Selective catalytic synthesis of glycerol monolaurate over silica gel-based sulfonic acid functionalized ionic liquid catalysts

Abstract

A series of silica gel supported sulfonic acid functionalized ionic liquid (SAFIL/SG) catalysts have been successfully synthesized through a sol–gel method by varying the organic amine loadings. The catalysts so fabricated were characterized by various physicochemical techniques such as FT-IR, XRD, TGA, FE-SEM, and solid-state 31P NMR probe molecule method and their catalytic performances during esterification of glycerol (GL) with lauric acid (LA) were assessed. The 20% N,N-dimethyl(benzyl)ammonium propyl sulfobetaine hydrosulfate embedded silica gel catalyst (20%[DMBPSH]HSO4/SG) was found to exhibit superior performance and durability during this eco-friendly synthesis of glycerol monolaurate (GML) owing to the high surface area and strong Brønsted acidity observed for the catalyst. Moreover, an experimental design was exploited via response surface methodology (RSM) for the optimization of process variables. Accordingly, a maximum GML yield of 83.9% was achieved for the 20%[DMBPSH]HSO4/SG catalyst under the optimal conditions: amount of catalyst 2.0 wt%, GL/LA molar ratio of 4.1, reaction temperature 418 K, and reaction time 45 min, which was in conformity with those predicted by a mathematical model. Further kinetic studies confirmed that the esterification of GL with LA to GML with an activation energy of 31.51 kJ/mol.