Simulation of Secondary Oxidation of p-Xylene in Liquid Phase

Abstract

Secondary oxidation of p-xylene (PX) plays an important role in the production of purifled terephthalic acid (PTA), including directly secondary oxidation (DSO) and nondirectly secondary oxidation (NDSO). Little is known about which kinds of kinetics, either PX oxidation or p-toluic acid (p-TA) oxidation, can be used to simulate these two types of secondary oxidation processes. In this work, the kinetic model of p-TA oxidation with only one parameter was first established, which exhibited good fitting accuracy to experiments. Next, semi-batch experiments were carried out to imitate the liquid phase oxidation in DSO and NDSO. The simulation results show that the direct prediction of liquor oxidation in DSO by PX oxidation kinetics has poor accuracy. But PX oxidation kinetics exhibits better prediction if choosing the free radical concentrations in the final phase of the primary PX oxidation process as the initial condition. And also, the kinetics of p-TA oxidation have a better capability of predicting liquor oxidation in DSO than the direct prediction by PX oxidation kinetics. Regarding the liquor oxidation in NDSO, the prediction given by p-TA oxidation kinetics was excellent, while that given by PX oxidation kinetics was unsatisfactory.