Insight into the interconversion mechanisms during the supercritical water gasification of bark

The clean and efficient utilization of biomass waste for hydrogen production conforms to social development in the future. In this work, hydrogen production from supercritical water gasification (SCWG) of fir bark (FB) was investigated systematically at various reaction temperatures (500–750 °C), feedstock concentrations (5 wt%–15 wt%), and retention time (0–40 min). The gaseous, liquid, and solid products were analyzed to master the gasification mechanism. The results demonstrated the maximum CE and H₂ selectivity of 95.34% and 0.99 were obtained at 700 °C-5 wt%-40 min. Reaction temperature was positively related to the gasification efficiency, and the effects of feedstock concentration and retention time were related to the reaction temperature. Increasing feedstock concentration contributed to the cyclisation and Diels-Alder reaction, with a cohesive aromatic structure. A benign conversion resulted in the enhancement of gasification efficiency with prolonging retention time in the high temperature SCWG. The vital reason for low gasification efficiency was due to the disorderly interconversions between organic matters.