Separation processes - Revision history

Jstolley: /* 4. Estimate the column diameter, based on flooding considerations. */

2016-02-23T05:58:50Z

4. Estimate the column diameter, based on flooding considerations.

← Older revision		Revision as of 05:58, 23 February 2016
Line 116:		Line 116:
	<math>u_f = K_1\sqrt{\frac{\rho_L - \rho_V}{\rho_V}}</math>		<math>u_f = K_1\sqrt{\frac{\rho_L - \rho_V}{\rho_V}}</math>

	[[File:Fig1129.jpg\|100px\|~~right~~\|frame\|Figure 4: Flooding velocity, sieve plates.]]		[[File:Fig1129.jpg\|100px\|center\|frame\|Figure 4: Flooding velocity, sieve plates.]]
	There is a range of vapor and liquid flow rates in which the column needs to be operated. Too low or too high of rates can result in various inefficiencies in the column operation, as shown in Figure 5. For example, if the vapor rate is too high, flooding will occur. However, it is not safe to operate on the flooding line. Instead, columns are typically designed for 80% of flooding at the maximum flow rate. <br />		There is a range of vapor and liquid flow rates in which the column needs to be operated. Too low or too high of rates can result in various inefficiencies in the column operation, as shown in Figure 5. For example, if the vapor rate is too high, flooding will occur. However, it is not safe to operate on the flooding line. Instead, columns are typically designed for 80% of flooding at the maximum flow rate. <br />

	Obtain a new velocity with this 80%, and use the velocity to calculate a a maximum volumetric flowrate. Using this and the velocity, we can calculate a net area necessary for vapor flow through the plate. Also need to assume a downcomer area. Now a column corss sectional area can be calculated.		Obtain a new velocity with this 80%, and use the velocity to calculate a a maximum volumetric flowrate. Using this and the velocity, we can calculate a net area necessary for vapor flow through the plate. Also need to assume a downcomer area. Now a column corss sectional area can be calculated.

	[[File:Fig1128.jpg\|400px\|~~right~~\|frame\|Figure 5: Sieve plate performance diagram.]]		[[File:Fig1128.jpg\|400px\|center\|frame\|Figure 5: Sieve plate performance diagram.]]

	=====5. Decide the liquid flow arrangement.=====		=====5. Decide the liquid flow arrangement.=====

Jstolley: /* 4. Estimate the column diameter, based on flooding considerations. */

2016-02-23T05:58:09Z

4. Estimate the column diameter, based on flooding considerations.

← Older revision		Revision as of 05:58, 23 February 2016
Line 106:		Line 106:
	<math>F_{\text{LV(bottom)}} = 0.072</math><br />		<math>F_{\text{LV(bottom)}} = 0.072</math><br />
	<math>F_{\text{LV(top)}} = 0.011</math><br />		<math>F_{\text{LV(top)}} = 0.011</math><br />

	Thus, K<sub>1_bottom</sub> = 0.90 and K<sub>1_top</sub> = 0.85 <br />		Thus, K<sub>1_bottom</sub> = 0.90 and K<sub>1_top</sub> = 0.85 <br />

Jstolley: /* 3. Select a Trial Plate Spacing */

2016-02-23T05:57:30Z

3. Select a Trial Plate Spacing

← Older revision		Revision as of 05:57, 23 February 2016
Line 99:		Line 99:
	=====3. Select a Trial Plate Spacing=====		=====3. Select a Trial Plate Spacing=====
	The plate spacing will depend on the column diameter and operating conditions. Plate spacings from 0.15 m to 1.0 m are typically used. The smaller the diameter, the smaller the spacing. Small columns will use close spacing. Columns with diameters above 1.0 m, plate spacings of 0.3 m to 0.6 m are normally used. A good initial estimate is 0.5 m.		The plate spacing will depend on the column diameter and operating conditions. Plate spacings from 0.15 m to 1.0 m are typically used. The smaller the diameter, the smaller the spacing. Small columns will use close spacing. Columns with diameters above 1.0 m, plate spacings of 0.3 m to 0.6 m are normally used. A good initial estimate is 0.5 m.
	[[File:trayspacing.jpg\|400px\|~~right~~\|frame\|Figure 3: Tray diagram.]]		[[File:trayspacing.jpg\|400px\|center\|frame\|Figure 3: Tray diagram.]]

