A comprehensive process for treating lignocellulosic biomass in order to separate the biomass into its component parts, the process comprising: a) contacting the lignocellulosic biomass with a first solvent for a period of time and at a first temperature at a severity in the range of about 2 to about 4 to remove extractive components and a portion of ash from the biomass; b) contacting the biomass from step (a) with a second solvent, and optional catalyst, at a second temperature at a severity in the range of about 1 to 5 to remove hemicelluloses and additional ash from the biomass; and c) separating the biomass from step (b) into a lignin product and a cellulose product by contacting the biomass from step (b) with a third solvent at a severity in the range of about 1.5 to 5 to provide a spent liquor product and a solid fraction containing cellulose.