Recovery tower

Abstract

The invention relates to a recovery column. A method of separating acrylonitrile from a mixture of acrylonitrile and acetonitrile includes providing the mixture of acrylonitrile and acetonitrile to a recovery column; contacting the mixture of acrylonitrile and acetonitrile with an aqueous solvent to provide an acrylonitrile-water azeotrope; and separating the acrylonitrile-water azeotrope from acetonitrile to provide an overhead stream comprising the acrylonitrile-water azeotrope and about 0.05 wt% or less acetonitrile, a bottom stream comprising about 0 to about 0.0075 wt% acetonitrile, and a side stream comprising about 5 to about 70 wt% acetonitrile.

Description

This application is a divisional application of the invention patent application with the application date of December 17, 2015, application number 201510947392.7, and invention name “Recovery Tower”.

[0001] A method for separating acrylonitrile from a mixture of acrylonitrile and acetonitrile is provided. More specifically, the method comprises contacting the mixture with a water-containing solvent to provide an acrylonitrile-water azeotrope and separating the acrylonitrile-water azeotrope from the acetonitrile. background Recovery and purification systems for acrylonitrile are known, see, for example, U.S. Pat. Nos. 4,234,510; 3,936,360; 3,885,928; 3,433,822; and 3,399,120. Typically, propylene, ammonia, and air are reacted in the vapor phase with an ammoxidation catalyst. The vaporous reactor effluent is then passed to a quench system, wherein the reactor effluent is directly contacted with an aqueous quench liquid, typically water. The quench removes unreacted ammonia and heavy polymers. The quench gas then travels to an absorber.

[0002] In the absorber, the gas is directly contacted with the absorption liquid (also usually water). Water, acrylonitrile, acetonitrile, HCN and related impurities are left in the aqueous solution at the bottom of the absorber. Inert gas is removed from the top of the absorber. The aqueous solution then travels to a recovery tower. The tower removes acetonitrile from the aqueous solution by extractive distillation.

[0003] Overview A method for separating acrylonitrile from a mixture of acrylonitrile and acetonitrile, comprising providing the mixture of acrylonitrile and acetonitrile to a recovery tower; contacting the mixture of acrylonitrile and acetonitrile with a water-containing solvent to provide an acrylonitrile-water azeotrope; and separating the acrylonitrile-water azeotrope from the acetonitrile to provide an overhead stream comprising the acrylonitrile-water azeotrope and about 0.05 weight percent or less of acetonitrile.

[0004] In another aspect, a method of separating acrylonitrile from a mixture of acrylonitrile and acetonitrile comprises providing the mixture of acrylonitrile and acetonitrile to a recovery column; contacting the mixture of acrylonitrile and acetonitrile with an aqueous solvent to provide an acrylonitrile-water azeotrope; and providing a bottom stream comprising about 0 to about 0.0075 weight percent acetonitrile, and a side stream comprising about 5 to about 70 weight percent acetonitrile.

[0005] In another aspect, a method for separating acrylonitrile from a mixture of acrylonitrile and acetonitrile comprises providing the mixture of acrylonitrile and acetonitrile to a recovery tower having a plurality of trays, wherein the plurality of trays comprises a top section of the trays, a middle section of the trays, and a bottom section of the trays; providing an aqueous solvent to the top section of the trays; contacting the mixture of acrylonitrile and acetonitrile with the aqueous solvent to provide an acrylonitrile-water azeotrope; and separating the acrylonitrile-water azeotrope from the acetonitrile to provide an overhead stream comprising the acrylonitrile-water azeotrope and about 0.05 wt % or less of acetonitrile.

[0006] In another aspect, a method for separating acrylonitrile from a mixture of acrylonitrile and acetonitrile comprises providing the mixture of acrylonitrile and acetonitrile to a recovery column having a plurality of trays, wherein the plurality of trays comprises a top section of trays, a middle section of trays, and a bottom section of trays; providing an aqueous solvent to the top of the trays; contacting the mixture of acrylonitrile and acetonitrile with the aqueous solvent to provide an acrylonitrile-water azeotrope; and providing a bottom stream comprising about 0 to about 0.0075 weight percent acetonitrile, and a side stream comprising about 5 to about 70 weight percent acetonitrile.

