WO2015191528A1

WO2015191528A1 - Fouling reduction in the acetonitrile removal steps of acrylonitrile recovery

Info

Publication number: WO2015191528A1
Application number: PCT/US2015/034826
Authority: WO
Inventors: Timothy Robert Mcdonel; Jay Robert COUCH; David Rudolph Wagner; Paul Trigg Wachtendorf
Original assignee: Ineos Europe Ag
Priority date: 2014-06-11
Filing date: 2015-06-09
Publication date: 2015-12-17
Also published as: CN104107559A; JP6761758B2; EA034228B1; CN109499085A; TR201617300T1; EA201692339A1; SA516380473B1; TWI715532B; TW201605774A; JP2017519002A

Abstract

A method is provided comprising adding acid to a reflux stream, and conveying the reflux stream to an acetonitrile fractionator, wherein the acid reduces fouling in the acetonitrile fractionator.

Description

FOULING REDUCTION IN THE ACETONITRILE REMOVAL STEPS OF ACRYLONITRILE RECOVERY

FIELD OF THE INVENTION

[1] The disclosure is directed to an improved process and system for the manufacture of acrylonitrile or methacrylonitrile. In particular, the disclosure is directed to improved reduction of fouling in the acetonitrile removal steps of acrylonitrile recovery.

BACKGROUND

[2] Various processes and systems for the manufacture of acrylonitrile and

methacrylonitrile are known; see for example, U.S. Patent Nos. 3,936,360;

3,433,822; 3,399,120; and 3,535,849. Propylene, ammonia, and oxygen (as an air component) are fed to an acrylonitrile reactor, which contains catalyst and operates as a fluidized bed. A conventional practice is to operate the reactor with an excess amount of ammonia in the feed with respect to the amount of propylene fed to the reactor. Some of the extra ammonia is burned in the reactor due to the extreme conditions before it can combine with propylene to form acrylonitrile. The remaining extra ammonia, commonly referred to as "excess ammonia," exits the reactor in the effluent gas. This gas then typically goes through a cooler and then to a quenching vessel to remove the excess ammonia. See e.g., U.S. Patent Nos. 3,936,360; 4,166,008, 4,334,965, 4,341,535, 5,895,635, and 6,793,776.

[3] Conventional processes typically involve recovery and purification of

acrylonitrile/methacrylonitrile produced by the direct reaction of a hydrocarbon selected from the group consisting of propane, propylene or isobutylene, ammonia and oxygen in the presence of a catalyst has been accomplished by transporting the reactor effluent containing acrylonitrile/methacrylonitrile to a first column (quench) where the reactor effluent is cooled with a first aqueous stream, transporting the cooled effluent containing acrylonitrile/methacrylonitrile into a second column (absorber) where the cooled effluent is contacted with a second aqueous stream to absorb the acrylonitrile/methacrylonitrile into the second aqueous stream, transporting the second aqueous stream containing the acrylonitrile/methacrylonitrile from the second column to a first distillation column (recovery column) for separation of the crude acrylonitrile/

methacrylonitrile from the second aqueous stream, and transporting the separated crude acrylonitrile/methacrylonitrile to a second distillation column (heads column) to remove at least some impurities from the crude acrylonitrile/ methacrylonitrile, and transporting the partially purified acrylonitrile/ methacrylonitrile to a third distillation column (product column) to obtain product acrylonitrile/methacrylonitrile. See e.g., U.S. Patent Nos. 4,334,295, and 4,238,295, which disclose conventional processes wherein separation of acetonitrile from acrylonitrile is performed in a single extractive distillation column. In such conventional processes, the bottoms stream of the acetonitrile fractionator is routed to the recovery column or extractive distillation column.

A problem encountered in conventional processes and systems is the

accumulation of hydrogen cyanide in a high boiling compound that breaks down at temperatures required in the acetonitrile fractionator. The breakdown of the high boiling compound releases hydrogen cyanide in free radical form that polymerizes and creates fouling in the acetonitrile fractionator. The fouling can cause poor operation of the acetonitrile fractionator, and result in unit shutdown to clean the acetonitrile fractionator column and remove the fouling. In addition, a small amount of ammonia passes through quench as the quenching reaction is not 100% efficient. This ammonia tends to accumulate.

