Taguchi optimization and life cycle assessment of biodiesel production from spent ground coffee

In this study, Vietnamese spent coffee ground (SCG) were subjected to produce biodiesel for fuel application. The extraction processes were conducted with three organic solvents, i.e., hexane, petroleum ether and dimethyl ether. The extraction oil seems to be favored in hexane solvent (17.06%) as compared with petroleum ether (16.62%) and dimethyl ether (16.18%). The extraction processes tend to sufficiently follow the empirical hyperbolic model with R2 of 0.973, 0.970 and 0.969 for hexane, petroleum ether, and dimethyl ether. The transesterification was optimized using Taguchi design with three variable molar ratios of MeOH and extracted oil (MeOH/EO), catalyst (NaOH) concentration and temperature. The transesterification reached the best yield 76.23% at MeOH of 6:1, NaOH of 0.75 wt% and temperature of 55 °C. Some acquired biodiesel quality was determined within the American Society for Testing and Materials and European standards (EN) norms for biodiesel. Life cycle assessment was also performed to evaluate the impact of the SCG biodiesel production; the industrial process was designed based on laboratory tests aimed with TRACI 2.1 tool. The obtained results indicated that oil extraction is the most effective on biodiesel production, contributing to global warming around 21.04 kg CO2 eq/kg.