Catalytic purification and recovery of dicarboxylic aromatic acids

Abstract

Processes using a titanium dioxide-supported purification catalyst are disclosed for purification of relatively impure dicarboxylic aromatic acid produced by liquid-phase oxidation of a suitable benzene or naphthalene having two oxidizable ring substituents, and/or by recovery from polyester resin comprising repeating units of the dicarboxylic aromatic acid residue and repeating units of dihydric alcohol residue. Purification comprises passing an aqueous solution of dicarboxylic aromatic acid with small amounts of organic impurities consisting of oxygen-containing aromatic co-products of oxidation and/or other organic components, through a particulate bed of purification catalyst comprising a noble metal on a titanium dioxide support under conditions suitable for decarbonylation of organic impurities. Generally, at least one weight percent of the titanium dioxide support is in the rutile crystalline phase. Optionally, effluent aqueous solution from the bed containing noble metal on the titanium dioxide support is passed through a subsequent particulate bed of another purification catalyst in the presence of a molecular hydrogen-containing gas. Hydrogenation of the aqueous solution subsequent to decarbonylation further reduces organic impurities in dicarboxylic aromatic acid recovered by crystallization and separation from the aqueous solution. The invention provides improved processes for preparation of purified terephthalic acid wherein purified terephthalic acid product is recovered from its mother liquor while maintaining temperatures within a range downward from about 100.degree. C. to about 25.degree. C. and pressures near or at atmospheric pressure.