Multiscale investigation of the mechanism of biomass deconstruction in the dimethyl isosorbide/water Co-solvent pretreatment system

In the context of promoting a circular bioeconomy, the development of green and efficient lignocellulosic biomass pretreatment technologies so as to realize high value-added biomass utilization is of intense interest. We demonstrated the potential of the bio-based green solvent dimethyl isosorbide (DMI) for the fractionation of Eucalyptus biomass with excellent performance. Here, to investigate the mechanisms involved in biomass fractionation, microimaging and microspectroscopic techniques were employed together with molecular dynamics (MD) simulation and COSMO-RS quantum chemical calculations to derive multiscale information. Both the microstructure and regional chemistry of the cell wall vary significantly with the volume ratio of DMI/H2O. The strongest effects were found at DMI/H2O = 9 : 1 and showed visible cell wall tearing cracks and cell wall deformation and collapse as well as the lowest values of cell wall thickness and circularity. From the MD simulations, lignin exhibits collapsed-like structure in pure H2O with low solvent accessibility surface area (SASA) and radius of gyration (Rg). In contrast, lignin in DMI/H2O shows extended structure with high SASA and solvent interactions dominated by van der Waals forces, with maximal contact in the 9 : 1 (v/v) system. Further, the COSMO-RS calculated sigma (sigma-) potential suggests the intermolecular interactions in DMI and DMI/H2O co-solvent are weak, leading to stronger interaction with lignin and correspondingly higher lignin dissolution. The radial distribution functions and sigma-potential all show that again DMI/H2O at 9 : 1 is an optimal volume ratio for high lignin dissolution. This study provides a solvent-ratio dependent mechanism for the action of polar aprotic solvents in the deconstruction of biomass. This study provides a fundamental understanding of the multiscale results on the biomass deconstruction mechanism by solvent DMI, contributing to the discovery of the green, efficient and sustainable lignocellulosic biomass pretreatment technologies.