An innovative method of extraction of coffee oil using an advanced microwave system: in comparison with conventional Soxhlet extraction method

Abstract: The production of energy and chemicals from waste biomass is an attractive alternative by comparison with first-generation biofuels and fossil feedstocks. This paper investigates oil extraction from spent coffee grounds (SCG) by means of an advanced microwave process and compares this with a conventional Soxhlet extraction (SE) method. Microwave-assisted oil extraction (MAE) from SCG was performed over different durations, varying solvent volumes and extraction temperatures. It was found that each of these parameters had an effect on the process, with the largest yield being over 11.54 wt%, oil extracted in 10 min using 160 mL of hexane at 95 °C. In 10 min, MAE was successful in extracting more oil than SE. MAE achieved a 24-fold decrease in duration for the extraction compared with SE and used less solvent per gram of oil produced. It is proposed that a certain moisture content in the SCG would be beneficial to the extraction process and might it also play a role in the heating process. The extracted oil can be converted into biodiesel and biochemicals leaving the remaining solids suitable for processing into bioethanol, fertiliser, adsorptive material and fuel pellets. Graphic Abstract: [Figure not available: see fulltext.].