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 SiO2 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 15 min when SrO was applied, while using SrO doped SiO2 (SrO/SiO2) further increased the conversion to 95% in 10 min. SrO/SiO2 also featured good water and free fatty acids (FFAs) tolerance, as the conversion was still higher than 90% (in 20 min) when the water and FFAs contents were increased to 3.23 and 3.14 wt.%, respectively. Addition of hexane significantly improved the reusability of SrO/SiO2 for transesterification, as the biodiesel production still reached nearly 80% after the catalyst was repeatedly used for four times.

► SrO has better catalytic ability for transesterification than CaO and MgO.
► The catalytic ability of SrO was enhanced by SiO2 or CaO doping.
► SrO doped with SiO2 featured good water and free fatty acid (FFA) tolerance.
► Co-solvent addition improved the recovery ability of the doped catalyst.