Defatted spent coffee grounds fast pyrolysis polygeneration system: Lipid extraction effect on energy yield and products characteristics

Spent coffee Grounds (SCG), residues after coffee brewing, are a biowaste diffused on a global scale rich of valuable extractives. Pyrolysis is an efficient process to valorize SCG energy content into biofuels. This study aims to experimentally investigate the impact of lipid extraction and conversion to biodiesel on energy yield of py-rolysis products. Microwave-assisted lipid extraction method was employed, and a two-step transesterification process was considered for conversion into biodiesel. Fast pyrolysis of defatted spent coffee grounds (DSCG) was performed with a 300 g/h screw reactor at the temperatures 400 degrees C and 550 degrees C. The results show an important impact of pyrolysis temperature on energy distribution of the pyrolysis products. The energy content of the organics from DSCG pyrolysis is very high (up to 32 MJ/kg) and the oxygen content is significatively reduced to 26%. Non-condensable gas composition is enriched of hydrogen and methane with temperature rise. Biodiesel energy contribution significantly improve the energy yield of the pyrolysis system, leading to a more than 10% increase of the energy efficiency at a 550 degrees C, while a limited increase of 4% in the case of 400 degrees C. This study outlines how lipids extraction significantly increases the economic potential of SCG pyrolysis-based poly-generation energy system.

Automated summary

This study investigates the impact of lipid extraction and conversion to biodiesel on the energy yield of pyrolysis products. The results show that the pyrolysis temperature has an important impact on the energy distribution of the products. The energy contribution of biodiesel significantly improves the energy yield of the pyrolysis system.