TH40952B - Methods for increasing ethanol production from microbial fermentation. - Google Patents

Abstract

DC60 is a stable, continuous method for ethanol production from anaerobic bacterial fermentation of a gaseous substrate containing at least one reducing gas. The bioreactor utilizes anaerobic and acetogenic bacteria in a liquid nutrient medium. The gaseous substrate is supplied to the bioreactor, and controlled bacterial growth is achieved by reducing the redox potential or increasing the NAD(P)H to NAD(P) ratio in the liquid fermentation medium. After the bacteria reach a steady state and a stable cell concentration in the bioreactor, the free acetic acid concentration is maintained at less than 5 g/L. This method allows for ethanol production in the liquid fermentation medium in the bioreactor at efficiencies greater than 10 g/L per day, producing both ethanol and other ethanol. And acetate in an ethanol-to-acetate ratio ranging from 1:1 to 20:1. A stable, continuous method for the production of ethanol from anaerobic fermentation by bacteria of a gaseous substrate containing at least one reducing gas related to culture in the bioreactor. Anaerobic biofermentation, acetogenic bacteria in a liquid nutrient medium. Supply of a gaseous substrate to the bioreactor and controlled use of bacteria in the bioreactor by reducing the redox potential or increasing the NAD(P)H to NAD(P) ratio in the liquid medium for fermentation. After the bacteria reach a steady state and a stable cell concentration in the bioreactor, maintain the free acetic acid concentration in the bioreactor at less than 5 g/L of free acid. This method allows for the production of ethanol in the liquid medium for fermentation in the bioreactor at efficiencies greater than 10 g/L per day, producing both ethanol and acetate. And the acetate content in the ethanol-to-acetate ratio ranges from 1:1 to 20:1.

Claims (22)

1. A continuous method for ethanol production from anaerobic bacterial fermentation of a gaseous substrate containing carbon monoxide is used. This method involves: culturing the acetogenic bacteria C. ljungdahlii in an anaerobic bioreactor in a continuously fed liquid nutrient medium to provide the liquid medium for fermentation; supplying the bioreactor with the gaseous substrate containing carbon monoxide (CO); maintaining the specific rate of CO2 consumption in the bioreactor at 0.3 to 2 mmol/g dry weight of bacterial cells/minute in the liquid medium for fermentation; and finally, ethanol production is carried out after the bacteria achieve a stable cell concentration in the bioreactor. The aforementioned free acetic acid concentration in the biofertilizer is less than 5 g/L of free acid. Ethanol production in the liquid fermentation medium has an efficiency greater than 10 g/L per day, and the production of both ethanol and acetate in the liquid fermentation medium is achieved at an ethanol-to-acetate ratio ranging from 1:1 to 20:1. 2. The method under claim 1, in which the aforementioned biofermentation reactor consists of a growth reactor which feeds the aforementioned liquid fermentation medium to a second biofermentation reactor which produces the majority of the aforementioned ethanol. 3. The methods under claim 1, which include the following steps: separation of the said fermentation liquid from the said biofermentation reactor, distillation of ethanol from the said liquid, and purification and recovery of the said ethanol. 4. The method under claim 3, which is further comprised of the reuse of the acetate-containing water from the aforementioned distillation step back to the aforementioned bioreactor. 5. The method pursuant to claim 1, which selected the aforementioned Clostridium ljungdahlii from the strains comprising PETC, ERI-2, O-52 and C-01. 6. The method under claim 1 which selects the aforementioned gaseous substrate from a group consisting of (a) carbon monoxide, (b) carbon monoxide and hydrogen, (c) carbon monoxide, carbon dioxide and hydrogen, 7. The method under claim 1 in which the aforementioned gaseous substrate is further incorporated with nitrogen or methane. 8. Method according to claim 1, where the pH is 4.5 to 5.5. 9. The method under claim 1, which includes the removal of the aforementioned bacteria from the aforementioned biofermentation equipment. 10. The method under claim 1, in which the specific rate of CO2 utilization is stated as 0.5 to 1.5 mmol/g dry bacterial cells in the stated bioreactor/minute. 11. The method pursuant to claim 1, in which the substrate is the aforementioned gas, consists of carbon monoxide, carbon dioxide, and hydrogen. 12. The procedure under claim 1, which involves feeding a certain amount of calcium pantothenate into the bioreactor in the range of 2 to 50 mcg of calcium pantothenate/g of dry bacterial cells produced in the aforementioned bioreactor. 13. The method pursuant to claim 12, in which the amount of calcium pantothenate mentioned is from 2 to 25 micrograms of calcium pantothenate/gram of dry cells of the produced bacteria. 14. The method under claim 12, in which the aforementioned gaseous substrate is further incorporated with hydrogen. 15. The method under claim 1, which includes the feeding into the aforementioned biofermentation reactor of cobalt in an amount of 5 to 100 mcg cobalt/g dry cell of bacteria produced in the aforementioned biofermentation reactor. 16. The method pursuant to claim 15, whereby the aforementioned amount of cobalt is from 20 to 50 micrograms of cobalt/gram of dry cells of the produced bacteria. 17. The method under claim 15, which includes further steps to prevent the alkleation of the aforementioned bacteria in the aforementioned bioreactor from the aforementioned amount of cobalt, by maintaining a constant cobalt concentration. 18. The method under claim 1, where the pH is greater than 4.5. 19. The method pursuant to claim 12, in which the amount of calcium pantothenate mentioned is from 10 to 30 micrograms of calcium pantothenate/gram of dry cells of the produced bacteria. 20. The method pursuant to claim 12, in which the amount of calcium pantothenate mentioned is from 10 to 50 micrograms of calcium pantothenate/gram of dry bacterial cells produced. 21. The method under claim 1, in which the specific rate of CO2 consumption is 0.5 to 1.5 mmol/g dry bacterial cells in the aforementioned bioreactor/minute, and calcium pantothenate is fed into the aforementioned bioreactor at a rate of 2 to 50 μg/g dry bacterial cells produced in the aforementioned bioreactor. 22. The method under claim 1, in which the specific rate of CO2 consumption as described is 0.5 to 1.5 mmol/g dry bacterial cells in the described bioreactor/minute, and calcium pantothenate is fed into the described bioreactor at a rate of 10 to 30 µm/g dry bacterial cells produced in the described bioreactor.