Grafting of acidic ionic liquids onto the NH2-UiO-66 for butyric acid glyceride synthesis through heterogeneous catalysis of esterification

Abstract

Immobilization of acid ionic liquid (AIL) for heterogeneous catalysis is benificial for products separation and recycling the AIL for continuing reuse. In this study, AIL was grafted onto the amino group functionalized zirconium-based metal organic framework (NH2-UiO-66) to catalyze esterification for short chain fatty acid glycerides synthesis. AIL of 1-(4-Sulfobutyl)-3-Methylimidazolium Hydrogen Sulfate ([HSO3-BMIM][HSO4]) was found suitable for short chain fatty acid glycerides after screening varied fatty acids with chain length from 4 to 18. [HSO3-BMIM][HSO4] was therefore grafted and butyric acid glyceride was synthesized. Reaction conditions were optimized by means of single factor study and orthogonal experiment. The reusability of the AIL@NH2-UiO-66 was evaluated. The AIL@NH2-UiO-66 showed good esterificaiton performance and fine reusability. Butyric acid conversion (converted into the glycerides of mono-, di- and tributyrin) at 62.16% was obtained under the optimum conditions. In addition, the present AIL@NH2-UiO-66 was quite stable, and 67.39% of its initial esterification activity was retained after 11 cycles of reuse, suggesting it was potential in the esterification reaction.