MODEL ESTERIFICATION OF ISOPHTHALIC AND TERPHTHALIC ACID WITH BENZYL ALCOHOL

The esterification kinetics of isophthalic and terephthalic acid, with benzyl alcohol, were studied in the melt phase, which is a heterogeneous system because of the low solubilities of the phthalic acids. The relative concentrations of components and their conversions, alpha, were determined with HPLC. The effect of insolubility of the phthalic acids on the reaction kinetics can be described in two ways. For terephthalic acid, at 0 less than or equal to alpha less than or equal to 1, and for isophthalic acid, at alpha < 0.6, the esterification kinetics can be described with equations for a homogeneous system with only a substitution effect. An improved and more complete description for isophthalic acid is obtained with equations for a heterogeneous system, with a surface reaction rate constant and a ratio of reactive (at the surface) over nonreactive monomers (in the core, i.e., the surface to volume ratio). This model fits data for alpha < 0.7. The model parameters depend on the reaction temperature and the solubility of the phthalic acid. (C) 1993 John Wiley & Sons, Inc.