Process and apparatus for recovery of acetic acid from methyl acetate

Abstract

An apparatus and process are described for recovery of a carboxylic acid by hydrolysis of an ester in a mixture comprising the ester, an alcohol and water. The apparatus comprises a catalytic distillation column containing an acidic catalyst and a distillation column. Simultaneously and interdependently the alcohol is catalytically dehydrated to the corresponding ether and water, and said water reacts with the ester to generate a carboxylic acid rich stream from the catalytic distillation column. The acid is recovered by distillation in the distillation column. The process requires no added water. A second embodiment of the apparatus and process has means to co-feed one or both of added methanol and/or water with the feed to maintain substantially optimum operation independent of feed composition.

1 . An apparatus for recovery of a carboxylic acid by hydrolysis of a corresponding ester in a feed containing one of:
 a mixture of the ester and an alcohol, or   a mixture of the ester, an alcohol and water;   the apparatus comprising a catalytic distillation column for catalytic hydrolysis of the ester and recovery of a carboxylic acid rich stream, and a distillation column for separation of the carboxylic acid rich stream to recover said carboxylic acid.   
     
     
         2 . The apparatus of  claim 1  wherein the acidic catalyst is an acidic form of a resin catalyst. 
     
     
         3 . The apparatus according to  claim 1  having means for co-feeding at least one of methanol and/or water in addition to the mixture containing the ester, an alcohol and water. 
     
     
         4 . A method for recovery of a carboxylic acid by hydrolysis of a corresponding ester in a mixture containing the ester, an alcohol and water, comprising:
 reacting the mixture over an acidic catalyst situated in a bed in a middle portion of a catalytic distillation column, wherein:
 the alcohol is in continuous reversible chemical reaction to the corresponding ether and water, and 
 the ester and water are in catalytic continuous reversible chemical reaction with the corresponding alcohol and carboxylic acid, so that: 
 the reaction mixture comprises an equilibrium mixture of the ester, the alcohol, the carboxylic acid, water and the ether, and the mixture is separated by distillation in the catalytic distillation column; 
   so that:
 a first volatiles stream recovered from a top portion of the catalytic distillation column comprises very pure ether, and 
 a first bottoms stream recovered from a bottom portion of the catalytic distillation column comprises a mixture rich in the carboxylic acid, with a smaller concentration of the ester and only trace amounts of the other components of the reaction mixture; and 
 there is separation of the carboxylic acid richer mixture using a distillation column to produce a second bottoms stream from the bottom portion of the distillation column that is essentially pure carboxylic acid, and a second volatiles stream from the top portion of the distillation column that is rich in the ester. 
   
     
     
         5 . The method according to  claim 4  wherein the acidic catalyst is an acidic form of a resin catalyst. 
     
     
         6 . The method according to  claim 4  wherein the ester is a component in a stream from a manufacturing facility producing at least one product selected from among polyvinyl alcohol and derivatives of polyvinyl alcohol. 
     
     
         7 . The method according to  claim 4  in which the ester is methyl acetate and the carboxylic acid recovered is acetic acid. 
     
     
         8 . The method according to  claim 7  wherein the mixture containing methyl acetate is a stream produced at a facility for manufacturing at least one product from among polyvinyl alcohol and derivatives of polyvinyl alcohol. 
     
     
         9 . The method according to  claim 7  wherein dimethyl ether is continuously removed from the system so that substantially all methyl species in the feed are converted to dimethyl ether and thereby removed from the reaction mixture, and the product stream is substantially pure acetic acid. 
     
     
         10 . A batch method for recovery of a carboxylic acid by refluxing a mixture of the corresponding methyl ester of the carboxylic acid and a sufficient amount of at least one of methanol and water, in which:
 dimethyl ether is removed by volatilization;   sufficient water is made available, as one of added water and water produced by dehydration of methanol to dimethyl ether, to effect hydrolysis of the methyl ester of the carboxylic acid to the carboxylic acid and methanol;   the combination of hydrolysis of the methyl ester and volatilization of dimethyl ether removes all methyl groups from the reaction mixture;   thus producing a liquid product rich in the carboxylic acid and a vapour product rich in dimethyl ether.   
     
     
         11 . The batch method according to  claim 10 , in which the ester is methyl acetate and the carboxylic acid recovered as product is acetic acid.