KR19990010948A - Improved Acrylonitrile Recovery Method - Google Patents

Abstract

The present invention allows the reactor discharge to pass through the absorption column and recovery column and stripper column, which is improved by increasing the recovery column top pressure by mechanical means to about 0.25 to 5 psi to enhance the recovery and stripper column capacity. The present invention relates to a process for the recovery of acrylonitrile or methacrylonitrile obtained from the reactor effluent of the darkening reaction of propylene or isobutylene.

Description

Improved Acrylonitrile Recovery Method

The present invention relates to an improved process for the preparation of acrylonitrile or methacrylonitrile. In particular, the present invention relates to an improvement in the recovery method used during the production of acrylonitrile and methacrylonitrile.

The recovery of acrylonitrile / methacrylonitrile produced by the agglomeration of propylene or isobutylene on a commercial scale involves quenching the reactor discharge with water followed by acrylonitrile or methacrylonitrile resulting from the quenching. It is carried out by passing a gaseous stream through the absorber, where water and gases are brought into contact with the countercurrent to remove substantially all of the acrylonitrile or methacrylonitrile and to substantially contain all of the acrylonitrile or methacrylonitrile. The gas stream is then passed through a series of distillation columns and connected with a decanter for the separation and purification of the product acrylonitrile or methacrylonitrile.

Typical recovery and purification systems used during the production of acrylonitrile or methacrylonitrile are U.S. Patents 4,234,510 and 3,885,928, which are incorporated herein by reference.

It is a primary object of the present invention to provide an improved process for the preparation of acrylonitrile or methacrylonitrile.

Another object of the present invention is to provide an improved recovery and purification process for use during the preparation of acrylonitrile or methacrylonitrile.

Another object of the present invention is to prepare acrylonitrile or methacrylonitrile which reduces waste gas and improves product yield, recovery efficiency and product quality while reducing the amount of organic impurities in the resulting final product. It is to provide an improved method.

Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention can be achieved and obtained by means of the instruments and combinations particularly pointed out in the appended claims.

In order to carry out the other objectives and also the objectives of the present invention as embodied and broadly described herein, the process of the present invention transfers the reactor effluent obtained during the darkening of propylene or isobutylene to a quench column to The effluent gas is brought into contact with an aqueous spray to cool and the cooled reactor discharge is then passed over an absorption column to absorb acrylonitrile or methacrylonitrile in water and an aqueous solution containing acrylonitrile or methacrylonitrile is added. This is followed by recovery of acrylonitrile or methacrylonitrile by passing through a recovery distillation column and a stripper distillation column, which improvement is achieved by increasing the pressure of the recovery distillation column by mechanical means of about 0.1-5 psi to recover and stripper. To increase the capacity of the column The. For example, in the recovery and purification portion of the acrylonitrile plant, typical recovery column overhead pressures are designed to operate at about 1 to 5 psig or less. The present invention mechanically increases the upper pressure of the recovery column to the above designed pressure of 0.1 to 5 psi, preferably 0.25 to 0.5 to 0.5, particularly preferably 1.0 to 5.0 psi, by addition of a pressure valve. It's about making things happen.

In a preferred embodiment of the invention, the recovery column top pressure is maintained at 5-10 psig, preferably at least 5-10 psig, particularly preferably 5.5-7.5 psig.

In a preferred embodiment of the invention, the process is carried out with reactor discharges obtained from the darkening of propylene, ammonia and oxygen to produce acrylonitrile.

In a more preferred embodiment of the invention, the reactor discharge is obtained by the reaction of propylene, ammonia and air in a fluidized bed reactor and is contacted with the fluidized bed catalyst.

Conventional fluidized bed darkening catalysts can be used in the practice of the present invention. For example, U.S. Pat. Fluid bed catalysts may be used in the practice of the present invention as described in patents 3,642,920 and 5,093,299.

In a conventional recovery purification method for recovery of acrylonitrile or methacrylonitrile, the maximum amount of lean water that jet plading can be circulated through the absorber, recovery and stripper columns in the recovery and stripper columns. It was found to determine typically. By operating the recovery and stripper columns at increased pressure, the present invention can increase the output from which jet plading occurs, thereby increasing the rate of reactor operation and lowering absorber off-gas losses. have. This is accomplished by increasing the flow of deflection water from the recovery and stripper columns to the absorber, with the surprising finding that the overall recovery method does not lose any process efficiency. The practice of the present invention maintains a minimum requirement for the ratio of product to deflection water (at least 11: 1) while allowing for a high rate of reaction production. The practice of the present invention is very advantageous when used in combination with recovery and purification columns in which the ratio of product to deflection water in the absorption column is performed from 12: 1 to 11: 1.

