Physical chemistry of the interactions between multicomponent solvents and biomass

Extraction of cellulose and lignin from plant biomass remains a major issue for enabling more economic and green production of lignocellulosic renewable fuels and byproducts. Although the use of multicomponent solvents has provided remarkable results in wood fractionation processes most of the currently used methods rely on empirically elaborated protocols. Understanding the physicochemical mechanisms of biomass breakdown and its interactions with solvent medium during fractionation will lead to more efficient use of biomass. This defined the focus in this thesis work on a systematic and detailed description of the interactions between ligoncellulose components with binary water-organic mixtures of ethanol and acetonitrile. Our results and their analysis were obtained predominantly with molecular dynamics (MD) simulations, and supported by additional studies of quantum chemical (Density Functional Theory) and mixed quantum mechanical (QM) and classical MD scheme (QM/MM). With these tools we first established a non-linear behavior of the mixed solvent structures, thermodynamic properties and dynamic hardness, as a measure for their global reactivity. The analysis of the average numbers of HBs with the liquid composition shows that alcohol molecules tend to substitute water molecules, allowing compensating for the loss of H-bonds in the water solvent domains. The role of organic component in water solvent mixtures on the conformational changes induced in the main wood components (cellulose, lignin and hemicellulose) is highlighted and their dependence on distinct solvent compositions is unveiled for each organic solvent component and its content in water. This dependence is explained by preferential solute-solvent interatomic interactions as a function of solvent compositions. Subsequently, the evolution of interaction forces in lignin-cellulose and lignin-xylan complexes are also found to have solvent-dependent profiles. All this supports the general conclusion about specific solvent actions on lignocellulose compounds being the driving factors in the observed macroscopic non-linear behavior in wood swelling in mixed water-organics.