WO2017087175A1

WO2017087175A1 - Hcn heads column pump around for acrylonitrile recovery

Info

Publication number: WO2017087175A1
Application number: PCT/US2016/060252
Authority: WO
Inventors: Timothy Robert Mcdonel; Lani JACKSON; David Rudolph WAGNER; Paul Trigg Wachtendorf; Jay Robert COUCH
Original assignee: Ineos Europe Ag
Priority date: 2015-11-16
Filing date: 2016-11-03
Publication date: 2017-05-26
Also published as: CN106699599A; RU2018120739A3; TR201806463T1; RU2721779C2; RU2018120739A; CN114870421A

Abstract

A process and system for acrylonitrile and HCN recovery includes a heads column system operated to reduce heads column condenser duty and reduce equipment while maintaining required purity and specifications with minimal increases in reboiler duty. In one aspect, the process includes providing a feed stream that includes acrylonitrile, HCN and water to a heads column; distilling the feed stream in the heads column to produce a heads column overhead stream that includes HCN and a bottom liquid stream that includes acrylonitrile; removing a sidestream from a side draw of the heads column that includes water and organics; separating at least some water and organics from the sidestream to provide an organic stream; returning the organic stream to the heads column; and adjusting a ratio of an amount of sidestream removed from a side draw of the heads column to an amount of organic stream returned to the heads column below the side draw to provide the bottom liquid stream with 500 ppm or less HCN.

Description

HCN HEADS COLUMN PUMP AROUND FOR

ACRYLONITRILE RECOVERY

[0001] A process and system are provided for acrylonitrile and HCN recovery. More specifically, a heads column system is operated to reduce heads column condenser duty, and reduce equipment requirements while maintaining required purity specifications with minimal increases in reboiler duty.

BACKGROUND

[0002] The acrylonitrile manufacturing process produces HCN. HCN must be removed in the process from the acrylonitrile in order to meet final acrylonitrile specifications. HCN can be a valuable co-product so it is desirable for the process to recover purified HCN. To minimize human exposure, systems are in place to remove HCN and reduce exposure to HCN during plant operation or maintenance. In some aspects, manufacturing systems utilize equipment that can handle HCN with low risk of leakage. For example, systems utilizing gravity flow help to eliminate the need for pumps in HCN handling. However, fouling, particularly of trays, is often a problem in acrylonitrile plants. Polymerization of HCN can be a problem in acrylonitrile production.

[0003] One important system for removing HCN in the acrylonitrile manufacturing process involves use of a heads column. Heads column 30 includes a plurality of trays. In an embodiment, heads column 30 includes between fifty (50) and seventy- five (75) trays, alternatively between fifty-five (55) and sixty-five (65) trays. In an embodiment, heads column 30 includes sixty-two (62) trays, alternatively sixty (60) or sixty-five (65) trays. Heads column 30 may be configured to receive crude nitriles feed stream 1 at tray 28. In an embodiment, tray 28 may be the located at between the thirty-fifth and forty- eighth tray, preferably between the trays forty and forty-four forty, in all cases from the bottom of heads column 30. Heads column 30 may be configured to remove a sidestream 44 from a side draw of the heads column that includes water and organics located at between the fifteenth and twenty-eighth tray, preferably between the trays eighteen and twenty five, in all cases from the bottom of heads column 30. In an alternative embodiment, tray 28 may be the forty-second or thirty-eighth tray from the bottom of heads column 12.

[0004] In an alternative embodiment, tray 28 may be the forty- seventh tray from the bottom of heads column 30 and heads column 30 may include sixty-seven trays. In an embodiment, the first through twenty bottom trays of heads column 30 dry the acrylonitrile product. In an embodiment, the twenty-first through forty- second tray from bottom of heads column 30 remove and purify HCN. In an embodiment, heads column 30 includes between forty (40) and sixty-five (65) trays. In an embodiment, and feed tray 28 may be between and including the twentieth and thirtieth tray from the bottom of the heads column.

[0005] In some designs, the heads column includes two column sections stacked on top of each other. In this design, the bottom section is called the drying

column/section and includes between 15 and 30 trays, preferably between 18 and 25, more preferably between 18 and 22. In another aspect, the heads column includes trays 1 through 20, where tray 1 is the lowest tray. The top column section is where HCN distills overhead, and it is called the heads column/section or HCN

column/section, and in one aspect, includes between 30 and 50 trays, preferably between 32 and 48, and more preferably between 38 and 48 trays. In another aspect, the column includes trays 21 through 62, where tray 62 is the highest tray. These numbers may be different in different heads columns.

