Reaction kinetics for the heterogeneously resin-catalyzed and homogeneously self-catalyzed esterification of thioglycolic acid with 2-ethyl-1-hexanol

Abstract

• Esterification of thioglycolic acid (TGA) with 2-ethyl-1-hexanol (EHL) was studied. • Heterogeneous and homogeneous reaction kinetics were determined. • The adsorption of water on resin catalyst improved the conversion of TGA. • Heterogeneous kinetics were well described by the PH, ER and LHHW models. • Homogeneous kinetics were described by an improved homogeneous model. Producing 2-ethyl-1-hexyl thioglycolate (ETE) via esterification reaction with thioglycolic acid (TGA) aqueous solution as raw material by reactive-separation coupling technology is a promising process intensification method. To choose suitable reactive-separation coupling strategy, the kinetic studies of the esterification of TGA with 2-ethyl-1-hexanol (EHL) were carried out in a batch system. The commercial ion exchange resin was employed as an eco-friendly catalyst. The effects of temperature, catalyst concentration and molar ratio were determined. It was interesting to observe that the equilibrium conversion of TGA increased with the increase of catalyst mass fraction due to the adsorption of product water onto resin surface. The activity-based pseudo-homogeneous (PH), Eley-Rideal (ER) and Langmuir-Hinshelwood-Hougen-Watson (LHHW) models were used to fit the kinetics data of the resin-catalyzed reaction. The models of ER and LHHW performed better than the PH model. The kinetics of the TGA-self-catalyzed reaction was also determined. An activity-based homogeneous kinetics model could well describe this self-catalyzed reaction. These results would be meaningful to the selection and design of an appropriate reaction-separation strategy for the production of ETE, to realize the process intensification.