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 WO₃ in the esterification reaction. The reaction conditions were optimized. A study for optimizing the reaction parameters such as the reaction temperature, stirring speed, WO₃ loading over ZrO₂ and reaction time, was carried out. The catalyst was characterized by BET, XRD, FT-IR, and NH₃-TPD. With increasing WO₃ loading over ZrO₂, the triclinic phase of WO₃ increased and the tetragonal phase of zirconia was clearly generated. The highest acid strength of 20wt% tungsten oxide zirconia catalyst was confirmed by NH₃-TPD analysis and the result was correlated to the highest catalytic activity of the esterification reaction.