Multiscale Molecular Simulation Strategies for Understanding the Delignification Mechanism of Biomass in Cyrene

In recent years, the cellulose-derived solvent Cyrene has piqued considerable interest in the green chemistry community despite only recently being available in the quantities required for solvent applications. Deconstruction of cellulose is an essential step in the production of fuel and value-added chemicals from lignocellulosic biomass. However, the high recalcitrance and heterogeneity of lignin hinder this process, necessitating the need to solubilize lignin. To understand the dissolution of lignin in Cyrene and Cyrene-cosolvent systems, multiscale molecular simulation approaches have been employed. Initially, the conductor-like screening model for real solvent (COSMO-RS) model was used to assess the thermodynamic properties of lignin in Cyrene and Cyrene-cosolvent systems. From the COSMO-RS calculations, the correlation between the predicted activity coefficient and the experimental lignin solubility was excellent. Further, classical molecular dynamics (MD) simulations were performed to evaluate the delignification of biomass by predicting structural and dynamic properties of lignin-solvent systems. The microscopic properties such as interaction energies, radius of gyration, solvent-accessible surface area, radial and spatial distribution functions (RDFs/SDFs), and hydrogen bonds were assessed to characterize lignin dissolution in these solvent mixtures and were validated with experimental data. From the MD simulations, it was observed that lignin adopts a coil-like structure in Cyrene and Cyrene:water mixtures, thereby dissolving the lignin, while lignin adopts a collapsed-like structure in the presence of water. The occupancy density of Cyrene is highly surrounded by the aryl and hydroxyl groups of lignin polymer rather than by water. The interaction energies between lignin and Cyrene and Cyrene-cosolvent were much stronger than that between lignin and water, explaining the higher biomass delignification in Cyrene-based solvents.