[0006] To help reduce fouling, a conventional heads drying column operates at reduced pressure (vacuum) operation. This mode of operation dramatically reduces fouling and extends the run time between cleanings of the HCN or heads column. Operation of the HCN or heads column at reduced pressure requires distillation at lower temperatures. The polymerization reaction rate to produce solids which foul process equipment is greatly reduced at lower temperatures. However, as a tradeoff, lower temperature distillation entails providing lower condensing temperatures. This necessitates a refrigerated coolant, for example, a chilled ethylene-glycol-water mixture, commonly referred to as "brine". The brine may need a temperature of about 0 °C for a heads column condenser and about -10 °C at a vent condenser.

SUMMARY

[0007] A process for acrylonitrile recovery includes providing a feed stream that includes acrylonitrile, HCN and water to a heads column; distilling the feed stream in the heads column to produce a heads column overhead stream that includes HCN and a bottom liquid stream that includes acrylonitrile; removing a sidestream from a side draw of the heads column that includes water and organics; separating at least some water and organics from the sidestream to provide an organic stream; returning the organic stream to the heads column; and adjusting a ratio of an amount of sidestream removed from a side draw of the heads column to an amount of organic stream returned to the heads column below the side draw to provide the bottom liquid stream with 500 ppm or less HCN.

[0008] A process for acrylonitrile recovery includes providing a feed stream that includes acrylonitrile, HCN and water to a heads column; distilling the feed stream in the heads column to produce a heads column overhead stream that includes HCN and a bottom liquid stream that includes acrylonitrile; removing a sidestream from a side draw of the heads column that includes water and organics; separating at least some water and organics from the sidestream; and splitting the organics into at least two streams and returning the streams to at least two separate locations on the heads column.

[0009] A process for operating a heads column includes providing a feed stream that includes acrylonitrile, HCN and water to the heads column; distilling the feed stream in the heads column to produce a heads column overhead stream and conveying the heads column overhead stream to a heads column condenser; removing a sidestream that includes water and organics from a side draw of the heads column and conveying the sidestream to a sidestream heat exchanger to provide a cooled sidestream;

separating at least some water and organics from the cooled sidestream; returning an organic stream to the heads column; and adjusting a ratio of an amount of sidestream removed from a side draw of the heads column to an amount of organic stream returned to the heads column below the side draw to provide a ratio of heat duty in the heads column condenser to heat duty in the sidestream heat exchanger of about 2.5 or less.

[0010] A process for acrylonitrile recovery includes providing a feed stream that includes acrylonitrile, HCN and water to a heads column; distilling the feed stream in the heads column to produce a heads column overhead stream that includes HCN, a bottom liquid stream that includes acrylonitrile, and a sidestream from a side draw of the heads column that includes water and organics; wherein a vapor/liquid molar rate in the column above the side draw of the column is about 0.25 to about 0.55 and a vapor/liquid rate in the column below the side draw of the column is about 0.50 to about 0.65.

[0011] A process for acrylonitrile recovery includes providing a feed stream that includes acrylonitrile, HCN and water to a heads column; distilling the feed stream in the heads column to produce a heads column overhead stream that includes HCN, a bottom liquid stream that includes acrylonitrile, and a sidestream from a side draw of the heads column that includes water and organics; wherein a ratio of a vapor/liquid molar rate in the column above the side draw of the column to a vapor/liquid molar rate in the column below the side draw of the column is about 0.40 to about 1.

[0012] A heads column system includes a heads column configured to receive a feed stream that includes acrylonitrile, HCN and water and further configured to distill the feed stream in the heads column to produce a heads column overhead stream that includes HCN and a bottom liquid stream that includes acrylonitrile; a sidedraw configured to remove a blend of water and organics from the heads column and cool the blend of water and organics prior to entry into a decanter; the decanter configured to separate the blend of water and organics in a water stream and an organic stream; a splitter configured to receive the organic stream from the decanter and split the organic stream into at least two streams; at least one return line configured to convey one of the organic streams to the heads column above the sidedraw; and at least one return line configured to convey one of the organic streams to the heads column below the sidedraw.

BRIEF DESCRIPTION OF FIGURES

[0013] The above and other aspects, features and advantages of several aspects of the process will be more apparent from the following figures.

[0014] Figure 1 illustrates a heads column system.

[0015] Figure 2 shows a heads column system with a pump around.

[0016] Figure 3 illustrates another aspect of heads column system with a pump around.

[0017] Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various aspects. Also, common but well-understood elements that are useful or necessary in a commercially feasible aspect are often not depicted in order to facilitate a less obstructed view of these various aspects.

DETAILED DESCRIPTION

[0018] The following description is not to be taken in a limiting sense, but is made merely for the purpose of describing the general principles of exemplary

embodiments. The scope of the invention should be determined with reference to the claims.

[0019] A process and apparatus includes a heads column. The heads column receives a crude nitriles feed stream (that includes acrylonitrile, HCN and water). Distillation in the heads column provides a heads column overhead stream that includes hydrogen cyanide (HCN) at the top of the heads column, and a heads column bottom liquid that includes acrylonitrile product at the bottom of the heads column. The column distillation results in both hydrogen cyanide and water removal from the acrylonitrile.

