Research On Oxidation Of MX To IPA Catalyzed By PW₁₂

As one of the most important aromatic compounds,isophthalic acid is widely used in organic synthesis,particularly in the polyester industry.Commercially,Co-Mn-Br was used as catalysis for m-xylene liquid-phase oxidation to isophthalic acid with high conversion and yield.However,the erosion caused by Br at a high temperature can sharply shorten the life of equipment.A bromine-free catalyst Co-Mn-PW12/AC was proved available for m-xylene oxidation,eliminating the erosion caused by Br at a high temperature.Firstly,PW12 was used as homogeneous catalyst and the effects of the reaction temperature,oxygen partial pressure,catalyst content,water content,stirring speed and air fluent were investigated and the results were listed as:(a) Either increasing the reaction temperatyre,pressure and stirring speed or decreasing the water concentration could fasten MX oxidation rate;(b)When the concentration of PW12,ratio of Mn/Co(wt) and air fluent were increased,the MX oxidation rate initially increased and then droped;(c)The optimal process conditions for MX oxidation catalyzed by PW12 were obtained,which is 215℃,3Mpa,0.52%(wt)PW12, 0.088%(wt)Co,2.46/1(wt)Mn/Co,4%H2O,1.2L/min air and 350rpm.Secondly,the semi-empirical kinetic model,based on some assumption,was proposed to describe the oxidation of MX. The kinetic paramerers were determined in a nonlinear optimization, minimizing the difference between the simulated and experimental time evolution of the products in a semibatch oxidation reactor.The results indicated that (a)the reaction temperature had a strong effect on each step of MX oxidation;(b)The activate energy of PIA to 3-CBA is highest(71.9636kj/mol),and that is the control step;The activate energy of MX to 3-IMA is the second highest(69.0418 kj/mol);The activate energy of 3-IMA to PIA is the lowest(42.6311 kj/mol);(c)The reaction orders of MX,3-IMA,PIA and 3-CBA is 0.9713,1.0605,0.7914 and 1.1892;Meanwhile, the reaction orders to oxygen partial pressure of each step are 0.2148,0.5699,0.1929 and 0.466.Finally,Co-Mn-PW12/AC including 4.5gAC and 13% PW12,which had been activated at 220℃for 4 hours,was used as heterogeneous catalyst for MX oxidation.Comparing to the homogeneous catalyst,the yield of IPA is 13.1% higher and the combustion rate is 25.25% lower.How to increase the reaction rate and meanwhile decrease the combustion rate with a heterogeneous catalyst still need some further research.