Carbon dioxide electrolysis device and method for controlling the carbon dioxide electrolysis device

Abstract

To provide a carbon dioxide electrolysis device with improved carbon dioxide utilization rates.SOLUTION: A carbon dioxide electrolysis device includes a carbon dioxide electrolysis cell having a cathode flow path, an anode flow path, a cathode, an anode, and a first diaphragm, a first current regulator that supplies a first current, a first gas-liquid separator that separates a first fluid discharged from the anode flow path into a first liquid and a first gas, an electrodialysis cell having a first housing, a first electrode, a second housing, a second electrode, a third housing, a fourth housing, a second diaphragm, a third diaphragm, and a fourth diaphragm, a second current regulator that supplies a second current, at least one of a first detector that detects a flow rate of the first gas or a concentration of carbon dioxide contained in the first gas and a second detector that detects a pH of the first fluid or a concentration of at least one ion, and a first controller that adjusts a value of the second current based on at least one detection signal.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] An embodiment of the present invention relates to a carbon dioxide electrolysis device and a method for controlling the carbon dioxide electrolysis device. [Background technology]

[0002] In recent years, carbon dioxide (CO 2 ) is electrochemically reduced to carbon monoxide (CO), formic acid (HCOOH), and methanol (CH 3 OH), methane (CH 4 ), ethanol (C 2 H 5 OH), ethane (C 2 H 6 ), ethylene (C 2 H 4 Carbon dioxide electrolysis technology, which converts carbon dioxide into chemical substances (chemical energy) such as nitrogen oxides, is attracting attention. Carbon dioxide electrolysis cells have two chambers separated by a membrane, but some of the carbon dioxide introduced into the electrolysis cell moves from the cathode flow path to the anode flow path, and then moves with the electrolyte and is discharged from the anode flow path, resulting in a problem of reduced carbon dioxide utilization rate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] European Patent Application Publication No. 2007-0761055 [Patent Document 2] Patent Publication No. 2021-46574 Summary of the Invention [Problem to be solved by the invention]

[0004] The problem to be solved by the present invention is to improve the carbon dioxide utilization rate of a carbon dioxide electrolysis device. [Means for solving the problem]

[0005] A carbon dioxide electrolysis device according to an embodiment includes a carbon dioxide electrolysis cell having a cathode flow path through which carbon dioxide flows, an anode flow path through which a water-containing electrolytic solution flows, a cathode facing the cathode flow path and reducing carbon dioxide to produce carbon compounds, an anode facing the anode and oxidizing water to produce oxygen, and a first diaphragm provided between the anode flow path and the cathode flow path, a first current regulator providing a first current between the anode and the cathode, a first gas-liquid separator separating a first fluid discharged from the anode flow path into a first liquid and a first gas, a first storage unit, a first electrode disposed in the first storage unit, a second storage unit, a second electrode disposed in the second storage unit, and a third storage unit provided between the first storage unit and the second storage unit and containing the first liquid supplied from the first gas-liquid separator. an electrodialysis cell having a first container, a fourth container provided between the third container and the second container, a second diaphragm provided between the first container and the third container, a third diaphragm provided between the second container and the fourth container, and a fourth diaphragm provided between the third container and the fourth container; a second current regulator for supplying a second current between the first electrode and the second electrode; at least one detector selected from the group consisting of a first detector for detecting a flow rate of the first gas or a concentration of carbon dioxide contained in the first gas, and a second detector for detecting a pH of the first fluid or a concentration of at least one ion contained in the first fluid; and a first controller for controlling the second current regulator to adjust a value of the second current based on at least one detection signal from the at least one detector. a second gas-liquid separator that separates the fourth fluid discharged from the third container into a second liquid containing the electrolyte and a second gas containing carbon dioxide; Equipped with: The second gas is supplied to the cathode flow passage. . [Brief description of the drawings]

[0006] [Figure 1] FIG. 1 is a schematic diagram illustrating a configuration example of a carbon dioxide electrolysis device according to a first embodiment. [Diagram 2] FIG. 1 is a schematic diagram illustrating an example of the structure of a carbon dioxide electrolysis cell 100 according to a first embodiment. [Diagram 3] FIG. 2 is a schematic diagram showing a structural example of an electrodialysis cell. [Figure 4]FIG. 2 is a schematic diagram showing another example of the structure of the electrodialysis cell. [Diagram 5] FIG. 1 is a schematic diagram illustrating an example of the structure of a carbon dioxide electrolysis cell 100 according to a second embodiment. [Figure 6] FIG. 1 is a schematic diagram showing an example of the structure of a carbon dioxide electrolysis cell 100 according to an embodiment of the present invention. [Figure 7] FIG. 4 is a graph showing the carbon dioxide concentration in the generated gas at each current density. [Figure 8] FIG. 13 is a graph showing the pH of the electrolyte after passing through the anode flow channel 102 at each current density. [Figure 9] FIG. 13 is a graph showing the relationship between the carbon dioxide concentration in the anode exhaust and the pH of the electrolyte. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] Hereinafter, carbon dioxide electrolysis devices according to the embodiments will be described with reference to the drawings. In each embodiment, substantially the same components are denoted by the same reference numerals, and their description may be omitted. The drawings are schematic, and the relationship between the thickness of each part and the planar dimensions, the thickness ratio of each part, etc. may differ from the actual ones.

[0008] In this specification, unless otherwise specified, "connect" includes not only direct connection but also indirect connection.

[0009] (First embodiment) Fig. 1 is a diagram showing a carbon dioxide electrolysis device of the first embodiment. The carbon dioxide electrolysis device 1 shown in Fig. 1 includes a carbon dioxide electrolysis cell 100, an electrodialysis cell 200, a carbon dioxide detector 41, a carbon dioxide detector 42, a pH / ion concentration detector 43, a gas-liquid separator 31, a gas-liquid separator 32, a water quality detector 44, a current regulator 51 that supplies current to the carbon dioxide electrolysis cell 100, a current regulator 52, a pump 61, a purge valve 62, a pump 63, a pump 64, a carbon dioxide supply source 71, a carbon dioxide flow regulator 72, a controller 81, a controller 82, and an electrolyte tank 93.

[0010] Figure 2 is a schematic diagram showing an example of the structure of a carbon dioxide electrolysis cell 100 in the first embodiment. The carbon dioxide electrolysis cell 100 shown in Figure 2 includes a cathode flow path 101, an anode flow path 102, a diaphragm 103, a cathode 104, an anode 105, a supply flow path 106, a supply flow path 107, a discharge flow path 108, a supply flow path 109, and a discharge flow path 110. Each flow path may be connected to a pump as necessary.

[0011] The cathode flow channel 101 is provided in a first storage unit capable of storing, for example, carbon dioxide. Carbon dioxide is stored in the cathode flow channel 101 as, for example, a first electrolytic solution containing carbon dioxide. The first electrolytic solution functions as a cathode solution and contains carbon dioxide as a substance to be reduced. The form of carbon dioxide present in the first electrolytic solution does not need to be in a gaseous state, and may be dissolved carbon dioxide or carbonate ions (CO 3 2- ) and bicarbonate ion (HCO 3 - The first electrolytic solution may contain hydrogen ions or hydroxide ions, and is preferably an aqueous solution.

[0012] The anode flow channel 102 is provided in a second container capable of containing, for example, a second electrolytic solution containing water or water vapor. The second electrolytic solution functions as an anode solution and contains, for example, water (H 2 O) and chloride ions (Cl - ), carbonate ion (CO 3 2- ) and bicarbonate ion (HCO 3 - The second electrolytic solution may be an aqueous solution of an alcohol, an aqueous solution of an organic substance such as an amine, or the like.

[0013] By changing the amount of water and the components of the electrolyte in the first and second electrolyte solutions, the reactivity can be changed, and the selectivity of the substance to be reduced and the ratio of the chemical substances to be generated can be changed. The first and second electrolyte solutions may contain a redox couple as necessary. Examples of the redox couple include Fe 3+ / Fe 2+ or IO 3 - / I - Examples include:

[0014] The first and second containers are formed of, for example, quartz white glass, acrylic resin (PMMA), polystyrene (PS), or the like. A light-transmitting material may be used for a portion of the cathode flow path 101 and the anode flow path 102, and a resin material may be used for the remaining portion. Examples of the resin material include, for example, polyetheretherketone (PEEK), polyamide (PA), polyvinylidene fluoride (PVDF), polyacetal (POM) (copolymer), polyphenylene ether (PPE), acrylonitrile-butadiene-styrene copolymer (ABS), polypropylene (PP), polyethylene (PE), and the like. The first and second containers may have a space for accommodating gas contained in the reactants and products.