SUMMARY

Accordingly, an aspect of this disclosure is to provide a safe, effective and cost efficient process and apparatus that reduces and/or removes fouling in the acetonitrile fractionator column.

In an aspect, a process is provided comprising adding acid to a reflux stream and conveying the reflux stream to an acetonitrile fractionator. [7] In another aspect, a process includes conveying a bottoms stream of an acetonitrile fractionation column to a quench column. In this aspect, the bottoms stream includes at least some acid.

[8] In another aspect, an apparatus includes an acetonitrile fractionator configured to produce an overhead stream comprising acetonitrile; a reflux line configured to convey a reflux stream to the acetonitrile fractionator; and an acid addition line configured to add acid to the reflux stream.

[9] The above and other aspects, features and advantages of the present disclosure will be apparent from the following detailed description of the illustrated embodiments thereof which are to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[10] A more complete understanding of the exemplary embodiments of the present invention and the advantages thereof may be acquired by referring to the following description in consideration of the accompanying drawings, in which like reference numbers indicate like features and wherein:

[11] FIG. 1 is a schematic flow diagram in accordance with at least one aspect of the disclosure.

[12] FIG. 2 is a schematic flow diagram in accordance with at least one aspect of the disclosure.

[13] FIG. 3 illustrates a flow diagram of a method 300 in accordance with aspects of the disclosure.

DETAILED DESCRIPTION

[14] In an aspect, a method or process is provided comprising the step of adding an acid in a reflux stream to an acetonitrile fractionator. In an aspect, the process comprises conveying the reflux stream to an acetonitrile fractionator comprising a top tray and multiple trays below the top tray, wherein the step of conveying comprises conveying the reflux stream to the top tray, wherein the acid reduces fouling in the acetonitrile fractionator.

[15] In an aspect, the process comprises routing a bottoms stream of the acetonitrile fractionator to a quench vessel. In an embodiment, the acid added in the reflux to the acetonitrile fractionator is acetic acid. In an aspect, the routing of the bottoms steam from the acetonitrile fractionator may include taking at least a portion of the acetonitrile fractionator bottoms stream otherwise routed to a recovery column, and rerouting at least one portion to the quench vessel. In an aspect, the acid may be added in the reflux steam at a low dosage rate to prevent or reduce polymer formation in the acetonitrile fractionator and reduce cleaning costs, as well as prolong operation of the acetonitrile fractionator.

[16] The routing of the bottom stream of the acetonitrile fractionator to the quench vessel may be performed so that the pH of a lower section of the recovery column is maintained at a predetermined level or range, e.g., below a neutral pH of 7, in another aspect, a pH of 5 to 7.5, and in another aspect, a pH of 6 to 7.5. The step of adding acid to the lower section of the recovery column may excessively lower the pH in the recovery column and upset the chemical balance of high boiling compounds present at this location in the process.

[17] In an aspect, the problem of hydrogen cyanide fouling is solved by the addition of acid to the reflux line returning to the top tray of the acetonitrile fractionator when the bottoms of the acetonitrile fractionator are returned to the quench column, and not back to the recovery column in the recovery section as conventional acrylonitrile processes.

[18] The acid serves as a polymer inhibitor by keeping the pH in a range such that the hydrogen cyanide present in the stream and the acetonitrile fractionator does not polymerize and cause fouling in the acetonitrile fractionator column. The acid then goes back to the quench vessel where the pH is already maintained in a lower than neutral range of about 4.5 to about 6, and can be used to help remove ammonia from the effluent stream of the reactor in an acrylonitrile plant. [19] FIG. 1 and FIG. 2 are schematic flow diagrams in accordance with at least one aspect of the disclosure. In particular, FIG. 1 and FIG. 2 are schematic representations of embodiments of the present disclosure in an acrylonitrile recovery process.

