Biodiesel synthesis via heterogeneous catalysis using modified strontium oxides as the catalysts

In this work, alkaline earth metal oxides (i.e., MgO, CaO, and SrO) were used as catalysts for the transesterification of olive oil with methanol. The most efficient catalyst was further doped with either CaO or SiO ₂ to improve its catalytic activity, which was evaluated by conducting transesterification at different reaction temperatures, different water content, and using different types of oils. Finally, repeated tests were conducted to evaluate the reusability of the doped catalyst. The results show that the conversion of refined olive oil to biodiesel was more than 80% in 15min when SrO was applied, while using SrO doped SiO ₂ (SrO/SiO ₂) further increased the conversion to 95% in 10min. SrO/SiO ₂ also featured good water and free fatty acids (FFAs) tolerance, as the conversion was still higher than 90% (in 20min) when the water and FFAs contents were increased to 3.23 and 3.14wt.%, respectively. Addition of hexane significantly improved the reusability of SrO/SiO ₂ for transesterification, as the biodiesel production still reached nearly 80% after the catalyst was repeatedly used for four times.