Process for the manufacture of trimellitic acid

Abstract

A continuous process is disclosed for producing trimellitic acid by the liquid-phase air oxidation of pseudocumene in an acetic acid medium in the presence of a cobalt-manganese-bromine catalyst or a zirconium-cobalt-manganese-bromine catalyst wherein the mole ratio of cobalt-to-manganese is about 1.0:0.1 to about 1:5 and the ratio of zirconium-to-cobalt is about 0.005:1 to about 0.20:1, and mole ratio of bromine to total metals of said cobalt-manganese-bromine catalyst or zirconium-cobalt-manganese-bromine catalyst is from about 0.2:1.0 to about 2.0:1.0, which process comprises conducting the reaction continuously in two stages comprising a first-stage reaction at a temperature of about 250.degree. F. to about 350.degree. F. and a second-stage reaction at a temperature of about 350.degree. F. to about 450.degree. F. and recycling the cobalt-manganese catalyst or the zirconium-cobalt-manganese catalyst by oxalate precipitation of the catalyst at temperatures of about 250.degree. F. to about 375.degree. F. prior to the separation of mother liquor and using about 0.25 to about 2.5 moles of oxalic acid per mole of cobalt and manganese or mole of zirconium-cobalt-manganese and continuously recycling the recovered catalyst metals to the first-stage oxidation. The product of this novel process, trimellitic acid, is useful for the manufacture of polyamide-imides which are used as fibers or molded articles, including automotive parts.