The present invention will now be described in detail. The reactor effluent obtained by contact with the fluidized bed ammonization catalyst while implicitly gasifying propylene or isobutylene, ammonia and oxygen containing gas in the fluidized bed reactor was transported to a quench column to bring hot discharge gases into contact with a water spray. Cool. Typically, any excess ammonia contained in the emissions is neutralized in contact with sulfuric acid upon quenching to remove ammonia, such as ammonium sulfate. The cooled off gas containing the desired product (acrylonitrile or methacrylonitrile and HCN) is then passed through the bottom of the absorption column, where the product is absorbed by the water introduced into the column from the top. Unabsorbed gases pass through the absorber through a pipe located on top of the absorber. The aqueous air stream containing the desired product is then passed from the bottom of the absorber to the top of the primary distillation column (recovery column) for purification of the further product. The product recovered from the top of the recovery column is then further purified and sent to a secondary distillation column for recovery of product acrylonitrile or methacrylonitrile. The bottoms air stream obtained from the recovery column is sent to a stripper column to recover the crude coproduct, crude acetonitrile.

In the practice of the present invention, an atomic pressure control valve can be installed in the overhead line of the recovery column to increase the upper pressure of the recovery column by about 0.1-5 psi, the above designed upper recovery column pressure. Typically, the recovery column top pressure is 1-5 psig or less, usually 4-4.5 psig. In a preferred implementation of the invention, the recovery column overhead pressure is operated at a constant pressure which can vary from 5 psig to about 10 psig, preferably 5.5 to 7.5 psig. Improvements of the present invention can be used to separate the recovery and stripper tower designs for recovery of acrylonitrile or methacrylonitrile as well as the integrated recovery / stripper tower designs, provided that tower hydraulicity is limited by jet plading. do. The pressure regulating valve used can be obtained from any regulating valve manufacturer. It can operate automatically or can be adjusted by hand.

Preferably, the darkening reaction is carried out in a fluidized bed reactor even if other forms of reactor such as transport lines are contemplated. Fluidized bed reactors for the production of acrylonitrile are already known in the prior art. For example, U.S. Reactor designs described in patent 3,230,246 are suitable.

Conditions for carrying out the darkening reaction can also be found in U.S. Patent Nos. 5,093,299; No. 4,863,891; It is already known in the prior art as evidenced by 4,767,878 and 4,503,001. Typically, the darkening process is performed by contacting propylene or isopropylene with a fluidized bed catalyst in the presence of ammonia and oxygen at elevated temperatures to produce acrylonitrile or methacrylonitrile. Any oxygen source can be used. However, it is desirable to use air for economic reasons. Typical molar ratios of oxygen to olefins in the injection should range from 0.5: 1 to 4: 1, preferably from 1: 1 to 3: 1. The molar ratio of ammonia to olefin in the introduction during the reaction can vary from 0.5: 1 to 5: 1. There is practically no upper limit to the ammonia-olefin ratio, but generally there is no reason to exceed the 5: 1 ratio for economic reasons.

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

In addition to the catalyst of U.S. Patent No. 3,642,930, other catalysts suitable for the practice of the present invention are described in U.S. Patent No. 5,093,299.

The conditions under which the absorption column, recovery column and stripper column are maintained are 5-7 psig (80 ° F-110 ° F), 1-4.5 psig (155 ° F-170 ° F), and 7-13 psig (170 ° F-210 ° F), respectively. Range.

The improvement of the present invention is distinguished from the prior art by operating the recovery column by mechanical control at the pressure, which is the normal desired pressure, during the execution of the darkening process for the production of acrylonitrile / methacrylonitrile. Conventional methods use a recovery column overhead pressure of 5 psig or less. In a preferred implementation of the invention, the recovery column overhead pressure is typically operated at a pressure in the range of 5 to 10 psig, preferably 5.5 to 7.0 psig.

The performance of the recovery and purification process of the present invention allows to achieve high production rates through the reactor without making any modifications to the recovery and purification system, including major expenses. The present invention not only brought about an unexpected increase in production rate but also achieved this increase without increasing the size of the tower used in the recovery and purification portion. In addition, an increase in by-products in the production rate does not result in any observed degradation in the performance of the absorption column during recovery of acrylonitrile or methacrylonitrile. The present invention exhibits improved efficiency of operation, increased production, and increased productivity without the need for major expenses.

As will be apparent to those skilled in the art, various modifications of the invention may be made or carried out in light of the preceding disclosure without departing from the spirit and scope of the disclosure or within the scope of the claims.

Claims (8)

The reactor discharge is passed through the absorption column and the recovery column and the stripper column, characterized by improvement by increasing the recovery column overhead pressure by mechanical means to about 0.1-5 psi to enhance the recovery and stripper column capacity. A process for the recovery of acrylonitrile or methacrylonitrile obtained from the reactor effluent of the darkening reaction of propylene or isobutylene. The process of claim 1 wherein the reactor discharge is obtained from the reaction of propylene, ammonia and oxygen containing gas in a fluidized bed reactor in contact with a fluidized bed darkening catalyst. The process of claim 1 wherein the reactor discharge is obtained from the reaction of isobutylene, ammonia and oxygen containing gas in the fluidized bed reactor while in contact with the fluidized bed darkening catalyst. The method of claim 1 wherein the recovery column is maintained at a top pressure of about 5 to about 10 psig. The method of claim 1, wherein the recovery column overhead pressure is maintained at about 5.5 to about 7.0 psig. The method of claim 1 wherein the recovery column top pressure is increased to about 0.25 to about 5 psi. The method of claim 1 wherein the recovery column top pressure is increased to about 0.5 to about 5 psi. The method of claim 1 wherein the recovery column top pressure is increased to about 1.0 to about 5 psi.