Esterification of acetic acid with isobutanol catalyzed by ionic liquid n-sulfopropyl-3-methylpyridinium trifluoromethanesulfonate: Experimental and kinetic study

As an important organic, isobutyl acetate (IbAc) has been widely used in industries because of its good biodegradability, low surface tension, and other properties. The industrial production of IbAc is usually catalyzed by sulfuric acid. However, the use of sulfuric acid has the drawbacks of causing considerable corrosion to equipment and being difficult to be separated. In this work, n-sulfopropyl-3-methylpyridinium trifluoromethanesulfonate ([HSO3-PMPY][CF3SO3]) Brönsted acidic ionic liquid (BAIL) was used as the catalyst and the catalytic activity, solubility, and corrosiveness were evaluated for the esterification of acetic acid with isobutanol. The reaction kinetics and chemical equilibrium were systemically studied. Compared to conventional acid catalysts, [HSO3-PMPY][CF3SO3] showed higher catalytic activity, more excellent reusability, more favorable phase separation, and non-corrosiveness. Three kinetic equations based on ideal homogeneous (IH), non-ideal homogeneous (NIH), and modified non-ideal homogeneous (NIH-M) models were established and correlated with the experimental data to determine the parameters and errors. The NIH-M model exhibited the best agreement with the experimental data, owing to its prediction considering the non-ideality and the self-catalysis effect of acetic acid in this system. Besides, the error of NIH-M model fitting was mainly caused by the difference in solubility between [HSO3-PMPY][CF3SO3] with reactants and products in the reaction system. Furthermore, the applicability of the NIH-M model was investigated by simulating the esterification of acetic acid with three short-chain alcohols (ethanol, n-butanol, and isobutanol) catalyzed by BAILs. The NIH-M model displayed an acceptable simulation for this type of acetic acid esterification reaction catalyzed by BAILs at different ranges of the BAILs concentration and temperature. This study confirmed the industrial prospects of [HSO3-PMPY][CF3SO3] in isobutyl acetate production and the applicability of the NIH-M kinetic model in the esterification of acetic acid.