[0015] The pressure in the first and second storage units is preferably set to a pressure at which carbon dioxide does not liquefy, and is preferably adjusted, for example, within a range of 0.1 MPa to 6.4 MPa. If the pressure in the storage units is less than 0.1 MPa, the efficiency of the carbon dioxide reduction reaction may decrease. If the pressure in the storage units exceeds 6.4 MPa, carbon dioxide may liquefy, and the efficiency of the carbon dioxide reduction reaction may decrease. Note that the pressure difference between the first and second storage units may cause damage to the diaphragm 103. For this reason, it is preferable that the pressure difference (differential pressure) between the first and second storage units is 1 MPa or less.

[0016] The lower the temperature of the electrolytic solution, the higher the amount of carbon dioxide dissolved; however, from the viewpoint of carbon dioxide electrolysis, low temperatures are disadvantageous because the solution resistance increases and the theoretical voltage of the reaction increases. On the other hand, a high temperature of the electrolytic solution reduces the amount of carbon dioxide dissolved, but is advantageous for carbon dioxide electrolysis. For this reason, the operating temperature condition of the carbon dioxide electrolysis cell 100 is preferably in the medium temperature range, for example, in the range from atmospheric temperature to the boiling point of the electrolytic solution. When the electrolytic solution is an aqueous solution, the temperature is preferably 10°C to 100°C, more preferably 25°C to 80°C. When the cathode flow channel 101 is filled with a raw gas containing carbon dioxide and the anode flow channel 102 is filled with water vapor, operation at a higher temperature is possible. In this case, the operating temperature is determined in consideration of the heat resistance of the members such as the diaphragm 103. When the diaphragm 103 is an ion exchange membrane or the like, the operating temperature is a maximum of 180°C, and when it is a polymer porous membrane such as Teflon (registered trademark), the maximum temperature is 300°C. The first and second electrolytic solutions may be electrolytic solutions containing different substances, or may be the same electrolytic solution containing the same substance. When the first and second electrolytic solutions contain the same substance and the same solvent, the first and second electrolytic solutions may be regarded as one electrolytic solution. The pH of the first electrolytic solution may be higher than the pH of the second electrolytic solution. This allows ions such as hydrogen ions and hydroxide ions to move easily through the membrane 103. In addition, the liquid junction potential difference caused by the difference in pH can effectively advance the redox reaction.

[0017] The first electrolytic solution is preferably a solution with a high carbon dioxide absorption rate. The form of carbon dioxide in the first electrolytic solution is not necessarily limited to a dissolved state, and carbon dioxide in the form of bubbles may be mixed and present in the first electrolytic solution. Examples of the electrolytic solution containing carbon dioxide include lithium bicarbonate (LiHCO 3 ), sodium bicarbonate (NaHCO 3 ), potassium bicarbonate (KHCO 3 ), Cesium bicarbonate (CsHCO 3 ), Sodium Carbonate (Na 2 CO 3 ), potassium carbonate (K 2 CO 3) containing hydrogen carbonate or carbonate, phosphoric acid, boric acid, etc. The electrolytic solution containing carbon dioxide may contain alcohols such as methanol, ethanol, acetone, etc., or may be an alcohol solution. The first electrolytic solution may be an electrolytic solution containing a carbon dioxide absorbent that reduces the reduction potential of carbon dioxide, has high ionic conductivity, and absorbs carbon dioxide.

[0018] The second electrolyte is water (H 2 A solution using phosphate ions (PO), for example, an aqueous solution containing any electrolyte, can be used. This solution is preferably an aqueous solution that promotes the oxidation reaction of water. An example of an aqueous solution containing an electrolyte is phosphate ions (PO 4 2- ), borate ion (BO 3 3- ), hydrogen ion (H + ), sodium ion (Na + ), potassium ion (K + ), calcium ion (Ca 2+ ), lithium ion (Li + ), Cesium ion (Cs + ), magnesium ion (Mg 2+ ), chloride ion (Cl - ), bicarbonate ion (HCO 3 - ), carbonate ion (CO 3 - ), hydroxide ion (OH - ) and the like.

[0019] The above-mentioned electrolyte solution may be, for example, a mixture of a cation such as an imidazolium ion or a pyridinium ion and BF 4 - or PF 6 -An ionic liquid or an aqueous solution thereof, which is composed of a salt with an anion such as ethanolamine, imidazole, pyridine, or the like and is in a liquid state over a wide temperature range, can be used. Further, other electrolyte solutions include amine solutions such as ethanolamine, imidazole, pyridine, or the like, or an aqueous solution thereof. Examples of amines include primary amines, secondary amines, and tertiary amines. These electrolyte solutions may have high ionic conductivity, a property of absorbing carbon dioxide, and a property of reducing reduction energy.

[0020] Examples of primary amines include methylamine, ethylamine, propylamine, butylamine, pentylamine, and hexylamine. The amine hydrocarbon may be substituted with an alcohol, a halogen, or the like. Examples of amines with substituted hydrocarbons include methanolamine, ethanolamine, and chloromethylamine. In addition, unsaturated bonds may be present. The same is true for secondary and tertiary amines.

[0021] Examples of secondary amines include dimethylamine, diethylamine, dipropylamine, dibutylamine, dipentylamine, dihexylamine, dimethanolamine, diethanolamine, dipropanolamine, etc. The substituted hydrocarbon may be different. This is also true for tertiary amines. For example, examples of amines with different hydrocarbons include methylethylamine, methylpropylamine, etc.

[0022] Examples of the tertiary amine include trimethylamine, triethylamine, tripropylamine, tributylamine, trihexylamine, trimethanolamine, triethanolamine, tripropanolamine, tributanolamine, trihexanolamine, methyldiethylamine, and methyldipropylamine.

[0023] Examples of the cation of the ionic liquid include a 1-ethyl-3-methylimidazolium ion, a 1-methyl-3-propylimidazolium ion, a 1-butyl-3-methylimidazole ion, a 1-methyl-3-pentylimidazolium ion, and a 1-hexyl-3-methylimidazolium ion.

[0024] The 2-position of the imidazolium ion may be substituted. Examples of cations substituted at the 2-position of the imidazolium ion include 1-ethyl-2,3-dimethylimidazolium ion, 1,2-dimethyl-3-propylimidazolium ion, 1-butyl-2,3-dimethylimidazolium ion, 1,2-dimethyl-3-pentylimidazolium ion, and 1-hexyl-2,3-dimethylimidazolium ion.

[0025] Examples of pyridinium ions include methylpyridinium, ethylpyridinium, propylpyridinium, butylpyridinium, pentylpyridinium, hexylpyridinium, etc. In both the imidazolium ion and the pyridinium ion, the alkyl group may be substituted, and an unsaturated bond may be present.

[0026] The anion is fluoride ion (F - ), chloride ion (Cl - ), bromide ion (Br - ), iodide ion (I - ), B.F. 4 - , P.F. 6 - , C.F. 3 COO - , C.F. 3 SO 3- , NO 3 - , SCN - , (CF 3 SO 2 ) 3 C -, bis(trifluoromethoxysulfonyl)imide, bis(trifluoromethoxysulfonyl)imide, bis(perfluoroethylsulfonyl)imide, etc. Zwitterions in which the cation and anion of the ionic liquid are connected by a hydrocarbon may also be used. A buffer solution such as a potassium phosphate solution may be supplied to the cathode flow channel 101 and the anode flow channel 102.

[0027] The diaphragm 103 is provided between the cathode flow channel 101 and the anode flow channel 102, and separates the cathode flow channel 101 from the anode flow channel 102. The diaphragm 103 is a membrane that separates hydrogen ions (H + ), hydroxide ion (OH - ), carbonate ion (CO 2 3- ), bicarbonate ion (HCO 3 - ) can be moved.

[0028] The diaphragm 103 is a membrane that allows anions or cations to pass selectively. This allows the electrolytes in contact with the cathode 104 and the anode 105 to contain different substances, and further allows the reduction reaction or oxidation reaction to be promoted by the difference in ionic strength, pH, or the like. The diaphragm 103 can be used to separate the first electrolyte solution from the second electrolyte solution. The diaphragm 103 may have a function of allowing some ions contained in the electrolyte solution in which both electrodes are immersed to pass through, that is, a function of blocking one or more types of ions contained in the electrolyte solution. This allows, for example, the two electrolyte solutions to be solutions with different pH values.

