Decrease of free fatty acid content in vegetable oil using silica supported ferric sulfate catalyst

A difficulty of biodiesel synthesis based on alkaline catalysts obviously exists if free fatty acids (FFAs) content in vegetable oil is above 0.5 wt.%. In this study, the ferric sulfate supported on silica (Fe2(SO4)3/SiO2) was synthesized, activated (at different temperature: 120–600 °C) and tested for heterogeneous esterification of FFA (oleic acid) present in sunflower oil (5 wt.%). The catalyst samples were characterized by BET, TG/DTG, XRD and FTIR analyses. Obtained results showed that catalyst activated at 500 °C for 2 h in air atmosphere gave the maximal conversion of oleic acid (∼97%). Repeated use of catalyst without additional catalyst treatment or re-activation indicated that catalyst posses desired stability and activity. A pseudo-homogeneous kinetic model was proposed with good agreement between calculated and experimental data.