Process for producing a high purity aromatic polycarboxylic acid

A process for producing a high purity aromatic polycarboxylic acid by purifying a crude aromatic polycarboxylic acid, comprising steps of:

• (I) forming a salt which comprises forming an amine salt of an aromatic polycarboxylic acid from the crude aromatic polycarboxylic acid and amine;
• (II) decomposing a salt which comprises simultaneously and continuously conducting in a salt decomposition reactor three operations of (i) supplying an aqueous solution of the amine salt of an aromatic polycarboxylic acid formed in the step of forming a salt, (ii) removing the amine and water by distillation under heating and (iii) taking out a slurry containing crystallized aromatic polycarboxylic acid in a condition, at steady state, that a concentration of crystals of the aromatic polycarboxylic acid is 5 to 50% by weight and that a fraction of decomposition of the amine salt of the carboxylic acid is 20 to 80%;
• and
• (III) separating crystals which comprises separating and recovering crystals of the aromatic polycarboxylic acid from the slurry which is taken out in the step of decomposing a salt, wherein at least a portion of a mother liquor, which is obtained after crystals of the aromatic polycarboxylic acid are separated in the step of separating crystals, is recycled to the step of decomposing a salt.