processdesign - User contributions [en]

Ethanol to Ethylene (B1)

2015-03-17T04:30:35Z

Hpoppick: /* References */

[[File:BFD_B1.png|600px|thumbnail|alt=Alt text|Conversion of Ethanol to Ethylene]]

Team B1 Final Report

Authors: Harry Poppick, Emm Fulk and Scott Smith

Instructors: Fengqi You, David Wegerer

March 13, 2015

=Executive Summary=

The following report outlines the design and analysis of a process converting ethanol to chemical-grade ethylene via catalytic dehydration. This process consumers 100,000 kg/hr of 95 wt% ethanol, 5 wt% water feedstock and produces 53,000 kg/hr of 99.7 wt% chemical-grade ethylene. The ethanol feed passes through two fixed-bed reactors, each packed with an aluminum oxide catalyst, and the resulting ethylene is purified by two flash tanks and by absorption with water. The process was modeled using Aspen HYSYS simulation software to estimate mass and energy flows and equipment sizing requirements. Based on results of this initial simulation, several alternatives are discussed for increasing the process efficiency and profitability. The use of a fluidized bed reactor or a more ethylene-selective catalyst could increase the production of ethylene per ethanol basis. Additionally, several methods of purification to more valuable polymer-grade ethylene are proposed.

The economic feasibility of this process was evaluated using Aspen Economic Analyzer with the Icarus economics package. Capital cost is approximately $16.4 million total with an operating cost of $465 million per year. The current market prices of the ethanol feed and ethylene sales price are $1.44/gallon and $1350/metric ton respectively. The cost of feed ethanol, process utilities and miscellaneous operational costs total to about $427 million/year. At full operation, revenue at current prices would be approximately $640 million per year. The predicted 10-year net present value of the process is approximately $391 million with an IRR of 79% and a payback period of 2.7 years. A sensitivity analysis indicates that the process is most sensitive to feed prices, product prices and operation cost.

Several recommendations are made for both cost reduction and profit maximization, including the design of a heat exchanger network and the optimization of fired heaters that require high capital investment and large amounts of fuel. A safety review of the process is recommended, as well as the minimization of flue gas effluent and wastewater. It is also suggested that the construction of an onsite wastewater treatment center be considered. Overall, the initial analysis indicates this to be a profitable process and it is recommended the project move forward.

=Introduction=

Ethylene is a critical chemical precursor to a number of different industrial products. It is often derived from petroleum sources and polymerized to polyethylene, one of the most ubiquitous plastics today. (American Chemistry Council, 2013) Recently there has been a significant effort to develop production pathways utilizing biologically-derived feedstocks, such as corn or cellulosic ethanol, rather than traditional fossil-fuel sources. Ethylene can be produced from bioethanol via catalytic dehydration over an aluminum oxide catalyst. The proposed process converts 100,000 kg/hr of 95 wt% ethanol, 5% water feed to 53,000 kg/hr of 99.7% chemical-grade ethylene when operating at full capacity. This process was found to be economically viable with a 10-year net present value (NPV) of $131 million (2014 USD) and a payback period of approximately 2.7 years. This memo will detail the proposed process, as well as outline potential alternatives and economic viability of the project.

=Technical Approach=

Many bioethanol plants are located in the Midwest where large amounts of feedstock crops, such as corn, are grown. As such, this plant will be located in Story county, Iowa, near a large-scale bioethanol production plant. (DuPont Nevada Site, 2012) It is assumed that the supply of bioethanol is consistent and readily available. It is also assumed that other reagents - namely, the aluminum oxide catalyst, heater fuel, utility water and freon refrigerant - are readily available, and that wastewater treatment facilities are located near enough to facilitate the off-site treatment of wastewater. Plant capacity was based on current mid-sized industrial ethylene plants. (Designing Ethylene Plants, 2014)

HYSYS simulations were performed with the NRTL fluid package and Peng-Robinson vapor model. The NRTL fluid package is an activity coefficient model that is especially useful to model the separations of alcohols in aqueous solutions. (Suppes, 2015) In addition, NRTL uses models of binary pairs of components, much like the Wilson equation, to predict chemical interactions at the molecular level. The NRTL package can thus be easily extended to ternary and higher order chemical systems, making it ideal for this type of simulation. The Peng-Robinson vapor model was selected as it is well-suited to account for the non-idealities of the vapor phase reactions and separations integral to this process. (ASPENtech, 2014)

It was assumed that the feed enters the process at ambient temperature and pressure (25 °C, 1 atm) and at a consistent rate and composition with negligible quantities of impurities. The ethanol feed was assumed to be 95% ethanol and 5% water by mass, which is the commercial standard for industrial ethanol. (190 Proof Ethanol, 2012) Storage vessels for the feed ethanol, waste streams and products are assumed to be located nearby to the process. An initial feed pump compensates for pressure drops through the process and reduces the duty on downstream compressors. (Hadawey, 2015)

Natural gas, assumed to consist of 83% methane, 16% ethane and 1% nitrogen by mass, was supplied to two fired heaters at a flow rate estimated by HYSYS. (Methane, 2015) Air fed to the process to enable combustion was assumed to be 23% oxygen and 77% nitrogen by mass. (Composition of Air, 2015) Air streams were fed at 50% molar excess in order to ensure complete combustion and prevent the formation of carbon monoxide in the heater exhaust. Total flue gases are assumed to be 230,000 kg/hr, or 2.2 million tons annually, and consist of 73.8% nitrogen gas, 10.5% carbon dioxide, 8.2% water vapor, and 7.5% oxygen by mass. The only compound of concern in these emissions is the carbon dioxide, a known greenhouse gas. At the time of this report, the quantities of carbon dioxide emitted by this plant annually are within acceptable EPA specifications. (Summary of the Clean Air Act, 2015)

Due to the difficulty of simulation equilibrium and conversion reactions in a single vessel in HYSYS, these two reaction types were simulated in separate equilibrium reactor and conversion reactor units in series. In addition, while HYSYS indicated that reactor units would output separate vapor and liquid streams, it was assumed that in practice this would take the form of a single, two phase stream between each unit. To account for this, mixers were installed downstream of each reactor to combine the liquid and vapor phases of the reactor effluent. The three consequent reactions considered are as follows:
[[File:Equation.PNG|300px|center]]
The optimal reaction temperature was determined to be 400 °C, which promotes the equilibrium reaction of ethanol to ethylene while minimizing byproducts. (Zhang and Yu, 2013) While other byproducts may be produced in this process, these reactions are typically taken to comprise of the bulk of the dehydration reaction. Heat losses over these reactors were assumed to be negligible. (Zhang and Yu, 2013)All major process equipment is assumed to be constructed of high strength carbon steel. (AspenTech, 2012)

The “Sizing Utility” within the Icarus Economic Evaluation module was used to estimate sizes of major equipment based on the process simulation. These values can serve as a benchmark for an initial plant design. Icarus KbaseTM implements a wide variety of mechanical design standards, including ASME and BS5500, in order to calculate accurate equipment sizing. The Icarus sizing module combines equipment prices for standard chemical processing equipment as well as correlations and sizing factors. The advantage of using a software package such as HYSYS to price out individual equipment is that it utilizes up-to-date prices from vendors and distributors when estimating costs. A more in-depth overview of the correlations included in this software can be found in Towler and Sinnott (2009).

=Process Flowsheet=
[[File:Squarepfd_B1.PNG|thumb|400px|alt=Alt text|Fig 1: PFD of the Proposed Process]]

The following process is based primarily on a 1983 US patent titled “Process for dehydration of a low molecular weight alcohol.” (Barrocas and Baratelli, 1983) The process flow diagram can be seen in Figure 1. A larger version of the PFD is included in Appendix I and the HYSYS simulation setup in Appendix II.

The feed enters the process at a rate of 100,000 kg/hr, a temperature and pressure of a 25 °C and 1 atm and at a composition of 95 wt% ethanol and 5 wt% water.It is initially pressurized to 4335 kPa by centrifugal pump P-101 and subsequently heated to 400 °C by fired heater F-101. The heated and pressurized feed enters fixed bed reactor R-101 and contacts with the aluminum oxide catalyst. At this point it dehydrates to form the product, ethylene, as well as the byproducts water, hydrogen, diethyl ether and acetaldehyde. Fired heater F-102 and reactor R-102 increase the overall conversion of the process. Both fired heaters F-101 and F-102 are fueled with natural gas and fed with excess air. The composition of the reactor train effluent is 54.5 wt% ethylene, 37.1 wt% water, 8.1 wt% unreacted ethanol and trace amounts of diethyl ether, acetaldehyde, and hydrogen contaminants.

The pressure of the reactor train effluent is increased to 4500 kPa by compressor K-102 and the temperature decreased to 100 °C by exchange with cold water in heat exchanger E-201. The stream then expands and flashes in flash vessel FL-201, which separates out 82.3% of the unreacted ethanol, 96.6% of the water and virtually all of the acetaldehyde contaminant in the bottoms while sending the ethylene-rich vapor phase out of the top. The top product of FL-202 is compressed to 3500 kPA by K-202 and cooled to 0.0 °C by a freon refrigerant in E-202. At this point the stream is flashed for a second time in vessel FL-202 to remove additional impurities. The top outlet stream consists of 99.5 wt% ethylene, which is fed to the bottom of a 10-tray absorption column that removes a fraction of the residual diethyl ether as well as the remainder of the unreacted ethanol. A stream of absorbent water is fed to the top of the column at 10,000 kg/hr. The product exits the top of the column at a rate of 54,600 kg/hr and has a purity of 99.7% ethylene. Diethyl ether makes up 0.2% of the remaining product stream and is the primary contaminant. Trace amounts of residual water and hydrogen are also present.

Full tables of material and energy streams can be found in Appendices III and IV respectively.

==Process Alternatives==
===Reactor Alternatives===
Two fixed bed reactors, alternating with fired heaters, are used in the dehydration reaction of ethanol to ethylene. However, a fluidized bed reactor can offer better mixing and temperature control than a fixed bed reactor and thus provide the highest possible conversion of ethanol with the greatest selectivity to ethylene. (Tsao and Zasloff, 1979) Fluidized bed reactors also provide a lower rate of catalyst coking and byproduct formation, minimizing separation and catalyst regeneration costs. (Morschbacker, 2009) The major downside of fluidized bed reactors is that few large-scale processes have been built since the technology was developed in the late 1970s. (Tsao and Zasloff, 1979; Morschbacker, 2009) Although implementation of fluidized bed reactors could potentially increase the purity of the ethylene product and/or decrease costs, a small scale pilot process would need to be built and tested before it would be possible to develop an industrial-scale facility.

===Catalyst Alternatives===
Aluminum oxide, specifically gamma alumina, is the most industrially-common catalyst and has been historically used due to its low cost and high stability. (Tsao and Zasloff, 1979; Fan and Dai, n.d.) Recent improvements in selectivity and catalyst stability of activated alumina have been achieved by incorporating titanium oxide into the catalyst, although this increases reaction temperature by approximately 50 °C and decreases catalyst lifespan. (Chen and Li, et. al. 2007) There is also significant ongoing research into HZSM-5 zeolite and heteropolyacids, which are being explored as potential alternatives to alumina oxide. A nanoscale HZSM-5 zeolite catalyst has been shown to operate at the relatively low temperature of 200-300°C, with a 100% ethanol conversion and 99.7% selectivity to ethylene. Initial research has also indicated that it maintains greater than 98% selectivity for 630 operational hours. (Fan and Dai, n.d.) However, the current low cost and ready availability of unmodified alumina oxide makes it a better choice for a process of this scale.

===Purification Alternatives===
As specified in this process, the reactor effluent is purified by two flash drums and absorption with water to produce chemical-grade ethylene. If chemical-grade ethylene is indeed the desired product, other purification options include caustic washing of the reactor effluent and water removal in a desiccant drying bed. (Morschbacker, 2009) While this purification train is relatively simple and does not require harsh chemical reagents, polymer grade ethylene is more commercially valuable and the additional cost of removing water and diethyl ether contaminants may be justified by increased revenue. Cryogenic distillation was initially simulated to produce polymer-grade ethylene, but utility requirements were found to render this separation economically unviable. (Barrocas and Baratelli, 1983) Further research and optimization may find this purification strategy to be a more valid process. Alternatively, the addition of a cryogenic turboexpander or the use of alternative adsorbents may increase product purity to polymer grade. (Jumonville, 2010) Initial HYSYS simulations indicate that these operations may be feasible with further refinement.

===Wastewater Treatment===
Due to the large volume of wastewater produced, building an on-site wastewater treatment facility may prove to be more economical than paying for third-party wastewater treatment. Flash vessel FL-201 produces 44,600 L/hr of wastewater contaminated with 18.7 vol% ethanol and 0.6 vol% acetaldehyde, while FL-202 produces 2940 L/hr of an aqueous waste consisting of 56.8 vol% ethanol, 42.0 vol% water and 0.9 vol% diethyl ether. The absorption column produces approximately 10,200 liters/hr of wastewater contaminated with 1.2 vol% ethanol, 0.2% diethyl ether and 0.2% acetaldehyde. Utilizing distillation to separate these streams into clean water and volatile organic waste could ultimately reduce the quantity of waste that requires disposal and reduce the overall costs of the process.

==Process Equipment==
Relevant sizing information for each unit operation, estimated by the method described in the “Technical Approach,” can be found in Appendix V. Equipment and piping is assumed to be constructed of carbon steel. It should be noted that the two fired heaters are proportionately large enough to heat the entirety of the process stream and are thus larger than standard equipment.

=Economic Analysis=
[[File:NPV_B1.png|400px|thumb|Fig 2. Projected Cash Flow]]
[[File:sensitivityanalysis_B1.png|400px|thumb| Fig 3. Results of the Sensitivity Analysis on 10 year NPV]]

==Economics Overview==
All final values are normalized to June 2014 USD by CEPCI scaling. It is assumed that all products produced are sold at current market prices.

The Aspen Economic Evaluation module within HYSYS v8.0 was used to estimate capital and operating costs for a 10-year plant life span with a construction start date of April 2015. The price of the 95% ethanol feed stream was estimated at $1.44 per gallon, while the chemical grade ethylene produced is currently selling for approximately $1350 per metric ton. (Today in Energy, 2015; Weddle, 2014) Mapping and sizing calculations were performed by the economics module and a preliminary economic evaluation was completed. Equipment sizes, also estimated by HYSYS, were reviewed to ensure that height, diameter, and volume specifications were within realistic ranges.

The process was ideally projected to operate 360 days per year with a start-up time of one year. In addition, the tax rate was approximated at 40%, an interest rate at 20%, and a salvage value of 20%. Escalation percentages were compounded yearly for the product, raw material, and operating costs. The total capital cost for this process is approximately $16.4 million, which includes all equipment and piping described in the process. The most expensive equipment used in this process are the two fired heaters F-101 and F-102, which have an exceptionally large heat exchange area to adequately heat the feed. Standard heaters may not suffice and additional costs may be incurred for the raw materials and manufacture of this equipment. Including a feed preheater or additional fired heaters may reduce this cost in subsequent design iterations.

The total operating cost is approximately $465 million per year, about $427 million of which is the cost of the ethanol feed and natural gas for the two fired heaters. An additional $1.73 million per year is used for utilities including the cooling water and refrigerant. The labor and maintenance costs of this industrial process were also accounted for within the simulation’s economic analysis. The HYSYS simulation software, in conjunction with the Icarus economic analyzer, estimated there should be 5 operators per 8 hour shift with a cost per operator of $20 per hour. This results in a total operating labor cost of approximately $880,000 per year. In addition, the process will require one supervisor per shift with an hourly rate of $35 for total supervisor salaries of $307,000 per year. Finally, a fixed maintenance rate was estimated at $205,000 per 8000 hours of operation for a total cost of $225,000 per year.

Total product sales are roughly $640 million per year at full operation. The estimated income for this process is thus approximately $175 million per year. After ten years, the plant is projected to have a net present value (NPV) of $391 million and an internal rate of return of approximately 79%. In addition the payout period for the initial investment is estimated to be about 2.7 years. Figure 2 shows the projected cash flow for the project.

==Sensitivity Analysis==
A sensitivity analysis was performed to investigate the effects of fluctuating capital costs, operating costs, raw materials, utility costs and ethylene sales price on the 10-year net present value (NPV) of the project. This analysis was performed by scaling these cost factors according to typical ranges given in Towler and Sinnott and calculating the adjusting the NPV accordingly. The results, illustrated in Figure 3, indicate that the project value is most sensitive to product sales, raw materials costs, and operating costs. Ethylene and ethanol prices are market-determined and cannot be controlled for in the process design, so further optimization should be focused on minimizing the operations cost of the process. (Today in Energy, 2015; Weddle, 2014) However, in feed and product prices do still have a profound effect on profitability and feasibility. A more rigorous market analysis will better inform the profitability outlook.

=Conclusions/Recommendations=

The proposed process produces approximately 460,000 metric tons of 99.7 wt% ethylene annually, with a 10-year net present value of $131 million. If current economic conditions hold, it is recommended that this project proceed to implementation following further design improvements and optimization.

Future design iterations should focus on process optimization, particularly in minimizing operating costs as prescribed by the results of the sensitivity analysis. The development of a heat-exchanger network, potentially with Aspen Energy Analyzer, is one option for decreasing utility requirements and increasing the efficiency of the process overall. Optimization of the fired heaters could also result in decreased operational costs. Although overall profitability is less sensitive to capital costs, reviewing and adjusting equipment sizing would also improve the economic outlook. In particular, exploring alternative heating strategies at the beginning of the process could significantly decrease capital costs. Although there are not any particularly dangerous chemicals utilized in the process, an overall process review should also consider potential failure modes to minimize the safety risk to plant workers and nearby residents.

In addition to economic and safety considerations, harmful emissions and waste streams should be minimized both to bring down the cost of treatment and to decrease environmental effects. The two fired heaters consume a large amount of natural gas per year, emitting about 200,000 tons of CO2 annually, and account for more than half of the capital cost of the process. Although no known toxic gases are produced, carbon capture or other emissions-reduction methods should be considered. Additionally, enough wastewater is produced by this process that building an onsite wastewater treatment center should be considered. This could not only decrease operating costs by eliminating the need for an external contract but also give the plant more control over the final purity of the treated wastewater.

Finally, the current model assumes that all ethylene produced will be sold at a current prices and price or product sales will not be affected by economic variability. A more detailed study of the chemical-grade ethylene market, as well as a more thorough understanding of sales and distribution logistics, would increase the surety of a profitable process.

In summary, the proposed process yields chemical grade ethylene via the catalytic dehydration of ethanol. A 100,000 kg/hr of 95 wt% ethanol, 5% water feed is converted to 53,000 kg/hr of 99.7% chemical-grade ethylene. After 10 years of operation, including a one-year startup time, the process has an NPV of $391 million with an IRR of 79% and a payback period of 2.7 years.
Pending further optimization, this process was determined to be viable and it is recommended for the project to move forward.

=References=

ASPENtech. Appendix A - Property Methods and Calculations. Simulation Basics; A-3 - A-26. 2014.

AspenTech. Aspen HYSYS Help File v8.0. Aspen Technology, Inc. 2012.

Barrocas H, Baratelli F, inventors; Petroleo Brasileiro S.A., assignee. Process for dehydration of a low molecular weight alcohol. US patent 4,396,789 A. August 2, 1983.

Chen G, Li S, Jiao F, Yuan Q. Catalytic dehydration of bioethanol to ethylene over TiO2/γ-Al2O3 catalysts in microchannel reactors. Catal. Today 2007, 125, 111–119.

Composition of Air [Internet]. Engineering Toolbox; [cited 13 Mar 2015]. Available from: http://www.engineeringtoolbox.com/air-composition-d_212.html.

Designing Ethylene Plants. Ethylene [Internet]. Technip; 2014 [cited 13 Mar 2015]. Available from: http://www.technip.com/en/our-business/onshore/ethylene.

DuPont Nevada Site Cellulosic Ethanol Facility [Internet]. DuPont Chemical; c2012-2015 [cited 11 Mar 2015]. Available from: http://biofuels.dupont.com/cellulosic-ethanol/nevada-site-ce-facility/.

Fan D, Dai DJ, Wu HS. Ethylene Formation by Catalytic Dehydration of Ethanol with Industrial Considerations. Materials. 2012 December;6:101-115.

Jumonville, J. Tutorial on Cryogenic Turboexpanders. Proceedings of the Thirty-Ninth Turbomachinery Symposium; 2010 Oct.

Britannica.com. Methane (Chemical Compound). Encyclopædia Britannica Online; c2015 [cited 13 Mar. 2015] Available from: http://www.britannica.com/EBchecked/topic/378264/methane.

Morschbacker, A. Bio-Ethanol Based Ethylene. Polymer Reviews. 2009; 49:79-84.

Statista.com. Production of chemicals and plastics in the U.S. in 2013, by type (in 1,000 metric tons) [Internet]. American Chemistry Council; c2014 [cited 15 Jan 2015]. Available from: http://www.statista.com/statistics/299725/total-us-plastics-and-chemicals-shipments-by-type/.

Epa.gov. Summary of the Clean Air Act, 2015. United States Environmental Protection Agency. [cited 13 Mar. 2015] Available from: http://www2.epa.gov/laws-regulations/summary-clean-air-act.

Suppes GJ. Selecting Thermodynamic Models for Process Simulation of Organic VLE and LLE Systems. The University of Missouri-Columbia, Dept of Chemical Engineering. [cited 13 Mar. 2015].

Today in Energy - Daily Prices. US Energy Information Administration website. http://www.eia.gov/todayinenergy/prices.cfm. Accessed March 3rd 2015.

Towler G, Sinnott R. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. 2nd ed. Boston: Elsevier; 2013.

Tsao U, Zasloff HB, inventors; The Lummus Company, assignee. Production of ethylene from ethanol. US patent 4,134,926. January 16, 1979.

Weddle, N. ICIS Pricing: Ethylene (Europe). Reed Business Limited. January 10 2014.

Zhang M, Yu Y. Dehydration of Ethanol to Ethylene. Industrial Engineering and Chemical Research. 2013; 52:9505-9514.

190 Proof Ethanol: Technical Data Sheet [Internet]. Decon Labs Inc; 2012 [cited 13 Mar 2015]. Available from: http://www.deconlabs.com/tds/ETHANOL%20190%20%20PROOF.pdf.

=Appendix I - Process Flow Diagram=
[[File:PFD B1.JPG|1200px|center]]

=Appendix II - HYSYS Simulation=
[[File:HYSYS_B1.PNG|center|1200px]]

=Appendix III - Material Streams=
[[File:Streams_B1.png|1200px]]

=Appendix IV - Energy Table=
[[File:Energy_B1.png|600px|center]]

[[File:Utilities.PNG|600px|center]]

=Appendix V - Equipment Sizing=
[[File:Equipment sizes.png|center]] 

=Appendix VI - Economics=
[[File:Econsummary_B1.png|center]] 

[[File:Capcost_B1.png|center]]

Ethanol to Ethylene (B1)

2015-03-17T04:28:31Z

Hpoppick: /* References */

[[File:BFD_B1.png|600px|thumbnail|alt=Alt text|Conversion of Ethanol to Ethylene]]

Team B1 Final Report

Authors: Harry Poppick, Emm Fulk and Scott Smith

Instructors: Fengqi You, David Wegerer

March 13, 2015

=Executive Summary=

The following report outlines the design and analysis of a process converting ethanol to chemical-grade ethylene via catalytic dehydration. This process consumers 100,000 kg/hr of 95 wt% ethanol, 5 wt% water feedstock and produces 53,000 kg/hr of 99.7 wt% chemical-grade ethylene. The ethanol feed passes through two fixed-bed reactors, each packed with an aluminum oxide catalyst, and the resulting ethylene is purified by two flash tanks and by absorption with water. The process was modeled using Aspen HYSYS simulation software to estimate mass and energy flows and equipment sizing requirements. Based on results of this initial simulation, several alternatives are discussed for increasing the process efficiency and profitability. The use of a fluidized bed reactor or a more ethylene-selective catalyst could increase the production of ethylene per ethanol basis. Additionally, several methods of purification to more valuable polymer-grade ethylene are proposed.

The economic feasibility of this process was evaluated using Aspen Economic Analyzer with the Icarus economics package. Capital cost is approximately $16.4 million total with an operating cost of $465 million per year. The current market prices of the ethanol feed and ethylene sales price are $1.44/gallon and $1350/metric ton respectively. The cost of feed ethanol, process utilities and miscellaneous operational costs total to about $427 million/year. At full operation, revenue at current prices would be approximately $640 million per year. The predicted 10-year net present value of the process is approximately $391 million with an IRR of 79% and a payback period of 2.7 years. A sensitivity analysis indicates that the process is most sensitive to feed prices, product prices and operation cost.

Several recommendations are made for both cost reduction and profit maximization, including the design of a heat exchanger network and the optimization of fired heaters that require high capital investment and large amounts of fuel. A safety review of the process is recommended, as well as the minimization of flue gas effluent and wastewater. It is also suggested that the construction of an onsite wastewater treatment center be considered. Overall, the initial analysis indicates this to be a profitable process and it is recommended the project move forward.

=Introduction=

Ethylene is a critical chemical precursor to a number of different industrial products. It is often derived from petroleum sources and polymerized to polyethylene, one of the most ubiquitous plastics today. (American Chemistry Council, 2013) Recently there has been a significant effort to develop production pathways utilizing biologically-derived feedstocks, such as corn or cellulosic ethanol, rather than traditional fossil-fuel sources. Ethylene can be produced from bioethanol via catalytic dehydration over an aluminum oxide catalyst. The proposed process converts 100,000 kg/hr of 95 wt% ethanol, 5% water feed to 53,000 kg/hr of 99.7% chemical-grade ethylene when operating at full capacity. This process was found to be economically viable with a 10-year net present value (NPV) of $131 million (2014 USD) and a payback period of approximately 2.7 years. This memo will detail the proposed process, as well as outline potential alternatives and economic viability of the project.

=Technical Approach=

Many bioethanol plants are located in the Midwest where large amounts of feedstock crops, such as corn, are grown. As such, this plant will be located in Story county, Iowa, near a large-scale bioethanol production plant. (DuPont Nevada Site, 2012) It is assumed that the supply of bioethanol is consistent and readily available. It is also assumed that other reagents - namely, the aluminum oxide catalyst, heater fuel, utility water and freon refrigerant - are readily available, and that wastewater treatment facilities are located near enough to facilitate the off-site treatment of wastewater. Plant capacity was based on current mid-sized industrial ethylene plants. (Designing Ethylene Plants, 2014)

HYSYS simulations were performed with the NRTL fluid package and Peng-Robinson vapor model. The NRTL fluid package is an activity coefficient model that is especially useful to model the separations of alcohols in aqueous solutions. (Suppes, 2015) In addition, NRTL uses models of binary pairs of components, much like the Wilson equation, to predict chemical interactions at the molecular level. The NRTL package can thus be easily extended to ternary and higher order chemical systems, making it ideal for this type of simulation. The Peng-Robinson vapor model was selected as it is well-suited to account for the non-idealities of the vapor phase reactions and separations integral to this process. (ASPENtech, 2014)

It was assumed that the feed enters the process at ambient temperature and pressure (25 °C, 1 atm) and at a consistent rate and composition with negligible quantities of impurities. The ethanol feed was assumed to be 95% ethanol and 5% water by mass, which is the commercial standard for industrial ethanol. (190 Proof Ethanol, 2012) Storage vessels for the feed ethanol, waste streams and products are assumed to be located nearby to the process. An initial feed pump compensates for pressure drops through the process and reduces the duty on downstream compressors. (Hadawey, 2015)

Natural gas, assumed to consist of 83% methane, 16% ethane and 1% nitrogen by mass, was supplied to two fired heaters at a flow rate estimated by HYSYS. (Methane, 2015) Air fed to the process to enable combustion was assumed to be 23% oxygen and 77% nitrogen by mass. (Composition of Air, 2015) Air streams were fed at 50% molar excess in order to ensure complete combustion and prevent the formation of carbon monoxide in the heater exhaust. Total flue gases are assumed to be 230,000 kg/hr, or 2.2 million tons annually, and consist of 73.8% nitrogen gas, 10.5% carbon dioxide, 8.2% water vapor, and 7.5% oxygen by mass. The only compound of concern in these emissions is the carbon dioxide, a known greenhouse gas. At the time of this report, the quantities of carbon dioxide emitted by this plant annually are within acceptable EPA specifications. (Summary of the Clean Air Act, 2015)

Due to the difficulty of simulation equilibrium and conversion reactions in a single vessel in HYSYS, these two reaction types were simulated in separate equilibrium reactor and conversion reactor units in series. In addition, while HYSYS indicated that reactor units would output separate vapor and liquid streams, it was assumed that in practice this would take the form of a single, two phase stream between each unit. To account for this, mixers were installed downstream of each reactor to combine the liquid and vapor phases of the reactor effluent. The three consequent reactions considered are as follows:
[[File:Equation.PNG|300px|center]]
The optimal reaction temperature was determined to be 400 °C, which promotes the equilibrium reaction of ethanol to ethylene while minimizing byproducts. (Zhang and Yu, 2013) While other byproducts may be produced in this process, these reactions are typically taken to comprise of the bulk of the dehydration reaction. Heat losses over these reactors were assumed to be negligible. (Zhang and Yu, 2013)All major process equipment is assumed to be constructed of high strength carbon steel. (AspenTech, 2012)

The “Sizing Utility” within the Icarus Economic Evaluation module was used to estimate sizes of major equipment based on the process simulation. These values can serve as a benchmark for an initial plant design. Icarus KbaseTM implements a wide variety of mechanical design standards, including ASME and BS5500, in order to calculate accurate equipment sizing. The Icarus sizing module combines equipment prices for standard chemical processing equipment as well as correlations and sizing factors. The advantage of using a software package such as HYSYS to price out individual equipment is that it utilizes up-to-date prices from vendors and distributors when estimating costs. A more in-depth overview of the correlations included in this software can be found in Towler and Sinnott (2009).

=Process Flowsheet=
[[File:Squarepfd_B1.PNG|thumb|400px|alt=Alt text|Fig 1: PFD of the Proposed Process]]

The following process is based primarily on a 1983 US patent titled “Process for dehydration of a low molecular weight alcohol.” (Barrocas and Baratelli, 1983) The process flow diagram can be seen in Figure 1. A larger version of the PFD is included in Appendix I and the HYSYS simulation setup in Appendix II.

The feed enters the process at a rate of 100,000 kg/hr, a temperature and pressure of a 25 °C and 1 atm and at a composition of 95 wt% ethanol and 5 wt% water.It is initially pressurized to 4335 kPa by centrifugal pump P-101 and subsequently heated to 400 °C by fired heater F-101. The heated and pressurized feed enters fixed bed reactor R-101 and contacts with the aluminum oxide catalyst. At this point it dehydrates to form the product, ethylene, as well as the byproducts water, hydrogen, diethyl ether and acetaldehyde. Fired heater F-102 and reactor R-102 increase the overall conversion of the process. Both fired heaters F-101 and F-102 are fueled with natural gas and fed with excess air. The composition of the reactor train effluent is 54.5 wt% ethylene, 37.1 wt% water, 8.1 wt% unreacted ethanol and trace amounts of diethyl ether, acetaldehyde, and hydrogen contaminants.

The pressure of the reactor train effluent is increased to 4500 kPa by compressor K-102 and the temperature decreased to 100 °C by exchange with cold water in heat exchanger E-201. The stream then expands and flashes in flash vessel FL-201, which separates out 82.3% of the unreacted ethanol, 96.6% of the water and virtually all of the acetaldehyde contaminant in the bottoms while sending the ethylene-rich vapor phase out of the top. The top product of FL-202 is compressed to 3500 kPA by K-202 and cooled to 0.0 °C by a freon refrigerant in E-202. At this point the stream is flashed for a second time in vessel FL-202 to remove additional impurities. The top outlet stream consists of 99.5 wt% ethylene, which is fed to the bottom of a 10-tray absorption column that removes a fraction of the residual diethyl ether as well as the remainder of the unreacted ethanol. A stream of absorbent water is fed to the top of the column at 10,000 kg/hr. The product exits the top of the column at a rate of 54,600 kg/hr and has a purity of 99.7% ethylene. Diethyl ether makes up 0.2% of the remaining product stream and is the primary contaminant. Trace amounts of residual water and hydrogen are also present.

Full tables of material and energy streams can be found in Appendices III and IV respectively.

==Process Alternatives==
===Reactor Alternatives===
Two fixed bed reactors, alternating with fired heaters, are used in the dehydration reaction of ethanol to ethylene. However, a fluidized bed reactor can offer better mixing and temperature control than a fixed bed reactor and thus provide the highest possible conversion of ethanol with the greatest selectivity to ethylene. (Tsao and Zasloff, 1979) Fluidized bed reactors also provide a lower rate of catalyst coking and byproduct formation, minimizing separation and catalyst regeneration costs. (Morschbacker, 2009) The major downside of fluidized bed reactors is that few large-scale processes have been built since the technology was developed in the late 1970s. (Tsao and Zasloff, 1979; Morschbacker, 2009) Although implementation of fluidized bed reactors could potentially increase the purity of the ethylene product and/or decrease costs, a small scale pilot process would need to be built and tested before it would be possible to develop an industrial-scale facility.

===Catalyst Alternatives===
Aluminum oxide, specifically gamma alumina, is the most industrially-common catalyst and has been historically used due to its low cost and high stability. (Tsao and Zasloff, 1979; Fan and Dai, n.d.) Recent improvements in selectivity and catalyst stability of activated alumina have been achieved by incorporating titanium oxide into the catalyst, although this increases reaction temperature by approximately 50 °C and decreases catalyst lifespan. (Chen and Li, et. al. 2007) There is also significant ongoing research into HZSM-5 zeolite and heteropolyacids, which are being explored as potential alternatives to alumina oxide. A nanoscale HZSM-5 zeolite catalyst has been shown to operate at the relatively low temperature of 200-300°C, with a 100% ethanol conversion and 99.7% selectivity to ethylene. Initial research has also indicated that it maintains greater than 98% selectivity for 630 operational hours. (Fan and Dai, n.d.) However, the current low cost and ready availability of unmodified alumina oxide makes it a better choice for a process of this scale.

===Purification Alternatives===
As specified in this process, the reactor effluent is purified by two flash drums and absorption with water to produce chemical-grade ethylene. If chemical-grade ethylene is indeed the desired product, other purification options include caustic washing of the reactor effluent and water removal in a desiccant drying bed. (Morschbacker, 2009) While this purification train is relatively simple and does not require harsh chemical reagents, polymer grade ethylene is more commercially valuable and the additional cost of removing water and diethyl ether contaminants may be justified by increased revenue. Cryogenic distillation was initially simulated to produce polymer-grade ethylene, but utility requirements were found to render this separation economically unviable. (Barrocas and Baratelli, 1983) Further research and optimization may find this purification strategy to be a more valid process. Alternatively, the addition of a cryogenic turboexpander or the use of alternative adsorbents may increase product purity to polymer grade. (Jumonville, 2010) Initial HYSYS simulations indicate that these operations may be feasible with further refinement.

===Wastewater Treatment===
Due to the large volume of wastewater produced, building an on-site wastewater treatment facility may prove to be more economical than paying for third-party wastewater treatment. Flash vessel FL-201 produces 44,600 L/hr of wastewater contaminated with 18.7 vol% ethanol and 0.6 vol% acetaldehyde, while FL-202 produces 2940 L/hr of an aqueous waste consisting of 56.8 vol% ethanol, 42.0 vol% water and 0.9 vol% diethyl ether. The absorption column produces approximately 10,200 liters/hr of wastewater contaminated with 1.2 vol% ethanol, 0.2% diethyl ether and 0.2% acetaldehyde. Utilizing distillation to separate these streams into clean water and volatile organic waste could ultimately reduce the quantity of waste that requires disposal and reduce the overall costs of the process.

==Process Equipment==
Relevant sizing information for each unit operation, estimated by the method described in the “Technical Approach,” can be found in Appendix V. Equipment and piping is assumed to be constructed of carbon steel. It should be noted that the two fired heaters are proportionately large enough to heat the entirety of the process stream and are thus larger than standard equipment.

=Economic Analysis=
[[File:NPV_B1.png|400px|thumb|Fig 2. Projected Cash Flow]]
[[File:sensitivityanalysis_B1.png|400px|thumb| Fig 3. Results of the Sensitivity Analysis on 10 year NPV]]

==Economics Overview==
All final values are normalized to June 2014 USD by CEPCI scaling. It is assumed that all products produced are sold at current market prices.

The Aspen Economic Evaluation module within HYSYS v8.0 was used to estimate capital and operating costs for a 10-year plant life span with a construction start date of April 2015. The price of the 95% ethanol feed stream was estimated at $1.44 per gallon, while the chemical grade ethylene produced is currently selling for approximately $1350 per metric ton. (Today in Energy, 2015; Weddle, 2014) Mapping and sizing calculations were performed by the economics module and a preliminary economic evaluation was completed. Equipment sizes, also estimated by HYSYS, were reviewed to ensure that height, diameter, and volume specifications were within realistic ranges.

The process was ideally projected to operate 360 days per year with a start-up time of one year. In addition, the tax rate was approximated at 40%, an interest rate at 20%, and a salvage value of 20%. Escalation percentages were compounded yearly for the product, raw material, and operating costs. The total capital cost for this process is approximately $16.4 million, which includes all equipment and piping described in the process. The most expensive equipment used in this process are the two fired heaters F-101 and F-102, which have an exceptionally large heat exchange area to adequately heat the feed. Standard heaters may not suffice and additional costs may be incurred for the raw materials and manufacture of this equipment. Including a feed preheater or additional fired heaters may reduce this cost in subsequent design iterations.

The total operating cost is approximately $465 million per year, about $427 million of which is the cost of the ethanol feed and natural gas for the two fired heaters. An additional $1.73 million per year is used for utilities including the cooling water and refrigerant. The labor and maintenance costs of this industrial process were also accounted for within the simulation’s economic analysis. The HYSYS simulation software, in conjunction with the Icarus economic analyzer, estimated there should be 5 operators per 8 hour shift with a cost per operator of $20 per hour. This results in a total operating labor cost of approximately $880,000 per year. In addition, the process will require one supervisor per shift with an hourly rate of $35 for total supervisor salaries of $307,000 per year. Finally, a fixed maintenance rate was estimated at $205,000 per 8000 hours of operation for a total cost of $225,000 per year.

Total product sales are roughly $640 million per year at full operation. The estimated income for this process is thus approximately $175 million per year. After ten years, the plant is projected to have a net present value (NPV) of $391 million and an internal rate of return of approximately 79%. In addition the payout period for the initial investment is estimated to be about 2.7 years. Figure 2 shows the projected cash flow for the project.

==Sensitivity Analysis==
A sensitivity analysis was performed to investigate the effects of fluctuating capital costs, operating costs, raw materials, utility costs and ethylene sales price on the 10-year net present value (NPV) of the project. This analysis was performed by scaling these cost factors according to typical ranges given in Towler and Sinnott and calculating the adjusting the NPV accordingly. The results, illustrated in Figure 3, indicate that the project value is most sensitive to product sales, raw materials costs, and operating costs. Ethylene and ethanol prices are market-determined and cannot be controlled for in the process design, so further optimization should be focused on minimizing the operations cost of the process. (Today in Energy, 2015; Weddle, 2014) However, in feed and product prices do still have a profound effect on profitability and feasibility. A more rigorous market analysis will better inform the profitability outlook.

=Conclusions/Recommendations=

The proposed process produces approximately 460,000 metric tons of 99.7 wt% ethylene annually, with a 10-year net present value of $131 million. If current economic conditions hold, it is recommended that this project proceed to implementation following further design improvements and optimization.

Future design iterations should focus on process optimization, particularly in minimizing operating costs as prescribed by the results of the sensitivity analysis. The development of a heat-exchanger network, potentially with Aspen Energy Analyzer, is one option for decreasing utility requirements and increasing the efficiency of the process overall. Optimization of the fired heaters could also result in decreased operational costs. Although overall profitability is less sensitive to capital costs, reviewing and adjusting equipment sizing would also improve the economic outlook. In particular, exploring alternative heating strategies at the beginning of the process could significantly decrease capital costs. Although there are not any particularly dangerous chemicals utilized in the process, an overall process review should also consider potential failure modes to minimize the safety risk to plant workers and nearby residents.

In addition to economic and safety considerations, harmful emissions and waste streams should be minimized both to bring down the cost of treatment and to decrease environmental effects. The two fired heaters consume a large amount of natural gas per year, emitting about 200,000 tons of CO2 annually, and account for more than half of the capital cost of the process. Although no known toxic gases are produced, carbon capture or other emissions-reduction methods should be considered. Additionally, enough wastewater is produced by this process that building an onsite wastewater treatment center should be considered. This could not only decrease operating costs by eliminating the need for an external contract but also give the plant more control over the final purity of the treated wastewater.

Finally, the current model assumes that all ethylene produced will be sold at a current prices and price or product sales will not be affected by economic variability. A more detailed study of the chemical-grade ethylene market, as well as a more thorough understanding of sales and distribution logistics, would increase the surety of a profitable process.

In summary, the proposed process yields chemical grade ethylene via the catalytic dehydration of ethanol. A 100,000 kg/hr of 95 wt% ethanol, 5% water feed is converted to 53,000 kg/hr of 99.7% chemical-grade ethylene. After 10 years of operation, including a one-year startup time, the process has an NPV of $391 million with an IRR of 79% and a payback period of 2.7 years.
Pending further optimization, this process was determined to be viable and it is recommended for the project to move forward.

=References=

ASPENtech. Appendix A - Property Methods and Calculations. Simulation Basics; A-3 - A-26. 2014.

AspenTech. Aspen HYSYS Help File v8.0. Aspen Technology, Inc. 2012.

Barrocas H, Baratelli F, inventors; Petroleo Brasileiro S.A., assignee. Process for dehydration of a low molecular weight alcohol. US patent 4,396,789 A. August 2, 1983.

Chen G, Li S, Jiao F, Yuan Q. Catalytic dehydration of bioethanol to ethylene over TiO2/γ-Al2O3 catalysts in microchannel reactors. Catal. Today 2007, 125, 111–119.

Composition of Air [Internet]. Engineering Toolbox; [cited 13 Mar 2015]. Available from: http://www.engineeringtoolbox.com/air-composition-d_212.html.

Designing Ethylene Plants. Ethylene [Internet]. Technip; 2014 [cited 13 Mar 2015]. Available from: http://www.technip.com/en/our-business/onshore/ethylene.

DuPont Nevada Site Cellulosic Ethanol Facility [Internet]. DuPont Chemical; c2012-2015 [cited 11 Mar 2015]. Available from: http://biofuels.dupont.com/cellulosic-ethanol/nevada-site-ce-facility/.

Fan D, Dai DJ, Wu HS. Ethylene Formation by Catalytic Dehydration of Ethanol with Industrial Considerations. Materials. 6, 101-115. doi: 10.3390/ma6010101.

Hadawey A, Ge Y, Tassou TSA. Energy Savings Through Liquid Pressure Amplification In A Dairy Plant Refrigeration System. The Centre for Energy and Built Environment Research.

Jumonville, J. Tutorial on Cryogenic Turboexpanders. Proceedings of the Thirty-Ninth Turbomachinery Symposium; 2010 Oct.

Britannica.com. Methane (Chemical Compound). Encyclopædia Britannica Online; c2015 [cited 13 Mar. 2015] Available from: http://www.britannica.com/EBchecked/topic/378264/methane.

Morschbacker, A. Bio-Ethanol Based Ethylene. Polymer Reviews. 2009; 49:79-84.

Statista.com. Production of chemicals and plastics in the U.S. in 2013, by type (in 1,000 metric tons) [Internet]. American Chemistry Council; c2014 [cited 15 Jan 2015]. Available from: http://www.statista.com/statistics/299725/total-us-plastics-and-chemicals-shipments-by-type/.

Epa.gov. Summary of the Clean Air Act, 2015. United States Environmental Protection Agency. [cited 13 Mar. 2015] Available from: http://www2.epa.gov/laws-regulations/summary-clean-air-act.

Suppes GJ. Selecting Thermodynamic Models for Process Simulation of Organic VLE and LLE Systems. The University of Missouri-Columbia, Dept of Chemical Engineering. [cited 13 Mar. 2015].

Today in Energy - Daily Prices. US Energy Information Administration website. http://www.eia.gov/todayinenergy/prices.cfm. Accessed March 3rd 2015.

Towler G, Sinnott R. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. 2nd ed. Boston: Elsevier; 2013.

Tsao U, Zasloff HB, inventors; The Lummus Company, assignee. Production of ethylene from ethanol. US patent 4,134,926. January 16, 1979.

Weddle, N. ICIS Pricing: Ethylene (Europe). Reed Business Limited. January 10 2014.

Zhang M, Yu Y. Dehydration of Ethanol to Ethylene. Industrial Engineering and Chemical Research. 2013; 52:9505-9514.

190 Proof Ethanol: Technical Data Sheet [Internet]. Decon Labs Inc; 2012 [cited 13 Mar 2015]. Available from: http://www.deconlabs.com/tds/ETHANOL%20190%20%20PROOF.pdf.

=Appendix I - Process Flow Diagram=
[[File:PFD B1.JPG|1200px|center]]

=Appendix II - HYSYS Simulation=
[[File:HYSYS_B1.PNG|center|1200px]]

=Appendix III - Material Streams=
[[File:Streams_B1.png|1200px]]

=Appendix IV - Energy Table=
[[File:Energy_B1.png|600px|center]]

[[File:Utilities.PNG|600px|center]]

=Appendix V - Equipment Sizing=
[[File:Equipment sizes.png|center]] 

=Appendix VI - Economics=
[[File:Econsummary_B1.png|center]] 

[[File:Capcost_B1.png|center]]

Ethanol to Ethylene (B1)

2015-03-17T04:24:40Z

Hpoppick:

[[File:BFD_B1.png|600px|thumbnail|alt=Alt text|Conversion of Ethanol to Ethylene]]

Team B1 Final Report

Authors: Harry Poppick, Emm Fulk and Scott Smith

Instructors: Fengqi You, David Wegerer

March 13, 2015

=Executive Summary=

The following report outlines the design and analysis of a process converting ethanol to chemical-grade ethylene via catalytic dehydration. This process consumers 100,000 kg/hr of 95 wt% ethanol, 5 wt% water feedstock and produces 53,000 kg/hr of 99.7 wt% chemical-grade ethylene. The ethanol feed passes through two fixed-bed reactors, each packed with an aluminum oxide catalyst, and the resulting ethylene is purified by two flash tanks and by absorption with water. The process was modeled using Aspen HYSYS simulation software to estimate mass and energy flows and equipment sizing requirements. Based on results of this initial simulation, several alternatives are discussed for increasing the process efficiency and profitability. The use of a fluidized bed reactor or a more ethylene-selective catalyst could increase the production of ethylene per ethanol basis. Additionally, several methods of purification to more valuable polymer-grade ethylene are proposed.

The economic feasibility of this process was evaluated using Aspen Economic Analyzer with the Icarus economics package. Capital cost is approximately $16.4 million total with an operating cost of $465 million per year. The current market prices of the ethanol feed and ethylene sales price are $1.44/gallon and $1350/metric ton respectively. The cost of feed ethanol, process utilities and miscellaneous operational costs total to about $427 million/year. At full operation, revenue at current prices would be approximately $640 million per year. The predicted 10-year net present value of the process is approximately $391 million with an IRR of 79% and a payback period of 2.7 years. A sensitivity analysis indicates that the process is most sensitive to feed prices, product prices and operation cost.

Several recommendations are made for both cost reduction and profit maximization, including the design of a heat exchanger network and the optimization of fired heaters that require high capital investment and large amounts of fuel. A safety review of the process is recommended, as well as the minimization of flue gas effluent and wastewater. It is also suggested that the construction of an onsite wastewater treatment center be considered. Overall, the initial analysis indicates this to be a profitable process and it is recommended the project move forward.

=Introduction=

Ethylene is a critical chemical precursor to a number of different industrial products. It is often derived from petroleum sources and polymerized to polyethylene, one of the most ubiquitous plastics today. (American Chemistry Council, 2013) Recently there has been a significant effort to develop production pathways utilizing biologically-derived feedstocks, such as corn or cellulosic ethanol, rather than traditional fossil-fuel sources. Ethylene can be produced from bioethanol via catalytic dehydration over an aluminum oxide catalyst. The proposed process converts 100,000 kg/hr of 95 wt% ethanol, 5% water feed to 53,000 kg/hr of 99.7% chemical-grade ethylene when operating at full capacity. This process was found to be economically viable with a 10-year net present value (NPV) of $131 million (2014 USD) and a payback period of approximately 2.7 years. This memo will detail the proposed process, as well as outline potential alternatives and economic viability of the project.

=Technical Approach=

Many bioethanol plants are located in the Midwest where large amounts of feedstock crops, such as corn, are grown. As such, this plant will be located in Story county, Iowa, near a large-scale bioethanol production plant. (DuPont Nevada Site, 2012) It is assumed that the supply of bioethanol is consistent and readily available. It is also assumed that other reagents - namely, the aluminum oxide catalyst, heater fuel, utility water and freon refrigerant - are readily available, and that wastewater treatment facilities are located near enough to facilitate the off-site treatment of wastewater. Plant capacity was based on current mid-sized industrial ethylene plants. (Designing Ethylene Plants, 2014)

HYSYS simulations were performed with the NRTL fluid package and Peng-Robinson vapor model. The NRTL fluid package is an activity coefficient model that is especially useful to model the separations of alcohols in aqueous solutions. (Suppes, 2015) In addition, NRTL uses models of binary pairs of components, much like the Wilson equation, to predict chemical interactions at the molecular level. The NRTL package can thus be easily extended to ternary and higher order chemical systems, making it ideal for this type of simulation. The Peng-Robinson vapor model was selected as it is well-suited to account for the non-idealities of the vapor phase reactions and separations integral to this process. (ASPENtech, 2014)

It was assumed that the feed enters the process at ambient temperature and pressure (25 °C, 1 atm) and at a consistent rate and composition with negligible quantities of impurities. The ethanol feed was assumed to be 95% ethanol and 5% water by mass, which is the commercial standard for industrial ethanol. (190 Proof Ethanol, 2012) Storage vessels for the feed ethanol, waste streams and products are assumed to be located nearby to the process. An initial feed pump compensates for pressure drops through the process and reduces the duty on downstream compressors. (Hadawey, 2015)

Natural gas, assumed to consist of 83% methane, 16% ethane and 1% nitrogen by mass, was supplied to two fired heaters at a flow rate estimated by HYSYS. (Methane, 2015) Air fed to the process to enable combustion was assumed to be 23% oxygen and 77% nitrogen by mass. (Composition of Air, 2015) Air streams were fed at 50% molar excess in order to ensure complete combustion and prevent the formation of carbon monoxide in the heater exhaust. Total flue gases are assumed to be 230,000 kg/hr, or 2.2 million tons annually, and consist of 73.8% nitrogen gas, 10.5% carbon dioxide, 8.2% water vapor, and 7.5% oxygen by mass. The only compound of concern in these emissions is the carbon dioxide, a known greenhouse gas. At the time of this report, the quantities of carbon dioxide emitted by this plant annually are within acceptable EPA specifications. (Summary of the Clean Air Act, 2015)

Due to the difficulty of simulation equilibrium and conversion reactions in a single vessel in HYSYS, these two reaction types were simulated in separate equilibrium reactor and conversion reactor units in series. In addition, while HYSYS indicated that reactor units would output separate vapor and liquid streams, it was assumed that in practice this would take the form of a single, two phase stream between each unit. To account for this, mixers were installed downstream of each reactor to combine the liquid and vapor phases of the reactor effluent. The three consequent reactions considered are as follows:
[[File:Equation.PNG|300px|center]]
The optimal reaction temperature was determined to be 400 °C, which promotes the equilibrium reaction of ethanol to ethylene while minimizing byproducts. (Zhang and Yu, 2013) While other byproducts may be produced in this process, these reactions are typically taken to comprise of the bulk of the dehydration reaction. Heat losses over these reactors were assumed to be negligible. (Zhang and Yu, 2013)All major process equipment is assumed to be constructed of high strength carbon steel. (AspenTech, 2012)

The “Sizing Utility” within the Icarus Economic Evaluation module was used to estimate sizes of major equipment based on the process simulation. These values can serve as a benchmark for an initial plant design. Icarus KbaseTM implements a wide variety of mechanical design standards, including ASME and BS5500, in order to calculate accurate equipment sizing. The Icarus sizing module combines equipment prices for standard chemical processing equipment as well as correlations and sizing factors. The advantage of using a software package such as HYSYS to price out individual equipment is that it utilizes up-to-date prices from vendors and distributors when estimating costs. A more in-depth overview of the correlations included in this software can be found in Towler and Sinnott (2009).

=Process Flowsheet=
[[File:Squarepfd_B1.PNG|thumb|400px|alt=Alt text|Fig 1: PFD of the Proposed Process]]

The following process is based primarily on a 1983 US patent titled “Process for dehydration of a low molecular weight alcohol.” (Barrocas and Baratelli, 1983) The process flow diagram can be seen in Figure 1. A larger version of the PFD is included in Appendix I and the HYSYS simulation setup in Appendix II.

The feed enters the process at a rate of 100,000 kg/hr, a temperature and pressure of a 25 °C and 1 atm and at a composition of 95 wt% ethanol and 5 wt% water.It is initially pressurized to 4335 kPa by centrifugal pump P-101 and subsequently heated to 400 °C by fired heater F-101. The heated and pressurized feed enters fixed bed reactor R-101 and contacts with the aluminum oxide catalyst. At this point it dehydrates to form the product, ethylene, as well as the byproducts water, hydrogen, diethyl ether and acetaldehyde. Fired heater F-102 and reactor R-102 increase the overall conversion of the process. Both fired heaters F-101 and F-102 are fueled with natural gas and fed with excess air. The composition of the reactor train effluent is 54.5 wt% ethylene, 37.1 wt% water, 8.1 wt% unreacted ethanol and trace amounts of diethyl ether, acetaldehyde, and hydrogen contaminants.

The pressure of the reactor train effluent is increased to 4500 kPa by compressor K-102 and the temperature decreased to 100 °C by exchange with cold water in heat exchanger E-201. The stream then expands and flashes in flash vessel FL-201, which separates out 82.3% of the unreacted ethanol, 96.6% of the water and virtually all of the acetaldehyde contaminant in the bottoms while sending the ethylene-rich vapor phase out of the top. The top product of FL-202 is compressed to 3500 kPA by K-202 and cooled to 0.0 °C by a freon refrigerant in E-202. At this point the stream is flashed for a second time in vessel FL-202 to remove additional impurities. The top outlet stream consists of 99.5 wt% ethylene, which is fed to the bottom of a 10-tray absorption column that removes a fraction of the residual diethyl ether as well as the remainder of the unreacted ethanol. A stream of absorbent water is fed to the top of the column at 10,000 kg/hr. The product exits the top of the column at a rate of 54,600 kg/hr and has a purity of 99.7% ethylene. Diethyl ether makes up 0.2% of the remaining product stream and is the primary contaminant. Trace amounts of residual water and hydrogen are also present.

Full tables of material and energy streams can be found in Appendices III and IV respectively.

==Process Alternatives==
===Reactor Alternatives===
Two fixed bed reactors, alternating with fired heaters, are used in the dehydration reaction of ethanol to ethylene. However, a fluidized bed reactor can offer better mixing and temperature control than a fixed bed reactor and thus provide the highest possible conversion of ethanol with the greatest selectivity to ethylene. (Tsao and Zasloff, 1979) Fluidized bed reactors also provide a lower rate of catalyst coking and byproduct formation, minimizing separation and catalyst regeneration costs. (Morschbacker, 2009) The major downside of fluidized bed reactors is that few large-scale processes have been built since the technology was developed in the late 1970s. (Tsao and Zasloff, 1979; Morschbacker, 2009) Although implementation of fluidized bed reactors could potentially increase the purity of the ethylene product and/or decrease costs, a small scale pilot process would need to be built and tested before it would be possible to develop an industrial-scale facility.

===Catalyst Alternatives===
Aluminum oxide, specifically gamma alumina, is the most industrially-common catalyst and has been historically used due to its low cost and high stability. (Tsao and Zasloff, 1979; Fan and Dai, n.d.) Recent improvements in selectivity and catalyst stability of activated alumina have been achieved by incorporating titanium oxide into the catalyst, although this increases reaction temperature by approximately 50 °C and decreases catalyst lifespan. (Chen and Li, et. al. 2007) There is also significant ongoing research into HZSM-5 zeolite and heteropolyacids, which are being explored as potential alternatives to alumina oxide. A nanoscale HZSM-5 zeolite catalyst has been shown to operate at the relatively low temperature of 200-300°C, with a 100% ethanol conversion and 99.7% selectivity to ethylene. Initial research has also indicated that it maintains greater than 98% selectivity for 630 operational hours. (Fan and Dai, n.d.) However, the current low cost and ready availability of unmodified alumina oxide makes it a better choice for a process of this scale.

===Purification Alternatives===
As specified in this process, the reactor effluent is purified by two flash drums and absorption with water to produce chemical-grade ethylene. If chemical-grade ethylene is indeed the desired product, other purification options include caustic washing of the reactor effluent and water removal in a desiccant drying bed. (Morschbacker, 2009) While this purification train is relatively simple and does not require harsh chemical reagents, polymer grade ethylene is more commercially valuable and the additional cost of removing water and diethyl ether contaminants may be justified by increased revenue. Cryogenic distillation was initially simulated to produce polymer-grade ethylene, but utility requirements were found to render this separation economically unviable. (Barrocas and Baratelli, 1983) Further research and optimization may find this purification strategy to be a more valid process. Alternatively, the addition of a cryogenic turboexpander or the use of alternative adsorbents may increase product purity to polymer grade. (Jumonville, 2010) Initial HYSYS simulations indicate that these operations may be feasible with further refinement.

===Wastewater Treatment===
Due to the large volume of wastewater produced, building an on-site wastewater treatment facility may prove to be more economical than paying for third-party wastewater treatment. Flash vessel FL-201 produces 44,600 L/hr of wastewater contaminated with 18.7 vol% ethanol and 0.6 vol% acetaldehyde, while FL-202 produces 2940 L/hr of an aqueous waste consisting of 56.8 vol% ethanol, 42.0 vol% water and 0.9 vol% diethyl ether. The absorption column produces approximately 10,200 liters/hr of wastewater contaminated with 1.2 vol% ethanol, 0.2% diethyl ether and 0.2% acetaldehyde. Utilizing distillation to separate these streams into clean water and volatile organic waste could ultimately reduce the quantity of waste that requires disposal and reduce the overall costs of the process.

==Process Equipment==
Relevant sizing information for each unit operation, estimated by the method described in the “Technical Approach,” can be found in Appendix V. Equipment and piping is assumed to be constructed of carbon steel. It should be noted that the two fired heaters are proportionately large enough to heat the entirety of the process stream and are thus larger than standard equipment.

=Economic Analysis=
[[File:NPV_B1.png|400px|thumb|Fig 2. Projected Cash Flow]]
[[File:sensitivityanalysis_B1.png|400px|thumb| Fig 3. Results of the Sensitivity Analysis on 10 year NPV]]

==Economics Overview==
All final values are normalized to June 2014 USD by CEPCI scaling. It is assumed that all products produced are sold at current market prices.

The Aspen Economic Evaluation module within HYSYS v8.0 was used to estimate capital and operating costs for a 10-year plant life span with a construction start date of April 2015. The price of the 95% ethanol feed stream was estimated at $1.44 per gallon, while the chemical grade ethylene produced is currently selling for approximately $1350 per metric ton. (Today in Energy, 2015; Weddle, 2014) Mapping and sizing calculations were performed by the economics module and a preliminary economic evaluation was completed. Equipment sizes, also estimated by HYSYS, were reviewed to ensure that height, diameter, and volume specifications were within realistic ranges.

The process was ideally projected to operate 360 days per year with a start-up time of one year. In addition, the tax rate was approximated at 40%, an interest rate at 20%, and a salvage value of 20%. Escalation percentages were compounded yearly for the product, raw material, and operating costs. The total capital cost for this process is approximately $16.4 million, which includes all equipment and piping described in the process. The most expensive equipment used in this process are the two fired heaters F-101 and F-102, which have an exceptionally large heat exchange area to adequately heat the feed. Standard heaters may not suffice and additional costs may be incurred for the raw materials and manufacture of this equipment. Including a feed preheater or additional fired heaters may reduce this cost in subsequent design iterations.

The total operating cost is approximately $465 million per year, about $427 million of which is the cost of the ethanol feed and natural gas for the two fired heaters. An additional $1.73 million per year is used for utilities including the cooling water and refrigerant. The labor and maintenance costs of this industrial process were also accounted for within the simulation’s economic analysis. The HYSYS simulation software, in conjunction with the Icarus economic analyzer, estimated there should be 5 operators per 8 hour shift with a cost per operator of $20 per hour. This results in a total operating labor cost of approximately $880,000 per year. In addition, the process will require one supervisor per shift with an hourly rate of $35 for total supervisor salaries of $307,000 per year. Finally, a fixed maintenance rate was estimated at $205,000 per 8000 hours of operation for a total cost of $225,000 per year.

Total product sales are roughly $640 million per year at full operation. The estimated income for this process is thus approximately $175 million per year. After ten years, the plant is projected to have a net present value (NPV) of $391 million and an internal rate of return of approximately 79%. In addition the payout period for the initial investment is estimated to be about 2.7 years. Figure 2 shows the projected cash flow for the project.

==Sensitivity Analysis==
A sensitivity analysis was performed to investigate the effects of fluctuating capital costs, operating costs, raw materials, utility costs and ethylene sales price on the 10-year net present value (NPV) of the project. This analysis was performed by scaling these cost factors according to typical ranges given in Towler and Sinnott and calculating the adjusting the NPV accordingly. The results, illustrated in Figure 3, indicate that the project value is most sensitive to product sales, raw materials costs, and operating costs. Ethylene and ethanol prices are market-determined and cannot be controlled for in the process design, so further optimization should be focused on minimizing the operations cost of the process. (Today in Energy, 2015; Weddle, 2014) However, in feed and product prices do still have a profound effect on profitability and feasibility. A more rigorous market analysis will better inform the profitability outlook.

=Conclusions/Recommendations=

The proposed process produces approximately 460,000 metric tons of 99.7 wt% ethylene annually, with a 10-year net present value of $131 million. If current economic conditions hold, it is recommended that this project proceed to implementation following further design improvements and optimization.

Future design iterations should focus on process optimization, particularly in minimizing operating costs as prescribed by the results of the sensitivity analysis. The development of a heat-exchanger network, potentially with Aspen Energy Analyzer, is one option for decreasing utility requirements and increasing the efficiency of the process overall. Optimization of the fired heaters could also result in decreased operational costs. Although overall profitability is less sensitive to capital costs, reviewing and adjusting equipment sizing would also improve the economic outlook. In particular, exploring alternative heating strategies at the beginning of the process could significantly decrease capital costs. Although there are not any particularly dangerous chemicals utilized in the process, an overall process review should also consider potential failure modes to minimize the safety risk to plant workers and nearby residents.

In addition to economic and safety considerations, harmful emissions and waste streams should be minimized both to bring down the cost of treatment and to decrease environmental effects. The two fired heaters consume a large amount of natural gas per year, emitting about 200,000 tons of CO2 annually, and account for more than half of the capital cost of the process. Although no known toxic gases are produced, carbon capture or other emissions-reduction methods should be considered. Additionally, enough wastewater is produced by this process that building an onsite wastewater treatment center should be considered. This could not only decrease operating costs by eliminating the need for an external contract but also give the plant more control over the final purity of the treated wastewater.

Finally, the current model assumes that all ethylene produced will be sold at a current prices and price or product sales will not be affected by economic variability. A more detailed study of the chemical-grade ethylene market, as well as a more thorough understanding of sales and distribution logistics, would increase the surety of a profitable process.

In summary, the proposed process yields chemical grade ethylene via the catalytic dehydration of ethanol. A 100,000 kg/hr of 95 wt% ethanol, 5% water feed is converted to 53,000 kg/hr of 99.7% chemical-grade ethylene. After 10 years of operation, including a one-year startup time, the process has an NPV of $391 million with an IRR of 79% and a payback period of 2.7 years.
Pending further optimization, this process was determined to be viable and it is recommended for the project to move forward.

=References=

ASPENtech. Appendix A - Property Methods and Calculations. Simulation Basics; A-3 - A-26. 2014.

AspenTech. Aspen HYSYS Help File v8.0. Aspen Technology, Inc. 2012.

Barrocas H, Baratelli F, inventors; Petroleo Brasileiro S.A., assignee. Process for dehydration of a low molecular weight alcohol. US patent 4,396,789 A. August 2, 1983.

Chen G, Li S, Jiao F, Yuan Q. Catalytic dehydration of bioethanol to ethylene over TiO2/γ-Al2O3 catalysts in microchannel reactors. Catal. Today 2007, 125, 111–119.

Composition of Air [Internet]. Engineering Toolbox; [cited 13 Mar 2015]. Available from: http://www.engineeringtoolbox.com/air-composition-d_212.html.

Designing Ethylene Plants. Ethylene [Internet]. Technip; 2014 [cited 13 Mar 2015]. Available from: http://www.technip.com/en/our-business/onshore/ethylene.

DuPont Nevada Site Cellulosic Ethanol Facility [Internet]. DuPont Chemical; c2012-2015 [cited 11 Mar 2015]. Available from: http://biofuels.dupont.com/cellulosic-ethanol/nevada-site-ce-facility/.

Fan D, Dai DJ, Wu HS. Ethylene Formation by Catalytic Dehydration of Ethanol with Industrial Considerations. Materials. 6, 101-115. doi: 10.3390/ma6010101.

Hadawey A, Ge Y, Tassou TSA. Energy Savings Through Liquid Pressure Amplification In A Dairy Plant Refrigeration System. The Centre for Energy and Built Environment Research [cited 13 Mar. 2015].

Jumonville, J. Tutorial on Cryogenic Turboexpanders. Proceedings of the Thirty-Ninth Turbomachinery Symposium; 2010 Oct 4-7; Houston, TX. Houston: Texas A&M University; 2010.

Britannica.com. Methane (Chemical Compound). Encyclopædia Britannica Online; c2015 [cited 13 Mar. 2015] Available from: http://www.britannica.com/EBchecked/topic/378264/methane.

Morschbacker, A. Bio-Ethanol Based Ethylene. Polymer Reviews. 2009; 49:79-84.

Statista.com. Production of chemicals and plastics in the U.S. in 2013, by type (in 1,000 metric tons) [Internet]. American Chemistry Council; c2014 [cited 15 Jan 2015]. Available from: http://www.statista.com/statistics/299725/total-us-plastics-and-chemicals-shipments-by-type/.

Epa.gov. Summary of the Clean Air Act, 2015. United States Environmental Protection Agency. [cited 13 Mar. 2015] Available from: http://www2.epa.gov/laws-regulations/summary-clean-air-act.

Suppes GJ. Selecting Thermodynamic Models for Process Simulation of Organic VLE and LLE Systems. The University of Missouri-Columbia, Dept of Chemical Engineering. [cited 13 Mar. 2015].

Today in Energy - Daily Prices. US Energy Information Administration website. http://www.eia.gov/todayinenergy/prices.cfm. Accessed March 3rd 2015.

Towler G, Sinnott R. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. 2nd ed. Boston: Elsevier; 2013.

Tsao U, Zasloff HB, inventors; The Lummus Company, assignee. Production of ethylene from ethanol. US patent 4,134,926. January 16, 1979.

Weddle, N. ICIS Pricing: Ethylene (Europe). Reed Business Limited. January 10 2014.

Zhang M, Yu Y. Dehydration of Ethanol to Ethylene. Industrial Engineering and Chemical Research. 2013; 52:9505-9514.

190 Proof Ethanol: Technical Data Sheet [Internet]. Decon Labs Inc; 2012 [cited 13 Mar 2015]. Available from: http://www.deconlabs.com/tds/ETHANOL%20190%20%20PROOF.pdf.

=Appendix I - Process Flow Diagram=
[[File:PFD B1.JPG|1200px|center]]

=Appendix II - HYSYS Simulation=
[[File:HYSYS_B1.PNG|center|1200px]]

=Appendix III - Material Streams=
[[File:Streams_B1.png|1200px]]

=Appendix IV - Energy Table=
[[File:Energy_B1.png|600px|center]]

[[File:Utilities.PNG|600px|center]]

=Appendix V - Equipment Sizing=
[[File:Equipment sizes.png|center]] 

=Appendix VI - Economics=
[[File:Econsummary_B1.png|center]] 

[[File:Capcost_B1.png|center]]

Ethanol to Ethylene (B1)

2015-03-14T05:00:28Z

Hpoppick:

[[File:BFD_B1.png|600px|thumbnail|alt=Alt text|Conversion of Ethanol to Ethylene]]

Team B1 Final Report

Authors: Harry Poppick, Emm Fulk and Scott Smith

Instructors: Fengqi You, David Wegerer

March 13, 2015

=Executive Summary=

The following report outlines the design and analysis of a process converting ethanol to chemical-grade ethylene via catalytic dehydration. This process consumers 100,000 kg/hr of 95 wt% ethanol, 5 wt% water feedstock and produces 53,000 kg/hr of 99.7 wt% chemical-grade ethylene. The ethanol feed passes through two fixed-bed reactors, each packed with an aluminum oxide catalyst, and the resulting ethylene is purified by two flash tanks and by absorption with water. The process was modeled using Aspen HYSYS simulation software to estimate mass and energy flows and equipment sizing requirements. Based on results of this initial simulation, several alternatives are discussed for increasing the process efficiency and profitability. The use of a fluidized bed reactor or a more ethylene-selective catalyst could increase the production of ethylene per ethanol basis. Additionally, several methods of purification to more valuable polymer-grade ethylene are proposed.

The economic feasibility of this process was evaluated using Aspen Economic Analyzer with the Icarus economics package. Capital cost is approximately $16.4 million total with an operating cost of $465 million per year. The current market prices of the ethanol feed and ethylene sales price are $1.44/gallon and $1350/metric ton respectively. The cost of feed ethanol, process utilities and miscellaneous operational costs total to about $427 million/year. At full operation, revenue at current prices would be approximately $640 million per year. The predicted 10-year net present value of the process is approximately $391 million with an IRR of 79% and a payback period of 2.7 years. A sensitivity analysis indicates that the process is most sensitive to feed prices, product prices and operation cost.

Several recommendations are made for both cost reduction and profit maximization, including the design of a heat exchanger network and the optimization of fired heaters that require high capital investment and large amounts of fuel. A safety review of the process is recommended, as well as the minimization of flue gas effluent and wastewater. It is also suggested that the construction of an onsite wastewater treatment center be considered. Overall, the initial analysis indicates this to be a profitable process and it is recommended the project move forward.

=Introduction=

Ethylene is a critical chemical precursor to a number of different industrial products. It is often derived from petroleum sources and polymerized to polyethylene, one of the most ubiquitous plastics today. (American Chemistry Council, 2013) Recently there has been a significant effort to develop production pathways utilizing biologically-derived feedstocks, such as corn or cellulosic ethanol, rather than traditional fossil-fuel sources. Ethylene can be produced from bioethanol via catalytic dehydration over an aluminum oxide catalyst. The proposed process converts 100,000 kg/hr of 95 wt% ethanol, 5% water feed to 53,000 kg/hr of 99.7% chemical-grade ethylene when operating at full capacity. This process was found to be economically viable with a 10-year net present value (NPV) of $131 million (2014 USD) and a payback period of approximately 2.7 years. This memo will detail the proposed process, as well as outline potential alternatives and economic viability of the project.

=Technical Approach=

Many bioethanol plants are located in the Midwest where large amounts of feedstock crops, such as corn, are grown. As such, this plant will be located in Story county, Iowa, near a large-scale bioethanol production plant. (DuPont Nevada Site, 2012) It is assumed that the supply of bioethanol is consistent and readily available. It is also assumed that other reagents - namely, the aluminum oxide catalyst, heater fuel, utility water and freon refrigerant - are readily available, and that wastewater treatment facilities are located near enough to facilitate the off-site treatment of wastewater. Plant capacity was based on current mid-sized industrial ethylene plants. (Designing Ethylene Plants, 2014)

HYSYS simulations were performed with the NRTL fluid package and Peng-Robinson vapor model. The NRTL fluid package is an activity coefficient model that is especially useful to model the separations of alcohols in aqueous solutions. (Suppes, 2015) In addition, NRTL uses models of binary pairs of components, much like the Wilson equation, to predict chemical interactions at the molecular level. The NRTL package can thus be easily extended to ternary and higher order chemical systems, making it ideal for this type of simulation. The Peng-Robinson vapor model was selected as it is well-suited to account for the non-idealities of the vapor phase reactions and separations integral to this process. (ASPENtech, 2014)

It was assumed that the feed enters the process at ambient temperature and pressure (25 °C, 1 atm) and at a consistent rate and composition with negligible quantities of impurities. The ethanol feed was assumed to be 95% ethanol and 5% water by mass, which is the commercial standard for industrial ethanol. (190 Proof Ethanol, 2012) Storage vessels for the feed ethanol, waste streams and products are assumed to be located nearby to the process. An initial feed pump compensates for pressure drops through the process and reduces the duty on downstream compressors. (Hadawey, 2015)

Natural gas, assumed to consist of 83% methane, 16% ethane and 1% nitrogen by mass, was supplied to two fired heaters at a flow rate estimated by HYSYS. (Methane, 2015) Air fed to the process to enable combustion was assumed to be 23% oxygen and 77% nitrogen by mass. (Composition of Air, 2015) Air streams were fed at 50% molar excess in order to ensure complete combustion and prevent the formation of carbon monoxide in the heater exhaust. Total flue gases are assumed to be 230,000 kg/hr, or 2.2 million tons annually, and consist of 73.8% nitrogen gas, 10.5% carbon dioxide, 8.2% water vapor, and 7.5% oxygen by mass. The only compound of concern in these emissions is the carbon dioxide, a known greenhouse gas. At the time of this report, the quantities of carbon dioxide emitted by this plant annually are within acceptable EPA specifications. (Summary of the Clean Air Act, 2015)

Due to the difficulty of simulation equilibrium and conversion reactions in a single vessel in HYSYS, these two reaction types were simulated in separate equilibrium reactor and conversion reactor units in series. In addition, while HYSYS indicated that reactor units would output separate vapor and liquid streams, it was assumed that in practice this would take the form of a single, two phase stream between each unit. To account for this, mixers were installed downstream of each reactor to combine the liquid and vapor phases of the reactor effluent. The three consequent reactions considered are as follows:
[[File:Equation.PNG|300px|center]]
The optimal reaction temperature was determined to be 400 °C, which promotes the equilibrium reaction of ethanol to ethylene while minimizing byproducts. (Zhang and Yu, 2013) While other byproducts may be produced in this process, these reactions are typically taken to comprise of the bulk of the dehydration reaction. Heat losses over these reactors were assumed to be negligible. (Zhang and Yu, 2013)All major process equipment is assumed to be constructed of high strength carbon steel. (AspenTech, 2012)

The “Sizing Utility” within the Icarus Economic Evaluation module was used to estimate sizes of major equipment based on the process simulation. These values can serve as a benchmark for an initial plant design. Icarus KbaseTM implements a wide variety of mechanical design standards, including ASME and BS5500, in order to calculate accurate equipment sizing. The Icarus sizing module combines equipment prices for standard chemical processing equipment as well as correlations and sizing factors. The advantage of using a software package such as HYSYS to price out individual equipment is that it utilizes up-to-date prices from vendors and distributors when estimating costs. A more in-depth overview of the correlations included in this software can be found in Towler and Sinnott (2009).

=Process Flowsheet=
[[File:Squarepfd_B1.PNG|thumb|400px|alt=Alt text|Fig 1: PFD of the Proposed Process]]

The following process is based primarily on a 1983 US patent titled “Process for dehydration of a low molecular weight alcohol.” (Barrocas and Baratelli, 1983) The process flow diagram can be seen in Figure 1. A larger version of the PFD is included in Appendix I and the HYSYS simulation setup in Appendix II.

The feed enters the process at a rate of 100,000 kg/hr, a temperature and pressure of a 25 °C and 1 atm and at a composition of 95 wt% ethanol and 5 wt% water.It is initially pressurized to 4335 kPa by centrifugal pump P-101 and subsequently heated to 400 °C by fired heater F-101. The heated and pressurized feed enters fixed bed reactor R-101 and contacts with the aluminum oxide catalyst. At this point it dehydrates to form the product, ethylene, as well as the byproducts water, hydrogen, diethyl ether and acetaldehyde. Fired heater F-102 and reactor R-102 increase the overall conversion of the process. Both fired heaters F-101 and F-102 are fueled with natural gas and fed with excess air. The composition of the reactor train effluent is 54.5 wt% ethylene, 37.1 wt% water, 8.1 wt% unreacted ethanol and trace amounts of diethyl ether, acetaldehyde, and hydrogen contaminants.

The pressure of the reactor train effluent is increased to 4500 kPa by compressor K-102 and the temperature decreased to 100 °C by exchange with cold water in heat exchanger E-201. The stream then expands and flashes in flash vessel FL-201, which separates out 82.3% of the unreacted ethanol, 96.6% of the water and virtually all of the acetaldehyde contaminant in the bottoms while sending the ethylene-rich vapor phase out of the top. The top product of FL-202 is compressed to 3500 kPA by K-202 and cooled to 0.0 °C by a freon refrigerant in E-202. At this point the stream is flashed for a second time in vessel FL-202 to remove additional impurities. The top outlet stream consists of 99.5 wt% ethylene, which is fed to the bottom of a 10-tray absorption column that removes a fraction of the residual diethyl ether as well as the remainder of the unreacted ethanol. A stream of absorbent water is fed to the top of the column at 10,000 kg/hr. The product exits the top of the column at a rate of 54,600 kg/hr and has a purity of 99.7% ethylene. Diethyl ether makes up 0.2% of the remaining product stream and is the primary contaminant. Trace amounts of residual water and hydrogen are also present.

Full tables of material and energy streams can be found in Appendices III and IV respectively.

==Process Alternatives==
===Reactor Alternatives===
Two fixed bed reactors, alternating with fired heaters, are used in the dehydration reaction of ethanol to ethylene. However, a fluidized bed reactor can offer better mixing and temperature control than a fixed bed reactor and thus provide the highest possible conversion of ethanol with the greatest selectivity to ethylene. (Tsao and Zasloff, 1979) Fluidized bed reactors also provide a lower rate of catalyst coking and byproduct formation, minimizing separation and catalyst regeneration costs. (Morschbacker, 2009) The major downside of fluidized bed reactors is that few large-scale processes have been built since the technology was developed in the late 1970s. (Tsao and Zasloff, 1979; Morschbacker, 2009) Although implementation of fluidized bed reactors could potentially increase the purity of the ethylene product and/or decrease costs, a small scale pilot process would need to be built and tested before it would be possible to develop an industrial-scale facility.

===Catalyst Alternatives===
Aluminum oxide, specifically gamma alumina, is the most industrially-common catalyst and has been historically used due to its low cost and high stability. (Tsao and Zasloff, 1979; Fan and Dai, n.d.) Recent improvements in selectivity and catalyst stability of activated alumina have been achieved by incorporating titanium oxide into the catalyst, although this increases reaction temperature by approximately 50 °C and decreases catalyst lifespan. (Chen and Li, et. al. 2007) There is also significant ongoing research into HZSM-5 zeolite and heteropolyacids, which are being explored as potential alternatives to alumina oxide. A nanoscale HZSM-5 zeolite catalyst has been shown to operate at the relatively low temperature of 200-300°C, with a 100% ethanol conversion and 99.7% selectivity to ethylene. Initial research has also indicated that it maintains greater than 98% selectivity for 630 operational hours. (Fan and Dai, n.d.) However, the current low cost and ready availability of unmodified alumina oxide makes it a better choice for a process of this scale.

===Purification Alternatives===
As specified in this process, the reactor effluent is purified by two flash drums and absorption with water to produce chemical-grade ethylene. If chemical-grade ethylene is indeed the desired product, other purification options include caustic washing of the reactor effluent and water removal in a desiccant drying bed. (Morschbacker, 2009) While this purification train is relatively simple and does not require harsh chemical reagents, polymer grade ethylene is more commercially valuable and the additional cost of removing water and diethyl ether contaminants may be justified by increased revenue. Cryogenic distillation was initially simulated to produce polymer-grade ethylene, but utility requirements were found to render this separation economically unviable. (Barrocas and Baratelli, 1983) Further research and optimization may find this purification strategy to be a more valid process. Alternatively, the addition of a cryogenic turboexpander or the use of alternative adsorbents may increase product purity to polymer grade. (Jumonville, 2010) Initial HYSYS simulations indicate that these operations may be feasible with further refinement.

===Wastewater Treatment===
Due to the large volume of wastewater produced, building an on-site wastewater treatment facility may prove to be more economical than paying for third-party wastewater treatment. Flash vessel FL-201 produces 44,600 L/hr of wastewater contaminated with 18.7 vol% ethanol and 0.6 vol% acetaldehyde, while FL-202 produces 2940 L/hr of an aqueous waste consisting of 56.8 vol% ethanol, 42.0 vol% water and 0.9 vol% diethyl ether. The absorption column produces approximately 10,200 liters/hr of wastewater contaminated with 1.2 vol% ethanol, 0.2% diethyl ether and 0.2% acetaldehyde. Utilizing distillation to separate these streams into clean water and volatile organic waste could ultimately reduce the quantity of waste that requires disposal and reduce the overall costs of the process.

==Process Equipment==
Relevant sizing information for each unit operation, estimated by the method described in the “Technical Approach,” can be found in Appendix V. Equipment and piping is assumed to be constructed of carbon steel. It should be noted that the two fired heaters are proportionately large enough to heat the entirety of the process stream and are thus larger than standard equipment.

=Economic Analysis=
[[File:NPV_B1.png|400px|thumb|Fig 2. Projected Cash Flow]]
[[File:sensitivityanalysis_B1.png|400px|thumb| Fig 3. Results of the Sensitivity Analysis on 10 year NPV]]

==Economics Overview==
All final values are normalized to June 2014 USD by CEPCI scaling. It is assumed that all products produced are sold at current market prices.

The Aspen Economic Evaluation module within HYSYS v8.0 was used to estimate capital and operating costs for a 10-year plant life span with a construction start date of April 2015. The price of the 95% ethanol feed stream was estimated at $1.44 per gallon, while the chemical grade ethylene produced is currently selling for approximately $1350 per metric ton. (Today in Energy, 2015; Weddle, 2014) Mapping and sizing calculations were performed by the economics module and a preliminary economic evaluation was completed. Equipment sizes, also estimated by HYSYS, were reviewed to ensure that height, diameter, and volume specifications were within realistic ranges.

The process was ideally projected to operate 360 days per year with a start-up time of one year. In addition, the tax rate was approximated at 40%, an interest rate at 20%, and a salvage value of 20%. Escalation percentages were compounded yearly for the product, raw material, and operating costs. The total capital cost for this process is approximately $16.4 million, which includes all equipment and piping described in the process. The most expensive equipment used in this process are the two fired heaters F-101 and F-102, which have an exceptionally large heat exchange area to adequately heat the feed. Standard heaters may not suffice and additional costs may be incurred for the raw materials and manufacture of this equipment. Including a feed preheater or additional fired heaters may reduce this cost in subsequent design iterations.

The total operating cost is approximately $465 million per year, about $427 million of which is the cost of the ethanol feed and natural gas for the two fired heaters. An additional $1.73 million per year is used for utilities including the cooling water and refrigerant. The labor and maintenance costs of this industrial process were also accounted for within the simulation’s economic analysis. The HYSYS simulation software, in conjunction with the Icarus economic analyzer, estimated there should be 5 operators per 8 hour shift with a cost per operator of $20 per hour. This results in a total operating labor cost of approximately $880,000 per year. In addition, the process will require one supervisor per shift with an hourly rate of $35 for total supervisor salaries of $307,000 per year. Finally, a fixed maintenance rate was estimated at $205,000 per 8000 hours of operation for a total cost of $225,000 per year.

Total product sales are roughly $640 million per year at full operation. The estimated income for this process is thus approximately $175 million per year. After ten years, the plant is projected to have a net present value (NPV) of $391 million and an internal rate of return of approximately 79%. In addition the payout period for the initial investment is estimated to be about 2.7 years. Figure 2 shows the projected cash flow for the project.

==Sensitivity Analysis==
A sensitivity analysis was performed to investigate the effects of fluctuating capital costs, operating costs, raw materials, utility costs and ethylene sales price on the 10-year net present value (NPV) of the project. This analysis was performed by scaling these cost factors according to typical ranges given in Towler and Sinnott and calculating the adjusting the NPV accordingly. The results, illustrated in Figure 3, indicate that the project value is most sensitive to product sales, raw materials costs, and operating costs. Ethylene and ethanol prices are market-determined and cannot be controlled for in the process design, so further optimization should be focused on minimizing the operations cost of the process. (Today in Energy, 2015; Weddle, 2014) However, in feed and product prices do still have a profound effect on profitability and feasibility. A more rigorous market analysis will better inform the profitability outlook.

=Conclusions/Recommendations=

The proposed process produces approximately 460,000 metric tons of 99.7 wt% ethylene annually, with a 10-year net present value of $131 million. If current economic conditions hold, it is recommended that this project proceed to implementation following further design improvements and optimization.

Future design iterations should focus on process optimization, particularly in minimizing operating costs as prescribed by the results of the sensitivity analysis. The development of a heat-exchanger network, potentially with Aspen Energy Analyzer, is one option for decreasing utility requirements and increasing the efficiency of the process overall. Optimization of the fired heaters could also result in decreased operational costs. Although overall profitability is less sensitive to capital costs, reviewing and adjusting equipment sizing would also improve the economic outlook. In particular, exploring alternative heating strategies at the beginning of the process could significantly decrease capital costs. Although there are not any particularly dangerous chemicals utilized in the process, an overall process review should also consider potential failure modes to minimize the safety risk to plant workers and nearby residents.

In addition to economic and safety considerations, harmful emissions and waste streams should be minimized both to bring down the cost of treatment and to decrease environmental effects. The two fired heaters consume a large amount of natural gas per year, emitting about 200,000 tons of CO2 annually, and account for more than half of the capital cost of the process. Although no known toxic gases are produced, carbon capture or other emissions-reduction methods should be considered. Additionally, enough wastewater is produced by this process that building an onsite wastewater treatment center should be considered. This could not only decrease operating costs by eliminating the need for an external contract but also give the plant more control over the final purity of the treated wastewater.

Finally, the current model assumes that all ethylene produced will be sold at a current prices and price or product sales will not be affected by economic variability. A more detailed study of the chemical-grade ethylene market, as well as a more thorough understanding of sales and distribution logistics, would increase the surety of a profitable process.

In summary, the proposed process yields chemical grade ethylene via the catalytic dehydration of ethanol. A 100,000 kg/hr of 95 wt% ethanol, 5% water feed is converted to 53,000 kg/hr of 99.7% chemical-grade ethylene. After 10 years of operation, including a one-year startup time, the process has an NPV of $391 million with an IRR of 79% and a payback period of 2.7 years.
Pending further optimization, this process was determined to be viable and it is recommended for the project to move forward.

=References=

[1] American Chemistry Council. Production of chemicals and plastics in the U.S. in 2013, by type (in 1,000 metric tons). In Statista - The Statistics Portal. August 2014. Available at http://www.statista.com/statistics/299725/total-us-plastics-and-chemicals-shipments-by-type/, Accessed January 15, 2015. – Relative proportions of plastics production.

[2] DuPont Nevada Site Cellulosic Ethanol Facility [Internet]. DuPont Chemical; c2012-2015 [cited 11 Mar. 2015]. Available from: http://biofuels.dupont.com/cellulosic-ethanol/nevada-site-ce-facility/. -- Information on ethanol production in Iowa.

[3] Designing Ethylene Plants. Ethylene [Internet]. Technip; 2014 [cited 13 Mar. 2015]. Available from: http://www.technip.com/en/our-business/onshore/ethylene -- Plant size ranges.

[4] Suppes GJ. Selecting Thermodynamic Models for Process Simulation of Organic VLE and LLE Systems. The University of Missouri-Columbia, Dept of Chemical Engineering. [cited 13 Mar. 2015]. -- Use of NRTL in alcohol separations.

[5] ASPENtech. Appendix A - Property Methods and Calculations. Simulation Basics; A-3 - A-26. 2014.

[6] 190 Proof Ethanol: Technical Data Sheet [Internet]. Decon Labs Inc; 2012 [cited 13 Mar. 2015]. Available from: http://www.deconlabs.com/tds/ETHANOL%20190%20%20PROOF.pdf -- Information regarding 95% ethanol

[7] Hadawey A, Ge Y, Tassou TSA. Energy Savings Through Liquid Pressure Amplification In A Dairy Plant Refrigeration System. The Centre for Energy and Built Environment Research [cited 13 Mar. 2015].

[8] Methane (Chemical Compound). 2015. Encyclopædia Britannica Online. [cited 13 Mar. 2015] Available from: http://www.britannica.com/EBchecked/topic/378264/methane -- Composition of Methane

[9] Composition of Air [Internet]. Engineering Toolbox; [cited 13 Mar. 2015]. Available from: http://www.engineeringtoolbox.com/air-composition-d_212.html. -- Composition of air.

[10] Summary of the Clean Air Act, 2015. United States Environmental Protection Agency. [cited 13 Mar. 2015] Available from: http://www2.epa.gov/laws-regulations/summary-clean-air-act -- Emissions requirements of chemical plants.

[11] Zhang M, Yu Y. Dehydration of Ethanol to Ethylene. Industrial Engineering and Chemical Research. 2013; 52:9505-9514. – Technical information on ethanol to ethylene conversion via dehydration.

[12] AspenTech. Aspen HYSYS Help File v8.0. Aspen Technology, Inc. 2012. - Aspen HYSYS help file used for troubleshooting and assistance on economic analysis.

[13] Towler G, Sinnott R. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. 2nd ed. Boston: Elsevier; 2013. -- General Reference Book

[14] Barrocas H, Baratelli F, inventors; Petroleo Brasileiro S.A., assignee. Process for dehydration of a low molecular weight alcohol. US patent 4,396,789 A. August 2, 1983. - Primary background for process design.

[15] Tsao U, Zasloff HB, inventors; The Lummus Company, assignee. Production of ethylene from ethanol. US patent 4,134,926. January 16, 1979. – Patent for catalytic dehydration of ethylene in a fluidized bed reactor.

[16] Morschbacker, A. Bio-Ethanol Based Ethylene. Polymer Reviews. 2009; 49:79-84. – Overview of bioethanol dehydration process development.

[17] Fan D, Dai DJ, Wu HS. Ethylene Formation by Catalytic Dehydration of Ethanol with Industrial Considerations. Materials. 6, 101-115. doi: 10.3390/ma6010101. - Comparison of types of catalysts used in the dehydration of ethanol and current research into new catalysts.

[18] Chen G, Li S, Jiao F, Yuan Q. Catalytic dehydration of bioethanol to ethylene over TiO2/γ-Al2O3 catalysts in microchannel reactors. Catal. Today 2007, 125, 111–119. - Paper introducing research on modified alumina catalyst for ethanol dehydration.

[19] Jumonville, J. Tutorial on Cryogenic Turboexpanders. Proceedings of the Thirty-Ninth Turbomachinery Symposium; 2010 Oct 4-7; Houston, TX. Houston: Texas A&M University; 2010. -- Use of turboexpander for cryogenic separations

[20] Today in Energy - Daily Prices. US Energy Information Administration website. http://www.eia.gov/todayinenergy/prices.cfm. Accessed March 3rd 2015. - Bulk market price for 95% ethanol.

[21] Weddle, N. ICIS Pricing: Ethylene (Europe). Reed Business Limited. January 10 2014. - Bulk market price for chemical grade ethylene.

=Appendix I - Process Flow Diagram=
[[File:PFD B1.JPG|1200px|center]]

=Appendix II - HYSYS Simulation=
[[File:HYSYS_B1.PNG|center|1200px]]

=Appendix III - Material Streams=
[[File:Streams_B1.png|1200px]]

=Appendix IV - Energy Table=
[[File:Energy_B1.png|600px|center]]

[[File:Utilities.PNG|600px|center]]

=Appendix V - Equipment Sizing=
[[File:Equipment sizes.png|center]] 

=Appendix VI - Economics=
[[File:Econsummary_B1.png|center]] 

[[File:Capcost_B1.png|center]]

File:Equipment sizes.png

2015-03-14T05:00:14Z

Hpoppick:

Ethanol to Ethylene (B1)

2015-03-14T04:59:39Z

Hpoppick:

[[File:BFD_B1.png|600px|thumbnail|alt=Alt text|Conversion of Ethanol to Ethylene]]

Team B1 Final Report

Authors: Harry Poppick, Emm Fulk and Scott Smith

Instructors: Fengqi You, David Wegerer

March 13, 2015

=Executive Summary=

The following report outlines the design and analysis of a process converting ethanol to chemical-grade ethylene via catalytic dehydration. This process consumers 100,000 kg/hr of 95 wt% ethanol, 5 wt% water feedstock and produces 53,000 kg/hr of 99.7 wt% chemical-grade ethylene. The ethanol feed passes through two fixed-bed reactors, each packed with an aluminum oxide catalyst, and the resulting ethylene is purified by two flash tanks and by absorption with water. The process was modeled using Aspen HYSYS simulation software to estimate mass and energy flows and equipment sizing requirements. Based on results of this initial simulation, several alternatives are discussed for increasing the process efficiency and profitability. The use of a fluidized bed reactor or a more ethylene-selective catalyst could increase the production of ethylene per ethanol basis. Additionally, several methods of purification to more valuable polymer-grade ethylene are proposed.

The economic feasibility of this process was evaluated using Aspen Economic Analyzer with the Icarus economics package. Capital cost is approximately $16.4 million total with an operating cost of $465 million per year. The current market prices of the ethanol feed and ethylene sales price are $1.44/gallon and $1350/metric ton respectively. The cost of feed ethanol, process utilities and miscellaneous operational costs total to about $427 million/year. At full operation, revenue at current prices would be approximately $640 million per year. The predicted 10-year net present value of the process is approximately $391 million with an IRR of 79% and a payback period of 2.7 years. A sensitivity analysis indicates that the process is most sensitive to feed prices, product prices and operation cost.

Several recommendations are made for both cost reduction and profit maximization, including the design of a heat exchanger network and the optimization of fired heaters that require high capital investment and large amounts of fuel. A safety review of the process is recommended, as well as the minimization of flue gas effluent and wastewater. It is also suggested that the construction of an onsite wastewater treatment center be considered. Overall, the initial analysis indicates this to be a profitable process and it is recommended the project move forward.

=Introduction=

Ethylene is a critical chemical precursor to a number of different industrial products. It is often derived from petroleum sources and polymerized to polyethylene, one of the most ubiquitous plastics today. (American Chemistry Council, 2013) Recently there has been a significant effort to develop production pathways utilizing biologically-derived feedstocks, such as corn or cellulosic ethanol, rather than traditional fossil-fuel sources. Ethylene can be produced from bioethanol via catalytic dehydration over an aluminum oxide catalyst. The proposed process converts 100,000 kg/hr of 95 wt% ethanol, 5% water feed to 53,000 kg/hr of 99.7% chemical-grade ethylene when operating at full capacity. This process was found to be economically viable with a 10-year net present value (NPV) of $131 million (2014 USD) and a payback period of approximately 2.7 years. This memo will detail the proposed process, as well as outline potential alternatives and economic viability of the project.

=Technical Approach=

Many bioethanol plants are located in the Midwest where large amounts of feedstock crops, such as corn, are grown. As such, this plant will be located in Story county, Iowa, near a large-scale bioethanol production plant. (DuPont Nevada Site, 2012) It is assumed that the supply of bioethanol is consistent and readily available. It is also assumed that other reagents - namely, the aluminum oxide catalyst, heater fuel, utility water and freon refrigerant - are readily available, and that wastewater treatment facilities are located near enough to facilitate the off-site treatment of wastewater. Plant capacity was based on current mid-sized industrial ethylene plants. (Designing Ethylene Plants, 2014)

HYSYS simulations were performed with the NRTL fluid package and Peng-Robinson vapor model. The NRTL fluid package is an activity coefficient model that is especially useful to model the separations of alcohols in aqueous solutions. (Suppes, 2015) In addition, NRTL uses models of binary pairs of components, much like the Wilson equation, to predict chemical interactions at the molecular level. The NRTL package can thus be easily extended to ternary and higher order chemical systems, making it ideal for this type of simulation. The Peng-Robinson vapor model was selected as it is well-suited to account for the non-idealities of the vapor phase reactions and separations integral to this process. (ASPENtech, 2014)

It was assumed that the feed enters the process at ambient temperature and pressure (25 °C, 1 atm) and at a consistent rate and composition with negligible quantities of impurities. The ethanol feed was assumed to be 95% ethanol and 5% water by mass, which is the commercial standard for industrial ethanol. (190 Proof Ethanol, 2012) Storage vessels for the feed ethanol, waste streams and products are assumed to be located nearby to the process. An initial feed pump compensates for pressure drops through the process and reduces the duty on downstream compressors. (Hadawey, 2015)

Natural gas, assumed to consist of 83% methane, 16% ethane and 1% nitrogen by mass, was supplied to two fired heaters at a flow rate estimated by HYSYS. (Methane, 2015) Air fed to the process to enable combustion was assumed to be 23% oxygen and 77% nitrogen by mass. (Composition of Air, 2015) Air streams were fed at 50% molar excess in order to ensure complete combustion and prevent the formation of carbon monoxide in the heater exhaust. Total flue gases are assumed to be 230,000 kg/hr, or 2.2 million tons annually, and consist of 73.8% nitrogen gas, 10.5% carbon dioxide, 8.2% water vapor, and 7.5% oxygen by mass. The only compound of concern in these emissions is the carbon dioxide, a known greenhouse gas. At the time of this report, the quantities of carbon dioxide emitted by this plant annually are within acceptable EPA specifications. (Summary of the Clean Air Act, 2015)

Due to the difficulty of simulation equilibrium and conversion reactions in a single vessel in HYSYS, these two reaction types were simulated in separate equilibrium reactor and conversion reactor units in series. In addition, while HYSYS indicated that reactor units would output separate vapor and liquid streams, it was assumed that in practice this would take the form of a single, two phase stream between each unit. To account for this, mixers were installed downstream of each reactor to combine the liquid and vapor phases of the reactor effluent. The three consequent reactions considered are as follows:
[[File:Equation.PNG|300px|center]]
The optimal reaction temperature was determined to be 400 °C, which promotes the equilibrium reaction of ethanol to ethylene while minimizing byproducts. (Zhang and Yu, 2013) While other byproducts may be produced in this process, these reactions are typically taken to comprise of the bulk of the dehydration reaction. Heat losses over these reactors were assumed to be negligible. (Zhang and Yu, 2013)All major process equipment is assumed to be constructed of high strength carbon steel. (AspenTech, 2012)

The “Sizing Utility” within the Icarus Economic Evaluation module was used to estimate sizes of major equipment based on the process simulation. These values can serve as a benchmark for an initial plant design. Icarus KbaseTM implements a wide variety of mechanical design standards, including ASME and BS5500, in order to calculate accurate equipment sizing. The Icarus sizing module combines equipment prices for standard chemical processing equipment as well as correlations and sizing factors. The advantage of using a software package such as HYSYS to price out individual equipment is that it utilizes up-to-date prices from vendors and distributors when estimating costs. A more in-depth overview of the correlations included in this software can be found in Towler and Sinnott (2009).

=Process Flowsheet=
[[File:Squarepfd_B1.PNG|thumb|400px|alt=Alt text|Fig 1: PFD of the Proposed Process]]

The following process is based primarily on a 1983 US patent titled “Process for dehydration of a low molecular weight alcohol.” (Barrocas and Baratelli, 1983) The process flow diagram can be seen in Figure 1. A larger version of the PFD is included in Appendix I and the HYSYS simulation setup in Appendix II.

The feed enters the process at a rate of 100,000 kg/hr, a temperature and pressure of a 25 °C and 1 atm and at a composition of 95 wt% ethanol and 5 wt% water.It is initially pressurized to 4335 kPa by centrifugal pump P-101 and subsequently heated to 400 °C by fired heater F-101. The heated and pressurized feed enters fixed bed reactor R-101 and contacts with the aluminum oxide catalyst. At this point it dehydrates to form the product, ethylene, as well as the byproducts water, hydrogen, diethyl ether and acetaldehyde. Fired heater F-102 and reactor R-102 increase the overall conversion of the process. Both fired heaters F-101 and F-102 are fueled with natural gas and fed with excess air. The composition of the reactor train effluent is 54.5 wt% ethylene, 37.1 wt% water, 8.1 wt% unreacted ethanol and trace amounts of diethyl ether, acetaldehyde, and hydrogen contaminants.

The pressure of the reactor train effluent is increased to 4500 kPa by compressor K-102 and the temperature decreased to 100 °C by exchange with cold water in heat exchanger E-201. The stream then expands and flashes in flash vessel FL-201, which separates out 82.3% of the unreacted ethanol, 96.6% of the water and virtually all of the acetaldehyde contaminant in the bottoms while sending the ethylene-rich vapor phase out of the top. The top product of FL-202 is compressed to 3500 kPA by K-202 and cooled to 0.0 °C by a freon refrigerant in E-202. At this point the stream is flashed for a second time in vessel FL-202 to remove additional impurities. The top outlet stream consists of 99.5 wt% ethylene, which is fed to the bottom of a 10-tray absorption column that removes a fraction of the residual diethyl ether as well as the remainder of the unreacted ethanol. A stream of absorbent water is fed to the top of the column at 10,000 kg/hr. The product exits the top of the column at a rate of 54,600 kg/hr and has a purity of 99.7% ethylene. Diethyl ether makes up 0.2% of the remaining product stream and is the primary contaminant. Trace amounts of residual water and hydrogen are also present.

Full tables of material and energy streams can be found in Appendices III and IV respectively.

==Process Alternatives==
===Reactor Alternatives===
Two fixed bed reactors, alternating with fired heaters, are used in the dehydration reaction of ethanol to ethylene. However, a fluidized bed reactor can offer better mixing and temperature control than a fixed bed reactor and thus provide the highest possible conversion of ethanol with the greatest selectivity to ethylene. (Tsao and Zasloff, 1979) Fluidized bed reactors also provide a lower rate of catalyst coking and byproduct formation, minimizing separation and catalyst regeneration costs. (Morschbacker, 2009) The major downside of fluidized bed reactors is that few large-scale processes have been built since the technology was developed in the late 1970s. (Tsao and Zasloff, 1979; Morschbacker, 2009) Although implementation of fluidized bed reactors could potentially increase the purity of the ethylene product and/or decrease costs, a small scale pilot process would need to be built and tested before it would be possible to develop an industrial-scale facility.

===Catalyst Alternatives===
Aluminum oxide, specifically gamma alumina, is the most industrially-common catalyst and has been historically used due to its low cost and high stability. (Tsao and Zasloff, 1979; Fan and Dai, n.d.) Recent improvements in selectivity and catalyst stability of activated alumina have been achieved by incorporating titanium oxide into the catalyst, although this increases reaction temperature by approximately 50 °C and decreases catalyst lifespan. (Chen and Li, et. al. 2007) There is also significant ongoing research into HZSM-5 zeolite and heteropolyacids, which are being explored as potential alternatives to alumina oxide. A nanoscale HZSM-5 zeolite catalyst has been shown to operate at the relatively low temperature of 200-300°C, with a 100% ethanol conversion and 99.7% selectivity to ethylene. Initial research has also indicated that it maintains greater than 98% selectivity for 630 operational hours. (Fan and Dai, n.d.) However, the current low cost and ready availability of unmodified alumina oxide makes it a better choice for a process of this scale.

===Purification Alternatives===
As specified in this process, the reactor effluent is purified by two flash drums and absorption with water to produce chemical-grade ethylene. If chemical-grade ethylene is indeed the desired product, other purification options include caustic washing of the reactor effluent and water removal in a desiccant drying bed. (Morschbacker, 2009) While this purification train is relatively simple and does not require harsh chemical reagents, polymer grade ethylene is more commercially valuable and the additional cost of removing water and diethyl ether contaminants may be justified by increased revenue. Cryogenic distillation was initially simulated to produce polymer-grade ethylene, but utility requirements were found to render this separation economically unviable. (Barrocas and Baratelli, 1983) Further research and optimization may find this purification strategy to be a more valid process. Alternatively, the addition of a cryogenic turboexpander or the use of alternative adsorbents may increase product purity to polymer grade. (Jumonville, 2010) Initial HYSYS simulations indicate that these operations may be feasible with further refinement.

===Wastewater Treatment===
Due to the large volume of wastewater produced, building an on-site wastewater treatment facility may prove to be more economical than paying for third-party wastewater treatment. Flash vessel FL-201 produces 44,600 L/hr of wastewater contaminated with 18.7 vol% ethanol and 0.6 vol% acetaldehyde, while FL-202 produces 2940 L/hr of an aqueous waste consisting of 56.8 vol% ethanol, 42.0 vol% water and 0.9 vol% diethyl ether. The absorption column produces approximately 10,200 liters/hr of wastewater contaminated with 1.2 vol% ethanol, 0.2% diethyl ether and 0.2% acetaldehyde. Utilizing distillation to separate these streams into clean water and volatile organic waste could ultimately reduce the quantity of waste that requires disposal and reduce the overall costs of the process.

==Process Equipment==
Relevant sizing information for each unit operation, estimated by the method described in the “Technical Approach,” can be found in Appendix V. Equipment and piping is assumed to be constructed of carbon steel. It should be noted that the two fired heaters are proportionately large enough to heat the entirety of the process stream and are thus larger than standard equipment.

=Economic Analysis=
[[File:NPV_B1.png|400px|thumb|Fig 2. Projected Cash Flow]]
[[File:sensitivityanalysis_B1.png|400px|thumb| Fig 3. Results of the Sensitivity Analysis on 10 year NPV]]

==Economics Overview==
All final values are normalized to June 2014 USD by CEPCI scaling. It is assumed that all products produced are sold at current market prices.

The Aspen Economic Evaluation module within HYSYS v8.0 was used to estimate capital and operating costs for a 10-year plant life span with a construction start date of April 2015. The price of the 95% ethanol feed stream was estimated at $1.44 per gallon, while the chemical grade ethylene produced is currently selling for approximately $1350 per metric ton. (Today in Energy, 2015; Weddle, 2014) Mapping and sizing calculations were performed by the economics module and a preliminary economic evaluation was completed. Equipment sizes, also estimated by HYSYS, were reviewed to ensure that height, diameter, and volume specifications were within realistic ranges.

The process was ideally projected to operate 360 days per year with a start-up time of one year. In addition, the tax rate was approximated at 40%, an interest rate at 20%, and a salvage value of 20%. Escalation percentages were compounded yearly for the product, raw material, and operating costs. The total capital cost for this process is approximately $16.4 million, which includes all equipment and piping described in the process. The most expensive equipment used in this process are the two fired heaters F-101 and F-102, which have an exceptionally large heat exchange area to adequately heat the feed. Standard heaters may not suffice and additional costs may be incurred for the raw materials and manufacture of this equipment. Including a feed preheater or additional fired heaters may reduce this cost in subsequent design iterations.

The total operating cost is approximately $465 million per year, about $427 million of which is the cost of the ethanol feed and natural gas for the two fired heaters. An additional $1.73 million per year is used for utilities including the cooling water and refrigerant. The labor and maintenance costs of this industrial process were also accounted for within the simulation’s economic analysis. The HYSYS simulation software, in conjunction with the Icarus economic analyzer, estimated there should be 5 operators per 8 hour shift with a cost per operator of $20 per hour. This results in a total operating labor cost of approximately $880,000 per year. In addition, the process will require one supervisor per shift with an hourly rate of $35 for total supervisor salaries of $307,000 per year. Finally, a fixed maintenance rate was estimated at $205,000 per 8000 hours of operation for a total cost of $225,000 per year.

Total product sales are roughly $640 million per year at full operation. The estimated income for this process is thus approximately $175 million per year. After ten years, the plant is projected to have a net present value (NPV) of $391 million and an internal rate of return of approximately 79%. In addition the payout period for the initial investment is estimated to be about 2.7 years. Figure 2 shows the projected cash flow for the project.

==Sensitivity Analysis==
A sensitivity analysis was performed to investigate the effects of fluctuating capital costs, operating costs, raw materials, utility costs and ethylene sales price on the 10-year net present value (NPV) of the project. This analysis was performed by scaling these cost factors according to typical ranges given in Towler and Sinnott and calculating the adjusting the NPV accordingly. The results, illustrated in Figure 3, indicate that the project value is most sensitive to product sales, raw materials costs, and operating costs. Ethylene and ethanol prices are market-determined and cannot be controlled for in the process design, so further optimization should be focused on minimizing the operations cost of the process. (Today in Energy, 2015; Weddle, 2014) However, in feed and product prices do still have a profound effect on profitability and feasibility. A more rigorous market analysis will better inform the profitability outlook.

=Conclusions/Recommendations=

The proposed process produces approximately 460,000 metric tons of 99.7 wt% ethylene annually, with a 10-year net present value of $131 million. If current economic conditions hold, it is recommended that this project proceed to implementation following further design improvements and optimization.

Future design iterations should focus on process optimization, particularly in minimizing operating costs as prescribed by the results of the sensitivity analysis. The development of a heat-exchanger network, potentially with Aspen Energy Analyzer, is one option for decreasing utility requirements and increasing the efficiency of the process overall. Optimization of the fired heaters could also result in decreased operational costs. Although overall profitability is less sensitive to capital costs, reviewing and adjusting equipment sizing would also improve the economic outlook. In particular, exploring alternative heating strategies at the beginning of the process could significantly decrease capital costs. Although there are not any particularly dangerous chemicals utilized in the process, an overall process review should also consider potential failure modes to minimize the safety risk to plant workers and nearby residents.

In addition to economic and safety considerations, harmful emissions and waste streams should be minimized both to bring down the cost of treatment and to decrease environmental effects. The two fired heaters consume a large amount of natural gas per year, emitting about 200,000 tons of CO2 annually, and account for more than half of the capital cost of the process. Although no known toxic gases are produced, carbon capture or other emissions-reduction methods should be considered. Additionally, enough wastewater is produced by this process that building an onsite wastewater treatment center should be considered. This could not only decrease operating costs by eliminating the need for an external contract but also give the plant more control over the final purity of the treated wastewater.

Finally, the current model assumes that all ethylene produced will be sold at a current prices and price or product sales will not be affected by economic variability. A more detailed study of the chemical-grade ethylene market, as well as a more thorough understanding of sales and distribution logistics, would increase the surety of a profitable process.

In summary, the proposed process yields chemical grade ethylene via the catalytic dehydration of ethanol. A 100,000 kg/hr of 95 wt% ethanol, 5% water feed is converted to 53,000 kg/hr of 99.7% chemical-grade ethylene. After 10 years of operation, including a one-year startup time, the process has an NPV of $391 million with an IRR of 79% and a payback period of 2.7 years.
Pending further optimization, this process was determined to be viable and it is recommended for the project to move forward.

=References=

[1] American Chemistry Council. Production of chemicals and plastics in the U.S. in 2013, by type (in 1,000 metric tons). In Statista - The Statistics Portal. August 2014. Available at http://www.statista.com/statistics/299725/total-us-plastics-and-chemicals-shipments-by-type/, Accessed January 15, 2015. – Relative proportions of plastics production.

[2] DuPont Nevada Site Cellulosic Ethanol Facility [Internet]. DuPont Chemical; c2012-2015 [cited 11 Mar. 2015]. Available from: http://biofuels.dupont.com/cellulosic-ethanol/nevada-site-ce-facility/. -- Information on ethanol production in Iowa.

[3] Designing Ethylene Plants. Ethylene [Internet]. Technip; 2014 [cited 13 Mar. 2015]. Available from: http://www.technip.com/en/our-business/onshore/ethylene -- Plant size ranges.

[4] Suppes GJ. Selecting Thermodynamic Models for Process Simulation of Organic VLE and LLE Systems. The University of Missouri-Columbia, Dept of Chemical Engineering. [cited 13 Mar. 2015]. -- Use of NRTL in alcohol separations.

[5] ASPENtech. Appendix A - Property Methods and Calculations. Simulation Basics; A-3 - A-26. 2014.

[6] 190 Proof Ethanol: Technical Data Sheet [Internet]. Decon Labs Inc; 2012 [cited 13 Mar. 2015]. Available from: http://www.deconlabs.com/tds/ETHANOL%20190%20%20PROOF.pdf -- Information regarding 95% ethanol

[7] Hadawey A, Ge Y, Tassou TSA. Energy Savings Through Liquid Pressure Amplification In A Dairy Plant Refrigeration System. The Centre for Energy and Built Environment Research [cited 13 Mar. 2015].

[8] Methane (Chemical Compound). 2015. Encyclopædia Britannica Online. [cited 13 Mar. 2015] Available from: http://www.britannica.com/EBchecked/topic/378264/methane -- Composition of Methane

[9] Composition of Air [Internet]. Engineering Toolbox; [cited 13 Mar. 2015]. Available from: http://www.engineeringtoolbox.com/air-composition-d_212.html. -- Composition of air.

[10] Summary of the Clean Air Act, 2015. United States Environmental Protection Agency. [cited 13 Mar. 2015] Available from: http://www2.epa.gov/laws-regulations/summary-clean-air-act -- Emissions requirements of chemical plants.

[11] Zhang M, Yu Y. Dehydration of Ethanol to Ethylene. Industrial Engineering and Chemical Research. 2013; 52:9505-9514. – Technical information on ethanol to ethylene conversion via dehydration.

[12] AspenTech. Aspen HYSYS Help File v8.0. Aspen Technology, Inc. 2012. - Aspen HYSYS help file used for troubleshooting and assistance on economic analysis.

[13] Towler G, Sinnott R. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. 2nd ed. Boston: Elsevier; 2013. -- General Reference Book

[14] Barrocas H, Baratelli F, inventors; Petroleo Brasileiro S.A., assignee. Process for dehydration of a low molecular weight alcohol. US patent 4,396,789 A. August 2, 1983. - Primary background for process design.

[15] Tsao U, Zasloff HB, inventors; The Lummus Company, assignee. Production of ethylene from ethanol. US patent 4,134,926. January 16, 1979. – Patent for catalytic dehydration of ethylene in a fluidized bed reactor.

[16] Morschbacker, A. Bio-Ethanol Based Ethylene. Polymer Reviews. 2009; 49:79-84. – Overview of bioethanol dehydration process development.

[17] Fan D, Dai DJ, Wu HS. Ethylene Formation by Catalytic Dehydration of Ethanol with Industrial Considerations. Materials. 6, 101-115. doi: 10.3390/ma6010101. - Comparison of types of catalysts used in the dehydration of ethanol and current research into new catalysts.

[18] Chen G, Li S, Jiao F, Yuan Q. Catalytic dehydration of bioethanol to ethylene over TiO2/γ-Al2O3 catalysts in microchannel reactors. Catal. Today 2007, 125, 111–119. - Paper introducing research on modified alumina catalyst for ethanol dehydration.

[19] Jumonville, J. Tutorial on Cryogenic Turboexpanders. Proceedings of the Thirty-Ninth Turbomachinery Symposium; 2010 Oct 4-7; Houston, TX. Houston: Texas A&M University; 2010. -- Use of turboexpander for cryogenic separations

[20] Today in Energy - Daily Prices. US Energy Information Administration website. http://www.eia.gov/todayinenergy/prices.cfm. Accessed March 3rd 2015. - Bulk market price for 95% ethanol.

[21] Weddle, N. ICIS Pricing: Ethylene (Europe). Reed Business Limited. January 10 2014. - Bulk market price for chemical grade ethylene.

=Appendix I - Process Flow Diagram=
[[File:PFD B1.JPG|1200px|center]]

=Appendix II - HYSYS Simulation=
[[File:HYSYS_B1.PNG|center|1200px]]

=Appendix III - Material Streams=
[[File:Streams_B1.png|1200px]]

=Appendix IV - Energy Table=
[[File:Energy_B1.png|600px|center]]

[[File:Utilities.PNG|600px|center]]

=Appendix V - Equipment Sizing=
[[File:Econsummary_B1.png|center]] 

=Appendix VI - Economics=
[[File:Econsummary_B1.png|center]] 

[[File:Capcost_B1.png|center]]

Ethanol to Ethylene (B1)

2015-03-14T04:58:47Z

Hpoppick: /* Appendix V - Economics */

[[File:BFD_B1.png|600px|thumbnail|alt=Alt text|Conversion of Ethanol to Ethylene]]

Team B1 Final Report

Authors: Harry Poppick, Emm Fulk and Scott Smith

Instructors: Fengqi You, David Wegerer

March 13, 2015

=Executive Summary=

The following report outlines the design and analysis of a process converting ethanol to chemical-grade ethylene via catalytic dehydration. This process consumers 100,000 kg/hr of 95 wt% ethanol, 5 wt% water feedstock and produces 53,000 kg/hr of 99.7 wt% chemical-grade ethylene. The ethanol feed passes through two fixed-bed reactors, each packed with an aluminum oxide catalyst, and the resulting ethylene is purified by two flash tanks and by absorption with water. The process was modeled using Aspen HYSYS simulation software to estimate mass and energy flows and equipment sizing requirements. Based on results of this initial simulation, several alternatives are discussed for increasing the process efficiency and profitability. The use of a fluidized bed reactor or a more ethylene-selective catalyst could increase the production of ethylene per ethanol basis. Additionally, several methods of purification to more valuable polymer-grade ethylene are proposed.

The economic feasibility of this process was evaluated using Aspen Economic Analyzer with the Icarus economics package. Capital cost is approximately $16.4 million total with an operating cost of $465 million per year. The current market prices of the ethanol feed and ethylene sales price are $1.44/gallon and $1350/metric ton respectively. The cost of feed ethanol, process utilities and miscellaneous operational costs total to about $427 million/year. At full operation, revenue at current prices would be approximately $640 million per year. The predicted 10-year net present value of the process is approximately $391 million with an IRR of 79% and a payback period of 2.7 years. A sensitivity analysis indicates that the process is most sensitive to feed prices, product prices and operation cost.

