Methods for increasing the production of ethanol from microbial fermentation

• US 20030211585A1
• Filed: 03/11/2003
• Published: 11/13/2003
• Est. Priority Date: 07/25/2000
• Status: Active Grant

• Current Assignee: Jupeng Bio (HK) Limited
• Original Assignee: Bioengineering Resources, Inc.
• Inventors: Ko, Ching-Whan, Basu, Rahul, Wikstrom, Carl V., Gaddy, James L., Arora, Dinesh K., Clausen, Edgar C., Phillips, John Randall
• Granted Patent: US 7,285,402 B2
• Time in Patent Office: Days
• US Class Current: 435/161
• CPC Class Codes: C12M 21/04 for producing gas, e.g. biogas digesters for manure with production of biogas A01C3/028, biological treatment of water, waste water or sewage C02F3/00, C02F11/02, preparation of natural gas or syngas C10L3/06, C10L3/10
• CPC Class Codes: C12M 21/12 for producing fuels or solvents C12M21/04 takes precedence; liquid carbonaceous fuels C10L1/00, solid fuels C10L5/00
• CPC Class Codes: C12M 29/02 Percolation
• CPC Class Codes: C12M 29/18 External loop; Means for reintroduction of fermented biomass or liquid percolate loop type reactors for chemical or physical processes B01J19/2435
• CPC Class Codes: C12M 43/02 Bioreactors or fermenters combined with devices for liquid fuel extraction; Biorefineries
• CPC Class Codes: C12P 7/065 with microorganisms other than yeasts
• 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 stable continuous method for producing ethanol from the anaerobic bacterial fermentation of a gaseous substrate containing at least one reducing gas involves culturing a fermentation bioreactor anaerobic, acetogenic bacteria in a liquid nutrient medium; supplying the gaseous substrate to the bioreactor; and manipulating the bacteria in the bioreactor by reducing the redox potential, or increasing the NAD(P)H TO NAD(P) ratio, in the fermentation broth after the bacteria achieves a steady state and stable cell concentration in the bioreactor. The free acetic acid concentration in the bioreactor is maintained at less than 5 g/L free acid. This method allows ethanol to be produced in the fermentation broth in the bioreactor at a productivity greater than 10 g/L per day. Both ethanol and acetate are produced in a ratio of ethanol to acetate ranging from 1:1 to 20:1.

Claims

1. A stable continuous method for producing ethanol from the anaerobic bacterial fermentation of a gaseous substrate, the method comprising:

culturing in a fermentation bioreactor anaerobic, acetogenic bacteria in a liquid nutrient medium and supplying to said bioreactor said gaseous substrate comprising at least one reducing gas selected from the group consisting of carbon monoxide and hydrogen; and

manipulating said bacteria in said bioreactor by reducing the redox potential, or increasing the NAD(P)H TO NAD(P) ratio, in the fermentation broth after said bacteria achieves a stable cell concentration in said bioreactor, wherein said free acetic acid concentration in said bioreactor is less than 5 g/L free acid,

said culturing and manipulating steps causing said bacteria in said bioreactor to produce ethanol in a fermentation broth at a productivity greater than 10 g/L per day and wherein both ethanol and acetate are produced in said fermentation broth in a ratio of ethanol to acetate ranging from 1;

1 to 20;

1.

2. The method according to claim 1, wherein said fermentation bioreactor comprises a growth reactor which feeds said fermentation broth to a second fermentation bioreactor in which most of said ethanol is produced.

3. The method according to claim 1, further comprising the steps of removing said fermentation broth from said bioreactor, distilling ethanol from said broth and recovering said ethanol.

4. The method according to claim 3, further comprising the steps of recycling water containing acetate from said distilling step back to the bioreactor.

5. The method according to claim 1, wherein said bacteria is selected from the group consisting of:

Acetobacterium woodii, Butyribacterium methylotrophicum, Clostridium aceticum, C. acetobutylicium, C. thermoaceticum, Eubacterium limosum, Clostridium ljungdahlii, and Peptostreptococcus productus.

6. The method according to claim 5, wherein said Clostridium ljungdahlii is selected from the strains consisting of PETC, ERI2, O-52 and C-01.

7. The method according to claim 1, wherein said gaseous substrate is selected from the group consisting of (a) carbon monoxide, (b) carbon monoxide and hydrogen, (c) carbon dioxide and hydrogen, and (d) carbon monoxide, carbon dioxide and hydrogen.

