JP2017519002A - Fouling reduction in the acetonitrile removal step of acrylonitrile recovery - Google Patents

Abstract

A method is provided for reducing fouling in an acetonitrile rectification column with an acid, the method comprising adding an acid to the reflux stream and conveying the reflux stream to an acetonitrile rectification column. [Selection] Figure 1

Description

  The present disclosure relates to improvements in methods and systems for producing acrylonitrile or methacrylonitrile. Specifically, the present disclosure relates to improved fouling reduction in the acetonitrile removal step of acrylonitrile recovery.

  Various methods and systems for producing acrylonitrile or methacrylonitrile are known, for example, U.S. Pat. Nos. 3,936,360, 3,433,822, 3,399,120 and third. , 535,849. Propylene, ammonia and oxygen (as an air component) are fed into an acrylonitrile reactor containing a catalyst and functioning as a fluidized bed. Conventional methods include operating the reactor with an excess of ammonia in the feed relative to the amount of propylene fed to the reactor. A portion of this excess ammonia is combusted in the reactor due to its extreme conditions and then combined with propylene to form acrylonitrile. The remaining excess ammonia, commonly referred to as “excess ammonia”, is contained in the exhaust gas and discharged from the reactor. Thereafter, this gas usually passes through a cooler and then reaches a quenching tank to remove excess ammonia. For example, U.S. Pat. Nos. 3,936,360, 4,166,008, 4,334,965, 4,341,535, 5,895,635 and 6,793,776. Please refer to the issue.

  Conventional methods usually recover and purify acrylonitrile / methacrylonitrile produced by direct reaction of a hydrocarbon selected from the group consisting of propane, propylene or isobutylene with ammonia and oxygen in the presence of a catalyst. The reactor effluent containing acrylonitrile / methacrylonitrile is transferred to the first tower (quenching tower) and cooled with the first water stream, and the cooling effluent containing acrylonitrile / methacrylonitrile is sent to the second tower ( In the absorption tower), the cooling waste water is brought into contact with the second water stream, the acrylonitrile / methacrylonitrile is absorbed in the second water stream, and the second water stream containing acrylonitrile / methacrylonitrile is absorbed in the second water stream. From the tower to the first distillation tower (recovery tower) to separate the crude acrylonitrile / methacrylonitrile from the second water stream, The separated crude acrylonitrile / methacrylonitrile is transferred to a second distillation column (head tower) to remove at least some impurities from the crude acrylonitrile / methacrylonitrile and partially purified acrylonitrile / methacrylonitrile to 3 is transferred to a distillation column (product column) 3 to obtain acrylonitrile / methacrylonitrile as a product. See, for example, US Pat. Nos. 4,334,295 and 4,238,295 which disclose conventional methods for separating acetonitrile from acrylonitrile in a single extractive distillation column. In such conventional methods, the bottom stream of the acetonitrile rectification column is routed to the recovery column or extractive distillation column.

US Pat. No. 3,936,360 US Pat. No. 3,433,822 US Pat. No. 3,399,120 US Pat. No. 3,535,849 US Pat. No. 4,166,008 U.S. Pat. No. 4,334,965 US Pat. No. 4,341,535 US Pat. No. 5,895,635 US Pat. No. 6,793,776 U.S. Pat. No. 4,334,295 U.S. Pat. No. 4,238,295

  A problem encountered with conventional methods and systems is that hydrogen cyanide accumulates in high boiling compounds that decompose at the required temperature of the acetonitrile rectification column. When the high-boiling compounds are decomposed, hydrogen cyanide is released in the form of free radicals, which are polymerized to produce fouling in the acetonitrile rectification column. Fouling causes the acetonitrile rectification column to malfunction, and the unit may be temporarily suspended to clean the acetonitrile rectification column and remove fouling. Further, since the efficiency of the quenching reaction is not 100%, a small amount of ammonia passes through the quenching tower. This ammonia tends to accumulate.