Several recommendations are made for both cost reduction and profit maximization, including the design of a heat exchanger network and the optimization of fired heaters that require high capital investment and large amounts of fuel. A safety review of the process is recommended, as well as the minimization of flue gas effluent and wastewater. It is also suggested that the construction of an onsite wastewater treatment center be considered. Overall, the initial analysis indicates this to be a profitable process and it is recommended the project move forward.

=Introduction=

Ethylene is a critical chemical precursor to a number of different industrial products. It is often derived from petroleum sources and polymerized to polyethylene, one of the most ubiquitous plastics today. (American Chemistry Council, 2013) Recently there has been a significant effort to develop production pathways utilizing biologically-derived feedstocks, such as corn or cellulosic ethanol, rather than traditional fossil-fuel sources. Ethylene can be produced from bioethanol via catalytic dehydration over an aluminum oxide catalyst. The proposed process converts 100,000 kg/hr of 95 wt% ethanol, 5% water feed to 53,000 kg/hr of 99.7% chemical-grade ethylene when operating at full capacity. This process was found to be economically viable with a 10-year net present value (NPV) of $131 million (2014 USD) and a payback period of approximately 2.7 years. This memo will detail the proposed process, as well as outline potential alternatives and economic viability of the project.

=Technical Approach=

Many bioethanol plants are located in the Midwest where large amounts of feedstock crops, such as corn, are grown. As such, this plant will be located in Story county, Iowa, near a large-scale bioethanol production plant. (DuPont Nevada Site, 2012) It is assumed that the supply of bioethanol is consistent and readily available. It is also assumed that other reagents - namely, the aluminum oxide catalyst, heater fuel, utility water and freon refrigerant - are readily available, and that wastewater treatment facilities are located near enough to facilitate the off-site treatment of wastewater. Plant capacity was based on current mid-sized industrial ethylene plants. (Designing Ethylene Plants, 2014)

HYSYS simulations were performed with the NRTL fluid package and Peng-Robinson vapor model. The NRTL fluid package is an activity coefficient model that is especially useful to model the separations of alcohols in aqueous solutions. (Suppes, 2015) In addition, NRTL uses models of binary pairs of components, much like the Wilson equation, to predict chemical interactions at the molecular level. The NRTL package can thus be easily extended to ternary and higher order chemical systems, making it ideal for this type of simulation. The Peng-Robinson vapor model was selected as it is well-suited to account for the non-idealities of the vapor phase reactions and separations integral to this process. (ASPENtech, 2014)

It was assumed that the feed enters the process at ambient temperature and pressure (25 °C, 1 atm) and at a consistent rate and composition with negligible quantities of impurities. The ethanol feed was assumed to be 95% ethanol and 5% water by mass, which is the commercial standard for industrial ethanol. (190 Proof Ethanol, 2012) Storage vessels for the feed ethanol, waste streams and products are assumed to be located nearby to the process. An initial feed pump compensates for pressure drops through the process and reduces the duty on downstream compressors. (Hadawey, 2015)

Natural gas, assumed to consist of 83% methane, 16% ethane and 1% nitrogen by mass, was supplied to two fired heaters at a flow rate estimated by HYSYS. (Methane, 2015) Air fed to the process to enable combustion was assumed to be 23% oxygen and 77% nitrogen by mass. (Composition of Air, 2015) Air streams were fed at 50% molar excess in order to ensure complete combustion and prevent the formation of carbon monoxide in the heater exhaust. Total flue gases are assumed to be 230,000 kg/hr, or 2.2 million tons annually, and consist of 73.8% nitrogen gas, 10.5% carbon dioxide, 8.2% water vapor, and 7.5% oxygen by mass. The only compound of concern in these emissions is the carbon dioxide, a known greenhouse gas. At the time of this report, the quantities of carbon dioxide emitted by this plant annually are within acceptable EPA specifications. (Summary of the Clean Air Act, 2015)

Due to the difficulty of simulation equilibrium and conversion reactions in a single vessel in HYSYS, these two reaction types were simulated in separate equilibrium reactor and conversion reactor units in series. In addition, while HYSYS indicated that reactor units would output separate vapor and liquid streams, it was assumed that in practice this would take the form of a single, two phase stream between each unit. To account for this, mixers were installed downstream of each reactor to combine the liquid and vapor phases of the reactor effluent. The three consequent reactions considered are as follows:
[[File:Equation.PNG|300px|center]]
The optimal reaction temperature was determined to be 400 °C, which promotes the equilibrium reaction of ethanol to ethylene while minimizing byproducts. (Zhang and Yu, 2013) While other byproducts may be produced in this process, these reactions are typically taken to comprise of the bulk of the dehydration reaction. Heat losses over these reactors were assumed to be negligible. (Zhang and Yu, 2013)All major process equipment is assumed to be constructed of high strength carbon steel. (AspenTech, 2012)

The “Sizing Utility” within the Icarus Economic Evaluation module was used to estimate sizes of major equipment based on the process simulation. These values can serve as a benchmark for an initial plant design. Icarus KbaseTM implements a wide variety of mechanical design standards, including ASME and BS5500, in order to calculate accurate equipment sizing. The Icarus sizing module combines equipment prices for standard chemical processing equipment as well as correlations and sizing factors. The advantage of using a software package such as HYSYS to price out individual equipment is that it utilizes up-to-date prices from vendors and distributors when estimating costs. A more in-depth overview of the correlations included in this software can be found in Towler and Sinnott (2009).

=Process Flowsheet=
[[File:Squarepfd_B1.PNG|thumb|400px|alt=Alt text|Fig 1: PFD of the Proposed Process]]

The following process is based primarily on a 1983 US patent titled “Process for dehydration of a low molecular weight alcohol.” (Barrocas and Baratelli, 1983) The process flow diagram can be seen in Figure 1. A larger version of the PFD is included in Appendix I and the HYSYS simulation setup in Appendix II.

The feed enters the process at a rate of 100,000 kg/hr, a temperature and pressure of a 25 °C and 1 atm and at a composition of 95 wt% ethanol and 5 wt% water.It is initially pressurized to 4335 kPa by centrifugal pump P-101 and subsequently heated to 400 °C by fired heater F-101. The heated and pressurized feed enters fixed bed reactor R-101 and contacts with the aluminum oxide catalyst. At this point it dehydrates to form the product, ethylene, as well as the byproducts water, hydrogen, diethyl ether and acetaldehyde. Fired heater F-102 and reactor R-102 increase the overall conversion of the process. Both fired heaters F-101 and F-102 are fueled with natural gas and fed with excess air. The composition of the reactor train effluent is 54.5 wt% ethylene, 37.1 wt% water, 8.1 wt% unreacted ethanol and trace amounts of diethyl ether, acetaldehyde, and hydrogen contaminants.

The pressure of the reactor train effluent is increased to 4500 kPa by compressor K-102 and the temperature decreased to 100 °C by exchange with cold water in heat exchanger E-201. The stream then expands and flashes in flash vessel FL-201, which separates out 82.3% of the unreacted ethanol, 96.6% of the water and virtually all of the acetaldehyde contaminant in the bottoms while sending the ethylene-rich vapor phase out of the top. The top product of FL-202 is compressed to 3500 kPA by K-202 and cooled to 0.0 °C by a freon refrigerant in E-202. At this point the stream is flashed for a second time in vessel FL-202 to remove additional impurities. The top outlet stream consists of 99.5 wt% ethylene, which is fed to the bottom of a 10-tray absorption column that removes a fraction of the residual diethyl ether as well as the remainder of the unreacted ethanol. A stream of absorbent water is fed to the top of the column at 10,000 kg/hr. The product exits the top of the column at a rate of 54,600 kg/hr and has a purity of 99.7% ethylene. Diethyl ether makes up 0.2% of the remaining product stream and is the primary contaminant. Trace amounts of residual water and hydrogen are also present.

Full tables of material and energy streams can be found in Appendices III and IV respectively.

==Process Alternatives==
===Reactor Alternatives===
Two fixed bed reactors, alternating with fired heaters, are used in the dehydration reaction of ethanol to ethylene. However, a fluidized bed reactor can offer better mixing and temperature control than a fixed bed reactor and thus provide the highest possible conversion of ethanol with the greatest selectivity to ethylene. (Tsao and Zasloff, 1979) Fluidized bed reactors also provide a lower rate of catalyst coking and byproduct formation, minimizing separation and catalyst regeneration costs. (Morschbacker, 2009) The major downside of fluidized bed reactors is that few large-scale processes have been built since the technology was developed in the late 1970s. (Tsao and Zasloff, 1979; Morschbacker, 2009) Although implementation of fluidized bed reactors could potentially increase the purity of the ethylene product and/or decrease costs, a small scale pilot process would need to be built and tested before it would be possible to develop an industrial-scale facility.

===Catalyst Alternatives===
Aluminum oxide, specifically gamma alumina, is the most industrially-common catalyst and has been historically used due to its low cost and high stability. (Tsao and Zasloff, 1979; Fan and Dai, n.d.) Recent improvements in selectivity and catalyst stability of activated alumina have been achieved by incorporating titanium oxide into the catalyst, although this increases reaction temperature by approximately 50 °C and decreases catalyst lifespan. (Chen and Li, et. al. 2007) There is also significant ongoing research into HZSM-5 zeolite and heteropolyacids, which are being explored as potential alternatives to alumina oxide. A nanoscale HZSM-5 zeolite catalyst has been shown to operate at the relatively low temperature of 200-300°C, with a 100% ethanol conversion and 99.7% selectivity to ethylene. Initial research has also indicated that it maintains greater than 98% selectivity for 630 operational hours. (Fan and Dai, n.d.) However, the current low cost and ready availability of unmodified alumina oxide makes it a better choice for a process of this scale.

===Purification Alternatives===
As specified in this process, the reactor effluent is purified by two flash drums and absorption with water to produce chemical-grade ethylene. If chemical-grade ethylene is indeed the desired product, other purification options include caustic washing of the reactor effluent and water removal in a desiccant drying bed. (Morschbacker, 2009) While this purification train is relatively simple and does not require harsh chemical reagents, polymer grade ethylene is more commercially valuable and the additional cost of removing water and diethyl ether contaminants may be justified by increased revenue. Cryogenic distillation was initially simulated to produce polymer-grade ethylene, but utility requirements were found to render this separation economically unviable. (Barrocas and Baratelli, 1983) Further research and optimization may find this purification strategy to be a more valid process. Alternatively, the addition of a cryogenic turboexpander or the use of alternative adsorbents may increase product purity to polymer grade. (Jumonville, 2010) Initial HYSYS simulations indicate that these operations may be feasible with further refinement.

===Wastewater Treatment===
Due to the large volume of wastewater produced, building an on-site wastewater treatment facility may prove to be more economical than paying for third-party wastewater treatment. Flash vessel FL-201 produces 44,600 L/hr of wastewater contaminated with 18.7 vol% ethanol and 0.6 vol% acetaldehyde, while FL-202 produces 2940 L/hr of an aqueous waste consisting of 56.8 vol% ethanol, 42.0 vol% water and 0.9 vol% diethyl ether. The absorption column produces approximately 10,200 liters/hr of wastewater contaminated with 1.2 vol% ethanol, 0.2% diethyl ether and 0.2% acetaldehyde. Utilizing distillation to separate these streams into clean water and volatile organic waste could ultimately reduce the quantity of waste that requires disposal and reduce the overall costs of the process.

==Process Equipment==
Relevant sizing information for each unit operation, estimated by the method described in the “Technical Approach,” can be found in Appendix V. Equipment and piping is assumed to be constructed of carbon steel. It should be noted that the two fired heaters are proportionately large enough to heat the entirety of the process stream and are thus larger than standard equipment.

=Economic Analysis=
[[File:NPV_B1.png|400px|thumb|Fig 2. Projected Cash Flow]]
[[File:sensitivityanalysis_B1.png|400px|thumb| Fig 3. Results of the Sensitivity Analysis on 10 year NPV]]

==Economics Overview==
All final values are normalized to June 2014 USD by CEPCI scaling. It is assumed that all products produced are sold at current market prices.

The Aspen Economic Evaluation module within HYSYS v8.0 was used to estimate capital and operating costs for a 10-year plant life span with a construction start date of April 2015. The price of the 95% ethanol feed stream was estimated at $1.44 per gallon, while the chemical grade ethylene produced is currently selling for approximately $1350 per metric ton. (Today in Energy, 2015; Weddle, 2014) Mapping and sizing calculations were performed by the economics module and a preliminary economic evaluation was completed. Equipment sizes, also estimated by HYSYS, were reviewed to ensure that height, diameter, and volume specifications were within realistic ranges.

The process was ideally projected to operate 360 days per year with a start-up time of one year. In addition, the tax rate was approximated at 40%, an interest rate at 20%, and a salvage value of 20%. Escalation percentages were compounded yearly for the product, raw material, and operating costs. The total capital cost for this process is approximately $16.4 million, which includes all equipment and piping described in the process. The most expensive equipment used in this process are the two fired heaters F-101 and F-102, which have an exceptionally large heat exchange area to adequately heat the feed. Standard heaters may not suffice and additional costs may be incurred for the raw materials and manufacture of this equipment. Including a feed preheater or additional fired heaters may reduce this cost in subsequent design iterations.

The total operating cost is approximately $465 million per year, about $427 million of which is the cost of the ethanol feed and natural gas for the two fired heaters. An additional $1.73 million per year is used for utilities including the cooling water and refrigerant. The labor and maintenance costs of this industrial process were also accounted for within the simulation’s economic analysis. The HYSYS simulation software, in conjunction with the Icarus economic analyzer, estimated there should be 5 operators per 8 hour shift with a cost per operator of $20 per hour. This results in a total operating labor cost of approximately $880,000 per year. In addition, the process will require one supervisor per shift with an hourly rate of $35 for total supervisor salaries of $307,000 per year. Finally, a fixed maintenance rate was estimated at $205,000 per 8000 hours of operation for a total cost of $225,000 per year.

Total product sales are roughly $640 million per year at full operation. The estimated income for this process is thus approximately $175 million per year. After ten years, the plant is projected to have a net present value (NPV) of $391 million and an internal rate of return of approximately 79%. In addition the payout period for the initial investment is estimated to be about 2.7 years. Figure 2 shows the projected cash flow for the project.

==Sensitivity Analysis==
A sensitivity analysis was performed to investigate the effects of fluctuating capital costs, operating costs, raw materials, utility costs and ethylene sales price on the 10-year net present value (NPV) of the project. This analysis was performed by scaling these cost factors according to typical ranges given in Towler and Sinnott and calculating the adjusting the NPV accordingly. The results, illustrated in Figure 3, indicate that the project value is most sensitive to product sales, raw materials costs, and operating costs. Ethylene and ethanol prices are market-determined and cannot be controlled for in the process design, so further optimization should be focused on minimizing the operations cost of the process. (Today in Energy, 2015; Weddle, 2014) However, in feed and product prices do still have a profound effect on profitability and feasibility. A more rigorous market analysis will better inform the profitability outlook.

=Conclusions/Recommendations=

The proposed process produces approximately 460,000 metric tons of 99.7 wt% ethylene annually, with a 10-year net present value of $131 million. If current economic conditions hold, it is recommended that this project proceed to implementation following further design improvements and optimization.

Future design iterations should focus on process optimization, particularly in minimizing operating costs as prescribed by the results of the sensitivity analysis. The development of a heat-exchanger network, potentially with Aspen Energy Analyzer, is one option for decreasing utility requirements and increasing the efficiency of the process overall. Optimization of the fired heaters could also result in decreased operational costs. Although overall profitability is less sensitive to capital costs, reviewing and adjusting equipment sizing would also improve the economic outlook. In particular, exploring alternative heating strategies at the beginning of the process could significantly decrease capital costs. Although there are not any particularly dangerous chemicals utilized in the process, an overall process review should also consider potential failure modes to minimize the safety risk to plant workers and nearby residents.

In addition to economic and safety considerations, harmful emissions and waste streams should be minimized both to bring down the cost of treatment and to decrease environmental effects. The two fired heaters consume a large amount of natural gas per year, emitting about 200,000 tons of CO2 annually, and account for more than half of the capital cost of the process. Although no known toxic gases are produced, carbon capture or other emissions-reduction methods should be considered. Additionally, enough wastewater is produced by this process that building an onsite wastewater treatment center should be considered. This could not only decrease operating costs by eliminating the need for an external contract but also give the plant more control over the final purity of the treated wastewater.

Finally, the current model assumes that all ethylene produced will be sold at a current prices and price or product sales will not be affected by economic variability. A more detailed study of the chemical-grade ethylene market, as well as a more thorough understanding of sales and distribution logistics, would increase the surety of a profitable process.

In summary, the proposed process yields chemical grade ethylene via the catalytic dehydration of ethanol. A 100,000 kg/hr of 95 wt% ethanol, 5% water feed is converted to 53,000 kg/hr of 99.7% chemical-grade ethylene. After 10 years of operation, including a one-year startup time, the process has an NPV of $391 million with an IRR of 79% and a payback period of 2.7 years.
Pending further optimization, this process was determined to be viable and it is recommended for the project to move forward.

=References=

[1] American Chemistry Council. Production of chemicals and plastics in the U.S. in 2013, by type (in 1,000 metric tons). In Statista - The Statistics Portal. August 2014. Available at http://www.statista.com/statistics/299725/total-us-plastics-and-chemicals-shipments-by-type/, Accessed January 15, 2015. – Relative proportions of plastics production.

[2] DuPont Nevada Site Cellulosic Ethanol Facility [Internet]. DuPont Chemical; c2012-2015 [cited 11 Mar. 2015]. Available from: http://biofuels.dupont.com/cellulosic-ethanol/nevada-site-ce-facility/. -- Information on ethanol production in Iowa.

[3] Designing Ethylene Plants. Ethylene [Internet]. Technip; 2014 [cited 13 Mar. 2015]. Available from: http://www.technip.com/en/our-business/onshore/ethylene -- Plant size ranges.

[4] Suppes GJ. Selecting Thermodynamic Models for Process Simulation of Organic VLE and LLE Systems. The University of Missouri-Columbia, Dept of Chemical Engineering. [cited 13 Mar. 2015]. -- Use of NRTL in alcohol separations.

[5] ASPENtech. Appendix A - Property Methods and Calculations. Simulation Basics; A-3 - A-26. 2014.

[6] 190 Proof Ethanol: Technical Data Sheet [Internet]. Decon Labs Inc; 2012 [cited 13 Mar. 2015]. Available from: http://www.deconlabs.com/tds/ETHANOL%20190%20%20PROOF.pdf -- Information regarding 95% ethanol

[7] Hadawey A, Ge Y, Tassou TSA. Energy Savings Through Liquid Pressure Amplification In A Dairy Plant Refrigeration System. The Centre for Energy and Built Environment Research [cited 13 Mar. 2015].

[8] Methane (Chemical Compound). 2015. Encyclopædia Britannica Online. [cited 13 Mar. 2015] Available from: http://www.britannica.com/EBchecked/topic/378264/methane -- Composition of Methane

[9] Composition of Air [Internet]. Engineering Toolbox; [cited 13 Mar. 2015]. Available from: http://www.engineeringtoolbox.com/air-composition-d_212.html. -- Composition of air.

[10] Summary of the Clean Air Act, 2015. United States Environmental Protection Agency. [cited 13 Mar. 2015] Available from: http://www2.epa.gov/laws-regulations/summary-clean-air-act -- Emissions requirements of chemical plants.

[11] Zhang M, Yu Y. Dehydration of Ethanol to Ethylene. Industrial Engineering and Chemical Research. 2013; 52:9505-9514. – Technical information on ethanol to ethylene conversion via dehydration.

[12] AspenTech. Aspen HYSYS Help File v8.0. Aspen Technology, Inc. 2012. - Aspen HYSYS help file used for troubleshooting and assistance on economic analysis.

[13] Towler G, Sinnott R. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. 2nd ed. Boston: Elsevier; 2013. -- General Reference Book

[14] Barrocas H, Baratelli F, inventors; Petroleo Brasileiro S.A., assignee. Process for dehydration of a low molecular weight alcohol. US patent 4,396,789 A. August 2, 1983. - Primary background for process design.

[15] Tsao U, Zasloff HB, inventors; The Lummus Company, assignee. Production of ethylene from ethanol. US patent 4,134,926. January 16, 1979. – Patent for catalytic dehydration of ethylene in a fluidized bed reactor.

[16] Morschbacker, A. Bio-Ethanol Based Ethylene. Polymer Reviews. 2009; 49:79-84. – Overview of bioethanol dehydration process development.

[17] Fan D, Dai DJ, Wu HS. Ethylene Formation by Catalytic Dehydration of Ethanol with Industrial Considerations. Materials. 6, 101-115. doi: 10.3390/ma6010101. - Comparison of types of catalysts used in the dehydration of ethanol and current research into new catalysts.

[18] Chen G, Li S, Jiao F, Yuan Q. Catalytic dehydration of bioethanol to ethylene over TiO2/γ-Al2O3 catalysts in microchannel reactors. Catal. Today 2007, 125, 111–119. - Paper introducing research on modified alumina catalyst for ethanol dehydration.

[19] Jumonville, J. Tutorial on Cryogenic Turboexpanders. Proceedings of the Thirty-Ninth Turbomachinery Symposium; 2010 Oct 4-7; Houston, TX. Houston: Texas A&M University; 2010. -- Use of turboexpander for cryogenic separations

[20] Today in Energy - Daily Prices. US Energy Information Administration website. http://www.eia.gov/todayinenergy/prices.cfm. Accessed March 3rd 2015. - Bulk market price for 95% ethanol.

[21] Weddle, N. ICIS Pricing: Ethylene (Europe). Reed Business Limited. January 10 2014. - Bulk market price for chemical grade ethylene.

=Appendix I - Process Flow Diagram=
[[File:PFD B1.JPG|1200px|center]]

=Appendix II - HYSYS Simulation=
[[File:HYSYS_B1.PNG|center|1200px]]

=Appendix III - Material Streams=
[[File:Streams_B1.png|1200px]]

=Appendix IV - Energy Table=
[[File:Energy_B1.png|600px|center]]

[[File:Utilities.PNG|600px|center]]

=Appendix V - Economics=
[[File:Econsummary_B1.png|center]] 

[[File:Capcost_B1.png|center]]

Ethanol to Ethylene (B1)

2015-03-14T04:55:09Z

Hpoppick: /* Appendix IV - Energy Table */

[[File:BFD_B1.png|600px|thumbnail|alt=Alt text|Conversion of Ethanol to Ethylene]]

Team B1 Final Report

Authors: Harry Poppick, Emm Fulk and Scott Smith

Instructors: Fengqi You, David Wegerer

March 13, 2015

=Executive Summary=

The following report outlines the design and analysis of a process converting ethanol to chemical-grade ethylene via catalytic dehydration. This process consumers 100,000 kg/hr of 95 wt% ethanol, 5 wt% water feedstock and produces 53,000 kg/hr of 99.7 wt% chemical-grade ethylene. The ethanol feed passes through two fixed-bed reactors, each packed with an aluminum oxide catalyst, and the resulting ethylene is purified by two flash tanks and by absorption with water. The process was modeled using Aspen HYSYS simulation software to estimate mass and energy flows and equipment sizing requirements. Based on results of this initial simulation, several alternatives are discussed for increasing the process efficiency and profitability. The use of a fluidized bed reactor or a more ethylene-selective catalyst could increase the production of ethylene per ethanol basis. Additionally, several methods of purification to more valuable polymer-grade ethylene are proposed.

The economic feasibility of this process was evaluated using Aspen Economic Analyzer with the Icarus economics package. Capital cost is approximately $16.4 million total with an operating cost of $465 million per year. The current market prices of the ethanol feed and ethylene sales price are $1.44/gallon and $1350/metric ton respectively. The cost of feed ethanol, process utilities and miscellaneous operational costs total to about $427 million/year. At full operation, revenue at current prices would be approximately $640 million per year. The predicted 10-year net present value of the process is approximately $391 million with an IRR of 79% and a payback period of 2.7 years. A sensitivity analysis indicates that the process is most sensitive to feed prices, product prices and operation cost.

Several recommendations are made for both cost reduction and profit maximization, including the design of a heat exchanger network and the optimization of fired heaters that require high capital investment and large amounts of fuel. A safety review of the process is recommended, as well as the minimization of flue gas effluent and wastewater. It is also suggested that the construction of an onsite wastewater treatment center be considered. Overall, the initial analysis indicates this to be a profitable process and it is recommended the project move forward.

=Introduction=

Ethylene is a critical chemical precursor to a number of different industrial products. It is often derived from petroleum sources and polymerized to polyethylene, one of the most ubiquitous plastics today. (American Chemistry Council, 2013) Recently there has been a significant effort to develop production pathways utilizing biologically-derived feedstocks, such as corn or cellulosic ethanol, rather than traditional fossil-fuel sources. Ethylene can be produced from bioethanol via catalytic dehydration over an aluminum oxide catalyst. The proposed process converts 100,000 kg/hr of 95 wt% ethanol, 5% water feed to 53,000 kg/hr of 99.7% chemical-grade ethylene when operating at full capacity. This process was found to be economically viable with a 10-year net present value (NPV) of $131 million (2014 USD) and a payback period of approximately 2.7 years. This memo will detail the proposed process, as well as outline potential alternatives and economic viability of the project.

=Technical Approach=

Many bioethanol plants are located in the Midwest where large amounts of feedstock crops, such as corn, are grown. As such, this plant will be located in Story county, Iowa, near a large-scale bioethanol production plant. (DuPont Nevada Site, 2012) It is assumed that the supply of bioethanol is consistent and readily available. It is also assumed that other reagents - namely, the aluminum oxide catalyst, heater fuel, utility water and freon refrigerant - are readily available, and that wastewater treatment facilities are located near enough to facilitate the off-site treatment of wastewater. Plant capacity was based on current mid-sized industrial ethylene plants. (Designing Ethylene Plants, 2014)

HYSYS simulations were performed with the NRTL fluid package and Peng-Robinson vapor model. The NRTL fluid package is an activity coefficient model that is especially useful to model the separations of alcohols in aqueous solutions. (Suppes, 2015) In addition, NRTL uses models of binary pairs of components, much like the Wilson equation, to predict chemical interactions at the molecular level. The NRTL package can thus be easily extended to ternary and higher order chemical systems, making it ideal for this type of simulation. The Peng-Robinson vapor model was selected as it is well-suited to account for the non-idealities of the vapor phase reactions and separations integral to this process. (ASPENtech, 2014)

It was assumed that the feed enters the process at ambient temperature and pressure (25 °C, 1 atm) and at a consistent rate and composition with negligible quantities of impurities. The ethanol feed was assumed to be 95% ethanol and 5% water by mass, which is the commercial standard for industrial ethanol. (190 Proof Ethanol, 2012) Storage vessels for the feed ethanol, waste streams and products are assumed to be located nearby to the process. An initial feed pump compensates for pressure drops through the process and reduces the duty on downstream compressors. (Hadawey, 2015)

Natural gas, assumed to consist of 83% methane, 16% ethane and 1% nitrogen by mass, was supplied to two fired heaters at a flow rate estimated by HYSYS. (Methane, 2015) Air fed to the process to enable combustion was assumed to be 23% oxygen and 77% nitrogen by mass. (Composition of Air, 2015) Air streams were fed at 50% molar excess in order to ensure complete combustion and prevent the formation of carbon monoxide in the heater exhaust. Total flue gases are assumed to be 230,000 kg/hr, or 2.2 million tons annually, and consist of 73.8% nitrogen gas, 10.5% carbon dioxide, 8.2% water vapor, and 7.5% oxygen by mass. The only compound of concern in these emissions is the carbon dioxide, a known greenhouse gas. At the time of this report, the quantities of carbon dioxide emitted by this plant annually are within acceptable EPA specifications. (Summary of the Clean Air Act, 2015)

Due to the difficulty of simulation equilibrium and conversion reactions in a single vessel in HYSYS, these two reaction types were simulated in separate equilibrium reactor and conversion reactor units in series. In addition, while HYSYS indicated that reactor units would output separate vapor and liquid streams, it was assumed that in practice this would take the form of a single, two phase stream between each unit. To account for this, mixers were installed downstream of each reactor to combine the liquid and vapor phases of the reactor effluent. The three consequent reactions considered are as follows:
[[File:Equation.PNG|300px|center]]
The optimal reaction temperature was determined to be 400 °C, which promotes the equilibrium reaction of ethanol to ethylene while minimizing byproducts. (Zhang and Yu, 2013) While other byproducts may be produced in this process, these reactions are typically taken to comprise of the bulk of the dehydration reaction. Heat losses over these reactors were assumed to be negligible. (Zhang and Yu, 2013)All major process equipment is assumed to be constructed of high strength carbon steel. (AspenTech, 2012)

The “Sizing Utility” within the Icarus Economic Evaluation module was used to estimate sizes of major equipment based on the process simulation. These values can serve as a benchmark for an initial plant design. Icarus KbaseTM implements a wide variety of mechanical design standards, including ASME and BS5500, in order to calculate accurate equipment sizing. The Icarus sizing module combines equipment prices for standard chemical processing equipment as well as correlations and sizing factors. The advantage of using a software package such as HYSYS to price out individual equipment is that it utilizes up-to-date prices from vendors and distributors when estimating costs. A more in-depth overview of the correlations included in this software can be found in Towler and Sinnott (2009).

=Process Flowsheet=
[[File:Squarepfd_B1.PNG|thumb|400px|alt=Alt text|Fig 1: PFD of the Proposed Process]]

The following process is based primarily on a 1983 US patent titled “Process for dehydration of a low molecular weight alcohol.” (Barrocas and Baratelli, 1983) The process flow diagram can be seen in Figure 1. A larger version of the PFD is included in Appendix I and the HYSYS simulation setup in Appendix II.

The feed enters the process at a rate of 100,000 kg/hr, a temperature and pressure of a 25 °C and 1 atm and at a composition of 95 wt% ethanol and 5 wt% water.It is initially pressurized to 4335 kPa by centrifugal pump P-101 and subsequently heated to 400 °C by fired heater F-101. The heated and pressurized feed enters fixed bed reactor R-101 and contacts with the aluminum oxide catalyst. At this point it dehydrates to form the product, ethylene, as well as the byproducts water, hydrogen, diethyl ether and acetaldehyde. Fired heater F-102 and reactor R-102 increase the overall conversion of the process. Both fired heaters F-101 and F-102 are fueled with natural gas and fed with excess air. The composition of the reactor train effluent is 54.5 wt% ethylene, 37.1 wt% water, 8.1 wt% unreacted ethanol and trace amounts of diethyl ether, acetaldehyde, and hydrogen contaminants.

The pressure of the reactor train effluent is increased to 4500 kPa by compressor K-102 and the temperature decreased to 100 °C by exchange with cold water in heat exchanger E-201. The stream then expands and flashes in flash vessel FL-201, which separates out 82.3% of the unreacted ethanol, 96.6% of the water and virtually all of the acetaldehyde contaminant in the bottoms while sending the ethylene-rich vapor phase out of the top. The top product of FL-202 is compressed to 3500 kPA by K-202 and cooled to 0.0 °C by a freon refrigerant in E-202. At this point the stream is flashed for a second time in vessel FL-202 to remove additional impurities. The top outlet stream consists of 99.5 wt% ethylene, which is fed to the bottom of a 10-tray absorption column that removes a fraction of the residual diethyl ether as well as the remainder of the unreacted ethanol. A stream of absorbent water is fed to the top of the column at 10,000 kg/hr. The product exits the top of the column at a rate of 54,600 kg/hr and has a purity of 99.7% ethylene. Diethyl ether makes up 0.2% of the remaining product stream and is the primary contaminant. Trace amounts of residual water and hydrogen are also present.

Full tables of material and energy streams can be found in Appendices III and IV respectively.

==Process Alternatives==
===Reactor Alternatives===
Two fixed bed reactors, alternating with fired heaters, are used in the dehydration reaction of ethanol to ethylene. However, a fluidized bed reactor can offer better mixing and temperature control than a fixed bed reactor and thus provide the highest possible conversion of ethanol with the greatest selectivity to ethylene. (Tsao and Zasloff, 1979) Fluidized bed reactors also provide a lower rate of catalyst coking and byproduct formation, minimizing separation and catalyst regeneration costs. (Morschbacker, 2009) The major downside of fluidized bed reactors is that few large-scale processes have been built since the technology was developed in the late 1970s. (Tsao and Zasloff, 1979; Morschbacker, 2009) Although implementation of fluidized bed reactors could potentially increase the purity of the ethylene product and/or decrease costs, a small scale pilot process would need to be built and tested before it would be possible to develop an industrial-scale facility.

===Catalyst Alternatives===
Aluminum oxide, specifically gamma alumina, is the most industrially-common catalyst and has been historically used due to its low cost and high stability. (Tsao and Zasloff, 1979; Fan and Dai, n.d.) Recent improvements in selectivity and catalyst stability of activated alumina have been achieved by incorporating titanium oxide into the catalyst, although this increases reaction temperature by approximately 50 °C and decreases catalyst lifespan. (Chen and Li, et. al. 2007) There is also significant ongoing research into HZSM-5 zeolite and heteropolyacids, which are being explored as potential alternatives to alumina oxide. A nanoscale HZSM-5 zeolite catalyst has been shown to operate at the relatively low temperature of 200-300°C, with a 100% ethanol conversion and 99.7% selectivity to ethylene. Initial research has also indicated that it maintains greater than 98% selectivity for 630 operational hours. (Fan and Dai, n.d.) However, the current low cost and ready availability of unmodified alumina oxide makes it a better choice for a process of this scale.

===Purification Alternatives===
As specified in this process, the reactor effluent is purified by two flash drums and absorption with water to produce chemical-grade ethylene. If chemical-grade ethylene is indeed the desired product, other purification options include caustic washing of the reactor effluent and water removal in a desiccant drying bed. (Morschbacker, 2009) While this purification train is relatively simple and does not require harsh chemical reagents, polymer grade ethylene is more commercially valuable and the additional cost of removing water and diethyl ether contaminants may be justified by increased revenue. Cryogenic distillation was initially simulated to produce polymer-grade ethylene, but utility requirements were found to render this separation economically unviable. (Barrocas and Baratelli, 1983) Further research and optimization may find this purification strategy to be a more valid process. Alternatively, the addition of a cryogenic turboexpander or the use of alternative adsorbents may increase product purity to polymer grade. (Jumonville, 2010) Initial HYSYS simulations indicate that these operations may be feasible with further refinement.

===Wastewater Treatment===
Due to the large volume of wastewater produced, building an on-site wastewater treatment facility may prove to be more economical than paying for third-party wastewater treatment. Flash vessel FL-201 produces 44,600 L/hr of wastewater contaminated with 18.7 vol% ethanol and 0.6 vol% acetaldehyde, while FL-202 produces 2940 L/hr of an aqueous waste consisting of 56.8 vol% ethanol, 42.0 vol% water and 0.9 vol% diethyl ether. The absorption column produces approximately 10,200 liters/hr of wastewater contaminated with 1.2 vol% ethanol, 0.2% diethyl ether and 0.2% acetaldehyde. Utilizing distillation to separate these streams into clean water and volatile organic waste could ultimately reduce the quantity of waste that requires disposal and reduce the overall costs of the process.

==Process Equipment==
Relevant sizing information for each unit operation, estimated by the method described in the “Technical Approach,” can be found in Appendix V. Equipment and piping is assumed to be constructed of carbon steel. It should be noted that the two fired heaters are proportionately large enough to heat the entirety of the process stream and are thus larger than standard equipment.

=Economic Analysis=
[[File:NPV_B1.png|400px|thumb|Fig 2. Projected Cash Flow]]
[[File:sensitivityanalysis_B1.png|400px|thumb| Fig 3. Results of the Sensitivity Analysis on 10 year NPV]]

==Economics Overview==
All final values are normalized to June 2014 USD by CEPCI scaling. It is assumed that all products produced are sold at current market prices.

The Aspen Economic Evaluation module within HYSYS v8.0 was used to estimate capital and operating costs for a 10-year plant life span with a construction start date of April 2015. The price of the 95% ethanol feed stream was estimated at $1.44 per gallon, while the chemical grade ethylene produced is currently selling for approximately $1350 per metric ton. (Today in Energy, 2015; Weddle, 2014) Mapping and sizing calculations were performed by the economics module and a preliminary economic evaluation was completed. Equipment sizes, also estimated by HYSYS, were reviewed to ensure that height, diameter, and volume specifications were within realistic ranges.

The process was ideally projected to operate 360 days per year with a start-up time of one year. In addition, the tax rate was approximated at 40%, an interest rate at 20%, and a salvage value of 20%. Escalation percentages were compounded yearly for the product, raw material, and operating costs. The total capital cost for this process is approximately $16.4 million, which includes all equipment and piping described in the process. The most expensive equipment used in this process are the two fired heaters F-101 and F-102, which have an exceptionally large heat exchange area to adequately heat the feed. Standard heaters may not suffice and additional costs may be incurred for the raw materials and manufacture of this equipment. Including a feed preheater or additional fired heaters may reduce this cost in subsequent design iterations.

The total operating cost is approximately $465 million per year, about $427 million of which is the cost of the ethanol feed and natural gas for the two fired heaters. An additional $1.73 million per year is used for utilities including the cooling water and refrigerant. The labor and maintenance costs of this industrial process were also accounted for within the simulation’s economic analysis. The HYSYS simulation software, in conjunction with the Icarus economic analyzer, estimated there should be 5 operators per 8 hour shift with a cost per operator of $20 per hour. This results in a total operating labor cost of approximately $880,000 per year. In addition, the process will require one supervisor per shift with an hourly rate of $35 for total supervisor salaries of $307,000 per year. Finally, a fixed maintenance rate was estimated at $205,000 per 8000 hours of operation for a total cost of $225,000 per year.

Total product sales are roughly $640 million per year at full operation. The estimated income for this process is thus approximately $175 million per year. After ten years, the plant is projected to have a net present value (NPV) of $391 million and an internal rate of return of approximately 79%. In addition the payout period for the initial investment is estimated to be about 2.7 years. Figure 2 shows the projected cash flow for the project.

==Sensitivity Analysis==
A sensitivity analysis was performed to investigate the effects of fluctuating capital costs, operating costs, raw materials, utility costs and ethylene sales price on the 10-year net present value (NPV) of the project. This analysis was performed by scaling these cost factors according to typical ranges given in Towler and Sinnott and calculating the adjusting the NPV accordingly. The results, illustrated in Figure 3, indicate that the project value is most sensitive to product sales, raw materials costs, and operating costs. Ethylene and ethanol prices are market-determined and cannot be controlled for in the process design, so further optimization should be focused on minimizing the operations cost of the process. (Today in Energy, 2015; Weddle, 2014) However, in feed and product prices do still have a profound effect on profitability and feasibility. A more rigorous market analysis will better inform the profitability outlook.

=Conclusions/Recommendations=

The proposed process produces approximately 460,000 metric tons of 99.7 wt% ethylene annually, with a 10-year net present value of $131 million. If current economic conditions hold, it is recommended that this project proceed to implementation following further design improvements and optimization.

Future design iterations should focus on process optimization, particularly in minimizing operating costs as prescribed by the results of the sensitivity analysis. The development of a heat-exchanger network, potentially with Aspen Energy Analyzer, is one option for decreasing utility requirements and increasing the efficiency of the process overall. Optimization of the fired heaters could also result in decreased operational costs. Although overall profitability is less sensitive to capital costs, reviewing and adjusting equipment sizing would also improve the economic outlook. In particular, exploring alternative heating strategies at the beginning of the process could significantly decrease capital costs. Although there are not any particularly dangerous chemicals utilized in the process, an overall process review should also consider potential failure modes to minimize the safety risk to plant workers and nearby residents.

In addition to economic and safety considerations, harmful emissions and waste streams should be minimized both to bring down the cost of treatment and to decrease environmental effects. The two fired heaters consume a large amount of natural gas per year, emitting about 200,000 tons of CO2 annually, and account for more than half of the capital cost of the process. Although no known toxic gases are produced, carbon capture or other emissions-reduction methods should be considered. Additionally, enough wastewater is produced by this process that building an onsite wastewater treatment center should be considered. This could not only decrease operating costs by eliminating the need for an external contract but also give the plant more control over the final purity of the treated wastewater.

Finally, the current model assumes that all ethylene produced will be sold at a current prices and price or product sales will not be affected by economic variability. A more detailed study of the chemical-grade ethylene market, as well as a more thorough understanding of sales and distribution logistics, would increase the surety of a profitable process.

In summary, the proposed process yields chemical grade ethylene via the catalytic dehydration of ethanol. A 100,000 kg/hr of 95 wt% ethanol, 5% water feed is converted to 53,000 kg/hr of 99.7% chemical-grade ethylene. After 10 years of operation, including a one-year startup time, the process has an NPV of $391 million with an IRR of 79% and a payback period of 2.7 years.
Pending further optimization, this process was determined to be viable and it is recommended for the project to move forward.

=References=

[1] American Chemistry Council. Production of chemicals and plastics in the U.S. in 2013, by type (in 1,000 metric tons). In Statista - The Statistics Portal. August 2014. Available at http://www.statista.com/statistics/299725/total-us-plastics-and-chemicals-shipments-by-type/, Accessed January 15, 2015. – Relative proportions of plastics production.

[2] DuPont Nevada Site Cellulosic Ethanol Facility [Internet]. DuPont Chemical; c2012-2015 [cited 11 Mar. 2015]. Available from: http://biofuels.dupont.com/cellulosic-ethanol/nevada-site-ce-facility/. -- Information on ethanol production in Iowa.

[3] Designing Ethylene Plants. Ethylene [Internet]. Technip; 2014 [cited 13 Mar. 2015]. Available from: http://www.technip.com/en/our-business/onshore/ethylene -- Plant size ranges.

[4] Suppes GJ. Selecting Thermodynamic Models for Process Simulation of Organic VLE and LLE Systems. The University of Missouri-Columbia, Dept of Chemical Engineering. [cited 13 Mar. 2015]. -- Use of NRTL in alcohol separations.

[5] ASPENtech. Appendix A - Property Methods and Calculations. Simulation Basics; A-3 - A-26. 2014.

[6] 190 Proof Ethanol: Technical Data Sheet [Internet]. Decon Labs Inc; 2012 [cited 13 Mar. 2015]. Available from: http://www.deconlabs.com/tds/ETHANOL%20190%20%20PROOF.pdf -- Information regarding 95% ethanol

[7] Hadawey A, Ge Y, Tassou TSA. Energy Savings Through Liquid Pressure Amplification In A Dairy Plant Refrigeration System. The Centre for Energy and Built Environment Research [cited 13 Mar. 2015].

[8] Methane (Chemical Compound). 2015. Encyclopædia Britannica Online. [cited 13 Mar. 2015] Available from: http://www.britannica.com/EBchecked/topic/378264/methane -- Composition of Methane

[9] Composition of Air [Internet]. Engineering Toolbox; [cited 13 Mar. 2015]. Available from: http://www.engineeringtoolbox.com/air-composition-d_212.html. -- Composition of air.

[10] Summary of the Clean Air Act, 2015. United States Environmental Protection Agency. [cited 13 Mar. 2015] Available from: http://www2.epa.gov/laws-regulations/summary-clean-air-act -- Emissions requirements of chemical plants.

[11] Zhang M, Yu Y. Dehydration of Ethanol to Ethylene. Industrial Engineering and Chemical Research. 2013; 52:9505-9514. – Technical information on ethanol to ethylene conversion via dehydration.

[12] AspenTech. Aspen HYSYS Help File v8.0. Aspen Technology, Inc. 2012. - Aspen HYSYS help file used for troubleshooting and assistance on economic analysis.

[13] Towler G, Sinnott R. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. 2nd ed. Boston: Elsevier; 2013. -- General Reference Book

[14] Barrocas H, Baratelli F, inventors; Petroleo Brasileiro S.A., assignee. Process for dehydration of a low molecular weight alcohol. US patent 4,396,789 A. August 2, 1983. - Primary background for process design.

[15] Tsao U, Zasloff HB, inventors; The Lummus Company, assignee. Production of ethylene from ethanol. US patent 4,134,926. January 16, 1979. – Patent for catalytic dehydration of ethylene in a fluidized bed reactor.

[16] Morschbacker, A. Bio-Ethanol Based Ethylene. Polymer Reviews. 2009; 49:79-84. – Overview of bioethanol dehydration process development.

[17] Fan D, Dai DJ, Wu HS. Ethylene Formation by Catalytic Dehydration of Ethanol with Industrial Considerations. Materials. 6, 101-115. doi: 10.3390/ma6010101. - Comparison of types of catalysts used in the dehydration of ethanol and current research into new catalysts.

[18] Chen G, Li S, Jiao F, Yuan Q. Catalytic dehydration of bioethanol to ethylene over TiO2/γ-Al2O3 catalysts in microchannel reactors. Catal. Today 2007, 125, 111–119. - Paper introducing research on modified alumina catalyst for ethanol dehydration.

[19] Jumonville, J. Tutorial on Cryogenic Turboexpanders. Proceedings of the Thirty-Ninth Turbomachinery Symposium; 2010 Oct 4-7; Houston, TX. Houston: Texas A&M University; 2010. -- Use of turboexpander for cryogenic separations

[20] Today in Energy - Daily Prices. US Energy Information Administration website. http://www.eia.gov/todayinenergy/prices.cfm. Accessed March 3rd 2015. - Bulk market price for 95% ethanol.

[21] Weddle, N. ICIS Pricing: Ethylene (Europe). Reed Business Limited. January 10 2014. - Bulk market price for chemical grade ethylene.

=Appendix I - Process Flow Diagram=
[[File:PFD B1.JPG|1200px|center]]

=Appendix II - HYSYS Simulation=
[[File:HYSYS_B1.PNG|center|1200px]]

=Appendix III - Material Streams=
[[File:Streams_B1.png|1200px]]

=Appendix IV - Energy Table=
[[File:Energy_B1.png|600px|center]]

[[File:Utilities.PNG|600px|center]]

=Appendix V - Economics=
[[File:Econsummary_B1.png|center]] 

[[File:Capcost_B1.png|center]] 

[[File:sensitivityanalysis_B1.png|600px|center]]

Ethanol to Ethylene (B1)

2015-03-14T04:54:14Z

Hpoppick: /* Appendix IV - Energy Table */

[[File:BFD_B1.png|600px|thumbnail|alt=Alt text|Conversion of Ethanol to Ethylene]]

Team B1 Final Report

Authors: Harry Poppick, Emm Fulk and Scott Smith

Instructors: Fengqi You, David Wegerer

March 13, 2015

=Executive Summary=

The following report outlines the design and analysis of a process converting ethanol to chemical-grade ethylene via catalytic dehydration. This process consumers 100,000 kg/hr of 95 wt% ethanol, 5 wt% water feedstock and produces 53,000 kg/hr of 99.7 wt% chemical-grade ethylene. The ethanol feed passes through two fixed-bed reactors, each packed with an aluminum oxide catalyst, and the resulting ethylene is purified by two flash tanks and by absorption with water. The process was modeled using Aspen HYSYS simulation software to estimate mass and energy flows and equipment sizing requirements. Based on results of this initial simulation, several alternatives are discussed for increasing the process efficiency and profitability. The use of a fluidized bed reactor or a more ethylene-selective catalyst could increase the production of ethylene per ethanol basis. Additionally, several methods of purification to more valuable polymer-grade ethylene are proposed.

The economic feasibility of this process was evaluated using Aspen Economic Analyzer with the Icarus economics package. Capital cost is approximately $16.4 million total with an operating cost of $465 million per year. The current market prices of the ethanol feed and ethylene sales price are $1.44/gallon and $1350/metric ton respectively. The cost of feed ethanol, process utilities and miscellaneous operational costs total to about $427 million/year. At full operation, revenue at current prices would be approximately $640 million per year. The predicted 10-year net present value of the process is approximately $391 million with an IRR of 79% and a payback period of 2.7 years. A sensitivity analysis indicates that the process is most sensitive to feed prices, product prices and operation cost.

Several recommendations are made for both cost reduction and profit maximization, including the design of a heat exchanger network and the optimization of fired heaters that require high capital investment and large amounts of fuel. A safety review of the process is recommended, as well as the minimization of flue gas effluent and wastewater. It is also suggested that the construction of an onsite wastewater treatment center be considered. Overall, the initial analysis indicates this to be a profitable process and it is recommended the project move forward.

=Introduction=

Ethylene is a critical chemical precursor to a number of different industrial products. It is often derived from petroleum sources and polymerized to polyethylene, one of the most ubiquitous plastics today. (American Chemistry Council, 2013) Recently there has been a significant effort to develop production pathways utilizing biologically-derived feedstocks, such as corn or cellulosic ethanol, rather than traditional fossil-fuel sources. Ethylene can be produced from bioethanol via catalytic dehydration over an aluminum oxide catalyst. The proposed process converts 100,000 kg/hr of 95 wt% ethanol, 5% water feed to 53,000 kg/hr of 99.7% chemical-grade ethylene when operating at full capacity. This process was found to be economically viable with a 10-year net present value (NPV) of $131 million (2014 USD) and a payback period of approximately 2.7 years. This memo will detail the proposed process, as well as outline potential alternatives and economic viability of the project.

=Technical Approach=

Many bioethanol plants are located in the Midwest where large amounts of feedstock crops, such as corn, are grown. As such, this plant will be located in Story county, Iowa, near a large-scale bioethanol production plant. (DuPont Nevada Site, 2012) It is assumed that the supply of bioethanol is consistent and readily available. It is also assumed that other reagents - namely, the aluminum oxide catalyst, heater fuel, utility water and freon refrigerant - are readily available, and that wastewater treatment facilities are located near enough to facilitate the off-site treatment of wastewater. Plant capacity was based on current mid-sized industrial ethylene plants. (Designing Ethylene Plants, 2014)

HYSYS simulations were performed with the NRTL fluid package and Peng-Robinson vapor model. The NRTL fluid package is an activity coefficient model that is especially useful to model the separations of alcohols in aqueous solutions. (Suppes, 2015) In addition, NRTL uses models of binary pairs of components, much like the Wilson equation, to predict chemical interactions at the molecular level. The NRTL package can thus be easily extended to ternary and higher order chemical systems, making it ideal for this type of simulation. The Peng-Robinson vapor model was selected as it is well-suited to account for the non-idealities of the vapor phase reactions and separations integral to this process. (ASPENtech, 2014)

It was assumed that the feed enters the process at ambient temperature and pressure (25 °C, 1 atm) and at a consistent rate and composition with negligible quantities of impurities. The ethanol feed was assumed to be 95% ethanol and 5% water by mass, which is the commercial standard for industrial ethanol. (190 Proof Ethanol, 2012) Storage vessels for the feed ethanol, waste streams and products are assumed to be located nearby to the process. An initial feed pump compensates for pressure drops through the process and reduces the duty on downstream compressors. (Hadawey, 2015)

Natural gas, assumed to consist of 83% methane, 16% ethane and 1% nitrogen by mass, was supplied to two fired heaters at a flow rate estimated by HYSYS. (Methane, 2015) Air fed to the process to enable combustion was assumed to be 23% oxygen and 77% nitrogen by mass. (Composition of Air, 2015) Air streams were fed at 50% molar excess in order to ensure complete combustion and prevent the formation of carbon monoxide in the heater exhaust. Total flue gases are assumed to be 230,000 kg/hr, or 2.2 million tons annually, and consist of 73.8% nitrogen gas, 10.5% carbon dioxide, 8.2% water vapor, and 7.5% oxygen by mass. The only compound of concern in these emissions is the carbon dioxide, a known greenhouse gas. At the time of this report, the quantities of carbon dioxide emitted by this plant annually are within acceptable EPA specifications. (Summary of the Clean Air Act, 2015)

Due to the difficulty of simulation equilibrium and conversion reactions in a single vessel in HYSYS, these two reaction types were simulated in separate equilibrium reactor and conversion reactor units in series. In addition, while HYSYS indicated that reactor units would output separate vapor and liquid streams, it was assumed that in practice this would take the form of a single, two phase stream between each unit. To account for this, mixers were installed downstream of each reactor to combine the liquid and vapor phases of the reactor effluent. The three consequent reactions considered are as follows:
[[File:Equation.PNG|300px|center]]
The optimal reaction temperature was determined to be 400 °C, which promotes the equilibrium reaction of ethanol to ethylene while minimizing byproducts. (Zhang and Yu, 2013) While other byproducts may be produced in this process, these reactions are typically taken to comprise of the bulk of the dehydration reaction. Heat losses over these reactors were assumed to be negligible. (Zhang and Yu, 2013)All major process equipment is assumed to be constructed of high strength carbon steel. (AspenTech, 2012)

The “Sizing Utility” within the Icarus Economic Evaluation module was used to estimate sizes of major equipment based on the process simulation. These values can serve as a benchmark for an initial plant design. Icarus KbaseTM implements a wide variety of mechanical design standards, including ASME and BS5500, in order to calculate accurate equipment sizing. The Icarus sizing module combines equipment prices for standard chemical processing equipment as well as correlations and sizing factors. The advantage of using a software package such as HYSYS to price out individual equipment is that it utilizes up-to-date prices from vendors and distributors when estimating costs. A more in-depth overview of the correlations included in this software can be found in Towler and Sinnott (2009).

=Process Flowsheet=
[[File:Squarepfd_B1.PNG|thumb|400px|alt=Alt text|Fig 1: PFD of the Proposed Process]]

The following process is based primarily on a 1983 US patent titled “Process for dehydration of a low molecular weight alcohol.” (Barrocas and Baratelli, 1983) The process flow diagram can be seen in Figure 1. A larger version of the PFD is included in Appendix I and the HYSYS simulation setup in Appendix II.

The feed enters the process at a rate of 100,000 kg/hr, a temperature and pressure of a 25 °C and 1 atm and at a composition of 95 wt% ethanol and 5 wt% water.It is initially pressurized to 4335 kPa by centrifugal pump P-101 and subsequently heated to 400 °C by fired heater F-101. The heated and pressurized feed enters fixed bed reactor R-101 and contacts with the aluminum oxide catalyst. At this point it dehydrates to form the product, ethylene, as well as the byproducts water, hydrogen, diethyl ether and acetaldehyde. Fired heater F-102 and reactor R-102 increase the overall conversion of the process. Both fired heaters F-101 and F-102 are fueled with natural gas and fed with excess air. The composition of the reactor train effluent is 54.5 wt% ethylene, 37.1 wt% water, 8.1 wt% unreacted ethanol and trace amounts of diethyl ether, acetaldehyde, and hydrogen contaminants.

The pressure of the reactor train effluent is increased to 4500 kPa by compressor K-102 and the temperature decreased to 100 °C by exchange with cold water in heat exchanger E-201. The stream then expands and flashes in flash vessel FL-201, which separates out 82.3% of the unreacted ethanol, 96.6% of the water and virtually all of the acetaldehyde contaminant in the bottoms while sending the ethylene-rich vapor phase out of the top. The top product of FL-202 is compressed to 3500 kPA by K-202 and cooled to 0.0 °C by a freon refrigerant in E-202. At this point the stream is flashed for a second time in vessel FL-202 to remove additional impurities. The top outlet stream consists of 99.5 wt% ethylene, which is fed to the bottom of a 10-tray absorption column that removes a fraction of the residual diethyl ether as well as the remainder of the unreacted ethanol. A stream of absorbent water is fed to the top of the column at 10,000 kg/hr. The product exits the top of the column at a rate of 54,600 kg/hr and has a purity of 99.7% ethylene. Diethyl ether makes up 0.2% of the remaining product stream and is the primary contaminant. Trace amounts of residual water and hydrogen are also present.

Full tables of material and energy streams can be found in Appendices III and IV respectively.

==Process Alternatives==
===Reactor Alternatives===
Two fixed bed reactors, alternating with fired heaters, are used in the dehydration reaction of ethanol to ethylene. However, a fluidized bed reactor can offer better mixing and temperature control than a fixed bed reactor and thus provide the highest possible conversion of ethanol with the greatest selectivity to ethylene. (Tsao and Zasloff, 1979) Fluidized bed reactors also provide a lower rate of catalyst coking and byproduct formation, minimizing separation and catalyst regeneration costs. (Morschbacker, 2009) The major downside of fluidized bed reactors is that few large-scale processes have been built since the technology was developed in the late 1970s. (Tsao and Zasloff, 1979; Morschbacker, 2009) Although implementation of fluidized bed reactors could potentially increase the purity of the ethylene product and/or decrease costs, a small scale pilot process would need to be built and tested before it would be possible to develop an industrial-scale facility.

===Catalyst Alternatives===
Aluminum oxide, specifically gamma alumina, is the most industrially-common catalyst and has been historically used due to its low cost and high stability. (Tsao and Zasloff, 1979; Fan and Dai, n.d.) Recent improvements in selectivity and catalyst stability of activated alumina have been achieved by incorporating titanium oxide into the catalyst, although this increases reaction temperature by approximately 50 °C and decreases catalyst lifespan. (Chen and Li, et. al. 2007) There is also significant ongoing research into HZSM-5 zeolite and heteropolyacids, which are being explored as potential alternatives to alumina oxide. A nanoscale HZSM-5 zeolite catalyst has been shown to operate at the relatively low temperature of 200-300°C, with a 100% ethanol conversion and 99.7% selectivity to ethylene. Initial research has also indicated that it maintains greater than 98% selectivity for 630 operational hours. (Fan and Dai, n.d.) However, the current low cost and ready availability of unmodified alumina oxide makes it a better choice for a process of this scale.

===Purification Alternatives===
As specified in this process, the reactor effluent is purified by two flash drums and absorption with water to produce chemical-grade ethylene. If chemical-grade ethylene is indeed the desired product, other purification options include caustic washing of the reactor effluent and water removal in a desiccant drying bed. (Morschbacker, 2009) While this purification train is relatively simple and does not require harsh chemical reagents, polymer grade ethylene is more commercially valuable and the additional cost of removing water and diethyl ether contaminants may be justified by increased revenue. Cryogenic distillation was initially simulated to produce polymer-grade ethylene, but utility requirements were found to render this separation economically unviable. (Barrocas and Baratelli, 1983) Further research and optimization may find this purification strategy to be a more valid process. Alternatively, the addition of a cryogenic turboexpander or the use of alternative adsorbents may increase product purity to polymer grade. (Jumonville, 2010) Initial HYSYS simulations indicate that these operations may be feasible with further refinement.

===Wastewater Treatment===
Due to the large volume of wastewater produced, building an on-site wastewater treatment facility may prove to be more economical than paying for third-party wastewater treatment. Flash vessel FL-201 produces 44,600 L/hr of wastewater contaminated with 18.7 vol% ethanol and 0.6 vol% acetaldehyde, while FL-202 produces 2940 L/hr of an aqueous waste consisting of 56.8 vol% ethanol, 42.0 vol% water and 0.9 vol% diethyl ether. The absorption column produces approximately 10,200 liters/hr of wastewater contaminated with 1.2 vol% ethanol, 0.2% diethyl ether and 0.2% acetaldehyde. Utilizing distillation to separate these streams into clean water and volatile organic waste could ultimately reduce the quantity of waste that requires disposal and reduce the overall costs of the process.

==Process Equipment==
Relevant sizing information for each unit operation, estimated by the method described in the “Technical Approach,” can be found in Appendix V. Equipment and piping is assumed to be constructed of carbon steel. It should be noted that the two fired heaters are proportionately large enough to heat the entirety of the process stream and are thus larger than standard equipment.

=Economic Analysis=
[[File:NPV_B1.png|400px|thumb|Fig 2. Projected Cash Flow]]
[[File:sensitivityanalysis_B1.png|400px|thumb| Fig 3. Results of the Sensitivity Analysis on 10 year NPV]]

==Economics Overview==
All final values are normalized to June 2014 USD by CEPCI scaling. It is assumed that all products produced are sold at current market prices.

The Aspen Economic Evaluation module within HYSYS v8.0 was used to estimate capital and operating costs for a 10-year plant life span with a construction start date of April 2015. The price of the 95% ethanol feed stream was estimated at $1.44 per gallon, while the chemical grade ethylene produced is currently selling for approximately $1350 per metric ton. (Today in Energy, 2015; Weddle, 2014) Mapping and sizing calculations were performed by the economics module and a preliminary economic evaluation was completed. Equipment sizes, also estimated by HYSYS, were reviewed to ensure that height, diameter, and volume specifications were within realistic ranges.

The process was ideally projected to operate 360 days per year with a start-up time of one year. In addition, the tax rate was approximated at 40%, an interest rate at 20%, and a salvage value of 20%. Escalation percentages were compounded yearly for the product, raw material, and operating costs. The total capital cost for this process is approximately $16.4 million, which includes all equipment and piping described in the process. The most expensive equipment used in this process are the two fired heaters F-101 and F-102, which have an exceptionally large heat exchange area to adequately heat the feed. Standard heaters may not suffice and additional costs may be incurred for the raw materials and manufacture of this equipment. Including a feed preheater or additional fired heaters may reduce this cost in subsequent design iterations.

The total operating cost is approximately $465 million per year, about $427 million of which is the cost of the ethanol feed and natural gas for the two fired heaters. An additional $1.73 million per year is used for utilities including the cooling water and refrigerant. The labor and maintenance costs of this industrial process were also accounted for within the simulation’s economic analysis. The HYSYS simulation software, in conjunction with the Icarus economic analyzer, estimated there should be 5 operators per 8 hour shift with a cost per operator of $20 per hour. This results in a total operating labor cost of approximately $880,000 per year. In addition, the process will require one supervisor per shift with an hourly rate of $35 for total supervisor salaries of $307,000 per year. Finally, a fixed maintenance rate was estimated at $205,000 per 8000 hours of operation for a total cost of $225,000 per year.

Total product sales are roughly $640 million per year at full operation. The estimated income for this process is thus approximately $175 million per year. After ten years, the plant is projected to have a net present value (NPV) of $391 million and an internal rate of return of approximately 79%. In addition the payout period for the initial investment is estimated to be about 2.7 years. Figure 2 shows the projected cash flow for the project.

==Sensitivity Analysis==
A sensitivity analysis was performed to investigate the effects of fluctuating capital costs, operating costs, raw materials, utility costs and ethylene sales price on the 10-year net present value (NPV) of the project. This analysis was performed by scaling these cost factors according to typical ranges given in Towler and Sinnott and calculating the adjusting the NPV accordingly. The results, illustrated in Figure 3, indicate that the project value is most sensitive to product sales, raw materials costs, and operating costs. Ethylene and ethanol prices are market-determined and cannot be controlled for in the process design, so further optimization should be focused on minimizing the operations cost of the process. (Today in Energy, 2015; Weddle, 2014) However, in feed and product prices do still have a profound effect on profitability and feasibility. A more rigorous market analysis will better inform the profitability outlook.

=Conclusions/Recommendations=

The proposed process produces approximately 460,000 metric tons of 99.7 wt% ethylene annually, with a 10-year net present value of $131 million. If current economic conditions hold, it is recommended that this project proceed to implementation following further design improvements and optimization.

Future design iterations should focus on process optimization, particularly in minimizing operating costs as prescribed by the results of the sensitivity analysis. The development of a heat-exchanger network, potentially with Aspen Energy Analyzer, is one option for decreasing utility requirements and increasing the efficiency of the process overall. Optimization of the fired heaters could also result in decreased operational costs. Although overall profitability is less sensitive to capital costs, reviewing and adjusting equipment sizing would also improve the economic outlook. In particular, exploring alternative heating strategies at the beginning of the process could significantly decrease capital costs. Although there are not any particularly dangerous chemicals utilized in the process, an overall process review should also consider potential failure modes to minimize the safety risk to plant workers and nearby residents.

In addition to economic and safety considerations, harmful emissions and waste streams should be minimized both to bring down the cost of treatment and to decrease environmental effects. The two fired heaters consume a large amount of natural gas per year, emitting about 200,000 tons of CO2 annually, and account for more than half of the capital cost of the process. Although no known toxic gases are produced, carbon capture or other emissions-reduction methods should be considered. Additionally, enough wastewater is produced by this process that building an onsite wastewater treatment center should be considered. This could not only decrease operating costs by eliminating the need for an external contract but also give the plant more control over the final purity of the treated wastewater.

Finally, the current model assumes that all ethylene produced will be sold at a current prices and price or product sales will not be affected by economic variability. A more detailed study of the chemical-grade ethylene market, as well as a more thorough understanding of sales and distribution logistics, would increase the surety of a profitable process.

In summary, the proposed process yields chemical grade ethylene via the catalytic dehydration of ethanol. A 100,000 kg/hr of 95 wt% ethanol, 5% water feed is converted to 53,000 kg/hr of 99.7% chemical-grade ethylene. After 10 years of operation, including a one-year startup time, the process has an NPV of $391 million with an IRR of 79% and a payback period of 2.7 years.
Pending further optimization, this process was determined to be viable and it is recommended for the project to move forward.

=References=

[1] American Chemistry Council. Production of chemicals and plastics in the U.S. in 2013, by type (in 1,000 metric tons). In Statista - The Statistics Portal. August 2014. Available at http://www.statista.com/statistics/299725/total-us-plastics-and-chemicals-shipments-by-type/, Accessed January 15, 2015. – Relative proportions of plastics production.

[2] DuPont Nevada Site Cellulosic Ethanol Facility [Internet]. DuPont Chemical; c2012-2015 [cited 11 Mar. 2015]. Available from: http://biofuels.dupont.com/cellulosic-ethanol/nevada-site-ce-facility/. -- Information on ethanol production in Iowa.

[3] Designing Ethylene Plants. Ethylene [Internet]. Technip; 2014 [cited 13 Mar. 2015]. Available from: http://www.technip.com/en/our-business/onshore/ethylene -- Plant size ranges.

[4] Suppes GJ. Selecting Thermodynamic Models for Process Simulation of Organic VLE and LLE Systems. The University of Missouri-Columbia, Dept of Chemical Engineering. [cited 13 Mar. 2015]. -- Use of NRTL in alcohol separations.

[5] ASPENtech. Appendix A - Property Methods and Calculations. Simulation Basics; A-3 - A-26. 2014.

[6] 190 Proof Ethanol: Technical Data Sheet [Internet]. Decon Labs Inc; 2012 [cited 13 Mar. 2015]. Available from: http://www.deconlabs.com/tds/ETHANOL%20190%20%20PROOF.pdf -- Information regarding 95% ethanol

[7] Hadawey A, Ge Y, Tassou TSA. Energy Savings Through Liquid Pressure Amplification In A Dairy Plant Refrigeration System. The Centre for Energy and Built Environment Research [cited 13 Mar. 2015].

[8] Methane (Chemical Compound). 2015. Encyclopædia Britannica Online. [cited 13 Mar. 2015] Available from: http://www.britannica.com/EBchecked/topic/378264/methane -- Composition of Methane

[9] Composition of Air [Internet]. Engineering Toolbox; [cited 13 Mar. 2015]. Available from: http://www.engineeringtoolbox.com/air-composition-d_212.html. -- Composition of air.

[10] Summary of the Clean Air Act, 2015. United States Environmental Protection Agency. [cited 13 Mar. 2015] Available from: http://www2.epa.gov/laws-regulations/summary-clean-air-act -- Emissions requirements of chemical plants.

[11] Zhang M, Yu Y. Dehydration of Ethanol to Ethylene. Industrial Engineering and Chemical Research. 2013; 52:9505-9514. – Technical information on ethanol to ethylene conversion via dehydration.

[12] AspenTech. Aspen HYSYS Help File v8.0. Aspen Technology, Inc. 2012. - Aspen HYSYS help file used for troubleshooting and assistance on economic analysis.

[13] Towler G, Sinnott R. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. 2nd ed. Boston: Elsevier; 2013. -- General Reference Book

[14] Barrocas H, Baratelli F, inventors; Petroleo Brasileiro S.A., assignee. Process for dehydration of a low molecular weight alcohol. US patent 4,396,789 A. August 2, 1983. - Primary background for process design.

[15] Tsao U, Zasloff HB, inventors; The Lummus Company, assignee. Production of ethylene from ethanol. US patent 4,134,926. January 16, 1979. – Patent for catalytic dehydration of ethylene in a fluidized bed reactor.

[16] Morschbacker, A. Bio-Ethanol Based Ethylene. Polymer Reviews. 2009; 49:79-84. – Overview of bioethanol dehydration process development.

[17] Fan D, Dai DJ, Wu HS. Ethylene Formation by Catalytic Dehydration of Ethanol with Industrial Considerations. Materials. 6, 101-115. doi: 10.3390/ma6010101. - Comparison of types of catalysts used in the dehydration of ethanol and current research into new catalysts.

[18] Chen G, Li S, Jiao F, Yuan Q. Catalytic dehydration of bioethanol to ethylene over TiO2/γ-Al2O3 catalysts in microchannel reactors. Catal. Today 2007, 125, 111–119. - Paper introducing research on modified alumina catalyst for ethanol dehydration.

[19] Jumonville, J. Tutorial on Cryogenic Turboexpanders. Proceedings of the Thirty-Ninth Turbomachinery Symposium; 2010 Oct 4-7; Houston, TX. Houston: Texas A&M University; 2010. -- Use of turboexpander for cryogenic separations

[20] Today in Energy - Daily Prices. US Energy Information Administration website. http://www.eia.gov/todayinenergy/prices.cfm. Accessed March 3rd 2015. - Bulk market price for 95% ethanol.

[21] Weddle, N. ICIS Pricing: Ethylene (Europe). Reed Business Limited. January 10 2014. - Bulk market price for chemical grade ethylene.

=Appendix I - Process Flow Diagram=
[[File:PFD B1.JPG|1200px|center]]

=Appendix II - HYSYS Simulation=
[[File:HYSYS_B1.PNG|center|1200px]]

=Appendix III - Material Streams=
[[File:Streams_B1.png|1200px]]

=Appendix IV - Energy Table=
[[File:Energy_B1.png|600px|center]]

[[File:Utilities.png|600px|center]]

=Appendix V - Economics=
[[File:Econsummary_B1.png|center]] 

[[File:Capcost_B1.png|center]] 

[[File:sensitivityanalysis_B1.png|600px|center]]

Ethanol to Ethylene (B1)

2015-03-14T04:53:32Z

Hpoppick: /* Appendix IV - Energy Table */

[[File:BFD_B1.png|600px|thumbnail|alt=Alt text|Conversion of Ethanol to Ethylene]]

Team B1 Final Report

Authors: Harry Poppick, Emm Fulk and Scott Smith

Instructors: Fengqi You, David Wegerer

March 13, 2015

=Executive Summary=

The following report outlines the design and analysis of a process converting ethanol to chemical-grade ethylene via catalytic dehydration. This process consumers 100,000 kg/hr of 95 wt% ethanol, 5 wt% water feedstock and produces 53,000 kg/hr of 99.7 wt% chemical-grade ethylene. The ethanol feed passes through two fixed-bed reactors, each packed with an aluminum oxide catalyst, and the resulting ethylene is purified by two flash tanks and by absorption with water. The process was modeled using Aspen HYSYS simulation software to estimate mass and energy flows and equipment sizing requirements. Based on results of this initial simulation, several alternatives are discussed for increasing the process efficiency and profitability. The use of a fluidized bed reactor or a more ethylene-selective catalyst could increase the production of ethylene per ethanol basis. Additionally, several methods of purification to more valuable polymer-grade ethylene are proposed.

The economic feasibility of this process was evaluated using Aspen Economic Analyzer with the Icarus economics package. Capital cost is approximately $16.4 million total with an operating cost of $465 million per year. The current market prices of the ethanol feed and ethylene sales price are $1.44/gallon and $1350/metric ton respectively. The cost of feed ethanol, process utilities and miscellaneous operational costs total to about $427 million/year. At full operation, revenue at current prices would be approximately $640 million per year. The predicted 10-year net present value of the process is approximately $391 million with an IRR of 79% and a payback period of 2.7 years. A sensitivity analysis indicates that the process is most sensitive to feed prices, product prices and operation cost.

Several recommendations are made for both cost reduction and profit maximization, including the design of a heat exchanger network and the optimization of fired heaters that require high capital investment and large amounts of fuel. A safety review of the process is recommended, as well as the minimization of flue gas effluent and wastewater. It is also suggested that the construction of an onsite wastewater treatment center be considered. Overall, the initial analysis indicates this to be a profitable process and it is recommended the project move forward.

=Introduction=

Ethylene is a critical chemical precursor to a number of different industrial products. It is often derived from petroleum sources and polymerized to polyethylene, one of the most ubiquitous plastics today. (American Chemistry Council, 2013) Recently there has been a significant effort to develop production pathways utilizing biologically-derived feedstocks, such as corn or cellulosic ethanol, rather than traditional fossil-fuel sources. Ethylene can be produced from bioethanol via catalytic dehydration over an aluminum oxide catalyst. The proposed process converts 100,000 kg/hr of 95 wt% ethanol, 5% water feed to 53,000 kg/hr of 99.7% chemical-grade ethylene when operating at full capacity. This process was found to be economically viable with a 10-year net present value (NPV) of $131 million (2014 USD) and a payback period of approximately 2.7 years. This memo will detail the proposed process, as well as outline potential alternatives and economic viability of the project.

=Technical Approach=

Many bioethanol plants are located in the Midwest where large amounts of feedstock crops, such as corn, are grown. As such, this plant will be located in Story county, Iowa, near a large-scale bioethanol production plant. (DuPont Nevada Site, 2012) It is assumed that the supply of bioethanol is consistent and readily available. It is also assumed that other reagents - namely, the aluminum oxide catalyst, heater fuel, utility water and freon refrigerant - are readily available, and that wastewater treatment facilities are located near enough to facilitate the off-site treatment of wastewater. Plant capacity was based on current mid-sized industrial ethylene plants. (Designing Ethylene Plants, 2014)

HYSYS simulations were performed with the NRTL fluid package and Peng-Robinson vapor model. The NRTL fluid package is an activity coefficient model that is especially useful to model the separations of alcohols in aqueous solutions. (Suppes, 2015) In addition, NRTL uses models of binary pairs of components, much like the Wilson equation, to predict chemical interactions at the molecular level. The NRTL package can thus be easily extended to ternary and higher order chemical systems, making it ideal for this type of simulation. The Peng-Robinson vapor model was selected as it is well-suited to account for the non-idealities of the vapor phase reactions and separations integral to this process. (ASPENtech, 2014)

It was assumed that the feed enters the process at ambient temperature and pressure (25 °C, 1 atm) and at a consistent rate and composition with negligible quantities of impurities. The ethanol feed was assumed to be 95% ethanol and 5% water by mass, which is the commercial standard for industrial ethanol. (190 Proof Ethanol, 2012) Storage vessels for the feed ethanol, waste streams and products are assumed to be located nearby to the process. An initial feed pump compensates for pressure drops through the process and reduces the duty on downstream compressors. (Hadawey, 2015)

Natural gas, assumed to consist of 83% methane, 16% ethane and 1% nitrogen by mass, was supplied to two fired heaters at a flow rate estimated by HYSYS. (Methane, 2015) Air fed to the process to enable combustion was assumed to be 23% oxygen and 77% nitrogen by mass. (Composition of Air, 2015) Air streams were fed at 50% molar excess in order to ensure complete combustion and prevent the formation of carbon monoxide in the heater exhaust. Total flue gases are assumed to be 230,000 kg/hr, or 2.2 million tons annually, and consist of 73.8% nitrogen gas, 10.5% carbon dioxide, 8.2% water vapor, and 7.5% oxygen by mass. The only compound of concern in these emissions is the carbon dioxide, a known greenhouse gas. At the time of this report, the quantities of carbon dioxide emitted by this plant annually are within acceptable EPA specifications. (Summary of the Clean Air Act, 2015)

Due to the difficulty of simulation equilibrium and conversion reactions in a single vessel in HYSYS, these two reaction types were simulated in separate equilibrium reactor and conversion reactor units in series. In addition, while HYSYS indicated that reactor units would output separate vapor and liquid streams, it was assumed that in practice this would take the form of a single, two phase stream between each unit. To account for this, mixers were installed downstream of each reactor to combine the liquid and vapor phases of the reactor effluent. The three consequent reactions considered are as follows:
[[File:Equation.PNG|300px|center]]
The optimal reaction temperature was determined to be 400 °C, which promotes the equilibrium reaction of ethanol to ethylene while minimizing byproducts. (Zhang and Yu, 2013) While other byproducts may be produced in this process, these reactions are typically taken to comprise of the bulk of the dehydration reaction. Heat losses over these reactors were assumed to be negligible. (Zhang and Yu, 2013)All major process equipment is assumed to be constructed of high strength carbon steel. (AspenTech, 2012)

The “Sizing Utility” within the Icarus Economic Evaluation module was used to estimate sizes of major equipment based on the process simulation. These values can serve as a benchmark for an initial plant design. Icarus KbaseTM implements a wide variety of mechanical design standards, including ASME and BS5500, in order to calculate accurate equipment sizing. The Icarus sizing module combines equipment prices for standard chemical processing equipment as well as correlations and sizing factors. The advantage of using a software package such as HYSYS to price out individual equipment is that it utilizes up-to-date prices from vendors and distributors when estimating costs. A more in-depth overview of the correlations included in this software can be found in Towler and Sinnott (2009).

=Process Flowsheet=
[[File:Squarepfd_B1.PNG|thumb|400px|alt=Alt text|Fig 1: PFD of the Proposed Process]]

The following process is based primarily on a 1983 US patent titled “Process for dehydration of a low molecular weight alcohol.” (Barrocas and Baratelli, 1983) The process flow diagram can be seen in Figure 1. A larger version of the PFD is included in Appendix I and the HYSYS simulation setup in Appendix II.

The feed enters the process at a rate of 100,000 kg/hr, a temperature and pressure of a 25 °C and 1 atm and at a composition of 95 wt% ethanol and 5 wt% water.It is initially pressurized to 4335 kPa by centrifugal pump P-101 and subsequently heated to 400 °C by fired heater F-101. The heated and pressurized feed enters fixed bed reactor R-101 and contacts with the aluminum oxide catalyst. At this point it dehydrates to form the product, ethylene, as well as the byproducts water, hydrogen, diethyl ether and acetaldehyde. Fired heater F-102 and reactor R-102 increase the overall conversion of the process. Both fired heaters F-101 and F-102 are fueled with natural gas and fed with excess air. The composition of the reactor train effluent is 54.5 wt% ethylene, 37.1 wt% water, 8.1 wt% unreacted ethanol and trace amounts of diethyl ether, acetaldehyde, and hydrogen contaminants.

The pressure of the reactor train effluent is increased to 4500 kPa by compressor K-102 and the temperature decreased to 100 °C by exchange with cold water in heat exchanger E-201. The stream then expands and flashes in flash vessel FL-201, which separates out 82.3% of the unreacted ethanol, 96.6% of the water and virtually all of the acetaldehyde contaminant in the bottoms while sending the ethylene-rich vapor phase out of the top. The top product of FL-202 is compressed to 3500 kPA by K-202 and cooled to 0.0 °C by a freon refrigerant in E-202. At this point the stream is flashed for a second time in vessel FL-202 to remove additional impurities. The top outlet stream consists of 99.5 wt% ethylene, which is fed to the bottom of a 10-tray absorption column that removes a fraction of the residual diethyl ether as well as the remainder of the unreacted ethanol. A stream of absorbent water is fed to the top of the column at 10,000 kg/hr. The product exits the top of the column at a rate of 54,600 kg/hr and has a purity of 99.7% ethylene. Diethyl ether makes up 0.2% of the remaining product stream and is the primary contaminant. Trace amounts of residual water and hydrogen are also present.

Full tables of material and energy streams can be found in Appendices III and IV respectively.

==Process Alternatives==
===Reactor Alternatives===
Two fixed bed reactors, alternating with fired heaters, are used in the dehydration reaction of ethanol to ethylene. However, a fluidized bed reactor can offer better mixing and temperature control than a fixed bed reactor and thus provide the highest possible conversion of ethanol with the greatest selectivity to ethylene. (Tsao and Zasloff, 1979) Fluidized bed reactors also provide a lower rate of catalyst coking and byproduct formation, minimizing separation and catalyst regeneration costs. (Morschbacker, 2009) The major downside of fluidized bed reactors is that few large-scale processes have been built since the technology was developed in the late 1970s. (Tsao and Zasloff, 1979; Morschbacker, 2009) Although implementation of fluidized bed reactors could potentially increase the purity of the ethylene product and/or decrease costs, a small scale pilot process would need to be built and tested before it would be possible to develop an industrial-scale facility.

===Catalyst Alternatives===
Aluminum oxide, specifically gamma alumina, is the most industrially-common catalyst and has been historically used due to its low cost and high stability. (Tsao and Zasloff, 1979; Fan and Dai, n.d.) Recent improvements in selectivity and catalyst stability of activated alumina have been achieved by incorporating titanium oxide into the catalyst, although this increases reaction temperature by approximately 50 °C and decreases catalyst lifespan. (Chen and Li, et. al. 2007) There is also significant ongoing research into HZSM-5 zeolite and heteropolyacids, which are being explored as potential alternatives to alumina oxide. A nanoscale HZSM-5 zeolite catalyst has been shown to operate at the relatively low temperature of 200-300°C, with a 100% ethanol conversion and 99.7% selectivity to ethylene. Initial research has also indicated that it maintains greater than 98% selectivity for 630 operational hours. (Fan and Dai, n.d.) However, the current low cost and ready availability of unmodified alumina oxide makes it a better choice for a process of this scale.

===Purification Alternatives===
As specified in this process, the reactor effluent is purified by two flash drums and absorption with water to produce chemical-grade ethylene. If chemical-grade ethylene is indeed the desired product, other purification options include caustic washing of the reactor effluent and water removal in a desiccant drying bed. (Morschbacker, 2009) While this purification train is relatively simple and does not require harsh chemical reagents, polymer grade ethylene is more commercially valuable and the additional cost of removing water and diethyl ether contaminants may be justified by increased revenue. Cryogenic distillation was initially simulated to produce polymer-grade ethylene, but utility requirements were found to render this separation economically unviable. (Barrocas and Baratelli, 1983) Further research and optimization may find this purification strategy to be a more valid process. Alternatively, the addition of a cryogenic turboexpander or the use of alternative adsorbents may increase product purity to polymer grade. (Jumonville, 2010) Initial HYSYS simulations indicate that these operations may be feasible with further refinement.

===Wastewater Treatment===
Due to the large volume of wastewater produced, building an on-site wastewater treatment facility may prove to be more economical than paying for third-party wastewater treatment. Flash vessel FL-201 produces 44,600 L/hr of wastewater contaminated with 18.7 vol% ethanol and 0.6 vol% acetaldehyde, while FL-202 produces 2940 L/hr of an aqueous waste consisting of 56.8 vol% ethanol, 42.0 vol% water and 0.9 vol% diethyl ether. The absorption column produces approximately 10,200 liters/hr of wastewater contaminated with 1.2 vol% ethanol, 0.2% diethyl ether and 0.2% acetaldehyde. Utilizing distillation to separate these streams into clean water and volatile organic waste could ultimately reduce the quantity of waste that requires disposal and reduce the overall costs of the process.

==Process Equipment==
Relevant sizing information for each unit operation, estimated by the method described in the “Technical Approach,” can be found in Appendix V. Equipment and piping is assumed to be constructed of carbon steel. It should be noted that the two fired heaters are proportionately large enough to heat the entirety of the process stream and are thus larger than standard equipment.

=Economic Analysis=
[[File:NPV_B1.png|400px|thumb|Fig 2. Projected Cash Flow]]
[[File:sensitivityanalysis_B1.png|400px|thumb| Fig 3. Results of the Sensitivity Analysis on 10 year NPV]]

==Economics Overview==
All final values are normalized to June 2014 USD by CEPCI scaling. It is assumed that all products produced are sold at current market prices.

The Aspen Economic Evaluation module within HYSYS v8.0 was used to estimate capital and operating costs for a 10-year plant life span with a construction start date of April 2015. The price of the 95% ethanol feed stream was estimated at $1.44 per gallon, while the chemical grade ethylene produced is currently selling for approximately $1350 per metric ton. (Today in Energy, 2015; Weddle, 2014) Mapping and sizing calculations were performed by the economics module and a preliminary economic evaluation was completed. Equipment sizes, also estimated by HYSYS, were reviewed to ensure that height, diameter, and volume specifications were within realistic ranges.

The process was ideally projected to operate 360 days per year with a start-up time of one year. In addition, the tax rate was approximated at 40%, an interest rate at 20%, and a salvage value of 20%. Escalation percentages were compounded yearly for the product, raw material, and operating costs. The total capital cost for this process is approximately $16.4 million, which includes all equipment and piping described in the process. The most expensive equipment used in this process are the two fired heaters F-101 and F-102, which have an exceptionally large heat exchange area to adequately heat the feed. Standard heaters may not suffice and additional costs may be incurred for the raw materials and manufacture of this equipment. Including a feed preheater or additional fired heaters may reduce this cost in subsequent design iterations.

The total operating cost is approximately $465 million per year, about $427 million of which is the cost of the ethanol feed and natural gas for the two fired heaters. An additional $1.73 million per year is used for utilities including the cooling water and refrigerant. The labor and maintenance costs of this industrial process were also accounted for within the simulation’s economic analysis. The HYSYS simulation software, in conjunction with the Icarus economic analyzer, estimated there should be 5 operators per 8 hour shift with a cost per operator of $20 per hour. This results in a total operating labor cost of approximately $880,000 per year. In addition, the process will require one supervisor per shift with an hourly rate of $35 for total supervisor salaries of $307,000 per year. Finally, a fixed maintenance rate was estimated at $205,000 per 8000 hours of operation for a total cost of $225,000 per year.

Total product sales are roughly $640 million per year at full operation. The estimated income for this process is thus approximately $175 million per year. After ten years, the plant is projected to have a net present value (NPV) of $391 million and an internal rate of return of approximately 79%. In addition the payout period for the initial investment is estimated to be about 2.7 years. Figure 2 shows the projected cash flow for the project.

==Sensitivity Analysis==
A sensitivity analysis was performed to investigate the effects of fluctuating capital costs, operating costs, raw materials, utility costs and ethylene sales price on the 10-year net present value (NPV) of the project. This analysis was performed by scaling these cost factors according to typical ranges given in Towler and Sinnott and calculating the adjusting the NPV accordingly. The results, illustrated in Figure 3, indicate that the project value is most sensitive to product sales, raw materials costs, and operating costs. Ethylene and ethanol prices are market-determined and cannot be controlled for in the process design, so further optimization should be focused on minimizing the operations cost of the process. (Today in Energy, 2015; Weddle, 2014) However, in feed and product prices do still have a profound effect on profitability and feasibility. A more rigorous market analysis will better inform the profitability outlook.

=Conclusions/Recommendations=

The proposed process produces approximately 460,000 metric tons of 99.7 wt% ethylene annually, with a 10-year net present value of $131 million. If current economic conditions hold, it is recommended that this project proceed to implementation following further design improvements and optimization.

Future design iterations should focus on process optimization, particularly in minimizing operating costs as prescribed by the results of the sensitivity analysis. The development of a heat-exchanger network, potentially with Aspen Energy Analyzer, is one option for decreasing utility requirements and increasing the efficiency of the process overall. Optimization of the fired heaters could also result in decreased operational costs. Although overall profitability is less sensitive to capital costs, reviewing and adjusting equipment sizing would also improve the economic outlook. In particular, exploring alternative heating strategies at the beginning of the process could significantly decrease capital costs. Although there are not any particularly dangerous chemicals utilized in the process, an overall process review should also consider potential failure modes to minimize the safety risk to plant workers and nearby residents.

In addition to economic and safety considerations, harmful emissions and waste streams should be minimized both to bring down the cost of treatment and to decrease environmental effects. The two fired heaters consume a large amount of natural gas per year, emitting about 200,000 tons of CO2 annually, and account for more than half of the capital cost of the process. Although no known toxic gases are produced, carbon capture or other emissions-reduction methods should be considered. Additionally, enough wastewater is produced by this process that building an onsite wastewater treatment center should be considered. This could not only decrease operating costs by eliminating the need for an external contract but also give the plant more control over the final purity of the treated wastewater.

Finally, the current model assumes that all ethylene produced will be sold at a current prices and price or product sales will not be affected by economic variability. A more detailed study of the chemical-grade ethylene market, as well as a more thorough understanding of sales and distribution logistics, would increase the surety of a profitable process.

In summary, the proposed process yields chemical grade ethylene via the catalytic dehydration of ethanol. A 100,000 kg/hr of 95 wt% ethanol, 5% water feed is converted to 53,000 kg/hr of 99.7% chemical-grade ethylene. After 10 years of operation, including a one-year startup time, the process has an NPV of $391 million with an IRR of 79% and a payback period of 2.7 years.
Pending further optimization, this process was determined to be viable and it is recommended for the project to move forward.

=References=

[1] American Chemistry Council. Production of chemicals and plastics in the U.S. in 2013, by type (in 1,000 metric tons). In Statista - The Statistics Portal. August 2014. Available at http://www.statista.com/statistics/299725/total-us-plastics-and-chemicals-shipments-by-type/, Accessed January 15, 2015. – Relative proportions of plastics production.

[2] DuPont Nevada Site Cellulosic Ethanol Facility [Internet]. DuPont Chemical; c2012-2015 [cited 11 Mar. 2015]. Available from: http://biofuels.dupont.com/cellulosic-ethanol/nevada-site-ce-facility/. -- Information on ethanol production in Iowa.

[3] Designing Ethylene Plants. Ethylene [Internet]. Technip; 2014 [cited 13 Mar. 2015]. Available from: http://www.technip.com/en/our-business/onshore/ethylene -- Plant size ranges.

[4] Suppes GJ. Selecting Thermodynamic Models for Process Simulation of Organic VLE and LLE Systems. The University of Missouri-Columbia, Dept of Chemical Engineering. [cited 13 Mar. 2015]. -- Use of NRTL in alcohol separations.

[5] ASPENtech. Appendix A - Property Methods and Calculations. Simulation Basics; A-3 - A-26. 2014.

[6] 190 Proof Ethanol: Technical Data Sheet [Internet]. Decon Labs Inc; 2012 [cited 13 Mar. 2015]. Available from: http://www.deconlabs.com/tds/ETHANOL%20190%20%20PROOF.pdf -- Information regarding 95% ethanol

[7] Hadawey A, Ge Y, Tassou TSA. Energy Savings Through Liquid Pressure Amplification In A Dairy Plant Refrigeration System. The Centre for Energy and Built Environment Research [cited 13 Mar. 2015].

[8] Methane (Chemical Compound). 2015. Encyclopædia Britannica Online. [cited 13 Mar. 2015] Available from: http://www.britannica.com/EBchecked/topic/378264/methane -- Composition of Methane

[9] Composition of Air [Internet]. Engineering Toolbox; [cited 13 Mar. 2015]. Available from: http://www.engineeringtoolbox.com/air-composition-d_212.html. -- Composition of air.

[10] Summary of the Clean Air Act, 2015. United States Environmental Protection Agency. [cited 13 Mar. 2015] Available from: http://www2.epa.gov/laws-regulations/summary-clean-air-act -- Emissions requirements of chemical plants.

[11] Zhang M, Yu Y. Dehydration of Ethanol to Ethylene. Industrial Engineering and Chemical Research. 2013; 52:9505-9514. – Technical information on ethanol to ethylene conversion via dehydration.

[12] AspenTech. Aspen HYSYS Help File v8.0. Aspen Technology, Inc. 2012. - Aspen HYSYS help file used for troubleshooting and assistance on economic analysis.

[13] Towler G, Sinnott R. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. 2nd ed. Boston: Elsevier; 2013. -- General Reference Book

[14] Barrocas H, Baratelli F, inventors; Petroleo Brasileiro S.A., assignee. Process for dehydration of a low molecular weight alcohol. US patent 4,396,789 A. August 2, 1983. - Primary background for process design.

[15] Tsao U, Zasloff HB, inventors; The Lummus Company, assignee. Production of ethylene from ethanol. US patent 4,134,926. January 16, 1979. – Patent for catalytic dehydration of ethylene in a fluidized bed reactor.

[16] Morschbacker, A. Bio-Ethanol Based Ethylene. Polymer Reviews. 2009; 49:79-84. – Overview of bioethanol dehydration process development.

[17] Fan D, Dai DJ, Wu HS. Ethylene Formation by Catalytic Dehydration of Ethanol with Industrial Considerations. Materials. 6, 101-115. doi: 10.3390/ma6010101. - Comparison of types of catalysts used in the dehydration of ethanol and current research into new catalysts.

[18] Chen G, Li S, Jiao F, Yuan Q. Catalytic dehydration of bioethanol to ethylene over TiO2/γ-Al2O3 catalysts in microchannel reactors. Catal. Today 2007, 125, 111–119. - Paper introducing research on modified alumina catalyst for ethanol dehydration.

[19] Jumonville, J. Tutorial on Cryogenic Turboexpanders. Proceedings of the Thirty-Ninth Turbomachinery Symposium; 2010 Oct 4-7; Houston, TX. Houston: Texas A&M University; 2010. -- Use of turboexpander for cryogenic separations

[20] Today in Energy - Daily Prices. US Energy Information Administration website. http://www.eia.gov/todayinenergy/prices.cfm. Accessed March 3rd 2015. - Bulk market price for 95% ethanol.

[21] Weddle, N. ICIS Pricing: Ethylene (Europe). Reed Business Limited. January 10 2014. - Bulk market price for chemical grade ethylene.

=Appendix I - Process Flow Diagram=
[[File:PFD B1.JPG|1200px|center]]

=Appendix II - HYSYS Simulation=
[[File:HYSYS_B1.PNG|center|1200px]]

=Appendix III - Material Streams=
[[File:Streams_B1.png|1200px]]

=Appendix IV - Energy Table=
[[File:Energy_B1.png|600px|center]]
[[File:Utilities.png|600px|center]]

=Appendix V - Economics=
[[File:Econsummary_B1.png|center]] 

[[File:Capcost_B1.png|center]] 

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2015-03-14T04:53:00Z

Hpoppick:

Ethanol to Ethylene (B1)

2015-03-14T04:45:49Z

Hpoppick: /* Technical Approach */

[[File:BFD_B1.png|600px|thumbnail|alt=Alt text|Conversion of Ethanol to Ethylene]]

Team B1 Final Report

Authors: Harry Poppick, Emm Fulk and Scott Smith

Instructors: Fengqi You, David Wegerer

March 13, 2015

=Executive Summary=

The following report outlines the design and analysis of a process converting ethanol to chemical-grade ethylene via catalytic dehydration. This process consumers 100,000 kg/hr of 95 wt% ethanol, 5 wt% water feedstock and produces 53,000 kg/hr of 99.7 wt% chemical-grade ethylene. The ethanol feed passes through two fixed-bed reactors, each packed with an aluminum oxide catalyst, and the resulting ethylene is purified by two flash tanks and by absorption with water. The process was modeled using Aspen HYSYS simulation software to estimate mass and energy flows and equipment sizing requirements. Based on results of this initial simulation, several alternatives are discussed for increasing the process efficiency and profitability. The use of a fluidized bed reactor or a more ethylene-selective catalyst could increase the production of ethylene per ethanol basis. Additionally, several methods of purification to more valuable polymer-grade ethylene are proposed.

The economic feasibility of this process was evaluated using Aspen Economic Analyzer with the Icarus economics package. Capital cost is approximately $16.4 million total with an operating cost of $465 million per year. The current market prices of the ethanol feed and ethylene sales price are $1.44/gallon and $1350/metric ton respectively. The cost of feed ethanol, process utilities and miscellaneous operational costs total to about $427 million/year. At full operation, revenue at current prices would be approximately $640 million per year. The predicted 10-year net present value of the process is approximately $391 million with an IRR of 79% and a payback period of 2.7 years. A sensitivity analysis indicates that the process is most sensitive to feed prices, product prices and operation cost.

Several recommendations are made for both cost reduction and profit maximization, including the design of a heat exchanger network and the optimization of fired heaters that require high capital investment and large amounts of fuel. A safety review of the process is recommended, as well as the minimization of flue gas effluent and wastewater. It is also suggested that the construction of an onsite wastewater treatment center be considered. Overall, the initial analysis indicates this to be a profitable process and it is recommended the project move forward.

=Introduction=

Ethylene is a critical chemical precursor to a number of different industrial products. It is often derived from petroleum sources and polymerized to polyethylene, one of the most ubiquitous plastics today. (American Chemistry Council, 2013) Recently there has been a significant effort to develop production pathways utilizing biologically-derived feedstocks, such as corn or cellulosic ethanol, rather than traditional fossil-fuel sources. Ethylene can be produced from bioethanol via catalytic dehydration over an aluminum oxide catalyst. The proposed process converts 100,000 kg/hr of 95 wt% ethanol, 5% water feed to 53,000 kg/hr of 99.7% chemical-grade ethylene when operating at full capacity. This process was found to be economically viable with a 10-year net present value (NPV) of $131 million (2014 USD) and a payback period of approximately 2.7 years. This memo will detail the proposed process, as well as outline potential alternatives and economic viability of the project.

=Technical Approach=

Many bioethanol plants are located in the Midwest where large amounts of feedstock crops, such as corn, are grown. As such, this plant will be located in Story county, Iowa, near a large-scale bioethanol production plant. (DuPont Nevada Site, 2012) It is assumed that the supply of bioethanol is consistent and readily available. It is also assumed that other reagents - namely, the aluminum oxide catalyst, heater fuel, utility water and freon refrigerant - are readily available, and that wastewater treatment facilities are located near enough to facilitate the off-site treatment of wastewater. Plant capacity was based on current mid-sized industrial ethylene plants. (Designing Ethylene Plants, 2014)

HYSYS simulations were performed with the NRTL fluid package and Peng-Robinson vapor model. The NRTL fluid package is an activity coefficient model that is especially useful to model the separations of alcohols in aqueous solutions. (Suppes, 2015) In addition, NRTL uses models of binary pairs of components, much like the Wilson equation, to predict chemical interactions at the molecular level. The NRTL package can thus be easily extended to ternary and higher order chemical systems, making it ideal for this type of simulation. The Peng-Robinson vapor model was selected as it is well-suited to account for the non-idealities of the vapor phase reactions and separations integral to this process. (ASPENtech, 2014)

It was assumed that the feed enters the process at ambient temperature and pressure (25 °C, 1 atm) and at a consistent rate and composition with negligible quantities of impurities. The ethanol feed was assumed to be 95% ethanol and 5% water by mass, which is the commercial standard for industrial ethanol. (190 Proof Ethanol, 2012) Storage vessels for the feed ethanol, waste streams and products are assumed to be located nearby to the process. An initial feed pump compensates for pressure drops through the process and reduces the duty on downstream compressors. (Hadawey, 2015)

Natural gas, assumed to consist of 83% methane, 16% ethane and 1% nitrogen by mass, was supplied to two fired heaters at a flow rate estimated by HYSYS. (Methane, 2015) Air fed to the process to enable combustion was assumed to be 23% oxygen and 77% nitrogen by mass. (Composition of Air, 2015) Air streams were fed at 50% molar excess in order to ensure complete combustion and prevent the formation of carbon monoxide in the heater exhaust. Total flue gases are assumed to be 230,000 kg/hr, or 2.2 million tons annually, and consist of 73.8% nitrogen gas, 10.5% carbon dioxide, 8.2% water vapor, and 7.5% oxygen by mass. The only compound of concern in these emissions is the carbon dioxide, a known greenhouse gas. At the time of this report, the quantities of carbon dioxide emitted by this plant annually are within acceptable EPA specifications. (Summary of the Clean Air Act, 2015)

Due to the difficulty of simulation equilibrium and conversion reactions in a single vessel in HYSYS, these two reaction types were simulated in separate equilibrium reactor and conversion reactor units in series. In addition, while HYSYS indicated that reactor units would output separate vapor and liquid streams, it was assumed that in practice this would take the form of a single, two phase stream between each unit. To account for this, mixers were installed downstream of each reactor to combine the liquid and vapor phases of the reactor effluent. The three consequent reactions considered are as follows:
[[File:Equation.PNG|300px|center]]
The optimal reaction temperature was determined to be 400 °C, which promotes the equilibrium reaction of ethanol to ethylene while minimizing byproducts. (Zhang and Yu, 2013) While other byproducts may be produced in this process, these reactions are typically taken to comprise of the bulk of the dehydration reaction. Heat losses over these reactors were assumed to be negligible. (Zhang and Yu, 2013)All major process equipment is assumed to be constructed of high strength carbon steel. (AspenTech, 2012)

The “Sizing Utility” within the Icarus Economic Evaluation module was used to estimate sizes of major equipment based on the process simulation. These values can serve as a benchmark for an initial plant design. Icarus KbaseTM implements a wide variety of mechanical design standards, including ASME and BS5500, in order to calculate accurate equipment sizing. The Icarus sizing module combines equipment prices for standard chemical processing equipment as well as correlations and sizing factors. The advantage of using a software package such as HYSYS to price out individual equipment is that it utilizes up-to-date prices from vendors and distributors when estimating costs. A more in-depth overview of the correlations included in this software can be found in Towler and Sinnott (2009).

=Process Flowsheet=
[[File:Squarepfd_B1.PNG|thumb|400px|alt=Alt text|Fig 1: PFD of the Proposed Process]]

The following process is based primarily on a 1983 US patent titled “Process for dehydration of a low molecular weight alcohol.” (Barrocas and Baratelli, 1983) The process flow diagram can be seen in Figure 1. A larger version of the PFD is included in Appendix I and the HYSYS simulation setup in Appendix II.

The feed enters the process at a rate of 100,000 kg/hr, a temperature and pressure of a 25 °C and 1 atm and at a composition of 95 wt% ethanol and 5 wt% water.It is initially pressurized to 4335 kPa by centrifugal pump P-101 and subsequently heated to 400 °C by fired heater F-101. The heated and pressurized feed enters fixed bed reactor R-101 and contacts with the aluminum oxide catalyst. At this point it dehydrates to form the product, ethylene, as well as the byproducts water, hydrogen, diethyl ether and acetaldehyde. Fired heater F-102 and reactor R-102 increase the overall conversion of the process. Both fired heaters F-101 and F-102 are fueled with natural gas and fed with excess air. The composition of the reactor train effluent is 54.5 wt% ethylene, 37.1 wt% water, 8.1 wt% unreacted ethanol and trace amounts of diethyl ether, acetaldehyde, and hydrogen contaminants.

The pressure of the reactor train effluent is increased to 4500 kPa by compressor K-102 and the temperature decreased to 100 °C by exchange with cold water in heat exchanger E-201. The stream then expands and flashes in flash vessel FL-201, which separates out 82.3% of the unreacted ethanol, 96.6% of the water and virtually all of the acetaldehyde contaminant in the bottoms while sending the ethylene-rich vapor phase out of the top. The top product of FL-202 is compressed to 3500 kPA by K-202 and cooled to 0.0 °C by a freon refrigerant in E-202. At this point the stream is flashed for a second time in vessel FL-202 to remove additional impurities. The top outlet stream consists of 99.5 wt% ethylene, which is fed to the bottom of a 10-tray absorption column that removes a fraction of the residual diethyl ether as well as the remainder of the unreacted ethanol. A stream of absorbent water is fed to the top of the column at 10,000 kg/hr. The product exits the top of the column at a rate of 54,600 kg/hr and has a purity of 99.7% ethylene. Diethyl ether makes up 0.2% of the remaining product stream and is the primary contaminant. Trace amounts of residual water and hydrogen are also present.

Full tables of material and energy streams can be found in Appendices III and IV respectively.

==Process Alternatives==
===Reactor Alternatives===
Two fixed bed reactors, alternating with fired heaters, are used in the dehydration reaction of ethanol to ethylene. However, a fluidized bed reactor can offer better mixing and temperature control than a fixed bed reactor and thus provide the highest possible conversion of ethanol with the greatest selectivity to ethylene. (Tsao and Zasloff, 1979) Fluidized bed reactors also provide a lower rate of catalyst coking and byproduct formation, minimizing separation and catalyst regeneration costs. (Morschbacker, 2009) The major downside of fluidized bed reactors is that few large-scale processes have been built since the technology was developed in the late 1970s. (Tsao and Zasloff, 1979; Morschbacker, 2009) Although implementation of fluidized bed reactors could potentially increase the purity of the ethylene product and/or decrease costs, a small scale pilot process would need to be built and tested before it would be possible to develop an industrial-scale facility.

===Catalyst Alternatives===
Aluminum oxide, specifically gamma alumina, is the most industrially-common catalyst and has been historically used due to its low cost and high stability. (Tsao and Zasloff, 1979; Fan and Dai, n.d.) Recent improvements in selectivity and catalyst stability of activated alumina have been achieved by incorporating titanium oxide into the catalyst, although this increases reaction temperature by approximately 50 °C and decreases catalyst lifespan. (Chen and Li, et. al. 2007) There is also significant ongoing research into HZSM-5 zeolite and heteropolyacids, which are being explored as potential alternatives to alumina oxide. A nanoscale HZSM-5 zeolite catalyst has been shown to operate at the relatively low temperature of 200-300°C, with a 100% ethanol conversion and 99.7% selectivity to ethylene. Initial research has also indicated that it maintains greater than 98% selectivity for 630 operational hours. (Fan and Dai, n.d.) However, the current low cost and ready availability of unmodified alumina oxide makes it a better choice for a process of this scale.

===Purification Alternatives===
As specified in this process, the reactor effluent is purified by two flash drums and absorption with water to produce chemical-grade ethylene. If chemical-grade ethylene is indeed the desired product, other purification options include caustic washing of the reactor effluent and water removal in a desiccant drying bed. (Morschbacker, 2009) While this purification train is relatively simple and does not require harsh chemical reagents, polymer grade ethylene is more commercially valuable and the additional cost of removing water and diethyl ether contaminants may be justified by increased revenue. Cryogenic distillation was initially simulated to produce polymer-grade ethylene, but utility requirements were found to render this separation economically unviable. (Barrocas and Baratelli, 1983) Further research and optimization may find this purification strategy to be a more valid process. Alternatively, the addition of a cryogenic turboexpander or the use of alternative adsorbents may increase product purity to polymer grade. (Jumonville, 2010) Initial HYSYS simulations indicate that these operations may be feasible with further refinement.

===Wastewater Treatment===
Due to the large volume of wastewater produced, building an on-site wastewater treatment facility may prove to be more economical than paying for third-party wastewater treatment. Flash vessel FL-201 produces 44,600 L/hr of wastewater contaminated with 18.7 vol% ethanol and 0.6 vol% acetaldehyde, while FL-202 produces 2940 L/hr of an aqueous waste consisting of 56.8 vol% ethanol, 42.0 vol% water and 0.9 vol% diethyl ether. The absorption column produces approximately 10,200 liters/hr of wastewater contaminated with 1.2 vol% ethanol, 0.2% diethyl ether and 0.2% acetaldehyde. Utilizing distillation to separate these streams into clean water and volatile organic waste could ultimately reduce the quantity of waste that requires disposal and reduce the overall costs of the process.

==Process Equipment==
Relevant sizing information for each unit operation, estimated by the method described in the “Technical Approach,” can be found in Appendix V. Equipment and piping is assumed to be constructed of carbon steel. It should be noted that the two fired heaters are proportionately large enough to heat the entirety of the process stream and are thus larger than standard equipment.

=Economic Analysis=
[[File:NPV_B1.png|400px|thumb|Fig 2. Projected Cash Flow]]
[[File:sensitivityanalysis_B1.png|400px|thumb| Fig 3. Results of the Sensitivity Analysis on 10 year NPV]]

==Economics Overview==
All final values are normalized to June 2014 USD by CEPCI scaling. It is assumed that all products produced are sold at current market prices.

The Aspen Economic Evaluation module within HYSYS v8.0 was used to estimate capital and operating costs for a 10-year plant life span with a construction start date of April 2015. The price of the 95% ethanol feed stream was estimated at $1.44 per gallon, while the chemical grade ethylene produced is currently selling for approximately $1350 per metric ton. (Today in Energy, 2015; Weddle, 2014) Mapping and sizing calculations were performed by the economics module and a preliminary economic evaluation was completed. Equipment sizes, also estimated by HYSYS, were reviewed to ensure that height, diameter, and volume specifications were within realistic ranges.

The process was ideally projected to operate 360 days per year with a start-up time of one year. In addition, the tax rate was approximated at 40%, an interest rate at 20%, and a salvage value of 20%. Escalation percentages were compounded yearly for the product, raw material, and operating costs. The total capital cost for this process is approximately $16.4 million, which includes all equipment and piping described in the process. The most expensive equipment used in this process are the two fired heaters F-101 and F-102, which have an exceptionally large heat exchange area to adequately heat the feed. Standard heaters may not suffice and additional costs may be incurred for the raw materials and manufacture of this equipment. Including a feed preheater or additional fired heaters may reduce this cost in subsequent design iterations.

The total operating cost is approximately $465 million per year, about $427 million of which is the cost of the ethanol feed and natural gas for the two fired heaters. An additional $1.73 million per year is used for utilities including the cooling water and refrigerant. The labor and maintenance costs of this industrial process were also accounted for within the simulation’s economic analysis. The HYSYS simulation software, in conjunction with the Icarus economic analyzer, estimated there should be 5 operators per 8 hour shift with a cost per operator of $20 per hour. This results in a total operating labor cost of approximately $880,000 per year. In addition, the process will require one supervisor per shift with an hourly rate of $35 for total supervisor salaries of $307,000 per year. Finally, a fixed maintenance rate was estimated at $205,000 per 8000 hours of operation for a total cost of $225,000 per year.

Total product sales are roughly $640 million per year at full operation. The estimated income for this process is thus approximately $175 million per year. After ten years, the plant is projected to have a net present value (NPV) of $391 million and an internal rate of return of approximately 79%. In addition the payout period for the initial investment is estimated to be about 2.7 years. Figure 2 shows the projected cash flow for the project.

==Sensitivity Analysis==
A sensitivity analysis was performed to investigate the effects of fluctuating capital costs, operating costs, raw materials, utility costs and ethylene sales price on the 10-year net present value (NPV) of the project. This analysis was performed by scaling these cost factors according to typical ranges given in Towler and Sinnott and calculating the adjusting the NPV accordingly. The results, illustrated in Figure 3, indicate that the project value is most sensitive to product sales, raw materials costs, and operating costs. Ethylene and ethanol prices are market-determined and cannot be controlled for in the process design, so further optimization should be focused on minimizing the operations cost of the process. (Today in Energy, 2015; Weddle, 2014) However, in feed and product prices do still have a profound effect on profitability and feasibility. A more rigorous market analysis will better inform the profitability outlook.

=Conclusions/Recommendations=

The proposed process produces approximately 460,000 metric tons of 99.7 wt% ethylene annually, with a 10-year net present value of $131 million. If current economic conditions hold, it is recommended that this project proceed to implementation following further design improvements and optimization.

Future design iterations should focus on process optimization, particularly in minimizing operating costs as prescribed by the results of the sensitivity analysis. The development of a heat-exchanger network, potentially with Aspen Energy Analyzer, is one option for decreasing utility requirements and increasing the efficiency of the process overall. Optimization of the fired heaters could also result in decreased operational costs. Although overall profitability is less sensitive to capital costs, reviewing and adjusting equipment sizing would also improve the economic outlook. In particular, exploring alternative heating strategies at the beginning of the process could significantly decrease capital costs. Although there are not any particularly dangerous chemicals utilized in the process, an overall process review should also consider potential failure modes to minimize the safety risk to plant workers and nearby residents.

In addition to economic and safety considerations, harmful emissions and waste streams should be minimized both to bring down the cost of treatment and to decrease environmental effects. The two fired heaters consume a large amount of natural gas per year, emitting about 200,000 tons of CO2 annually, and account for more than half of the capital cost of the process. Although no known toxic gases are produced, carbon capture or other emissions-reduction methods should be considered. Additionally, enough wastewater is produced by this process that building an onsite wastewater treatment center should be considered. This could not only decrease operating costs by eliminating the need for an external contract but also give the plant more control over the final purity of the treated wastewater.

Finally, the current model assumes that all ethylene produced will be sold at a current prices and price or product sales will not be affected by economic variability. A more detailed study of the chemical-grade ethylene market, as well as a more thorough understanding of sales and distribution logistics, would increase the surety of a profitable process.

In summary, the proposed process yields chemical grade ethylene via the catalytic dehydration of ethanol. A 100,000 kg/hr of 95 wt% ethanol, 5% water feed is converted to 53,000 kg/hr of 99.7% chemical-grade ethylene. After 10 years of operation, including a one-year startup time, the process has an NPV of $391 million with an IRR of 79% and a payback period of 2.7 years.
Pending further optimization, this process was determined to be viable and it is recommended for the project to move forward.

=References=

[1] American Chemistry Council. Production of chemicals and plastics in the U.S. in 2013, by type (in 1,000 metric tons). In Statista - The Statistics Portal. August 2014. Available at http://www.statista.com/statistics/299725/total-us-plastics-and-chemicals-shipments-by-type/, Accessed January 15, 2015. – Relative proportions of plastics production.

[2] DuPont Nevada Site Cellulosic Ethanol Facility [Internet]. DuPont Chemical; c2012-2015 [cited 11 Mar. 2015]. Available from: http://biofuels.dupont.com/cellulosic-ethanol/nevada-site-ce-facility/. -- Information on ethanol production in Iowa.

[3] Designing Ethylene Plants. Ethylene [Internet]. Technip; 2014 [cited 13 Mar. 2015]. Available from: http://www.technip.com/en/our-business/onshore/ethylene -- Plant size ranges.

[4] Suppes GJ. Selecting Thermodynamic Models for Process Simulation of Organic VLE and LLE Systems. The University of Missouri-Columbia, Dept of Chemical Engineering. [cited 13 Mar. 2015]. -- Use of NRTL in alcohol separations.

[5] ASPENtech. Appendix A - Property Methods and Calculations. Simulation Basics; A-3 - A-26. 2014.

[6] 190 Proof Ethanol: Technical Data Sheet [Internet]. Decon Labs Inc; 2012 [cited 13 Mar. 2015]. Available from: http://www.deconlabs.com/tds/ETHANOL%20190%20%20PROOF.pdf -- Information regarding 95% ethanol

[7] Hadawey A, Ge Y, Tassou TSA. Energy Savings Through Liquid Pressure Amplification In A Dairy Plant Refrigeration System. The Centre for Energy and Built Environment Research [cited 13 Mar. 2015].

[8] Methane (Chemical Compound). 2015. Encyclopædia Britannica Online. [cited 13 Mar. 2015] Available from: http://www.britannica.com/EBchecked/topic/378264/methane -- Composition of Methane

[9] Composition of Air [Internet]. Engineering Toolbox; [cited 13 Mar. 2015]. Available from: http://www.engineeringtoolbox.com/air-composition-d_212.html. -- Composition of air.

[10] Summary of the Clean Air Act, 2015. United States Environmental Protection Agency. [cited 13 Mar. 2015] Available from: http://www2.epa.gov/laws-regulations/summary-clean-air-act -- Emissions requirements of chemical plants.

[11] Zhang M, Yu Y. Dehydration of Ethanol to Ethylene. Industrial Engineering and Chemical Research. 2013; 52:9505-9514. – Technical information on ethanol to ethylene conversion via dehydration.

[12] AspenTech. Aspen HYSYS Help File v8.0. Aspen Technology, Inc. 2012. - Aspen HYSYS help file used for troubleshooting and assistance on economic analysis.

[13] Towler G, Sinnott R. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. 2nd ed. Boston: Elsevier; 2013. -- General Reference Book

[14] Barrocas H, Baratelli F, inventors; Petroleo Brasileiro S.A., assignee. Process for dehydration of a low molecular weight alcohol. US patent 4,396,789 A. August 2, 1983. - Primary background for process design.

[15] Tsao U, Zasloff HB, inventors; The Lummus Company, assignee. Production of ethylene from ethanol. US patent 4,134,926. January 16, 1979. – Patent for catalytic dehydration of ethylene in a fluidized bed reactor.

[16] Morschbacker, A. Bio-Ethanol Based Ethylene. Polymer Reviews. 2009; 49:79-84. – Overview of bioethanol dehydration process development.

[17] Fan D, Dai DJ, Wu HS. Ethylene Formation by Catalytic Dehydration of Ethanol with Industrial Considerations. Materials. 6, 101-115. doi: 10.3390/ma6010101. - Comparison of types of catalysts used in the dehydration of ethanol and current research into new catalysts.

[18] Chen G, Li S, Jiao F, Yuan Q. Catalytic dehydration of bioethanol to ethylene over TiO2/γ-Al2O3 catalysts in microchannel reactors. Catal. Today 2007, 125, 111–119. - Paper introducing research on modified alumina catalyst for ethanol dehydration.

[19] Jumonville, J. Tutorial on Cryogenic Turboexpanders. Proceedings of the Thirty-Ninth Turbomachinery Symposium; 2010 Oct 4-7; Houston, TX. Houston: Texas A&M University; 2010. -- Use of turboexpander for cryogenic separations

[20] Today in Energy - Daily Prices. US Energy Information Administration website. http://www.eia.gov/todayinenergy/prices.cfm. Accessed March 3rd 2015. - Bulk market price for 95% ethanol.

[21] Weddle, N. ICIS Pricing: Ethylene (Europe). Reed Business Limited. January 10 2014. - Bulk market price for chemical grade ethylene.

=Appendix I - Process Flow Diagram=
[[File:PFD B1.JPG|1200px|center]]

=Appendix II - HYSYS Simulation=
[[File:HYSYS_B1.PNG|center|1200px]]

=Appendix III - Material Streams=
[[File:Streams_B1.png|1200px]]

=Appendix IV - Energy Table=
[[File:Energy_B1.png|600px|center]]

=Appendix V - Economics=
[[File:Econsummary_B1.png|center]] 

[[File:Capcost_B1.png|center]] 

[[File:sensitivityanalysis_B1.png|600px|center]]

Ethanol to Ethylene (B1)

2015-03-14T04:45:38Z

Hpoppick: /* Technical Approach */

[[File:BFD_B1.png|600px|thumbnail|alt=Alt text|Conversion of Ethanol to Ethylene]]

Team B1 Final Report

Authors: Harry Poppick, Emm Fulk and Scott Smith

Instructors: Fengqi You, David Wegerer

March 13, 2015

=Executive Summary=

The following report outlines the design and analysis of a process converting ethanol to chemical-grade ethylene via catalytic dehydration. This process consumers 100,000 kg/hr of 95 wt% ethanol, 5 wt% water feedstock and produces 53,000 kg/hr of 99.7 wt% chemical-grade ethylene. The ethanol feed passes through two fixed-bed reactors, each packed with an aluminum oxide catalyst, and the resulting ethylene is purified by two flash tanks and by absorption with water. The process was modeled using Aspen HYSYS simulation software to estimate mass and energy flows and equipment sizing requirements. Based on results of this initial simulation, several alternatives are discussed for increasing the process efficiency and profitability. The use of a fluidized bed reactor or a more ethylene-selective catalyst could increase the production of ethylene per ethanol basis. Additionally, several methods of purification to more valuable polymer-grade ethylene are proposed.