[20] A rich water or aqueous solution from absorber 300 containing acrylonitrile, acetonitrile, HCN, water and impurities is passed through line 2 to heat exchanger 4, wherein the rich water is preheated by lean/solvent water 222 from line 223 to heat exchanger 4. After pre-heating, the rich water leaves exchanger 4 via line 6 and is passed to recovery column 7. Extractive distillation is performed in recovery column 7 with the addition of solvent water passed to recovery column through line 8. The lean/solvent water 222, upon or after passing from heat exchanger 4 may be split into a solvent water stream that passes through heat exchanger 236 and line 8 to a top portion 207 of recovery column 7, and a lean water stream that passes through line 224. Lean/solvent water 222 may be provided from heat recovery apparatus 226. Heat recovery apparatus 226 may receive a steam 228 from recovery column 7 via line 230. Steam 228 may be taken recovery column 7 from a predetermined location, such as just above or at tray 232 in bottom portion 227 of recovery column 7. Tray 232 may be the bottommost tray in recovery column 7, also called the first tray of recovery column 7. Steam 228 may be transferred by pump 229 from recovery column 7 to heat recovery apparatus 226.

[21] Lean water stream passing through line 224 may be sent to an absorber 300. Heat exchange may occur at heat exchanger 234 before lean water stream passing through line 224 is sent to absorber 300. Heat may be supplied through exchanger 210 for the distillation in recovery column 7. Three streams are removed from the recovery column 7. First, an overhead stream of acrylonitrile, HCN, water and some impurities is removed from recovery column 7 via line 212. Side stream 214 may be removed from recovery column 7 and passed to stripper or acetonitrile fractionator 215. Overhead stream 203 comprising acetonitrile may be removed from a top portion of acetonitrile fractionator 215 via line 216. Liquid bottoms 209 from bottom 205 of acetonitrile fractionator 215 may be returned to recovery column 7 through line 218. Pump 219 may be used for this return of liquid through line 218 to recovery column 7. It has been found, however, to be preferable to convey bottoms 209 from the bottom 205 to quench vessel 10 through line 221. A bottoms stream from recovery column 7 may be removed via line 51, and transferred by pump 53 through line 220 to quench column vessel 10 or waste disposal.

[22] In an embodiment, the stream comprising acetonitrile in line 216 may be

conveyed to condenser 235, and exit as condenser bottom stream 245. Condenser bottom stream 245 may be split at juncture 247 into reflux stream 251 in reflux line 217 and a crude acetonitrile stream 253 in crude acetonitrile line 237. In an aspect, reflux stream 251 in reflux line 217 may be returned to the top tray 241 of acetonitrile fractionator 215. A portion of stream 215 may be provided to line 216 via line 239.

[23] In one aspect, vapor phase containing acetonitrile, water and trace amounts of

HCN are withdrawn from recovery column 7 as sidestream 214 and conveyed to acetonitrile fractionator 215. Acetonitrile fractionator 215 may be a column that comprises multiple trays. Pump 225 may be used to pump reflux through reflux line 217 and/or crude acetonitrile line 237.

[24] In one aspect, the process includes adding acid to a reflux stream. As further described, "adding acid to a reflux stream" may include adding acid to reflux line 217, adding acid to overhead in line 216, adding acid to reflux line 239, and combinations of each. In another aspect, acid may be added upstream or downstream of the condenser 235. Addition of acid upstream of the condenser 235 provides a more dilute concentration of acid. Addition of acid downstream of the condenser would provide a higher concentration of acid to the acetonitrile fractionator 215.

[25] In another aspect, acid is provided to the condenser 235 to reduce fouling in the condenser. In this aspect, acid conveyed to the condenser 235 is most effective when a spray of acid to a tube sheet in the condenser is completely covered with with a spray of the acid. Acid may be conveyed to the tube sheet in condenser 235 by a spray nozzle, such as for example a full cone spary nozzle. Spray nozzles may be angle to effect spray coverage of the tube sheet. For example, the nozzle may be perpendicular to the tube sheet and up to about a 60° angle from perpendicular to the tube sheet.

