Kinetic study of the esterification of propionic acid and ethanol catalyzed by ionic liquid 1-sulfopropyl-3-methylimidazole p-toluene sulfonic acid

Abstract

Ethyl propionate (EtPr) is an important organic compound in the chemical industry. Conventionally, EtPr is synthesized via esterification of propionic acid (PrAc) and ethanol (EtOH) with concentrated sulfuric acid as the catalyst. Nevertheless, this conventional route suffers from multiple drawbacks, including low reactant conversion, severe equipment corrosion, and hazardous environmental pollution. Accordingly, exploring novel eco-friendly catalysts is highly desirable. In this work, a Brönsted acid ionic liquid (BAIL), 1-sulfopropyl-3-methylimidazole p-toluene sulfonic acid ([HSO₃-PMIM][PTSA]), was selected as the catalyst for the esterification reaction to produce EtPr from PrAc and EtOH. TGA, DSC, ¹H NMR, and FTIR were used to characterize [HSO₃-PMIM][PTSA]. Meanwhile, the COSMO software was employed to calculate the σ-potential of all the components of the reaction system. Furthermore, the reusability and corrosive property of this IL catalyst were systematically evaluated. Reaction kinetic measurements were carried out to investigate the influences of catalyst concentration, reaction temperature, and initial PrAc/EtOH molar ratio on PrAc conversion. The NIH-M kinetic model was applied to correlate the experimental data and derive the corresponding esterification kinetic equation. A low mean squared error (MSE) of 1.19 × 10⁻³ between model-fitted values and experimental observations was obtained, which verifies the reliable fitting capability and satisfactory precision of the NIH-M model. This study indicates that [HSO₃-PMIM][PTSA] is a promising candidate catalyst for industrial esterification synthesis of EtPr.