Solvo-thermal in situ transesterification of wet spent coffee grounds for the production of biodiesel

•Solvo-thermal in situ transesterification of SCG is introduced.•The solvo-thermal process induces the DCE hydrolysis leading to acid conditions.•The in situ induced acid catalyst enhances FAEE production from SCG.•Water in SCG is critical for maximizing acidity and FAEE yield.•FAEE yield is 11.8 wt% due to the DCE hydrolysis. This work addresses non-catalytic biodiesel production from spent coffee ground (SCG) by integrating solvo-thermal effect of 1,2-dichloroethane (DCE) with in situ transesterification over 160 °C. The SCG water content has a positive effect on the DCE hydrolysis up to 60 wt% due to the bimolecular substitution mechanism. The hydrolysis gives an acidic environment favorable for cellulose decomposition, SCG particle size reduction and lipid conversion. The optimal fatty acid ethyl ester yield was 11.8 wt% based on the mass of dried SCG with 3.36 ml ethanol and 3.16 ml DCE at 196.8 °C through the response surface methodology. Using the solvo-thermal effect, direct utilization of wet SCG as a biodiesel feedstock provides not only economic feasibility without using drying process and additional acid catalyst but also environmental advantage of recycling the municipal waste.