Patent Application
20240301568
This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2023-034938, filed on Mar. 7, 2023; the entire contents of which are incorporated herein by reference.
Embodiments relate to a carbon dioxide conversion apparatus and a carbon dioxide conversion method.
Fossil fuels such as natural gas, coal, and petroleum is combusted to generate carbon dioxide (CO2) which is considered the main factor behind global warming due to a greenhouse effect, and thus the fossil fuels should be used less. Know example methods of reducing the carbon dioxide are performed by removing carbon dioxide from an exhaust gas from a carbon dioxide generation source to reduce an amount of the carbon dioxide emitted to the air and then chemically synthesizing a product from the carbon dioxide removed from the exhaust. An example method of the know example methods is performed by reducing carbon dioxide to produce carbon monoxide (CO), and synthesizing an organic substance from the produced carbon monoxide (CO) and hydrogen (H2), and the example method has developed.
The gas produced in a cathode chamber, which is included in gases produced in a carbon dioxide electrolysis device, contains CO, hydrogen (H2) and unreacted CO2, the CO being produced by reducing CO2, the H2 being produced by co-electrolysis of H2O and CO2. The gas produced in an anode chamber contains oxygen (O2) and by-produced CO2, the O2 being produced by oxidizing a carbonate ion (CO32−) and a hydroxide ion (OH−) which are a part of the reduction products produced by reducing CO2, the by-produced CO2 being secondarily produced by the electrolysis. Thus, the products through CO2 electrolysis contain main products such as CO, H2, and O2, and the unreacted CO2 and the by-produced CO2. Emitting a purge gas as it is after purifying and capturing active ingredients such as CO and H2 from such gases produced in the CO2 electrolysis device prevents a reduction in the emission of CO2 into the air, and lowers effective usability of CO2. Therefore, the reduction in the emission of CO2 in the air and an increase in the effective usability of CO2 are required.
Hereinafter, a carbon dioxide conversion apparatus of an embodiment will be described with reference to the drawings. In each embodiment presented below, substantially the same constituent parts are denoted by the same reference signs, and a description thereof may be partially omitted. The drawings are schematic, and the relation of the thickness and planar dimension, a thickness ratio among the parts, and so on may be different from actual ones. Note that a symbol of “˜” in the following description indicates a range between an upper limit value and a lower limit value of respective numerical values. In this case, the range of the numerical values includes the upper limit value and the lower limit value.
A carbon dioxide conversion apparatus of an embodiment includes: a carbon dioxide supply part configured to capture carbon dioxide from a carbon dioxide containing gas and supply the carbon dioxide; a carbon dioxide electrolysis part that includes: a cathode chamber configured to receive the carbon dioxide from the carbon dioxide supply part and reduce the carbon dioxide to produce carbon monoxide; and an anode chamber configured to oxidize an oxidizable substance to produce oxygen and carbon dioxide; a carbon dioxide capture part configured to separate and capture the carbon dioxide from an oxygen-carbon dioxide containing gas to be produced in the anode chamber; a carbon monoxide purification part configured to purify the carbon monoxide in a carbon monoxide containing gas to be produced in the cathode chamber; and an oxidation part configured to perform a reaction between a reducing gas and a carbon dioxide containing gas, the reducing gas being discharged from the carbon monoxide purification part and containing a residual carbon monoxide, and the carbon dioxide containing gas being separated and captured in the carbon dioxide capture part and containing a residual oxygen.
The CO2 supply part 2 is configured to separate and capture CO2 from an emission gas G1 containing CO2 (CO2 containing gas) emitted from a thermal power plant, a waste incineration plant, a steel plant, and the like, and supply a CO2 gas G2 having an increased CO2 concentration to the CO2 electrolysis part 3. The CO2 supply part 2 can be constituted by applying, for example, a chemical absorption method of using a chemical absorption solution such as an amine aqueous solution, a physical absorption method of using a physical absorption solution such as methanol or a polyethylene glycol solution, a solid absorption method of using a solid absorbent such as an amine compound, a membrane separation method of using a CO2 separation membrane, a physical adsorption method of using an inorganic substance such as zeolite as an adsorbent, a PSA (Pressure Swing Adsorption method), a TSA (Thermal Swing Adsorption method), or the like is applied. For example, the chemical absorption method and a chemical absorber which use the amine aqueous solution can supply the emission gas G1 to an absorption tower in which the amine aqueous solution is sprayed, and heat the amine aqueous solution absorbing CO2 in a regeneration tower to capture CO2 emitted from the amine aqueous solution.
