Deactivation Kinetic Modeling on Liquid Phase Oxidation of Durene to Pyromellitic Acid Using a Co/Mn/Br Catalyst

Pyromellitic acid (PMA) is a critical monomer in the synthesis of high-performance polyimides (PIs). A viable approach for the preparation of PMA is the synthesis of durene (DR) by liquid-phase oxidation using a Co/Mn/Br catalyst and acetic acid/water as solvents. Due to interaction between the transition metals Co/Mn and PMA, the catalytic effect is diminished, restricting industrial application of the liquid-phase oxidation method in the production of PMA. Based on the catalyst deactivation mechanism, the effects of different bromine sources, catalyst concentrations, solvent ratios, temperatures, and water contents on the liquid-phase oxidation of DR to PMA were systematically investigated in this work. A deactivation mechanistic model was developed covering DR, PMA, and other pivotal intermediates. Using hydrogen bromide as the bromine source and under conditions of a high solvent ratio, the yield of PMA was enhanced from 34.25 to 78.13 mol %. The kinetic model was utilized to conduct a comprehensive investigation into the impact of catalyst concentrations, temperature, and water content on the reaction and deactivation process. It was determined that the initiation of the DR oxidation chain is a rate-determining step and that the reaction rate increases while the deactivation rate decreases under high temperature and high-Co conditions. Furthermore, it is demonstrated that the optimum water content for the yield of PMA is 5%, with a concomitant slower deactivation reaction rate constant. Hopefully, the results obtained in this work can provide valuable insights into the liquid phase oxidation of polyalkyl aromatic hydrocarbons.