	=====4. Estimate the column diameter, based on flooding considerations.=====		=====4. Estimate the column diameter, based on flooding considerations.=====

Jstolley: /* Sieve Tray Design Procedure */

2016-02-23T05:55:42Z

Sieve Tray Design Procedure

← Older revision		Revision as of 05:55, 23 February 2016
Line 99:		Line 99:
	=====3. Select a Trial Plate Spacing=====		=====3. Select a Trial Plate Spacing=====
	The plate spacing will depend on the column diameter and operating conditions. Plate spacings from 0.15 m to 1.0 m are typically used. The smaller the diameter, the smaller the spacing. Small columns will use close spacing. Columns with diameters above 1.0 m, plate spacings of 0.3 m to 0.6 m are normally used. A good initial estimate is 0.5 m.		The plate spacing will depend on the column diameter and operating conditions. Plate spacings from 0.15 m to 1.0 m are typically used. The smaller the diameter, the smaller the spacing. Small columns will use close spacing. Columns with diameters above 1.0 m, plate spacings of 0.3 m to 0.6 m are normally used. A good initial estimate is 0.5 m.
	[[File:trayspacing.jpg\|400px\|~~center~~\|frame\|Figure 3: Tray diagram.]]		[[File:trayspacing.jpg\|400px\|right\|frame\|Figure 3: Tray diagram.]]

	=====4. Estimate the column diameter, based on flooding considerations.=====		=====4. Estimate the column diameter, based on flooding considerations.=====
	Vapor and liquid flow rates will vary along the column, so plate design needs to be considered both above and below the feed. Using plate spacing and F<sub>LV</sub> ~~(which is the square root of the ratio of the liquid to vapor flow rates)~~, you can obtain the value of K from ~~the plot~~.		Vapor and liquid flow rates will vary along the column, so plate design needs to be considered both above and below the feed. Using plate spacing and F<sub>LV</sub>, you can obtain the value of K from Figure 4.<br />
			<math>F_{\text{LV}} = (slope_{\text{operating line}})*\sqrt{\frac{\rho_v}{\rho_L}}</math><br />
			<math>F_{\text{LV(bottom)}} = 0.072</math><br />
			<math>F_{\text{LV(top)}} = 0.011</math><br />
			Thus, K<sub>1_bottom</sub> = 0.90 and K<sub>1_top</sub> = 0.85 <br />

	[[File:Fig1129.jpg\|100px\|~~center~~\|frame\|Figure 4: Flooding velocity, sieve plates.]]		<dfn>Next, correct those values of K<sub>1</sub> for surface tensions:</dfn>
	There is a range of vapor and liquid flow rates in which the column needs to be operated. Too low or too high of rates can result in various inefficiencies in the column operation, as shown in ~~the figure below~~. For example, if the vapor rate is too high, flooding will occur. However, it is not safe to operate on the flooding line. Instead, columns are typically designed for 80% of flooding at the maximum flow rate.		<math>K_1' = K_1*(\frac{\sigma}{\sigma_{\text{water}}})^{\text{0.2}}</math><br />
	[[File:Fig1128.jpg\|400px\|~~center~~\|frame\|Figure 5: Sieve plate performance diagram.]]		<math>\sigma = {\text{surface tension}} </math><br />

			<dfn>Next, calculate u<sub>f</sub>, the vapor velocity through the net area at flooding:</dfn><br />
			<math>u_f = K_1\sqrt{\frac{\rho_L - \rho_V}{\rho_V}}</math>

			[[File:Fig1129.jpg\|100px\|right\|frame\|Figure 4: Flooding velocity, sieve plates.]]
			There is a range of vapor and liquid flow rates in which the column needs to be operated. Too low or too high of rates can result in various inefficiencies in the column operation, as shown in Figure 5. For example, if the vapor rate is too high, flooding will occur. However, it is not safe to operate on the flooding line. Instead, columns are typically designed for 80% of flooding at the maximum flow rate. <br />

			Obtain a new velocity with this 80%, and use the velocity to calculate a a maximum volumetric flowrate. Using this and the velocity, we can calculate a net area necessary for vapor flow through the plate. Also need to assume a downcomer area. Now a column corss sectional area can be calculated.

			[[File:Fig1128.jpg\|400px\|right\|frame\|Figure 5: Sieve plate performance diagram.]]

