Studies On Effects Of Catalysts On P-Xylene Oxidation

Pure terephthalic acid is an important raw stuff used for synthetic preparation of polyester fibre and plastic, which is produced via air oxidation of p-xylene in acetic acid with cobalt/manganese/bromide catalyst. Catalyst effects on the oxidation process are researched and discussed in this paper. The work includes two parts. Firstly, effects of Co-Mn-Br components on each step of the main reactions were investigated experimentally, and the related kinetic constants for typical industrial reaction conditions, such as that of Amoco and Mitsui technologies, were obtained. Secondly, various kinds of catalytic additives were developed and tested in order to find a new ternary-component catalyst system. It is shown that increase of the concentration of Co-Mn-Br catalyst will accelerate both main reactions and combustion reactions, and Br is the most sensitive catalytic component in Co-Mn-Br influencing the reaction rates; ratio of Co/Mn has more remarkable effects on combustion reactions than that on main reactions, and low ratio of Co/Mn can reduce the combustion, its optimum value depends on practical reaction conditions. These results were treated as expressions of rate constants vs total concentration of Co-Mn-Br, mole ratio of Co/Mn as well as mole ratio of Br/Co. For the catalyst development and test, a serial of new additives with a fourth metal or non-metal compound were considered. Experiments show that KAc, NaOH, Hf(Ac)4, Zr(Ac)4, HC1, NaCl and C5H5N can accelerate p-xylene oxidation; acetates of Nd, Pr, Gd, Dy, Sm, La, Ce and HNC>3 do not change the reaction rates, but Ce acetate can prevent Mn from precipitation; EDTA will introduce an induction period at the beginning of p-xylene oxidation; Fe ion does not influence the reaction rates under the low concentration of 30ppm, beyond l00ppm it will slow the main reactions perceptibly.