Micro kinetics and mass transfer in poly(ethylene terephthalate) synthesis

The polycondensation of PET through ester interchange is a process strongly limited by mass transport effects. Therefore, design and scale up of industrial PET plants require a detailed knowledge of micro and macro kinetics. In this work, a comprehensive model for the polycondensation of PET has been developed taking into account 1) kinetic data, 2) equilibrium data, 3) diffusion processes for the major by-products EG and water in the molten PET. The model was validated using own experimental data determined by thermogravimetric analysis. As a sample, so called “PET-prepolymer ” was used. The kinetic parameters for the ester interchange reaction, for the water formation through esterification as well as for the most significant side reactions were taken from the literature. The mass transport was described using the classical diffusion equation according to Fick’s law and a modified Wilke-Chang diffusion model. Diffusion coefficients were then calculated as a function of temperature and degree of polycondensation to give a good explanation of the process phenomena