Process and apparatus for recovery of acetic acid from a feed stream containing the corresponding ester

Abstract

An apparatus and process for recovery of a carboxylic acid e.g. acetic acid, from an aqueous feed stream containing the corresponding ester, an alcohol and a small amount of water, and in some cases the carboxylic acid includes a catalytic distillation column containing an acidic catalyst and a distillation column. The alcohol is catalytically dehydrated to the corresponding ether and water, and the water reacts with the ester to generate a liquid carboxylic acid rich product stream. The acid is recovered by distillation in the distillation column. In a second embodiment, additional methanol and/or water are co-fed with the feed or fed directly to the catalytic distillation column, resulting in a liquid bottoms product stream of substantially pure acetic acid and a tops distillate stream of substantially pure ether.

1 . An apparatus for recovery of acetic acid from an aqueous feed stream containing methyl acetate and methyl alcohol and a small amount of water, and in some cases acetic acid, by catalytic distillation of the aqueous stream to form acetic acid and dimethyl ether, the apparatus comprising a catalytic distillation column containing an acidic catalyst for acid catalyzed chemical reactions, and a recovery distillation column for recovery of acetic acid as a liquid bottoms product stream. 
     
     
         2 . An apparatus according to  claim 1 , wherein the catalytic distillation column includes a top portion, a middle portion including a reactive zone containing the acidic catalyst and a bottom portion. 
     
     
         3 . An apparatus according to  claim 2 , wherein the acidic catalyst is any one of several acidic resin catalysts suitable for use in the catalytic hydration of methyl acetate, selected from the acidic forms of commercially available resins, containing SO 3 H+ reactive sites attached to a styrene divinyl benzene copolymer. 
     
     
         4 . An apparatus according to  claim 3 , additionally comprising a first condenser for condensing a portion of vapors exiting the top portion, from which a fraction is recycled to the catalytic distillation column and another fraction comprising substantially pure dimethyl ether is recovered as first volatiles product. 
     
     
         5 . An apparatus according to  claim 4 , additionally comprising a first reboiler to reboil a first liquid bottoms product stream exiting the bottom portion of the catalytic distillation column to produce a first fraction for recycle thereto, and another fraction comprising acetic acid and methyl acetate for removal and directing to the recovery distillation column. 
     
     
         6 . An apparatus according to  claim 5 , wherein the recovery distillation column includes a top portion, a middle portion and a bottom portion, and additionally comprising a second condenser for condensing vapors exiting the top portion, from which a fraction is recycled to the recovery distillation column and another fraction comprising dimethyl acetate is recovered as second volatiles product, and a second reboiler to reboil a second liquid bottoms product stream exiting the bottom portion of the recovery distillation column, to produce a fraction for recycle thereto, and another fraction is recovered as substantially pure acetic acid. 
     
     
         7 . An apparatus for recovery of acetic acid from an aqueous feed stream containing methyl acetate and methyl alcohol and a small amount of water, and in some cases acetic acid, by catalytic distillation of the aqueous stream to form acetic acid and dimethyl ether, the apparatus comprising a catalytic distillation column containing an acidic catalyst for acid catalyzed chemical reactions, and means for addition of a supplemental amount of methanol and/or water, either to the feed stream before it is fed into the catalytic distillation column, or directly into the column at an appropriate location on the column, to maintain optimum operation independent of the composition of the ester containing feed stream from which the acetic acid is to be recovered, to provide a volatile tops product stream that is substantially pure dimethyl ether, and a liquid bottoms product stream that is substantially pure acetic acid. 
     
     
         8 . An apparatus according to  claim 7 , additionally comprising a feed line for supplying the feed stream to the catalytic distillation column at a location on the column, closely below the middle portion. 
     
     
         9 . A process for the recovery of acetic acid from an aqueous feed stream containing methyl acetate, methyl alcohol and a small amount of water and in some cases acetic acid, comprising
 (a) supplying the aqueous feed stream to a catalytic distillation column containing an acidic catalyst, wherein in one reaction the alcohol is dehydrated to produce dimethyl ether and water, and in another reaction the water is used to hydrolyze the methyl acetate to methyl alcohol and acetic acid, wherein both reactions proceed concurrently in reversible equilibrium, to produce a liquid bottoms product stream containing the acid exiting the catalytic distillation column, and   (b) transferring the liquid bottoms product stream to a recovery distillation column from which substantially pure acetic acid is recovered as a liquid bottoms product stream.   
     
     
         10 . A process for the recovery of acetic acid from an aqueous feed stream containing methyl acetate, methyl alcohol and a small amount of water and in some cases acetic acid, comprising
 (a) supplying the aqueous feed stream to a catalytic distillation column containing an acidic catalyst, wherein in one reaction the alcohol is dehydrated to produce dimethyl ether and water, and in another reaction this water is used to hydrolyze the methyl acetate to methyl alcohol and acetic acid, wherein both reactions proceed concurrently in reversible equilibrium, and   (b) adding a supplemental amount of methanol and/or water, either to the feed stream before it is fed into the catalytic distillation column, or directly into the column at an appropriate location on the column, to maintain optimum operation of the process independent of the composition of the ester containing feed stream from which the acetic acid, is to be recovered, to provide a volatile tops product stream that is substantially pure dimethyl ether, and a liquid bottoms product stream that is substantially pure acetic acid.   
     
     
         11 . A process according to  claim 10 , wherein the acidic catalyst is any one of several acidic resin catalysts suitable for use in the catalytic hydration of methyl acetate, selected from the acidic forms of commercially available resins, containing SO 3 H+ reactive sites attached to a styrene divinyl benzene copolymer. 
     
     
         12 . A process according to  claim 11 , wherein the aqueous feed stream is a stream produced at a facility for manufacturing at least one product from among polyvinyl alcohol and derivatives of polyvinyl alcohol. 
     
     
         13 . A process according to  claim 10 , wherein dimethyl ether is continuously removed from the system so that substantially all methyl species in the feed stream are converted to dimethyl ether and thereby removed from the reaction mixture, and the liquid product stream is substantially pure acetic acid.