The capture method and device of CO2 applied to the CO2 supply part 2 are not particularly limited, and various methods and devices which allow the capture of CO2 from the emission gas (CO2 containing gas) G1 can be applied. The CO2 supply part 2 is connected to a cathode chamber (reducing part) 8 of the CO2 electrolysis part 3 via a gas mixer 7. The CO2 supply part 2 is configured to supply a CO2 gas G2 to the cathode chamber 8 via the gas mixer 7.
The CO2 electrolysis part 3 is a CO2 electrolysis device having an electrolysis cell, and includes the cathode chamber (reducing part) 8 and an anode chamber (oxidizing part) 9. The cathode chamber 8 includes a reduction electrode (cathode), the anode chamber 9 includes an oxidation electrode (anode), and an electrolytic solution is made to flow through at least the anode chamber 9. A CO2 gas is made to flow through the cathode chamber 8. Examples of the electrolytic solution supplied into the anode chamber 9, include a solution using water (H2O), and an aqueous solution containing an optional electrolyte. Examples of the aqueous solution containing the electrolyte, include an aqueous solution containing at least one ion selected from a phosphate ion (PO42−), a borate ion (BO33−), a sodium ion (Na+), a potassium ion (K+), a calcium ion (Ca2+), a lithium ion (Li+), a cesium ion (Cs+), a magnesium ion (Mg2+), a chloride ion (Cl−), a hydrogen carbonate ion (HCO3−), a carbonate ion (CO32−), and a hydroxide ion (OH−). Examples of the electrolytic solution include an alkaline aqueous solution containing at least one dissolved compound selected from KOH, KHCO3, and K2CO3.
The cathode chamber 8 can receives the CO2 gas G2 captured in the CO2 supply part 2. The cathode chamber 8 has a gas flow path facing a reduction electrode which is not illustrated in
Each of the reduction electrode and the oxidation electrode of the CO2 electrolysis part 3 are connected to a direct-current power supply which is not illustrated in
The carbonate ion (CO32−) produced in the cathode chamber 8 moves to the anode chamber 9 via the diaphragm 10. The anode chamber 9 can perform an oxidation reaction of the carbonate ion (CO32−) produced in the cathode chamber 8 and moved via the diaphragm 10 to produce CO2 and O2, as presented in the following formula (2).
Moreover, the cathode chamber 8 can perform an electrolytic reaction of H2O in the electrolytic solution to produce hydrogen (H2) and hydroxide ions (OH−), as presented in the following formula (3).
The hydroxide ions (OH−) produced in the cathode chamber 8 move to the anode chamber 9 via the diaphragm 10. Then, the anode chamber 9 can produce water (H2O) and oxygen (O2), as presented in the following formula (4).
Further, The anode chamber 9 can electrolyze water (H2O) in the electrolytic solution to produce oxygen (O2) and hydrogen ions (H+), as presented in the following formula (5).
The produced hydrogen ions (H+) move to the cathode chamber 8 via the diaphragm 10. The hydrogen ions (H+) reach the cathode chamber 8, and electrons (e) reach the cathode chamber 8 through an external circuit, and then the cathode chamber 8 can perform a reaction presented in the following formula (6) to produce hydrogen.
The cathode chamber 8 can perform the CO2 reduction reaction presented in the formula (1) to produce CO, and can perform the H2O electrolytic reaction presented in the formula (3) and the reaction presented in the formula (6) to produce H2. The CO and H2 produced in the cathode chamber 8 are discharged from the cathode chamber 8 with unreacted CO2 and saturated steam. A mixed gas G3 discharged from the cathode chamber 8 and containing CO, H2, CO2, and the saturated steam (H2O) is cooled by a cooler 11, and thereafter fed to a first gas/liquid separator 12. The first gas/liquid separator 12 removes the water (H2O) condensed in the cooled mixed gas G3 from the cooled mixed gas G3 to form a mixed gas G4 containing CO, H2, and CO2. The mixed gas G4 is fed to the CO purification part 4.
