JP6761758B2 - Reduced fouling in the acetonitrile removal step of acrylonitrile recovery - Google Patents

Description

The present disclosure relates to improvements in acrylonitrile or methacrylonitrile production methods and systems. 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, US Pat. Nos. 3,936,360, 3,433,822, 3,399,120 and 3. , 535, 849. Propylene, ammonia and oxygen (as an air component) are supplied to an acrylonitrile reactor that contains a catalyst and functions as a fluidized bed. The conventional method operates the reactor by including an excess amount of ammonia in the feed with respect to the amount of propylene supplied to the reactor. A part of this excess ammonia burns in the reactor due to its extreme state and then combines 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. After that, the gas usually reaches the quenching tank after passing through the cooler 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.

Usually, conventional methods recover and purify acrylonitrile / methacrylonitrile produced by directly reacting acrylonitrile / methacrylonitrile produced by directly reacting a hydrocarbon selected from the group consisting of propane, propylene or isobutylene with ammonia and oxygen in the presence of a catalyst. The reactor wastewater containing acrylonitrile / methacrylonitrile is transferred to the first tower (quenching tower) and cooled by the first water stream, and the cooling wastewater containing acrylonitrile / methacrylonitrile is transferred to the second tower (quenched tower). Transfer into the absorption tower), bring the cooling effluent into contact with the second stream of water, absorb acrylonitrile / methacrylonitrile in the second stream of water, and transfer the second stream of water containing acrylonitrile / methacrylonitrile to the second stream. Transfer from the tower to the first distillation tower (recovery tower) to separate crude acrylonitrile / methacrylonitrile from the second stream, and transfer the separated crude acrylonitrile / methacrylonitrile to the second distillation tower (head tower). At least some impurities are removed from the crude acrylonitrile / methacrylonitrile, and the partially purified acrylonitrile / methacrylonitrile is transferred to a third distillation column (product column) to produce acrylonitrile / methacrylonitrile as a product. Is done by getting. 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 extraction distillation column. In such a conventional method, the bottom flow of the acetonitrile rectification column is routed to the recovery column or the extraction distillation column.

U.S. Pat. No. 3,936,360 U.S. Pat. No. 3,433,822 U.S. Pat. No. 3,399,120 U.S. Pat. No. 3,535,849 U.S. Pat. No. 4,166,008 U.S. Pat. No. 4,334,965 U.S. Pat. No. 4,341,535 U.S. Pat. No. 5,895,635 U.S. Pat. No. 6,793,7776 U.S. Pat. No. 4,334,295 U.S. Pat. No. 4,238,295

The problem faced by conventional methods and systems is that hydrogen cyanide accumulates in high boiling point compounds that decompose at the required temperature of the acetonitrile rectification column. When the high boiling point compound is decomposed, hydrogen cyanide is released in the form of free radicals, which polymerize to cause fouling in the acetonitrile rectification column. Fowling causes malfunction of the acetonitrile rectification column, and the operation of the unit may be suspended in order to clean the acetonitrile rectification column and remove the fouling. Also, 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 safe, effective and cost-effective methods and devices for reducing and / or eliminating fouling in an acetonitrile rectification column.

In some embodiments, the method comprises adding an acid to the reflux stream and transporting the reflux stream to an acetonitrile rectification column.

In another aspect, the method comprises transporting the bottom flow of the acetonitrile rectification column to a quenching column. In this aspect, the column bottom flow contains at least some acid.

In another aspect, the apparatus comprises an acetonitrile rectification column configured to produce an apical stream containing acetonitrile, a reflux conduit configured to carry the reflux stream to the acetonitrile rectification column, and a reflux stream. Includes an acid addition pipeline configured to add acid to.

Reading the detailed description of the exemplary embodiments below in connection with the accompanying drawings will reveal the above and other aspects, features and advantages of the present disclosure.

An exemplary embodiment of the present disclosure and its advantages can be fully understood by reference to the following description with reference to the accompanying drawings showing the same features by the same reference number.

