Solid acid catalyzed biodiesel production by simultaneous esterification and transesterification

12-Tungstophosphoric acid (TPA) impregnated on four different supports such as hydrous zirconia, silica, alumina and activated carbon was evaluated as solid acid catalysts for the biodiesel production from low quality canola oil containing upto 20 wt% free fatty acids. The hydrous zirconia supported TPA was found to be the most promising catalyst exhibiting the highest ester yield (∼77%). The FTIR, XRD and nitrogen adsorption analysis revealed that the Lewis acid sites generated by the strong interaction of TPA and surface hydroxyl groups of zirconia are responsible for their higher activity. Further, the optimization of reaction parameters was carried out with the most active catalysts i.e. TPA supported hydrous zirconia and it was found that at 200 °C, 1 : 9 oil to alcohol molar ratio and 3 wt% catalysts loading a maximum ester yield of 90 wt% could be obtained. The catalysts were recycled and reused with negligible loss in activity.