Patent ID: 8192549

Claim:
A method for extracting C 5 sugars comprising pentose from a slurry of cellulosic material comprising cellulose and water, the method comprising the steps of: feeding the slurry of cellulosic material comprising cellulose and water to a first stage via an inlet at a top of a vessel, wherein the step of feeding the slurry of cellulosic material comprising cellulose and water to the first stage via the inlet at the top of the vessel does not comprise adding acid to the slurry; exposing the slurry in the first stage to a first temperature between 170° C. and 190° C. for a first period of time ranging between 10 minutes and 120 minutes; passing the slurry to a second stage; exposing the slurry in the second stage to a second temperature between 100° C. and 170° C. for a second period of time ranging between 30 minutes and 120 minutes; extracting liquid comprising C 5 sugars including pentose and C 6 sugars including hemicellulose from the slurry in the second stage; and extracting the slurry containing lignin via an outlet at the bottom of a vessel.