[0020] The heads column overhead stream is sent to a heads column condenser where a portion condenses using a coolant. The uncondensed vapor from the heads column condenser is sent to the heads column vent condenser where a portion is condensed using coolant. The process includes combining the two condensed liquid streams from the heads column condenser and the heads column vent condenser and conveying those streams to a heads column reflux pump. A portion of this combined liquid stream returns as reflux to the top of the heads column, and the rest is either used as product or goes to disposal.

[0021] The process includes removing a total liquid-draw off at a middle section of the heads column and sending that draw-off to a side stream cooler and then to a decanter. Previously, the liquid draw-off would first go to a heat interchanger, where a cooler organic stream from the decanter would cool the total liquid draw-off stream. The total liquid draw-off stream would then proceed to the heads column decanter where a phase separation takes place. The water phase from the water side of the decanter may go to the recovery column feed manifold. The acrylonitrile phase from the organic side of the decanter goes back to the heads column.

[0022] In one aspect, the process includes providing a feed stream that includes acrylonitrile, HCN and water to a heads column. As shown in Fig. 1, a feed stream 34 enters a heads column 30 at an upper section of the heads column 30 at heads column feed stream inlet 36. In one aspect, the feed stream inlet 36 may correspond to any one of tray numbers 40 to 45 of the heads column 30, and in another aspect, tray number 42 of the heads column 30. The feed stream 34 may include about 82 to about 90 weight percent acrylonitrile and about 5 to about 13 weight percent HCN.

[0023] The process includes distilling the feed stream 34 in the heads column 30 to produce a heads column overhead stream 51 that includes HCN and a bottom liquid stream 58 that includes acrylonitrile. The process includes removing a sidestream 46 from a side draw 44 of the heads column 30. In one aspect, the side draw 44 is at a middle section of the heads column 30. In another aspect, the side draw 44 may correspond to any one of tray numbers 18 to 23 of the heads column 30 (that includes 62 trays), and in another aspect, tray number 21 of the heads column 30. The sidestream 46 includes water and organics.

[0024] In one aspect, the side draw 44 is at a height in the column that allows for withdrawal of a sidestream 46 that includes about 90 to about 95 weight percent acrylonitrile, and in another aspect, about 92 to about 93 weight percent acrylonitrile, and about 5 to about 10 weight percent water, and in another aspect, about 7 to about 8 percent water.

[0025] As shown in Fig. 1, the process may include continuously removing the sidestream 46 from the heads column 30 using a sidestream pump 39. The process includes cooling the sidestream 46 to provide a cooled sidestream 49. The process shown in Fig. 1 includes passing the sidestream 46 through a first heat exchanger 35 and a second heat exchanger 37. The process provides a cooled sidestream 49 having a temperature of about 35°C to about 45°C, and in another aspect, about 38°C to about 42°C prior to entering a decanter 33. Providing the cooled sidestream 49 to the decanter 33 improves separation of water and organics.

[0026] Water and organic materials separate in the decanter 33. A pump (not shown) removes a water phase 42 from the decanter 33. An organic stream pump 31 removes organic stream 48 from decanter 33. In the decanter 33, one phase is predominantly water (about 93%), and the other phase acrylonitrile (about 95%). The water phase is pumped from the water side of the decanter 33 to a recovery column feed manifold (not shown). The acrylonitrile phase from the organic side of the decanter 33 is pumped back to the heads columns 30. [0027] A decanter vent stream 47 may be sent to a scrubber (not shown). Organic stream 48 is conveyed to first heat exchanger 35 where it provides a cooling stream. The organic stream 48 enters heads column 30 at organic stream inlet 54. Organic stream inlet 54 may be at a middle section of heads column 30. In this aspect, organic stream inlet 54 is below side draw 44.

[0028] In another aspect, the process includes conveying the heads column overhead stream 51 to a heads column condenser 55. The heads column overhead stream 51 condenses in the heads column condenser 55 using a condenser coolant stream 53. In this aspect, the condenser coolant stream 53 may be antifreeze or refrigerated water. The condenser coolant stream 53 has a temperature of about -10°C to about +10°C, in another aspect, about -10°C to about +5°C. A vapor/liquid stream 92 is sent to a vapor/liquid separator 94. The uncondensed vapor 58 from the vapor/liquid separator 94 is sent to a heads column vent condenser 90. The uncondensed vapor 58 condenses in heads column vent condenser 90 which is cooled by a vent coolant stream 61. In this aspect, vent coolant stream 61 may be antifreeze or refrigerated water. The vent coolant stream 61 has a temperature of about -10°C to about +10°C, in another aspect, about -10°C to about +5°C. A vapor/liquid stream 96 is sent to second liquid/vapor separator 98.

