Abstract: Improved acid yield and product quality are realized in the oxidation of aromatic hydrocarbons in a two-stage process, employing an aqueous solvent system and an increased proportion of bromine, and, optionally, of catalytic metals, in the second stage.

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.