Systems and methods for acid recycle
Methods and systems for pretreating lignocellulosic biomass are disclosed. An acid solution between 1% to 1.6% sulfuric acid is applied to the biomass. The biomass is subjected to an elevated temperature to cause the production of xylose, glucose, and furfural. Adjustments to temperature, acid concentration, and time can generate at least 80% or 90% of theoretical xylose, 45% or 50% of the theoretical glucose, and less than 4000 ppm of furfural in the xylose liquor. A portion of the resulting xylose liquor may be separated from the glucan solids. The xylose liquor, still highly acidic, can be recycled to reduce subsequent acid loading requirements. Makeup acid solution is added to the xylose liquor and subsequent biomass to ensure a proper solids to liquids ratio. The biomass is again treated to higher temperatures to yield sugars. The process may be repeated for each subsequent cycle.
1. A method for pretreating lignocellulosic biomass, comprising:
a) conveying a first portion of a lignocellulosic biomass feedstock to a pretreatment reactor, wherein the lignocellulosic biomass feedstock comprises ground corn cobs and corn stover;
b) applying an acid solution to the first portion of lignocellulosic biomass feedstock;
c) treating the first portion of lignocellulosic biomass feedstock under a first set of conditions to produce a first hydrolysate, wherein the treating under the first set of conditions hydrolyzes hemicellulose present in the lignocellulosic biomass feedstock,
d) separating the first hydrolysate into a xylose liquor and a glucan solid;
e) conveying a second portion of the lignocellulosic biomass feedstock to the pretreatment reactor;
f) recycling a fraction of the xylose liquor that is separated from the first hydrolysate and applying the fraction of the xylose liquor to the second portion of the lignocellulosic biomass feedstock, wherein the fraction of the xylose liquor that is recycled is 70% or more of the total xylose liquor that is separated from the glucan solid;
g) applying makeup acid and water to the second portion of the lignocellulosic biomass feedstock; and
h) enzymatically hydrolyzing the glucan solid under a second set of conditions to produce a second hydrolysate comprising glucose.
2. The method of claim 1 , wherein at step b) the acid solution comprises between about 0.8% to 1.6% acid.
3. The method of claim 1 , wherein the acid solution comprises an acid selected from the group consisting of sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, and acetic acid.
4. The method of claim 1 , wherein the acid solution comprises sulfuric acid.
5. The method of claim 1 , wherein at step c) a xylose yield of greater than about 80% of theoretical is achieved.
6. The method of claim 1 , wherein at step c) furfural is present in the xylose liquor in an amount of 4000 ppm or less.
7. The method of claim 1 , wherein at step c) the second temperature is about 120° C.
8. The method of claim 1 , wherein at step c) maintaining the second temperature for at least about 10 minutes.
9. The method of claim 1 , wherein at step c) maintaining the second temperature for at least about 120 minutes.
10. The method of claim 1 , wherein recycling the xylose liquor reduces the amount of water and acid solution required to pretreat the second portion of the biomass feedstock.
11. The method of claim 1 , wherein recycling the fraction of the xylose liquor results in a 35%-70% reduction in water and acid solution.
12. The method of claim 1 , wherein the recycled xylose liquor reaches a steady state xylose concentration of from about 6.5 to 11.4% w/v.
13. A method for pretreating lignocellulosic biomass to be supplied to a fermentation system for production of a fermentation product, comprising:
a) applying a first xylose liquor to lignocellulosic biomass feedstock, wherein the lignocellulosic biomass feedstock comprises ground corn cobs and corn stover;
b) applying a makeup acid solution to the lignocellulosic biomass feedstock;
c) treating the lignocellulosic biomass feedstock under a first set of conditions to produce a first hydrolysate, wherein the treating under the first set of conditions to hydrolyzes hemicellulose present in the lignocellulosic biomass feedstock;
d) separating the first hydrolysate into a the second xylose liquor and a glucan solid;
e) recycling a fraction of the second xylose liquor that is separated from the first hydrolysate and applying the fraction of the second xylose liquor to a subsequent portion of the lignocellulosic biomass feedstock, wherein the fraction of the second xylose liquor that is recycled is 70% or more of the total xylose liquor that is separated from the glucan solid; and
f) enzymatically hydrolyzing the glucan solid under a second set of conditions to produce a second hydrolysate comprising glucose.
14. The method of claim 13 , wherein at step b) the makeup acid solution comprises sulfuric between about 0.8% to 1.6% acid.
15. The method of claim 13 , wherein at step c) furfural is present in the second xylose liquor in an amount of 4000 ppm or less.
16. The method of claim 13 , wherein at step c) the second temperature is about 120° C.
17. The method of claim 13 , wherein recycling the xylose liquor reduces the amount of water and acid required to pretreat the subsequent portion of the lignocellulosic biomass feedstock about 35%-70% and the recycled xylose liquor reaches a steady state xylose concentration of from about 6.5 to 11.4% w/v.