Kinetic Studies On Buring Reactions In The Oxidation Of P-Xylene

High-temperature liquid phase catalytic oxidation of p-xylene to produce purified terephthalic acid is an important industry process which often carries out at 180-224 癈 and 10~25atm by using cobalt acetate, manganic acetate and bromine as catalyst and dioxygen as oxidant. During the process, the intermediate product oxidized from p--xylene and solvent acetic acid are decarboxylated to form carbon dioxide and decarbonylated to form carbon monoxide which is called buring reaction. This thesis concentrates on three major industry processes and studies how the factors such as the p-xylene concentration, temperature, catalyst concentration and ratio, water content and oxygen concentration in vent gas affect the burning reaction rate. The experiments show that in the reaction the generating rate of COX had two maximums, and the lower the reactant concentraion is, the higher the generating rate of COX will be. Detailed analysis on decarboxylation and /7-xylene oxidation mechanisms shows that the increased concentration of trivalent metal ions oxidized by peroxide radicals greatly enhances the decarboxylation, and the effect of abstracting hydrogen atoms from the carboxy group of acetic acid when aldehyde is oxidized results in the appearance of two maximums on the COX curve. With reference to the kinetic model of />-xylene oxidation, the fractional kinetic model of buring reaction was developed, which is used to fit experiments data. It is found that the buring rate will increase along with the temperature and catalyst concentration. The active energy of the burning reaction was obtained, which is similar in amplitude to the main reaction. Increasing the cobalt acetate and bromine concentration will also accelerate the burning reaction, but increasing the bromine concentration will decrease the whole COX amount produced from buring reaction. Water content is another important factor affecting the burning reaction that a little increase of water content will greatly inhibit the buring. The burning reaction will also increase with the oxygen concentration in vent gas. The kinetic data and model obtained in this paper can be utilized for the innovation and optimization of industrial process.