	=====5. Decide the liquid flow arrangement.=====		=====5. Decide the liquid flow arrangement.=====

Jstolley: /* Clarifiers */

2016-02-23T05:09:39Z

Clarifiers

← Older revision		Revision as of 05:09, 23 February 2016
Line 643:		Line 643:

	====Clarifiers====		====Clarifiers====
	[[File:Circular_Clarifier.png\|300px\|thumb\|bottom\|Figure 9: Circular clarifier with some components labelled.]] [[File:Rectangular_Clarifier.png\|300px\|thumb\|bottom\|Figure 10: Rectangular clarifier with some components labelled.]]		[[File:Circular_Clarifier.png\|300px\|thumb\|bottom\|Figure 30: Circular clarifier with some components labelled.]] [[File:Rectangular_Clarifier.png\|300px\|thumb\|bottom\|Figure 31: Rectangular clarifier with some components labelled.]]

	Clarifiers are one of the methods used for the continuous removal of particulate solids from liquids through sedimentation by gravity. Applications include process water pretreatment, waste water treatment, and drinking water purification. Historically, clarifiers were originally developed to limit nutrient input into surface water due to fear of eutrophication. Today, they have a number of uses, particularly in wastewater treatment processes, metal removal, disinfection, and membrane pretreatment. The process helps removed dissolved solids, silt, and undesirable metals from the water, making it more suitable for downstream processes as well as human consumption (Wilson, 2005).		Clarifiers are one of the methods used for the continuous removal of particulate solids from liquids through sedimentation by gravity. Applications include process water pretreatment, waste water treatment, and drinking water purification. Historically, clarifiers were originally developed to limit nutrient input into surface water due to fear of eutrophication. Today, they have a number of uses, particularly in wastewater treatment processes, metal removal, disinfection, and membrane pretreatment. The process helps removed dissolved solids, silt, and undesirable metals from the water, making it more suitable for downstream processes as well as human consumption (Wilson, 2005).
Line 657:		Line 657:
	where <math>E_{TSS}</math> is the efficiency of total suspended solids (TSS) removal, <math>E_{TSSmax}</math> is the maximum possible efficiency, <math>\lambda \left [\frac{m}{d} \right ]</math> is the settling constant, and <math>SOR \left [\frac{m^3}{m^2 d} \right ]</math> is the surface overflow rate. The effect of flocculation chemicals on TSS can be seen in figure 11. However, it should be noted that chemical addition will increase sludge quantity and may have an adverse effect on plant aesthetics, which increases maintenance costs (Wilson, 2005).		where <math>E_{TSS}</math> is the efficiency of total suspended solids (TSS) removal, <math>E_{TSSmax}</math> is the maximum possible efficiency, <math>\lambda \left [\frac{m}{d} \right ]</math> is the settling constant, and <math>SOR \left [\frac{m^3}{m^2 d} \right ]</math> is the surface overflow rate. The effect of flocculation chemicals on TSS can be seen in figure 11. However, it should be noted that chemical addition will increase sludge quantity and may have an adverse effect on plant aesthetics, which increases maintenance costs (Wilson, 2005).

	[[File:Chem_Addition.png\|200px\|thumb\|bottom\|Figure 11: The effect of flocculating agents on total suspended solids removal in clarifiers.]]		[[File:Chem_Addition.png\|200px\|thumb\|bottom\|Figure 32: The effect of flocculating agents on total suspended solids removal in clarifiers.]]

	=====Lamella Clarifiers=====		=====Lamella Clarifiers=====
Line 663:		Line 663:
	Lamella clarifiers use inclined plates in order to maximize the settling area for solids. Solids continue to settle into a hopper at the bottom of the tank while clarified water exits up through the inclined plates. This allows for the design of a smaller tank, which leads to large savings in capital costs. A lamella clarifier is pictured in figure 12.		Lamella clarifiers use inclined plates in order to maximize the settling area for solids. Solids continue to settle into a hopper at the bottom of the tank while clarified water exits up through the inclined plates. This allows for the design of a smaller tank, which leads to large savings in capital costs. A lamella clarifier is pictured in figure 12.

	[[File:Lamella_Clarifier.png\|300px\|thumb\|bottom\|Figure 12: A lamella clarifier with components labeled.]]		[[File:Lamella_Clarifier.png\|300px\|thumb\|bottom\|Figure 33: A lamella clarifier with components labeled.]]

