Pure terephthalic acid prodn - by hydrogenating ammonium terephthalate soln and acidifying

摘要

Terephthalic acid is purified by (a) dissolving it at 20-200, pref. 80-180 degrees C in aq. ammonia in stoichiometric excess of 0.100% pref. 1-10% to form ammonium terephthalate soln. of pH 7.5-11, pref. 8-9, (b) treating the soln. with H2 (partial press. 1-200 atm) using hydrogenation catalyst at 130-230, pref. 150-180 degrees C, and (c) converting the ammonium terephthalate to the free acid by contact with H2SO4. Ammonium, terephthalate is more soluble than the acid and concn. of soln. can be increased from 10 to 30%. The product is suitable for polyester prepn.