Process Simulation And Analysis Of Oxidation Unit Of PTA Plant

Process simulation and analysis of oxidation unit of purified terephthalic acid (PTA) plant using Aspen Plus have been conducted, which could provide development platform for design and optimization for para-Xylene oxidation unit.Firstly, the methods and models including thermodynamic property and solubility involved in PX oxidation system were studied, and the corresponding parameters were regressed based on literature data.Secondly, modeling blocks of major sections in oxidation unit, including oxidation reaction section, oxidation and crystallization section, solvent dehydration section, solvent recovery section, filtering and drying section, have been built. Kinetic model of PX oxidation based on free radical reaction mechanism was applied, and side reactions were also considered. Meanwhile salt precipitation reactions were selected to describe the formation and dissolution of solids in equilibrium. Therefore, an oxidation reactor model coupling reaction, crystallization and evaporation was established. The simulation of oxidation reaction section was further completed with four circulation loops. So both composition information and solid product content of slurry is figured out. Similarly, the model of the first crystallizer involving secondary oxidation, crystallization and evaporation also has been built, and the oxidation and crystallization section was simulated, the effect of residence time on reaction and crystallization in the first crystallizer was investigated, the result of operation pressure influence on crystallization under adiabatic condition showed that reducing pressure would benefit the formation of solid. What’s more, a model of solvent dehydration section containing four circulation loops was generated, all of the loops could converged with appropriate tears and reasonable convergence method. It was verified that the calculated results of major subsidiary models of each sections were in good agreement with design value of industrial plant.Finally, segment partition of oxidation unit was carried out following the theory of hierarchical mechanism, and a hierarchical model for the whole process was created. With appropriate convergence method and sequence, the simulation of oxidation unit was realized. The calculated results also indicated a good fit with design value.