[26] In one aspect, an organic acid or organic acid derivative, such as for example, acetic acid or glycol acid, may be added via line 213 to reflux line 217. In another aspect, an organic acid or organic acid derivative, such as for example, acetic acid or glycol acid, may be added via line 233 to overhead in line 216 from acetonitrile fractionator 215. In another aspect, an organic acid or organic acid derivative, such as for example, acetic acid or glycol acid, may be added via line 243 to reflux line 239. In another aspect, the addition of organic acid or organic acid derivative, such as for example, acetic acid or glycol acid, via line 213 to reflux line 217 and/or via line 233 and/or via line 243 to reflux line 239, to line 216 prior to entry of the overhead to condenser 235 may be useful to reduce polymerization and fouling in acetonitrile fractionator 215, condenser 235, and/or other apparatus, such as, for example, when the bottoms of acetonitrile fractionator 215 are routed to a quench vessel, as opposed to recovery column 7. Acetonitrile fractionator 215 may be designed or configured to concentrate a dilute water/acetonitrile stream that may be sent to other apparatus for further purification and/or recovery of acetonitrile. In an embodiment, bottoms 211 of acetonitrile fractionator 215 may be transferred by pump 55 through line 221 to quench vessel 10. In an embodiment, bottoms 211 of acetonitrile fractionator 215 may be joined via line 9 with recovery column bottoms in line 51, wherein the combined bottoms may be transferred by pump 53 through line 220 to the quench vessel 10 or to waste disposal.

[27] As shown in FIG. 2, quench vessel 10 is configured to receive reactor effluent gas or gaseous stream 12 through conduit 14. Reactor effluent gas 12 may comprise acrylonitrile and ammonia. Reactor effluent gas 12 may be cooled in a reactor effluent cooler before entering quench vessel 10. In quench vessel 10, the quench liquid comprising the bottoms stream of the acetonitrile fractionator contacts and quenches reactor effluent gas 12. [28] An acid 36 (e.g., 98% sulfuric acid) may be added via line 38 to quench liquid 16. Due to acid in bottoms 21 1 that is routed to quench vessel 10, the amount of acid added through line 38 may be reduced. Quench liquid 16 comprises liquid effluent exiting bottom 42 of quench vessel 10 through line 44. Water may be added via line 46 to quench vessel 10 through inlet 48, or otherwise may be added to quench liquid 16 or elsewhere in the liquid recycle loop formed by streams 17, 44, and 65. Quench liquid 16 is circulated through line 44 and back to lines 65 and 17 using pump 50. A stream 67 may be withdrawn as part of the liquid effluent exiting through line 44, in order to maintain a relatively constant mass flow in the liquid recycle loop by offsetting the liquid added via lines 38, 46, 220 and 221. Stream 67 removes formed neutralization reaction products (e.g. , ammonium sulfate) and is also useful for preventing the accumulation of unwanted products in the liquid recycle loop, such as corrosion products.

Effluent exiting bottom 42 of quench vessel 10 may be drawn from line 44 at siphon point 52.

[29] Overhead stream 13 may flow through line 15 from quench vessel 10 to quench after cooler 240. Cold water may be used to quench after cooler 240 to cool overhead stream 13 quench after cooler condensate. Rich water may be transferred by pump 242 from bottom portion 250 of quench after cooler 240 to rich water line 2 and/or to recirculation line 248 and back to upper portion 252 of quench after cooler 240. After being cooled by quench after cooler 240, overhead stream 13 may exit quench after cooler 240 as stream 244. Stream 244 may be conveyed via line 246 to absorber 300. Lean water from line 224 may enter upper portion 254 of absorber 300. Off gas 256 from absorber 300 may be sent to an incinerator (not shown). Stream 258 from bottom 262 of absorber 300 may comprise rich water as previously described. This rich water may be transferred via pump 260 to line 2. Stream 258 may be combined with rich water from quench after cooler 240, such as at junction 264.