The economic feasibility of this process was evaluated using Aspen Economic Analyzer with the Icarus economics package. Capital cost is approximately $16.4 million total with an operating cost of $465 million per year. The current market prices of the ethanol feed and ethylene sales price are $1.44/gallon and $1350/metric ton respectively. The cost of feed ethanol, process utilities and miscellaneous operational costs total to about $427 million/year. At full operation, revenue at current prices would be approximately $640 million per year. The predicted 10-year net present value of the process is approximately $391 million with an IRR of 79% and a payback period of 2.7 years. A sensitivity analysis indicates that the process is most sensitive to feed prices, product prices and operation cost.

Several recommendations are made for both cost reduction and profit maximization, including the design of a heat exchanger network and the optimization of fired heaters that require high capital investment and large amounts of fuel. A safety review of the process is recommended, as well as the minimization of flue gas effluent and wastewater. It is also suggested that the construction of an onsite wastewater treatment center be considered. Overall, the initial analysis indicates this to be a profitable process and it is recommended the project move forward.

=Introduction=

Ethylene is a critical chemical precursor to a number of different industrial products. It is often derived from petroleum sources and polymerized to polyethylene, one of the most ubiquitous plastics today. (American Chemistry Council, 2013) Recently there has been a significant effort to develop production pathways utilizing biologically-derived feedstocks, such as corn or cellulosic ethanol, rather than traditional fossil-fuel sources. Ethylene can be produced from bioethanol via catalytic dehydration over an aluminum oxide catalyst. The proposed process converts 100,000 kg/hr of 95 wt% ethanol, 5% water feed to 53,000 kg/hr of 99.7% chemical-grade ethylene when operating at full capacity. This process was found to be economically viable with a 10-year net present value (NPV) of $131 million (2014 USD) and a payback period of approximately 2.7 years. This memo will detail the proposed process, as well as outline potential alternatives and economic viability of the project.

=Technical Approach=

Many bioethanol plants are located in the Midwest where large amounts of feedstock crops, such as corn, are grown. As such, this plant will be located in Story county, Iowa, near a large-scale bioethanol production plant. (DuPont Nevada Site, 2012) It is assumed that the supply of bioethanol is consistent and readily available. It is also assumed that other reagents - namely, the aluminum oxide catalyst, heater fuel, utility water and freon refrigerant - are readily available, and that wastewater treatment facilities are located near enough to facilitate the off-site treatment of wastewater. Plant capacity was based on current mid-sized industrial ethylene plants. (Designing Ethylene Plants, 2014)

HYSYS simulations were performed with the NRTL fluid package and Peng-Robinson vapor model. The NRTL fluid package is an activity coefficient model that is especially useful to model the separations of alcohols in aqueous solutions. (Suppes, 2015) In addition, NRTL uses models of binary pairs of components, much like the Wilson equation, to predict chemical interactions at the molecular level. The NRTL package can thus be easily extended to ternary and higher order chemical systems, making it ideal for this type of simulation. The Peng-Robinson vapor model was selected as it is well-suited to account for the non-idealities of the vapor phase reactions and separations integral to this process. (ASPENtech, 2014)

It was assumed that the feed enters the process at ambient temperature and pressure (25 °C, 1 atm) and at a consistent rate and composition with negligible quantities of impurities. The ethanol feed was assumed to be 95% ethanol and 5% water by mass, which is the commercial standard for industrial ethanol. (190 Proof Ethanol, 2012) Storage vessels for the feed ethanol, waste streams and products are assumed to be located nearby to the process. An initial feed pump compensates for pressure drops through the process and reduces the duty on downstream compressors. (Hadawey, 2015)

Natural gas, assumed to consist of 83% methane, 16% ethane and 1% nitrogen by mass, was supplied to two fired heaters at a flow rate estimated by HYSYS. (Methane, 2015) Air fed to the process to enable combustion was assumed to be 23% oxygen and 77% nitrogen by mass. (Composition of Air, 2015) Air streams were fed at 50% molar excess in order to ensure complete combustion and prevent the formation of carbon monoxide in the heater exhaust. Total flue gases are assumed to be 230,000 kg/hr, or 2.2 million tons annually, and consist of 73.8% nitrogen gas, 10.5% carbon dioxide, 8.2% water vapor, and 7.5% oxygen by mass. The only compound of concern in these emissions is the carbon dioxide, a known greenhouse gas. At the time of this report, the quantities of carbon dioxide emitted by this plant annually are within acceptable EPA specifications. (Summary of the Clean Air Act, 2015)

Due to the difficulty of simulation equilibrium and conversion reactions in a single vessel in HYSYS, these two reaction types were simulated in separate equilibrium reactor and conversion reactor units in series. In addition, while HYSYS indicated that reactor units would output separate vapor and liquid streams, it was assumed that in practice this would take the form of a single, two phase stream between each unit. To account for this, mixers were installed downstream of each reactor to combine the liquid and vapor phases of the reactor effluent. The three consequent reactions considered are as follows:

[[File:Equation.PNG|400px|center]]

The optimal reaction temperature was determined to be 400 °C, which promotes the equilibrium reaction of ethanol to ethylene while minimizing byproducts. (Zhang and Yu, 2013) While other byproducts may be produced in this process, these reactions are typically taken to comprise of the bulk of the dehydration reaction. Heat losses over these reactors were assumed to be negligible. (Zhang and Yu, 2013)All major process equipment is assumed to be constructed of high strength carbon steel. (AspenTech, 2012)

The “Sizing Utility” within the Icarus Economic Evaluation module was used to estimate sizes of major equipment based on the process simulation. These values can serve as a benchmark for an initial plant design. Icarus KbaseTM implements a wide variety of mechanical design standards, including ASME and BS5500, in order to calculate accurate equipment sizing. The Icarus sizing module combines equipment prices for standard chemical processing equipment as well as correlations and sizing factors. The advantage of using a software package such as HYSYS to price out individual equipment is that it utilizes up-to-date prices from vendors and distributors when estimating costs. A more in-depth overview of the correlations included in this software can be found in Towler and Sinnott (2009).

=Process Flowsheet=
[[File:Squarepfd_B1.PNG|thumb|400px|alt=Alt text|Fig 1: PFD of the Proposed Process]]

The following process is based primarily on a 1983 US patent titled “Process for dehydration of a low molecular weight alcohol.” (Barrocas and Baratelli, 1983) The process flow diagram can be seen in Figure 1. A larger version of the PFD is included in Appendix I and the HYSYS simulation setup in Appendix II.

The feed enters the process at a rate of 100,000 kg/hr, a temperature and pressure of a 25 °C and 1 atm and at a composition of 95 wt% ethanol and 5 wt% water.It is initially pressurized to 4335 kPa by centrifugal pump P-101 and subsequently heated to 400 °C by fired heater F-101. The heated and pressurized feed enters fixed bed reactor R-101 and contacts with the aluminum oxide catalyst. At this point it dehydrates to form the product, ethylene, as well as the byproducts water, hydrogen, diethyl ether and acetaldehyde. Fired heater F-102 and reactor R-102 increase the overall conversion of the process. Both fired heaters F-101 and F-102 are fueled with natural gas and fed with excess air. The composition of the reactor train effluent is 54.5 wt% ethylene, 37.1 wt% water, 8.1 wt% unreacted ethanol and trace amounts of diethyl ether, acetaldehyde, and hydrogen contaminants.

The pressure of the reactor train effluent is increased to 4500 kPa by compressor K-102 and the temperature decreased to 100 °C by exchange with cold water in heat exchanger E-201. The stream then expands and flashes in flash vessel FL-201, which separates out 82.3% of the unreacted ethanol, 96.6% of the water and virtually all of the acetaldehyde contaminant in the bottoms while sending the ethylene-rich vapor phase out of the top. The top product of FL-202 is compressed to 3500 kPA by K-202 and cooled to 0.0 °C by a freon refrigerant in E-202. At this point the stream is flashed for a second time in vessel FL-202 to remove additional impurities. The top outlet stream consists of 99.5 wt% ethylene, which is fed to the bottom of a 10-tray absorption column that removes a fraction of the residual diethyl ether as well as the remainder of the unreacted ethanol. A stream of absorbent water is fed to the top of the column at 10,000 kg/hr. The product exits the top of the column at a rate of 54,600 kg/hr and has a purity of 99.7% ethylene. Diethyl ether makes up 0.2% of the remaining product stream and is the primary contaminant. Trace amounts of residual water and hydrogen are also present.

Full tables of material and energy streams can be found in Appendices III and IV respectively.

==Process Alternatives==
===Reactor Alternatives===
Two fixed bed reactors, alternating with fired heaters, are used in the dehydration reaction of ethanol to ethylene. However, a fluidized bed reactor can offer better mixing and temperature control than a fixed bed reactor and thus provide the highest possible conversion of ethanol with the greatest selectivity to ethylene. (Tsao and Zasloff, 1979) Fluidized bed reactors also provide a lower rate of catalyst coking and byproduct formation, minimizing separation and catalyst regeneration costs. (Morschbacker, 2009) The major downside of fluidized bed reactors is that few large-scale processes have been built since the technology was developed in the late 1970s. (Tsao and Zasloff, 1979; Morschbacker, 2009) Although implementation of fluidized bed reactors could potentially increase the purity of the ethylene product and/or decrease costs, a small scale pilot process would need to be built and tested before it would be possible to develop an industrial-scale facility.

===Catalyst Alternatives===
Aluminum oxide, specifically gamma alumina, is the most industrially-common catalyst and has been historically used due to its low cost and high stability. (Tsao and Zasloff, 1979; Fan and Dai, n.d.) Recent improvements in selectivity and catalyst stability of activated alumina have been achieved by incorporating titanium oxide into the catalyst, although this increases reaction temperature by approximately 50 °C and decreases catalyst lifespan. (Chen and Li, et. al. 2007) There is also significant ongoing research into HZSM-5 zeolite and heteropolyacids, which are being explored as potential alternatives to alumina oxide. A nanoscale HZSM-5 zeolite catalyst has been shown to operate at the relatively low temperature of 200-300°C, with a 100% ethanol conversion and 99.7% selectivity to ethylene. Initial research has also indicated that it maintains greater than 98% selectivity for 630 operational hours. (Fan and Dai, n.d.) However, the current low cost and ready availability of unmodified alumina oxide makes it a better choice for a process of this scale.

===Purification Alternatives===
As specified in this process, the reactor effluent is purified by two flash drums and absorption with water to produce chemical-grade ethylene. If chemical-grade ethylene is indeed the desired product, other purification options include caustic washing of the reactor effluent and water removal in a desiccant drying bed. (Morschbacker, 2009) While this purification train is relatively simple and does not require harsh chemical reagents, polymer grade ethylene is more commercially valuable and the additional cost of removing water and diethyl ether contaminants may be justified by increased revenue. Cryogenic distillation was initially simulated to produce polymer-grade ethylene, but utility requirements were found to render this separation economically unviable. (Barrocas and Baratelli, 1983) Further research and optimization may find this purification strategy to be a more valid process. Alternatively, the addition of a cryogenic turboexpander or the use of alternative adsorbents may increase product purity to polymer grade. (Jumonville, 2010) Initial HYSYS simulations indicate that these operations may be feasible with further refinement.

===Wastewater Treatment===
Due to the large volume of wastewater produced, building an on-site wastewater treatment facility may prove to be more economical than paying for third-party wastewater treatment. Flash vessel FL-201 produces 44,600 L/hr of wastewater contaminated with 18.7 vol% ethanol and 0.6 vol% acetaldehyde, while FL-202 produces 2940 L/hr of an aqueous waste consisting of 56.8 vol% ethanol, 42.0 vol% water and 0.9 vol% diethyl ether. The absorption column produces approximately 10,200 liters/hr of wastewater contaminated with 1.2 vol% ethanol, 0.2% diethyl ether and 0.2% acetaldehyde. Utilizing distillation to separate these streams into clean water and volatile organic waste could ultimately reduce the quantity of waste that requires disposal and reduce the overall costs of the process.

==Process Equipment==
Relevant sizing information for each unit operation, estimated by the method described in the “Technical Approach,” can be found in Appendix V. Equipment and piping is assumed to be constructed of carbon steel. It should be noted that the two fired heaters are proportionately large enough to heat the entirety of the process stream and are thus larger than standard equipment.

=Economic Analysis=
[[File:NPV_B1.png|400px|thumb|Fig 2. Projected Cash Flow]]
[[File:sensitivityanalysis_B1.png|400px|thumb| Fig 3. Results of the Sensitivity Analysis on 10 year NPV]]

==Economics Overview==
All final values are normalized to June 2014 USD by CEPCI scaling. It is assumed that all products produced are sold at current market prices.

The Aspen Economic Evaluation module within HYSYS v8.0 was used to estimate capital and operating costs for a 10-year plant life span with a construction start date of April 2015. The price of the 95% ethanol feed stream was estimated at $1.44 per gallon, while the chemical grade ethylene produced is currently selling for approximately $1350 per metric ton. (Today in Energy, 2015; Weddle, 2014) Mapping and sizing calculations were performed by the economics module and a preliminary economic evaluation was completed. Equipment sizes, also estimated by HYSYS, were reviewed to ensure that height, diameter, and volume specifications were within realistic ranges.

The process was ideally projected to operate 360 days per year with a start-up time of one year. In addition, the tax rate was approximated at 40%, an interest rate at 20%, and a salvage value of 20%. Escalation percentages were compounded yearly for the product, raw material, and operating costs. The total capital cost for this process is approximately $16.4 million, which includes all equipment and piping described in the process. The most expensive equipment used in this process are the two fired heaters F-101 and F-102, which have an exceptionally large heat exchange area to adequately heat the feed. Standard heaters may not suffice and additional costs may be incurred for the raw materials and manufacture of this equipment. Including a feed preheater or additional fired heaters may reduce this cost in subsequent design iterations.

The total operating cost is approximately $465 million per year, about $427 million of which is the cost of the ethanol feed and natural gas for the two fired heaters. An additional $1.73 million per year is used for utilities including the cooling water and refrigerant. The labor and maintenance costs of this industrial process were also accounted for within the simulation’s economic analysis. The HYSYS simulation software, in conjunction with the Icarus economic analyzer, estimated there should be 5 operators per 8 hour shift with a cost per operator of $20 per hour. This results in a total operating labor cost of approximately $880,000 per year. In addition, the process will require one supervisor per shift with an hourly rate of $35 for total supervisor salaries of $307,000 per year. Finally, a fixed maintenance rate was estimated at $205,000 per 8000 hours of operation for a total cost of $225,000 per year.

Total product sales are roughly $640 million per year at full operation. The estimated income for this process is thus approximately $175 million per year. After ten years, the plant is projected to have a net present value (NPV) of $391 million and an internal rate of return of approximately 79%. In addition the payout period for the initial investment is estimated to be about 2.7 years. Figure 2 shows the projected cash flow for the project.

==Sensitivity Analysis==
A sensitivity analysis was performed to investigate the effects of fluctuating capital costs, operating costs, raw materials, utility costs and ethylene sales price on the 10-year net present value (NPV) of the project. This analysis was performed by scaling these cost factors according to typical ranges given in Towler and Sinnott and calculating the adjusting the NPV accordingly. The results, illustrated in Figure 3, indicate that the project value is most sensitive to product sales, raw materials costs, and operating costs. Ethylene and ethanol prices are market-determined and cannot be controlled for in the process design, so further optimization should be focused on minimizing the operations cost of the process. (Today in Energy, 2015; Weddle, 2014) However, in feed and product prices do still have a profound effect on profitability and feasibility. A more rigorous market analysis will better inform the profitability outlook.

=Conclusions/Recommendations=

The proposed process produces approximately 460,000 metric tons of 99.7 wt% ethylene annually, with a 10-year net present value of $131 million. If current economic conditions hold, it is recommended that this project proceed to implementation following further design improvements and optimization.

Future design iterations should focus on process optimization, particularly in minimizing operating costs as prescribed by the results of the sensitivity analysis. The development of a heat-exchanger network, potentially with Aspen Energy Analyzer, is one option for decreasing utility requirements and increasing the efficiency of the process overall. Optimization of the fired heaters could also result in decreased operational costs. Although overall profitability is less sensitive to capital costs, reviewing and adjusting equipment sizing would also improve the economic outlook. In particular, exploring alternative heating strategies at the beginning of the process could significantly decrease capital costs. Although there are not any particularly dangerous chemicals utilized in the process, an overall process review should also consider potential failure modes to minimize the safety risk to plant workers and nearby residents.

In addition to economic and safety considerations, harmful emissions and waste streams should be minimized both to bring down the cost of treatment and to decrease environmental effects. The two fired heaters consume a large amount of natural gas per year, emitting about 200,000 tons of CO2 annually, and account for more than half of the capital cost of the process. Although no known toxic gases are produced, carbon capture or other emissions-reduction methods should be considered. Additionally, enough wastewater is produced by this process that building an onsite wastewater treatment center should be considered. This could not only decrease operating costs by eliminating the need for an external contract but also give the plant more control over the final purity of the treated wastewater.

Finally, the current model assumes that all ethylene produced will be sold at a current prices and price or product sales will not be affected by economic variability. A more detailed study of the chemical-grade ethylene market, as well as a more thorough understanding of sales and distribution logistics, would increase the surety of a profitable process.

In summary, the proposed process yields chemical grade ethylene via the catalytic dehydration of ethanol. A 100,000 kg/hr of 95 wt% ethanol, 5% water feed is converted to 53,000 kg/hr of 99.7% chemical-grade ethylene. After 10 years of operation, including a one-year startup time, the process has an NPV of $391 million with an IRR of 79% and a payback period of 2.7 years.
Pending further optimization, this process was determined to be viable and it is recommended for the project to move forward.

=References=

[1] American Chemistry Council. Production of chemicals and plastics in the U.S. in 2013, by type (in 1,000 metric tons). In Statista - The Statistics Portal. August 2014. Available at http://www.statista.com/statistics/299725/total-us-plastics-and-chemicals-shipments-by-type/, Accessed January 15, 2015. – Relative proportions of plastics production.

[2] DuPont Nevada Site Cellulosic Ethanol Facility [Internet]. DuPont Chemical; c2012-2015 [cited 11 Mar. 2015]. Available from: http://biofuels.dupont.com/cellulosic-ethanol/nevada-site-ce-facility/. -- Information on ethanol production in Iowa.

[3] Designing Ethylene Plants. Ethylene [Internet]. Technip; 2014 [cited 13 Mar. 2015]. Available from: http://www.technip.com/en/our-business/onshore/ethylene -- Plant size ranges.

[4] Suppes GJ. Selecting Thermodynamic Models for Process Simulation of Organic VLE and LLE Systems. The University of Missouri-Columbia, Dept of Chemical Engineering. [cited 13 Mar. 2015]. -- Use of NRTL in alcohol separations.

[5] ASPENtech. Appendix A - Property Methods and Calculations. Simulation Basics; A-3 - A-26. 2014.

[6] 190 Proof Ethanol: Technical Data Sheet [Internet]. Decon Labs Inc; 2012 [cited 13 Mar. 2015]. Available from: http://www.deconlabs.com/tds/ETHANOL%20190%20%20PROOF.pdf -- Information regarding 95% ethanol

[7] Hadawey A, Ge Y, Tassou TSA. Energy Savings Through Liquid Pressure Amplification In A Dairy Plant Refrigeration System. The Centre for Energy and Built Environment Research [cited 13 Mar. 2015].

[8] Methane (Chemical Compound). 2015. Encyclopædia Britannica Online. [cited 13 Mar. 2015] Available from: http://www.britannica.com/EBchecked/topic/378264/methane -- Composition of Methane

[9] Composition of Air [Internet]. Engineering Toolbox; [cited 13 Mar. 2015]. Available from: http://www.engineeringtoolbox.com/air-composition-d_212.html. -- Composition of air.

[10] Summary of the Clean Air Act, 2015. United States Environmental Protection Agency. [cited 13 Mar. 2015] Available from: http://www2.epa.gov/laws-regulations/summary-clean-air-act -- Emissions requirements of chemical plants.

[11] Zhang M, Yu Y. Dehydration of Ethanol to Ethylene. Industrial Engineering and Chemical Research. 2013; 52:9505-9514. – Technical information on ethanol to ethylene conversion via dehydration.

[12] AspenTech. Aspen HYSYS Help File v8.0. Aspen Technology, Inc. 2012. - Aspen HYSYS help file used for troubleshooting and assistance on economic analysis.

[13] Towler G, Sinnott R. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. 2nd ed. Boston: Elsevier; 2013. -- General Reference Book

[14] Barrocas H, Baratelli F, inventors; Petroleo Brasileiro S.A., assignee. Process for dehydration of a low molecular weight alcohol. US patent 4,396,789 A. August 2, 1983. - Primary background for process design.

[15] Tsao U, Zasloff HB, inventors; The Lummus Company, assignee. Production of ethylene from ethanol. US patent 4,134,926. January 16, 1979. – Patent for catalytic dehydration of ethylene in a fluidized bed reactor.

[16] Morschbacker, A. Bio-Ethanol Based Ethylene. Polymer Reviews. 2009; 49:79-84. – Overview of bioethanol dehydration process development.

[17] Fan D, Dai DJ, Wu HS. Ethylene Formation by Catalytic Dehydration of Ethanol with Industrial Considerations. Materials. 6, 101-115. doi: 10.3390/ma6010101. - Comparison of types of catalysts used in the dehydration of ethanol and current research into new catalysts.

[18] Chen G, Li S, Jiao F, Yuan Q. Catalytic dehydration of bioethanol to ethylene over TiO2/γ-Al2O3 catalysts in microchannel reactors. Catal. Today 2007, 125, 111–119. - Paper introducing research on modified alumina catalyst for ethanol dehydration.

[19] Jumonville, J. Tutorial on Cryogenic Turboexpanders. Proceedings of the Thirty-Ninth Turbomachinery Symposium; 2010 Oct 4-7; Houston, TX. Houston: Texas A&M University; 2010. -- Use of turboexpander for cryogenic separations

[20] Today in Energy - Daily Prices. US Energy Information Administration website. http://www.eia.gov/todayinenergy/prices.cfm. Accessed March 3rd 2015. - Bulk market price for 95% ethanol.

[21] Weddle, N. ICIS Pricing: Ethylene (Europe). Reed Business Limited. January 10 2014. - Bulk market price for chemical grade ethylene.

=Appendix I - Process Flow Diagram=
[[File:PFD B1.JPG|1200px|center]]

=Appendix II - HYSYS Simulation=
[[File:HYSYS_B1.PNG|center|1200px]]

=Appendix III - Material Streams=
[[File:Streams_B1.png|1200px]]

=Appendix IV - Energy Table=
[[File:Energy_B1.png|600px|center]]

=Appendix V - Economics=
[[File:Econsummary_B1.png|center]] 

[[File:Capcost_B1.png|center]] 

[[File:sensitivityanalysis_B1.png|600px|center]]

Ethanol to Ethylene (B1)

2015-03-14T04:45:25Z

Hpoppick: /* Technical Approach */

[[File:BFD_B1.png|600px|thumbnail|alt=Alt text|Conversion of Ethanol to Ethylene]]

Team B1 Final Report

Authors: Harry Poppick, Emm Fulk and Scott Smith

Instructors: Fengqi You, David Wegerer

March 13, 2015

=Executive Summary=

The following report outlines the design and analysis of a process converting ethanol to chemical-grade ethylene via catalytic dehydration. This process consumers 100,000 kg/hr of 95 wt% ethanol, 5 wt% water feedstock and produces 53,000 kg/hr of 99.7 wt% chemical-grade ethylene. The ethanol feed passes through two fixed-bed reactors, each packed with an aluminum oxide catalyst, and the resulting ethylene is purified by two flash tanks and by absorption with water. The process was modeled using Aspen HYSYS simulation software to estimate mass and energy flows and equipment sizing requirements. Based on results of this initial simulation, several alternatives are discussed for increasing the process efficiency and profitability. The use of a fluidized bed reactor or a more ethylene-selective catalyst could increase the production of ethylene per ethanol basis. Additionally, several methods of purification to more valuable polymer-grade ethylene are proposed.

The economic feasibility of this process was evaluated using Aspen Economic Analyzer with the Icarus economics package. Capital cost is approximately $16.4 million total with an operating cost of $465 million per year. The current market prices of the ethanol feed and ethylene sales price are $1.44/gallon and $1350/metric ton respectively. The cost of feed ethanol, process utilities and miscellaneous operational costs total to about $427 million/year. At full operation, revenue at current prices would be approximately $640 million per year. The predicted 10-year net present value of the process is approximately $391 million with an IRR of 79% and a payback period of 2.7 years. A sensitivity analysis indicates that the process is most sensitive to feed prices, product prices and operation cost.

Several recommendations are made for both cost reduction and profit maximization, including the design of a heat exchanger network and the optimization of fired heaters that require high capital investment and large amounts of fuel. A safety review of the process is recommended, as well as the minimization of flue gas effluent and wastewater. It is also suggested that the construction of an onsite wastewater treatment center be considered. Overall, the initial analysis indicates this to be a profitable process and it is recommended the project move forward.

=Introduction=

Ethylene is a critical chemical precursor to a number of different industrial products. It is often derived from petroleum sources and polymerized to polyethylene, one of the most ubiquitous plastics today. (American Chemistry Council, 2013) Recently there has been a significant effort to develop production pathways utilizing biologically-derived feedstocks, such as corn or cellulosic ethanol, rather than traditional fossil-fuel sources. Ethylene can be produced from bioethanol via catalytic dehydration over an aluminum oxide catalyst. The proposed process converts 100,000 kg/hr of 95 wt% ethanol, 5% water feed to 53,000 kg/hr of 99.7% chemical-grade ethylene when operating at full capacity. This process was found to be economically viable with a 10-year net present value (NPV) of $131 million (2014 USD) and a payback period of approximately 2.7 years. This memo will detail the proposed process, as well as outline potential alternatives and economic viability of the project.

=Technical Approach=

Many bioethanol plants are located in the Midwest where large amounts of feedstock crops, such as corn, are grown. As such, this plant will be located in Story county, Iowa, near a large-scale bioethanol production plant. (DuPont Nevada Site, 2012) It is assumed that the supply of bioethanol is consistent and readily available. It is also assumed that other reagents - namely, the aluminum oxide catalyst, heater fuel, utility water and freon refrigerant - are readily available, and that wastewater treatment facilities are located near enough to facilitate the off-site treatment of wastewater. Plant capacity was based on current mid-sized industrial ethylene plants. (Designing Ethylene Plants, 2014)

HYSYS simulations were performed with the NRTL fluid package and Peng-Robinson vapor model. The NRTL fluid package is an activity coefficient model that is especially useful to model the separations of alcohols in aqueous solutions. (Suppes, 2015) In addition, NRTL uses models of binary pairs of components, much like the Wilson equation, to predict chemical interactions at the molecular level. The NRTL package can thus be easily extended to ternary and higher order chemical systems, making it ideal for this type of simulation. The Peng-Robinson vapor model was selected as it is well-suited to account for the non-idealities of the vapor phase reactions and separations integral to this process. (ASPENtech, 2014)

It was assumed that the feed enters the process at ambient temperature and pressure (25 °C, 1 atm) and at a consistent rate and composition with negligible quantities of impurities. The ethanol feed was assumed to be 95% ethanol and 5% water by mass, which is the commercial standard for industrial ethanol. (190 Proof Ethanol, 2012) Storage vessels for the feed ethanol, waste streams and products are assumed to be located nearby to the process. An initial feed pump compensates for pressure drops through the process and reduces the duty on downstream compressors. (Hadawey, 2015)

Natural gas, assumed to consist of 83% methane, 16% ethane and 1% nitrogen by mass, was supplied to two fired heaters at a flow rate estimated by HYSYS. (Methane, 2015) Air fed to the process to enable combustion was assumed to be 23% oxygen and 77% nitrogen by mass. (Composition of Air, 2015) Air streams were fed at 50% molar excess in order to ensure complete combustion and prevent the formation of carbon monoxide in the heater exhaust. Total flue gases are assumed to be 230,000 kg/hr, or 2.2 million tons annually, and consist of 73.8% nitrogen gas, 10.5% carbon dioxide, 8.2% water vapor, and 7.5% oxygen by mass. The only compound of concern in these emissions is the carbon dioxide, a known greenhouse gas. At the time of this report, the quantities of carbon dioxide emitted by this plant annually are within acceptable EPA specifications. (Summary of the Clean Air Act, 2015)

Due to the difficulty of simulation equilibrium and conversion reactions in a single vessel in HYSYS, these two reaction types were simulated in separate equilibrium reactor and conversion reactor units in series. In addition, while HYSYS indicated that reactor units would output separate vapor and liquid streams, it was assumed that in practice this would take the form of a single, two phase stream between each unit. To account for this, mixers were installed downstream of each reactor to combine the liquid and vapor phases of the reactor effluent. The three consequent reactions considered are as follows:

[[File:Equation.PNG|500px|center]]

The optimal reaction temperature was determined to be 400 °C, which promotes the equilibrium reaction of ethanol to ethylene while minimizing byproducts. (Zhang and Yu, 2013) While other byproducts may be produced in this process, these reactions are typically taken to comprise of the bulk of the dehydration reaction. Heat losses over these reactors were assumed to be negligible. (Zhang and Yu, 2013)All major process equipment is assumed to be constructed of high strength carbon steel. (AspenTech, 2012)

The “Sizing Utility” within the Icarus Economic Evaluation module was used to estimate sizes of major equipment based on the process simulation. These values can serve as a benchmark for an initial plant design. Icarus KbaseTM implements a wide variety of mechanical design standards, including ASME and BS5500, in order to calculate accurate equipment sizing. The Icarus sizing module combines equipment prices for standard chemical processing equipment as well as correlations and sizing factors. The advantage of using a software package such as HYSYS to price out individual equipment is that it utilizes up-to-date prices from vendors and distributors when estimating costs. A more in-depth overview of the correlations included in this software can be found in Towler and Sinnott (2009).

=Process Flowsheet=
[[File:Squarepfd_B1.PNG|thumb|400px|alt=Alt text|Fig 1: PFD of the Proposed Process]]

The following process is based primarily on a 1983 US patent titled “Process for dehydration of a low molecular weight alcohol.” (Barrocas and Baratelli, 1983) The process flow diagram can be seen in Figure 1. A larger version of the PFD is included in Appendix I and the HYSYS simulation setup in Appendix II.

The feed enters the process at a rate of 100,000 kg/hr, a temperature and pressure of a 25 °C and 1 atm and at a composition of 95 wt% ethanol and 5 wt% water.It is initially pressurized to 4335 kPa by centrifugal pump P-101 and subsequently heated to 400 °C by fired heater F-101. The heated and pressurized feed enters fixed bed reactor R-101 and contacts with the aluminum oxide catalyst. At this point it dehydrates to form the product, ethylene, as well as the byproducts water, hydrogen, diethyl ether and acetaldehyde. Fired heater F-102 and reactor R-102 increase the overall conversion of the process. Both fired heaters F-101 and F-102 are fueled with natural gas and fed with excess air. The composition of the reactor train effluent is 54.5 wt% ethylene, 37.1 wt% water, 8.1 wt% unreacted ethanol and trace amounts of diethyl ether, acetaldehyde, and hydrogen contaminants.

The pressure of the reactor train effluent is increased to 4500 kPa by compressor K-102 and the temperature decreased to 100 °C by exchange with cold water in heat exchanger E-201. The stream then expands and flashes in flash vessel FL-201, which separates out 82.3% of the unreacted ethanol, 96.6% of the water and virtually all of the acetaldehyde contaminant in the bottoms while sending the ethylene-rich vapor phase out of the top. The top product of FL-202 is compressed to 3500 kPA by K-202 and cooled to 0.0 °C by a freon refrigerant in E-202. At this point the stream is flashed for a second time in vessel FL-202 to remove additional impurities. The top outlet stream consists of 99.5 wt% ethylene, which is fed to the bottom of a 10-tray absorption column that removes a fraction of the residual diethyl ether as well as the remainder of the unreacted ethanol. A stream of absorbent water is fed to the top of the column at 10,000 kg/hr. The product exits the top of the column at a rate of 54,600 kg/hr and has a purity of 99.7% ethylene. Diethyl ether makes up 0.2% of the remaining product stream and is the primary contaminant. Trace amounts of residual water and hydrogen are also present.

Full tables of material and energy streams can be found in Appendices III and IV respectively.

==Process Alternatives==
===Reactor Alternatives===
Two fixed bed reactors, alternating with fired heaters, are used in the dehydration reaction of ethanol to ethylene. However, a fluidized bed reactor can offer better mixing and temperature control than a fixed bed reactor and thus provide the highest possible conversion of ethanol with the greatest selectivity to ethylene. (Tsao and Zasloff, 1979) Fluidized bed reactors also provide a lower rate of catalyst coking and byproduct formation, minimizing separation and catalyst regeneration costs. (Morschbacker, 2009) The major downside of fluidized bed reactors is that few large-scale processes have been built since the technology was developed in the late 1970s. (Tsao and Zasloff, 1979; Morschbacker, 2009) Although implementation of fluidized bed reactors could potentially increase the purity of the ethylene product and/or decrease costs, a small scale pilot process would need to be built and tested before it would be possible to develop an industrial-scale facility.

===Catalyst Alternatives===
Aluminum oxide, specifically gamma alumina, is the most industrially-common catalyst and has been historically used due to its low cost and high stability. (Tsao and Zasloff, 1979; Fan and Dai, n.d.) Recent improvements in selectivity and catalyst stability of activated alumina have been achieved by incorporating titanium oxide into the catalyst, although this increases reaction temperature by approximately 50 °C and decreases catalyst lifespan. (Chen and Li, et. al. 2007) There is also significant ongoing research into HZSM-5 zeolite and heteropolyacids, which are being explored as potential alternatives to alumina oxide. A nanoscale HZSM-5 zeolite catalyst has been shown to operate at the relatively low temperature of 200-300°C, with a 100% ethanol conversion and 99.7% selectivity to ethylene. Initial research has also indicated that it maintains greater than 98% selectivity for 630 operational hours. (Fan and Dai, n.d.) However, the current low cost and ready availability of unmodified alumina oxide makes it a better choice for a process of this scale.

===Purification Alternatives===
As specified in this process, the reactor effluent is purified by two flash drums and absorption with water to produce chemical-grade ethylene. If chemical-grade ethylene is indeed the desired product, other purification options include caustic washing of the reactor effluent and water removal in a desiccant drying bed. (Morschbacker, 2009) While this purification train is relatively simple and does not require harsh chemical reagents, polymer grade ethylene is more commercially valuable and the additional cost of removing water and diethyl ether contaminants may be justified by increased revenue. Cryogenic distillation was initially simulated to produce polymer-grade ethylene, but utility requirements were found to render this separation economically unviable. (Barrocas and Baratelli, 1983) Further research and optimization may find this purification strategy to be a more valid process. Alternatively, the addition of a cryogenic turboexpander or the use of alternative adsorbents may increase product purity to polymer grade. (Jumonville, 2010) Initial HYSYS simulations indicate that these operations may be feasible with further refinement.

===Wastewater Treatment===
Due to the large volume of wastewater produced, building an on-site wastewater treatment facility may prove to be more economical than paying for third-party wastewater treatment. Flash vessel FL-201 produces 44,600 L/hr of wastewater contaminated with 18.7 vol% ethanol and 0.6 vol% acetaldehyde, while FL-202 produces 2940 L/hr of an aqueous waste consisting of 56.8 vol% ethanol, 42.0 vol% water and 0.9 vol% diethyl ether. The absorption column produces approximately 10,200 liters/hr of wastewater contaminated with 1.2 vol% ethanol, 0.2% diethyl ether and 0.2% acetaldehyde. Utilizing distillation to separate these streams into clean water and volatile organic waste could ultimately reduce the quantity of waste that requires disposal and reduce the overall costs of the process.

==Process Equipment==
Relevant sizing information for each unit operation, estimated by the method described in the “Technical Approach,” can be found in Appendix V. Equipment and piping is assumed to be constructed of carbon steel. It should be noted that the two fired heaters are proportionately large enough to heat the entirety of the process stream and are thus larger than standard equipment.

=Economic Analysis=
[[File:NPV_B1.png|400px|thumb|Fig 2. Projected Cash Flow]]
[[File:sensitivityanalysis_B1.png|400px|thumb| Fig 3. Results of the Sensitivity Analysis on 10 year NPV]]

==Economics Overview==
All final values are normalized to June 2014 USD by CEPCI scaling. It is assumed that all products produced are sold at current market prices.

The Aspen Economic Evaluation module within HYSYS v8.0 was used to estimate capital and operating costs for a 10-year plant life span with a construction start date of April 2015. The price of the 95% ethanol feed stream was estimated at $1.44 per gallon, while the chemical grade ethylene produced is currently selling for approximately $1350 per metric ton. (Today in Energy, 2015; Weddle, 2014) Mapping and sizing calculations were performed by the economics module and a preliminary economic evaluation was completed. Equipment sizes, also estimated by HYSYS, were reviewed to ensure that height, diameter, and volume specifications were within realistic ranges.

The process was ideally projected to operate 360 days per year with a start-up time of one year. In addition, the tax rate was approximated at 40%, an interest rate at 20%, and a salvage value of 20%. Escalation percentages were compounded yearly for the product, raw material, and operating costs. The total capital cost for this process is approximately $16.4 million, which includes all equipment and piping described in the process. The most expensive equipment used in this process are the two fired heaters F-101 and F-102, which have an exceptionally large heat exchange area to adequately heat the feed. Standard heaters may not suffice and additional costs may be incurred for the raw materials and manufacture of this equipment. Including a feed preheater or additional fired heaters may reduce this cost in subsequent design iterations.

The total operating cost is approximately $465 million per year, about $427 million of which is the cost of the ethanol feed and natural gas for the two fired heaters. An additional $1.73 million per year is used for utilities including the cooling water and refrigerant. The labor and maintenance costs of this industrial process were also accounted for within the simulation’s economic analysis. The HYSYS simulation software, in conjunction with the Icarus economic analyzer, estimated there should be 5 operators per 8 hour shift with a cost per operator of $20 per hour. This results in a total operating labor cost of approximately $880,000 per year. In addition, the process will require one supervisor per shift with an hourly rate of $35 for total supervisor salaries of $307,000 per year. Finally, a fixed maintenance rate was estimated at $205,000 per 8000 hours of operation for a total cost of $225,000 per year.

Total product sales are roughly $640 million per year at full operation. The estimated income for this process is thus approximately $175 million per year. After ten years, the plant is projected to have a net present value (NPV) of $391 million and an internal rate of return of approximately 79%. In addition the payout period for the initial investment is estimated to be about 2.7 years. Figure 2 shows the projected cash flow for the project.

==Sensitivity Analysis==
A sensitivity analysis was performed to investigate the effects of fluctuating capital costs, operating costs, raw materials, utility costs and ethylene sales price on the 10-year net present value (NPV) of the project. This analysis was performed by scaling these cost factors according to typical ranges given in Towler and Sinnott and calculating the adjusting the NPV accordingly. The results, illustrated in Figure 3, indicate that the project value is most sensitive to product sales, raw materials costs, and operating costs. Ethylene and ethanol prices are market-determined and cannot be controlled for in the process design, so further optimization should be focused on minimizing the operations cost of the process. (Today in Energy, 2015; Weddle, 2014) However, in feed and product prices do still have a profound effect on profitability and feasibility. A more rigorous market analysis will better inform the profitability outlook.

=Conclusions/Recommendations=

The proposed process produces approximately 460,000 metric tons of 99.7 wt% ethylene annually, with a 10-year net present value of $131 million. If current economic conditions hold, it is recommended that this project proceed to implementation following further design improvements and optimization.

Future design iterations should focus on process optimization, particularly in minimizing operating costs as prescribed by the results of the sensitivity analysis. The development of a heat-exchanger network, potentially with Aspen Energy Analyzer, is one option for decreasing utility requirements and increasing the efficiency of the process overall. Optimization of the fired heaters could also result in decreased operational costs. Although overall profitability is less sensitive to capital costs, reviewing and adjusting equipment sizing would also improve the economic outlook. In particular, exploring alternative heating strategies at the beginning of the process could significantly decrease capital costs. Although there are not any particularly dangerous chemicals utilized in the process, an overall process review should also consider potential failure modes to minimize the safety risk to plant workers and nearby residents.

In addition to economic and safety considerations, harmful emissions and waste streams should be minimized both to bring down the cost of treatment and to decrease environmental effects. The two fired heaters consume a large amount of natural gas per year, emitting about 200,000 tons of CO2 annually, and account for more than half of the capital cost of the process. Although no known toxic gases are produced, carbon capture or other emissions-reduction methods should be considered. Additionally, enough wastewater is produced by this process that building an onsite wastewater treatment center should be considered. This could not only decrease operating costs by eliminating the need for an external contract but also give the plant more control over the final purity of the treated wastewater.

Finally, the current model assumes that all ethylene produced will be sold at a current prices and price or product sales will not be affected by economic variability. A more detailed study of the chemical-grade ethylene market, as well as a more thorough understanding of sales and distribution logistics, would increase the surety of a profitable process.

In summary, the proposed process yields chemical grade ethylene via the catalytic dehydration of ethanol. A 100,000 kg/hr of 95 wt% ethanol, 5% water feed is converted to 53,000 kg/hr of 99.7% chemical-grade ethylene. After 10 years of operation, including a one-year startup time, the process has an NPV of $391 million with an IRR of 79% and a payback period of 2.7 years.
Pending further optimization, this process was determined to be viable and it is recommended for the project to move forward.

=References=

[1] American Chemistry Council. Production of chemicals and plastics in the U.S. in 2013, by type (in 1,000 metric tons). In Statista - The Statistics Portal. August 2014. Available at http://www.statista.com/statistics/299725/total-us-plastics-and-chemicals-shipments-by-type/, Accessed January 15, 2015. – Relative proportions of plastics production.

[2] DuPont Nevada Site Cellulosic Ethanol Facility [Internet]. DuPont Chemical; c2012-2015 [cited 11 Mar. 2015]. Available from: http://biofuels.dupont.com/cellulosic-ethanol/nevada-site-ce-facility/. -- Information on ethanol production in Iowa.

[3] Designing Ethylene Plants. Ethylene [Internet]. Technip; 2014 [cited 13 Mar. 2015]. Available from: http://www.technip.com/en/our-business/onshore/ethylene -- Plant size ranges.

[4] Suppes GJ. Selecting Thermodynamic Models for Process Simulation of Organic VLE and LLE Systems. The University of Missouri-Columbia, Dept of Chemical Engineering. [cited 13 Mar. 2015]. -- Use of NRTL in alcohol separations.

[5] ASPENtech. Appendix A - Property Methods and Calculations. Simulation Basics; A-3 - A-26. 2014.

[6] 190 Proof Ethanol: Technical Data Sheet [Internet]. Decon Labs Inc; 2012 [cited 13 Mar. 2015]. Available from: http://www.deconlabs.com/tds/ETHANOL%20190%20%20PROOF.pdf -- Information regarding 95% ethanol

[7] Hadawey A, Ge Y, Tassou TSA. Energy Savings Through Liquid Pressure Amplification In A Dairy Plant Refrigeration System. The Centre for Energy and Built Environment Research [cited 13 Mar. 2015].

[8] Methane (Chemical Compound). 2015. Encyclopædia Britannica Online. [cited 13 Mar. 2015] Available from: http://www.britannica.com/EBchecked/topic/378264/methane -- Composition of Methane

[9] Composition of Air [Internet]. Engineering Toolbox; [cited 13 Mar. 2015]. Available from: http://www.engineeringtoolbox.com/air-composition-d_212.html. -- Composition of air.

[10] Summary of the Clean Air Act, 2015. United States Environmental Protection Agency. [cited 13 Mar. 2015] Available from: http://www2.epa.gov/laws-regulations/summary-clean-air-act -- Emissions requirements of chemical plants.

[11] Zhang M, Yu Y. Dehydration of Ethanol to Ethylene. Industrial Engineering and Chemical Research. 2013; 52:9505-9514. – Technical information on ethanol to ethylene conversion via dehydration.

[12] AspenTech. Aspen HYSYS Help File v8.0. Aspen Technology, Inc. 2012. - Aspen HYSYS help file used for troubleshooting and assistance on economic analysis.

[13] Towler G, Sinnott R. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. 2nd ed. Boston: Elsevier; 2013. -- General Reference Book

[14] Barrocas H, Baratelli F, inventors; Petroleo Brasileiro S.A., assignee. Process for dehydration of a low molecular weight alcohol. US patent 4,396,789 A. August 2, 1983. - Primary background for process design.

[15] Tsao U, Zasloff HB, inventors; The Lummus Company, assignee. Production of ethylene from ethanol. US patent 4,134,926. January 16, 1979. – Patent for catalytic dehydration of ethylene in a fluidized bed reactor.

[16] Morschbacker, A. Bio-Ethanol Based Ethylene. Polymer Reviews. 2009; 49:79-84. – Overview of bioethanol dehydration process development.

[17] Fan D, Dai DJ, Wu HS. Ethylene Formation by Catalytic Dehydration of Ethanol with Industrial Considerations. Materials. 6, 101-115. doi: 10.3390/ma6010101. - Comparison of types of catalysts used in the dehydration of ethanol and current research into new catalysts.

[18] Chen G, Li S, Jiao F, Yuan Q. Catalytic dehydration of bioethanol to ethylene over TiO2/γ-Al2O3 catalysts in microchannel reactors. Catal. Today 2007, 125, 111–119. - Paper introducing research on modified alumina catalyst for ethanol dehydration.

[19] Jumonville, J. Tutorial on Cryogenic Turboexpanders. Proceedings of the Thirty-Ninth Turbomachinery Symposium; 2010 Oct 4-7; Houston, TX. Houston: Texas A&M University; 2010. -- Use of turboexpander for cryogenic separations

[20] Today in Energy - Daily Prices. US Energy Information Administration website. http://www.eia.gov/todayinenergy/prices.cfm. Accessed March 3rd 2015. - Bulk market price for 95% ethanol.

[21] Weddle, N. ICIS Pricing: Ethylene (Europe). Reed Business Limited. January 10 2014. - Bulk market price for chemical grade ethylene.

=Appendix I - Process Flow Diagram=
[[File:PFD B1.JPG|1200px|center]]

=Appendix II - HYSYS Simulation=
[[File:HYSYS_B1.PNG|center|1200px]]

=Appendix III - Material Streams=
[[File:Streams_B1.png|1200px]]

=Appendix IV - Energy Table=
[[File:Energy_B1.png|600px|center]]

=Appendix V - Economics=
[[File:Econsummary_B1.png|center]] 

[[File:Capcost_B1.png|center]] 

[[File:sensitivityanalysis_B1.png|600px|center]]

Ethanol to Ethylene (B1)

2015-03-14T04:45:16Z

Hpoppick: /* Technical Approach */

[[File:BFD_B1.png|600px|thumbnail|alt=Alt text|Conversion of Ethanol to Ethylene]]

Team B1 Final Report

Authors: Harry Poppick, Emm Fulk and Scott Smith

Instructors: Fengqi You, David Wegerer

March 13, 2015

=Executive Summary=

The following report outlines the design and analysis of a process converting ethanol to chemical-grade ethylene via catalytic dehydration. This process consumers 100,000 kg/hr of 95 wt% ethanol, 5 wt% water feedstock and produces 53,000 kg/hr of 99.7 wt% chemical-grade ethylene. The ethanol feed passes through two fixed-bed reactors, each packed with an aluminum oxide catalyst, and the resulting ethylene is purified by two flash tanks and by absorption with water. The process was modeled using Aspen HYSYS simulation software to estimate mass and energy flows and equipment sizing requirements. Based on results of this initial simulation, several alternatives are discussed for increasing the process efficiency and profitability. The use of a fluidized bed reactor or a more ethylene-selective catalyst could increase the production of ethylene per ethanol basis. Additionally, several methods of purification to more valuable polymer-grade ethylene are proposed.

The economic feasibility of this process was evaluated using Aspen Economic Analyzer with the Icarus economics package. Capital cost is approximately $16.4 million total with an operating cost of $465 million per year. The current market prices of the ethanol feed and ethylene sales price are $1.44/gallon and $1350/metric ton respectively. The cost of feed ethanol, process utilities and miscellaneous operational costs total to about $427 million/year. At full operation, revenue at current prices would be approximately $640 million per year. The predicted 10-year net present value of the process is approximately $391 million with an IRR of 79% and a payback period of 2.7 years. A sensitivity analysis indicates that the process is most sensitive to feed prices, product prices and operation cost.

Several recommendations are made for both cost reduction and profit maximization, including the design of a heat exchanger network and the optimization of fired heaters that require high capital investment and large amounts of fuel. A safety review of the process is recommended, as well as the minimization of flue gas effluent and wastewater. It is also suggested that the construction of an onsite wastewater treatment center be considered. Overall, the initial analysis indicates this to be a profitable process and it is recommended the project move forward.

=Introduction=

Ethylene is a critical chemical precursor to a number of different industrial products. It is often derived from petroleum sources and polymerized to polyethylene, one of the most ubiquitous plastics today. (American Chemistry Council, 2013) Recently there has been a significant effort to develop production pathways utilizing biologically-derived feedstocks, such as corn or cellulosic ethanol, rather than traditional fossil-fuel sources. Ethylene can be produced from bioethanol via catalytic dehydration over an aluminum oxide catalyst. The proposed process converts 100,000 kg/hr of 95 wt% ethanol, 5% water feed to 53,000 kg/hr of 99.7% chemical-grade ethylene when operating at full capacity. This process was found to be economically viable with a 10-year net present value (NPV) of $131 million (2014 USD) and a payback period of approximately 2.7 years. This memo will detail the proposed process, as well as outline potential alternatives and economic viability of the project.

=Technical Approach=

Many bioethanol plants are located in the Midwest where large amounts of feedstock crops, such as corn, are grown. As such, this plant will be located in Story county, Iowa, near a large-scale bioethanol production plant. (DuPont Nevada Site, 2012) It is assumed that the supply of bioethanol is consistent and readily available. It is also assumed that other reagents - namely, the aluminum oxide catalyst, heater fuel, utility water and freon refrigerant - are readily available, and that wastewater treatment facilities are located near enough to facilitate the off-site treatment of wastewater. Plant capacity was based on current mid-sized industrial ethylene plants. (Designing Ethylene Plants, 2014)

HYSYS simulations were performed with the NRTL fluid package and Peng-Robinson vapor model. The NRTL fluid package is an activity coefficient model that is especially useful to model the separations of alcohols in aqueous solutions. (Suppes, 2015) In addition, NRTL uses models of binary pairs of components, much like the Wilson equation, to predict chemical interactions at the molecular level. The NRTL package can thus be easily extended to ternary and higher order chemical systems, making it ideal for this type of simulation. The Peng-Robinson vapor model was selected as it is well-suited to account for the non-idealities of the vapor phase reactions and separations integral to this process. (ASPENtech, 2014)

It was assumed that the feed enters the process at ambient temperature and pressure (25 °C, 1 atm) and at a consistent rate and composition with negligible quantities of impurities. The ethanol feed was assumed to be 95% ethanol and 5% water by mass, which is the commercial standard for industrial ethanol. (190 Proof Ethanol, 2012) Storage vessels for the feed ethanol, waste streams and products are assumed to be located nearby to the process. An initial feed pump compensates for pressure drops through the process and reduces the duty on downstream compressors. (Hadawey, 2015)

Natural gas, assumed to consist of 83% methane, 16% ethane and 1% nitrogen by mass, was supplied to two fired heaters at a flow rate estimated by HYSYS. (Methane, 2015) Air fed to the process to enable combustion was assumed to be 23% oxygen and 77% nitrogen by mass. (Composition of Air, 2015) Air streams were fed at 50% molar excess in order to ensure complete combustion and prevent the formation of carbon monoxide in the heater exhaust. Total flue gases are assumed to be 230,000 kg/hr, or 2.2 million tons annually, and consist of 73.8% nitrogen gas, 10.5% carbon dioxide, 8.2% water vapor, and 7.5% oxygen by mass. The only compound of concern in these emissions is the carbon dioxide, a known greenhouse gas. At the time of this report, the quantities of carbon dioxide emitted by this plant annually are within acceptable EPA specifications. (Summary of the Clean Air Act, 2015)

Due to the difficulty of simulation equilibrium and conversion reactions in a single vessel in HYSYS, these two reaction types were simulated in separate equilibrium reactor and conversion reactor units in series. In addition, while HYSYS indicated that reactor units would output separate vapor and liquid streams, it was assumed that in practice this would take the form of a single, two phase stream between each unit. To account for this, mixers were installed downstream of each reactor to combine the liquid and vapor phases of the reactor effluent. The three consequent reactions considered are as follows:

[[File:Equation.PNG|300px|center]]

The optimal reaction temperature was determined to be 400 °C, which promotes the equilibrium reaction of ethanol to ethylene while minimizing byproducts. (Zhang and Yu, 2013) While other byproducts may be produced in this process, these reactions are typically taken to comprise of the bulk of the dehydration reaction. Heat losses over these reactors were assumed to be negligible. (Zhang and Yu, 2013)All major process equipment is assumed to be constructed of high strength carbon steel. (AspenTech, 2012)

The “Sizing Utility” within the Icarus Economic Evaluation module was used to estimate sizes of major equipment based on the process simulation. These values can serve as a benchmark for an initial plant design. Icarus KbaseTM implements a wide variety of mechanical design standards, including ASME and BS5500, in order to calculate accurate equipment sizing. The Icarus sizing module combines equipment prices for standard chemical processing equipment as well as correlations and sizing factors. The advantage of using a software package such as HYSYS to price out individual equipment is that it utilizes up-to-date prices from vendors and distributors when estimating costs. A more in-depth overview of the correlations included in this software can be found in Towler and Sinnott (2009).

=Process Flowsheet=
[[File:Squarepfd_B1.PNG|thumb|400px|alt=Alt text|Fig 1: PFD of the Proposed Process]]

The following process is based primarily on a 1983 US patent titled “Process for dehydration of a low molecular weight alcohol.” (Barrocas and Baratelli, 1983) The process flow diagram can be seen in Figure 1. A larger version of the PFD is included in Appendix I and the HYSYS simulation setup in Appendix II.

The feed enters the process at a rate of 100,000 kg/hr, a temperature and pressure of a 25 °C and 1 atm and at a composition of 95 wt% ethanol and 5 wt% water.It is initially pressurized to 4335 kPa by centrifugal pump P-101 and subsequently heated to 400 °C by fired heater F-101. The heated and pressurized feed enters fixed bed reactor R-101 and contacts with the aluminum oxide catalyst. At this point it dehydrates to form the product, ethylene, as well as the byproducts water, hydrogen, diethyl ether and acetaldehyde. Fired heater F-102 and reactor R-102 increase the overall conversion of the process. Both fired heaters F-101 and F-102 are fueled with natural gas and fed with excess air. The composition of the reactor train effluent is 54.5 wt% ethylene, 37.1 wt% water, 8.1 wt% unreacted ethanol and trace amounts of diethyl ether, acetaldehyde, and hydrogen contaminants.

The pressure of the reactor train effluent is increased to 4500 kPa by compressor K-102 and the temperature decreased to 100 °C by exchange with cold water in heat exchanger E-201. The stream then expands and flashes in flash vessel FL-201, which separates out 82.3% of the unreacted ethanol, 96.6% of the water and virtually all of the acetaldehyde contaminant in the bottoms while sending the ethylene-rich vapor phase out of the top. The top product of FL-202 is compressed to 3500 kPA by K-202 and cooled to 0.0 °C by a freon refrigerant in E-202. At this point the stream is flashed for a second time in vessel FL-202 to remove additional impurities. The top outlet stream consists of 99.5 wt% ethylene, which is fed to the bottom of a 10-tray absorption column that removes a fraction of the residual diethyl ether as well as the remainder of the unreacted ethanol. A stream of absorbent water is fed to the top of the column at 10,000 kg/hr. The product exits the top of the column at a rate of 54,600 kg/hr and has a purity of 99.7% ethylene. Diethyl ether makes up 0.2% of the remaining product stream and is the primary contaminant. Trace amounts of residual water and hydrogen are also present.

Full tables of material and energy streams can be found in Appendices III and IV respectively.

==Process Alternatives==
===Reactor Alternatives===
Two fixed bed reactors, alternating with fired heaters, are used in the dehydration reaction of ethanol to ethylene. However, a fluidized bed reactor can offer better mixing and temperature control than a fixed bed reactor and thus provide the highest possible conversion of ethanol with the greatest selectivity to ethylene. (Tsao and Zasloff, 1979) Fluidized bed reactors also provide a lower rate of catalyst coking and byproduct formation, minimizing separation and catalyst regeneration costs. (Morschbacker, 2009) The major downside of fluidized bed reactors is that few large-scale processes have been built since the technology was developed in the late 1970s. (Tsao and Zasloff, 1979; Morschbacker, 2009) Although implementation of fluidized bed reactors could potentially increase the purity of the ethylene product and/or decrease costs, a small scale pilot process would need to be built and tested before it would be possible to develop an industrial-scale facility.

===Catalyst Alternatives===
Aluminum oxide, specifically gamma alumina, is the most industrially-common catalyst and has been historically used due to its low cost and high stability. (Tsao and Zasloff, 1979; Fan and Dai, n.d.) Recent improvements in selectivity and catalyst stability of activated alumina have been achieved by incorporating titanium oxide into the catalyst, although this increases reaction temperature by approximately 50 °C and decreases catalyst lifespan. (Chen and Li, et. al. 2007) There is also significant ongoing research into HZSM-5 zeolite and heteropolyacids, which are being explored as potential alternatives to alumina oxide. A nanoscale HZSM-5 zeolite catalyst has been shown to operate at the relatively low temperature of 200-300°C, with a 100% ethanol conversion and 99.7% selectivity to ethylene. Initial research has also indicated that it maintains greater than 98% selectivity for 630 operational hours. (Fan and Dai, n.d.) However, the current low cost and ready availability of unmodified alumina oxide makes it a better choice for a process of this scale.

===Purification Alternatives===
As specified in this process, the reactor effluent is purified by two flash drums and absorption with water to produce chemical-grade ethylene. If chemical-grade ethylene is indeed the desired product, other purification options include caustic washing of the reactor effluent and water removal in a desiccant drying bed. (Morschbacker, 2009) While this purification train is relatively simple and does not require harsh chemical reagents, polymer grade ethylene is more commercially valuable and the additional cost of removing water and diethyl ether contaminants may be justified by increased revenue. Cryogenic distillation was initially simulated to produce polymer-grade ethylene, but utility requirements were found to render this separation economically unviable. (Barrocas and Baratelli, 1983) Further research and optimization may find this purification strategy to be a more valid process. Alternatively, the addition of a cryogenic turboexpander or the use of alternative adsorbents may increase product purity to polymer grade. (Jumonville, 2010) Initial HYSYS simulations indicate that these operations may be feasible with further refinement.

===Wastewater Treatment===
Due to the large volume of wastewater produced, building an on-site wastewater treatment facility may prove to be more economical than paying for third-party wastewater treatment. Flash vessel FL-201 produces 44,600 L/hr of wastewater contaminated with 18.7 vol% ethanol and 0.6 vol% acetaldehyde, while FL-202 produces 2940 L/hr of an aqueous waste consisting of 56.8 vol% ethanol, 42.0 vol% water and 0.9 vol% diethyl ether. The absorption column produces approximately 10,200 liters/hr of wastewater contaminated with 1.2 vol% ethanol, 0.2% diethyl ether and 0.2% acetaldehyde. Utilizing distillation to separate these streams into clean water and volatile organic waste could ultimately reduce the quantity of waste that requires disposal and reduce the overall costs of the process.

==Process Equipment==
Relevant sizing information for each unit operation, estimated by the method described in the “Technical Approach,” can be found in Appendix V. Equipment and piping is assumed to be constructed of carbon steel. It should be noted that the two fired heaters are proportionately large enough to heat the entirety of the process stream and are thus larger than standard equipment.

=Economic Analysis=
[[File:NPV_B1.png|400px|thumb|Fig 2. Projected Cash Flow]]
[[File:sensitivityanalysis_B1.png|400px|thumb| Fig 3. Results of the Sensitivity Analysis on 10 year NPV]]

==Economics Overview==
All final values are normalized to June 2014 USD by CEPCI scaling. It is assumed that all products produced are sold at current market prices.

The Aspen Economic Evaluation module within HYSYS v8.0 was used to estimate capital and operating costs for a 10-year plant life span with a construction start date of April 2015. The price of the 95% ethanol feed stream was estimated at $1.44 per gallon, while the chemical grade ethylene produced is currently selling for approximately $1350 per metric ton. (Today in Energy, 2015; Weddle, 2014) Mapping and sizing calculations were performed by the economics module and a preliminary economic evaluation was completed. Equipment sizes, also estimated by HYSYS, were reviewed to ensure that height, diameter, and volume specifications were within realistic ranges.

The process was ideally projected to operate 360 days per year with a start-up time of one year. In addition, the tax rate was approximated at 40%, an interest rate at 20%, and a salvage value of 20%. Escalation percentages were compounded yearly for the product, raw material, and operating costs. The total capital cost for this process is approximately $16.4 million, which includes all equipment and piping described in the process. The most expensive equipment used in this process are the two fired heaters F-101 and F-102, which have an exceptionally large heat exchange area to adequately heat the feed. Standard heaters may not suffice and additional costs may be incurred for the raw materials and manufacture of this equipment. Including a feed preheater or additional fired heaters may reduce this cost in subsequent design iterations.

The total operating cost is approximately $465 million per year, about $427 million of which is the cost of the ethanol feed and natural gas for the two fired heaters. An additional $1.73 million per year is used for utilities including the cooling water and refrigerant. The labor and maintenance costs of this industrial process were also accounted for within the simulation’s economic analysis. The HYSYS simulation software, in conjunction with the Icarus economic analyzer, estimated there should be 5 operators per 8 hour shift with a cost per operator of $20 per hour. This results in a total operating labor cost of approximately $880,000 per year. In addition, the process will require one supervisor per shift with an hourly rate of $35 for total supervisor salaries of $307,000 per year. Finally, a fixed maintenance rate was estimated at $205,000 per 8000 hours of operation for a total cost of $225,000 per year.

Total product sales are roughly $640 million per year at full operation. The estimated income for this process is thus approximately $175 million per year. After ten years, the plant is projected to have a net present value (NPV) of $391 million and an internal rate of return of approximately 79%. In addition the payout period for the initial investment is estimated to be about 2.7 years. Figure 2 shows the projected cash flow for the project.

==Sensitivity Analysis==
A sensitivity analysis was performed to investigate the effects of fluctuating capital costs, operating costs, raw materials, utility costs and ethylene sales price on the 10-year net present value (NPV) of the project. This analysis was performed by scaling these cost factors according to typical ranges given in Towler and Sinnott and calculating the adjusting the NPV accordingly. The results, illustrated in Figure 3, indicate that the project value is most sensitive to product sales, raw materials costs, and operating costs. Ethylene and ethanol prices are market-determined and cannot be controlled for in the process design, so further optimization should be focused on minimizing the operations cost of the process. (Today in Energy, 2015; Weddle, 2014) However, in feed and product prices do still have a profound effect on profitability and feasibility. A more rigorous market analysis will better inform the profitability outlook.

=Conclusions/Recommendations=

The proposed process produces approximately 460,000 metric tons of 99.7 wt% ethylene annually, with a 10-year net present value of $131 million. If current economic conditions hold, it is recommended that this project proceed to implementation following further design improvements and optimization.

Future design iterations should focus on process optimization, particularly in minimizing operating costs as prescribed by the results of the sensitivity analysis. The development of a heat-exchanger network, potentially with Aspen Energy Analyzer, is one option for decreasing utility requirements and increasing the efficiency of the process overall. Optimization of the fired heaters could also result in decreased operational costs. Although overall profitability is less sensitive to capital costs, reviewing and adjusting equipment sizing would also improve the economic outlook. In particular, exploring alternative heating strategies at the beginning of the process could significantly decrease capital costs. Although there are not any particularly dangerous chemicals utilized in the process, an overall process review should also consider potential failure modes to minimize the safety risk to plant workers and nearby residents.

In addition to economic and safety considerations, harmful emissions and waste streams should be minimized both to bring down the cost of treatment and to decrease environmental effects. The two fired heaters consume a large amount of natural gas per year, emitting about 200,000 tons of CO2 annually, and account for more than half of the capital cost of the process. Although no known toxic gases are produced, carbon capture or other emissions-reduction methods should be considered. Additionally, enough wastewater is produced by this process that building an onsite wastewater treatment center should be considered. This could not only decrease operating costs by eliminating the need for an external contract but also give the plant more control over the final purity of the treated wastewater.

Finally, the current model assumes that all ethylene produced will be sold at a current prices and price or product sales will not be affected by economic variability. A more detailed study of the chemical-grade ethylene market, as well as a more thorough understanding of sales and distribution logistics, would increase the surety of a profitable process.

In summary, the proposed process yields chemical grade ethylene via the catalytic dehydration of ethanol. A 100,000 kg/hr of 95 wt% ethanol, 5% water feed is converted to 53,000 kg/hr of 99.7% chemical-grade ethylene. After 10 years of operation, including a one-year startup time, the process has an NPV of $391 million with an IRR of 79% and a payback period of 2.7 years.
Pending further optimization, this process was determined to be viable and it is recommended for the project to move forward.

=References=

[1] American Chemistry Council. Production of chemicals and plastics in the U.S. in 2013, by type (in 1,000 metric tons). In Statista - The Statistics Portal. August 2014. Available at http://www.statista.com/statistics/299725/total-us-plastics-and-chemicals-shipments-by-type/, Accessed January 15, 2015. – Relative proportions of plastics production.

[2] DuPont Nevada Site Cellulosic Ethanol Facility [Internet]. DuPont Chemical; c2012-2015 [cited 11 Mar. 2015]. Available from: http://biofuels.dupont.com/cellulosic-ethanol/nevada-site-ce-facility/. -- Information on ethanol production in Iowa.

[3] Designing Ethylene Plants. Ethylene [Internet]. Technip; 2014 [cited 13 Mar. 2015]. Available from: http://www.technip.com/en/our-business/onshore/ethylene -- Plant size ranges.

[4] Suppes GJ. Selecting Thermodynamic Models for Process Simulation of Organic VLE and LLE Systems. The University of Missouri-Columbia, Dept of Chemical Engineering. [cited 13 Mar. 2015]. -- Use of NRTL in alcohol separations.

[5] ASPENtech. Appendix A - Property Methods and Calculations. Simulation Basics; A-3 - A-26. 2014.

[6] 190 Proof Ethanol: Technical Data Sheet [Internet]. Decon Labs Inc; 2012 [cited 13 Mar. 2015]. Available from: http://www.deconlabs.com/tds/ETHANOL%20190%20%20PROOF.pdf -- Information regarding 95% ethanol

[7] Hadawey A, Ge Y, Tassou TSA. Energy Savings Through Liquid Pressure Amplification In A Dairy Plant Refrigeration System. The Centre for Energy and Built Environment Research [cited 13 Mar. 2015].

[8] Methane (Chemical Compound). 2015. Encyclopædia Britannica Online. [cited 13 Mar. 2015] Available from: http://www.britannica.com/EBchecked/topic/378264/methane -- Composition of Methane

[9] Composition of Air [Internet]. Engineering Toolbox; [cited 13 Mar. 2015]. Available from: http://www.engineeringtoolbox.com/air-composition-d_212.html. -- Composition of air.

[10] Summary of the Clean Air Act, 2015. United States Environmental Protection Agency. [cited 13 Mar. 2015] Available from: http://www2.epa.gov/laws-regulations/summary-clean-air-act -- Emissions requirements of chemical plants.

[11] Zhang M, Yu Y. Dehydration of Ethanol to Ethylene. Industrial Engineering and Chemical Research. 2013; 52:9505-9514. – Technical information on ethanol to ethylene conversion via dehydration.

[12] AspenTech. Aspen HYSYS Help File v8.0. Aspen Technology, Inc. 2012. - Aspen HYSYS help file used for troubleshooting and assistance on economic analysis.

[13] Towler G, Sinnott R. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. 2nd ed. Boston: Elsevier; 2013. -- General Reference Book

[14] Barrocas H, Baratelli F, inventors; Petroleo Brasileiro S.A., assignee. Process for dehydration of a low molecular weight alcohol. US patent 4,396,789 A. August 2, 1983. - Primary background for process design.

[15] Tsao U, Zasloff HB, inventors; The Lummus Company, assignee. Production of ethylene from ethanol. US patent 4,134,926. January 16, 1979. – Patent for catalytic dehydration of ethylene in a fluidized bed reactor.

[16] Morschbacker, A. Bio-Ethanol Based Ethylene. Polymer Reviews. 2009; 49:79-84. – Overview of bioethanol dehydration process development.

[17] Fan D, Dai DJ, Wu HS. Ethylene Formation by Catalytic Dehydration of Ethanol with Industrial Considerations. Materials. 6, 101-115. doi: 10.3390/ma6010101. - Comparison of types of catalysts used in the dehydration of ethanol and current research into new catalysts.

[18] Chen G, Li S, Jiao F, Yuan Q. Catalytic dehydration of bioethanol to ethylene over TiO2/γ-Al2O3 catalysts in microchannel reactors. Catal. Today 2007, 125, 111–119. - Paper introducing research on modified alumina catalyst for ethanol dehydration.

[19] Jumonville, J. Tutorial on Cryogenic Turboexpanders. Proceedings of the Thirty-Ninth Turbomachinery Symposium; 2010 Oct 4-7; Houston, TX. Houston: Texas A&M University; 2010. -- Use of turboexpander for cryogenic separations

[20] Today in Energy - Daily Prices. US Energy Information Administration website. http://www.eia.gov/todayinenergy/prices.cfm. Accessed March 3rd 2015. - Bulk market price for 95% ethanol.

[21] Weddle, N. ICIS Pricing: Ethylene (Europe). Reed Business Limited. January 10 2014. - Bulk market price for chemical grade ethylene.

=Appendix I - Process Flow Diagram=
[[File:PFD B1.JPG|1200px|center]]

=Appendix II - HYSYS Simulation=
[[File:HYSYS_B1.PNG|center|1200px]]

=Appendix III - Material Streams=
[[File:Streams_B1.png|1200px]]

=Appendix IV - Energy Table=
[[File:Energy_B1.png|600px|center]]

=Appendix V - Economics=
[[File:Econsummary_B1.png|center]] 

[[File:Capcost_B1.png|center]] 

[[File:sensitivityanalysis_B1.png|600px|center]]

Ethanol to Ethylene (B1)

2015-03-14T04:45:06Z

Hpoppick: /* Technical Approach */

[[File:BFD_B1.png|600px|thumbnail|alt=Alt text|Conversion of Ethanol to Ethylene]]

Team B1 Final Report

Authors: Harry Poppick, Emm Fulk and Scott Smith

Instructors: Fengqi You, David Wegerer

March 13, 2015

=Executive Summary=

The following report outlines the design and analysis of a process converting ethanol to chemical-grade ethylene via catalytic dehydration. This process consumers 100,000 kg/hr of 95 wt% ethanol, 5 wt% water feedstock and produces 53,000 kg/hr of 99.7 wt% chemical-grade ethylene. The ethanol feed passes through two fixed-bed reactors, each packed with an aluminum oxide catalyst, and the resulting ethylene is purified by two flash tanks and by absorption with water. The process was modeled using Aspen HYSYS simulation software to estimate mass and energy flows and equipment sizing requirements. Based on results of this initial simulation, several alternatives are discussed for increasing the process efficiency and profitability. The use of a fluidized bed reactor or a more ethylene-selective catalyst could increase the production of ethylene per ethanol basis. Additionally, several methods of purification to more valuable polymer-grade ethylene are proposed.

The economic feasibility of this process was evaluated using Aspen Economic Analyzer with the Icarus economics package. Capital cost is approximately $16.4 million total with an operating cost of $465 million per year. The current market prices of the ethanol feed and ethylene sales price are $1.44/gallon and $1350/metric ton respectively. The cost of feed ethanol, process utilities and miscellaneous operational costs total to about $427 million/year. At full operation, revenue at current prices would be approximately $640 million per year. The predicted 10-year net present value of the process is approximately $391 million with an IRR of 79% and a payback period of 2.7 years. A sensitivity analysis indicates that the process is most sensitive to feed prices, product prices and operation cost.

Several recommendations are made for both cost reduction and profit maximization, including the design of a heat exchanger network and the optimization of fired heaters that require high capital investment and large amounts of fuel. A safety review of the process is recommended, as well as the minimization of flue gas effluent and wastewater. It is also suggested that the construction of an onsite wastewater treatment center be considered. Overall, the initial analysis indicates this to be a profitable process and it is recommended the project move forward.

=Introduction=

Ethylene is a critical chemical precursor to a number of different industrial products. It is often derived from petroleum sources and polymerized to polyethylene, one of the most ubiquitous plastics today. (American Chemistry Council, 2013) Recently there has been a significant effort to develop production pathways utilizing biologically-derived feedstocks, such as corn or cellulosic ethanol, rather than traditional fossil-fuel sources. Ethylene can be produced from bioethanol via catalytic dehydration over an aluminum oxide catalyst. The proposed process converts 100,000 kg/hr of 95 wt% ethanol, 5% water feed to 53,000 kg/hr of 99.7% chemical-grade ethylene when operating at full capacity. This process was found to be economically viable with a 10-year net present value (NPV) of $131 million (2014 USD) and a payback period of approximately 2.7 years. This memo will detail the proposed process, as well as outline potential alternatives and economic viability of the project.

=Technical Approach=

Many bioethanol plants are located in the Midwest where large amounts of feedstock crops, such as corn, are grown. As such, this plant will be located in Story county, Iowa, near a large-scale bioethanol production plant. (DuPont Nevada Site, 2012) It is assumed that the supply of bioethanol is consistent and readily available. It is also assumed that other reagents - namely, the aluminum oxide catalyst, heater fuel, utility water and freon refrigerant - are readily available, and that wastewater treatment facilities are located near enough to facilitate the off-site treatment of wastewater. Plant capacity was based on current mid-sized industrial ethylene plants. (Designing Ethylene Plants, 2014)

HYSYS simulations were performed with the NRTL fluid package and Peng-Robinson vapor model. The NRTL fluid package is an activity coefficient model that is especially useful to model the separations of alcohols in aqueous solutions. (Suppes, 2015) In addition, NRTL uses models of binary pairs of components, much like the Wilson equation, to predict chemical interactions at the molecular level. The NRTL package can thus be easily extended to ternary and higher order chemical systems, making it ideal for this type of simulation. The Peng-Robinson vapor model was selected as it is well-suited to account for the non-idealities of the vapor phase reactions and separations integral to this process. (ASPENtech, 2014)

It was assumed that the feed enters the process at ambient temperature and pressure (25 °C, 1 atm) and at a consistent rate and composition with negligible quantities of impurities. The ethanol feed was assumed to be 95% ethanol and 5% water by mass, which is the commercial standard for industrial ethanol. (190 Proof Ethanol, 2012) Storage vessels for the feed ethanol, waste streams and products are assumed to be located nearby to the process. An initial feed pump compensates for pressure drops through the process and reduces the duty on downstream compressors. (Hadawey, 2015)

Natural gas, assumed to consist of 83% methane, 16% ethane and 1% nitrogen by mass, was supplied to two fired heaters at a flow rate estimated by HYSYS. (Methane, 2015) Air fed to the process to enable combustion was assumed to be 23% oxygen and 77% nitrogen by mass. (Composition of Air, 2015) Air streams were fed at 50% molar excess in order to ensure complete combustion and prevent the formation of carbon monoxide in the heater exhaust. Total flue gases are assumed to be 230,000 kg/hr, or 2.2 million tons annually, and consist of 73.8% nitrogen gas, 10.5% carbon dioxide, 8.2% water vapor, and 7.5% oxygen by mass. The only compound of concern in these emissions is the carbon dioxide, a known greenhouse gas. At the time of this report, the quantities of carbon dioxide emitted by this plant annually are within acceptable EPA specifications. (Summary of the Clean Air Act, 2015)

Due to the difficulty of simulation equilibrium and conversion reactions in a single vessel in HYSYS, these two reaction types were simulated in separate equilibrium reactor and conversion reactor units in series. In addition, while HYSYS indicated that reactor units would output separate vapor and liquid streams, it was assumed that in practice this would take the form of a single, two phase stream between each unit. To account for this, mixers were installed downstream of each reactor to combine the liquid and vapor phases of the reactor effluent. The three consequent reactions considered are as follows:

[[File:Equation.PNG|1200px|center]]

The optimal reaction temperature was determined to be 400 °C, which promotes the equilibrium reaction of ethanol to ethylene while minimizing byproducts. (Zhang and Yu, 2013) While other byproducts may be produced in this process, these reactions are typically taken to comprise of the bulk of the dehydration reaction. Heat losses over these reactors were assumed to be negligible. (Zhang and Yu, 2013)All major process equipment is assumed to be constructed of high strength carbon steel. (AspenTech, 2012)

The “Sizing Utility” within the Icarus Economic Evaluation module was used to estimate sizes of major equipment based on the process simulation. These values can serve as a benchmark for an initial plant design. Icarus KbaseTM implements a wide variety of mechanical design standards, including ASME and BS5500, in order to calculate accurate equipment sizing. The Icarus sizing module combines equipment prices for standard chemical processing equipment as well as correlations and sizing factors. The advantage of using a software package such as HYSYS to price out individual equipment is that it utilizes up-to-date prices from vendors and distributors when estimating costs. A more in-depth overview of the correlations included in this software can be found in Towler and Sinnott (2009).

=Process Flowsheet=
[[File:Squarepfd_B1.PNG|thumb|400px|alt=Alt text|Fig 1: PFD of the Proposed Process]]

The following process is based primarily on a 1983 US patent titled “Process for dehydration of a low molecular weight alcohol.” (Barrocas and Baratelli, 1983) The process flow diagram can be seen in Figure 1. A larger version of the PFD is included in Appendix I and the HYSYS simulation setup in Appendix II.

The feed enters the process at a rate of 100,000 kg/hr, a temperature and pressure of a 25 °C and 1 atm and at a composition of 95 wt% ethanol and 5 wt% water.It is initially pressurized to 4335 kPa by centrifugal pump P-101 and subsequently heated to 400 °C by fired heater F-101. The heated and pressurized feed enters fixed bed reactor R-101 and contacts with the aluminum oxide catalyst. At this point it dehydrates to form the product, ethylene, as well as the byproducts water, hydrogen, diethyl ether and acetaldehyde. Fired heater F-102 and reactor R-102 increase the overall conversion of the process. Both fired heaters F-101 and F-102 are fueled with natural gas and fed with excess air. The composition of the reactor train effluent is 54.5 wt% ethylene, 37.1 wt% water, 8.1 wt% unreacted ethanol and trace amounts of diethyl ether, acetaldehyde, and hydrogen contaminants.

The pressure of the reactor train effluent is increased to 4500 kPa by compressor K-102 and the temperature decreased to 100 °C by exchange with cold water in heat exchanger E-201. The stream then expands and flashes in flash vessel FL-201, which separates out 82.3% of the unreacted ethanol, 96.6% of the water and virtually all of the acetaldehyde contaminant in the bottoms while sending the ethylene-rich vapor phase out of the top. The top product of FL-202 is compressed to 3500 kPA by K-202 and cooled to 0.0 °C by a freon refrigerant in E-202. At this point the stream is flashed for a second time in vessel FL-202 to remove additional impurities. The top outlet stream consists of 99.5 wt% ethylene, which is fed to the bottom of a 10-tray absorption column that removes a fraction of the residual diethyl ether as well as the remainder of the unreacted ethanol. A stream of absorbent water is fed to the top of the column at 10,000 kg/hr. The product exits the top of the column at a rate of 54,600 kg/hr and has a purity of 99.7% ethylene. Diethyl ether makes up 0.2% of the remaining product stream and is the primary contaminant. Trace amounts of residual water and hydrogen are also present.

Full tables of material and energy streams can be found in Appendices III and IV respectively.

==Process Alternatives==
===Reactor Alternatives===
Two fixed bed reactors, alternating with fired heaters, are used in the dehydration reaction of ethanol to ethylene. However, a fluidized bed reactor can offer better mixing and temperature control than a fixed bed reactor and thus provide the highest possible conversion of ethanol with the greatest selectivity to ethylene. (Tsao and Zasloff, 1979) Fluidized bed reactors also provide a lower rate of catalyst coking and byproduct formation, minimizing separation and catalyst regeneration costs. (Morschbacker, 2009) The major downside of fluidized bed reactors is that few large-scale processes have been built since the technology was developed in the late 1970s. (Tsao and Zasloff, 1979; Morschbacker, 2009) Although implementation of fluidized bed reactors could potentially increase the purity of the ethylene product and/or decrease costs, a small scale pilot process would need to be built and tested before it would be possible to develop an industrial-scale facility.

===Catalyst Alternatives===
Aluminum oxide, specifically gamma alumina, is the most industrially-common catalyst and has been historically used due to its low cost and high stability. (Tsao and Zasloff, 1979; Fan and Dai, n.d.) Recent improvements in selectivity and catalyst stability of activated alumina have been achieved by incorporating titanium oxide into the catalyst, although this increases reaction temperature by approximately 50 °C and decreases catalyst lifespan. (Chen and Li, et. al. 2007) There is also significant ongoing research into HZSM-5 zeolite and heteropolyacids, which are being explored as potential alternatives to alumina oxide. A nanoscale HZSM-5 zeolite catalyst has been shown to operate at the relatively low temperature of 200-300°C, with a 100% ethanol conversion and 99.7% selectivity to ethylene. Initial research has also indicated that it maintains greater than 98% selectivity for 630 operational hours. (Fan and Dai, n.d.) However, the current low cost and ready availability of unmodified alumina oxide makes it a better choice for a process of this scale.

===Purification Alternatives===
As specified in this process, the reactor effluent is purified by two flash drums and absorption with water to produce chemical-grade ethylene. If chemical-grade ethylene is indeed the desired product, other purification options include caustic washing of the reactor effluent and water removal in a desiccant drying bed. (Morschbacker, 2009) While this purification train is relatively simple and does not require harsh chemical reagents, polymer grade ethylene is more commercially valuable and the additional cost of removing water and diethyl ether contaminants may be justified by increased revenue. Cryogenic distillation was initially simulated to produce polymer-grade ethylene, but utility requirements were found to render this separation economically unviable. (Barrocas and Baratelli, 1983) Further research and optimization may find this purification strategy to be a more valid process. Alternatively, the addition of a cryogenic turboexpander or the use of alternative adsorbents may increase product purity to polymer grade. (Jumonville, 2010) Initial HYSYS simulations indicate that these operations may be feasible with further refinement.

===Wastewater Treatment===
Due to the large volume of wastewater produced, building an on-site wastewater treatment facility may prove to be more economical than paying for third-party wastewater treatment. Flash vessel FL-201 produces 44,600 L/hr of wastewater contaminated with 18.7 vol% ethanol and 0.6 vol% acetaldehyde, while FL-202 produces 2940 L/hr of an aqueous waste consisting of 56.8 vol% ethanol, 42.0 vol% water and 0.9 vol% diethyl ether. The absorption column produces approximately 10,200 liters/hr of wastewater contaminated with 1.2 vol% ethanol, 0.2% diethyl ether and 0.2% acetaldehyde. Utilizing distillation to separate these streams into clean water and volatile organic waste could ultimately reduce the quantity of waste that requires disposal and reduce the overall costs of the process.

==Process Equipment==
Relevant sizing information for each unit operation, estimated by the method described in the “Technical Approach,” can be found in Appendix V. Equipment and piping is assumed to be constructed of carbon steel. It should be noted that the two fired heaters are proportionately large enough to heat the entirety of the process stream and are thus larger than standard equipment.

=Economic Analysis=
[[File:NPV_B1.png|400px|thumb|Fig 2. Projected Cash Flow]]
[[File:sensitivityanalysis_B1.png|400px|thumb| Fig 3. Results of the Sensitivity Analysis on 10 year NPV]]

==Economics Overview==
All final values are normalized to June 2014 USD by CEPCI scaling. It is assumed that all products produced are sold at current market prices.

The Aspen Economic Evaluation module within HYSYS v8.0 was used to estimate capital and operating costs for a 10-year plant life span with a construction start date of April 2015. The price of the 95% ethanol feed stream was estimated at $1.44 per gallon, while the chemical grade ethylene produced is currently selling for approximately $1350 per metric ton. (Today in Energy, 2015; Weddle, 2014) Mapping and sizing calculations were performed by the economics module and a preliminary economic evaluation was completed. Equipment sizes, also estimated by HYSYS, were reviewed to ensure that height, diameter, and volume specifications were within realistic ranges.

The process was ideally projected to operate 360 days per year with a start-up time of one year. In addition, the tax rate was approximated at 40%, an interest rate at 20%, and a salvage value of 20%. Escalation percentages were compounded yearly for the product, raw material, and operating costs. The total capital cost for this process is approximately $16.4 million, which includes all equipment and piping described in the process. The most expensive equipment used in this process are the two fired heaters F-101 and F-102, which have an exceptionally large heat exchange area to adequately heat the feed. Standard heaters may not suffice and additional costs may be incurred for the raw materials and manufacture of this equipment. Including a feed preheater or additional fired heaters may reduce this cost in subsequent design iterations.

The total operating cost is approximately $465 million per year, about $427 million of which is the cost of the ethanol feed and natural gas for the two fired heaters. An additional $1.73 million per year is used for utilities including the cooling water and refrigerant. The labor and maintenance costs of this industrial process were also accounted for within the simulation’s economic analysis. The HYSYS simulation software, in conjunction with the Icarus economic analyzer, estimated there should be 5 operators per 8 hour shift with a cost per operator of $20 per hour. This results in a total operating labor cost of approximately $880,000 per year. In addition, the process will require one supervisor per shift with an hourly rate of $35 for total supervisor salaries of $307,000 per year. Finally, a fixed maintenance rate was estimated at $205,000 per 8000 hours of operation for a total cost of $225,000 per year.

Total product sales are roughly $640 million per year at full operation. The estimated income for this process is thus approximately $175 million per year. After ten years, the plant is projected to have a net present value (NPV) of $391 million and an internal rate of return of approximately 79%. In addition the payout period for the initial investment is estimated to be about 2.7 years. Figure 2 shows the projected cash flow for the project.

==Sensitivity Analysis==
A sensitivity analysis was performed to investigate the effects of fluctuating capital costs, operating costs, raw materials, utility costs and ethylene sales price on the 10-year net present value (NPV) of the project. This analysis was performed by scaling these cost factors according to typical ranges given in Towler and Sinnott and calculating the adjusting the NPV accordingly. The results, illustrated in Figure 3, indicate that the project value is most sensitive to product sales, raw materials costs, and operating costs. Ethylene and ethanol prices are market-determined and cannot be controlled for in the process design, so further optimization should be focused on minimizing the operations cost of the process. (Today in Energy, 2015; Weddle, 2014) However, in feed and product prices do still have a profound effect on profitability and feasibility. A more rigorous market analysis will better inform the profitability outlook.

=Conclusions/Recommendations=

The proposed process produces approximately 460,000 metric tons of 99.7 wt% ethylene annually, with a 10-year net present value of $131 million. If current economic conditions hold, it is recommended that this project proceed to implementation following further design improvements and optimization.

Future design iterations should focus on process optimization, particularly in minimizing operating costs as prescribed by the results of the sensitivity analysis. The development of a heat-exchanger network, potentially with Aspen Energy Analyzer, is one option for decreasing utility requirements and increasing the efficiency of the process overall. Optimization of the fired heaters could also result in decreased operational costs. Although overall profitability is less sensitive to capital costs, reviewing and adjusting equipment sizing would also improve the economic outlook. In particular, exploring alternative heating strategies at the beginning of the process could significantly decrease capital costs. Although there are not any particularly dangerous chemicals utilized in the process, an overall process review should also consider potential failure modes to minimize the safety risk to plant workers and nearby residents.

In addition to economic and safety considerations, harmful emissions and waste streams should be minimized both to bring down the cost of treatment and to decrease environmental effects. The two fired heaters consume a large amount of natural gas per year, emitting about 200,000 tons of CO2 annually, and account for more than half of the capital cost of the process. Although no known toxic gases are produced, carbon capture or other emissions-reduction methods should be considered. Additionally, enough wastewater is produced by this process that building an onsite wastewater treatment center should be considered. This could not only decrease operating costs by eliminating the need for an external contract but also give the plant more control over the final purity of the treated wastewater.

Finally, the current model assumes that all ethylene produced will be sold at a current prices and price or product sales will not be affected by economic variability. A more detailed study of the chemical-grade ethylene market, as well as a more thorough understanding of sales and distribution logistics, would increase the surety of a profitable process.

In summary, the proposed process yields chemical grade ethylene via the catalytic dehydration of ethanol. A 100,000 kg/hr of 95 wt% ethanol, 5% water feed is converted to 53,000 kg/hr of 99.7% chemical-grade ethylene. After 10 years of operation, including a one-year startup time, the process has an NPV of $391 million with an IRR of 79% and a payback period of 2.7 years.
Pending further optimization, this process was determined to be viable and it is recommended for the project to move forward.

=References=

[1] American Chemistry Council. Production of chemicals and plastics in the U.S. in 2013, by type (in 1,000 metric tons). In Statista - The Statistics Portal. August 2014. Available at http://www.statista.com/statistics/299725/total-us-plastics-and-chemicals-shipments-by-type/, Accessed January 15, 2015. – Relative proportions of plastics production.

[2] DuPont Nevada Site Cellulosic Ethanol Facility [Internet]. DuPont Chemical; c2012-2015 [cited 11 Mar. 2015]. Available from: http://biofuels.dupont.com/cellulosic-ethanol/nevada-site-ce-facility/. -- Information on ethanol production in Iowa.

[3] Designing Ethylene Plants. Ethylene [Internet]. Technip; 2014 [cited 13 Mar. 2015]. Available from: http://www.technip.com/en/our-business/onshore/ethylene -- Plant size ranges.

[4] Suppes GJ. Selecting Thermodynamic Models for Process Simulation of Organic VLE and LLE Systems. The University of Missouri-Columbia, Dept of Chemical Engineering. [cited 13 Mar. 2015]. -- Use of NRTL in alcohol separations.

[5] ASPENtech. Appendix A - Property Methods and Calculations. Simulation Basics; A-3 - A-26. 2014.

[6] 190 Proof Ethanol: Technical Data Sheet [Internet]. Decon Labs Inc; 2012 [cited 13 Mar. 2015]. Available from: http://www.deconlabs.com/tds/ETHANOL%20190%20%20PROOF.pdf -- Information regarding 95% ethanol

[7] Hadawey A, Ge Y, Tassou TSA. Energy Savings Through Liquid Pressure Amplification In A Dairy Plant Refrigeration System. The Centre for Energy and Built Environment Research [cited 13 Mar. 2015].

[8] Methane (Chemical Compound). 2015. Encyclopædia Britannica Online. [cited 13 Mar. 2015] Available from: http://www.britannica.com/EBchecked/topic/378264/methane -- Composition of Methane

[9] Composition of Air [Internet]. Engineering Toolbox; [cited 13 Mar. 2015]. Available from: http://www.engineeringtoolbox.com/air-composition-d_212.html. -- Composition of air.

[10] Summary of the Clean Air Act, 2015. United States Environmental Protection Agency. [cited 13 Mar. 2015] Available from: http://www2.epa.gov/laws-regulations/summary-clean-air-act -- Emissions requirements of chemical plants.

[11] Zhang M, Yu Y. Dehydration of Ethanol to Ethylene. Industrial Engineering and Chemical Research. 2013; 52:9505-9514. – Technical information on ethanol to ethylene conversion via dehydration.

[12] AspenTech. Aspen HYSYS Help File v8.0. Aspen Technology, Inc. 2012. - Aspen HYSYS help file used for troubleshooting and assistance on economic analysis.

[13] Towler G, Sinnott R. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. 2nd ed. Boston: Elsevier; 2013. -- General Reference Book

[14] Barrocas H, Baratelli F, inventors; Petroleo Brasileiro S.A., assignee. Process for dehydration of a low molecular weight alcohol. US patent 4,396,789 A. August 2, 1983. - Primary background for process design.

[15] Tsao U, Zasloff HB, inventors; The Lummus Company, assignee. Production of ethylene from ethanol. US patent 4,134,926. January 16, 1979. – Patent for catalytic dehydration of ethylene in a fluidized bed reactor.

[16] Morschbacker, A. Bio-Ethanol Based Ethylene. Polymer Reviews. 2009; 49:79-84. – Overview of bioethanol dehydration process development.

[17] Fan D, Dai DJ, Wu HS. Ethylene Formation by Catalytic Dehydration of Ethanol with Industrial Considerations. Materials. 6, 101-115. doi: 10.3390/ma6010101. - Comparison of types of catalysts used in the dehydration of ethanol and current research into new catalysts.

[18] Chen G, Li S, Jiao F, Yuan Q. Catalytic dehydration of bioethanol to ethylene over TiO2/γ-Al2O3 catalysts in microchannel reactors. Catal. Today 2007, 125, 111–119. - Paper introducing research on modified alumina catalyst for ethanol dehydration.

[19] Jumonville, J. Tutorial on Cryogenic Turboexpanders. Proceedings of the Thirty-Ninth Turbomachinery Symposium; 2010 Oct 4-7; Houston, TX. Houston: Texas A&M University; 2010. -- Use of turboexpander for cryogenic separations

[20] Today in Energy - Daily Prices. US Energy Information Administration website. http://www.eia.gov/todayinenergy/prices.cfm. Accessed March 3rd 2015. - Bulk market price for 95% ethanol.

[21] Weddle, N. ICIS Pricing: Ethylene (Europe). Reed Business Limited. January 10 2014. - Bulk market price for chemical grade ethylene.

=Appendix I - Process Flow Diagram=
[[File:PFD B1.JPG|1200px|center]]

=Appendix II - HYSYS Simulation=
[[File:HYSYS_B1.PNG|center|1200px]]

=Appendix III - Material Streams=
[[File:Streams_B1.png|1200px]]

=Appendix IV - Energy Table=
[[File:Energy_B1.png|600px|center]]

=Appendix V - Economics=
[[File:Econsummary_B1.png|center]] 

[[File:Capcost_B1.png|center]] 

[[File:sensitivityanalysis_B1.png|600px|center]]

Ethanol to Ethylene (B1)

2015-03-14T04:44:55Z

Hpoppick: /* Technical Approach */

[[File:BFD_B1.png|600px|thumbnail|alt=Alt text|Conversion of Ethanol to Ethylene]]

Team B1 Final Report

Authors: Harry Poppick, Emm Fulk and Scott Smith

Instructors: Fengqi You, David Wegerer

March 13, 2015

=Executive Summary=

The following report outlines the design and analysis of a process converting ethanol to chemical-grade ethylene via catalytic dehydration. This process consumers 100,000 kg/hr of 95 wt% ethanol, 5 wt% water feedstock and produces 53,000 kg/hr of 99.7 wt% chemical-grade ethylene. The ethanol feed passes through two fixed-bed reactors, each packed with an aluminum oxide catalyst, and the resulting ethylene is purified by two flash tanks and by absorption with water. The process was modeled using Aspen HYSYS simulation software to estimate mass and energy flows and equipment sizing requirements. Based on results of this initial simulation, several alternatives are discussed for increasing the process efficiency and profitability. The use of a fluidized bed reactor or a more ethylene-selective catalyst could increase the production of ethylene per ethanol basis. Additionally, several methods of purification to more valuable polymer-grade ethylene are proposed.

The economic feasibility of this process was evaluated using Aspen Economic Analyzer with the Icarus economics package. Capital cost is approximately $16.4 million total with an operating cost of $465 million per year. The current market prices of the ethanol feed and ethylene sales price are $1.44/gallon and $1350/metric ton respectively. The cost of feed ethanol, process utilities and miscellaneous operational costs total to about $427 million/year. At full operation, revenue at current prices would be approximately $640 million per year. The predicted 10-year net present value of the process is approximately $391 million with an IRR of 79% and a payback period of 2.7 years. A sensitivity analysis indicates that the process is most sensitive to feed prices, product prices and operation cost.

Several recommendations are made for both cost reduction and profit maximization, including the design of a heat exchanger network and the optimization of fired heaters that require high capital investment and large amounts of fuel. A safety review of the process is recommended, as well as the minimization of flue gas effluent and wastewater. It is also suggested that the construction of an onsite wastewater treatment center be considered. Overall, the initial analysis indicates this to be a profitable process and it is recommended the project move forward.

=Introduction=

Ethylene is a critical chemical precursor to a number of different industrial products. It is often derived from petroleum sources and polymerized to polyethylene, one of the most ubiquitous plastics today. (American Chemistry Council, 2013) Recently there has been a significant effort to develop production pathways utilizing biologically-derived feedstocks, such as corn or cellulosic ethanol, rather than traditional fossil-fuel sources. Ethylene can be produced from bioethanol via catalytic dehydration over an aluminum oxide catalyst. The proposed process converts 100,000 kg/hr of 95 wt% ethanol, 5% water feed to 53,000 kg/hr of 99.7% chemical-grade ethylene when operating at full capacity. This process was found to be economically viable with a 10-year net present value (NPV) of $131 million (2014 USD) and a payback period of approximately 2.7 years. This memo will detail the proposed process, as well as outline potential alternatives and economic viability of the project.

=Technical Approach=

Many bioethanol plants are located in the Midwest where large amounts of feedstock crops, such as corn, are grown. As such, this plant will be located in Story county, Iowa, near a large-scale bioethanol production plant. (DuPont Nevada Site, 2012) It is assumed that the supply of bioethanol is consistent and readily available. It is also assumed that other reagents - namely, the aluminum oxide catalyst, heater fuel, utility water and freon refrigerant - are readily available, and that wastewater treatment facilities are located near enough to facilitate the off-site treatment of wastewater. Plant capacity was based on current mid-sized industrial ethylene plants. (Designing Ethylene Plants, 2014)

HYSYS simulations were performed with the NRTL fluid package and Peng-Robinson vapor model. The NRTL fluid package is an activity coefficient model that is especially useful to model the separations of alcohols in aqueous solutions. (Suppes, 2015) In addition, NRTL uses models of binary pairs of components, much like the Wilson equation, to predict chemical interactions at the molecular level. The NRTL package can thus be easily extended to ternary and higher order chemical systems, making it ideal for this type of simulation. The Peng-Robinson vapor model was selected as it is well-suited to account for the non-idealities of the vapor phase reactions and separations integral to this process. (ASPENtech, 2014)

It was assumed that the feed enters the process at ambient temperature and pressure (25 °C, 1 atm) and at a consistent rate and composition with negligible quantities of impurities. The ethanol feed was assumed to be 95% ethanol and 5% water by mass, which is the commercial standard for industrial ethanol. (190 Proof Ethanol, 2012) Storage vessels for the feed ethanol, waste streams and products are assumed to be located nearby to the process. An initial feed pump compensates for pressure drops through the process and reduces the duty on downstream compressors. (Hadawey, 2015)

Natural gas, assumed to consist of 83% methane, 16% ethane and 1% nitrogen by mass, was supplied to two fired heaters at a flow rate estimated by HYSYS. (Methane, 2015) Air fed to the process to enable combustion was assumed to be 23% oxygen and 77% nitrogen by mass. (Composition of Air, 2015) Air streams were fed at 50% molar excess in order to ensure complete combustion and prevent the formation of carbon monoxide in the heater exhaust. Total flue gases are assumed to be 230,000 kg/hr, or 2.2 million tons annually, and consist of 73.8% nitrogen gas, 10.5% carbon dioxide, 8.2% water vapor, and 7.5% oxygen by mass. The only compound of concern in these emissions is the carbon dioxide, a known greenhouse gas. At the time of this report, the quantities of carbon dioxide emitted by this plant annually are within acceptable EPA specifications. (Summary of the Clean Air Act, 2015)

Due to the difficulty of simulation equilibrium and conversion reactions in a single vessel in HYSYS, these two reaction types were simulated in separate equilibrium reactor and conversion reactor units in series. In addition, while HYSYS indicated that reactor units would output separate vapor and liquid streams, it was assumed that in practice this would take the form of a single, two phase stream between each unit. To account for this, mixers were installed downstream of each reactor to combine the liquid and vapor phases of the reactor effluent. The three consequent reactions considered are as follows:

[[File:Equation.JPG|1200px|center]]

The optimal reaction temperature was determined to be 400 °C, which promotes the equilibrium reaction of ethanol to ethylene while minimizing byproducts. (Zhang and Yu, 2013) While other byproducts may be produced in this process, these reactions are typically taken to comprise of the bulk of the dehydration reaction. Heat losses over these reactors were assumed to be negligible. (Zhang and Yu, 2013)All major process equipment is assumed to be constructed of high strength carbon steel. (AspenTech, 2012)

The “Sizing Utility” within the Icarus Economic Evaluation module was used to estimate sizes of major equipment based on the process simulation. These values can serve as a benchmark for an initial plant design. Icarus KbaseTM implements a wide variety of mechanical design standards, including ASME and BS5500, in order to calculate accurate equipment sizing. The Icarus sizing module combines equipment prices for standard chemical processing equipment as well as correlations and sizing factors. The advantage of using a software package such as HYSYS to price out individual equipment is that it utilizes up-to-date prices from vendors and distributors when estimating costs. A more in-depth overview of the correlations included in this software can be found in Towler and Sinnott (2009).

=Process Flowsheet=
[[File:Squarepfd_B1.PNG|thumb|400px|alt=Alt text|Fig 1: PFD of the Proposed Process]]

The following process is based primarily on a 1983 US patent titled “Process for dehydration of a low molecular weight alcohol.” (Barrocas and Baratelli, 1983) The process flow diagram can be seen in Figure 1. A larger version of the PFD is included in Appendix I and the HYSYS simulation setup in Appendix II.

The feed enters the process at a rate of 100,000 kg/hr, a temperature and pressure of a 25 °C and 1 atm and at a composition of 95 wt% ethanol and 5 wt% water.It is initially pressurized to 4335 kPa by centrifugal pump P-101 and subsequently heated to 400 °C by fired heater F-101. The heated and pressurized feed enters fixed bed reactor R-101 and contacts with the aluminum oxide catalyst. At this point it dehydrates to form the product, ethylene, as well as the byproducts water, hydrogen, diethyl ether and acetaldehyde. Fired heater F-102 and reactor R-102 increase the overall conversion of the process. Both fired heaters F-101 and F-102 are fueled with natural gas and fed with excess air. The composition of the reactor train effluent is 54.5 wt% ethylene, 37.1 wt% water, 8.1 wt% unreacted ethanol and trace amounts of diethyl ether, acetaldehyde, and hydrogen contaminants.

The pressure of the reactor train effluent is increased to 4500 kPa by compressor K-102 and the temperature decreased to 100 °C by exchange with cold water in heat exchanger E-201. The stream then expands and flashes in flash vessel FL-201, which separates out 82.3% of the unreacted ethanol, 96.6% of the water and virtually all of the acetaldehyde contaminant in the bottoms while sending the ethylene-rich vapor phase out of the top. The top product of FL-202 is compressed to 3500 kPA by K-202 and cooled to 0.0 °C by a freon refrigerant in E-202. At this point the stream is flashed for a second time in vessel FL-202 to remove additional impurities. The top outlet stream consists of 99.5 wt% ethylene, which is fed to the bottom of a 10-tray absorption column that removes a fraction of the residual diethyl ether as well as the remainder of the unreacted ethanol. A stream of absorbent water is fed to the top of the column at 10,000 kg/hr. The product exits the top of the column at a rate of 54,600 kg/hr and has a purity of 99.7% ethylene. Diethyl ether makes up 0.2% of the remaining product stream and is the primary contaminant. Trace amounts of residual water and hydrogen are also present.

Full tables of material and energy streams can be found in Appendices III and IV respectively.

==Process Alternatives==
===Reactor Alternatives===
Two fixed bed reactors, alternating with fired heaters, are used in the dehydration reaction of ethanol to ethylene. However, a fluidized bed reactor can offer better mixing and temperature control than a fixed bed reactor and thus provide the highest possible conversion of ethanol with the greatest selectivity to ethylene. (Tsao and Zasloff, 1979) Fluidized bed reactors also provide a lower rate of catalyst coking and byproduct formation, minimizing separation and catalyst regeneration costs. (Morschbacker, 2009) The major downside of fluidized bed reactors is that few large-scale processes have been built since the technology was developed in the late 1970s. (Tsao and Zasloff, 1979; Morschbacker, 2009) Although implementation of fluidized bed reactors could potentially increase the purity of the ethylene product and/or decrease costs, a small scale pilot process would need to be built and tested before it would be possible to develop an industrial-scale facility.

===Catalyst Alternatives===
Aluminum oxide, specifically gamma alumina, is the most industrially-common catalyst and has been historically used due to its low cost and high stability. (Tsao and Zasloff, 1979; Fan and Dai, n.d.) Recent improvements in selectivity and catalyst stability of activated alumina have been achieved by incorporating titanium oxide into the catalyst, although this increases reaction temperature by approximately 50 °C and decreases catalyst lifespan. (Chen and Li, et. al. 2007) There is also significant ongoing research into HZSM-5 zeolite and heteropolyacids, which are being explored as potential alternatives to alumina oxide. A nanoscale HZSM-5 zeolite catalyst has been shown to operate at the relatively low temperature of 200-300°C, with a 100% ethanol conversion and 99.7% selectivity to ethylene. Initial research has also indicated that it maintains greater than 98% selectivity for 630 operational hours. (Fan and Dai, n.d.) However, the current low cost and ready availability of unmodified alumina oxide makes it a better choice for a process of this scale.

===Purification Alternatives===
As specified in this process, the reactor effluent is purified by two flash drums and absorption with water to produce chemical-grade ethylene. If chemical-grade ethylene is indeed the desired product, other purification options include caustic washing of the reactor effluent and water removal in a desiccant drying bed. (Morschbacker, 2009) While this purification train is relatively simple and does not require harsh chemical reagents, polymer grade ethylene is more commercially valuable and the additional cost of removing water and diethyl ether contaminants may be justified by increased revenue. Cryogenic distillation was initially simulated to produce polymer-grade ethylene, but utility requirements were found to render this separation economically unviable. (Barrocas and Baratelli, 1983) Further research and optimization may find this purification strategy to be a more valid process. Alternatively, the addition of a cryogenic turboexpander or the use of alternative adsorbents may increase product purity to polymer grade. (Jumonville, 2010) Initial HYSYS simulations indicate that these operations may be feasible with further refinement.

===Wastewater Treatment===
Due to the large volume of wastewater produced, building an on-site wastewater treatment facility may prove to be more economical than paying for third-party wastewater treatment. Flash vessel FL-201 produces 44,600 L/hr of wastewater contaminated with 18.7 vol% ethanol and 0.6 vol% acetaldehyde, while FL-202 produces 2940 L/hr of an aqueous waste consisting of 56.8 vol% ethanol, 42.0 vol% water and 0.9 vol% diethyl ether. The absorption column produces approximately 10,200 liters/hr of wastewater contaminated with 1.2 vol% ethanol, 0.2% diethyl ether and 0.2% acetaldehyde. Utilizing distillation to separate these streams into clean water and volatile organic waste could ultimately reduce the quantity of waste that requires disposal and reduce the overall costs of the process.

==Process Equipment==
Relevant sizing information for each unit operation, estimated by the method described in the “Technical Approach,” can be found in Appendix V. Equipment and piping is assumed to be constructed of carbon steel. It should be noted that the two fired heaters are proportionately large enough to heat the entirety of the process stream and are thus larger than standard equipment.

=Economic Analysis=
[[File:NPV_B1.png|400px|thumb|Fig 2. Projected Cash Flow]]
[[File:sensitivityanalysis_B1.png|400px|thumb| Fig 3. Results of the Sensitivity Analysis on 10 year NPV]]

==Economics Overview==
All final values are normalized to June 2014 USD by CEPCI scaling. It is assumed that all products produced are sold at current market prices.

The Aspen Economic Evaluation module within HYSYS v8.0 was used to estimate capital and operating costs for a 10-year plant life span with a construction start date of April 2015. The price of the 95% ethanol feed stream was estimated at $1.44 per gallon, while the chemical grade ethylene produced is currently selling for approximately $1350 per metric ton. (Today in Energy, 2015; Weddle, 2014) Mapping and sizing calculations were performed by the economics module and a preliminary economic evaluation was completed. Equipment sizes, also estimated by HYSYS, were reviewed to ensure that height, diameter, and volume specifications were within realistic ranges.

The process was ideally projected to operate 360 days per year with a start-up time of one year. In addition, the tax rate was approximated at 40%, an interest rate at 20%, and a salvage value of 20%. Escalation percentages were compounded yearly for the product, raw material, and operating costs. The total capital cost for this process is approximately $16.4 million, which includes all equipment and piping described in the process. The most expensive equipment used in this process are the two fired heaters F-101 and F-102, which have an exceptionally large heat exchange area to adequately heat the feed. Standard heaters may not suffice and additional costs may be incurred for the raw materials and manufacture of this equipment. Including a feed preheater or additional fired heaters may reduce this cost in subsequent design iterations.

The total operating cost is approximately $465 million per year, about $427 million of which is the cost of the ethanol feed and natural gas for the two fired heaters. An additional $1.73 million per year is used for utilities including the cooling water and refrigerant. The labor and maintenance costs of this industrial process were also accounted for within the simulation’s economic analysis. The HYSYS simulation software, in conjunction with the Icarus economic analyzer, estimated there should be 5 operators per 8 hour shift with a cost per operator of $20 per hour. This results in a total operating labor cost of approximately $880,000 per year. In addition, the process will require one supervisor per shift with an hourly rate of $35 for total supervisor salaries of $307,000 per year. Finally, a fixed maintenance rate was estimated at $205,000 per 8000 hours of operation for a total cost of $225,000 per year.

Total product sales are roughly $640 million per year at full operation. The estimated income for this process is thus approximately $175 million per year. After ten years, the plant is projected to have a net present value (NPV) of $391 million and an internal rate of return of approximately 79%. In addition the payout period for the initial investment is estimated to be about 2.7 years. Figure 2 shows the projected cash flow for the project.

==Sensitivity Analysis==
A sensitivity analysis was performed to investigate the effects of fluctuating capital costs, operating costs, raw materials, utility costs and ethylene sales price on the 10-year net present value (NPV) of the project. This analysis was performed by scaling these cost factors according to typical ranges given in Towler and Sinnott and calculating the adjusting the NPV accordingly. The results, illustrated in Figure 3, indicate that the project value is most sensitive to product sales, raw materials costs, and operating costs. Ethylene and ethanol prices are market-determined and cannot be controlled for in the process design, so further optimization should be focused on minimizing the operations cost of the process. (Today in Energy, 2015; Weddle, 2014) However, in feed and product prices do still have a profound effect on profitability and feasibility. A more rigorous market analysis will better inform the profitability outlook.

=Conclusions/Recommendations=

The proposed process produces approximately 460,000 metric tons of 99.7 wt% ethylene annually, with a 10-year net present value of $131 million. If current economic conditions hold, it is recommended that this project proceed to implementation following further design improvements and optimization.

Future design iterations should focus on process optimization, particularly in minimizing operating costs as prescribed by the results of the sensitivity analysis. The development of a heat-exchanger network, potentially with Aspen Energy Analyzer, is one option for decreasing utility requirements and increasing the efficiency of the process overall. Optimization of the fired heaters could also result in decreased operational costs. Although overall profitability is less sensitive to capital costs, reviewing and adjusting equipment sizing would also improve the economic outlook. In particular, exploring alternative heating strategies at the beginning of the process could significantly decrease capital costs. Although there are not any particularly dangerous chemicals utilized in the process, an overall process review should also consider potential failure modes to minimize the safety risk to plant workers and nearby residents.

In addition to economic and safety considerations, harmful emissions and waste streams should be minimized both to bring down the cost of treatment and to decrease environmental effects. The two fired heaters consume a large amount of natural gas per year, emitting about 200,000 tons of CO2 annually, and account for more than half of the capital cost of the process. Although no known toxic gases are produced, carbon capture or other emissions-reduction methods should be considered. Additionally, enough wastewater is produced by this process that building an onsite wastewater treatment center should be considered. This could not only decrease operating costs by eliminating the need for an external contract but also give the plant more control over the final purity of the treated wastewater.

Finally, the current model assumes that all ethylene produced will be sold at a current prices and price or product sales will not be affected by economic variability. A more detailed study of the chemical-grade ethylene market, as well as a more thorough understanding of sales and distribution logistics, would increase the surety of a profitable process.

In summary, the proposed process yields chemical grade ethylene via the catalytic dehydration of ethanol. A 100,000 kg/hr of 95 wt% ethanol, 5% water feed is converted to 53,000 kg/hr of 99.7% chemical-grade ethylene. After 10 years of operation, including a one-year startup time, the process has an NPV of $391 million with an IRR of 79% and a payback period of 2.7 years.
Pending further optimization, this process was determined to be viable and it is recommended for the project to move forward.

=References=

[1] American Chemistry Council. Production of chemicals and plastics in the U.S. in 2013, by type (in 1,000 metric tons). In Statista - The Statistics Portal. August 2014. Available at http://www.statista.com/statistics/299725/total-us-plastics-and-chemicals-shipments-by-type/, Accessed January 15, 2015. – Relative proportions of plastics production.

[2] DuPont Nevada Site Cellulosic Ethanol Facility [Internet]. DuPont Chemical; c2012-2015 [cited 11 Mar. 2015]. Available from: http://biofuels.dupont.com/cellulosic-ethanol/nevada-site-ce-facility/. -- Information on ethanol production in Iowa.

[3] Designing Ethylene Plants. Ethylene [Internet]. Technip; 2014 [cited 13 Mar. 2015]. Available from: http://www.technip.com/en/our-business/onshore/ethylene -- Plant size ranges.

[4] Suppes GJ. Selecting Thermodynamic Models for Process Simulation of Organic VLE and LLE Systems. The University of Missouri-Columbia, Dept of Chemical Engineering. [cited 13 Mar. 2015]. -- Use of NRTL in alcohol separations.

[5] ASPENtech. Appendix A - Property Methods and Calculations. Simulation Basics; A-3 - A-26. 2014.

[6] 190 Proof Ethanol: Technical Data Sheet [Internet]. Decon Labs Inc; 2012 [cited 13 Mar. 2015]. Available from: http://www.deconlabs.com/tds/ETHANOL%20190%20%20PROOF.pdf -- Information regarding 95% ethanol

[7] Hadawey A, Ge Y, Tassou TSA. Energy Savings Through Liquid Pressure Amplification In A Dairy Plant Refrigeration System. The Centre for Energy and Built Environment Research [cited 13 Mar. 2015].

[8] Methane (Chemical Compound). 2015. Encyclopædia Britannica Online. [cited 13 Mar. 2015] Available from: http://www.britannica.com/EBchecked/topic/378264/methane -- Composition of Methane

[9] Composition of Air [Internet]. Engineering Toolbox; [cited 13 Mar. 2015]. Available from: http://www.engineeringtoolbox.com/air-composition-d_212.html. -- Composition of air.

[10] Summary of the Clean Air Act, 2015. United States Environmental Protection Agency. [cited 13 Mar. 2015] Available from: http://www2.epa.gov/laws-regulations/summary-clean-air-act -- Emissions requirements of chemical plants.

[11] Zhang M, Yu Y. Dehydration of Ethanol to Ethylene. Industrial Engineering and Chemical Research. 2013; 52:9505-9514. – Technical information on ethanol to ethylene conversion via dehydration.

[12] AspenTech. Aspen HYSYS Help File v8.0. Aspen Technology, Inc. 2012. - Aspen HYSYS help file used for troubleshooting and assistance on economic analysis.

[13] Towler G, Sinnott R. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. 2nd ed. Boston: Elsevier; 2013. -- General Reference Book

[14] Barrocas H, Baratelli F, inventors; Petroleo Brasileiro S.A., assignee. Process for dehydration of a low molecular weight alcohol. US patent 4,396,789 A. August 2, 1983. - Primary background for process design.

[15] Tsao U, Zasloff HB, inventors; The Lummus Company, assignee. Production of ethylene from ethanol. US patent 4,134,926. January 16, 1979. – Patent for catalytic dehydration of ethylene in a fluidized bed reactor.

[16] Morschbacker, A. Bio-Ethanol Based Ethylene. Polymer Reviews. 2009; 49:79-84. – Overview of bioethanol dehydration process development.

[17] Fan D, Dai DJ, Wu HS. Ethylene Formation by Catalytic Dehydration of Ethanol with Industrial Considerations. Materials. 6, 101-115. doi: 10.3390/ma6010101. - Comparison of types of catalysts used in the dehydration of ethanol and current research into new catalysts.

[18] Chen G, Li S, Jiao F, Yuan Q. Catalytic dehydration of bioethanol to ethylene over TiO2/γ-Al2O3 catalysts in microchannel reactors. Catal. Today 2007, 125, 111–119. - Paper introducing research on modified alumina catalyst for ethanol dehydration.

[19] Jumonville, J. Tutorial on Cryogenic Turboexpanders. Proceedings of the Thirty-Ninth Turbomachinery Symposium; 2010 Oct 4-7; Houston, TX. Houston: Texas A&M University; 2010. -- Use of turboexpander for cryogenic separations

[20] Today in Energy - Daily Prices. US Energy Information Administration website. http://www.eia.gov/todayinenergy/prices.cfm. Accessed March 3rd 2015. - Bulk market price for 95% ethanol.

[21] Weddle, N. ICIS Pricing: Ethylene (Europe). Reed Business Limited. January 10 2014. - Bulk market price for chemical grade ethylene.

