Gas Phase Air Oxidation of Durene with V-P-O Catalysts

Abstract

Gas phase air oxidation of durene to pyromellitic dianhydride (PMDA) has been studied with catalysts of vanadium oxide on porous alundum. Simple V2O5 catalysts had some selectivity for formation of PMDA, and by addition of a little amount of P2O5-component the selectivity increased though the activity for oxidation slightly decreased. The optimum amount of P2O5 to be added was 15% on the weight of V2O5, and the addition of the P2O5 in excess of the optimum amount resulted only in the decrease of the oxidation-activity.Formation of PMDA on V-P-O catalyst proceeded mainly via 3, 4-dimethylphthalic anhydride. Trimethylbenzene carboxylic acid and monomethylbenzene tricarboxylic acid expected to come from durene were formed in small quantities, and most of the adjacent methyl groups in the molecule of durene seemed to be oxidized at the same time.Oxidation of durene was compared with those of toluene, o-xylene and pseudocumene, and the following results were obtained. (1) Oxidizability was in the order: durene>pseudocumene>o-xylene_??_toluene. (2) Yields of benzene carboxylic acids, φ-(COOH)n (or anhydrides), in oxidation of the hydrocarbons, φ-(CH3)n, were in the order: o-xylene>durene>toluene>pseudocumene. Good yield of PMDA may be at least partly due to the high stability of the anhydride-structure to oxidation. (3) Yield of maleic anhydride was in the order: toluene>o-xylene>pseudocumene>durene.