[30] In an aspect, controller 1 1 may be configured to process one or more signals corresponding to a measured parameter, e.g., the pH of acetonitrile fractionator bottoms 209 in bottom 205 of acetonitrile fractionator 215, or the pH of the acetonitrile fractionator bottoms 211 in line 221 or line 9, as measured by a pH sensor (not shown in FIG. 1). Controller 11 may be configured to determine whether the measured parameter is above or below a predetermined parameter range. Those skilled in the art will recognize that in accordance with the disclosure, the measured parameter may be any suitable parameter useful in operation of the acetonitrile fractionator, e.g., a pH of acetonitrile fractionator bottoms 209 or 211 as previously discussed, or a or a liquid level measured by a level controller (not shown in FIG. 1) in bottom 205 of acetonitrile fractionator 215, or a flow controller (not shown in FIG. 1) associated with the flow of fluid in a line or lines discussed herein. Controller 11 may be configured to adjust operation of one or more devices via communication lines or wireless communications (not shown in FIG. 1) if the measured parameter is below or above a predetermined parameter range. For example, controller 11 may be configured to adjust the amount of acid added through lines 213 or 233 to achieve a desired pH in reflux stream 251 in order to reduce fouling in acetonitrile fractionator 215. Those skilled in the art will recognize that in accordance with the disclosure, controller 11 may be configured to control operation of pump(s) and/or valves associated with the addition of acid through lines 213 and/or 233 in order to meet the predetermined range(s). Those skilled in the art will recognize that controller 11 or a similar controller may be located remote from a level controller or flow controller (not shown in FIG. 1), or may be located at and comprise a level controller, or a flow controller. Those skilled in the art will recognize that in accordance with the disclosure, controller 11 may be configured to operation of devices shown in FIG. 2 and pump(s) and/or valves associated with those devices.

Testing was performed to demonstrate the advantages of acid addition to acetonitrile fractionator 215, and routing acetonitrile fractionator bottoms to quench vessel 10 instead of routing acetonitrile fractionator bottoms to recovery column 7 in accordance with conventional practice and without acid addition to acetonitrile fractionator 215. The following test data was obtained. [32] Test Data - A plant 1 comprising a quench vessel shown in FIG. 1 was operated in accordance with the disclosure to show the reduction in the formation of ammonia in the overhead line 216 of acetonitrile fractionator 215. Ammonia in overhead line 216 is a byproduct of the polymerization reaction of hydrogen cyanide, and thus indicative of undesirable polymer formation in the acetonitrile fractionator 215. Plant 1 "with acid" was operated with the addition of acetic acid as described above to the top tray of acetonitrile fractionator 215, and acetonitrile fractionator bottoms were sent via line 211 to quench vessel 10. Plant 1 "no acid" was operated with no addition of acetic or other acid, wherein the acetonitrile fractionator bottoms were sent back to recovery column 7 via line 18.

[33] The results obtained in running Plant 1 "with acid" and running Plant 1 "without acid" as described above is shown in the Table below.

Acetonitrile 6.2 Not determined 7.1 Not determined

Fractionator

(AF)

Bottoms

Acetonitrile 6.4 9 8.9 188

Fractionator

(AF)

Overhead

[34] The test data presented above shows the effects of the addition of the acetic acid to the acetonitrile fractionator overhead where the pH of the stream is lowered from a pH of 8.9 to a pH of 6.4. In an aspect, the lowering of pH in the recovery column reduces undesirable polymerization. There is a corresponding reduction in the ammonia concentration in the acetonitrile fractionator overhead, i.e., from 188 ppm to 9 ppm when the acetic acid is added. This drop in ammonia in the acetonitrile fractionator overhead, i.e., the stream flowing through line 216 is believed to be a result of the acetic acid capturing the ammonia as ammonium acetate and removing it in stream 211 to quench 10. It may also partially a result of hydrogen cyanide staying in solution as a cyanohydrin and not breaking down to its original components and then polymerizing, which releases ammonia. Ammonia is a byproduct of the polymerization reaction of hydrogen cyanide. The addition of the acetic acid to the stream clearly reduces the amount of ammonia present and demonstrates the effectiveness of the present disclosure.