  Accordingly, aspects of the present disclosure provide a safe, effective and cost effective method and apparatus that reduces and / or eliminates fouling in an acetonitrile rectification column.

  In one aspect, a method is provided that includes adding an acid to the reflux stream and conveying the reflux stream to an acetonitrile rectification column.

  In another aspect, the method includes conveying a bottom stream of an acetonitrile rectification column to a quench tower. In this embodiment, the bottom stream contains at least some acid.

  In another aspect, the apparatus comprises an acetonitrile rectification column configured to produce a top stream comprising acetonitrile, a reflux line configured to convey the reflux stream to the acetonitrile rectification column, and a reflux stream. And an acid addition line configured to add acid.

  The foregoing and other aspects, features, and advantages of the present disclosure will become apparent when the following detailed description of the exemplary embodiments is read in conjunction with the accompanying drawings.

  The exemplary embodiments of the present disclosure and their advantages can be more fully understood by reference to the following description, taken in conjunction with the accompanying drawings, in which like features are indicated by like reference numerals, and in which:

FIG. 3 is a schematic flow diagram according to at least one aspect of the present disclosure. FIG. 3 is a schematic flow diagram according to at least one aspect of the present disclosure. FIG. 5 is a flow diagram of a method 300 according to aspects of the present disclosure.

  In one aspect, a method or process is provided that includes adding an acid to the reflux stream to the acetonitrile rectification column. In one aspect, the method includes conveying a reflux stream to an acetonitrile rectification column that includes an uppermost tray and a plurality of trays below the uppermost tray, the conveying step comprising refluxing the uppermost tray. And the acid reduces fouling in the acetonitrile rectification column.

  In some embodiments, the method includes routing the bottom stream of the acetonitrile rectification column to a quench bath. In certain embodiments, the acid added to the reflux to the acetonitrile rectification column is acetic acid. In one aspect, the bottom stream routing from the acetonitrile rectification column involves at least part of the bottom stream of the acetonitrile rectification column that would have been routed to the recovery tower, and quenching at least a portion thereof. Rerouting the bath. In certain embodiments, a low dose of acid can be added to the reflux stream to prevent or reduce polymer formation in the acetonitrile rectification column to reduce washing costs and to prolong the operation of the acetonitrile rectification column.

  The routing of the bottom stream of the acetonitrile rectification column to the quenching tank is such that the pH at the bottom of the recovery column is less than 7 neutral pH, in another embodiment pH 5 to 7.5, in another embodiment pH 6 to 7,5. Etc. so that it is maintained at a predetermined level or range. The step of adding acid to the bottom of the recovery tower can excessively lower the pH in the recovery tower and upset the chemical equilibrium of high boiling compounds present at this location during processing.

  In one embodiment, the problem of hydrogen cyanide fouling is that when the bottom liquid of the acetonitrile rectification column returns to the quenching tower and does not return to the recovery column in the recovery unit as in the case of conventional acrylonitrile treatment, the uppermost tray of the acetonitrile rectification column. This is solved by adding an acid to the reflux line back to.

  The acid serves as a polymerization inhibitor by maintaining the pH within a range in which the flow and hydrogen cyanide present in the acetonitrile rectification column do not polymerize and fouling does not occur in the acetonitrile rectification column. The acid is then returned to the quench tank where the pH is already maintained below the neutral range of about 4.5 to about 6, and this acid is used to discharge the reactor discharge stream in the acrylonitrile plant. Can be used to remove ammonia from water.

  1 and 2 are schematic flow diagrams according to at least one aspect of the present disclosure. Specifically, FIGS. 1 and 2 are schematic diagrams of embodiments of the present disclosure in an acrylonitrile recovery process.

