Ultrasound-assisted production of biodiesel and ethanol from spent coffee grounds

This study evaluates the production of biodiesel and ethanol from spent coffee grounds (SCG). The extraction of oil from SCG, biodiesel production and ethanol production processes were studied. The liquid-to-solid ratio and temperature were evaluated in the ultrasound-assisted extraction of the oil from SCG. The highest yield (12%) was obtained using 4 mL g−1 liquid-to-solid ratio at 60 °C for 45 min. The process to produce biodiesel showed a yield of 97% into fatty acid methyl esters (FAME). The highest glucose yield (192 mg gSCG−1) was obtained by hydrolysis with 0.4 mol L−1 sulfuric acid at 121 °C for 15 min. The hydrolysate was used as fermentation medium for ethanol production by Saccharomyces cerevisiae obtaining 19.0 g L−1 at 10 h of process of ethanol with a yield of ethanol and productivity of 0.50 g g−1 and 1.90 g L−1 h−1, respectively. Spent coffee grounds were considered a potential feedstock for biodiesel and ethanol production.