KINETIC-MODEL FOR MAIN AND SIDE REACTIONS IN THE POLYESTERIFICATION OF DICARBOXYLIC-ACIDS WITH DIOLS

A rate model based on a reaction mechanism was proposed for the melt p olyesterification of dicarboxylic acids with diols for the case that n o catalyst is added. The model includes the esterification, the cis-tr ans isomerization and the double bond saturation reactions. All three reactions are acid catalyzed. The overall reaction order of the main r eaction increases with conversion due to a shift of the ionic equilibr ia in the liquid phase. This increase of the reaction order was descri bed with a semi-empirical function. Experiments were carried out for t he esterification of maleic acid with propylene glycol at 160-220 degr ees C in a laboratory scale batch reactor. The derived rate model succ essfully described the isomerization of maleic acid to fumaric acid, t he saturation of the double bonds, and the polyesterification of malei c and fumaric acids. The model included two parameters for each of the three types of reactions taking place simultaneously.