Carbon Capture in Fermentation
The present invention provides methods and systems for improving carbon capture from a gas stream comprising methane. Further, the invention provides a method for the production of at least one alcohol, and at least one acid from a gas stream comprising methane, the method comprising reforming a gas stream comprising methane to provide a syngas, in a first bioreactor fermenting the syngas to produce at least one acid and a tail gas comprising CO 2 and H 2 , and, in a second bioreactor fermenting the tail gas to produce at least one acid.
1 . A method for producing at least one alcohol and at least one acid from a gas stream comprising methane, the method comprising;
a) Flowing the gas stream to a reforming module and reforming the gas stream to produce a syngas substrate comprising CO, CO 2 and H 2 ;
b) Flowing the syngas substrate to a first bioreactor, the first bioreactor comprising a liquid nutrient media comprising a culture of one or more carboxydotrophic micro-organisms;
c) Fermenting the syngas substrate to produce at least one alcohol and a tail gas stream comprising H 2 and CO 2 ;
d) Flowing the tail gas stream to a second bioreactor, the second bioreactor comprising a liquid nutrient medium comprising a culture of one or more microorganism; and
e) Fermenting the tail gas stream to produce one or more acids;
wherein the composition of the tail gas stream exiting the first bioreactor is controlled at a desired ratio of H 2 :CO 2 by measuring the amount of CO and H 2 consumed by the one or more carboxydotrophic microorganism and adjusting the syngas substrate in response to changes in the amount of CO and H 2 consumed.
2 . The method of claim 1 wherein the reforming module is selected from the group comprising: dry reforming, steam reforming, partial oxidation and auto thermal reforming.
3 . The method of claim 1 wherein the syngas substrate provided to the first bioreactor comprise CO, CO 2 and H 2 at a composition such that the tail gas stream exiting the first bioreactor comprises H 2 and CO 2 at a ratio of between 1:2 and 3:1.
4 . The method of claim 3 wherein additional H 2 and/or CO 2 is added to the tail gas exiting the first bioreactor to provide a H 2 and CO 2 substrate having a H 2 :CO 2 ratio of 2:1.
5 . The method of claim 1 wherein the syngas substrate provided to the first bioreactor comprises H 2 and CO at a ratio of between 0.5:1 and 5:1.
6 . The method of claim 5 wherein the syngas substrate provided to the first bioreactor comprises H 2 and CO at a ratio of 0.7:1 to 1.9:1.
7 . The method of claim 1 where the gas stream is a natural gas stream.
8 . The method of claim 1 wherein CO 2 and/or H 2 is blended with the tail gas exiting the bioreactor to provide a substrate having a H 2 :CO 2 ratio of 2:1.
9 . The method of claim 1 wherein at least a portion of CO 2 and/or H 2 is separated from the tail gas exiting the first bioreactor to provide a substrate having a H 2 :CO 2 ratio of 2:1.
10 . The method of claim 1 wherein the syngas substrate exiting the gas reformer is sent to a water gas shift module to increase the hydrogen composition of the syngas substrate.
11 . The method of claim 1 wherein the tail gas exiting the first bioreactor is sent to a water gas shift module to increase the hydrogen composition of the tail gas stream.
12 . The method of claim 1 wherein at least a portion of hydrogen in the syngas substrate is separated from the syngas stream to provide a hydrogen depleted syngas stream and a separated hydrogen stream.
13 . The method of claim 12 wherein at least a portion of the separated hydrogen stream is blended with the tail gas stream exiting the first bioreactor to increase the hydrogen composition of the tail gas stream.
14 . The method of claim 1 wherein the at least one alcohol produced in the first bioreactor is ethanol.
15 . The method of claim 1 wherein the one or more carboxydotrophic microorganisms provided in the first bioreactor is selected from the group consisting of Clostridium autoethanogenum, Clostridium ljungdahlii, Clostridium ragsdalei and Clostridium carboxydivorans.
16 . The method of claim 1 wherein the at least one acid produced in the second bioreactor is acetic acid.
17 . The method of claim 1 wherein the carboxydotrophic micro-organism in the second bioreactor is Acetobacterium woodii.