CONTINUOUS PROCESS FOR THE PRODUCTION OF ETHANOL FROM LIGNOCELLULOSIC BIOMASS

• US 20120115200A1
• Filed: 11/08/2011
• Published: 05/10/2012
• Est. Priority Date: 11/09/2010
• Status: Active Grant

• Current Assignee: GreenField Specialty Alcohols Inc.
• Original Assignee: GreenField Ethanol Inc.
• Inventors: DOTTORI, Frank A., BENSON, Robert Ashley Cooper, BENECH, Régis-Olivier
• Granted Patent: US 9,434,961 B2
• Time in Patent Office: Days
• US Class Current: 435/165
• CPC Class Codes: C12P 7/10 substrate containing cellulosic material
• CPC Class Codes: Y02E 50/10 Biofuels, e.g. bio-diesel

Abstract

A continuous process for the recovery of ethanol from hemicellulose and cellulose from lignocellulosic biomass. Yield of fermentable sugars can be maximized by continuous operation of the pre-treatment system and careful selection of pretreatment conditions including the addition of only small amounts of dilute mineral acid and low pressure. With this approach, the xylose component that is mainly present in its unfermentable oligomeric form in known pre-hydrolysis Kraft processes can be recovered more efficiently and as a monomer that can be fermented by xylose fermenting yeasts and bacteria. Due to the use of only dilute acids, there is a very low loss of glucose and xylose hence very low production of toxic chemicals (e.g. HMF, furfural) in the pretreatment step. The resulting overall fermentation efficiency of both hexose and pentose sugars is 90% of the theoretical maximum.

Claims

1. A continuous process for converting carbohydrates from lignocellulosic biomass to ethanol, comprising the steps of:

a) cutting the biomass to a prescribed size

b) steaming the sized biomass at atmospheric pressure

c) squeezing the steamed biomass for removing a first liquid stream and generating squeezed biomass

d) adding mineral or organic acid to the squeezed biomass in an amount of 0.5% to 0.9% w/w on an incoming biomass dry matter basis, to obtain acidified biomass;

e) adjusting a moisture content of the acidified biomass to 50% to 80% w/w water;

f) pretreating the acidified biomass in a continuous treatment vessel by steam treatment under pressure;

at a preselected pretreatment temperature for a preselected pretreatment time and at a preselected pretreatment pressure that depends on the feedstock used

g) continuously purging from the treatment vessel under pressure volatile components generated by the pressurized steam treatment and liquid condensate formed in the vessel and containing soluble biomass components;

h) submitting to explosive decompression the biomass exiting the continuous pre-treatment vessel prior to or after the washing step

i) extracting the pre-treated biomass with water to recover a cellulose rich solids stream and a liquid stream;

k) heating the liquid stream for simultaneously concentrating the liquid stream and removing inhibitory compounds by evaporation of volatile components, to obtain a concentrated liquid stream containing at most 6 gpl acetic acid, the evaporation being carried out at pressure and temperature conditions selected from the group consisting of;

(i) under vacuum at a temperature of 70°

C.-85°

C., and at 50 mbar to 250 mbar;

or under pressure of 5 psig to 35 psig, and combinations thereof;

l) optionally further hydrolyzing xylo-oligosaccharides in the liquid stream before, during or after the concentrating step.

m) hydrolyzing the solids stream with a mixture of cellulases and hemicellulases to obtain a hydrolyzed solids stream;

n) combining the hydrolyzed solids stream with the concentrated liquid stream to obtain a combined hydrolysate stream;

o) co-fermenting hexose and pentose sugars in the combined hydrolysate stream to ethanol; and

p) distilling the ethanol from the fermentation broth to recover ethanol and a de-ethanolized slurry.

2. The process of claim 1, wherein the moisture is adjusted in step e) 65% to 80% prior to continuous steam treatment.

3. The process of claim 1, wherein the moisture is adjusted in step e) 70% to 80% prior to continuous steam treatment.

4. The process of claim 1, wherein the mineral or organic acid is added to the biomass in step d) in an amount of 0.7% to 0.9% w/w.