It is a schematic flow chart by at least one aspect of this disclosure. It is a schematic flow chart by at least one aspect of this disclosure. It is a flow chart of the method 300 by the aspect of this disclosure.

In some embodiments, the method or process comprises adding an acid to the reflux stream to the acetonitrile rectification column. In some embodiments, the method comprises transporting a reflux stream to an acetonitrile rectifying column that includes a top tray and a plurality of trays below the top tray, the transport step comprising transporting the reflux stream to the top tray. The acid reduces fouling in the acetonitrile rectification column, including the step of transporting.

In some embodiments, the method comprises routing the bottom flow of an acetonitrile rectification column to a quenching tank. In some embodiments, the acid added to reflux into the acetonitrile rectification column is acetic acid. In some embodiments, the routing of the underflow from the acetonitrile rectification column involves the step of extracting at least a portion of the underflow of the acetonitrile rectification column that was supposed to be routed to the recovery column, and quenching at least a portion thereof. It can include a step of rerouting to the tank. In some embodiments, a low dose of acid can be added to the reflux stream to prevent or reduce polymer formation in the acetonitrile rectification column, reducing cleaning costs and prolonging the operation of the acetonitrile rectification column.

The routing of the bottom flow of the acetonitrile rectification column to the quenching tank is that the pH at the bottom of the recovery column is less than the neutral pH of 7, pH 5 to 7.5 in another embodiment, pH 6 to 7.5 in another embodiment. It can be done so as to be maintained at a predetermined level or range such as. 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 the high boiling point compounds present at this position during the treatment.

In some embodiments, the problem of hydrogen cyanide fouling is that when the bottom fluid of the acetonitrile rectification column returns to the quenching column and does not return to the recovery column in the recovery section as in conventional acrylonitrile treatment, the top tray of the acetonitrile rectification column. It is solved by adding acid to the reflux conduit.

The acid plays a role as a polymerization inhibitor by maintaining the pH within a range in which hydrogen cyanide present in the flow and the acetonitrile rectification column does not polymerize and fouling does not occur in the acetonitrile rectification column. The acid is then returned to a quencher where the pH is already maintained below the neutral region of about 4.5 to about 6, and the acid is used to drain the reactor in the acrylonitrile plant. Can help remove ammonia from.

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

Fertile water (rich water) or aqueous solution from the absorption tower 300, which contains acrylonitrile, acetonitrile, HCN, water and impurities, passes through the conduit 2 to the heat exchanger 4, where the heat exchanger from the conduit 223. Preheated with lean water / solvent water 222 to 4. After preheating, the fertilized water separates from the heat exchanger 4 via the pipeline 6 and moves to the recovery tower 7. In the recovery tower 7, the solvent water that has moved to the recovery tower 7 via the pipeline 8 is added to perform extraction distillation. The dilute water / solvent water 222 includes a solvent water flow that advances to the top 207 of the recovery tower 7 through the heat exchanger 236 and the pipeline 8 and a dilute water flow that passes through the pipeline 224 when or after passing through the heat exchanger 4. 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 steam 228 from the recovery tower 7 via the pipeline 230. The steam 228 can be taken out from a predetermined position of the recovery tower 7, such as tray 232 or directly above the tray 232 present at the bottom 227 of the recovery tower 7. The tray 232 can be the bottom tray of the recovery tower 7, and is also called 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 flow passing through the pipeline 224 can be sent to the absorption tower 300. Heat exchange can be performed in the heat exchanger 234 before the dilute water flow passing through the pipeline 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 taken out from the recovery tower 7. First, the top current consisting of acrylonitrile, HCN, water and some impurities is taken out from the recovery tower 7 via the pipeline 212. The column side stream 214 can also be taken out from the recovery column 7 and sent to a stripper or an acetonitrile rectifying column 215. From the top of the acetonitrile rectification column 215, the column top stream 203 containing acetonitrile can be taken out through the pipeline 216. The bottom fluid 209 from the bottom 205 of the acetonitrile rectification column 215 can be returned to the recovery column 7 via the conduit 218. Pump 219 can be used to return the liquid to the recovery tower 7 via pipeline 218. However, it has been found that the column bottom liquid 209 is preferably conveyed from the bottom 205 to the quenching tank 10 via the pipeline 221. The bottom flow from the recovery tower 7 can be taken out through the pipeline 51 and transferred to the quenching tank 10 or the waste treatment apparatus via the pipeline 220 by the pump 53.

