Methods for hydrothermal digestion of cellulosic biomass solids in the presence of a slurry catalyst and a digestible filter aid

A method comprising:

• providing cellulosic biomass solids and a slurry catalyst in a hydrothermal digestion unit, the slurry catalyst being capable of activating molecular hydrogen and the cellulosic biomass solids comprising a digestible filter aid comprising cellulosic biomass particulates capable of forming a filter cake suitable for retaining at least a portion of the slurry catalyst thereon;
• heating the cellulosic biomass solids in the hydrothermal digestion unit in the presence of the slurry catalyst, a digestion solvent, and molecular hydrogen, thereby forming a liquor phase comprising soluble carbohydrates;
• allowing a portion of the liquor phase to exit the hydrothermal digestion unit;
• forming a filter cake comprising the digestible filter aid on a solids retention mechanism configured to allow the liquor phase to pass therethrough;
• collecting at least a portion of the slurry catalyst on the filter cake;
• and
• performing a first catalytic reduction reaction on the soluble carbohydrates in the hydrothermal digestion unit, thereby at least partially forming a reaction product comprising a triol, a diol, a monohydric alcohol, or any combination thereof in the hydrothermal digestion unit.