Transesterification of soybean oil over WO3 supported on AlPO4 as a solid acid catalyst.

WO(3)/AlPO(4) catalysts were prepared by impregnation of AlPO(4) with ammonium metatungstate. Powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and thermo gravimetric and differential thermal analysis (TG-DTA) demonstrated that the tungsten compound was incorporated into AlPO(4) forming the catalyst with an enhanced acidity. When transesterification of soybean oil over the catalysts was performed, the catalyst with 30 wt.% WO(3) loading and calcined at 1073 K, exhibited the best catalytic activity with a conversion of 72.5%. The transesterification was optimal at 453 K for 5h with a methanol/oil ratio of 30:1 and catalyst dosage of 5 wt.%. Free fatty acid (FFA) and water did not affect the catalytic activity. The catalyst proved to be stable over four transesterification cycles as it lost only 4% of its activity after being reused four times. The catalyst could be used for the transesterification of low-cost oils for biodiesel production.