Molecular-scale elucidating of lignocellulose biomass char steam gasification for ultimately converting to syngas

Abstract

Lignocellulosic biomass char gasification plays an irreplaceable role in alleviating environmental problems caused by greenhouse effects. Elucidating the molecular-scale gasification mechanism is significant in ultimately converting the lignocellulosic biomass char to clean syngas and reducing pollutant emissions. In this study, the molecular-scale structure of sawdust char (SC) is carefully established using 13C NMR, FTIR, and XPS. The results compare well with the results of previous work. The mechanism of its steam gasification is investigated by molecular dynamics simulation. Results show that the main products of the gasification process after complete reaction are H2 and CO, and CO is always released before H2. The gasification equivalent ratio decreases, H2 increases significantly and is more from steam. The maximum carbon number of single molecule in the product is re-increased, and the increase of H2O molecules hinders the decomposition of light tar into small molecules of gas. The reaction mechanism is clearly defined: the aromatic carbon rings substituted by oxygen-containing functional groups are firstly gasified, followed by bridge bond breakage of the macromolecular char into several multiple aromatic rings. Each of the rings is gasified separately and ring-opening to form C5-C13 (light tar). Finally, C5-C13 completes the conversion to generate a large amount of H2, accompanied by CH4 reforming and dehydrogenating small molecule compounds. The migration paths of N elements are pyrrole (N)→CN→CON→C1-3H1-3N→HCN. This work elucidates the steam gasification process of lignocellulosic biomass char at a molecular scale, which provides a theoretical basis for the clean utilization of biomass and CO2 reduction.