Method for producing organic acid

Abstract

A novel method is provided whereby a free organic acid can be produced particularly from an ammonium salt of an organic acid having a high melting point obtainable by bioconversion of a carbon source in the presence of a neutralizing agent, efficiently at a low cost, and the used material for reaction and a byproduct can be recycled for reuse without being disposed. An ammonium salt of organic acid A such as a dicarboxylic acid, a tricarboxylic acid or an amino acid is subjected to reactive crystallization by means of acid B such as a monocarboxylic acid satisfying the following formula (1), to separate free organic acid A in solid form: pKa( A )≦pKa( B )  (1) where pKa(A) and pKa(B) represent ionization indices of organic acid A and acid B, respectively, provided that when they have plural values, they represent the minimum pKa among them. The crystallization mother liquor after precipitating and separating organic acid A is, after separating acid B and then an ammonium salt of acid B, recycled for use in the reactive crystallization step. The ammonium salt of acid B is decomposed into acid B and ammonia, which are recycled for use in the reactive crystallization step and as a neutralizing agent in the bioconversion step, respectively.

1 - 22 . (canceled)  
   
   
       23 . A method for producing organic acid A, which comprises subjecting an ammonium salt of organic acid A to reactive crystallization by means of acid B satisfying the following formula (1), to separate organic acid A in solid form: 
       pKa( A )≦pKa( B )  (1) where pKa(A) and pKa(B) represent ionization indices of organic acid A and acid B, respectively provided that when they have plural values, they represent the minimum pKa among them,    wherein the ammonium salt of organic acid A is one obtained in the form of an aqueous solution of the ammonium salt of organic acid A in such a manner that a reaction solution containing an alkali metal and/or alkaline earth metal salt of organic acid A is obtained via a bioconversion step in which a carbon source is converted by a microorganism in the presence of at least one neutralizing agent selected from the group consisting of an alkali metal hydroxide, an alkaline earth metal hydroxide, an alkali metal carbonate and an alkaline earth metal carbonate; ammonia and carbon dioxide, and/or ammonium carbonate, is added to said reaction solution containing an alkali metal and/or alkaline earth metal salt of organic acid A to carry out reactive crystallization to precipitate an alkali metal and/or alkaline earth metal carbonate (Solvay process step); and the precipitated carbonate is separated; organic acid A precipitated by the reactive crystallization carried out by adding acid B, is separated; after the separation, the ammonium salt of acid B in the crystallization mother liquor, is decomposed to obtain ammonia; and the ammonia is used as an ammonia source for the Solvay process step.    
   
   
       24 . The method according to  claim 23 , wherein the reactive crystallization is carried out in multi-stages, and in reactive crystallization in the second or subsequent stage, the crystallization mother liquor after separating the precipitated organic acid A is, directly or after concentrating the ammonium salt of acid B by vaporization of the reactive crystallization solvent containing acid B, or after separating organic acid A or its salt dissolved in the mother liquor, recycled to a crystallizer for reactive crystallization in a preceding stage.  
   
   
       25 - 30 . (canceled)  
   
   
       31 . The method according to  claim 23 , wherein the alkali metal and/or alkaline earth metal constituting the alkali metal and/or alkaline earth metal salt of acid B, is at least one member selected from the group consisting of Na, K, Ca and Mg.  
   
   
       32 . The method according to  claim 23 , wherein acid B is at least one member selected from the group consisting of formic acid, acetic acid, propionic acid and butyric acid.  
   
   
       33 - 36 . (canceled)