  Rich water or an aqueous solution from the absorption tower 300 containing acrylonitrile, acetonitrile, HCN, water and impurities passes through the line 2 to the heat exchanger 4 where the line 223 heats the heat exchanger. Preheated with lean water / solvent water 222 to 4. After preheating, the fertilized water leaves the heat exchanger 4 through the pipe 6 and moves to the recovery tower 7. In the recovery tower 7, extractive distillation is performed by adding the solvent water moved to the recovery tower 7 via the pipe line 8. The dilute water / solvent water 222 passes through the heat exchanger 236 and the pipe 8 to the top 207 of the recovery tower 7 when passing through the heat exchanger 4 or after passing, and the dilute water stream passing through the pipe 224. It is divided into. The dilute water / solvent water 222 can be supplied from the heat recovery device 226. The heat recovery device 226 can receive the steam 228 from the recovery tower 7 via the pipe line 230. The steam 228 can be taken out from a predetermined position of the recovery tower 7 such as the tray 232 present at the bottom 227 of the recovery tower 7 or directly above the tray 232. The tray 232 can be the bottommost tray in the recovery tower 7 and is also referred to as the first tray of the recovery tower 7. The steam 228 can be transferred from the recovery tower 7 to the heat recovery device 226 by the pump 229.

  The dilute water stream that passes through line 224 can be sent to absorption tower 300. Heat exchange can be performed in the heat exchanger 234 before the dilute water stream passing through the conduit 224 is sent to the absorption tower 300. Heat can be supplied through the exchanger 210 for distillation in the recovery tower 7. Three streams are extracted from the recovery tower 7. First, a tower top stream composed of acrylonitrile, HCN, water and some impurities is taken out from the recovery tower 7 via a pipe 212. From the recovery tower 7, the tower side stream 214 can be taken out and sent to a stripper or acetonitrile rectification tower 215. From the top of the acetonitrile rectification column 215, a column top stream 203 containing acetonitrile can be taken out via a pipe line 216. The column bottom liquid 209 from the bottom 205 of the acetonitrile rectification column 215 can be returned to the recovery column 7 via the pipe line 218. A pump 219 can be used to return the liquid to the recovery tower 7 via line 218. However, it has been found that the bottom liquid 209 is preferably transported from the bottom 205 to the quenching tank 10 via the pipe 221. The tower bottom flow from the recovery tower 7 can be taken out via the pipe 51 and transferred to the quenching tank 10 or the waste treatment apparatus via the pipe 220 by the pump 53.

  In some embodiments, the stream containing acetonitrile in line 216 can be conveyed to condenser 235 and discharged as condenser tower bottom stream 245. The condenser tower bottom stream 245 can be split at the junction 247 into a reflux stream 251 in the reflux line 217 and a crude acrylonitrile stream 253 in the crude acetonitrile line 237. In one embodiment, the reflux stream 251 in the reflux line 217 can be returned to the uppermost tray 241 of the acetonitrile rectification column 215. A portion of stream 215 can be supplied to line 216 via line 239.

  In one embodiment, a gas phase containing acetonitrile, water and a small amount of HCN is taken out from the recovery tower 7 as a tower side stream 214 and conveyed to the acetonitrile rectification tower 215. The acetonitrile rectification column 215 can be a column including a plurality of trays. Reflux can be pumped using a pump 225 through a reflux line 217 and / or a crude acrylonitrile line 237.

  In some embodiments, the method includes adding an acid to the reflux stream. As will be further explained, “adding acid to the reflux stream” means adding acid to the reflux line 217, adding acid to the top liquid in the line 216, and adding acid to the reflux line 239. Additions and combinations of each of these. In another aspect, the acid can be added upstream or downstream of the condenser 235. When acid is added upstream of the condenser 235, the acid concentration decreases. As acid is added downstream of the condenser, a higher concentration of acid is supplied to the acetonitrile rectification column 215.

  In another aspect, an acid is provided to the condenser 235 to reduce condenser fouling. In this embodiment, the acid conveyed to the condenser 235 is most effective when the tube plate in the condenser is completely covered by the spray of acid. The acid can be conveyed to the tube plate in the condenser 235 by a spray nozzle such as a circular full surface spray nozzle. The spray nozzle can be tilted to cover the tube sheet with spray. For example, the nozzle can be perpendicular to the tube sheet and at an angle of up to about 60 ° from the normal to the tube sheet.

