Studies On Modeling And Simuation Of Purified Terephthalic Acid Process

Purified terephthalic acid (PTA), one of the most important materials of polyester, is usually produced by liquid oxidization of p-xylene (PX). The purity of oxidation product can't achieve industrial requirement, because the concentration of 4-carboxybenzaldehyd (4-CBA) is too high. By hydrogenating of 4-CBA, its concentration can be decreased from 3000 ppm to 25 ppm. Our group has done some research on PX oxidation process, but hydrogenation process has never been studied.This thesis focuses on the modeling of critical units and studying of the chemical engineering problem. Based on these work, the whole PTA process simulation and analysis will be conducted.The thesis includes mainly following five parts. The Liquid-liquid Equilibrium for the Ternary System HAc + H2O + EntrainerIn order to simulate the azeotropic distillation correctly, the phase behavior of acetic acid + water + acetate was studied in this thesis. Two different entrainers, n-propyl acetate and n-butyl acetate, were considered. Experiments related to the phase behavior were conducted at different temperatures under atmospheric pressure. The experimental data were correlated with the UNIQUAC model, and a good agreement was obtained.Studies on Azeotropic DistillationAzeotropic distillation is used to recover acetic acid and trash organic impurites. By analyzing the stability of the ternary system acetic acid + water + acetate, the criteria of phase splitting was given. Applying the thermodynamic model, considering mass balance, enthalpy balance, phase equilibrium and summation equations, the azeotropic distillation model was built. The comparison between calculated results and industrial data shows good agreement.Mechanism Modeling for CTA Hydrofining ReactorCrude terephthalic acid (CTA) hydrofining reactor, a crucial unit in PTA process, decides the purity of PTA product. By using chemical engineering method, this thesis considered the reactor model from hydrogenation reaction kinetics and reactor transport phenomena. Combining reactor's industrial character, themechanism model was built and was used to simulate the industrial reactor. Calculated results agree well with industrial data.Mechanism Modeling for PTA Series CrystallizersPTA series crystallizers decide the average particle size and size distribution of the product. Using the industrial data, the parameters of the crystallization kinetics were regressed. Considering mass balance, enthalpy balance, particle balance equations, the mechanism model was built. Operation parameters influence on the crystallization process was studied.PTA Whole Process Simulation and AnalysisIn this part, other physical treatment units were modeled. Combining PX oxidizer model built by our group before and the models discussed in the former parts, the whole PTA process was simulated. Newton-Raphson method was used to solve the non-linear equations. Simulation results agreed well with the field data.