[0029] As the diaphragm 103, for example, ion exchange membranes such as NeoSepta (registered trademark) from Astom Corporation, Selemion (registered trademark) and Aciplex (registered trademark) from Asahi Glass Co., Ltd., Fumasep (registered trademark) and fumapem (registered trademark) from Fumatech Corporation, Nafion (registered trademark) which is a fluororesin obtained by sulfonating and polymerizing tetrafluoroethylene from DuPont Corporation, lewabrane (registered trademark) from LANXESS Corporation, IONSEP (registered trademark) from IONTECH Corporation, Mustang (registered trademark) from PALL Corporation, ralex (registered trademark) from mega Corporation, and Gore-Tex (registered trademark) from Gore-Tex Corporation can be used. In addition, the ion exchange membrane may be formed using a membrane having a basic skeleton of a hydrocarbon, or a membrane having an amine group for anion exchange. When there is a pH difference between the first and second electrolyte solutions, the pH of each electrolyte solution can be stably maintained while it is used by using a bipolar membrane in which a cation exchange membrane and an anion exchange membrane are laminated.

[0030] As the diaphragm 103, other than an ion exchange membrane, for example, a silicone resin, a fluorine-based resin (perfluoroalkoxyalkane (PFA), perfluoroethylenepropene copolymer (FEP), polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene copolymer (ETFE), polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), polyethersulfone (PES), etc., a ceramic porous membrane, a glass filter, a packing filled with agar or the like, an insulating porous body such as zeolite or an oxide, etc. can be used. In particular, a hydrophilic porous membrane is preferable as the diaphragm 103 because it does not cause clogging due to air bubbles.

[0031] The cathode 104 faces the cathode flow path 101. The cathode 104 is an electrode (reduction electrode) that reduces carbon dioxide to produce a carbon compound. The cathode 104 is disposed inside the first housing and immersed in the first electrolytic solution. The cathode 104 includes, for example, a reduction catalyst for producing a carbon compound by a reduction reaction of carbon dioxide. The reduction catalyst may be a material that reduces the activation energy for reducing carbon dioxide. In other words, it may be a material that reduces the overvoltage when producing a carbon compound by a reduction reaction of carbon dioxide.

[0032] For example, a metal material or a carbon material can be used as the cathode 104. For example, a metal such as gold, aluminum, copper, silver, platinum, palladium, zinc, mercury, indium, nickel, or titanium, or an alloy containing the metal can be used as the metal material. For example, a graphene, a carbon nanotube (CNT), a fullerene, or Ketjen black can be used as the carbon material. In addition, the present invention is not limited to these, and a metal complex such as a Ru complex or a Re complex, or an organic molecule having an imidazole skeleton or a pyridine skeleton can be used as the reduction catalyst. The reduction catalyst may be a mixture of a plurality of materials. For example, the cathode 104 may have a structure in which a reduction catalyst in the form of a thin film, a lattice, a particle, a wire, or the like is provided on a conductive base material.

[0033] The carbon compounds generated by the reduction reaction at the cathode 104 vary depending on the type of reduction catalyst, and include, for example, carbon monoxide (CO), formic acid (HCOOH), methane (CH 4 ), methanol (CH 3 OH), ethane (C 2 H 6 ), ethylene (C 2 H 4 ), ethanol (C 2 H 5 OH), formaldehyde (HCHO), ethylene glycol (C 2 H 6 O 2 ) and the like. In addition, carbon dioxide (CO 2) reduction reaction, and hydrogen (H 2 ) side reactions may occur.

[0034] The anode 105 faces the anode flow path 102. The anode 105 is an electrode (oxidation electrode) that oxidizes substances to be oxidized, such as substances and ions, in the second electrolyte solution. For example, the anode 105 oxidizes water to generate oxygen or hydrogen peroxide solution, or oxidizes chloride ions (Cl - ) to generate chlorine. The anode 105 is placed inside the second housing and immersed in the second electrolyte. The anode 105 includes an oxidation catalyst for the substance to be oxidized. As the oxidation catalyst, a material that reduces the activation energy when the substance to be oxidized is oxidized, in other words, a material that reduces the reaction overvoltage, is used.

[0035] Examples of the oxidation catalyst include metals such as ruthenium, iridium, platinum, cobalt, nickel, iron, and manganese. In addition, binary metal oxides, ternary metal oxides, and quaternary metal oxides can be used. Examples of the binary metal oxides include manganese oxide (Mn-O), iridium oxide (Ir-O), nickel oxide (Ni-O), cobalt oxide (Co-O), iron oxide (Fe-O), tin oxide (Sn-O), indium oxide (In-O), and ruthenium oxide (Ru-O). Examples of the ternary metal oxides include Ni-Fe-O, Ni-Co-O, La-Co-O, Ni-La-O, and Sr-Fe-O. Examples of the quaternary metal oxides include Pb-Ru-Ir-O, La-Sr-Co-O, and the like. However, the oxidation catalyst is not limited to these, and metal hydroxides containing cobalt, nickel, iron, manganese, etc., and metal complexes such as Ru complexes and Fe complexes can also be used. A mixture of multiple materials can also be used.

[0036] The anode 105 may be a composite material including both an oxidation catalyst and a conductive material. Examples of the conductive material include carbon materials such as carbon black, activated carbon, fullerene, carbon nanotubes, graphene, ketjen black, and diamond; transparent conductive oxides such as indium tin oxide (ITO), zinc oxide (ZnO), fluorine-doped tin oxide (FTO), aluminum-doped zinc oxide (AZO), and antimony-doped tin oxide (ATO); metals such as Cu, Al, Ti, Ni, Ag, W, Co, and Au; and alloys including at least one of these metals. The anode 105 may have a structure in which an oxidation catalyst is provided on a conductive substrate in the form of a thin film, a lattice, a particle, a wire, or the like. The conductive substrate may be, for example, a metal material including titanium, a titanium alloy, or stainless steel.

[0037] The supply flow path 106 is connected to the cathode flow path 101. The carbon dioxide electrolysis cell 100 is capable of supplying a raw material gas containing carbon dioxide from the supply flow path 106 to the cathode flow path 101. The supply flow path 106 shown in FIG. 2 extends inside the cathode flow path 101, but the position of the supply flow path 106 is not limited to the position shown in FIG. 2.

[0038] The supply flow path 107 is connected to the cathode flow path 101. The carbon dioxide electrolysis cell 100 is capable of supplying the first electrolytic solution to the container 101 via the supply flow path 107.

[0039] The exhaust flow path is connected to the cathode flow path 101. The carbon dioxide electrolysis cell 100 is capable of exhausting a fluid containing a reactant gas and a first electrolytic solution from the cathode flow path 101 via the exhaust flow path .

[0040] The supply flow path 109 is connected to the anode flow path 102. The carbon dioxide electrolysis cell 100 is capable of supplying a second electrolytic solution to the anode flow path 102 via the supply flow path 109.

[0041] The exhaust flow path 110 is connected to the anode flow path 102. The carbon dioxide electrolysis cell 100 is capable of exhausting a fluid including a reactant gas and a second electrolyte from the anode flow path 102 via the exhaust flow path 110.

[0042] 3 and 4 are schematic diagrams showing a structural example of an electrodialysis cell 200. The electrodialysis cell 200 shown in Fig. 3 includes a storage section 201, a storage section 202, a storage section 203, a storage section 204, an electrode 205, an electrode 206, a diaphragm 207, a diaphragm 208, a diaphragm 209, a supply flow path 211, a discharge flow path 212, a supply flow path 213, a discharge flow path 214, a supply flow path 215, a discharge flow path 216, a supply flow path 217, and a discharge flow path 218.

[0043] The housing portion 201 is disposed outside the housing portion 203 .

[0044] The housing portion 202 is disposed outside the housing portion 204 .

[0045] The storage unit 203 is provided between the storage unit 201 and the storage unit 202. The storage unit 203 is capable of storing a liquid including, for example, ionized carbon dioxide.

[0046] The container 204 is provided between the container 202 and the container 203. The container 204 is capable of containing, for example, an electrolyte.

[0047] Electrode 205 is disposed in housing 201. Electrode 206 is disposed in housing 202. The polarities of electrode 205 and electrode 206 change depending on the device configuration. That is, when one of electrode 205 and electrode 206 is an anode, the other is a cathode.

[0048] Examples of materials that can be used for the electrodes 205 and 206 include metal materials such as elemental metals such as gold, aluminum, copper, silver, platinum, palladium, zinc, mercury, indium, nickel, and titanium, and alloys containing these metals, as well as carbon materials such as graphene and carbon nanotubes.

[0049] The diaphragm 207 is provided between the housing portion 201 and the housing portion 203 and separates the housing portion 201 from the housing portion 203 .

[0050] The diaphragm 208 is provided between the housing portion 202 and the housing portion 204 and separates the housing portion 202 and the housing portion 204 .

[0051] The diaphragm 209 is provided between the housing portion 203 and the housing portion 204 and separates the housing portion 203 and the housing portion 204 .