[0007] In another aspect, a method for separating acrylonitrile from a mixture of acrylonitrile and acetonitrile comprises providing the mixture of acrylonitrile and acetonitrile to a recovery tower and contacting the mixture of acrylonitrile and acetonitrile with a water-containing solvent to provide an acrylonitrile-water azeotrope; maintaining a temperature of about 55 to about 80° C. at a top portion of a top section of the recovery tower; maintaining a temperature of about 65 to about 85° C. at a top portion of a middle section of the recovery tower and maintaining a temperature of about 100 to about 120° C. at a bottom portion of the middle section of the recovery tower; maintaining a temperature of about 105 to about 125° C. at a bottom portion of a bottom section of the recovery tower; and separating the acrylonitrile-water azeotrope from the acetonitrile to provide an overhead stream, a bottoms stream, and a side stream comprising the acrylonitrile-water azeotrope.

[0008] In another aspect, a method of operating a recovery column includes providing a temperature of about 100 to about 105° C. to a control plate in the recovery column and then introducing a feed stream into the recovery column.

[0009] In another aspect, a method of operating a recovery column includes providing a temperature of about 100° C. or less in a top section of the recovery column and then introducing a feed stream into the recovery column.

[0010] In another aspect, a method of operating a recovery column includes providing a temperature of about 100 to about 105° C. to a control plate of the recovery column and then introducing a mixture of acrylonitrile and acetonitrile into the recovery column; providing the mixture of acrylonitrile and acetonitrile to the recovery column and contacting the mixture of acrylonitrile and acetonitrile with an aqueous solvent to provide an acrylonitrile-water azeotrope; maintaining a temperature of about 55 to about 80° C. at a top portion of a top section of the recovery column; maintaining a temperature of about 65 to about 85° C. at a top portion of a middle section of the recovery column, and maintaining a temperature of about 100 to about 120° C. at a bottom portion of the middle section of the recovery column; maintaining a temperature of about 105 to about 125° C. at a bottom portion of a bottom section of the recovery column; and separating the acrylonitrile-water azeotrope from the acetonitrile to provide an overhead stream, a bottom stream, and a side stream comprising the acrylonitrile-water azeotrope. BRIEF DESCRIPTION OF THE DRAWINGS The above and other aspects, features and advantages of the method will become more apparent from the following drawings.

[0011] Figure 1 An overall view of the recovery tower is provided.

[0012] Figure 2 Another view of the recovery tower is illustrated.

[0013] Figure 3 A recovery column including an acetonitrile concentration zone is illustrated; and Figure 4 The recovery tower temperature distribution is illustrated.

[0014] Throughout the several views of the drawings, corresponding reference numerals indicate corresponding components. It will be appreciated by those skilled in the art that the elements in the drawings are illustrated for simplicity and clarity, and need not be depicted to scale. For example, the dimensions of some elements in the drawings may be exaggerated relative to other elements to help improve understanding of the various aspects. In addition, common but well-understood elements that are useful or necessary in commercially feasible aspects are generally not depicted to facilitate a more unimpeded viewing of these various aspects.

[0015] Details The following description should not be taken in a limiting sense, but is merely made for the purpose of illustrating the general principles of exemplary embodiments. The scope of the present invention should be defined with reference to the claims.

[0016] Recovery tower Any type of recovery column may be used in conjunction with the present method.Several types of recovery column configurations are described herein as examples.

