A molecular view of lignin fractionation in organic–water co-solvents: the effect of the van der Waals over electrostatic ratio of lignin–solvent interactions

With the escalating demand for green and sustainable development driven by resource depletion 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 the molecular level. Integrating molecular dynamics simulations with previous experimental data in multiple solvents has revealed that van der Waals interactions between lignin and solvent promote 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 has indicated that water mainly provided the electrostatic interactions, and organic solvents provided mainly van der Waals interactions in organic-water co-solvents. Effective appreciable fractionation results occurred when van der Waals interaction constituted approximately 0.55 of the lignin-solvent interactions. This finding provides a molecular-level guidance for rationally designing lignin fractionation solvent systems, offering a theoretical foundation for subsequent AI-driven prediction development.