Synthesis and Optimization of Methyl Laurate Using Sulfonated Pyrrolidonium Ionic Liquid as a Catalyst

Abstract

Abstract Methyl laurate was synthesized from lauric acid and methanol using Brønsted acid ionic liquids as catalysts, by an esterification reaction. The efficiencies of four different catalysts, 1-methylimidazolium hydrogen sulfate ([Hmim]HSO4), 2-pyrrolidonium hydrogen sulfate ([Hnhp]HSO4), 1-(3-sulfonic acid) propyl-2-pyrrolidonium hydrogen sulfate ([C3SO3Hnhp]HSO4) and H2SO4 were compared. The effect of the methanol/lauric acid molar ratio, reaction temperature, reaction time, and catalyst dosage on the lauric acid conversion was investigated by single-factor experiments. On the basis of single-factor experiments, the esterification of lauric acid and methanol was optimized using response surface methodology (RSM) based on central composite design (CCD). The results showed that the most effective catalyst was the ionic liquid [C3SO3Hnhp]HSO4. The optimal conditions were as follows: [C3SO3Hnhp]HSO4 dosage of 10 % (based on the mass of lauric acid), methanol/lauric acid molar ratio of 9:1, reaction time of 1 h and reaction temperature of 70 °C. Under these conditions, the lauric acid conversion reached 95.33 %. The catalytic activity of [C3SO3Hnhp]HSO4 still remained high after 5 cycles.