[0052] Each of diaphragm 207, diaphragm 208, and diaphragm 209 is, for example, a cation exchange membrane, an anion exchange membrane, or a bipolar membrane formed by laminating a cation exchange membrane and an anion exchange membrane. The polarity direction when current is supplied from current regulator 52 between electrode 205 and electrode 206, and whether the discharged carbon dioxide regenerated liquid and alkali regenerated liquid correspond to discharge flow path 212 or discharge flow path 214 are determined by the position and type of the diaphragm used.

[0053] The supply flow path 211 is connected to the container 201. The electrodialysis cell 200 is capable of supplying the electrolyte from the electrolyte tank 93 to the container 201 via the supply flow path 211 using the pump 63.

[0054] The discharge flow path 212 is connected to the storage unit 201. The electrodialysis cell 200 is capable of discharging from the storage unit 201 a fluid containing the gas generated in the storage unit 201 and the first electrolytic solution or the second electrolytic solution.

[0055] The supply flow path 213 is connected to the container 202. The electrodialysis cell 200 is capable of supplying the electrolyte from the electrolyte tank 93 to the container 202 via the supply flow path 213 using the pump 64.

[0056] The discharge flow path 214 is connected to the container 202. The electrodialysis cell 200 is capable of discharging from the container 202 a fluid containing the gas generated in the container 202 and the first electrolytic solution or the second electrolytic solution.

[0057] The supply flow path 215 is connected to the storage unit 203. The supply flow path 215 may be connected to the gas-liquid separator 31. The electrodialysis cell 200 is capable of supplying the anode effluent, which has been separated from the fluid containing the reactant gas and the second electrolytic solution discharged from the discharge flow path 108, to the storage unit 203 via the supply flow path 215.

[0058] The discharge flow path 216 is connected to the container 203. The supply flow path 215 may be connected to the gas-liquid separator 32. The electrodialysis cell 200 is capable of discharging a fluid including gas and liquid from the container 203 via the discharge flow path 216.

[0059] The supply flow path 217 is connected to the storage unit 204. The supply flow path 217 may be connected to the gas-liquid separator 32. The electrodialysis cell 200 can supply the liquid separated by the gas-liquid separator 32 as a circulating liquid to the storage unit 204 via the supply flow path 217.

[0060] The discharge flow path 218 is connected to the container 204. The discharge flow path 218 may be connected to the pump 61. The electrodialysis cell 200 is capable of discharging fluids including gas and liquid via the discharge flow path 218.

[0061] 4, the electrodialysis cell 200 may have a structure in which a constituent unit consisting of the storage section 203, the storage section 204, the diaphragm 207, the diaphragm 209, the supply flow path 215, the discharge flow path 216, the supply flow path 217, and the discharge flow path 218 is defined as a cell constituent unit U, and a plurality of cell constituent units U are arranged in a sandwiched manner between the storage section 201 and the storage section 202. In the structure shown in FIG. 4, the diaphragm 208 may be used instead of the diaphragm 207 included in the cell constituent unit U in order to achieve left-right symmetry. In addition, the positional relationship between the storage section 203 and the storage section 204 may be reversed depending on the combination of diaphragms and the sign of the voltage applied to the electrodes.

[0062] The gas-liquid separator 31 is disposed downstream of the carbon dioxide electrolysis cell 100. The gas-liquid separator 31 separates the fluid discharged from the anode flow channel 102 of the carbon dioxide electrolysis cell 100 into a first liquid (anode effluent) and a first gas (anode exhaust). The gas-liquid separator 31 has, for example, a gas-liquid separation membrane.

[0063] The gas-liquid separator 32 is disposed downstream of the electrodialysis cell 200. The gas-liquid separator 32 separates the fluid discharged from the discharge flow path 216 of the electrodialysis cell 200 into a second liquid and a second gas. The gas-liquid separator 32 has, for example, a gas-liquid separation membrane.

[0064] The carbon dioxide detector 41 is capable of detecting the concentration of carbon dioxide contained in the fluid discharged from the cathode flow path 101 of the carbon dioxide electrolysis cell 100. The carbon dioxide concentration in the fluid discharged from the cathode flow path 101 may be adjusted to an optimal value by changing the flow rate of carbon dioxide supplied to the cathode flow path 101 of the carbon dioxide electrolysis cell 100 in accordance with the carbon dioxide concentration measured by the carbon dioxide detector 41. This can simplify or eliminate the mechanism or process for adjusting the carbon dioxide concentration in the fluid discharged from the cathode flow path 101, thereby reducing the costs of the carbon dioxide electrolysis device 1 and the valuable resource production system.

[0065] The carbon dioxide detector 42 is capable of detecting the concentration of carbon dioxide contained in the fluid discharged from the container 203 of the electrodialysis cell 200 .

[0066] As for each of the carbon dioxide detectors 41 and 42, the carbon dioxide detector 41 may be, for example, a carbon dioxide concentration meter using a gas chromatography (GC) method, specific heat, IR absorption method, or the like.

[0067] The pH / ion concentration detector 43 is capable of detecting the pH of the fluid discharged from the anode flow path 102 of the carbon dioxide electrolysis cell 100, or at least one type of ion contained in the fluid. The pH / ion concentration detector 43 may be connected to the discharge flow path 110 or a stage downstream of the gas-liquid separator 31.

[0068] The water quality detector 44 can monitor the quality of the anode effluent by detecting the concentration of at least one component contained in the anode effluent separated by the gas-liquid separator 31. The detection method of the water quality detector 44 may be a method of separating a portion of the liquid and analyzing it by liquid chromatography, or a method of detecting a specific compound. The water quality detector 44 may be connected downstream of the gas-liquid separator 31, or may be connected upstream or downstream of the pump 61.

[0069] The current regulator 51 is connected to the carbon dioxide electrolysis cell 100. The current regulator 51 is capable of providing a first current between the cathode 104 and the anode 105 of the carbon dioxide electrolysis cell 100.

[0070] The current regulator 52 is connected to the electrodialysis cell 200. The current regulator 52 is capable of providing a second current between the electrode 205 and the electrode 206 of the electrodialysis cell 200.

[0071] The current regulators 51 and 52 may have, for example, an AC power source supplied from a power plant, a DC power source via a converter circuit, or a variable power source, i.e., a power source that converts renewable energy into electrical energy and supplies it. Examples of such power sources include a power source that converts kinetic energy or potential energy such as wind power, hydroelectric power, geothermal power, and tidal power into electrical energy, a power source such as a solar cell having a photoelectric conversion element that converts light energy into electrical energy, a power source such as a fuel cell or a storage battery that converts chemical energy into electrical energy, and a device that converts vibration energy such as sound into electrical energy. Furthermore, the current regulators 51 and 52 may have a power controller that controls the above power sources.

[0072] The pump 61 is disposed downstream of the electrodialysis cell 200. The pump 61 is capable of supplying the fluid discharged from the container 204 to the anode flow path 102 of the carbon dioxide electrolysis cell 100.

[0073] The purge valve 62 is disposed after the electrodialysis cell 200. The purge valve 62 can supply the first electrolyte from the electrolyte path 92 or discharge a portion of the anode waste liquid.

[0074] The purge valve 62 may be connected downstream of the gas-liquid separator 31 , or may be connected upstream or downstream of the pump 61 .

[0075] The pump 63 is disposed, for example, in the middle of the supply flow path 211. The pump 63 is capable of supplying the electrolyte from the electrolyte tank 93, from which gas has been removed, to the container 201.

[0076] The pump 64 is disposed, for example, in the middle of the supply flow path 213. The pump 64 is capable of supplying the electrolyte from the electrolyte tank 93, from which gas has been removed, to the container 201.

[0077] The carbon dioxide source 71 is capable of containing carbon dioxide for supply to the cathode flow channel 101 of the carbon dioxide electrolysis cell 100 .

[0078] The carbon dioxide flow regulator 72 is provided between the carbon dioxide supply source 71 and the carbon dioxide flow regulator 72. The carbon dioxide flow regulator 72 adjusts the flow rate of the fluid containing carbon dioxide supplied to the cathode flow channel 101 using a mass flow controller or the like. By increasing or decreasing the amount of carbon dioxide supplied to the cathode flow channel 101 by the carbon dioxide flow regulator 72, it is possible to adjust the concentration of unreacted carbon dioxide in the fluid discharged from the cathode flow channel 101, thereby making it possible to improve the carbon dioxide utilization rate and stabilize the carbon dioxide concentration in the generated gas.

