Kinetic Modeling of Liquid Phase Oxidation of 2,6-Dimethylnaphthalene to 2,6-Naphthalenedicarboxylic Acid

2,6-Naphthalenedicarboxylic acid (2,6-NDA) is an important monomer for high-performance polyester materials. In this work, 2,6-NDA was prepared through liquid phase oxidation of 2,6-dimethylnaphthalene (2,6-DMN) using Co/Mn/Br as catalysts, acetic acid/water as solvents, and air as oxidant. The effects of catalysts, temperature, and water content on oxidation kinetics were investigated. Based on the free radical chain reaction mechanism, a simplified kinetic model was developed, which involves 2,6-DMN, 2,6-NDA, and other important intermediates. Model fitting results show that the kinetic model fits experimental data well under the conditions of various catalysts, temperatures, and solvent compositions. It was found that rate constants k2 through k9 regarding to chain propagation and termination are independent of catalyst and solvent compositions due to the absence of catalyst and water in these steps. These reaction steps show to be insensitive to temperatures within a certain range due to a very low reaction activation energy of the reactions between peroxy-radicals and α-carbon atoms. Hopefully, the model fitting results obtained in this work can provide valuable insights into the industrial reactor design and process optimization of the liquid phase oxidation of 2,6-DMN.