[35] In one aspect, selction of pH level is a balance between reduction of fouling and use of desirable materials of construction. In this aspect, use of pH levels as described herein allows for use of carbon steel construction.

[36] FIG. 3 illustrates a flow diagram of a method 300 in accordance with aspects of the disclosure. Method 300 may be carried out using apparatus previously described. Step 301 comprises routing a bottoms stream of an acetonitrile fractionator column to a quench vessel. Step 302 comprises adding acid to a reflux stream to the acetonitrile fractionator. In an aspect, the acetonitrile fractionator comprises multiple trays, and the step of adding acid to the reflux stream to the acetonitrile fractionator column comprises adding the acid to the top tray of the multiple trays of the acetonitrile fractionator. In an aspect, the step of adding acid to the reflux stream to the acetonitrile fractionator comprises adding acetic acid to the reflux stream. In an aspect, the step of adding acid to the reflux is performed to lower the pH of overhead of the acetonitrile fractionator.

[37] In an aspect, the step of adding acid to the reflux results in lowering the pH of the overhead of the acetonitrile fractionator from above 7.0 to a pH below 7.0. In an aspect, the step of adding acid to the reflux results in lowering the pH of the overhead of the acetonitrile fractionator from above 8.0 and to a pH below 6.5. In an aspect, the step of adding acid to the reflux results in lowering the pH of the overhead of the acetonitrile fractionator column from above 7.0 and to a pH of about 6.4.

[38] In an aspect, the steps of routing a bottoms stream of an acetonitrile fractionator to a quench vessel further comprises rerouting the bottoms stream of the acetonitrile fractionator from flowing to a recovery column so that the bottom stream of the acetonitrile fractionator column flows to the quench vessel.

[39] The present invention is applicable to any process for the recovery of acrylonitrile that has a recovery column and one or more additional distillation columns. The additional distillation columns typically consist of an HCN column, a drying column for removing water, and a product column for recovering the product- quality acrylonitrile. However, these separate operations may be combined as shown in the drawing wherein one distillation column removes both HCN and water.

[40] While in the foregoing specification this disclosure has been described in relation to certain preferred embodiments thereof, and many details have been set forth for purpose of illustration, it will be apparent to those skilled in the art that the disclosure is susceptible to additional embodiments and that certain of the details described herein can be varied considerably without departing from the basic principles of the disclosure. It should be understood that the features of the disclosure are susceptible to modification, alteration, changes or substitution without departing from the spirit and scope of the disclosure or from the scope of the claims. For example, the dimensions, number, size and shape of the various components may be altered to fit specific applications. Accordingly, the specific embodiments illustrated and described herein are for illustrative purposes only.

Claims

WE CLAIM:

1. A process comprising:

adding acid to a reflux stream; and

conveying the reflux stream to an acetonitrile fractionator.

2. The process of claim 1 , wherein the acid reduces fouling in the acetonitrile fractionator.

3. The process of claim 1, wherein the acetonitrile fractionator comprises a top tray and multiple trays below the top tray, wherein the step of conveying comprises conveying the reflux stream to the top tray.

4. The process of claim 1 , wherein the acid comprises an organic acid, an organic acid derivative, and mixtures thereof, wherein the organic acid is selected from the group consisting of acetic acid, glycolic acid, and mixtures thereof.

5. The process of claim 1, wherein the step of adding acid to the reflux stream lowers a pH of an overhead stream of the acetonitrile fractionator.

6. The process of claim 1, wherein the step of adding acid to the reflux stream maintains the pH of an overhead stream of the acetonitrile fractionator within a predetermined range.

7. The process of claim 5, wherein the step of adding acid to the reflux lowers the pH of the overhead stream of the acetonitrile fractionator column from above 7.0 to a pH below 7.0.

8. The process of claim 5, wherein the step of adding acid to the reflux stream lowers the pH of the overhead stream of the acetonitrile fractionator column from above 8.0 and to a pH below 6.5.

9. The process of claim 5, wherein the step of adding acid to the reflux stream lowers the pH of the overhead stream of the acetonitrile fractionator column from above 7.0 and to a pH of about 6.4.