[0079] The controller 81 is connected to each of the carbon dioxide detector 41, the water quality detector 44, the purge valve 62, and the carbon dioxide flow regulator 72. In FIG. 1, the flow of signals in the controller 81 is indicated by dotted lines. The controller 81 can adjust the flow rate of the fluid supplied from the carbon dioxide supply source 71 to the cathode flow path 101 to an appropriate value by controlling the carbon dioxide flow regulator 72 using a control signal generated based on a detection signal from the carbon dioxide detector 41. The controller 81 can control the purge valve 62 based on a detection signal from the water quality detector 44 to replenish liquid such as an electrolyte from the electrolyte path 92, or discharge the first liquid to the electrolyte path 92.

[0080] The controller 82 is connected to each of the carbon dioxide detector 42, the pH / ion concentration detector 43, the water quality detector 44, the current regulator 52, and the pump 61. In Fig. 1, the signal flow in the controller 82 is indicated by dotted lines. The controller 82 can adjust the value of the second current supplied to the electrodialysis cell 200 by controlling the current regulator 52 according to a control signal generated based on at least one detection signal from at least one of the carbon dioxide detector 42, the pH / ion concentration detector 43, and the water quality detector 44, and can adjust the flow rate of the fluid supplied to the anode flow path 102 by controlling the pump 61 according to the generated control signal.

[0081] The electrolytic solution tank 93 can contain the electrolytic solution discharged from the discharge flow path 212 and the discharge flow path 214. The electrolytic solution tank 93 may have a gas discharge part and a gas-liquid separation membrane for removing gas from the fluid discharged from the discharge flow path 212 and the discharge flow path 214.

[0082] Next, an example of the operation of the carbon dioxide electrolysis cell 100 will be described. Here, the case will be described where an aqueous solution containing carbon dioxide is used as the first electrolytic solution, an aqueous solution of potassium hydroxide is used as the second electrolytic solution, carbon dioxide is reduced by the cathode 104 to produce mainly ethylene, and water or hydroxide ions are oxidized by the anode 105 to produce oxygen.

[0083] When a voltage equal to or greater than the electrolysis voltage is applied between the cathode 104 and the anode 105, a reduction reaction of carbon dioxide occurs near the cathode 104 in contact with the first electrolyte. As shown in the following formula (1), electrons (e - ) reduces the carbon dioxide contained in the first electrolyte solution to produce ethylene (C 2 H 4 ) and hydroxide ion (OH - ) is produced. The hydroxide ion (OH - ) reacts with carbon dioxide to produce bicarbonate ions (HCO 3 - ), carbonate ion (CO 3 2- ) are produced (Equations (2) and (3)). A portion of the hydroxide ions, hydrogen carbonate ions, and carbonate ions move into the second electrolytic solution through the diaphragm 103 due to the voltage between the cathode 104 and the anode 105. The reduction reaction of carbon dioxide is not limited to a reaction for producing ethylene, and may be a reaction for producing carbon monoxide, ethanol, ethane, methane, methanol, formic acid, acetic acid, propanol, etc. 2CO 2 +8H 2 O+12e - →C 2 H 4 +12OH - …(1) 12CO 2 +12OH - →12HCO 3 - …(2) HCO 3 - +OH - ←→CO 3 2- +H 2 O…(3)

[0084] In the vicinity of the anode 105 in contact with the second electrolyte solution, an oxidation reaction of water occurs. As shown in the following formula (4), H 2 The oxidation reaction of O occurs, electrons are lost, and oxygen (O 2 ) and hydrogen ions (H + ) is generated. 6H2 O→12H + +3O 2 +12e - …(4)

[0085] The hydrogen ions (H + ) neutralizes the second electrolyte and determines the pH near the anode 105. 3 - ) or carbonate ion (CO 3 2- ) is discharged from the discharge flow path 110 either as it is dissolved as a liquid or together with the oxygen generated as carbon dioxide through the equilibrium reaction of formula (5) depending on the pH near the anode 105. In the equilibrium reaction of formula (5), the higher the pH (closer to alkalinity), the more the equilibrium shifts to the right. CO 2 +H 2 O←→HCO 3 - +H + ←→CO 3 2- +2H + …(5)

[0086] When hydroxide ions are generated at the cathode 104 as described above, the greater the amount of current supplied, the more hydroxide ions are generated, and more carbon dioxide dissolves in the first electrolytic solution and moves to the anode 105 side. In other words, the greater the amount of current, the less carbon dioxide is used in the carbon dioxide reduction reaction, and the lower the carbon dioxide utilization rate. It is also possible that a phenomenon (crossover) will occur in which part of the carbon dioxide supplied to the cathode 104 side dissolves in the electrolytic solution and moves to the anode 105 through the diaphragm 103.

[0087] In the carbon dioxide electrolysis device 1, carbon dioxide that has migrated to the anode 105 side either as carbon dioxide gas or as hydrogen carbonate ions or carbonate ions is regenerated into carbon dioxide gas in the electrodialysis cell 200 and supplied again to the carbon dioxide electrolysis cell 100, thereby improving the carbon dioxide utilization rate of the entire device.

[0088] A known method for recovering carbon dioxide not used in the carbon dioxide reduction reaction is to absorb carbon dioxide gas in a scrubber and regenerate it in an electrodialysis cell. In contrast, the carbon dioxide electrolysis device 1 can regenerate carbon dioxide gas without using a scrubber.

[0089] In the electrodialysis cell 200, in order to regenerate the carbonate ions or bicarbonate ions dissolved in the second electrolyte into carbon dioxide, the carbon dioxide gas that has moved to the anode 105 side needs to be dissolved in the solution as carbonate ions or bicarbonate ions through the equilibrium reaction of formula (5). For this purpose, the pH of the fluid near the anode 105 needs to be adjusted to shift the equilibrium reaction of formula (5) to the right. The pH of the fluid near the anode 105 is determined by the flow rate of the fluid supplied to the anode flow path 102 from the pump 61 connected to the supply flow path 109, the pH of the second electrolyte before it passes through the anode flow path 102, and the amount of current supplied to the carbon dioxide electrolysis cell 100.

[0090] The pH of the fluid near the anode 105 , which causes the equilibrium reaction of equation (5), is measured by the pH / ion concentration detector 43 .

[0091] When the pH is lower than the pH at which carbon dioxide exists as bicarbonate ions or carbonate ions in the equilibrium reaction of formula (5), i.e., when the carbon dioxide that has moved to the anode 105 side is not completely dissolved in the solution, it is possible to adjust the pH to a level at which most of the carbon dioxide that has moved to the anode 105 side exists as bicarbonate ions or carbonate ions by adjusting the flow rate of the fluid supplied from the pump 61 to the anode flow path 102 or the amount of current supplied to the electrodialysis cell 200, i.e., the pH of the second electrolyte before passing through the anode flow path 102. When the pH is about 8.35 or higher, most of the carbon dioxide in the aqueous solution exists as bicarbonate ions or carbonate ions, so it is possible to control the pH measured by the pH / ion concentration detector 43 to be 8.35 or higher.

[0092] The gas-liquid two-phase fluid discharged from the discharge flow path 110 is separated into anode exhaust and anode waste liquid by the gas-liquid separator 31, the anode exhaust is recovered or discarded through a gas exhaust path 91 connected to the gas-liquid separator 31, and the anode waste liquid is supplied to the container 203 of the electrodialysis cell 200 through the subsequent supply flow path 215.

[0093] Examples of the anode exhaust include a mixed gas produced by the gaseous product of the carbon dioxide reduction reaction, such as oxygen, carbon dioxide, carbon monoxide, and ethylene, which move to the anode 105 side through the diaphragm 103 and are mixed. The gas components of the anode exhaust are measured by the carbon dioxide detector 42, and when the carbon dioxide concentration reaches a certain level or higher, the pH of the electrolyte can be controlled so that the carbon dioxide contained in the anode exhaust is dissolved in the anode effluent by adjusting the flow rate of the pump 61 or the amount of current supplied to the electrodialysis cell 200. From the viewpoint of secondary use of the oxygen gas generated at the anode 105, it is desirable that the anode exhaust discharged from the gas exhaust path 91 is a high-purity oxygen gas, and it is possible to divert it to an intake gas or a reaction gas.

[0094] The components of the anode effluent separated in the gas-liquid separator 31 are measured by the water quality detector 44. Since liquid products such as methanol, ethanol, formic acid, etc. that may be generated by the carbon dioxide reduction reaction may affect various electrodes and diaphragms and deteriorate their performance, if the concentration of these compounds in the liquid exceeds a certain concentration (prescribed value), it is possible to control the discharge and supply of liquid via the purge valve 62 so that the concentration of these compounds becomes equal to or lower than the prescribed value. The liquid to be supplied is the aqueous solution used in the second electrolyte, or an ionic liquid.

