Mechanism insights into hardwood lignin pyrolysis via ReaxFF molecular dynamics simulations

Lignin pyrolysis is an effective approach for producing high-value chemicals and fuels. In this study, reactive molecular dynamics simulations were conducted to investigate the pyrolytic behavior of hardwood lignin, focusing on gas product distribution, generation pathways of major gas species, and the evolutions of bonds, benzene rings, β-O-4 linkages, and key functional groups. Furthermore, the morphology of char and kinetic analysis were examined. The results reveal that hydroxyl groups, methoxy groups, and benzene rings are the primary hydrogen sources in H₂ formation. In contrast, methoxy groups, hydroxyl groups and linkages are the main contributors of oxygen atoms in CO. The quantities of initial β-O-4 linkages, methoxy groups, and hydroxyl groups consistently decrease throughout pyrolysis. Char growth is primarily driven by carbon chain extension and bonding with other fragments. Additionally, the estimated activation energy for hardwood lignin pyrolysis is 113.42 kJ/mol. These findings provide detailed insights into the hardwood lignin pyrolysis mechanisms, laying a foundation for optimizing pyrolysis processes.