Molecular View on Lignin Fractionation in Organic-water Co-solvent: Effect of the Ratio of Van Der Waals over Electrostatic of Lignin-Solvent Interactions

Abstract

With the escalating demand for green and sustainable development driven by resource depleting and worldwide climate upheavals, the conversion of lignin—a naturally occurring, widely distributed, renewable aromatic chemical feedstock—has long attracted significant attention. The rational design of efficient solvent systems for the hierarchical separation of lignin remains a persistent research challenge. In this study, the key physicochemical factors influencing the fractionation of lignin in organic-water solvent were identified at molecular level. Integrating molecular dynamics simulations with previous experimental data in multiple solvents revealed that van der Waals interactions between lignin and solvent promoted extensive surface contact, while electrostatic interactions effectively disrupt hydrogen bonds between lignin chains. These synergistic interactions collectively enhance lignin dispersion and dissolution within the solvent. Quantitative analysis indicated that water mainly provided the electrostatic interactions, and organic solvent provided mainly van der Waals interactions in organic-water co-solvent. Effective appreciate fractionation results occurred when van der Waals interaction constituted approximately 0.55 of the Lignin-Solvent interactions. This finding provides a molecular-level rationale for rationally designing lignin fractionation solvent systems, offering a theoretical foundation for subsequent AI-driven prediction development.