	Typically, inclined plates are installed at an angle of 45 to 60 degrees and spaced 40 to 120 mm apart, which increases effective settling surface area by a factor of 6 to 12 compared to traditional clarifiers. For effective use, it is recommended that the Reynolds number be below 2000, Froude number higher than 10<sup>-5</sup>,and detention time be longer than 3 to 5 minutes. For this implementation, the equations are as follows:		Typically, inclined plates are installed at an angle of 45 to 60 degrees and spaced 40 to 120 mm apart, which increases effective settling surface area by a factor of 6 to 12 compared to traditional clarifiers. For effective use, it is recommended that the Reynolds number be below 2000, Froude number higher than 10<sup>-5</sup>,and detention time be longer than 3 to 5 minutes. For this implementation, the equations are as follows:

Jstolley: /* Cyclones */

2016-02-23T05:08:35Z

Cyclones

← Older revision		Revision as of 05:08, 23 February 2016
Line 510:		Line 510:
	Centrifugal Separators, more commonly know as Cyclones, are one of the most widely used gas-solid separators. They are typically used for particles that are 5μm or larger, but if agglomeration occurs they can sometimes separate particles as small as particles as small as .5μm. These cyclones can be designed for high efficiency separations or for high throughput (Towler, 2013).		Centrifugal Separators, more commonly know as Cyclones, are one of the most widely used gas-solid separators. They are typically used for particles that are 5μm or larger, but if agglomeration occurs they can sometimes separate particles as small as particles as small as .5μm. These cyclones can be designed for high efficiency separations or for high throughput (Towler, 2013).

	[[File:cyclone.png\|thumb\|center\|Reverse-flow Cyclone (Towler, 2013)\|500x300px]]		[[File:cyclone.png\|thumb\|center\|Figure 23. Reverse-flow Cyclone (Towler, 2013)\|500x300px]]


Line 540:		Line 540:
	The diameter of particles separated by cyclones are governed by this design equation. This equation is dependent upon the standards of the cyclone and how much you are trying to deviate from its standard operating conditions. Looking into the equation it shows that a larger internal cyclone diameter, higher flowrate, higher difference in density, and lower viscosity result in smaller particles being seperated. The whole term after d<sub>1</sub> is known as a scale up factor. When designing a cyclone you would determine the flow rate, viscosity, particle size, and density difference would be known prior to using this design equation, so this would be used to optimize the diameter of the cyclone you were designing (Towler, 2012).		The diameter of particles separated by cyclones are governed by this design equation. This equation is dependent upon the standards of the cyclone and how much you are trying to deviate from its standard operating conditions. Looking into the equation it shows that a larger internal cyclone diameter, higher flowrate, higher difference in density, and lower viscosity result in smaller particles being seperated. The whole term after d<sub>1</sub> is known as a scale up factor. When designing a cyclone you would determine the flow rate, viscosity, particle size, and density difference would be known prior to using this design equation, so this would be used to optimize the diameter of the cyclone you were designing (Towler, 2012).

	[[File:Towler 10.8.PNG\|center\|Reverse-flow Cyclone (Towler, 2013)\|500x300px]]		[[File:Towler 10.8.PNG\|center\|Figure 24. Reverse-flow Cyclone (Towler, 2013)\|500x300px]]


Line 566:		Line 566:


	[[File:Towler10.44.PNG\|\|thumb\|center\|(a) Standard Cyclone Dimensions (b) High Gas Rate Cyclone (Towler, 2013)\|500x300px]]		[[File:Towler10.44.PNG\|\|thumb\|center\|Figure 25. (a) Standard Cyclone Dimensions (b) High Gas Rate Cyclone (Towler, 2013)\|500x300px]]

	====Efficiency====		====Efficiency====
Line 572:		Line 572:


	[[File:Towler10.45.PNG\|\|thumb\|center\|Performance curves, standard conditions. (a) High-efficiency cyclone performance curves, standard conditions. (b) High gas-rate cyclone (Towler, 2013)\|600x400px]]		[[File:Towler10.45.PNG\|\|thumb\|center\|Figure 26. Performance curves, standard conditions. (a) High-efficiency cyclone performance curves, standard conditions. (b) High gas-rate cyclone (Towler, 2013)\|600x400px]]


	If you have to scale the efficiency it can be estimated by the point where a horizontal line from the efficiency of the original particle size intersects the new particle size. A demonstration is on the graph below.		If you have to scale the efficiency it can be estimated by the point where a horizontal line from the efficiency of the original particle size intersects the new particle size. A demonstration is on the graph below.