=Appendix I - Process Flow Diagram=
[[File:PFD B1.JPG|1200px|center]]

=Appendix II - HYSYS Simulation=
[[File:HYSYS_B1.PNG|center|1200px]]

=Appendix III - Material Streams=
[[File:Streams_B1.png|1200px]]

=Appendix IV - Energy Table=
[[File:Energy_B1.png|600px|center]]

=Appendix V - Economics=
[[File:Econsummary_B1.png|center]] 

[[File:Capcost_B1.png|center]] 

[[File:sensitivityanalysis_B1.png|600px|center]]

File:Equation.PNG

2015-03-14T04:44:16Z

Hpoppick:

Ethanol to Ethylene (B1)

2015-03-14T04:35:52Z

Hpoppick: /* Technical Approach */

[[File:BFD_B1.png|600px|thumbnail|alt=Alt text|Conversion of Ethanol to Ethylene]]

Team B1 Final Report

Authors: Harry Poppick, Emm Fulk and Scott Smith

Instructors: Fengqi You, David Wegerer

March 13, 2015

=Executive Summary=

The following report outlines the design and analysis of a process converting ethanol to chemical-grade ethylene via catalytic dehydration. This process consumers 100,000 kg/hr of 95 wt% ethanol, 5 wt% water feedstock and produces 53,000 kg/hr of 99.7 wt% chemical-grade ethylene. The ethanol feed passes through two fixed-bed reactors, each packed with an aluminum oxide catalyst, and the resulting ethylene is purified by two flash tanks and by absorption with water. The process was modeled using Aspen HYSYS simulation software to estimate mass and energy flows and equipment sizing requirements. Based on results of this initial simulation, several alternatives are discussed for increasing the process efficiency and profitability. The use of a fluidized bed reactor or a more ethylene-selective catalyst could increase the production of ethylene per ethanol basis. Additionally, several methods of purification to more valuable polymer-grade ethylene are proposed.

The economic feasibility of this process was evaluated using Aspen Economic Analyzer with the Icarus economics package. Capital cost is approximately $16.4 million total with an operating cost of $465 million per year. The current market prices of the ethanol feed and ethylene sales price are $1.44/gallon and $1350/metric ton respectively. The cost of feed ethanol, process utilities and miscellaneous operational costs total to about $427 million/year. At full operation, revenue at current prices would be approximately $640 million per year. The predicted 10-year net present value of the process is approximately $391 million with an IRR of 79% and a payback period of 2.7 years. A sensitivity analysis indicates that the process is most sensitive to feed prices, product prices and operation cost.

Several recommendations are made for both cost reduction and profit maximization, including the design of a heat exchanger network and the optimization of fired heaters that require high capital investment and large amounts of fuel. A safety review of the process is recommended, as well as the minimization of flue gas effluent and wastewater. It is also suggested that the construction of an onsite wastewater treatment center be considered. Overall, the initial analysis indicates this to be a profitable process and it is recommended the project move forward.

=Introduction=

Ethylene is a critical chemical precursor to a number of different industrial products. It is often derived from petroleum sources and polymerized to polyethylene, one of the most ubiquitous plastics today. (American Chemistry Council, 2013) Recently there has been a significant effort to develop production pathways utilizing biologically-derived feedstocks, such as corn or cellulosic ethanol, rather than traditional fossil-fuel sources. Ethylene can be produced from bioethanol via catalytic dehydration over an aluminum oxide catalyst. The proposed process converts 100,000 kg/hr of 95 wt% ethanol, 5% water feed to 53,000 kg/hr of 99.7% chemical-grade ethylene when operating at full capacity. This process was found to be economically viable with a 10-year net present value (NPV) of $131 million (2014 USD) and a payback period of approximately 2.7 years. This memo will detail the proposed process, as well as outline potential alternatives and economic viability of the project.

=Technical Approach=

Many bioethanol plants are located in the Midwest where large amounts of feedstock crops, such as corn, are grown. As such, this plant will be located in Story county, Iowa, near a large-scale bioethanol production plant. (DuPont Nevada Site, 2012) It is assumed that the supply of bioethanol is consistent and readily available. It is also assumed that other reagents - namely, the aluminum oxide catalyst, heater fuel, utility water and freon refrigerant - are readily available, and that wastewater treatment facilities are located near enough to facilitate the off-site treatment of wastewater. Plant capacity was based on current mid-sized industrial ethylene plants. (Designing Ethylene Plants, 2014)

HYSYS simulations were performed with the NRTL fluid package and Peng-Robinson vapor model. The NRTL fluid package is an activity coefficient model that is especially useful to model the separations of alcohols in aqueous solutions. (Suppes, 2015) In addition, NRTL uses models of binary pairs of components, much like the Wilson equation, to predict chemical interactions at the molecular level. The NRTL package can thus be easily extended to ternary and higher order chemical systems, making it ideal for this type of simulation. The Peng-Robinson vapor model was selected as it is well-suited to account for the non-idealities of the vapor phase reactions and separations integral to this process. (ASPENtech, 2014)

It was assumed that the feed enters the process at ambient temperature and pressure (25 °C, 1 atm) and at a consistent rate and composition with negligible quantities of impurities. The ethanol feed was assumed to be 95% ethanol and 5% water by mass, which is the commercial standard for industrial ethanol. (190 Proof Ethanol, 2012) Storage vessels for the feed ethanol, waste streams and products are assumed to be located nearby to the process. An initial feed pump compensates for pressure drops through the process and reduces the duty on downstream compressors. (Hadawey, 2015)

Natural gas, assumed to consist of 83% methane, 16% ethane and 1% nitrogen by mass, was supplied to two fired heaters at a flow rate estimated by HYSYS. (Methane, 2015) Air fed to the process to enable combustion was assumed to be 23% oxygen and 77% nitrogen by mass. (Composition of Air, 2015) Air streams were fed at 50% molar excess in order to ensure complete combustion and prevent the formation of carbon monoxide in the heater exhaust. Total flue gases are assumed to be 230,000 kg/hr, or 2.2 million tons annually, and consist of 73.8% nitrogen gas, 10.5% carbon dioxide, 8.2% water vapor, and 7.5% oxygen by mass. The only compound of concern in these emissions is the carbon dioxide, a known greenhouse gas. At the time of this report, the quantities of carbon dioxide emitted by this plant annually are within acceptable EPA specifications. (Summary of the Clean Air Act, 2015)

Due to the difficulty of simulation equilibrium and conversion reactions in a single vessel in HYSYS, these two reaction types were simulated in separate equilibrium reactor and conversion reactor units in series. In addition, while HYSYS indicated that reactor units would output separate vapor and liquid streams, it was assumed that in practice this would take the form of a single, two phase stream between each unit. To account for this, mixers were installed downstream of each reactor to combine the liquid and vapor phases of the reactor effluent. The three consequent reactions considered are as follows:

Ethanol ↔ Ethylene + Water

Ethanol → Acetaldehyde + Hydrogen

2 Ethanol → Diethyl Ether + Water

The optimal reaction temperature was determined to be 400 °C, which promotes the equilibrium reaction of ethanol to ethylene while minimizing byproducts. (Zhang and Yu, 2013) While other byproducts may be produced in this process, these reactions are typically taken to comprise of the bulk of the dehydration reaction. Heat losses over these reactors were assumed to be negligible. (Zhang and Yu, 2013)All major process equipment is assumed to be constructed of high strength carbon steel. (AspenTech, 2012)

The “Sizing Utility” within the Icarus Economic Evaluation module was used to estimate sizes of major equipment based on the process simulation. These values can serve as a benchmark for an initial plant design. Icarus KbaseTM implements a wide variety of mechanical design standards, including ASME and BS5500, in order to calculate accurate equipment sizing. The Icarus sizing module combines equipment prices for standard chemical processing equipment as well as correlations and sizing factors. The advantage of using a software package such as HYSYS to price out individual equipment is that it utilizes up-to-date prices from vendors and distributors when estimating costs. A more in-depth overview of the correlations included in this software can be found in Towler and Sinnott (2009).

=Process Flowsheet=
[[File:Squarepfd_B1.PNG|thumb|400px|alt=Alt text|Fig 1: PFD of the Proposed Process]]

The following process is based primarily on a 1983 US patent titled “Process for dehydration of a low molecular weight alcohol.” (Barrocas and Baratelli, 1983) The process flow diagram can be seen in Figure 1. A larger version of the PFD is included in Appendix I and the HYSYS simulation setup in Appendix II.

The feed enters the process at a rate of 100,000 kg/hr, a temperature and pressure of a 25 °C and 1 atm and at a composition of 95 wt% ethanol and 5 wt% water.It is initially pressurized to 4335 kPa by centrifugal pump P-101 and subsequently heated to 400 °C by fired heater F-101. The heated and pressurized feed enters fixed bed reactor R-101 and contacts with the aluminum oxide catalyst. At this point it dehydrates to form the product, ethylene, as well as the byproducts water, hydrogen, diethyl ether and acetaldehyde. Fired heater F-102 and reactor R-102 increase the overall conversion of the process. Both fired heaters F-101 and F-102 are fueled with natural gas and fed with excess air. The composition of the reactor train effluent is 54.5 wt% ethylene, 37.1 wt% water, 8.1 wt% unreacted ethanol and trace amounts of diethyl ether, acetaldehyde, and hydrogen contaminants.

The pressure of the reactor train effluent is increased to 4500 kPa by compressor K-102 and the temperature decreased to 100 °C by exchange with cold water in heat exchanger E-201. The stream then expands and flashes in flash vessel FL-201, which separates out 82.3% of the unreacted ethanol, 96.6% of the water and virtually all of the acetaldehyde contaminant in the bottoms while sending the ethylene-rich vapor phase out of the top. The top product of FL-202 is compressed to 3500 kPA by K-202 and cooled to 0.0 °C by a freon refrigerant in E-202. At this point the stream is flashed for a second time in vessel FL-202 to remove additional impurities. The top outlet stream consists of 99.5 wt% ethylene, which is fed to the bottom of a 10-tray absorption column that removes a fraction of the residual diethyl ether as well as the remainder of the unreacted ethanol. A stream of absorbent water is fed to the top of the column at 10,000 kg/hr. The product exits the top of the column at a rate of 54,600 kg/hr and has a purity of 99.7% ethylene. Diethyl ether makes up 0.2% of the remaining product stream and is the primary contaminant. Trace amounts of residual water and hydrogen are also present.

Full tables of material and energy streams can be found in Appendices III and IV respectively.

==Process Alternatives==
===Reactor Alternatives===
Two fixed bed reactors, alternating with fired heaters, are used in the dehydration reaction of ethanol to ethylene. However, a fluidized bed reactor can offer better mixing and temperature control than a fixed bed reactor and thus provide the highest possible conversion of ethanol with the greatest selectivity to ethylene. (Tsao and Zasloff, 1979) Fluidized bed reactors also provide a lower rate of catalyst coking and byproduct formation, minimizing separation and catalyst regeneration costs. (Morschbacker, 2009) The major downside of fluidized bed reactors is that few large-scale processes have been built since the technology was developed in the late 1970s. (Tsao and Zasloff, 1979; Morschbacker, 2009) Although implementation of fluidized bed reactors could potentially increase the purity of the ethylene product and/or decrease costs, a small scale pilot process would need to be built and tested before it would be possible to develop an industrial-scale facility.

===Catalyst Alternatives===
Aluminum oxide, specifically gamma alumina, is the most industrially-common catalyst and has been historically used due to its low cost and high stability. (Tsao and Zasloff, 1979; Fan and Dai, n.d.) Recent improvements in selectivity and catalyst stability of activated alumina have been achieved by incorporating titanium oxide into the catalyst, although this increases reaction temperature by approximately 50 °C and decreases catalyst lifespan. (Chen and Li, et. al. 2007) There is also significant ongoing research into HZSM-5 zeolite and heteropolyacids, which are being explored as potential alternatives to alumina oxide. A nanoscale HZSM-5 zeolite catalyst has been shown to operate at the relatively low temperature of 200-300°C, with a 100% ethanol conversion and 99.7% selectivity to ethylene. Initial research has also indicated that it maintains greater than 98% selectivity for 630 operational hours. (Fan and Dai, n.d.) However, the current low cost and ready availability of unmodified alumina oxide makes it a better choice for a process of this scale.

===Purification Alternatives===
As specified in this process, the reactor effluent is purified by two flash drums and absorption with water to produce chemical-grade ethylene. If chemical-grade ethylene is indeed the desired product, other purification options include caustic washing of the reactor effluent and water removal in a desiccant drying bed. (Morschbacker, 2009) While this purification train is relatively simple and does not require harsh chemical reagents, polymer grade ethylene is more commercially valuable and the additional cost of removing water and diethyl ether contaminants may be justified by increased revenue. Cryogenic distillation was initially simulated to produce polymer-grade ethylene, but utility requirements were found to render this separation economically unviable. (Barrocas and Baratelli, 1983) Further research and optimization may find this purification strategy to be a more valid process. Alternatively, the addition of a cryogenic turboexpander or the use of alternative adsorbents may increase product purity to polymer grade. (Jumonville, 2010) Initial HYSYS simulations indicate that these operations may be feasible with further refinement.

===Wastewater Treatment===
Due to the large volume of wastewater produced, building an on-site wastewater treatment facility may prove to be more economical than paying for third-party wastewater treatment. Flash vessel FL-201 produces 44,600 L/hr of wastewater contaminated with 18.7 vol% ethanol and 0.6 vol% acetaldehyde, while FL-202 produces 2940 L/hr of an aqueous waste consisting of 56.8 vol% ethanol, 42.0 vol% water and 0.9 vol% diethyl ether. The absorption column produces approximately 10,200 liters/hr of wastewater contaminated with 1.2 vol% ethanol, 0.2% diethyl ether and 0.2% acetaldehyde. Utilizing distillation to separate these streams into clean water and volatile organic waste could ultimately reduce the quantity of waste that requires disposal and reduce the overall costs of the process.

==Process Equipment==
Relevant sizing information for each unit operation, estimated by the method described in the “Technical Approach,” can be found in Appendix V. Equipment and piping is assumed to be constructed of carbon steel. It should be noted that the two fired heaters are proportionately large enough to heat the entirety of the process stream and are thus larger than standard equipment.

=Economic Analysis=
[[File:NPV_B1.png|400px|thumb|Fig 2. Projected Cash Flow]]
[[File:sensitivityanalysis_B1.png|400px|thumb| Fig 3. Results of the Sensitivity Analysis on 10 year NPV]]

==Economics Overview==
All final values are normalized to June 2014 USD by CEPCI scaling. It is assumed that all products produced are sold at current market prices.

The Aspen Economic Evaluation module within HYSYS v8.0 was used to estimate capital and operating costs for a 10-year plant life span with a construction start date of April 2015. The price of the 95% ethanol feed stream was estimated at $1.44 per gallon, while the chemical grade ethylene produced is currently selling for approximately $1350 per metric ton. (Today in Energy, 2015; Weddle, 2014) Mapping and sizing calculations were performed by the economics module and a preliminary economic evaluation was completed. Equipment sizes, also estimated by HYSYS, were reviewed to ensure that height, diameter, and volume specifications were within realistic ranges.

The process was ideally projected to operate 360 days per year with a start-up time of one year. In addition, the tax rate was approximated at 40%, an interest rate at 20%, and a salvage value of 20%. Escalation percentages were compounded yearly for the product, raw material, and operating costs. The total capital cost for this process is approximately $16.4 million, which includes all equipment and piping described in the process. The most expensive equipment used in this process are the two fired heaters F-101 and F-102, which have an exceptionally large heat exchange area to adequately heat the feed. Standard heaters may not suffice and additional costs may be incurred for the raw materials and manufacture of this equipment. Including a feed preheater or additional fired heaters may reduce this cost in subsequent design iterations.

The total operating cost is approximately $465 million per year, about $427 million of which is the cost of the ethanol feed and natural gas for the two fired heaters. An additional $1.73 million per year is used for utilities including the cooling water and refrigerant. The labor and maintenance costs of this industrial process were also accounted for within the simulation’s economic analysis. The HYSYS simulation software, in conjunction with the Icarus economic analyzer, estimated there should be 5 operators per 8 hour shift with a cost per operator of $20 per hour. This results in a total operating labor cost of approximately $880,000 per year. In addition, the process will require one supervisor per shift with an hourly rate of $35 for total supervisor salaries of $307,000 per year. Finally, a fixed maintenance rate was estimated at $205,000 per 8000 hours of operation for a total cost of $225,000 per year.

Total product sales are roughly $640 million per year at full operation. The estimated income for this process is thus approximately $175 million per year. After ten years, the plant is projected to have a net present value (NPV) of $391 million and an internal rate of return of approximately 79%. In addition the payout period for the initial investment is estimated to be about 2.7 years. Figure 2 shows the projected cash flow for the project.

==Sensitivity Analysis==
A sensitivity analysis was performed to investigate the effects of fluctuating capital costs, operating costs, raw materials, utility costs and ethylene sales price on the 10-year net present value (NPV) of the project. This analysis was performed by scaling these cost factors according to typical ranges given in Towler and Sinnott and calculating the adjusting the NPV accordingly. The results, illustrated in Figure 3, indicate that the project value is most sensitive to product sales, raw materials costs, and operating costs. Ethylene and ethanol prices are market-determined and cannot be controlled for in the process design, so further optimization should be focused on minimizing the operations cost of the process. (Today in Energy, 2015; Weddle, 2014) However, in feed and product prices do still have a profound effect on profitability and feasibility. A more rigorous market analysis will better inform the profitability outlook.

=Conclusions/Recommendations=

The proposed process produces approximately 460,000 metric tons of 99.7 wt% ethylene annually, with a 10-year net present value of $131 million. If current economic conditions hold, it is recommended that this project proceed to implementation following further design improvements and optimization.

Future design iterations should focus on process optimization, particularly in minimizing operating costs as prescribed by the results of the sensitivity analysis. The development of a heat-exchanger network, potentially with Aspen Energy Analyzer, is one option for decreasing utility requirements and increasing the efficiency of the process overall. Optimization of the fired heaters could also result in decreased operational costs. Although overall profitability is less sensitive to capital costs, reviewing and adjusting equipment sizing would also improve the economic outlook. In particular, exploring alternative heating strategies at the beginning of the process could significantly decrease capital costs. Although there are not any particularly dangerous chemicals utilized in the process, an overall process review should also consider potential failure modes to minimize the safety risk to plant workers and nearby residents.

In addition to economic and safety considerations, harmful emissions and waste streams should be minimized both to bring down the cost of treatment and to decrease environmental effects. The two fired heaters consume a large amount of natural gas per year, emitting about 200,000 tons of CO2 annually, and account for more than half of the capital cost of the process. Although no known toxic gases are produced, carbon capture or other emissions-reduction methods should be considered. Additionally, enough wastewater is produced by this process that building an onsite wastewater treatment center should be considered. This could not only decrease operating costs by eliminating the need for an external contract but also give the plant more control over the final purity of the treated wastewater.

Finally, the current model assumes that all ethylene produced will be sold at a current prices and price or product sales will not be affected by economic variability. A more detailed study of the chemical-grade ethylene market, as well as a more thorough understanding of sales and distribution logistics, would increase the surety of a profitable process.

In summary, the proposed process yields chemical grade ethylene via the catalytic dehydration of ethanol. A 100,000 kg/hr of 95 wt% ethanol, 5% water feed is converted to 53,000 kg/hr of 99.7% chemical-grade ethylene. After 10 years of operation, including a one-year startup time, the process has an NPV of $391 million with an IRR of 79% and a payback period of 2.7 years.
Pending further optimization, this process was determined to be viable and it is recommended for the project to move forward.

=References=

[1] American Chemistry Council. Production of chemicals and plastics in the U.S. in 2013, by type (in 1,000 metric tons). In Statista - The Statistics Portal. August 2014. Available at http://www.statista.com/statistics/299725/total-us-plastics-and-chemicals-shipments-by-type/, Accessed January 15, 2015. – Relative proportions of plastics production.

[2] DuPont Nevada Site Cellulosic Ethanol Facility [Internet]. DuPont Chemical; c2012-2015 [cited 11 Mar. 2015]. Available from: http://biofuels.dupont.com/cellulosic-ethanol/nevada-site-ce-facility/. -- Information on ethanol production in Iowa.

[3] Designing Ethylene Plants. Ethylene [Internet]. Technip; 2014 [cited 13 Mar. 2015]. Available from: http://www.technip.com/en/our-business/onshore/ethylene -- Plant size ranges.

[4] Suppes GJ. Selecting Thermodynamic Models for Process Simulation of Organic VLE and LLE Systems. The University of Missouri-Columbia, Dept of Chemical Engineering. [cited 13 Mar. 2015]. -- Use of NRTL in alcohol separations.

[5] ASPENtech. Appendix A - Property Methods and Calculations. Simulation Basics; A-3 - A-26. 2014.

[6] 190 Proof Ethanol: Technical Data Sheet [Internet]. Decon Labs Inc; 2012 [cited 13 Mar. 2015]. Available from: http://www.deconlabs.com/tds/ETHANOL%20190%20%20PROOF.pdf -- Information regarding 95% ethanol

[7] Hadawey A, Ge Y, Tassou TSA. Energy Savings Through Liquid Pressure Amplification In A Dairy Plant Refrigeration System. The Centre for Energy and Built Environment Research [cited 13 Mar. 2015].

[8] Methane (Chemical Compound). 2015. Encyclopædia Britannica Online. [cited 13 Mar. 2015] Available from: http://www.britannica.com/EBchecked/topic/378264/methane -- Composition of Methane

[9] Composition of Air [Internet]. Engineering Toolbox; [cited 13 Mar. 2015]. Available from: http://www.engineeringtoolbox.com/air-composition-d_212.html. -- Composition of air.

[10] Summary of the Clean Air Act, 2015. United States Environmental Protection Agency. [cited 13 Mar. 2015] Available from: http://www2.epa.gov/laws-regulations/summary-clean-air-act -- Emissions requirements of chemical plants.

[11] Zhang M, Yu Y. Dehydration of Ethanol to Ethylene. Industrial Engineering and Chemical Research. 2013; 52:9505-9514. – Technical information on ethanol to ethylene conversion via dehydration.

[12] AspenTech. Aspen HYSYS Help File v8.0. Aspen Technology, Inc. 2012. - Aspen HYSYS help file used for troubleshooting and assistance on economic analysis.

[13] Towler G, Sinnott R. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. 2nd ed. Boston: Elsevier; 2013. -- General Reference Book

[14] Barrocas H, Baratelli F, inventors; Petroleo Brasileiro S.A., assignee. Process for dehydration of a low molecular weight alcohol. US patent 4,396,789 A. August 2, 1983. - Primary background for process design.

[15] Tsao U, Zasloff HB, inventors; The Lummus Company, assignee. Production of ethylene from ethanol. US patent 4,134,926. January 16, 1979. – Patent for catalytic dehydration of ethylene in a fluidized bed reactor.

[16] Morschbacker, A. Bio-Ethanol Based Ethylene. Polymer Reviews. 2009; 49:79-84. – Overview of bioethanol dehydration process development.

[17] Fan D, Dai DJ, Wu HS. Ethylene Formation by Catalytic Dehydration of Ethanol with Industrial Considerations. Materials. 6, 101-115. doi: 10.3390/ma6010101. - Comparison of types of catalysts used in the dehydration of ethanol and current research into new catalysts.

[18] Chen G, Li S, Jiao F, Yuan Q. Catalytic dehydration of bioethanol to ethylene over TiO2/γ-Al2O3 catalysts in microchannel reactors. Catal. Today 2007, 125, 111–119. - Paper introducing research on modified alumina catalyst for ethanol dehydration.

[19] Jumonville, J. Tutorial on Cryogenic Turboexpanders. Proceedings of the Thirty-Ninth Turbomachinery Symposium; 2010 Oct 4-7; Houston, TX. Houston: Texas A&M University; 2010. -- Use of turboexpander for cryogenic separations

[20] Today in Energy - Daily Prices. US Energy Information Administration website. http://www.eia.gov/todayinenergy/prices.cfm. Accessed March 3rd 2015. - Bulk market price for 95% ethanol.

[21] Weddle, N. ICIS Pricing: Ethylene (Europe). Reed Business Limited. January 10 2014. - Bulk market price for chemical grade ethylene.

=Appendix I - Process Flow Diagram=
[[File:PFD B1.JPG|1200px|center]]

=Appendix II - HYSYS Simulation=
[[File:HYSYS_B1.PNG|center|1200px]]

=Appendix III - Material Streams=
[[File:Streams_B1.png|1200px]]

=Appendix IV - Energy Table=
[[File:Energy_B1.png|600px|center]]

=Appendix V - Economics=
[[File:Econsummary_B1.png|center]] 

[[File:Capcost_B1.png|center]] 

[[File:sensitivityanalysis_B1.png|600px|center]]

Ethanol to Ethylene (B1)

2015-03-14T04:35:22Z

Hpoppick: /* Technical Approach */

[[File:BFD_B1.png|600px|thumbnail|alt=Alt text|Conversion of Ethanol to Ethylene]]

Team B1 Final Report

Authors: Harry Poppick, Emm Fulk and Scott Smith

Instructors: Fengqi You, David Wegerer

March 13, 2015

=Executive Summary=

The following report outlines the design and analysis of a process converting ethanol to chemical-grade ethylene via catalytic dehydration. This process consumers 100,000 kg/hr of 95 wt% ethanol, 5 wt% water feedstock and produces 53,000 kg/hr of 99.7 wt% chemical-grade ethylene. The ethanol feed passes through two fixed-bed reactors, each packed with an aluminum oxide catalyst, and the resulting ethylene is purified by two flash tanks and by absorption with water. The process was modeled using Aspen HYSYS simulation software to estimate mass and energy flows and equipment sizing requirements. Based on results of this initial simulation, several alternatives are discussed for increasing the process efficiency and profitability. The use of a fluidized bed reactor or a more ethylene-selective catalyst could increase the production of ethylene per ethanol basis. Additionally, several methods of purification to more valuable polymer-grade ethylene are proposed.

The economic feasibility of this process was evaluated using Aspen Economic Analyzer with the Icarus economics package. Capital cost is approximately $16.4 million total with an operating cost of $465 million per year. The current market prices of the ethanol feed and ethylene sales price are $1.44/gallon and $1350/metric ton respectively. The cost of feed ethanol, process utilities and miscellaneous operational costs total to about $427 million/year. At full operation, revenue at current prices would be approximately $640 million per year. The predicted 10-year net present value of the process is approximately $391 million with an IRR of 79% and a payback period of 2.7 years. A sensitivity analysis indicates that the process is most sensitive to feed prices, product prices and operation cost.

Several recommendations are made for both cost reduction and profit maximization, including the design of a heat exchanger network and the optimization of fired heaters that require high capital investment and large amounts of fuel. A safety review of the process is recommended, as well as the minimization of flue gas effluent and wastewater. It is also suggested that the construction of an onsite wastewater treatment center be considered. Overall, the initial analysis indicates this to be a profitable process and it is recommended the project move forward.

=Introduction=

Ethylene is a critical chemical precursor to a number of different industrial products. It is often derived from petroleum sources and polymerized to polyethylene, one of the most ubiquitous plastics today. (American Chemistry Council, 2013) Recently there has been a significant effort to develop production pathways utilizing biologically-derived feedstocks, such as corn or cellulosic ethanol, rather than traditional fossil-fuel sources. Ethylene can be produced from bioethanol via catalytic dehydration over an aluminum oxide catalyst. The proposed process converts 100,000 kg/hr of 95 wt% ethanol, 5% water feed to 53,000 kg/hr of 99.7% chemical-grade ethylene when operating at full capacity. This process was found to be economically viable with a 10-year net present value (NPV) of $131 million (2014 USD) and a payback period of approximately 2.7 years. This memo will detail the proposed process, as well as outline potential alternatives and economic viability of the project.

=Technical Approach=

Many bioethanol plants are located in the Midwest where large amounts of feedstock crops, such as corn, are grown. As such, this plant will be located in Story county, Iowa, near a large-scale bioethanol production plant. (DuPont Nevada Site, 2012) It is assumed that the supply of bioethanol is consistent and readily available. It is also assumed that other reagents - namely, the aluminum oxide catalyst, heater fuel, utility water and freon refrigerant - are readily available, and that wastewater treatment facilities are located near enough to facilitate the off-site treatment of wastewater. Plant capacity was based on current mid-sized industrial ethylene plants. (Designing Ethylene Plants, 2014)

HYSYS simulations were performed with the NRTL fluid package and Peng-Robinson vapor model. The NRTL fluid package is an activity coefficient model that is especially useful to model the separations of alcohols in aqueous solutions. (Suppes, 2015) In addition, NRTL uses models of binary pairs of components, much like the Wilson equation, to predict chemical interactions at the molecular level. The NRTL package can thus be easily extended to ternary and higher order chemical systems, making it ideal for this type of simulation. The Peng-Robinson vapor model was selected as it is well-suited to account for the non-idealities of the vapor phase reactions and separations integral to this process. (ASPENtech, 2014)

It was assumed that the feed enters the process at ambient temperature and pressure (25 °C, 1 atm) and at a consistent rate and composition with negligible quantities of impurities. The ethanol feed was assumed to be 95% ethanol and 5% water by mass, which is the commercial standard for industrial ethanol. (190 Proof Ethanol, 2012) Storage vessels for the feed ethanol, waste streams and products are assumed to be located nearby to the process. An initial feed pump compensates for pressure drops through the process and reduces the duty on downstream compressors. (Hadawey, 2015)

Natural gas, assumed to consist of 83% methane, 16% ethane and 1% nitrogen by mass, was supplied to two fired heaters at a flow rate estimated by HYSYS. (Methane, 2015) Air fed to the process to enable combustion was assumed to be 23% oxygen and 77% nitrogen by mass. (Composition of Air, 2015) Air streams were fed at 50% molar excess in order to ensure complete combustion and prevent the formation of carbon monoxide in the heater exhaust. Total flue gases are assumed to be 230,000 kg/hr, or 2.2 million tons annually, and consist of 73.8% nitrogen gas, 10.5% carbon dioxide, 8.2% water vapor, and 7.5% oxygen by mass. The only compound of concern in these emissions is the carbon dioxide, a known greenhouse gas. At the time of this report, the quantities of carbon dioxide emitted by this plant annually are within acceptable EPA specifications. (Summary of the Clean Air Act, 2015)

Due to the difficulty of simulation equilibrium and conversion reactions in a single vessel in HYSYS, these two reaction types were simulated in separate equilibrium reactor and conversion reactor units in series. In addition, while HYSYS indicated that reactor units would output separate vapor and liquid streams, it was assumed that in practice this would take the form of a single, two phase stream between each unit. To account for this, mixers were installed downstream of each reactor to combine the liquid and vapor phases of the reactor effluent. The three consequent reactions considered are as follows:

<math> Ethanol ↔ Ethylene + Water </math>

Ethanol → Acetaldehyde + Hydrogen

2 Ethanol → Diethyl Ether + Water

The optimal reaction temperature was determined to be 400 °C, which promotes the equilibrium reaction of ethanol to ethylene while minimizing byproducts. (Zhang and Yu, 2013) While other byproducts may be produced in this process, these reactions are typically taken to comprise of the bulk of the dehydration reaction. Heat losses over these reactors were assumed to be negligible. (Zhang and Yu, 2013)All major process equipment is assumed to be constructed of high strength carbon steel. (AspenTech, 2012)

The “Sizing Utility” within the Icarus Economic Evaluation module was used to estimate sizes of major equipment based on the process simulation. These values can serve as a benchmark for an initial plant design. Icarus KbaseTM implements a wide variety of mechanical design standards, including ASME and BS5500, in order to calculate accurate equipment sizing. The Icarus sizing module combines equipment prices for standard chemical processing equipment as well as correlations and sizing factors. The advantage of using a software package such as HYSYS to price out individual equipment is that it utilizes up-to-date prices from vendors and distributors when estimating costs. A more in-depth overview of the correlations included in this software can be found in Towler and Sinnott (2009).

=Process Flowsheet=
[[File:Squarepfd_B1.PNG|thumb|400px|alt=Alt text|Fig 1: PFD of the Proposed Process]]

The following process is based primarily on a 1983 US patent titled “Process for dehydration of a low molecular weight alcohol.” (Barrocas and Baratelli, 1983) The process flow diagram can be seen in Figure 1. A larger version of the PFD is included in Appendix I and the HYSYS simulation setup in Appendix II.

The feed enters the process at a rate of 100,000 kg/hr, a temperature and pressure of a 25 °C and 1 atm and at a composition of 95 wt% ethanol and 5 wt% water.It is initially pressurized to 4335 kPa by centrifugal pump P-101 and subsequently heated to 400 °C by fired heater F-101. The heated and pressurized feed enters fixed bed reactor R-101 and contacts with the aluminum oxide catalyst. At this point it dehydrates to form the product, ethylene, as well as the byproducts water, hydrogen, diethyl ether and acetaldehyde. Fired heater F-102 and reactor R-102 increase the overall conversion of the process. Both fired heaters F-101 and F-102 are fueled with natural gas and fed with excess air. The composition of the reactor train effluent is 54.5 wt% ethylene, 37.1 wt% water, 8.1 wt% unreacted ethanol and trace amounts of diethyl ether, acetaldehyde, and hydrogen contaminants.

The pressure of the reactor train effluent is increased to 4500 kPa by compressor K-102 and the temperature decreased to 100 °C by exchange with cold water in heat exchanger E-201. The stream then expands and flashes in flash vessel FL-201, which separates out 82.3% of the unreacted ethanol, 96.6% of the water and virtually all of the acetaldehyde contaminant in the bottoms while sending the ethylene-rich vapor phase out of the top. The top product of FL-202 is compressed to 3500 kPA by K-202 and cooled to 0.0 °C by a freon refrigerant in E-202. At this point the stream is flashed for a second time in vessel FL-202 to remove additional impurities. The top outlet stream consists of 99.5 wt% ethylene, which is fed to the bottom of a 10-tray absorption column that removes a fraction of the residual diethyl ether as well as the remainder of the unreacted ethanol. A stream of absorbent water is fed to the top of the column at 10,000 kg/hr. The product exits the top of the column at a rate of 54,600 kg/hr and has a purity of 99.7% ethylene. Diethyl ether makes up 0.2% of the remaining product stream and is the primary contaminant. Trace amounts of residual water and hydrogen are also present.

Full tables of material and energy streams can be found in Appendices III and IV respectively.

==Process Alternatives==
===Reactor Alternatives===
Two fixed bed reactors, alternating with fired heaters, are used in the dehydration reaction of ethanol to ethylene. However, a fluidized bed reactor can offer better mixing and temperature control than a fixed bed reactor and thus provide the highest possible conversion of ethanol with the greatest selectivity to ethylene. (Tsao and Zasloff, 1979) Fluidized bed reactors also provide a lower rate of catalyst coking and byproduct formation, minimizing separation and catalyst regeneration costs. (Morschbacker, 2009) The major downside of fluidized bed reactors is that few large-scale processes have been built since the technology was developed in the late 1970s. (Tsao and Zasloff, 1979; Morschbacker, 2009) Although implementation of fluidized bed reactors could potentially increase the purity of the ethylene product and/or decrease costs, a small scale pilot process would need to be built and tested before it would be possible to develop an industrial-scale facility.

===Catalyst Alternatives===
Aluminum oxide, specifically gamma alumina, is the most industrially-common catalyst and has been historically used due to its low cost and high stability. (Tsao and Zasloff, 1979; Fan and Dai, n.d.) Recent improvements in selectivity and catalyst stability of activated alumina have been achieved by incorporating titanium oxide into the catalyst, although this increases reaction temperature by approximately 50 °C and decreases catalyst lifespan. (Chen and Li, et. al. 2007) There is also significant ongoing research into HZSM-5 zeolite and heteropolyacids, which are being explored as potential alternatives to alumina oxide. A nanoscale HZSM-5 zeolite catalyst has been shown to operate at the relatively low temperature of 200-300°C, with a 100% ethanol conversion and 99.7% selectivity to ethylene. Initial research has also indicated that it maintains greater than 98% selectivity for 630 operational hours. (Fan and Dai, n.d.) However, the current low cost and ready availability of unmodified alumina oxide makes it a better choice for a process of this scale.

===Purification Alternatives===
As specified in this process, the reactor effluent is purified by two flash drums and absorption with water to produce chemical-grade ethylene. If chemical-grade ethylene is indeed the desired product, other purification options include caustic washing of the reactor effluent and water removal in a desiccant drying bed. (Morschbacker, 2009) While this purification train is relatively simple and does not require harsh chemical reagents, polymer grade ethylene is more commercially valuable and the additional cost of removing water and diethyl ether contaminants may be justified by increased revenue. Cryogenic distillation was initially simulated to produce polymer-grade ethylene, but utility requirements were found to render this separation economically unviable. (Barrocas and Baratelli, 1983) Further research and optimization may find this purification strategy to be a more valid process. Alternatively, the addition of a cryogenic turboexpander or the use of alternative adsorbents may increase product purity to polymer grade. (Jumonville, 2010) Initial HYSYS simulations indicate that these operations may be feasible with further refinement.

===Wastewater Treatment===
Due to the large volume of wastewater produced, building an on-site wastewater treatment facility may prove to be more economical than paying for third-party wastewater treatment. Flash vessel FL-201 produces 44,600 L/hr of wastewater contaminated with 18.7 vol% ethanol and 0.6 vol% acetaldehyde, while FL-202 produces 2940 L/hr of an aqueous waste consisting of 56.8 vol% ethanol, 42.0 vol% water and 0.9 vol% diethyl ether. The absorption column produces approximately 10,200 liters/hr of wastewater contaminated with 1.2 vol% ethanol, 0.2% diethyl ether and 0.2% acetaldehyde. Utilizing distillation to separate these streams into clean water and volatile organic waste could ultimately reduce the quantity of waste that requires disposal and reduce the overall costs of the process.

==Process Equipment==
Relevant sizing information for each unit operation, estimated by the method described in the “Technical Approach,” can be found in Appendix V. Equipment and piping is assumed to be constructed of carbon steel. It should be noted that the two fired heaters are proportionately large enough to heat the entirety of the process stream and are thus larger than standard equipment.

=Economic Analysis=
[[File:NPV_B1.png|400px|thumb|Fig 2. Projected Cash Flow]]
[[File:sensitivityanalysis_B1.png|400px|thumb| Fig 3. Results of the Sensitivity Analysis on 10 year NPV]]

==Economics Overview==
All final values are normalized to June 2014 USD by CEPCI scaling. It is assumed that all products produced are sold at current market prices.

The Aspen Economic Evaluation module within HYSYS v8.0 was used to estimate capital and operating costs for a 10-year plant life span with a construction start date of April 2015. The price of the 95% ethanol feed stream was estimated at $1.44 per gallon, while the chemical grade ethylene produced is currently selling for approximately $1350 per metric ton. (Today in Energy, 2015; Weddle, 2014) Mapping and sizing calculations were performed by the economics module and a preliminary economic evaluation was completed. Equipment sizes, also estimated by HYSYS, were reviewed to ensure that height, diameter, and volume specifications were within realistic ranges.

The process was ideally projected to operate 360 days per year with a start-up time of one year. In addition, the tax rate was approximated at 40%, an interest rate at 20%, and a salvage value of 20%. Escalation percentages were compounded yearly for the product, raw material, and operating costs. The total capital cost for this process is approximately $16.4 million, which includes all equipment and piping described in the process. The most expensive equipment used in this process are the two fired heaters F-101 and F-102, which have an exceptionally large heat exchange area to adequately heat the feed. Standard heaters may not suffice and additional costs may be incurred for the raw materials and manufacture of this equipment. Including a feed preheater or additional fired heaters may reduce this cost in subsequent design iterations.

The total operating cost is approximately $465 million per year, about $427 million of which is the cost of the ethanol feed and natural gas for the two fired heaters. An additional $1.73 million per year is used for utilities including the cooling water and refrigerant. The labor and maintenance costs of this industrial process were also accounted for within the simulation’s economic analysis. The HYSYS simulation software, in conjunction with the Icarus economic analyzer, estimated there should be 5 operators per 8 hour shift with a cost per operator of $20 per hour. This results in a total operating labor cost of approximately $880,000 per year. In addition, the process will require one supervisor per shift with an hourly rate of $35 for total supervisor salaries of $307,000 per year. Finally, a fixed maintenance rate was estimated at $205,000 per 8000 hours of operation for a total cost of $225,000 per year.

Total product sales are roughly $640 million per year at full operation. The estimated income for this process is thus approximately $175 million per year. After ten years, the plant is projected to have a net present value (NPV) of $391 million and an internal rate of return of approximately 79%. In addition the payout period for the initial investment is estimated to be about 2.7 years. Figure 2 shows the projected cash flow for the project.

==Sensitivity Analysis==
A sensitivity analysis was performed to investigate the effects of fluctuating capital costs, operating costs, raw materials, utility costs and ethylene sales price on the 10-year net present value (NPV) of the project. This analysis was performed by scaling these cost factors according to typical ranges given in Towler and Sinnott and calculating the adjusting the NPV accordingly. The results, illustrated in Figure 3, indicate that the project value is most sensitive to product sales, raw materials costs, and operating costs. Ethylene and ethanol prices are market-determined and cannot be controlled for in the process design, so further optimization should be focused on minimizing the operations cost of the process. (Today in Energy, 2015; Weddle, 2014) However, in feed and product prices do still have a profound effect on profitability and feasibility. A more rigorous market analysis will better inform the profitability outlook.

=Conclusions/Recommendations=

The proposed process produces approximately 460,000 metric tons of 99.7 wt% ethylene annually, with a 10-year net present value of $131 million. If current economic conditions hold, it is recommended that this project proceed to implementation following further design improvements and optimization.

Future design iterations should focus on process optimization, particularly in minimizing operating costs as prescribed by the results of the sensitivity analysis. The development of a heat-exchanger network, potentially with Aspen Energy Analyzer, is one option for decreasing utility requirements and increasing the efficiency of the process overall. Optimization of the fired heaters could also result in decreased operational costs. Although overall profitability is less sensitive to capital costs, reviewing and adjusting equipment sizing would also improve the economic outlook. In particular, exploring alternative heating strategies at the beginning of the process could significantly decrease capital costs. Although there are not any particularly dangerous chemicals utilized in the process, an overall process review should also consider potential failure modes to minimize the safety risk to plant workers and nearby residents.

In addition to economic and safety considerations, harmful emissions and waste streams should be minimized both to bring down the cost of treatment and to decrease environmental effects. The two fired heaters consume a large amount of natural gas per year, emitting about 200,000 tons of CO2 annually, and account for more than half of the capital cost of the process. Although no known toxic gases are produced, carbon capture or other emissions-reduction methods should be considered. Additionally, enough wastewater is produced by this process that building an onsite wastewater treatment center should be considered. This could not only decrease operating costs by eliminating the need for an external contract but also give the plant more control over the final purity of the treated wastewater.

Finally, the current model assumes that all ethylene produced will be sold at a current prices and price or product sales will not be affected by economic variability. A more detailed study of the chemical-grade ethylene market, as well as a more thorough understanding of sales and distribution logistics, would increase the surety of a profitable process.

In summary, the proposed process yields chemical grade ethylene via the catalytic dehydration of ethanol. A 100,000 kg/hr of 95 wt% ethanol, 5% water feed is converted to 53,000 kg/hr of 99.7% chemical-grade ethylene. After 10 years of operation, including a one-year startup time, the process has an NPV of $391 million with an IRR of 79% and a payback period of 2.7 years.
Pending further optimization, this process was determined to be viable and it is recommended for the project to move forward.

=References=

[1] American Chemistry Council. Production of chemicals and plastics in the U.S. in 2013, by type (in 1,000 metric tons). In Statista - The Statistics Portal. August 2014. Available at http://www.statista.com/statistics/299725/total-us-plastics-and-chemicals-shipments-by-type/, Accessed January 15, 2015. – Relative proportions of plastics production.

[2] DuPont Nevada Site Cellulosic Ethanol Facility [Internet]. DuPont Chemical; c2012-2015 [cited 11 Mar. 2015]. Available from: http://biofuels.dupont.com/cellulosic-ethanol/nevada-site-ce-facility/. -- Information on ethanol production in Iowa.

[3] Designing Ethylene Plants. Ethylene [Internet]. Technip; 2014 [cited 13 Mar. 2015]. Available from: http://www.technip.com/en/our-business/onshore/ethylene -- Plant size ranges.

[4] Suppes GJ. Selecting Thermodynamic Models for Process Simulation of Organic VLE and LLE Systems. The University of Missouri-Columbia, Dept of Chemical Engineering. [cited 13 Mar. 2015]. -- Use of NRTL in alcohol separations.

[5] ASPENtech. Appendix A - Property Methods and Calculations. Simulation Basics; A-3 - A-26. 2014.

[6] 190 Proof Ethanol: Technical Data Sheet [Internet]. Decon Labs Inc; 2012 [cited 13 Mar. 2015]. Available from: http://www.deconlabs.com/tds/ETHANOL%20190%20%20PROOF.pdf -- Information regarding 95% ethanol

[7] Hadawey A, Ge Y, Tassou TSA. Energy Savings Through Liquid Pressure Amplification In A Dairy Plant Refrigeration System. The Centre for Energy and Built Environment Research [cited 13 Mar. 2015].

[8] Methane (Chemical Compound). 2015. Encyclopædia Britannica Online. [cited 13 Mar. 2015] Available from: http://www.britannica.com/EBchecked/topic/378264/methane -- Composition of Methane

[9] Composition of Air [Internet]. Engineering Toolbox; [cited 13 Mar. 2015]. Available from: http://www.engineeringtoolbox.com/air-composition-d_212.html. -- Composition of air.

[10] Summary of the Clean Air Act, 2015. United States Environmental Protection Agency. [cited 13 Mar. 2015] Available from: http://www2.epa.gov/laws-regulations/summary-clean-air-act -- Emissions requirements of chemical plants.

[11] Zhang M, Yu Y. Dehydration of Ethanol to Ethylene. Industrial Engineering and Chemical Research. 2013; 52:9505-9514. – Technical information on ethanol to ethylene conversion via dehydration.

[12] AspenTech. Aspen HYSYS Help File v8.0. Aspen Technology, Inc. 2012. - Aspen HYSYS help file used for troubleshooting and assistance on economic analysis.

[13] Towler G, Sinnott R. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. 2nd ed. Boston: Elsevier; 2013. -- General Reference Book

[14] Barrocas H, Baratelli F, inventors; Petroleo Brasileiro S.A., assignee. Process for dehydration of a low molecular weight alcohol. US patent 4,396,789 A. August 2, 1983. - Primary background for process design.

[15] Tsao U, Zasloff HB, inventors; The Lummus Company, assignee. Production of ethylene from ethanol. US patent 4,134,926. January 16, 1979. – Patent for catalytic dehydration of ethylene in a fluidized bed reactor.

[16] Morschbacker, A. Bio-Ethanol Based Ethylene. Polymer Reviews. 2009; 49:79-84. – Overview of bioethanol dehydration process development.

[17] Fan D, Dai DJ, Wu HS. Ethylene Formation by Catalytic Dehydration of Ethanol with Industrial Considerations. Materials. 6, 101-115. doi: 10.3390/ma6010101. - Comparison of types of catalysts used in the dehydration of ethanol and current research into new catalysts.

[18] Chen G, Li S, Jiao F, Yuan Q. Catalytic dehydration of bioethanol to ethylene over TiO2/γ-Al2O3 catalysts in microchannel reactors. Catal. Today 2007, 125, 111–119. - Paper introducing research on modified alumina catalyst for ethanol dehydration.

[19] Jumonville, J. Tutorial on Cryogenic Turboexpanders. Proceedings of the Thirty-Ninth Turbomachinery Symposium; 2010 Oct 4-7; Houston, TX. Houston: Texas A&M University; 2010. -- Use of turboexpander for cryogenic separations

[20] Today in Energy - Daily Prices. US Energy Information Administration website. http://www.eia.gov/todayinenergy/prices.cfm. Accessed March 3rd 2015. - Bulk market price for 95% ethanol.

[21] Weddle, N. ICIS Pricing: Ethylene (Europe). Reed Business Limited. January 10 2014. - Bulk market price for chemical grade ethylene.

=Appendix I - Process Flow Diagram=
[[File:PFD B1.JPG|1200px|center]]

=Appendix II - HYSYS Simulation=
[[File:HYSYS_B1.PNG|center|1200px]]

=Appendix III - Material Streams=
[[File:Streams_B1.png|1200px]]

=Appendix IV - Energy Table=
[[File:Energy_B1.png|600px|center]]

=Appendix V - Economics=
[[File:Econsummary_B1.png|center]] 

[[File:Capcost_B1.png|center]] 

[[File:sensitivityanalysis_B1.png|600px|center]]

Ethanol to Ethylene (B1)

2015-03-14T04:31:49Z

Hpoppick: /* Technical Approach */

[[File:BFD_B1.png|600px|thumbnail|alt=Alt text|Conversion of Ethanol to Ethylene]]

Team B1 Final Report

Authors: Harry Poppick, Emm Fulk and Scott Smith

Instructors: Fengqi You, David Wegerer

March 13, 2015

=Executive Summary=

The following report outlines the design and analysis of a process converting ethanol to chemical-grade ethylene via catalytic dehydration. This process consumers 100,000 kg/hr of 95 wt% ethanol, 5 wt% water feedstock and produces 53,000 kg/hr of 99.7 wt% chemical-grade ethylene. The ethanol feed passes through two fixed-bed reactors, each packed with an aluminum oxide catalyst, and the resulting ethylene is purified by two flash tanks and by absorption with water. The process was modeled using Aspen HYSYS simulation software to estimate mass and energy flows and equipment sizing requirements. Based on results of this initial simulation, several alternatives are discussed for increasing the process efficiency and profitability. The use of a fluidized bed reactor or a more ethylene-selective catalyst could increase the production of ethylene per ethanol basis. Additionally, several methods of purification to more valuable polymer-grade ethylene are proposed.

The economic feasibility of this process was evaluated using Aspen Economic Analyzer with the Icarus economics package. Capital cost is approximately $16.4 million total with an operating cost of $465 million per year. The current market prices of the ethanol feed and ethylene sales price are $1.44/gallon and $1350/metric ton respectively. The cost of feed ethanol, process utilities and miscellaneous operational costs total to about $427 million/year. At full operation, revenue at current prices would be approximately $640 million per year. The predicted 10-year net present value of the process is approximately $391 million with an IRR of 79% and a payback period of 2.7 years. A sensitivity analysis indicates that the process is most sensitive to feed prices, product prices and operation cost.

Several recommendations are made for both cost reduction and profit maximization, including the design of a heat exchanger network and the optimization of fired heaters that require high capital investment and large amounts of fuel. A safety review of the process is recommended, as well as the minimization of flue gas effluent and wastewater. It is also suggested that the construction of an onsite wastewater treatment center be considered. Overall, the initial analysis indicates this to be a profitable process and it is recommended the project move forward.

=Introduction=

Ethylene is a critical chemical precursor to a number of different industrial products. It is often derived from petroleum sources and polymerized to polyethylene, one of the most ubiquitous plastics today. (American Chemistry Council, 2013) Recently there has been a significant effort to develop production pathways utilizing biologically-derived feedstocks, such as corn or cellulosic ethanol, rather than traditional fossil-fuel sources. Ethylene can be produced from bioethanol via catalytic dehydration over an aluminum oxide catalyst. The proposed process converts 100,000 kg/hr of 95 wt% ethanol, 5% water feed to 53,000 kg/hr of 99.7% chemical-grade ethylene when operating at full capacity. This process was found to be economically viable with a 10-year net present value (NPV) of $131 million (2014 USD) and a payback period of approximately 2.7 years. This memo will detail the proposed process, as well as outline potential alternatives and economic viability of the project.

=Technical Approach=

Many bioethanol plants are located in the Midwest where large amounts of feedstock crops, such as corn, are grown. As such, this plant will be located in Story county, Iowa, near a large-scale bioethanol production plant. (DuPont Nevada Site, 2012) It is assumed that the supply of bioethanol is consistent and readily available. It is also assumed that other reagents - namely, the aluminum oxide catalyst, heater fuel, utility water and freon refrigerant - are readily available, and that wastewater treatment facilities are located near enough to facilitate the off-site treatment of wastewater. Plant capacity was based on current mid-sized industrial ethylene plants. (Designing Ethylene Plants, 2014)

HYSYS simulations were performed with the NRTL fluid package and Peng-Robinson vapor model. The NRTL fluid package is an activity coefficient model that is especially useful to model the separations of alcohols in aqueous solutions. (Suppes, 2015) In addition, NRTL uses models of binary pairs of components, much like the Wilson equation, to predict chemical interactions at the molecular level. The NRTL package can thus be easily extended to ternary and higher order chemical systems, making it ideal for this type of simulation. The Peng-Robinson vapor model was selected as it is well-suited to account for the non-idealities of the vapor phase reactions and separations integral to this process. (ASPENtech, 2014)

It was assumed that the feed enters the process at ambient temperature and pressure (25 °C, 1 atm) and at a consistent rate and composition with negligible quantities of impurities. The ethanol feed was assumed to be 95% ethanol and 5% water by mass, which is the commercial standard for industrial ethanol. (190 Proof Ethanol, 2012) Storage vessels for the feed ethanol, waste streams and products are assumed to be located nearby to the process. An initial feed pump compensates for pressure drops through the process and reduces the duty on downstream compressors. (Hadawey, 2015)

Natural gas, assumed to consist of 83% methane, 16% ethane and 1% nitrogen by mass, was supplied to two fired heaters at a flow rate estimated by HYSYS. (Methane, 2015) Air fed to the process to enable combustion was assumed to be 23% oxygen and 77% nitrogen by mass. (Composition of Air, 2015) Air streams were fed at 50% molar excess in order to ensure complete combustion and prevent the formation of carbon monoxide in the heater exhaust. Total flue gases are assumed to be 230,000 kg/hr, or 2.2 million tons annually, and consist of 73.8% nitrogen gas, 10.5% carbon dioxide, 8.2% water vapor, and 7.5% oxygen by mass. The only compound of concern in these emissions is the carbon dioxide, a known greenhouse gas. At the time of this report, the quantities of carbon dioxide emitted by this plant annually are within acceptable EPA specifications. (Summary of the Clean Air Act, 2015)

Due to the difficulty of simulation equilibrium and conversion reactions in a single vessel in HYSYS, these two reaction types were simulated in separate equilibrium reactor and conversion reactor units in series. In addition, while HYSYS indicated that reactor units would output separate vapor and liquid streams, it was assumed that in practice this would take the form of a single, two phase stream between each unit. To account for this, mixers were installed downstream of each reactor to combine the liquid and vapor phases of the reactor effluent. The three consequent reactions considered are as follows:

Ethanol ↔ Ethylene + Water

Ethanol → Acetaldehyde + Hydrogen

2 Ethanol → Diethyl Ether + Water

The optimal reaction temperature was determined to be 400 °C, which promotes the equilibrium reaction of ethanol to ethylene while minimizing byproducts. (Zhang and Yu, 2013) While other byproducts may be produced in this process, these reactions are typically taken to comprise of the bulk of the dehydration reaction. Heat losses over these reactors were assumed to be negligible. (Zhang and Yu, 2013)All major process equipment is assumed to be constructed of high strength carbon steel. (AspenTech, 2012)

The “Sizing Utility” within the Icarus Economic Evaluation module was used to estimate sizes of major equipment based on the process simulation. These values can serve as a benchmark for an initial plant design. Icarus KbaseTM implements a wide variety of mechanical design standards, including ASME and BS5500, in order to calculate accurate equipment sizing. The Icarus sizing module combines equipment prices for standard chemical processing equipment as well as correlations and sizing factors. The advantage of using a software package such as HYSYS to price out individual equipment is that it utilizes up-to-date prices from vendors and distributors when estimating costs. A more in-depth overview of the correlations included in this software can be found in Towler and Sinnott (2009).

=Process Flowsheet=
[[File:Squarepfd_B1.PNG|thumb|400px|alt=Alt text|Fig 1: PFD of the Proposed Process]]

The following process is based primarily on a 1983 US patent titled “Process for dehydration of a low molecular weight alcohol.” (Barrocas and Baratelli, 1983) The process flow diagram can be seen in Figure 1. A larger version of the PFD is included in Appendix I and the HYSYS simulation setup in Appendix II.

The feed enters the process at a rate of 100,000 kg/hr, a temperature and pressure of a 25 °C and 1 atm and at a composition of 95 wt% ethanol and 5 wt% water.It is initially pressurized to 4335 kPa by centrifugal pump P-101 and subsequently heated to 400 °C by fired heater F-101. The heated and pressurized feed enters fixed bed reactor R-101 and contacts with the aluminum oxide catalyst. At this point it dehydrates to form the product, ethylene, as well as the byproducts water, hydrogen, diethyl ether and acetaldehyde. Fired heater F-102 and reactor R-102 increase the overall conversion of the process. Both fired heaters F-101 and F-102 are fueled with natural gas and fed with excess air. The composition of the reactor train effluent is 54.5 wt% ethylene, 37.1 wt% water, 8.1 wt% unreacted ethanol and trace amounts of diethyl ether, acetaldehyde, and hydrogen contaminants.

The pressure of the reactor train effluent is increased to 4500 kPa by compressor K-102 and the temperature decreased to 100 °C by exchange with cold water in heat exchanger E-201. The stream then expands and flashes in flash vessel FL-201, which separates out 82.3% of the unreacted ethanol, 96.6% of the water and virtually all of the acetaldehyde contaminant in the bottoms while sending the ethylene-rich vapor phase out of the top. The top product of FL-202 is compressed to 3500 kPA by K-202 and cooled to 0.0 °C by a freon refrigerant in E-202. At this point the stream is flashed for a second time in vessel FL-202 to remove additional impurities. The top outlet stream consists of 99.5 wt% ethylene, which is fed to the bottom of a 10-tray absorption column that removes a fraction of the residual diethyl ether as well as the remainder of the unreacted ethanol. A stream of absorbent water is fed to the top of the column at 10,000 kg/hr. The product exits the top of the column at a rate of 54,600 kg/hr and has a purity of 99.7% ethylene. Diethyl ether makes up 0.2% of the remaining product stream and is the primary contaminant. Trace amounts of residual water and hydrogen are also present.

Full tables of material and energy streams can be found in Appendices III and IV respectively.

==Process Alternatives==
===Reactor Alternatives===
Two fixed bed reactors, alternating with fired heaters, are used in the dehydration reaction of ethanol to ethylene. However, a fluidized bed reactor can offer better mixing and temperature control than a fixed bed reactor and thus provide the highest possible conversion of ethanol with the greatest selectivity to ethylene. (Tsao and Zasloff, 1979) Fluidized bed reactors also provide a lower rate of catalyst coking and byproduct formation, minimizing separation and catalyst regeneration costs. (Morschbacker, 2009) The major downside of fluidized bed reactors is that few large-scale processes have been built since the technology was developed in the late 1970s. (Tsao and Zasloff, 1979; Morschbacker, 2009) Although implementation of fluidized bed reactors could potentially increase the purity of the ethylene product and/or decrease costs, a small scale pilot process would need to be built and tested before it would be possible to develop an industrial-scale facility.

===Catalyst Alternatives===
Aluminum oxide, specifically gamma alumina, is the most industrially-common catalyst and has been historically used due to its low cost and high stability. (Tsao and Zasloff, 1979; Fan and Dai, n.d.) Recent improvements in selectivity and catalyst stability of activated alumina have been achieved by incorporating titanium oxide into the catalyst, although this increases reaction temperature by approximately 50 °C and decreases catalyst lifespan. (Chen and Li, et. al. 2007) There is also significant ongoing research into HZSM-5 zeolite and heteropolyacids, which are being explored as potential alternatives to alumina oxide. A nanoscale HZSM-5 zeolite catalyst has been shown to operate at the relatively low temperature of 200-300°C, with a 100% ethanol conversion and 99.7% selectivity to ethylene. Initial research has also indicated that it maintains greater than 98% selectivity for 630 operational hours. (Fan and Dai, n.d.) However, the current low cost and ready availability of unmodified alumina oxide makes it a better choice for a process of this scale.

===Purification Alternatives===
As specified in this process, the reactor effluent is purified by two flash drums and absorption with water to produce chemical-grade ethylene. If chemical-grade ethylene is indeed the desired product, other purification options include caustic washing of the reactor effluent and water removal in a desiccant drying bed. (Morschbacker, 2009) While this purification train is relatively simple and does not require harsh chemical reagents, polymer grade ethylene is more commercially valuable and the additional cost of removing water and diethyl ether contaminants may be justified by increased revenue. Cryogenic distillation was initially simulated to produce polymer-grade ethylene, but utility requirements were found to render this separation economically unviable. (Barrocas and Baratelli, 1983) Further research and optimization may find this purification strategy to be a more valid process. Alternatively, the addition of a cryogenic turboexpander or the use of alternative adsorbents may increase product purity to polymer grade. (Jumonville, 2010) Initial HYSYS simulations indicate that these operations may be feasible with further refinement.

===Wastewater Treatment===
Due to the large volume of wastewater produced, building an on-site wastewater treatment facility may prove to be more economical than paying for third-party wastewater treatment. Flash vessel FL-201 produces 44,600 L/hr of wastewater contaminated with 18.7 vol% ethanol and 0.6 vol% acetaldehyde, while FL-202 produces 2940 L/hr of an aqueous waste consisting of 56.8 vol% ethanol, 42.0 vol% water and 0.9 vol% diethyl ether. The absorption column produces approximately 10,200 liters/hr of wastewater contaminated with 1.2 vol% ethanol, 0.2% diethyl ether and 0.2% acetaldehyde. Utilizing distillation to separate these streams into clean water and volatile organic waste could ultimately reduce the quantity of waste that requires disposal and reduce the overall costs of the process.

==Process Equipment==
Relevant sizing information for each unit operation, estimated by the method described in the “Technical Approach,” can be found in Appendix V. Equipment and piping is assumed to be constructed of carbon steel. It should be noted that the two fired heaters are proportionately large enough to heat the entirety of the process stream and are thus larger than standard equipment.

=Economic Analysis=
[[File:NPV_B1.png|400px|thumb|Fig 2. Projected Cash Flow]]
[[File:sensitivityanalysis_B1.png|400px|thumb| Fig 3. Results of the Sensitivity Analysis on 10 year NPV]]

==Economics Overview==
All final values are normalized to June 2014 USD by CEPCI scaling. It is assumed that all products produced are sold at current market prices.

The Aspen Economic Evaluation module within HYSYS v8.0 was used to estimate capital and operating costs for a 10-year plant life span with a construction start date of April 2015. The price of the 95% ethanol feed stream was estimated at $1.44 per gallon, while the chemical grade ethylene produced is currently selling for approximately $1350 per metric ton. (Today in Energy, 2015; Weddle, 2014) Mapping and sizing calculations were performed by the economics module and a preliminary economic evaluation was completed. Equipment sizes, also estimated by HYSYS, were reviewed to ensure that height, diameter, and volume specifications were within realistic ranges.

The process was ideally projected to operate 360 days per year with a start-up time of one year. In addition, the tax rate was approximated at 40%, an interest rate at 20%, and a salvage value of 20%. Escalation percentages were compounded yearly for the product, raw material, and operating costs. The total capital cost for this process is approximately $16.4 million, which includes all equipment and piping described in the process. The most expensive equipment used in this process are the two fired heaters F-101 and F-102, which have an exceptionally large heat exchange area to adequately heat the feed. Standard heaters may not suffice and additional costs may be incurred for the raw materials and manufacture of this equipment. Including a feed preheater or additional fired heaters may reduce this cost in subsequent design iterations.

The total operating cost is approximately $465 million per year, about $427 million of which is the cost of the ethanol feed and natural gas for the two fired heaters. An additional $1.73 million per year is used for utilities including the cooling water and refrigerant. The labor and maintenance costs of this industrial process were also accounted for within the simulation’s economic analysis. The HYSYS simulation software, in conjunction with the Icarus economic analyzer, estimated there should be 5 operators per 8 hour shift with a cost per operator of $20 per hour. This results in a total operating labor cost of approximately $880,000 per year. In addition, the process will require one supervisor per shift with an hourly rate of $35 for total supervisor salaries of $307,000 per year. Finally, a fixed maintenance rate was estimated at $205,000 per 8000 hours of operation for a total cost of $225,000 per year.

Total product sales are roughly $640 million per year at full operation. The estimated income for this process is thus approximately $175 million per year. After ten years, the plant is projected to have a net present value (NPV) of $391 million and an internal rate of return of approximately 79%. In addition the payout period for the initial investment is estimated to be about 2.7 years. Figure 2 shows the projected cash flow for the project.

==Sensitivity Analysis==
A sensitivity analysis was performed to investigate the effects of fluctuating capital costs, operating costs, raw materials, utility costs and ethylene sales price on the 10-year net present value (NPV) of the project. This analysis was performed by scaling these cost factors according to typical ranges given in Towler and Sinnott and calculating the adjusting the NPV accordingly. The results, illustrated in Figure 3, indicate that the project value is most sensitive to product sales, raw materials costs, and operating costs. Ethylene and ethanol prices are market-determined and cannot be controlled for in the process design, so further optimization should be focused on minimizing the operations cost of the process. (Today in Energy, 2015; Weddle, 2014) However, in feed and product prices do still have a profound effect on profitability and feasibility. A more rigorous market analysis will better inform the profitability outlook.

=Conclusions/Recommendations=

The proposed process produces approximately 460,000 metric tons of 99.7 wt% ethylene annually, with a 10-year net present value of $131 million. If current economic conditions hold, it is recommended that this project proceed to implementation following further design improvements and optimization.

Future design iterations should focus on process optimization, particularly in minimizing operating costs as prescribed by the results of the sensitivity analysis. The development of a heat-exchanger network, potentially with Aspen Energy Analyzer, is one option for decreasing utility requirements and increasing the efficiency of the process overall. Optimization of the fired heaters could also result in decreased operational costs. Although overall profitability is less sensitive to capital costs, reviewing and adjusting equipment sizing would also improve the economic outlook. In particular, exploring alternative heating strategies at the beginning of the process could significantly decrease capital costs. Although there are not any particularly dangerous chemicals utilized in the process, an overall process review should also consider potential failure modes to minimize the safety risk to plant workers and nearby residents.

In addition to economic and safety considerations, harmful emissions and waste streams should be minimized both to bring down the cost of treatment and to decrease environmental effects. The two fired heaters consume a large amount of natural gas per year, emitting about 200,000 tons of CO2 annually, and account for more than half of the capital cost of the process. Although no known toxic gases are produced, carbon capture or other emissions-reduction methods should be considered. Additionally, enough wastewater is produced by this process that building an onsite wastewater treatment center should be considered. This could not only decrease operating costs by eliminating the need for an external contract but also give the plant more control over the final purity of the treated wastewater.

Finally, the current model assumes that all ethylene produced will be sold at a current prices and price or product sales will not be affected by economic variability. A more detailed study of the chemical-grade ethylene market, as well as a more thorough understanding of sales and distribution logistics, would increase the surety of a profitable process.

In summary, the proposed process yields chemical grade ethylene via the catalytic dehydration of ethanol. A 100,000 kg/hr of 95 wt% ethanol, 5% water feed is converted to 53,000 kg/hr of 99.7% chemical-grade ethylene. After 10 years of operation, including a one-year startup time, the process has an NPV of $391 million with an IRR of 79% and a payback period of 2.7 years.
Pending further optimization, this process was determined to be viable and it is recommended for the project to move forward.

=References=

[1] American Chemistry Council. Production of chemicals and plastics in the U.S. in 2013, by type (in 1,000 metric tons). In Statista - The Statistics Portal. August 2014. Available at http://www.statista.com/statistics/299725/total-us-plastics-and-chemicals-shipments-by-type/, Accessed January 15, 2015. – Relative proportions of plastics production.

[2] DuPont Nevada Site Cellulosic Ethanol Facility [Internet]. DuPont Chemical; c2012-2015 [cited 11 Mar. 2015]. Available from: http://biofuels.dupont.com/cellulosic-ethanol/nevada-site-ce-facility/. -- Information on ethanol production in Iowa.

[3] Designing Ethylene Plants. Ethylene [Internet]. Technip; 2014 [cited 13 Mar. 2015]. Available from: http://www.technip.com/en/our-business/onshore/ethylene -- Plant size ranges.

[4] Suppes GJ. Selecting Thermodynamic Models for Process Simulation of Organic VLE and LLE Systems. The University of Missouri-Columbia, Dept of Chemical Engineering. [cited 13 Mar. 2015]. -- Use of NRTL in alcohol separations.

[5] ASPENtech. Appendix A - Property Methods and Calculations. Simulation Basics; A-3 - A-26. 2014.

[6] 190 Proof Ethanol: Technical Data Sheet [Internet]. Decon Labs Inc; 2012 [cited 13 Mar. 2015]. Available from: http://www.deconlabs.com/tds/ETHANOL%20190%20%20PROOF.pdf -- Information regarding 95% ethanol

[7] Hadawey A, Ge Y, Tassou TSA. Energy Savings Through Liquid Pressure Amplification In A Dairy Plant Refrigeration System. The Centre for Energy and Built Environment Research [cited 13 Mar. 2015].

[8] Methane (Chemical Compound). 2015. Encyclopædia Britannica Online. [cited 13 Mar. 2015] Available from: http://www.britannica.com/EBchecked/topic/378264/methane -- Composition of Methane

[9] Composition of Air [Internet]. Engineering Toolbox; [cited 13 Mar. 2015]. Available from: http://www.engineeringtoolbox.com/air-composition-d_212.html. -- Composition of air.

[10] Summary of the Clean Air Act, 2015. United States Environmental Protection Agency. [cited 13 Mar. 2015] Available from: http://www2.epa.gov/laws-regulations/summary-clean-air-act -- Emissions requirements of chemical plants.

[11] Zhang M, Yu Y. Dehydration of Ethanol to Ethylene. Industrial Engineering and Chemical Research. 2013; 52:9505-9514. – Technical information on ethanol to ethylene conversion via dehydration.

[12] AspenTech. Aspen HYSYS Help File v8.0. Aspen Technology, Inc. 2012. - Aspen HYSYS help file used for troubleshooting and assistance on economic analysis.

[13] Towler G, Sinnott R. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. 2nd ed. Boston: Elsevier; 2013. -- General Reference Book

[14] Barrocas H, Baratelli F, inventors; Petroleo Brasileiro S.A., assignee. Process for dehydration of a low molecular weight alcohol. US patent 4,396,789 A. August 2, 1983. - Primary background for process design.

[15] Tsao U, Zasloff HB, inventors; The Lummus Company, assignee. Production of ethylene from ethanol. US patent 4,134,926. January 16, 1979. – Patent for catalytic dehydration of ethylene in a fluidized bed reactor.

[16] Morschbacker, A. Bio-Ethanol Based Ethylene. Polymer Reviews. 2009; 49:79-84. – Overview of bioethanol dehydration process development.

[17] Fan D, Dai DJ, Wu HS. Ethylene Formation by Catalytic Dehydration of Ethanol with Industrial Considerations. Materials. 6, 101-115. doi: 10.3390/ma6010101. - Comparison of types of catalysts used in the dehydration of ethanol and current research into new catalysts.

[18] Chen G, Li S, Jiao F, Yuan Q. Catalytic dehydration of bioethanol to ethylene over TiO2/γ-Al2O3 catalysts in microchannel reactors. Catal. Today 2007, 125, 111–119. - Paper introducing research on modified alumina catalyst for ethanol dehydration.

[19] Jumonville, J. Tutorial on Cryogenic Turboexpanders. Proceedings of the Thirty-Ninth Turbomachinery Symposium; 2010 Oct 4-7; Houston, TX. Houston: Texas A&M University; 2010. -- Use of turboexpander for cryogenic separations

[20] Today in Energy - Daily Prices. US Energy Information Administration website. http://www.eia.gov/todayinenergy/prices.cfm. Accessed March 3rd 2015. - Bulk market price for 95% ethanol.

[21] Weddle, N. ICIS Pricing: Ethylene (Europe). Reed Business Limited. January 10 2014. - Bulk market price for chemical grade ethylene.

=Appendix I - Process Flow Diagram=
[[File:PFD B1.JPG|1200px|center]]

=Appendix II - HYSYS Simulation=
[[File:HYSYS_B1.PNG|center|1200px]]

=Appendix III - Material Streams=
[[File:Streams_B1.png|1200px]]

=Appendix IV - Energy Table=
[[File:Energy_B1.png|600px|center]]

=Appendix V - Economics=
[[File:Econsummary_B1.png|center]] 

[[File:Capcost_B1.png|center]] 

[[File:sensitivityanalysis_B1.png|600px|center]]

Ethanol to Ethylene (B1)

2015-03-14T04:25:15Z

Hpoppick: /* Economic Analysis */

[[File:BFD_B1.png|600px|thumbnail|alt=Alt text|Conversion of Ethanol to Ethylene]]

Team B1 Final Report

Authors: Harry Poppick, Emm Fulk and Scott Smith

Instructors: Fengqi You, David Wegerer

March 13, 2015

=Executive Summary=

The following report outlines the design and analysis of a process converting ethanol to chemical-grade ethylene via catalytic dehydration. This process consumers 100,000 kg/hr of 95 wt% ethanol, 5 wt% water feedstock and produces 53,000 kg/hr of 99.7 wt% chemical-grade ethylene. The ethanol feed passes through two fixed-bed reactors, each packed with an aluminum oxide catalyst, and the resulting ethylene is purified by two flash tanks and by absorption with water. The process was modeled using Aspen HYSYS simulation software to estimate mass and energy flows and equipment sizing requirements. Based on results of this initial simulation, several alternatives are discussed for increasing the process efficiency and profitability. The use of a fluidized bed reactor or a more ethylene-selective catalyst could increase the production of ethylene per ethanol basis. Additionally, several methods of purification to more valuable polymer-grade ethylene are proposed.

The economic feasibility of this process was evaluated using Aspen Economic Analyzer with the Icarus economics package. Capital cost is approximately $16.4 million total with an operating cost of $465 million per year. The current market prices of the ethanol feed and ethylene sales price are $1.44/gallon and $1350/metric ton respectively. The cost of feed ethanol, process utilities and miscellaneous operational costs total to about $427 million/year. At full operation, revenue at current prices would be approximately $640 million per year. The predicted 10-year net present value of the process is approximately $391 million with an IRR of 79% and a payback period of 2.7 years. A sensitivity analysis indicates that the process is most sensitive to feed prices, product prices and operation cost.

Several recommendations are made for both cost reduction and profit maximization, including the design of a heat exchanger network and the optimization of fired heaters that require high capital investment and large amounts of fuel. A safety review of the process is recommended, as well as the minimization of flue gas effluent and wastewater. It is also suggested that the construction of an onsite wastewater treatment center be considered. Overall, the initial analysis indicates this to be a profitable process and it is recommended the project move forward.

=Introduction=

Ethylene is a critical chemical precursor to a number of different industrial products. It is often derived from petroleum sources and polymerized to polyethylene, one of the most ubiquitous plastics today. (American Chemistry Council, 2013) Recently there has been a significant effort to develop production pathways utilizing biologically-derived feedstocks, such as corn or cellulosic ethanol, rather than traditional fossil-fuel sources. Ethylene can be produced from bioethanol via catalytic dehydration over an aluminum oxide catalyst. The proposed process converts 100,000 kg/hr of 95 wt% ethanol, 5% water feed to 53,000 kg/hr of 99.7% chemical-grade ethylene when operating at full capacity. This process was found to be economically viable with a 10-year net present value (NPV) of $131 million (2014 USD) and a payback period of approximately 2.7 years. This memo will detail the proposed process, as well as outline potential alternatives and economic viability of the project.

=Technical Approach=

Many bioethanol plants are located in the Midwest where large amounts of feedstock crops, such as corn, are grown. As such, this plant will be located in Story county, Iowa, near a large-scale bioethanol production plant. (DuPont Nevada Site, 2012) It is assumed that the supply of bioethanol is consistent and readily available. It is also assumed that other reagents - namely, the aluminum oxide catalyst, heater fuel, utility water and freon refrigerant - are readily available, and that wastewater treatment facilities are located near enough to facilitate the off-site treatment of wastewater. Plant capacity was based on current mid-sized industrial ethylene plants. (Designing Ethylene Plants, 2014)

HYSYS simulations were performed with the NRTL fluid package and Peng-Robinson vapor model. The NRTL fluid package is an activity coefficient model that is especially useful to model the separations of alcohols in aqueous solutions. (Suppes, 2015) In addition, NRTL uses models of binary pairs of components, much like the Wilson equation, to predict chemical interactions at the molecular level. The NRTL package can thus be easily extended to ternary and higher order chemical systems, making it ideal for this type of simulation. The Peng-Robinson vapor model was selected as it is well-suited to account for the non-idealities of the vapor phase reactions and separations integral to this process. (ASPENtech, 2014)

It was assumed that the feed enters the process at ambient temperature and pressure (25 °C, 1 atm) and at a consistent rate and composition with negligible quantities of impurities. The ethanol feed was assumed to be 95% ethanol and 5% water by mass, which is the commercial standard for industrial ethanol. (190 Proof Ethanol, 2012) Storage vessels for the feed ethanol, waste streams and products are assumed to be located nearby to the process. An initial feed pump compensates for pressure drops through the process and reduces the duty on downstream compressors. (Hadawey, 2015)

Natural gas, assumed to consist of 83% methane, 16% ethane and 1% nitrogen by mass, was supplied to two fired heaters at a flow rate estimated by HYSYS. (Methane, 2015) Air fed to the process to enable combustion was assumed to be 23% oxygen and 77% nitrogen by mass. (Composition of Air, 2015) Air streams were fed at 50% molar excess in order to ensure complete combustion and prevent the formation of carbon monoxide in the heater exhaust. Total flue gases are assumed to be 230,000 kg/hr, or 2.2 million tons annually, and consist of 73.8% nitrogen gas, 10.5% carbon dioxide, 8.2% water vapor, and 7.5% oxygen by mass. The only compound of concern in these emissions is the carbon dioxide, a known greenhouse gas. At the time of this report, the quantities of carbon dioxide emitted by this plant annually are within acceptable EPA specifications. (Summary of the Clean Air Act, 2015)

Due to the difficulty of simulation equilibrium and conversion reactions in a single vessel in HYSYS, these two reaction types were simulated in separate equilibrium reactor and conversion reactor units in series. In addition, while HYSYS indicated that reactor units would output separate vapor and liquid streams, it was assumed that in practice this would take the form of a single, two phase stream between each unit. To account for this, mixers were installed downstream of each reactor to combine the liquid and vapor phases of the reactor effluent. The three consequent reactions considered are as follows:

Ethanol ↔ Ethylene + Water
Ethanol → Acetaldehyde + Hydrogen
2 Ethanol → Diethyl Ether + Water

The optimal reaction temperature was determined to be 400 °C, which promotes the equilibrium reaction of ethanol to ethylene while minimizing byproducts. (Zhang and Yu, 2013) While other byproducts may be produced in this process, these reactions are typically taken to comprise of the bulk of the dehydration reaction. Heat losses over these reactors were assumed to be negligible. (Zhang and Yu, 2013)All major process equipment is assumed to be constructed of high strength carbon steel. (AspenTech, 2012)

The “Sizing Utility” within the Icarus Economic Evaluation module was used to estimate sizes of major equipment based on the process simulation. These values can serve as a benchmark for an initial plant design. Icarus KbaseTM implements a wide variety of mechanical design standards, including ASME and BS5500, in order to calculate accurate equipment sizing. The Icarus sizing module combines equipment prices for standard chemical processing equipment as well as correlations and sizing factors. The advantage of using a software package such as HYSYS to price out individual equipment is that it utilizes up-to-date prices from vendors and distributors when estimating costs. A more in-depth overview of the correlations included in this software can be found in Towler and Sinnott (2009).

=Process Flowsheet=
[[File:Squarepfd_B1.PNG|thumb|400px|alt=Alt text|Fig 1: PFD of the Proposed Process]]

The following process is based primarily on a 1983 US patent titled “Process for dehydration of a low molecular weight alcohol.” (Barrocas and Baratelli, 1983) The process flow diagram can be seen in Figure 1. A larger version of the PFD is included in Appendix I and the HYSYS simulation setup in Appendix II.

The feed enters the process at a rate of 100,000 kg/hr, a temperature and pressure of a 25 °C and 1 atm and at a composition of 95 wt% ethanol and 5 wt% water.It is initially pressurized to 4335 kPa by centrifugal pump P-101 and subsequently heated to 400 °C by fired heater F-101. The heated and pressurized feed enters fixed bed reactor R-101 and contacts with the aluminum oxide catalyst. At this point it dehydrates to form the product, ethylene, as well as the byproducts water, hydrogen, diethyl ether and acetaldehyde. Fired heater F-102 and reactor R-102 increase the overall conversion of the process. Both fired heaters F-101 and F-102 are fueled with natural gas and fed with excess air. The composition of the reactor train effluent is 54.5 wt% ethylene, 37.1 wt% water, 8.1 wt% unreacted ethanol and trace amounts of diethyl ether, acetaldehyde, and hydrogen contaminants.

The pressure of the reactor train effluent is increased to 4500 kPa by compressor K-102 and the temperature decreased to 100 °C by exchange with cold water in heat exchanger E-201. The stream then expands and flashes in flash vessel FL-201, which separates out 82.3% of the unreacted ethanol, 96.6% of the water and virtually all of the acetaldehyde contaminant in the bottoms while sending the ethylene-rich vapor phase out of the top. The top product of FL-202 is compressed to 3500 kPA by K-202 and cooled to 0.0 °C by a freon refrigerant in E-202. At this point the stream is flashed for a second time in vessel FL-202 to remove additional impurities. The top outlet stream consists of 99.5 wt% ethylene, which is fed to the bottom of a 10-tray absorption column that removes a fraction of the residual diethyl ether as well as the remainder of the unreacted ethanol. A stream of absorbent water is fed to the top of the column at 10,000 kg/hr. The product exits the top of the column at a rate of 54,600 kg/hr and has a purity of 99.7% ethylene. Diethyl ether makes up 0.2% of the remaining product stream and is the primary contaminant. Trace amounts of residual water and hydrogen are also present.

Full tables of material and energy streams can be found in Appendices III and IV respectively.

==Process Alternatives==
===Reactor Alternatives===
Two fixed bed reactors, alternating with fired heaters, are used in the dehydration reaction of ethanol to ethylene. However, a fluidized bed reactor can offer better mixing and temperature control than a fixed bed reactor and thus provide the highest possible conversion of ethanol with the greatest selectivity to ethylene. (Tsao and Zasloff, 1979) Fluidized bed reactors also provide a lower rate of catalyst coking and byproduct formation, minimizing separation and catalyst regeneration costs. (Morschbacker, 2009) The major downside of fluidized bed reactors is that few large-scale processes have been built since the technology was developed in the late 1970s. (Tsao and Zasloff, 1979; Morschbacker, 2009) Although implementation of fluidized bed reactors could potentially increase the purity of the ethylene product and/or decrease costs, a small scale pilot process would need to be built and tested before it would be possible to develop an industrial-scale facility.

===Catalyst Alternatives===
Aluminum oxide, specifically gamma alumina, is the most industrially-common catalyst and has been historically used due to its low cost and high stability. (Tsao and Zasloff, 1979; Fan and Dai, n.d.) Recent improvements in selectivity and catalyst stability of activated alumina have been achieved by incorporating titanium oxide into the catalyst, although this increases reaction temperature by approximately 50 °C and decreases catalyst lifespan. (Chen and Li, et. al. 2007) There is also significant ongoing research into HZSM-5 zeolite and heteropolyacids, which are being explored as potential alternatives to alumina oxide. A nanoscale HZSM-5 zeolite catalyst has been shown to operate at the relatively low temperature of 200-300°C, with a 100% ethanol conversion and 99.7% selectivity to ethylene. Initial research has also indicated that it maintains greater than 98% selectivity for 630 operational hours. (Fan and Dai, n.d.) However, the current low cost and ready availability of unmodified alumina oxide makes it a better choice for a process of this scale.

===Purification Alternatives===
As specified in this process, the reactor effluent is purified by two flash drums and absorption with water to produce chemical-grade ethylene. If chemical-grade ethylene is indeed the desired product, other purification options include caustic washing of the reactor effluent and water removal in a desiccant drying bed. (Morschbacker, 2009) While this purification train is relatively simple and does not require harsh chemical reagents, polymer grade ethylene is more commercially valuable and the additional cost of removing water and diethyl ether contaminants may be justified by increased revenue. Cryogenic distillation was initially simulated to produce polymer-grade ethylene, but utility requirements were found to render this separation economically unviable. (Barrocas and Baratelli, 1983) Further research and optimization may find this purification strategy to be a more valid process. Alternatively, the addition of a cryogenic turboexpander or the use of alternative adsorbents may increase product purity to polymer grade. (Jumonville, 2010) Initial HYSYS simulations indicate that these operations may be feasible with further refinement.

===Wastewater Treatment===
Due to the large volume of wastewater produced, building an on-site wastewater treatment facility may prove to be more economical than paying for third-party wastewater treatment. Flash vessel FL-201 produces 44,600 L/hr of wastewater contaminated with 18.7 vol% ethanol and 0.6 vol% acetaldehyde, while FL-202 produces 2940 L/hr of an aqueous waste consisting of 56.8 vol% ethanol, 42.0 vol% water and 0.9 vol% diethyl ether. The absorption column produces approximately 10,200 liters/hr of wastewater contaminated with 1.2 vol% ethanol, 0.2% diethyl ether and 0.2% acetaldehyde. Utilizing distillation to separate these streams into clean water and volatile organic waste could ultimately reduce the quantity of waste that requires disposal and reduce the overall costs of the process.

==Process Equipment==
Relevant sizing information for each unit operation, estimated by the method described in the “Technical Approach,” can be found in Appendix V. Equipment and piping is assumed to be constructed of carbon steel. It should be noted that the two fired heaters are proportionately large enough to heat the entirety of the process stream and are thus larger than standard equipment.

=Economic Analysis=
[[File:NPV_B1.png|400px|thumb|Fig 2. Projected Cash Flow]]
[[File:sensitivityanalysis_B1.png|400px|thumb| Fig 3. Results of the Sensitivity Analysis on 10 year NPV]]

==Economics Overview==
All final values are normalized to June 2014 USD by CEPCI scaling. It is assumed that all products produced are sold at current market prices.

The Aspen Economic Evaluation module within HYSYS v8.0 was used to estimate capital and operating costs for a 10-year plant life span with a construction start date of April 2015. The price of the 95% ethanol feed stream was estimated at $1.44 per gallon, while the chemical grade ethylene produced is currently selling for approximately $1350 per metric ton. (Today in Energy, 2015; Weddle, 2014) Mapping and sizing calculations were performed by the economics module and a preliminary economic evaluation was completed. Equipment sizes, also estimated by HYSYS, were reviewed to ensure that height, diameter, and volume specifications were within realistic ranges.

The process was ideally projected to operate 360 days per year with a start-up time of one year. In addition, the tax rate was approximated at 40%, an interest rate at 20%, and a salvage value of 20%. Escalation percentages were compounded yearly for the product, raw material, and operating costs. The total capital cost for this process is approximately $16.4 million, which includes all equipment and piping described in the process. The most expensive equipment used in this process are the two fired heaters F-101 and F-102, which have an exceptionally large heat exchange area to adequately heat the feed. Standard heaters may not suffice and additional costs may be incurred for the raw materials and manufacture of this equipment. Including a feed preheater or additional fired heaters may reduce this cost in subsequent design iterations.

The total operating cost is approximately $465 million per year, about $427 million of which is the cost of the ethanol feed and natural gas for the two fired heaters. An additional $1.73 million per year is used for utilities including the cooling water and refrigerant. The labor and maintenance costs of this industrial process were also accounted for within the simulation’s economic analysis. The HYSYS simulation software, in conjunction with the Icarus economic analyzer, estimated there should be 5 operators per 8 hour shift with a cost per operator of $20 per hour. This results in a total operating labor cost of approximately $880,000 per year. In addition, the process will require one supervisor per shift with an hourly rate of $35 for total supervisor salaries of $307,000 per year. Finally, a fixed maintenance rate was estimated at $205,000 per 8000 hours of operation for a total cost of $225,000 per year.

Total product sales are roughly $640 million per year at full operation. The estimated income for this process is thus approximately $175 million per year. After ten years, the plant is projected to have a net present value (NPV) of $391 million and an internal rate of return of approximately 79%. In addition the payout period for the initial investment is estimated to be about 2.7 years. Figure 2 shows the projected cash flow for the project.

==Sensitivity Analysis==
A sensitivity analysis was performed to investigate the effects of fluctuating capital costs, operating costs, raw materials, utility costs and ethylene sales price on the 10-year net present value (NPV) of the project. This analysis was performed by scaling these cost factors according to typical ranges given in Towler and Sinnott and calculating the adjusting the NPV accordingly. The results, illustrated in Figure 3, indicate that the project value is most sensitive to product sales, raw materials costs, and operating costs. Ethylene and ethanol prices are market-determined and cannot be controlled for in the process design, so further optimization should be focused on minimizing the operations cost of the process. (Today in Energy, 2015; Weddle, 2014) However, in feed and product prices do still have a profound effect on profitability and feasibility. A more rigorous market analysis will better inform the profitability outlook.

=Conclusions/Recommendations=

The proposed process produces approximately 460,000 metric tons of 99.7 wt% ethylene annually, with a 10-year net present value of $131 million. If current economic conditions hold, it is recommended that this project proceed to implementation following further design improvements and optimization.

Future design iterations should focus on process optimization, particularly in minimizing operating costs as prescribed by the results of the sensitivity analysis. The development of a heat-exchanger network, potentially with Aspen Energy Analyzer, is one option for decreasing utility requirements and increasing the efficiency of the process overall. Optimization of the fired heaters could also result in decreased operational costs. Although overall profitability is less sensitive to capital costs, reviewing and adjusting equipment sizing would also improve the economic outlook. In particular, exploring alternative heating strategies at the beginning of the process could significantly decrease capital costs. Although there are not any particularly dangerous chemicals utilized in the process, an overall process review should also consider potential failure modes to minimize the safety risk to plant workers and nearby residents.

In addition to economic and safety considerations, harmful emissions and waste streams should be minimized both to bring down the cost of treatment and to decrease environmental effects. The two fired heaters consume a large amount of natural gas per year, emitting about 200,000 tons of CO2 annually, and account for more than half of the capital cost of the process. Although no known toxic gases are produced, carbon capture or other emissions-reduction methods should be considered. Additionally, enough wastewater is produced by this process that building an onsite wastewater treatment center should be considered. This could not only decrease operating costs by eliminating the need for an external contract but also give the plant more control over the final purity of the treated wastewater.

Finally, the current model assumes that all ethylene produced will be sold at a current prices and price or product sales will not be affected by economic variability. A more detailed study of the chemical-grade ethylene market, as well as a more thorough understanding of sales and distribution logistics, would increase the surety of a profitable process.

In summary, the proposed process yields chemical grade ethylene via the catalytic dehydration of ethanol. A 100,000 kg/hr of 95 wt% ethanol, 5% water feed is converted to 53,000 kg/hr of 99.7% chemical-grade ethylene. After 10 years of operation, including a one-year startup time, the process has an NPV of $391 million with an IRR of 79% and a payback period of 2.7 years.
Pending further optimization, this process was determined to be viable and it is recommended for the project to move forward.

=References=

[1] American Chemistry Council. Production of chemicals and plastics in the U.S. in 2013, by type (in 1,000 metric tons). In Statista - The Statistics Portal. August 2014. Available at http://www.statista.com/statistics/299725/total-us-plastics-and-chemicals-shipments-by-type/, Accessed January 15, 2015. – Relative proportions of plastics production.

[2] DuPont Nevada Site Cellulosic Ethanol Facility [Internet]. DuPont Chemical; c2012-2015 [cited 11 Mar. 2015]. Available from: http://biofuels.dupont.com/cellulosic-ethanol/nevada-site-ce-facility/. -- Information on ethanol production in Iowa.

[3] Designing Ethylene Plants. Ethylene [Internet]. Technip; 2014 [cited 13 Mar. 2015]. Available from: http://www.technip.com/en/our-business/onshore/ethylene -- Plant size ranges.

[4] Suppes GJ. Selecting Thermodynamic Models for Process Simulation of Organic VLE and LLE Systems. The University of Missouri-Columbia, Dept of Chemical Engineering. [cited 13 Mar. 2015]. -- Use of NRTL in alcohol separations.

[5] ASPENtech. Appendix A - Property Methods and Calculations. Simulation Basics; A-3 - A-26. 2014.

[6] 190 Proof Ethanol: Technical Data Sheet [Internet]. Decon Labs Inc; 2012 [cited 13 Mar. 2015]. Available from: http://www.deconlabs.com/tds/ETHANOL%20190%20%20PROOF.pdf -- Information regarding 95% ethanol

[7] Hadawey A, Ge Y, Tassou TSA. Energy Savings Through Liquid Pressure Amplification In A Dairy Plant Refrigeration System. The Centre for Energy and Built Environment Research [cited 13 Mar. 2015].

[8] Methane (Chemical Compound). 2015. Encyclopædia Britannica Online. [cited 13 Mar. 2015] Available from: http://www.britannica.com/EBchecked/topic/378264/methane -- Composition of Methane

[9] Composition of Air [Internet]. Engineering Toolbox; [cited 13 Mar. 2015]. Available from: http://www.engineeringtoolbox.com/air-composition-d_212.html. -- Composition of air.

[10] Summary of the Clean Air Act, 2015. United States Environmental Protection Agency. [cited 13 Mar. 2015] Available from: http://www2.epa.gov/laws-regulations/summary-clean-air-act -- Emissions requirements of chemical plants.

[11] Zhang M, Yu Y. Dehydration of Ethanol to Ethylene. Industrial Engineering and Chemical Research. 2013; 52:9505-9514. – Technical information on ethanol to ethylene conversion via dehydration.

[12] AspenTech. Aspen HYSYS Help File v8.0. Aspen Technology, Inc. 2012. - Aspen HYSYS help file used for troubleshooting and assistance on economic analysis.

[13] Towler G, Sinnott R. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. 2nd ed. Boston: Elsevier; 2013. -- General Reference Book

[14] Barrocas H, Baratelli F, inventors; Petroleo Brasileiro S.A., assignee. Process for dehydration of a low molecular weight alcohol. US patent 4,396,789 A. August 2, 1983. - Primary background for process design.

[15] Tsao U, Zasloff HB, inventors; The Lummus Company, assignee. Production of ethylene from ethanol. US patent 4,134,926. January 16, 1979. – Patent for catalytic dehydration of ethylene in a fluidized bed reactor.

[16] Morschbacker, A. Bio-Ethanol Based Ethylene. Polymer Reviews. 2009; 49:79-84. – Overview of bioethanol dehydration process development.

[17] Fan D, Dai DJ, Wu HS. Ethylene Formation by Catalytic Dehydration of Ethanol with Industrial Considerations. Materials. 6, 101-115. doi: 10.3390/ma6010101. - Comparison of types of catalysts used in the dehydration of ethanol and current research into new catalysts.

[18] Chen G, Li S, Jiao F, Yuan Q. Catalytic dehydration of bioethanol to ethylene over TiO2/γ-Al2O3 catalysts in microchannel reactors. Catal. Today 2007, 125, 111–119. - Paper introducing research on modified alumina catalyst for ethanol dehydration.

[19] Jumonville, J. Tutorial on Cryogenic Turboexpanders. Proceedings of the Thirty-Ninth Turbomachinery Symposium; 2010 Oct 4-7; Houston, TX. Houston: Texas A&M University; 2010. -- Use of turboexpander for cryogenic separations

[20] Today in Energy - Daily Prices. US Energy Information Administration website. http://www.eia.gov/todayinenergy/prices.cfm. Accessed March 3rd 2015. - Bulk market price for 95% ethanol.

[21] Weddle, N. ICIS Pricing: Ethylene (Europe). Reed Business Limited. January 10 2014. - Bulk market price for chemical grade ethylene.

=Appendix I - Process Flow Diagram=
[[File:PFD B1.JPG|1300px|center]]

=Appendix II - HYSYS Simulation=
[[File:HYSYS_B1.PNG|center]]

=Appendix III - Material Streams=
[[File:Streams_B1.png|1200px]]

=Appendix IV - Energy Table=
[[File:Energy_B1.png|600px|center]]

=Appendix V - Economics=
[[File:Econsummary_B1.png|center]] 

[[File:Capcost_B1.png|center]] 

[[File:sensitivityanalysis_B1.png|600px|center]]

Ethanol to Ethylene (B1)

2015-03-14T04:24:26Z

Hpoppick: /* Process Flowsheet */

[[File:BFD_B1.png|600px|thumbnail|alt=Alt text|Conversion of Ethanol to Ethylene]]

Team B1 Final Report

Authors: Harry Poppick, Emm Fulk and Scott Smith

Instructors: Fengqi You, David Wegerer

March 13, 2015

=Executive Summary=

The following report outlines the design and analysis of a process converting ethanol to chemical-grade ethylene via catalytic dehydration. This process consumers 100,000 kg/hr of 95 wt% ethanol, 5 wt% water feedstock and produces 53,000 kg/hr of 99.7 wt% chemical-grade ethylene. The ethanol feed passes through two fixed-bed reactors, each packed with an aluminum oxide catalyst, and the resulting ethylene is purified by two flash tanks and by absorption with water. The process was modeled using Aspen HYSYS simulation software to estimate mass and energy flows and equipment sizing requirements. Based on results of this initial simulation, several alternatives are discussed for increasing the process efficiency and profitability. The use of a fluidized bed reactor or a more ethylene-selective catalyst could increase the production of ethylene per ethanol basis. Additionally, several methods of purification to more valuable polymer-grade ethylene are proposed.

The economic feasibility of this process was evaluated using Aspen Economic Analyzer with the Icarus economics package. Capital cost is approximately $16.4 million total with an operating cost of $465 million per year. The current market prices of the ethanol feed and ethylene sales price are $1.44/gallon and $1350/metric ton respectively. The cost of feed ethanol, process utilities and miscellaneous operational costs total to about $427 million/year. At full operation, revenue at current prices would be approximately $640 million per year. The predicted 10-year net present value of the process is approximately $391 million with an IRR of 79% and a payback period of 2.7 years. A sensitivity analysis indicates that the process is most sensitive to feed prices, product prices and operation cost.

Several recommendations are made for both cost reduction and profit maximization, including the design of a heat exchanger network and the optimization of fired heaters that require high capital investment and large amounts of fuel. A safety review of the process is recommended, as well as the minimization of flue gas effluent and wastewater. It is also suggested that the construction of an onsite wastewater treatment center be considered. Overall, the initial analysis indicates this to be a profitable process and it is recommended the project move forward.

=Introduction=

Ethylene is a critical chemical precursor to a number of different industrial products. It is often derived from petroleum sources and polymerized to polyethylene, one of the most ubiquitous plastics today. (American Chemistry Council, 2013) Recently there has been a significant effort to develop production pathways utilizing biologically-derived feedstocks, such as corn or cellulosic ethanol, rather than traditional fossil-fuel sources. Ethylene can be produced from bioethanol via catalytic dehydration over an aluminum oxide catalyst. The proposed process converts 100,000 kg/hr of 95 wt% ethanol, 5% water feed to 53,000 kg/hr of 99.7% chemical-grade ethylene when operating at full capacity. This process was found to be economically viable with a 10-year net present value (NPV) of $131 million (2014 USD) and a payback period of approximately 2.7 years. This memo will detail the proposed process, as well as outline potential alternatives and economic viability of the project.

=Technical Approach=

Many bioethanol plants are located in the Midwest where large amounts of feedstock crops, such as corn, are grown. As such, this plant will be located in Story county, Iowa, near a large-scale bioethanol production plant. (DuPont Nevada Site, 2012) It is assumed that the supply of bioethanol is consistent and readily available. It is also assumed that other reagents - namely, the aluminum oxide catalyst, heater fuel, utility water and freon refrigerant - are readily available, and that wastewater treatment facilities are located near enough to facilitate the off-site treatment of wastewater. Plant capacity was based on current mid-sized industrial ethylene plants. (Designing Ethylene Plants, 2014)

HYSYS simulations were performed with the NRTL fluid package and Peng-Robinson vapor model. The NRTL fluid package is an activity coefficient model that is especially useful to model the separations of alcohols in aqueous solutions. (Suppes, 2015) In addition, NRTL uses models of binary pairs of components, much like the Wilson equation, to predict chemical interactions at the molecular level. The NRTL package can thus be easily extended to ternary and higher order chemical systems, making it ideal for this type of simulation. The Peng-Robinson vapor model was selected as it is well-suited to account for the non-idealities of the vapor phase reactions and separations integral to this process. (ASPENtech, 2014)

It was assumed that the feed enters the process at ambient temperature and pressure (25 °C, 1 atm) and at a consistent rate and composition with negligible quantities of impurities. The ethanol feed was assumed to be 95% ethanol and 5% water by mass, which is the commercial standard for industrial ethanol. (190 Proof Ethanol, 2012) Storage vessels for the feed ethanol, waste streams and products are assumed to be located nearby to the process. An initial feed pump compensates for pressure drops through the process and reduces the duty on downstream compressors. (Hadawey, 2015)

Natural gas, assumed to consist of 83% methane, 16% ethane and 1% nitrogen by mass, was supplied to two fired heaters at a flow rate estimated by HYSYS. (Methane, 2015) Air fed to the process to enable combustion was assumed to be 23% oxygen and 77% nitrogen by mass. (Composition of Air, 2015) Air streams were fed at 50% molar excess in order to ensure complete combustion and prevent the formation of carbon monoxide in the heater exhaust. Total flue gases are assumed to be 230,000 kg/hr, or 2.2 million tons annually, and consist of 73.8% nitrogen gas, 10.5% carbon dioxide, 8.2% water vapor, and 7.5% oxygen by mass. The only compound of concern in these emissions is the carbon dioxide, a known greenhouse gas. At the time of this report, the quantities of carbon dioxide emitted by this plant annually are within acceptable EPA specifications. (Summary of the Clean Air Act, 2015)

Due to the difficulty of simulation equilibrium and conversion reactions in a single vessel in HYSYS, these two reaction types were simulated in separate equilibrium reactor and conversion reactor units in series. In addition, while HYSYS indicated that reactor units would output separate vapor and liquid streams, it was assumed that in practice this would take the form of a single, two phase stream between each unit. To account for this, mixers were installed downstream of each reactor to combine the liquid and vapor phases of the reactor effluent. The three consequent reactions considered are as follows:

Ethanol ↔ Ethylene + Water
Ethanol → Acetaldehyde + Hydrogen
2 Ethanol → Diethyl Ether + Water

The optimal reaction temperature was determined to be 400 °C, which promotes the equilibrium reaction of ethanol to ethylene while minimizing byproducts. (Zhang and Yu, 2013) While other byproducts may be produced in this process, these reactions are typically taken to comprise of the bulk of the dehydration reaction. Heat losses over these reactors were assumed to be negligible. (Zhang and Yu, 2013)All major process equipment is assumed to be constructed of high strength carbon steel. (AspenTech, 2012)

The “Sizing Utility” within the Icarus Economic Evaluation module was used to estimate sizes of major equipment based on the process simulation. These values can serve as a benchmark for an initial plant design. Icarus KbaseTM implements a wide variety of mechanical design standards, including ASME and BS5500, in order to calculate accurate equipment sizing. The Icarus sizing module combines equipment prices for standard chemical processing equipment as well as correlations and sizing factors. The advantage of using a software package such as HYSYS to price out individual equipment is that it utilizes up-to-date prices from vendors and distributors when estimating costs. A more in-depth overview of the correlations included in this software can be found in Towler and Sinnott (2009).

=Process Flowsheet=
[[File:Squarepfd_B1.PNG|thumb|400px|Fig 1. PFD of the Proposed Process]]

The following process is based primarily on a 1983 US patent titled “Process for dehydration of a low molecular weight alcohol.” (Barrocas and Baratelli, 1983) The process flow diagram can be seen in Figure 1. A larger version of the PFD is included in Appendix I and the HYSYS simulation setup in Appendix II.

The feed enters the process at a rate of 100,000 kg/hr, a temperature and pressure of a 25 °C and 1 atm and at a composition of 95 wt% ethanol and 5 wt% water.It is initially pressurized to 4335 kPa by centrifugal pump P-101 and subsequently heated to 400 °C by fired heater F-101. The heated and pressurized feed enters fixed bed reactor R-101 and contacts with the aluminum oxide catalyst. At this point it dehydrates to form the product, ethylene, as well as the byproducts water, hydrogen, diethyl ether and acetaldehyde. Fired heater F-102 and reactor R-102 increase the overall conversion of the process. Both fired heaters F-101 and F-102 are fueled with natural gas and fed with excess air. The composition of the reactor train effluent is 54.5 wt% ethylene, 37.1 wt% water, 8.1 wt% unreacted ethanol and trace amounts of diethyl ether, acetaldehyde, and hydrogen contaminants.

The pressure of the reactor train effluent is increased to 4500 kPa by compressor K-102 and the temperature decreased to 100 °C by exchange with cold water in heat exchanger E-201. The stream then expands and flashes in flash vessel FL-201, which separates out 82.3% of the unreacted ethanol, 96.6% of the water and virtually all of the acetaldehyde contaminant in the bottoms while sending the ethylene-rich vapor phase out of the top. The top product of FL-202 is compressed to 3500 kPA by K-202 and cooled to 0.0 °C by a freon refrigerant in E-202. At this point the stream is flashed for a second time in vessel FL-202 to remove additional impurities. The top outlet stream consists of 99.5 wt% ethylene, which is fed to the bottom of a 10-tray absorption column that removes a fraction of the residual diethyl ether as well as the remainder of the unreacted ethanol. A stream of absorbent water is fed to the top of the column at 10,000 kg/hr. The product exits the top of the column at a rate of 54,600 kg/hr and has a purity of 99.7% ethylene. Diethyl ether makes up 0.2% of the remaining product stream and is the primary contaminant. Trace amounts of residual water and hydrogen are also present.

Full tables of material and energy streams can be found in Appendices III and IV respectively.

==Process Alternatives==
===Reactor Alternatives===
Two fixed bed reactors, alternating with fired heaters, are used in the dehydration reaction of ethanol to ethylene. However, a fluidized bed reactor can offer better mixing and temperature control than a fixed bed reactor and thus provide the highest possible conversion of ethanol with the greatest selectivity to ethylene. (Tsao and Zasloff, 1979) Fluidized bed reactors also provide a lower rate of catalyst coking and byproduct formation, minimizing separation and catalyst regeneration costs. (Morschbacker, 2009) The major downside of fluidized bed reactors is that few large-scale processes have been built since the technology was developed in the late 1970s. (Tsao and Zasloff, 1979; Morschbacker, 2009) Although implementation of fluidized bed reactors could potentially increase the purity of the ethylene product and/or decrease costs, a small scale pilot process would need to be built and tested before it would be possible to develop an industrial-scale facility.

===Catalyst Alternatives===
Aluminum oxide, specifically gamma alumina, is the most industrially-common catalyst and has been historically used due to its low cost and high stability. (Tsao and Zasloff, 1979; Fan and Dai, n.d.) Recent improvements in selectivity and catalyst stability of activated alumina have been achieved by incorporating titanium oxide into the catalyst, although this increases reaction temperature by approximately 50 °C and decreases catalyst lifespan. (Chen and Li, et. al. 2007) There is also significant ongoing research into HZSM-5 zeolite and heteropolyacids, which are being explored as potential alternatives to alumina oxide. A nanoscale HZSM-5 zeolite catalyst has been shown to operate at the relatively low temperature of 200-300°C, with a 100% ethanol conversion and 99.7% selectivity to ethylene. Initial research has also indicated that it maintains greater than 98% selectivity for 630 operational hours. (Fan and Dai, n.d.) However, the current low cost and ready availability of unmodified alumina oxide makes it a better choice for a process of this scale.

===Purification Alternatives===
As specified in this process, the reactor effluent is purified by two flash drums and absorption with water to produce chemical-grade ethylene. If chemical-grade ethylene is indeed the desired product, other purification options include caustic washing of the reactor effluent and water removal in a desiccant drying bed. (Morschbacker, 2009) While this purification train is relatively simple and does not require harsh chemical reagents, polymer grade ethylene is more commercially valuable and the additional cost of removing water and diethyl ether contaminants may be justified by increased revenue. Cryogenic distillation was initially simulated to produce polymer-grade ethylene, but utility requirements were found to render this separation economically unviable. (Barrocas and Baratelli, 1983) Further research and optimization may find this purification strategy to be a more valid process. Alternatively, the addition of a cryogenic turboexpander or the use of alternative adsorbents may increase product purity to polymer grade. (Jumonville, 2010) Initial HYSYS simulations indicate that these operations may be feasible with further refinement.

===Wastewater Treatment===
Due to the large volume of wastewater produced, building an on-site wastewater treatment facility may prove to be more economical than paying for third-party wastewater treatment. Flash vessel FL-201 produces 44,600 L/hr of wastewater contaminated with 18.7 vol% ethanol and 0.6 vol% acetaldehyde, while FL-202 produces 2940 L/hr of an aqueous waste consisting of 56.8 vol% ethanol, 42.0 vol% water and 0.9 vol% diethyl ether. The absorption column produces approximately 10,200 liters/hr of wastewater contaminated with 1.2 vol% ethanol, 0.2% diethyl ether and 0.2% acetaldehyde. Utilizing distillation to separate these streams into clean water and volatile organic waste could ultimately reduce the quantity of waste that requires disposal and reduce the overall costs of the process.

==Process Equipment==
Relevant sizing information for each unit operation, estimated by the method described in the “Technical Approach,” can be found in Appendix V. Equipment and piping is assumed to be constructed of carbon steel. It should be noted that the two fired heaters are proportionately large enough to heat the entirety of the process stream and are thus larger than standard equipment.

=Economic Analysis=
[[File:NPV_B1.png|400px|thumb]]
[[File:sensitivityanalysis_B1.png|400px|thumb]]

==Economics Overview==
All final values are normalized to June 2014 USD by CEPCI scaling. It is assumed that all products produced are sold at current market prices.

The Aspen Economic Evaluation module within HYSYS v8.0 was used to estimate capital and operating costs for a 10-year plant life span with a construction start date of April 2015. The price of the 95% ethanol feed stream was estimated at $1.44 per gallon, while the chemical grade ethylene produced is currently selling for approximately $1350 per metric ton. (Today in Energy, 2015; Weddle, 2014) Mapping and sizing calculations were performed by the economics module and a preliminary economic evaluation was completed. Equipment sizes, also estimated by HYSYS, were reviewed to ensure that height, diameter, and volume specifications were within realistic ranges.

The process was ideally projected to operate 360 days per year with a start-up time of one year. In addition, the tax rate was approximated at 40%, an interest rate at 20%, and a salvage value of 20%. Escalation percentages were compounded yearly for the product, raw material, and operating costs. The total capital cost for this process is approximately $16.4 million, which includes all equipment and piping described in the process. The most expensive equipment used in this process are the two fired heaters F-101 and F-102, which have an exceptionally large heat exchange area to adequately heat the feed. Standard heaters may not suffice and additional costs may be incurred for the raw materials and manufacture of this equipment. Including a feed preheater or additional fired heaters may reduce this cost in subsequent design iterations.

The total operating cost is approximately $465 million per year, about $427 million of which is the cost of the ethanol feed and natural gas for the two fired heaters. An additional $1.73 million per year is used for utilities including the cooling water and refrigerant. The labor and maintenance costs of this industrial process were also accounted for within the simulation’s economic analysis. The HYSYS simulation software, in conjunction with the Icarus economic analyzer, estimated there should be 5 operators per 8 hour shift with a cost per operator of $20 per hour. This results in a total operating labor cost of approximately $880,000 per year. In addition, the process will require one supervisor per shift with an hourly rate of $35 for total supervisor salaries of $307,000 per year. Finally, a fixed maintenance rate was estimated at $205,000 per 8000 hours of operation for a total cost of $225,000 per year.

Total product sales are roughly $640 million per year at full operation. The estimated income for this process is thus approximately $175 million per year. After ten years, the plant is projected to have a net present value (NPV) of $391 million and an internal rate of return of approximately 79%. In addition the payout period for the initial investment is estimated to be about 2.7 years. Figure 2 shows the projected cash flow for the project.

==Sensitivity Analysis==
A sensitivity analysis was performed to investigate the effects of fluctuating capital costs, operating costs, raw materials, utility costs and ethylene sales price on the 10-year net present value (NPV) of the project. This analysis was performed by scaling these cost factors according to typical ranges given in Towler and Sinnott and calculating the adjusting the NPV accordingly. The results, illustrated in Figure 3, indicate that the project value is most sensitive to product sales, raw materials costs, and operating costs. Ethylene and ethanol prices are market-determined and cannot be controlled for in the process design, so further optimization should be focused on minimizing the operations cost of the process. (Today in Energy, 2015; Weddle, 2014) However, in feed and product prices do still have a profound effect on profitability and feasibility. A more rigorous market analysis will better inform the profitability outlook.

=Conclusions/Recommendations=

The proposed process produces approximately 460,000 metric tons of 99.7 wt% ethylene annually, with a 10-year net present value of $131 million. If current economic conditions hold, it is recommended that this project proceed to implementation following further design improvements and optimization.

Future design iterations should focus on process optimization, particularly in minimizing operating costs as prescribed by the results of the sensitivity analysis. The development of a heat-exchanger network, potentially with Aspen Energy Analyzer, is one option for decreasing utility requirements and increasing the efficiency of the process overall. Optimization of the fired heaters could also result in decreased operational costs. Although overall profitability is less sensitive to capital costs, reviewing and adjusting equipment sizing would also improve the economic outlook. In particular, exploring alternative heating strategies at the beginning of the process could significantly decrease capital costs. Although there are not any particularly dangerous chemicals utilized in the process, an overall process review should also consider potential failure modes to minimize the safety risk to plant workers and nearby residents.

In addition to economic and safety considerations, harmful emissions and waste streams should be minimized both to bring down the cost of treatment and to decrease environmental effects. The two fired heaters consume a large amount of natural gas per year, emitting about 200,000 tons of CO2 annually, and account for more than half of the capital cost of the process. Although no known toxic gases are produced, carbon capture or other emissions-reduction methods should be considered. Additionally, enough wastewater is produced by this process that building an onsite wastewater treatment center should be considered. This could not only decrease operating costs by eliminating the need for an external contract but also give the plant more control over the final purity of the treated wastewater.

Finally, the current model assumes that all ethylene produced will be sold at a current prices and price or product sales will not be affected by economic variability. A more detailed study of the chemical-grade ethylene market, as well as a more thorough understanding of sales and distribution logistics, would increase the surety of a profitable process.

In summary, the proposed process yields chemical grade ethylene via the catalytic dehydration of ethanol. A 100,000 kg/hr of 95 wt% ethanol, 5% water feed is converted to 53,000 kg/hr of 99.7% chemical-grade ethylene. After 10 years of operation, including a one-year startup time, the process has an NPV of $391 million with an IRR of 79% and a payback period of 2.7 years.
Pending further optimization, this process was determined to be viable and it is recommended for the project to move forward.

=References=

[1] American Chemistry Council. Production of chemicals and plastics in the U.S. in 2013, by type (in 1,000 metric tons). In Statista - The Statistics Portal. August 2014. Available at http://www.statista.com/statistics/299725/total-us-plastics-and-chemicals-shipments-by-type/, Accessed January 15, 2015. – Relative proportions of plastics production.

[2] DuPont Nevada Site Cellulosic Ethanol Facility [Internet]. DuPont Chemical; c2012-2015 [cited 11 Mar. 2015]. Available from: http://biofuels.dupont.com/cellulosic-ethanol/nevada-site-ce-facility/. -- Information on ethanol production in Iowa.

[3] Designing Ethylene Plants. Ethylene [Internet]. Technip; 2014 [cited 13 Mar. 2015]. Available from: http://www.technip.com/en/our-business/onshore/ethylene -- Plant size ranges.

[4] Suppes GJ. Selecting Thermodynamic Models for Process Simulation of Organic VLE and LLE Systems. The University of Missouri-Columbia, Dept of Chemical Engineering. [cited 13 Mar. 2015]. -- Use of NRTL in alcohol separations.

[5] ASPENtech. Appendix A - Property Methods and Calculations. Simulation Basics; A-3 - A-26. 2014.

[6] 190 Proof Ethanol: Technical Data Sheet [Internet]. Decon Labs Inc; 2012 [cited 13 Mar. 2015]. Available from: http://www.deconlabs.com/tds/ETHANOL%20190%20%20PROOF.pdf -- Information regarding 95% ethanol

[7] Hadawey A, Ge Y, Tassou TSA. Energy Savings Through Liquid Pressure Amplification In A Dairy Plant Refrigeration System. The Centre for Energy and Built Environment Research [cited 13 Mar. 2015].

[8] Methane (Chemical Compound). 2015. Encyclopædia Britannica Online. [cited 13 Mar. 2015] Available from: http://www.britannica.com/EBchecked/topic/378264/methane -- Composition of Methane

[9] Composition of Air [Internet]. Engineering Toolbox; [cited 13 Mar. 2015]. Available from: http://www.engineeringtoolbox.com/air-composition-d_212.html. -- Composition of air.

[10] Summary of the Clean Air Act, 2015. United States Environmental Protection Agency. [cited 13 Mar. 2015] Available from: http://www2.epa.gov/laws-regulations/summary-clean-air-act -- Emissions requirements of chemical plants.

[11] Zhang M, Yu Y. Dehydration of Ethanol to Ethylene. Industrial Engineering and Chemical Research. 2013; 52:9505-9514. – Technical information on ethanol to ethylene conversion via dehydration.

[12] AspenTech. Aspen HYSYS Help File v8.0. Aspen Technology, Inc. 2012. - Aspen HYSYS help file used for troubleshooting and assistance on economic analysis.

[13] Towler G, Sinnott R. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. 2nd ed. Boston: Elsevier; 2013. -- General Reference Book

[14] Barrocas H, Baratelli F, inventors; Petroleo Brasileiro S.A., assignee. Process for dehydration of a low molecular weight alcohol. US patent 4,396,789 A. August 2, 1983. - Primary background for process design.

[15] Tsao U, Zasloff HB, inventors; The Lummus Company, assignee. Production of ethylene from ethanol. US patent 4,134,926. January 16, 1979. – Patent for catalytic dehydration of ethylene in a fluidized bed reactor.

