Study Finds Used Coffee Grounds Can Create Fuel

Scientists from Universitat Rovira i Virgili (URV) have discovered a method for extracting oil from spent coffee grounds, which could then be used in other renewable fuels and bio-based products. Coffee beans generate about 10 million metric tons annually, but much of the solid residue after brewing is thrown away. Used coffee grounds contain around 15% lipids, which could be converted into biodiesel.

Researchers studied how temperature, extraction time, and solvent amount impacted oil recovery. They used n-hexane, a solvent often utilized for extracting fats. By employing a temperature of 45°C for 60 minutes with 35 milliliters of hexane per gram of dry coffee residue, the team managed to recover around 90% of the available oil, compared to 90% through conventional Soxhlet extraction, but with significantly less energy and time.

The recovered oil was cleaner, with only 0.3% impurities, while Soxhlet extraction left 3.9% impurities.

More importantly, the remaining coffee grounds contained valuable lignocellulosic material that could be utilized to produce bioethanol, lactic acid, bioplastics, phenolic compounds, and sustainable aviation fuel precursors. Removing the oil could also facilitate subsequent processing by providing better access to solvents, enzymes, and catalysts for the remaining biomass.

The technique of moderate-temperature batch extraction with n-hexane emerged as a feasible option for biorefineries aiming to convert spent coffee grounds into various useful fuels, chemicals, and materials, rather than simply disposing of them as waste.