	[[File:Towler 10.46.PNG\|\|thumb\|center\|Scaled Performance Curve(Towler, 2013)\|500x300px]]		[[File:Towler 10.46.PNG\|\|thumb\|center\|Figure 27. Scaled Performance Curve(Towler, 2013)\|500x300px]]

	====Pressure Drop====		====Pressure Drop====
	One of the most important design factors in a cyclone is its pressure drop. The pressure drop occurs because entry and exit losses, kinetic energy losses, and friction losses that occur inside the cyclone. The pressure drop can be calculated using the following equation (Towler, 2013).		One of the most important design factors in a cyclone is its pressure drop. The pressure drop occurs because entry and exit losses, kinetic energy losses, and friction losses that occur inside the cyclone. The pressure drop can be calculated using the following equation (Towler, 2013).

	[[File:Towler 10.9.PNG\|center\|Reverse-flow Cyclone (Towler, 2013)\|500x300px]]		[[File:Towler 10.9.PNG\|center\|Figure 28. Reverse-flow Cyclone (Towler, 2013)\|500x300px]]

	The variables are defined as follows:		The variables are defined as follows:
Line 606:		Line 606:
	A<sub>1</sub> = area of inlet duct		A<sub>1</sub> = area of inlet duct

	[[File:Towler_10.47.PNG\|thumb\|center\|Cyclone Pressure Drop Factor (Towler, 2013)\|600x400px]]		[[File:Towler_10.47.PNG\|thumb\|center\|Figure 29. Cyclone Pressure Drop Factor (Towler, 2013)\|600x400px]]

	====Cost Estimation====		====Cost Estimation====

Jstolley: /* Membrane Separation */

2016-02-23T05:05:42Z

Membrane Separation

Jstolley: /* Affinity Separations */

2016-02-23T05:04:14Z

Affinity Separations

← Older revision		Revision as of 05:04, 23 February 2016
Line 381:		Line 381:
	Proteins can be separated from very complex and unrefined mixtures using this method because of the great specificity. Antibody-protein interactions are so specific that individual proteins can be isolated from blood samples as shown in the figure below. The main drawback of this method is simply that specific interactions between proteins and binding targets do not always exist. Antibodies exist for many proteins, but for others they must be customized or created using some sort of evolution process. This is not a trivial task and can require a significant capital investment (Hage, 1999).		Proteins can be separated from very complex and unrefined mixtures using this method because of the great specificity. Antibody-protein interactions are so specific that individual proteins can be isolated from blood samples as shown in the figure below. The main drawback of this method is simply that specific interactions between proteins and binding targets do not always exist. Antibodies exist for many proteins, but for others they must be customized or created using some sort of evolution process. This is not a trivial task and can require a significant capital investment (Hage, 1999).

	[[File:Affinity_Chromatography_Example.PNG\|frame\|center\|Fig. 9: Affinity purification separating fibrinogen from human plasma using an anti-fibrinogen antibody (Hage, 1999).]]		[[File:Affinity_Chromatography_Example.PNG\|frame\|center\|Fig. 17: Affinity purification separating fibrinogen from human plasma using an anti-fibrinogen antibody (Hage, 1999).]]


Line 389:		Line 389:


	[[File:HisTagPurification.PNG\|frame\|center\|Fig. 10: Protein gel demonstrating the separation of proteins from a sample. The far left column represents the most efficient separating conditions using cobalt and the far right column represents a negative control with no purification performed (HisPur Cobalt Resin - Thermo Fisher Scientific, 2016).]]		[[File:HisTagPurification.PNG\|frame\|center\|Fig. 18: Protein gel demonstrating the separation of proteins from a sample. The far left column represents the most efficient separating conditions using cobalt and the far right column represents a negative control with no purification performed (HisPur Cobalt Resin - Thermo Fisher Scientific, 2016).]]