[0017] The conventional method for separating acrylonitrile from acetonitrile is shown in Figure 1 In. Figure 1As shown, feed stream 1 is sent to the first tower 10 from an acrylonitrile absorber (not shown). Feed stream 1 generally contains acrylonitrile, hydrogen cyanide (HCN), acetonitrile and water. A water stream 2 substantially free of acetonitrile is recycled from the bottom or vicinity of the second tower 20 to the upper portion of the first tower 10 to facilitate separation of acetonitrile from acrylonitrile and HCN by extractive distillation. A stream 3 comprising acrylonitrile, HCN and a portion of water from feed 1 is removed from the top of the first tower 10. A liquid stream 4 comprising water and acetonitrile is sent to the second tower 20 from the bottom of the first tower 10 as a feed. A vapor stream 5 is sent to the first tower 10 from the second tower 20 to provide the heat required for distillation in the first tower 10. A vapor side stream 4v moves upward to the second tower 20 and includes acetonitrile. A crude acetonitrile stream 6 comprising acetonitrile, water and a small amount of acrylonitrile and HCN is removed from the top of the second tower 20. The remaining water stream 7 is substantially free of acrylonitrile, HCN and acetonitrile and is not recycled back to the first column 10 as water stream 2, which exits the second column 20 at or near the bottom thereof.

[0018] Another conventional method for separating acrylonitrile from crude acetonitrile is shown in Figure 2 In. Figure 2 As shown, feed stream 101 is sent from an acrylonitrile absorber (not shown) to tower 110. Feed stream 101 typically contains acrylonitrile, hydrogen cyanide (HCN), acetonitrile, and water. A bottom stream 102 substantially free of acetonitrile is recycled from the bottom or near the top of tower 110 to the top of tower 110 to facilitate separation of acetonitrile from acrylonitrile and HCN by extractive distillation. The portion of bottom stream 102 that is not recycled to the top of tower 110 is discharged from tower 110 as stream 107. A top stream 103 comprising acrylonitrile, HCN, and a portion of water from feed stream 101 is removed from the top of tower 110. A vapor side stream 5v moves upward to tower 110 and a side stream 104 (corresponding to Figure 1 4v) is removed from column 110.

[0019] Another example of a recovery tower is shown in Figure 3In this regard, the apparatus 300 includes a tower 310. The tower 310 includes a top section 330, a middle section 340, and a bottom section 350. The middle section 340 of the single tower 310 can be configured to receive a feed stream 301. In one aspect, the tower includes a top section and a middle section, and the ratio of the diameter of the middle section to the top section is about 0.8 to about 1.2, in another aspect, about 0.9 to about 1.1, in another aspect, about 1.5 to about 2.5, in another aspect, about 1.75 to about 2.25, and in another aspect, about 1.8 to about 2. In one aspect, the column comprises a middle section and a bottom section, and the ratio of the diameter of the bottom section to the middle section is from about 0.8 to about 1.2, in another aspect, from about 0.9 to about 1.1, in another aspect, from about 1.5 to about 2.5, in another aspect, from about 1.75 to about 2.25, and in another aspect, from about 1.8 to about 2. In one aspect, the column comprises a top section and a bottom section, and the ratio of the diameter of the bottom section to the top section is from about 0.8 to about 1.2, in another aspect, from about 0.9 to about 1.1, in another aspect, from about 1.5 to about 2.5, in another aspect, from about 1.75 to about 2.25, and in another aspect, from about 1.8 to about 2. In one aspect, the top section, the middle section, and the bottom section are each about 25 to about 40% of the height of the recovery column (tangent to tangent).

[0020] like Figure 3 As shown, the overhead stream 303 comprising acrylonitrile, HCN and water is removed from the top of tower 310. Recovery tower may include a crude acetonitrile concentration region 342. Crude acetonitrile concentration region 342 includes an internal vertical baffle 344. Crude acetonitrile concentration region may include a plurality of trays. The trays are located at different heights of the tower, and each tray includes a horizontal plane extending across crude acetonitrile concentration region 342 cross sections. Crude acetonitrile region 342 includes an upper outlet, which is configured to allow side stream 306 to flow out of the crude acetonitrile concentration region 342 of tower 310. Steam may flow upward as stream 304 or vapor stream 5v along either side of baffle 344. The part that is not recycled to the top of tower 310 in bottom stream 302 is discharged as stream 307.

