Abstract
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 20 wt% tungsten oxide zirconia catalyst was confirmed by NH3-TPD analysis and the result was correlated to the highest catalytic activity of the esterification reaction. (C) 2009 Elsevier Ltd. All rights reserved.