Comprehensive recovery of biocrude, bioactives, and solid fuel from wet coffee grounds using liquefied dimethyl ether

Spent coffee grounds (SCG), rich in lipids, antioxidants, and other valuable compounds, are a potential renewable resource for energy and functional products. This study introduces an environmentally benign and energy-efficient technique for separating lipids, bioactive species, and highly calorific solid residues from wet SCG using liquefied dimethyl ether (L-DME) without any pretreatment. This L-DME extraction process was performed semi-continuously under various temperatures, pressures, and DME consumption levels to optimize recovery performance. The process efficiently removed 95.9–97.1 wt% of the moisture from wet SCG. The biocrude exhibited a high FAME content (988.4 mg/g), while the removed water contained significant caffeine (93.44 mg/g dry extract) and antioxidant activity (2534.4 μmol TE/g dry extract), highlighting their potential applications in biodiesel production and the cosmetic and food industry. Furthermore, the defatted dry solid residue showed high heating value and low ash content, making it suitable for combustion as a solid fuel. Additionally, a techno-economic analysis was conducted to evaluate the scalability and economic viability of the L-DME extraction process. Overall, this work demonstrates the potential of L-DME as a versatile and scalable biorefinery platform for converting coffee waste into valuable fuel and functional products.