Effect of Sr concentration in SrK/CaO oyster shell derived catalysts for biodiesel production

This study examined the effect of the Sr concentration in SrK/CaO catalysts based on oyster shells for the transesterification of canola oil. The CaO support was obtained by mixing 800 °C calcined oyster shell and limestone. Then, K and Sr were impregnated simultaneously at three different Sr/(Sr + K) molar ratios, 0.2, 0.3, and 0.4, and calcined at 800 °C. XRD, SEM, and Hammett indicators were used to characterize the catalysts. The reaction conditions were 60 °C, 1 h, met/oil = 12.5, and a catalyst loading of 7 wt%. The results showed that a Sr/(Sr + K) = 0.3 produces larger K 2 Sr(CO 3 ) 2 crystals that contribute synergistically to the catalytic activity. At Sr/(Sr + K) > 0.3, the K and Sr are segregated, decreasing the alkaline character and activity. Also, the optimization of WCO transesterification conditions was carried out by Box–Behnken response surface design with SrK/CaO-0.3 catalyst. The theoretical optimal conditions were 70 °C, 1.5 h, and a met/oil = 10, which achieved 79 % of biodiesel yield. Nonetheless, the produced WCO biodiesel did not present acceptable quality, and this reactive system increased the lixiviation of the active phases.