[0021] The recovery tower may include a top section, a middle section and a bottom section. In one aspect, the top section, the middle section and the bottom section are each about 25-about 40% (tangent: tangent) of the recovery tower height. Each recovery tower part can be further divided into a plurality of parts. For example, the middle section of the recovery tower includes a top portion, a middle portion and a bottom portion. In this regard, the top portion, the middle portion and the bottom portion are each about 25-about 40% of the height of the recovery tower middle section. On the other hand, the top section of the recovery tower includes a top portion and a bottom portion, each of which is about 40-about 60% of the height of the recovery tower top section. On the other hand, the bottom section of the recovery tower includes a top portion and a bottom portion, each of which is about 40-about 60% of the height of the recovery tower bottom section.

[0022] In another aspect, the recovery column can include from about 80 to about 120 trays, and in another aspect, from about 80 to about 100 trays. The plurality of trays in the recovery column includes a top section of trays, a middle section of trays, and a bottom section of trays. In this aspect, the top section of trays, the middle section of trays, and the bottom section of trays are each about 25 to about 40% of the total number of trays in the recovery column.

[0023] The top section of the tower plate of the recovery tower includes the top part of the tower plate and the bottom part of the tower plate, each of which is about 40-about 60% of the total number of tower plates in the top section of the tower plate of the recovery tower. The middle section of the tower plate includes the top part of the tower plate, the middle part of the tower plate and the bottom part of the tower plate. The top part of the tower plate, the middle part of the tower plate and the bottom part of the tower plate are each about 25-about 40% of the total number of tower plates in the middle section of the tower plate of the recovery tower. The bottom section of the tower plate of the recovery tower includes the top part of the tower plate and the bottom part of the tower plate, each of which is about 40-about 60% of the total number of tower plates in the bottom section of the tower plate of the recovery tower.

[0024] Recovery Tower Operation The feed stream provided to the recovery column typically contains acrylonitrile, hydrogen cyanide (HCN), acetonitrile and water (in Figure 1 In the figure, the feed stream 1 is shown. Figure 2 is shown as feed stream 101, and in Figure 3 301). In this regard, the feed stream provided to the recovery tower includes about 2 to about 10 weight % acrylonitrile, in another aspect, about 3 to about 7 weight %, and in another aspect, about 4 to about 6 weight % acrylonitrile. The mixture also includes acetonitrile in an amount of about 0.1 to about 0.3 weight % acetonitrile, and in another aspect, about 0.15 to about 0.25 weight % acetonitrile. The mixture may also include other ingredients, for example, lesser amounts of acrolein and / or oxazole.

[0025] The solvent water enters the recovery tower at the top of the tower ( Figure 1 It is shown as water flow 2 in Figure 2 The water flow 102 and Figure 3 302 in FIG. 30). The solvent water introduced into the top of the recovery tower flows downward along the tower across the tray, condenses and extracts acetonitrile when it moves to the bottom of the recovery tower. When the liquid descends across the tray in the recovery tower to the bottom of the tower, the hot steam from the stripper and the heat increased from the fresh steam move upward along the tower through the tray holes, making close contact with the liquid thereon. Heat transfer occurs between the liquid and the steam transport and tends to move all organic matter (except acetonitrile) upward to the top of the tower.

[0026] Through the recovery tower (in Figure 1 It is shown as stream 3 in Figure 2 103 in the Figure 3 The overhead stream produced by the recovery column (shown as stream 303 in FIG. 1 ) may include acrylonitrile, HCN and a portion of the water from the feed stream. The recovery column may provide a vapor side stream comprising water and acetonitrile, which is substantially free of acrylonitrile and HCN (at Figure 2 is shown as flow 104, and in Figure 3 The recovery column may also provide a bottoms stream (shown as stream 304 in FIG. Figure 1 The bottom stream 2 is shown in Figure 2 is shown as bottom flow 102, and in Figure 3 The bottom stream 302 is shown in the figure as bottom stream 302, which leaves the bottom portion of the recovery column. At least a portion of the bottom stream can be recycled back to the top portion of the recovery column. Known methods for heating the recovery column include, for example, steam, steam heated reboilers and / or heat exchange with other process streams.

