Organic-Exchanged Silicotungstic Acid Compounds as Efficient and Environmental-Friendly Catalysts for Synthesis of Glycerol Monolaurate

A series of organic-exchanged silicotungstic acid catalysts were synthesized by changing the variety and amount of organic compounds. The structure, thermal stability and acidic properties of the catalysts were characterized by FT-IR, XRD, TGA and 31P-MAS NMR. The catalytic performances of the catalysts were investigated on the selective esterification of lauric acid with glycerol to glycerol monolaurate. Among the various catalysts, [QuH]1H3SiW12O40 with molar ratio of quinoline to silicotungstic acid of 1:1 showed excellent activity and reusability due to strong Bronsted acidity and "pseudo-liquid" catalytic modes. The optimal conditions optimized by response surface methodology were as follows: the molar ratio of glycerol to lauric acid was 5.3:1, the amount of catalyst was 4.8 wt%, the reaction temperature was 424 K, and the reaction time was 1.5 h. Under these conditions, the average yield of glycerol monolaurate was 79.7%, which was basically consistent with the values predicted by the mathematical model. Moreover, the kinetic data of this reaction were fitted to a second-order kinetic model and the apparent activation energy Ea was 52.35 kJ / mol.