Methods for digestion of cellulosic biomass solids in the presence of a phenolic solvent generated in situ from lignin

A method comprising:

• providing cellulosic biomass solids in a digestion medium comprising about 50% or more of an organic solvent by volume, the cellulosic biomass solids comprising water in an amount up to about 50% by mass;
• heating the cellulosic biomass solids and the digestion medium in a digestion unit in the presence of molecular hydrogen and a slurry catalyst capable of activating molecular hydrogen, thereby forming an alcoholic component derived from the cellulosic biomass solids and liberating lignin from the cellulosic biomass solids into the digestion medium;
• wherein the water from the cellulosic biomass solids forms a biphasic mixture with the digestion medium as the cellulosic biomass solids are heated, the biphasic mixture comprising an organic phase and an aqueous phase;
• removing at least a portion of the biphasic mixture from the digestion unit, the biphasic mixture containing the alcoholic component, the lignin and the slurry catalyst;
• converting at least a portion of the lignin into a phenolic solvent;
• and
• returning at least a portion of the phenolic solvent to the digestion unit while heating the cellulosic biomass solids and the digestion medium.