Patent ID: 8268125

Claim:
A process for fractionating a lignocellulosic material, said process comprising: (a) providing a liquid solution comprising an aliphatic alcohol, water, and sulfur dioxide, wherein said sulfur dioxide is present in a concentration of from 9 wt % to 25 wt % of said liquid solution; (b) contacting a lignocellulosic material with a vapor phase of said liquid solution in a cooking stage, wherein said vapor phase comprises water vapor, alcohol vapor, and sulfur dioxide gas, and wherein a mass ratio of said liquid solution to said lignocellulosic material is from 1 to 3; (c) delignifying said lignocellulosic material with said vapor phase in said cooking stage at a cooking temperature selected from 120° C. to 160° C. and a cooking time selected from 5 minutes to 3 hours, to produce a mixture comprising cellulose, hemicellulose oligomers, and lignin; and (d) removing cellulose from said mixture and washing said cellulose with a washing solution comprising a second amount of said aliphatic alcohol and a second amount of water, to produce a chemical pulp product and a liquid hydrolyzate stream comprising sugars and lignin.