[16] Morschbacker, A. Bio-Ethanol Based Ethylene. Polymer Reviews. 2009; 49:79-84. – Overview of bioethanol dehydration process development.

[17] Fan D, Dai DJ, Wu HS. Ethylene Formation by Catalytic Dehydration of Ethanol with Industrial Considerations. Materials. 6, 101-115. doi: 10.3390/ma6010101. - Comparison of types of catalysts used in the dehydration of ethanol and current research into new catalysts.

[18] Chen G, Li S, Jiao F, Yuan Q. Catalytic dehydration of bioethanol to ethylene over TiO2/γ-Al2O3 catalysts in microchannel reactors. Catal. Today 2007, 125, 111–119. - Paper introducing research on modified alumina catalyst for ethanol dehydration.

[19] Jumonville, J. Tutorial on Cryogenic Turboexpanders. Proceedings of the Thirty-Ninth Turbomachinery Symposium; 2010 Oct 4-7; Houston, TX. Houston: Texas A&M University; 2010. -- Use of turboexpander for cryogenic separations

[20] Today in Energy - Daily Prices. US Energy Information Administration website. http://www.eia.gov/todayinenergy/prices.cfm. Accessed March 3rd 2015. - Bulk market price for 95% ethanol.

[21] Weddle, N. ICIS Pricing: Ethylene (Europe). Reed Business Limited. January 10 2014. - Bulk market price for chemical grade ethylene.

=Appendix I - Process Flow Diagram=
[[File:PFD B1.JPG|1300px|center]]

=Appendix II - HYSYS Simulation=
[[File:HYSYS_B1.PNG|center]]

=Appendix III - Material Streams=
[[File:Streams_B1.png|1200px]]

=Appendix IV - Energy Table=
[[File:Energy_B1.png|600px|center]]

=Appendix V - Economics=
[[File:Econsummary_B1.png|center]] 

[[File:Capcost_B1.png|center]] 

[[File:sensitivityanalysis_B1.png|600px|center]]

Ethanol to Ethylene (B1)

2015-03-14T04:23:45Z

Hpoppick: /* Process Flowsheet */

[[File:BFD_B1.png|600px|thumbnail|alt=Alt text|Conversion of Ethanol to Ethylene]]

Team B1 Final Report

Authors: Harry Poppick, Emm Fulk and Scott Smith

Instructors: Fengqi You, David Wegerer

March 13, 2015

=Executive Summary=

The following report outlines the design and analysis of a process converting ethanol to chemical-grade ethylene via catalytic dehydration. This process consumers 100,000 kg/hr of 95 wt% ethanol, 5 wt% water feedstock and produces 53,000 kg/hr of 99.7 wt% chemical-grade ethylene. The ethanol feed passes through two fixed-bed reactors, each packed with an aluminum oxide catalyst, and the resulting ethylene is purified by two flash tanks and by absorption with water. The process was modeled using Aspen HYSYS simulation software to estimate mass and energy flows and equipment sizing requirements. Based on results of this initial simulation, several alternatives are discussed for increasing the process efficiency and profitability. The use of a fluidized bed reactor or a more ethylene-selective catalyst could increase the production of ethylene per ethanol basis. Additionally, several methods of purification to more valuable polymer-grade ethylene are proposed.

The economic feasibility of this process was evaluated using Aspen Economic Analyzer with the Icarus economics package. Capital cost is approximately $16.4 million total with an operating cost of $465 million per year. The current market prices of the ethanol feed and ethylene sales price are $1.44/gallon and $1350/metric ton respectively. The cost of feed ethanol, process utilities and miscellaneous operational costs total to about $427 million/year. At full operation, revenue at current prices would be approximately $640 million per year. The predicted 10-year net present value of the process is approximately $391 million with an IRR of 79% and a payback period of 2.7 years. A sensitivity analysis indicates that the process is most sensitive to feed prices, product prices and operation cost.

Several recommendations are made for both cost reduction and profit maximization, including the design of a heat exchanger network and the optimization of fired heaters that require high capital investment and large amounts of fuel. A safety review of the process is recommended, as well as the minimization of flue gas effluent and wastewater. It is also suggested that the construction of an onsite wastewater treatment center be considered. Overall, the initial analysis indicates this to be a profitable process and it is recommended the project move forward.

=Introduction=

Ethylene is a critical chemical precursor to a number of different industrial products. It is often derived from petroleum sources and polymerized to polyethylene, one of the most ubiquitous plastics today. (American Chemistry Council, 2013) Recently there has been a significant effort to develop production pathways utilizing biologically-derived feedstocks, such as corn or cellulosic ethanol, rather than traditional fossil-fuel sources. Ethylene can be produced from bioethanol via catalytic dehydration over an aluminum oxide catalyst. The proposed process converts 100,000 kg/hr of 95 wt% ethanol, 5% water feed to 53,000 kg/hr of 99.7% chemical-grade ethylene when operating at full capacity. This process was found to be economically viable with a 10-year net present value (NPV) of $131 million (2014 USD) and a payback period of approximately 2.7 years. This memo will detail the proposed process, as well as outline potential alternatives and economic viability of the project.

=Technical Approach=

Many bioethanol plants are located in the Midwest where large amounts of feedstock crops, such as corn, are grown. As such, this plant will be located in Story county, Iowa, near a large-scale bioethanol production plant. (DuPont Nevada Site, 2012) It is assumed that the supply of bioethanol is consistent and readily available. It is also assumed that other reagents - namely, the aluminum oxide catalyst, heater fuel, utility water and freon refrigerant - are readily available, and that wastewater treatment facilities are located near enough to facilitate the off-site treatment of wastewater. Plant capacity was based on current mid-sized industrial ethylene plants. (Designing Ethylene Plants, 2014)

HYSYS simulations were performed with the NRTL fluid package and Peng-Robinson vapor model. The NRTL fluid package is an activity coefficient model that is especially useful to model the separations of alcohols in aqueous solutions. (Suppes, 2015) In addition, NRTL uses models of binary pairs of components, much like the Wilson equation, to predict chemical interactions at the molecular level. The NRTL package can thus be easily extended to ternary and higher order chemical systems, making it ideal for this type of simulation. The Peng-Robinson vapor model was selected as it is well-suited to account for the non-idealities of the vapor phase reactions and separations integral to this process. (ASPENtech, 2014)

It was assumed that the feed enters the process at ambient temperature and pressure (25 °C, 1 atm) and at a consistent rate and composition with negligible quantities of impurities. The ethanol feed was assumed to be 95% ethanol and 5% water by mass, which is the commercial standard for industrial ethanol. (190 Proof Ethanol, 2012) Storage vessels for the feed ethanol, waste streams and products are assumed to be located nearby to the process. An initial feed pump compensates for pressure drops through the process and reduces the duty on downstream compressors. (Hadawey, 2015)

Natural gas, assumed to consist of 83% methane, 16% ethane and 1% nitrogen by mass, was supplied to two fired heaters at a flow rate estimated by HYSYS. (Methane, 2015) Air fed to the process to enable combustion was assumed to be 23% oxygen and 77% nitrogen by mass. (Composition of Air, 2015) Air streams were fed at 50% molar excess in order to ensure complete combustion and prevent the formation of carbon monoxide in the heater exhaust. Total flue gases are assumed to be 230,000 kg/hr, or 2.2 million tons annually, and consist of 73.8% nitrogen gas, 10.5% carbon dioxide, 8.2% water vapor, and 7.5% oxygen by mass. The only compound of concern in these emissions is the carbon dioxide, a known greenhouse gas. At the time of this report, the quantities of carbon dioxide emitted by this plant annually are within acceptable EPA specifications. (Summary of the Clean Air Act, 2015)

Due to the difficulty of simulation equilibrium and conversion reactions in a single vessel in HYSYS, these two reaction types were simulated in separate equilibrium reactor and conversion reactor units in series. In addition, while HYSYS indicated that reactor units would output separate vapor and liquid streams, it was assumed that in practice this would take the form of a single, two phase stream between each unit. To account for this, mixers were installed downstream of each reactor to combine the liquid and vapor phases of the reactor effluent. The three consequent reactions considered are as follows:

Ethanol ↔ Ethylene + Water
Ethanol → Acetaldehyde + Hydrogen
2 Ethanol → Diethyl Ether + Water

The optimal reaction temperature was determined to be 400 °C, which promotes the equilibrium reaction of ethanol to ethylene while minimizing byproducts. (Zhang and Yu, 2013) While other byproducts may be produced in this process, these reactions are typically taken to comprise of the bulk of the dehydration reaction. Heat losses over these reactors were assumed to be negligible. (Zhang and Yu, 2013)All major process equipment is assumed to be constructed of high strength carbon steel. (AspenTech, 2012)

The “Sizing Utility” within the Icarus Economic Evaluation module was used to estimate sizes of major equipment based on the process simulation. These values can serve as a benchmark for an initial plant design. Icarus KbaseTM implements a wide variety of mechanical design standards, including ASME and BS5500, in order to calculate accurate equipment sizing. The Icarus sizing module combines equipment prices for standard chemical processing equipment as well as correlations and sizing factors. The advantage of using a software package such as HYSYS to price out individual equipment is that it utilizes up-to-date prices from vendors and distributors when estimating costs. A more in-depth overview of the correlations included in this software can be found in Towler and Sinnott (2009).

=Process Flowsheet=
[[File:Squarepfd_B1.PNG|thumb|400px]]

The following process is based primarily on a 1983 US patent titled “Process for dehydration of a low molecular weight alcohol.” (Barrocas and Baratelli, 1983) The process flow diagram can be seen in Figure 1. A larger version of the PFD is included in Appendix I and the HYSYS simulation setup in Appendix II.

The feed enters the process at a rate of 100,000 kg/hr, a temperature and pressure of a 25 °C and 1 atm and at a composition of 95 wt% ethanol and 5 wt% water.It is initially pressurized to 4335 kPa by centrifugal pump P-101 and subsequently heated to 400 °C by fired heater F-101. The heated and pressurized feed enters fixed bed reactor R-101 and contacts with the aluminum oxide catalyst. At this point it dehydrates to form the product, ethylene, as well as the byproducts water, hydrogen, diethyl ether and acetaldehyde. Fired heater F-102 and reactor R-102 increase the overall conversion of the process. Both fired heaters F-101 and F-102 are fueled with natural gas and fed with excess air. The composition of the reactor train effluent is 54.5 wt% ethylene, 37.1 wt% water, 8.1 wt% unreacted ethanol and trace amounts of diethyl ether, acetaldehyde, and hydrogen contaminants.

The pressure of the reactor train effluent is increased to 4500 kPa by compressor K-102 and the temperature decreased to 100 °C by exchange with cold water in heat exchanger E-201. The stream then expands and flashes in flash vessel FL-201, which separates out 82.3% of the unreacted ethanol, 96.6% of the water and virtually all of the acetaldehyde contaminant in the bottoms while sending the ethylene-rich vapor phase out of the top. The top product of FL-202 is compressed to 3500 kPA by K-202 and cooled to 0.0 °C by a freon refrigerant in E-202. At this point the stream is flashed for a second time in vessel FL-202 to remove additional impurities. The top outlet stream consists of 99.5 wt% ethylene, which is fed to the bottom of a 10-tray absorption column that removes a fraction of the residual diethyl ether as well as the remainder of the unreacted ethanol. A stream of absorbent water is fed to the top of the column at 10,000 kg/hr. The product exits the top of the column at a rate of 54,600 kg/hr and has a purity of 99.7% ethylene. Diethyl ether makes up 0.2% of the remaining product stream and is the primary contaminant. Trace amounts of residual water and hydrogen are also present.

Full tables of material and energy streams can be found in Appendices III and IV respectively.

==Process Alternatives==
===Reactor Alternatives===
Two fixed bed reactors, alternating with fired heaters, are used in the dehydration reaction of ethanol to ethylene. However, a fluidized bed reactor can offer better mixing and temperature control than a fixed bed reactor and thus provide the highest possible conversion of ethanol with the greatest selectivity to ethylene. (Tsao and Zasloff, 1979) Fluidized bed reactors also provide a lower rate of catalyst coking and byproduct formation, minimizing separation and catalyst regeneration costs. (Morschbacker, 2009) The major downside of fluidized bed reactors is that few large-scale processes have been built since the technology was developed in the late 1970s. (Tsao and Zasloff, 1979; Morschbacker, 2009) Although implementation of fluidized bed reactors could potentially increase the purity of the ethylene product and/or decrease costs, a small scale pilot process would need to be built and tested before it would be possible to develop an industrial-scale facility.

===Catalyst Alternatives===
Aluminum oxide, specifically gamma alumina, is the most industrially-common catalyst and has been historically used due to its low cost and high stability. (Tsao and Zasloff, 1979; Fan and Dai, n.d.) Recent improvements in selectivity and catalyst stability of activated alumina have been achieved by incorporating titanium oxide into the catalyst, although this increases reaction temperature by approximately 50 °C and decreases catalyst lifespan. (Chen and Li, et. al. 2007) There is also significant ongoing research into HZSM-5 zeolite and heteropolyacids, which are being explored as potential alternatives to alumina oxide. A nanoscale HZSM-5 zeolite catalyst has been shown to operate at the relatively low temperature of 200-300°C, with a 100% ethanol conversion and 99.7% selectivity to ethylene. Initial research has also indicated that it maintains greater than 98% selectivity for 630 operational hours. (Fan and Dai, n.d.) However, the current low cost and ready availability of unmodified alumina oxide makes it a better choice for a process of this scale.

===Purification Alternatives===
As specified in this process, the reactor effluent is purified by two flash drums and absorption with water to produce chemical-grade ethylene. If chemical-grade ethylene is indeed the desired product, other purification options include caustic washing of the reactor effluent and water removal in a desiccant drying bed. (Morschbacker, 2009) While this purification train is relatively simple and does not require harsh chemical reagents, polymer grade ethylene is more commercially valuable and the additional cost of removing water and diethyl ether contaminants may be justified by increased revenue. Cryogenic distillation was initially simulated to produce polymer-grade ethylene, but utility requirements were found to render this separation economically unviable. (Barrocas and Baratelli, 1983) Further research and optimization may find this purification strategy to be a more valid process. Alternatively, the addition of a cryogenic turboexpander or the use of alternative adsorbents may increase product purity to polymer grade. (Jumonville, 2010) Initial HYSYS simulations indicate that these operations may be feasible with further refinement.

===Wastewater Treatment===
Due to the large volume of wastewater produced, building an on-site wastewater treatment facility may prove to be more economical than paying for third-party wastewater treatment. Flash vessel FL-201 produces 44,600 L/hr of wastewater contaminated with 18.7 vol% ethanol and 0.6 vol% acetaldehyde, while FL-202 produces 2940 L/hr of an aqueous waste consisting of 56.8 vol% ethanol, 42.0 vol% water and 0.9 vol% diethyl ether. The absorption column produces approximately 10,200 liters/hr of wastewater contaminated with 1.2 vol% ethanol, 0.2% diethyl ether and 0.2% acetaldehyde. Utilizing distillation to separate these streams into clean water and volatile organic waste could ultimately reduce the quantity of waste that requires disposal and reduce the overall costs of the process.

==Process Equipment==
Relevant sizing information for each unit operation, estimated by the method described in the “Technical Approach,” can be found in Appendix V. Equipment and piping is assumed to be constructed of carbon steel. It should be noted that the two fired heaters are proportionately large enough to heat the entirety of the process stream and are thus larger than standard equipment.

=Economic Analysis=
[[File:NPV_B1.png|400px|thumb]]
[[File:sensitivityanalysis_B1.png|400px|thumb]]

==Economics Overview==
All final values are normalized to June 2014 USD by CEPCI scaling. It is assumed that all products produced are sold at current market prices.

The Aspen Economic Evaluation module within HYSYS v8.0 was used to estimate capital and operating costs for a 10-year plant life span with a construction start date of April 2015. The price of the 95% ethanol feed stream was estimated at $1.44 per gallon, while the chemical grade ethylene produced is currently selling for approximately $1350 per metric ton. (Today in Energy, 2015; Weddle, 2014) Mapping and sizing calculations were performed by the economics module and a preliminary economic evaluation was completed. Equipment sizes, also estimated by HYSYS, were reviewed to ensure that height, diameter, and volume specifications were within realistic ranges.

The process was ideally projected to operate 360 days per year with a start-up time of one year. In addition, the tax rate was approximated at 40%, an interest rate at 20%, and a salvage value of 20%. Escalation percentages were compounded yearly for the product, raw material, and operating costs. The total capital cost for this process is approximately $16.4 million, which includes all equipment and piping described in the process. The most expensive equipment used in this process are the two fired heaters F-101 and F-102, which have an exceptionally large heat exchange area to adequately heat the feed. Standard heaters may not suffice and additional costs may be incurred for the raw materials and manufacture of this equipment. Including a feed preheater or additional fired heaters may reduce this cost in subsequent design iterations.

The total operating cost is approximately $465 million per year, about $427 million of which is the cost of the ethanol feed and natural gas for the two fired heaters. An additional $1.73 million per year is used for utilities including the cooling water and refrigerant. The labor and maintenance costs of this industrial process were also accounted for within the simulation’s economic analysis. The HYSYS simulation software, in conjunction with the Icarus economic analyzer, estimated there should be 5 operators per 8 hour shift with a cost per operator of $20 per hour. This results in a total operating labor cost of approximately $880,000 per year. In addition, the process will require one supervisor per shift with an hourly rate of $35 for total supervisor salaries of $307,000 per year. Finally, a fixed maintenance rate was estimated at $205,000 per 8000 hours of operation for a total cost of $225,000 per year.

Total product sales are roughly $640 million per year at full operation. The estimated income for this process is thus approximately $175 million per year. After ten years, the plant is projected to have a net present value (NPV) of $391 million and an internal rate of return of approximately 79%. In addition the payout period for the initial investment is estimated to be about 2.7 years. Figure 2 shows the projected cash flow for the project.

==Sensitivity Analysis==
A sensitivity analysis was performed to investigate the effects of fluctuating capital costs, operating costs, raw materials, utility costs and ethylene sales price on the 10-year net present value (NPV) of the project. This analysis was performed by scaling these cost factors according to typical ranges given in Towler and Sinnott and calculating the adjusting the NPV accordingly. The results, illustrated in Figure 3, indicate that the project value is most sensitive to product sales, raw materials costs, and operating costs. Ethylene and ethanol prices are market-determined and cannot be controlled for in the process design, so further optimization should be focused on minimizing the operations cost of the process. (Today in Energy, 2015; Weddle, 2014) However, in feed and product prices do still have a profound effect on profitability and feasibility. A more rigorous market analysis will better inform the profitability outlook.

=Conclusions/Recommendations=

The proposed process produces approximately 460,000 metric tons of 99.7 wt% ethylene annually, with a 10-year net present value of $131 million. If current economic conditions hold, it is recommended that this project proceed to implementation following further design improvements and optimization.

Future design iterations should focus on process optimization, particularly in minimizing operating costs as prescribed by the results of the sensitivity analysis. The development of a heat-exchanger network, potentially with Aspen Energy Analyzer, is one option for decreasing utility requirements and increasing the efficiency of the process overall. Optimization of the fired heaters could also result in decreased operational costs. Although overall profitability is less sensitive to capital costs, reviewing and adjusting equipment sizing would also improve the economic outlook. In particular, exploring alternative heating strategies at the beginning of the process could significantly decrease capital costs. Although there are not any particularly dangerous chemicals utilized in the process, an overall process review should also consider potential failure modes to minimize the safety risk to plant workers and nearby residents.

In addition to economic and safety considerations, harmful emissions and waste streams should be minimized both to bring down the cost of treatment and to decrease environmental effects. The two fired heaters consume a large amount of natural gas per year, emitting about 200,000 tons of CO2 annually, and account for more than half of the capital cost of the process. Although no known toxic gases are produced, carbon capture or other emissions-reduction methods should be considered. Additionally, enough wastewater is produced by this process that building an onsite wastewater treatment center should be considered. This could not only decrease operating costs by eliminating the need for an external contract but also give the plant more control over the final purity of the treated wastewater.

Finally, the current model assumes that all ethylene produced will be sold at a current prices and price or product sales will not be affected by economic variability. A more detailed study of the chemical-grade ethylene market, as well as a more thorough understanding of sales and distribution logistics, would increase the surety of a profitable process.

In summary, the proposed process yields chemical grade ethylene via the catalytic dehydration of ethanol. A 100,000 kg/hr of 95 wt% ethanol, 5% water feed is converted to 53,000 kg/hr of 99.7% chemical-grade ethylene. After 10 years of operation, including a one-year startup time, the process has an NPV of $391 million with an IRR of 79% and a payback period of 2.7 years.
Pending further optimization, this process was determined to be viable and it is recommended for the project to move forward.

=References=

[1] American Chemistry Council. Production of chemicals and plastics in the U.S. in 2013, by type (in 1,000 metric tons). In Statista - The Statistics Portal. August 2014. Available at http://www.statista.com/statistics/299725/total-us-plastics-and-chemicals-shipments-by-type/, Accessed January 15, 2015. – Relative proportions of plastics production.

[2] DuPont Nevada Site Cellulosic Ethanol Facility [Internet]. DuPont Chemical; c2012-2015 [cited 11 Mar. 2015]. Available from: http://biofuels.dupont.com/cellulosic-ethanol/nevada-site-ce-facility/. -- Information on ethanol production in Iowa.

[3] Designing Ethylene Plants. Ethylene [Internet]. Technip; 2014 [cited 13 Mar. 2015]. Available from: http://www.technip.com/en/our-business/onshore/ethylene -- Plant size ranges.

[4] Suppes GJ. Selecting Thermodynamic Models for Process Simulation of Organic VLE and LLE Systems. The University of Missouri-Columbia, Dept of Chemical Engineering. [cited 13 Mar. 2015]. -- Use of NRTL in alcohol separations.

[5] ASPENtech. Appendix A - Property Methods and Calculations. Simulation Basics; A-3 - A-26. 2014.

[6] 190 Proof Ethanol: Technical Data Sheet [Internet]. Decon Labs Inc; 2012 [cited 13 Mar. 2015]. Available from: http://www.deconlabs.com/tds/ETHANOL%20190%20%20PROOF.pdf -- Information regarding 95% ethanol

[7] Hadawey A, Ge Y, Tassou TSA. Energy Savings Through Liquid Pressure Amplification In A Dairy Plant Refrigeration System. The Centre for Energy and Built Environment Research [cited 13 Mar. 2015].

[8] Methane (Chemical Compound). 2015. Encyclopædia Britannica Online. [cited 13 Mar. 2015] Available from: http://www.britannica.com/EBchecked/topic/378264/methane -- Composition of Methane

[9] Composition of Air [Internet]. Engineering Toolbox; [cited 13 Mar. 2015]. Available from: http://www.engineeringtoolbox.com/air-composition-d_212.html. -- Composition of air.

[10] Summary of the Clean Air Act, 2015. United States Environmental Protection Agency. [cited 13 Mar. 2015] Available from: http://www2.epa.gov/laws-regulations/summary-clean-air-act -- Emissions requirements of chemical plants.

[11] Zhang M, Yu Y. Dehydration of Ethanol to Ethylene. Industrial Engineering and Chemical Research. 2013; 52:9505-9514. – Technical information on ethanol to ethylene conversion via dehydration.

[12] AspenTech. Aspen HYSYS Help File v8.0. Aspen Technology, Inc. 2012. - Aspen HYSYS help file used for troubleshooting and assistance on economic analysis.

[13] Towler G, Sinnott R. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. 2nd ed. Boston: Elsevier; 2013. -- General Reference Book

[14] Barrocas H, Baratelli F, inventors; Petroleo Brasileiro S.A., assignee. Process for dehydration of a low molecular weight alcohol. US patent 4,396,789 A. August 2, 1983. - Primary background for process design.

[15] Tsao U, Zasloff HB, inventors; The Lummus Company, assignee. Production of ethylene from ethanol. US patent 4,134,926. January 16, 1979. – Patent for catalytic dehydration of ethylene in a fluidized bed reactor.

[16] Morschbacker, A. Bio-Ethanol Based Ethylene. Polymer Reviews. 2009; 49:79-84. – Overview of bioethanol dehydration process development.

[17] Fan D, Dai DJ, Wu HS. Ethylene Formation by Catalytic Dehydration of Ethanol with Industrial Considerations. Materials. 6, 101-115. doi: 10.3390/ma6010101. - Comparison of types of catalysts used in the dehydration of ethanol and current research into new catalysts.

[18] Chen G, Li S, Jiao F, Yuan Q. Catalytic dehydration of bioethanol to ethylene over TiO2/γ-Al2O3 catalysts in microchannel reactors. Catal. Today 2007, 125, 111–119. - Paper introducing research on modified alumina catalyst for ethanol dehydration.

[19] Jumonville, J. Tutorial on Cryogenic Turboexpanders. Proceedings of the Thirty-Ninth Turbomachinery Symposium; 2010 Oct 4-7; Houston, TX. Houston: Texas A&M University; 2010. -- Use of turboexpander for cryogenic separations

[20] Today in Energy - Daily Prices. US Energy Information Administration website. http://www.eia.gov/todayinenergy/prices.cfm. Accessed March 3rd 2015. - Bulk market price for 95% ethanol.

[21] Weddle, N. ICIS Pricing: Ethylene (Europe). Reed Business Limited. January 10 2014. - Bulk market price for chemical grade ethylene.

=Appendix I - Process Flow Diagram=
[[File:PFD B1.JPG|1300px|center]]

=Appendix II - HYSYS Simulation=
[[File:HYSYS_B1.PNG|center]]

=Appendix III - Material Streams=
[[File:Streams_B1.png|1200px]]

=Appendix IV - Energy Table=
[[File:Energy_B1.png|600px|center]]

=Appendix V - Economics=
[[File:Econsummary_B1.png|center]] 

[[File:Capcost_B1.png|center]] 

[[File:sensitivityanalysis_B1.png|600px|center]]

Ethanol to Ethylene (B1)

2015-03-14T04:23:23Z

Hpoppick: /* Process Flowsheet */

[[File:BFD_B1.png|600px|thumbnail|alt=Alt text|Conversion of Ethanol to Ethylene]]

Team B1 Final Report

Authors: Harry Poppick, Emm Fulk and Scott Smith

Instructors: Fengqi You, David Wegerer

March 13, 2015

=Executive Summary=

The following report outlines the design and analysis of a process converting ethanol to chemical-grade ethylene via catalytic dehydration. This process consumers 100,000 kg/hr of 95 wt% ethanol, 5 wt% water feedstock and produces 53,000 kg/hr of 99.7 wt% chemical-grade ethylene. The ethanol feed passes through two fixed-bed reactors, each packed with an aluminum oxide catalyst, and the resulting ethylene is purified by two flash tanks and by absorption with water. The process was modeled using Aspen HYSYS simulation software to estimate mass and energy flows and equipment sizing requirements. Based on results of this initial simulation, several alternatives are discussed for increasing the process efficiency and profitability. The use of a fluidized bed reactor or a more ethylene-selective catalyst could increase the production of ethylene per ethanol basis. Additionally, several methods of purification to more valuable polymer-grade ethylene are proposed.

The economic feasibility of this process was evaluated using Aspen Economic Analyzer with the Icarus economics package. Capital cost is approximately $16.4 million total with an operating cost of $465 million per year. The current market prices of the ethanol feed and ethylene sales price are $1.44/gallon and $1350/metric ton respectively. The cost of feed ethanol, process utilities and miscellaneous operational costs total to about $427 million/year. At full operation, revenue at current prices would be approximately $640 million per year. The predicted 10-year net present value of the process is approximately $391 million with an IRR of 79% and a payback period of 2.7 years. A sensitivity analysis indicates that the process is most sensitive to feed prices, product prices and operation cost.

Several recommendations are made for both cost reduction and profit maximization, including the design of a heat exchanger network and the optimization of fired heaters that require high capital investment and large amounts of fuel. A safety review of the process is recommended, as well as the minimization of flue gas effluent and wastewater. It is also suggested that the construction of an onsite wastewater treatment center be considered. Overall, the initial analysis indicates this to be a profitable process and it is recommended the project move forward.

=Introduction=

Ethylene is a critical chemical precursor to a number of different industrial products. It is often derived from petroleum sources and polymerized to polyethylene, one of the most ubiquitous plastics today. (American Chemistry Council, 2013) Recently there has been a significant effort to develop production pathways utilizing biologically-derived feedstocks, such as corn or cellulosic ethanol, rather than traditional fossil-fuel sources. Ethylene can be produced from bioethanol via catalytic dehydration over an aluminum oxide catalyst. The proposed process converts 100,000 kg/hr of 95 wt% ethanol, 5% water feed to 53,000 kg/hr of 99.7% chemical-grade ethylene when operating at full capacity. This process was found to be economically viable with a 10-year net present value (NPV) of $131 million (2014 USD) and a payback period of approximately 2.7 years. This memo will detail the proposed process, as well as outline potential alternatives and economic viability of the project.

=Technical Approach=

Many bioethanol plants are located in the Midwest where large amounts of feedstock crops, such as corn, are grown. As such, this plant will be located in Story county, Iowa, near a large-scale bioethanol production plant. (DuPont Nevada Site, 2012) It is assumed that the supply of bioethanol is consistent and readily available. It is also assumed that other reagents - namely, the aluminum oxide catalyst, heater fuel, utility water and freon refrigerant - are readily available, and that wastewater treatment facilities are located near enough to facilitate the off-site treatment of wastewater. Plant capacity was based on current mid-sized industrial ethylene plants. (Designing Ethylene Plants, 2014)

HYSYS simulations were performed with the NRTL fluid package and Peng-Robinson vapor model. The NRTL fluid package is an activity coefficient model that is especially useful to model the separations of alcohols in aqueous solutions. (Suppes, 2015) In addition, NRTL uses models of binary pairs of components, much like the Wilson equation, to predict chemical interactions at the molecular level. The NRTL package can thus be easily extended to ternary and higher order chemical systems, making it ideal for this type of simulation. The Peng-Robinson vapor model was selected as it is well-suited to account for the non-idealities of the vapor phase reactions and separations integral to this process. (ASPENtech, 2014)

It was assumed that the feed enters the process at ambient temperature and pressure (25 °C, 1 atm) and at a consistent rate and composition with negligible quantities of impurities. The ethanol feed was assumed to be 95% ethanol and 5% water by mass, which is the commercial standard for industrial ethanol. (190 Proof Ethanol, 2012) Storage vessels for the feed ethanol, waste streams and products are assumed to be located nearby to the process. An initial feed pump compensates for pressure drops through the process and reduces the duty on downstream compressors. (Hadawey, 2015)

Natural gas, assumed to consist of 83% methane, 16% ethane and 1% nitrogen by mass, was supplied to two fired heaters at a flow rate estimated by HYSYS. (Methane, 2015) Air fed to the process to enable combustion was assumed to be 23% oxygen and 77% nitrogen by mass. (Composition of Air, 2015) Air streams were fed at 50% molar excess in order to ensure complete combustion and prevent the formation of carbon monoxide in the heater exhaust. Total flue gases are assumed to be 230,000 kg/hr, or 2.2 million tons annually, and consist of 73.8% nitrogen gas, 10.5% carbon dioxide, 8.2% water vapor, and 7.5% oxygen by mass. The only compound of concern in these emissions is the carbon dioxide, a known greenhouse gas. At the time of this report, the quantities of carbon dioxide emitted by this plant annually are within acceptable EPA specifications. (Summary of the Clean Air Act, 2015)

Due to the difficulty of simulation equilibrium and conversion reactions in a single vessel in HYSYS, these two reaction types were simulated in separate equilibrium reactor and conversion reactor units in series. In addition, while HYSYS indicated that reactor units would output separate vapor and liquid streams, it was assumed that in practice this would take the form of a single, two phase stream between each unit. To account for this, mixers were installed downstream of each reactor to combine the liquid and vapor phases of the reactor effluent. The three consequent reactions considered are as follows:

Ethanol ↔ Ethylene + Water
Ethanol → Acetaldehyde + Hydrogen
2 Ethanol → Diethyl Ether + Water

The optimal reaction temperature was determined to be 400 °C, which promotes the equilibrium reaction of ethanol to ethylene while minimizing byproducts. (Zhang and Yu, 2013) While other byproducts may be produced in this process, these reactions are typically taken to comprise of the bulk of the dehydration reaction. Heat losses over these reactors were assumed to be negligible. (Zhang and Yu, 2013)All major process equipment is assumed to be constructed of high strength carbon steel. (AspenTech, 2012)

The “Sizing Utility” within the Icarus Economic Evaluation module was used to estimate sizes of major equipment based on the process simulation. These values can serve as a benchmark for an initial plant design. Icarus KbaseTM implements a wide variety of mechanical design standards, including ASME and BS5500, in order to calculate accurate equipment sizing. The Icarus sizing module combines equipment prices for standard chemical processing equipment as well as correlations and sizing factors. The advantage of using a software package such as HYSYS to price out individual equipment is that it utilizes up-to-date prices from vendors and distributors when estimating costs. A more in-depth overview of the correlations included in this software can be found in Towler and Sinnott (2009).

=Process Flowsheet=
[[File:Squarepfd_B1.PNG|thumb|400px] Fig 1. PFD of the Proposed Process]

The following process is based primarily on a 1983 US patent titled “Process for dehydration of a low molecular weight alcohol.” (Barrocas and Baratelli, 1983) The process flow diagram can be seen in Figure 1. A larger version of the PFD is included in Appendix I and the HYSYS simulation setup in Appendix II.

The feed enters the process at a rate of 100,000 kg/hr, a temperature and pressure of a 25 °C and 1 atm and at a composition of 95 wt% ethanol and 5 wt% water.It is initially pressurized to 4335 kPa by centrifugal pump P-101 and subsequently heated to 400 °C by fired heater F-101. The heated and pressurized feed enters fixed bed reactor R-101 and contacts with the aluminum oxide catalyst. At this point it dehydrates to form the product, ethylene, as well as the byproducts water, hydrogen, diethyl ether and acetaldehyde. Fired heater F-102 and reactor R-102 increase the overall conversion of the process. Both fired heaters F-101 and F-102 are fueled with natural gas and fed with excess air. The composition of the reactor train effluent is 54.5 wt% ethylene, 37.1 wt% water, 8.1 wt% unreacted ethanol and trace amounts of diethyl ether, acetaldehyde, and hydrogen contaminants.

The pressure of the reactor train effluent is increased to 4500 kPa by compressor K-102 and the temperature decreased to 100 °C by exchange with cold water in heat exchanger E-201. The stream then expands and flashes in flash vessel FL-201, which separates out 82.3% of the unreacted ethanol, 96.6% of the water and virtually all of the acetaldehyde contaminant in the bottoms while sending the ethylene-rich vapor phase out of the top. The top product of FL-202 is compressed to 3500 kPA by K-202 and cooled to 0.0 °C by a freon refrigerant in E-202. At this point the stream is flashed for a second time in vessel FL-202 to remove additional impurities. The top outlet stream consists of 99.5 wt% ethylene, which is fed to the bottom of a 10-tray absorption column that removes a fraction of the residual diethyl ether as well as the remainder of the unreacted ethanol. A stream of absorbent water is fed to the top of the column at 10,000 kg/hr. The product exits the top of the column at a rate of 54,600 kg/hr and has a purity of 99.7% ethylene. Diethyl ether makes up 0.2% of the remaining product stream and is the primary contaminant. Trace amounts of residual water and hydrogen are also present.

Full tables of material and energy streams can be found in Appendices III and IV respectively.

==Process Alternatives==
===Reactor Alternatives===
Two fixed bed reactors, alternating with fired heaters, are used in the dehydration reaction of ethanol to ethylene. However, a fluidized bed reactor can offer better mixing and temperature control than a fixed bed reactor and thus provide the highest possible conversion of ethanol with the greatest selectivity to ethylene. (Tsao and Zasloff, 1979) Fluidized bed reactors also provide a lower rate of catalyst coking and byproduct formation, minimizing separation and catalyst regeneration costs. (Morschbacker, 2009) The major downside of fluidized bed reactors is that few large-scale processes have been built since the technology was developed in the late 1970s. (Tsao and Zasloff, 1979; Morschbacker, 2009) Although implementation of fluidized bed reactors could potentially increase the purity of the ethylene product and/or decrease costs, a small scale pilot process would need to be built and tested before it would be possible to develop an industrial-scale facility.

===Catalyst Alternatives===
Aluminum oxide, specifically gamma alumina, is the most industrially-common catalyst and has been historically used due to its low cost and high stability. (Tsao and Zasloff, 1979; Fan and Dai, n.d.) Recent improvements in selectivity and catalyst stability of activated alumina have been achieved by incorporating titanium oxide into the catalyst, although this increases reaction temperature by approximately 50 °C and decreases catalyst lifespan. (Chen and Li, et. al. 2007) There is also significant ongoing research into HZSM-5 zeolite and heteropolyacids, which are being explored as potential alternatives to alumina oxide. A nanoscale HZSM-5 zeolite catalyst has been shown to operate at the relatively low temperature of 200-300°C, with a 100% ethanol conversion and 99.7% selectivity to ethylene. Initial research has also indicated that it maintains greater than 98% selectivity for 630 operational hours. (Fan and Dai, n.d.) However, the current low cost and ready availability of unmodified alumina oxide makes it a better choice for a process of this scale.

===Purification Alternatives===
As specified in this process, the reactor effluent is purified by two flash drums and absorption with water to produce chemical-grade ethylene. If chemical-grade ethylene is indeed the desired product, other purification options include caustic washing of the reactor effluent and water removal in a desiccant drying bed. (Morschbacker, 2009) While this purification train is relatively simple and does not require harsh chemical reagents, polymer grade ethylene is more commercially valuable and the additional cost of removing water and diethyl ether contaminants may be justified by increased revenue. Cryogenic distillation was initially simulated to produce polymer-grade ethylene, but utility requirements were found to render this separation economically unviable. (Barrocas and Baratelli, 1983) Further research and optimization may find this purification strategy to be a more valid process. Alternatively, the addition of a cryogenic turboexpander or the use of alternative adsorbents may increase product purity to polymer grade. (Jumonville, 2010) Initial HYSYS simulations indicate that these operations may be feasible with further refinement.

===Wastewater Treatment===
Due to the large volume of wastewater produced, building an on-site wastewater treatment facility may prove to be more economical than paying for third-party wastewater treatment. Flash vessel FL-201 produces 44,600 L/hr of wastewater contaminated with 18.7 vol% ethanol and 0.6 vol% acetaldehyde, while FL-202 produces 2940 L/hr of an aqueous waste consisting of 56.8 vol% ethanol, 42.0 vol% water and 0.9 vol% diethyl ether. The absorption column produces approximately 10,200 liters/hr of wastewater contaminated with 1.2 vol% ethanol, 0.2% diethyl ether and 0.2% acetaldehyde. Utilizing distillation to separate these streams into clean water and volatile organic waste could ultimately reduce the quantity of waste that requires disposal and reduce the overall costs of the process.

==Process Equipment==
Relevant sizing information for each unit operation, estimated by the method described in the “Technical Approach,” can be found in Appendix V. Equipment and piping is assumed to be constructed of carbon steel. It should be noted that the two fired heaters are proportionately large enough to heat the entirety of the process stream and are thus larger than standard equipment.

=Economic Analysis=
[[File:NPV_B1.png|400px|thumb]]
[[File:sensitivityanalysis_B1.png|400px|thumb]]

==Economics Overview==
All final values are normalized to June 2014 USD by CEPCI scaling. It is assumed that all products produced are sold at current market prices.

The Aspen Economic Evaluation module within HYSYS v8.0 was used to estimate capital and operating costs for a 10-year plant life span with a construction start date of April 2015. The price of the 95% ethanol feed stream was estimated at $1.44 per gallon, while the chemical grade ethylene produced is currently selling for approximately $1350 per metric ton. (Today in Energy, 2015; Weddle, 2014) Mapping and sizing calculations were performed by the economics module and a preliminary economic evaluation was completed. Equipment sizes, also estimated by HYSYS, were reviewed to ensure that height, diameter, and volume specifications were within realistic ranges.

The process was ideally projected to operate 360 days per year with a start-up time of one year. In addition, the tax rate was approximated at 40%, an interest rate at 20%, and a salvage value of 20%. Escalation percentages were compounded yearly for the product, raw material, and operating costs. The total capital cost for this process is approximately $16.4 million, which includes all equipment and piping described in the process. The most expensive equipment used in this process are the two fired heaters F-101 and F-102, which have an exceptionally large heat exchange area to adequately heat the feed. Standard heaters may not suffice and additional costs may be incurred for the raw materials and manufacture of this equipment. Including a feed preheater or additional fired heaters may reduce this cost in subsequent design iterations.

The total operating cost is approximately $465 million per year, about $427 million of which is the cost of the ethanol feed and natural gas for the two fired heaters. An additional $1.73 million per year is used for utilities including the cooling water and refrigerant. The labor and maintenance costs of this industrial process were also accounted for within the simulation’s economic analysis. The HYSYS simulation software, in conjunction with the Icarus economic analyzer, estimated there should be 5 operators per 8 hour shift with a cost per operator of $20 per hour. This results in a total operating labor cost of approximately $880,000 per year. In addition, the process will require one supervisor per shift with an hourly rate of $35 for total supervisor salaries of $307,000 per year. Finally, a fixed maintenance rate was estimated at $205,000 per 8000 hours of operation for a total cost of $225,000 per year.

Total product sales are roughly $640 million per year at full operation. The estimated income for this process is thus approximately $175 million per year. After ten years, the plant is projected to have a net present value (NPV) of $391 million and an internal rate of return of approximately 79%. In addition the payout period for the initial investment is estimated to be about 2.7 years. Figure 2 shows the projected cash flow for the project.

==Sensitivity Analysis==
A sensitivity analysis was performed to investigate the effects of fluctuating capital costs, operating costs, raw materials, utility costs and ethylene sales price on the 10-year net present value (NPV) of the project. This analysis was performed by scaling these cost factors according to typical ranges given in Towler and Sinnott and calculating the adjusting the NPV accordingly. The results, illustrated in Figure 3, indicate that the project value is most sensitive to product sales, raw materials costs, and operating costs. Ethylene and ethanol prices are market-determined and cannot be controlled for in the process design, so further optimization should be focused on minimizing the operations cost of the process. (Today in Energy, 2015; Weddle, 2014) However, in feed and product prices do still have a profound effect on profitability and feasibility. A more rigorous market analysis will better inform the profitability outlook.

=Conclusions/Recommendations=

The proposed process produces approximately 460,000 metric tons of 99.7 wt% ethylene annually, with a 10-year net present value of $131 million. If current economic conditions hold, it is recommended that this project proceed to implementation following further design improvements and optimization.

Future design iterations should focus on process optimization, particularly in minimizing operating costs as prescribed by the results of the sensitivity analysis. The development of a heat-exchanger network, potentially with Aspen Energy Analyzer, is one option for decreasing utility requirements and increasing the efficiency of the process overall. Optimization of the fired heaters could also result in decreased operational costs. Although overall profitability is less sensitive to capital costs, reviewing and adjusting equipment sizing would also improve the economic outlook. In particular, exploring alternative heating strategies at the beginning of the process could significantly decrease capital costs. Although there are not any particularly dangerous chemicals utilized in the process, an overall process review should also consider potential failure modes to minimize the safety risk to plant workers and nearby residents.

In addition to economic and safety considerations, harmful emissions and waste streams should be minimized both to bring down the cost of treatment and to decrease environmental effects. The two fired heaters consume a large amount of natural gas per year, emitting about 200,000 tons of CO2 annually, and account for more than half of the capital cost of the process. Although no known toxic gases are produced, carbon capture or other emissions-reduction methods should be considered. Additionally, enough wastewater is produced by this process that building an onsite wastewater treatment center should be considered. This could not only decrease operating costs by eliminating the need for an external contract but also give the plant more control over the final purity of the treated wastewater.

Finally, the current model assumes that all ethylene produced will be sold at a current prices and price or product sales will not be affected by economic variability. A more detailed study of the chemical-grade ethylene market, as well as a more thorough understanding of sales and distribution logistics, would increase the surety of a profitable process.

In summary, the proposed process yields chemical grade ethylene via the catalytic dehydration of ethanol. A 100,000 kg/hr of 95 wt% ethanol, 5% water feed is converted to 53,000 kg/hr of 99.7% chemical-grade ethylene. After 10 years of operation, including a one-year startup time, the process has an NPV of $391 million with an IRR of 79% and a payback period of 2.7 years.
Pending further optimization, this process was determined to be viable and it is recommended for the project to move forward.

=References=

[1] American Chemistry Council. Production of chemicals and plastics in the U.S. in 2013, by type (in 1,000 metric tons). In Statista - The Statistics Portal. August 2014. Available at http://www.statista.com/statistics/299725/total-us-plastics-and-chemicals-shipments-by-type/, Accessed January 15, 2015. – Relative proportions of plastics production.

[2] DuPont Nevada Site Cellulosic Ethanol Facility [Internet]. DuPont Chemical; c2012-2015 [cited 11 Mar. 2015]. Available from: http://biofuels.dupont.com/cellulosic-ethanol/nevada-site-ce-facility/. -- Information on ethanol production in Iowa.

[3] Designing Ethylene Plants. Ethylene [Internet]. Technip; 2014 [cited 13 Mar. 2015]. Available from: http://www.technip.com/en/our-business/onshore/ethylene -- Plant size ranges.

[4] Suppes GJ. Selecting Thermodynamic Models for Process Simulation of Organic VLE and LLE Systems. The University of Missouri-Columbia, Dept of Chemical Engineering. [cited 13 Mar. 2015]. -- Use of NRTL in alcohol separations.

[5] ASPENtech. Appendix A - Property Methods and Calculations. Simulation Basics; A-3 - A-26. 2014.

[6] 190 Proof Ethanol: Technical Data Sheet [Internet]. Decon Labs Inc; 2012 [cited 13 Mar. 2015]. Available from: http://www.deconlabs.com/tds/ETHANOL%20190%20%20PROOF.pdf -- Information regarding 95% ethanol

[7] Hadawey A, Ge Y, Tassou TSA. Energy Savings Through Liquid Pressure Amplification In A Dairy Plant Refrigeration System. The Centre for Energy and Built Environment Research [cited 13 Mar. 2015].

[8] Methane (Chemical Compound). 2015. Encyclopædia Britannica Online. [cited 13 Mar. 2015] Available from: http://www.britannica.com/EBchecked/topic/378264/methane -- Composition of Methane

[9] Composition of Air [Internet]. Engineering Toolbox; [cited 13 Mar. 2015]. Available from: http://www.engineeringtoolbox.com/air-composition-d_212.html. -- Composition of air.

[10] Summary of the Clean Air Act, 2015. United States Environmental Protection Agency. [cited 13 Mar. 2015] Available from: http://www2.epa.gov/laws-regulations/summary-clean-air-act -- Emissions requirements of chemical plants.

[11] Zhang M, Yu Y. Dehydration of Ethanol to Ethylene. Industrial Engineering and Chemical Research. 2013; 52:9505-9514. – Technical information on ethanol to ethylene conversion via dehydration.

[12] AspenTech. Aspen HYSYS Help File v8.0. Aspen Technology, Inc. 2012. - Aspen HYSYS help file used for troubleshooting and assistance on economic analysis.

[13] Towler G, Sinnott R. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. 2nd ed. Boston: Elsevier; 2013. -- General Reference Book

[14] Barrocas H, Baratelli F, inventors; Petroleo Brasileiro S.A., assignee. Process for dehydration of a low molecular weight alcohol. US patent 4,396,789 A. August 2, 1983. - Primary background for process design.

[15] Tsao U, Zasloff HB, inventors; The Lummus Company, assignee. Production of ethylene from ethanol. US patent 4,134,926. January 16, 1979. – Patent for catalytic dehydration of ethylene in a fluidized bed reactor.

[16] Morschbacker, A. Bio-Ethanol Based Ethylene. Polymer Reviews. 2009; 49:79-84. – Overview of bioethanol dehydration process development.

[17] Fan D, Dai DJ, Wu HS. Ethylene Formation by Catalytic Dehydration of Ethanol with Industrial Considerations. Materials. 6, 101-115. doi: 10.3390/ma6010101. - Comparison of types of catalysts used in the dehydration of ethanol and current research into new catalysts.

[18] Chen G, Li S, Jiao F, Yuan Q. Catalytic dehydration of bioethanol to ethylene over TiO2/γ-Al2O3 catalysts in microchannel reactors. Catal. Today 2007, 125, 111–119. - Paper introducing research on modified alumina catalyst for ethanol dehydration.

[19] Jumonville, J. Tutorial on Cryogenic Turboexpanders. Proceedings of the Thirty-Ninth Turbomachinery Symposium; 2010 Oct 4-7; Houston, TX. Houston: Texas A&M University; 2010. -- Use of turboexpander for cryogenic separations

[20] Today in Energy - Daily Prices. US Energy Information Administration website. http://www.eia.gov/todayinenergy/prices.cfm. Accessed March 3rd 2015. - Bulk market price for 95% ethanol.

[21] Weddle, N. ICIS Pricing: Ethylene (Europe). Reed Business Limited. January 10 2014. - Bulk market price for chemical grade ethylene.

=Appendix I - Process Flow Diagram=
[[File:PFD B1.JPG|1300px|center]]

=Appendix II - HYSYS Simulation=
[[File:HYSYS_B1.PNG|center]]

=Appendix III - Material Streams=
[[File:Streams_B1.png|1200px]]

=Appendix IV - Energy Table=
[[File:Energy_B1.png|600px|center]]

=Appendix V - Economics=
[[File:Econsummary_B1.png|center]] 

[[File:Capcost_B1.png|center]] 

[[File:sensitivityanalysis_B1.png|600px|center]]

Ethanol to Ethylene (B1)

2015-03-14T04:22:23Z

Hpoppick: /* Appendix II - HYSYS Simulation */

[[File:BFD_B1.png|600px|thumbnail|alt=Alt text|Conversion of Ethanol to Ethylene]]

Team B1 Final Report

Authors: Harry Poppick, Emm Fulk and Scott Smith

Instructors: Fengqi You, David Wegerer

March 13, 2015

=Executive Summary=

The following report outlines the design and analysis of a process converting ethanol to chemical-grade ethylene via catalytic dehydration. This process consumers 100,000 kg/hr of 95 wt% ethanol, 5 wt% water feedstock and produces 53,000 kg/hr of 99.7 wt% chemical-grade ethylene. The ethanol feed passes through two fixed-bed reactors, each packed with an aluminum oxide catalyst, and the resulting ethylene is purified by two flash tanks and by absorption with water. The process was modeled using Aspen HYSYS simulation software to estimate mass and energy flows and equipment sizing requirements. Based on results of this initial simulation, several alternatives are discussed for increasing the process efficiency and profitability. The use of a fluidized bed reactor or a more ethylene-selective catalyst could increase the production of ethylene per ethanol basis. Additionally, several methods of purification to more valuable polymer-grade ethylene are proposed.

The economic feasibility of this process was evaluated using Aspen Economic Analyzer with the Icarus economics package. Capital cost is approximately $16.4 million total with an operating cost of $465 million per year. The current market prices of the ethanol feed and ethylene sales price are $1.44/gallon and $1350/metric ton respectively. The cost of feed ethanol, process utilities and miscellaneous operational costs total to about $427 million/year. At full operation, revenue at current prices would be approximately $640 million per year. The predicted 10-year net present value of the process is approximately $391 million with an IRR of 79% and a payback period of 2.7 years. A sensitivity analysis indicates that the process is most sensitive to feed prices, product prices and operation cost.

Several recommendations are made for both cost reduction and profit maximization, including the design of a heat exchanger network and the optimization of fired heaters that require high capital investment and large amounts of fuel. A safety review of the process is recommended, as well as the minimization of flue gas effluent and wastewater. It is also suggested that the construction of an onsite wastewater treatment center be considered. Overall, the initial analysis indicates this to be a profitable process and it is recommended the project move forward.

=Introduction=

Ethylene is a critical chemical precursor to a number of different industrial products. It is often derived from petroleum sources and polymerized to polyethylene, one of the most ubiquitous plastics today. (American Chemistry Council, 2013) Recently there has been a significant effort to develop production pathways utilizing biologically-derived feedstocks, such as corn or cellulosic ethanol, rather than traditional fossil-fuel sources. Ethylene can be produced from bioethanol via catalytic dehydration over an aluminum oxide catalyst. The proposed process converts 100,000 kg/hr of 95 wt% ethanol, 5% water feed to 53,000 kg/hr of 99.7% chemical-grade ethylene when operating at full capacity. This process was found to be economically viable with a 10-year net present value (NPV) of $131 million (2014 USD) and a payback period of approximately 2.7 years. This memo will detail the proposed process, as well as outline potential alternatives and economic viability of the project.

=Technical Approach=

Many bioethanol plants are located in the Midwest where large amounts of feedstock crops, such as corn, are grown. As such, this plant will be located in Story county, Iowa, near a large-scale bioethanol production plant. (DuPont Nevada Site, 2012) It is assumed that the supply of bioethanol is consistent and readily available. It is also assumed that other reagents - namely, the aluminum oxide catalyst, heater fuel, utility water and freon refrigerant - are readily available, and that wastewater treatment facilities are located near enough to facilitate the off-site treatment of wastewater. Plant capacity was based on current mid-sized industrial ethylene plants. (Designing Ethylene Plants, 2014)

HYSYS simulations were performed with the NRTL fluid package and Peng-Robinson vapor model. The NRTL fluid package is an activity coefficient model that is especially useful to model the separations of alcohols in aqueous solutions. (Suppes, 2015) In addition, NRTL uses models of binary pairs of components, much like the Wilson equation, to predict chemical interactions at the molecular level. The NRTL package can thus be easily extended to ternary and higher order chemical systems, making it ideal for this type of simulation. The Peng-Robinson vapor model was selected as it is well-suited to account for the non-idealities of the vapor phase reactions and separations integral to this process. (ASPENtech, 2014)

It was assumed that the feed enters the process at ambient temperature and pressure (25 °C, 1 atm) and at a consistent rate and composition with negligible quantities of impurities. The ethanol feed was assumed to be 95% ethanol and 5% water by mass, which is the commercial standard for industrial ethanol. (190 Proof Ethanol, 2012) Storage vessels for the feed ethanol, waste streams and products are assumed to be located nearby to the process. An initial feed pump compensates for pressure drops through the process and reduces the duty on downstream compressors. (Hadawey, 2015)

Natural gas, assumed to consist of 83% methane, 16% ethane and 1% nitrogen by mass, was supplied to two fired heaters at a flow rate estimated by HYSYS. (Methane, 2015) Air fed to the process to enable combustion was assumed to be 23% oxygen and 77% nitrogen by mass. (Composition of Air, 2015) Air streams were fed at 50% molar excess in order to ensure complete combustion and prevent the formation of carbon monoxide in the heater exhaust. Total flue gases are assumed to be 230,000 kg/hr, or 2.2 million tons annually, and consist of 73.8% nitrogen gas, 10.5% carbon dioxide, 8.2% water vapor, and 7.5% oxygen by mass. The only compound of concern in these emissions is the carbon dioxide, a known greenhouse gas. At the time of this report, the quantities of carbon dioxide emitted by this plant annually are within acceptable EPA specifications. (Summary of the Clean Air Act, 2015)

Due to the difficulty of simulation equilibrium and conversion reactions in a single vessel in HYSYS, these two reaction types were simulated in separate equilibrium reactor and conversion reactor units in series. In addition, while HYSYS indicated that reactor units would output separate vapor and liquid streams, it was assumed that in practice this would take the form of a single, two phase stream between each unit. To account for this, mixers were installed downstream of each reactor to combine the liquid and vapor phases of the reactor effluent. The three consequent reactions considered are as follows:

Ethanol ↔ Ethylene + Water
Ethanol → Acetaldehyde + Hydrogen
2 Ethanol → Diethyl Ether + Water

The optimal reaction temperature was determined to be 400 °C, which promotes the equilibrium reaction of ethanol to ethylene while minimizing byproducts. (Zhang and Yu, 2013) While other byproducts may be produced in this process, these reactions are typically taken to comprise of the bulk of the dehydration reaction. Heat losses over these reactors were assumed to be negligible. (Zhang and Yu, 2013)All major process equipment is assumed to be constructed of high strength carbon steel. (AspenTech, 2012)

The “Sizing Utility” within the Icarus Economic Evaluation module was used to estimate sizes of major equipment based on the process simulation. These values can serve as a benchmark for an initial plant design. Icarus KbaseTM implements a wide variety of mechanical design standards, including ASME and BS5500, in order to calculate accurate equipment sizing. The Icarus sizing module combines equipment prices for standard chemical processing equipment as well as correlations and sizing factors. The advantage of using a software package such as HYSYS to price out individual equipment is that it utilizes up-to-date prices from vendors and distributors when estimating costs. A more in-depth overview of the correlations included in this software can be found in Towler and Sinnott (2009).

=Process Flowsheet=
[[File:Squarepfd_B1.PNG|thumb|400px]]

The following process is based primarily on a 1983 US patent titled “Process for dehydration of a low molecular weight alcohol.” (Barrocas and Baratelli, 1983) The process flow diagram can be seen in Figure 1. A larger version of the PFD is included in Appendix I and the HYSYS simulation setup in Appendix II.

The feed enters the process at a rate of 100,000 kg/hr, a temperature and pressure of a 25 °C and 1 atm and at a composition of 95 wt% ethanol and 5 wt% water.It is initially pressurized to 4335 kPa by centrifugal pump P-101 and subsequently heated to 400 °C by fired heater F-101. The heated and pressurized feed enters fixed bed reactor R-101 and contacts with the aluminum oxide catalyst. At this point it dehydrates to form the product, ethylene, as well as the byproducts water, hydrogen, diethyl ether and acetaldehyde. Fired heater F-102 and reactor R-102 increase the overall conversion of the process. Both fired heaters F-101 and F-102 are fueled with natural gas and fed with excess air. The composition of the reactor train effluent is 54.5 wt% ethylene, 37.1 wt% water, 8.1 wt% unreacted ethanol and trace amounts of diethyl ether, acetaldehyde, and hydrogen contaminants.

The pressure of the reactor train effluent is increased to 4500 kPa by compressor K-102 and the temperature decreased to 100 °C by exchange with cold water in heat exchanger E-201. The stream then expands and flashes in flash vessel FL-201, which separates out 82.3% of the unreacted ethanol, 96.6% of the water and virtually all of the acetaldehyde contaminant in the bottoms while sending the ethylene-rich vapor phase out of the top. The top product of FL-202 is compressed to 3500 kPA by K-202 and cooled to 0.0 °C by a freon refrigerant in E-202. At this point the stream is flashed for a second time in vessel FL-202 to remove additional impurities. The top outlet stream consists of 99.5 wt% ethylene, which is fed to the bottom of a 10-tray absorption column that removes a fraction of the residual diethyl ether as well as the remainder of the unreacted ethanol. A stream of absorbent water is fed to the top of the column at 10,000 kg/hr. The product exits the top of the column at a rate of 54,600 kg/hr and has a purity of 99.7% ethylene. Diethyl ether makes up 0.2% of the remaining product stream and is the primary contaminant. Trace amounts of residual water and hydrogen are also present.

Full tables of material and energy streams can be found in Appendices III and IV respectively.

==Process Alternatives==
===Reactor Alternatives===
Two fixed bed reactors, alternating with fired heaters, are used in the dehydration reaction of ethanol to ethylene. However, a fluidized bed reactor can offer better mixing and temperature control than a fixed bed reactor and thus provide the highest possible conversion of ethanol with the greatest selectivity to ethylene. (Tsao and Zasloff, 1979) Fluidized bed reactors also provide a lower rate of catalyst coking and byproduct formation, minimizing separation and catalyst regeneration costs. (Morschbacker, 2009) The major downside of fluidized bed reactors is that few large-scale processes have been built since the technology was developed in the late 1970s. (Tsao and Zasloff, 1979; Morschbacker, 2009) Although implementation of fluidized bed reactors could potentially increase the purity of the ethylene product and/or decrease costs, a small scale pilot process would need to be built and tested before it would be possible to develop an industrial-scale facility.

===Catalyst Alternatives===
Aluminum oxide, specifically gamma alumina, is the most industrially-common catalyst and has been historically used due to its low cost and high stability. (Tsao and Zasloff, 1979; Fan and Dai, n.d.) Recent improvements in selectivity and catalyst stability of activated alumina have been achieved by incorporating titanium oxide into the catalyst, although this increases reaction temperature by approximately 50 °C and decreases catalyst lifespan. (Chen and Li, et. al. 2007) There is also significant ongoing research into HZSM-5 zeolite and heteropolyacids, which are being explored as potential alternatives to alumina oxide. A nanoscale HZSM-5 zeolite catalyst has been shown to operate at the relatively low temperature of 200-300°C, with a 100% ethanol conversion and 99.7% selectivity to ethylene. Initial research has also indicated that it maintains greater than 98% selectivity for 630 operational hours. (Fan and Dai, n.d.) However, the current low cost and ready availability of unmodified alumina oxide makes it a better choice for a process of this scale.

===Purification Alternatives===
As specified in this process, the reactor effluent is purified by two flash drums and absorption with water to produce chemical-grade ethylene. If chemical-grade ethylene is indeed the desired product, other purification options include caustic washing of the reactor effluent and water removal in a desiccant drying bed. (Morschbacker, 2009) While this purification train is relatively simple and does not require harsh chemical reagents, polymer grade ethylene is more commercially valuable and the additional cost of removing water and diethyl ether contaminants may be justified by increased revenue. Cryogenic distillation was initially simulated to produce polymer-grade ethylene, but utility requirements were found to render this separation economically unviable. (Barrocas and Baratelli, 1983) Further research and optimization may find this purification strategy to be a more valid process. Alternatively, the addition of a cryogenic turboexpander or the use of alternative adsorbents may increase product purity to polymer grade. (Jumonville, 2010) Initial HYSYS simulations indicate that these operations may be feasible with further refinement.

===Wastewater Treatment===
Due to the large volume of wastewater produced, building an on-site wastewater treatment facility may prove to be more economical than paying for third-party wastewater treatment. Flash vessel FL-201 produces 44,600 L/hr of wastewater contaminated with 18.7 vol% ethanol and 0.6 vol% acetaldehyde, while FL-202 produces 2940 L/hr of an aqueous waste consisting of 56.8 vol% ethanol, 42.0 vol% water and 0.9 vol% diethyl ether. The absorption column produces approximately 10,200 liters/hr of wastewater contaminated with 1.2 vol% ethanol, 0.2% diethyl ether and 0.2% acetaldehyde. Utilizing distillation to separate these streams into clean water and volatile organic waste could ultimately reduce the quantity of waste that requires disposal and reduce the overall costs of the process.

==Process Equipment==
Relevant sizing information for each unit operation, estimated by the method described in the “Technical Approach,” can be found in Appendix V. Equipment and piping is assumed to be constructed of carbon steel. It should be noted that the two fired heaters are proportionately large enough to heat the entirety of the process stream and are thus larger than standard equipment.

=Economic Analysis=
[[File:NPV_B1.png|400px|thumb]]
[[File:sensitivityanalysis_B1.png|400px|thumb]]

==Economics Overview==
All final values are normalized to June 2014 USD by CEPCI scaling. It is assumed that all products produced are sold at current market prices.

The Aspen Economic Evaluation module within HYSYS v8.0 was used to estimate capital and operating costs for a 10-year plant life span with a construction start date of April 2015. The price of the 95% ethanol feed stream was estimated at $1.44 per gallon, while the chemical grade ethylene produced is currently selling for approximately $1350 per metric ton. (Today in Energy, 2015; Weddle, 2014) Mapping and sizing calculations were performed by the economics module and a preliminary economic evaluation was completed. Equipment sizes, also estimated by HYSYS, were reviewed to ensure that height, diameter, and volume specifications were within realistic ranges.

The process was ideally projected to operate 360 days per year with a start-up time of one year. In addition, the tax rate was approximated at 40%, an interest rate at 20%, and a salvage value of 20%. Escalation percentages were compounded yearly for the product, raw material, and operating costs. The total capital cost for this process is approximately $16.4 million, which includes all equipment and piping described in the process. The most expensive equipment used in this process are the two fired heaters F-101 and F-102, which have an exceptionally large heat exchange area to adequately heat the feed. Standard heaters may not suffice and additional costs may be incurred for the raw materials and manufacture of this equipment. Including a feed preheater or additional fired heaters may reduce this cost in subsequent design iterations.

The total operating cost is approximately $465 million per year, about $427 million of which is the cost of the ethanol feed and natural gas for the two fired heaters. An additional $1.73 million per year is used for utilities including the cooling water and refrigerant. The labor and maintenance costs of this industrial process were also accounted for within the simulation’s economic analysis. The HYSYS simulation software, in conjunction with the Icarus economic analyzer, estimated there should be 5 operators per 8 hour shift with a cost per operator of $20 per hour. This results in a total operating labor cost of approximately $880,000 per year. In addition, the process will require one supervisor per shift with an hourly rate of $35 for total supervisor salaries of $307,000 per year. Finally, a fixed maintenance rate was estimated at $205,000 per 8000 hours of operation for a total cost of $225,000 per year.

Total product sales are roughly $640 million per year at full operation. The estimated income for this process is thus approximately $175 million per year. After ten years, the plant is projected to have a net present value (NPV) of $391 million and an internal rate of return of approximately 79%. In addition the payout period for the initial investment is estimated to be about 2.7 years. Figure 2 shows the projected cash flow for the project.

==Sensitivity Analysis==
A sensitivity analysis was performed to investigate the effects of fluctuating capital costs, operating costs, raw materials, utility costs and ethylene sales price on the 10-year net present value (NPV) of the project. This analysis was performed by scaling these cost factors according to typical ranges given in Towler and Sinnott and calculating the adjusting the NPV accordingly. The results, illustrated in Figure 3, indicate that the project value is most sensitive to product sales, raw materials costs, and operating costs. Ethylene and ethanol prices are market-determined and cannot be controlled for in the process design, so further optimization should be focused on minimizing the operations cost of the process. (Today in Energy, 2015; Weddle, 2014) However, in feed and product prices do still have a profound effect on profitability and feasibility. A more rigorous market analysis will better inform the profitability outlook.

=Conclusions/Recommendations=

The proposed process produces approximately 460,000 metric tons of 99.7 wt% ethylene annually, with a 10-year net present value of $131 million. If current economic conditions hold, it is recommended that this project proceed to implementation following further design improvements and optimization.

Future design iterations should focus on process optimization, particularly in minimizing operating costs as prescribed by the results of the sensitivity analysis. The development of a heat-exchanger network, potentially with Aspen Energy Analyzer, is one option for decreasing utility requirements and increasing the efficiency of the process overall. Optimization of the fired heaters could also result in decreased operational costs. Although overall profitability is less sensitive to capital costs, reviewing and adjusting equipment sizing would also improve the economic outlook. In particular, exploring alternative heating strategies at the beginning of the process could significantly decrease capital costs. Although there are not any particularly dangerous chemicals utilized in the process, an overall process review should also consider potential failure modes to minimize the safety risk to plant workers and nearby residents.

In addition to economic and safety considerations, harmful emissions and waste streams should be minimized both to bring down the cost of treatment and to decrease environmental effects. The two fired heaters consume a large amount of natural gas per year, emitting about 200,000 tons of CO2 annually, and account for more than half of the capital cost of the process. Although no known toxic gases are produced, carbon capture or other emissions-reduction methods should be considered. Additionally, enough wastewater is produced by this process that building an onsite wastewater treatment center should be considered. This could not only decrease operating costs by eliminating the need for an external contract but also give the plant more control over the final purity of the treated wastewater.

Finally, the current model assumes that all ethylene produced will be sold at a current prices and price or product sales will not be affected by economic variability. A more detailed study of the chemical-grade ethylene market, as well as a more thorough understanding of sales and distribution logistics, would increase the surety of a profitable process.

In summary, the proposed process yields chemical grade ethylene via the catalytic dehydration of ethanol. A 100,000 kg/hr of 95 wt% ethanol, 5% water feed is converted to 53,000 kg/hr of 99.7% chemical-grade ethylene. After 10 years of operation, including a one-year startup time, the process has an NPV of $391 million with an IRR of 79% and a payback period of 2.7 years.
Pending further optimization, this process was determined to be viable and it is recommended for the project to move forward.

=References=

[1] American Chemistry Council. Production of chemicals and plastics in the U.S. in 2013, by type (in 1,000 metric tons). In Statista - The Statistics Portal. August 2014. Available at http://www.statista.com/statistics/299725/total-us-plastics-and-chemicals-shipments-by-type/, Accessed January 15, 2015. – Relative proportions of plastics production.

[2] DuPont Nevada Site Cellulosic Ethanol Facility [Internet]. DuPont Chemical; c2012-2015 [cited 11 Mar. 2015]. Available from: http://biofuels.dupont.com/cellulosic-ethanol/nevada-site-ce-facility/. -- Information on ethanol production in Iowa.

[3] Designing Ethylene Plants. Ethylene [Internet]. Technip; 2014 [cited 13 Mar. 2015]. Available from: http://www.technip.com/en/our-business/onshore/ethylene -- Plant size ranges.

[4] Suppes GJ. Selecting Thermodynamic Models for Process Simulation of Organic VLE and LLE Systems. The University of Missouri-Columbia, Dept of Chemical Engineering. [cited 13 Mar. 2015]. -- Use of NRTL in alcohol separations.

[5] ASPENtech. Appendix A - Property Methods and Calculations. Simulation Basics; A-3 - A-26. 2014.

[6] 190 Proof Ethanol: Technical Data Sheet [Internet]. Decon Labs Inc; 2012 [cited 13 Mar. 2015]. Available from: http://www.deconlabs.com/tds/ETHANOL%20190%20%20PROOF.pdf -- Information regarding 95% ethanol

[7] Hadawey A, Ge Y, Tassou TSA. Energy Savings Through Liquid Pressure Amplification In A Dairy Plant Refrigeration System. The Centre for Energy and Built Environment Research [cited 13 Mar. 2015].

[8] Methane (Chemical Compound). 2015. Encyclopædia Britannica Online. [cited 13 Mar. 2015] Available from: http://www.britannica.com/EBchecked/topic/378264/methane -- Composition of Methane

[9] Composition of Air [Internet]. Engineering Toolbox; [cited 13 Mar. 2015]. Available from: http://www.engineeringtoolbox.com/air-composition-d_212.html. -- Composition of air.

[10] Summary of the Clean Air Act, 2015. United States Environmental Protection Agency. [cited 13 Mar. 2015] Available from: http://www2.epa.gov/laws-regulations/summary-clean-air-act -- Emissions requirements of chemical plants.

[11] Zhang M, Yu Y. Dehydration of Ethanol to Ethylene. Industrial Engineering and Chemical Research. 2013; 52:9505-9514. – Technical information on ethanol to ethylene conversion via dehydration.

[12] AspenTech. Aspen HYSYS Help File v8.0. Aspen Technology, Inc. 2012. - Aspen HYSYS help file used for troubleshooting and assistance on economic analysis.

[13] Towler G, Sinnott R. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. 2nd ed. Boston: Elsevier; 2013. -- General Reference Book

[14] Barrocas H, Baratelli F, inventors; Petroleo Brasileiro S.A., assignee. Process for dehydration of a low molecular weight alcohol. US patent 4,396,789 A. August 2, 1983. - Primary background for process design.

[15] Tsao U, Zasloff HB, inventors; The Lummus Company, assignee. Production of ethylene from ethanol. US patent 4,134,926. January 16, 1979. – Patent for catalytic dehydration of ethylene in a fluidized bed reactor.

[16] Morschbacker, A. Bio-Ethanol Based Ethylene. Polymer Reviews. 2009; 49:79-84. – Overview of bioethanol dehydration process development.

[17] Fan D, Dai DJ, Wu HS. Ethylene Formation by Catalytic Dehydration of Ethanol with Industrial Considerations. Materials. 6, 101-115. doi: 10.3390/ma6010101. - Comparison of types of catalysts used in the dehydration of ethanol and current research into new catalysts.

[18] Chen G, Li S, Jiao F, Yuan Q. Catalytic dehydration of bioethanol to ethylene over TiO2/γ-Al2O3 catalysts in microchannel reactors. Catal. Today 2007, 125, 111–119. - Paper introducing research on modified alumina catalyst for ethanol dehydration.

[19] Jumonville, J. Tutorial on Cryogenic Turboexpanders. Proceedings of the Thirty-Ninth Turbomachinery Symposium; 2010 Oct 4-7; Houston, TX. Houston: Texas A&M University; 2010. -- Use of turboexpander for cryogenic separations

[20] Today in Energy - Daily Prices. US Energy Information Administration website. http://www.eia.gov/todayinenergy/prices.cfm. Accessed March 3rd 2015. - Bulk market price for 95% ethanol.

[21] Weddle, N. ICIS Pricing: Ethylene (Europe). Reed Business Limited. January 10 2014. - Bulk market price for chemical grade ethylene.

=Appendix I - Process Flow Diagram=
[[File:PFD B1.JPG|1300px|center]]

=Appendix II - HYSYS Simulation=
[[File:HYSYS_B1.PNG|center]]

=Appendix III - Material Streams=
[[File:Streams_B1.png|1200px]]

=Appendix IV - Energy Table=
[[File:Energy_B1.png|600px|center]]

=Appendix V - Economics=
[[File:Econsummary_B1.png|center]] 

[[File:Capcost_B1.png|center]] 

[[File:sensitivityanalysis_B1.png|600px|center]]

Ethanol to Ethylene (B1)

2015-03-14T04:22:13Z

Hpoppick: /* Appendix I - Process Flow Diagram */

[[File:BFD_B1.png|600px|thumbnail|alt=Alt text|Conversion of Ethanol to Ethylene]]

Team B1 Final Report

Authors: Harry Poppick, Emm Fulk and Scott Smith

Instructors: Fengqi You, David Wegerer

March 13, 2015

=Executive Summary=

The following report outlines the design and analysis of a process converting ethanol to chemical-grade ethylene via catalytic dehydration. This process consumers 100,000 kg/hr of 95 wt% ethanol, 5 wt% water feedstock and produces 53,000 kg/hr of 99.7 wt% chemical-grade ethylene. The ethanol feed passes through two fixed-bed reactors, each packed with an aluminum oxide catalyst, and the resulting ethylene is purified by two flash tanks and by absorption with water. The process was modeled using Aspen HYSYS simulation software to estimate mass and energy flows and equipment sizing requirements. Based on results of this initial simulation, several alternatives are discussed for increasing the process efficiency and profitability. The use of a fluidized bed reactor or a more ethylene-selective catalyst could increase the production of ethylene per ethanol basis. Additionally, several methods of purification to more valuable polymer-grade ethylene are proposed.

The economic feasibility of this process was evaluated using Aspen Economic Analyzer with the Icarus economics package. Capital cost is approximately $16.4 million total with an operating cost of $465 million per year. The current market prices of the ethanol feed and ethylene sales price are $1.44/gallon and $1350/metric ton respectively. The cost of feed ethanol, process utilities and miscellaneous operational costs total to about $427 million/year. At full operation, revenue at current prices would be approximately $640 million per year. The predicted 10-year net present value of the process is approximately $391 million with an IRR of 79% and a payback period of 2.7 years. A sensitivity analysis indicates that the process is most sensitive to feed prices, product prices and operation cost.

Several recommendations are made for both cost reduction and profit maximization, including the design of a heat exchanger network and the optimization of fired heaters that require high capital investment and large amounts of fuel. A safety review of the process is recommended, as well as the minimization of flue gas effluent and wastewater. It is also suggested that the construction of an onsite wastewater treatment center be considered. Overall, the initial analysis indicates this to be a profitable process and it is recommended the project move forward.

=Introduction=

Ethylene is a critical chemical precursor to a number of different industrial products. It is often derived from petroleum sources and polymerized to polyethylene, one of the most ubiquitous plastics today. (American Chemistry Council, 2013) Recently there has been a significant effort to develop production pathways utilizing biologically-derived feedstocks, such as corn or cellulosic ethanol, rather than traditional fossil-fuel sources. Ethylene can be produced from bioethanol via catalytic dehydration over an aluminum oxide catalyst. The proposed process converts 100,000 kg/hr of 95 wt% ethanol, 5% water feed to 53,000 kg/hr of 99.7% chemical-grade ethylene when operating at full capacity. This process was found to be economically viable with a 10-year net present value (NPV) of $131 million (2014 USD) and a payback period of approximately 2.7 years. This memo will detail the proposed process, as well as outline potential alternatives and economic viability of the project.

=Technical Approach=

Many bioethanol plants are located in the Midwest where large amounts of feedstock crops, such as corn, are grown. As such, this plant will be located in Story county, Iowa, near a large-scale bioethanol production plant. (DuPont Nevada Site, 2012) It is assumed that the supply of bioethanol is consistent and readily available. It is also assumed that other reagents - namely, the aluminum oxide catalyst, heater fuel, utility water and freon refrigerant - are readily available, and that wastewater treatment facilities are located near enough to facilitate the off-site treatment of wastewater. Plant capacity was based on current mid-sized industrial ethylene plants. (Designing Ethylene Plants, 2014)

HYSYS simulations were performed with the NRTL fluid package and Peng-Robinson vapor model. The NRTL fluid package is an activity coefficient model that is especially useful to model the separations of alcohols in aqueous solutions. (Suppes, 2015) In addition, NRTL uses models of binary pairs of components, much like the Wilson equation, to predict chemical interactions at the molecular level. The NRTL package can thus be easily extended to ternary and higher order chemical systems, making it ideal for this type of simulation. The Peng-Robinson vapor model was selected as it is well-suited to account for the non-idealities of the vapor phase reactions and separations integral to this process. (ASPENtech, 2014)

It was assumed that the feed enters the process at ambient temperature and pressure (25 °C, 1 atm) and at a consistent rate and composition with negligible quantities of impurities. The ethanol feed was assumed to be 95% ethanol and 5% water by mass, which is the commercial standard for industrial ethanol. (190 Proof Ethanol, 2012) Storage vessels for the feed ethanol, waste streams and products are assumed to be located nearby to the process. An initial feed pump compensates for pressure drops through the process and reduces the duty on downstream compressors. (Hadawey, 2015)

Natural gas, assumed to consist of 83% methane, 16% ethane and 1% nitrogen by mass, was supplied to two fired heaters at a flow rate estimated by HYSYS. (Methane, 2015) Air fed to the process to enable combustion was assumed to be 23% oxygen and 77% nitrogen by mass. (Composition of Air, 2015) Air streams were fed at 50% molar excess in order to ensure complete combustion and prevent the formation of carbon monoxide in the heater exhaust. Total flue gases are assumed to be 230,000 kg/hr, or 2.2 million tons annually, and consist of 73.8% nitrogen gas, 10.5% carbon dioxide, 8.2% water vapor, and 7.5% oxygen by mass. The only compound of concern in these emissions is the carbon dioxide, a known greenhouse gas. At the time of this report, the quantities of carbon dioxide emitted by this plant annually are within acceptable EPA specifications. (Summary of the Clean Air Act, 2015)

Due to the difficulty of simulation equilibrium and conversion reactions in a single vessel in HYSYS, these two reaction types were simulated in separate equilibrium reactor and conversion reactor units in series. In addition, while HYSYS indicated that reactor units would output separate vapor and liquid streams, it was assumed that in practice this would take the form of a single, two phase stream between each unit. To account for this, mixers were installed downstream of each reactor to combine the liquid and vapor phases of the reactor effluent. The three consequent reactions considered are as follows:

Ethanol ↔ Ethylene + Water
Ethanol → Acetaldehyde + Hydrogen
2 Ethanol → Diethyl Ether + Water

The optimal reaction temperature was determined to be 400 °C, which promotes the equilibrium reaction of ethanol to ethylene while minimizing byproducts. (Zhang and Yu, 2013) While other byproducts may be produced in this process, these reactions are typically taken to comprise of the bulk of the dehydration reaction. Heat losses over these reactors were assumed to be negligible. (Zhang and Yu, 2013)All major process equipment is assumed to be constructed of high strength carbon steel. (AspenTech, 2012)

The “Sizing Utility” within the Icarus Economic Evaluation module was used to estimate sizes of major equipment based on the process simulation. These values can serve as a benchmark for an initial plant design. Icarus KbaseTM implements a wide variety of mechanical design standards, including ASME and BS5500, in order to calculate accurate equipment sizing. The Icarus sizing module combines equipment prices for standard chemical processing equipment as well as correlations and sizing factors. The advantage of using a software package such as HYSYS to price out individual equipment is that it utilizes up-to-date prices from vendors and distributors when estimating costs. A more in-depth overview of the correlations included in this software can be found in Towler and Sinnott (2009).

=Process Flowsheet=
[[File:Squarepfd_B1.PNG|thumb|400px]]

The following process is based primarily on a 1983 US patent titled “Process for dehydration of a low molecular weight alcohol.” (Barrocas and Baratelli, 1983) The process flow diagram can be seen in Figure 1. A larger version of the PFD is included in Appendix I and the HYSYS simulation setup in Appendix II.

The feed enters the process at a rate of 100,000 kg/hr, a temperature and pressure of a 25 °C and 1 atm and at a composition of 95 wt% ethanol and 5 wt% water.It is initially pressurized to 4335 kPa by centrifugal pump P-101 and subsequently heated to 400 °C by fired heater F-101. The heated and pressurized feed enters fixed bed reactor R-101 and contacts with the aluminum oxide catalyst. At this point it dehydrates to form the product, ethylene, as well as the byproducts water, hydrogen, diethyl ether and acetaldehyde. Fired heater F-102 and reactor R-102 increase the overall conversion of the process. Both fired heaters F-101 and F-102 are fueled with natural gas and fed with excess air. The composition of the reactor train effluent is 54.5 wt% ethylene, 37.1 wt% water, 8.1 wt% unreacted ethanol and trace amounts of diethyl ether, acetaldehyde, and hydrogen contaminants.

The pressure of the reactor train effluent is increased to 4500 kPa by compressor K-102 and the temperature decreased to 100 °C by exchange with cold water in heat exchanger E-201. The stream then expands and flashes in flash vessel FL-201, which separates out 82.3% of the unreacted ethanol, 96.6% of the water and virtually all of the acetaldehyde contaminant in the bottoms while sending the ethylene-rich vapor phase out of the top. The top product of FL-202 is compressed to 3500 kPA by K-202 and cooled to 0.0 °C by a freon refrigerant in E-202. At this point the stream is flashed for a second time in vessel FL-202 to remove additional impurities. The top outlet stream consists of 99.5 wt% ethylene, which is fed to the bottom of a 10-tray absorption column that removes a fraction of the residual diethyl ether as well as the remainder of the unreacted ethanol. A stream of absorbent water is fed to the top of the column at 10,000 kg/hr. The product exits the top of the column at a rate of 54,600 kg/hr and has a purity of 99.7% ethylene. Diethyl ether makes up 0.2% of the remaining product stream and is the primary contaminant. Trace amounts of residual water and hydrogen are also present.

Full tables of material and energy streams can be found in Appendices III and IV respectively.

==Process Alternatives==
===Reactor Alternatives===
Two fixed bed reactors, alternating with fired heaters, are used in the dehydration reaction of ethanol to ethylene. However, a fluidized bed reactor can offer better mixing and temperature control than a fixed bed reactor and thus provide the highest possible conversion of ethanol with the greatest selectivity to ethylene. (Tsao and Zasloff, 1979) Fluidized bed reactors also provide a lower rate of catalyst coking and byproduct formation, minimizing separation and catalyst regeneration costs. (Morschbacker, 2009) The major downside of fluidized bed reactors is that few large-scale processes have been built since the technology was developed in the late 1970s. (Tsao and Zasloff, 1979; Morschbacker, 2009) Although implementation of fluidized bed reactors could potentially increase the purity of the ethylene product and/or decrease costs, a small scale pilot process would need to be built and tested before it would be possible to develop an industrial-scale facility.

===Catalyst Alternatives===
Aluminum oxide, specifically gamma alumina, is the most industrially-common catalyst and has been historically used due to its low cost and high stability. (Tsao and Zasloff, 1979; Fan and Dai, n.d.) Recent improvements in selectivity and catalyst stability of activated alumina have been achieved by incorporating titanium oxide into the catalyst, although this increases reaction temperature by approximately 50 °C and decreases catalyst lifespan. (Chen and Li, et. al. 2007) There is also significant ongoing research into HZSM-5 zeolite and heteropolyacids, which are being explored as potential alternatives to alumina oxide. A nanoscale HZSM-5 zeolite catalyst has been shown to operate at the relatively low temperature of 200-300°C, with a 100% ethanol conversion and 99.7% selectivity to ethylene. Initial research has also indicated that it maintains greater than 98% selectivity for 630 operational hours. (Fan and Dai, n.d.) However, the current low cost and ready availability of unmodified alumina oxide makes it a better choice for a process of this scale.

===Purification Alternatives===
As specified in this process, the reactor effluent is purified by two flash drums and absorption with water to produce chemical-grade ethylene. If chemical-grade ethylene is indeed the desired product, other purification options include caustic washing of the reactor effluent and water removal in a desiccant drying bed. (Morschbacker, 2009) While this purification train is relatively simple and does not require harsh chemical reagents, polymer grade ethylene is more commercially valuable and the additional cost of removing water and diethyl ether contaminants may be justified by increased revenue. Cryogenic distillation was initially simulated to produce polymer-grade ethylene, but utility requirements were found to render this separation economically unviable. (Barrocas and Baratelli, 1983) Further research and optimization may find this purification strategy to be a more valid process. Alternatively, the addition of a cryogenic turboexpander or the use of alternative adsorbents may increase product purity to polymer grade. (Jumonville, 2010) Initial HYSYS simulations indicate that these operations may be feasible with further refinement.

===Wastewater Treatment===
Due to the large volume of wastewater produced, building an on-site wastewater treatment facility may prove to be more economical than paying for third-party wastewater treatment. Flash vessel FL-201 produces 44,600 L/hr of wastewater contaminated with 18.7 vol% ethanol and 0.6 vol% acetaldehyde, while FL-202 produces 2940 L/hr of an aqueous waste consisting of 56.8 vol% ethanol, 42.0 vol% water and 0.9 vol% diethyl ether. The absorption column produces approximately 10,200 liters/hr of wastewater contaminated with 1.2 vol% ethanol, 0.2% diethyl ether and 0.2% acetaldehyde. Utilizing distillation to separate these streams into clean water and volatile organic waste could ultimately reduce the quantity of waste that requires disposal and reduce the overall costs of the process.

==Process Equipment==
Relevant sizing information for each unit operation, estimated by the method described in the “Technical Approach,” can be found in Appendix V. Equipment and piping is assumed to be constructed of carbon steel. It should be noted that the two fired heaters are proportionately large enough to heat the entirety of the process stream and are thus larger than standard equipment.

=Economic Analysis=
[[File:NPV_B1.png|400px|thumb]]
[[File:sensitivityanalysis_B1.png|400px|thumb]]

==Economics Overview==
All final values are normalized to June 2014 USD by CEPCI scaling. It is assumed that all products produced are sold at current market prices.

The Aspen Economic Evaluation module within HYSYS v8.0 was used to estimate capital and operating costs for a 10-year plant life span with a construction start date of April 2015. The price of the 95% ethanol feed stream was estimated at $1.44 per gallon, while the chemical grade ethylene produced is currently selling for approximately $1350 per metric ton. (Today in Energy, 2015; Weddle, 2014) Mapping and sizing calculations were performed by the economics module and a preliminary economic evaluation was completed. Equipment sizes, also estimated by HYSYS, were reviewed to ensure that height, diameter, and volume specifications were within realistic ranges.

The process was ideally projected to operate 360 days per year with a start-up time of one year. In addition, the tax rate was approximated at 40%, an interest rate at 20%, and a salvage value of 20%. Escalation percentages were compounded yearly for the product, raw material, and operating costs. The total capital cost for this process is approximately $16.4 million, which includes all equipment and piping described in the process. The most expensive equipment used in this process are the two fired heaters F-101 and F-102, which have an exceptionally large heat exchange area to adequately heat the feed. Standard heaters may not suffice and additional costs may be incurred for the raw materials and manufacture of this equipment. Including a feed preheater or additional fired heaters may reduce this cost in subsequent design iterations.

The total operating cost is approximately $465 million per year, about $427 million of which is the cost of the ethanol feed and natural gas for the two fired heaters. An additional $1.73 million per year is used for utilities including the cooling water and refrigerant. The labor and maintenance costs of this industrial process were also accounted for within the simulation’s economic analysis. The HYSYS simulation software, in conjunction with the Icarus economic analyzer, estimated there should be 5 operators per 8 hour shift with a cost per operator of $20 per hour. This results in a total operating labor cost of approximately $880,000 per year. In addition, the process will require one supervisor per shift with an hourly rate of $35 for total supervisor salaries of $307,000 per year. Finally, a fixed maintenance rate was estimated at $205,000 per 8000 hours of operation for a total cost of $225,000 per year.

Total product sales are roughly $640 million per year at full operation. The estimated income for this process is thus approximately $175 million per year. After ten years, the plant is projected to have a net present value (NPV) of $391 million and an internal rate of return of approximately 79%. In addition the payout period for the initial investment is estimated to be about 2.7 years. Figure 2 shows the projected cash flow for the project.

==Sensitivity Analysis==
A sensitivity analysis was performed to investigate the effects of fluctuating capital costs, operating costs, raw materials, utility costs and ethylene sales price on the 10-year net present value (NPV) of the project. This analysis was performed by scaling these cost factors according to typical ranges given in Towler and Sinnott and calculating the adjusting the NPV accordingly. The results, illustrated in Figure 3, indicate that the project value is most sensitive to product sales, raw materials costs, and operating costs. Ethylene and ethanol prices are market-determined and cannot be controlled for in the process design, so further optimization should be focused on minimizing the operations cost of the process. (Today in Energy, 2015; Weddle, 2014) However, in feed and product prices do still have a profound effect on profitability and feasibility. A more rigorous market analysis will better inform the profitability outlook.

=Conclusions/Recommendations=

The proposed process produces approximately 460,000 metric tons of 99.7 wt% ethylene annually, with a 10-year net present value of $131 million. If current economic conditions hold, it is recommended that this project proceed to implementation following further design improvements and optimization.

Future design iterations should focus on process optimization, particularly in minimizing operating costs as prescribed by the results of the sensitivity analysis. The development of a heat-exchanger network, potentially with Aspen Energy Analyzer, is one option for decreasing utility requirements and increasing the efficiency of the process overall. Optimization of the fired heaters could also result in decreased operational costs. Although overall profitability is less sensitive to capital costs, reviewing and adjusting equipment sizing would also improve the economic outlook. In particular, exploring alternative heating strategies at the beginning of the process could significantly decrease capital costs. Although there are not any particularly dangerous chemicals utilized in the process, an overall process review should also consider potential failure modes to minimize the safety risk to plant workers and nearby residents.

In addition to economic and safety considerations, harmful emissions and waste streams should be minimized both to bring down the cost of treatment and to decrease environmental effects. The two fired heaters consume a large amount of natural gas per year, emitting about 200,000 tons of CO2 annually, and account for more than half of the capital cost of the process. Although no known toxic gases are produced, carbon capture or other emissions-reduction methods should be considered. Additionally, enough wastewater is produced by this process that building an onsite wastewater treatment center should be considered. This could not only decrease operating costs by eliminating the need for an external contract but also give the plant more control over the final purity of the treated wastewater.

Finally, the current model assumes that all ethylene produced will be sold at a current prices and price or product sales will not be affected by economic variability. A more detailed study of the chemical-grade ethylene market, as well as a more thorough understanding of sales and distribution logistics, would increase the surety of a profitable process.

In summary, the proposed process yields chemical grade ethylene via the catalytic dehydration of ethanol. A 100,000 kg/hr of 95 wt% ethanol, 5% water feed is converted to 53,000 kg/hr of 99.7% chemical-grade ethylene. After 10 years of operation, including a one-year startup time, the process has an NPV of $391 million with an IRR of 79% and a payback period of 2.7 years.
Pending further optimization, this process was determined to be viable and it is recommended for the project to move forward.

=References=

[1] American Chemistry Council. Production of chemicals and plastics in the U.S. in 2013, by type (in 1,000 metric tons). In Statista - The Statistics Portal. August 2014. Available at http://www.statista.com/statistics/299725/total-us-plastics-and-chemicals-shipments-by-type/, Accessed January 15, 2015. – Relative proportions of plastics production.

[2] DuPont Nevada Site Cellulosic Ethanol Facility [Internet]. DuPont Chemical; c2012-2015 [cited 11 Mar. 2015]. Available from: http://biofuels.dupont.com/cellulosic-ethanol/nevada-site-ce-facility/. -- Information on ethanol production in Iowa.

[3] Designing Ethylene Plants. Ethylene [Internet]. Technip; 2014 [cited 13 Mar. 2015]. Available from: http://www.technip.com/en/our-business/onshore/ethylene -- Plant size ranges.

[4] Suppes GJ. Selecting Thermodynamic Models for Process Simulation of Organic VLE and LLE Systems. The University of Missouri-Columbia, Dept of Chemical Engineering. [cited 13 Mar. 2015]. -- Use of NRTL in alcohol separations.

[5] ASPENtech. Appendix A - Property Methods and Calculations. Simulation Basics; A-3 - A-26. 2014.

[6] 190 Proof Ethanol: Technical Data Sheet [Internet]. Decon Labs Inc; 2012 [cited 13 Mar. 2015]. Available from: http://www.deconlabs.com/tds/ETHANOL%20190%20%20PROOF.pdf -- Information regarding 95% ethanol

[7] Hadawey A, Ge Y, Tassou TSA. Energy Savings Through Liquid Pressure Amplification In A Dairy Plant Refrigeration System. The Centre for Energy and Built Environment Research [cited 13 Mar. 2015].

[8] Methane (Chemical Compound). 2015. Encyclopædia Britannica Online. [cited 13 Mar. 2015] Available from: http://www.britannica.com/EBchecked/topic/378264/methane -- Composition of Methane

[9] Composition of Air [Internet]. Engineering Toolbox; [cited 13 Mar. 2015]. Available from: http://www.engineeringtoolbox.com/air-composition-d_212.html. -- Composition of air.

[10] Summary of the Clean Air Act, 2015. United States Environmental Protection Agency. [cited 13 Mar. 2015] Available from: http://www2.epa.gov/laws-regulations/summary-clean-air-act -- Emissions requirements of chemical plants.

[11] Zhang M, Yu Y. Dehydration of Ethanol to Ethylene. Industrial Engineering and Chemical Research. 2013; 52:9505-9514. – Technical information on ethanol to ethylene conversion via dehydration.

[12] AspenTech. Aspen HYSYS Help File v8.0. Aspen Technology, Inc. 2012. - Aspen HYSYS help file used for troubleshooting and assistance on economic analysis.

[13] Towler G, Sinnott R. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. 2nd ed. Boston: Elsevier; 2013. -- General Reference Book

[14] Barrocas H, Baratelli F, inventors; Petroleo Brasileiro S.A., assignee. Process for dehydration of a low molecular weight alcohol. US patent 4,396,789 A. August 2, 1983. - Primary background for process design.

[15] Tsao U, Zasloff HB, inventors; The Lummus Company, assignee. Production of ethylene from ethanol. US patent 4,134,926. January 16, 1979. – Patent for catalytic dehydration of ethylene in a fluidized bed reactor.

[16] Morschbacker, A. Bio-Ethanol Based Ethylene. Polymer Reviews. 2009; 49:79-84. – Overview of bioethanol dehydration process development.

[17] Fan D, Dai DJ, Wu HS. Ethylene Formation by Catalytic Dehydration of Ethanol with Industrial Considerations. Materials. 6, 101-115. doi: 10.3390/ma6010101. - Comparison of types of catalysts used in the dehydration of ethanol and current research into new catalysts.

[18] Chen G, Li S, Jiao F, Yuan Q. Catalytic dehydration of bioethanol to ethylene over TiO2/γ-Al2O3 catalysts in microchannel reactors. Catal. Today 2007, 125, 111–119. - Paper introducing research on modified alumina catalyst for ethanol dehydration.

[19] Jumonville, J. Tutorial on Cryogenic Turboexpanders. Proceedings of the Thirty-Ninth Turbomachinery Symposium; 2010 Oct 4-7; Houston, TX. Houston: Texas A&M University; 2010. -- Use of turboexpander for cryogenic separations

[20] Today in Energy - Daily Prices. US Energy Information Administration website. http://www.eia.gov/todayinenergy/prices.cfm. Accessed March 3rd 2015. - Bulk market price for 95% ethanol.

[21] Weddle, N. ICIS Pricing: Ethylene (Europe). Reed Business Limited. January 10 2014. - Bulk market price for chemical grade ethylene.

=Appendix I - Process Flow Diagram=
[[File:PFD B1.JPG|1300px|center]]

=Appendix II - HYSYS Simulation=
[[File:HYSYS_B1.PNG]]

=Appendix III - Material Streams=
[[File:Streams_B1.png|1200px]]

=Appendix IV - Energy Table=
[[File:Energy_B1.png|600px|center]]

=Appendix V - Economics=
[[File:Econsummary_B1.png|center]] 

[[File:Capcost_B1.png|center]] 

[[File:sensitivityanalysis_B1.png|600px|center]]

Ethanol to Ethylene (B1)

2015-03-14T04:22:03Z

Hpoppick: /* Appendix I - Process Flow Diagram */

[[File:BFD_B1.png|600px|thumbnail|alt=Alt text|Conversion of Ethanol to Ethylene]]

Team B1 Final Report

Authors: Harry Poppick, Emm Fulk and Scott Smith

Instructors: Fengqi You, David Wegerer

March 13, 2015

=Executive Summary=

The following report outlines the design and analysis of a process converting ethanol to chemical-grade ethylene via catalytic dehydration. This process consumers 100,000 kg/hr of 95 wt% ethanol, 5 wt% water feedstock and produces 53,000 kg/hr of 99.7 wt% chemical-grade ethylene. The ethanol feed passes through two fixed-bed reactors, each packed with an aluminum oxide catalyst, and the resulting ethylene is purified by two flash tanks and by absorption with water. The process was modeled using Aspen HYSYS simulation software to estimate mass and energy flows and equipment sizing requirements. Based on results of this initial simulation, several alternatives are discussed for increasing the process efficiency and profitability. The use of a fluidized bed reactor or a more ethylene-selective catalyst could increase the production of ethylene per ethanol basis. Additionally, several methods of purification to more valuable polymer-grade ethylene are proposed.

The economic feasibility of this process was evaluated using Aspen Economic Analyzer with the Icarus economics package. Capital cost is approximately $16.4 million total with an operating cost of $465 million per year. The current market prices of the ethanol feed and ethylene sales price are $1.44/gallon and $1350/metric ton respectively. The cost of feed ethanol, process utilities and miscellaneous operational costs total to about $427 million/year. At full operation, revenue at current prices would be approximately $640 million per year. The predicted 10-year net present value of the process is approximately $391 million with an IRR of 79% and a payback period of 2.7 years. A sensitivity analysis indicates that the process is most sensitive to feed prices, product prices and operation cost.

Several recommendations are made for both cost reduction and profit maximization, including the design of a heat exchanger network and the optimization of fired heaters that require high capital investment and large amounts of fuel. A safety review of the process is recommended, as well as the minimization of flue gas effluent and wastewater. It is also suggested that the construction of an onsite wastewater treatment center be considered. Overall, the initial analysis indicates this to be a profitable process and it is recommended the project move forward.

=Introduction=

Ethylene is a critical chemical precursor to a number of different industrial products. It is often derived from petroleum sources and polymerized to polyethylene, one of the most ubiquitous plastics today. (American Chemistry Council, 2013) Recently there has been a significant effort to develop production pathways utilizing biologically-derived feedstocks, such as corn or cellulosic ethanol, rather than traditional fossil-fuel sources. Ethylene can be produced from bioethanol via catalytic dehydration over an aluminum oxide catalyst. The proposed process converts 100,000 kg/hr of 95 wt% ethanol, 5% water feed to 53,000 kg/hr of 99.7% chemical-grade ethylene when operating at full capacity. This process was found to be economically viable with a 10-year net present value (NPV) of $131 million (2014 USD) and a payback period of approximately 2.7 years. This memo will detail the proposed process, as well as outline potential alternatives and economic viability of the project.

=Technical Approach=

Many bioethanol plants are located in the Midwest where large amounts of feedstock crops, such as corn, are grown. As such, this plant will be located in Story county, Iowa, near a large-scale bioethanol production plant. (DuPont Nevada Site, 2012) It is assumed that the supply of bioethanol is consistent and readily available. It is also assumed that other reagents - namely, the aluminum oxide catalyst, heater fuel, utility water and freon refrigerant - are readily available, and that wastewater treatment facilities are located near enough to facilitate the off-site treatment of wastewater. Plant capacity was based on current mid-sized industrial ethylene plants. (Designing Ethylene Plants, 2014)

HYSYS simulations were performed with the NRTL fluid package and Peng-Robinson vapor model. The NRTL fluid package is an activity coefficient model that is especially useful to model the separations of alcohols in aqueous solutions. (Suppes, 2015) In addition, NRTL uses models of binary pairs of components, much like the Wilson equation, to predict chemical interactions at the molecular level. The NRTL package can thus be easily extended to ternary and higher order chemical systems, making it ideal for this type of simulation. The Peng-Robinson vapor model was selected as it is well-suited to account for the non-idealities of the vapor phase reactions and separations integral to this process. (ASPENtech, 2014)

It was assumed that the feed enters the process at ambient temperature and pressure (25 °C, 1 atm) and at a consistent rate and composition with negligible quantities of impurities. The ethanol feed was assumed to be 95% ethanol and 5% water by mass, which is the commercial standard for industrial ethanol. (190 Proof Ethanol, 2012) Storage vessels for the feed ethanol, waste streams and products are assumed to be located nearby to the process. An initial feed pump compensates for pressure drops through the process and reduces the duty on downstream compressors. (Hadawey, 2015)

Natural gas, assumed to consist of 83% methane, 16% ethane and 1% nitrogen by mass, was supplied to two fired heaters at a flow rate estimated by HYSYS. (Methane, 2015) Air fed to the process to enable combustion was assumed to be 23% oxygen and 77% nitrogen by mass. (Composition of Air, 2015) Air streams were fed at 50% molar excess in order to ensure complete combustion and prevent the formation of carbon monoxide in the heater exhaust. Total flue gases are assumed to be 230,000 kg/hr, or 2.2 million tons annually, and consist of 73.8% nitrogen gas, 10.5% carbon dioxide, 8.2% water vapor, and 7.5% oxygen by mass. The only compound of concern in these emissions is the carbon dioxide, a known greenhouse gas. At the time of this report, the quantities of carbon dioxide emitted by this plant annually are within acceptable EPA specifications. (Summary of the Clean Air Act, 2015)

Due to the difficulty of simulation equilibrium and conversion reactions in a single vessel in HYSYS, these two reaction types were simulated in separate equilibrium reactor and conversion reactor units in series. In addition, while HYSYS indicated that reactor units would output separate vapor and liquid streams, it was assumed that in practice this would take the form of a single, two phase stream between each unit. To account for this, mixers were installed downstream of each reactor to combine the liquid and vapor phases of the reactor effluent. The three consequent reactions considered are as follows:

Ethanol ↔ Ethylene + Water
Ethanol → Acetaldehyde + Hydrogen
2 Ethanol → Diethyl Ether + Water

The optimal reaction temperature was determined to be 400 °C, which promotes the equilibrium reaction of ethanol to ethylene while minimizing byproducts. (Zhang and Yu, 2013) While other byproducts may be produced in this process, these reactions are typically taken to comprise of the bulk of the dehydration reaction. Heat losses over these reactors were assumed to be negligible. (Zhang and Yu, 2013)All major process equipment is assumed to be constructed of high strength carbon steel. (AspenTech, 2012)

The “Sizing Utility” within the Icarus Economic Evaluation module was used to estimate sizes of major equipment based on the process simulation. These values can serve as a benchmark for an initial plant design. Icarus KbaseTM implements a wide variety of mechanical design standards, including ASME and BS5500, in order to calculate accurate equipment sizing. The Icarus sizing module combines equipment prices for standard chemical processing equipment as well as correlations and sizing factors. The advantage of using a software package such as HYSYS to price out individual equipment is that it utilizes up-to-date prices from vendors and distributors when estimating costs. A more in-depth overview of the correlations included in this software can be found in Towler and Sinnott (2009).

=Process Flowsheet=
[[File:Squarepfd_B1.PNG|thumb|400px]]

The following process is based primarily on a 1983 US patent titled “Process for dehydration of a low molecular weight alcohol.” (Barrocas and Baratelli, 1983) The process flow diagram can be seen in Figure 1. A larger version of the PFD is included in Appendix I and the HYSYS simulation setup in Appendix II.

The feed enters the process at a rate of 100,000 kg/hr, a temperature and pressure of a 25 °C and 1 atm and at a composition of 95 wt% ethanol and 5 wt% water.It is initially pressurized to 4335 kPa by centrifugal pump P-101 and subsequently heated to 400 °C by fired heater F-101. The heated and pressurized feed enters fixed bed reactor R-101 and contacts with the aluminum oxide catalyst. At this point it dehydrates to form the product, ethylene, as well as the byproducts water, hydrogen, diethyl ether and acetaldehyde. Fired heater F-102 and reactor R-102 increase the overall conversion of the process. Both fired heaters F-101 and F-102 are fueled with natural gas and fed with excess air. The composition of the reactor train effluent is 54.5 wt% ethylene, 37.1 wt% water, 8.1 wt% unreacted ethanol and trace amounts of diethyl ether, acetaldehyde, and hydrogen contaminants.

The pressure of the reactor train effluent is increased to 4500 kPa by compressor K-102 and the temperature decreased to 100 °C by exchange with cold water in heat exchanger E-201. The stream then expands and flashes in flash vessel FL-201, which separates out 82.3% of the unreacted ethanol, 96.6% of the water and virtually all of the acetaldehyde contaminant in the bottoms while sending the ethylene-rich vapor phase out of the top. The top product of FL-202 is compressed to 3500 kPA by K-202 and cooled to 0.0 °C by a freon refrigerant in E-202. At this point the stream is flashed for a second time in vessel FL-202 to remove additional impurities. The top outlet stream consists of 99.5 wt% ethylene, which is fed to the bottom of a 10-tray absorption column that removes a fraction of the residual diethyl ether as well as the remainder of the unreacted ethanol. A stream of absorbent water is fed to the top of the column at 10,000 kg/hr. The product exits the top of the column at a rate of 54,600 kg/hr and has a purity of 99.7% ethylene. Diethyl ether makes up 0.2% of the remaining product stream and is the primary contaminant. Trace amounts of residual water and hydrogen are also present.

Full tables of material and energy streams can be found in Appendices III and IV respectively.

==Process Alternatives==
===Reactor Alternatives===
Two fixed bed reactors, alternating with fired heaters, are used in the dehydration reaction of ethanol to ethylene. However, a fluidized bed reactor can offer better mixing and temperature control than a fixed bed reactor and thus provide the highest possible conversion of ethanol with the greatest selectivity to ethylene. (Tsao and Zasloff, 1979) Fluidized bed reactors also provide a lower rate of catalyst coking and byproduct formation, minimizing separation and catalyst regeneration costs. (Morschbacker, 2009) The major downside of fluidized bed reactors is that few large-scale processes have been built since the technology was developed in the late 1970s. (Tsao and Zasloff, 1979; Morschbacker, 2009) Although implementation of fluidized bed reactors could potentially increase the purity of the ethylene product and/or decrease costs, a small scale pilot process would need to be built and tested before it would be possible to develop an industrial-scale facility.

===Catalyst Alternatives===
Aluminum oxide, specifically gamma alumina, is the most industrially-common catalyst and has been historically used due to its low cost and high stability. (Tsao and Zasloff, 1979; Fan and Dai, n.d.) Recent improvements in selectivity and catalyst stability of activated alumina have been achieved by incorporating titanium oxide into the catalyst, although this increases reaction temperature by approximately 50 °C and decreases catalyst lifespan. (Chen and Li, et. al. 2007) There is also significant ongoing research into HZSM-5 zeolite and heteropolyacids, which are being explored as potential alternatives to alumina oxide. A nanoscale HZSM-5 zeolite catalyst has been shown to operate at the relatively low temperature of 200-300°C, with a 100% ethanol conversion and 99.7% selectivity to ethylene. Initial research has also indicated that it maintains greater than 98% selectivity for 630 operational hours. (Fan and Dai, n.d.) However, the current low cost and ready availability of unmodified alumina oxide makes it a better choice for a process of this scale.

===Purification Alternatives===
As specified in this process, the reactor effluent is purified by two flash drums and absorption with water to produce chemical-grade ethylene. If chemical-grade ethylene is indeed the desired product, other purification options include caustic washing of the reactor effluent and water removal in a desiccant drying bed. (Morschbacker, 2009) While this purification train is relatively simple and does not require harsh chemical reagents, polymer grade ethylene is more commercially valuable and the additional cost of removing water and diethyl ether contaminants may be justified by increased revenue. Cryogenic distillation was initially simulated to produce polymer-grade ethylene, but utility requirements were found to render this separation economically unviable. (Barrocas and Baratelli, 1983) Further research and optimization may find this purification strategy to be a more valid process. Alternatively, the addition of a cryogenic turboexpander or the use of alternative adsorbents may increase product purity to polymer grade. (Jumonville, 2010) Initial HYSYS simulations indicate that these operations may be feasible with further refinement.

===Wastewater Treatment===
Due to the large volume of wastewater produced, building an on-site wastewater treatment facility may prove to be more economical than paying for third-party wastewater treatment. Flash vessel FL-201 produces 44,600 L/hr of wastewater contaminated with 18.7 vol% ethanol and 0.6 vol% acetaldehyde, while FL-202 produces 2940 L/hr of an aqueous waste consisting of 56.8 vol% ethanol, 42.0 vol% water and 0.9 vol% diethyl ether. The absorption column produces approximately 10,200 liters/hr of wastewater contaminated with 1.2 vol% ethanol, 0.2% diethyl ether and 0.2% acetaldehyde. Utilizing distillation to separate these streams into clean water and volatile organic waste could ultimately reduce the quantity of waste that requires disposal and reduce the overall costs of the process.

==Process Equipment==
Relevant sizing information for each unit operation, estimated by the method described in the “Technical Approach,” can be found in Appendix V. Equipment and piping is assumed to be constructed of carbon steel. It should be noted that the two fired heaters are proportionately large enough to heat the entirety of the process stream and are thus larger than standard equipment.

=Economic Analysis=
[[File:NPV_B1.png|400px|thumb]]
[[File:sensitivityanalysis_B1.png|400px|thumb]]

==Economics Overview==
All final values are normalized to June 2014 USD by CEPCI scaling. It is assumed that all products produced are sold at current market prices.

The Aspen Economic Evaluation module within HYSYS v8.0 was used to estimate capital and operating costs for a 10-year plant life span with a construction start date of April 2015. The price of the 95% ethanol feed stream was estimated at $1.44 per gallon, while the chemical grade ethylene produced is currently selling for approximately $1350 per metric ton. (Today in Energy, 2015; Weddle, 2014) Mapping and sizing calculations were performed by the economics module and a preliminary economic evaluation was completed. Equipment sizes, also estimated by HYSYS, were reviewed to ensure that height, diameter, and volume specifications were within realistic ranges.

The process was ideally projected to operate 360 days per year with a start-up time of one year. In addition, the tax rate was approximated at 40%, an interest rate at 20%, and a salvage value of 20%. Escalation percentages were compounded yearly for the product, raw material, and operating costs. The total capital cost for this process is approximately $16.4 million, which includes all equipment and piping described in the process. The most expensive equipment used in this process are the two fired heaters F-101 and F-102, which have an exceptionally large heat exchange area to adequately heat the feed. Standard heaters may not suffice and additional costs may be incurred for the raw materials and manufacture of this equipment. Including a feed preheater or additional fired heaters may reduce this cost in subsequent design iterations.

The total operating cost is approximately $465 million per year, about $427 million of which is the cost of the ethanol feed and natural gas for the two fired heaters. An additional $1.73 million per year is used for utilities including the cooling water and refrigerant. The labor and maintenance costs of this industrial process were also accounted for within the simulation’s economic analysis. The HYSYS simulation software, in conjunction with the Icarus economic analyzer, estimated there should be 5 operators per 8 hour shift with a cost per operator of $20 per hour. This results in a total operating labor cost of approximately $880,000 per year. In addition, the process will require one supervisor per shift with an hourly rate of $35 for total supervisor salaries of $307,000 per year. Finally, a fixed maintenance rate was estimated at $205,000 per 8000 hours of operation for a total cost of $225,000 per year.

Total product sales are roughly $640 million per year at full operation. The estimated income for this process is thus approximately $175 million per year. After ten years, the plant is projected to have a net present value (NPV) of $391 million and an internal rate of return of approximately 79%. In addition the payout period for the initial investment is estimated to be about 2.7 years. Figure 2 shows the projected cash flow for the project.

==Sensitivity Analysis==
A sensitivity analysis was performed to investigate the effects of fluctuating capital costs, operating costs, raw materials, utility costs and ethylene sales price on the 10-year net present value (NPV) of the project. This analysis was performed by scaling these cost factors according to typical ranges given in Towler and Sinnott and calculating the adjusting the NPV accordingly. The results, illustrated in Figure 3, indicate that the project value is most sensitive to product sales, raw materials costs, and operating costs. Ethylene and ethanol prices are market-determined and cannot be controlled for in the process design, so further optimization should be focused on minimizing the operations cost of the process. (Today in Energy, 2015; Weddle, 2014) However, in feed and product prices do still have a profound effect on profitability and feasibility. A more rigorous market analysis will better inform the profitability outlook.

=Conclusions/Recommendations=

The proposed process produces approximately 460,000 metric tons of 99.7 wt% ethylene annually, with a 10-year net present value of $131 million. If current economic conditions hold, it is recommended that this project proceed to implementation following further design improvements and optimization.

Future design iterations should focus on process optimization, particularly in minimizing operating costs as prescribed by the results of the sensitivity analysis. The development of a heat-exchanger network, potentially with Aspen Energy Analyzer, is one option for decreasing utility requirements and increasing the efficiency of the process overall. Optimization of the fired heaters could also result in decreased operational costs. Although overall profitability is less sensitive to capital costs, reviewing and adjusting equipment sizing would also improve the economic outlook. In particular, exploring alternative heating strategies at the beginning of the process could significantly decrease capital costs. Although there are not any particularly dangerous chemicals utilized in the process, an overall process review should also consider potential failure modes to minimize the safety risk to plant workers and nearby residents.

In addition to economic and safety considerations, harmful emissions and waste streams should be minimized both to bring down the cost of treatment and to decrease environmental effects. The two fired heaters consume a large amount of natural gas per year, emitting about 200,000 tons of CO2 annually, and account for more than half of the capital cost of the process. Although no known toxic gases are produced, carbon capture or other emissions-reduction methods should be considered. Additionally, enough wastewater is produced by this process that building an onsite wastewater treatment center should be considered. This could not only decrease operating costs by eliminating the need for an external contract but also give the plant more control over the final purity of the treated wastewater.

Finally, the current model assumes that all ethylene produced will be sold at a current prices and price or product sales will not be affected by economic variability. A more detailed study of the chemical-grade ethylene market, as well as a more thorough understanding of sales and distribution logistics, would increase the surety of a profitable process.

In summary, the proposed process yields chemical grade ethylene via the catalytic dehydration of ethanol. A 100,000 kg/hr of 95 wt% ethanol, 5% water feed is converted to 53,000 kg/hr of 99.7% chemical-grade ethylene. After 10 years of operation, including a one-year startup time, the process has an NPV of $391 million with an IRR of 79% and a payback period of 2.7 years.
Pending further optimization, this process was determined to be viable and it is recommended for the project to move forward.

=References=

[1] American Chemistry Council. Production of chemicals and plastics in the U.S. in 2013, by type (in 1,000 metric tons). In Statista - The Statistics Portal. August 2014. Available at http://www.statista.com/statistics/299725/total-us-plastics-and-chemicals-shipments-by-type/, Accessed January 15, 2015. – Relative proportions of plastics production.

[2] DuPont Nevada Site Cellulosic Ethanol Facility [Internet]. DuPont Chemical; c2012-2015 [cited 11 Mar. 2015]. Available from: http://biofuels.dupont.com/cellulosic-ethanol/nevada-site-ce-facility/. -- Information on ethanol production in Iowa.

[3] Designing Ethylene Plants. Ethylene [Internet]. Technip; 2014 [cited 13 Mar. 2015]. Available from: http://www.technip.com/en/our-business/onshore/ethylene -- Plant size ranges.

[4] Suppes GJ. Selecting Thermodynamic Models for Process Simulation of Organic VLE and LLE Systems. The University of Missouri-Columbia, Dept of Chemical Engineering. [cited 13 Mar. 2015]. -- Use of NRTL in alcohol separations.

[5] ASPENtech. Appendix A - Property Methods and Calculations. Simulation Basics; A-3 - A-26. 2014.

[6] 190 Proof Ethanol: Technical Data Sheet [Internet]. Decon Labs Inc; 2012 [cited 13 Mar. 2015]. Available from: http://www.deconlabs.com/tds/ETHANOL%20190%20%20PROOF.pdf -- Information regarding 95% ethanol

[7] Hadawey A, Ge Y, Tassou TSA. Energy Savings Through Liquid Pressure Amplification In A Dairy Plant Refrigeration System. The Centre for Energy and Built Environment Research [cited 13 Mar. 2015].

[8] Methane (Chemical Compound). 2015. Encyclopædia Britannica Online. [cited 13 Mar. 2015] Available from: http://www.britannica.com/EBchecked/topic/378264/methane -- Composition of Methane

[9] Composition of Air [Internet]. Engineering Toolbox; [cited 13 Mar. 2015]. Available from: http://www.engineeringtoolbox.com/air-composition-d_212.html. -- Composition of air.

[10] Summary of the Clean Air Act, 2015. United States Environmental Protection Agency. [cited 13 Mar. 2015] Available from: http://www2.epa.gov/laws-regulations/summary-clean-air-act -- Emissions requirements of chemical plants.

[11] Zhang M, Yu Y. Dehydration of Ethanol to Ethylene. Industrial Engineering and Chemical Research. 2013; 52:9505-9514. – Technical information on ethanol to ethylene conversion via dehydration.