  In some embodiments, an organic acid or organic acid derivative such as, for example, acetic acid or glycolic acid can be added to reflux line 217 via line 213. In some embodiments, an organic acid or organic acid derivative such as acetic acid or glycolic acid can be added to the top liquid in line 216 from acetonitrile rectification column 215 via line 233. In some embodiments, an organic acid or organic acid derivative such as, for example, acetic acid or glycolic acid can be added to reflux line 239 via line 243. In another embodiment, an organic acid or organic acid derivative such as acetic acid or glycolic acid, for example, when the bottom liquid of acetonitrile rectification column 215 is routed to a quench bath rather than the recovery column 7 Adding to the reflux line 217 via line 213 and / or to the reflux line 239, line 216 via line 233 and / or line 243 before the overhead liquid enters the condenser 235, It may be useful to reduce polymerization and fouling in the rectification column 215, the condenser 235 and / or other equipment. The acetonitrile rectification column 215 can be designed or configured such that the dilute water / acetonitrile stream can be concentrated and sent to other equipment for further purification and / or recovery of acetonitrile. In an embodiment, the bottom liquid 211 of the acetonitrile rectification column 215 can be transferred to the quenching column 10 via the pipe 221 by the pump 55. In one embodiment, the bottom liquid 211 of the acetonitrile rectifying column 215 is connected to the recovery tower bottom liquid in the pipe 51 via the pipe 9, and this connected tower bottom liquid is connected to the pipe line by the pump 53. 220 can be transferred to quenching tank 10 or waste disposal.

  As shown in FIG. 2, the quench bath 10 is configured to receive a reactor exhaust gas or gas stream 12 via a conduit 14. The reactor exhaust gas 12 can contain acrylonitrile and ammonia. The reactor exhaust gas 12 can be cooled in the reactor exhaust gas cooler before entering the quench bath 10. In the quenching tank 10, the quenching liquid containing the bottom stream of the acetonitrile rectification column can contact the reactor exhaust gas 12 and quench it.

  An acid 36 (eg, 98% sulfuric acid) can be added to the quench liquid 16 via line 38. The amount of acid added via line 38 can be reduced by the acid in the bottom liquid 211 routed to the quench bath 10. The quench liquid 16 can include a liquid discharge discharged from the bottom 42 of the quench bath 10 via the conduit 44. Water can be added to the quench bath 10 through an inlet 48 via line 46, or this water can be added separately to the quench liquid 16, or the liquid formed by the streams 17, 44 and 65. It can also be added elsewhere in the recirculation loop. The quench liquid 16 is circulated through the conduit 44 and returned to the conduits 65 and 17 using the pump 50. A portion of the liquid effluent discharged through line 44 to maintain a relatively constant mass flow in the liquid recirculation loop by correcting the liquid added through lines 38, 46, 220 and 221. The flow 67 can be taken out. Stream 67 serves to remove neutralization reaction products that are formed (eg, ammonium sulfate) and to prevent the accumulation of undesirable products such as corrosion products in the liquid recycle loop. Exhaust discharged from the bottom 42 of the quenching tank 10 can be drawn from the conduit 44 at the suction point 52.

  The tower top stream 13 can flow from the quenching tank 10 through the conduit 15 to the quenching final cooler 240. The quench final cooler 240 can use cold water to cool the overhead stream 13 to the quench final cooler condensate. From the bottom 250 of the quench final cooler 240, the fertilized water can be transferred to the fertilizer conduit 2 and / or the recirculation conduit 248 by the pump 242 and returned to the upper portion 252 of the quench final cooler 240. After cooling by the quench final cooler 240, the tower top stream 13 can be discharged from the quench final cooler 240 as stream 244. Stream 244 can be conveyed to absorption tower 300 via line 246. Diluted water from line 224 can enter the upper portion 254 of the absorption tower 300. The off gas 256 from the absorption tower 300 can be sent to an incinerator (not shown). As described above, the stream 258 from the bottom 262 of the absorption tower 300 can include fertilized water. This fertilized water can be transferred to the pipe line 2 via the pump 260. Stream 258 may be combined with fertilized water from quench final cooler 240, such as at joint 264.

