Process to treat a carbon dioxide comprising gas
The invention is directed to a process to convert carbon dioxide to methane by contacting an aqueous solution comprising dissolved carbon dioxide with an electron charged packed bed comprising of a carrier, suitably activated carbon granules, and a biofilm of microorganisms under anaerobic conditions, wherein more than 90 mol % of the dissolved carbon dioxide in the aqueous solution is present as a bicarbonate ion and/or as a carbonate ion.
1 . A process to convert carbon dioxide to methane by contacting an aqueous solution comprising dissolved carbon dioxide with an electron charged packed bed comprising of a carrier and a biofilm of microorganisms under anaerobic conditions, wherein the aqueous solution comprises:
a) between 0.3 and 4 M sodium cations, or
b) between 0.3 and 4 M sodium and potassium cations,
such that more than 90 mol % of the dissolved carbon dioxide in the aqueous solution is present as a bicarbonate ion and/or as a carbonate ion.
2 . The process according to claim 1 , wherein the carrier is activated carbon granules or activated biochar granules.
3 . The process according to claim 1 , wherein no power is supplied to the electron charged packed bed.
4 . The process according to claim 3 , wherein the electron charged packed bed is part of a biocathode in a bioelectrochemical system further comprising an anode, an ion exchange membrane, and a cathode;
wherein the packed bed is charged by applying a potential to the bioelectrochemical system resulting in a current between biocathode and anode for a certain time.
5 . The process according to claim 4 , wherein the aqueous solution as present at the anode is referred to as the anolyte and the aqueous solution as present at the cathode is referred to as the catholyte and wherein a recirculation is performed where part of the catholyte is fed to the anode to become part of the anolyte and part of the anolyte is fed to the cathode to become part of the catholyte.
6 . The process according to claim 4 , wherein the process is performed in more than one bioelectrochemical systems, each system comprising of the biocathode and an anode; and
wherein in one or more bioelectrochemical systems the process is performed while no power is supplied to the electron charged packed bed of these one or more bioelectrochemical systems; and
wherein power is supplied to the packed bed of one or more other bioelectrochemical system of the more than one bioelectrochemical systems such that these packed beds are charged with electrons while the process is not performed.
7 . The process according to claim 4 , wherein the packed bed is charged by applying a cathode potential to the cathode electrode of between −0.50 and −0.60V vs. Ag/AgCl (3M KCl) or by applying a current density to the cathode electrode of between 5 and 200 A/m 2 .
8 . The process according to claim 4 , wherein the anode is a titanium mesh coated with iridium and/or tantalum.
9 . The process according to claim 4 , wherein the power supply is generated by a chemical reaction at the anode.
10 . The process according to claim 4 , wherein the carrier and a biofilm of microorganisms is obtained in an activation step which activation step is performed at a pH greater than 8 and under anaerobic conditions and by supplying an amount of current at a cathode potential which is more positive than the theoretical hydrogen evolution potential at −0.61 V vs Ag/AgCl (3M KCl) at a pH of 7 to the packed bed comprising of carrier and biofilm of microorganisms; and
wherein the microorganisms are a mixed culture microorganisms from a sludge of an anaerobic wastewater treatment plant.
11 . The process according to claim 1 , wherein the electron charged packed bed is part of a biocathode in a bioelectrochemical system further comprising an anode; and
wherein at one moment in time the process is performed when the packed bed is charged by applying a potential to the bioelectrochemical system resulting in a current between biocathode and anode; and
wherein at another moment in time the process is performed when no power is supplied to the electron charged packed bed.
12 . The process according to claim 11 , wherein the process is performed for between 0.03 and 12 hours when no power is supplied to the electron charged packed.
13 . The process according to claim 11 , wherein the power supply is electricity generated by solar and/or wind.
14 . The process according to claim 1 , wherein the packed bed is a packed bed of activated carbon granules having an activated surface area of between 500 and 1500 m 2 /g; and
wherein the microorganisms are present as a biofilm on the surface of the activated surface area.
15 . The process according to claim 1 , wherein the pH of the aqueous solution is above 7.7.
16 . The process according to claim 15 , wherein the pH of the aqueous solution is above 8.
17 . The process according to claim 1 , wherein the aqueous solution comprises between 0.5 and 1.5 M sodium cations or between 0.5 and 1.5 M sodium and potassium cations.
18 . The process according to claim 1 , wherein the aqueous solution comprising dissolved carbon dioxide is obtained by contacting a gas comprising carbon dioxide with an aqueous solution having a pH of above 8 to obtain an aqueous solution wherein a major part of the dissolved carbon dioxide is present as a bicarbonate ion and/or as a carbonate ion.
19 . The process according to claim 18 , wherein the gas comprising carbon dioxide is counter currently contacted with the aqueous solution having a pH of above 8 and comprising dissolved methane as obtained a process comprising:
contacting an aqueous solution comprising dissolved carbon dioxide with an electron charged packed bed comprising of a carrier and a biofilm of microorganisms under anaerobic conditions,
wherein more than 90 mol % of the dissolved carbon dioxide in the aqueous solution is present as a bicarbonate ion and/or as a carbonate ion; and
wherein the gas strips the methane from the aqueous solution to obtain a gas comprising methane.