Selective esterification of glycerol with acetic acid to diacetin using antimony pentoxide as reusable catalyst

Glycerol can be obtained as a by-product during biodiesel manufacture. It is important to convert glycerol to value-added products. Glycerol esterification with acetic acid is one of the most promising approaches for glycerol utilization. It is usually difficult to obtain diacetin with good activity and selectivity. In this work, glycerol esterification with acetic acid over different metal oxides , such as Bi 2 O 3 , Sb 2 O 3 , SnO 2 , TiO 2 , Nb 2 O 5 and Sb 2 O 5 , was investigated. It was found that in the six investigated metal oxides, only Sb 2 O 5 resulted in good activity and selectivity to diacetin. Under the 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 Sb 2 O 5 possessed Brønsted acid sites strong enough to protonate adsorbed pyridine. The good catalytic activity and selectivity to diacetin might be mainly attributable to the Brønsted acid sites of Sb 2 O 5 . Reusability tests showed that with Sb 2 O 5 as catalyst, after six reaction cycles, no significant change in the glycerol conversion and the selectivity to diacetin was observed.