NOVELTY - An organosolv process for treating lignocellulosic biomass involves adding biomass to reaction vessel and exposing to a solvent, where ratio of solvent to biomass is 10:1 to 4:1, the solvent comprises ethanol (40-60 wt./wt.%), and acid (1.5-2.5 wt.%) is added; elevating temperature of the biomass/solvent mixture to 140-170 degrees C for 50-200 minutes to form pulp and extraction liquor, where liquor comprises extracted derivatives of native lignin; recovering at least portion of extraction liquor; and recovering at least portion of pulp, where pressure in vessel is less than about 22 bar.    USE - As organosolv process for treating a lignocellulosic biomass (containing softwood feedstock, hardwood feedstock or annual fiber feedstock), to separate lignin and other useful materials from biomass.    ADVANTAGE - The yield of lignin recovered from the extraction liquor is greater than or equal to 60 (preferably greater than or equal to 70, especially greater than or equal to 80)% of the theoretical maximum yield. The organosolv processes operate within relatively narrow ranges of process conditions and offer improved glucose yield, lignin yield, and/or reduced production of acetic acid. The present process operates at significantly lower temperature and pressure than typical for organosolv biorefining with consequent savings in capital, operating and/or energy expenditure; demonstrates significantly less fouling than seen in prior art organosolv processes. When the present process utilizes softwood feedstock there is a marked reduction in the amount of self precipitated lignins (SPLs) seen. A reduction in the amount of SPLs can result in lower equipment fouling. This offers the possibility of an improved commercial scale organosolv plant that has the ability to process softwood and other types of biomass that suffer from problems with SPLs. The process offers surprisingly high lignin yields which increases the value derivable from the lignin stream of a particular process and also reduces the amount of non-recovered lignin contaminating product streams from the process.    DETAILED DESCRIPTION - An organosolv process for treating a lignocellulosic biomass involves either: adding the biomass to a reaction vessel and exposing the biomass to a solvent, where the ratio of solvent to biomass is 10:1 to 4:1, the solvent comprises ethanol (40-60 wt./wt.%), and an acid (1.5-2.5 wt.%) is added; elevating the temperature of the biomass/solvent mixture to 140-170 degrees C for a total period of 50-200 minutes to form a pulp and an extraction liquor, where the liquor comprises extracted derivatives of native lignin; recovering at least a portion of the extraction liquor; and recovering at least a portion of the pulp, where the pressure in the reaction vessel is less than about 22 bar; or adding the biomass to a reaction vessel and exposing the biomass to a solvent, where the ratio of solvent to biomass is 10:1 to 4:1, the solvent comprises ethanol (40-60 wt./wt.%), and the pH of the biomass/solvent mixture is 2.5-2.7; elevating the temperature of the biomass/solvent mixture to 150-170 degrees C for a total period of 50-200 minutes to form a pulp and an extraction liquor, where the liquor comprises extracted derivatives of native lignin; recovering the extraction liquor; and recovering the pulp, where the pressure in the reaction vessel is greater than or equal to 22 bar.