Molybdenum-Based Catalysts Catalyzed Oils And Fatty Acids For The Synthesis Of Biodiesel

Biodiesel is an environmentally friendly fuel, which is obtained by the transesterification of vegetable oils or animal fats with methanol. Heterogeneous acid catalysts can be used both in esterification and transesterification for biodiesel production. Being environmental friendly, easily separated and undemanding to raw materials, the catalysts have received more and more attentions in recent years. In this study, a heterogeneous acid, MoO₃, is proposed in biodiesel production as a catalyst for the first time. In stainless steel reactor, MoO₃ catalyzes both transesterification (soybean oil and methanol as raw material) and esterification (oleic acid and methanol as raw material); meanwhile, WO₃ doped MoO₃ (WO₃/MoO₃) was applied in the transesterification of castor oil and methanol. The results of our research are as follows:1. MoO₃ was applied in the transesterification of soybean oil and methanol, at the reaction conditions of 150℃, methanol/oil molar ratio 9:1, catalyst amount 2wt.%, reaction time 5h, the free acid methyl ester (FAME) yield up to 85%. MoO₃ performed well to high acid value raw oil. For example, at 150℃, after 5h, the FAME yield could be up to 90% when the acid value of the raw oil was more than 150mg KOH. After recycled 10 times, the activity of the catalyst decreased no more than 12%. The reasons of deactivation is mainly due to the oils covered on the catalyst or (and) the carbonaceous species formed on the catalyst surface, which were proved by XPS and XRD analysis. The deactivated catalyst was easily regenerated by calcinated in air.2. MoO₃ was applied in the esterification of oleic acid and methanol, at the reaction conditions of 150℃, methanol/oil molar ratio 9:1, catalyst amount 1wt.%, reaction time 3h, the conversion of oleic oil is up to 95%. It was observed in XPS analysis that the catalyst was reduced during the esterification from Mo⁶⁺ to Mo⁴⁺, which lead to the leaching of the catalyst. The huge polarity of the reactants system and the existence of the reduced matter might be the reasons of the catalyst leaching. The doped of Bi₂O₃ could combine with MoO₃ and enhance the stability of the MoO₃.3. WO₃/MoO₃ was applied in the transesterification of castor oil and methanol, at the reaction conditions of 150℃, methanol/oil mass ratio 1.5:1, catalyst amount 2wt.%, reaction time 5h, the FAME yield up to 85%. WO₃/MoO₃ was stable even when high water content oils or high acid value oils as raw materials. For example, when the raw oils of the water content of 10 wt.%, the FAME yield could up to 78%; when the acid value of the raw oil was more than 80mg KOH, the acid value of the products could down to 2mg KOH. The deactivated catalyst was easily regenerated by calcinated in air.The MoO₃ catalyst, which was a high catalytic activity,stable,easily separated and environment friendly catalyst, can be applied in biodiesel production from cheap raw feedstocks with high free fatty acids (FFAs) or water. It can be expected that MoO₃ catalyst will have widespread applications on an industrial scale.