Canola oil transesterification for biodiesel production using potassium and strontium supported on calcium oxide catalysts synthesized from oyster shell residues

This work studied the effect of K precursor comparing KNO3 and KHCO3 and the combination with SrO, supported on CaO from oyster shell and limestone (1:1 mass ratio) for transesterification canola oil to produce biodiesel. The loading of Sr and K were 9 wt% and were calcined at 800 °C. The catalytic transesterification evaluations were conducted at 60 °C, methanol/oil of 10, 8 wt% of the catalyst for 1 h, where SrK/CaO catalysts presented biodiesel yields above 80 %. Moreover, the Box-Behnken response surface design was used with reaction time, methanol-to-oil ratio, and temperature as factors using SrKH/CaO catalyst. In comparison to using KNO3, the KHCO3 increase the concentration of CaO. However, basicity and biodiesel yield were the same regardless of the K precursor. Incorporating K into Sr/CaO increased the particle size, the basicity, and the biodiesel yield. Furthermore, the design of experiments successfully showed an optimum methanol-to-oil ratio of 15, 46 °C, and 3 h. Nonetheless, the SrK/CaO catalysts presented a reusability of only two cycles. The incorporation of Sr and K did not avoid the lixiviation of the active sites, but they may retard this process the catalyst may be more active at low reaction times.