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 . In a process for separating and recovering an acid B and ammonia by decomposing an ammonium salt of acid B to the acid B and ammonia, a method for decomposing the ammonium salt of acid B, wherein said method comprises:
 heating a liquid comprising water, the ammonium salt of acid B, and a metal salt of acid B, by supplying the liquid to a site of a distillation column having at least two plates as the real number of plates to produce a gas of a basic aqueous solution and a remaining liquid, wherein the temperature of the site of the distillation column is not higher than the melting point of the ammonium salt of acid B, and wherein the metal of the metal salt of acid B is one or more metals selected from the group consisting of Na, K, Ca and Mg; and   withdrawing the gas of the basic aqueous solution from the top of the distillation column.   
   
   
       2 . The method according to  claim 1 , wherein the acid B is at least one acid selected from the group consisting of formic acid, acetic acid, propionic acid and butyric acid. 
   
   
       3 . The method according to  claim 1 , wherein said method further comprises recovering the acid B by subjecting the remaining liquid, after said withdrawing, to a temperature of at least 125° C. under reduced pressure or atmospheric pressure, and separating the acid B from a residual liquid. 
   
   
       4 . The method according to  claim 3 , wherein said method further comprises mixing the residual liquid, after said separating, with an aqueous system to hydrolyze an amide compound formed as a byproduct in said heating and said separating; and recycling the residual liquid, after said mixing, to said heating. 
   
   
       5 . The method according to  claim 1 , wherein said method further comprises withdrawing the gas of the basic aqueous solution from the remaining liquid. 
   
   
       6 . The method according to  claim 1 , wherein said method further comprises subjecting the gas of the basic aqueous solution, either directly or after condensation, to a gas separation carried out at a temperature of not higher than the melting point of the ammonium salt of acid B, wherein said gas separation is selected from the group consisting of a gas/liquid separation, a gas/solid separation and a gas/liquid/solid separation.