Side Reactions In Liquid-phase Oxidation Of P-Xylene

With complicated reaction mechanism, side reactions in liquid-phase oxidation of p-xylene (PX) have a close relationship with main reactions. According to characteristic of by-products, side reactions were investigated separately, including the influences on the formations of benzoic acid (BA) and methyl acetate, and kinetic experiments and model of burning side reaction.Due to the difficulty in sample collecting caused by the sublimation of BA and the low boiling point of methyl acetate, a batch device with good air-tightness was established. The influences of temperature, water content, and catalyst on the formations of BA and methyl acetate were systematically investigated, in which the temperatures ranged from 180 to 195℃, the content of water from 2 to 10wt%, and the concentration ranges of Co, Mn, and Br were 200～1000 ppm,200～800 ppm, and 300～1200 ppm, respectively. Results showed that the formations of BA and methyl acetate increased with the rising of temperature and there existed optimal water content for inhibiting the formation of BA. Besides, the increasing of the ratio of Co/Mn caused side reactions such as decarboxylation and decarbonylation to be aggravated, and the formation of BA can be kept lower when the concentration of Br was enhanced.By tail gas online measurement in semi-continuous experimental setup, the influences of temperature, water content and catalyst on kinetics of COx formation were investigated, in which the temperatures ranged from 180 to 200℃, the mass content of water from 2 to 10wt%, and the concentration ranges of Co, Mn, and Br were 350-700 ppm,350-700 ppm, and 700-1400 ppm, respectively. The results indicated that lower temperatures helped to reduce the formation rate of COx, and water content inhibited side reactions. With the increasing of the ratio of Co/Mn, burning'side reactions were greatly intensified, and those were reduced by raising the Br concentration. By combining main reactions in PX oxidation process with side reactions, the kinetic model of COx formation was established. Fitting results showed that calculated values were in good agreement with experimental ones. And also, the kinetics of COx formation gave satisfactory predictions to industrial reactors in three kinds of technologies.