Sorbitol dehydration in 1,4-dioxane: study of reaction conditions and kinetic analysis including mass transfer control

Abstract

This work assesses the influence of temperature, catalyst loading and water content on the dehydration of sorbitol to isosorbide using a commercially available porous strong acid resin (Amberlyst A70). The results from the catalytic tests show that the presence of water critically drops the reaction efficiency. Water not only participates in the dehydration reaction but also interacts with the sulfonic acid groups of the catalyst, competing for the adsorption to the catalytic sites with the substrate and intermediate products, varying the performance of the sulfonic acid resin. This has a strong influence on the kinetics of the transformation, so that a comprehensive assessment of different kinetic models for heterogeneous catalytic systems evaluating the role of saturation of catalytic sites, different adsorption isotherms, and different controls in the mass transfer has been carried out. Among all the studied alternatives, the model that describes the best the reaction performance is a Langmuir-Hinshelwood-Hougen-Watson model with saturation on the catalytic sites featured by mass transfer control in the desorption of the intermediate and final products. Despite the experimental tests have been performed in stirred tanks and other studies have not addressed mass transfer from the pores to the solvent core, the control mostly occurs at the catalyst pores. This is particularly observed for the sorbitans acting as intermediate products since they suffer from limitations in desorption and the latter adsorption to continue with the reaction to sorbitans. This study sheds light on the behaviour of strong cation exchange resins as heterogeneous acid catalysts in dehydration reactions, quite common transformations, specially important in the conversion of highly oxygenated biomass-derived molecules.