| Isophthalic acid is an important raw material in the polyeaster industry. The most popular method of producing isophthalic acid is the liquid-phase catalytic oxidation of m-xylene, in which acetic acid is used as solvent, cobalt/manganese/bromide as catalyst. The two methyls are oxidized into corresponding aldehyde and acid. In this paper a mechanism model is used to describe the oxidation of m-xylene. The effect of reactant concentration, catalyst composition, catalyst concentration and temperature on the oxidation is investigated. It is found that the oxidation rate of m-xylene does not vary significantly with the variation of m-xylene concentration. There exists an optimal ratio of cobalt and manganese. The activation energies of four steps range from 50kJ/mol to 60kJ /mol. Among them, the activation energy of 3-carboxybenzaldehyde to isophthalic acid step is the highest. Because of the difference of the position of two methyls the oxidation character of m-xylene and p-xylene also has some difference.The content of m-xylene is the highest among the C8 aromatic hydrocarbon. Yet most is isomerized to produce p-xylene. In this paper a novel process to produce cheap PIA is proposed. In this process the mixture of m-xylene and p-xylene is oxidized. The feasibility experiments show that the m-xylene and p-xylene is oxidized through the respective reaction path into PIA and PTA. The solubility of PIA and PTA in water at high temperature is significantly different and the solubility of PTA in water is sensitive to temperature. Therefore, cheap PIA can be obtained through crystallization.
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