Process for the production of trimellitic anhydride

A process for the oxidation of pseudocumene to trimellitic acid anhydride is disclosed which comprises catalytic oxidation of pseudocumene with air in the presence of acetic acid in an oxidation zone in the liquid phase wherein the weight ratio of acetic acid to pseudocumene is in the range of about 0.5-4.0:1.0 and the catalyst comprises one or more heavy metal oxidation catalysts comprising zirconium, cobalt, and manganese to provide about 0.1 to about 0.4 weight percent total metals based on pseudocumene and a source of bromine. The addition of the bromine component is controlled to provide a total of about 0.10 to about 0.30 weight percent total bromine based on pseudocumene. The total weight ratio of bromine ions to total metals ions is about 0.5 to about 2.0. The zirconium content is about 1 to about 5% and the manganese content is about 14 to about 60% each by weight of the total metals. The reaction temperature is about 100 DEG C. to about 250 DEG C. The acetic acid and water of reaction are withdrawn during the last 5 to about 20% of the reaction.