PURIFICATION OF TEREPHTHALIC ACID TO RELATIVELY LOW LEVELS OF 4-CARBOXYBENZALDEHYDE AND CATALYST THEREFOR

摘要

Aqueous solutions of crude terephthalic acid are purified to relatively low 4-carboxybenzaldehyde levels under hydrogenation conditions by using a layered catalyst bed. The aqueous terephthalic acid solution to be purified is first passed through a particulate primary catalyst layer constituted by palladium on active carbon and thereafter through a particulate secondary catalyst bed constituted by rhodium on active carbon.