10. The process of claim 6, wherein the step of adding acid to the reflux stream maintains the pH of the overhead stream of the acetonitrile fractionator below about 7.0.

11. The process of claim 6, wherein the step of adding acid to the reflux stream maintains the pH of the overhead stream of the acetonitrile fractionator below about 6.5.

12. The process of claim 6, wherein the step of adding acid to the reflux stream maintains the pH of the overhead stream of the acetonitrile fractionator below about 6.4.

13. The process of claim 1, further comprising condensing an overhead stream to provide the reflux stream.

14. The process of claim 13, wherein the step of adding acid to the reflux stream comprises adding acid to the overhead stream of the acetonitrile fractionator.

15. The process of claim 14, further comprising routing a bottoms stream of the acetonitrile fractionator to a quench vessel.

16. The process of claim 15, wherein the bottoms stream of the acetonitrile fractionator comprises at least some acid added to the reflux stream during the step of adding acid to the reflux stream.

17. The process of claim 16 further comprising providing a gaseous stream that includes acrylonitrile and ammonia to the quench vessel, and contacting the gaseous stream with a quench liquid, the quench liquid comprising the bottoms stream of the acetonitrile fractionator.

18. The process of claim 15, wherein the step of routing comprises rerouting at least a portion of the bottoms stream of the acetonitrile fractionator from being conveyed to a recovery column so that the bottom stream of the acetonitrile fractionator is conveyed to the quench vessel.

19. The process of claim 1, further comprising conveying at least a portion of the reflux stream to an overhead stream of the acetonitrile fractionator upstream of a condenser.

20. A process comprising conveying a bottoms stream of an acetonitrile fractionation column to a quench column, wherein the bottoms stream includes at least some acid.

21. The process of claim 20, wherein the bottoms stream has a pH of about 7 or less.

22. The process of claim 20, wherein the bottoms stream has a pH of about 5 to about 7.5.

23. The process of claim 20, wherein the bottoms stream has a pH of about 6 to about 7.

24. An apparatus comprising:

an acetonitrile fractionator configured to produce an overhead stream comprising acetonitrile;

a reflux line configured to convey a reflux stream to the acetonitrile fractionator, the reflux stream; and

an acid addition line configured to add acid to the reflux stream.

25. The apparatus of claim 24, further comprising a condenser configured to cool the overhead stream and generate a condensed crude acetonitrile product, wherein the reflux stream comprises at least a portion of the condensed acetonitrile product.

26. The apparatus of claim 24 wherein the acetonitrile fractionator comprises a top tray and multiple trays below the top tray, and the reflux line is configured to convey the reflux stream to the top tray.

27. The apparatus of claim 24, wherein the acid comprises acetic acid.

28. The apparatus of claim 24 comprising a controller configured to control acid addition to the reflux stream.

29. The apparatus of claim 28, wherein the controller is configured to control acid addition to lower the pH of the overhead stream.

30. The apparatus of claim 29, wherein the controller is configured to maintain the pH of the overhead stream within a predetermined range.

31. The apparatus of claim 29, wherein the controller is configured to lower the pH of the overhead stream from above 7.0 to a pH below 7.0.

32. The apparatus of claim 29, wherein the controller is configured to lower the pH of the overhead stream from above 8.0 to a pH below 6.5.

33. The apparatus of claim 29, wherein the controller is configured to lower the pH of the overhead stream from above 7.0 to a pH of about 6.4.

34. The apparatus of claim 25, wherein the acid line is configured to add acid the overhead stream.

35. The apparatus of claim 24, further comprising a routing line configured to route at least a portion of bottoms stream of the acetonitrile fractionator to a quench vessel.

36. The apparatus of claim 35, wherein the bottoms stream comprises at least some acid added to the reflux stream.

37. The apparatus of claim 36, wherein the quench vessel is configured to receive a gaseous stream comprising acrylonitrile and ammonia, and contact the gaseous stream with a quench liquid, the quench liquid comprising the bottoms stream of the acetonitrile fractionator.