Efficient preparation of hydrogen-rich fuel gas from food waste through hydrothermal carbonization coupled with hydrothermal gasification

Hydrothermal gasification has emerged as one of the most promising technologies for clean energy production, offering a potential solution to the environmental problems associated with massive food waste generation, yet it still suffers from low gasification benefits due to the low feed content. In this study, the hydrothermal cascade process that integrated hydrothermal carbonization with hydrothermal gasification was thus proposed for efficient hydrogen-rich fuel gas production from food waste at a high solid content. Hydrothermal carbonization provided an effective means of partitioning complex organic components into readily gasifiable soluble organics in the process water and a relatively recalcitrant hydrochar. The hydrothermal cascade process allowed hydrothermal gasification of food waste at a solid content as high as 30%, with a dry basis hydrogen-rich fuel gas production of 24.36 mol/kg and a higher heating value of 441.13 kJ/mol. The hydrochar showed almost identical contributions to gasification as the process water. Hydrothermal carbonization at 240 °C for over 4 h reduced overall gasification performance, whereas higher gasification temperature and increased Raney Ni catalyst loading improved the process. The process achieved a higher effective carbon mass gasification efficiency (29.06%) and energy efficiency (28.55%) when compared with direct hydrothermal gasification of food waste and mixed products from hydrothermal carbonization, showing dry basis CH 4 and H 2 yields of 10.82 and 5.82 mol/kg, respectively. More importantly, the hydrothermal cascade process suppressed the char formation and significantly reduced the total organic carbon content of wastewater after hydrothermal gasification, creating favorable conditions for stable gasification and recycling of wastewater.