Ethanol production with dilute acid hydrolysis using partially dried lignocellulosics

• US 6,660,506 B2
• Filed: 02/07/2003
• Issued: 12/09/2003
• Est. Priority Date: 08/09/2000
• Status: Expired due to Term

• Current Assignee: Midwest Research Institute
• Original Assignee: Midwest Research Institute
• Inventors: Nguyen, Quang A., Tucker, Melvin P., Keller, Fred A.
• Primary Examiner(s): BRUNSMAN, DAVID M
• Application Number:
  US10/344,091
• Publication Number:
  US 20030199049A1
• Time in Patent Office: 305 Days
• Field of Search: 127/37, 435/165
• US Class Current: 435/165
• CPC Class Codes: C12P 2201/00 Pretreatment of cellulosic or lignocellulosic material for subsequent enzymatic treatment or hydrolysis
• CPC Class Codes: C12P 7/08 produced as by-product or from waste or cellulosic material substrate
• CPC Class Codes: C12P 7/10 substrate containing cellulosic material
• CPC Class Codes: C13K 1/02 obtained by saccharification of cellulosic materials manufacture of fodder A23K10/32
• CPC Class Codes: Y02E 50/10 Biofuels, e.g. bio-diesel
• CPC Class Codes: Y02E 50/30 Fuel from waste, e.g. synthetic alcohol or diesel

Abstract

A process of converting lignocellulosic biomass to ethanol, comprising hydrolyzing lignocellulosic materials by subjecting dried lignocellulosic material in a reactor to a catalyst comprised of a dilute solution of a strong acid and a metal salt to lower the activation energy (i.e., the temperature) of cellulose hydrolysis and ultimately obtain higher sugar yields.

Claims

1. In a process for converting lignocellulosic biomass to ethanol, the improvement of obtaining higher fermentable soluble sugar yields by drying acid impregnated biomass particles, comprising:

a) feeding a moist lignocellulosic biomass feedstock into a dilute strong acid impregnator to effect pH values below about 3 for a sufficient residence time to render it acid-soaked and draining the acid-soaked biomass to about 30% to about 35% by weight solids;

b) dewatering said acid-soaked biomass by drying or centrifugation in a manner so as to prevent densifying the biomass particles and obtain a solids content of about 40% to 60% wet weight basis;

c) subjecting said acid-impregnated biomass to a first-stage hydrolysis reactor at a temperature sufficient to commence hydrolysis and discharging the formed hydrolysate into a first flash tank at a temperature sufficient to hydrolyze most of the soluble oligosaccharides to monomeric sugars and flashing remaining hydrolysate to a second flash tank at a lower temperature than the first flash tank—

said second flash tank serving as a feed surge tank for a counter-current extractor;

d) washing the hydrolysate, recovering more than about 95% of the soluble sugars in the first-stage hydrolysate slurry by a counter-current extractor, and adjusting the pH of the extract to about 5;

e) subjecting remaining washed first stage pretreated solids to a second-stage acid and metal salt impregnator and dewatering by drying or centrifugation in a manner so as to prevent compaction of the biomass particles and obtain a solids content of about 40% to 60% wet weight basis;

f) subjecting said acid and metal salt-impregnated biomass to a second-stage hydrolysis reactor at a temperature of from about 190°

C. to about 240°

C. and discharging the formed hydrolysate into a flash tank at about 120°

C. to about 140°

C. to hydrolyze most of the remaining soluble oligosaccharides to monomeric sugars and flashing remaining hydrolysate to a second flash tank at a lower temperature than the first flash tank—

said second flash tank serving as a feed surge tank for second-stage fermentors;

g) cooling the pH-adjusted extract from said counter-current extractor, feeding the extract to a first-stage fermentor and air sparging the first-stage fermentor at a rate sufficient to promote enough yeast growth to compensate for loss through second-stage fermentors;

h) pH adjusting second-stage hydrolysate slurry to about 4.5, cooling the slurry and adding it into the top of the first fermentor of the second-stage fermentation train, pumping broth from the bottom of the first fermentor to the top of a second fermentor for a period sufficient for the carried over yeast to consume over about 95% of fermentable sugars; and

i) recovering ethanol.

