Study on the mechanisms of hydrogen production from alkali lignin gasification in supercritical water by ReaxFF molecular dynamics simulation

Lignin is a major polymer in the black liquor of paper mill and one of the most important components of biomass. Supercritical water gasification (SCWG) technology, which is an efficient and clean method for waste lignin treatment, has a good application prospect. To improve the conversion efficiency of lignin, it is necessary to reveal the detail mechanisms of lignin gasification in supercritical water (SCW). Based on the actual molecular structure of lignin, a model of complex lignin was constructed by using Materials Studio (MS). The effects of different reaction parameters on gasification results were analyzed with the reactive force field molecular dynamics method (ReaxFF MD). The simulation results show that higher reaction temperature and lower reactant concentration lead to higher efficiency of lignin gasification in SCW, and lignin has the highest gasification efficiency at 3500 K and 15 wt%. Additionally, the decomposition pathway of lignin and the generation paths of CO2, H2 were clarified. This work will provide theoretical guidance for further research to improve the SCWG efficiency of lignin.