NOVELTY - Fractionation (m1) of lignocellulosic biomass involves (a1) combining a first solvent with a lignocellulosic biomass, where the first solvent dissolves at least some of the cellulose present in the lignocellulosic biomass; and (b1) combining a second solvent with the resultant material, where at least some of the cellulose that is dissolved by the first solvent, precipitates out of the liquid phase.    USE - For fractionating lignocellulosic biomass (such as hardwood, softwood, recycled paper, waste paper, forest trimmings, pulp and paper waste, corn stover, corn fiber, wheat straw, rice straw, sugarcane bagasse, and/or switchgrass) which is useful for producing hemicellulose sugars, lignin, acetic acid, and amorphous cellulose that is hydrolyzed into glucose or fermented directly (claimed). Also in biorefining industry.    ADVANTAGE - The method provides high amorphous cellulose which is readily converted into glucose using known methods; and carried out by using modest process conditions and low solvent/solid ratio, thus has advantage of relatively low capital and processing costs. The obtained lignin is high-quality, relatively pure, low-molecular weight lignin that does not contain sulfur.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) a solvent combination (c2) for fractionating lignocellulosic biomass, comprising: a first solvent (s1) is selected from hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, polyphosphoric acid, acetic acid, sulfur dioxide, zinc chloride, sodium hydroxide, potassium hydroxide, ammonia, lithium chloride/N,N-dimethylacetamide, 1-butyl-3-methylimidazolium hexafluorophosphate, dimethylsulfoxide/tetrabutylammonium fluoride trihydrate, N-methylmorpholine-N-oxide, or cadmium monoxide/ethylenediamine (cadoxen); and a second solvent is selected from methanol, ethanol, 1-propanol, 2-propanol, acetone, propanal, 1-butanol, 2-butanol, butanal, butanone (methyl ethyl ketone), tert-butanol, or water; and    (2) system for fractionating lignocellulosic biomass, comprising: a device for separately containing a first and second solvent; reaction vessel where the first solvent is combined with the lignocellulosic biomass, and the first solvent dissolves at least 90% of the cellulose present in the lignocellulosic biomass; a precipitation vessel where the second solvent is combined with the material from the reaction vessel, and at least 90% of the cellulose that is dissolved by the first solvent in the reaction vessel, precipitates out of the liquid phase; and a device for recovering the precipitated amorphous cellulose.