2. The process of claim 1 wherein said reactor is a batch steam explosion reactor.

3. The process of claim 1 wherein said reactor is a continuous reactor.

4. The process of claim 1 wherein said lignocellulosic feedstock is selected from the group consisting of softwood, hardwood, agricultural residues, corn refining residues and grasses.

5. The process of claim 4 wherein said softwood is Douglas Fir, White Fir, Ponderosa Pine, Sitka spruce, and Hemlock.

6. The process of claim 4 wherein said municipal solid waste is construction lumber.

7. The process of claim 1 wherein said dilute(acid is selected from the group consisting of H₂SO₄, HCl, HNO₃, SO₂, and said metal salt catalyst is selected from the group consisting of ferrous sulfate, ferric sulfate, ferric chloride, aluminum sulfate, aluminum chloride, and magnesium sulfate.

8. The process of claim 7 wherein said acid is H₂SO₄ and said residence time is about 1 to about 60 minutes for first stage hydrolysis and about 1 to about 10 minutes for second stage hydrolysis.

9. The process of claim 8 wherein said temperature sufficient to commence hydrolysis is from about 130°

C. to about 220°

C. for first stage hydrolysis, and from about 190°

C. to about 240°

C. for second stage hydrolysis.

10. The process of claim 9 wherein said temperature sufficient to hydrolyze most of the soluble oligosaccharides to monomeric sugars in first flash tank is from about 120°

C. to about 140°

C., and the residence time of hydrolysate in the flash tank is from about 1 to about 3 hours.

11. The process of claim 7 wherein said acid is SO₂ and said residence time is about 1 to about 60 minutes.

12. The process of claim 11 wherein said temperature sufficient to commence hydrolysis is from about 130°

C. to about 220°

C. for first stage hydrolysis, and from about 190°

C. to about 240°

C. for second stage hydrolysis.

13. The process of claim 12 wherein said temperature sufficient to hydrolyze most of the soluble oligosaccharides to monomeric sugars in first flash tank is from about 120°

C. to about 140°

C., and the residence time of hydrolysate in the flash tank is from about 1 to about 3 hours.

14. The process of claim 7 wherein said acid is H₂SO₄, dewatering is by drying, and the acid concentration in the liquid in the biomass before subjecting to first stage or second stage hydrolysis is between about 0.3% to about 4.0% by weight, and the concentration of said metal salt is between about 0.2 to about 25.0 mmole/L.

15. The process of claim 7 wherein said acid is SO₂ and the feedstock is dewatered (if necessary) to 40% to 60% wet weight basis prior to SO₂ impregnation, and the acid concentration in the liquid in the biomass before subjecting to first stage or second stage hydrolysis is between about 0.3% to about 6.0% by weight.

16. The process of claim 1 wherein in step g) air sparging in the first fermentor of the first-stage fermentation train sufficient to promote yeast growth is about 0.05 wvm.

17. The process of claim 1 wherein in step g) air sparging sufficient to promote yeast growth is about 0.05 vvm.

18. The process of claim 1 wherein in step f) said lower temperature in said second flash tank is about 95°

C.

19. The process in claim 1 wherein in step h) said whole slurry from the second stage hydrolysis reactor is fermented in the second train of fermentors using yeasts from the first stage fermentors.

20. The process of claim 1 wherein in step a) gaseous SO₂ is used as the acid, the solid content of biomass is between about 40% to about 60% by weight, and the dewatering step b) is omitted.

21. The process of claim 1 wherein said drying is done using heated air, nitrogen, carbon dioxide, superheated steam or any combination thereof.

22. The process of claim 1 wherein in step d) said extract is recovered hydrolysate liquor.

23. The process of claim 1 wherein in step e) said pretreated solids are insoluble solids.