Co-gasification of waste lignin and plastics in supercritical liquids: Comparison of water and carbon dioxide

Waste lignin and plastic can be converted into useful syngas by co-gasified in supercritical liquids. In this work, lignin with beta-O-4 linkages and two kinds of common plastics, polyethylene and polypropylene, were simulated in the process of co-gasification. The processes in supercritical water (SCW) or supercritical carbon dioxide (SCCO2) environment at different temperatures and ratios of reactants were studied comparatively using ReaxFF mo-lecular dynamics simulations. The composition of products has been analyzed, the co-gasification synergistic effect has been explored, and the reaction mechanisms were provided and compared. The addition of plastic increased the production of H2 in both the SCW and SCCO2 systems The effect of adding plastics on the initial pyrolysis of lignin in SCW was greater than that in SCCO2, resulting in the production of more H2 and CH4 and less CO in the SCW system.