[12] AspenTech. Aspen HYSYS Help File v8.0. Aspen Technology, Inc. 2012. - Aspen HYSYS help file used for troubleshooting and assistance on economic analysis.

[13] Towler G, Sinnott R. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. 2nd ed. Boston: Elsevier; 2013. -- General Reference Book

[14] Barrocas H, Baratelli F, inventors; Petroleo Brasileiro S.A., assignee. Process for dehydration of a low molecular weight alcohol. US patent 4,396,789 A. August 2, 1983. - Primary background for process design.

[15] Tsao U, Zasloff HB, inventors; The Lummus Company, assignee. Production of ethylene from ethanol. US patent 4,134,926. January 16, 1979. – Patent for catalytic dehydration of ethylene in a fluidized bed reactor.

[16] Morschbacker, A. Bio-Ethanol Based Ethylene. Polymer Reviews. 2009; 49:79-84. – Overview of bioethanol dehydration process development.

[17] Fan D, Dai DJ, Wu HS. Ethylene Formation by Catalytic Dehydration of Ethanol with Industrial Considerations. Materials. 6, 101-115. doi: 10.3390/ma6010101. - Comparison of types of catalysts used in the dehydration of ethanol and current research into new catalysts.

[18] Chen G, Li S, Jiao F, Yuan Q. Catalytic dehydration of bioethanol to ethylene over TiO2/γ-Al2O3 catalysts in microchannel reactors. Catal. Today 2007, 125, 111–119. - Paper introducing research on modified alumina catalyst for ethanol dehydration.

[19] Jumonville, J. Tutorial on Cryogenic Turboexpanders. Proceedings of the Thirty-Ninth Turbomachinery Symposium; 2010 Oct 4-7; Houston, TX. Houston: Texas A&M University; 2010. -- Use of turboexpander for cryogenic separations

[20] Today in Energy - Daily Prices. US Energy Information Administration website. http://www.eia.gov/todayinenergy/prices.cfm. Accessed March 3rd 2015. - Bulk market price for 95% ethanol.

[21] Weddle, N. ICIS Pricing: Ethylene (Europe). Reed Business Limited. January 10 2014. - Bulk market price for chemical grade ethylene.

=Appendix I - Process Flow Diagram=
[[File:PFD B1.JPG|1300px]]

=Appendix II - HYSYS Simulation=
[[File:HYSYS_B1.PNG]]

=Appendix III - Material Streams=
[[File:Streams_B1.png|1200px]]

=Appendix IV - Energy Table=
[[File:Energy_B1.png|600px|center]]

=Appendix V - Economics=
[[File:Econsummary_B1.png|center]] 

[[File:Capcost_B1.png|center]] 

[[File:sensitivityanalysis_B1.png|600px|center]]

Ethanol to Ethylene (B1)

2015-03-14T04:21:43Z

Hpoppick: /* Appendix I - Process Flow Diagram */

[[File:BFD_B1.png|600px|thumbnail|alt=Alt text|Conversion of Ethanol to Ethylene]]

Team B1 Final Report

Authors: Harry Poppick, Emm Fulk and Scott Smith

Instructors: Fengqi You, David Wegerer

March 13, 2015

=Executive Summary=

The following report outlines the design and analysis of a process converting ethanol to chemical-grade ethylene via catalytic dehydration. This process consumers 100,000 kg/hr of 95 wt% ethanol, 5 wt% water feedstock and produces 53,000 kg/hr of 99.7 wt% chemical-grade ethylene. The ethanol feed passes through two fixed-bed reactors, each packed with an aluminum oxide catalyst, and the resulting ethylene is purified by two flash tanks and by absorption with water. The process was modeled using Aspen HYSYS simulation software to estimate mass and energy flows and equipment sizing requirements. Based on results of this initial simulation, several alternatives are discussed for increasing the process efficiency and profitability. The use of a fluidized bed reactor or a more ethylene-selective catalyst could increase the production of ethylene per ethanol basis. Additionally, several methods of purification to more valuable polymer-grade ethylene are proposed.

The economic feasibility of this process was evaluated using Aspen Economic Analyzer with the Icarus economics package. Capital cost is approximately $16.4 million total with an operating cost of $465 million per year. The current market prices of the ethanol feed and ethylene sales price are $1.44/gallon and $1350/metric ton respectively. The cost of feed ethanol, process utilities and miscellaneous operational costs total to about $427 million/year. At full operation, revenue at current prices would be approximately $640 million per year. The predicted 10-year net present value of the process is approximately $391 million with an IRR of 79% and a payback period of 2.7 years. A sensitivity analysis indicates that the process is most sensitive to feed prices, product prices and operation cost.

Several recommendations are made for both cost reduction and profit maximization, including the design of a heat exchanger network and the optimization of fired heaters that require high capital investment and large amounts of fuel. A safety review of the process is recommended, as well as the minimization of flue gas effluent and wastewater. It is also suggested that the construction of an onsite wastewater treatment center be considered. Overall, the initial analysis indicates this to be a profitable process and it is recommended the project move forward.

=Introduction=

Ethylene is a critical chemical precursor to a number of different industrial products. It is often derived from petroleum sources and polymerized to polyethylene, one of the most ubiquitous plastics today. (American Chemistry Council, 2013) Recently there has been a significant effort to develop production pathways utilizing biologically-derived feedstocks, such as corn or cellulosic ethanol, rather than traditional fossil-fuel sources. Ethylene can be produced from bioethanol via catalytic dehydration over an aluminum oxide catalyst. The proposed process converts 100,000 kg/hr of 95 wt% ethanol, 5% water feed to 53,000 kg/hr of 99.7% chemical-grade ethylene when operating at full capacity. This process was found to be economically viable with a 10-year net present value (NPV) of $131 million (2014 USD) and a payback period of approximately 2.7 years. This memo will detail the proposed process, as well as outline potential alternatives and economic viability of the project.

=Technical Approach=

Many bioethanol plants are located in the Midwest where large amounts of feedstock crops, such as corn, are grown. As such, this plant will be located in Story county, Iowa, near a large-scale bioethanol production plant. (DuPont Nevada Site, 2012) It is assumed that the supply of bioethanol is consistent and readily available. It is also assumed that other reagents - namely, the aluminum oxide catalyst, heater fuel, utility water and freon refrigerant - are readily available, and that wastewater treatment facilities are located near enough to facilitate the off-site treatment of wastewater. Plant capacity was based on current mid-sized industrial ethylene plants. (Designing Ethylene Plants, 2014)

HYSYS simulations were performed with the NRTL fluid package and Peng-Robinson vapor model. The NRTL fluid package is an activity coefficient model that is especially useful to model the separations of alcohols in aqueous solutions. (Suppes, 2015) In addition, NRTL uses models of binary pairs of components, much like the Wilson equation, to predict chemical interactions at the molecular level. The NRTL package can thus be easily extended to ternary and higher order chemical systems, making it ideal for this type of simulation. The Peng-Robinson vapor model was selected as it is well-suited to account for the non-idealities of the vapor phase reactions and separations integral to this process. (ASPENtech, 2014)

It was assumed that the feed enters the process at ambient temperature and pressure (25 °C, 1 atm) and at a consistent rate and composition with negligible quantities of impurities. The ethanol feed was assumed to be 95% ethanol and 5% water by mass, which is the commercial standard for industrial ethanol. (190 Proof Ethanol, 2012) Storage vessels for the feed ethanol, waste streams and products are assumed to be located nearby to the process. An initial feed pump compensates for pressure drops through the process and reduces the duty on downstream compressors. (Hadawey, 2015)

Natural gas, assumed to consist of 83% methane, 16% ethane and 1% nitrogen by mass, was supplied to two fired heaters at a flow rate estimated by HYSYS. (Methane, 2015) Air fed to the process to enable combustion was assumed to be 23% oxygen and 77% nitrogen by mass. (Composition of Air, 2015) Air streams were fed at 50% molar excess in order to ensure complete combustion and prevent the formation of carbon monoxide in the heater exhaust. Total flue gases are assumed to be 230,000 kg/hr, or 2.2 million tons annually, and consist of 73.8% nitrogen gas, 10.5% carbon dioxide, 8.2% water vapor, and 7.5% oxygen by mass. The only compound of concern in these emissions is the carbon dioxide, a known greenhouse gas. At the time of this report, the quantities of carbon dioxide emitted by this plant annually are within acceptable EPA specifications. (Summary of the Clean Air Act, 2015)

Due to the difficulty of simulation equilibrium and conversion reactions in a single vessel in HYSYS, these two reaction types were simulated in separate equilibrium reactor and conversion reactor units in series. In addition, while HYSYS indicated that reactor units would output separate vapor and liquid streams, it was assumed that in practice this would take the form of a single, two phase stream between each unit. To account for this, mixers were installed downstream of each reactor to combine the liquid and vapor phases of the reactor effluent. The three consequent reactions considered are as follows:

Ethanol ↔ Ethylene + Water
Ethanol → Acetaldehyde + Hydrogen
2 Ethanol → Diethyl Ether + Water

The optimal reaction temperature was determined to be 400 °C, which promotes the equilibrium reaction of ethanol to ethylene while minimizing byproducts. (Zhang and Yu, 2013) While other byproducts may be produced in this process, these reactions are typically taken to comprise of the bulk of the dehydration reaction. Heat losses over these reactors were assumed to be negligible. (Zhang and Yu, 2013)All major process equipment is assumed to be constructed of high strength carbon steel. (AspenTech, 2012)

The “Sizing Utility” within the Icarus Economic Evaluation module was used to estimate sizes of major equipment based on the process simulation. These values can serve as a benchmark for an initial plant design. Icarus KbaseTM implements a wide variety of mechanical design standards, including ASME and BS5500, in order to calculate accurate equipment sizing. The Icarus sizing module combines equipment prices for standard chemical processing equipment as well as correlations and sizing factors. The advantage of using a software package such as HYSYS to price out individual equipment is that it utilizes up-to-date prices from vendors and distributors when estimating costs. A more in-depth overview of the correlations included in this software can be found in Towler and Sinnott (2009).

=Process Flowsheet=
[[File:Squarepfd_B1.PNG|thumb|400px]]

The following process is based primarily on a 1983 US patent titled “Process for dehydration of a low molecular weight alcohol.” (Barrocas and Baratelli, 1983) The process flow diagram can be seen in Figure 1. A larger version of the PFD is included in Appendix I and the HYSYS simulation setup in Appendix II.

The feed enters the process at a rate of 100,000 kg/hr, a temperature and pressure of a 25 °C and 1 atm and at a composition of 95 wt% ethanol and 5 wt% water.It is initially pressurized to 4335 kPa by centrifugal pump P-101 and subsequently heated to 400 °C by fired heater F-101. The heated and pressurized feed enters fixed bed reactor R-101 and contacts with the aluminum oxide catalyst. At this point it dehydrates to form the product, ethylene, as well as the byproducts water, hydrogen, diethyl ether and acetaldehyde. Fired heater F-102 and reactor R-102 increase the overall conversion of the process. Both fired heaters F-101 and F-102 are fueled with natural gas and fed with excess air. The composition of the reactor train effluent is 54.5 wt% ethylene, 37.1 wt% water, 8.1 wt% unreacted ethanol and trace amounts of diethyl ether, acetaldehyde, and hydrogen contaminants.

The pressure of the reactor train effluent is increased to 4500 kPa by compressor K-102 and the temperature decreased to 100 °C by exchange with cold water in heat exchanger E-201. The stream then expands and flashes in flash vessel FL-201, which separates out 82.3% of the unreacted ethanol, 96.6% of the water and virtually all of the acetaldehyde contaminant in the bottoms while sending the ethylene-rich vapor phase out of the top. The top product of FL-202 is compressed to 3500 kPA by K-202 and cooled to 0.0 °C by a freon refrigerant in E-202. At this point the stream is flashed for a second time in vessel FL-202 to remove additional impurities. The top outlet stream consists of 99.5 wt% ethylene, which is fed to the bottom of a 10-tray absorption column that removes a fraction of the residual diethyl ether as well as the remainder of the unreacted ethanol. A stream of absorbent water is fed to the top of the column at 10,000 kg/hr. The product exits the top of the column at a rate of 54,600 kg/hr and has a purity of 99.7% ethylene. Diethyl ether makes up 0.2% of the remaining product stream and is the primary contaminant. Trace amounts of residual water and hydrogen are also present.

Full tables of material and energy streams can be found in Appendices III and IV respectively.

==Process Alternatives==
===Reactor Alternatives===
Two fixed bed reactors, alternating with fired heaters, are used in the dehydration reaction of ethanol to ethylene. However, a fluidized bed reactor can offer better mixing and temperature control than a fixed bed reactor and thus provide the highest possible conversion of ethanol with the greatest selectivity to ethylene. (Tsao and Zasloff, 1979) Fluidized bed reactors also provide a lower rate of catalyst coking and byproduct formation, minimizing separation and catalyst regeneration costs. (Morschbacker, 2009) The major downside of fluidized bed reactors is that few large-scale processes have been built since the technology was developed in the late 1970s. (Tsao and Zasloff, 1979; Morschbacker, 2009) Although implementation of fluidized bed reactors could potentially increase the purity of the ethylene product and/or decrease costs, a small scale pilot process would need to be built and tested before it would be possible to develop an industrial-scale facility.

===Catalyst Alternatives===
Aluminum oxide, specifically gamma alumina, is the most industrially-common catalyst and has been historically used due to its low cost and high stability. (Tsao and Zasloff, 1979; Fan and Dai, n.d.) Recent improvements in selectivity and catalyst stability of activated alumina have been achieved by incorporating titanium oxide into the catalyst, although this increases reaction temperature by approximately 50 °C and decreases catalyst lifespan. (Chen and Li, et. al. 2007) There is also significant ongoing research into HZSM-5 zeolite and heteropolyacids, which are being explored as potential alternatives to alumina oxide. A nanoscale HZSM-5 zeolite catalyst has been shown to operate at the relatively low temperature of 200-300°C, with a 100% ethanol conversion and 99.7% selectivity to ethylene. Initial research has also indicated that it maintains greater than 98% selectivity for 630 operational hours. (Fan and Dai, n.d.) However, the current low cost and ready availability of unmodified alumina oxide makes it a better choice for a process of this scale.

===Purification Alternatives===
As specified in this process, the reactor effluent is purified by two flash drums and absorption with water to produce chemical-grade ethylene. If chemical-grade ethylene is indeed the desired product, other purification options include caustic washing of the reactor effluent and water removal in a desiccant drying bed. (Morschbacker, 2009) While this purification train is relatively simple and does not require harsh chemical reagents, polymer grade ethylene is more commercially valuable and the additional cost of removing water and diethyl ether contaminants may be justified by increased revenue. Cryogenic distillation was initially simulated to produce polymer-grade ethylene, but utility requirements were found to render this separation economically unviable. (Barrocas and Baratelli, 1983) Further research and optimization may find this purification strategy to be a more valid process. Alternatively, the addition of a cryogenic turboexpander or the use of alternative adsorbents may increase product purity to polymer grade. (Jumonville, 2010) Initial HYSYS simulations indicate that these operations may be feasible with further refinement.

===Wastewater Treatment===
Due to the large volume of wastewater produced, building an on-site wastewater treatment facility may prove to be more economical than paying for third-party wastewater treatment. Flash vessel FL-201 produces 44,600 L/hr of wastewater contaminated with 18.7 vol% ethanol and 0.6 vol% acetaldehyde, while FL-202 produces 2940 L/hr of an aqueous waste consisting of 56.8 vol% ethanol, 42.0 vol% water and 0.9 vol% diethyl ether. The absorption column produces approximately 10,200 liters/hr of wastewater contaminated with 1.2 vol% ethanol, 0.2% diethyl ether and 0.2% acetaldehyde. Utilizing distillation to separate these streams into clean water and volatile organic waste could ultimately reduce the quantity of waste that requires disposal and reduce the overall costs of the process.

==Process Equipment==
Relevant sizing information for each unit operation, estimated by the method described in the “Technical Approach,” can be found in Appendix V. Equipment and piping is assumed to be constructed of carbon steel. It should be noted that the two fired heaters are proportionately large enough to heat the entirety of the process stream and are thus larger than standard equipment.

=Economic Analysis=
[[File:sensitivityanalysis_B1.png|400px|thumb]]

==Economics Overview==
All final values are normalized to June 2014 USD by CEPCI scaling. It is assumed that all products produced are sold at current market prices.

The Aspen Economic Evaluation module within HYSYS v8.0 was used to estimate capital and operating costs for a 10-year plant life span with a construction start date of April 2015. The price of the 95% ethanol feed stream was estimated at $1.44 per gallon, while the chemical grade ethylene produced is currently selling for approximately $1350 per metric ton. (Today in Energy, 2015; Weddle, 2014) Mapping and sizing calculations were performed by the economics module and a preliminary economic evaluation was completed. Equipment sizes, also estimated by HYSYS, were reviewed to ensure that height, diameter, and volume specifications were within realistic ranges.

The process was ideally projected to operate 360 days per year with a start-up time of one year. In addition, the tax rate was approximated at 40%, an interest rate at 20%, and a salvage value of 20%. Escalation percentages were compounded yearly for the product, raw material, and operating costs. The total capital cost for this process is approximately $16.4 million, which includes all equipment and piping described in the process. The most expensive equipment used in this process are the two fired heaters F-101 and F-102, which have an exceptionally large heat exchange area to adequately heat the feed. Standard heaters may not suffice and additional costs may be incurred for the raw materials and manufacture of this equipment. Including a feed preheater or additional fired heaters may reduce this cost in subsequent design iterations.

The total operating cost is approximately $465 million per year, about $427 million of which is the cost of the ethanol feed and natural gas for the two fired heaters. An additional $1.73 million per year is used for utilities including the cooling water and refrigerant. The labor and maintenance costs of this industrial process were also accounted for within the simulation’s economic analysis. The HYSYS simulation software, in conjunction with the Icarus economic analyzer, estimated there should be 5 operators per 8 hour shift with a cost per operator of $20 per hour. This results in a total operating labor cost of approximately $880,000 per year. In addition, the process will require one supervisor per shift with an hourly rate of $35 for total supervisor salaries of $307,000 per year. Finally, a fixed maintenance rate was estimated at $205,000 per 8000 hours of operation for a total cost of $225,000 per year.

Total product sales are roughly $640 million per year at full operation. The estimated income for this process is thus approximately $175 million per year. After ten years, the plant is projected to have a net present value (NPV) of $391 million and an internal rate of return of approximately 79%. In addition the payout period for the initial investment is estimated to be about 2.7 years. Figure 2 shows the projected cash flow for the project.

==Sensitivity Analysis==
A sensitivity analysis was performed to investigate the effects of fluctuating capital costs, operating costs, raw materials, utility costs and ethylene sales price on the 10-year net present value (NPV) of the project. This analysis was performed by scaling these cost factors according to typical ranges given in Towler and Sinnott and calculating the adjusting the NPV accordingly. The results, illustrated in Figure 3, indicate that the project value is most sensitive to product sales, raw materials costs, and operating costs. Ethylene and ethanol prices are market-determined and cannot be controlled for in the process design, so further optimization should be focused on minimizing the operations cost of the process. (Today in Energy, 2015; Weddle, 2014) However, in feed and product prices do still have a profound effect on profitability and feasibility. A more rigorous market analysis will better inform the profitability outlook.

=Conclusions/Recommendations=

The proposed process produces approximately 460,000 metric tons of 99.7 wt% ethylene annually, with a 10-year net present value of $131 million. If current economic conditions hold, it is recommended that this project proceed to implementation following further design improvements and optimization.

Future design iterations should focus on process optimization, particularly in minimizing operating costs as prescribed by the results of the sensitivity analysis. The development of a heat-exchanger network, potentially with Aspen Energy Analyzer, is one option for decreasing utility requirements and increasing the efficiency of the process overall. Optimization of the fired heaters could also result in decreased operational costs. Although overall profitability is less sensitive to capital costs, reviewing and adjusting equipment sizing would also improve the economic outlook. In particular, exploring alternative heating strategies at the beginning of the process could significantly decrease capital costs. Although there are not any particularly dangerous chemicals utilized in the process, an overall process review should also consider potential failure modes to minimize the safety risk to plant workers and nearby residents.

In addition to economic and safety considerations, harmful emissions and waste streams should be minimized both to bring down the cost of treatment and to decrease environmental effects. The two fired heaters consume a large amount of natural gas per year, emitting about 200,000 tons of CO2 annually, and account for more than half of the capital cost of the process. Although no known toxic gases are produced, carbon capture or other emissions-reduction methods should be considered. Additionally, enough wastewater is produced by this process that building an onsite wastewater treatment center should be considered. This could not only decrease operating costs by eliminating the need for an external contract but also give the plant more control over the final purity of the treated wastewater.

Finally, the current model assumes that all ethylene produced will be sold at a current prices and price or product sales will not be affected by economic variability. A more detailed study of the chemical-grade ethylene market, as well as a more thorough understanding of sales and distribution logistics, would increase the surety of a profitable process.

In summary, the proposed process yields chemical grade ethylene via the catalytic dehydration of ethanol. A 100,000 kg/hr of 95 wt% ethanol, 5% water feed is converted to 53,000 kg/hr of 99.7% chemical-grade ethylene. After 10 years of operation, including a one-year startup time, the process has an NPV of $391 million with an IRR of 79% and a payback period of 2.7 years.
Pending further optimization, this process was determined to be viable and it is recommended for the project to move forward.

=References=

[1] American Chemistry Council. Production of chemicals and plastics in the U.S. in 2013, by type (in 1,000 metric tons). In Statista - The Statistics Portal. August 2014. Available at http://www.statista.com/statistics/299725/total-us-plastics-and-chemicals-shipments-by-type/, Accessed January 15, 2015. – Relative proportions of plastics production.

[2] DuPont Nevada Site Cellulosic Ethanol Facility [Internet]. DuPont Chemical; c2012-2015 [cited 11 Mar. 2015]. Available from: http://biofuels.dupont.com/cellulosic-ethanol/nevada-site-ce-facility/. -- Information on ethanol production in Iowa.

[3] Designing Ethylene Plants. Ethylene [Internet]. Technip; 2014 [cited 13 Mar. 2015]. Available from: http://www.technip.com/en/our-business/onshore/ethylene -- Plant size ranges.

[4] Suppes GJ. Selecting Thermodynamic Models for Process Simulation of Organic VLE and LLE Systems. The University of Missouri-Columbia, Dept of Chemical Engineering. [cited 13 Mar. 2015]. -- Use of NRTL in alcohol separations.

[5] ASPENtech. Appendix A - Property Methods and Calculations. Simulation Basics; A-3 - A-26. 2014.

[6] 190 Proof Ethanol: Technical Data Sheet [Internet]. Decon Labs Inc; 2012 [cited 13 Mar. 2015]. Available from: http://www.deconlabs.com/tds/ETHANOL%20190%20%20PROOF.pdf -- Information regarding 95% ethanol

[7] Hadawey A, Ge Y, Tassou TSA. Energy Savings Through Liquid Pressure Amplification In A Dairy Plant Refrigeration System. The Centre for Energy and Built Environment Research [cited 13 Mar. 2015].

[8] Methane (Chemical Compound). 2015. Encyclopædia Britannica Online. [cited 13 Mar. 2015] Available from: http://www.britannica.com/EBchecked/topic/378264/methane -- Composition of Methane

[9] Composition of Air [Internet]. Engineering Toolbox; [cited 13 Mar. 2015]. Available from: http://www.engineeringtoolbox.com/air-composition-d_212.html. -- Composition of air.

[10] Summary of the Clean Air Act, 2015. United States Environmental Protection Agency. [cited 13 Mar. 2015] Available from: http://www2.epa.gov/laws-regulations/summary-clean-air-act -- Emissions requirements of chemical plants.

[11] Zhang M, Yu Y. Dehydration of Ethanol to Ethylene. Industrial Engineering and Chemical Research. 2013; 52:9505-9514. – Technical information on ethanol to ethylene conversion via dehydration.

[12] AspenTech. Aspen HYSYS Help File v8.0. Aspen Technology, Inc. 2012. - Aspen HYSYS help file used for troubleshooting and assistance on economic analysis.

[13] Towler G, Sinnott R. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. 2nd ed. Boston: Elsevier; 2013. -- General Reference Book

[14] Barrocas H, Baratelli F, inventors; Petroleo Brasileiro S.A., assignee. Process for dehydration of a low molecular weight alcohol. US patent 4,396,789 A. August 2, 1983. - Primary background for process design.

[15] Tsao U, Zasloff HB, inventors; The Lummus Company, assignee. Production of ethylene from ethanol. US patent 4,134,926. January 16, 1979. – Patent for catalytic dehydration of ethylene in a fluidized bed reactor.

[16] Morschbacker, A. Bio-Ethanol Based Ethylene. Polymer Reviews. 2009; 49:79-84. – Overview of bioethanol dehydration process development.

[17] Fan D, Dai DJ, Wu HS. Ethylene Formation by Catalytic Dehydration of Ethanol with Industrial Considerations. Materials. 6, 101-115. doi: 10.3390/ma6010101. - Comparison of types of catalysts used in the dehydration of ethanol and current research into new catalysts.

[18] Chen G, Li S, Jiao F, Yuan Q. Catalytic dehydration of bioethanol to ethylene over TiO2/γ-Al2O3 catalysts in microchannel reactors. Catal. Today 2007, 125, 111–119. - Paper introducing research on modified alumina catalyst for ethanol dehydration.

[19] Jumonville, J. Tutorial on Cryogenic Turboexpanders. Proceedings of the Thirty-Ninth Turbomachinery Symposium; 2010 Oct 4-7; Houston, TX. Houston: Texas A&M University; 2010. -- Use of turboexpander for cryogenic separations

[20] Today in Energy - Daily Prices. US Energy Information Administration website. http://www.eia.gov/todayinenergy/prices.cfm. Accessed March 3rd 2015. - Bulk market price for 95% ethanol.

[21] Weddle, N. ICIS Pricing: Ethylene (Europe). Reed Business Limited. January 10 2014. - Bulk market price for chemical grade ethylene.

=Appendix I - Process Flow Diagram=
[[File:PFD B1.JPG]]

=Appendix II - HYSYS Simulation=
[[File:HYSYS_B1.PNG]]

=Appendix III - Material Streams=
[[File:Streams_B1.png|1200px]]

=Appendix IV - Energy Table=
[[File:Energy_B1.png|600px|center]]

=Appendix V - Economics=
[[File:Econsummary_B1.png|center]] 

[[File:Capcost_B1.png|center]] 

[[File:sensitivityanalysis_B1.png|600px|center]]

Ethanol to Ethylene (B1)

2015-03-14T04:21:35Z

Hpoppick: /* Appendix I - Process Flow Diagram */

[[File:BFD_B1.png|600px|thumbnail|alt=Alt text|Conversion of Ethanol to Ethylene]]

Team B1 Final Report

Authors: Harry Poppick, Emm Fulk and Scott Smith

Instructors: Fengqi You, David Wegerer

March 13, 2015

=Executive Summary=

The following report outlines the design and analysis of a process converting ethanol to chemical-grade ethylene via catalytic dehydration. This process consumers 100,000 kg/hr of 95 wt% ethanol, 5 wt% water feedstock and produces 53,000 kg/hr of 99.7 wt% chemical-grade ethylene. The ethanol feed passes through two fixed-bed reactors, each packed with an aluminum oxide catalyst, and the resulting ethylene is purified by two flash tanks and by absorption with water. The process was modeled using Aspen HYSYS simulation software to estimate mass and energy flows and equipment sizing requirements. Based on results of this initial simulation, several alternatives are discussed for increasing the process efficiency and profitability. The use of a fluidized bed reactor or a more ethylene-selective catalyst could increase the production of ethylene per ethanol basis. Additionally, several methods of purification to more valuable polymer-grade ethylene are proposed.

The economic feasibility of this process was evaluated using Aspen Economic Analyzer with the Icarus economics package. Capital cost is approximately $16.4 million total with an operating cost of $465 million per year. The current market prices of the ethanol feed and ethylene sales price are $1.44/gallon and $1350/metric ton respectively. The cost of feed ethanol, process utilities and miscellaneous operational costs total to about $427 million/year. At full operation, revenue at current prices would be approximately $640 million per year. The predicted 10-year net present value of the process is approximately $391 million with an IRR of 79% and a payback period of 2.7 years. A sensitivity analysis indicates that the process is most sensitive to feed prices, product prices and operation cost.

Several recommendations are made for both cost reduction and profit maximization, including the design of a heat exchanger network and the optimization of fired heaters that require high capital investment and large amounts of fuel. A safety review of the process is recommended, as well as the minimization of flue gas effluent and wastewater. It is also suggested that the construction of an onsite wastewater treatment center be considered. Overall, the initial analysis indicates this to be a profitable process and it is recommended the project move forward.

=Introduction=

Ethylene is a critical chemical precursor to a number of different industrial products. It is often derived from petroleum sources and polymerized to polyethylene, one of the most ubiquitous plastics today. (American Chemistry Council, 2013) Recently there has been a significant effort to develop production pathways utilizing biologically-derived feedstocks, such as corn or cellulosic ethanol, rather than traditional fossil-fuel sources. Ethylene can be produced from bioethanol via catalytic dehydration over an aluminum oxide catalyst. The proposed process converts 100,000 kg/hr of 95 wt% ethanol, 5% water feed to 53,000 kg/hr of 99.7% chemical-grade ethylene when operating at full capacity. This process was found to be economically viable with a 10-year net present value (NPV) of $131 million (2014 USD) and a payback period of approximately 2.7 years. This memo will detail the proposed process, as well as outline potential alternatives and economic viability of the project.

=Technical Approach=

Many bioethanol plants are located in the Midwest where large amounts of feedstock crops, such as corn, are grown. As such, this plant will be located in Story county, Iowa, near a large-scale bioethanol production plant. (DuPont Nevada Site, 2012) It is assumed that the supply of bioethanol is consistent and readily available. It is also assumed that other reagents - namely, the aluminum oxide catalyst, heater fuel, utility water and freon refrigerant - are readily available, and that wastewater treatment facilities are located near enough to facilitate the off-site treatment of wastewater. Plant capacity was based on current mid-sized industrial ethylene plants. (Designing Ethylene Plants, 2014)

HYSYS simulations were performed with the NRTL fluid package and Peng-Robinson vapor model. The NRTL fluid package is an activity coefficient model that is especially useful to model the separations of alcohols in aqueous solutions. (Suppes, 2015) In addition, NRTL uses models of binary pairs of components, much like the Wilson equation, to predict chemical interactions at the molecular level. The NRTL package can thus be easily extended to ternary and higher order chemical systems, making it ideal for this type of simulation. The Peng-Robinson vapor model was selected as it is well-suited to account for the non-idealities of the vapor phase reactions and separations integral to this process. (ASPENtech, 2014)

It was assumed that the feed enters the process at ambient temperature and pressure (25 °C, 1 atm) and at a consistent rate and composition with negligible quantities of impurities. The ethanol feed was assumed to be 95% ethanol and 5% water by mass, which is the commercial standard for industrial ethanol. (190 Proof Ethanol, 2012) Storage vessels for the feed ethanol, waste streams and products are assumed to be located nearby to the process. An initial feed pump compensates for pressure drops through the process and reduces the duty on downstream compressors. (Hadawey, 2015)

Natural gas, assumed to consist of 83% methane, 16% ethane and 1% nitrogen by mass, was supplied to two fired heaters at a flow rate estimated by HYSYS. (Methane, 2015) Air fed to the process to enable combustion was assumed to be 23% oxygen and 77% nitrogen by mass. (Composition of Air, 2015) Air streams were fed at 50% molar excess in order to ensure complete combustion and prevent the formation of carbon monoxide in the heater exhaust. Total flue gases are assumed to be 230,000 kg/hr, or 2.2 million tons annually, and consist of 73.8% nitrogen gas, 10.5% carbon dioxide, 8.2% water vapor, and 7.5% oxygen by mass. The only compound of concern in these emissions is the carbon dioxide, a known greenhouse gas. At the time of this report, the quantities of carbon dioxide emitted by this plant annually are within acceptable EPA specifications. (Summary of the Clean Air Act, 2015)

Due to the difficulty of simulation equilibrium and conversion reactions in a single vessel in HYSYS, these two reaction types were simulated in separate equilibrium reactor and conversion reactor units in series. In addition, while HYSYS indicated that reactor units would output separate vapor and liquid streams, it was assumed that in practice this would take the form of a single, two phase stream between each unit. To account for this, mixers were installed downstream of each reactor to combine the liquid and vapor phases of the reactor effluent. The three consequent reactions considered are as follows:

Ethanol ↔ Ethylene + Water
Ethanol → Acetaldehyde + Hydrogen
2 Ethanol → Diethyl Ether + Water

The optimal reaction temperature was determined to be 400 °C, which promotes the equilibrium reaction of ethanol to ethylene while minimizing byproducts. (Zhang and Yu, 2013) While other byproducts may be produced in this process, these reactions are typically taken to comprise of the bulk of the dehydration reaction. Heat losses over these reactors were assumed to be negligible. (Zhang and Yu, 2013)All major process equipment is assumed to be constructed of high strength carbon steel. (AspenTech, 2012)

The “Sizing Utility” within the Icarus Economic Evaluation module was used to estimate sizes of major equipment based on the process simulation. These values can serve as a benchmark for an initial plant design. Icarus KbaseTM implements a wide variety of mechanical design standards, including ASME and BS5500, in order to calculate accurate equipment sizing. The Icarus sizing module combines equipment prices for standard chemical processing equipment as well as correlations and sizing factors. The advantage of using a software package such as HYSYS to price out individual equipment is that it utilizes up-to-date prices from vendors and distributors when estimating costs. A more in-depth overview of the correlations included in this software can be found in Towler and Sinnott (2009).

=Process Flowsheet=
[[File:Squarepfd_B1.PNG|thumb|400px]]

The following process is based primarily on a 1983 US patent titled “Process for dehydration of a low molecular weight alcohol.” (Barrocas and Baratelli, 1983) The process flow diagram can be seen in Figure 1. A larger version of the PFD is included in Appendix I and the HYSYS simulation setup in Appendix II.

The feed enters the process at a rate of 100,000 kg/hr, a temperature and pressure of a 25 °C and 1 atm and at a composition of 95 wt% ethanol and 5 wt% water.It is initially pressurized to 4335 kPa by centrifugal pump P-101 and subsequently heated to 400 °C by fired heater F-101. The heated and pressurized feed enters fixed bed reactor R-101 and contacts with the aluminum oxide catalyst. At this point it dehydrates to form the product, ethylene, as well as the byproducts water, hydrogen, diethyl ether and acetaldehyde. Fired heater F-102 and reactor R-102 increase the overall conversion of the process. Both fired heaters F-101 and F-102 are fueled with natural gas and fed with excess air. The composition of the reactor train effluent is 54.5 wt% ethylene, 37.1 wt% water, 8.1 wt% unreacted ethanol and trace amounts of diethyl ether, acetaldehyde, and hydrogen contaminants.

The pressure of the reactor train effluent is increased to 4500 kPa by compressor K-102 and the temperature decreased to 100 °C by exchange with cold water in heat exchanger E-201. The stream then expands and flashes in flash vessel FL-201, which separates out 82.3% of the unreacted ethanol, 96.6% of the water and virtually all of the acetaldehyde contaminant in the bottoms while sending the ethylene-rich vapor phase out of the top. The top product of FL-202 is compressed to 3500 kPA by K-202 and cooled to 0.0 °C by a freon refrigerant in E-202. At this point the stream is flashed for a second time in vessel FL-202 to remove additional impurities. The top outlet stream consists of 99.5 wt% ethylene, which is fed to the bottom of a 10-tray absorption column that removes a fraction of the residual diethyl ether as well as the remainder of the unreacted ethanol. A stream of absorbent water is fed to the top of the column at 10,000 kg/hr. The product exits the top of the column at a rate of 54,600 kg/hr and has a purity of 99.7% ethylene. Diethyl ether makes up 0.2% of the remaining product stream and is the primary contaminant. Trace amounts of residual water and hydrogen are also present.

Full tables of material and energy streams can be found in Appendices III and IV respectively.

==Process Alternatives==
===Reactor Alternatives===
Two fixed bed reactors, alternating with fired heaters, are used in the dehydration reaction of ethanol to ethylene. However, a fluidized bed reactor can offer better mixing and temperature control than a fixed bed reactor and thus provide the highest possible conversion of ethanol with the greatest selectivity to ethylene. (Tsao and Zasloff, 1979) Fluidized bed reactors also provide a lower rate of catalyst coking and byproduct formation, minimizing separation and catalyst regeneration costs. (Morschbacker, 2009) The major downside of fluidized bed reactors is that few large-scale processes have been built since the technology was developed in the late 1970s. (Tsao and Zasloff, 1979; Morschbacker, 2009) Although implementation of fluidized bed reactors could potentially increase the purity of the ethylene product and/or decrease costs, a small scale pilot process would need to be built and tested before it would be possible to develop an industrial-scale facility.

===Catalyst Alternatives===
Aluminum oxide, specifically gamma alumina, is the most industrially-common catalyst and has been historically used due to its low cost and high stability. (Tsao and Zasloff, 1979; Fan and Dai, n.d.) Recent improvements in selectivity and catalyst stability of activated alumina have been achieved by incorporating titanium oxide into the catalyst, although this increases reaction temperature by approximately 50 °C and decreases catalyst lifespan. (Chen and Li, et. al. 2007) There is also significant ongoing research into HZSM-5 zeolite and heteropolyacids, which are being explored as potential alternatives to alumina oxide. A nanoscale HZSM-5 zeolite catalyst has been shown to operate at the relatively low temperature of 200-300°C, with a 100% ethanol conversion and 99.7% selectivity to ethylene. Initial research has also indicated that it maintains greater than 98% selectivity for 630 operational hours. (Fan and Dai, n.d.) However, the current low cost and ready availability of unmodified alumina oxide makes it a better choice for a process of this scale.

===Purification Alternatives===
As specified in this process, the reactor effluent is purified by two flash drums and absorption with water to produce chemical-grade ethylene. If chemical-grade ethylene is indeed the desired product, other purification options include caustic washing of the reactor effluent and water removal in a desiccant drying bed. (Morschbacker, 2009) While this purification train is relatively simple and does not require harsh chemical reagents, polymer grade ethylene is more commercially valuable and the additional cost of removing water and diethyl ether contaminants may be justified by increased revenue. Cryogenic distillation was initially simulated to produce polymer-grade ethylene, but utility requirements were found to render this separation economically unviable. (Barrocas and Baratelli, 1983) Further research and optimization may find this purification strategy to be a more valid process. Alternatively, the addition of a cryogenic turboexpander or the use of alternative adsorbents may increase product purity to polymer grade. (Jumonville, 2010) Initial HYSYS simulations indicate that these operations may be feasible with further refinement.

===Wastewater Treatment===
Due to the large volume of wastewater produced, building an on-site wastewater treatment facility may prove to be more economical than paying for third-party wastewater treatment. Flash vessel FL-201 produces 44,600 L/hr of wastewater contaminated with 18.7 vol% ethanol and 0.6 vol% acetaldehyde, while FL-202 produces 2940 L/hr of an aqueous waste consisting of 56.8 vol% ethanol, 42.0 vol% water and 0.9 vol% diethyl ether. The absorption column produces approximately 10,200 liters/hr of wastewater contaminated with 1.2 vol% ethanol, 0.2% diethyl ether and 0.2% acetaldehyde. Utilizing distillation to separate these streams into clean water and volatile organic waste could ultimately reduce the quantity of waste that requires disposal and reduce the overall costs of the process.

==Process Equipment==
Relevant sizing information for each unit operation, estimated by the method described in the “Technical Approach,” can be found in Appendix V. Equipment and piping is assumed to be constructed of carbon steel. It should be noted that the two fired heaters are proportionately large enough to heat the entirety of the process stream and are thus larger than standard equipment.

=Economic Analysis=
[[File:sensitivityanalysis_B1.png|400px|thumb]]

==Economics Overview==
All final values are normalized to June 2014 USD by CEPCI scaling. It is assumed that all products produced are sold at current market prices.

The Aspen Economic Evaluation module within HYSYS v8.0 was used to estimate capital and operating costs for a 10-year plant life span with a construction start date of April 2015. The price of the 95% ethanol feed stream was estimated at $1.44 per gallon, while the chemical grade ethylene produced is currently selling for approximately $1350 per metric ton. (Today in Energy, 2015; Weddle, 2014) Mapping and sizing calculations were performed by the economics module and a preliminary economic evaluation was completed. Equipment sizes, also estimated by HYSYS, were reviewed to ensure that height, diameter, and volume specifications were within realistic ranges.

The process was ideally projected to operate 360 days per year with a start-up time of one year. In addition, the tax rate was approximated at 40%, an interest rate at 20%, and a salvage value of 20%. Escalation percentages were compounded yearly for the product, raw material, and operating costs. The total capital cost for this process is approximately $16.4 million, which includes all equipment and piping described in the process. The most expensive equipment used in this process are the two fired heaters F-101 and F-102, which have an exceptionally large heat exchange area to adequately heat the feed. Standard heaters may not suffice and additional costs may be incurred for the raw materials and manufacture of this equipment. Including a feed preheater or additional fired heaters may reduce this cost in subsequent design iterations.

The total operating cost is approximately $465 million per year, about $427 million of which is the cost of the ethanol feed and natural gas for the two fired heaters. An additional $1.73 million per year is used for utilities including the cooling water and refrigerant. The labor and maintenance costs of this industrial process were also accounted for within the simulation’s economic analysis. The HYSYS simulation software, in conjunction with the Icarus economic analyzer, estimated there should be 5 operators per 8 hour shift with a cost per operator of $20 per hour. This results in a total operating labor cost of approximately $880,000 per year. In addition, the process will require one supervisor per shift with an hourly rate of $35 for total supervisor salaries of $307,000 per year. Finally, a fixed maintenance rate was estimated at $205,000 per 8000 hours of operation for a total cost of $225,000 per year.

Total product sales are roughly $640 million per year at full operation. The estimated income for this process is thus approximately $175 million per year. After ten years, the plant is projected to have a net present value (NPV) of $391 million and an internal rate of return of approximately 79%. In addition the payout period for the initial investment is estimated to be about 2.7 years. Figure 2 shows the projected cash flow for the project.

==Sensitivity Analysis==
A sensitivity analysis was performed to investigate the effects of fluctuating capital costs, operating costs, raw materials, utility costs and ethylene sales price on the 10-year net present value (NPV) of the project. This analysis was performed by scaling these cost factors according to typical ranges given in Towler and Sinnott and calculating the adjusting the NPV accordingly. The results, illustrated in Figure 3, indicate that the project value is most sensitive to product sales, raw materials costs, and operating costs. Ethylene and ethanol prices are market-determined and cannot be controlled for in the process design, so further optimization should be focused on minimizing the operations cost of the process. (Today in Energy, 2015; Weddle, 2014) However, in feed and product prices do still have a profound effect on profitability and feasibility. A more rigorous market analysis will better inform the profitability outlook.

=Conclusions/Recommendations=

The proposed process produces approximately 460,000 metric tons of 99.7 wt% ethylene annually, with a 10-year net present value of $131 million. If current economic conditions hold, it is recommended that this project proceed to implementation following further design improvements and optimization.

Future design iterations should focus on process optimization, particularly in minimizing operating costs as prescribed by the results of the sensitivity analysis. The development of a heat-exchanger network, potentially with Aspen Energy Analyzer, is one option for decreasing utility requirements and increasing the efficiency of the process overall. Optimization of the fired heaters could also result in decreased operational costs. Although overall profitability is less sensitive to capital costs, reviewing and adjusting equipment sizing would also improve the economic outlook. In particular, exploring alternative heating strategies at the beginning of the process could significantly decrease capital costs. Although there are not any particularly dangerous chemicals utilized in the process, an overall process review should also consider potential failure modes to minimize the safety risk to plant workers and nearby residents.

In addition to economic and safety considerations, harmful emissions and waste streams should be minimized both to bring down the cost of treatment and to decrease environmental effects. The two fired heaters consume a large amount of natural gas per year, emitting about 200,000 tons of CO2 annually, and account for more than half of the capital cost of the process. Although no known toxic gases are produced, carbon capture or other emissions-reduction methods should be considered. Additionally, enough wastewater is produced by this process that building an onsite wastewater treatment center should be considered. This could not only decrease operating costs by eliminating the need for an external contract but also give the plant more control over the final purity of the treated wastewater.

Finally, the current model assumes that all ethylene produced will be sold at a current prices and price or product sales will not be affected by economic variability. A more detailed study of the chemical-grade ethylene market, as well as a more thorough understanding of sales and distribution logistics, would increase the surety of a profitable process.

In summary, the proposed process yields chemical grade ethylene via the catalytic dehydration of ethanol. A 100,000 kg/hr of 95 wt% ethanol, 5% water feed is converted to 53,000 kg/hr of 99.7% chemical-grade ethylene. After 10 years of operation, including a one-year startup time, the process has an NPV of $391 million with an IRR of 79% and a payback period of 2.7 years.
Pending further optimization, this process was determined to be viable and it is recommended for the project to move forward.

=References=

[1] American Chemistry Council. Production of chemicals and plastics in the U.S. in 2013, by type (in 1,000 metric tons). In Statista - The Statistics Portal. August 2014. Available at http://www.statista.com/statistics/299725/total-us-plastics-and-chemicals-shipments-by-type/, Accessed January 15, 2015. – Relative proportions of plastics production.

[2] DuPont Nevada Site Cellulosic Ethanol Facility [Internet]. DuPont Chemical; c2012-2015 [cited 11 Mar. 2015]. Available from: http://biofuels.dupont.com/cellulosic-ethanol/nevada-site-ce-facility/. -- Information on ethanol production in Iowa.

[3] Designing Ethylene Plants. Ethylene [Internet]. Technip; 2014 [cited 13 Mar. 2015]. Available from: http://www.technip.com/en/our-business/onshore/ethylene -- Plant size ranges.

[4] Suppes GJ. Selecting Thermodynamic Models for Process Simulation of Organic VLE and LLE Systems. The University of Missouri-Columbia, Dept of Chemical Engineering. [cited 13 Mar. 2015]. -- Use of NRTL in alcohol separations.

[5] ASPENtech. Appendix A - Property Methods and Calculations. Simulation Basics; A-3 - A-26. 2014.

[6] 190 Proof Ethanol: Technical Data Sheet [Internet]. Decon Labs Inc; 2012 [cited 13 Mar. 2015]. Available from: http://www.deconlabs.com/tds/ETHANOL%20190%20%20PROOF.pdf -- Information regarding 95% ethanol

[7] Hadawey A, Ge Y, Tassou TSA. Energy Savings Through Liquid Pressure Amplification In A Dairy Plant Refrigeration System. The Centre for Energy and Built Environment Research [cited 13 Mar. 2015].

[8] Methane (Chemical Compound). 2015. Encyclopædia Britannica Online. [cited 13 Mar. 2015] Available from: http://www.britannica.com/EBchecked/topic/378264/methane -- Composition of Methane

[9] Composition of Air [Internet]. Engineering Toolbox; [cited 13 Mar. 2015]. Available from: http://www.engineeringtoolbox.com/air-composition-d_212.html. -- Composition of air.

[10] Summary of the Clean Air Act, 2015. United States Environmental Protection Agency. [cited 13 Mar. 2015] Available from: http://www2.epa.gov/laws-regulations/summary-clean-air-act -- Emissions requirements of chemical plants.

[11] Zhang M, Yu Y. Dehydration of Ethanol to Ethylene. Industrial Engineering and Chemical Research. 2013; 52:9505-9514. – Technical information on ethanol to ethylene conversion via dehydration.

[12] AspenTech. Aspen HYSYS Help File v8.0. Aspen Technology, Inc. 2012. - Aspen HYSYS help file used for troubleshooting and assistance on economic analysis.

[13] Towler G, Sinnott R. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. 2nd ed. Boston: Elsevier; 2013. -- General Reference Book

[14] Barrocas H, Baratelli F, inventors; Petroleo Brasileiro S.A., assignee. Process for dehydration of a low molecular weight alcohol. US patent 4,396,789 A. August 2, 1983. - Primary background for process design.

[15] Tsao U, Zasloff HB, inventors; The Lummus Company, assignee. Production of ethylene from ethanol. US patent 4,134,926. January 16, 1979. – Patent for catalytic dehydration of ethylene in a fluidized bed reactor.

[16] Morschbacker, A. Bio-Ethanol Based Ethylene. Polymer Reviews. 2009; 49:79-84. – Overview of bioethanol dehydration process development.

[17] Fan D, Dai DJ, Wu HS. Ethylene Formation by Catalytic Dehydration of Ethanol with Industrial Considerations. Materials. 6, 101-115. doi: 10.3390/ma6010101. - Comparison of types of catalysts used in the dehydration of ethanol and current research into new catalysts.

[18] Chen G, Li S, Jiao F, Yuan Q. Catalytic dehydration of bioethanol to ethylene over TiO2/γ-Al2O3 catalysts in microchannel reactors. Catal. Today 2007, 125, 111–119. - Paper introducing research on modified alumina catalyst for ethanol dehydration.

[19] Jumonville, J. Tutorial on Cryogenic Turboexpanders. Proceedings of the Thirty-Ninth Turbomachinery Symposium; 2010 Oct 4-7; Houston, TX. Houston: Texas A&M University; 2010. -- Use of turboexpander for cryogenic separations

[20] Today in Energy - Daily Prices. US Energy Information Administration website. http://www.eia.gov/todayinenergy/prices.cfm. Accessed March 3rd 2015. - Bulk market price for 95% ethanol.

[21] Weddle, N. ICIS Pricing: Ethylene (Europe). Reed Business Limited. January 10 2014. - Bulk market price for chemical grade ethylene.

=Appendix I - Process Flow Diagram=
[[File:PFD B1.JPG]|center]

=Appendix II - HYSYS Simulation=
[[File:HYSYS_B1.PNG]]

=Appendix III - Material Streams=
[[File:Streams_B1.png|1200px]]

=Appendix IV - Energy Table=
[[File:Energy_B1.png|600px|center]]

=Appendix V - Economics=
[[File:Econsummary_B1.png|center]] 

[[File:Capcost_B1.png|center]] 

[[File:sensitivityanalysis_B1.png|600px|center]]

Ethanol to Ethylene (B1)

2015-03-14T04:21:11Z

Hpoppick: /* Appendix II - HYSYS Simulation */

[[File:BFD_B1.png|600px|thumbnail|alt=Alt text|Conversion of Ethanol to Ethylene]]

Team B1 Final Report

Authors: Harry Poppick, Emm Fulk and Scott Smith

Instructors: Fengqi You, David Wegerer

March 13, 2015

=Executive Summary=

The following report outlines the design and analysis of a process converting ethanol to chemical-grade ethylene via catalytic dehydration. This process consumers 100,000 kg/hr of 95 wt% ethanol, 5 wt% water feedstock and produces 53,000 kg/hr of 99.7 wt% chemical-grade ethylene. The ethanol feed passes through two fixed-bed reactors, each packed with an aluminum oxide catalyst, and the resulting ethylene is purified by two flash tanks and by absorption with water. The process was modeled using Aspen HYSYS simulation software to estimate mass and energy flows and equipment sizing requirements. Based on results of this initial simulation, several alternatives are discussed for increasing the process efficiency and profitability. The use of a fluidized bed reactor or a more ethylene-selective catalyst could increase the production of ethylene per ethanol basis. Additionally, several methods of purification to more valuable polymer-grade ethylene are proposed.

The economic feasibility of this process was evaluated using Aspen Economic Analyzer with the Icarus economics package. Capital cost is approximately $16.4 million total with an operating cost of $465 million per year. The current market prices of the ethanol feed and ethylene sales price are $1.44/gallon and $1350/metric ton respectively. The cost of feed ethanol, process utilities and miscellaneous operational costs total to about $427 million/year. At full operation, revenue at current prices would be approximately $640 million per year. The predicted 10-year net present value of the process is approximately $391 million with an IRR of 79% and a payback period of 2.7 years. A sensitivity analysis indicates that the process is most sensitive to feed prices, product prices and operation cost.

Several recommendations are made for both cost reduction and profit maximization, including the design of a heat exchanger network and the optimization of fired heaters that require high capital investment and large amounts of fuel. A safety review of the process is recommended, as well as the minimization of flue gas effluent and wastewater. It is also suggested that the construction of an onsite wastewater treatment center be considered. Overall, the initial analysis indicates this to be a profitable process and it is recommended the project move forward.

=Introduction=

Ethylene is a critical chemical precursor to a number of different industrial products. It is often derived from petroleum sources and polymerized to polyethylene, one of the most ubiquitous plastics today. (American Chemistry Council, 2013) Recently there has been a significant effort to develop production pathways utilizing biologically-derived feedstocks, such as corn or cellulosic ethanol, rather than traditional fossil-fuel sources. Ethylene can be produced from bioethanol via catalytic dehydration over an aluminum oxide catalyst. The proposed process converts 100,000 kg/hr of 95 wt% ethanol, 5% water feed to 53,000 kg/hr of 99.7% chemical-grade ethylene when operating at full capacity. This process was found to be economically viable with a 10-year net present value (NPV) of $131 million (2014 USD) and a payback period of approximately 2.7 years. This memo will detail the proposed process, as well as outline potential alternatives and economic viability of the project.

=Technical Approach=

Many bioethanol plants are located in the Midwest where large amounts of feedstock crops, such as corn, are grown. As such, this plant will be located in Story county, Iowa, near a large-scale bioethanol production plant. (DuPont Nevada Site, 2012) It is assumed that the supply of bioethanol is consistent and readily available. It is also assumed that other reagents - namely, the aluminum oxide catalyst, heater fuel, utility water and freon refrigerant - are readily available, and that wastewater treatment facilities are located near enough to facilitate the off-site treatment of wastewater. Plant capacity was based on current mid-sized industrial ethylene plants. (Designing Ethylene Plants, 2014)

HYSYS simulations were performed with the NRTL fluid package and Peng-Robinson vapor model. The NRTL fluid package is an activity coefficient model that is especially useful to model the separations of alcohols in aqueous solutions. (Suppes, 2015) In addition, NRTL uses models of binary pairs of components, much like the Wilson equation, to predict chemical interactions at the molecular level. The NRTL package can thus be easily extended to ternary and higher order chemical systems, making it ideal for this type of simulation. The Peng-Robinson vapor model was selected as it is well-suited to account for the non-idealities of the vapor phase reactions and separations integral to this process. (ASPENtech, 2014)

It was assumed that the feed enters the process at ambient temperature and pressure (25 °C, 1 atm) and at a consistent rate and composition with negligible quantities of impurities. The ethanol feed was assumed to be 95% ethanol and 5% water by mass, which is the commercial standard for industrial ethanol. (190 Proof Ethanol, 2012) Storage vessels for the feed ethanol, waste streams and products are assumed to be located nearby to the process. An initial feed pump compensates for pressure drops through the process and reduces the duty on downstream compressors. (Hadawey, 2015)

Natural gas, assumed to consist of 83% methane, 16% ethane and 1% nitrogen by mass, was supplied to two fired heaters at a flow rate estimated by HYSYS. (Methane, 2015) Air fed to the process to enable combustion was assumed to be 23% oxygen and 77% nitrogen by mass. (Composition of Air, 2015) Air streams were fed at 50% molar excess in order to ensure complete combustion and prevent the formation of carbon monoxide in the heater exhaust. Total flue gases are assumed to be 230,000 kg/hr, or 2.2 million tons annually, and consist of 73.8% nitrogen gas, 10.5% carbon dioxide, 8.2% water vapor, and 7.5% oxygen by mass. The only compound of concern in these emissions is the carbon dioxide, a known greenhouse gas. At the time of this report, the quantities of carbon dioxide emitted by this plant annually are within acceptable EPA specifications. (Summary of the Clean Air Act, 2015)

Due to the difficulty of simulation equilibrium and conversion reactions in a single vessel in HYSYS, these two reaction types were simulated in separate equilibrium reactor and conversion reactor units in series. In addition, while HYSYS indicated that reactor units would output separate vapor and liquid streams, it was assumed that in practice this would take the form of a single, two phase stream between each unit. To account for this, mixers were installed downstream of each reactor to combine the liquid and vapor phases of the reactor effluent. The three consequent reactions considered are as follows:

Ethanol ↔ Ethylene + Water
Ethanol → Acetaldehyde + Hydrogen
2 Ethanol → Diethyl Ether + Water

The optimal reaction temperature was determined to be 400 °C, which promotes the equilibrium reaction of ethanol to ethylene while minimizing byproducts. (Zhang and Yu, 2013) While other byproducts may be produced in this process, these reactions are typically taken to comprise of the bulk of the dehydration reaction. Heat losses over these reactors were assumed to be negligible. (Zhang and Yu, 2013)All major process equipment is assumed to be constructed of high strength carbon steel. (AspenTech, 2012)

The “Sizing Utility” within the Icarus Economic Evaluation module was used to estimate sizes of major equipment based on the process simulation. These values can serve as a benchmark for an initial plant design. Icarus KbaseTM implements a wide variety of mechanical design standards, including ASME and BS5500, in order to calculate accurate equipment sizing. The Icarus sizing module combines equipment prices for standard chemical processing equipment as well as correlations and sizing factors. The advantage of using a software package such as HYSYS to price out individual equipment is that it utilizes up-to-date prices from vendors and distributors when estimating costs. A more in-depth overview of the correlations included in this software can be found in Towler and Sinnott (2009).

=Process Flowsheet=
[[File:Squarepfd_B1.PNG|thumb|400px]]

The following process is based primarily on a 1983 US patent titled “Process for dehydration of a low molecular weight alcohol.” (Barrocas and Baratelli, 1983) The process flow diagram can be seen in Figure 1. A larger version of the PFD is included in Appendix I and the HYSYS simulation setup in Appendix II.

The feed enters the process at a rate of 100,000 kg/hr, a temperature and pressure of a 25 °C and 1 atm and at a composition of 95 wt% ethanol and 5 wt% water.It is initially pressurized to 4335 kPa by centrifugal pump P-101 and subsequently heated to 400 °C by fired heater F-101. The heated and pressurized feed enters fixed bed reactor R-101 and contacts with the aluminum oxide catalyst. At this point it dehydrates to form the product, ethylene, as well as the byproducts water, hydrogen, diethyl ether and acetaldehyde. Fired heater F-102 and reactor R-102 increase the overall conversion of the process. Both fired heaters F-101 and F-102 are fueled with natural gas and fed with excess air. The composition of the reactor train effluent is 54.5 wt% ethylene, 37.1 wt% water, 8.1 wt% unreacted ethanol and trace amounts of diethyl ether, acetaldehyde, and hydrogen contaminants.

The pressure of the reactor train effluent is increased to 4500 kPa by compressor K-102 and the temperature decreased to 100 °C by exchange with cold water in heat exchanger E-201. The stream then expands and flashes in flash vessel FL-201, which separates out 82.3% of the unreacted ethanol, 96.6% of the water and virtually all of the acetaldehyde contaminant in the bottoms while sending the ethylene-rich vapor phase out of the top. The top product of FL-202 is compressed to 3500 kPA by K-202 and cooled to 0.0 °C by a freon refrigerant in E-202. At this point the stream is flashed for a second time in vessel FL-202 to remove additional impurities. The top outlet stream consists of 99.5 wt% ethylene, which is fed to the bottom of a 10-tray absorption column that removes a fraction of the residual diethyl ether as well as the remainder of the unreacted ethanol. A stream of absorbent water is fed to the top of the column at 10,000 kg/hr. The product exits the top of the column at a rate of 54,600 kg/hr and has a purity of 99.7% ethylene. Diethyl ether makes up 0.2% of the remaining product stream and is the primary contaminant. Trace amounts of residual water and hydrogen are also present.

Full tables of material and energy streams can be found in Appendices III and IV respectively.

==Process Alternatives==
===Reactor Alternatives===
Two fixed bed reactors, alternating with fired heaters, are used in the dehydration reaction of ethanol to ethylene. However, a fluidized bed reactor can offer better mixing and temperature control than a fixed bed reactor and thus provide the highest possible conversion of ethanol with the greatest selectivity to ethylene. (Tsao and Zasloff, 1979) Fluidized bed reactors also provide a lower rate of catalyst coking and byproduct formation, minimizing separation and catalyst regeneration costs. (Morschbacker, 2009) The major downside of fluidized bed reactors is that few large-scale processes have been built since the technology was developed in the late 1970s. (Tsao and Zasloff, 1979; Morschbacker, 2009) Although implementation of fluidized bed reactors could potentially increase the purity of the ethylene product and/or decrease costs, a small scale pilot process would need to be built and tested before it would be possible to develop an industrial-scale facility.

===Catalyst Alternatives===
Aluminum oxide, specifically gamma alumina, is the most industrially-common catalyst and has been historically used due to its low cost and high stability. (Tsao and Zasloff, 1979; Fan and Dai, n.d.) Recent improvements in selectivity and catalyst stability of activated alumina have been achieved by incorporating titanium oxide into the catalyst, although this increases reaction temperature by approximately 50 °C and decreases catalyst lifespan. (Chen and Li, et. al. 2007) There is also significant ongoing research into HZSM-5 zeolite and heteropolyacids, which are being explored as potential alternatives to alumina oxide. A nanoscale HZSM-5 zeolite catalyst has been shown to operate at the relatively low temperature of 200-300°C, with a 100% ethanol conversion and 99.7% selectivity to ethylene. Initial research has also indicated that it maintains greater than 98% selectivity for 630 operational hours. (Fan and Dai, n.d.) However, the current low cost and ready availability of unmodified alumina oxide makes it a better choice for a process of this scale.

===Purification Alternatives===
As specified in this process, the reactor effluent is purified by two flash drums and absorption with water to produce chemical-grade ethylene. If chemical-grade ethylene is indeed the desired product, other purification options include caustic washing of the reactor effluent and water removal in a desiccant drying bed. (Morschbacker, 2009) While this purification train is relatively simple and does not require harsh chemical reagents, polymer grade ethylene is more commercially valuable and the additional cost of removing water and diethyl ether contaminants may be justified by increased revenue. Cryogenic distillation was initially simulated to produce polymer-grade ethylene, but utility requirements were found to render this separation economically unviable. (Barrocas and Baratelli, 1983) Further research and optimization may find this purification strategy to be a more valid process. Alternatively, the addition of a cryogenic turboexpander or the use of alternative adsorbents may increase product purity to polymer grade. (Jumonville, 2010) Initial HYSYS simulations indicate that these operations may be feasible with further refinement.

===Wastewater Treatment===
Due to the large volume of wastewater produced, building an on-site wastewater treatment facility may prove to be more economical than paying for third-party wastewater treatment. Flash vessel FL-201 produces 44,600 L/hr of wastewater contaminated with 18.7 vol% ethanol and 0.6 vol% acetaldehyde, while FL-202 produces 2940 L/hr of an aqueous waste consisting of 56.8 vol% ethanol, 42.0 vol% water and 0.9 vol% diethyl ether. The absorption column produces approximately 10,200 liters/hr of wastewater contaminated with 1.2 vol% ethanol, 0.2% diethyl ether and 0.2% acetaldehyde. Utilizing distillation to separate these streams into clean water and volatile organic waste could ultimately reduce the quantity of waste that requires disposal and reduce the overall costs of the process.

==Process Equipment==
Relevant sizing information for each unit operation, estimated by the method described in the “Technical Approach,” can be found in Appendix V. Equipment and piping is assumed to be constructed of carbon steel. It should be noted that the two fired heaters are proportionately large enough to heat the entirety of the process stream and are thus larger than standard equipment.

=Economic Analysis=
[[File:sensitivityanalysis_B1.png|400px|thumb]]

==Economics Overview==
All final values are normalized to June 2014 USD by CEPCI scaling. It is assumed that all products produced are sold at current market prices.

The Aspen Economic Evaluation module within HYSYS v8.0 was used to estimate capital and operating costs for a 10-year plant life span with a construction start date of April 2015. The price of the 95% ethanol feed stream was estimated at $1.44 per gallon, while the chemical grade ethylene produced is currently selling for approximately $1350 per metric ton. (Today in Energy, 2015; Weddle, 2014) Mapping and sizing calculations were performed by the economics module and a preliminary economic evaluation was completed. Equipment sizes, also estimated by HYSYS, were reviewed to ensure that height, diameter, and volume specifications were within realistic ranges.

The process was ideally projected to operate 360 days per year with a start-up time of one year. In addition, the tax rate was approximated at 40%, an interest rate at 20%, and a salvage value of 20%. Escalation percentages were compounded yearly for the product, raw material, and operating costs. The total capital cost for this process is approximately $16.4 million, which includes all equipment and piping described in the process. The most expensive equipment used in this process are the two fired heaters F-101 and F-102, which have an exceptionally large heat exchange area to adequately heat the feed. Standard heaters may not suffice and additional costs may be incurred for the raw materials and manufacture of this equipment. Including a feed preheater or additional fired heaters may reduce this cost in subsequent design iterations.

The total operating cost is approximately $465 million per year, about $427 million of which is the cost of the ethanol feed and natural gas for the two fired heaters. An additional $1.73 million per year is used for utilities including the cooling water and refrigerant. The labor and maintenance costs of this industrial process were also accounted for within the simulation’s economic analysis. The HYSYS simulation software, in conjunction with the Icarus economic analyzer, estimated there should be 5 operators per 8 hour shift with a cost per operator of $20 per hour. This results in a total operating labor cost of approximately $880,000 per year. In addition, the process will require one supervisor per shift with an hourly rate of $35 for total supervisor salaries of $307,000 per year. Finally, a fixed maintenance rate was estimated at $205,000 per 8000 hours of operation for a total cost of $225,000 per year.

Total product sales are roughly $640 million per year at full operation. The estimated income for this process is thus approximately $175 million per year. After ten years, the plant is projected to have a net present value (NPV) of $391 million and an internal rate of return of approximately 79%. In addition the payout period for the initial investment is estimated to be about 2.7 years. Figure 2 shows the projected cash flow for the project.

==Sensitivity Analysis==
A sensitivity analysis was performed to investigate the effects of fluctuating capital costs, operating costs, raw materials, utility costs and ethylene sales price on the 10-year net present value (NPV) of the project. This analysis was performed by scaling these cost factors according to typical ranges given in Towler and Sinnott and calculating the adjusting the NPV accordingly. The results, illustrated in Figure 3, indicate that the project value is most sensitive to product sales, raw materials costs, and operating costs. Ethylene and ethanol prices are market-determined and cannot be controlled for in the process design, so further optimization should be focused on minimizing the operations cost of the process. (Today in Energy, 2015; Weddle, 2014) However, in feed and product prices do still have a profound effect on profitability and feasibility. A more rigorous market analysis will better inform the profitability outlook.

=Conclusions/Recommendations=

The proposed process produces approximately 460,000 metric tons of 99.7 wt% ethylene annually, with a 10-year net present value of $131 million. If current economic conditions hold, it is recommended that this project proceed to implementation following further design improvements and optimization.

Future design iterations should focus on process optimization, particularly in minimizing operating costs as prescribed by the results of the sensitivity analysis. The development of a heat-exchanger network, potentially with Aspen Energy Analyzer, is one option for decreasing utility requirements and increasing the efficiency of the process overall. Optimization of the fired heaters could also result in decreased operational costs. Although overall profitability is less sensitive to capital costs, reviewing and adjusting equipment sizing would also improve the economic outlook. In particular, exploring alternative heating strategies at the beginning of the process could significantly decrease capital costs. Although there are not any particularly dangerous chemicals utilized in the process, an overall process review should also consider potential failure modes to minimize the safety risk to plant workers and nearby residents.

In addition to economic and safety considerations, harmful emissions and waste streams should be minimized both to bring down the cost of treatment and to decrease environmental effects. The two fired heaters consume a large amount of natural gas per year, emitting about 200,000 tons of CO2 annually, and account for more than half of the capital cost of the process. Although no known toxic gases are produced, carbon capture or other emissions-reduction methods should be considered. Additionally, enough wastewater is produced by this process that building an onsite wastewater treatment center should be considered. This could not only decrease operating costs by eliminating the need for an external contract but also give the plant more control over the final purity of the treated wastewater.

Finally, the current model assumes that all ethylene produced will be sold at a current prices and price or product sales will not be affected by economic variability. A more detailed study of the chemical-grade ethylene market, as well as a more thorough understanding of sales and distribution logistics, would increase the surety of a profitable process.

In summary, the proposed process yields chemical grade ethylene via the catalytic dehydration of ethanol. A 100,000 kg/hr of 95 wt% ethanol, 5% water feed is converted to 53,000 kg/hr of 99.7% chemical-grade ethylene. After 10 years of operation, including a one-year startup time, the process has an NPV of $391 million with an IRR of 79% and a payback period of 2.7 years.
Pending further optimization, this process was determined to be viable and it is recommended for the project to move forward.

=References=

[1] American Chemistry Council. Production of chemicals and plastics in the U.S. in 2013, by type (in 1,000 metric tons). In Statista - The Statistics Portal. August 2014. Available at http://www.statista.com/statistics/299725/total-us-plastics-and-chemicals-shipments-by-type/, Accessed January 15, 2015. – Relative proportions of plastics production.

[2] DuPont Nevada Site Cellulosic Ethanol Facility [Internet]. DuPont Chemical; c2012-2015 [cited 11 Mar. 2015]. Available from: http://biofuels.dupont.com/cellulosic-ethanol/nevada-site-ce-facility/. -- Information on ethanol production in Iowa.

[3] Designing Ethylene Plants. Ethylene [Internet]. Technip; 2014 [cited 13 Mar. 2015]. Available from: http://www.technip.com/en/our-business/onshore/ethylene -- Plant size ranges.

[4] Suppes GJ. Selecting Thermodynamic Models for Process Simulation of Organic VLE and LLE Systems. The University of Missouri-Columbia, Dept of Chemical Engineering. [cited 13 Mar. 2015]. -- Use of NRTL in alcohol separations.

[5] ASPENtech. Appendix A - Property Methods and Calculations. Simulation Basics; A-3 - A-26. 2014.

[6] 190 Proof Ethanol: Technical Data Sheet [Internet]. Decon Labs Inc; 2012 [cited 13 Mar. 2015]. Available from: http://www.deconlabs.com/tds/ETHANOL%20190%20%20PROOF.pdf -- Information regarding 95% ethanol

[7] Hadawey A, Ge Y, Tassou TSA. Energy Savings Through Liquid Pressure Amplification In A Dairy Plant Refrigeration System. The Centre for Energy and Built Environment Research [cited 13 Mar. 2015].

[8] Methane (Chemical Compound). 2015. Encyclopædia Britannica Online. [cited 13 Mar. 2015] Available from: http://www.britannica.com/EBchecked/topic/378264/methane -- Composition of Methane

[9] Composition of Air [Internet]. Engineering Toolbox; [cited 13 Mar. 2015]. Available from: http://www.engineeringtoolbox.com/air-composition-d_212.html. -- Composition of air.

[10] Summary of the Clean Air Act, 2015. United States Environmental Protection Agency. [cited 13 Mar. 2015] Available from: http://www2.epa.gov/laws-regulations/summary-clean-air-act -- Emissions requirements of chemical plants.

[11] Zhang M, Yu Y. Dehydration of Ethanol to Ethylene. Industrial Engineering and Chemical Research. 2013; 52:9505-9514. – Technical information on ethanol to ethylene conversion via dehydration.

[12] AspenTech. Aspen HYSYS Help File v8.0. Aspen Technology, Inc. 2012. - Aspen HYSYS help file used for troubleshooting and assistance on economic analysis.

[13] Towler G, Sinnott R. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. 2nd ed. Boston: Elsevier; 2013. -- General Reference Book

[14] Barrocas H, Baratelli F, inventors; Petroleo Brasileiro S.A., assignee. Process for dehydration of a low molecular weight alcohol. US patent 4,396,789 A. August 2, 1983. - Primary background for process design.

[15] Tsao U, Zasloff HB, inventors; The Lummus Company, assignee. Production of ethylene from ethanol. US patent 4,134,926. January 16, 1979. – Patent for catalytic dehydration of ethylene in a fluidized bed reactor.

[16] Morschbacker, A. Bio-Ethanol Based Ethylene. Polymer Reviews. 2009; 49:79-84. – Overview of bioethanol dehydration process development.

[17] Fan D, Dai DJ, Wu HS. Ethylene Formation by Catalytic Dehydration of Ethanol with Industrial Considerations. Materials. 6, 101-115. doi: 10.3390/ma6010101. - Comparison of types of catalysts used in the dehydration of ethanol and current research into new catalysts.

[18] Chen G, Li S, Jiao F, Yuan Q. Catalytic dehydration of bioethanol to ethylene over TiO2/γ-Al2O3 catalysts in microchannel reactors. Catal. Today 2007, 125, 111–119. - Paper introducing research on modified alumina catalyst for ethanol dehydration.

[19] Jumonville, J. Tutorial on Cryogenic Turboexpanders. Proceedings of the Thirty-Ninth Turbomachinery Symposium; 2010 Oct 4-7; Houston, TX. Houston: Texas A&M University; 2010. -- Use of turboexpander for cryogenic separations

[20] Today in Energy - Daily Prices. US Energy Information Administration website. http://www.eia.gov/todayinenergy/prices.cfm. Accessed March 3rd 2015. - Bulk market price for 95% ethanol.

[21] Weddle, N. ICIS Pricing: Ethylene (Europe). Reed Business Limited. January 10 2014. - Bulk market price for chemical grade ethylene.

=Appendix I - Process Flow Diagram=
[[File:PFD B1.JPG|1200px]]

=Appendix II - HYSYS Simulation=
[[File:HYSYS_B1.PNG]]

=Appendix III - Material Streams=
[[File:Streams_B1.png|1200px]]

=Appendix IV - Energy Table=
[[File:Energy_B1.png|600px|center]]

=Appendix V - Economics=
[[File:Econsummary_B1.png|center]] 

[[File:Capcost_B1.png|center]] 

[[File:sensitivityanalysis_B1.png|600px|center]]

Ethanol to Ethylene (B1)

2015-03-14T04:20:18Z

Hpoppick:

[[File:BFD_B1.png|600px|thumbnail|alt=Alt text|Conversion of Ethanol to Ethylene]]

Team B1 Final Report

Authors: Harry Poppick, Emm Fulk and Scott Smith

Instructors: Fengqi You, David Wegerer

March 13, 2015

=Executive Summary=

The following report outlines the design and analysis of a process converting ethanol to chemical-grade ethylene via catalytic dehydration. This process consumers 100,000 kg/hr of 95 wt% ethanol, 5 wt% water feedstock and produces 53,000 kg/hr of 99.7 wt% chemical-grade ethylene. The ethanol feed passes through two fixed-bed reactors, each packed with an aluminum oxide catalyst, and the resulting ethylene is purified by two flash tanks and by absorption with water. The process was modeled using Aspen HYSYS simulation software to estimate mass and energy flows and equipment sizing requirements. Based on results of this initial simulation, several alternatives are discussed for increasing the process efficiency and profitability. The use of a fluidized bed reactor or a more ethylene-selective catalyst could increase the production of ethylene per ethanol basis. Additionally, several methods of purification to more valuable polymer-grade ethylene are proposed.

The economic feasibility of this process was evaluated using Aspen Economic Analyzer with the Icarus economics package. Capital cost is approximately $16.4 million total with an operating cost of $465 million per year. The current market prices of the ethanol feed and ethylene sales price are $1.44/gallon and $1350/metric ton respectively. The cost of feed ethanol, process utilities and miscellaneous operational costs total to about $427 million/year. At full operation, revenue at current prices would be approximately $640 million per year. The predicted 10-year net present value of the process is approximately $391 million with an IRR of 79% and a payback period of 2.7 years. A sensitivity analysis indicates that the process is most sensitive to feed prices, product prices and operation cost.

Several recommendations are made for both cost reduction and profit maximization, including the design of a heat exchanger network and the optimization of fired heaters that require high capital investment and large amounts of fuel. A safety review of the process is recommended, as well as the minimization of flue gas effluent and wastewater. It is also suggested that the construction of an onsite wastewater treatment center be considered. Overall, the initial analysis indicates this to be a profitable process and it is recommended the project move forward.

=Introduction=

Ethylene is a critical chemical precursor to a number of different industrial products. It is often derived from petroleum sources and polymerized to polyethylene, one of the most ubiquitous plastics today. (American Chemistry Council, 2013) Recently there has been a significant effort to develop production pathways utilizing biologically-derived feedstocks, such as corn or cellulosic ethanol, rather than traditional fossil-fuel sources. Ethylene can be produced from bioethanol via catalytic dehydration over an aluminum oxide catalyst. The proposed process converts 100,000 kg/hr of 95 wt% ethanol, 5% water feed to 53,000 kg/hr of 99.7% chemical-grade ethylene when operating at full capacity. This process was found to be economically viable with a 10-year net present value (NPV) of $131 million (2014 USD) and a payback period of approximately 2.7 years. This memo will detail the proposed process, as well as outline potential alternatives and economic viability of the project.

=Technical Approach=

Many bioethanol plants are located in the Midwest where large amounts of feedstock crops, such as corn, are grown. As such, this plant will be located in Story county, Iowa, near a large-scale bioethanol production plant. (DuPont Nevada Site, 2012) It is assumed that the supply of bioethanol is consistent and readily available. It is also assumed that other reagents - namely, the aluminum oxide catalyst, heater fuel, utility water and freon refrigerant - are readily available, and that wastewater treatment facilities are located near enough to facilitate the off-site treatment of wastewater. Plant capacity was based on current mid-sized industrial ethylene plants. (Designing Ethylene Plants, 2014)

HYSYS simulations were performed with the NRTL fluid package and Peng-Robinson vapor model. The NRTL fluid package is an activity coefficient model that is especially useful to model the separations of alcohols in aqueous solutions. (Suppes, 2015) In addition, NRTL uses models of binary pairs of components, much like the Wilson equation, to predict chemical interactions at the molecular level. The NRTL package can thus be easily extended to ternary and higher order chemical systems, making it ideal for this type of simulation. The Peng-Robinson vapor model was selected as it is well-suited to account for the non-idealities of the vapor phase reactions and separations integral to this process. (ASPENtech, 2014)

It was assumed that the feed enters the process at ambient temperature and pressure (25 °C, 1 atm) and at a consistent rate and composition with negligible quantities of impurities. The ethanol feed was assumed to be 95% ethanol and 5% water by mass, which is the commercial standard for industrial ethanol. (190 Proof Ethanol, 2012) Storage vessels for the feed ethanol, waste streams and products are assumed to be located nearby to the process. An initial feed pump compensates for pressure drops through the process and reduces the duty on downstream compressors. (Hadawey, 2015)

Natural gas, assumed to consist of 83% methane, 16% ethane and 1% nitrogen by mass, was supplied to two fired heaters at a flow rate estimated by HYSYS. (Methane, 2015) Air fed to the process to enable combustion was assumed to be 23% oxygen and 77% nitrogen by mass. (Composition of Air, 2015) Air streams were fed at 50% molar excess in order to ensure complete combustion and prevent the formation of carbon monoxide in the heater exhaust. Total flue gases are assumed to be 230,000 kg/hr, or 2.2 million tons annually, and consist of 73.8% nitrogen gas, 10.5% carbon dioxide, 8.2% water vapor, and 7.5% oxygen by mass. The only compound of concern in these emissions is the carbon dioxide, a known greenhouse gas. At the time of this report, the quantities of carbon dioxide emitted by this plant annually are within acceptable EPA specifications. (Summary of the Clean Air Act, 2015)

Due to the difficulty of simulation equilibrium and conversion reactions in a single vessel in HYSYS, these two reaction types were simulated in separate equilibrium reactor and conversion reactor units in series. In addition, while HYSYS indicated that reactor units would output separate vapor and liquid streams, it was assumed that in practice this would take the form of a single, two phase stream between each unit. To account for this, mixers were installed downstream of each reactor to combine the liquid and vapor phases of the reactor effluent. The three consequent reactions considered are as follows:

Ethanol ↔ Ethylene + Water
Ethanol → Acetaldehyde + Hydrogen
2 Ethanol → Diethyl Ether + Water

The optimal reaction temperature was determined to be 400 °C, which promotes the equilibrium reaction of ethanol to ethylene while minimizing byproducts. (Zhang and Yu, 2013) While other byproducts may be produced in this process, these reactions are typically taken to comprise of the bulk of the dehydration reaction. Heat losses over these reactors were assumed to be negligible. (Zhang and Yu, 2013)All major process equipment is assumed to be constructed of high strength carbon steel. (AspenTech, 2012)

The “Sizing Utility” within the Icarus Economic Evaluation module was used to estimate sizes of major equipment based on the process simulation. These values can serve as a benchmark for an initial plant design. Icarus KbaseTM implements a wide variety of mechanical design standards, including ASME and BS5500, in order to calculate accurate equipment sizing. The Icarus sizing module combines equipment prices for standard chemical processing equipment as well as correlations and sizing factors. The advantage of using a software package such as HYSYS to price out individual equipment is that it utilizes up-to-date prices from vendors and distributors when estimating costs. A more in-depth overview of the correlations included in this software can be found in Towler and Sinnott (2009).

=Process Flowsheet=
[[File:Squarepfd_B1.PNG|thumb|400px]]

The following process is based primarily on a 1983 US patent titled “Process for dehydration of a low molecular weight alcohol.” (Barrocas and Baratelli, 1983) The process flow diagram can be seen in Figure 1. A larger version of the PFD is included in Appendix I and the HYSYS simulation setup in Appendix II.

The feed enters the process at a rate of 100,000 kg/hr, a temperature and pressure of a 25 °C and 1 atm and at a composition of 95 wt% ethanol and 5 wt% water.It is initially pressurized to 4335 kPa by centrifugal pump P-101 and subsequently heated to 400 °C by fired heater F-101. The heated and pressurized feed enters fixed bed reactor R-101 and contacts with the aluminum oxide catalyst. At this point it dehydrates to form the product, ethylene, as well as the byproducts water, hydrogen, diethyl ether and acetaldehyde. Fired heater F-102 and reactor R-102 increase the overall conversion of the process. Both fired heaters F-101 and F-102 are fueled with natural gas and fed with excess air. The composition of the reactor train effluent is 54.5 wt% ethylene, 37.1 wt% water, 8.1 wt% unreacted ethanol and trace amounts of diethyl ether, acetaldehyde, and hydrogen contaminants.

The pressure of the reactor train effluent is increased to 4500 kPa by compressor K-102 and the temperature decreased to 100 °C by exchange with cold water in heat exchanger E-201. The stream then expands and flashes in flash vessel FL-201, which separates out 82.3% of the unreacted ethanol, 96.6% of the water and virtually all of the acetaldehyde contaminant in the bottoms while sending the ethylene-rich vapor phase out of the top. The top product of FL-202 is compressed to 3500 kPA by K-202 and cooled to 0.0 °C by a freon refrigerant in E-202. At this point the stream is flashed for a second time in vessel FL-202 to remove additional impurities. The top outlet stream consists of 99.5 wt% ethylene, which is fed to the bottom of a 10-tray absorption column that removes a fraction of the residual diethyl ether as well as the remainder of the unreacted ethanol. A stream of absorbent water is fed to the top of the column at 10,000 kg/hr. The product exits the top of the column at a rate of 54,600 kg/hr and has a purity of 99.7% ethylene. Diethyl ether makes up 0.2% of the remaining product stream and is the primary contaminant. Trace amounts of residual water and hydrogen are also present.

Full tables of material and energy streams can be found in Appendices III and IV respectively.

==Process Alternatives==
===Reactor Alternatives===
Two fixed bed reactors, alternating with fired heaters, are used in the dehydration reaction of ethanol to ethylene. However, a fluidized bed reactor can offer better mixing and temperature control than a fixed bed reactor and thus provide the highest possible conversion of ethanol with the greatest selectivity to ethylene. (Tsao and Zasloff, 1979) Fluidized bed reactors also provide a lower rate of catalyst coking and byproduct formation, minimizing separation and catalyst regeneration costs. (Morschbacker, 2009) The major downside of fluidized bed reactors is that few large-scale processes have been built since the technology was developed in the late 1970s. (Tsao and Zasloff, 1979; Morschbacker, 2009) Although implementation of fluidized bed reactors could potentially increase the purity of the ethylene product and/or decrease costs, a small scale pilot process would need to be built and tested before it would be possible to develop an industrial-scale facility.

===Catalyst Alternatives===
Aluminum oxide, specifically gamma alumina, is the most industrially-common catalyst and has been historically used due to its low cost and high stability. (Tsao and Zasloff, 1979; Fan and Dai, n.d.) Recent improvements in selectivity and catalyst stability of activated alumina have been achieved by incorporating titanium oxide into the catalyst, although this increases reaction temperature by approximately 50 °C and decreases catalyst lifespan. (Chen and Li, et. al. 2007) There is also significant ongoing research into HZSM-5 zeolite and heteropolyacids, which are being explored as potential alternatives to alumina oxide. A nanoscale HZSM-5 zeolite catalyst has been shown to operate at the relatively low temperature of 200-300°C, with a 100% ethanol conversion and 99.7% selectivity to ethylene. Initial research has also indicated that it maintains greater than 98% selectivity for 630 operational hours. (Fan and Dai, n.d.) However, the current low cost and ready availability of unmodified alumina oxide makes it a better choice for a process of this scale.

===Purification Alternatives===
As specified in this process, the reactor effluent is purified by two flash drums and absorption with water to produce chemical-grade ethylene. If chemical-grade ethylene is indeed the desired product, other purification options include caustic washing of the reactor effluent and water removal in a desiccant drying bed. (Morschbacker, 2009) While this purification train is relatively simple and does not require harsh chemical reagents, polymer grade ethylene is more commercially valuable and the additional cost of removing water and diethyl ether contaminants may be justified by increased revenue. Cryogenic distillation was initially simulated to produce polymer-grade ethylene, but utility requirements were found to render this separation economically unviable. (Barrocas and Baratelli, 1983) Further research and optimization may find this purification strategy to be a more valid process. Alternatively, the addition of a cryogenic turboexpander or the use of alternative adsorbents may increase product purity to polymer grade. (Jumonville, 2010) Initial HYSYS simulations indicate that these operations may be feasible with further refinement.

===Wastewater Treatment===
Due to the large volume of wastewater produced, building an on-site wastewater treatment facility may prove to be more economical than paying for third-party wastewater treatment. Flash vessel FL-201 produces 44,600 L/hr of wastewater contaminated with 18.7 vol% ethanol and 0.6 vol% acetaldehyde, while FL-202 produces 2940 L/hr of an aqueous waste consisting of 56.8 vol% ethanol, 42.0 vol% water and 0.9 vol% diethyl ether. The absorption column produces approximately 10,200 liters/hr of wastewater contaminated with 1.2 vol% ethanol, 0.2% diethyl ether and 0.2% acetaldehyde. Utilizing distillation to separate these streams into clean water and volatile organic waste could ultimately reduce the quantity of waste that requires disposal and reduce the overall costs of the process.

==Process Equipment==
Relevant sizing information for each unit operation, estimated by the method described in the “Technical Approach,” can be found in Appendix V. Equipment and piping is assumed to be constructed of carbon steel. It should be noted that the two fired heaters are proportionately large enough to heat the entirety of the process stream and are thus larger than standard equipment.

=Economic Analysis=
[[File:sensitivityanalysis_B1.png|400px|thumb]]

==Economics Overview==
All final values are normalized to June 2014 USD by CEPCI scaling. It is assumed that all products produced are sold at current market prices.

The Aspen Economic Evaluation module within HYSYS v8.0 was used to estimate capital and operating costs for a 10-year plant life span with a construction start date of April 2015. The price of the 95% ethanol feed stream was estimated at $1.44 per gallon, while the chemical grade ethylene produced is currently selling for approximately $1350 per metric ton. (Today in Energy, 2015; Weddle, 2014) Mapping and sizing calculations were performed by the economics module and a preliminary economic evaluation was completed. Equipment sizes, also estimated by HYSYS, were reviewed to ensure that height, diameter, and volume specifications were within realistic ranges.

The process was ideally projected to operate 360 days per year with a start-up time of one year. In addition, the tax rate was approximated at 40%, an interest rate at 20%, and a salvage value of 20%. Escalation percentages were compounded yearly for the product, raw material, and operating costs. The total capital cost for this process is approximately $16.4 million, which includes all equipment and piping described in the process. The most expensive equipment used in this process are the two fired heaters F-101 and F-102, which have an exceptionally large heat exchange area to adequately heat the feed. Standard heaters may not suffice and additional costs may be incurred for the raw materials and manufacture of this equipment. Including a feed preheater or additional fired heaters may reduce this cost in subsequent design iterations.

The total operating cost is approximately $465 million per year, about $427 million of which is the cost of the ethanol feed and natural gas for the two fired heaters. An additional $1.73 million per year is used for utilities including the cooling water and refrigerant. The labor and maintenance costs of this industrial process were also accounted for within the simulation’s economic analysis. The HYSYS simulation software, in conjunction with the Icarus economic analyzer, estimated there should be 5 operators per 8 hour shift with a cost per operator of $20 per hour. This results in a total operating labor cost of approximately $880,000 per year. In addition, the process will require one supervisor per shift with an hourly rate of $35 for total supervisor salaries of $307,000 per year. Finally, a fixed maintenance rate was estimated at $205,000 per 8000 hours of operation for a total cost of $225,000 per year.

Total product sales are roughly $640 million per year at full operation. The estimated income for this process is thus approximately $175 million per year. After ten years, the plant is projected to have a net present value (NPV) of $391 million and an internal rate of return of approximately 79%. In addition the payout period for the initial investment is estimated to be about 2.7 years. Figure 2 shows the projected cash flow for the project.

==Sensitivity Analysis==
A sensitivity analysis was performed to investigate the effects of fluctuating capital costs, operating costs, raw materials, utility costs and ethylene sales price on the 10-year net present value (NPV) of the project. This analysis was performed by scaling these cost factors according to typical ranges given in Towler and Sinnott and calculating the adjusting the NPV accordingly. The results, illustrated in Figure 3, indicate that the project value is most sensitive to product sales, raw materials costs, and operating costs. Ethylene and ethanol prices are market-determined and cannot be controlled for in the process design, so further optimization should be focused on minimizing the operations cost of the process. (Today in Energy, 2015; Weddle, 2014) However, in feed and product prices do still have a profound effect on profitability and feasibility. A more rigorous market analysis will better inform the profitability outlook.

=Conclusions/Recommendations=

The proposed process produces approximately 460,000 metric tons of 99.7 wt% ethylene annually, with a 10-year net present value of $131 million. If current economic conditions hold, it is recommended that this project proceed to implementation following further design improvements and optimization.

Future design iterations should focus on process optimization, particularly in minimizing operating costs as prescribed by the results of the sensitivity analysis. The development of a heat-exchanger network, potentially with Aspen Energy Analyzer, is one option for decreasing utility requirements and increasing the efficiency of the process overall. Optimization of the fired heaters could also result in decreased operational costs. Although overall profitability is less sensitive to capital costs, reviewing and adjusting equipment sizing would also improve the economic outlook. In particular, exploring alternative heating strategies at the beginning of the process could significantly decrease capital costs. Although there are not any particularly dangerous chemicals utilized in the process, an overall process review should also consider potential failure modes to minimize the safety risk to plant workers and nearby residents.

In addition to economic and safety considerations, harmful emissions and waste streams should be minimized both to bring down the cost of treatment and to decrease environmental effects. The two fired heaters consume a large amount of natural gas per year, emitting about 200,000 tons of CO2 annually, and account for more than half of the capital cost of the process. Although no known toxic gases are produced, carbon capture or other emissions-reduction methods should be considered. Additionally, enough wastewater is produced by this process that building an onsite wastewater treatment center should be considered. This could not only decrease operating costs by eliminating the need for an external contract but also give the plant more control over the final purity of the treated wastewater.

Finally, the current model assumes that all ethylene produced will be sold at a current prices and price or product sales will not be affected by economic variability. A more detailed study of the chemical-grade ethylene market, as well as a more thorough understanding of sales and distribution logistics, would increase the surety of a profitable process.

In summary, the proposed process yields chemical grade ethylene via the catalytic dehydration of ethanol. A 100,000 kg/hr of 95 wt% ethanol, 5% water feed is converted to 53,000 kg/hr of 99.7% chemical-grade ethylene. After 10 years of operation, including a one-year startup time, the process has an NPV of $391 million with an IRR of 79% and a payback period of 2.7 years.
Pending further optimization, this process was determined to be viable and it is recommended for the project to move forward.

=References=

[1] American Chemistry Council. Production of chemicals and plastics in the U.S. in 2013, by type (in 1,000 metric tons). In Statista - The Statistics Portal. August 2014. Available at http://www.statista.com/statistics/299725/total-us-plastics-and-chemicals-shipments-by-type/, Accessed January 15, 2015. – Relative proportions of plastics production.

[2] DuPont Nevada Site Cellulosic Ethanol Facility [Internet]. DuPont Chemical; c2012-2015 [cited 11 Mar. 2015]. Available from: http://biofuels.dupont.com/cellulosic-ethanol/nevada-site-ce-facility/. -- Information on ethanol production in Iowa.

[3] Designing Ethylene Plants. Ethylene [Internet]. Technip; 2014 [cited 13 Mar. 2015]. Available from: http://www.technip.com/en/our-business/onshore/ethylene -- Plant size ranges.

[4] Suppes GJ. Selecting Thermodynamic Models for Process Simulation of Organic VLE and LLE Systems. The University of Missouri-Columbia, Dept of Chemical Engineering. [cited 13 Mar. 2015]. -- Use of NRTL in alcohol separations.

[5] ASPENtech. Appendix A - Property Methods and Calculations. Simulation Basics; A-3 - A-26. 2014.

[6] 190 Proof Ethanol: Technical Data Sheet [Internet]. Decon Labs Inc; 2012 [cited 13 Mar. 2015]. Available from: http://www.deconlabs.com/tds/ETHANOL%20190%20%20PROOF.pdf -- Information regarding 95% ethanol

[7] Hadawey A, Ge Y, Tassou TSA. Energy Savings Through Liquid Pressure Amplification In A Dairy Plant Refrigeration System. The Centre for Energy and Built Environment Research [cited 13 Mar. 2015].

[8] Methane (Chemical Compound). 2015. Encyclopædia Britannica Online. [cited 13 Mar. 2015] Available from: http://www.britannica.com/EBchecked/topic/378264/methane -- Composition of Methane

[9] Composition of Air [Internet]. Engineering Toolbox; [cited 13 Mar. 2015]. Available from: http://www.engineeringtoolbox.com/air-composition-d_212.html. -- Composition of air.

[10] Summary of the Clean Air Act, 2015. United States Environmental Protection Agency. [cited 13 Mar. 2015] Available from: http://www2.epa.gov/laws-regulations/summary-clean-air-act -- Emissions requirements of chemical plants.

[11] Zhang M, Yu Y. Dehydration of Ethanol to Ethylene. Industrial Engineering and Chemical Research. 2013; 52:9505-9514. – Technical information on ethanol to ethylene conversion via dehydration.

[12] AspenTech. Aspen HYSYS Help File v8.0. Aspen Technology, Inc. 2012. - Aspen HYSYS help file used for troubleshooting and assistance on economic analysis.

[13] Towler G, Sinnott R. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. 2nd ed. Boston: Elsevier; 2013. -- General Reference Book

[14] Barrocas H, Baratelli F, inventors; Petroleo Brasileiro S.A., assignee. Process for dehydration of a low molecular weight alcohol. US patent 4,396,789 A. August 2, 1983. - Primary background for process design.

[15] Tsao U, Zasloff HB, inventors; The Lummus Company, assignee. Production of ethylene from ethanol. US patent 4,134,926. January 16, 1979. – Patent for catalytic dehydration of ethylene in a fluidized bed reactor.

[16] Morschbacker, A. Bio-Ethanol Based Ethylene. Polymer Reviews. 2009; 49:79-84. – Overview of bioethanol dehydration process development.

[17] Fan D, Dai DJ, Wu HS. Ethylene Formation by Catalytic Dehydration of Ethanol with Industrial Considerations. Materials. 6, 101-115. doi: 10.3390/ma6010101. - Comparison of types of catalysts used in the dehydration of ethanol and current research into new catalysts.

[18] Chen G, Li S, Jiao F, Yuan Q. Catalytic dehydration of bioethanol to ethylene over TiO2/γ-Al2O3 catalysts in microchannel reactors. Catal. Today 2007, 125, 111–119. - Paper introducing research on modified alumina catalyst for ethanol dehydration.

[19] Jumonville, J. Tutorial on Cryogenic Turboexpanders. Proceedings of the Thirty-Ninth Turbomachinery Symposium; 2010 Oct 4-7; Houston, TX. Houston: Texas A&M University; 2010. -- Use of turboexpander for cryogenic separations

[20] Today in Energy - Daily Prices. US Energy Information Administration website. http://www.eia.gov/todayinenergy/prices.cfm. Accessed March 3rd 2015. - Bulk market price for 95% ethanol.

[21] Weddle, N. ICIS Pricing: Ethylene (Europe). Reed Business Limited. January 10 2014. - Bulk market price for chemical grade ethylene.

=Appendix I - Process Flow Diagram=
[[File:PFD B1.JPG|1200px]]

=Appendix II - HYSYS Simulation=
[[File:HYSYS_B1.PNG|1200px]]

=Appendix III - Material Streams=
[[File:Streams_B1.png|1200px]]

=Appendix IV - Energy Table=
[[File:Energy_B1.png|600px|center]]

=Appendix V - Economics=
[[File:Econsummary_B1.png|center]] 

[[File:Capcost_B1.png|center]] 

[[File:sensitivityanalysis_B1.png|600px|center]]

Ethanol to Ethylene (B1)

2015-03-14T04:20:07Z

Hpoppick:

[[File:BFD_B1.png|600px|thumbnail|alt=Alt text|Conversion of Ethanol to Ethylene]]

Team B1 Final Report
Authors: Harry Poppick, Emm Fulk and Scott Smith
Instructors: Fengqi You, David Wegerer
March 13, 2015

=Executive Summary=

The following report outlines the design and analysis of a process converting ethanol to chemical-grade ethylene via catalytic dehydration. This process consumers 100,000 kg/hr of 95 wt% ethanol, 5 wt% water feedstock and produces 53,000 kg/hr of 99.7 wt% chemical-grade ethylene. The ethanol feed passes through two fixed-bed reactors, each packed with an aluminum oxide catalyst, and the resulting ethylene is purified by two flash tanks and by absorption with water. The process was modeled using Aspen HYSYS simulation software to estimate mass and energy flows and equipment sizing requirements. Based on results of this initial simulation, several alternatives are discussed for increasing the process efficiency and profitability. The use of a fluidized bed reactor or a more ethylene-selective catalyst could increase the production of ethylene per ethanol basis. Additionally, several methods of purification to more valuable polymer-grade ethylene are proposed.

The economic feasibility of this process was evaluated using Aspen Economic Analyzer with the Icarus economics package. Capital cost is approximately $16.4 million total with an operating cost of $465 million per year. The current market prices of the ethanol feed and ethylene sales price are $1.44/gallon and $1350/metric ton respectively. The cost of feed ethanol, process utilities and miscellaneous operational costs total to about $427 million/year. At full operation, revenue at current prices would be approximately $640 million per year. The predicted 10-year net present value of the process is approximately $391 million with an IRR of 79% and a payback period of 2.7 years. A sensitivity analysis indicates that the process is most sensitive to feed prices, product prices and operation cost.

Several recommendations are made for both cost reduction and profit maximization, including the design of a heat exchanger network and the optimization of fired heaters that require high capital investment and large amounts of fuel. A safety review of the process is recommended, as well as the minimization of flue gas effluent and wastewater. It is also suggested that the construction of an onsite wastewater treatment center be considered. Overall, the initial analysis indicates this to be a profitable process and it is recommended the project move forward.

=Introduction=

Ethylene is a critical chemical precursor to a number of different industrial products. It is often derived from petroleum sources and polymerized to polyethylene, one of the most ubiquitous plastics today. (American Chemistry Council, 2013) Recently there has been a significant effort to develop production pathways utilizing biologically-derived feedstocks, such as corn or cellulosic ethanol, rather than traditional fossil-fuel sources. Ethylene can be produced from bioethanol via catalytic dehydration over an aluminum oxide catalyst. The proposed process converts 100,000 kg/hr of 95 wt% ethanol, 5% water feed to 53,000 kg/hr of 99.7% chemical-grade ethylene when operating at full capacity. This process was found to be economically viable with a 10-year net present value (NPV) of $131 million (2014 USD) and a payback period of approximately 2.7 years. This memo will detail the proposed process, as well as outline potential alternatives and economic viability of the project.

=Technical Approach=

Many bioethanol plants are located in the Midwest where large amounts of feedstock crops, such as corn, are grown. As such, this plant will be located in Story county, Iowa, near a large-scale bioethanol production plant. (DuPont Nevada Site, 2012) It is assumed that the supply of bioethanol is consistent and readily available. It is also assumed that other reagents - namely, the aluminum oxide catalyst, heater fuel, utility water and freon refrigerant - are readily available, and that wastewater treatment facilities are located near enough to facilitate the off-site treatment of wastewater. Plant capacity was based on current mid-sized industrial ethylene plants. (Designing Ethylene Plants, 2014)

HYSYS simulations were performed with the NRTL fluid package and Peng-Robinson vapor model. The NRTL fluid package is an activity coefficient model that is especially useful to model the separations of alcohols in aqueous solutions. (Suppes, 2015) In addition, NRTL uses models of binary pairs of components, much like the Wilson equation, to predict chemical interactions at the molecular level. The NRTL package can thus be easily extended to ternary and higher order chemical systems, making it ideal for this type of simulation. The Peng-Robinson vapor model was selected as it is well-suited to account for the non-idealities of the vapor phase reactions and separations integral to this process. (ASPENtech, 2014)

It was assumed that the feed enters the process at ambient temperature and pressure (25 °C, 1 atm) and at a consistent rate and composition with negligible quantities of impurities. The ethanol feed was assumed to be 95% ethanol and 5% water by mass, which is the commercial standard for industrial ethanol. (190 Proof Ethanol, 2012) Storage vessels for the feed ethanol, waste streams and products are assumed to be located nearby to the process. An initial feed pump compensates for pressure drops through the process and reduces the duty on downstream compressors. (Hadawey, 2015)

Natural gas, assumed to consist of 83% methane, 16% ethane and 1% nitrogen by mass, was supplied to two fired heaters at a flow rate estimated by HYSYS. (Methane, 2015) Air fed to the process to enable combustion was assumed to be 23% oxygen and 77% nitrogen by mass. (Composition of Air, 2015) Air streams were fed at 50% molar excess in order to ensure complete combustion and prevent the formation of carbon monoxide in the heater exhaust. Total flue gases are assumed to be 230,000 kg/hr, or 2.2 million tons annually, and consist of 73.8% nitrogen gas, 10.5% carbon dioxide, 8.2% water vapor, and 7.5% oxygen by mass. The only compound of concern in these emissions is the carbon dioxide, a known greenhouse gas. At the time of this report, the quantities of carbon dioxide emitted by this plant annually are within acceptable EPA specifications. (Summary of the Clean Air Act, 2015)

Due to the difficulty of simulation equilibrium and conversion reactions in a single vessel in HYSYS, these two reaction types were simulated in separate equilibrium reactor and conversion reactor units in series. In addition, while HYSYS indicated that reactor units would output separate vapor and liquid streams, it was assumed that in practice this would take the form of a single, two phase stream between each unit. To account for this, mixers were installed downstream of each reactor to combine the liquid and vapor phases of the reactor effluent. The three consequent reactions considered are as follows:

Ethanol ↔ Ethylene + Water
Ethanol → Acetaldehyde + Hydrogen
2 Ethanol → Diethyl Ether + Water

The optimal reaction temperature was determined to be 400 °C, which promotes the equilibrium reaction of ethanol to ethylene while minimizing byproducts. (Zhang and Yu, 2013) While other byproducts may be produced in this process, these reactions are typically taken to comprise of the bulk of the dehydration reaction. Heat losses over these reactors were assumed to be negligible. (Zhang and Yu, 2013)All major process equipment is assumed to be constructed of high strength carbon steel. (AspenTech, 2012)

The “Sizing Utility” within the Icarus Economic Evaluation module was used to estimate sizes of major equipment based on the process simulation. These values can serve as a benchmark for an initial plant design. Icarus KbaseTM implements a wide variety of mechanical design standards, including ASME and BS5500, in order to calculate accurate equipment sizing. The Icarus sizing module combines equipment prices for standard chemical processing equipment as well as correlations and sizing factors. The advantage of using a software package such as HYSYS to price out individual equipment is that it utilizes up-to-date prices from vendors and distributors when estimating costs. A more in-depth overview of the correlations included in this software can be found in Towler and Sinnott (2009).

=Process Flowsheet=
[[File:Squarepfd_B1.PNG|thumb|400px]]

The following process is based primarily on a 1983 US patent titled “Process for dehydration of a low molecular weight alcohol.” (Barrocas and Baratelli, 1983) The process flow diagram can be seen in Figure 1. A larger version of the PFD is included in Appendix I and the HYSYS simulation setup in Appendix II.

The feed enters the process at a rate of 100,000 kg/hr, a temperature and pressure of a 25 °C and 1 atm and at a composition of 95 wt% ethanol and 5 wt% water.It is initially pressurized to 4335 kPa by centrifugal pump P-101 and subsequently heated to 400 °C by fired heater F-101. The heated and pressurized feed enters fixed bed reactor R-101 and contacts with the aluminum oxide catalyst. At this point it dehydrates to form the product, ethylene, as well as the byproducts water, hydrogen, diethyl ether and acetaldehyde. Fired heater F-102 and reactor R-102 increase the overall conversion of the process. Both fired heaters F-101 and F-102 are fueled with natural gas and fed with excess air. The composition of the reactor train effluent is 54.5 wt% ethylene, 37.1 wt% water, 8.1 wt% unreacted ethanol and trace amounts of diethyl ether, acetaldehyde, and hydrogen contaminants.

The pressure of the reactor train effluent is increased to 4500 kPa by compressor K-102 and the temperature decreased to 100 °C by exchange with cold water in heat exchanger E-201. The stream then expands and flashes in flash vessel FL-201, which separates out 82.3% of the unreacted ethanol, 96.6% of the water and virtually all of the acetaldehyde contaminant in the bottoms while sending the ethylene-rich vapor phase out of the top. The top product of FL-202 is compressed to 3500 kPA by K-202 and cooled to 0.0 °C by a freon refrigerant in E-202. At this point the stream is flashed for a second time in vessel FL-202 to remove additional impurities. The top outlet stream consists of 99.5 wt% ethylene, which is fed to the bottom of a 10-tray absorption column that removes a fraction of the residual diethyl ether as well as the remainder of the unreacted ethanol. A stream of absorbent water is fed to the top of the column at 10,000 kg/hr. The product exits the top of the column at a rate of 54,600 kg/hr and has a purity of 99.7% ethylene. Diethyl ether makes up 0.2% of the remaining product stream and is the primary contaminant. Trace amounts of residual water and hydrogen are also present.

Full tables of material and energy streams can be found in Appendices III and IV respectively.

==Process Alternatives==
===Reactor Alternatives===
Two fixed bed reactors, alternating with fired heaters, are used in the dehydration reaction of ethanol to ethylene. However, a fluidized bed reactor can offer better mixing and temperature control than a fixed bed reactor and thus provide the highest possible conversion of ethanol with the greatest selectivity to ethylene. (Tsao and Zasloff, 1979) Fluidized bed reactors also provide a lower rate of catalyst coking and byproduct formation, minimizing separation and catalyst regeneration costs. (Morschbacker, 2009) The major downside of fluidized bed reactors is that few large-scale processes have been built since the technology was developed in the late 1970s. (Tsao and Zasloff, 1979; Morschbacker, 2009) Although implementation of fluidized bed reactors could potentially increase the purity of the ethylene product and/or decrease costs, a small scale pilot process would need to be built and tested before it would be possible to develop an industrial-scale facility.

===Catalyst Alternatives===
Aluminum oxide, specifically gamma alumina, is the most industrially-common catalyst and has been historically used due to its low cost and high stability. (Tsao and Zasloff, 1979; Fan and Dai, n.d.) Recent improvements in selectivity and catalyst stability of activated alumina have been achieved by incorporating titanium oxide into the catalyst, although this increases reaction temperature by approximately 50 °C and decreases catalyst lifespan. (Chen and Li, et. al. 2007) There is also significant ongoing research into HZSM-5 zeolite and heteropolyacids, which are being explored as potential alternatives to alumina oxide. A nanoscale HZSM-5 zeolite catalyst has been shown to operate at the relatively low temperature of 200-300°C, with a 100% ethanol conversion and 99.7% selectivity to ethylene. Initial research has also indicated that it maintains greater than 98% selectivity for 630 operational hours. (Fan and Dai, n.d.) However, the current low cost and ready availability of unmodified alumina oxide makes it a better choice for a process of this scale.

===Purification Alternatives===
As specified in this process, the reactor effluent is purified by two flash drums and absorption with water to produce chemical-grade ethylene. If chemical-grade ethylene is indeed the desired product, other purification options include caustic washing of the reactor effluent and water removal in a desiccant drying bed. (Morschbacker, 2009) While this purification train is relatively simple and does not require harsh chemical reagents, polymer grade ethylene is more commercially valuable and the additional cost of removing water and diethyl ether contaminants may be justified by increased revenue. Cryogenic distillation was initially simulated to produce polymer-grade ethylene, but utility requirements were found to render this separation economically unviable. (Barrocas and Baratelli, 1983) Further research and optimization may find this purification strategy to be a more valid process. Alternatively, the addition of a cryogenic turboexpander or the use of alternative adsorbents may increase product purity to polymer grade. (Jumonville, 2010) Initial HYSYS simulations indicate that these operations may be feasible with further refinement.

===Wastewater Treatment===
Due to the large volume of wastewater produced, building an on-site wastewater treatment facility may prove to be more economical than paying for third-party wastewater treatment. Flash vessel FL-201 produces 44,600 L/hr of wastewater contaminated with 18.7 vol% ethanol and 0.6 vol% acetaldehyde, while FL-202 produces 2940 L/hr of an aqueous waste consisting of 56.8 vol% ethanol, 42.0 vol% water and 0.9 vol% diethyl ether. The absorption column produces approximately 10,200 liters/hr of wastewater contaminated with 1.2 vol% ethanol, 0.2% diethyl ether and 0.2% acetaldehyde. Utilizing distillation to separate these streams into clean water and volatile organic waste could ultimately reduce the quantity of waste that requires disposal and reduce the overall costs of the process.

==Process Equipment==
Relevant sizing information for each unit operation, estimated by the method described in the “Technical Approach,” can be found in Appendix V. Equipment and piping is assumed to be constructed of carbon steel. It should be noted that the two fired heaters are proportionately large enough to heat the entirety of the process stream and are thus larger than standard equipment.

=Economic Analysis=
[[File:sensitivityanalysis_B1.png|400px|thumb]]

==Economics Overview==
All final values are normalized to June 2014 USD by CEPCI scaling. It is assumed that all products produced are sold at current market prices.

The Aspen Economic Evaluation module within HYSYS v8.0 was used to estimate capital and operating costs for a 10-year plant life span with a construction start date of April 2015. The price of the 95% ethanol feed stream was estimated at $1.44 per gallon, while the chemical grade ethylene produced is currently selling for approximately $1350 per metric ton. (Today in Energy, 2015; Weddle, 2014) Mapping and sizing calculations were performed by the economics module and a preliminary economic evaluation was completed. Equipment sizes, also estimated by HYSYS, were reviewed to ensure that height, diameter, and volume specifications were within realistic ranges.

The process was ideally projected to operate 360 days per year with a start-up time of one year. In addition, the tax rate was approximated at 40%, an interest rate at 20%, and a salvage value of 20%. Escalation percentages were compounded yearly for the product, raw material, and operating costs. The total capital cost for this process is approximately $16.4 million, which includes all equipment and piping described in the process. The most expensive equipment used in this process are the two fired heaters F-101 and F-102, which have an exceptionally large heat exchange area to adequately heat the feed. Standard heaters may not suffice and additional costs may be incurred for the raw materials and manufacture of this equipment. Including a feed preheater or additional fired heaters may reduce this cost in subsequent design iterations.

The total operating cost is approximately $465 million per year, about $427 million of which is the cost of the ethanol feed and natural gas for the two fired heaters. An additional $1.73 million per year is used for utilities including the cooling water and refrigerant. The labor and maintenance costs of this industrial process were also accounted for within the simulation’s economic analysis. The HYSYS simulation software, in conjunction with the Icarus economic analyzer, estimated there should be 5 operators per 8 hour shift with a cost per operator of $20 per hour. This results in a total operating labor cost of approximately $880,000 per year. In addition, the process will require one supervisor per shift with an hourly rate of $35 for total supervisor salaries of $307,000 per year. Finally, a fixed maintenance rate was estimated at $205,000 per 8000 hours of operation for a total cost of $225,000 per year.

Total product sales are roughly $640 million per year at full operation. The estimated income for this process is thus approximately $175 million per year. After ten years, the plant is projected to have a net present value (NPV) of $391 million and an internal rate of return of approximately 79%. In addition the payout period for the initial investment is estimated to be about 2.7 years. Figure 2 shows the projected cash flow for the project.

==Sensitivity Analysis==
A sensitivity analysis was performed to investigate the effects of fluctuating capital costs, operating costs, raw materials, utility costs and ethylene sales price on the 10-year net present value (NPV) of the project. This analysis was performed by scaling these cost factors according to typical ranges given in Towler and Sinnott and calculating the adjusting the NPV accordingly. The results, illustrated in Figure 3, indicate that the project value is most sensitive to product sales, raw materials costs, and operating costs. Ethylene and ethanol prices are market-determined and cannot be controlled for in the process design, so further optimization should be focused on minimizing the operations cost of the process. (Today in Energy, 2015; Weddle, 2014) However, in feed and product prices do still have a profound effect on profitability and feasibility. A more rigorous market analysis will better inform the profitability outlook.

=Conclusions/Recommendations=

The proposed process produces approximately 460,000 metric tons of 99.7 wt% ethylene annually, with a 10-year net present value of $131 million. If current economic conditions hold, it is recommended that this project proceed to implementation following further design improvements and optimization.

Future design iterations should focus on process optimization, particularly in minimizing operating costs as prescribed by the results of the sensitivity analysis. The development of a heat-exchanger network, potentially with Aspen Energy Analyzer, is one option for decreasing utility requirements and increasing the efficiency of the process overall. Optimization of the fired heaters could also result in decreased operational costs. Although overall profitability is less sensitive to capital costs, reviewing and adjusting equipment sizing would also improve the economic outlook. In particular, exploring alternative heating strategies at the beginning of the process could significantly decrease capital costs. Although there are not any particularly dangerous chemicals utilized in the process, an overall process review should also consider potential failure modes to minimize the safety risk to plant workers and nearby residents.

In addition to economic and safety considerations, harmful emissions and waste streams should be minimized both to bring down the cost of treatment and to decrease environmental effects. The two fired heaters consume a large amount of natural gas per year, emitting about 200,000 tons of CO2 annually, and account for more than half of the capital cost of the process. Although no known toxic gases are produced, carbon capture or other emissions-reduction methods should be considered. Additionally, enough wastewater is produced by this process that building an onsite wastewater treatment center should be considered. This could not only decrease operating costs by eliminating the need for an external contract but also give the plant more control over the final purity of the treated wastewater.

Finally, the current model assumes that all ethylene produced will be sold at a current prices and price or product sales will not be affected by economic variability. A more detailed study of the chemical-grade ethylene market, as well as a more thorough understanding of sales and distribution logistics, would increase the surety of a profitable process.

In summary, the proposed process yields chemical grade ethylene via the catalytic dehydration of ethanol. A 100,000 kg/hr of 95 wt% ethanol, 5% water feed is converted to 53,000 kg/hr of 99.7% chemical-grade ethylene. After 10 years of operation, including a one-year startup time, the process has an NPV of $391 million with an IRR of 79% and a payback period of 2.7 years.
Pending further optimization, this process was determined to be viable and it is recommended for the project to move forward.

=References=

[1] American Chemistry Council. Production of chemicals and plastics in the U.S. in 2013, by type (in 1,000 metric tons). In Statista - The Statistics Portal. August 2014. Available at http://www.statista.com/statistics/299725/total-us-plastics-and-chemicals-shipments-by-type/, Accessed January 15, 2015. – Relative proportions of plastics production.

[2] DuPont Nevada Site Cellulosic Ethanol Facility [Internet]. DuPont Chemical; c2012-2015 [cited 11 Mar. 2015]. Available from: http://biofuels.dupont.com/cellulosic-ethanol/nevada-site-ce-facility/. -- Information on ethanol production in Iowa.

[3] Designing Ethylene Plants. Ethylene [Internet]. Technip; 2014 [cited 13 Mar. 2015]. Available from: http://www.technip.com/en/our-business/onshore/ethylene -- Plant size ranges.

[4] Suppes GJ. Selecting Thermodynamic Models for Process Simulation of Organic VLE and LLE Systems. The University of Missouri-Columbia, Dept of Chemical Engineering. [cited 13 Mar. 2015]. -- Use of NRTL in alcohol separations.

[5] ASPENtech. Appendix A - Property Methods and Calculations. Simulation Basics; A-3 - A-26. 2014.

[6] 190 Proof Ethanol: Technical Data Sheet [Internet]. Decon Labs Inc; 2012 [cited 13 Mar. 2015]. Available from: http://www.deconlabs.com/tds/ETHANOL%20190%20%20PROOF.pdf -- Information regarding 95% ethanol

[7] Hadawey A, Ge Y, Tassou TSA. Energy Savings Through Liquid Pressure Amplification In A Dairy Plant Refrigeration System. The Centre for Energy and Built Environment Research [cited 13 Mar. 2015].

[8] Methane (Chemical Compound). 2015. Encyclopædia Britannica Online. [cited 13 Mar. 2015] Available from: http://www.britannica.com/EBchecked/topic/378264/methane -- Composition of Methane

[9] Composition of Air [Internet]. Engineering Toolbox; [cited 13 Mar. 2015]. Available from: http://www.engineeringtoolbox.com/air-composition-d_212.html. -- Composition of air.

[10] Summary of the Clean Air Act, 2015. United States Environmental Protection Agency. [cited 13 Mar. 2015] Available from: http://www2.epa.gov/laws-regulations/summary-clean-air-act -- Emissions requirements of chemical plants.

