Blocky shapes Ca-Mg mixed oxides as a water-resistant catalyst for effective synthesis of biodiesel by transesterification

•Mixed oxide alkaline catalyst from oxalic acid salt decomposition synthesis.•Significant improvement of basic sites as compared with conventional ones.•Effective biodiesel production via methanolysis of soybean oil.•The yield of biodiesel above 98% within 2 h and at mild reaction temperature of 70 °C.•Little loss on catalytic activity when the catalyst was used several times.

The Ca-Mg mixed oxides were synthetized from a new method using calcium oxalate and magnesium oxalate as the precursors for transesterification of soybean oil. To elucidate their composition, morphology and basic properties, the resulting materials were characterized using: XRD, SEM, TEM, CO2-TPD and Nitrogen adsorption-desorption. The results showed that the catalyst with neat blocky structure had better water-resistance compared to the pure calcium oxide. And the CaO-MgO exhibited higher amounts of basic site and provided higher catalytic activity in the methanolysis process. The highest biodiesel yield reached 98.4% over CaO-MgO with a Ca-to-Mg molar ratio of 1:3 under the optimal reaction conditions: 1.0 wt% of catalyst adding, 12:1 of methanol/oil and reacting at 70 °C for 2 h. Hopefully, this kind of stable solid base catalyst could confirm the yield of FAME still above 90% after using 5 times which demonstrated the good reusability of mixed oxide CaO-MgO catalyst.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slide