  In some embodiments, the controller 11 may be configured to control, for example, the pH of the acetonitrile rectification column bottom liquid 209 at the bottom 205 of the acetonitrile rectification column 215 or the pH of the acetonitrile rectification column bottom liquid 211 in the line 221 or the line 9. Or the like, may be configured to process one or more signals corresponding to measurement parameters measured by a pH sensor (not shown in FIG. 1). The controller 11 can be configured to determine whether the measurement parameter is above or below a predetermined parameter range. For those skilled in the art, according to the present disclosure, this measurement parameter may be, for example, the pH of the acetonitrile rectification column bottom liquid 209 or 211 as described above, or the water level adjuster at the bottom 205 of the acetonitrile rectification column 215 ( Acetonitrile, such as a liquid level measured by a flow regulator (not shown in FIG. 1) associated with the fluid flow in one or more conduits described herein or not shown in FIG. It will be appreciated that any suitable parameter useful for the operation of the rectification column may be used. The controller 11 adjusts the operation of one or more devices via a communication line or wireless communication (not shown in FIG. 1) when the measured parameter is below or above a predetermined parameter range. Can be configured to. For example, the controller 11 is configured to adjust the amount of acid added through line 213 or 233 to achieve the desired pH in the reflux stream 251 to reduce fouling in the acetonitrile rectification column 215. be able to. A person skilled in the art, in accordance with the present disclosure, may have controller 11 associated with these addition (s) to meet a predetermined range (s) of acid added through lines 213 and / or 233. It will be appreciated that the pump and / or valve can be configured to control the operation. A person skilled in the art can locate the controller 11 or similar controller away from the water level regulator or flow regulator (not shown in FIG. 1) or at the same position as the water level regulator or flow regulator. It will be appreciated that they can be arranged to include these. One skilled in the art, in accordance with the present disclosure, may configure the controller 11 to control the operation of the apparatus and pump (s) shown in FIG. 2 and / or the valves associated with these apparatuses. You will recognize that you can.

  The advantage of adding acid to the acetonitrile rectifying column 215, and the bottom liquid of the acetonitrile rectifying column to the quenching tank 10 instead of being routed to the recovery column 7 without adding acid to the acetonitrile rectifying column 215 as usual. Tests were conducted to demonstrate the benefits of routing. The following test data were obtained.

  Test Data—Plant 1 with the quench tank shown in FIG. 1 was operated in accordance with the present disclosure to show reduced ammonia formation in the overhead liquid line 216 of the acetonitrile rectification column 215. Ammonia in the top liquid line 216 is a byproduct of the hydrogen cyanide polymerization reaction, thus indicating undesirable polymer formation in the acetonitrile rectification column 215. For the plant 1 “with acid”, acetic acid as described above was added to the uppermost tray of the acetonitrile rectifying column 215 to operate, and the bottom liquid of the acetonitrile rectifying column was transferred to the quenching tank 10 via the pipe 211. sent. Plant 1 “no acid” was operated without adding acetic acid or other acids, and the bottom liquid of the acetonitrile rectification column was returned to the recovery column 7 via the line 218.

The following table shows the results obtained by operating plant 1 “with acid” and plant 1 “without acid” as described above.

  The test data showed that the pH of the stream dropped from pH 8.9 to pH 6.4 due to the effect of adding acetic acid to the top liquid of the acetonitrile rectification column. In some embodiments, undesired polymerization is reduced by lowering the pH of the recovery tower. Correspondingly, the ammonia concentration in the top liquid of the acetonitrile rectification column decreases, that is, when acetic acid is added, the ammonia concentration decreases from 188 ppm to 9 ppm. The decrease in ammonia in the flow through the acetonitrile rectification column, i.e., the stream through line 216, appears to be the result of acetic acid taking up ammonia as ammonium acetate, which was removed in stream 211 to quench bath 10. . In part, hydrogen cyanide remains in the solution as cyanohydrin and is not polymerized after being decomposed into its original components, and may not be released as a result. Ammonia is a by-product of the hydrogen cyanide polymerization reaction. Adding acetic acid to the stream clearly reduces the amount of ammonia present, thus demonstrating the effectiveness of the present disclosure.