The CO purification part 4 can purify the mixed gas G4 to form purified CO. The CO purification part 4 can be constituted by applying, for example, a CO-PSA (Pressure Swing Adsorption method) of using a copper ion-zeolite adsorbent, a copper ion activated carbon adsorbent, a copper chloride-aluminum-crosslinked polystyrene solid adsorbent, a copper chloride-aluminum-activated carbon adsorbent, or the like, a cuprammonium cleaning method, a copper aluminum chloride complex solution absorption method, a copper chloride-aluminum-polystyrene polymer complex solution absorption method, a low-temperature method, or the like is applied. The purified CO is accommodated in a storage container such as a tank which is not illustrated, for example, or is fed to an organic-substance synthesis reactor such as a methane synthesis reactor, an alcohol synthesizer, or a Fischer-Tropsch reactor which perform a reaction between CO and H2, for example. The CO purification part 4 constituted by applying the CO-PSA or the like may be replaced by one of these organic-substance synthesis reactors. The CO purification part 4 can discharge a purification residual gas G5 left by purifying the CO. The purification residual gas G5 contains residual CO, residual H2, and residual CO2. The purification residual gas G5 discharged from the CO purification part 4 is fed to the oxidation part 6.
Meanwhile, The anode chamber 9 of the CO2 electrolysis part 3 can perform the oxidation of a carbonate ion (CO32−) and hydroxide ions (OH) to produce oxygen (O2) and carbon dioxide (CO2), as presented in the formula (2) and formula (4). A gas (O2—CO2 containing gas) containing the O2 and CO2, which is produced in the anode chamber 9, is discharged from the anode chamber 9 with the electrolytic solution. The electrolytic solution containing the O2—CO2 containing gas is fed to a second gas/liquid separator 13. The second gas/liquid separator 13 can separate the O2—CO2 containing gas from the electrolytic solution. The O2—CO2 containing gas G6 separated by the second gas/liquid separator 13 is cooled to a predetermined temperature by a cooler 14, and thereafter fed to a third gas/liquid separator 15. The electrolytic solution separated by the second gas/liquid separator 13 is cooled to a predetermined temperature by a cooler 16, and thereafter fed to a buffer tank 17. In addition to electrolytic solution, the condensed water (H2O) separated by the third gas/liquid separator 15 is also fed to the buffer tank 17. The electrolytic solution fed to the buffer tank 17 is supplied with water from a makeup tank 18 as necessary, and thereafter fed to the anode chamber 9 of the CO2 electrolysis part 3 via a pump 19 again.
The O2—CO2 containing gas G6 separated by the second and third gas/liquid separators 13, 15 is subjected to a removal of residual H2O in a H2O removal part 20, and thereafter fed to the CO2 capture part 5. The H2O removal part 20 can have a water vapor-removing polymer membrane or a water vapor adsorbent such as zeolite, silica gel, mesoporous silica or activated carbon. In the CO2 capture part 5, for example, as a CO2 adsorbent, a primary or secondary amine-supported material, FAU-type zeolite, or GIS-type zeolite is used, and as an organic ligand, a benzene-1,4-dicarbohydroxamic acid is used, at the same time, as an ancillary ligand, an isonicotinic acid is used, and Co-MOF (Metal Organic Frameworks) obtained by a reaction with cobalt nitrate, ZIF-69 (CAS No. 1018477-10-5, chemical formula: C10H6N5O2ClZn), Cubic[Zn4O(piperazine dicarbamate)3], or the like is used, and thereby CO2 is separated and captured by the pressure swing adsorption (PSA) method, or the temperature swing adsorption (TSA) method depending on the adsorbent.
In the CO2 capture part 5, with use of, as an oxygen adsorbent, an organic semiconductor such as a tetracyanoquinodimethane (CAS No. 1518-16-7, chemical formula: (NC)2CC6H4C(CN)2) pore material, O2 may be separated and captured by the pressure swing adsorption (PSA) method or the temperature swing adsorption (TSA) method, resulting in capturing CO2. To CO2 capture part 5, a faradaic electro-swing reactive adsorption method in which polyvinylferrocene is used as a counter electrode with poly-1,4-anthraquinone used as a CO2 adsorption electrode may be applied.