[0029] In another aspect, the process includes combining the heads column condenser condensate 63 and the heads column vent condenser condensate 65 to form a combined condensate stream 67. The process further includes conveying the combined condensate stream 67 to a top portion of the heads column 30 with a condensate pump 71. The process may include drawing off a portion of the combined condensate stream 67 at a draw-off 74. The combined condensate stream 67 may be returned to a top portion of the heads column 30 at a heads column condensate inlet 76.

[0030] As shown in Fig. 2, and similar to Fig. 1, the process includes providing a feed stream that includes acrylonitrile, HCN and water to a heads column. As shown in Fig. 2, the feed stream 34 enters the heads column 30 at an upper section of the heads column 30 at a heads column feed stream inlet 36. In one aspect, the feed stream inlet 36 may correspond to any one of tray numbers 40 to 45 of the heads column 30 (that includes 62 trays), and in one aspect, tray number 42 of heads column 30. The process includes distilling the feed stream 34 in the heads column 30 to produce a heads column overhead stream 51 that includes HCN and a bottom liquid stream 58 that includes acrylonitrile. In this aspect, the bottom liquid stream 58 includes about 500 ppm or less HCN, in another aspect, about 0 to about 500 ppm HCN, in another aspect, about 1 to about 400 ppm HCN, in another aspect, about 1 to about 250 ppm HCN, and in another aspect, about 1 to about 100 ppm HCN. The bottom liquid stream 58 may also include about 0.1 to about 0.5 weight percent water, in another aspect, about 0.1 to about 0.25 weight percent water.

[0031] The heads column overhead stream 51 includes about 100 ppm or less acrylonitrile, in another aspect, about 0 to about 100 ppm acrylonitrile, in another aspect, about 1 to about 90 ppm acrylonitrile, in another aspect, about 5 to about 50 ppm acrylonitrile, in another aspect, about 5 to about 25 ppm acrylonitrile, and in another aspect, about 1 to about 10 ppm acrylonitrile. The heads column overhead stream 51 may include about 0.25 to about 0.75 weight percent water, in another aspect, about 0.4 to about 0.6 weight percent water.

[0032] The process includes removing a sidestream 46 from a side draw 44 of the heads column 30. In one aspect, the side draw 44 is at a middle section of the heads column 30. In another aspect, the side draw 44 may correspond to any one of tray numbers 18 to 23 of heads column 30, and in one aspect, tray number 21 of the heads column 30. The sidestream 46 includes water and organics.

[0033] In one aspect and in contrast to the process of Fig. 1, the process shown in Fig. 2 includes conveying sidestream 46 to a heat exchanger 38. In this aspect, the sidestream 46 may flow to heat exchanger 38 with gravity feed. The process provides a cooled sidestream 49 having a temperature of about 35°C to about 45°C, and in another aspect, about 38°C to about 42°C prior to entering a decanter 33. In the aspect of the process illustrated in Fig. 2, the process does not require a pump to convey the sidestream 46 to the heat exchanger 38, and only requires a single heat exchanger prior to entry into the decanter 33.

[0034] In another aspect, water and organic materials separate in the decanter 33. A pump (not shown) removes water phase 42 from decanter 33. An organic stream pump 31 removes organic stream 48 from decanter 33. In contrast to Fig. 1, the process shown in Fig. 2 includes conveying organic stream 48 to a splitter 71. The splitter divides the organic stream 48 into a first organic stream 73 and a second organic stream 75. In this aspect, the splitter 71 provides the first organic stream 73 or the second organic stream 75 with about 40 to about 60 weight % of the organic stream 48.

[0035] In another aspect, the process includes returning the first organic stream 73 and second organic stream 75 to the heads column 30 at two separate locations on the heads column 30. In this aspect, the process includes returning the first organic stream 73 to a heads column first organic stream inlet 77, and the second organic stream 75 to a heads column second organic stream inlet 79. In one aspect, the process includes returning the first organic stream 73 to the first organic stream inlet 77 which is about 5 to about 1 tray above the side draw 44 of the heads column 30, in another aspect, about 4 to about 1 tray, in another aspect about 3 to about 1 tray, in another aspect, about 2 to about 1 tray, and in another aspect, about 1 tray above the side draw 44 of the heads column 30. In another aspect, the process includes returning the second organic stream 75 to the second organic stream inlet 79 which is about 5 to about 1 tray below the side draw 44 of the heads column 30, about 4 to about 1 tray, in another aspect about 3 to about 1 tray, in another aspect, about 2 to about 1 tray, and in another aspect, about 1 tray below the side draw 44 of the heads column 30. [0036] In another aspect and in contrast to Fig. l, the process shown in Fig. 2 includes conveying a decanter vent stream 47 to the heads column 30. In this aspect, the decanter vent stream 47 may enter the heads column 30 at a decanter vent stream inlet 81. The decanter vent stream inlet 81 may correspond to a location on the heads column that is the same tray as the side draw 44. The decanter vent stream 47 may function as an equilibrium line as liquid is removed from the side draw 44.

