Carbon capture in fermentation
The invention provides processes and methods for utilization of carbon dioxide (CO 2 ) in the fermentation of a gaseous substrate comprising hydrogen (H 2 ) and CO 2 . In particular, the invention allows for the conversion of at least a portion of the CO 2 in the gaseous substrate to one or more products, such as ethanol, acetate, and/or 2,3-butanediol.
1. A fermentation process comprising:
a) passing a gaseous substrate stream comprising CO, H 2 , and CO 2 to a bioreactor comprising a carboxydotrophic bacterial culture in a liquid nutrient medium; wherein the ratio of H 2 :CO in the gaseous substrate stream is at least 3:1 and the ratio of CO 2 :CO in the gaseous substrate stream is between 1:1 and 4:1;
b) fermenting the culture wherein at least a portion of the CO 2 in the gaseous substrate stream is converted to at least one product selected from alcohols and acids; and
c) removing the at least one product from the bioreactor, the process characterized in that the specific uptake of H 2 by the culture exceeds specific uptake of CO by the culture and the amount of CO 2 consumed by the culture exceeds or is equal to the amount of CO 2 produced by the culture.
2. The process of claim 1 , wherein the gaseous substrate comprises 30-90% H 2 .
3. The process of claim 1 , wherein the at least one product comprises one or more of ethanol, acetate, and 2,3-butanediol.
4. The process of claim 1 , wherein the bacterial culture comprises one or more of Clostridium, Moorella, Oxobacter, Peptostreptococcus, Acetobacterium, Eubacterium , or Butyribacterium.
5. The process of claim 4 , wherein the bacterial culture comprises Clostridium autoethanogenum or Clostridium ljungdahlii.
6. The process of claim 5 , wherein the bacterial culture comprises Clostridium autoethanogenum deposited under DSMZ accession number DSM23693 or bacteria derived therefrom.
7. The process of claim 1 , wherein specific uptake of H 2 :CO by the culture is at least 1.4:1.
8. The process of claim 1 , wherein specific uptake of CO 2 by the culture is at least 500 mmol/L/day of CO 2 .
9. The process of claim 1 , wherein the amount of CO 2 exiting the reactor is at least 5% lower than an amount of CO 2 entering the bioreactor.
10. The process of claim 1 , wherein at least 5% of carbon in the at least one product is derived from CO 2 .
11. The process of claim 1 , where specific uptake H 2 :CO by the culture is at least 2:1.
12. The process of claim 1 , wherein the ratio of H 2 :CO in the gaseous substrate is at least 5:1.
13. The process of claim 1 , wherein the gaseous substrate is a pressure swing adsorption (PSA) tail gas.
14. The process of claim 1 , further comprising monitoring a mass transfer rate of the gaseous substrate.
15. The process of claim 14 , wherein the mass transfer rate of the gaseous substrate is controlled by controlling the partial pressure of the gaseous substrate passed to the bioreactor.
16. The process of claim 1 , wherein fermenting the culture is performed at a pressure higher than ambient pressure.