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

The polycondensation of poly(ethylene terephthalate) (PET) through ester in terchange is a process strongly limited by mass transport effects. Therefor e, design and scale up of industrial PET plants require a detailed knowledg e 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, and (3) diffusion processes for the major by-p roducts EG and water in the molten PET. The model was validated using own e xperimental data determined by thermogravimetric analysis. As a sample, the so-called "PET-prepolymer" was used. The kinetic parameters for the ester interchange reaction, for the water formation through esterification as wel l as for the most significant side reactions were taken from the literature . The mass transport was described using a classical diffusion equation acc ording to Fick's law and a modified Wilke-Chang diffusion model. Diffusion coefficients where then calculated as a function of temperature and degree of polycondensation to give a good explanation of the process phenomena. (C ) 2001 Elsevier Science Ltd. All rights reserved.