Sulfite pretreatment for biorefining biomass
The present invention relates to a method using sulfite pretreatment to overcome recalcitrance of lignocellulose (SPORL). More specifically, it relates to a sulfite-based chemical process for pretreating biomass in solutions to reduce access barriers of enzymes to the lignocellulose, resulting in efficient conversion through enzymatic saccharification.
1. A method for treating a cellulose-containing material to produce sugars comprising the steps of:
(a) providing cellulose-containing woody biomass comprising hemicellulose and lignin;
(b) treating the woody biomass of step (a) for 0.1 to 120 minutes with a solution comprising a base of sulfite or bisulfite adjusted to have an initial pH of from about 1.5 to 5.0, wherein said treating is at a temperature of about 150 to 250° C., wherein sulfite or bisulfite charge (w/w), based on oven dried woody biomass, is no more than 9%, but greater than 0, and wherein treating removes hemicellulose and produces only partial delignification; and
(c) enzymatically hydrolyzing the resultant treated biomass of step (b) to produce sugars,
wherein the woody biomass is mechanically size-reduced or treated by steam explosion prior to or during step (a) or (b).
2. The method of claim 1 , wherein the temperature of step (b) is about 150 to 220° C.
3. The method of claim 1 , wherein the sulfite or bisulfite base further comprises sulfur dioxide.
4. The method of claim 1 , wherein the mass ratio between the sulfite or bisulfite base and the woody biomass in step (b) is about 1:100 to about 1:10.
5. The method of claim 1 , wherein the bisulfite is sodium bisulfite, magnesium bisulfite, ammonium bisulfite, calcium bisulfite, or potassium bisulfite.
6. The method of claim 1 , wherein the mechanical size reduction comprises disk milling or hammer milling.
7. The method of claim 1 , wherein step (b) takes place in a feeder coupled to a device used for the mechanical size reduction.
8. The method of claim 1 , wherein the method comprises treating the woody biomass with steam explosion at the same time as step (b).
9. The method of claim 1 , where the method further comprises fermenting the sugars into ethanol.
10. The method of claim 1 , wherein the method further comprises chemically converting the sugars to a biofuel or a biochemical.
11. The method of claim 1 , wherein the biomass ratio between the sulfite or bisulfite base and the woody biomass in step (b) is about 1:40 to about 1:15.