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

In some embodiments, the gas phase containing acetonitrile, water and trace amounts of HCN is removed from the recovery column 7 as column sideflow 214 and transported to the acetonitrile rectification column 215. The acetonitrile rectification column 215 can be a column including a plurality of trays. Reflux can be pumped through the reflux line 217 and / or the crude acrylonitrile line 237 using a pump 225.

In some embodiments, the method comprises adding acid to the reflux stream. As further explained, "adding acid to the reflux stream" means adding acid to the reflux line 217, adding acid to the top fluid in the line 216, and adding acid to the return line 239. Additions and combinations of each of these can be included. In another aspect, the acid can be added upstream or downstream of the condenser 235. Adding acid upstream of the condenser 235 reduces the acid concentration. Addition of acid downstream of the condenser provides a higher concentration of acid to the acetonitrile rectification column 215.

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

In some embodiments, an organic acid or organic acid derivative, such as acetic acid or glycolic acid, can be added to the 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 fluid in the conduit 216 from the acetonitrile rectification column 215 via the conduit 233. In some embodiments, an organic acid or organic acid derivative, such as acetic acid or glycolic acid, can be added to the reflux line 239 via line 243. In another embodiment, for example, when the bottom liquid of the acetonitrile rectification column 215 is routed to a quenching tank instead of the recovery column 7, an organic acid or an organic acid derivative such as acetic acid or glycolic acid is piped. Acetic acid can be added to the reflux line 217 via 213 and / or to the return line 239, line 216 via line 233 and / or line 243 before the top fluid enters the condenser 235. It can be useful for reducing polymerization and fouling in the rectification column 215, condenser 235 and / or other equipment. The acetonitrile rectification column 215 can be designed or configured to concentrate the flow of diluted water / acetonitrile and send it to another device for further purification and / or recovery of acetonitrile. In one embodiment, the bottom liquid 211 of the acetonitrile rectification column 215 can be transferred to the quenching column 10 by the pump 55 via the pipeline 221. In one embodiment, the bottom liquid 211 of the acetonitrile rectification column 215 is connected to the recovery tower bottom liquid in the pipe 51 via the pipe 9, and the connected bottom liquid is connected to the pipe by a pump 53. It can be transferred to the quenching tank 10 or waste treatment via 220.

As shown in FIG. 2, the quenching tank 10 is configured to receive the reactor exhaust gas or the gas stream 12 via the 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 quenching tank 10. In the quenching tank 10, the quenching liquid containing the bottom flow of the acetonitrile rectification column comes into contact with the reactor exhaust gas 12 and can be rapidly cooled.

Acid 36 (for example, 98% sulfuric acid) can be added to the quenching liquid 16 via the conduit 38. The amount of acid added through the conduit 38 can be reduced by the acid in the bottom liquid 211 routed to the quenching tank 10. The quenching liquid 16 can include a liquid discharge discharged from the bottom 42 of the quenching tank 10 through the pipeline 44. Water can be added to the quenching tank 10 through the inlet 48 via the conduit 46, or this water can be added separately to the quenching liquid 16 or the liquid formed by the flows 17, 44 and 65. It can also be added elsewhere in the recirculation loop. The quenching liquid 16 circulates through the conduit 44 and returns to the conduits 65 and 17 using the pump 50. Part of the liquid discharge discharged through the line 44 to maintain a relatively constant mass flow in the liquid recirculation loop by compensating for the liquid added through the lines 38, 46, 220 and 221. Flow 67 can be taken out. The flow 67 also helps to remove the neutralization reaction products formed (eg, ammonium sulphate) and also prevent the accumulation of unwanted products such as corrosion products in the liquid recirculation loop. The discharge discharged from the bottom 42 of the quenching tank 10 can be withdrawn from the pipeline 44 at the suction point 52.