[0027] Temperature control Figure 4 The temperature profile of the recovery tower operation is described. Figure 4 Proper temperature control and temperature profile as described in are important for proper column operation. Changes in temperature profile, such as Figure 4 The dashed line in the middle can be affected by a combination of changes including solvent water and feed temperature, solvent water rate, and steam rate. Column pressure can also change the profile.

[0028] The changes above point "A" on the curve are mainly due to changes in composition and pressure. The temperature changes above point "A" are not critical, but the top temperature should be kept as low as possible to minimize the amount of oxazole, acetonitrile, acetone and water going to the top of the column. The temperature changes below point "B" are mainly due to changes in pressure of the column plate, because the composition in this section is mostly water.

[0029] The temperature control of the recovery tower includes a known temperature control system, which may include a reboiler and a heat exchanger. In one aspect, the heat load required for the necessary boiling at the bottom of the recovery tower can be provided by heat transfer in any conventional reboiler. Conventional reboilers may include some variants of shell-and-tube heat exchangers. Some examples of reboiler configurations include kettles, thermosyphons, pressure loops, bundled heating rods, horizontal, vertical and descending films. In one aspect, the method includes controlling the temperature by removing liquid at or near the bottom of the recovery tower and exchanging liquid in a thermosyphon reboiler. In this regard, the effluent from the thermosyphon reboiler is returned to the recovery tower. Fresh steam can be injected to supplement or replace the heat load required for the recovery tower. On the other hand, the method includes reboiling the recovery tower using pressurized steam derived from turbine exhaust by two parallel vertical thermosyphon reboilers.

[0030] In one aspect, the recovery column temperature is maintained as follows: The top portion of the middle section of the recovery column is maintained at a temperature of about 65 to about 85°C, and in another aspect, about 70 to about 80°C; The bottom portion of the middle section of the recovery column is maintained at about 100 to about 120° C., and in another aspect, about 105 to about 115° C.; The top portion of the top section of the recovery column is maintained at about 55 to about 80° C., and in another aspect, about 60 to about 75° C.; The top portion and the bottom portion of the top section of the recovery column have a temperature difference of about 0 to about 20°C, and in another aspect, about 5 to about 15°C; The bottom portion of the bottom section of the recovery column is maintained at about 105 to about 125°C, and in another aspect, about 110 to about 120°C; and The top portion and the bottom portion of the bottom section of the recovery column have a temperature difference of about 0 to about 15°C, and in another aspect, about 7 to about 13°C.

[0031] On the other hand, the recovery column temperature is maintained as follows: The top portion of the trays of the middle section of the recovery column is maintained at a temperature of about 65 to about 85°C, and in another aspect, about 70 to about 80°C; The bottom portion of the trays of the middle section of the recovery column is maintained at about 100 to about 120° C., and in another aspect, about 105 to about 115° C.; The top portion of the trays of the top section of the recovery column is maintained at about 55 to about 80° C., and in another aspect, about 60 to about 75° C.; The top portion of the tray and the bottom portion of the tray of the top section of the recovery column have a temperature difference of about 0 to about 20°C, and in another aspect, about 5 to about 15°C; The bottom portion of the trays of the bottom section of the recovery column is maintained at about 105 to about 125° C., and in another aspect, about 110 to about 120° C.; and The top portion of the tray and the bottom portion of the tray of the bottom section of the recovery column have a temperature difference of about 0 to about 15°C, and in another aspect, about 7 to about 13°C.