[0037] A comparison of heat duty between the process of Fig. 1 and Fig. 2 was as follows.

Heat Duty (kw)

Split Return Single Return %

(Fig. 2) (Fig. 1) Change Change

Condenser (55 in Figs 1 and 2) 5541.78 6377.61 -835.83 -13.11

Vent Condenser (90 in Figs. 1 and 2) 31.80 31.80 -0.0016 -0.01

Exchanger (37 in Fig.l, 38 in Fig 2) 2265.07 1381.22 883.85 63.99

Reboiler (21 in Figs 1 and 2) 9038.10 8999.62 38.48 0.43

Net Change Cooling 7838.65 7790.63 48.01 0.62

[0038] A comparison of the process of Fig. 1 and Fig. 2 shows that condenser duty for the heads column decreases by about 13% with the split return shown in Fig. 2. This change in heat duty translates to savings on refrigeration. This change in heat duty essentially gets transferred to the sidestream heat exchanger 38, which uses cooling water, which is the cheaper utility. Although the heat balance around the heads column changed significantly due to process equipment and operational changes, the overall net change in cooling and reboiler duties between Fig. 1 and Fig. 2 is small, 0.62% and 0.43%, which is expected. In this aspect, the sidestream heat exchanger 38 has a heat duty of 3165 kw or less, in another aspect, about 1410 to about 2350 kw, and in another aspect, about 2350 to about 3165 kw (based on 260 - 350 kta production of acrylonitrile). In another aspect, a ratio of heat duty in the heads column condenser 55 to heat duty in the sidestream heat exchanger 38 is about 4.7 or less, in another aspect, about 2.5 or less, in another aspect, about 2 to about 3, and in another aspect, about 2.5 to about 4.7.

[0039] In one aspect, the process shown in Fig. 2 provides for removal of one heat exchanger and pump, and reduction in the refrigeration utility requirement. A practical example of the benefit can be illustrated during conditions of fouling. When the heads column begins to foul, the operation of the column tends to require more and more reflux to maintain the same purity specs, until eventually the tower must be shut down for cleaning. Since the pumparound to Tray 22 is a source of increased reflux, this leads to a lower condenser duty associated with fouling conditions in the heads column.

[0040] In another aspect, the process includes operating the heads column at certain vapor/liquid molar rates. In this aspect, a vapor/liquid molar rate in the heads column 30 above the side draw 44 is about 0.25 to about 0.55, in another aspect, about 0.26 to about 0.51, in another aspect, 0.26 to about 0.48, in another aspect, about 0.45 to about 0.55, in another aspect, about 0.46 to about 0.51, and in another aspect, about 0.49 to about 0.51. In one aspect, the vapor/liquid molar rates above the side draw for a process that includes a split return is about 0.25 to about 0.50, and in another aspect, about 0.26 to about 0.48. In another aspect, the vapor/liquid molar rates above the side draw for a process that includes a single return is about 0.49 to about 0.51.

[0041] A vapor/liquid molar rate in the heads column 30 below the side draw 44 is about 0.4 to about 1, in another aspect, about 0.5 to about 0.65, in another aspect, about 0.55 to about 0.65, in another aspect, about 0.54 to about 0.61, in another aspect, about 0.56 to about 0.62, and in another aspect, about 0.58 to about 0.61. In one aspect, the vapor/liquid molar rates below the side draw for a process that includes a split return is about 0.5 to about 0.65, and in another aspect, about 0.54 to about 0.61. In another aspect, the vapor/liquid molar rates below the side draw for a process that includes a single return is about 0.58 to about 0.61. [0042] In another aspect, the process includes operating the heads column at certain ratios of vapor/liquid molar rates. In this aspect, a ratio of vapor/liquid molar rate in the heads column 30 above side draw 44 to a vapor/liquid molar rate in the heads column 30 below side draw 44 is about 0.4 to about 0.9, in another aspect, about 0.44 to about 0.88, in another aspect, about 0.75 to about 0.90, in another aspect, about 0.77 to about 0.82, and in another aspect, about 0.82 to about 0.87. In another aspect, in a process that includes a split return, a ratio of vapor/liquid molar rate in the heads column 30 above side draw 44 to a vapor/liquid molar rate in the heads column 30 below side draw 44 is about 0.4 to about 0.85, and in another aspect, about 0.44 to about 0.83. In another aspect, in a process that includes a single return, a ratio of vapor/liquid molar rate in the heads column 30 above side draw 44 to a vapor/liquid molar rate in the heads column 30 below side draw 44 is about 0.8 to about 0.9, and in another aspect, about 0.81 to about 0.83.