5. The process of claim 1, wherein the mineral or organic acid is added to the biomass in step d) in an amount of 0.8% w/w.

6. The process of claim 1, wherein the biomass is steamed at atmospheric pressure for 10 to 60 min prior to subjecting the acidified biomass to steam treatment under pressure in a continuous treatment vessel.

7. The process of any one of claims 1 to 6, further comprising the step of drying the de-ethanolized slurry.

8. The process of claim 7, further comprising the step of recovering energy from the pretreatment and drying steps.

9. The process of claim 1, wherein the amount of mineral acid added to the squeezed biomass in step d) is adjusted to achieve a pH of 1.8 to 2.5 in the acidified biomass.

10. The process of claim 9, wherein the acidified biomass is adjusted at a pH of 2.0.

11. The process of claim 9, wherein the mineral acid is selected from the group consisting of sulfuric acid, phosphoric acid, and sulfur dioxide.

12. The process of claim 1, wherein the acidified biomass is pre-treated in step f) with steam in a continuous process vessel.

13. The process of claim 12, wherein the continuous pretreatment in step f) occurs at a pretreatment temperature between 130°

C. to 180°

C.

14. The process of claim 13, wherein the pretreatment temperature is between 150°

C. and 170°

C. and the pressure above 100 psig.

15. The process of claim 13, wherein the pretreatment temperature is 160°

C. for hardwoods and 150°

C. for agricultural residues.

16. The process of claim 1, wherein the pretreatment time is between 0.5 to 4 hours.

17. The process of claim 16, wherein the pretreatment time is 45 minutes to 3 hours.

18. The process of claim 16, wherein the pretreatment time is 45 minutes for hardwoods and 2 hours for agricultural residues.

19. The process of claim 1, wherein a severity index of the continuous pretreatment step f) is between 3.5 to 3.7.

20. The process of claim 19 wherein the severity index is between 3.5 to 3.6.

21. The process of claim 1, wherein the continuous extraction step i) comprises squeezing, water washing, or a combination thereof either before or after explosive decomposition or both.

22. The process of claim 21, wherein in the continuous extraction step i) the solid cellulose rich stream contains only between 4% to 8% w/w xylose from remaining Xylose, Xylooligosaccharides and Xylans .

23. The process of claim 19 or 20, wherein the continuous extraction step i) is carried out at a pressure between atmospheric pressure and the pre-treatment pressure.

24. The process of claim 1, wherein the liquid stream extracted in step i) is concentrated in step k) by evaporation to a concentration of soluble solids between 100 to 300 grams per litre.

25. The process of claim 24 wherein the extracted liquid stream is held at a temperature of 90°

C. to 125°

C. for 1 hour to 3 hours in step k).

26. The process of claim 1, wherein the liquid stream extracted in step k) is hydrolyzed in step I) prior to being mixed back with the solids stream.

27. The process of claim 24, wherein energy required for the concentrating step k) is derived from recovered energy from the continuous pre-treatment step f).

28. The process of claim 24, wherein vapors created in the concentrating step k) from the evaporation of the soluble solids are recovered.

29. The process of claim 1, wherein a consistency of the solids stream obtained in step i) is adjusted within a range of 10% to 25%, consistency.

30. The process of claim 29, wherein the solids stream is adjusted to between 15% and 25% consistency.

31. The process of claim 29, wherein the solids stream is adjusted to 17% consistency.

32. The process of claim 1, wherein the combined hydrolysate stream is co-fermented to ethanol with bacteria or yeast that converts both glucose and xylose to ethanol.

33. The process of claim 7 wherein the drying of the slurry takes place in a dryer for recovering heat as low pressure steam for use in other parts of the process such the distilling step p).

34. The process of claim 1, wherein step k) is carried out at atmospheric pressure and a temperature of 98°

C.

35. The process of claim 1, wherein step k) is carried out under a vacuum of 150 mba and a temperature of 80°

C.

36. The process of claim 1, wherein step k) is carried out at a pressure of 20 psig.