NOVELTY - Producing purified cellulose, comprises (a) providing a feedstock comprising lignocellulosic biomass, (b) contacting the feedstock with sulfur dioxide or sulfurous acid, water, and a solvent for lignin, to produce delignified intermediate solids and a liquid phase comprising hemicelluloses and lignin, (c) bleaching the intermediate solids to further delignify the intermediate solids to generate cellulose-rich solids, (d) washing the cellulose-rich solids to generate purified cellulose, and (e) recovering the purified cellulose.    USE - The process is useful for producing purified cellulose, which is useful for making a cellulose derivative or nanocellulose to produce monomeric sugars such as glucose (all claimed) and xylose, which can be fermented to a wide variety of fuels and chemicals, used to grow organisms or produce enzymes, converted catalytically to chemicals, or recovered and sold to the market.    ADVANTAGE - The process is capable of economically producing purified cellulose with high yield and very low lignin content.    DETAILED DESCRIPTION - Producing purified cellulose, comprises: either (a) providing a feedstock comprising lignocellulosic biomass, (b) contacting the feedstock with sulfur dioxide or sulfurous acid, water, and a solvent for lignin, to produce delignified intermediate solids and a liquid phase comprising hemicelluloses and lignin, (c) bleaching the intermediate solids to further delignify the intermediate solids to generate cellulose-rich solids, (d) washing the cellulose-rich solids to generate purified cellulose, and (e) recovering the purified cellulose; or (a1) the step (a) as above per se, (b1) bleaching the feedstock to generate delignified intermediate solids, (c1) contacting the intermediate solids with sulfur dioxide or sulfurous acid, water, and a solvent for lignin, to produce cellulose-rich solids and a liquid phase comprising hemicelluloses and lignin, and (d1) the steps (d) and (e) as above per se.    DESCRIPTION OF DRAWING(S) - The figure shows a block flow diagram of a process for producing purified cellulose.