Abstract
Understanding and controlling the physical adsorption of lignin compounds on cellulose pulp is a key parameter for a successful optimization of organosolv processes. The effect of binary organic-aqueous solvents on the coordination of lignin to cellulose was studied with molecular dynamics simulations, considering ethanol and acetonitrile as organic co-solvents in aqueous solutions in comparison to their mono-component counterparts. The structures of the solvation shells around cellulose and lignin, as well as the energetics of the lignin-cellulose adhesion, indicate a more effective disruption of lignin-cellulose binding by binary solvents. The synergic effect between solvent components is explained by their preferential interactions with cellulose-lignin complexes. In the presence of pure water, long-lasting H-bonds in the lignin-cellulose complex are observed, promoted by the non-favorable interactions of lignin with water. Ethanol and acetonitrile compete with water and lignin for cellulose oxygen binding sites, causing a non-linear decrease of the cellulose-lignin interactions with the amount of the organic component. This effect is modulated by the water exclusion from the cellulose solvation shell by the organic solvent component. The amount and rate of water exclusion depend on the type of organic cosolvent and its concentration.