Kinetics Study Of The Aerobic Oxidation Of P-Xylene Catalyzed By Metalloporphyrin And Cobalt Acetate

p-Xylene(PX) liquid phase oxidation reaction is an important industrial production process, terephthalic acid(TA) which is the main oxidation products of p-xylene oxidation has recently become an important, fast-growing chemical as a raw material for polyethylene terephthalate(PET), worldwide production of terephthalic acid is 30 million tons per year. Commercially, the majority of terephthalic acid is produced by the air oxidation of p-xylene in acetic acid in the temperature range from 150 to 210°C, catalyzed by cobalt and manganese salts and promoted by bromine (MC process). This process, however, has some disadvantages:i. e., the use of bromine as a promoter which corrodes the reactor and pollutes the environment, and the use of acetic acid as solvent which is large consumption by oxidized to carbon dioxide in the terephthalic acid production process. From economical and environmental points of view, the development of a new oxidation system, which overcomes these disadvantages for the production of terephthalic acid, is desired. In recent years, metalloporphyrin biomimetic catalyst in the selective oxidation of hydrocarbons drew more and more attention, because it has an environmentally friendly, good product selectivity and other characteristics,. In our group's preceding papers, we showed that metalloporphyrin promotes the aerobic oxidation of p-xylene in the presence of cobalt acetate, which shows good catalytic effect. To gain better insight into the reaction mechanism and identify the effects of different parameters on the progress of the reaction, it is essential to study the kinetics.In this paper, the basis of previous work, in solvent-free conditions, the metalloporphyrin and cobalt acetate co-catalytic aerobic p-xylene oxidation system as a research system, Systematic study of the reaction mechanism and kinetics of the aerobic oxidation of p-xylene catalyzed by metalloporphyrin and cobalt acetate. The main work of this paper is as follows:1, In order to raises the experimental efficiency, we have improved the reactor, through the design of the continuous sampling device of the reactor. And also we have improved the HPLC analysis of p-xylene to increase accuracy and reduce the analysis time。2,p-Xylene conversion and selectivity of terephthalic acid of the metalloporphyrin and cobalt acetate co-catalytic p-xylene oxidation reaction was improved through experimental research. After the study of the exclusion of oxygen gas mass transfer resistance effects, we have also researched the components of the p-xylene oxidation reaction change with time under different conditions. And it provides experimental data for the kinetics of this reaction.3, Based on our previous work, we proposes a new reaction mechanism of aerobic p-xylene oxidation catalyzed by metalloporphyrin and cobalt acetate. We believe that the metalloporphyrin cobalt acetate co-catalytic aerobic oxidation of p-xylene has two competing reaction paths, the radicals escape way and the radicals capture way.4, Using the steady-state approximation, a simple kinetic model was derived from the our assumed reaction mechanism for the first time. Then apply our experimental data to regress the kinetic model parameters, which made the uniquely determination of the model parameters by fitting of experimental data available and feasible. The derived kinetic model can explain and correlate our experimental results satisfactorily.