Line 439:		Line 439:
	\|}		\|}

	Unfortunately, based on the contents of the solution, the characteristics of the protein, and the specific product being used, there are extremely large amounts of variation in yield and purity for each type of tag. Therefore, it is crucial to allocate time towards preliminary tests and scale-up experiments with the exact solution from which the protein of interest is being separated. The his tag is typically the most used because, as seen in the table above, it has one of the lowest costs and highest yields. In addition, because it is only a 6 amino acids, it often is not cleaved from the protein of interest which minimizes the number of steps required in the overall purification process (Lichty et al., 2005).		Unfortunately, based on the contents of the solution, the characteristics of the protein, and the specific product being used, there are extremely large amounts of variation in yield and purity for each type of tag. Therefore, it is crucial to allocate time towards preliminary tests and scale-up experiments with the exact solution from which the protein of interest is being separated. The his tag is typically the most used because, as seen in the table above, it has one of the lowest costs and highest yields. In addition, because it is only a 6 amino acids, it often is not cleaved from the protein of interest which minimizes the number of steps required in the overall purification process (Lichty et al., 2005).

	==== Crystallization ====		==== Crystallization ====

Jstolley: /* Ion Exchange Chromatography */

2016-02-23T05:03:05Z

Ion Exchange Chromatography

← Older revision		Revision as of 05:03, 23 February 2016
Line 366:		Line 366:


	There are two main types of ion exchange columns—anion and cation. Anion exchange resins have a positive charge and are used to retain products with a negative charge. Cation exchange resins have a negative charge and are used to retain products with a positive charge. The pH of the elution buffer is change to force a specific solute to wash out, depending on whether the pH of the buffer is above or below the isoelectric point of the solute (Belter et al., 1998). This is especially useful for the separation of protein product (including antibodies), nucleic acids, and other charged molecules. When the solutes have sufficiently different isoelectric points, the pH of the buffer is manipulated to affect the solute charge and force the product to elute while the solute remains preferentially bound to the resin, or vice versa (Harrison et al., 2003). In general, the most strongly charged molecules will remain in the column for a longer period of time. Elution washes through the weakly bound ions before the more strongly bound ions. Different speeds of elution can be visualized as in figure 8.		There are two main types of ion exchange columns—anion and cation. Anion exchange resins have a positive charge and are used to retain products with a negative charge. Cation exchange resins have a negative charge and are used to retain products with a positive charge. The pH of the elution buffer is change to force a specific solute to wash out, depending on whether the pH of the buffer is above or below the isoelectric point of the solute (Belter et al., 1998). This is especially useful for the separation of protein product (including antibodies), nucleic acids, and other charged molecules. When the solutes have sufficiently different isoelectric points, the pH of the buffer is manipulated to affect the solute charge and force the product to elute while the solute remains preferentially bound to the resin, or vice versa (Harrison et al., 2003). In general, the most strongly charged molecules will remain in the column for a longer period of time. Elution washes through the weakly bound ions before the more strongly bound ions. Different speeds of elution can be visualized as in figure 16.


	[[File:chromatography.png\|frame\|center\|Fig. 8: Illustration of product bands in an elution chromatography column (Belter et al., 1998).]]		[[File:chromatography.png\|frame\|center\|Fig. 16: Illustration of product bands in an elution chromatography column (Belter et al., 1998).]]


	==== Size Exclusion Chromatography ====		==== Size Exclusion Chromatography ====

Jstolley: /* Centrifugation */

2016-02-23T05:02:22Z

Centrifugation

← Older revision		Revision as of 05:02, 23 February 2016
Line 325:		Line 325:

	====Centrifugation====		====Centrifugation====
	Centrifuges are widely utilized across many processes, and thus a wide variety of scales and designs have been developed. <i> Disk-stack centrifuges</i>, in which the solid phase is deposited onto “shelves” in the center of the spinner and liquid phase is pushed to the outside, are some of the most commonly used centrifuges in industry. They are especially suited to biomass separation processes because they can be built on a large scale and are ideal for separating fine solids from liquids. [[File: Disk_stack_centrifuge_towler.png\|frame\|center\|Fig. 6: Diagram of a disk-stack centrifuge (Tolwer et al, 1997).]] <i>Tubular bowl centrifuges</i> are also common and can reach separation efficiencies of up to 90%. Heavier products accumulate along the sides of the bowl, while the light phase flows out the top. They separate products by can be used both to separate solids from liquids and immiscible liquids, such as and oil product and an aqueous broth (Tolwer and Sinnott, 2013). [[File: tubular bowl centrifuge towler.png\|frame\|center\|Fig. 7: Diagram of a tubular bowl centrifuge centrifuge (Tolwer and Sinnott, 2013).]]		Centrifuges are widely utilized across many processes, and thus a wide variety of scales and designs have been developed. <i> Disk-stack centrifuges</i>, in which the solid phase is deposited onto “shelves” in the center of the spinner and liquid phase is pushed to the outside, are some of the most commonly used centrifuges in industry. They are especially suited to biomass separation processes because they can be built on a large scale and are ideal for separating fine solids from liquids. [[File: Disk_stack_centrifuge_towler.png\|frame\|center\|Fig. 14: Diagram of a disk-stack centrifuge (Tolwer et al, 1997).]] <i>Tubular bowl centrifuges</i> are also common and can reach separation efficiencies of up to 90%. Heavier products accumulate along the sides of the bowl, while the light phase flows out the top. They separate products by can be used both to separate solids from liquids and immiscible liquids, such as and oil product and an aqueous broth (Tolwer and Sinnott, 2013). [[File: tubular bowl centrifuge towler.png\|frame\|center\|Fig. 15: Diagram of a tubular bowl centrifuge centrifuge (Tolwer and Sinnott, 2013).]]

	Centrifugation scale-up is made easier by <i>sigma analysis</i>, which allows for the estimation of appropriate feed rates for different size centrifuges. The sigma factor is dependent on the inner and outer radius of the centrifuge, the angular velocity, and the sedimentation velocity of the solid particles being separated. It can be thought of as the characteristic cross-sectional area with units of [length]<sup>2</sup>. The sedimentation velocity can be calculated by		Centrifugation scale-up is made easier by <i>sigma analysis</i>, which allows for the estimation of appropriate feed rates for different size centrifuges. The sigma factor is dependent on the inner and outer radius of the centrifuge, the angular velocity, and the sedimentation velocity of the solid particles being separated. It can be thought of as the characteristic cross-sectional area with units of [length]<sup>2</sup>. The sedimentation velocity can be calculated by

← Older revision		Revision as of 05:05, 23 February 2016
Line 448:		Line 448:
	Membrane separation takes advantage of the selective permeability of membranes; they allow certain particles to pass through and selectively stop other, generally unwanted, particles. The component that passes through is called the permeate and the component stream that is rejected is called the retentate or concentrate. The applicability of membranes comes from the fact that their selectivity is determined by their pore size, which can be controlled during the creation of the membranes. Additionally, Membrane processes do not require heat meaning they generally require less energy than conventional separations technology such as distillation and crystallization. Membrane separations processes are generally classified as microfiltration, ultrafiltration, or nanofiltration depending on the size of the particles to be filtered out.		Membrane separation takes advantage of the selective permeability of membranes; they allow certain particles to pass through and selectively stop other, generally unwanted, particles. The component that passes through is called the permeate and the component stream that is rejected is called the retentate or concentrate. The applicability of membranes comes from the fact that their selectivity is determined by their pore size, which can be controlled during the creation of the membranes. Additionally, Membrane processes do not require heat meaning they generally require less energy than conventional separations technology such as distillation and crystallization. Membrane separations processes are generally classified as microfiltration, ultrafiltration, or nanofiltration depending on the size of the particles to be filtered out.

	[[File:membrane techs.png\|frame\|center\|Figure. Cutoffs for different membrane categories]]		[[File:membrane techs.png\|frame\|center\|Figure 19. Cutoffs for different membrane categories]]

	===Membrane Selection, Construction, and Flow Geometries===		===Membrane Selection, Construction, and Flow Geometries===
Line 455:		Line 455:
	The two most commonly utilized membrane configurations are hollow fiber and spiral wound. Hollow fiber is generally the most commonly utilized module for gas separations. These are formed by gluing the two ends of the hollow fiber to a resin forming a closure. The fibers are housed in a shell much like a heat exchanger. The feed flows past thousands of tubes with the permeate flowing into the hollow tubes and out the closure. The retentate then flows out of the shell not having gotten through the membrane.		The two most commonly utilized membrane configurations are hollow fiber and spiral wound. Hollow fiber is generally the most commonly utilized module for gas separations. These are formed by gluing the two ends of the hollow fiber to a resin forming a closure. The fibers are housed in a shell much like a heat exchanger. The feed flows past thousands of tubes with the permeate flowing into the hollow tubes and out the closure. The retentate then flows out of the shell not having gotten through the membrane.