[0095] Anode waste liquid is supplied to storage unit 203 of electrodialysis cell 200 through supply flow path 215, and gas and liquid are discharged through discharge flow path 216. Circulating liquid is supplied to storage unit 204 through supply flow path 217, and gas and liquid are discharged through discharge flow path 218. Storage unit 203 and storage unit 204 contain a first electrolytic solution and a second electrolytic solution.

[0096] When a cation exchange membrane is used for diaphragm 209 and a bipolar membrane is used for each of diaphragms 207 and 208, electrode 205 is an anode, electrode 206 is a cathode, and the carbon dioxide regenerated liquid is discharged through discharge flow path 212 and the alkali regenerated liquid is discharged through discharge flow path 214.

[0097] When a bipolar membrane is used for diaphragm 209 and a cation exchange membrane is used for each of diaphragms 207 and 208, electrode 205 is a cathode, electrode 206 is an anode, and the carbon dioxide regenerated liquid is discharged through discharge flow path 212 and the alkali regenerated liquid is discharged through discharge flow path 214.

[0098] When an anion exchange membrane is used for diaphragm 209 and bipolar membranes are used for diaphragms 207 and 208, electrode 205 is a cathode, electrode 206 is an anode, and the alkaline regenerated liquid is discharged through discharge flow path 212 and the carbon dioxide regenerated liquid is discharged through discharge flow path 214.

[0099] When a bipolar membrane is used for diaphragm 209 and anion exchange membranes are used for diaphragms 207 and 208, electrode 205 is an anode, electrode 206 is a cathode, the alkaline regenerated liquid is discharged through discharge flow path 212, and the carbon dioxide regenerated liquid is discharged through discharge flow path 214.

[0100] The anion exchange membrane side of the bipolar membrane is arranged facing the anode and the cation exchange membrane side facing the cathode. By applying a positive potential to the anode using a current regulator 52, cations pass through the cation exchange membrane to move to the cathode side, and anions pass through the anion exchange membrane to move to the anode side.

[0101] The carbon dioxide regenerated liquid is separated by the gas-liquid separator 32 into a liquid containing water (second liquid) and a gas containing carbon dioxide (second gas), the second liquid is supplied as a circulating liquid to the storage unit 204 via the supply flow path 213, and the second gas is supplied to the cathode flow path 101 of the carbon dioxide electrolysis cell 100. That is, carbon dioxide that is dissolved in the second electrolytic solution in the carbon dioxide electrolysis cell 100 and is not used in the carbon dioxide reduction reaction is regenerated as carbon dioxide gas in the electrodialysis cell 200 and is used again in the carbon dioxide reduction reaction in the carbon dioxide electrolysis cell 100, thereby improving the carbon dioxide utilization rate in the carbon dioxide reduction reaction in the entire apparatus. The alkaline regenerated liquid is sent by the pump 61 via a corresponding discharge flow path to the anode flow path 102 of the carbon dioxide electrolysis cell 100 as the second electrolytic solution.

[0102] The bipolar membrane converts water into hydrogen ions (H + ) and hydroxide ion (OH - ), the hydrogen ions react with the anions remaining in the container, and the hydroxide ions react with the cations remaining in the container to form products. H 2 O→H + +OH - …(6)

[0103] At this time, an oxidation-reduction reaction occurs at the electrodes 205 and 206, an oxidation reaction occurs at the anode, and a reduction reaction occurs at the cathode. When an aqueous solution is used, the main oxidation reaction is an oxygen production reaction, and the main reduction reaction is a hydrogen production reaction, and there is a possibility that other oxidation-reduction reactions may occur depending on the remaining ion species.

[0104] The current regulator 52 can change the value of the current supplied to the electrodialysis cell 200. This makes it possible to control the rates of the water dissociation reaction in the bipolar membrane and the oxidation-reduction reaction at the electrodes, i.e., to adjust the carbon dioxide concentration in the carbon dioxide regenerated solution and the pH of the alkaline regenerated solution. As described above, the higher the current value in the carbon dioxide electrolysis cell 100, the lower the pH of the second electrolyte solution. However, in order to regenerate carbon dioxide in the electrodialysis cell 200, it is necessary to keep the pH of the electrolyte supplied to the carbon dioxide electrolysis cell 100, i.e., the alkaline regenerated solution, sufficiently high so that carbon dioxide is completely dissolved in the electrolyte as hydrogen carbonate ions or carbonate ions.

[0105] The circulating fluid and the electrode solution are pure water or an aqueous solution, and are preferably aqueous solutions having the same components as the second electrolytic solution, but may be aqueous solutions containing ions of the same cation species but different anion species when a cation exchange membrane is used, or aqueous solutions containing ions of the same anion species but different cation species when an anion exchange membrane is used. It is preferable that the aqueous solution has a low solution resistance so as to have little effect on the diaphragm and reduce the resistance between the electrodes.

[0106] Next, as a result of the operation of the carbon dioxide electrolysis cell 100, an aqueous solution containing potassium ions, bicarbonate ions, and carbonate ions is obtained as the anode discharge liquid, and 0.02M KHCO 3 Aqueous solution, electrode solution: 1M K 2 CO 3 An example of the operation of the electrodialysis cell 200 using an aqueous solution, a cation exchange membrane for the diaphragm 209, and bipolar membranes for each of the diaphragms 207 and 208 will be described.

[0107] Potassium ions in the anode effluent stored in storage section 203 move to storage section 204 due to the voltage applied between electrodes 205 and 206, and storage section 203 changes to a state in which there are many bicarbonate ions and carbonate ions, and storage section 204 changes to a state in which there are many potassium ions. A water dissociation reaction occurs in diaphragms 207 and 208 due to the electric potential, and hydrogen ions move to storage section 203, and hydroxide ions move to storage section 204. As a result, the pH of the anode effluent decreases in storage section 203 due to the hydrogen ions, and the equilibrium reaction of formula (5) shifts to the left, resulting in water and carbon dioxide. Alternatively, hydrogen ions react with bicarbonate ions or carbonate ions to produce water and carbon dioxide, as shown in formulas (7) and (8). In storage section 204, potassium ions react with hydroxide ions to produce potassium hydroxide, as shown in formula (9). H + +HCO 3 - →H 2 O+CO 2 …(7) 2H + +CO 3 2- →H 2 O+CO 2 …(8) K + +OH - →KOH…(9)

[0108] As a result of the water dissociation reaction occurring in diaphragms 207 and 208, hydroxide ions move to storage section 201, causing the first electrolytic solution in storage section 201 to change to a state in which the content of hydroxide ions is greater, and hydrogen ions move to storage section 202, causing the second electrolytic solution in storage section 202 to change to a state in which the content of hydrogen ions is greater. At electrode 205 in storage section 201 to which a positive potential is applied, an oxidation reaction of hydroxide ions occurs, generating oxygen gas, and at electrode 206 in storage section 202 to which a negative potential is applied, a reduction reaction of hydrogen ions occurs, generating hydrogen gas. These generated gases are discharged via discharge flow paths 212 and 214 and are discarded or recovered for reuse.

[0109] In this way, of the carbon dioxide supplied to the carbon dioxide electrolysis cell 100, in addition to the carbon dioxide that is not used in the reaction and remains in the product gas, carbon dioxide dissolved in the liquid at the cathode 104 moves to the anode 105 and is formed, and when an alkaline solution is used as the electrolyte, carbon dioxide dissolves in the alkaline solution and becomes carbon dioxide gas at the anode 105, which is then discharged as a gas, is not used in the electrolytic reaction and reduces the carbon dioxide utilization rate of the entire device.

[0110] In this embodiment, in an electric field device in which an electrodialysis cell 200 is combined with a carbon dioxide electrolysis cell 100, the carbon dioxide concentration in the generated gas, the pH of the electrolytic solution, and the carbon dioxide concentration in the anode exhaust are monitored, and the flow rate of carbon dioxide supplied to the carbon dioxide electrolysis cell 100, the value of the current supplied to the electrodialysis cell 200, and the flow rate of the fluid supplied from the pump 61 to the anode flow path 102 are adjusted according to the monitored values, thereby improving the carbon dioxide utilization rate. Furthermore, the power supplied to the electrodialysis cell can also be reduced.

[0111] Second Embodiment The carbon dioxide electrolysis device of the second embodiment differs from the carbon dioxide electrolysis device of the first embodiment in the structure of the carbon dioxide electrolysis cell 100.

