Modeling And Simulation Of Esterification Section In Industrial Poly(Ethylene Terephthalate) Process

Developing a mathematic model can be an important method to improve industrial processes. An appropriate model can be applied to analyze the operating conditions and optimize the existing process. In this thesis, a steady model has been developed for esterification section of Gimmer technique. It has taken into account the complexity and characteristics of the process such as physical properties and kinetics mechanism. The main results are as follows:An appropriate property model for the polyethylene terephthalate esterification system was developed. The esterification system included ethylene glycol, terephthalic acid, water, diethylene glycol, acetaldehyde, bis(hydroxyethyl) terephtalate, poly(ethylene terephthalate) and catalyst. The equation of UNIFAC based on group contribution theory was applied to predict thermodynamic properties and phase equilibrium of the system. The group binary parameters of UNIFAC were re-parameterized through regressing data from literature. The results of pure component property, vapor-liquid equilibrium and solid-liquid equilibrium calculating with the re-parameterized UNIFAC model agree with those in literature. The maximum average relative error is lower than 3% between prediction result and literature data. The re-parameterized UNIFAC EOS can be used to predict the vapor-liquid-solid equilibrium and physical properties involved in the PET esterification system with sufficient accuracy.Esterification reactor models were developed. The two esterification reactors are standard stirred-tank reactors type with a heating jacket. Each esterification reactor was divided into an inner chamber and an outer chamber by a ring baffle. According to the previous researchers' study, the inner chamber can be represented as a CSTR unit module, and the outer chamber can be represented as a CSTR unit module or a PFR unit module. Comparing the results from different combinations of reactor unit module including two CSTR modules, one CSTR module plus one PFR module and one CSTR, it turned out that 2 CSTR unit modules should be used to represent an esterification reactor. A kinetic model was developed for industrial PET esterification process. The kinetic mechanisms and kinetic parameters of both main reactions and side reactions were discussed. The adjustable ranges of kinetic constant were determined. A set of kinetic constants from literature was used as original parameters. The key parameters were finetuned within the adjustable ranges to fit the plant data including components flow, esterification rate of terephthalic acid and diethylene glycol content. The process model included kinetic and thermodynamic parameters can simulate the esterification process well at different capacities. The results of main product qualities agreed well with plant data.A steady model was developed and applied for analysis of operating conditions and optimization of residence time combination. It was found that esterification rate increased with increasing mole ratio of EG/TPA in feed, temperature, pressure and residence time in two esterification reactors, and DEG content increased with increasing mole ratio of EG/TPA in feed, temperature, pressure and residence time in the first esterification reactor but decreased with increasing residence time in the second esterification reactor. The residence time combination of esterification reactors at the highest esterification conversion efficiency was determined.