[0043] A vapor/liquid rate in the heads column 30 above the side draw 44 may be calculated as follows:

flow rate in the heads column overhead stream 51 / (flow rate in feed stream 34) +

(flow rate combined condensate stream 67 at heads column inlet 76)

A vapor/liquid rate in the heads column 30 below the side draw 44 may be calculated as follows:

flow rate in heads column overhead stream 51 / flow rate of the second organic stream 75

[0044] Figure 3 is similar to Figure 1 except that Figure 3 includes an additional heat exchanger 99.

[0045] While the invention herein disclosed has been described by means of specific embodiments, examples and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.

Claims

What is claimed is:

1. A process for acrylonitrile recovery comprising:

providing a feed stream that includes acrylonitrile, HCN and water to a heads column; distilling the feed stream in the heads column to produce a heads column overhead stream that includes HCN and a bottom liquid stream that includes acrylonitrile;

removing a sidestream from a side draw of the heads column that includes water and organics;

separating at least some water and organics from the sidestream to provide an organic stream;

returning the organic stream to the heads column; and

adjusting a ratio of an amount of sidestream removed from a side draw of the heads column to an amount of organic stream returned to the heads column below the side draw to provide the bottom liquid stream with 500 ppm or less HCN.

2. The process of claim 1 wherein the organic stream is split into at least two streams before it is returned to the heads column.

3. The process of claim 2 wherein one of the organics streams is returned to the heads column above the side draw of the heads column and one is returned below the side draw of the heads column.

4. The process of claim 3 wherein one of the organic streams is returned to the heads column from about 5 to about 1 tray above the side draw of the heads column.

5. The process of claim 3 wherein one of the organic streams is returned to the heads column about 1 tray below the side draw of the heads column.

6. The process of claim 2 wherein one of the two organic streams being returned to the heads column includes about 40 to about 60 weight % of the organics.

7. The process of claim 1 wherein the sidestream is cooled after removal from the heads column.

8. The process of claim 7 wherein the sidestream is cooled in at least one heat exchanger.

9. The process of claim 8 wherein the sidestream is cooled in at least two heat exchangers.

10. The process of claim 8 wherein the sidestream is conveyed to the heat exchanger by a gravity feed.

11. The process of claim 1 wherein water and organics in the side stream are separated in a decanter.

12. The process of claim 11 wherein a vent stream from the decanter is returned to the heads column.

13. The process of claim 8 wherein the heads column overhead stream is conveyed to a heads column condenser.

14. The process of claim 13 wherein a ratio of heat duty in the heads column condenser to heat duty in the sidestream heat exchanger is about 2.5 or less.

15. The process of claim 1 wherein the heads column overhead stream has 100 ppm or less acrylonitrile.

16. A process for acrylonitrile recovery comprising:

providing a feed stream that includes acrylonitrile, HCN and water to a heads column; distilling the feed stream in the heads column to produce a heads column overhead stream that includes HCN and a bottom liquid stream that includes acrylonitrile; removing a sidestream from a side draw of the heads column that includes water and organics;

separating at least some water and organics from the sidestream; and

splitting the organics into at least two streams and returning the streams to at least two separate locations on the heads column.

17. The process of claim 16 wherein one of the organics streams is returned to the heads column above the side draw of the heads column and one is returned below the side draw of the heads column.

18. The process of claim 17 wherein one of the organic streams is returned to the heads column from about 5 to about 1 tray above the side draw of the heads column.

19. The process of claim 17 wherein one of the organic streams is returned to the heads column about 1 tray below the side draw of the heads column.

20. The process of claim 17 wherein one of the two streams being returned to the heads column includes about 40 to about 60 weight % of the organics.

21. The process of claim 16 wherein the sidestream is cooled after removal from the heads column.

22. The process of claim 21 wherein the sidestream is cooled in at least one heat exchanger.

23. The process of claim 22 wherein the sidestream is cooled in at least two heat exchangers.

24. The process of claim 22 wherein the sidestream is conveyed to the heat exchanger by a gravity feed.

25. The process of claim 16 wherein water and organics are separated in a decanter.

26. The process of claim 25 wherein a vent stream from the decanter is returned to the heads column.

27. The process of claim 22 wherein the heads column overhead stream is conveyed to a heads column condenser.

28. The process of claim 27 wherein a ratio of heat duty in the heads column condenser to heat duty in the sidestream heat exchanger is about 2.5 or less.

29. The process of claim 16 wherein the bottoms liquid stream has 500 ppm or less

HCN.

