Sustainable biodiesel production from waste cooking oil using oyster shell-derived superparamagnetic acid-base bifunctional biochar

Abstract

This study evaluates the catalytic potential of a waste-derived magnetic acid-base bifunctional nanocatalyst, CaO-Fe2O3-based biochar (CaO-Fe2O3/BC), synthesized from oyster shells, for the conversion of waste cooking oil (WCO) into biodiesel. The research aims to mitigate waste generation and reduce the environmental impact of fossil fuel consumption, thereby promoting sustainable energy utilization. The catalyst's properties were comprehensively analyzed using various characterization techniques, while the effects of experimental reaction variables including catalyst loading, methanol-to-oil molar ratios, reaction temperatures and times were evaluated to enhance the transesterification. Additionally, response surface methodology was employed to optimize and enhance the efficiency of the transesterification process. N2 physisorption measurement revealed its suitability for ester exchange reactions, boasting a higher specific surface area (48.82 m2 g−1) and pore size (19.26 nm) than those (2.643 m2 g−1 and 9.385 nm, respectively) of traditional CaO catalysts. A biodiesel yield of 95.6 % was obtained under optimized conditions of 65 ℃, 4 wt% catalyst loading, a methanol-to-oil molar ratio of 17:1 and a reaction time of 2.5 h. Response surface methodology (RSM) determined optimal conditions: 4.30 wt% catalyst loading, 17.60 alcohol-to-oil molar ratio, 66.50 °C, and 2.65 h, yielding 96.8 % biodiesel. With a magnetic strength of 14.26 emu g−1, CaO-Fe2O3/BC allowed efficient recovery through magnetic decantation. The work further analyzes the mechanism of CaO-Fe2O3/BC-catalyzed transesterification and assesses the repeatability of the catalyst. CaO-Fe2O3/BC demonstrated satisfactory stability and reusability, maintaining a biodiesel yield of 72.3 % even after 8 cycles. Additionally, the fuel properties of the produced biodiesel complied with ASTM and EN standards, highlighting the catalyst's significant potential for industrial applications.