In-situ transesterification of wet spent coffee grounds for sustainable biodiesel production

•Wet in-situ transesterification of SCG is firstly proposed to produce biodiesel.•Wet in-situ transesterification integrates lipid extraction and conversion in one pot.•The maximum FAME yield was 16.75 wt.% at 95 °C.•Non-oxidative strong acid catalyst was effective for wet in-situ transesterification.•Organic solvent having a moderate polarity can be proper as a co-solvent.

This work addresses in-situ transesterification of wet spent coffee grounds (SCGs) for the production of biodiesel. For in-situ transesterification process, the methanol, organic solvent and acid catalyst were mixed with wet SCG in one pot and the mixture was heated for simultaneous lipid extraction and transesterification. Maximum yield of fatty acid methyl esters (FAME) was 16.75 wt.% based on the weight of dry SCG at 95 °C. Comprehensive experiments were conducted with varying temperatures and various amounts of moisture, methanol, co-solvent and acid catalyst. Moderate polar and alcohol-miscible organic solvent is suitable for the high FAME yield. Unsaturated FAMEs are subject to oxidative cleavage by nitric acid and shorter chain (C6 and C10) FAMEs were mainly produced while sulfuric acid yielded long chain unsaturated FAMEs (C16 and C18). Utilization of wet SCGs as a biodiesel feedstock gives economic and environmental benefits by recycling the municipal waste.