30. The process of claim 16 wherein the heads column overhead stream has 100 ppm or less acrylonitrile.

31. A process for operating a heads column comprising:

providing a feed stream that includes acrylonitrile, HCN and water to the heads column; distilling the feed stream in the heads column to produce a heads column overhead stream and conveying the heads column overhead stream to a heads column condenser;

removing a sidestream that includes water and organics from a side draw of the head column and conveying the sidestream to a sidestream heat exchanger to provide a cooled sidestream;

separating at least some water and organics from the cooled sidestream;

returning an organic stream to the heads column; and

adjusting a ratio of an amount of organic stream returned above the side draw of the heads column to an amount of organic stream returned to the heads column below the side draw to provide a ratio of heat duty in the heads column condenser to heat duty in the sidestream heat exchanger of about 2.5 or less.

32. The process of claim 31 wherein the organic stream is split into at least two streams before it is returned to the heads column.

33. The process of claim 31 wherein the column includes between about 15 to about 30 trays below the side draw.

34. The process of claim 33 wherein the column includes between about 18 to about 25 trays below the side draw.

35. The process of claim 34 wherein the column includes between about 18 to about 22 trays below the side draw.

36. The process of claim 31 wherein the column includes between about 30 to about 50 trays above the side draw.

37. The process of claim 36 wherein the column includes between about 32 to about 48 trays above the side draw.

38. The process of claim 37 wherein the column includes between about 38 to about 44 trays above the side draw.

39. The process of claim 32 wherein one of the organics streams is returned to the heads column above the side draw of the heads column and one is returned below the side draw of the heads column.

40. The process of claim 39 wherein one of the organic streams is returned to the heads column from about 5 to about 1 tray above the side draw of the heads column.

41. The process of claim 39 wherein one of the organic streams is returned to the heads column about 1 tray below the side draw of the heads column.

42. The process of claim 32 wherein one of the two organic streams being returned to the heads column includes about 40 to about 60 weight % of the organics.

43. The process of claim 31 wherein the sidestream is cooled in at least one heat exchanger.

44. The process of claim 43 wherein the sidestream is cooled in at least two heat exchangers.

45. The process of claim 43 wherein the sidestream is conveyed to the heat exchanger by a gravity feed.

46. The process of claim 31 wherein water and organics in the side stream are separated in a decanter.

47. The process of claim 46 wherein a vent stream from the decanter is returned to the heads column.

48. The process of claim 31 wherein the heads column overhead stream is conveyed to a heads column condenser.

49. The process of claim 31 wherein the bottoms liquid stream has 500 ppm or less

HCN.

50. The process of claim 31 wherein the heads column overhead stream has 100 ppm or less acrylonitrile.

51. A process for acrylonitrile recovery comprising:

providing a feed stream that includes acrylonitrile, HCN and water to a heads column; distilling the feed stream in the heads column to produce a heads column overhead stream that includes HCN, a bottom liquid stream that includes acrylonitrile, and a sidestream from a side draw of the heads column that includes water and organics;

wherein a vapor/liquid molar rate in the column above the side draw of the column is about 0.25 to about 0.55 and a vapor/liquid molar rate in the column below the side draw of the column is about 0.50 to about 0.65.

52. The process of claim 51 wherein the column includes between about 15 to about 30 trays below the side draw.

53. The process of claim 52 wherein the column includes between about 18 to about 25 trays below the side draw.

54. The process of claim 53 wherein the column includes between about 18 to about 22 trays below the side draw.

55. The process of claim 51 wherein the column includes between about 30 to about 50 trays above the side draw.

56. The process of claim 55 wherein the column includes between about 32 to about 48 trays above the side draw.

57. The process of claim 56 wherein the column includes between about 38 to about 44 trays above the side draw.

58. The process of claim 51 wherein the process includes cooling the sidestream to provide a cooled sidestream.

59. The process of claim 58 wherein the process includes separating water and organics from the cooled sidestream.

60. The process of claim 51 wherein the organic stream is split into at least two streams and returned to the heads column.

61. The process of claim 60 wherein one of the organics streams is returned to the heads column above the side draw of the heads column and one is returned below the side draw of the heads column.

62. The process of claim 61 wherein one of the organic streams is returned to the heads column from about 5 to about 1 tray above the side draw of the heads column.

63. The process of claim 61 wherein one of the organic streams is returned to the heads column about 1 tray below the side draw of the heads column.

64. The process of claim 60 wherein one of the two organic streams being returned to the heads column includes about 40 to about 60 weight % of the organics.

65. The process of claim 58 wherein the sidestream is cooled in at least one heat exchanger.

66. The process of claim 65 wherein the sidestream is cooled in at least two heat exchangers.

67. The process of claim 65 wherein the sidestream is conveyed to the heat exchanger by a gravity feed.

68. The process of claim 59 wherein water and organics in the side stream are separated in a decanter.

69. The process of claim 68 wherein a vent stream from the decanter is returned to the heads column.

70. The process of claim 65 wherein the heads column overhead stream is conveyed to a heads column condenser.

71. The process of claim 70 a ratio of heat duty in the heads column condenser to heat duty in the sidestream heat exchanger is about 2.5 or less.

