Modeling And Analysis Of The Industrial Poly (Ethylene Terephthalate) Plant

Modeling the industrial processes, which can improve existing process and increase economic efficiency, has great significance. The steady-state model of the whole polyester production process based on the reaction mechanism is established for the five-tank polyester continuous production process on the esterification section, pre-polycondensation section and final polycondensation section.This model takes account of the complexity and specificity of polymer properties, polymerization kinetics, mass transfer and other aspects, which can solve the modeling difficulties of reaction mechanism, kinetic parameters, mass transfer model and parameters. The model has been used to analyze process parameters, i.e., feed mole ratio, reaction temperature and pressure, and can provide guidance for the adjustment of polyester production process parameters. Specific innovative results are as follows:1. On the basis of inductive analysis of the reported reaction mechanism and kinetics of the esterification stage, the rate constants for the proton acid and Sb3+ catalytic system are drawn under a reasonable range. With the help of industrial production data correction to the esterification reaction and polycondensation reaction kinetic constants, the mechanism model for large-scale PET plant esterification process is established with the relative deviation of less than 3%. The influences of operating conditions on mass flow, the esterification rate, content of diethylene glycol are studied. Increasing the feed molar ratio of ethylene glycol to terephthalic acid, temperature, pressure and residence time will cause the increase in the esterification rate and mass flow of PET, and inhibit the formation of diethylene glycol.2. The main concerned side reaction in pre-polycondensation system is the formation of DEG and AA. Through the analysis of sensitivities of kinetic constants on the main quality indexes, including the average molecular weight(MWN) of polymer, esterifacation rate, mass fraction of DEG, and kinetic constants of esterification reactions and plycondensation for process modeling have been modified. The model was validated according to the industrial production data, the error of main parameters between plant data and simulation were less than 0.1%. Using the modified model to investigate the effects of operating conditions such as ethylene glycol and terephthalic (EG/TPA) molar ratio, temperature, pressure and residence time on PET mass flow, esterification rate(ES%) and mass fraction(DEGwt%). Increasing the temperature, pressure, residence time could enhance ES%, DEGwt% and MWN.3. The main reaction and the main side reaction involved in the final stage were poly condensation and thermal degradation, respectively. According to the analyzing of vacuum-finishing reactors, model including diffusivity and volatilization of EG has been established. Through investigation of the mass-transfer coefficient and kinetic constants on the main quality indexes, including the average molecular weight of polymer, mass flow of acetaldehyde and diethylene glycol, and basic model parameters for process modeling have been modified. The model of polycondensation section of PET process was developed based on kinetic mechanism and the mass-transfer model. The error between plant data and simulation was less than 1%. By the sensitivity analysis of the impacts of operating conditions on the average molecular weight(MWN) and DEGwt%, it was informed that if we wanted to increase MWN can raise the mass-transfer coefficient and vacuum, and if we want to decrease DEGwt% can take measures of reducing the residence time.4. The impacts of operating conditions on the qualities of products, including EG/TPA feed molar ratio, temperature, pressure and residence time in esterification stage and pre-polycondensation stage were obtained. The EG/TPA molar greatly affected the DEGwt%, followed by residence time, pressure and temperature. The greatest impact factor for PET mass flow was EG/TPA molar ratio. The EG/TPA molar ratio greatly affected the MWN, followed by pressure and residence time of esterification reactor, and residence time of pre-polycondensation reactor.