[0032] On the other hand, the temperature of the middle section of the recovery column is controlled as follows: In one aspect, the temperature drop in the middle section of the recovery column is about 35% or greater of the temperature drop between the top tray and the bottom tray of the recovery column; In another aspect, the temperature drop in the middle section of the recovery column is about 50% or greater of the temperature drop between the top tray and the bottom tray of the recovery column; In another aspect, the temperature drop in the middle section of the recovery column is about 75% or greater of the temperature drop between the top tray and the bottom tray of the recovery column; In another aspect, the temperature drop in the middle section of the recovery column is about 75% of the temperature drop between the top tray and the bottom tray of the recovery column; and In another aspect, the temperature drop in the middle section of the recovery column is about 80% of the temperature drop between the top tray and the bottom tray of the recovery column.

[0033] Temperature control of the recovery column provides an overhead stream, a bottoms stream, and a side stream having the following composition: an overhead stream comprising an acrylonitrile-water azeotrope and about 0.05 wt % or less of acetonitrile, in another aspect, about 0.03 wt % or less of acetonitrile, and in another aspect, about 0.01 wt % or less of acetonitrile; an overhead stream comprising from about 70 weight percent to about 90 weight percent acrylonitrile, and in another aspect, from about 75 to about 85 weight percent acrylonitrile; a bottoms stream comprising from about 0 to about 0.0075 weight percent acetonitrile, in another aspect, from about 0.0025 to about 0.007 weight percent acetonitrile, and in another aspect, from about 0.0025 to about 0.005 weight percent acetonitrile; and A side stream comprising about 5 to about 70 weight percent acetonitrile, in another aspect, about 5 to about 50 weight percent acetonitrile, and in another aspect, about 6 to about 12 weight percent acetonitrile.

[0034] A method of operating a recovery tower, the method comprising providing a temperature of about 100 to about 105°C to a control tray in the recovery tower, and then introducing a feed stream to the recovery tower. In this regard, the control tray is located in the middle section of the recovery tower. The method also includes providing a temperature of about 100°C or less in the top section of the recovery tower, and then introducing the feed stream to the recovery tower. In another aspect, the top section of the recovery tower is about 70 to about 90°C, and then introducing the feed stream to the recovery tower. In this regard, the feed stream includes organic matter. The organic matter may include acrylonitrile, methacrylonitrile, acetonitrile, and mixtures thereof.

[0035] After providing the temperature as described, the method includes providing a mixture of acrylonitrile and acetonitrile to a recovery tower; contacting the mixture of acrylonitrile and acetonitrile with a water-containing solvent to provide an acrylonitrile-water azeotrope; separating the acrylonitrile-water azeotrope from the acetonitrile to provide an overhead stream comprising the acrylonitrile-water azeotrope and about 0.05 wt % or less of acetonitrile. The method provides a bottom stream comprising about 0 to about 0.0075 wt % acetonitrile, and a side stream comprising about 5 to about 70 wt % acetonitrile.

[0036] In another aspect, the method of operating a recovery column includes providing a temperature of about 100°C or less in the top section of the recovery column and then introducing the feed stream into the recovery column. In this aspect, the top section of the recovery column is about 70 to about 90°C and then the feed stream is introduced into the recovery column.

[0037] After providing the temperature as described, the method includes providing a mixture of acrylonitrile and acetonitrile to a recovery tower; contacting the mixture of acrylonitrile and acetonitrile with a water-containing solvent to provide an acrylonitrile-water azeotrope; separating the acrylonitrile-water azeotrope from the acetonitrile to provide an overhead stream comprising the acrylonitrile-water azeotrope and about 0.05 wt % or less of acetonitrile. The method provides a bottom stream comprising about 0 to about 0.0075 wt % acetonitrile, and a side stream comprising about 5 to about 70 wt % acetonitrile.

[0038] While the invention disclosed herein has been described by way of specific embodiments, examples, and applications thereof, numerous modifications and variations may be made thereto by those skilled in the art without departing from the scope of the invention as set forth in the claims.