72. The process of claim 51 wherein the bottoms liquid stream has 500 ppm or less

HCN.

73. The process of claim 51 wherein the heads column overhead stream has 100 ppm or less acrylonitrile.

74. A process for acrylonitrile recovery comprising:

wherein a ratio of a vapor/liquid molar rate in the column above the side draw of the column to a vapor/liquid molar rate in the column below the side draw of the column is about 0.40 to about 1.0.

75. The process of claim 74 wherein the column includes between about 15 to about 30 trays below the side draw.

76. The process of claim 75 wherein the column includes between about 18 to about 25 trays below the side draw.

77. The process of claim 76 wherein the column includes between about 18 to about 22 trays below the side draw.

78. The process of claim 74 wherein the column includes between about 30 to about 50 trays above the side draw.

79. The process of claim 78 wherein the column includes between about 32 to about 48 trays above the side draw.

80. The process of claim 79 wherein the column includes between about 38 to about 44 trays above the side draw.

81. The process of claim 74 wherein the process includes cooling the sidestream to provide a cooled sidestream.

82. The process of claim 81 wherein the process includes separating water and organics from the cooled sidestream.

83. The process of claim 82 wherein the organic stream is split into at least two streams and returned to the heads column.

84. The process of claim 83 wherein one of the organics streams is returned to the heads column above the side draw of the heads column and one is returned below the side draw of the heads column.

85. The process of claim 84 wherein one of the organic streams is returned to the heads column from about 5 to about 1 tray above the side draw of the heads column.

86. The process of claim 84 wherein one of the organic streams is returned to the heads column about 1 tray below the side draw of the heads column.

87. The process of claim 83 wherein one of the two organic streams being returned to the heads column includes about 40 to about 60 weight % of the organics.

88. The process of claim 81 wherein the sidestream is cooled in at least one heat exchanger.

89. The process of claim 88 wherein the sidestream is cooled in at least two heat exchangers.

90. The process of claim 89 wherein the sidestream is conveyed to the heat exchanger by a gravity feed.

91. The process of claim 74 wherein water and organics in the side stream are separated in a decanter.

92. The process of claim 91 wherein a vent stream from the decanter is returned to the heads column.

93. The process of claim 88 wherein the heads column overhead stream is conveyed to a heads column condenser.

94. The process of claim 93 wherein a ratio of heat duty in the heads column condenser to heat duty in the sidestream heat exchanger is about 2.5 or less.

95. The process of claim 74 wherein the bottoms liquid stream has 500 ppm or less

HCN.

96. The process of claim 74 wherein the heads column overhead stream has 100 ppm or less acrylonitrile.

97. A heads column system comprising:

a heads column configured to receive a feed stream that includes acrylonitrile, HCN and water and further configured to distill the feed stream in the heads column to produce a heads column overhead stream that includes HCN and a bottom liquid stream that includes acrylonitrile;

a sidedraw configured to remove a blend of water and organics from the heads column and cool the blend of water and organics prior to entry into a decanter;

the decanter configured to separate the blend of water and organics in a water stream and an organic stream;

a splitter configured to receive the organic stream from the decanter and split the organic stream into at least two streams;

at least one return line configured to convey one of the organic streams to the heads column above the sidedraw; and

at least one return line configured to convey one of the organic streams to the heads column below the sidedraw.

98. The system of claim 97 wherein one of the organic streams is returned to the heads column from about 5 to about 1 tray above the sidedraw of the heads column.

99. The system of claim 97 wherein one of the organic streams is returned to the heads column about 1 tray below the sidedraw of the heads column.

100. The system of claim 97 wherein one of the two streams being returned to the heads column includes about 40 to about 60 weight % of the organics.

101. The system of claim 97 wherein the sidedraw is cooled in at least one heat exchanger.

102. The system of claim 101 wherein the sidedraw is conveyed to the heat exchanger by a gravity feed.

103. The system of claim 97 wherein a vent stream from the decanter is returned to the heads column.

104. The system of claim 101 wherein the heads column overhead stream is conveyed to a heads column condenser.

105. The system of claim 104 wherein a ratio of heat duty in the heads column condenser to heat duty in the sidesdraw heat exchanger is about 2.5 or less.

106. The system of claim 97 wherein the column includes between about 15 to about 30 trays below the side draw.

107. The system of claim 106 wherein the column includes between about 18 to about 25 trays below the side draw.

108. The system of claim 107 wherein the column includes between about 18 to about 22 trays below the side draw.

109. The system of claim 97 wherein the column includes between about 30 to about 50 trays above the side draw.

110. The process of claim 109 wherein the column includes between about 32 to about 48 trays above the side draw.

111. The process of claim 110 wherein the column includes between about 38 to about 44 trays above the side draw.