  In one aspect, the choice of pH level is a balance between reduced fouling and the use of desirable constituent materials. In this embodiment, the use of a pH level as described herein allows the use of a carbon steel structure.

  FIG. 3 shows a flow diagram of a method 300 according to aspects of the present disclosure. Method 300 can be performed using the apparatus described above. Step 301 includes routing the bottom stream of the acetonitrile rectification column to a quench bath. Step 302 includes adding an acid to the reflux stream to the acetonitrile rectification column. In one aspect, the acetonitrile rectification column includes a plurality of trays, and the step of adding acid to the reflux stream to the acetonitrile rectification column comprises the step of adding acid to the uppermost tray of the plurality of trays of the acetonitrile rectification column. Including. In some embodiments, adding the acid to the reflux stream to the acetonitrile rectification column comprises adding the acid to the reflux stream. In some embodiments, the step of adding an acid to the reflux is performed to lower the pH of the acetonitrile rectifier overhead.

  In some embodiments, the step of adding an acid to the reflux lowers the pH of the acetonitrile rectifier overhead from greater than 7.0 to less than 7.0. In some embodiments, the step of adding an acid to the reflux lowers the pH of the acetonitrile rectifier overhead from greater than 8.0 to less than 6.5. In some embodiments, the step of adding an acid to the reflux reduces the pH of the acetonitrile rectifier overhead to a pH of greater than 7.0 to about 6.4.

  In some embodiments, routing the bottoms flow of the acetonitrile rectification column to the quenching tank further comprises rerouting the bottoms flow of the acetonitrile rectification tower to flow from the flow to the recovery tower to the quenching tank.

  The present invention is applicable to any acrylonitrile recovery process having a recovery tower and one or more additional distillation towers. The further distillation column usually consists of an HCN column, a drying column to remove water, and a product column to recover product quality acrylonitrile. However, these separate operations can be combined as shown in the figure so that a single distillation column removes both HCN and water.

  In the foregoing specification, the disclosure has been described with reference to several preferred embodiments thereof, and numerous details have been set forth for purposes of illustration, but those skilled in the art will recognize the present disclosure without departing from the basic principles of the disclosure. It will be apparent that further embodiments of the disclosure are possible and that some of the details described herein may be varied significantly. It should be understood that the features of the present disclosure may be modified, altered, changed or substituted without departing from the spirit or scope of the disclosure and the claims. For example, the dimensions, number, size and shape of various components can be varied to suit a particular application. Accordingly, the specific embodiments illustrated and described herein are for illustrative purposes only.

Claims (37)

