JPH1135543A - Improved recovering process of acrylonitrile - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an improved method for manufacturing acrylonitrile or methacrylonitrile. SOLUTION: This method is adopted for recovering acetonitrile or methacrylonitrile obtained from a reactor effluent from an ammoxidation of propylene with isobutylene. The process includes processes passing the reactor effluent through an absorbing column, a recovering column and a stripping column. The improving points include increasing a top pressure of the recovering column from about 0.1 psi to about 5 psi by a mechanical means and improving hydraulic capacity of the recovering column and the stripping column.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an improved process for producing acrylonitrile or methacrylonitrile. In particular, the present invention relates to improved recovery procedures used in the production of acrylonitrile and methacrylonitrile.

[0002]

BACKGROUND OF THE INVENTION Commercial scale recovery of acrylonitrile / methacrylonitrile produced by the ammoxidation of propylene or isobutylene is carried out in the following procedure: quenching the reactor effluent with water; Passing the acrylonitrile or methacrylonitrile-containing gas stream obtained in the above through an absorber and contacting water and gas flowing in opposite directions to remove substantially all acrylonitrile or methacrylonitrile from the gas;
The aqueous stream containing substantially all acrylonitrile or methacrylonitrile is then passed through a series of distillation columns and associated decanters to separate and purify the acrylonitrile or methacrylonitrile product.

A typical recovery and purification system used in the manufacture of acrylonitrile or methacrylonitrile is described in US Pat. No. 4,234,51 assigned to the assignee of the present invention.
Nos. 0 and 3,885,928, which are incorporated herein by reference.

[0004]

SUMMARY OF THE INVENTION It is a primary object of the present invention to provide an improved process for producing acrylonitrile or methacrylonitrile.

It is another object of the present invention to provide an improved recovery and purification procedure used in the production of acrylonitrile or methacrylonitrile.

It is a further object of the present invention to reduce the amount of organic impurities in the final product obtained, thereby reducing gas waste and improving product throughput, recovery efficiency and product quality. It is to provide an improved acrylonitrile or methacrylonitrile manufacturing process.

Some of the further objects, advantages and novel features of the invention will be set forth in the description which follows, and in part will be obvious to those skilled in the art from a consideration of the following description, or may be learned by the practice of the invention. It can be understood by practice. The objects and advantages of the invention may be achieved by means and combinations particularly pointed out in the appended claims.
And can be obtained.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above and other objects, and in accordance with the objects of the invention specifically and broadly described herein, the process of the present invention comprises: Transferring the reactor effluent obtained during the ammoxidation of propylene or isobutylene to a quench column and cooling the hot effluent gas by contacting it with an aqueous spray; then cooling Passing the reactor effluent through an absorption column from overhead to absorb acrylonitrile or methacrylonitrile in water; and then adding an aqueous solution containing acrylonitrile or methacrylonitrile to
Recovering the acrylonitrile or methacrylonitrile product through a recovery (distillation) column and a stripping (distillation) column. Here, as an improvement, the top pressure of the recovery column is increased from about 0.1 psi to 5 psi by mechanical means, and the water capacity (hydraulic capa) of the recovery column and the stripping column is increased.
city). For example, typically the collection column top pressure in the collection and purification section of an acrylonitrile plant is designed to operate at about 1 psig to less than 5 psig. The present invention provides for a collection column top pressure of between 0.1 psi and 5 psi, preferably 0.25 psi.
5.0, more preferably 0.5 to 5.0, particularly preferably 1.0ps
i-5.0 psi relates to mechanically increasing (e.g., by installing a pressure valve) above a designed pressure.

In a preferred embodiment of the present invention, the top pressure of the collection column is between 5 psig and 10 psig, preferably greater than 5 psig to 10 psig, more preferably 5.5 psig.
It is maintained at sig to 7.5 psig, particularly preferably 5.5 psig to 7.0 psig.

In a preferred embodiment of the present invention, the process is carried out using the reactor effluent obtained by ammoxidation of propylene, ammonia and oxygen to produce acrylonitrile.

[0011] In another preferred embodiment of the present invention, the reactor effluent is obtained by the reaction of propylene, ammonia and air in a fluidized bed reactor contacting a fluidized bed catalyst.

The process for recovering acetonitrile or methacrylonitrile obtained from the reactor effluent of the ammoxidation reaction of propylene or isobutylene according to the present invention comprises passing the reactor effluent through an absorption column, a recovery column and a stripping column. As an improvement, the top pressure of the collection column may be increased by mechanical means from about 0.1 psi to 5 psi.
increasing the psi to improve the water capacity of the recovery and stripping columns.

