Patent ID: 8889384

Claim:
A process for producing alcohol is provided comprising: (a) providing a biomass containing cellulose fibers and at least 15 weight percent of lignin; (b) contacting said biomass, in at least one digester, with a cooking liquor comprising 1 to 20 wt %, based on the cooking liquor, of sodium hydroxide, and water, wherein said cooking liquor having an active alkali of between 5 to 25%, and a sodium carbonate concentration of less than 3.5 wt% based on cooking liquor, at a cooking liquor to biomass ratio within the range of 2:1 to 6:1, at a temperature within the range of 100° C. to 230° C. with a residence time within 0.25h to 4h under conditions effective to provide a pulp stream containing pulp having a lignin content of 5% to 20% by weight, based on the pulp, and a chemical liquor stream containing sodium compounds; (c) washing the pulp stream with a water stream thereby removing at least a portion of lignin and hemicellulosic material and producing washed pulp stream; (d) hydrolyzing the washed pulp stream by treating the streams with an enzyme solution comprising cellulases and optionally xylanases at a pH within the range of about 3 to about 7 at a temperature within the range of 30° C. to 90° C. to produce a hydrolyzate containing from about 4% to 30% by weight of fermentable sugar; (e) fermenting the hydrolyzate in the presence of a microorganism at a temperature with the range of about 25° C. to about 55° C. at a pH within the range of about 4 to about 6 thereby producing an alcohol stream containing at least one alcohol having 2 to 18 carbon atoms; and (f) recovering at least one of said alcohol from the alcohol stream.