Kinetic study and simulation of the precopolytransesterification step in the copoly(ethylene-polyoxyethylene terephthalate) production process

Abstract

The kinetics of the precopolytransesterification step for the production process of the copoly(ethylene-polyoxyethylene terephthalate), COPEPOET, has been analyzed. The prepolytransesterification step involves two competitive parallel reactions generating the same by-product, ethylene glycol: 1. Prehomopolytransesterification reaction of bis (2-hydroxyethylene terephthalate), BHET, with itself and 2. Precopolytransesterification reaction of BHET with poly(oxyethylene), POE. The kinetic constants of both reactions, BHET with BHET and BHET with POE, were calculated. The analysis was made as follows: 1. A kinetic model was developed in order to calculate the kinetic constants k_H and k_C of the prehomopolytransesterification and precopolytransesterification reactions; 2. The simulation of the precopolytransesterification step was carried out by integrating the differential equations, which describe the prepolytransesterification step. A fourth-order Runge-Kutta method was used for this integration. Several values that fall within the interval of 0.05 to 1.5 were assigned to the rate constant ratio k_H/k_C value, a set of k_H/k_C value, a set of k_H and k_C values were obtained. The parameters of the Arrhenius equation A and E were evaluated by means of a multiple regression analytical method; and 3. By comparison between theoretical and experimental data the best k_H/k_C value was obtained. The k_H value was found to be several times smaller than that of k_C.