Combining experiment and theory to study the mechanism of lignin supercritical water gasification

Supercritical water gasification (SCWG) presents notable advantages in biomass energy utilization. The exploration of the reaction mechanism of lignin in supercritical water holds significance in advancing and refining the biomass SCWG process. In this work, syringol was selected as a lignin model compound to study the SCWG mechanism of lignin through a combination of molecular simulation and experiments. The results show that the ether bond is rapidly cleaved in the reaction initial stages. While the phenolics dearomatization has a slower rate and temperature exerts a considerable influence on the dearomatization process. Four degradation pathways are proposed based on the molecular simulations. In the context of the dearomatization reaction, DFT calculations are performed to determine the energy barriers associated with each of the four pathways. Notably, the energy barrier for the most favorable pathway is found to be 291.96 kJ/mol. A lumped kinetic model is constructed based on the reaction pathway, and the reliability of the model is verified by both experiments and DFT calculations. This paper offers valuable assistance in optimizing reaction pathways.