Transesterification of rapeseed oil with ethanol over heterogeneous heteropolyacids

Abstract

Heterogeneized heteropolyacids, H3PW12O40/SiO2 and Cs2HPW12O40 were shown to catalyze rapeseed oil transesterification with ethanol in mild conditions. The number and the strength of the acid sites were evaluated by calorimetry. Over anhydrous H3PW12O40 and Cs2HPW12O40, acid sites of homogeneous strength with heat of ammonia adsorption near 200 kJ mol 1 were measured. By contrast, H3PW12O40/ SiO2 showed sites of lower strength with a heterogeneous distribution. The catalytic activity did not correlate the acid strength of solid catalysts. Indeed, equivalent TOF were determined on H3PW12O40 and silica supported H3PW12O40 while lower TOF were measured on microporous Cs2HPW12O40. The TOF values were interpreted in terms of leaching of the active phase in the case of H3PW12O40/SiO2 while reduced acid sites accessibility might explain the lower TOF measured on Cs2HPW12O40.