Esterification of used vegetable oils using the heterogeneous WO3/ZrO2 catalyst for production of biodiesel.

Tungsten oxide zirconia, sulfated zirconia and Amberlyst-15 were examined as a catalyst for a conversion of used vegetable oils (VOs) to fatty acid methyl esters (FAMEs). Among them, tungsten oxide zirconia was a promising heterogeneous catalyst for the production of biodiesel fuels from used VOs because of high activity in the conversion over 93% and no leaching WO(3) in the esterification reaction. The reaction conditions were optimized. A study for optimizing the reaction parameters such as the reaction temperature, stirring speed, WO(3) loading over ZrO(2) and reaction time, was carried out. The catalyst was characterized by BET, XRD, FT-IR, and NH(3)-TPD. With increasing WO(3) loading over ZrO(2), the triclinic phase of WO(3) increased and the tetragonal phase of zirconia was clearly generated. The highest acid strength of 20 wt% tungsten oxide zirconia catalyst was confirmed by NH(3)-TPD analysis and the result was correlated to the highest catalytic activity of the esterification reaction.