Esterification Of Glycerol To Acetin Catalyzed By Solid Acid

As the fossil energy is decreasing, the development of renewable energy has been paid more and more attention. Biodiesel is a renewable and clean energy, which mainly prepared from transesterification of animal or vegetable oil with methanol or ethanol. The production process of biodiesel will generate large amounts of by-product glycerol. The conversion of glycerol into high value-added chemicals is conducive to improve the overall efficiency of biodiesel industry. Esterification of glycerol with acetic acid is one of the important ways to utilize glycerol. Glycerol acetates, especially diacetate has important uses. Therefore, the research on esterification of glycerol to produce glycerol acetate（especially diacetin） has a great significance in science and applied prospectIn this paper, SBA-15 supported different loading tungstophosphoric heteropoly acid catalysts for esterification of glycerol with acetic acid were prepared, and the catalysts were characterized by IR, XRD, BET and NH3-TPD. The effects of reaction conditions, such as temperature, catalyst loading, the molar ratio of acetic acid to glycerol, time, were investigated. The results showed that the loading of H3PW12O₄0 had great influence on its catalytic activity. The catalyst with 30 wt% H3PW12O₄0 supported on SBA-15 showed the best performance. Under the optimized conditions, the glycerol conversion reached 95.8%, and the selectivity to diacetin reached 53.2%, while the selectivity to monoacetin and triacetin was 36.2% and 10.6%, respectively.In addition, glycerol esterification with acetic acid over different metal oxides, such as Bi₂O₃, Sb₂O₃, SnO₂, TiO₂, Nb₂O₅ and Sb₂O₅, were investigated. It was found that in the six investigated metal oxides, only Sb₂O₅ resulted in good activity and selectivity to diacetin. Under optimized conditions, the glycerol conversion reached 96.8%, and the selectivity to diacetin reached 54.2%, while the selectivity to monoacetin and triacetin was 33.2% and 12.6%, respectively. The catalysts were characterized with FT-IR spectra of adsorbed pyridine, which indicated that in the six investigated metal oxides, only Sb₂O₅ possessed Br?nsted acid sites strong enough to protonate adsorbed pyridine. The good catalytic activity and selectivity to diacetin might be mainly attributable to the Br?nsted acid sites of Sb₂O₅. Reusability tests showed that with Sb₂O₅ as catalyst, after six reaction cycles, no significant change in the glycerol conversion and the selectivity to diacetin was observed.