The tower top flow 13 can flow from the quenching tank 10 to the quenching final cooler 240 through the pipeline 15. In the quenching final cooler 240, cold water can be used to cool the tower top stream 13 into the quenching final cooler condensate. From the bottom 250 of the quenching final cooler 240, the fertilizer water can be transferred to the fertilizer water line 2 and / or the recirculation line 248 by the pump 242 and returned to the top 252 of the quenching final cooler 240. After cooling by the quenching final cooler 240, the tower top stream 13 can be discharged from the quenching final cooler 240 as a flow 244. The flow 244 can be conveyed to the absorption tower 300 via the pipeline 246. The dilute water from the pipeline 224 can enter the upper part 254 of the absorption tower 300. The off-gas 256 from the absorption tower 300 can be sent to an incinerator (not shown). As mentioned above, the flow 258 from the bottom 262 of the absorption tower 300 can contain fertile water. This fertile water can be transferred to the pipeline 2 via the pump 260. The flow 258 can be combined with fertile water from the quenching final cooler 240, such as at the joint 264.

In some embodiments, the controller 11 is set to, for example, the pH of the acetonitrile rectification column bottom fluid 209 at the bottom 205 of the acetonitrile rectification column 215, or the pH of the acetonitrile rectification column bottom fluid 211 in the conduit 221 or the conduit 9. Etc., can be configured to process one or more signals corresponding to the measurement parameters measured by a pH sensor (not shown in FIG. 1). The controller 11 can be configured to determine whether the measurement parameters are 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 fluid 209 or 211 as described above, or the water level regulator at the bottom 205 of the acetonitrile rectification column 215. Acetonitrile, such as (not shown in FIG. 1) or the liquid level measured by a flow regulator (not shown in FIG. 1) associated with the fluid flow in one or more conduits described herein. It will be recognized 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 communication lines or wireless communication (not shown in FIG. 1) when the measurement parameters are below or above a predetermined parameter range. Can be configured to: For example, controller 11 is configured to adjust the amount of acid added through line 213 or 233 to achieve the desired pH in reflux stream 251 in order to reduce fouling in the acetonitrile rectification column 215. be able to. One of ordinary skill in the art will use the controller 11 in connection with these additions in order to meet a predetermined range of acids added through pipelines 213 and / or 233, according to the present disclosure. You will recognize that it can be configured to control the operation of the pump and / or valve. Those skilled in the art may place the controller 11 or similar controller away from the water level regulator or flow rate regulator (not shown in FIG. 1) or in the same position as the water level regulator or flow rate regulator. You will recognize that it can also be placed to include these. For those skilled in the art, according to the present disclosure, the controller 11 is configured to control the operation of the device and (s) pumps shown in FIG. 2 and / or the operation of valves associated with these devices. You will recognize that you can.

The advantage of adding acid to the acetonitrile rectification column 215, and the bottom fluid of the acetonitrile rectification column, is placed in the quenching tank 10 instead of being routed to the recovery column 7 without adding acid to the acetonitrile rectification column 215 as before. Testing was done to demonstrate the benefits of routing. The following test data were obtained.

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

The table below shows the results obtained by operating Plant 1 "with acid" and Plant 1 "without acid" as described above.

