Co-processing of Waste Cooking Oil and Hemp-shives for an Intensified Production of Advanced Biodiesel

Biodiesel production from waste cooking oil (WCO) is a sustainable alternative to fossil fuels that reduces waste and greenhouse gas emissions, specifically that WCO has no competition with food industry. However, the oxidation stability and cold flow properties of WCO-derived biodiesel are the main limiting factors. This study investigates a novel co-processing approach that incorporates the valorisation of hemp shives, an abundant agricultural residue with a natural antioxidant activity, to improve biodiesel quality. Hemp shives and WCO were subjected to direct ethanolysis with aluminium triflate as a green catalyst, yielding biodiesel blended with ethyl levulinate, a valuable biobased additive. The addition of ethyl levulinate to WCO-based biodiesel is expected to improve its oxidative stability and cold flow properties. Response surface methodology (RSM) was used to optimise the reaction conditions for both ethyl levulinate production from hemp shives and biodiesel synthesis from WCO. The optimal conditions were found to be 180 °C, a 30:1 ethanol:oil molar ratio, and 0.01 g aluminium triflate catalyst. Under these conditions, the biodiesel had a 99% ester content, with a 23% yield of ethyl levulinate from hemp shives and a 96% yield of biodiesel (primarily ethyl palmitate and ethyl oleate). This coprocessing strategy offers a promising route for increased biodiesel production with improved fuel properties by utilising agricultural waste in a sustainable manner.