Exploiting the potential of calcined sodium citrate as a novel and efficient heterogeneous catalyst for biodiesel synthesis†

Environmental concerns have emphasized the necessity of pursuing renewable energy in order to reduce reliance on fossil fuel-derived sources. Biodiesel, a promising renewable fuel, still faces challenges in its production associated with the feedstock and the dependence on homogeneous catalysts. Herein, for the first time, sodium citrate, a bio-based and environmentally friendly compound, is calcined at mild temperatures to create a novel basic heterogeneous catalyst for the transesterification of refined canola and waste cooking oils. The catalyst demonstrated excellent performance with a 99% conversion of canola oil. Moreover, a conversion of 98% was obtained under optimized conditions (1 : 36 oil to methanol molar ratio, 10 wt% catalyst loading, 3 h, and 90 °C) when waste cooking oil was used as the feedstock. The catalyst further exhibited remarkable tolerance up to 10 wt% free fatty acids. Kinetics studies indicated that the reaction is governed by a pseudo-first-order kinetic model. Notably, the catalyst exhibits high turnover frequencies of 6.22 h⁻¹ and 1.86 h⁻¹ for the transesterification of canola and waste cooking oils, respectively, proving its efficiency. Finally, a possible mechanism for the reaction using calcined sodium citrate as a basic heterogeneous catalyst was proposed.