Microscopic mechanism for CO2-assisted co-gasification of polyethylene and softwood lignin: A reactive force field molecular dynamics study

Co-gasification of biomass and waste plastic to produce syngas and value-added products is an attractive technology for renewable energy utilization and waste disposal. CO2 as a gasifying agent has received much attention as it can act as carbon source and oxidant in the reaction. In this paper, the feasibility and characteristics of CO2-assisted co-gasification of polyethylene and softwood lignin were explored. Simulation results showed that the lignin macromolecule began to decompose through C–O–C bond breaking and the PE chain gradually decomposed through C–C bond breaking. CO2-assisted co-gasification showed a negative synergistic effect on gas yield at the early stage, which delayed the reaction, but showed a positive synergistic effect at the late stage. The reaction between CO2 and carbon-containing fragments greatly promoted CO production. The hydrogen and hydrocarbon radicals from PE were actively involved in H2 and hydrocarbon gas production. Compared with O2-assisted co-gasification, the CO2-assisted and CO2/O2-assisted co-gasification yielded more CO, hydrocarbon gases and combustible gases and increased the lower heating value of gas product. This work sheds light on the underlying mechanisms of CO2-assisted co-gasification of polyethylene and softwood, and would be helpful for the development of this technology.