A gas G7 containing CO2 separated and captured in the CO2 capture part 5 contains residual O2. The gas G7 containing CO2 and the residual O2 is fed to the oxidation part 6. The oxidation part 6 can perform a reaction between the purification residual gas (reducing gas) G5 and the gas G7, the purification residual gas G5 being discharged from the CO purification part 4 and containing residual CO and unreacted CO2, and the gas G7 being separated and captured in the CO2 capture part 5 and containing CO2 and residual O2. The residual CO in the gas G5 is oxidized by O2 in the gas G7, and converted into CO2. In addition, the O2 in the gas G7 separated and captured in the CO2 capture part 5 is removed. This allows a reduction and moreover a further reduction in an O2 amount in a CO2 gas G8 returned from the oxidation part 6 to the cathode chamber 8 of the CO2 electrolysis part 3.
That is, when the CO2 gas supplied to the cathode chamber 8 of the CO2 electrolysis part 3 contains O2, O2 degrades carbon materials forming the reduction electrode (cathode) disposed in the cathode chamber 8, O2 aggregates metal particles such as gold, silver or copper particles contained as a reduction catalyst in the reduction electrode (cathode), or the like, thereby lowering performance of the reduction electrode. Thus, when the gas G7 containing CO2 separated and captured in the CO2 capture part 5 contains the residual O2, the CO2 gas G8 cannot be fed to the cathode chamber 8 again. In contrast to this, a removal of O2 in the gas G7 separated and captured in the CO2 capture part 5 by the reaction of the purification residual gas (reducing gas) G5 containing the residual CO and the unreacted CO2 and the gas G7 containing CO2 and the residual O2 separated and captured in the CO2 capture part 5 in the oxidation part 6 allows the mixed gas G8 of the gas G7 containing CO2 and the gas G5 containing the unreacted CO2 and CO2 newly produced by the oxidation of CO to be resupplied to the cathode chamber 8 of the CO2 electrolysis part 3 without adversely affecting the cathode chamber 8.
The CO2 gas G8 is cooled by a cooler 21, and thereafter fed to a fourth gas/liquid separator 22. Saturated steam and condensed water (H2O) are removed by the fourth gas/liquid separator 22, and thereafter the CO2 gas G8 is fed to the gas mixer 7. The CO2 gas G8 is mixed with the CO2 gas G2 supplied from the CO2 supply part 2 by the gas mixer 7, and is thereafter supplied to the cathode chamber 8 of the CO2 electrolysis part 3. The oxidation part 6 may be constituted by applying a hydrogen-oxygen recombination catalyst or a combustion catalyst such as Ni—Ce2O3—Pt to enable enhancing removability of oxygen. Depending on a residual O2 concentration in the CO2 containing gas G7 supplied from the CO2 capture part 5 or a residual CO concentration in the purification residual gas G5 discharged from the CO purification part 4, as illustrated in
To control an amount of water vapor of the CO2 gas G2, and reduce an amount of diffusing water vapor from the electrolytic solution, the CO2 gas may be appropriately humidified in the gas mixer 7, or a removal amount of water vapor from the CO2 gas G8 may be controlled by an outlet temperature of the cooler 21. For a reduction in load of the cooler 21 and/or a reduction in heating amount of the oxidation part 6, heat may be exchanged between the gas G8 and the gases G5, G7.
As described above, according to the CO2 conversion apparatus 1 of the embodiment, the residual O2 in the CO2 gas G7 separated and captured in the CO2 capture part 5 can be reacted with the residual CO in the purification residual gas G5 in the oxidation part 6 to remove the residual O2 in the CO2 gas G7 and capture the residual CO as CO2. In addition to this, the unreacted CO2 contained in the purification residual gas G5 can be captured. These allow a further stable reduction in the O2 concentration in the CO2 gas G8 adversely affecting the cathode chamber 8 in addition to a promotion of effective use of CO2. That is, the unreacted and reproduced CO2 can be effectively used with electrolysis ability of CO2 by using the CO2 electrolysis part 3 maintained.
Note that though not described and illustrated in the embodiment, and,
Note that the configurations of the above-described embodiments are applicable in combination with each other, and parts thereof are also replaceable. While certain embodiments of the present invention have been described above, these embodiments have been presented by way of example only, and are not intended to limit the scope of the invention. Indeed these embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions, and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2023-034938 | Mar 2023 | JP | national |