[0112] Fig. 5 is a schematic diagram showing an example of the structure of a carbon dioxide electrolysis cell 100 according to the second embodiment. The carbon dioxide electrolysis cell 100 shown in Fig. 5 has a solid polymer structure and includes a flow path plate 121, a flow path plate 122, a diaphragm 103, a cathode 104, an anode 105, a supply flow path 106, a supply flow path 107, a discharge flow path 108, a supply flow path 109, a discharge flow path 110, a current collector 125, and a current collector 126.

[0113] The flow channel plate 121 forms a cathode flow channel 123 including a groove facing the cathode 104. The cathode flow channel 123 is connected to the supply flow channel 106 and the exhaust flow channel 108.

[0114] The flow channel plate 122 forms an anode flow channel 124 including a groove facing the anode 105. The anode flow channel 124 is connected to the supply flow channel 109 and the exhaust flow channel 110.

[0115] The current collector 125 is electrically connected to the flow path plate 121 and the cathode 104. The current collector 126 is electrically connected to the flow path plate 122 and the anode 105. The current collector 125 and the current collector 126 are electrically connected to each other via wiring.

[0116] The flow path plate 121, the flow path plate 122, the diaphragm 103, the cathode 104, and the anode 105 are integrated together under a certain pressure.

[0117] The rest of the description is the same as that of the carbon dioxide electrolysis cell 100 of the first embodiment, and the description of the first embodiment can be used as appropriate.

[0118] During operation of the carbon dioxide electrolysis cell 100, products of the reduction of carbon dioxide and components of the second electrolytic solution that migrate to the cathode 104 side may solidify and precipitate in the cathode flow path 123, causing the cathode flow path 123 to become clogged and the supply of the carbon dioxide-containing gas to stop. For this reason, it is preferable that moisture be present in the carbon dioxide-containing gas to suppress the formation of precipitates.

[0119] On the other hand, if the water content of the gas containing carbon dioxide is too high, it is not preferable because a large amount of water is supplied to the catalyst surface in the cathode 104, which makes it easier for hydrogen to be generated. Therefore, the water content in the gas containing carbon dioxide is preferably 20% or more and 90% or less in relative humidity, and more preferably 30% or more and 70% or less.

[0120] A gas containing carbon dioxide is supplied to the cathode flow channel 123 via the supply flow channel 106, and the product of the cathode 104 is discharged via the discharge flow channel 108. As described above, it is preferable for the gas containing carbon dioxide to contain a certain amount of moisture, so it is preferable to connect a humidifier to the supply flow channel 106 and control the humidity of the supply gas. A second electrolytic solution is supplied to the anode flow channel 124 via the supply flow channel 109, and the product of the anode 105 and carbon dioxide moving from the cathode 104 are discharged via the discharge flow channel 110 together with the second electrolytic solution.

[0121] 2, the carbon dioxide utilization rate of the entire device can be improved by dissolving carbon dioxide that is not used in the carbon dioxide reduction reaction in the carbon dioxide electrolysis cell 100 in the electrolytic solution. In particular, the carbon dioxide utilization rate can be improved by measuring the carbon dioxide concentrations in the generated gas and the anode exhaust gas, and the pH of the anode effluent, and controlling the amount of carbon dioxide supplied to the carbon dioxide electrolysis cell 100 and the flow rate of the pump 61.

[0122] 2, carbon dioxide not used in the carbon dioxide reduction reaction in the carbon dioxide electrolysis cell 100 can be dissolved in the electrolytic solution, thereby regenerating carbon dioxide in the electrodialysis cell 200. In particular, the carbon dioxide utilization rate can be improved by measuring the carbon dioxide concentration in the generated gas, the carbon dioxide concentration in the anode exhaust gas, and the pH of the anode effluent, and controlling the flow rate of carbon dioxide supplied to the carbon dioxide electrolysis cell 100, the value of the current supplied to the electrodialysis cell 200, and the flow rate of the fluid supplied from the pump 61 to the anode flow path 102.

[0123] It should be noted that this embodiment can be appropriately combined with other embodiments. EXAMPLES

[0124] Next, examples and their evaluation results will be described.

[0125] (Examples 1 to 9) Fig. 6 is a schematic diagram showing an example of the structure of the carbon dioxide electrolysis device of Example 1. The carbon dioxide electrolysis device 1A shown in Fig. 6 includes a carbon dioxide electrolysis cell 100, a carbon dioxide detector 41, a carbon dioxide detector 42, a gas-liquid separator 31, a flow meter 34, a pH / ion concentration detector 43, a current regulator 51, a pump 61, a carbon dioxide supply source 71, a carbon dioxide flow regulator 72, an argon supply source 73, and an electrolyte supply source 94.

[0126] The carbon dioxide electrolysis cell 100 has the configuration shown in Figure 5. The cathode 104 is 4 cm 2 The anode 105 is a 4 cm square piece of carbon paper coated with copper nanoparticles. 2 IrO on Ti nonwoven fabric cut into a corner 2 The electrodes are coated with nanoparticles. The diaphragm 103 is an anion exchange membrane. The rest of the description of the carbon dioxide electrolysis cell 100 can be appropriately referred to the description of FIG.

[0127] The carbon dioxide detector 41 is connected to the exhaust flow path 108 of the carbon dioxide electrolysis cell 100 via a flow meter 34. The carbon dioxide detector 41 is a gas chromatograph. Other details of the carbon dioxide detector 41 can be explained with reference to the explanation of FIG. 1 as appropriate.

[0128] The carbon dioxide detector 42 is connected to the gas-liquid separator 31. The carbon dioxide detector 42 is a gas chromatograph. The rest of the description of the carbon dioxide detector 42 can be appropriately referred to the description of FIG.

[0129] The pH / ion concentration detector 43 is connected to the gas-liquid separator 31. The pH / ion concentration detector 43 is a pH sensor.

[0130] The current regulator 51 has a galvanostat. The galvanostat applies a constant current to the carbon dioxide electrolysis cell 100. The rest of the description of the current regulator 51 can be appropriately cited from the description of FIG.

[0131] The pump 61 is provided to supply the electrolyte solution supplied from the electrolyte solution supply source 94 to the supply flow path 109 of the carbon dioxide electrolysis cell 100. For other details of the pump 61, the description of FIG. 1 can be used as appropriate.

[0132] The carbon dioxide supply source 71 includes a carbon dioxide tank that stores carbon dioxide gas. The carbon dioxide supply source 71 may include a pump for supplying carbon dioxide.

[0133] The carbon dioxide flow regulator 72 is a mass flow controller.

[0134] The argon supply source 73 includes an argon tank that stores argon gas, and may include a pump for supplying argon.

[0135] The electrolyte supply 94 includes an electrolyte tank that contains an electrolyte.

[0136] Using the carbon dioxide electrolysis device 1A, the pH and flow rate of the electrolyte required for carbon dioxide to exist in a state dissolved in the electrolyte as hydrogen carbonate ions or carbonate ions were investigated. A galvanostat was used as the current regulator, and a constant current was applied to the carbon dioxide electrolysis cell 100.

[0137] The carbon dioxide electrolysis device 1A was operated under the following conditions. Carbon dioxide gas with a purity of more than 99.9% was introduced into the cathode flow passage 123 at a predetermined flow rate. The product gas discharged from the cathode flow passage 123 was diluted 10 times with argon gas and then introduced into the carbon dioxide detector 41. The electrolyte was introduced from the electrolyte supply source 94 into the anode flow passage 124 at a predetermined flow rate. A current density of 0 mA / cm was maintained between the cathode 104 and anode 105 of the carbon dioxide electrolysis cell 100 by a galvanostat. 2 、 50mA / cm 2 , 100mA / cm 2 , 200mA / cm 2 , 300mA / cm 2Voltage was applied under different conditions so that the pH of the anode effluent discharged from gas-liquid separator 31 and the components of the generated gas after a certain time for each current value were measured by water quality detector 41. Measurements were performed using a 0.1 M potassium hydroxide aqueous solution, a 0.1 M potassium carbonate aqueous solution, and a 0.1 M potassium bicarbonate aqueous solution as the electrolyte, with the carbon dioxide flow rate changed to 20 mL / min and 40 mL / min, and the electrolyte flow rate changed to 5 mL / min and 10 mL / min. The conditions for each example are as shown in Table 1.