The test data showed that the effect of adding acetic acid to the top liquor of the acetonitrile rectification column reduced the pH of the stream from pH 8.9 to pH 6.4. In some embodiments, lowering the pH of the recovery column reduces unwanted polymerization. Correspondingly, the ammonia concentration in the top solution of the acetonitrile rectification column decreases, that is, when acetic acid is added, it decreases from 188 ppm to 9 ppm. The decrease in ammonia in the flow through the top liquid of the acetonitrile rectification column, that is, the conduit 216, is believed to be the result of acetic acid taking up ammonia as ammonium acetate, which was removed in the flow 211 to the quenching tank 10. .. Partially, it is also considered that hydrogen cyanide remains in the solution as cyanohydrin, decomposes into its original components, and then does not polymerize and does not release ammonia. Ammonia is a by-product of the polymerization reaction of hydrogen cyanide. The addition of acetic acid to the stream clearly reduces the amount of ammonia present, thus demonstrating the effectiveness of the present disclosure.

In one embodiment, the choice of pH level is the balance between reducing fouling and using the desired constituent material. In this aspect, the use of pH levels as described herein allows the use of carbon steel structures.

FIG. 3 shows a flow chart of the method 300 according to the aspect of the present disclosure. Method 300 can be performed using the device described above. Step 301 includes routing the bottom flow of the acetonitrile rectification column to the quenching tank. Step 302 includes adding acid to the reflux stream to the acetonitrile rectification column. In some embodiments, the acetonitrile rectification column comprises multiple trays, the step of adding acid to the reflux stream to the acetonitrile rectification column is the step of adding acid to the top tray of the plurality of trays of the acetonitrile rectification column. Including. In some embodiments, the step of adding acid to the reflux stream to the acetonitrile rectification column comprises adding acid to the reflux stream. In some embodiments, the step of adding acid to reflux is performed to reduce the pH of the top solution of the acetonitrile rectification column.

In some embodiments, the step of adding acid to reflux reduces the pH of the top solution of the acetonitrile rectification column from greater than 7.0 to less than 7.0. In some embodiments, the step of adding acid to reflux reduces the pH of the top solution of the acetonitrile rectification column from greater than 8.0 to less than 6.5. In some embodiments, the step of adding acid to reflux reduces the pH of the top solution of the acetonitrile rectification column from greater than 7.0 to a pH of about 6.4.

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

The present invention is applicable to any acrylonitrile recovery method having a recovery column and one or more additional distillation columns. Usually, the additional distillation column is composed of an HCN column, a drying column for removing water, and a product column for recovering product quality acrylonitrile. However, these separate actions can be combined as shown in the drawing so that one distillation column removes both HCN and water.

Although the present disclosure has been described in the context of some preferred embodiments thereof and provided many details for illustrative purposes, those skilled in the art will appreciate this without departing from the basic principles of the present disclosure. Further embodiments of the disclosure are possible, and it will be apparent that some of the details described herein can be modified significantly. It should be understood that the features of the present disclosure can be modified, modified, modified or substituted without departing from the spirit or scope of the disclosure and the claims. For example, the dimensions, number, size and shape of the various components can be modified to suit a particular application. Therefore, the particular embodiments illustrated and described herein are for illustration purposes only.

Claims (33)