[11] Zhang M, Yu Y. Dehydration of Ethanol to Ethylene. Industrial Engineering and Chemical Research. 2013; 52:9505-9514. – Technical information on ethanol to ethylene conversion via dehydration.

[12] AspenTech. Aspen HYSYS Help File v8.0. Aspen Technology, Inc. 2012. - Aspen HYSYS help file used for troubleshooting and assistance on economic analysis.

[13] Towler G, Sinnott R. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. 2nd ed. Boston: Elsevier; 2013. -- General Reference Book

[14] Barrocas H, Baratelli F, inventors; Petroleo Brasileiro S.A., assignee. Process for dehydration of a low molecular weight alcohol. US patent 4,396,789 A. August 2, 1983. - Primary background for process design.

[15] Tsao U, Zasloff HB, inventors; The Lummus Company, assignee. Production of ethylene from ethanol. US patent 4,134,926. January 16, 1979. – Patent for catalytic dehydration of ethylene in a fluidized bed reactor.

[16] Morschbacker, A. Bio-Ethanol Based Ethylene. Polymer Reviews. 2009; 49:79-84. – Overview of bioethanol dehydration process development.

[17] Fan D, Dai DJ, Wu HS. Ethylene Formation by Catalytic Dehydration of Ethanol with Industrial Considerations. Materials. 6, 101-115. doi: 10.3390/ma6010101. - Comparison of types of catalysts used in the dehydration of ethanol and current research into new catalysts.

[18] Chen G, Li S, Jiao F, Yuan Q. Catalytic dehydration of bioethanol to ethylene over TiO2/γ-Al2O3 catalysts in microchannel reactors. Catal. Today 2007, 125, 111–119. - Paper introducing research on modified alumina catalyst for ethanol dehydration.

[19] Jumonville, J. Tutorial on Cryogenic Turboexpanders. Proceedings of the Thirty-Ninth Turbomachinery Symposium; 2010 Oct 4-7; Houston, TX. Houston: Texas A&M University; 2010. -- Use of turboexpander for cryogenic separations

[20] Today in Energy - Daily Prices. US Energy Information Administration website. http://www.eia.gov/todayinenergy/prices.cfm. Accessed March 3rd 2015. - Bulk market price for 95% ethanol.

[21] Weddle, N. ICIS Pricing: Ethylene (Europe). Reed Business Limited. January 10 2014. - Bulk market price for chemical grade ethylene.

=Appendix I - Process Flow Diagram=
[[File:PFD B1.JPG|1200px]]

=Appendix II - HYSYS Simulation=
[[File:HYSYS_B1.PNG|1200px]]

=Appendix III - Material Streams=
[[File:Streams_B1.png|1200px]]

=Appendix IV - Energy Table=
[[File:Energy_B1.png|600px|center]]

=Appendix V - Economics=
[[File:Econsummary_B1.png|center]] 

[[File:Capcost_B1.png|center]] 

[[File:sensitivityanalysis_B1.png|600px|center]]

Ethanol to Ethylene (B1)

2015-03-14T04:19:29Z

Hpoppick:

[[File:BFD_B1.png|600px|thumbnail|alt=Alt text|Conversion of Ethanol to Ethylene]]

by Harry Poppick, Emm Fulk and Scott Smith

=Executive Summary=

The following report outlines the design and analysis of a process converting ethanol to chemical-grade ethylene via catalytic dehydration. This process consumers 100,000 kg/hr of 95 wt% ethanol, 5 wt% water feedstock and produces 53,000 kg/hr of 99.7 wt% chemical-grade ethylene. The ethanol feed passes through two fixed-bed reactors, each packed with an aluminum oxide catalyst, and the resulting ethylene is purified by two flash tanks and by absorption with water. The process was modeled using Aspen HYSYS simulation software to estimate mass and energy flows and equipment sizing requirements. Based on results of this initial simulation, several alternatives are discussed for increasing the process efficiency and profitability. The use of a fluidized bed reactor or a more ethylene-selective catalyst could increase the production of ethylene per ethanol basis. Additionally, several methods of purification to more valuable polymer-grade ethylene are proposed.

The economic feasibility of this process was evaluated using Aspen Economic Analyzer with the Icarus economics package. Capital cost is approximately $16.4 million total with an operating cost of $465 million per year. The current market prices of the ethanol feed and ethylene sales price are $1.44/gallon and $1350/metric ton respectively. The cost of feed ethanol, process utilities and miscellaneous operational costs total to about $427 million/year. At full operation, revenue at current prices would be approximately $640 million per year. The predicted 10-year net present value of the process is approximately $391 million with an IRR of 79% and a payback period of 2.7 years. A sensitivity analysis indicates that the process is most sensitive to feed prices, product prices and operation cost.

Several recommendations are made for both cost reduction and profit maximization, including the design of a heat exchanger network and the optimization of fired heaters that require high capital investment and large amounts of fuel. A safety review of the process is recommended, as well as the minimization of flue gas effluent and wastewater. It is also suggested that the construction of an onsite wastewater treatment center be considered. Overall, the initial analysis indicates this to be a profitable process and it is recommended the project move forward.

=Introduction=

Ethylene is a critical chemical precursor to a number of different industrial products. It is often derived from petroleum sources and polymerized to polyethylene, one of the most ubiquitous plastics today. (American Chemistry Council, 2013) Recently there has been a significant effort to develop production pathways utilizing biologically-derived feedstocks, such as corn or cellulosic ethanol, rather than traditional fossil-fuel sources. Ethylene can be produced from bioethanol via catalytic dehydration over an aluminum oxide catalyst. The proposed process converts 100,000 kg/hr of 95 wt% ethanol, 5% water feed to 53,000 kg/hr of 99.7% chemical-grade ethylene when operating at full capacity. This process was found to be economically viable with a 10-year net present value (NPV) of $131 million (2014 USD) and a payback period of approximately 2.7 years. This memo will detail the proposed process, as well as outline potential alternatives and economic viability of the project.

=Technical Approach=

Many bioethanol plants are located in the Midwest where large amounts of feedstock crops, such as corn, are grown. As such, this plant will be located in Story county, Iowa, near a large-scale bioethanol production plant. (DuPont Nevada Site, 2012) It is assumed that the supply of bioethanol is consistent and readily available. It is also assumed that other reagents - namely, the aluminum oxide catalyst, heater fuel, utility water and freon refrigerant - are readily available, and that wastewater treatment facilities are located near enough to facilitate the off-site treatment of wastewater. Plant capacity was based on current mid-sized industrial ethylene plants. (Designing Ethylene Plants, 2014)

HYSYS simulations were performed with the NRTL fluid package and Peng-Robinson vapor model. The NRTL fluid package is an activity coefficient model that is especially useful to model the separations of alcohols in aqueous solutions. (Suppes, 2015) In addition, NRTL uses models of binary pairs of components, much like the Wilson equation, to predict chemical interactions at the molecular level. The NRTL package can thus be easily extended to ternary and higher order chemical systems, making it ideal for this type of simulation. The Peng-Robinson vapor model was selected as it is well-suited to account for the non-idealities of the vapor phase reactions and separations integral to this process. (ASPENtech, 2014)

It was assumed that the feed enters the process at ambient temperature and pressure (25 °C, 1 atm) and at a consistent rate and composition with negligible quantities of impurities. The ethanol feed was assumed to be 95% ethanol and 5% water by mass, which is the commercial standard for industrial ethanol. (190 Proof Ethanol, 2012) Storage vessels for the feed ethanol, waste streams and products are assumed to be located nearby to the process. An initial feed pump compensates for pressure drops through the process and reduces the duty on downstream compressors. (Hadawey, 2015)

Natural gas, assumed to consist of 83% methane, 16% ethane and 1% nitrogen by mass, was supplied to two fired heaters at a flow rate estimated by HYSYS. (Methane, 2015) Air fed to the process to enable combustion was assumed to be 23% oxygen and 77% nitrogen by mass. (Composition of Air, 2015) Air streams were fed at 50% molar excess in order to ensure complete combustion and prevent the formation of carbon monoxide in the heater exhaust. Total flue gases are assumed to be 230,000 kg/hr, or 2.2 million tons annually, and consist of 73.8% nitrogen gas, 10.5% carbon dioxide, 8.2% water vapor, and 7.5% oxygen by mass. The only compound of concern in these emissions is the carbon dioxide, a known greenhouse gas. At the time of this report, the quantities of carbon dioxide emitted by this plant annually are within acceptable EPA specifications. (Summary of the Clean Air Act, 2015)

Due to the difficulty of simulation equilibrium and conversion reactions in a single vessel in HYSYS, these two reaction types were simulated in separate equilibrium reactor and conversion reactor units in series. In addition, while HYSYS indicated that reactor units would output separate vapor and liquid streams, it was assumed that in practice this would take the form of a single, two phase stream between each unit. To account for this, mixers were installed downstream of each reactor to combine the liquid and vapor phases of the reactor effluent. The three consequent reactions considered are as follows:

Ethanol ↔ Ethylene + Water
Ethanol → Acetaldehyde + Hydrogen
2 Ethanol → Diethyl Ether + Water

The optimal reaction temperature was determined to be 400 °C, which promotes the equilibrium reaction of ethanol to ethylene while minimizing byproducts. (Zhang and Yu, 2013) While other byproducts may be produced in this process, these reactions are typically taken to comprise of the bulk of the dehydration reaction. Heat losses over these reactors were assumed to be negligible. (Zhang and Yu, 2013)All major process equipment is assumed to be constructed of high strength carbon steel. (AspenTech, 2012)

The “Sizing Utility” within the Icarus Economic Evaluation module was used to estimate sizes of major equipment based on the process simulation. These values can serve as a benchmark for an initial plant design. Icarus KbaseTM implements a wide variety of mechanical design standards, including ASME and BS5500, in order to calculate accurate equipment sizing. The Icarus sizing module combines equipment prices for standard chemical processing equipment as well as correlations and sizing factors. The advantage of using a software package such as HYSYS to price out individual equipment is that it utilizes up-to-date prices from vendors and distributors when estimating costs. A more in-depth overview of the correlations included in this software can be found in Towler and Sinnott (2009).

=Process Flowsheet=
[[File:Squarepfd_B1.PNG|thumb|400px]]

The following process is based primarily on a 1983 US patent titled “Process for dehydration of a low molecular weight alcohol.” (Barrocas and Baratelli, 1983) The process flow diagram can be seen in Figure 1. A larger version of the PFD is included in Appendix I and the HYSYS simulation setup in Appendix II.

The feed enters the process at a rate of 100,000 kg/hr, a temperature and pressure of a 25 °C and 1 atm and at a composition of 95 wt% ethanol and 5 wt% water.It is initially pressurized to 4335 kPa by centrifugal pump P-101 and subsequently heated to 400 °C by fired heater F-101. The heated and pressurized feed enters fixed bed reactor R-101 and contacts with the aluminum oxide catalyst. At this point it dehydrates to form the product, ethylene, as well as the byproducts water, hydrogen, diethyl ether and acetaldehyde. Fired heater F-102 and reactor R-102 increase the overall conversion of the process. Both fired heaters F-101 and F-102 are fueled with natural gas and fed with excess air. The composition of the reactor train effluent is 54.5 wt% ethylene, 37.1 wt% water, 8.1 wt% unreacted ethanol and trace amounts of diethyl ether, acetaldehyde, and hydrogen contaminants.

The pressure of the reactor train effluent is increased to 4500 kPa by compressor K-102 and the temperature decreased to 100 °C by exchange with cold water in heat exchanger E-201. The stream then expands and flashes in flash vessel FL-201, which separates out 82.3% of the unreacted ethanol, 96.6% of the water and virtually all of the acetaldehyde contaminant in the bottoms while sending the ethylene-rich vapor phase out of the top. The top product of FL-202 is compressed to 3500 kPA by K-202 and cooled to 0.0 °C by a freon refrigerant in E-202. At this point the stream is flashed for a second time in vessel FL-202 to remove additional impurities. The top outlet stream consists of 99.5 wt% ethylene, which is fed to the bottom of a 10-tray absorption column that removes a fraction of the residual diethyl ether as well as the remainder of the unreacted ethanol. A stream of absorbent water is fed to the top of the column at 10,000 kg/hr. The product exits the top of the column at a rate of 54,600 kg/hr and has a purity of 99.7% ethylene. Diethyl ether makes up 0.2% of the remaining product stream and is the primary contaminant. Trace amounts of residual water and hydrogen are also present.

Full tables of material and energy streams can be found in Appendices III and IV respectively.

==Process Alternatives==
===Reactor Alternatives===
Two fixed bed reactors, alternating with fired heaters, are used in the dehydration reaction of ethanol to ethylene. However, a fluidized bed reactor can offer better mixing and temperature control than a fixed bed reactor and thus provide the highest possible conversion of ethanol with the greatest selectivity to ethylene. (Tsao and Zasloff, 1979) Fluidized bed reactors also provide a lower rate of catalyst coking and byproduct formation, minimizing separation and catalyst regeneration costs. (Morschbacker, 2009) The major downside of fluidized bed reactors is that few large-scale processes have been built since the technology was developed in the late 1970s. (Tsao and Zasloff, 1979; Morschbacker, 2009) Although implementation of fluidized bed reactors could potentially increase the purity of the ethylene product and/or decrease costs, a small scale pilot process would need to be built and tested before it would be possible to develop an industrial-scale facility.

===Catalyst Alternatives===
Aluminum oxide, specifically gamma alumina, is the most industrially-common catalyst and has been historically used due to its low cost and high stability. (Tsao and Zasloff, 1979; Fan and Dai, n.d.) Recent improvements in selectivity and catalyst stability of activated alumina have been achieved by incorporating titanium oxide into the catalyst, although this increases reaction temperature by approximately 50 °C and decreases catalyst lifespan. (Chen and Li, et. al. 2007) There is also significant ongoing research into HZSM-5 zeolite and heteropolyacids, which are being explored as potential alternatives to alumina oxide. A nanoscale HZSM-5 zeolite catalyst has been shown to operate at the relatively low temperature of 200-300°C, with a 100% ethanol conversion and 99.7% selectivity to ethylene. Initial research has also indicated that it maintains greater than 98% selectivity for 630 operational hours. (Fan and Dai, n.d.) However, the current low cost and ready availability of unmodified alumina oxide makes it a better choice for a process of this scale.

===Purification Alternatives===
As specified in this process, the reactor effluent is purified by two flash drums and absorption with water to produce chemical-grade ethylene. If chemical-grade ethylene is indeed the desired product, other purification options include caustic washing of the reactor effluent and water removal in a desiccant drying bed. (Morschbacker, 2009) While this purification train is relatively simple and does not require harsh chemical reagents, polymer grade ethylene is more commercially valuable and the additional cost of removing water and diethyl ether contaminants may be justified by increased revenue. Cryogenic distillation was initially simulated to produce polymer-grade ethylene, but utility requirements were found to render this separation economically unviable. (Barrocas and Baratelli, 1983) Further research and optimization may find this purification strategy to be a more valid process. Alternatively, the addition of a cryogenic turboexpander or the use of alternative adsorbents may increase product purity to polymer grade. (Jumonville, 2010) Initial HYSYS simulations indicate that these operations may be feasible with further refinement.

===Wastewater Treatment===
Due to the large volume of wastewater produced, building an on-site wastewater treatment facility may prove to be more economical than paying for third-party wastewater treatment. Flash vessel FL-201 produces 44,600 L/hr of wastewater contaminated with 18.7 vol% ethanol and 0.6 vol% acetaldehyde, while FL-202 produces 2940 L/hr of an aqueous waste consisting of 56.8 vol% ethanol, 42.0 vol% water and 0.9 vol% diethyl ether. The absorption column produces approximately 10,200 liters/hr of wastewater contaminated with 1.2 vol% ethanol, 0.2% diethyl ether and 0.2% acetaldehyde. Utilizing distillation to separate these streams into clean water and volatile organic waste could ultimately reduce the quantity of waste that requires disposal and reduce the overall costs of the process.

==Process Equipment==
Relevant sizing information for each unit operation, estimated by the method described in the “Technical Approach,” can be found in Appendix V. Equipment and piping is assumed to be constructed of carbon steel. It should be noted that the two fired heaters are proportionately large enough to heat the entirety of the process stream and are thus larger than standard equipment.

=Economic Analysis=
[[File:sensitivityanalysis_B1.png|400px|thumb]]

==Economics Overview==
All final values are normalized to June 2014 USD by CEPCI scaling. It is assumed that all products produced are sold at current market prices.

The Aspen Economic Evaluation module within HYSYS v8.0 was used to estimate capital and operating costs for a 10-year plant life span with a construction start date of April 2015. The price of the 95% ethanol feed stream was estimated at $1.44 per gallon, while the chemical grade ethylene produced is currently selling for approximately $1350 per metric ton. (Today in Energy, 2015; Weddle, 2014) Mapping and sizing calculations were performed by the economics module and a preliminary economic evaluation was completed. Equipment sizes, also estimated by HYSYS, were reviewed to ensure that height, diameter, and volume specifications were within realistic ranges.

The process was ideally projected to operate 360 days per year with a start-up time of one year. In addition, the tax rate was approximated at 40%, an interest rate at 20%, and a salvage value of 20%. Escalation percentages were compounded yearly for the product, raw material, and operating costs. The total capital cost for this process is approximately $16.4 million, which includes all equipment and piping described in the process. The most expensive equipment used in this process are the two fired heaters F-101 and F-102, which have an exceptionally large heat exchange area to adequately heat the feed. Standard heaters may not suffice and additional costs may be incurred for the raw materials and manufacture of this equipment. Including a feed preheater or additional fired heaters may reduce this cost in subsequent design iterations.

The total operating cost is approximately $465 million per year, about $427 million of which is the cost of the ethanol feed and natural gas for the two fired heaters. An additional $1.73 million per year is used for utilities including the cooling water and refrigerant. The labor and maintenance costs of this industrial process were also accounted for within the simulation’s economic analysis. The HYSYS simulation software, in conjunction with the Icarus economic analyzer, estimated there should be 5 operators per 8 hour shift with a cost per operator of $20 per hour. This results in a total operating labor cost of approximately $880,000 per year. In addition, the process will require one supervisor per shift with an hourly rate of $35 for total supervisor salaries of $307,000 per year. Finally, a fixed maintenance rate was estimated at $205,000 per 8000 hours of operation for a total cost of $225,000 per year.

Total product sales are roughly $640 million per year at full operation. The estimated income for this process is thus approximately $175 million per year. After ten years, the plant is projected to have a net present value (NPV) of $391 million and an internal rate of return of approximately 79%. In addition the payout period for the initial investment is estimated to be about 2.7 years. Figure 2 shows the projected cash flow for the project.

==Sensitivity Analysis==
A sensitivity analysis was performed to investigate the effects of fluctuating capital costs, operating costs, raw materials, utility costs and ethylene sales price on the 10-year net present value (NPV) of the project. This analysis was performed by scaling these cost factors according to typical ranges given in Towler and Sinnott and calculating the adjusting the NPV accordingly. The results, illustrated in Figure 3, indicate that the project value is most sensitive to product sales, raw materials costs, and operating costs. Ethylene and ethanol prices are market-determined and cannot be controlled for in the process design, so further optimization should be focused on minimizing the operations cost of the process. (Today in Energy, 2015; Weddle, 2014) However, in feed and product prices do still have a profound effect on profitability and feasibility. A more rigorous market analysis will better inform the profitability outlook.

=Conclusions/Recommendations=

The proposed process produces approximately 460,000 metric tons of 99.7 wt% ethylene annually, with a 10-year net present value of $131 million. If current economic conditions hold, it is recommended that this project proceed to implementation following further design improvements and optimization.

Future design iterations should focus on process optimization, particularly in minimizing operating costs as prescribed by the results of the sensitivity analysis. The development of a heat-exchanger network, potentially with Aspen Energy Analyzer, is one option for decreasing utility requirements and increasing the efficiency of the process overall. Optimization of the fired heaters could also result in decreased operational costs. Although overall profitability is less sensitive to capital costs, reviewing and adjusting equipment sizing would also improve the economic outlook. In particular, exploring alternative heating strategies at the beginning of the process could significantly decrease capital costs. Although there are not any particularly dangerous chemicals utilized in the process, an overall process review should also consider potential failure modes to minimize the safety risk to plant workers and nearby residents.

In addition to economic and safety considerations, harmful emissions and waste streams should be minimized both to bring down the cost of treatment and to decrease environmental effects. The two fired heaters consume a large amount of natural gas per year, emitting about 200,000 tons of CO2 annually, and account for more than half of the capital cost of the process. Although no known toxic gases are produced, carbon capture or other emissions-reduction methods should be considered. Additionally, enough wastewater is produced by this process that building an onsite wastewater treatment center should be considered. This could not only decrease operating costs by eliminating the need for an external contract but also give the plant more control over the final purity of the treated wastewater.

Finally, the current model assumes that all ethylene produced will be sold at a current prices and price or product sales will not be affected by economic variability. A more detailed study of the chemical-grade ethylene market, as well as a more thorough understanding of sales and distribution logistics, would increase the surety of a profitable process.

In summary, the proposed process yields chemical grade ethylene via the catalytic dehydration of ethanol. A 100,000 kg/hr of 95 wt% ethanol, 5% water feed is converted to 53,000 kg/hr of 99.7% chemical-grade ethylene. After 10 years of operation, including a one-year startup time, the process has an NPV of $391 million with an IRR of 79% and a payback period of 2.7 years.
Pending further optimization, this process was determined to be viable and it is recommended for the project to move forward.

=References=

[1] American Chemistry Council. Production of chemicals and plastics in the U.S. in 2013, by type (in 1,000 metric tons). In Statista - The Statistics Portal. August 2014. Available at http://www.statista.com/statistics/299725/total-us-plastics-and-chemicals-shipments-by-type/, Accessed January 15, 2015. – Relative proportions of plastics production.

[2] DuPont Nevada Site Cellulosic Ethanol Facility [Internet]. DuPont Chemical; c2012-2015 [cited 11 Mar. 2015]. Available from: http://biofuels.dupont.com/cellulosic-ethanol/nevada-site-ce-facility/. -- Information on ethanol production in Iowa.

[3] Designing Ethylene Plants. Ethylene [Internet]. Technip; 2014 [cited 13 Mar. 2015]. Available from: http://www.technip.com/en/our-business/onshore/ethylene -- Plant size ranges.

[4] Suppes GJ. Selecting Thermodynamic Models for Process Simulation of Organic VLE and LLE Systems. The University of Missouri-Columbia, Dept of Chemical Engineering. [cited 13 Mar. 2015]. -- Use of NRTL in alcohol separations.

[5] ASPENtech. Appendix A - Property Methods and Calculations. Simulation Basics; A-3 - A-26. 2014.

[6] 190 Proof Ethanol: Technical Data Sheet [Internet]. Decon Labs Inc; 2012 [cited 13 Mar. 2015]. Available from: http://www.deconlabs.com/tds/ETHANOL%20190%20%20PROOF.pdf -- Information regarding 95% ethanol

[7] Hadawey A, Ge Y, Tassou TSA. Energy Savings Through Liquid Pressure Amplification In A Dairy Plant Refrigeration System. The Centre for Energy and Built Environment Research [cited 13 Mar. 2015].

[8] Methane (Chemical Compound). 2015. Encyclopædia Britannica Online. [cited 13 Mar. 2015] Available from: http://www.britannica.com/EBchecked/topic/378264/methane -- Composition of Methane

[9] Composition of Air [Internet]. Engineering Toolbox; [cited 13 Mar. 2015]. Available from: http://www.engineeringtoolbox.com/air-composition-d_212.html. -- Composition of air.

[10] Summary of the Clean Air Act, 2015. United States Environmental Protection Agency. [cited 13 Mar. 2015] Available from: http://www2.epa.gov/laws-regulations/summary-clean-air-act -- Emissions requirements of chemical plants.

[11] Zhang M, Yu Y. Dehydration of Ethanol to Ethylene. Industrial Engineering and Chemical Research. 2013; 52:9505-9514. – Technical information on ethanol to ethylene conversion via dehydration.

[12] AspenTech. Aspen HYSYS Help File v8.0. Aspen Technology, Inc. 2012. - Aspen HYSYS help file used for troubleshooting and assistance on economic analysis.

[13] Towler G, Sinnott R. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. 2nd ed. Boston: Elsevier; 2013. -- General Reference Book

[14] Barrocas H, Baratelli F, inventors; Petroleo Brasileiro S.A., assignee. Process for dehydration of a low molecular weight alcohol. US patent 4,396,789 A. August 2, 1983. - Primary background for process design.

[15] Tsao U, Zasloff HB, inventors; The Lummus Company, assignee. Production of ethylene from ethanol. US patent 4,134,926. January 16, 1979. – Patent for catalytic dehydration of ethylene in a fluidized bed reactor.

[16] Morschbacker, A. Bio-Ethanol Based Ethylene. Polymer Reviews. 2009; 49:79-84. – Overview of bioethanol dehydration process development.

[17] Fan D, Dai DJ, Wu HS. Ethylene Formation by Catalytic Dehydration of Ethanol with Industrial Considerations. Materials. 6, 101-115. doi: 10.3390/ma6010101. - Comparison of types of catalysts used in the dehydration of ethanol and current research into new catalysts.

[18] Chen G, Li S, Jiao F, Yuan Q. Catalytic dehydration of bioethanol to ethylene over TiO2/γ-Al2O3 catalysts in microchannel reactors. Catal. Today 2007, 125, 111–119. - Paper introducing research on modified alumina catalyst for ethanol dehydration.

[19] Jumonville, J. Tutorial on Cryogenic Turboexpanders. Proceedings of the Thirty-Ninth Turbomachinery Symposium; 2010 Oct 4-7; Houston, TX. Houston: Texas A&M University; 2010. -- Use of turboexpander for cryogenic separations

[20] Today in Energy - Daily Prices. US Energy Information Administration website. http://www.eia.gov/todayinenergy/prices.cfm. Accessed March 3rd 2015. - Bulk market price for 95% ethanol.

[21] Weddle, N. ICIS Pricing: Ethylene (Europe). Reed Business Limited. January 10 2014. - Bulk market price for chemical grade ethylene.

=Appendix I - Process Flow Diagram=
[[File:PFD B1.JPG|1200px]]

=Appendix II - HYSYS Simulation=
[[File:HYSYS_B1.PNG|1200px]]

=Appendix III - Material Streams=
[[File:Streams_B1.png|1200px]]

=Appendix IV - Energy Table=
[[File:Energy_B1.png|600px|center]]

=Appendix V - Economics=
[[File:Econsummary_B1.png|center]] 

[[File:Capcost_B1.png|center]] 

[[File:sensitivityanalysis_B1.png|600px|center]]

Ethanol to Ethylene (B1)

2015-03-14T04:19:05Z

Hpoppick:

[[File:BFD_B1.png|600px|thumbnail|alt=Alt text|Conversion of Ethanol to Ethylene]]
=Executive Summary=

The following report outlines the design and analysis of a process converting ethanol to chemical-grade ethylene via catalytic dehydration. This process consumers 100,000 kg/hr of 95 wt% ethanol, 5 wt% water feedstock and produces 53,000 kg/hr of 99.7 wt% chemical-grade ethylene. The ethanol feed passes through two fixed-bed reactors, each packed with an aluminum oxide catalyst, and the resulting ethylene is purified by two flash tanks and by absorption with water. The process was modeled using Aspen HYSYS simulation software to estimate mass and energy flows and equipment sizing requirements. Based on results of this initial simulation, several alternatives are discussed for increasing the process efficiency and profitability. The use of a fluidized bed reactor or a more ethylene-selective catalyst could increase the production of ethylene per ethanol basis. Additionally, several methods of purification to more valuable polymer-grade ethylene are proposed.

The economic feasibility of this process was evaluated using Aspen Economic Analyzer with the Icarus economics package. Capital cost is approximately $16.4 million total with an operating cost of $465 million per year. The current market prices of the ethanol feed and ethylene sales price are $1.44/gallon and $1350/metric ton respectively. The cost of feed ethanol, process utilities and miscellaneous operational costs total to about $427 million/year. At full operation, revenue at current prices would be approximately $640 million per year. The predicted 10-year net present value of the process is approximately $391 million with an IRR of 79% and a payback period of 2.7 years. A sensitivity analysis indicates that the process is most sensitive to feed prices, product prices and operation cost.

Several recommendations are made for both cost reduction and profit maximization, including the design of a heat exchanger network and the optimization of fired heaters that require high capital investment and large amounts of fuel. A safety review of the process is recommended, as well as the minimization of flue gas effluent and wastewater. It is also suggested that the construction of an onsite wastewater treatment center be considered. Overall, the initial analysis indicates this to be a profitable process and it is recommended the project move forward.

=Introduction=

Ethylene is a critical chemical precursor to a number of different industrial products. It is often derived from petroleum sources and polymerized to polyethylene, one of the most ubiquitous plastics today. (American Chemistry Council, 2013) Recently there has been a significant effort to develop production pathways utilizing biologically-derived feedstocks, such as corn or cellulosic ethanol, rather than traditional fossil-fuel sources. Ethylene can be produced from bioethanol via catalytic dehydration over an aluminum oxide catalyst. The proposed process converts 100,000 kg/hr of 95 wt% ethanol, 5% water feed to 53,000 kg/hr of 99.7% chemical-grade ethylene when operating at full capacity. This process was found to be economically viable with a 10-year net present value (NPV) of $131 million (2014 USD) and a payback period of approximately 2.7 years. This memo will detail the proposed process, as well as outline potential alternatives and economic viability of the project.

=Technical Approach=

Many bioethanol plants are located in the Midwest where large amounts of feedstock crops, such as corn, are grown. As such, this plant will be located in Story county, Iowa, near a large-scale bioethanol production plant. (DuPont Nevada Site, 2012) It is assumed that the supply of bioethanol is consistent and readily available. It is also assumed that other reagents - namely, the aluminum oxide catalyst, heater fuel, utility water and freon refrigerant - are readily available, and that wastewater treatment facilities are located near enough to facilitate the off-site treatment of wastewater. Plant capacity was based on current mid-sized industrial ethylene plants. (Designing Ethylene Plants, 2014)

HYSYS simulations were performed with the NRTL fluid package and Peng-Robinson vapor model. The NRTL fluid package is an activity coefficient model that is especially useful to model the separations of alcohols in aqueous solutions. (Suppes, 2015) In addition, NRTL uses models of binary pairs of components, much like the Wilson equation, to predict chemical interactions at the molecular level. The NRTL package can thus be easily extended to ternary and higher order chemical systems, making it ideal for this type of simulation. The Peng-Robinson vapor model was selected as it is well-suited to account for the non-idealities of the vapor phase reactions and separations integral to this process. (ASPENtech, 2014)

It was assumed that the feed enters the process at ambient temperature and pressure (25 °C, 1 atm) and at a consistent rate and composition with negligible quantities of impurities. The ethanol feed was assumed to be 95% ethanol and 5% water by mass, which is the commercial standard for industrial ethanol. (190 Proof Ethanol, 2012) Storage vessels for the feed ethanol, waste streams and products are assumed to be located nearby to the process. An initial feed pump compensates for pressure drops through the process and reduces the duty on downstream compressors. (Hadawey, 2015)

Natural gas, assumed to consist of 83% methane, 16% ethane and 1% nitrogen by mass, was supplied to two fired heaters at a flow rate estimated by HYSYS. (Methane, 2015) Air fed to the process to enable combustion was assumed to be 23% oxygen and 77% nitrogen by mass. (Composition of Air, 2015) Air streams were fed at 50% molar excess in order to ensure complete combustion and prevent the formation of carbon monoxide in the heater exhaust. Total flue gases are assumed to be 230,000 kg/hr, or 2.2 million tons annually, and consist of 73.8% nitrogen gas, 10.5% carbon dioxide, 8.2% water vapor, and 7.5% oxygen by mass. The only compound of concern in these emissions is the carbon dioxide, a known greenhouse gas. At the time of this report, the quantities of carbon dioxide emitted by this plant annually are within acceptable EPA specifications. (Summary of the Clean Air Act, 2015)

Due to the difficulty of simulation equilibrium and conversion reactions in a single vessel in HYSYS, these two reaction types were simulated in separate equilibrium reactor and conversion reactor units in series. In addition, while HYSYS indicated that reactor units would output separate vapor and liquid streams, it was assumed that in practice this would take the form of a single, two phase stream between each unit. To account for this, mixers were installed downstream of each reactor to combine the liquid and vapor phases of the reactor effluent. The three consequent reactions considered are as follows:

Ethanol ↔ Ethylene + Water
Ethanol → Acetaldehyde + Hydrogen
2 Ethanol → Diethyl Ether + Water

The optimal reaction temperature was determined to be 400 °C, which promotes the equilibrium reaction of ethanol to ethylene while minimizing byproducts. (Zhang and Yu, 2013) While other byproducts may be produced in this process, these reactions are typically taken to comprise of the bulk of the dehydration reaction. Heat losses over these reactors were assumed to be negligible. (Zhang and Yu, 2013)All major process equipment is assumed to be constructed of high strength carbon steel. (AspenTech, 2012)

The “Sizing Utility” within the Icarus Economic Evaluation module was used to estimate sizes of major equipment based on the process simulation. These values can serve as a benchmark for an initial plant design. Icarus KbaseTM implements a wide variety of mechanical design standards, including ASME and BS5500, in order to calculate accurate equipment sizing. The Icarus sizing module combines equipment prices for standard chemical processing equipment as well as correlations and sizing factors. The advantage of using a software package such as HYSYS to price out individual equipment is that it utilizes up-to-date prices from vendors and distributors when estimating costs. A more in-depth overview of the correlations included in this software can be found in Towler and Sinnott (2009).

=Process Flowsheet=
[[File:Squarepfd_B1.PNG|thumb|400px]]

The following process is based primarily on a 1983 US patent titled “Process for dehydration of a low molecular weight alcohol.” (Barrocas and Baratelli, 1983) The process flow diagram can be seen in Figure 1. A larger version of the PFD is included in Appendix I and the HYSYS simulation setup in Appendix II.

The feed enters the process at a rate of 100,000 kg/hr, a temperature and pressure of a 25 °C and 1 atm and at a composition of 95 wt% ethanol and 5 wt% water.It is initially pressurized to 4335 kPa by centrifugal pump P-101 and subsequently heated to 400 °C by fired heater F-101. The heated and pressurized feed enters fixed bed reactor R-101 and contacts with the aluminum oxide catalyst. At this point it dehydrates to form the product, ethylene, as well as the byproducts water, hydrogen, diethyl ether and acetaldehyde. Fired heater F-102 and reactor R-102 increase the overall conversion of the process. Both fired heaters F-101 and F-102 are fueled with natural gas and fed with excess air. The composition of the reactor train effluent is 54.5 wt% ethylene, 37.1 wt% water, 8.1 wt% unreacted ethanol and trace amounts of diethyl ether, acetaldehyde, and hydrogen contaminants.

The pressure of the reactor train effluent is increased to 4500 kPa by compressor K-102 and the temperature decreased to 100 °C by exchange with cold water in heat exchanger E-201. The stream then expands and flashes in flash vessel FL-201, which separates out 82.3% of the unreacted ethanol, 96.6% of the water and virtually all of the acetaldehyde contaminant in the bottoms while sending the ethylene-rich vapor phase out of the top. The top product of FL-202 is compressed to 3500 kPA by K-202 and cooled to 0.0 °C by a freon refrigerant in E-202. At this point the stream is flashed for a second time in vessel FL-202 to remove additional impurities. The top outlet stream consists of 99.5 wt% ethylene, which is fed to the bottom of a 10-tray absorption column that removes a fraction of the residual diethyl ether as well as the remainder of the unreacted ethanol. A stream of absorbent water is fed to the top of the column at 10,000 kg/hr. The product exits the top of the column at a rate of 54,600 kg/hr and has a purity of 99.7% ethylene. Diethyl ether makes up 0.2% of the remaining product stream and is the primary contaminant. Trace amounts of residual water and hydrogen are also present.

Full tables of material and energy streams can be found in Appendices III and IV respectively.

==Process Alternatives==
===Reactor Alternatives===
Two fixed bed reactors, alternating with fired heaters, are used in the dehydration reaction of ethanol to ethylene. However, a fluidized bed reactor can offer better mixing and temperature control than a fixed bed reactor and thus provide the highest possible conversion of ethanol with the greatest selectivity to ethylene. (Tsao and Zasloff, 1979) Fluidized bed reactors also provide a lower rate of catalyst coking and byproduct formation, minimizing separation and catalyst regeneration costs. (Morschbacker, 2009) The major downside of fluidized bed reactors is that few large-scale processes have been built since the technology was developed in the late 1970s. (Tsao and Zasloff, 1979; Morschbacker, 2009) Although implementation of fluidized bed reactors could potentially increase the purity of the ethylene product and/or decrease costs, a small scale pilot process would need to be built and tested before it would be possible to develop an industrial-scale facility.

===Catalyst Alternatives===
Aluminum oxide, specifically gamma alumina, is the most industrially-common catalyst and has been historically used due to its low cost and high stability. (Tsao and Zasloff, 1979; Fan and Dai, n.d.) Recent improvements in selectivity and catalyst stability of activated alumina have been achieved by incorporating titanium oxide into the catalyst, although this increases reaction temperature by approximately 50 °C and decreases catalyst lifespan. (Chen and Li, et. al. 2007) There is also significant ongoing research into HZSM-5 zeolite and heteropolyacids, which are being explored as potential alternatives to alumina oxide. A nanoscale HZSM-5 zeolite catalyst has been shown to operate at the relatively low temperature of 200-300°C, with a 100% ethanol conversion and 99.7% selectivity to ethylene. Initial research has also indicated that it maintains greater than 98% selectivity for 630 operational hours. (Fan and Dai, n.d.) However, the current low cost and ready availability of unmodified alumina oxide makes it a better choice for a process of this scale.

===Purification Alternatives===
As specified in this process, the reactor effluent is purified by two flash drums and absorption with water to produce chemical-grade ethylene. If chemical-grade ethylene is indeed the desired product, other purification options include caustic washing of the reactor effluent and water removal in a desiccant drying bed. (Morschbacker, 2009) While this purification train is relatively simple and does not require harsh chemical reagents, polymer grade ethylene is more commercially valuable and the additional cost of removing water and diethyl ether contaminants may be justified by increased revenue. Cryogenic distillation was initially simulated to produce polymer-grade ethylene, but utility requirements were found to render this separation economically unviable. (Barrocas and Baratelli, 1983) Further research and optimization may find this purification strategy to be a more valid process. Alternatively, the addition of a cryogenic turboexpander or the use of alternative adsorbents may increase product purity to polymer grade. (Jumonville, 2010) Initial HYSYS simulations indicate that these operations may be feasible with further refinement.

===Wastewater Treatment===
Due to the large volume of wastewater produced, building an on-site wastewater treatment facility may prove to be more economical than paying for third-party wastewater treatment. Flash vessel FL-201 produces 44,600 L/hr of wastewater contaminated with 18.7 vol% ethanol and 0.6 vol% acetaldehyde, while FL-202 produces 2940 L/hr of an aqueous waste consisting of 56.8 vol% ethanol, 42.0 vol% water and 0.9 vol% diethyl ether. The absorption column produces approximately 10,200 liters/hr of wastewater contaminated with 1.2 vol% ethanol, 0.2% diethyl ether and 0.2% acetaldehyde. Utilizing distillation to separate these streams into clean water and volatile organic waste could ultimately reduce the quantity of waste that requires disposal and reduce the overall costs of the process.

==Process Equipment==
Relevant sizing information for each unit operation, estimated by the method described in the “Technical Approach,” can be found in Appendix V. Equipment and piping is assumed to be constructed of carbon steel. It should be noted that the two fired heaters are proportionately large enough to heat the entirety of the process stream and are thus larger than standard equipment.

=Economic Analysis=
[[File:sensitivityanalysis_B1.png|400px|thumb]]

==Economics Overview==
All final values are normalized to June 2014 USD by CEPCI scaling. It is assumed that all products produced are sold at current market prices.

The Aspen Economic Evaluation module within HYSYS v8.0 was used to estimate capital and operating costs for a 10-year plant life span with a construction start date of April 2015. The price of the 95% ethanol feed stream was estimated at $1.44 per gallon, while the chemical grade ethylene produced is currently selling for approximately $1350 per metric ton. (Today in Energy, 2015; Weddle, 2014) Mapping and sizing calculations were performed by the economics module and a preliminary economic evaluation was completed. Equipment sizes, also estimated by HYSYS, were reviewed to ensure that height, diameter, and volume specifications were within realistic ranges.

The process was ideally projected to operate 360 days per year with a start-up time of one year. In addition, the tax rate was approximated at 40%, an interest rate at 20%, and a salvage value of 20%. Escalation percentages were compounded yearly for the product, raw material, and operating costs. The total capital cost for this process is approximately $16.4 million, which includes all equipment and piping described in the process. The most expensive equipment used in this process are the two fired heaters F-101 and F-102, which have an exceptionally large heat exchange area to adequately heat the feed. Standard heaters may not suffice and additional costs may be incurred for the raw materials and manufacture of this equipment. Including a feed preheater or additional fired heaters may reduce this cost in subsequent design iterations.

The total operating cost is approximately $465 million per year, about $427 million of which is the cost of the ethanol feed and natural gas for the two fired heaters. An additional $1.73 million per year is used for utilities including the cooling water and refrigerant. The labor and maintenance costs of this industrial process were also accounted for within the simulation’s economic analysis. The HYSYS simulation software, in conjunction with the Icarus economic analyzer, estimated there should be 5 operators per 8 hour shift with a cost per operator of $20 per hour. This results in a total operating labor cost of approximately $880,000 per year. In addition, the process will require one supervisor per shift with an hourly rate of $35 for total supervisor salaries of $307,000 per year. Finally, a fixed maintenance rate was estimated at $205,000 per 8000 hours of operation for a total cost of $225,000 per year.

Total product sales are roughly $640 million per year at full operation. The estimated income for this process is thus approximately $175 million per year. After ten years, the plant is projected to have a net present value (NPV) of $391 million and an internal rate of return of approximately 79%. In addition the payout period for the initial investment is estimated to be about 2.7 years. Figure 2 shows the projected cash flow for the project.

==Sensitivity Analysis==
A sensitivity analysis was performed to investigate the effects of fluctuating capital costs, operating costs, raw materials, utility costs and ethylene sales price on the 10-year net present value (NPV) of the project. This analysis was performed by scaling these cost factors according to typical ranges given in Towler and Sinnott and calculating the adjusting the NPV accordingly. The results, illustrated in Figure 3, indicate that the project value is most sensitive to product sales, raw materials costs, and operating costs. Ethylene and ethanol prices are market-determined and cannot be controlled for in the process design, so further optimization should be focused on minimizing the operations cost of the process. (Today in Energy, 2015; Weddle, 2014) However, in feed and product prices do still have a profound effect on profitability and feasibility. A more rigorous market analysis will better inform the profitability outlook.

=Conclusions/Recommendations=

The proposed process produces approximately 460,000 metric tons of 99.7 wt% ethylene annually, with a 10-year net present value of $131 million. If current economic conditions hold, it is recommended that this project proceed to implementation following further design improvements and optimization.

Future design iterations should focus on process optimization, particularly in minimizing operating costs as prescribed by the results of the sensitivity analysis. The development of a heat-exchanger network, potentially with Aspen Energy Analyzer, is one option for decreasing utility requirements and increasing the efficiency of the process overall. Optimization of the fired heaters could also result in decreased operational costs. Although overall profitability is less sensitive to capital costs, reviewing and adjusting equipment sizing would also improve the economic outlook. In particular, exploring alternative heating strategies at the beginning of the process could significantly decrease capital costs. Although there are not any particularly dangerous chemicals utilized in the process, an overall process review should also consider potential failure modes to minimize the safety risk to plant workers and nearby residents.

In addition to economic and safety considerations, harmful emissions and waste streams should be minimized both to bring down the cost of treatment and to decrease environmental effects. The two fired heaters consume a large amount of natural gas per year, emitting about 200,000 tons of CO2 annually, and account for more than half of the capital cost of the process. Although no known toxic gases are produced, carbon capture or other emissions-reduction methods should be considered. Additionally, enough wastewater is produced by this process that building an onsite wastewater treatment center should be considered. This could not only decrease operating costs by eliminating the need for an external contract but also give the plant more control over the final purity of the treated wastewater.

Finally, the current model assumes that all ethylene produced will be sold at a current prices and price or product sales will not be affected by economic variability. A more detailed study of the chemical-grade ethylene market, as well as a more thorough understanding of sales and distribution logistics, would increase the surety of a profitable process.

In summary, the proposed process yields chemical grade ethylene via the catalytic dehydration of ethanol. A 100,000 kg/hr of 95 wt% ethanol, 5% water feed is converted to 53,000 kg/hr of 99.7% chemical-grade ethylene. After 10 years of operation, including a one-year startup time, the process has an NPV of $391 million with an IRR of 79% and a payback period of 2.7 years.
Pending further optimization, this process was determined to be viable and it is recommended for the project to move forward.

=References=

[1] American Chemistry Council. Production of chemicals and plastics in the U.S. in 2013, by type (in 1,000 metric tons). In Statista - The Statistics Portal. August 2014. Available at http://www.statista.com/statistics/299725/total-us-plastics-and-chemicals-shipments-by-type/, Accessed January 15, 2015. – Relative proportions of plastics production.

[2] DuPont Nevada Site Cellulosic Ethanol Facility [Internet]. DuPont Chemical; c2012-2015 [cited 11 Mar. 2015]. Available from: http://biofuels.dupont.com/cellulosic-ethanol/nevada-site-ce-facility/. -- Information on ethanol production in Iowa.

[3] Designing Ethylene Plants. Ethylene [Internet]. Technip; 2014 [cited 13 Mar. 2015]. Available from: http://www.technip.com/en/our-business/onshore/ethylene -- Plant size ranges.

[4] Suppes GJ. Selecting Thermodynamic Models for Process Simulation of Organic VLE and LLE Systems. The University of Missouri-Columbia, Dept of Chemical Engineering. [cited 13 Mar. 2015]. -- Use of NRTL in alcohol separations.

[5] ASPENtech. Appendix A - Property Methods and Calculations. Simulation Basics; A-3 - A-26. 2014.

[6] 190 Proof Ethanol: Technical Data Sheet [Internet]. Decon Labs Inc; 2012 [cited 13 Mar. 2015]. Available from: http://www.deconlabs.com/tds/ETHANOL%20190%20%20PROOF.pdf -- Information regarding 95% ethanol

[7] Hadawey A, Ge Y, Tassou TSA. Energy Savings Through Liquid Pressure Amplification In A Dairy Plant Refrigeration System. The Centre for Energy and Built Environment Research [cited 13 Mar. 2015].

[8] Methane (Chemical Compound). 2015. Encyclopædia Britannica Online. [cited 13 Mar. 2015] Available from: http://www.britannica.com/EBchecked/topic/378264/methane -- Composition of Methane

[9] Composition of Air [Internet]. Engineering Toolbox; [cited 13 Mar. 2015]. Available from: http://www.engineeringtoolbox.com/air-composition-d_212.html. -- Composition of air.

[10] Summary of the Clean Air Act, 2015. United States Environmental Protection Agency. [cited 13 Mar. 2015] Available from: http://www2.epa.gov/laws-regulations/summary-clean-air-act -- Emissions requirements of chemical plants.

[11] Zhang M, Yu Y. Dehydration of Ethanol to Ethylene. Industrial Engineering and Chemical Research. 2013; 52:9505-9514. – Technical information on ethanol to ethylene conversion via dehydration.

[12] AspenTech. Aspen HYSYS Help File v8.0. Aspen Technology, Inc. 2012. - Aspen HYSYS help file used for troubleshooting and assistance on economic analysis.

[13] Towler G, Sinnott R. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. 2nd ed. Boston: Elsevier; 2013. -- General Reference Book

[14] Barrocas H, Baratelli F, inventors; Petroleo Brasileiro S.A., assignee. Process for dehydration of a low molecular weight alcohol. US patent 4,396,789 A. August 2, 1983. - Primary background for process design.

[15] Tsao U, Zasloff HB, inventors; The Lummus Company, assignee. Production of ethylene from ethanol. US patent 4,134,926. January 16, 1979. – Patent for catalytic dehydration of ethylene in a fluidized bed reactor.

[16] Morschbacker, A. Bio-Ethanol Based Ethylene. Polymer Reviews. 2009; 49:79-84. – Overview of bioethanol dehydration process development.

[17] Fan D, Dai DJ, Wu HS. Ethylene Formation by Catalytic Dehydration of Ethanol with Industrial Considerations. Materials. 6, 101-115. doi: 10.3390/ma6010101. - Comparison of types of catalysts used in the dehydration of ethanol and current research into new catalysts.

[18] Chen G, Li S, Jiao F, Yuan Q. Catalytic dehydration of bioethanol to ethylene over TiO2/γ-Al2O3 catalysts in microchannel reactors. Catal. Today 2007, 125, 111–119. - Paper introducing research on modified alumina catalyst for ethanol dehydration.

[19] Jumonville, J. Tutorial on Cryogenic Turboexpanders. Proceedings of the Thirty-Ninth Turbomachinery Symposium; 2010 Oct 4-7; Houston, TX. Houston: Texas A&M University; 2010. -- Use of turboexpander for cryogenic separations

[20] Today in Energy - Daily Prices. US Energy Information Administration website. http://www.eia.gov/todayinenergy/prices.cfm. Accessed March 3rd 2015. - Bulk market price for 95% ethanol.

[21] Weddle, N. ICIS Pricing: Ethylene (Europe). Reed Business Limited. January 10 2014. - Bulk market price for chemical grade ethylene.

=Appendix I - Process Flow Diagram=
[[File:PFD B1.JPG|1200px]]

=Appendix II - HYSYS Simulation=
[[File:HYSYS_B1.PNG|1200px]]

=Appendix III - Material Streams=
[[File:Streams_B1.png|1200px]]

=Appendix IV - Energy Table=
[[File:Energy_B1.png|600px|center]]

=Appendix V - Economics=
[[File:Econsummary_B1.png|center]] 

[[File:Capcost_B1.png|center]] 

[[File:sensitivityanalysis_B1.png|600px|center]]

Ethanol to Ethylene (B1)

2015-03-14T04:18:25Z

Hpoppick: /* Process Alternatives/Recommendations */

[[File:BFD_B1.png|600px|thumbnail|alt=Alt text|Conversion of Ethanol to Ethylene]]
=Executive Summary=

The following report outlines the design and analysis of a process converting ethanol to chemical-grade ethylene via catalytic dehydration. This process consumers 100,000 kg/hr of 95 wt% ethanol, 5 wt% water feedstock and produces 53,000 kg/hr of 99.7 wt% chemical-grade ethylene. The ethanol feed passes through two fixed-bed reactors, each packed with an aluminum oxide catalyst, and the resulting ethylene is purified by two flash tanks and by absorption with water. The process was modeled using Aspen HYSYS simulation software to estimate mass and energy flows and equipment sizing requirements. Based on results of this initial simulation, several alternatives are discussed for increasing the process efficiency and profitability. The use of a fluidized bed reactor or a more ethylene-selective catalyst could increase the production of ethylene per ethanol basis. Additionally, several methods of purification to more valuable polymer-grade ethylene are proposed.

The economic feasibility of this process was evaluated using Aspen Economic Analyzer with the Icarus economics package. Capital cost is approximately $16.4 million total with an operating cost of $465 million per year. The current market prices of the ethanol feed and ethylene sales price are $1.44/gallon and $1350/metric ton respectively. The cost of feed ethanol, process utilities and miscellaneous operational costs total to about $427 million/year. At full operation, revenue at current prices would be approximately $640 million per year. The predicted 10-year net present value of the process is approximately $391 million with an IRR of 79% and a payback period of 2.7 years. A sensitivity analysis indicates that the process is most sensitive to feed prices, product prices and operation cost.

Several recommendations are made for both cost reduction and profit maximization, including the design of a heat exchanger network and the optimization of fired heaters that require high capital investment and large amounts of fuel. A safety review of the process is recommended, as well as the minimization of flue gas effluent and wastewater. It is also suggested that the construction of an onsite wastewater treatment center be considered. Overall, the initial analysis indicates this to be a profitable process and it is recommended the project move forward.

=Introduction=

Ethylene is a critical chemical precursor to a number of different industrial products. It is often derived from petroleum sources and polymerized to polyethylene, one of the most ubiquitous plastics today. (American Chemistry Council, 2013) Recently there has been a significant effort to develop production pathways utilizing biologically-derived feedstocks, such as corn or cellulosic ethanol, rather than traditional fossil-fuel sources. Ethylene can be produced from bioethanol via catalytic dehydration over an aluminum oxide catalyst. The proposed process converts 100,000 kg/hr of 95 wt% ethanol, 5% water feed to 53,000 kg/hr of 99.7% chemical-grade ethylene when operating at full capacity. This process was found to be economically viable with a 10-year net present value (NPV) of $131 million (2014 USD) and a payback period of approximately 2.7 years. This memo will detail the proposed process, as well as outline potential alternatives and economic viability of the project.

=Technical Approach=

Many bioethanol plants are located in the Midwest where large amounts of feedstock crops, such as corn, are grown. As such, this plant will be located in Story county, Iowa, near a large-scale bioethanol production plant. (DuPont Nevada Site, 2012) It is assumed that the supply of bioethanol is consistent and readily available. It is also assumed that other reagents - namely, the aluminum oxide catalyst, heater fuel, utility water and freon refrigerant - are readily available, and that wastewater treatment facilities are located near enough to facilitate the off-site treatment of wastewater. Plant capacity was based on current mid-sized industrial ethylene plants. (Designing Ethylene Plants, 2014)

HYSYS simulations were performed with the NRTL fluid package and Peng-Robinson vapor model. The NRTL fluid package is an activity coefficient model that is especially useful to model the separations of alcohols in aqueous solutions. (Suppes, 2015) In addition, NRTL uses models of binary pairs of components, much like the Wilson equation, to predict chemical interactions at the molecular level. The NRTL package can thus be easily extended to ternary and higher order chemical systems, making it ideal for this type of simulation. The Peng-Robinson vapor model was selected as it is well-suited to account for the non-idealities of the vapor phase reactions and separations integral to this process. (ASPENtech, 2014)

It was assumed that the feed enters the process at ambient temperature and pressure (25 °C, 1 atm) and at a consistent rate and composition with negligible quantities of impurities. The ethanol feed was assumed to be 95% ethanol and 5% water by mass, which is the commercial standard for industrial ethanol. (190 Proof Ethanol, 2012) Storage vessels for the feed ethanol, waste streams and products are assumed to be located nearby to the process. An initial feed pump compensates for pressure drops through the process and reduces the duty on downstream compressors. (Hadawey, 2015)

Natural gas, assumed to consist of 83% methane, 16% ethane and 1% nitrogen by mass, was supplied to two fired heaters at a flow rate estimated by HYSYS. (Methane, 2015) Air fed to the process to enable combustion was assumed to be 23% oxygen and 77% nitrogen by mass. (Composition of Air, 2015) Air streams were fed at 50% molar excess in order to ensure complete combustion and prevent the formation of carbon monoxide in the heater exhaust. Total flue gases are assumed to be 230,000 kg/hr, or 2.2 million tons annually, and consist of 73.8% nitrogen gas, 10.5% carbon dioxide, 8.2% water vapor, and 7.5% oxygen by mass. The only compound of concern in these emissions is the carbon dioxide, a known greenhouse gas. At the time of this report, the quantities of carbon dioxide emitted by this plant annually are within acceptable EPA specifications. (Summary of the Clean Air Act, 2015)

Due to the difficulty of simulation equilibrium and conversion reactions in a single vessel in HYSYS, these two reaction types were simulated in separate equilibrium reactor and conversion reactor units in series. In addition, while HYSYS indicated that reactor units would output separate vapor and liquid streams, it was assumed that in practice this would take the form of a single, two phase stream between each unit. To account for this, mixers were installed downstream of each reactor to combine the liquid and vapor phases of the reactor effluent. The three consequent reactions considered are as follows:

Ethanol ↔ Ethylene + Water
Ethanol → Acetaldehyde + Hydrogen
2 Ethanol → Diethyl Ether + Water

The optimal reaction temperature was determined to be 400 °C, which promotes the equilibrium reaction of ethanol to ethylene while minimizing byproducts. (Zhang and Yu, 2013) While other byproducts may be produced in this process, these reactions are typically taken to comprise of the bulk of the dehydration reaction. Heat losses over these reactors were assumed to be negligible. (Zhang and Yu, 2013)All major process equipment is assumed to be constructed of high strength carbon steel. (AspenTech, 2012)

The “Sizing Utility” within the Icarus Economic Evaluation module was used to estimate sizes of major equipment based on the process simulation. These values can serve as a benchmark for an initial plant design. Icarus KbaseTM implements a wide variety of mechanical design standards, including ASME and BS5500, in order to calculate accurate equipment sizing. The Icarus sizing module combines equipment prices for standard chemical processing equipment as well as correlations and sizing factors. The advantage of using a software package such as HYSYS to price out individual equipment is that it utilizes up-to-date prices from vendors and distributors when estimating costs. A more in-depth overview of the correlations included in this software can be found in Towler and Sinnott (2009).

=Process Flowsheet=
[[File:Squarepfd_B1.PNG|thumb|400px]]

The following process is based primarily on a 1983 US patent titled “Process for dehydration of a low molecular weight alcohol.” (Barrocas and Baratelli, 1983) The process flow diagram can be seen in Figure 1. A larger version of the PFD is included in Appendix I and the HYSYS simulation setup in Appendix II.

The feed enters the process at a rate of 100,000 kg/hr, a temperature and pressure of a 25 °C and 1 atm and at a composition of 95 wt% ethanol and 5 wt% water.It is initially pressurized to 4335 kPa by centrifugal pump P-101 and subsequently heated to 400 °C by fired heater F-101. The heated and pressurized feed enters fixed bed reactor R-101 and contacts with the aluminum oxide catalyst. At this point it dehydrates to form the product, ethylene, as well as the byproducts water, hydrogen, diethyl ether and acetaldehyde. Fired heater F-102 and reactor R-102 increase the overall conversion of the process. Both fired heaters F-101 and F-102 are fueled with natural gas and fed with excess air. The composition of the reactor train effluent is 54.5 wt% ethylene, 37.1 wt% water, 8.1 wt% unreacted ethanol and trace amounts of diethyl ether, acetaldehyde, and hydrogen contaminants.

The pressure of the reactor train effluent is increased to 4500 kPa by compressor K-102 and the temperature decreased to 100 °C by exchange with cold water in heat exchanger E-201. The stream then expands and flashes in flash vessel FL-201, which separates out 82.3% of the unreacted ethanol, 96.6% of the water and virtually all of the acetaldehyde contaminant in the bottoms while sending the ethylene-rich vapor phase out of the top. The top product of FL-202 is compressed to 3500 kPA by K-202 and cooled to 0.0 °C by a freon refrigerant in E-202. At this point the stream is flashed for a second time in vessel FL-202 to remove additional impurities. The top outlet stream consists of 99.5 wt% ethylene, which is fed to the bottom of a 10-tray absorption column that removes a fraction of the residual diethyl ether as well as the remainder of the unreacted ethanol. A stream of absorbent water is fed to the top of the column at 10,000 kg/hr. The product exits the top of the column at a rate of 54,600 kg/hr and has a purity of 99.7% ethylene. Diethyl ether makes up 0.2% of the remaining product stream and is the primary contaminant. Trace amounts of residual water and hydrogen are also present.

Full tables of material and energy streams can be found in Appendices III and IV respectively.

==Process Alternatives==
===Reactor Alternatives===
Two fixed bed reactors, alternating with fired heaters, are used in the dehydration reaction of ethanol to ethylene. However, a fluidized bed reactor can offer better mixing and temperature control than a fixed bed reactor and thus provide the highest possible conversion of ethanol with the greatest selectivity to ethylene. (Tsao and Zasloff, 1979) Fluidized bed reactors also provide a lower rate of catalyst coking and byproduct formation, minimizing separation and catalyst regeneration costs. (Morschbacker, 2009) The major downside of fluidized bed reactors is that few large-scale processes have been built since the technology was developed in the late 1970s. (Tsao and Zasloff, 1979; Morschbacker, 2009) Although implementation of fluidized bed reactors could potentially increase the purity of the ethylene product and/or decrease costs, a small scale pilot process would need to be built and tested before it would be possible to develop an industrial-scale facility.

===Catalyst Alternatives===
Aluminum oxide, specifically gamma alumina, is the most industrially-common catalyst and has been historically used due to its low cost and high stability. (Tsao and Zasloff, 1979; Fan and Dai, n.d.) Recent improvements in selectivity and catalyst stability of activated alumina have been achieved by incorporating titanium oxide into the catalyst, although this increases reaction temperature by approximately 50 °C and decreases catalyst lifespan. (Chen and Li, et. al. 2007) There is also significant ongoing research into HZSM-5 zeolite and heteropolyacids, which are being explored as potential alternatives to alumina oxide. A nanoscale HZSM-5 zeolite catalyst has been shown to operate at the relatively low temperature of 200-300°C, with a 100% ethanol conversion and 99.7% selectivity to ethylene. Initial research has also indicated that it maintains greater than 98% selectivity for 630 operational hours. (Fan and Dai, n.d.) However, the current low cost and ready availability of unmodified alumina oxide makes it a better choice for a process of this scale.

===Purification Alternatives===
As specified in this process, the reactor effluent is purified by two flash drums and absorption with water to produce chemical-grade ethylene. If chemical-grade ethylene is indeed the desired product, other purification options include caustic washing of the reactor effluent and water removal in a desiccant drying bed. (Morschbacker, 2009) While this purification train is relatively simple and does not require harsh chemical reagents, polymer grade ethylene is more commercially valuable and the additional cost of removing water and diethyl ether contaminants may be justified by increased revenue. Cryogenic distillation was initially simulated to produce polymer-grade ethylene, but utility requirements were found to render this separation economically unviable. (Barrocas and Baratelli, 1983) Further research and optimization may find this purification strategy to be a more valid process. Alternatively, the addition of a cryogenic turboexpander or the use of alternative adsorbents may increase product purity to polymer grade. (Jumonville, 2010) Initial HYSYS simulations indicate that these operations may be feasible with further refinement.

===Wastewater Treatment===
Due to the large volume of wastewater produced, building an on-site wastewater treatment facility may prove to be more economical than paying for third-party wastewater treatment. Flash vessel FL-201 produces 44,600 L/hr of wastewater contaminated with 18.7 vol% ethanol and 0.6 vol% acetaldehyde, while FL-202 produces 2940 L/hr of an aqueous waste consisting of 56.8 vol% ethanol, 42.0 vol% water and 0.9 vol% diethyl ether. The absorption column produces approximately 10,200 liters/hr of wastewater contaminated with 1.2 vol% ethanol, 0.2% diethyl ether and 0.2% acetaldehyde. Utilizing distillation to separate these streams into clean water and volatile organic waste could ultimately reduce the quantity of waste that requires disposal and reduce the overall costs of the process.

==Process Equipment==
Relevant sizing information for each unit operation, estimated by the method described in the “Technical Approach,” can be found in Appendix V. Equipment and piping is assumed to be constructed of carbon steel. It should be noted that the two fired heaters are proportionately large enough to heat the entirety of the process stream and are thus larger than standard equipment.

=Economic Analysis=
[[File:sensitivityanalysis_B1.png|400px|thumb]]

==Economics Overview==
All final values are normalized to June 2014 USD by CEPCI scaling. It is assumed that all products produced are sold at current market prices.

The Aspen Economic Evaluation module within HYSYS v8.0 was used to estimate capital and operating costs for a 10-year plant life span with a construction start date of April 2015. The price of the 95% ethanol feed stream was estimated at $1.44 per gallon, while the chemical grade ethylene produced is currently selling for approximately $1350 per metric ton. (Today in Energy, 2015; Weddle, 2014) Mapping and sizing calculations were performed by the economics module and a preliminary economic evaluation was completed. Equipment sizes, also estimated by HYSYS, were reviewed to ensure that height, diameter, and volume specifications were within realistic ranges.

The process was ideally projected to operate 360 days per year with a start-up time of one year. In addition, the tax rate was approximated at 40%, an interest rate at 20%, and a salvage value of 20%. Escalation percentages were compounded yearly for the product, raw material, and operating costs. The total capital cost for this process is approximately $16.4 million, which includes all equipment and piping described in the process. The most expensive equipment used in this process are the two fired heaters F-101 and F-102, which have an exceptionally large heat exchange area to adequately heat the feed. Standard heaters may not suffice and additional costs may be incurred for the raw materials and manufacture of this equipment. Including a feed preheater or additional fired heaters may reduce this cost in subsequent design iterations.

The total operating cost is approximately $465 million per year, about $427 million of which is the cost of the ethanol feed and natural gas for the two fired heaters. An additional $1.73 million per year is used for utilities including the cooling water and refrigerant. The labor and maintenance costs of this industrial process were also accounted for within the simulation’s economic analysis. The HYSYS simulation software, in conjunction with the Icarus economic analyzer, estimated there should be 5 operators per 8 hour shift with a cost per operator of $20 per hour. This results in a total operating labor cost of approximately $880,000 per year. In addition, the process will require one supervisor per shift with an hourly rate of $35 for total supervisor salaries of $307,000 per year. Finally, a fixed maintenance rate was estimated at $205,000 per 8000 hours of operation for a total cost of $225,000 per year.

Total product sales are roughly $640 million per year at full operation. The estimated income for this process is thus approximately $175 million per year. After ten years, the plant is projected to have a net present value (NPV) of $391 million and an internal rate of return of approximately 79%. In addition the payout period for the initial investment is estimated to be about 2.7 years. Figure 2 shows the projected cash flow for the project.

==Sensitivity Analysis==
A sensitivity analysis was performed to investigate the effects of fluctuating capital costs, operating costs, raw materials, utility costs and ethylene sales price on the 10-year net present value (NPV) of the project. This analysis was performed by scaling these cost factors according to typical ranges given in Towler and Sinnott and calculating the adjusting the NPV accordingly. The results, illustrated in Figure 3, indicate that the project value is most sensitive to product sales, raw materials costs, and operating costs. Ethylene and ethanol prices are market-determined and cannot be controlled for in the process design, so further optimization should be focused on minimizing the operations cost of the process. (Today in Energy, 2015; Weddle, 2014) However, in feed and product prices do still have a profound effect on profitability and feasibility. A more rigorous market analysis will better inform the profitability outlook.

=Conclusions/Recommendations=

The proposed process produces approximately 460,000 metric tons of 99.7 wt% ethylene annually, with a 10-year net present value of $131 million. If current economic conditions hold, it is recommended that this project proceed to implementation following further design improvements and optimization.

Future design iterations should focus on process optimization, particularly in minimizing operating costs as prescribed by the results of the sensitivity analysis. The development of a heat-exchanger network, potentially with Aspen Energy Analyzer, is one option for decreasing utility requirements and increasing the efficiency of the process overall. Optimization of the fired heaters could also result in decreased operational costs. Although overall profitability is less sensitive to capital costs, reviewing and adjusting equipment sizing would also improve the economic outlook. In particular, exploring alternative heating strategies at the beginning of the process could significantly decrease capital costs. Although there are not any particularly dangerous chemicals utilized in the process, an overall process review should also consider potential failure modes to minimize the safety risk to plant workers and nearby residents.

In addition to economic and safety considerations, harmful emissions and waste streams should be minimized both to bring down the cost of treatment and to decrease environmental effects. The two fired heaters consume a large amount of natural gas per year, emitting about 200,000 tons of CO2 annually, and account for more than half of the capital cost of the process. Although no known toxic gases are produced, carbon capture or other emissions-reduction methods should be considered. Additionally, enough wastewater is produced by this process that building an onsite wastewater treatment center should be considered. This could not only decrease operating costs by eliminating the need for an external contract but also give the plant more control over the final purity of the treated wastewater.

Finally, the current model assumes that all ethylene produced will be sold at a current prices and price or product sales will not be affected by economic variability. A more detailed study of the chemical-grade ethylene market, as well as a more thorough understanding of sales and distribution logistics, would increase the surety of a profitable process.

In summary, the proposed process yields chemical grade ethylene via the catalytic dehydration of ethanol. A 100,000 kg/hr of 95 wt% ethanol, 5% water feed is converted to 53,000 kg/hr of 99.7% chemical-grade ethylene. After 10 years of operation, including a one-year startup time, the process has an NPV of $391 million with an IRR of 79% and a payback period of 2.7 years.
Pending further optimization, this process was determined to be viable and it is recommended for the project to move forward.

=Conclusion=
=References=

[1] American Chemistry Council. Production of chemicals and plastics in the U.S. in 2013, by type (in 1,000 metric tons). In Statista - The Statistics Portal. August 2014. Available at http://www.statista.com/statistics/299725/total-us-plastics-and-chemicals-shipments-by-type/, Accessed January 15, 2015. – Relative proportions of plastics production.

[2] DuPont Nevada Site Cellulosic Ethanol Facility [Internet]. DuPont Chemical; c2012-2015 [cited 11 Mar. 2015]. Available from: http://biofuels.dupont.com/cellulosic-ethanol/nevada-site-ce-facility/. -- Information on ethanol production in Iowa.

[3] Designing Ethylene Plants. Ethylene [Internet]. Technip; 2014 [cited 13 Mar. 2015]. Available from: http://www.technip.com/en/our-business/onshore/ethylene -- Plant size ranges.

[4] Suppes GJ. Selecting Thermodynamic Models for Process Simulation of Organic VLE and LLE Systems. The University of Missouri-Columbia, Dept of Chemical Engineering. [cited 13 Mar. 2015]. -- Use of NRTL in alcohol separations.

[5] ASPENtech. Appendix A - Property Methods and Calculations. Simulation Basics; A-3 - A-26. 2014.

[6] 190 Proof Ethanol: Technical Data Sheet [Internet]. Decon Labs Inc; 2012 [cited 13 Mar. 2015]. Available from: http://www.deconlabs.com/tds/ETHANOL%20190%20%20PROOF.pdf -- Information regarding 95% ethanol

[7] Hadawey A, Ge Y, Tassou TSA. Energy Savings Through Liquid Pressure Amplification In A Dairy Plant Refrigeration System. The Centre for Energy and Built Environment Research [cited 13 Mar. 2015].

[8] Methane (Chemical Compound). 2015. Encyclopædia Britannica Online. [cited 13 Mar. 2015] Available from: http://www.britannica.com/EBchecked/topic/378264/methane -- Composition of Methane

[9] Composition of Air [Internet]. Engineering Toolbox; [cited 13 Mar. 2015]. Available from: http://www.engineeringtoolbox.com/air-composition-d_212.html. -- Composition of air.

[10] Summary of the Clean Air Act, 2015. United States Environmental Protection Agency. [cited 13 Mar. 2015] Available from: http://www2.epa.gov/laws-regulations/summary-clean-air-act -- Emissions requirements of chemical plants.

[11] Zhang M, Yu Y. Dehydration of Ethanol to Ethylene. Industrial Engineering and Chemical Research. 2013; 52:9505-9514. – Technical information on ethanol to ethylene conversion via dehydration.

[12] AspenTech. Aspen HYSYS Help File v8.0. Aspen Technology, Inc. 2012. - Aspen HYSYS help file used for troubleshooting and assistance on economic analysis.

[13] Towler G, Sinnott R. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. 2nd ed. Boston: Elsevier; 2013. -- General Reference Book

[14] Barrocas H, Baratelli F, inventors; Petroleo Brasileiro S.A., assignee. Process for dehydration of a low molecular weight alcohol. US patent 4,396,789 A. August 2, 1983. - Primary background for process design.

[15] Tsao U, Zasloff HB, inventors; The Lummus Company, assignee. Production of ethylene from ethanol. US patent 4,134,926. January 16, 1979. – Patent for catalytic dehydration of ethylene in a fluidized bed reactor.

[16] Morschbacker, A. Bio-Ethanol Based Ethylene. Polymer Reviews. 2009; 49:79-84. – Overview of bioethanol dehydration process development.

[17] Fan D, Dai DJ, Wu HS. Ethylene Formation by Catalytic Dehydration of Ethanol with Industrial Considerations. Materials. 6, 101-115. doi: 10.3390/ma6010101. - Comparison of types of catalysts used in the dehydration of ethanol and current research into new catalysts.

[18] Chen G, Li S, Jiao F, Yuan Q. Catalytic dehydration of bioethanol to ethylene over TiO2/γ-Al2O3 catalysts in microchannel reactors. Catal. Today 2007, 125, 111–119. - Paper introducing research on modified alumina catalyst for ethanol dehydration.

[19] Jumonville, J. Tutorial on Cryogenic Turboexpanders. Proceedings of the Thirty-Ninth Turbomachinery Symposium; 2010 Oct 4-7; Houston, TX. Houston: Texas A&M University; 2010. -- Use of turboexpander for cryogenic separations

[20] Today in Energy - Daily Prices. US Energy Information Administration website. http://www.eia.gov/todayinenergy/prices.cfm. Accessed March 3rd 2015. - Bulk market price for 95% ethanol.

[21] Weddle, N. ICIS Pricing: Ethylene (Europe). Reed Business Limited. January 10 2014. - Bulk market price for chemical grade ethylene.

=Appendix I - Process Flow Diagram=
[[File:PFD B1.JPG|1200px]]

=Appendix II - HYSYS Simulation=
[[File:HYSYS_B1.PNG|1200px]]

=Appendix III - Material Streams=
[[File:Streams_B1.png|1200px]]

=Appendix IV - Energy Table=
[[File:Energy_B1.png|600px|center]]

=Appendix V - Economics=
[[File:Econsummary_B1.png|center]] 

[[File:Capcost_B1.png|center]] 

[[File:sensitivityanalysis_B1.png|600px|center]]

Ethanol to Ethylene (B1)

2015-03-14T04:17:49Z

Hpoppick: /* Economic Analysis */

[[File:BFD_B1.png|600px|thumbnail|alt=Alt text|Conversion of Ethanol to Ethylene]]
=Executive Summary=

The following report outlines the design and analysis of a process converting ethanol to chemical-grade ethylene via catalytic dehydration. This process consumers 100,000 kg/hr of 95 wt% ethanol, 5 wt% water feedstock and produces 53,000 kg/hr of 99.7 wt% chemical-grade ethylene. The ethanol feed passes through two fixed-bed reactors, each packed with an aluminum oxide catalyst, and the resulting ethylene is purified by two flash tanks and by absorption with water. The process was modeled using Aspen HYSYS simulation software to estimate mass and energy flows and equipment sizing requirements. Based on results of this initial simulation, several alternatives are discussed for increasing the process efficiency and profitability. The use of a fluidized bed reactor or a more ethylene-selective catalyst could increase the production of ethylene per ethanol basis. Additionally, several methods of purification to more valuable polymer-grade ethylene are proposed.

The economic feasibility of this process was evaluated using Aspen Economic Analyzer with the Icarus economics package. Capital cost is approximately $16.4 million total with an operating cost of $465 million per year. The current market prices of the ethanol feed and ethylene sales price are $1.44/gallon and $1350/metric ton respectively. The cost of feed ethanol, process utilities and miscellaneous operational costs total to about $427 million/year. At full operation, revenue at current prices would be approximately $640 million per year. The predicted 10-year net present value of the process is approximately $391 million with an IRR of 79% and a payback period of 2.7 years. A sensitivity analysis indicates that the process is most sensitive to feed prices, product prices and operation cost.

Several recommendations are made for both cost reduction and profit maximization, including the design of a heat exchanger network and the optimization of fired heaters that require high capital investment and large amounts of fuel. A safety review of the process is recommended, as well as the minimization of flue gas effluent and wastewater. It is also suggested that the construction of an onsite wastewater treatment center be considered. Overall, the initial analysis indicates this to be a profitable process and it is recommended the project move forward.

=Introduction=

Ethylene is a critical chemical precursor to a number of different industrial products. It is often derived from petroleum sources and polymerized to polyethylene, one of the most ubiquitous plastics today. (American Chemistry Council, 2013) Recently there has been a significant effort to develop production pathways utilizing biologically-derived feedstocks, such as corn or cellulosic ethanol, rather than traditional fossil-fuel sources. Ethylene can be produced from bioethanol via catalytic dehydration over an aluminum oxide catalyst. The proposed process converts 100,000 kg/hr of 95 wt% ethanol, 5% water feed to 53,000 kg/hr of 99.7% chemical-grade ethylene when operating at full capacity. This process was found to be economically viable with a 10-year net present value (NPV) of $131 million (2014 USD) and a payback period of approximately 2.7 years. This memo will detail the proposed process, as well as outline potential alternatives and economic viability of the project.

=Technical Approach=

Many bioethanol plants are located in the Midwest where large amounts of feedstock crops, such as corn, are grown. As such, this plant will be located in Story county, Iowa, near a large-scale bioethanol production plant. (DuPont Nevada Site, 2012) It is assumed that the supply of bioethanol is consistent and readily available. It is also assumed that other reagents - namely, the aluminum oxide catalyst, heater fuel, utility water and freon refrigerant - are readily available, and that wastewater treatment facilities are located near enough to facilitate the off-site treatment of wastewater. Plant capacity was based on current mid-sized industrial ethylene plants. (Designing Ethylene Plants, 2014)

HYSYS simulations were performed with the NRTL fluid package and Peng-Robinson vapor model. The NRTL fluid package is an activity coefficient model that is especially useful to model the separations of alcohols in aqueous solutions. (Suppes, 2015) In addition, NRTL uses models of binary pairs of components, much like the Wilson equation, to predict chemical interactions at the molecular level. The NRTL package can thus be easily extended to ternary and higher order chemical systems, making it ideal for this type of simulation. The Peng-Robinson vapor model was selected as it is well-suited to account for the non-idealities of the vapor phase reactions and separations integral to this process. (ASPENtech, 2014)

It was assumed that the feed enters the process at ambient temperature and pressure (25 °C, 1 atm) and at a consistent rate and composition with negligible quantities of impurities. The ethanol feed was assumed to be 95% ethanol and 5% water by mass, which is the commercial standard for industrial ethanol. (190 Proof Ethanol, 2012) Storage vessels for the feed ethanol, waste streams and products are assumed to be located nearby to the process. An initial feed pump compensates for pressure drops through the process and reduces the duty on downstream compressors. (Hadawey, 2015)

Natural gas, assumed to consist of 83% methane, 16% ethane and 1% nitrogen by mass, was supplied to two fired heaters at a flow rate estimated by HYSYS. (Methane, 2015) Air fed to the process to enable combustion was assumed to be 23% oxygen and 77% nitrogen by mass. (Composition of Air, 2015) Air streams were fed at 50% molar excess in order to ensure complete combustion and prevent the formation of carbon monoxide in the heater exhaust. Total flue gases are assumed to be 230,000 kg/hr, or 2.2 million tons annually, and consist of 73.8% nitrogen gas, 10.5% carbon dioxide, 8.2% water vapor, and 7.5% oxygen by mass. The only compound of concern in these emissions is the carbon dioxide, a known greenhouse gas. At the time of this report, the quantities of carbon dioxide emitted by this plant annually are within acceptable EPA specifications. (Summary of the Clean Air Act, 2015)

Due to the difficulty of simulation equilibrium and conversion reactions in a single vessel in HYSYS, these two reaction types were simulated in separate equilibrium reactor and conversion reactor units in series. In addition, while HYSYS indicated that reactor units would output separate vapor and liquid streams, it was assumed that in practice this would take the form of a single, two phase stream between each unit. To account for this, mixers were installed downstream of each reactor to combine the liquid and vapor phases of the reactor effluent. The three consequent reactions considered are as follows:

Ethanol ↔ Ethylene + Water
Ethanol → Acetaldehyde + Hydrogen
2 Ethanol → Diethyl Ether + Water

The optimal reaction temperature was determined to be 400 °C, which promotes the equilibrium reaction of ethanol to ethylene while minimizing byproducts. (Zhang and Yu, 2013) While other byproducts may be produced in this process, these reactions are typically taken to comprise of the bulk of the dehydration reaction. Heat losses over these reactors were assumed to be negligible. (Zhang and Yu, 2013)All major process equipment is assumed to be constructed of high strength carbon steel. (AspenTech, 2012)

The “Sizing Utility” within the Icarus Economic Evaluation module was used to estimate sizes of major equipment based on the process simulation. These values can serve as a benchmark for an initial plant design. Icarus KbaseTM implements a wide variety of mechanical design standards, including ASME and BS5500, in order to calculate accurate equipment sizing. The Icarus sizing module combines equipment prices for standard chemical processing equipment as well as correlations and sizing factors. The advantage of using a software package such as HYSYS to price out individual equipment is that it utilizes up-to-date prices from vendors and distributors when estimating costs. A more in-depth overview of the correlations included in this software can be found in Towler and Sinnott (2009).

=Process Flowsheet=
[[File:Squarepfd_B1.PNG|thumb|400px]]

The following process is based primarily on a 1983 US patent titled “Process for dehydration of a low molecular weight alcohol.” (Barrocas and Baratelli, 1983) The process flow diagram can be seen in Figure 1. A larger version of the PFD is included in Appendix I and the HYSYS simulation setup in Appendix II.

The feed enters the process at a rate of 100,000 kg/hr, a temperature and pressure of a 25 °C and 1 atm and at a composition of 95 wt% ethanol and 5 wt% water.It is initially pressurized to 4335 kPa by centrifugal pump P-101 and subsequently heated to 400 °C by fired heater F-101. The heated and pressurized feed enters fixed bed reactor R-101 and contacts with the aluminum oxide catalyst. At this point it dehydrates to form the product, ethylene, as well as the byproducts water, hydrogen, diethyl ether and acetaldehyde. Fired heater F-102 and reactor R-102 increase the overall conversion of the process. Both fired heaters F-101 and F-102 are fueled with natural gas and fed with excess air. The composition of the reactor train effluent is 54.5 wt% ethylene, 37.1 wt% water, 8.1 wt% unreacted ethanol and trace amounts of diethyl ether, acetaldehyde, and hydrogen contaminants.

The pressure of the reactor train effluent is increased to 4500 kPa by compressor K-102 and the temperature decreased to 100 °C by exchange with cold water in heat exchanger E-201. The stream then expands and flashes in flash vessel FL-201, which separates out 82.3% of the unreacted ethanol, 96.6% of the water and virtually all of the acetaldehyde contaminant in the bottoms while sending the ethylene-rich vapor phase out of the top. The top product of FL-202 is compressed to 3500 kPA by K-202 and cooled to 0.0 °C by a freon refrigerant in E-202. At this point the stream is flashed for a second time in vessel FL-202 to remove additional impurities. The top outlet stream consists of 99.5 wt% ethylene, which is fed to the bottom of a 10-tray absorption column that removes a fraction of the residual diethyl ether as well as the remainder of the unreacted ethanol. A stream of absorbent water is fed to the top of the column at 10,000 kg/hr. The product exits the top of the column at a rate of 54,600 kg/hr and has a purity of 99.7% ethylene. Diethyl ether makes up 0.2% of the remaining product stream and is the primary contaminant. Trace amounts of residual water and hydrogen are also present.

Full tables of material and energy streams can be found in Appendices III and IV respectively.

==Process Alternatives==
===Reactor Alternatives===
Two fixed bed reactors, alternating with fired heaters, are used in the dehydration reaction of ethanol to ethylene. However, a fluidized bed reactor can offer better mixing and temperature control than a fixed bed reactor and thus provide the highest possible conversion of ethanol with the greatest selectivity to ethylene. (Tsao and Zasloff, 1979) Fluidized bed reactors also provide a lower rate of catalyst coking and byproduct formation, minimizing separation and catalyst regeneration costs. (Morschbacker, 2009) The major downside of fluidized bed reactors is that few large-scale processes have been built since the technology was developed in the late 1970s. (Tsao and Zasloff, 1979; Morschbacker, 2009) Although implementation of fluidized bed reactors could potentially increase the purity of the ethylene product and/or decrease costs, a small scale pilot process would need to be built and tested before it would be possible to develop an industrial-scale facility.

===Catalyst Alternatives===
Aluminum oxide, specifically gamma alumina, is the most industrially-common catalyst and has been historically used due to its low cost and high stability. (Tsao and Zasloff, 1979; Fan and Dai, n.d.) Recent improvements in selectivity and catalyst stability of activated alumina have been achieved by incorporating titanium oxide into the catalyst, although this increases reaction temperature by approximately 50 °C and decreases catalyst lifespan. (Chen and Li, et. al. 2007) There is also significant ongoing research into HZSM-5 zeolite and heteropolyacids, which are being explored as potential alternatives to alumina oxide. A nanoscale HZSM-5 zeolite catalyst has been shown to operate at the relatively low temperature of 200-300°C, with a 100% ethanol conversion and 99.7% selectivity to ethylene. Initial research has also indicated that it maintains greater than 98% selectivity for 630 operational hours. (Fan and Dai, n.d.) However, the current low cost and ready availability of unmodified alumina oxide makes it a better choice for a process of this scale.

===Purification Alternatives===
As specified in this process, the reactor effluent is purified by two flash drums and absorption with water to produce chemical-grade ethylene. If chemical-grade ethylene is indeed the desired product, other purification options include caustic washing of the reactor effluent and water removal in a desiccant drying bed. (Morschbacker, 2009) While this purification train is relatively simple and does not require harsh chemical reagents, polymer grade ethylene is more commercially valuable and the additional cost of removing water and diethyl ether contaminants may be justified by increased revenue. Cryogenic distillation was initially simulated to produce polymer-grade ethylene, but utility requirements were found to render this separation economically unviable. (Barrocas and Baratelli, 1983) Further research and optimization may find this purification strategy to be a more valid process. Alternatively, the addition of a cryogenic turboexpander or the use of alternative adsorbents may increase product purity to polymer grade. (Jumonville, 2010) Initial HYSYS simulations indicate that these operations may be feasible with further refinement.

===Wastewater Treatment===
Due to the large volume of wastewater produced, building an on-site wastewater treatment facility may prove to be more economical than paying for third-party wastewater treatment. Flash vessel FL-201 produces 44,600 L/hr of wastewater contaminated with 18.7 vol% ethanol and 0.6 vol% acetaldehyde, while FL-202 produces 2940 L/hr of an aqueous waste consisting of 56.8 vol% ethanol, 42.0 vol% water and 0.9 vol% diethyl ether. The absorption column produces approximately 10,200 liters/hr of wastewater contaminated with 1.2 vol% ethanol, 0.2% diethyl ether and 0.2% acetaldehyde. Utilizing distillation to separate these streams into clean water and volatile organic waste could ultimately reduce the quantity of waste that requires disposal and reduce the overall costs of the process.

==Process Equipment==
Relevant sizing information for each unit operation, estimated by the method described in the “Technical Approach,” can be found in Appendix V. Equipment and piping is assumed to be constructed of carbon steel. It should be noted that the two fired heaters are proportionately large enough to heat the entirety of the process stream and are thus larger than standard equipment.

=Economic Analysis=
[[File:sensitivityanalysis_B1.png|400px|thumb]]

==Economics Overview==
All final values are normalized to June 2014 USD by CEPCI scaling. It is assumed that all products produced are sold at current market prices.

The Aspen Economic Evaluation module within HYSYS v8.0 was used to estimate capital and operating costs for a 10-year plant life span with a construction start date of April 2015. The price of the 95% ethanol feed stream was estimated at $1.44 per gallon, while the chemical grade ethylene produced is currently selling for approximately $1350 per metric ton. (Today in Energy, 2015; Weddle, 2014) Mapping and sizing calculations were performed by the economics module and a preliminary economic evaluation was completed. Equipment sizes, also estimated by HYSYS, were reviewed to ensure that height, diameter, and volume specifications were within realistic ranges.

The process was ideally projected to operate 360 days per year with a start-up time of one year. In addition, the tax rate was approximated at 40%, an interest rate at 20%, and a salvage value of 20%. Escalation percentages were compounded yearly for the product, raw material, and operating costs. The total capital cost for this process is approximately $16.4 million, which includes all equipment and piping described in the process. The most expensive equipment used in this process are the two fired heaters F-101 and F-102, which have an exceptionally large heat exchange area to adequately heat the feed. Standard heaters may not suffice and additional costs may be incurred for the raw materials and manufacture of this equipment. Including a feed preheater or additional fired heaters may reduce this cost in subsequent design iterations.

The total operating cost is approximately $465 million per year, about $427 million of which is the cost of the ethanol feed and natural gas for the two fired heaters. An additional $1.73 million per year is used for utilities including the cooling water and refrigerant. The labor and maintenance costs of this industrial process were also accounted for within the simulation’s economic analysis. The HYSYS simulation software, in conjunction with the Icarus economic analyzer, estimated there should be 5 operators per 8 hour shift with a cost per operator of $20 per hour. This results in a total operating labor cost of approximately $880,000 per year. In addition, the process will require one supervisor per shift with an hourly rate of $35 for total supervisor salaries of $307,000 per year. Finally, a fixed maintenance rate was estimated at $205,000 per 8000 hours of operation for a total cost of $225,000 per year.

Total product sales are roughly $640 million per year at full operation. The estimated income for this process is thus approximately $175 million per year. After ten years, the plant is projected to have a net present value (NPV) of $391 million and an internal rate of return of approximately 79%. In addition the payout period for the initial investment is estimated to be about 2.7 years. Figure 2 shows the projected cash flow for the project.

==Sensitivity Analysis==
A sensitivity analysis was performed to investigate the effects of fluctuating capital costs, operating costs, raw materials, utility costs and ethylene sales price on the 10-year net present value (NPV) of the project. This analysis was performed by scaling these cost factors according to typical ranges given in Towler and Sinnott and calculating the adjusting the NPV accordingly. The results, illustrated in Figure 3, indicate that the project value is most sensitive to product sales, raw materials costs, and operating costs. Ethylene and ethanol prices are market-determined and cannot be controlled for in the process design, so further optimization should be focused on minimizing the operations cost of the process. (Today in Energy, 2015; Weddle, 2014) However, in feed and product prices do still have a profound effect on profitability and feasibility. A more rigorous market analysis will better inform the profitability outlook.

=Process Alternatives/Recommendations=
=Conclusion=
=References=

[1] American Chemistry Council. Production of chemicals and plastics in the U.S. in 2013, by type (in 1,000 metric tons). In Statista - The Statistics Portal. August 2014. Available at http://www.statista.com/statistics/299725/total-us-plastics-and-chemicals-shipments-by-type/, Accessed January 15, 2015. – Relative proportions of plastics production.

[2] DuPont Nevada Site Cellulosic Ethanol Facility [Internet]. DuPont Chemical; c2012-2015 [cited 11 Mar. 2015]. Available from: http://biofuels.dupont.com/cellulosic-ethanol/nevada-site-ce-facility/. -- Information on ethanol production in Iowa.

[3] Designing Ethylene Plants. Ethylene [Internet]. Technip; 2014 [cited 13 Mar. 2015]. Available from: http://www.technip.com/en/our-business/onshore/ethylene -- Plant size ranges.

[4] Suppes GJ. Selecting Thermodynamic Models for Process Simulation of Organic VLE and LLE Systems. The University of Missouri-Columbia, Dept of Chemical Engineering. [cited 13 Mar. 2015]. -- Use of NRTL in alcohol separations.

[5] ASPENtech. Appendix A - Property Methods and Calculations. Simulation Basics; A-3 - A-26. 2014.

[6] 190 Proof Ethanol: Technical Data Sheet [Internet]. Decon Labs Inc; 2012 [cited 13 Mar. 2015]. Available from: http://www.deconlabs.com/tds/ETHANOL%20190%20%20PROOF.pdf -- Information regarding 95% ethanol

[7] Hadawey A, Ge Y, Tassou TSA. Energy Savings Through Liquid Pressure Amplification In A Dairy Plant Refrigeration System. The Centre for Energy and Built Environment Research [cited 13 Mar. 2015].

[8] Methane (Chemical Compound). 2015. Encyclopædia Britannica Online. [cited 13 Mar. 2015] Available from: http://www.britannica.com/EBchecked/topic/378264/methane -- Composition of Methane

[9] Composition of Air [Internet]. Engineering Toolbox; [cited 13 Mar. 2015]. Available from: http://www.engineeringtoolbox.com/air-composition-d_212.html. -- Composition of air.

[10] Summary of the Clean Air Act, 2015. United States Environmental Protection Agency. [cited 13 Mar. 2015] Available from: http://www2.epa.gov/laws-regulations/summary-clean-air-act -- Emissions requirements of chemical plants.

[11] Zhang M, Yu Y. Dehydration of Ethanol to Ethylene. Industrial Engineering and Chemical Research. 2013; 52:9505-9514. – Technical information on ethanol to ethylene conversion via dehydration.

[12] AspenTech. Aspen HYSYS Help File v8.0. Aspen Technology, Inc. 2012. - Aspen HYSYS help file used for troubleshooting and assistance on economic analysis.

[13] Towler G, Sinnott R. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. 2nd ed. Boston: Elsevier; 2013. -- General Reference Book

[14] Barrocas H, Baratelli F, inventors; Petroleo Brasileiro S.A., assignee. Process for dehydration of a low molecular weight alcohol. US patent 4,396,789 A. August 2, 1983. - Primary background for process design.

[15] Tsao U, Zasloff HB, inventors; The Lummus Company, assignee. Production of ethylene from ethanol. US patent 4,134,926. January 16, 1979. – Patent for catalytic dehydration of ethylene in a fluidized bed reactor.

[16] Morschbacker, A. Bio-Ethanol Based Ethylene. Polymer Reviews. 2009; 49:79-84. – Overview of bioethanol dehydration process development.

[17] Fan D, Dai DJ, Wu HS. Ethylene Formation by Catalytic Dehydration of Ethanol with Industrial Considerations. Materials. 6, 101-115. doi: 10.3390/ma6010101. - Comparison of types of catalysts used in the dehydration of ethanol and current research into new catalysts.

[18] Chen G, Li S, Jiao F, Yuan Q. Catalytic dehydration of bioethanol to ethylene over TiO2/γ-Al2O3 catalysts in microchannel reactors. Catal. Today 2007, 125, 111–119. - Paper introducing research on modified alumina catalyst for ethanol dehydration.

[19] Jumonville, J. Tutorial on Cryogenic Turboexpanders. Proceedings of the Thirty-Ninth Turbomachinery Symposium; 2010 Oct 4-7; Houston, TX. Houston: Texas A&M University; 2010. -- Use of turboexpander for cryogenic separations

[20] Today in Energy - Daily Prices. US Energy Information Administration website. http://www.eia.gov/todayinenergy/prices.cfm. Accessed March 3rd 2015. - Bulk market price for 95% ethanol.

[21] Weddle, N. ICIS Pricing: Ethylene (Europe). Reed Business Limited. January 10 2014. - Bulk market price for chemical grade ethylene.

=Appendix I - Process Flow Diagram=
[[File:PFD B1.JPG|1200px]]

=Appendix II - HYSYS Simulation=
[[File:HYSYS_B1.PNG|1200px]]

=Appendix III - Material Streams=
[[File:Streams_B1.png|1200px]]

=Appendix IV - Energy Table=
[[File:Energy_B1.png|600px|center]]

=Appendix V - Economics=
[[File:Econsummary_B1.png|center]] 

[[File:Capcost_B1.png|center]] 

[[File:sensitivityanalysis_B1.png|600px|center]]

Ethanol to Ethylene (B1)

2015-03-14T04:17:07Z

Hpoppick: /* Process Alternatives */

[[File:BFD_B1.png|600px|thumbnail|alt=Alt text|Conversion of Ethanol to Ethylene]]
=Executive Summary=

The following report outlines the design and analysis of a process converting ethanol to chemical-grade ethylene via catalytic dehydration. This process consumers 100,000 kg/hr of 95 wt% ethanol, 5 wt% water feedstock and produces 53,000 kg/hr of 99.7 wt% chemical-grade ethylene. The ethanol feed passes through two fixed-bed reactors, each packed with an aluminum oxide catalyst, and the resulting ethylene is purified by two flash tanks and by absorption with water. The process was modeled using Aspen HYSYS simulation software to estimate mass and energy flows and equipment sizing requirements. Based on results of this initial simulation, several alternatives are discussed for increasing the process efficiency and profitability. The use of a fluidized bed reactor or a more ethylene-selective catalyst could increase the production of ethylene per ethanol basis. Additionally, several methods of purification to more valuable polymer-grade ethylene are proposed.

The economic feasibility of this process was evaluated using Aspen Economic Analyzer with the Icarus economics package. Capital cost is approximately $16.4 million total with an operating cost of $465 million per year. The current market prices of the ethanol feed and ethylene sales price are $1.44/gallon and $1350/metric ton respectively. The cost of feed ethanol, process utilities and miscellaneous operational costs total to about $427 million/year. At full operation, revenue at current prices would be approximately $640 million per year. The predicted 10-year net present value of the process is approximately $391 million with an IRR of 79% and a payback period of 2.7 years. A sensitivity analysis indicates that the process is most sensitive to feed prices, product prices and operation cost.

Several recommendations are made for both cost reduction and profit maximization, including the design of a heat exchanger network and the optimization of fired heaters that require high capital investment and large amounts of fuel. A safety review of the process is recommended, as well as the minimization of flue gas effluent and wastewater. It is also suggested that the construction of an onsite wastewater treatment center be considered. Overall, the initial analysis indicates this to be a profitable process and it is recommended the project move forward.

=Introduction=

Ethylene is a critical chemical precursor to a number of different industrial products. It is often derived from petroleum sources and polymerized to polyethylene, one of the most ubiquitous plastics today. (American Chemistry Council, 2013) Recently there has been a significant effort to develop production pathways utilizing biologically-derived feedstocks, such as corn or cellulosic ethanol, rather than traditional fossil-fuel sources. Ethylene can be produced from bioethanol via catalytic dehydration over an aluminum oxide catalyst. The proposed process converts 100,000 kg/hr of 95 wt% ethanol, 5% water feed to 53,000 kg/hr of 99.7% chemical-grade ethylene when operating at full capacity. This process was found to be economically viable with a 10-year net present value (NPV) of $131 million (2014 USD) and a payback period of approximately 2.7 years. This memo will detail the proposed process, as well as outline potential alternatives and economic viability of the project.

=Technical Approach=

Many bioethanol plants are located in the Midwest where large amounts of feedstock crops, such as corn, are grown. As such, this plant will be located in Story county, Iowa, near a large-scale bioethanol production plant. (DuPont Nevada Site, 2012) It is assumed that the supply of bioethanol is consistent and readily available. It is also assumed that other reagents - namely, the aluminum oxide catalyst, heater fuel, utility water and freon refrigerant - are readily available, and that wastewater treatment facilities are located near enough to facilitate the off-site treatment of wastewater. Plant capacity was based on current mid-sized industrial ethylene plants. (Designing Ethylene Plants, 2014)

HYSYS simulations were performed with the NRTL fluid package and Peng-Robinson vapor model. The NRTL fluid package is an activity coefficient model that is especially useful to model the separations of alcohols in aqueous solutions. (Suppes, 2015) In addition, NRTL uses models of binary pairs of components, much like the Wilson equation, to predict chemical interactions at the molecular level. The NRTL package can thus be easily extended to ternary and higher order chemical systems, making it ideal for this type of simulation. The Peng-Robinson vapor model was selected as it is well-suited to account for the non-idealities of the vapor phase reactions and separations integral to this process. (ASPENtech, 2014)

It was assumed that the feed enters the process at ambient temperature and pressure (25 °C, 1 atm) and at a consistent rate and composition with negligible quantities of impurities. The ethanol feed was assumed to be 95% ethanol and 5% water by mass, which is the commercial standard for industrial ethanol. (190 Proof Ethanol, 2012) Storage vessels for the feed ethanol, waste streams and products are assumed to be located nearby to the process. An initial feed pump compensates for pressure drops through the process and reduces the duty on downstream compressors. (Hadawey, 2015)

Natural gas, assumed to consist of 83% methane, 16% ethane and 1% nitrogen by mass, was supplied to two fired heaters at a flow rate estimated by HYSYS. (Methane, 2015) Air fed to the process to enable combustion was assumed to be 23% oxygen and 77% nitrogen by mass. (Composition of Air, 2015) Air streams were fed at 50% molar excess in order to ensure complete combustion and prevent the formation of carbon monoxide in the heater exhaust. Total flue gases are assumed to be 230,000 kg/hr, or 2.2 million tons annually, and consist of 73.8% nitrogen gas, 10.5% carbon dioxide, 8.2% water vapor, and 7.5% oxygen by mass. The only compound of concern in these emissions is the carbon dioxide, a known greenhouse gas. At the time of this report, the quantities of carbon dioxide emitted by this plant annually are within acceptable EPA specifications. (Summary of the Clean Air Act, 2015)

Due to the difficulty of simulation equilibrium and conversion reactions in a single vessel in HYSYS, these two reaction types were simulated in separate equilibrium reactor and conversion reactor units in series. In addition, while HYSYS indicated that reactor units would output separate vapor and liquid streams, it was assumed that in practice this would take the form of a single, two phase stream between each unit. To account for this, mixers were installed downstream of each reactor to combine the liquid and vapor phases of the reactor effluent. The three consequent reactions considered are as follows:

Ethanol ↔ Ethylene + Water
Ethanol → Acetaldehyde + Hydrogen
2 Ethanol → Diethyl Ether + Water

The optimal reaction temperature was determined to be 400 °C, which promotes the equilibrium reaction of ethanol to ethylene while minimizing byproducts. (Zhang and Yu, 2013) While other byproducts may be produced in this process, these reactions are typically taken to comprise of the bulk of the dehydration reaction. Heat losses over these reactors were assumed to be negligible. (Zhang and Yu, 2013)All major process equipment is assumed to be constructed of high strength carbon steel. (AspenTech, 2012)

The “Sizing Utility” within the Icarus Economic Evaluation module was used to estimate sizes of major equipment based on the process simulation. These values can serve as a benchmark for an initial plant design. Icarus KbaseTM implements a wide variety of mechanical design standards, including ASME and BS5500, in order to calculate accurate equipment sizing. The Icarus sizing module combines equipment prices for standard chemical processing equipment as well as correlations and sizing factors. The advantage of using a software package such as HYSYS to price out individual equipment is that it utilizes up-to-date prices from vendors and distributors when estimating costs. A more in-depth overview of the correlations included in this software can be found in Towler and Sinnott (2009).

=Process Flowsheet=
[[File:Squarepfd_B1.PNG|thumb|400px]]

The following process is based primarily on a 1983 US patent titled “Process for dehydration of a low molecular weight alcohol.” (Barrocas and Baratelli, 1983) The process flow diagram can be seen in Figure 1. A larger version of the PFD is included in Appendix I and the HYSYS simulation setup in Appendix II.

The feed enters the process at a rate of 100,000 kg/hr, a temperature and pressure of a 25 °C and 1 atm and at a composition of 95 wt% ethanol and 5 wt% water.It is initially pressurized to 4335 kPa by centrifugal pump P-101 and subsequently heated to 400 °C by fired heater F-101. The heated and pressurized feed enters fixed bed reactor R-101 and contacts with the aluminum oxide catalyst. At this point it dehydrates to form the product, ethylene, as well as the byproducts water, hydrogen, diethyl ether and acetaldehyde. Fired heater F-102 and reactor R-102 increase the overall conversion of the process. Both fired heaters F-101 and F-102 are fueled with natural gas and fed with excess air. The composition of the reactor train effluent is 54.5 wt% ethylene, 37.1 wt% water, 8.1 wt% unreacted ethanol and trace amounts of diethyl ether, acetaldehyde, and hydrogen contaminants.

The pressure of the reactor train effluent is increased to 4500 kPa by compressor K-102 and the temperature decreased to 100 °C by exchange with cold water in heat exchanger E-201. The stream then expands and flashes in flash vessel FL-201, which separates out 82.3% of the unreacted ethanol, 96.6% of the water and virtually all of the acetaldehyde contaminant in the bottoms while sending the ethylene-rich vapor phase out of the top. The top product of FL-202 is compressed to 3500 kPA by K-202 and cooled to 0.0 °C by a freon refrigerant in E-202. At this point the stream is flashed for a second time in vessel FL-202 to remove additional impurities. The top outlet stream consists of 99.5 wt% ethylene, which is fed to the bottom of a 10-tray absorption column that removes a fraction of the residual diethyl ether as well as the remainder of the unreacted ethanol. A stream of absorbent water is fed to the top of the column at 10,000 kg/hr. The product exits the top of the column at a rate of 54,600 kg/hr and has a purity of 99.7% ethylene. Diethyl ether makes up 0.2% of the remaining product stream and is the primary contaminant. Trace amounts of residual water and hydrogen are also present.

Full tables of material and energy streams can be found in Appendices III and IV respectively.

==Process Alternatives==
===Reactor Alternatives===
Two fixed bed reactors, alternating with fired heaters, are used in the dehydration reaction of ethanol to ethylene. However, a fluidized bed reactor can offer better mixing and temperature control than a fixed bed reactor and thus provide the highest possible conversion of ethanol with the greatest selectivity to ethylene. (Tsao and Zasloff, 1979) Fluidized bed reactors also provide a lower rate of catalyst coking and byproduct formation, minimizing separation and catalyst regeneration costs. (Morschbacker, 2009) The major downside of fluidized bed reactors is that few large-scale processes have been built since the technology was developed in the late 1970s. (Tsao and Zasloff, 1979; Morschbacker, 2009) Although implementation of fluidized bed reactors could potentially increase the purity of the ethylene product and/or decrease costs, a small scale pilot process would need to be built and tested before it would be possible to develop an industrial-scale facility.

===Catalyst Alternatives===
Aluminum oxide, specifically gamma alumina, is the most industrially-common catalyst and has been historically used due to its low cost and high stability. (Tsao and Zasloff, 1979; Fan and Dai, n.d.) Recent improvements in selectivity and catalyst stability of activated alumina have been achieved by incorporating titanium oxide into the catalyst, although this increases reaction temperature by approximately 50 °C and decreases catalyst lifespan. (Chen and Li, et. al. 2007) There is also significant ongoing research into HZSM-5 zeolite and heteropolyacids, which are being explored as potential alternatives to alumina oxide. A nanoscale HZSM-5 zeolite catalyst has been shown to operate at the relatively low temperature of 200-300°C, with a 100% ethanol conversion and 99.7% selectivity to ethylene. Initial research has also indicated that it maintains greater than 98% selectivity for 630 operational hours. (Fan and Dai, n.d.) However, the current low cost and ready availability of unmodified alumina oxide makes it a better choice for a process of this scale.

===Purification Alternatives===
As specified in this process, the reactor effluent is purified by two flash drums and absorption with water to produce chemical-grade ethylene. If chemical-grade ethylene is indeed the desired product, other purification options include caustic washing of the reactor effluent and water removal in a desiccant drying bed. (Morschbacker, 2009) While this purification train is relatively simple and does not require harsh chemical reagents, polymer grade ethylene is more commercially valuable and the additional cost of removing water and diethyl ether contaminants may be justified by increased revenue. Cryogenic distillation was initially simulated to produce polymer-grade ethylene, but utility requirements were found to render this separation economically unviable. (Barrocas and Baratelli, 1983) Further research and optimization may find this purification strategy to be a more valid process. Alternatively, the addition of a cryogenic turboexpander or the use of alternative adsorbents may increase product purity to polymer grade. (Jumonville, 2010) Initial HYSYS simulations indicate that these operations may be feasible with further refinement.

===Wastewater Treatment===
Due to the large volume of wastewater produced, building an on-site wastewater treatment facility may prove to be more economical than paying for third-party wastewater treatment. Flash vessel FL-201 produces 44,600 L/hr of wastewater contaminated with 18.7 vol% ethanol and 0.6 vol% acetaldehyde, while FL-202 produces 2940 L/hr of an aqueous waste consisting of 56.8 vol% ethanol, 42.0 vol% water and 0.9 vol% diethyl ether. The absorption column produces approximately 10,200 liters/hr of wastewater contaminated with 1.2 vol% ethanol, 0.2% diethyl ether and 0.2% acetaldehyde. Utilizing distillation to separate these streams into clean water and volatile organic waste could ultimately reduce the quantity of waste that requires disposal and reduce the overall costs of the process.

==Process Equipment==
Relevant sizing information for each unit operation, estimated by the method described in the “Technical Approach,” can be found in Appendix V. Equipment and piping is assumed to be constructed of carbon steel. It should be noted that the two fired heaters are proportionately large enough to heat the entirety of the process stream and are thus larger than standard equipment.

=Economic Analysis=
[[File:sensitivityanalysis_B1.png|400px|thumb]]

=Process Alternatives/Recommendations=
=Conclusion=
=References=

[1] American Chemistry Council. Production of chemicals and plastics in the U.S. in 2013, by type (in 1,000 metric tons). In Statista - The Statistics Portal. August 2014. Available at http://www.statista.com/statistics/299725/total-us-plastics-and-chemicals-shipments-by-type/, Accessed January 15, 2015. – Relative proportions of plastics production.

[2] DuPont Nevada Site Cellulosic Ethanol Facility [Internet]. DuPont Chemical; c2012-2015 [cited 11 Mar. 2015]. Available from: http://biofuels.dupont.com/cellulosic-ethanol/nevada-site-ce-facility/. -- Information on ethanol production in Iowa.

[3] Designing Ethylene Plants. Ethylene [Internet]. Technip; 2014 [cited 13 Mar. 2015]. Available from: http://www.technip.com/en/our-business/onshore/ethylene -- Plant size ranges.

[4] Suppes GJ. Selecting Thermodynamic Models for Process Simulation of Organic VLE and LLE Systems. The University of Missouri-Columbia, Dept of Chemical Engineering. [cited 13 Mar. 2015]. -- Use of NRTL in alcohol separations.

[5] ASPENtech. Appendix A - Property Methods and Calculations. Simulation Basics; A-3 - A-26. 2014.

[6] 190 Proof Ethanol: Technical Data Sheet [Internet]. Decon Labs Inc; 2012 [cited 13 Mar. 2015]. Available from: http://www.deconlabs.com/tds/ETHANOL%20190%20%20PROOF.pdf -- Information regarding 95% ethanol

[7] Hadawey A, Ge Y, Tassou TSA. Energy Savings Through Liquid Pressure Amplification In A Dairy Plant Refrigeration System. The Centre for Energy and Built Environment Research [cited 13 Mar. 2015].

[8] Methane (Chemical Compound). 2015. Encyclopædia Britannica Online. [cited 13 Mar. 2015] Available from: http://www.britannica.com/EBchecked/topic/378264/methane -- Composition of Methane

[9] Composition of Air [Internet]. Engineering Toolbox; [cited 13 Mar. 2015]. Available from: http://www.engineeringtoolbox.com/air-composition-d_212.html. -- Composition of air.

[10] Summary of the Clean Air Act, 2015. United States Environmental Protection Agency. [cited 13 Mar. 2015] Available from: http://www2.epa.gov/laws-regulations/summary-clean-air-act -- Emissions requirements of chemical plants.

[11] Zhang M, Yu Y. Dehydration of Ethanol to Ethylene. Industrial Engineering and Chemical Research. 2013; 52:9505-9514. – Technical information on ethanol to ethylene conversion via dehydration.

[12] AspenTech. Aspen HYSYS Help File v8.0. Aspen Technology, Inc. 2012. - Aspen HYSYS help file used for troubleshooting and assistance on economic analysis.

[13] Towler G, Sinnott R. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. 2nd ed. Boston: Elsevier; 2013. -- General Reference Book

[14] Barrocas H, Baratelli F, inventors; Petroleo Brasileiro S.A., assignee. Process for dehydration of a low molecular weight alcohol. US patent 4,396,789 A. August 2, 1983. - Primary background for process design.

[15] Tsao U, Zasloff HB, inventors; The Lummus Company, assignee. Production of ethylene from ethanol. US patent 4,134,926. January 16, 1979. – Patent for catalytic dehydration of ethylene in a fluidized bed reactor.

[16] Morschbacker, A. Bio-Ethanol Based Ethylene. Polymer Reviews. 2009; 49:79-84. – Overview of bioethanol dehydration process development.

[17] Fan D, Dai DJ, Wu HS. Ethylene Formation by Catalytic Dehydration of Ethanol with Industrial Considerations. Materials. 6, 101-115. doi: 10.3390/ma6010101. - Comparison of types of catalysts used in the dehydration of ethanol and current research into new catalysts.

[18] Chen G, Li S, Jiao F, Yuan Q. Catalytic dehydration of bioethanol to ethylene over TiO2/γ-Al2O3 catalysts in microchannel reactors. Catal. Today 2007, 125, 111–119. - Paper introducing research on modified alumina catalyst for ethanol dehydration.

[19] Jumonville, J. Tutorial on Cryogenic Turboexpanders. Proceedings of the Thirty-Ninth Turbomachinery Symposium; 2010 Oct 4-7; Houston, TX. Houston: Texas A&M University; 2010. -- Use of turboexpander for cryogenic separations

[20] Today in Energy - Daily Prices. US Energy Information Administration website. http://www.eia.gov/todayinenergy/prices.cfm. Accessed March 3rd 2015. - Bulk market price for 95% ethanol.

[21] Weddle, N. ICIS Pricing: Ethylene (Europe). Reed Business Limited. January 10 2014. - Bulk market price for chemical grade ethylene.

=Appendix I - Process Flow Diagram=
[[File:PFD B1.JPG|1200px]]

=Appendix II - HYSYS Simulation=
[[File:HYSYS_B1.PNG|1200px]]

=Appendix III - Material Streams=
[[File:Streams_B1.png|1200px]]

=Appendix IV - Energy Table=
[[File:Energy_B1.png|600px|center]]

=Appendix V - Economics=
[[File:Econsummary_B1.png|center]] 

[[File:Capcost_B1.png|center]] 

[[File:sensitivityanalysis_B1.png|600px|center]]

Ethanol to Ethylene (B1)

2015-03-14T04:16:47Z

Hpoppick: /* Process Flowsheet */

[[File:BFD_B1.png|600px|thumbnail|alt=Alt text|Conversion of Ethanol to Ethylene]]
=Executive Summary=

The following report outlines the design and analysis of a process converting ethanol to chemical-grade ethylene via catalytic dehydration. This process consumers 100,000 kg/hr of 95 wt% ethanol, 5 wt% water feedstock and produces 53,000 kg/hr of 99.7 wt% chemical-grade ethylene. The ethanol feed passes through two fixed-bed reactors, each packed with an aluminum oxide catalyst, and the resulting ethylene is purified by two flash tanks and by absorption with water. The process was modeled using Aspen HYSYS simulation software to estimate mass and energy flows and equipment sizing requirements. Based on results of this initial simulation, several alternatives are discussed for increasing the process efficiency and profitability. The use of a fluidized bed reactor or a more ethylene-selective catalyst could increase the production of ethylene per ethanol basis. Additionally, several methods of purification to more valuable polymer-grade ethylene are proposed.

The economic feasibility of this process was evaluated using Aspen Economic Analyzer with the Icarus economics package. Capital cost is approximately $16.4 million total with an operating cost of $465 million per year. The current market prices of the ethanol feed and ethylene sales price are $1.44/gallon and $1350/metric ton respectively. The cost of feed ethanol, process utilities and miscellaneous operational costs total to about $427 million/year. At full operation, revenue at current prices would be approximately $640 million per year. The predicted 10-year net present value of the process is approximately $391 million with an IRR of 79% and a payback period of 2.7 years. A sensitivity analysis indicates that the process is most sensitive to feed prices, product prices and operation cost.

Several recommendations are made for both cost reduction and profit maximization, including the design of a heat exchanger network and the optimization of fired heaters that require high capital investment and large amounts of fuel. A safety review of the process is recommended, as well as the minimization of flue gas effluent and wastewater. It is also suggested that the construction of an onsite wastewater treatment center be considered. Overall, the initial analysis indicates this to be a profitable process and it is recommended the project move forward.

=Introduction=

Ethylene is a critical chemical precursor to a number of different industrial products. It is often derived from petroleum sources and polymerized to polyethylene, one of the most ubiquitous plastics today. (American Chemistry Council, 2013) Recently there has been a significant effort to develop production pathways utilizing biologically-derived feedstocks, such as corn or cellulosic ethanol, rather than traditional fossil-fuel sources. Ethylene can be produced from bioethanol via catalytic dehydration over an aluminum oxide catalyst. The proposed process converts 100,000 kg/hr of 95 wt% ethanol, 5% water feed to 53,000 kg/hr of 99.7% chemical-grade ethylene when operating at full capacity. This process was found to be economically viable with a 10-year net present value (NPV) of $131 million (2014 USD) and a payback period of approximately 2.7 years. This memo will detail the proposed process, as well as outline potential alternatives and economic viability of the project.