According to one embodiment of the present invention, the reactor effluent is obtained from the reaction of propylene, ammonia and an oxygen-containing gas in a fluidized bed reactor contacting a fluidized bed ammoxidation catalyst.

According to another embodiment of the present invention, the reactor effluent is obtained from the reaction of isobutylene, ammonia and an oxygen-containing gas in a fluidized bed reactor contacting a fluidized bed ammoxidation catalyst.

According to a preferred embodiment of the present invention, the top pressure of the collection column is maintained between about 5 psig and about 10 psig, more preferably between about 5.5 psig and about 7.0 psig.

According to a preferred embodiment of the present invention, the top pressure of the recovery column is between about 0.25 psi and about 5 psi, more preferably between about 0.5 psi and about 5 psi, and even more preferably between about 1.0 psi and about 5 psi. Rise between.

In the practice of the present invention, a conventional fluidized bed ammoxidation catalyst may be used. For example, U.S. Pat.
Fluid bed catalysts described in US Pat. Nos. 2,930 and 5,093,299, which are incorporated herein by reference, may be used in the practice of the present invention.

[0018] In conventional recovery and purification procedures for the recovery of acrylonitrile or methacrylonitrile, typically jet flooding in the recovery and stripping columns is based on absorption, recovery and stripping columns. It has been found to define the maximum amount of lean water that can circulate through the water. The present invention operates the recovery and stripping columns at elevated pressure. Thereby, the throughput at which jet flooding occurs increases, thus increasing the operating speed of the reactor and reducing the gas lost by the absorber. This is achieved by increasing the flow rate of poor water from the recovery column and the stripping column to the absorber. It has now surprisingly been found that the entire recovery procedure has no loss of operating efficiency. The practice of the present invention allows for a high rate of reaction formation, while maintaining the ratio of poor water to product to the minimum required (at least 11: 1). The practice of the present invention is highly beneficial when used in combination with a recovery and purification procedure (operating in an absorption column with a poor water: product ratio of 12: 1 to 11: 1).

[0019]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail. The reactor effluent obtained by ammoxidation of propylene or isobutylene, ammonia and oxygen-containing gas in a fluidized bed reactor while in contact with the fluidized bed ammoxidation catalyst is transferred to a quench column. In this quench column, the hot effluent gas is cooled by contact with the water smoke. Typically, any excess ammonia in the effluent will
It is neutralized by contact with sulfuric acid in a quench column to remove ammonia as ammonium sulfate. The cooled effluent gas containing the desired products (acrylonitrile or methacrylonitrile, and HCN) is then passed to the bottom of the absorption column. Where the product is
Absorbed by water entering the column from the top. Unabsorbed gas passes from the absorber through a pipe located at the top of the absorber. The water stream containing the desired product is then passed from the bottom of the absorber to the top of the first distillation column (recovery column) for further purification of the product. The product recovered from the top of the recovery column is then sent to a second distillation column for further purification and recovery of the product (acrylonitrile or methacrylonitrile). The bottom stream from the recovery column is sent to a stripping distillation column to recover the valuable by-product, crude acetonitrile.

In the practice of the present invention, an automatic pressure control valve is attached to the collection column overhead tube so that the top pressure of the collection column is about 0.
Allows climbing from 1 psi to over 5 psi.
Typically, the recovery column top pressure is between 1 psig and less than 5 psig, typically between 4 psig and 4.5 psig.
In a preferred practice of the invention, the top pressure of the recovery column is a constant pressure (5 psig to about 10 psig, preferably 5.5 psig).
得 る 7.5 psig). The improvements of the present invention include separate recovery and stripping tower designs, and a stacked recovery / recovery system for recovering acrylonitrile or methacrylonitrile, as long as the column hydraulics are limited by jet flooding. Applicable to stripping tower design.
The pressure control valve used can be obtained from any control valve manufacturer. It may be automatic operation or manual control.

Preferably, the ammoxidation reaction is performed in a fluidized bed reactor, although other types of reactors are also contemplated (eg, transport tube reactors). Fluid bed reactors for acrylonitrile production are well known in the prior art. For example, the reactor design described in US Pat. No. 3,230,246, which is incorporated herein by reference, is suitable.

The conditions under which the ammoxidation reaction takes place are also well known, as shown in the following prior art: US Pat.
Nos. 093,299, 4,863,891, 4,767,878 and 4,503,001, which are incorporated herein by reference. Typically, the ammoxidation process is performed by contacting propylene or isobutylene at elevated temperatures with a fluidized bed catalyst in the presence of ammonia and oxygen to obtain acrylonitrile or methacrylonitrile. Although any source of oxygen may be employed, it is preferred to use air for economic reasons. A typical molar ratio of oxygen to olefin in the feed should be in the range 0.5: 1 to 4: 1, preferably 1: 1 to 3: 1. In the reaction, the molar ratio of ammonia to olefin in the feed can vary from 0.5: 1 to 5: 1. There is no practical upper limit for the ammonia-olefin ratio, but generally, 5: 1
Ratios above are almost meaningless for economic reasons.