A method of reducing fouling in the acetonitrile removal step of acrylonitrile recovery.
The step of transporting the column side stream containing acetonitrile from the recovery column to the acetonitrile rectification column,
The step of transporting the top stream from the acetonitrile rectification column to the condenser,
The step of condensing the tower top flow to supply the reflux flow,
The step of adding acid to the reflux stream and
The step of transporting the reflux stream to the acetonitrile rectification column, and
A step of transporting at least a part of the bottom flow of the acetonitrile rectification column to a quenching tank, and
A method characterized by including. The acid reduces fouling in the acetonitrile rectification column.
The method according to claim 1. The acetonitrile rectification column includes a top tray and a plurality of trays below the top tray, and the transport step includes a step of transporting the reflux stream to the top tray.
The method according to claim 1. The acid comprises an organic acid selected from the group consisting of acetic acid, glycolic acid and mixtures thereof.
The method according to claim 1. The step of adding acid to the reflux stream lowers the pH of the top stream of the acetonitrile rectification column.
The method according to claim 1. The step of adding acid to the reflux stream keeps the pH of the top stream of the acetonitrile rectification column within a predetermined range.
The method according to claim 1. The step of adding acid to the reflux stream reduces the pH of the top stream of the acetonitrile rectification column from greater than 7.0 to less than 7.0.
The method according to claim 5. The step of adding an acid to the reflux stream reduces the pH of the top stream of the acetonitrile rectification column from greater than 8.0 to less than 6.5.
The method according to claim 5. The step of adding an acid to the reflux stream reduces the pH of the top stream of the acetonitrile rectification column from more than 7.0 to a pH of about 6.4.
The method according to claim 5. The step of adding acid to the reflux stream keeps the pH of the top stream of the acetonitrile rectification column below about 7.0.
The method according to claim 6. The step of adding acid to the reflux stream keeps the pH of the top stream of the acetonitrile rectification column below about 6.5.
The method according to claim 6. The step of adding acid to the reflux stream maintains the pH of the top stream of the acetonitrile rectification column below about 6.4.
The method according to claim 6. The step of adding acid to the reflux stream comprises adding acid to the top stream of the acetonitrile rectification column.
The method according to claim 1. The bottom flow 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 according to claim 1. The step further comprises supplying a gas stream containing acrylonitrile and ammonia to the quenching tank, and bringing the gas stream into contact with a quenching solution containing the bottom flow of the acetonitrile rectification column.
The method according to claim 14. At least a part of the bottom flow of the acetonitrile rectification column is transported to the quenching tank, and at least a part of the bottom flow of the acetonitrile rectification column is transferred to the recovery tower.
The method according to claim 1. Further comprising transporting at least a portion of the reflux stream upstream of the condenser to the top stream of the acetonitrile rectification column.
The method according to claim 1. The column bottom flow has a pH of about 7 or less.
The method according to claim 1. The column bottom flow has a pH of about 5 to about 7.5.
The method according to claim 1. The column bottom flow has a pH of about 6 to about 7.
The method according to claim 1. A device that reduces fouling in the acetonitrile removal step of acrylonitrile recovery.
An acetonitrile rectification column configured to generate an apical stream containing acetonitrile,
A reflux line configured to carry the reflux stream to the acetonitrile rectification column, and
An acid addition pipeline configured to add acid to the reflux stream,
A routing pipeline configured to transport at least a portion of the bottom flow of the acetonitrile rectification column to a quenching tank.
A device characterized by comprising. Further comprising a condenser configured to cool the column top stream to produce a condensed crude acetonitrile product, the reflux stream comprises at least a portion of the condensed acetonitrile product.
The device according to claim 21. The acetonitrile rectification column includes an uppermost tray and a plurality of trays below the uppermost tray, and the reflux pipe is configured to convey the reflux flow to the uppermost tray.
The device according to claim 21. The acid comprises acetic acid.
The device according to claim 21. A controller configured to control the addition of acid to the reflux stream.
The device according to claim 21. The controller is configured to control the addition of acid to lower the pH of the tower apex.
25. The apparatus of claim 25. The controller is configured to keep the pH of the tower top stream within a predetermined range.
The device according to claim 26. The controller is configured to reduce the pH of the tower apex stream from more than about 7.0 to less than 7.0.
The device according to claim 27. The controller is configured to reduce the pH of the tower apex stream from more than about 8.0 to less than 6.5.
The device according to claim 26. The controller is configured to reduce the pH of the tower apex stream from above about 7.0 to a pH of about 6.4.
The device according to claim 26. The acid addition line is configured to add acid to the tower apex.
The device according to claim 21. The column bottom stream contains at least some acid added to the reflux stream.
The device according to claim 21. The quenching tank is configured to receive a gas stream containing acrylonitrile and ammonia and bring the gas stream into contact with a quenching solution containing the bottom flow of the acetonitrile rectification column.
The device according to claim 21.

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