Claims

1. A method for separating acrylonitrile from a mixture comprising acrylonitrile and acetonitrile, the method comprising: providing a mixture of acrylonitrile and acetonitrile to at least one recovery column and contacting the mixture of acrylonitrile and acetonitrile with an aqueous solvent to provide an acrylonitrile-water azeotrope, wherein the aqueous solvent is provided to a top section of the recovery column; Maintaining the temperature in the top portion of the recovery tower top section at 55-80° C.; The temperature in the top portion of the middle section of the recovery tower is maintained at 65-85° C., and the temperature in the bottom portion of the middle section of the recovery tower is maintained at 100-120° C.; maintaining the temperature within the bottom portion of the recovery column bottom section at 105-125°C; and The acrylonitrile-water azeotrope is separated from the acetonitrile to provide an overhead stream, a bottoms stream, and a vapor side stream comprising the acrylonitrile-water azeotrope, and wherein The recovery column includes a crude acetonitrile concentration region, the crude acetonitrile concentration region includes an upper outlet configured to allow a side stream to flow out of the recovery column from the crude acetonitrile concentration region, and The overhead stream includes the acrylonitrile-water azeotrope, 0.05 wt % or less of acetonitrile, and has 70-90 wt % of acrylonitrile; The bottom stream comprises 0-0.0075 wt % acetonitrile, and The side stream comprises 5-70 wt% acetonitrile.

2. The process of claim 1, wherein the recovery column is a single column.

3. The method of claim 1, wherein the recovery column comprises a first column and a second column.

4. The process of claim 1, wherein the top section, middle section, and bottom section are each 25-40% of the tangent to tangent height of the recovery column.

5. The method of claim 1, wherein the middle section comprises a top portion, a middle portion, and a bottom portion.

6. The process of claim 5, wherein the top portion, the middle portion, and the bottom portion are each 25-40% of the tangent to tangent height of the recovery column middle section.

7. The process of claim 1, wherein the mixture of acrylonitrile and acetonitrile is provided to a middle section of the recovery column.

8. The process of claim 1, wherein the top portion of the recovery tower middle section is maintained at 70-80°C.

9. The process of claim 1, wherein the bottom portion of the recovery tower middle section is maintained at 105-115°C.

10. The process of claim 1, wherein the top section of the recovery column comprises a top portion and a bottom portion, each of which is 40-60% of the tangent to tangent height of the top section of the recovery column.

11. The process of claim 1, wherein the top portion of the recovery column top section is maintained at 60-75°C.

12. The method of claim 1, wherein the top portion and the bottom portion of the recovery tower top section have a temperature difference of 0-20°C.

13. The method of claim 12, wherein the top portion and the bottom portion of the recovery tower top section have a temperature difference of 5-15°C.

14. The process of claim 1, wherein the bottom section of the recovery column comprises a top portion and a bottom portion, each of which is 40-60% of the tangent to tangent height of the bottom section of the recovery column.

15. The process of claim 1, wherein the bottom portion of the bottom section of the recovery tower is maintained at 110-120°C.

16. The method of claim 1, wherein the top portion and the bottom portion of the recovery column bottom section have a temperature difference of 0-15°C.

17. The method of claim 16, wherein the top portion and the bottom portion of the recovery column bottom section have a temperature difference of 7-13°C.

18. The process of claim 1 wherein the overhead stream comprises 0.03 wt% or less acetonitrile.

19. The process of claim 18, wherein the overhead stream comprises 0.01 wt% or less acetonitrile.

20. The process of claim 1 wherein the overhead stream has 75 to 85 weight percent acrylonitrile.

21. The process of claim 1 wherein the bottoms stream comprises 0.0025-0.007 wt % acetonitrile.

22. The process of claim 21, wherein the bottom stream comprises 0.0025-0.005 wt% acetonitrile.

23. The process of claim 1, wherein the side stream comprises 5-50 wt% acetonitrile.

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