Study on the reaction mechanism for hydrogen production from rice straw gasification in supercritical water based on ReaxFF

Supercritical Water Gasification (SCWG) is an efficient technology for converting biomass waste into hydrogen-rich gas. In this study, we investigated the gasification process of rice straw under SCW conditions using ReaxFF reactive force field molecular dynamics (MD) simulations combined with experimental validation. The effects of temperature, reactant concentration, and reaction time on gasification efficiency were explored. The results show that under conditions of 4500 K, 3 wt%, and 500 ps, the gasification rate reaches its optimum, with the selectivity proportion of three gases comprising approximately 70 % of the total gas yield. Furthermore, we focused on the radical reactions of water in SCW and the decomposition pathways of cellulose and hemicellulose. Radicals (such as H, OH, and H₃O⁺) generated from water under supercritical conditions drive hydrogen production through dynamic equilibrium reactions. In the reaction pathway, hemicellulose, cellulose, and lignin in rice straw are first hydrolyzed into small molecular monomers, which subsequently undergo dehydrogenation, deoxygenation, ring-opening, and free radical reactions to produce hydrogen and other gaseous products. This study not only provides in-depth insights into the reaction mechanisms of rice straw during SCWG but also offers theoretical guidance for optimizing SCWG systems and advancing their industrial applications.