Process for producing a concentrated sugar solution by enzymatic saccharification of polysaccharide enriched biomass

1. A method of producing a concentrated sugar solution from biomass, the method comprising:

a) delignifying biomass comprising the substeps of

i) contacting with water and at least one nucleophilic base, a biomass comprising lignin and having a glucan/xylan weight ratio G 1 /X 1 to form a biomass slurry having a pH of about 12.5 to about 13.0; and

ii) maintaining the biomass slurry under reaction conditions such that the slurry attains a pH of about 9.5 to about 10.0 and has a glucan/xylan weight ratio G 2 /X 2 within 10% of the value of G 1 /X 1 , and wherein the slurry comprises a lignin-containing liquid fraction and a solid fraction comprising a polysaccharide enriched biomass;

wherein G 1 and G 2 are grams of glucan per 100 grams of biomass and biomass slurry respectively, and X 1 and X 2 are grams of xylan per 100 grams of biomass and biomass slurry respectively; and

wherein the water soluble metal hydroxide is selected from the group consisting of sodium hydroxide, and the metal carbonate or the organic hydroxide is selected from the group consisting of sodium carbonate, potassium carbonate, ammonium hydroxide; and

wherein the reaction conditions include a temperature from about 20° C. to about 110° C. and a reaction time of about 4 hours to about 30 days; and

b) adding an additive selected from the group consisting of polyethylene glycols, fatty acid esters, fatty acid ethoxylates, nonionic surfactants derived from polyethoxylated sorbitan and a fatty acid, sodium lauriminodipropionate, sodium cocoamphoacetate, sodium tridecyl ether sulfate, and a combination of these, such that the enzyme loading of the saccharification enzyme consortium is reduced relative to the loading of the saccharification enzyme consortium when none of the additives is added; and

c) contacting with a saccharification enzyme consortium an aqueous suspension of at least a portion of the solid fraction of the polysaccharide enriched biomass,

the solid fraction of the polysaccharide enriched biomass being 13 weight percent to about 30 weight percent of the aqueous suspension,

at reaction conditions sufficient to produce a saccharification product comprising at least about 7 percent by weight sugars, based on the total weight of the saccharification product, in 24 hours of contact with the saccharification enzyme consortium.

2. The method of claim 1 wherein the saccharification product comprises at least about 18 percent by weight sugars in 168 hours.

3. The method of claim 1 wherein the additive is from about 0.1 weight percent to about 5 weight percent, based on the weight of the solid fraction of the polysaccharide enriched biomass solid fraction in the aqueous suspension.

4. The method of claim 3 , wherein the additive is a polyethylene glycol of molecular weight 500 to 50,000 Daltons, a fatty acid ester selected from the group consisting of methyl esters of C 12 to C 30 fatty acid esters, fatty acid ethoxylates of C 12 to C 30 fatty acids, nonionic surfactants derived from polyethoxylated sorbitan and a C 12 to C 30 fatty acid, and a combination of these.

5. The method of claim 1 wherein at least about 70 percent of the lignin in the biomass is delignified in the solid fraction of the polysaccharide enriched biomass.

6. The method of claim 1 wherein the concentration of the solid fraction in the aqueous suspension is from about 21 weight percent to about 30 weight percent, and the saccharification product comprises sugars corresponding to at least a 65% saccharification yield based on the sum of glucan and xylan in the polysaccharide enriched biomass.

7. The method of claim 1 wherein the sugars comprise at least one sugar monomer selected from the group consisting of glucose, arabinose, xylose, mannose, and galactose, and a combination of these.