8. The method according to claim 7, wherein said substrate additionally comprises nitrogen or methane.

9. The method according to claim 1, wherein said manipulating step further comprises altering at least one parameter selected from the group consisting of nutrient medium contents, nutrient feed rate, aqueous feed rate, operating pressure, operating pH, gaseous substrate contents, gas feed rate, fermentation broth agitation rate, product inhibition step, cell density, substrate inhibition and combinations thereof.

10. The method according to claim 9, wherein said manipulating step comprises raising the pH of said culture above 4.5.

11. The method according to claim 9, wherein said manipulating step comprises periodically purging bacterial cells from said bioreactor to a cell concentration less than said stable concentration that utilizes all reducing gas or nutrient substrates in said bioreactor.

12. The method according to claim 9, comprising increasing the aqueous feed rate when the free acetic acid portion of the acetate present in the fermentation broth exceeds 2 g/L, thereby inhibiting any unwanted increase in the concentration of said free acetic acid.

13. The method according to claim 9, comprising reducing said gaseous substrate feed rate to eliminate excess carbon monoxide, to relieve substrate inhibition and maintain said productivity.

14. The method according to claim 9, wherein said agitation rate is reduced to eliminate excess carbon monoxide, to relieve substrate inhibition and maintain said productivity.

15. The method according to claim 9, wherein said manipulating step comprises supplying to said bioreactor said gaseous substrate comprising the reducing gas carbon monoxide at a rate of from 0.3 to 2 mmol CO/gram of dry cell of bacteria in said bioreactor/minute.

16. The method according to claim 15, wherein said the amount of CO present in said bioreactor is greater than the amount required to maintain said bacteria at a stable bacterial concentration that would fully utilize the CO provided.

17. The method according to claim 15, wherein said the amount of CO present in said bioreactor maintains ethanol production in preference to acetate production.

18. The method according to claim 15, wherein said rate is in the range of 0.5 to 1.5 mmol CO/gram of dry cell of bacteria in said bioreactor/minute.

19. The method according to claim 15, wherein said gaseous substrate further comprises an excess of hydrogen reducing gas relative to said carbon monoxide, wherein said excess hydrogen causes said bacteria to produce a high ethanol to acetate ratio in said fermentation broth.

20. The method according to claim 9, wherein said manipulating step comprises feeding into said fermentation bioreactor said nutrient medium comprising an amount of calcium pantothenate in a range of from 0.5 to 50 μ

g/grams of dry cell of bacteria produced in said bioreactor.

21. The method according to claim 20, wherein said amount of calcium pantothenate is less than required to maintain said bacteria at a stable bacterial concentration that would fully utilize the calcium pantothenate provided.

22. The method according to claim 20, wherein said amount of calcium pantothenate maintains ethanol production in preference to acetate production.

23. The method according to claim 20, wherein said amount is from 1 to 25 μ

g calcium pantothenate/grams of dry cell of bacteria produced.

24. The method according to claim 20, wherein said amount is from 2 to 25 μ

g calcium pantothenate/grains of dry cell of bacteria produced.

25. The method according to claim 20, further comprising the step of preventing acclimation of said bacteria in said bioreactor to said calcium pantothenate amount by maintaining a constant calcium pantothenate concentration and adjusting the parameters selected from the group consisting of gas rate, liquid rate, agitation rate and hydrogen gas partial pressure.

26. The method according to claim 20, further comprising supplying excess hydrogen reducing gas to said bioreactor prior to providing said amount of calcium pantothenate.

27. The method according to claim 9, wherein said manipulating step comprises feeding into said fermentation bioreactor said nutrient medium comprising an amount of cobalt in a range of from 5 to 100 μ

g cobalt/grams of dry cell of bacteria produced in said bioreactor.

28. The method according to claim 27, wherein said amount of cobalt is less than required to maintain said bacteria at a stable bacterial concentration that would fully utilize the cobalt provided.

29. The method according to claim 27, wherein said amount of cobalt maintains ethanol production in preference to acetate

30. The method according to claim 27, wherein said amount is from 20 to 50 μ

g calcium pantothenate/grams of dry cell of bacteria produced.

31. The method according to claim 27, further comprising the step of preventing acclimation of said bacteria in said bioreactor to said amount of cobalt by maintaining a constant cobalt concentration and adjusting the parameters selected from the group consisting of gas rate, liquid rate, agitation rate and hydrogen gas partial pressure.