Synthesis of Sn-CaO as a bifunctional catalyst and its application for biodiesel production from waste cooking oil

Herein, a simple solid-state method was employed to synthesize a bifunctional tin (Sn) supported calcium oxide (CaO) catalyst. The synthesized catalyst (Sn-CaO) was found to be suitable for the conversion of waste cooking oil to biodiesel in a single-step reaction procedure. To achieve maximum conversion, the physicochemical and surface morphological characteristics of the catalyst were investigated using FTIR, XRD and FESEM-EDX. Box-Behnken Design based on Response Surface Methodology was used to optimize biodiesel conversion. At optimized conditions, the variables affecting the reaction were, methanol to oil molar ratio (16.15:1), time (3.42 h), temperature (85.15 °C) and catalyst concentration (2.22% with respect to oil) that led to biodiesel conversion amounting to 97.39%. Three experiments were carried out under these conditions to validate the predicted model. The experimental value of biodiesel conversion in this setting was 96.72 ± 0.61%. The acid value and kinematic viscosity of biodiesel were measured at 40 °C and were determined to be 0.48 mg KOH g−1 and 5.3 mm2 s−1, respectively, fulfilling the ASTM and EN standards. The simultaneous esterification and transesterification reaction mechanism were also described. The finding of this study leads to an economical and environmentally benign approach to biodiesel production.