Microbial fermentation of gaseous substrates to produce alcohols
View Patent ↗The present invention relates to methods for increasing the efficiency of anaerobic fermentation processes (1) that produce acetate as a by-product in addition to a desired product, and (2) that can utilize hydrogen and/or carbon dioxide in the fermentation. The method comprises the steps of converting acetate produced by the fermentation process into hydrogen gas and carbon dioxide gas, and utilizing hydrogen gas and/or carbon dioxide gas obtained from the acetate conversion in the anaerobic fermentation process. In particular aspects, the invention relates to processes of producing alcohols, particularly ethanol.
1. A process for producing one or more alcohols from a gaseous substrate comprising CO, the process comprising the following steps:
(a) in a bioreactor, anaerobically fermenting the gaseous substrate to produce one or more alcohols and acetate;
(b) converting acetate obtained from step (a) into H 2 and CO 2 gases; and
(c) using H 2 and/or CO 2 obtained from step (b) as a co-substrate in the fermentation process.
2. A process according to claim 1 , wherein the one or more alcohols comprises ethanol.
3. A process according to claim 1 , wherein the fermentation is carried out by one or more strains of bacteria selected from Clostridium, Moorella and Carboxydothermus.
4. A process according to claim 1 , wherein the fermentation is carried out by Clostridium autoethanogenum.
5. A process according to claim 1 , wherein acetate is removed from the bioreactor before the acetate is converted into H 2 and CO 2 , and step (c) includes introducing either H 2 or a mixture of CO 2 and H 2 obtained from the acetate conversion into the bioreactor during the fermentation process.
6. A process according to claim 1 , wherein step (a) is carried out in a first bioreactor and step (b) is carried out in a second bioreactor.
7. A process according to claim 1 , wherein the conversion of acetate to H 2 and CO 2 is carried out by one or more strains of bacteria selected from Clostridium and Geobacter.
8. A process according to claim 1 , wherein the conversion of acetate to H 2 and CO 2 is carried out by Geobacter sulfurreducens.
9. A process according to claim 1 , wherein the gaseous substrate comprises a gas obtained as the result of an industrial process.
10. A process according to claim 1 , wherein the gaseous substrate comprises a waste gas obtained from a steel mill.
11. A process according to claim 1 , wherein acetate and the one or more alcohols are both recovered from the bioreactor before converting the acetate into H 2 and CO 2 .
12. A process according to claim 1 , the process further comprising, before step (a),
capturing a gaseous substrate comprising CO produced as a result of an industrial process, before the gaseous substrate is released into the atmosphere.
13. The process of claim 4 , wherein the fermentation is carried out by Clostridium autoethanogenum having all of the identifying characteristics of DSMZ deposit number DSMZ 10061.
14. The process of claim 1 , wherein converting acetate into H 2 and CO 2 is carried out by microbial oxidation.
15. The process of claim 1 , wherein the gaseous substrate comprises at least 70% CO and less than 15% H 2 by volume.