A novel circular waste-to-energy pathway via cascading valorization of spent coffee grounds through non-catalytic supercritical transesterification of pyrolytic oil for liquid hydrocarbon

The ever-growing global consumption of coffee generates millions of tons of spent coffee grounds (SCGs) annually, posing a significant waste disposal problem. While some SCGs find use in composting or biogas production, a large portion remains underutilized. This study introduces a novel circular waste-to-energy pathway to tackle this challenge. Our proposed technology employs a cascading valorization approach, utilizing non-catalytic supercritical transesterification of pyrolytic oil derived from SCGs for liquid hydrocarbon production. The process begins with pyrolysis, which converts SCGs into pyrolytic oil. This oil is then upgraded via supercritical transesterification with methanol. Experiments were conducted using a 1:6 oil-to-methanol ratio at precisely controlled conditions of 239.4°C and 1200 psi for 20 minutes. This optimized process yielded an impressive 96% of valuable liquid hydrocarbons. The resulting product exhibited highly favorable characteristics, including a density of 755.7 kg/m³, a viscosity of 0.7297 mm²/s, and a high heating value (HHV) of 48.86 MJ/kg. These properties are remarkably comparable to conventional biofuels and standard fossil fuels, demonstrating the product's potential as a viable energy source. These compelling results unequivocally demonstrate that non-catalytic supercritical transesterification effectively upgrades SCG-derived pyrolytic oil into valuable liquid hydrocarbons. This innovative approach offers a sustainable solution for SCG waste management, significantly contributes to a circular bioeconomy, and presents a promising alternative for renewable fuel production, thereby potentially reducing global reliance on fossil fuels.