Terephthalic acid purificn - by catalytic hydrogenation

摘要

Crude terephthalic acid is purified by dissolving it at moderately elevated temp. in N-methyl pyrrolidone followed by treatment of the soln. with H2 in the presence of a noble metal contg. catalyst at normal press. andmoderately elevated temp. The terephthalic acid is pptd. out of soln. after sepn. of the catalyst. A suitable catalyst is Pd/charcoal. The process is partic. suitable for purifying acid contg. 4-carboxybenzaldehyde as the main impurity.