Selective esterification of glycerol diacetin and triacetin over rice husk biosilica catalyst with microwave heating

Abstract

Selectivity towards diacetin and triacetin was investigated in esterification of glycerol using rice husk biosilica catalyst. The reaction was carried out in a microwave-irradiated batch reactor using acetic acid to glycerol molar ratio of 1:3, catalyst amount of 3% and 5% of the glycerol volume, and reaction time of 20 and 30 minutes. The biosilica catalyst was prepared by treating rice husk with hydrochloric acid and followed by calcination at 600°C. SEM analysis of the resulted catalyst reveals significant change of rice husk morphology and its XRD analysis shows the characteristics of amorphous silica. Furthermore, FTIR analysis of the reaction sample reveals the presence of an ester group of triacetin at 1709.5 cm−1. Product distribution of the glycerol esterification identified by GC-MS shows the highest total selectivity for diacetin and triacetin of 79.3% at the reaction condition of 30 minutes and 3% catalyst loading. However, individual selectivity for triacetin as the final product of this consecutive esterification steps was low, less than 5%.