[0138] [Table 1]

[0139] FIG. 7 is a graph showing the carbon dioxide concentration in the generated gas at each current density. 2 The value is the concentration measured without current flow, and the mass concentration of the generated gas is about 10% because it was diluted 10 times with argon after passing through 100 carbon dioxide electrolysis cells and then measured by GC. The plots indicated by circle markers are the results at a carbon dioxide flow rate of 40 mL / min and an electrolyte flow rate of 10 mL / min, the plots indicated by triangle markers are the results at a carbon dioxide flow rate of 40 mL / min and an electrolyte flow rate of 5 mL / min, and the plots indicated by square markers are the results at a carbon dioxide flow rate of 20 mL / min and an electrolyte flow rate of 10 mL / min. In all results, as the current density increases, the amount of carbon dioxide used in the carbon dioxide electrolysis reaction increases, and the carbon dioxide concentration in the generated gas decreases. When the carbon dioxide flow rate is reduced, the carbon dioxide concentration in the generated gas decreases relatively, and it can be seen that it is possible to control the amount of carbon dioxide in the generated gas by controlling the carbon dioxide supply to an optimal amount according to the current density.

[0140] 8 is a graph showing the pH of the electrolyte after passing through the anode flow channel 102 at each current density. 2The value of indicates the pH of the electrolyte in the electrolyte tank before measurement. The measurement conditions for each plot are as described above. For all electrolytes, the pH of the electrolyte decreased as the current density increased. This is more noticeable when the electrolyte flow rate is low, and is thought to be because the electrolyte remains near the anode 105 where hydrogen ions are generated for a long time. This shows that the pH of the electrolyte after passing through the anode 105 can be kept high by increasing the flow rate of the pump 61, and conversely, the pH of the electrolyte after passing through the anode 105 decreases by decreasing the flow rate.

[0141] FIG. 9 shows a carbon dioxide electrolysis cell 100 with a current density of 300 mA / cm 2 1 shows the relationship between the carbon dioxide concentration in the anode exhaust separated by the gas-liquid separator 31 and the pH of the electrolyte when a current density of 10 V is applied. Since all measurements were performed at the same current density, the total amount of carbon dioxide that moved from the cathode flow path 101 to the anode flow path 102 was the same at each point. However, it can be seen that the lower the pH of the electrolyte after passing through the carbon dioxide electrolysis cell 100, the greater the amount of carbon dioxide present as a gas, and when the pH exceeds 9, the carbon dioxide concentration in the gas on the anode 105 side can be suppressed to 1% or less. This example demonstrates that it is possible to control the pH of the anode effluent by controlling the pH of the electrolyte supplied to the carbon dioxide electrolysis cell 100, the current value supplied to the electrodialysis cell 200, and the flow rate of the pump 61, and that it is possible to reduce the amount of carbon dioxide that is not used in the reaction and is exhausted as a gas by controlling the pH of the anode effluent and the amount of carbon dioxide introduced into the cathode 104. This shows that the carbon dioxide utilization rate of the carbon dioxide electrolysis device can be improved by the method of this embodiment.

[0142] The above embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0143] 1...carbon dioxide electrolysis device, 1A...carbon dioxide electrolysis device, 31...gas-liquid separator, 32...gas-liquid separator, 34...flow meter, 41...carbon dioxide detector, 42...carbon dioxide detector, 43...pH·ion concentration detector, 44...water quality detector, 51...current regulator, 52...current regulator, 61...pump, 62...purge valve, 63...pump, 64...pump, 71...carbon dioxide supply source, 72...carbon dioxide flow regulator, 73...argon supply source, 81...controller, 82...controller, 91...gas exhaust path, 92...electrolyte path, 93...electrolyte tank, 94...electrolyte supply source, 100...carbon dioxide electrolysis cell, 101...cathode flow path, 102...anode flow path, 10 3...diaphragm, 104...cathode, 105...anode, 106...supply flow path, 107...supply flow path, 108...discharge flow path, 109...supply flow path, 110...discharge flow path, 121...flow path plate, 122...flow path plate, 123...cathode flow path, 124...anode flow path, 124...flow path plate, 125...current collector, 126...current collector, 200...electrodialysis cell, 201...receptacle, 202...receptacle, 203...receptacle, 204...receptacle, 205...electrode, 206...electrode, 207...diaphragm, 208...diaphragm, 209...diaphragm, 211...supply flow path, 212...discharge flow path, 213...supply flow path, 214...discharge flow path, 215...supply flow path, 216...discharge flow path, 217...supply flow path, 218...discharge flow path.

Claims

1. a carbon dioxide electrolysis cell including: a cathode flow path through which carbon dioxide flows; an anode flow path through which a water-containing electrolytic solution flows; a cathode facing the cathode flow path and for reducing the carbon dioxide to produce a carbon compound; an anode facing the anode flow path and for oxidizing the water to produce oxygen; and a first diaphragm provided between the anode flow path and the cathode flow path; a first current regulator for supplying a first current to the carbon dioxide electrolysis cell; a first gas-liquid separator that separates a first fluid discharged from the anode flow channel into a first liquid and a first gas; an electrodialysis cell having a first container, a first electrode disposed in the first container, a second container, a second electrode disposed in the second container, a third container provided between the first container and the second container and configured to accommodate the first liquid supplied from the first gas-liquid separator, a fourth container provided between the third container and the second container, a second diaphragm provided between the first container and the third container, a third diaphragm provided between the second container and the fourth container, and a fourth diaphragm provided between the third container and the fourth container; a second current regulator supplying a second current to the electrodialysis cell; At least one detector selected from the group consisting of a first detector that detects the flow rate of the first gas or the concentration of carbon dioxide contained in the first gas, and a second detector that detects the pH of the first fluid or the concentration of at least one type of ion contained in the first fluid; a first controller that controls the second current regulator to adjust a value of the second current based on at least one detection signal from the at least one detector; a second gas-liquid separator that separates the fourth fluid discharged from the third storage unit into a second liquid containing the electrolytic solution and a second gas containing the carbon dioxide; Equipped with The second gas is supplied to the cathode flow path.

2. a third detector for detecting a concentration of carbon dioxide contained in the first fluid; a second controller that controls the first current regulator to adjust the value of the first current based on a detection signal from the third detector; The carbon dioxide electrolysis device of claim 1 further comprising:

3. The cathode flow channel further includes a flow rate regulator that regulates a flow rate of a second fluid containing carbon dioxide. The carbon dioxide electrolysis device according to claim 2 , wherein the second controller controls the flow regulator to adjust the flow rate of the second fluid based on a detection signal from the third detector.

4. a pump for supplying a third fluid discharged from the fourth storage section to the anode flow path; 4. The carbon dioxide electrolysis device according to claim 1, wherein the first controller controls the pump to adjust a flow rate of the third fluid supplied to the anode flow channel, based on at least one detection signal from the at least one detector.

5. A carbon dioxide electrolysis device as described in any one of claims 1 to 4, wherein the second liquid is supplied to the fourth storage section.

6. 6. The carbon dioxide electrolysis device according to claim 1, wherein the electrolytic solution contains at least one ion selected from the group consisting of hydroxide ions, carbonate ions, and bicarbonate ions.

7. a fourth detector for detecting a concentration of at least one component contained in the first liquid; a purge valve for replenishing the first liquid with electrolyte or for draining a portion of the first liquid; Further comprising:

7. The carbon dioxide electrolysis device according to claim 1, wherein the first controller controls the purge valve to replenish the electrolytic solution or to discharge a part of the first liquid so that a concentration of at least one component contained in the first liquid becomes equal to or lower than a specified value, based on a detection signal from the fourth detector.

8. A method for controlling a carbon dioxide electrolysis device, comprising: The carbon dioxide electrolysis device comprises: a carbon dioxide electrolysis cell including: a cathode flow path through which carbon dioxide flows; an anode flow path through which a water-containing electrolytic solution flows; a cathode facing the cathode flow path and for reducing the carbon dioxide to produce a carbon compound; an anode facing the anode flow path and for oxidizing the water to produce oxygen; and a first diaphragm provided between the anode flow path and the cathode flow path; a first gas-liquid separator that separates a first fluid discharged from the anode flow channel into a first liquid and a second gas; an electrodialysis cell having a first container, a first electrode disposed in the first container, a second container, a second electrode disposed in the second container, a third container provided between the first container and the second container and configured to accommodate the first liquid supplied from the first gas-liquid separator, a fourth container provided between the third container and the second container, a second diaphragm provided between the first container and the third container, a third diaphragm provided between the second container and the fourth container, and a fourth diaphragm provided between the third container and the fourth container; a second gas-liquid separator that separates the fourth fluid discharged from the third storage unit into a second liquid containing the electrolytic solution and a second gas containing the carbon dioxide; Equipped with The method comprises: separating the first fluid discharged from the anode flow channel into a first liquid and a first gas, and detecting at least one selected from the group consisting of a flow rate of the first gas or a concentration of carbon dioxide contained in the first gas, a pH of the first fluid, and a concentration of at least one type of ion contained in the first fluid; adjusting a value of the current supplied to the electrodialysis cell based on the at least one sensing result; Equipped with The second gas is supplied to the cathode flow path.

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