Catalytic evaluation of eggshell-based calcium methoxide over Al2O3 for biodiesel generation from waste cooking oil

Shell-derived materials are promising heterogeneous catalysts for biodiesel production due to their nontoxic and renewable nature, but they have the disadvantage of being highly leachable. To overcome this issue, Ca(OCH₃)₂ formed through the reaction of CaO with methanol, and supported in turn on Al₂O₃ is proposed as a catalytic system for the transesterification of fresh soybean oil and waste cooking oil (WCO). First, catalysts with several Al/Ca molar ratios (0.2, 0.5, and 0.8-AC), as well as their precursors (CaO and Al₂O₃) alone, were tested at 60 °C, catalyst loading 6% wt, methanol-to-oil molar ratio (MOR) 10, for 1 h for fresh oil, and 3 h for WCO. The 0.2-AC catalyst generated the highest biodiesel yield for both oils. The optimum operating conditions for WCO transesterification, determined by using a univariable approach, were 60 °C, 9 wt% catalyst loading, MOR of 12.5, and a reaction time of 3 h. These improved conditions led to yields higher than 90% for pure CaO and the 0.2, 0.5, and 0.8-AC catalysts. The density, kinematic viscosity, and refractive index of the biodiesel obtained were measured.