Systematic screening of bifunctional ionic liquid for intensifying esterification of methyl heptanoate in the reactive extraction process

Abstract

For long-chain ester formation, reactive extraction intensified by a bifunctional solvent is a proper process concept as the product ester is usually not soluble in water. To screen a bifunctional ionic liquid (IL), both extraction performance and catalytic activity are considered, taking esterification of methanol and heptanoic acid as example. Based on solute-in-IL infinite dilution activity coefficient generated from DNN-based recommender system, infinite dilution selectivity between product and reactant in ILs is adopted to evaluate extraction performance. The acid dissociation constant (pKa) obtained by quantum chemical calculation is used to evaluate the catalytic activity of ILs. The screened IL, 1-propyl-2,3-dimethylimidazol-3-ium hydrogen sulfate ([IM-3,1,1][HSO4]), has a high infinite dilution selectivity of 710.77 and pKa of 5.81. Both UNIFAC-IL calculation and experimental validation are performed to examine phase splitting and reaction results. The screened IL gives higher ester yield and ester phase purity than the most commonly used bifunctional IL [BMIM][HSO4].