Adding an acid to the reflux stream;
Conveying the reflux stream to an acetonitrile rectification column;
A method comprising the steps of: The acid reduces fouling in the acetonitrile rectification column;
The method of claim 1. The acetonitrile rectification column includes an uppermost tray and a plurality of trays below the uppermost tray, and the transporting step includes a step of transporting the reflux stream to the uppermost tray.
The method of claim 1. The acid includes an organic acid, an organic acid derivative, and a mixture thereof, and the organic acid is selected from the group consisting of acetic acid, glycolic acid, and a mixture thereof.
The method of claim 1. The step of adding acid to the reflux stream reduces the pH of the overhead stream of the acetonitrile rectification column;
The method of claim 1. The step of adding acid to the reflux stream maintains the pH of the overhead stream of the acetonitrile rectification column within a predetermined range;
The method of claim 1. The step of adding an acid to the reflux reduces the pH of the overhead stream of the acetonitrile rectification column to a pH greater than 7.0 and less than 7.0;
The method of claim 5. The step of adding an acid to the reflux reduces the pH of the overhead stream of the acetonitrile rectification column to a pH greater than 8.0 and less than 6.5;
The method of claim 5. The step of adding an acid to the reflux reduces the pH of the overhead stream of the acetonitrile rectification column from greater than 7.0 to a pH of about 6.4;
The method of claim 5. The step of adding acid to the reflux maintains the pH of the overhead stream of the acetonitrile rectification column below about 7.0;
The method of claim 6. The step of adding acid to the reflux maintains the pH of the overhead stream of the acetonitrile rectification column below about 6.5;
The method of claim 6. The step of adding acid to the reflux maintains the pH of the overhead stream of the acetonitrile rectification column below about 6.4;
The method of claim 6. Further comprising condensing the overhead stream to provide the reflux stream.
The method of claim 1. Adding the acid to the reflux stream comprises adding an acid to the overhead stream of the acetonitrile rectification column;
The method of claim 13. Routing the bottoms stream of the acetonitrile fractionator to a quench bath;
The method according to claim 14. The bottom stream of the acetonitrile rectification column comprises at least some acid added to the reflux stream during the step of adding acid to the reflux stream.
The method of claim 15. Further comprising: supplying a gas stream comprising acrylonitrile and ammonia to the quenching tank; and contacting the gas stream with a quench liquid comprising the bottom stream of the acetonitrile rectification column.
The method of claim 16. The routing step reroutes at least a portion of the bottom stream of the acetonitrile rectifying column from transport to the recovery tower so that the bottom stream of the acetonitrile rectifying column is transported to the quenching tank. Further comprising steps,
The method of claim 15. Conveying at least a portion of the reflux stream to the overhead stream of the acetonitrile rectification column upstream of the condenser;
The method of claim 1. Conveying the bottom stream of the acetonitrile rectification column to a quench tower, the bottom stream comprising at least some acid;
A method characterized by that. The bottom stream has a pH of about 7 or less;
The method of claim 20. The bottom stream has a pH of about 5 to about 7.5;
The method of claim 20. The bottoms stream has a pH of about 6 to about 7;
The method of claim 20. An acetonitrile rectification column configured to produce a top stream comprising acetonitrile;
A reflux line configured to convey a reflux stream to the acetonitrile rectification column;
An acid addition line configured to add acid to the reflux stream;
A device comprising: Further comprising a condenser configured to cool the overhead stream to produce a condensed crude acetonitrile product, wherein the reflux stream comprises at least a portion of the condensed acetonitrile product;
25. The device according to claim 24. The acetonitrile rectification column includes an uppermost tray and a plurality of trays below the uppermost tray, and the reflux line is configured to convey the reflux flow to the uppermost tray.
25. The device according to claim 24. The acid includes acetic acid,
25. The device according to claim 24. A controller configured to control the addition of acid to the reflux stream;
25. The device according to claim 24. The controller is configured to control acid addition to reduce the pH of the overhead stream.
30. The apparatus of claim 28. The controller is configured to maintain the pH of the overhead stream within a predetermined range;
30. Apparatus according to claim 29. The controller is configured to reduce the pH of the overhead stream to a pH greater than about 7.0 and less than 7.0.
30. Apparatus according to claim 29. The controller is configured to reduce the pH of the overhead stream to a pH greater than about 8.0 to less than 6.5.
30. Apparatus according to claim 29. The controller is configured to reduce the pH of the overhead stream from greater than about 7.0 to a pH of about 6.4.
30. Apparatus according to claim 29. The acid conduit is configured to add acid to the overhead stream;
26. The device of claim 25. Further comprising a routing line configured to route at least a portion of the bottom stream of the acetonitrile rectification column to a quench bath;
25. The device according to claim 24. The bottoms stream comprises at least some acid added to the reflux stream;
36. Apparatus according to claim 35. The quench bath is configured to receive a gas stream comprising acrylonitrile and ammonia and to contact the gas stream with a quench liquid comprising the bottom stream of the acetonitrile rectification column;
37. The device according to claim 36.

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