=Technical Approach=

Many bioethanol plants are located in the Midwest where large amounts of feedstock crops, such as corn, are grown. As such, this plant will be located in Story county, Iowa, near a large-scale bioethanol production plant. (DuPont Nevada Site, 2012) It is assumed that the supply of bioethanol is consistent and readily available. It is also assumed that other reagents - namely, the aluminum oxide catalyst, heater fuel, utility water and freon refrigerant - are readily available, and that wastewater treatment facilities are located near enough to facilitate the off-site treatment of wastewater. Plant capacity was based on current mid-sized industrial ethylene plants. (Designing Ethylene Plants, 2014)

HYSYS simulations were performed with the NRTL fluid package and Peng-Robinson vapor model. The NRTL fluid package is an activity coefficient model that is especially useful to model the separations of alcohols in aqueous solutions. (Suppes, 2015) In addition, NRTL uses models of binary pairs of components, much like the Wilson equation, to predict chemical interactions at the molecular level. The NRTL package can thus be easily extended to ternary and higher order chemical systems, making it ideal for this type of simulation. The Peng-Robinson vapor model was selected as it is well-suited to account for the non-idealities of the vapor phase reactions and separations integral to this process. (ASPENtech, 2014)

It was assumed that the feed enters the process at ambient temperature and pressure (25 °C, 1 atm) and at a consistent rate and composition with negligible quantities of impurities. The ethanol feed was assumed to be 95% ethanol and 5% water by mass, which is the commercial standard for industrial ethanol. (190 Proof Ethanol, 2012) Storage vessels for the feed ethanol, waste streams and products are assumed to be located nearby to the process. An initial feed pump compensates for pressure drops through the process and reduces the duty on downstream compressors. (Hadawey, 2015)

Natural gas, assumed to consist of 83% methane, 16% ethane and 1% nitrogen by mass, was supplied to two fired heaters at a flow rate estimated by HYSYS. (Methane, 2015) Air fed to the process to enable combustion was assumed to be 23% oxygen and 77% nitrogen by mass. (Composition of Air, 2015) Air streams were fed at 50% molar excess in order to ensure complete combustion and prevent the formation of carbon monoxide in the heater exhaust. Total flue gases are assumed to be 230,000 kg/hr, or 2.2 million tons annually, and consist of 73.8% nitrogen gas, 10.5% carbon dioxide, 8.2% water vapor, and 7.5% oxygen by mass. The only compound of concern in these emissions is the carbon dioxide, a known greenhouse gas. At the time of this report, the quantities of carbon dioxide emitted by this plant annually are within acceptable EPA specifications. (Summary of the Clean Air Act, 2015)

Due to the difficulty of simulation equilibrium and conversion reactions in a single vessel in HYSYS, these two reaction types were simulated in separate equilibrium reactor and conversion reactor units in series. In addition, while HYSYS indicated that reactor units would output separate vapor and liquid streams, it was assumed that in practice this would take the form of a single, two phase stream between each unit. To account for this, mixers were installed downstream of each reactor to combine the liquid and vapor phases of the reactor effluent. The three consequent reactions considered are as follows:

Ethanol ↔ Ethylene + Water
Ethanol → Acetaldehyde + Hydrogen
2 Ethanol → Diethyl Ether + Water

The optimal reaction temperature was determined to be 400 °C, which promotes the equilibrium reaction of ethanol to ethylene while minimizing byproducts. (Zhang and Yu, 2013) While other byproducts may be produced in this process, these reactions are typically taken to comprise of the bulk of the dehydration reaction. Heat losses over these reactors were assumed to be negligible. (Zhang and Yu, 2013)All major process equipment is assumed to be constructed of high strength carbon steel. (AspenTech, 2012)

The “Sizing Utility” within the Icarus Economic Evaluation module was used to estimate sizes of major equipment based on the process simulation. These values can serve as a benchmark for an initial plant design. Icarus KbaseTM implements a wide variety of mechanical design standards, including ASME and BS5500, in order to calculate accurate equipment sizing. The Icarus sizing module combines equipment prices for standard chemical processing equipment as well as correlations and sizing factors. The advantage of using a software package such as HYSYS to price out individual equipment is that it utilizes up-to-date prices from vendors and distributors when estimating costs. A more in-depth overview of the correlations included in this software can be found in Towler and Sinnott (2009).

=Process Flowsheet=
[[File:Squarepfd_B1.PNG|thumb|400px]]

The following process is based primarily on a 1983 US patent titled “Process for dehydration of a low molecular weight alcohol.” (Barrocas and Baratelli, 1983) The process flow diagram can be seen in Figure 1. A larger version of the PFD is included in Appendix I and the HYSYS simulation setup in Appendix II.

The feed enters the process at a rate of 100,000 kg/hr, a temperature and pressure of a 25 °C and 1 atm and at a composition of 95 wt% ethanol and 5 wt% water.It is initially pressurized to 4335 kPa by centrifugal pump P-101 and subsequently heated to 400 °C by fired heater F-101. The heated and pressurized feed enters fixed bed reactor R-101 and contacts with the aluminum oxide catalyst. At this point it dehydrates to form the product, ethylene, as well as the byproducts water, hydrogen, diethyl ether and acetaldehyde. Fired heater F-102 and reactor R-102 increase the overall conversion of the process. Both fired heaters F-101 and F-102 are fueled with natural gas and fed with excess air. The composition of the reactor train effluent is 54.5 wt% ethylene, 37.1 wt% water, 8.1 wt% unreacted ethanol and trace amounts of diethyl ether, acetaldehyde, and hydrogen contaminants.

The pressure of the reactor train effluent is increased to 4500 kPa by compressor K-102 and the temperature decreased to 100 °C by exchange with cold water in heat exchanger E-201. The stream then expands and flashes in flash vessel FL-201, which separates out 82.3% of the unreacted ethanol, 96.6% of the water and virtually all of the acetaldehyde contaminant in the bottoms while sending the ethylene-rich vapor phase out of the top. The top product of FL-202 is compressed to 3500 kPA by K-202 and cooled to 0.0 °C by a freon refrigerant in E-202. At this point the stream is flashed for a second time in vessel FL-202 to remove additional impurities. The top outlet stream consists of 99.5 wt% ethylene, which is fed to the bottom of a 10-tray absorption column that removes a fraction of the residual diethyl ether as well as the remainder of the unreacted ethanol. A stream of absorbent water is fed to the top of the column at 10,000 kg/hr. The product exits the top of the column at a rate of 54,600 kg/hr and has a purity of 99.7% ethylene. Diethyl ether makes up 0.2% of the remaining product stream and is the primary contaminant. Trace amounts of residual water and hydrogen are also present.

Full tables of material and energy streams can be found in Appendices III and IV respectively.

==Process Alternatives==
===Reactor Alternatives===
Two fixed bed reactors, alternating with fired heaters, are used in the dehydration reaction of ethanol to ethylene. However, a fluidized bed reactor can offer better mixing and temperature control than a fixed bed reactor and thus provide the highest possible conversion of ethanol with the greatest selectivity to ethylene. (Tsao and Zasloff, 1979) Fluidized bed reactors also provide a lower rate of catalyst coking and byproduct formation, minimizing separation and catalyst regeneration costs. (Morschbacker, 2009) The major downside of fluidized bed reactors is that few large-scale processes have been built since the technology was developed in the late 1970s. (Tsao and Zasloff, 1979; Morschbacker, 2009) Although implementation of fluidized bed reactors could potentially increase the purity of the ethylene product and/or decrease costs, a small scale pilot process would need to be built and tested before it would be possible to develop an industrial-scale facility.

===Catalyst Alternatives===
Aluminum oxide, specifically gamma alumina, is the most industrially-common catalyst and has been historically used due to its low cost and high stability. (Tsao and Zasloff, 1979; Fan and Dai, n.d.) Recent improvements in selectivity and catalyst stability of activated alumina have been achieved by incorporating titanium oxide into the catalyst, although this increases reaction temperature by approximately 50 °C and decreases catalyst lifespan. (Chen and Li, et. al. 2007) There is also significant ongoing research into HZSM-5 zeolite and heteropolyacids, which are being explored as potential alternatives to alumina oxide. A nanoscale HZSM-5 zeolite catalyst has been shown to operate at the relatively low temperature of 200-300°C, with a 100% ethanol conversion and 99.7% selectivity to ethylene. Initial research has also indicated that it maintains greater than 98% selectivity for 630 operational hours. (Fan and Dai, n.d.) However, the current low cost and ready availability of unmodified alumina oxide makes it a better choice for a process of this scale.

===Purification Alternatives===
As specified in this process, the reactor effluent is purified by two flash drums and absorption with water to produce chemical-grade ethylene. If chemical-grade ethylene is indeed the desired product, other purification options include caustic washing of the reactor effluent and water removal in a desiccant drying bed. (Morschbacker, 2009) While this purification train is relatively simple and does not require harsh chemical reagents, polymer grade ethylene is more commercially valuable and the additional cost of removing water and diethyl ether contaminants may be justified by increased revenue. Cryogenic distillation was initially simulated to produce polymer-grade ethylene, but utility requirements were found to render this separation economically unviable. (Barrocas and Baratelli, 1983) Further research and optimization may find this purification strategy to be a more valid process. Alternatively, the addition of a cryogenic turboexpander or the use of alternative adsorbents may increase product purity to polymer grade. (Jumonville, 2010) Initial HYSYS simulations indicate that these operations may be feasible with further refinement.

===Wastewater Treatment===
Due to the large volume of wastewater produced, building an on-site wastewater treatment facility may prove to be more economical than paying for third-party wastewater treatment. Flash vessel FL-201 produces 44,600 L/hr of wastewater contaminated with 18.7 vol% ethanol and 0.6 vol% acetaldehyde, while FL-202 produces 2940 L/hr of an aqueous waste consisting of 56.8 vol% ethanol, 42.0 vol% water and 0.9 vol% diethyl ether. The absorption column produces approximately 10,200 liters/hr of wastewater contaminated with 1.2 vol% ethanol, 0.2% diethyl ether and 0.2% acetaldehyde. Utilizing distillation to separate these streams into clean water and volatile organic waste could ultimately reduce the quantity of waste that requires disposal and reduce the overall costs of the process.

===Process Equipment===
Relevant sizing information for each unit operation, estimated by the method described in the “Technical Approach,” can be found in Appendix V. Equipment and piping is assumed to be constructed of carbon steel. It should be noted that the two fired heaters are proportionately large enough to heat the entirety of the process stream and are thus larger than standard equipment.

=Economic Analysis=
[[File:sensitivityanalysis_B1.png|400px|thumb]]

=Process Alternatives/Recommendations=
=Conclusion=
=References=

[1] American Chemistry Council. Production of chemicals and plastics in the U.S. in 2013, by type (in 1,000 metric tons). In Statista - The Statistics Portal. August 2014. Available at http://www.statista.com/statistics/299725/total-us-plastics-and-chemicals-shipments-by-type/, Accessed January 15, 2015. – Relative proportions of plastics production.

[2] DuPont Nevada Site Cellulosic Ethanol Facility [Internet]. DuPont Chemical; c2012-2015 [cited 11 Mar. 2015]. Available from: http://biofuels.dupont.com/cellulosic-ethanol/nevada-site-ce-facility/. -- Information on ethanol production in Iowa.

[3] Designing Ethylene Plants. Ethylene [Internet]. Technip; 2014 [cited 13 Mar. 2015]. Available from: http://www.technip.com/en/our-business/onshore/ethylene -- Plant size ranges.

[4] Suppes GJ. Selecting Thermodynamic Models for Process Simulation of Organic VLE and LLE Systems. The University of Missouri-Columbia, Dept of Chemical Engineering. [cited 13 Mar. 2015]. -- Use of NRTL in alcohol separations.

[5] ASPENtech. Appendix A - Property Methods and Calculations. Simulation Basics; A-3 - A-26. 2014.

[6] 190 Proof Ethanol: Technical Data Sheet [Internet]. Decon Labs Inc; 2012 [cited 13 Mar. 2015]. Available from: http://www.deconlabs.com/tds/ETHANOL%20190%20%20PROOF.pdf -- Information regarding 95% ethanol

[7] Hadawey A, Ge Y, Tassou TSA. Energy Savings Through Liquid Pressure Amplification In A Dairy Plant Refrigeration System. The Centre for Energy and Built Environment Research [cited 13 Mar. 2015].

[8] Methane (Chemical Compound). 2015. Encyclopædia Britannica Online. [cited 13 Mar. 2015] Available from: http://www.britannica.com/EBchecked/topic/378264/methane -- Composition of Methane

[9] Composition of Air [Internet]. Engineering Toolbox; [cited 13 Mar. 2015]. Available from: http://www.engineeringtoolbox.com/air-composition-d_212.html. -- Composition of air.

[10] Summary of the Clean Air Act, 2015. United States Environmental Protection Agency. [cited 13 Mar. 2015] Available from: http://www2.epa.gov/laws-regulations/summary-clean-air-act -- Emissions requirements of chemical plants.

[11] Zhang M, Yu Y. Dehydration of Ethanol to Ethylene. Industrial Engineering and Chemical Research. 2013; 52:9505-9514. – Technical information on ethanol to ethylene conversion via dehydration.

[12] AspenTech. Aspen HYSYS Help File v8.0. Aspen Technology, Inc. 2012. - Aspen HYSYS help file used for troubleshooting and assistance on economic analysis.

[13] Towler G, Sinnott R. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. 2nd ed. Boston: Elsevier; 2013. -- General Reference Book

[14] Barrocas H, Baratelli F, inventors; Petroleo Brasileiro S.A., assignee. Process for dehydration of a low molecular weight alcohol. US patent 4,396,789 A. August 2, 1983. - Primary background for process design.

[15] Tsao U, Zasloff HB, inventors; The Lummus Company, assignee. Production of ethylene from ethanol. US patent 4,134,926. January 16, 1979. – Patent for catalytic dehydration of ethylene in a fluidized bed reactor.

[16] Morschbacker, A. Bio-Ethanol Based Ethylene. Polymer Reviews. 2009; 49:79-84. – Overview of bioethanol dehydration process development.

[17] Fan D, Dai DJ, Wu HS. Ethylene Formation by Catalytic Dehydration of Ethanol with Industrial Considerations. Materials. 6, 101-115. doi: 10.3390/ma6010101. - Comparison of types of catalysts used in the dehydration of ethanol and current research into new catalysts.

[18] Chen G, Li S, Jiao F, Yuan Q. Catalytic dehydration of bioethanol to ethylene over TiO2/γ-Al2O3 catalysts in microchannel reactors. Catal. Today 2007, 125, 111–119. - Paper introducing research on modified alumina catalyst for ethanol dehydration.

[19] Jumonville, J. Tutorial on Cryogenic Turboexpanders. Proceedings of the Thirty-Ninth Turbomachinery Symposium; 2010 Oct 4-7; Houston, TX. Houston: Texas A&M University; 2010. -- Use of turboexpander for cryogenic separations

[20] Today in Energy - Daily Prices. US Energy Information Administration website. http://www.eia.gov/todayinenergy/prices.cfm. Accessed March 3rd 2015. - Bulk market price for 95% ethanol.

[21] Weddle, N. ICIS Pricing: Ethylene (Europe). Reed Business Limited. January 10 2014. - Bulk market price for chemical grade ethylene.

=Appendix I - Process Flow Diagram=
[[File:PFD B1.JPG|1200px]]

=Appendix II - HYSYS Simulation=
[[File:HYSYS_B1.PNG|1200px]]

=Appendix III - Material Streams=
[[File:Streams_B1.png|1200px]]

=Appendix IV - Energy Table=
[[File:Energy_B1.png|600px|center]]

=Appendix V - Economics=
[[File:Econsummary_B1.png|center]] 

[[File:Capcost_B1.png|center]] 

[[File:sensitivityanalysis_B1.png|600px|center]]

Ethanol to Ethylene (B1)

2015-03-14T04:16:33Z

Hpoppick: /* Process Flowsheet */

[[File:BFD_B1.png|600px|thumbnail|alt=Alt text|Conversion of Ethanol to Ethylene]]
=Executive Summary=

The following report outlines the design and analysis of a process converting ethanol to chemical-grade ethylene via catalytic dehydration. This process consumers 100,000 kg/hr of 95 wt% ethanol, 5 wt% water feedstock and produces 53,000 kg/hr of 99.7 wt% chemical-grade ethylene. The ethanol feed passes through two fixed-bed reactors, each packed with an aluminum oxide catalyst, and the resulting ethylene is purified by two flash tanks and by absorption with water. The process was modeled using Aspen HYSYS simulation software to estimate mass and energy flows and equipment sizing requirements. Based on results of this initial simulation, several alternatives are discussed for increasing the process efficiency and profitability. The use of a fluidized bed reactor or a more ethylene-selective catalyst could increase the production of ethylene per ethanol basis. Additionally, several methods of purification to more valuable polymer-grade ethylene are proposed.

The economic feasibility of this process was evaluated using Aspen Economic Analyzer with the Icarus economics package. Capital cost is approximately $16.4 million total with an operating cost of $465 million per year. The current market prices of the ethanol feed and ethylene sales price are $1.44/gallon and $1350/metric ton respectively. The cost of feed ethanol, process utilities and miscellaneous operational costs total to about $427 million/year. At full operation, revenue at current prices would be approximately $640 million per year. The predicted 10-year net present value of the process is approximately $391 million with an IRR of 79% and a payback period of 2.7 years. A sensitivity analysis indicates that the process is most sensitive to feed prices, product prices and operation cost.

Several recommendations are made for both cost reduction and profit maximization, including the design of a heat exchanger network and the optimization of fired heaters that require high capital investment and large amounts of fuel. A safety review of the process is recommended, as well as the minimization of flue gas effluent and wastewater. It is also suggested that the construction of an onsite wastewater treatment center be considered. Overall, the initial analysis indicates this to be a profitable process and it is recommended the project move forward.

=Introduction=

Ethylene is a critical chemical precursor to a number of different industrial products. It is often derived from petroleum sources and polymerized to polyethylene, one of the most ubiquitous plastics today. (American Chemistry Council, 2013) Recently there has been a significant effort to develop production pathways utilizing biologically-derived feedstocks, such as corn or cellulosic ethanol, rather than traditional fossil-fuel sources. Ethylene can be produced from bioethanol via catalytic dehydration over an aluminum oxide catalyst. The proposed process converts 100,000 kg/hr of 95 wt% ethanol, 5% water feed to 53,000 kg/hr of 99.7% chemical-grade ethylene when operating at full capacity. This process was found to be economically viable with a 10-year net present value (NPV) of $131 million (2014 USD) and a payback period of approximately 2.7 years. This memo will detail the proposed process, as well as outline potential alternatives and economic viability of the project.

=Technical Approach=

Many bioethanol plants are located in the Midwest where large amounts of feedstock crops, such as corn, are grown. As such, this plant will be located in Story county, Iowa, near a large-scale bioethanol production plant. (DuPont Nevada Site, 2012) It is assumed that the supply of bioethanol is consistent and readily available. It is also assumed that other reagents - namely, the aluminum oxide catalyst, heater fuel, utility water and freon refrigerant - are readily available, and that wastewater treatment facilities are located near enough to facilitate the off-site treatment of wastewater. Plant capacity was based on current mid-sized industrial ethylene plants. (Designing Ethylene Plants, 2014)

HYSYS simulations were performed with the NRTL fluid package and Peng-Robinson vapor model. The NRTL fluid package is an activity coefficient model that is especially useful to model the separations of alcohols in aqueous solutions. (Suppes, 2015) In addition, NRTL uses models of binary pairs of components, much like the Wilson equation, to predict chemical interactions at the molecular level. The NRTL package can thus be easily extended to ternary and higher order chemical systems, making it ideal for this type of simulation. The Peng-Robinson vapor model was selected as it is well-suited to account for the non-idealities of the vapor phase reactions and separations integral to this process. (ASPENtech, 2014)

It was assumed that the feed enters the process at ambient temperature and pressure (25 °C, 1 atm) and at a consistent rate and composition with negligible quantities of impurities. The ethanol feed was assumed to be 95% ethanol and 5% water by mass, which is the commercial standard for industrial ethanol. (190 Proof Ethanol, 2012) Storage vessels for the feed ethanol, waste streams and products are assumed to be located nearby to the process. An initial feed pump compensates for pressure drops through the process and reduces the duty on downstream compressors. (Hadawey, 2015)

Natural gas, assumed to consist of 83% methane, 16% ethane and 1% nitrogen by mass, was supplied to two fired heaters at a flow rate estimated by HYSYS. (Methane, 2015) Air fed to the process to enable combustion was assumed to be 23% oxygen and 77% nitrogen by mass. (Composition of Air, 2015) Air streams were fed at 50% molar excess in order to ensure complete combustion and prevent the formation of carbon monoxide in the heater exhaust. Total flue gases are assumed to be 230,000 kg/hr, or 2.2 million tons annually, and consist of 73.8% nitrogen gas, 10.5% carbon dioxide, 8.2% water vapor, and 7.5% oxygen by mass. The only compound of concern in these emissions is the carbon dioxide, a known greenhouse gas. At the time of this report, the quantities of carbon dioxide emitted by this plant annually are within acceptable EPA specifications. (Summary of the Clean Air Act, 2015)

Due to the difficulty of simulation equilibrium and conversion reactions in a single vessel in HYSYS, these two reaction types were simulated in separate equilibrium reactor and conversion reactor units in series. In addition, while HYSYS indicated that reactor units would output separate vapor and liquid streams, it was assumed that in practice this would take the form of a single, two phase stream between each unit. To account for this, mixers were installed downstream of each reactor to combine the liquid and vapor phases of the reactor effluent. The three consequent reactions considered are as follows:

Ethanol ↔ Ethylene + Water
Ethanol → Acetaldehyde + Hydrogen
2 Ethanol → Diethyl Ether + Water

The optimal reaction temperature was determined to be 400 °C, which promotes the equilibrium reaction of ethanol to ethylene while minimizing byproducts. (Zhang and Yu, 2013) While other byproducts may be produced in this process, these reactions are typically taken to comprise of the bulk of the dehydration reaction. Heat losses over these reactors were assumed to be negligible. (Zhang and Yu, 2013)All major process equipment is assumed to be constructed of high strength carbon steel. (AspenTech, 2012)

The “Sizing Utility” within the Icarus Economic Evaluation module was used to estimate sizes of major equipment based on the process simulation. These values can serve as a benchmark for an initial plant design. Icarus KbaseTM implements a wide variety of mechanical design standards, including ASME and BS5500, in order to calculate accurate equipment sizing. The Icarus sizing module combines equipment prices for standard chemical processing equipment as well as correlations and sizing factors. The advantage of using a software package such as HYSYS to price out individual equipment is that it utilizes up-to-date prices from vendors and distributors when estimating costs. A more in-depth overview of the correlations included in this software can be found in Towler and Sinnott (2009).

=Process Flowsheet=
[[File:Squarepfd_B1.PNG|thumb|400px]]

The following process is based primarily on a 1983 US patent titled “Process for dehydration of a low molecular weight alcohol.” (Barrocas and Baratelli, 1983) The process flow diagram can be seen in Figure 1. A larger version of the PFD is included in Appendix I and the HYSYS simulation setup in Appendix II.

The feed enters the process at a rate of 100,000 kg/hr, a temperature and pressure of a 25 °C and 1 atm and at a composition of 95 wt% ethanol and 5 wt% water.It is initially pressurized to 4335 kPa by centrifugal pump P-101 and subsequently heated to 400 °C by fired heater F-101. The heated and pressurized feed enters fixed bed reactor R-101 and contacts with the aluminum oxide catalyst. At this point it dehydrates to form the product, ethylene, as well as the byproducts water, hydrogen, diethyl ether and acetaldehyde. Fired heater F-102 and reactor R-102 increase the overall conversion of the process. Both fired heaters F-101 and F-102 are fueled with natural gas and fed with excess air. The composition of the reactor train effluent is 54.5 wt% ethylene, 37.1 wt% water, 8.1 wt% unreacted ethanol and trace amounts of diethyl ether, acetaldehyde, and hydrogen contaminants.

The pressure of the reactor train effluent is increased to 4500 kPa by compressor K-102 and the temperature decreased to 100 °C by exchange with cold water in heat exchanger E-201. The stream then expands and flashes in flash vessel FL-201, which separates out 82.3% of the unreacted ethanol, 96.6% of the water and virtually all of the acetaldehyde contaminant in the bottoms while sending the ethylene-rich vapor phase out of the top. The top product of FL-202 is compressed to 3500 kPA by K-202 and cooled to 0.0 °C by a freon refrigerant in E-202. At this point the stream is flashed for a second time in vessel FL-202 to remove additional impurities. The top outlet stream consists of 99.5 wt% ethylene, which is fed to the bottom of a 10-tray absorption column that removes a fraction of the residual diethyl ether as well as the remainder of the unreacted ethanol. A stream of absorbent water is fed to the top of the column at 10,000 kg/hr. The product exits the top of the column at a rate of 54,600 kg/hr and has a purity of 99.7% ethylene. Diethyl ether makes up 0.2% of the remaining product stream and is the primary contaminant. Trace amounts of residual water and hydrogen are also present.

Full tables of material and energy streams can be found in Appendices III and IV respectively.

==Process Alternatives==
===Reactor Alternatives===
Two fixed bed reactors, alternating with fired heaters, are used in the dehydration reaction of ethanol to ethylene. However, a fluidized bed reactor can offer better mixing and temperature control than a fixed bed reactor and thus provide the highest possible conversion of ethanol with the greatest selectivity to ethylene. (Tsao and Zasloff, 1979) Fluidized bed reactors also provide a lower rate of catalyst coking and byproduct formation, minimizing separation and catalyst regeneration costs. (Morschbacker, 2009) The major downside of fluidized bed reactors is that few large-scale processes have been built since the technology was developed in the late 1970s. (Tsao and Zasloff, 1979; Morschbacker, 2009) Although implementation of fluidized bed reactors could potentially increase the purity of the ethylene product and/or decrease costs, a small scale pilot process would need to be built and tested before it would be possible to develop an industrial-scale facility.

===Catalyst Alternatives===
Aluminum oxide, specifically gamma alumina, is the most industrially-common catalyst and has been historically used due to its low cost and high stability. (Tsao and Zasloff, 1979; Fan and Dai, n.d.) Recent improvements in selectivity and catalyst stability of activated alumina have been achieved by incorporating titanium oxide into the catalyst, although this increases reaction temperature by approximately 50 °C and decreases catalyst lifespan. (Chen and Li, et. al. 2007) There is also significant ongoing research into HZSM-5 zeolite and heteropolyacids, which are being explored as potential alternatives to alumina oxide. A nanoscale HZSM-5 zeolite catalyst has been shown to operate at the relatively low temperature of 200-300°C, with a 100% ethanol conversion and 99.7% selectivity to ethylene. Initial research has also indicated that it maintains greater than 98% selectivity for 630 operational hours. (Fan and Dai, n.d.) However, the current low cost and ready availability of unmodified alumina oxide makes it a better choice for a process of this scale.

===Purification Alternatives===
As specified in this process, the reactor effluent is purified by two flash drums and absorption with water to produce chemical-grade ethylene. If chemical-grade ethylene is indeed the desired product, other purification options include caustic washing of the reactor effluent and water removal in a desiccant drying bed. (Morschbacker, 2009) While this purification train is relatively simple and does not require harsh chemical reagents, polymer grade ethylene is more commercially valuable and the additional cost of removing water and diethyl ether contaminants may be justified by increased revenue. Cryogenic distillation was initially simulated to produce polymer-grade ethylene, but utility requirements were found to render this separation economically unviable. (Barrocas and Baratelli, 1983) Further research and optimization may find this purification strategy to be a more valid process. Alternatively, the addition of a cryogenic turboexpander or the use of alternative adsorbents may increase product purity to polymer grade. (Jumonville, 2010) Initial HYSYS simulations indicate that these operations may be feasible with further refinement.

===Wastewater Treatment===
Due to the large volume of wastewater produced, building an on-site wastewater treatment facility may prove to be more economical than paying for third-party wastewater treatment. Flash vessel FL-201 produces 44,600 L/hr of wastewater contaminated with 18.7 vol% ethanol and 0.6 vol% acetaldehyde, while FL-202 produces 2940 L/hr of an aqueous waste consisting of 56.8 vol% ethanol, 42.0 vol% water and 0.9 vol% diethyl ether. The absorption column produces approximately 10,200 liters/hr of wastewater contaminated with 1.2 vol% ethanol, 0.2% diethyl ether and 0.2% acetaldehyde. Utilizing distillation to separate these streams into clean water and volatile organic waste could ultimately reduce the quantity of waste that requires disposal and reduce the overall costs of the process.

===Process Equipment===
Relevant sizing information for each unit operation, estimated by the method described in the “Technical Approach,” can be found in Appendix V. Equipment and piping is assumed to be constructed of carbon steel. It should be noted that the two fired heaters are proportionately large enough to heat the entirety of the process stream and are thus larger than standard equipment.

=Economic Analysis=
[[File:sensitivityanalysis_B1.png|400px|thumb]]

=Process Alternatives/Recommendations=
=Conclusion=
=References=

[1] American Chemistry Council. Production of chemicals and plastics in the U.S. in 2013, by type (in 1,000 metric tons). In Statista - The Statistics Portal. August 2014. Available at http://www.statista.com/statistics/299725/total-us-plastics-and-chemicals-shipments-by-type/, Accessed January 15, 2015. – Relative proportions of plastics production.

[2] DuPont Nevada Site Cellulosic Ethanol Facility [Internet]. DuPont Chemical; c2012-2015 [cited 11 Mar. 2015]. Available from: http://biofuels.dupont.com/cellulosic-ethanol/nevada-site-ce-facility/. -- Information on ethanol production in Iowa.

[3] Designing Ethylene Plants. Ethylene [Internet]. Technip; 2014 [cited 13 Mar. 2015]. Available from: http://www.technip.com/en/our-business/onshore/ethylene -- Plant size ranges.

[4] Suppes GJ. Selecting Thermodynamic Models for Process Simulation of Organic VLE and LLE Systems. The University of Missouri-Columbia, Dept of Chemical Engineering. [cited 13 Mar. 2015]. -- Use of NRTL in alcohol separations.

[5] ASPENtech. Appendix A - Property Methods and Calculations. Simulation Basics; A-3 - A-26. 2014.

[6] 190 Proof Ethanol: Technical Data Sheet [Internet]. Decon Labs Inc; 2012 [cited 13 Mar. 2015]. Available from: http://www.deconlabs.com/tds/ETHANOL%20190%20%20PROOF.pdf -- Information regarding 95% ethanol

[7] Hadawey A, Ge Y, Tassou TSA. Energy Savings Through Liquid Pressure Amplification In A Dairy Plant Refrigeration System. The Centre for Energy and Built Environment Research [cited 13 Mar. 2015].

[8] Methane (Chemical Compound). 2015. Encyclopædia Britannica Online. [cited 13 Mar. 2015] Available from: http://www.britannica.com/EBchecked/topic/378264/methane -- Composition of Methane

[9] Composition of Air [Internet]. Engineering Toolbox; [cited 13 Mar. 2015]. Available from: http://www.engineeringtoolbox.com/air-composition-d_212.html. -- Composition of air.

[10] Summary of the Clean Air Act, 2015. United States Environmental Protection Agency. [cited 13 Mar. 2015] Available from: http://www2.epa.gov/laws-regulations/summary-clean-air-act -- Emissions requirements of chemical plants.

[11] Zhang M, Yu Y. Dehydration of Ethanol to Ethylene. Industrial Engineering and Chemical Research. 2013; 52:9505-9514. – Technical information on ethanol to ethylene conversion via dehydration.

[12] AspenTech. Aspen HYSYS Help File v8.0. Aspen Technology, Inc. 2012. - Aspen HYSYS help file used for troubleshooting and assistance on economic analysis.

[13] Towler G, Sinnott R. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. 2nd ed. Boston: Elsevier; 2013. -- General Reference Book

[14] Barrocas H, Baratelli F, inventors; Petroleo Brasileiro S.A., assignee. Process for dehydration of a low molecular weight alcohol. US patent 4,396,789 A. August 2, 1983. - Primary background for process design.

[15] Tsao U, Zasloff HB, inventors; The Lummus Company, assignee. Production of ethylene from ethanol. US patent 4,134,926. January 16, 1979. – Patent for catalytic dehydration of ethylene in a fluidized bed reactor.

[16] Morschbacker, A. Bio-Ethanol Based Ethylene. Polymer Reviews. 2009; 49:79-84. – Overview of bioethanol dehydration process development.

[17] Fan D, Dai DJ, Wu HS. Ethylene Formation by Catalytic Dehydration of Ethanol with Industrial Considerations. Materials. 6, 101-115. doi: 10.3390/ma6010101. - Comparison of types of catalysts used in the dehydration of ethanol and current research into new catalysts.

[18] Chen G, Li S, Jiao F, Yuan Q. Catalytic dehydration of bioethanol to ethylene over TiO2/γ-Al2O3 catalysts in microchannel reactors. Catal. Today 2007, 125, 111–119. - Paper introducing research on modified alumina catalyst for ethanol dehydration.

[19] Jumonville, J. Tutorial on Cryogenic Turboexpanders. Proceedings of the Thirty-Ninth Turbomachinery Symposium; 2010 Oct 4-7; Houston, TX. Houston: Texas A&M University; 2010. -- Use of turboexpander for cryogenic separations

[20] Today in Energy - Daily Prices. US Energy Information Administration website. http://www.eia.gov/todayinenergy/prices.cfm. Accessed March 3rd 2015. - Bulk market price for 95% ethanol.

[21] Weddle, N. ICIS Pricing: Ethylene (Europe). Reed Business Limited. January 10 2014. - Bulk market price for chemical grade ethylene.

=Appendix I - Process Flow Diagram=
[[File:PFD B1.JPG|1200px]]

=Appendix II - HYSYS Simulation=
[[File:HYSYS_B1.PNG|1200px]]

=Appendix III - Material Streams=
[[File:Streams_B1.png|1200px]]

=Appendix IV - Energy Table=
[[File:Energy_B1.png|600px|center]]

=Appendix V - Economics=
[[File:Econsummary_B1.png|center]] 

[[File:Capcost_B1.png|center]] 

[[File:sensitivityanalysis_B1.png|600px|center]]

Ethanol to Ethylene (B1)

2015-03-14T04:14:45Z

Hpoppick: /* Technical Approach */

Ethanol to Ethylene (B1)

2015-03-14T04:14:23Z

Hpoppick: /* Introduction */

Ethanol to Ethylene (B1)

2015-03-14T04:14:01Z

Hpoppick: /* Executive Summary */

Ethanol to Ethylene (B1)

2015-03-14T03:42:48Z

Hpoppick: /* References */

[[File:BFD_B1.png|600px|thumbnail]]
=Executive Summary=
=Introduction=
=Technical Approach=
=Process Flowsheet=
=Economic Analysis=
=Process Alternatives/Recommendations=
=Conclusion=
=References=

[1] American Chemistry Council. Production of chemicals and plastics in the U.S. in 2013, by type (in 1,000 metric tons). In Statista - The Statistics Portal. August 2014. Available at http://www.statista.com/statistics/299725/total-us-plastics-and-chemicals-shipments-by-type/, Accessed January 15, 2015. – Relative proportions of plastics production.

[2] DuPont Nevada Site Cellulosic Ethanol Facility [Internet]. DuPont Chemical; c2012-2015 [cited 11 Mar. 2015]. Available from: http://biofuels.dupont.com/cellulosic-ethanol/nevada-site-ce-facility/. -- Information on ethanol production in Iowa.

[3] Designing Ethylene Plants. Ethylene [Internet]. Technip; 2014 [cited 13 Mar. 2015]. Available from: http://www.technip.com/en/our-business/onshore/ethylene -- Plant size ranges.

[4] Suppes GJ. Selecting Thermodynamic Models for Process Simulation of Organic VLE and LLE Systems. The University of Missouri-Columbia, Dept of Chemical Engineering. [cited 13 Mar. 2015]. -- Use of NRTL in alcohol separations.

[5] ASPENtech. Appendix A - Property Methods and Calculations. Simulation Basics; A-3 - A-26. 2014.

[6] 190 Proof Ethanol: Technical Data Sheet [Internet]. Decon Labs Inc; 2012 [cited 13 Mar. 2015]. Available from: http://www.deconlabs.com/tds/ETHANOL%20190%20%20PROOF.pdf -- Information regarding 95% ethanol

[7] Hadawey A, Ge Y, Tassou TSA. Energy Savings Through Liquid Pressure Amplification In A Dairy Plant Refrigeration System. The Centre for Energy and Built Environment Research [cited 13 Mar. 2015].

[8] Methane (Chemical Compound). 2015. Encyclopædia Britannica Online. [cited 13 Mar. 2015] Available from: http://www.britannica.com/EBchecked/topic/378264/methane -- Composition of Methane

[9] Composition of Air [Internet]. Engineering Toolbox; [cited 13 Mar. 2015]. Available from: http://www.engineeringtoolbox.com/air-composition-d_212.html. -- Composition of air.

[10] Summary of the Clean Air Act, 2015. United States Environmental Protection Agency. [cited 13 Mar. 2015] Available from: http://www2.epa.gov/laws-regulations/summary-clean-air-act -- Emissions requirements of chemical plants.

[11] Zhang M, Yu Y. Dehydration of Ethanol to Ethylene. Industrial Engineering and Chemical Research. 2013; 52:9505-9514. – Technical information on ethanol to ethylene conversion via dehydration.

[12] AspenTech. Aspen HYSYS Help File v8.0. Aspen Technology, Inc. 2012. - Aspen HYSYS help file used for troubleshooting and assistance on economic analysis.

[13] Towler G, Sinnott R. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design. 2nd ed. Boston: Elsevier; 2013. -- General Reference Book

[14] Barrocas H, Baratelli F, inventors; Petroleo Brasileiro S.A., assignee. Process for dehydration of a low molecular weight alcohol. US patent 4,396,789 A. August 2, 1983. - Primary background for process design.

[15] Tsao U, Zasloff HB, inventors; The Lummus Company, assignee. Production of ethylene from ethanol. US patent 4,134,926. January 16, 1979. – Patent for catalytic dehydration of ethylene in a fluidized bed reactor.

[16] Morschbacker, A. Bio-Ethanol Based Ethylene. Polymer Reviews. 2009; 49:79-84. – Overview of bioethanol dehydration process development.

[17] Fan D, Dai DJ, Wu HS. Ethylene Formation by Catalytic Dehydration of Ethanol with Industrial Considerations. Materials. 6, 101-115. doi: 10.3390/ma6010101. - Comparison of types of catalysts used in the dehydration of ethanol and current research into new catalysts.

[18] Chen G, Li S, Jiao F, Yuan Q. Catalytic dehydration of bioethanol to ethylene over TiO2/γ-Al2O3 catalysts in microchannel reactors. Catal. Today 2007, 125, 111–119. - Paper introducing research on modified alumina catalyst for ethanol dehydration.

[19] Jumonville, J. Tutorial on Cryogenic Turboexpanders. Proceedings of the Thirty-Ninth Turbomachinery Symposium; 2010 Oct 4-7; Houston, TX. Houston: Texas A&M University; 2010. -- Use of turboexpander for cryogenic separations

[20] Today in Energy - Daily Prices. US Energy Information Administration website. http://www.eia.gov/todayinenergy/prices.cfm. Accessed March 3rd 2015. - Bulk market price for 95% ethanol.

[21] Weddle, N. ICIS Pricing: Ethylene (Europe). Reed Business Limited. January 10 2014. - Bulk market price for chemical grade ethylene.

=Appendix I - Process Flow Diagram=
[[File:PFD B1.JPG|1200px]]

=Appendix II - HYSYS Simulation=
[[File:HYSYS_B1.PNG|1200px]]

=Appendix III - Material Streams=
[[File:Streams_B1.png|1200px]]

=Appendix IV - Energy Tables=
=Appendix V - Economics=
[[File:Econsummary_B1.png|center]] 

[[File:Capcost_B1.png|center]] 

[[File:sensitivityanalysis_B1.png|600px|center]]

Column

2015-02-28T21:47:32Z

Hpoppick:

[[File:Distillationcolumn_singlefeed.png|thumb|right|300px|Figure 1. Distillation Column]]
Authors: Scott Smith [2015] and Harry Poppick [2015] 

Stewards: Jian Gong and Fengqi You

The column utilities in HYSYS can be used to model a wide variety of chemical separation techniques including absorption, liquid-liquid extraction and three-phase distillation. This article highlights the use of HYSYS for simulations of standard chemical distillation. The two primary distillation simulation utilities are the shortcut column, which is useful for quick and cursory simulations, and the full column utility, for more involved simulations.

==HYSYS Column Types==
{| border="1" class="wikitable"
|+ Varieties of Separators in HYSYS
! Name
! Icon
! Description
|-
! Absorption Column
| [[File:Absorber.JPG|center|35px|]]|| Utility to model absorption and stripping (liquid/vapor) separations.
|-
! Refluxed Absorption Column
| [[File:RefluxedAbsorb.JPG|center|35px|]]|| Utility to model absorption and stripping (liquid/vapor) operations with condensed top products.
|-
! Absorption with Reboil
| [[File:ReboiledAbsorber.JPG|center|35px|]]|| Utility to model absorption and stripping (liquid/vapor) operations with reboiled bottoms.
|-
! Liquid Liquid Extractor
| [[File:LiquidLiquid.JPG|center|35px|]]|| Utility to model liquid-liquid phase separations.
|-
! Three Phase Distillation
| [[File:ThreePhase.JPG|center|35px|]]|| Utility to model distillation consisting of three phases internally.
|-
! Distillation Sub-Flowsheet
| [[File:DistillationColumn.JPG|center|35px|]]|| Overall two-phase distillation utility.
|-
! Shortcut Column
| [[File:ShortcutDistillation.JPG|center|35px|]]|| Approximate model of distillation processes.
|-
! Component Splitter
| [[File:ComponentSplitter.JPG|center|35px|]]|| Utility to force components to separate with no equilibrium considerations.
|}

==Distillation Column HYSYS Simulation==
===Shortcut Distillation Column<ref name = "HYSYS"> Aspentech. "Aspen HYSYS V8.0 Help Documentation". Published 2014 </ref>===

The shortcut distillation utility within HYSYS allows users to quickly model a distillation separation of a stream with relatively little known information. Once the user attaches a fully defined inlet stream to the shortcut distillation column, the essential information that must be specified are as follows:

* The vapor/liquid quality of the top product
* The light key component and composition in the bottoms product
* The heavy key component and composition in the distillate (top) product
* The condenser pressure
* The reboiler pressure
* The external reflux ratio

With this information, the utility will run and, if possible, converge on a solution that will meet the key component specifications. The critical information that the utility will calculate are as follows:

* Fully specified distillate product stream (temperature, pressure, flow rate, composition)
* Fully specified bottom product stream (temperature, pressure, flow rate, composition)
* Condenser operating temperature and heat duty
* Reboiler operating temperature and heat duty
* Minimum number of trays
* Actual number of trays
* Optimum feed tray location

The primary purpose of the shortcut distillation is to allow for users to perform a first pass estimate on the performance requirements of a given system for a specified reflux ratio. The values gathered from the shortcut distillation utility can be used to assist the user when setting up the complete distillation utility in HYSYS, or when attempting to find reasonable column properties to allow the system to converge (e.g. number of trays, feed location, etc.)

====Tutorial====

This example will simulate the separation of benzene, toluene and p-xylene from some upstream process.<ref name = "HYSYS" />

'''Initialize'''

[[File:AddComponents.PNG|thumb|center|600px|Figure 2. Adding Components in HYSYS]]

#Start Aspen HYSYS v.8 and click “new” on the main screen to open a new simulation window.
#Once on the component list screen, select “add” near the bottom of the screen
#Search the database for the desired components using the search bar, and add them to the component list by clicking “add.” In this case, we wish to add Benzene, Toluene and p-Xylene.
#On the left hand “properties” menu, click the “fluid packages” tab and select “add” to add a new package.
#Select the desired fluid package. In this case we are using Peng-Robinson
#In the bottom, left-hand corner of the screen, click “simulation” to enter the simulation environment.

'''Setup Streams'''

[[File:Streams.PNG|thumb|center|300px|Figure 3. Add Streams]]

#Start by clicking the blue arrow at the top of the “palette” window and then clicking on the main flowsheet to produce a new material stream. This will create our feed stream. It is a good idea to place your other streams as well: one for distillate product and one for bottoms product.
#Add two energy streams that will be the condenser and reboiler duties.
#Double click on the newly created feed stream to pull up the worksheet for the stream. Please note that we are specifying this feed stream to demonstrate how the column would behaved with a fully specified inlet stream. The temperature, pressure, flow rate and composition of the feed stream can be specified by the user.

[[File:FeedConditions.PNG|thumb|center|300px|Figure 4. Define Feed]]

#We will make the following changes within this worksheet to specify the feed stream:
#Enter “feed” into the stream name.
#Set the temperature to 20 degrees C.
#Set the pressure to 1 atm. (Be sure to select the “atm” unit from the dropdown when you begin to enter this value)
#Set the mass flow to 500 kg/hr

[[File:Compositions.PNG|thumb|center|600px|Figure 5. Define Compositions]]

#On the left hand column within the worksheet, click “composition” to enter the composition tab.
#Click “edit” on the composition tab to change the composition of the feed stream
#Enter .25 to Toluene, .35 to Benzene and .40 to p-Xylene.

The worksheet should indicate that the stream is fully specified with a green “ok” indicator at the bottom. Close the worksheet.

'''Fully Specify Shortcut Column'''

[[File:ConnectStreams.PNG|thumb|center|600px|Figure 6. Connect the inlet and outlet streams]]

#Create the shortcut column by clicking on the "columns" tab within the palette and selecting "shortcut column"
#Click on the simulation environment to place the column
#The shortcut column should currently appear red to represent that it is not currently specified.
#Double click on the column to pull up the column worksheet
#Under each drop down, add the appropriate stream: E.g. Under "Distillate" add the distillate product stream that was defined earlier.
#Additionally, be sure to specify the quality of the top product stream: whether it is liquid or vapor phase. In this case, select "liquid."

[[File:Set Keys.PNG|thumb|center|600px|Figure 7. Set the key specifications]]

#On the left hand side of the worksheet, select "Parameters."
#This will move you to the parameters section of the column window where column specifications can be added.
#At this point it is important to identify which components are most volatile. In this case, benzene is most volatile, xylene is the least volatile and toluene rests in between the two. One rule of thumb is that more volatile components tend to be more valuable, and so in this example we will be purifying benzene in the distillate stream. In order to do this we will specify that benzene is the light key in the bottoms and that toluene is the heavy key in the distillate. This arrangement makes sense since it will force the heavier xylene and toluene products to drop out in the bottoms.
#Set the Light Key in Bottoms to Benzene and the mole fraction to .001 and set the Heavy Key in Distillate to Toluene and the mole fraction to .001.
#Set the condenser and reboiler pressure to the approximate values that they would be. In this case, we are assuming that our column is sufficiently small that atmospheric pressure is a fair assumption for both values. Enter 1 atm for both of these values.

[[File:Worksheet.PNG|thumb|center|600px|Figure 8. Viewing the Worksheet]]

#Finally set the reflux ratio to a value that is higher than the minimum reflux ratio that HYSYS calculates. In this case the minimum reflux ratio was calculated to be 2.119 and so it is best to input around 2.5. This value can be tweaked later to see how performance is changed for different reflux ratios.
#At this point it is worthwhile to see what outputs the column is producing, since this is one of the primary uses of the shortcut distillation column.
#Click on the "worksheet" tab at the top of the window. This will bring you to your stream information where you can view the temperatures and flow rates of your outgoing streams.
#Now click on the "compositions" tab on the left side to view the compositions of the outgoing stream. As expected, the benzene is leaving in the distillate stream at 99.9% purity with a .1% toluene impurity, while all of the xylene is leaving out in the bottoms.

[[File:Performance.PNG|thumb|center|600px|Figure 9. View the Performance Tab]]

#At this point it is valuable to record the calculated minimum number of trays, actual number of trays, as well as the condenser/reboiler temperatures.
#To view these values click on the "performance" tab
#You can observe here that the minimum number of trays calculated was around 15.7, the actual number of trays used was 35.7 the optimal feed stage was around 20.5, the condenser temperature was found to be around 80 C, while the reboiler was calculated to be around 123 C.

===Standard Distillation Column<ref name = "HYSYS" />===
The standard distillation column, found under the "Columns" tab on the equipment palette, may be used to perform a more rigorous simulation of your process than that offered by the shortcut column. In addition, the shortcut column may be used as a "first pass" analysis and then these specification estimations can used as the starting point for the standard column.

====Tutorial====
In this example, we will be setting up a basic distillation column in HYSYS to simulate the separation of benzene and toluene.

# Start a new case in HYSYS by clicking on the button on the top menu bar.
# On the Components screen, add Benzene and Toluene.
# On the Fluid Package screen, you have a wide range of options with which to simulate vapor-liquid equilibrium. For this example, choose the Peng-Robinson fluid package and enter the simulation environment.

[[File:Columncomponents.PNG|thumb|right|300px|Figure 10. Component Selection in HYSYS]] [[File:Fluidpkg.PNG|thumb|right|400px|Figure 12. Fluid Package Selection in HYSYS]]

We are using the simple distillation column and thus we only need a single feed stream into the distillation column as well as a distillate stream and a bottoms stream. We will also need 2 energy streams for the condenser and reboiler. <ref name = "HYSYS" />

# Add the material and energy streams to the simulation environment. Naming them appropriately will make it easer to keep everything straight as we move forward with the tutorial.
# Select the distillation column from the palette and place anywhere in the simulation environment.
# Switch to “Attach Mode” and attach the mass and energy streams to their appropriate locations on the distillation column. NOTE: You could also complete this step by double-clicking on the column itself and selecting each respective stream from the drop down menus.
# Double click on the column and select the condenser type. For this example, select “total condenser” and click next
# This next page is where the pressures of the column are specified. For this example, we will assume that the column is run at 1 atm with no pressure drops within the column. Therefore, specify reboiler pressure and condenser pressure to 101.3 kPa and the condenser pressure drop to 0 kPa.
# The next page has fields where temperature estimates can be made for the condenser, top stage, and reboiler. As these are optional fields, simply click next.
# The final screen of the distillation column setup is where the reflux ratio and distillate flow rates should be specified. For this example, specify the distillate flow rate as 1000 kgmol/hr and the reflux ratio as 1.5.
# Click “Done” at the bottom of the screen and the simulation page should be back in full view.

[[File:Simulationview.PNG|thumb|center|400px|Figure 11. Simulation View of Distillation Column in HYSYS]]

We are now ready to specify the flow rates and compositions of the streams coming in and out of the column.
# Double click on the feed stream coming into the column. A specifications page should come up.
# This page allows you specify a number of parameters pertaining to the feed stream, including temperature, pressure, and compositions. Specify the temperature as 37C and pressure as 101.3 kPa (1 atm). In addition, specify the molar flow as 3500 kgmole/h.
# Now click on the composition tab on the left side of the window. Here specify, the benzene as 70 mass % and the toluene as 30 mass %. The stream should be fully specified. Close the window to return to the simulation.

[[File:Configurationpage.PNG|thumb|center|400px|Figure 13. Column Configuration Page]]

The column and feed stream should now be fully specified. It is now time to run the simulation.
# If the solver is not already activated, click the green traffic light at the top of the simulation window.
# Now double click on the distillation column to bring up the main column window. A feed stage and total number of stages should already be specified.
# Click the “Run” button of the window to start the simulation. The small rectangle to the right of this button should light up green and say “converged” when it finds a solution.

[[File:Columncompositions.PNG|thumb|center|400px|Figure 14. Outlet compositions in HYSYS]]

===Manipulating Column Specifications===

''Information taken from Towler Chapter 17'' <ref name = "Towler"> Towler, G. Sinnott, "Chemical Engineering Design". Elsevier, 2012, Chapter 17: R. Separation Columns (Distillation, Absorption, and Extraction). </ref>

Parameters that directly impact the design and operation of the distillation column include:
*Reflux ratio
*Feed point location
*Column Pressure
*Number of equilibrium stages/real stages

Assuming that we have already specified a desired specification for either the distillate or bottoms stream, we can manipulate the above parameters when running our simulation within HYSYS.

'''Reflux Ratio'''

The number of stages required for separation is directly affected by the reflux ratio that can be defined as follows:

<math> R=\frac {Flow\ returned\ as\ reflux} {Flow\ of\ top\ product\ taken\ off} </math>

Increasing the reflux ratio will reduce the total number of stages required but will increase the utility costs for the column. Therefore, when simulating a distillation column, special care should be taken to strike a balance between capital and operating costs.

When starting a new distillation column simulation within HYSYS, it is a good idea to calculate a minimum reflux ratio to advise the specification of the reflux ratio. The minimum reflux ratio can be calculated through use of a McCabe-Thiele diagram. According to Towler, a reflux ratio of 1.15 times the minimum reflux ratio should be used as a first approximation. Once this ratio is inputted into the simulation environment, it can be further manipulated to fine-tune the optimum reflux ratio for the system. <ref name = "Towler" />

'''Feed Point Location'''

The column simulation environment within HYSYS allows for manipulation of the feed point location. The general rule for designating feed point location is to have the feed enter the column at the stage which best matches the composition of the feed. There can be some uncertainty when it comes to finding the precise feed point location. Instead, a trial-and-error method may be useful when using HYSYS to determine which feed stage results in the desired distillate and bottoms conditions.

'''Column Pressure'''

When specifying the distillation column within the HYSYS simulation environment, you must specify the operating pressure as well as any pressure drops. If you are running a HYSYS simulation to get a first-pass approximation of compositions and flow rates, it is a typical practice to assume the pressure in the column is constant. If you are running a more intensive and rigorous simulation, you can approximate the pressure drop per tray using the following equation:

<math> \Delta P_{\text{tray}} = 2 \rho_L g h_w </math>

where <math> \rho_L </math> is the liquid density, g is gravitational acceleration, and <math> h_w </math> is the weir height.

==References==
<references />

Column

2015-02-28T21:38:11Z

Hpoppick: /* HYSYS Column Types */

[[File:Distillationcolumn_singlefeed.png|thumb|right|300px|Figure 1. Distillation Column]]
Authors: Scott Smith [2015] and Harry Poppick [2015] 

Stewards: Jian Gong and Fengqi You

This article highlights the use of HYSYS for simulations of chemical distillation. The two primary distillation simulation utilities are the shortcut column, which is useful for quick and cursory simulations, and the full column utility, for more involved simulations.

==HYSYS Column Types==
{| border="1" class="wikitable"
|+ Varieties of Separators in HYSYS
! Name
! Icon
! Description
|-
! Absorption Column
| [[File:Absorber.JPG|center|35px|]]|| Utility to model absorption and stripping (liquid/vapor) separations.
|-
! Refluxed Absorption Column
| [[File:RefluxedAbsorb.JPG|center|35px|]]|| Utility to model absorption and stripping (liquid/vapor) operations with condensed top products.
|-
! Absorption with Reboil
| [[File:ReboiledAbsorber.JPG|center|35px|]]|| Utility to model absorption and stripping (liquid/vapor) operations with reboiled bottoms.
|-
! Liquid Liquid Extractor
| [[File:LiquidLiquid.JPG|center|35px|]]|| Utility to model liquid-liquid phase separations.
|-
! Three Phase Distillation
| [[File:ThreePhase.JPG|center|35px|]]|| Utility to model distillation consisting of three phases internally.
|-
! Distillation Sub-Flowsheet
| [[File:DistillationColumn.JPG|center|35px|]]|| Overall two-phase distillation utility.
|-
! Shortcut Column
| [[File:ShortcutDistillation.JPG|center|35px|]]|| Approximate model of distillation processes.
|-
! Component Splitter
| [[File:ComponentSplitter.JPG|center|35px|]]|| Utility to force components to separate with no equilibrium considerations.
|}

==Distillation Column HYSYS Simulation==
===Shortcut Distillation Column===

The shortcut distillation utility within HYSYS allows users to quickly model a distillation separation of a stream with relatively little known information. Once the user attaches a fully defined inlet stream to the shortcut distillation column, the essential information that must be specified are as follows:

* The vapor/liquid quality of the top product
* The light key component and composition in the bottoms product
* The heavy key component and composition in the distillate (top) product
* The condenser pressure
* The reboiler pressure
* The external reflux ratio

With this information, the utility will run and, if possible, converge on a solution that will meet the key component specifications. The critical information that the utility will calculate are as follows:

* Fully specified distillate product stream (temperature, pressure, flow rate, composition)
* Fully specified bottom product stream (temperature, pressure, flow rate, composition)
* Condenser operating temperature and heat duty
* Reboiler operating temperature and heat duty
* Minimum number of trays
* Actual number of trays
* Optimum feed tray location

The primary purpose of the shortcut distillation is to allow for users to perform a first pass estimate on the performance requirements of a given system for a specified reflux ratio. The values gathered from the shortcut distillation utility can be used to assist the user when setting up the complete distillation utility in HYSYS, or when attempting to find reasonable column properties to allow the system to converge (e.g. number of trays, feed location, etc.)

====Tutorial====

This example will simulate the separation of benzene, toluene and p-xylene from some upstream process.

'''Initialize'''

[[File:AddComponents.PNG|thumb|center|600px|Figure 2. Adding Components in HYSYS]]

#Start Aspen HYSYS v.8 and click “new” on the main screen to open a new simulation window.
#Once on the component list screen, select “add” near the bottom of the screen
#Search the database for the desired components using the search bar, and add them to the component list by clicking “add.” In this case, we wish to add Benzene, Toluene and p-Xylene.
#On the left hand “properties” menu, click the “fluid packages” tab and select “add” to add a new package.
#Select the desired fluid package. In this case we are using Peng-Robinson
#In the bottom, left-hand corner of the screen, click “simulation” to enter the simulation environment.

'''Setup Streams'''

[[File:Streams.PNG|thumb|center|300px|Figure 3. Add Streams]]

#Start by clicking the blue arrow at the top of the “palette” window and then clicking on the main flowsheet to produce a new material stream. This will create our feed stream. It is a good idea to place your other streams as well: one for distillate product and one for bottoms product.
#Add two energy streams that will be the condenser and reboiler duties.
#Double click on the newly created feed stream to pull up the worksheet for the stream. Please note that we are specifying this feed stream to demonstrate how the column would behaved with a fully specified inlet stream. The temperature, pressure, flow rate and composition of the feed stream can be specified by the user.

[[File:FeedConditions.PNG|thumb|center|300px|Figure 4. Define Feed]]

#We will make the following changes within this worksheet to specify the feed stream:
#Enter “feed” into the stream name.
#Set the temperature to 20 degrees C.
#Set the pressure to 1 atm. (Be sure to select the “atm” unit from the dropdown when you begin to enter this value)
#Set the mass flow to 500 kg/hr

[[File:Compositions.PNG|thumb|center|600px|Figure 5. Define Compositions]]

#On the left hand column within the worksheet, click “composition” to enter the composition tab.
#Click “edit” on the composition tab to change the composition of the feed stream
#Enter .25 to Toluene, .35 to Benzene and .40 to p-Xylene.

The worksheet should indicate that the stream is fully specified with a green “ok” indicator at the bottom. Close the worksheet.

'''Fully Specify Shortcut Column'''

[[File:ConnectStreams.PNG|thumb|center|600px|Figure 6. Connect the inlet and outlet streams]]

#Create the shortcut column by clicking on the "columns" tab within the palette and selecting "shortcut column"
#Click on the simulation environment to place the column
#The shortcut column should currently appear red to represent that it is not currently specified.
#Double click on the column to pull up the column worksheet
#Under each drop down, add the appropriate stream: E.g. Under "Distillate" add the distillate product stream that was defined earlier.
#Additionally, be sure to specify the quality of the top product stream: whether it is liquid or vapor phase. In this case, select "liquid."

[[File:Set Keys.PNG|thumb|center|600px|Figure 7. Set the key specifications]]

#On the left hand side of the worksheet, select "Parameters."
#This will move you to the parameters section of the column window where column specifications can be added.
#At this point it is important to identify which components are most volatile. In this case, benzene is most volatile, xylene is the least volatile and toluene rests in between the two. One rule of thumb is that more volatile components tend to be more valuable, and so in this example we will be purifying benzene in the distillate stream. In order to do this we will specify that benzene is the light key in the bottoms and that toluene is the heavy key in the distillate. This arrangement makes sense since it will force the heavier xylene and toluene products to drop out in the bottoms.
#Set the Light Key in Bottoms to Benzene and the mole fraction to .001 and set the Heavy Key in Distillate to Toluene and the mole fraction to .001.
#Set the condenser and reboiler pressure to the approximate values that they would be. In this case, we are assuming that our column is sufficiently small that atmospheric pressure is a fair assumption for both values. Enter 1 atm for both of these values.

[[File:Worksheet.PNG|thumb|center|600px|Figure 8. Viewing the Worksheet]]

#Finally set the reflux ratio to a value that is higher than the minimum reflux ratio that HYSYS calculates. In this case the minimum reflux ratio was calculated to be 2.119 and so it is best to input around 2.5. This value can be tweaked later to see how performance is changed for different reflux ratios.
#At this point it is worthwhile to see what outputs the column is producing, since this is one of the primary uses of the shortcut distillation column.
#Click on the "worksheet" tab at the top of the window. This will bring you to your stream information where you can view the temperatures and flow rates of your outgoing streams.
#Now click on the "compositions" tab on the left side to view the compositions of the outgoing stream. As expected, the benzene is leaving in the distillate stream at 99.9% purity with a .1% toluene impurity, while all of the xylene is leaving out in the bottoms.

[[File:Performance.PNG|thumb|center|600px|Figure 9. View the Performance Tab]]

#At this point it is valuable to record the calculated minimum number of trays, actual number of trays, as well as the condenser/reboiler temperatures.
#To view these values click on the "performance" tab
#You can observe here that the minimum number of trays calculated was around 15.7, the actual number of trays used was 35.7 the optimal feed stage was around 20.5, the condenser temperature was found to be around 80 C, while the reboiler was calculated to be around 123 C.

===Standard Distillation Column===
The standard distillation column, found under the "Columns" tab on the equipment palette, may be used to perform a more rigorous simulation of your process than that offered by the shortcut column. In addition, the shortcut column may be used as a "first pass" analysis and then these specification estimations can used as the starting point for the standard column.

====Tutorial====
In this example, we will be setting up a basic distillation column in HYSYS to simulate the separation of benzene and toluene.

# Start a new case in HYSYS by clicking on the button on the top menu bar.
# On the Components screen, add Benzene and Toluene.
# On the Fluid Package screen, you have a wide range of options with which to simulate vapor-liquid equilibrium. For this example, choose the Peng-Robinson fluid package and enter the simulation environment.

[[File:Columncomponents.PNG|thumb|right|300px|Figure 10. Component Selection in HYSYS]] [[File:Fluidpkg.PNG|thumb|right|400px|Figure 12. Fluid Package Selection in HYSYS]]

We are using the simple distillation column and thus we only need a single feed stream into the distillation column as well as a distillate stream and a bottoms stream. We will also need 2 energy streams for the condenser and reboiler.

# Add the material and energy streams to the simulation environment. Naming them appropriately will make it easer to keep everything straight as we move forward with the tutorial.
# Select the distillation column from the palette and place anywhere in the simulation environment.
# Switch to “Attach Mode” and attach the mass and energy streams to their appropriate locations on the distillation column. NOTE: You could also complete this step by double-clicking on the column itself and selecting each respective stream from the drop down menus.
# Double click on the column and select the condenser type. For this example, select “total condenser” and click next
# This next page is where the pressures of the column are specified. For this example, we will assume that the column is run at 1 atm with no pressure drops within the column. Therefore, specify reboiler pressure and condenser pressure to 101.3 kPa and the condenser pressure drop to 0 kPa.
# The next page has fields where temperature estimates can be made for the condenser, top stage, and reboiler. As these are optional fields, simply click next.
# The final screen of the distillation column setup is where the reflux ratio and distillate flow rates should be specified. For this example, specify the distillate flow rate as 1000 kgmol/hr and the reflux ratio as 1.5.
# Click “Done” at the bottom of the screen and the simulation page should be back in full view.

[[File:Simulationview.PNG|thumb|center|400px|Figure 11. Simulation View of Distillation Column in HYSYS]]

We are now ready to specify the flow rates and compositions of the streams coming in and out of the column.
# Double click on the feed stream coming into the column. A specifications page should come up.
# This page allows you specify a number of parameters pertaining to the feed stream, including temperature, pressure, and compositions. Specify the temperature as 37C and pressure as 101.3 kPa (1 atm). In addition, specify the molar flow as 3500 kgmole/h.
# Now click on the composition tab on the left side of the window. Here specify, the benzene as 70 mass % and the toluene as 30 mass %. The stream should be fully specified. Close the window to return to the simulation.

[[File:Configurationpage.PNG|thumb|center|400px|Figure 13. Column Configuration Page]]

The column and feed stream should now be fully specified. It is now time to run the simulation.
# If the solver is not already activated, click the green traffic light at the top of the simulation window.
# Now double click on the distillation column to bring up the main column window. A feed stage and total number of stages should already be specified.
# Click the “Run” button of the window to start the simulation. The small rectangle to the right of this button should light up green and say “converged” when it finds a solution.

[[File:Columncompositions.PNG|thumb|center|400px|Figure 14. Outlet compositions in HYSYS]]

===Manipulating Column Specifications===

''Information taken from Towler Chapter 17'' <ref name = "Towler"> Towler, G. Sinnott, "Chemical Engineering Design". Elsevier, 2012, Chapter 17: R. Separation Columns (Distillation, Absorption, and Extraction). </ref>

Parameters that directly impact the design and operation of the distillation column include:
*Reflux ratio
*Feed point location
*Column Pressure
*Number of equilibrium stages/real stages

Assuming that we have already specified a desired specification for either the distillate or bottoms stream, we can manipulate the above parameters when running our simulation within HYSYS.

'''Reflux Ratio'''

The number of stages required for separation is directly affected by the reflux ratio that can be defined as follows:

<math> R=\frac {Flow\ returned\ as\ reflux} {Flow\ of\ top\ product\ taken\ off} </math>

Increasing the reflux ratio will reduce the total number of stages required but will increase the utility costs for the column. Therefore, when simulating a distillation column, special care should be taken to strike a balance between capital and operating costs.

When starting a new distillation column simulation within HYSYS, it is a good idea to calculate a minimum reflux ratio to advise the specification of the reflux ratio. The minimum reflux ratio can be calculated through use of a McCabe-Thiele diagram. According to Towler, a reflux ratio of 1.15 times the minimum reflux ratio should be used as a first approximation. Once this ratio is inputted into the simulation environment, it can be further manipulated to fine-tune the optimum reflux ratio for the system. <ref name = "Towler" />

'''Feed Point Location'''

The column simulation environment within HYSYS allows for manipulation of the feed point location. The general rule for designating feed point location is to have the feed enter the column at the stage which best matches the composition of the feed. There can be some uncertainty when it comes to finding the precise feed point location. Instead, a trial-and-error method may be useful when using HYSYS to determine which feed stage results in the desired distillate and bottoms conditions.

'''Column Pressure'''

When specifying the distillation column within the HYSYS simulation environment, you must specify the operating pressure as well as any pressure drops. If you are running a HYSYS simulation to get a first-pass approximation of compositions and flow rates, it is a typical practice to assume the pressure in the column is constant. If you are running a more intensive and rigorous simulation, you can approximate the pressure drop per tray using the following equation:

<math> \Delta P_{\text{tray}} = 2 \rho_L g h_w </math>

where <math> \rho_L </math> is the liquid density, g is gravitational acceleration, and <math> h_w </math> is the weir height.

==References==
<references />

Column

2015-02-28T21:33:02Z

Hpoppick: /* HYSYS Column Types */

[[File:Distillationcolumn_singlefeed.png|thumb|right|300px|Figure 1. Distillation Column]]
Authors: Scott Smith [2015] and Harry Poppick [2015] 

Stewards: Jian Gong and Fengqi You

This article highlights the use of HYSYS for simulations of chemical distillation. The two primary distillation simulation utilities are the shortcut column, which is useful for quick and cursory simulations, and the full column utility, for more involved simulations.

==HYSYS Column Types==
{| border="1" class="wikitable"
|+ Varieties of Separators in HYSYS
! Name
! Icon
! Description
|-
! Absorption Column
| [[File:Absorber.JPG|center|35px|]]|| Cell 3
|-
! Refluxed Absorption Column
| [[File:RefluxedAbsorb.JPG|center|35px|]]|| Cell 3
|-
! Absorption with Reboil
| [[File:ReboiledAbsorber.JPG|center|35px|]]|| Cell 3
|-
! Liquid Liquid Extractor
| [[File:LiquidLiquid.JPG|center|35px|]]|| Cell 3
|-
! Three Phase Distillation
| [[File:ThreePhase.JPG|center|35px|]]|| Cell 3
|-
! Distillation Sub-Flowsheet
| [[File:DistillationColumn.JPG|center|35px|]]|| Cell 3
|-
! Shortcut Column
| [[File:ShortcutDistillation.JPG|center|35px|]]|| Cell 3
|-
! Component Splitter
| [[File:ComponentSplitter.JPG|center|35px|]]|| Cell 3
|}

==Distillation Column HYSYS Simulation==
===Shortcut Distillation Column===

The shortcut distillation utility within HYSYS allows users to quickly model a distillation separation of a stream with relatively little known information. Once the user attaches a fully defined inlet stream to the shortcut distillation column, the essential information that must be specified are as follows:

* The vapor/liquid quality of the top product
* The light key component and composition in the bottoms product
* The heavy key component and composition in the distillate (top) product
* The condenser pressure
* The reboiler pressure
* The external reflux ratio

With this information, the utility will run and, if possible, converge on a solution that will meet the key component specifications. The critical information that the utility will calculate are as follows:

* Fully specified distillate product stream (temperature, pressure, flow rate, composition)
* Fully specified bottom product stream (temperature, pressure, flow rate, composition)
* Condenser operating temperature and heat duty
* Reboiler operating temperature and heat duty
* Minimum number of trays
* Actual number of trays
* Optimum feed tray location

The primary purpose of the shortcut distillation is to allow for users to perform a first pass estimate on the performance requirements of a given system for a specified reflux ratio. The values gathered from the shortcut distillation utility can be used to assist the user when setting up the complete distillation utility in HYSYS, or when attempting to find reasonable column properties to allow the system to converge (e.g. number of trays, feed location, etc.)

====Tutorial====

This example will simulate the separation of benzene, toluene and p-xylene from some upstream process.

'''Initialize'''

[[File:AddComponents.PNG|thumb|center|600px|Figure 2. Adding Components in HYSYS]]

#Start Aspen HYSYS v.8 and click “new” on the main screen to open a new simulation window.
#Once on the component list screen, select “add” near the bottom of the screen
#Search the database for the desired components using the search bar, and add them to the component list by clicking “add.” In this case, we wish to add Benzene, Toluene and p-Xylene.
#On the left hand “properties” menu, click the “fluid packages” tab and select “add” to add a new package.
#Select the desired fluid package. In this case we are using Peng-Robinson
#In the bottom, left-hand corner of the screen, click “simulation” to enter the simulation environment.

'''Setup Streams'''

[[File:Streams.PNG|thumb|center|300px|Figure 3. Add Streams]]

#Start by clicking the blue arrow at the top of the “palette” window and then clicking on the main flowsheet to produce a new material stream. This will create our feed stream. It is a good idea to place your other streams as well: one for distillate product and one for bottoms product.
#Add two energy streams that will be the condenser and reboiler duties.
#Double click on the newly created feed stream to pull up the worksheet for the stream. Please note that we are specifying this feed stream to demonstrate how the column would behaved with a fully specified inlet stream. The temperature, pressure, flow rate and composition of the feed stream can be specified by the user.

[[File:FeedConditions.PNG|thumb|center|300px|Figure 4. Define Feed]]

#We will make the following changes within this worksheet to specify the feed stream:
#Enter “feed” into the stream name.
#Set the temperature to 20 degrees C.
#Set the pressure to 1 atm. (Be sure to select the “atm” unit from the dropdown when you begin to enter this value)
#Set the mass flow to 500 kg/hr

[[File:Compositions.PNG|thumb|center|600px|Figure 5. Define Compositions]]

#On the left hand column within the worksheet, click “composition” to enter the composition tab.
#Click “edit” on the composition tab to change the composition of the feed stream
#Enter .25 to Toluene, .35 to Benzene and .40 to p-Xylene.

The worksheet should indicate that the stream is fully specified with a green “ok” indicator at the bottom. Close the worksheet.

'''Fully Specify Shortcut Column'''

[[File:ConnectStreams.PNG|thumb|center|600px|Figure 6. Connect the inlet and outlet streams]]

#Create the shortcut column by clicking on the "columns" tab within the palette and selecting "shortcut column"
#Click on the simulation environment to place the column
#The shortcut column should currently appear red to represent that it is not currently specified.
#Double click on the column to pull up the column worksheet
#Under each drop down, add the appropriate stream: E.g. Under "Distillate" add the distillate product stream that was defined earlier.
#Additionally, be sure to specify the quality of the top product stream: whether it is liquid or vapor phase. In this case, select "liquid."

[[File:Set Keys.PNG|thumb|center|600px|Figure 7. Set the key specifications]]

#On the left hand side of the worksheet, select "Parameters."
#This will move you to the parameters section of the column window where column specifications can be added.
#At this point it is important to identify which components are most volatile. In this case, benzene is most volatile, xylene is the least volatile and toluene rests in between the two. One rule of thumb is that more volatile components tend to be more valuable, and so in this example we will be purifying benzene in the distillate stream. In order to do this we will specify that benzene is the light key in the bottoms and that toluene is the heavy key in the distillate. This arrangement makes sense since it will force the heavier xylene and toluene products to drop out in the bottoms.
#Set the Light Key in Bottoms to Benzene and the mole fraction to .001 and set the Heavy Key in Distillate to Toluene and the mole fraction to .001.
#Set the condenser and reboiler pressure to the approximate values that they would be. In this case, we are assuming that our column is sufficiently small that atmospheric pressure is a fair assumption for both values. Enter 1 atm for both of these values.

[[File:Worksheet.PNG|thumb|center|600px|Figure 8. Viewing the Worksheet]]

#Finally set the reflux ratio to a value that is higher than the minimum reflux ratio that HYSYS calculates. In this case the minimum reflux ratio was calculated to be 2.119 and so it is best to input around 2.5. This value can be tweaked later to see how performance is changed for different reflux ratios.
#At this point it is worthwhile to see what outputs the column is producing, since this is one of the primary uses of the shortcut distillation column.
#Click on the "worksheet" tab at the top of the window. This will bring you to your stream information where you can view the temperatures and flow rates of your outgoing streams.
#Now click on the "compositions" tab on the left side to view the compositions of the outgoing stream. As expected, the benzene is leaving in the distillate stream at 99.9% purity with a .1% toluene impurity, while all of the xylene is leaving out in the bottoms.

[[File:Performance.PNG|thumb|center|600px|Figure 9. View the Performance Tab]]

#At this point it is valuable to record the calculated minimum number of trays, actual number of trays, as well as the condenser/reboiler temperatures.
#To view these values click on the "performance" tab
#You can observe here that the minimum number of trays calculated was around 15.7, the actual number of trays used was 35.7 the optimal feed stage was around 20.5, the condenser temperature was found to be around 80 C, while the reboiler was calculated to be around 123 C.

===Standard Distillation Column===
The standard distillation column, found under the "Columns" tab on the equipment palette, may be used to perform a more rigorous simulation of your process than that offered by the shortcut column. In addition, the shortcut column may be used as a "first pass" analysis and then these specification estimations can used as the starting point for the standard column.

====Tutorial====
In this example, we will be setting up a basic distillation column in HYSYS to simulate the separation of benzene and toluene.

# Start a new case in HYSYS by clicking on the button on the top menu bar.
# On the Components screen, add Benzene and Toluene.
# On the Fluid Package screen, you have a wide range of options with which to simulate vapor-liquid equilibrium. For this example, choose the Peng-Robinson fluid package and enter the simulation environment.

[[File:Columncomponents.PNG|thumb|right|300px|Figure 10. Component Selection in HYSYS]] [[File:Fluidpkg.PNG|thumb|right|400px|Figure 12. Fluid Package Selection in HYSYS]]

We are using the simple distillation column and thus we only need a single feed stream into the distillation column as well as a distillate stream and a bottoms stream. We will also need 2 energy streams for the condenser and reboiler.

# Add the material and energy streams to the simulation environment. Naming them appropriately will make it easer to keep everything straight as we move forward with the tutorial.
# Select the distillation column from the palette and place anywhere in the simulation environment.
# Switch to “Attach Mode” and attach the mass and energy streams to their appropriate locations on the distillation column. NOTE: You could also complete this step by double-clicking on the column itself and selecting each respective stream from the drop down menus.
# Double click on the column and select the condenser type. For this example, select “total condenser” and click next
# This next page is where the pressures of the column are specified. For this example, we will assume that the column is run at 1 atm with no pressure drops within the column. Therefore, specify reboiler pressure and condenser pressure to 101.3 kPa and the condenser pressure drop to 0 kPa.
# The next page has fields where temperature estimates can be made for the condenser, top stage, and reboiler. As these are optional fields, simply click next.
# The final screen of the distillation column setup is where the reflux ratio and distillate flow rates should be specified. For this example, specify the distillate flow rate as 1000 kgmol/hr and the reflux ratio as 1.5.
# Click “Done” at the bottom of the screen and the simulation page should be back in full view.

[[File:Simulationview.PNG|thumb|center|400px|Figure 11. Simulation View of Distillation Column in HYSYS]]

We are now ready to specify the flow rates and compositions of the streams coming in and out of the column.
# Double click on the feed stream coming into the column. A specifications page should come up.
# This page allows you specify a number of parameters pertaining to the feed stream, including temperature, pressure, and compositions. Specify the temperature as 37C and pressure as 101.3 kPa (1 atm). In addition, specify the molar flow as 3500 kgmole/h.
# Now click on the composition tab on the left side of the window. Here specify, the benzene as 70 mass % and the toluene as 30 mass %. The stream should be fully specified. Close the window to return to the simulation.

[[File:Configurationpage.PNG|thumb|center|400px|Figure 13. Column Configuration Page]]

The column and feed stream should now be fully specified. It is now time to run the simulation.
# If the solver is not already activated, click the green traffic light at the top of the simulation window.
# Now double click on the distillation column to bring up the main column window. A feed stage and total number of stages should already be specified.
# Click the “Run” button of the window to start the simulation. The small rectangle to the right of this button should light up green and say “converged” when it finds a solution.

[[File:Columncompositions.PNG|thumb|center|400px|Figure 14. Outlet compositions in HYSYS]]

===Manipulating Column Specifications===

''Information taken from Towler Chapter 17''

Parameters that directly impact the design and operation of the distillation column include:
*Reflux ratio
*Feed point location
*Column Pressure
*Number of equilibrium stages/real stages

Assuming that we have already specified a desired specification for either the distillate or bottoms stream, we can manipulate the above parameters when running our simulation within HYSYS.

'''Reflux Ratio'''

The number of stages required for separation is directly affected by the reflux ratio that can be defined as follows:

<math> R=\frac {Flow\ returned\ as\ reflux} {Flow\ of\ top\ product\ taken\ off} </math>

Increasing the reflux ratio will reduce the total number of stages required but will increase the utility costs for the column. Therefore, when simulating a distillation column, special care should be taken to strike a balance between capital and operating costs.

When starting a new distillation column simulation within HYSYS, it is a good idea to calculate a minimum reflux ratio to advise the specification of the reflux ratio. The minimum reflux ratio can be calculated through use of a McCabe-Thiele diagram. According to Towler, a reflux ratio of 1.15 times the minimum reflux ratio should be used as a first approximation. Once this ratio is inputted into the simulation environment, it can be further manipulated to fine-tune the optimum reflux ratio for the system.

'''Feed Point Location'''

The column simulation environment within HYSYS allows for manipulation of the feed point location. The general rule for designating feed point location is to have the feed enter the column at the stage which best matches the composition of the feed. There can be some uncertainty when it comes to finding the precise feed point location. Instead, a trial-and-error method may be useful when using HYSYS to determine which feed stage results in the desired distillate and bottoms conditions.

'''Column Pressure'''

When specifying the distillation column within the HYSYS simulation environment, you must specify the operating pressure as well as any pressure drops. If you are running a HYSYS simulation to get a first-pass approximation of compositions and flow rates, it is a typical practice to assume the pressure in the column is constant. If you are running a more intensive and rigorous simulation, you can approximate the pressure drop per tray using the following equation:

<math> \Delta P_{\text{tray}} = 2 \rho_L g h_w </math>

where <math> \rho_L </math> is the liquid density, g is gravitational acceleration, and <math> h_w </math> is the weir height.

Column

2015-02-28T21:32:06Z

Hpoppick: /* HYSYS Column Types */

[[File:Distillationcolumn_singlefeed.png|thumb|right|300px|Figure 1. Distillation Column]]
Authors: Scott Smith [2015] and Harry Poppick [2015] 

Stewards: Jian Gong and Fengqi You

This article highlights the use of HYSYS for simulations of chemical distillation. The two primary distillation simulation utilities are the shortcut column, which is useful for quick and cursory simulations, and the full column utility, for more involved simulations.

==HYSYS Column Types==
{| border="1" class="wikitable"
|+ Varieties of Separators in HYSYS
! Name
! Icon
! Description
|-
! Absorption Column
| [[File:Absorber.JPG|center|35px|]]|| Cell 3
|-
! Refluxed Absorption Column
| [[File:RefluxedAbsorb.JPG|center|35px|]]|| Cell 3
|-
! Row heading 1
| [[File:ReboiledAbsorber.JPG|center|35px|]]|| Cell 3
|-
! Row heading 1
| [[File:LiquidLiquid.JPG|center|35px|]]|| Cell 3
|-
! Row heading 1
| [[File:ThreePhase.JPG|center|35px|]]|| Cell 3
|-
! Row heading 1
| [[File:DistillationColumn.JPG|center|35px|]]|| Cell 3
|-
! Row heading 1
| [[File:ShortcutDistillation.JPG|center|35px|]]|| Cell 3
|-
! Row heading 1
| [[File:ComponentSplitter.JPG|center|35px|]]|| Cell 3
|}

==Distillation Column HYSYS Simulation==
===Shortcut Distillation Column===

The shortcut distillation utility within HYSYS allows users to quickly model a distillation separation of a stream with relatively little known information. Once the user attaches a fully defined inlet stream to the shortcut distillation column, the essential information that must be specified are as follows:

* The vapor/liquid quality of the top product
* The light key component and composition in the bottoms product
* The heavy key component and composition in the distillate (top) product
* The condenser pressure
* The reboiler pressure
* The external reflux ratio

With this information, the utility will run and, if possible, converge on a solution that will meet the key component specifications. The critical information that the utility will calculate are as follows:

* Fully specified distillate product stream (temperature, pressure, flow rate, composition)
* Fully specified bottom product stream (temperature, pressure, flow rate, composition)
* Condenser operating temperature and heat duty
* Reboiler operating temperature and heat duty
* Minimum number of trays
* Actual number of trays
* Optimum feed tray location

The primary purpose of the shortcut distillation is to allow for users to perform a first pass estimate on the performance requirements of a given system for a specified reflux ratio. The values gathered from the shortcut distillation utility can be used to assist the user when setting up the complete distillation utility in HYSYS, or when attempting to find reasonable column properties to allow the system to converge (e.g. number of trays, feed location, etc.)

====Tutorial====

This example will simulate the separation of benzene, toluene and p-xylene from some upstream process.

'''Initialize'''

[[File:AddComponents.PNG|thumb|center|600px|Figure 2. Adding Components in HYSYS]]

#Start Aspen HYSYS v.8 and click “new” on the main screen to open a new simulation window.
#Once on the component list screen, select “add” near the bottom of the screen
#Search the database for the desired components using the search bar, and add them to the component list by clicking “add.” In this case, we wish to add Benzene, Toluene and p-Xylene.
#On the left hand “properties” menu, click the “fluid packages” tab and select “add” to add a new package.
#Select the desired fluid package. In this case we are using Peng-Robinson
#In the bottom, left-hand corner of the screen, click “simulation” to enter the simulation environment.

'''Setup Streams'''

[[File:Streams.PNG|thumb|center|300px|Figure 3. Add Streams]]

#Start by clicking the blue arrow at the top of the “palette” window and then clicking on the main flowsheet to produce a new material stream. This will create our feed stream. It is a good idea to place your other streams as well: one for distillate product and one for bottoms product.
#Add two energy streams that will be the condenser and reboiler duties.
#Double click on the newly created feed stream to pull up the worksheet for the stream. Please note that we are specifying this feed stream to demonstrate how the column would behaved with a fully specified inlet stream. The temperature, pressure, flow rate and composition of the feed stream can be specified by the user.

[[File:FeedConditions.PNG|thumb|center|300px|Figure 4. Define Feed]]

#We will make the following changes within this worksheet to specify the feed stream:
#Enter “feed” into the stream name.
#Set the temperature to 20 degrees C.
#Set the pressure to 1 atm. (Be sure to select the “atm” unit from the dropdown when you begin to enter this value)
#Set the mass flow to 500 kg/hr

[[File:Compositions.PNG|thumb|center|600px|Figure 5. Define Compositions]]

#On the left hand column within the worksheet, click “composition” to enter the composition tab.
#Click “edit” on the composition tab to change the composition of the feed stream
#Enter .25 to Toluene, .35 to Benzene and .40 to p-Xylene.

The worksheet should indicate that the stream is fully specified with a green “ok” indicator at the bottom. Close the worksheet.

'''Fully Specify Shortcut Column'''

[[File:ConnectStreams.PNG|thumb|center|600px|Figure 6. Connect the inlet and outlet streams]]

#Create the shortcut column by clicking on the "columns" tab within the palette and selecting "shortcut column"
#Click on the simulation environment to place the column
#The shortcut column should currently appear red to represent that it is not currently specified.
#Double click on the column to pull up the column worksheet
#Under each drop down, add the appropriate stream: E.g. Under "Distillate" add the distillate product stream that was defined earlier.
#Additionally, be sure to specify the quality of the top product stream: whether it is liquid or vapor phase. In this case, select "liquid."

[[File:Set Keys.PNG|thumb|center|600px|Figure 7. Set the key specifications]]

#On the left hand side of the worksheet, select "Parameters."
#This will move you to the parameters section of the column window where column specifications can be added.
#At this point it is important to identify which components are most volatile. In this case, benzene is most volatile, xylene is the least volatile and toluene rests in between the two. One rule of thumb is that more volatile components tend to be more valuable, and so in this example we will be purifying benzene in the distillate stream. In order to do this we will specify that benzene is the light key in the bottoms and that toluene is the heavy key in the distillate. This arrangement makes sense since it will force the heavier xylene and toluene products to drop out in the bottoms.
#Set the Light Key in Bottoms to Benzene and the mole fraction to .001 and set the Heavy Key in Distillate to Toluene and the mole fraction to .001.
#Set the condenser and reboiler pressure to the approximate values that they would be. In this case, we are assuming that our column is sufficiently small that atmospheric pressure is a fair assumption for both values. Enter 1 atm for both of these values.

[[File:Worksheet.PNG|thumb|center|600px|Figure 8. Viewing the Worksheet]]

#Finally set the reflux ratio to a value that is higher than the minimum reflux ratio that HYSYS calculates. In this case the minimum reflux ratio was calculated to be 2.119 and so it is best to input around 2.5. This value can be tweaked later to see how performance is changed for different reflux ratios.
#At this point it is worthwhile to see what outputs the column is producing, since this is one of the primary uses of the shortcut distillation column.
#Click on the "worksheet" tab at the top of the window. This will bring you to your stream information where you can view the temperatures and flow rates of your outgoing streams.
#Now click on the "compositions" tab on the left side to view the compositions of the outgoing stream. As expected, the benzene is leaving in the distillate stream at 99.9% purity with a .1% toluene impurity, while all of the xylene is leaving out in the bottoms.

[[File:Performance.PNG|thumb|center|600px|Figure 9. View the Performance Tab]]

#At this point it is valuable to record the calculated minimum number of trays, actual number of trays, as well as the condenser/reboiler temperatures.
#To view these values click on the "performance" tab
#You can observe here that the minimum number of trays calculated was around 15.7, the actual number of trays used was 35.7 the optimal feed stage was around 20.5, the condenser temperature was found to be around 80 C, while the reboiler was calculated to be around 123 C.

===Standard Distillation Column===
The standard distillation column, found under the "Columns" tab on the equipment palette, may be used to perform a more rigorous simulation of your process than that offered by the shortcut column. In addition, the shortcut column may be used as a "first pass" analysis and then these specification estimations can used as the starting point for the standard column.

====Tutorial====
In this example, we will be setting up a basic distillation column in HYSYS to simulate the separation of benzene and toluene.

# Start a new case in HYSYS by clicking on the button on the top menu bar.
# On the Components screen, add Benzene and Toluene.
# On the Fluid Package screen, you have a wide range of options with which to simulate vapor-liquid equilibrium. For this example, choose the Peng-Robinson fluid package and enter the simulation environment.

[[File:Columncomponents.PNG|thumb|right|300px|Figure 10. Component Selection in HYSYS]] [[File:Fluidpkg.PNG|thumb|right|400px|Figure 12. Fluid Package Selection in HYSYS]]

We are using the simple distillation column and thus we only need a single feed stream into the distillation column as well as a distillate stream and a bottoms stream. We will also need 2 energy streams for the condenser and reboiler.

# Add the material and energy streams to the simulation environment. Naming them appropriately will make it easer to keep everything straight as we move forward with the tutorial.
# Select the distillation column from the palette and place anywhere in the simulation environment.
# Switch to “Attach Mode” and attach the mass and energy streams to their appropriate locations on the distillation column. NOTE: You could also complete this step by double-clicking on the column itself and selecting each respective stream from the drop down menus.
# Double click on the column and select the condenser type. For this example, select “total condenser” and click next
# This next page is where the pressures of the column are specified. For this example, we will assume that the column is run at 1 atm with no pressure drops within the column. Therefore, specify reboiler pressure and condenser pressure to 101.3 kPa and the condenser pressure drop to 0 kPa.
# The next page has fields where temperature estimates can be made for the condenser, top stage, and reboiler. As these are optional fields, simply click next.
# The final screen of the distillation column setup is where the reflux ratio and distillate flow rates should be specified. For this example, specify the distillate flow rate as 1000 kgmol/hr and the reflux ratio as 1.5.
# Click “Done” at the bottom of the screen and the simulation page should be back in full view.

[[File:Simulationview.PNG|thumb|center|400px|Figure 11. Simulation View of Distillation Column in HYSYS]]

We are now ready to specify the flow rates and compositions of the streams coming in and out of the column.
# Double click on the feed stream coming into the column. A specifications page should come up.
# This page allows you specify a number of parameters pertaining to the feed stream, including temperature, pressure, and compositions. Specify the temperature as 37C and pressure as 101.3 kPa (1 atm). In addition, specify the molar flow as 3500 kgmole/h.
# Now click on the composition tab on the left side of the window. Here specify, the benzene as 70 mass % and the toluene as 30 mass %. The stream should be fully specified. Close the window to return to the simulation.

[[File:Configurationpage.PNG|thumb|center|400px|Figure 13. Column Configuration Page]]

The column and feed stream should now be fully specified. It is now time to run the simulation.
# If the solver is not already activated, click the green traffic light at the top of the simulation window.
# Now double click on the distillation column to bring up the main column window. A feed stage and total number of stages should already be specified.
# Click the “Run” button of the window to start the simulation. The small rectangle to the right of this button should light up green and say “converged” when it finds a solution.

[[File:Columncompositions.PNG|thumb|center|400px|Figure 14. Outlet compositions in HYSYS]]

===Manipulating Column Specifications===

''Information taken from Towler Chapter 17''

Parameters that directly impact the design and operation of the distillation column include:
*Reflux ratio
*Feed point location
*Column Pressure
*Number of equilibrium stages/real stages

Assuming that we have already specified a desired specification for either the distillate or bottoms stream, we can manipulate the above parameters when running our simulation within HYSYS.

'''Reflux Ratio'''

The number of stages required for separation is directly affected by the reflux ratio that can be defined as follows:

<math> R=\frac {Flow\ returned\ as\ reflux} {Flow\ of\ top\ product\ taken\ off} </math>

Increasing the reflux ratio will reduce the total number of stages required but will increase the utility costs for the column. Therefore, when simulating a distillation column, special care should be taken to strike a balance between capital and operating costs.

When starting a new distillation column simulation within HYSYS, it is a good idea to calculate a minimum reflux ratio to advise the specification of the reflux ratio. The minimum reflux ratio can be calculated through use of a McCabe-Thiele diagram. According to Towler, a reflux ratio of 1.15 times the minimum reflux ratio should be used as a first approximation. Once this ratio is inputted into the simulation environment, it can be further manipulated to fine-tune the optimum reflux ratio for the system.

'''Feed Point Location'''

The column simulation environment within HYSYS allows for manipulation of the feed point location. The general rule for designating feed point location is to have the feed enter the column at the stage which best matches the composition of the feed. There can be some uncertainty when it comes to finding the precise feed point location. Instead, a trial-and-error method may be useful when using HYSYS to determine which feed stage results in the desired distillate and bottoms conditions.

'''Column Pressure'''

When specifying the distillation column within the HYSYS simulation environment, you must specify the operating pressure as well as any pressure drops. If you are running a HYSYS simulation to get a first-pass approximation of compositions and flow rates, it is a typical practice to assume the pressure in the column is constant. If you are running a more intensive and rigorous simulation, you can approximate the pressure drop per tray using the following equation:

<math> \Delta P_{\text{tray}} = 2 \rho_L g h_w </math>

where <math> \rho_L </math> is the liquid density, g is gravitational acceleration, and <math> h_w </math> is the weir height.

Column

2015-02-28T21:31:24Z

Hpoppick: /* HYSYS Column Types */

[[File:Distillationcolumn_singlefeed.png|thumb|right|300px|Figure 1. Distillation Column]]
Authors: Scott Smith [2015] and Harry Poppick [2015] 

Stewards: Jian Gong and Fengqi You

This article highlights the use of HYSYS for simulations of chemical distillation. The two primary distillation simulation utilities are the shortcut column, which is useful for quick and cursory simulations, and the full column utility, for more involved simulations.

==HYSYS Column Types==
{| border="1" class="wikitable"
|+ Varieties of Separators in HYSYS
! Name
! Icon
! Description
|-
! Row heading 1
| [[File:Absorber.JPG|center|35px|]]|| Cell 3
|-
! Row heading 1
| [[File:RefluxedAbsorb.JPG|center|35px|]]|| Cell 3
|-
! Row heading 1
| [[File:ReboiledAbsorber.JPG|center|35px|]]|| Cell 3
|-
! Row heading 1
| [[File:LiquidLiquid.JPG|center|35px|]]|| Cell 3
|-
! Row heading 1
| [[File:ThreePhase.JPG|center|35px|]]|| Cell 3
|-
! Row heading 1
| [[File:DistillationColumn.JPG|center|35px|]]|| Cell 3
|-
! Row heading 1
| [[File:ShortcutDistillation.JPG|center|35px|]]|| Cell 3
|-
! Row heading 1
| [[File:ComponentSplitter.JPG|center|35px|]]|| Cell 3
|}

==Distillation Column HYSYS Simulation==
===Shortcut Distillation Column===

The shortcut distillation utility within HYSYS allows users to quickly model a distillation separation of a stream with relatively little known information. Once the user attaches a fully defined inlet stream to the shortcut distillation column, the essential information that must be specified are as follows:

* The vapor/liquid quality of the top product
* The light key component and composition in the bottoms product
* The heavy key component and composition in the distillate (top) product
* The condenser pressure
* The reboiler pressure
* The external reflux ratio

With this information, the utility will run and, if possible, converge on a solution that will meet the key component specifications. The critical information that the utility will calculate are as follows:

* Fully specified distillate product stream (temperature, pressure, flow rate, composition)
* Fully specified bottom product stream (temperature, pressure, flow rate, composition)
* Condenser operating temperature and heat duty
* Reboiler operating temperature and heat duty
* Minimum number of trays
* Actual number of trays
* Optimum feed tray location

The primary purpose of the shortcut distillation is to allow for users to perform a first pass estimate on the performance requirements of a given system for a specified reflux ratio. The values gathered from the shortcut distillation utility can be used to assist the user when setting up the complete distillation utility in HYSYS, or when attempting to find reasonable column properties to allow the system to converge (e.g. number of trays, feed location, etc.)

====Tutorial====

This example will simulate the separation of benzene, toluene and p-xylene from some upstream process.

'''Initialize'''

[[File:AddComponents.PNG|thumb|center|600px|Figure 2. Adding Components in HYSYS]]

#Start Aspen HYSYS v.8 and click “new” on the main screen to open a new simulation window.
#Once on the component list screen, select “add” near the bottom of the screen
#Search the database for the desired components using the search bar, and add them to the component list by clicking “add.” In this case, we wish to add Benzene, Toluene and p-Xylene.
#On the left hand “properties” menu, click the “fluid packages” tab and select “add” to add a new package.
#Select the desired fluid package. In this case we are using Peng-Robinson
#In the bottom, left-hand corner of the screen, click “simulation” to enter the simulation environment.

'''Setup Streams'''

[[File:Streams.PNG|thumb|center|300px|Figure 3. Add Streams]]

#Start by clicking the blue arrow at the top of the “palette” window and then clicking on the main flowsheet to produce a new material stream. This will create our feed stream. It is a good idea to place your other streams as well: one for distillate product and one for bottoms product.
#Add two energy streams that will be the condenser and reboiler duties.
#Double click on the newly created feed stream to pull up the worksheet for the stream. Please note that we are specifying this feed stream to demonstrate how the column would behaved with a fully specified inlet stream. The temperature, pressure, flow rate and composition of the feed stream can be specified by the user.

[[File:FeedConditions.PNG|thumb|center|300px|Figure 4. Define Feed]]

#We will make the following changes within this worksheet to specify the feed stream:
#Enter “feed” into the stream name.
#Set the temperature to 20 degrees C.
#Set the pressure to 1 atm. (Be sure to select the “atm” unit from the dropdown when you begin to enter this value)
#Set the mass flow to 500 kg/hr

[[File:Compositions.PNG|thumb|center|600px|Figure 5. Define Compositions]]

#On the left hand column within the worksheet, click “composition” to enter the composition tab.
#Click “edit” on the composition tab to change the composition of the feed stream
#Enter .25 to Toluene, .35 to Benzene and .40 to p-Xylene.

The worksheet should indicate that the stream is fully specified with a green “ok” indicator at the bottom. Close the worksheet.

'''Fully Specify Shortcut Column'''

[[File:ConnectStreams.PNG|thumb|center|600px|Figure 6. Connect the inlet and outlet streams]]

#Create the shortcut column by clicking on the "columns" tab within the palette and selecting "shortcut column"
#Click on the simulation environment to place the column
#The shortcut column should currently appear red to represent that it is not currently specified.
#Double click on the column to pull up the column worksheet
#Under each drop down, add the appropriate stream: E.g. Under "Distillate" add the distillate product stream that was defined earlier.
#Additionally, be sure to specify the quality of the top product stream: whether it is liquid or vapor phase. In this case, select "liquid."

[[File:Set Keys.PNG|thumb|center|600px|Figure 7. Set the key specifications]]

#On the left hand side of the worksheet, select "Parameters."
#This will move you to the parameters section of the column window where column specifications can be added.
#At this point it is important to identify which components are most volatile. In this case, benzene is most volatile, xylene is the least volatile and toluene rests in between the two. One rule of thumb is that more volatile components tend to be more valuable, and so in this example we will be purifying benzene in the distillate stream. In order to do this we will specify that benzene is the light key in the bottoms and that toluene is the heavy key in the distillate. This arrangement makes sense since it will force the heavier xylene and toluene products to drop out in the bottoms.
#Set the Light Key in Bottoms to Benzene and the mole fraction to .001 and set the Heavy Key in Distillate to Toluene and the mole fraction to .001.
#Set the condenser and reboiler pressure to the approximate values that they would be. In this case, we are assuming that our column is sufficiently small that atmospheric pressure is a fair assumption for both values. Enter 1 atm for both of these values.

[[File:Worksheet.PNG|thumb|center|600px|Figure 8. Viewing the Worksheet]]

#Finally set the reflux ratio to a value that is higher than the minimum reflux ratio that HYSYS calculates. In this case the minimum reflux ratio was calculated to be 2.119 and so it is best to input around 2.5. This value can be tweaked later to see how performance is changed for different reflux ratios.
#At this point it is worthwhile to see what outputs the column is producing, since this is one of the primary uses of the shortcut distillation column.
#Click on the "worksheet" tab at the top of the window. This will bring you to your stream information where you can view the temperatures and flow rates of your outgoing streams.
#Now click on the "compositions" tab on the left side to view the compositions of the outgoing stream. As expected, the benzene is leaving in the distillate stream at 99.9% purity with a .1% toluene impurity, while all of the xylene is leaving out in the bottoms.

[[File:Performance.PNG|thumb|center|600px|Figure 9. View the Performance Tab]]

#At this point it is valuable to record the calculated minimum number of trays, actual number of trays, as well as the condenser/reboiler temperatures.
#To view these values click on the "performance" tab
#You can observe here that the minimum number of trays calculated was around 15.7, the actual number of trays used was 35.7 the optimal feed stage was around 20.5, the condenser temperature was found to be around 80 C, while the reboiler was calculated to be around 123 C.

===Standard Distillation Column===
The standard distillation column, found under the "Columns" tab on the equipment palette, may be used to perform a more rigorous simulation of your process than that offered by the shortcut column. In addition, the shortcut column may be used as a "first pass" analysis and then these specification estimations can used as the starting point for the standard column.

====Tutorial====
In this example, we will be setting up a basic distillation column in HYSYS to simulate the separation of benzene and toluene.

# Start a new case in HYSYS by clicking on the button on the top menu bar.
# On the Components screen, add Benzene and Toluene.
# On the Fluid Package screen, you have a wide range of options with which to simulate vapor-liquid equilibrium. For this example, choose the Peng-Robinson fluid package and enter the simulation environment.

[[File:Columncomponents.PNG|thumb|right|300px|Figure 10. Component Selection in HYSYS]] [[File:Fluidpkg.PNG|thumb|right|400px|Figure 12. Fluid Package Selection in HYSYS]]

We are using the simple distillation column and thus we only need a single feed stream into the distillation column as well as a distillate stream and a bottoms stream. We will also need 2 energy streams for the condenser and reboiler.

# Add the material and energy streams to the simulation environment. Naming them appropriately will make it easer to keep everything straight as we move forward with the tutorial.
# Select the distillation column from the palette and place anywhere in the simulation environment.
# Switch to “Attach Mode” and attach the mass and energy streams to their appropriate locations on the distillation column. NOTE: You could also complete this step by double-clicking on the column itself and selecting each respective stream from the drop down menus.
# Double click on the column and select the condenser type. For this example, select “total condenser” and click next
# This next page is where the pressures of the column are specified. For this example, we will assume that the column is run at 1 atm with no pressure drops within the column. Therefore, specify reboiler pressure and condenser pressure to 101.3 kPa and the condenser pressure drop to 0 kPa.
# The next page has fields where temperature estimates can be made for the condenser, top stage, and reboiler. As these are optional fields, simply click next.
# The final screen of the distillation column setup is where the reflux ratio and distillate flow rates should be specified. For this example, specify the distillate flow rate as 1000 kgmol/hr and the reflux ratio as 1.5.
# Click “Done” at the bottom of the screen and the simulation page should be back in full view.

[[File:Simulationview.PNG|thumb|center|400px|Figure 11. Simulation View of Distillation Column in HYSYS]]

We are now ready to specify the flow rates and compositions of the streams coming in and out of the column.
# Double click on the feed stream coming into the column. A specifications page should come up.
# This page allows you specify a number of parameters pertaining to the feed stream, including temperature, pressure, and compositions. Specify the temperature as 37C and pressure as 101.3 kPa (1 atm). In addition, specify the molar flow as 3500 kgmole/h.
# Now click on the composition tab on the left side of the window. Here specify, the benzene as 70 mass % and the toluene as 30 mass %. The stream should be fully specified. Close the window to return to the simulation.

[[File:Configurationpage.PNG|thumb|center|400px|Figure 13. Column Configuration Page]]

The column and feed stream should now be fully specified. It is now time to run the simulation.
# If the solver is not already activated, click the green traffic light at the top of the simulation window.
# Now double click on the distillation column to bring up the main column window. A feed stage and total number of stages should already be specified.
# Click the “Run” button of the window to start the simulation. The small rectangle to the right of this button should light up green and say “converged” when it finds a solution.

[[File:Columncompositions.PNG|thumb|center|400px|Figure 14. Outlet compositions in HYSYS]]

===Manipulating Column Specifications===

''Information taken from Towler Chapter 17''

Parameters that directly impact the design and operation of the distillation column include:
*Reflux ratio
*Feed point location
*Column Pressure
*Number of equilibrium stages/real stages

Assuming that we have already specified a desired specification for either the distillate or bottoms stream, we can manipulate the above parameters when running our simulation within HYSYS.

'''Reflux Ratio'''

The number of stages required for separation is directly affected by the reflux ratio that can be defined as follows:

<math> R=\frac {Flow\ returned\ as\ reflux} {Flow\ of\ top\ product\ taken\ off} </math>

Increasing the reflux ratio will reduce the total number of stages required but will increase the utility costs for the column. Therefore, when simulating a distillation column, special care should be taken to strike a balance between capital and operating costs.

When starting a new distillation column simulation within HYSYS, it is a good idea to calculate a minimum reflux ratio to advise the specification of the reflux ratio. The minimum reflux ratio can be calculated through use of a McCabe-Thiele diagram. According to Towler, a reflux ratio of 1.15 times the minimum reflux ratio should be used as a first approximation. Once this ratio is inputted into the simulation environment, it can be further manipulated to fine-tune the optimum reflux ratio for the system.

'''Feed Point Location'''

The column simulation environment within HYSYS allows for manipulation of the feed point location. The general rule for designating feed point location is to have the feed enter the column at the stage which best matches the composition of the feed. There can be some uncertainty when it comes to finding the precise feed point location. Instead, a trial-and-error method may be useful when using HYSYS to determine which feed stage results in the desired distillate and bottoms conditions.

'''Column Pressure'''

When specifying the distillation column within the HYSYS simulation environment, you must specify the operating pressure as well as any pressure drops. If you are running a HYSYS simulation to get a first-pass approximation of compositions and flow rates, it is a typical practice to assume the pressure in the column is constant. If you are running a more intensive and rigorous simulation, you can approximate the pressure drop per tray using the following equation:

<math> \Delta P_{\text{tray}} = 2 \rho_L g h_w </math>

where <math> \rho_L </math> is the liquid density, g is gravitational acceleration, and <math> h_w </math> is the weir height.

Column

2015-02-28T21:30:30Z

Hpoppick: /* HYSYS Column Types */

[[File:Distillationcolumn_singlefeed.png|thumb|right|300px|Figure 1. Distillation Column]]
Authors: Scott Smith [2015] and Harry Poppick [2015] 

Stewards: Jian Gong and Fengqi You

This article highlights the use of HYSYS for simulations of chemical distillation. The two primary distillation simulation utilities are the shortcut column, which is useful for quick and cursory simulations, and the full column utility, for more involved simulations.

==HYSYS Column Types==
{| border="1" class="wikitable"
|+ The table's caption
! Column heading 1
! Column heading 2
! Column heading 3
|-
! Row heading 1
| [[File:Absorber.JPG|center|35px|]]|| Cell 3
|-
! Row heading 1
| [[File:RefluxedAbsorb.JPG|center|35px|]]|| Cell 3
|-
! Row heading 1
| [[File:ReboiledAbsorber.JPG|center|35px|]]|| Cell 3
|-
! Row heading 1
| [[File:LiquidLiquid.JPG|center|35px|]]|| Cell 3
|-
! Row heading 1
| [[File:ThreePhase.JPG|center|35px|]]|| Cell 3
|-
! Row heading 1
| [[File:DistillationColumn.JPG|center|35px|]]|| Cell 3
|-
! Row heading 1
| [[File:ShortcutDistillation.JPG|center|35px|]]|| Cell 3
|-
! Row heading 1
| [[File:ComponentSplitter.JPG|center|35px|]]|| Cell 3
|}

==Distillation Column HYSYS Simulation==
===Shortcut Distillation Column===

The shortcut distillation utility within HYSYS allows users to quickly model a distillation separation of a stream with relatively little known information. Once the user attaches a fully defined inlet stream to the shortcut distillation column, the essential information that must be specified are as follows:

* The vapor/liquid quality of the top product
* The light key component and composition in the bottoms product
* The heavy key component and composition in the distillate (top) product
* The condenser pressure
* The reboiler pressure
* The external reflux ratio

With this information, the utility will run and, if possible, converge on a solution that will meet the key component specifications. The critical information that the utility will calculate are as follows:

* Fully specified distillate product stream (temperature, pressure, flow rate, composition)
* Fully specified bottom product stream (temperature, pressure, flow rate, composition)
* Condenser operating temperature and heat duty
* Reboiler operating temperature and heat duty
* Minimum number of trays
* Actual number of trays
* Optimum feed tray location

The primary purpose of the shortcut distillation is to allow for users to perform a first pass estimate on the performance requirements of a given system for a specified reflux ratio. The values gathered from the shortcut distillation utility can be used to assist the user when setting up the complete distillation utility in HYSYS, or when attempting to find reasonable column properties to allow the system to converge (e.g. number of trays, feed location, etc.)

====Tutorial====

This example will simulate the separation of benzene, toluene and p-xylene from some upstream process.

'''Initialize'''

[[File:AddComponents.PNG|thumb|center|600px|Figure 2. Adding Components in HYSYS]]

#Start Aspen HYSYS v.8 and click “new” on the main screen to open a new simulation window.
#Once on the component list screen, select “add” near the bottom of the screen
#Search the database for the desired components using the search bar, and add them to the component list by clicking “add.” In this case, we wish to add Benzene, Toluene and p-Xylene.
#On the left hand “properties” menu, click the “fluid packages” tab and select “add” to add a new package.
#Select the desired fluid package. In this case we are using Peng-Robinson
#In the bottom, left-hand corner of the screen, click “simulation” to enter the simulation environment.

'''Setup Streams'''

[[File:Streams.PNG|thumb|center|300px|Figure 3. Add Streams]]

#Start by clicking the blue arrow at the top of the “palette” window and then clicking on the main flowsheet to produce a new material stream. This will create our feed stream. It is a good idea to place your other streams as well: one for distillate product and one for bottoms product.
#Add two energy streams that will be the condenser and reboiler duties.
#Double click on the newly created feed stream to pull up the worksheet for the stream. Please note that we are specifying this feed stream to demonstrate how the column would behaved with a fully specified inlet stream. The temperature, pressure, flow rate and composition of the feed stream can be specified by the user.

[[File:FeedConditions.PNG|thumb|center|300px|Figure 4. Define Feed]]

#We will make the following changes within this worksheet to specify the feed stream:
#Enter “feed” into the stream name.
#Set the temperature to 20 degrees C.
#Set the pressure to 1 atm. (Be sure to select the “atm” unit from the dropdown when you begin to enter this value)
#Set the mass flow to 500 kg/hr

[[File:Compositions.PNG|thumb|center|600px|Figure 5. Define Compositions]]

#On the left hand column within the worksheet, click “composition” to enter the composition tab.
#Click “edit” on the composition tab to change the composition of the feed stream
#Enter .25 to Toluene, .35 to Benzene and .40 to p-Xylene.

The worksheet should indicate that the stream is fully specified with a green “ok” indicator at the bottom. Close the worksheet.

'''Fully Specify Shortcut Column'''

[[File:ConnectStreams.PNG|thumb|center|600px|Figure 6. Connect the inlet and outlet streams]]

#Create the shortcut column by clicking on the "columns" tab within the palette and selecting "shortcut column"
#Click on the simulation environment to place the column
#The shortcut column should currently appear red to represent that it is not currently specified.
#Double click on the column to pull up the column worksheet
#Under each drop down, add the appropriate stream: E.g. Under "Distillate" add the distillate product stream that was defined earlier.
#Additionally, be sure to specify the quality of the top product stream: whether it is liquid or vapor phase. In this case, select "liquid."

[[File:Set Keys.PNG|thumb|center|600px|Figure 7. Set the key specifications]]

#On the left hand side of the worksheet, select "Parameters."
#This will move you to the parameters section of the column window where column specifications can be added.
#At this point it is important to identify which components are most volatile. In this case, benzene is most volatile, xylene is the least volatile and toluene rests in between the two. One rule of thumb is that more volatile components tend to be more valuable, and so in this example we will be purifying benzene in the distillate stream. In order to do this we will specify that benzene is the light key in the bottoms and that toluene is the heavy key in the distillate. This arrangement makes sense since it will force the heavier xylene and toluene products to drop out in the bottoms.
#Set the Light Key in Bottoms to Benzene and the mole fraction to .001 and set the Heavy Key in Distillate to Toluene and the mole fraction to .001.
#Set the condenser and reboiler pressure to the approximate values that they would be. In this case, we are assuming that our column is sufficiently small that atmospheric pressure is a fair assumption for both values. Enter 1 atm for both of these values.

[[File:Worksheet.PNG|thumb|center|600px|Figure 8. Viewing the Worksheet]]

#Finally set the reflux ratio to a value that is higher than the minimum reflux ratio that HYSYS calculates. In this case the minimum reflux ratio was calculated to be 2.119 and so it is best to input around 2.5. This value can be tweaked later to see how performance is changed for different reflux ratios.
#At this point it is worthwhile to see what outputs the column is producing, since this is one of the primary uses of the shortcut distillation column.
#Click on the "worksheet" tab at the top of the window. This will bring you to your stream information where you can view the temperatures and flow rates of your outgoing streams.
#Now click on the "compositions" tab on the left side to view the compositions of the outgoing stream. As expected, the benzene is leaving in the distillate stream at 99.9% purity with a .1% toluene impurity, while all of the xylene is leaving out in the bottoms.

[[File:Performance.PNG|thumb|center|600px|Figure 9. View the Performance Tab]]

#At this point it is valuable to record the calculated minimum number of trays, actual number of trays, as well as the condenser/reboiler temperatures.
#To view these values click on the "performance" tab
#You can observe here that the minimum number of trays calculated was around 15.7, the actual number of trays used was 35.7 the optimal feed stage was around 20.5, the condenser temperature was found to be around 80 C, while the reboiler was calculated to be around 123 C.

===Standard Distillation Column===
The standard distillation column, found under the "Columns" tab on the equipment palette, may be used to perform a more rigorous simulation of your process than that offered by the shortcut column. In addition, the shortcut column may be used as a "first pass" analysis and then these specification estimations can used as the starting point for the standard column.

====Tutorial====
In this example, we will be setting up a basic distillation column in HYSYS to simulate the separation of benzene and toluene.

# Start a new case in HYSYS by clicking on the button on the top menu bar.
# On the Components screen, add Benzene and Toluene.
# On the Fluid Package screen, you have a wide range of options with which to simulate vapor-liquid equilibrium. For this example, choose the Peng-Robinson fluid package and enter the simulation environment.

[[File:Columncomponents.PNG|thumb|right|300px|Figure 10. Component Selection in HYSYS]] [[File:Fluidpkg.PNG|thumb|right|400px|Figure 12. Fluid Package Selection in HYSYS]]

We are using the simple distillation column and thus we only need a single feed stream into the distillation column as well as a distillate stream and a bottoms stream. We will also need 2 energy streams for the condenser and reboiler.

# Add the material and energy streams to the simulation environment. Naming them appropriately will make it easer to keep everything straight as we move forward with the tutorial.
# Select the distillation column from the palette and place anywhere in the simulation environment.
# Switch to “Attach Mode” and attach the mass and energy streams to their appropriate locations on the distillation column. NOTE: You could also complete this step by double-clicking on the column itself and selecting each respective stream from the drop down menus.
# Double click on the column and select the condenser type. For this example, select “total condenser” and click next
# This next page is where the pressures of the column are specified. For this example, we will assume that the column is run at 1 atm with no pressure drops within the column. Therefore, specify reboiler pressure and condenser pressure to 101.3 kPa and the condenser pressure drop to 0 kPa.
# The next page has fields where temperature estimates can be made for the condenser, top stage, and reboiler. As these are optional fields, simply click next.
# The final screen of the distillation column setup is where the reflux ratio and distillate flow rates should be specified. For this example, specify the distillate flow rate as 1000 kgmol/hr and the reflux ratio as 1.5.
# Click “Done” at the bottom of the screen and the simulation page should be back in full view.

[[File:Simulationview.PNG|thumb|center|400px|Figure 11. Simulation View of Distillation Column in HYSYS]]

We are now ready to specify the flow rates and compositions of the streams coming in and out of the column.
# Double click on the feed stream coming into the column. A specifications page should come up.
# This page allows you specify a number of parameters pertaining to the feed stream, including temperature, pressure, and compositions. Specify the temperature as 37C and pressure as 101.3 kPa (1 atm). In addition, specify the molar flow as 3500 kgmole/h.
# Now click on the composition tab on the left side of the window. Here specify, the benzene as 70 mass % and the toluene as 30 mass %. The stream should be fully specified. Close the window to return to the simulation.

[[File:Configurationpage.PNG|thumb|center|400px|Figure 13. Column Configuration Page]]

The column and feed stream should now be fully specified. It is now time to run the simulation.
# If the solver is not already activated, click the green traffic light at the top of the simulation window.
# Now double click on the distillation column to bring up the main column window. A feed stage and total number of stages should already be specified.
# Click the “Run” button of the window to start the simulation. The small rectangle to the right of this button should light up green and say “converged” when it finds a solution.

[[File:Columncompositions.PNG|thumb|center|400px|Figure 14. Outlet compositions in HYSYS]]

===Manipulating Column Specifications===

''Information taken from Towler Chapter 17''

Parameters that directly impact the design and operation of the distillation column include:
*Reflux ratio
*Feed point location
*Column Pressure
*Number of equilibrium stages/real stages

Assuming that we have already specified a desired specification for either the distillate or bottoms stream, we can manipulate the above parameters when running our simulation within HYSYS.

'''Reflux Ratio'''

The number of stages required for separation is directly affected by the reflux ratio that can be defined as follows:

<math> R=\frac {Flow\ returned\ as\ reflux} {Flow\ of\ top\ product\ taken\ off} </math>

Increasing the reflux ratio will reduce the total number of stages required but will increase the utility costs for the column. Therefore, when simulating a distillation column, special care should be taken to strike a balance between capital and operating costs.

When starting a new distillation column simulation within HYSYS, it is a good idea to calculate a minimum reflux ratio to advise the specification of the reflux ratio. The minimum reflux ratio can be calculated through use of a McCabe-Thiele diagram. According to Towler, a reflux ratio of 1.15 times the minimum reflux ratio should be used as a first approximation. Once this ratio is inputted into the simulation environment, it can be further manipulated to fine-tune the optimum reflux ratio for the system.

'''Feed Point Location'''

The column simulation environment within HYSYS allows for manipulation of the feed point location. The general rule for designating feed point location is to have the feed enter the column at the stage which best matches the composition of the feed. There can be some uncertainty when it comes to finding the precise feed point location. Instead, a trial-and-error method may be useful when using HYSYS to determine which feed stage results in the desired distillate and bottoms conditions.

'''Column Pressure'''

When specifying the distillation column within the HYSYS simulation environment, you must specify the operating pressure as well as any pressure drops. If you are running a HYSYS simulation to get a first-pass approximation of compositions and flow rates, it is a typical practice to assume the pressure in the column is constant. If you are running a more intensive and rigorous simulation, you can approximate the pressure drop per tray using the following equation:

<math> \Delta P_{\text{tray}} = 2 \rho_L g h_w </math>

where <math> \rho_L </math> is the liquid density, g is gravitational acceleration, and <math> h_w </math> is the weir height.