The reaction is carried out at a temperature in the range from about 260 ° C. to about 600 ° C., but is preferably carried out in the range from 310 ° C. to 500 ° C., particularly preferably in the range from 350 ° C. to 480 ° C. The contact time is not critical, but is generally in the range 0.1 seconds to 50 seconds, preferably in the range 1 second to 15 seconds.

In addition to the catalyst of US Pat. No. 3,642,930,
Other catalysts suitable for practicing the present invention are described in U.S. Pat.No. 5,093,29.
No. 9 (incorporated herein by reference).

The conditions for maintaining the absorption column, the recovery column and the stripping column are 5 psig to 7 psi, respectively.
psig (80 ° F to 110 ° F), 1 psig to 4.5psig (155 ° F to 170
° F), and ranges from 7 to 13 psig (170 ° F to 210 ° F).

The improvement of the present invention is achieved by operating the recovery column mechanically at a pressure above the normal design pressure when performing the ammoxidation process for the production of acrylonitrile / methacrylonitrile by operating the recovery column. Is distinguished. Conventional procedures used a recovery column top pressure of less than 5 psig. In a preferred practice of the invention, the top pressure of the recovery column is operated at a pressure typically in the range of 5 psig to 10 psig, preferably 5.5 psig to 7.0 psig.

[0027]

The present invention relates to a process for recovering acetonitrile or methacrylonitrile from a reactor effluent of an ammoxidation reaction of propylene or isobutylene, the process comprising the steps of removing the reactor effluent from an absorption column, a recovery column and a storage column. Passing through a ripping column. Here, the improvement of the present invention is that the pressure at the top of the recovery column is
Increasing from about 0.1 psi to 5 psi by mechanical means to improve the water capacity of the recovery and stripping columns.

As a result of the operation of the recovery and purification process of the present invention, a high reactor throughput can be achieved without any costly modifications to the recovery and purification system. The present invention not only provides an unexpected improvement in production rate, but also achieves this improvement without increasing the size of the column used in the recovery and purification section.
Furthermore, the resulting increase in the production rate does not result in degradation of the performance of the absorption column during recovery, or of acrylonitrile or methacrylonitrile. As a result, the present invention improves operating efficiency, improves throughput, and increases productivity without requiring capital.

As will be apparent to those skilled in the art, various modifications of the present invention can be made in light of the above disclosure and discussion without departing from the spirit and scope of the disclosure or the scope of the claims. Can be followed.

 ──────────────────────────────────────────────────続 き Continuation of the front page (71) Applicant 595017584 200 Public Square, 39G BP Building, Clevel and, Ohio 44114, U.S.A. S. A. (72) Inventor Sanjay Palshottam Godball USA 44139, Solon, Winchester Drive 7260 (72) Inventor Jeffrey Earl Linker USA 45807, Elida, Astor Street 5189

Claims (8)

[Claims] 1. A process for recovering acetonitrile or methacrylonitrile obtained from a reactor effluent of an ammoxidation reaction of propylene or isobutylene, comprising passing the reactor effluent through an absorption column, a recovery column and a stripping column. A process comprising, as an improvement, raising the top pressure of the collection column by about 0.1 psi to 5 psi by mechanical means to improve the water capacity of the collection column and the stripping column. 2. The reactor effluent is obtained from the reaction of propylene, ammonia and an oxygen-containing gas in a fluidized bed reactor in contact with a fluidized bed ammoxidation catalyst.
The process described in. 3. The process of claim 1, wherein the reactor effluent is obtained from the reaction of isobutylene, ammonia and an oxygen-containing gas in a fluidized bed reactor contacted with a fluidized bed ammoxidation catalyst. 4. The collection column has a top pressure of about 5 psig to about 5 psig.
The process of claim 1, wherein the process is maintained between 10 psig. 5. The process of claim 1, wherein the top pressure of the collection column is maintained between about 5.5 psig and about 7.0 psig. 6. The process of claim 1, wherein the recovery column top pressure is increased between about 0.25 psi to about 5 psi. 7. The process of claim 1, wherein the recovery column top pressure is increased between about 0.5 psi to about 5 psi. 8. The process of claim 1, wherein the recovery column top pressure is increased between about 1.0 psi to about 5 psi.