Semicontinuous Studies on the Reaction Mechanism and Kinetics for the Liquid-Phase Oxidation of p-Xylene to Terephthalic Acid

The reaction mechanism and kinetics for the liquid-phase catalytic oxidation of p -xylene to terephthalic acid are briefly reviewed, which indicates that the available literature is not complete when one looks for the industrially applicable mechanism and kinetics. In this work, a detailed radical chain reaction mechanism for the liquid-phase catalytic oxidation of p -xylene to terephthalic acid is proposed. Using several assumptions, a simple fractional-like kinetic model is derived from the assumed reaction mechanism. Several semicontinuous oxidation experiments are carried out at different reactant feed rates and temperatures. The experimental results show that the measured concentrations of liquid-phase reactants increase approximately linearly with time, which indicates that the reaction rate for the liquid-phase reactants is approximately independent from its concentration. The derived kinetic model can explain and correlate these experimental results satisfactorily. By combining the results determined in batch oxidation experiments with the semicontinuous experimental results, the kinetic model parameters are determined by data fitting. The correlated results generally agree with both the semicontinuous and the batch experimental results satisfactorily.