	[[File:hollow membrane.jpg\|frame\|Figure. Hollow fiber membrane module]]		[[File:hollow membrane.jpg\|frame\|Figure 20. Hollow fiber membrane module]]

	Spiral wound membranes are created by sealing two membrane sheets back to back on three edges to form a sort of pocket. This fourth open edge is then attached to a porous tube which allows permeate to go through it. Several membrane pockets are attached to a single tube and wrapped around in a spiral.		Spiral wound membranes are created by sealing two membrane sheets back to back on three edges to form a sort of pocket. This fourth open edge is then attached to a porous tube which allows permeate to go through it. Several membrane pockets are attached to a single tube and wrapped around in a spiral.

	[[File:spiral membrane.jpg\|frame\|Figure. Spiral wound membrane module]]		[[File:spiral membrane.jpg\|frame\|Figure 21. Spiral wound membrane module]]

	Flow geometry is usually either dead-end geometry or cross flow geometry. In dead end, the fluid flow is normal to the membrane surface while cross flow is parallel to the membrane surface. Dead end geometry is usually used with hollow fiber membranes while cross flow is used with spiral wound membranes. Each geometry has advantages and disadvantages. Dead end geometry is generally cheaper to set up and therefore has lower initial capital costs. However, it is very vulnerable to membrane fouling, which reduces the effectiveness of the membrane. This is usually the geometry set up for small scale lab experiments. The tangential flow devices are more cost and labor-intensive, but they are less susceptible to fouling due to the sweeping effects and high shear rates of the passing flow. Most commercial industrial membrane separations are done using spiral wound cross flow membrane modules.		Flow geometry is usually either dead-end geometry or cross flow geometry. In dead end, the fluid flow is normal to the membrane surface while cross flow is parallel to the membrane surface. Dead end geometry is usually used with hollow fiber membranes while cross flow is used with spiral wound membranes. Each geometry has advantages and disadvantages. Dead end geometry is generally cheaper to set up and therefore has lower initial capital costs. However, it is very vulnerable to membrane fouling, which reduces the effectiveness of the membrane. This is usually the geometry set up for small scale lab experiments. The tangential flow devices are more cost and labor-intensive, but they are less susceptible to fouling due to the sweeping effects and high shear rates of the passing flow. Most commercial industrial membrane separations are done using spiral wound cross flow membrane modules.
Line 465:		Line 465:
	The first big breakthrough for membrane technology was the creation of the asymmetric membrane. In this type of membrane, there is a very thin dense polymer portion of the membrane that is cross linked with less dense, spongier, support polymer. The dense part of the membrane does most of the filtering while the spongy section provides structural support ensuring the membrane will not break. This allows the dense portion to be thinner which increases overall flux through the membrane. The early asymmetric membranes were made with all the same polymer. State of the art membranes are called thin film composite membranes. They are essentially asymmetric membranes were the dense thin portion is made from a different polymer than the spongy support. This enables the best support polymer to be paired with the best filtering polymer allowing for much more effective membranes. Current thin film composite membranes are usually made with a polyamide thin film layer supported by polysulfone.		The first big breakthrough for membrane technology was the creation of the asymmetric membrane. In this type of membrane, there is a very thin dense polymer portion of the membrane that is cross linked with less dense, spongier, support polymer. The dense part of the membrane does most of the filtering while the spongy section provides structural support ensuring the membrane will not break. This allows the dense portion to be thinner which increases overall flux through the membrane. The early asymmetric membranes were made with all the same polymer. State of the art membranes are called thin film composite membranes. They are essentially asymmetric membranes were the dense thin portion is made from a different polymer than the spongy support. This enables the best support polymer to be paired with the best filtering polymer allowing for much more effective membranes. Current thin film composite membranes are usually made with a polyamide thin film layer supported by polysulfone.

	[[File:Asymmetric_membrane.PNG\|frame\|Figure. Asymmetric membrane structure]]		[[File:Asymmetric_membrane.PNG\|frame\|Figure 22. Asymmetric membrane structure]]

	===Designing a Membrane System===		===Designing a Membrane System===