PURIFICATION OF NAPHTHALENEDICARBOXYLIC ACID

摘要

PROBLEM TO BE SOLVED: To accomplish purity improvement and yield improvement for naphthalenedicarboxylic acid simultaneously through purification of crude naphthalenedicarboxylic acrid by converting the CHO group in formylnaphthoic acid, a typical impurity found in the crude naphthalenedicarboxylic acid, into COOH group. SOLUTION: Crude naphthalenedicarboxylic acid is subjected to molecular oxygen at such a level as to be at least 0.5 equivalent of the amount of oxygen required for oxidizing the substituents being in incompletely oxidized state in the crude naphthalenedicarboxylic acid to carboxyl groups (pref. 1-15 equivalents) in a high-temperature aqueous reaction medium in the presence of a noble metal catalyst such as platinum. Subsequently, the reaction liquid is separated from the catalyst while the resultant naphthalenedicarboxylic acid lies dissolved in the high-temperature aqueous reaction medium, and gradually allowed to cool to effect crystallization of the naphthalenedicarboxylic acid which is the recovered to obtain the objective purified product.