Enhanced production of syngas from supercritical water gasification of lignin in a CO2 atmosphere: ReaxFF molecular dynamic simulation and DFT calculation study.

Supercritical water gasification (SCWG) emerged as a promising route to tackle solid pollution induced by lignin to obtain syngas. Combined with the characteristics of SCWG technology for hydrogen-rich generation and CO2 gasification technology for CO-rich generation, the use of CO2 atmosphere in the SCWG of biomass could effectively regulate the H2/CO molar ratio in syngas. The study of the SCWG mechanism of lignin in CO2 atmosphere was conducive to the understanding and optimization of the lignin conversion process and reaction pathways. The effects of temperature, lignin content and CO2 atmosphere on the distributions of gasification products were studied using ReaxFF reactive molecular dynamic simulation and density functional theory calculation. The results indicated that the molar ratio of H2 to CO increased with the increase of lignin content, while the molar ratio of H2 to CO decreased with the increase of temperature and CO2 content. However, the overall generation of syngas increased with the improvement of these parameters. The addition of CO2 effectively promoted the generation of syngas and also adjusted the molar ratio of H2 to CO in syngas. Hydrogen bonds formed between lignin and H2O molecules, and CO2 and H2O molecules to promote the decomposition of lignin and CO2.