Carbon dioxide electrolysis device, carbon dioxide electrolysis method, and valuable substance manufacturing system

Abstract

The carbon dioxide electrolysis device of the embodiment includes: an electrolytic cell (including: a first accommodation portion for accommodating carbon dioxide, a second accommodation portion for accommodating an electrolyte containing water or water vapor, a diaphragm provided between the first accommodation portion and the second accommodation portion, a reduction electrode arranged in the first accommodation portion, and an oxidation electrode arranged in the second accommodation portion); a first power supply control portion (capable of being connected with a first power supply for supplying power to the electrolytic cell); a second power supply control portion (capable of being connected with a second power supply for supplying power to the electrolytic cell); and a comprehensive control portion (controlling the first power supply control portion and the second power supply control portion, and switching the power supply from the first power supply or the second power supply to the electrolytic cell).

Description

[0001] This application is based on Japanese Patent Application No. 2021-151516 (Filing date: September 16, 2021) the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present embodiment relates to a carbon dioxide electrolysis device, a carbon dioxide electrolysis method, and a valuable substance manufacturing system. BACKGROUND

[0003] In recent years, there are concerns about the depletion of fossil fuels such as oil and coal, and expectations for renewable energy that can be used sustainably are increasing. As renewable energy, solar power generation, hydroelectric power generation, wind power generation, geothermal power generation, and the like can be cited. They are power sources (fluctuating power sources) whose output fluctuates depending on weather and natural conditions and the like. Therefore, attempts are being made to combine fluctuating power sources with storage batteries to adjust the power. However, when storing power, there are problems that the storage battery requires cost, and that loss occurs when storing power.

[0004] Further, as an attempt to decarbonize, carbon dioxide (CO2) electrolysis technology that electrochemically reduces CO2 into chemical substances (chemical energy) such as carbon compounds such as carbon monoxide (CO), formic acid (HCOOH), methanol (CH3OH), methane (CH4), acetic acid (CH3COOH), ethanol (C2H5OH), ethane (C2H6), ethylene (C2H4) is attracting attention. By connecting a fluctuating power source using renewable energy to a carbon dioxide electrolysis device, it has an advantage that power adjustment and resource utilization of carbon dioxide can be performed at the same time. When combining a fluctuating power source and a carbon dioxide electrolysis device, development of a system that suppresses fluctuation in the concentration of unreacted CO2 in the generated gas is being conducted.

[0005] When electrochemically reducing CO2 using renewable energy, as described above, power is likely to fluctuate due to changes in weather, wind conditions, and the like. Along with such power fluctuation, there are problems that the operation of the carbon dioxide electrolysis device is unstable, the amount of reaction of CO2 in the carbon dioxide electrolysis device changes, and the concentration of unreacted CO2 gas in the generated gas easily fluctuates. Fluctuation in the concentration of unreacted CO2 gas in the generated gas is a major cause of reduction in the manufacturability and manufacturing efficiency of valuable substances and the like when manufacturing valuable substances such as gasoline, jet fuel, or methanol using the gas generated by the carbon dioxide electrolysis device and the like. SUMMARY

[0006] PROBLEMS TO BE SOLVED BY THE INVENTION

[0007] An object of the present application is to provide a carbon dioxide electrolysis device and a carbon dioxide electrolysis method capable of suppressing destabilization of operation accompanying power fluctuations, and a valuable substance manufacturing system using such a carbon dioxide electrolysis device.

[0008] Means for solving the problem

[0009] The carbon dioxide electrolysis device of the embodiment includes:

[0010] an electrolytic cell including a first accommodation portion for accommodating at least carbon dioxide, a second accommodation portion for accommodating an electrolyte containing water or water vapor, a separator provided between the first accommodation portion and the second accommodation portion, a reduction electrode disposed in the first accommodation portion, and an oxidation electrode disposed in the second accommodation portion,

[0011] a first power supply control portion connectable to a first power supply that supplies power to the electrolytic cell,

[0012] a second power supply control portion connectable to a second power supply that supplies power to the electrolytic cell, and

[0013] a comprehensive control portion that controls the first power supply control portion and the second power supply control portion, and switches the supply of power to the electrolytic cell from the first power supply or the second power supply. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is a view that shows a carbon dioxide electrolysis device of a first embodiment.

[0015] Figure 2 is a view that shows an electrolytic cell in the carbon dioxide electrolysis device of the first embodiment.

[0016] Figure 3 is a view that shows an operation process of the carbon dioxide electrolysis device of the first embodiment.

[0017] Figure 4 is a view that shows a carbon dioxide electrolysis device of a second embodiment.

[0018] Figure 5 is a view that shows an electrolytic cell in the carbon dioxide electrolysis device of the second embodiment.

[0019] Figure 6 is a view that shows a carbon dioxide electrolysis device of a third embodiment.

[0020] Figure 7 is a view that shows a carbon dioxide electrolysis device of a fourth embodiment.

[0021] Figure 8 is a view that shows a carbon dioxide electrolysis device of a fifth embodiment.

[0022] Figure 9 is a graph showing an electrolytic cell in the carbon dioxide electrolysis device of the 5th embodiment.

[0023] Figure 10 is a graph showing a carbon dioxide electrolysis device of the 6th embodiment.

[0024] Figure 11 is a graph showing a carbon dioxide electrolysis device used in the example.

[0025] Figure 12 is a graph showing a time change of the current in Example 1.

[0026] Figure 13 is a graph showing changes in the cell voltage, the reduction electrode potential, and the oxidation electrode potential when the time (Δtl) in which the current of the 1st power source in Example 1 is made zero is changed.

[0027] Figure 14 is a table showing the results of the investigation whether or not the start-up can be promptly made when Δtl in Example 1 is changed.

[0028] Figure 15 is a table showing the results of the investigation whether or not the start-up can be promptly made when Δtl and the current at the time of the warm-up operation in Example 1 are changed.

[0029] Figure 16 is a graph showing a current change at the time of the low-speed start-up in Example 2.

[0030] Figure 17 is a graph showing the results of the measurement of the cell voltage when the current rise time Δt2 in Example 2 is changed.

[0031] Figure 18 is a table showing the results of the investigation whether or not the start-up can be promptly made when Δt2 in Example 2 is changed.

[0032] (Symbol explanation)

[0033] 1... carbon dioxide electrolysis device, 2... cathode portion, 3... anode portion, 4... electrolytic cell, 5... 1st power source, 6... 1st power source control portion, 7... 2nd power source, 8... 2nd power source control portion, 9... detection portion, 10... gas control portion, 11... integrated control portion, 13... 1st housing portion, 14... reduction electrode 3, 16... 2nd housing portion, 17... oxidation electrode, 18... separator, 31... 1st flow path, 32... 2nd flow path, 60... valuable substance manufacturing system, 61... chemical synthesis device, 63... chemical synthesis portion. DETAILED DESCRIPTION

[0034] Hereinafter, a carbon dioxide electrolysis device, a carbon dioxide electrolysis method, and a valuable substance manufacturing system according to an embodiment will be described with reference to the drawings. In each of the embodiments shown below, the same constituent parts are basically denoted by the same reference symbols, and the description thereof will be sometimes omitted. The drawings are schematic, and the relationship between the thickness and the planar dimensions, the ratio of the thickness of each part, and the like are sometimes different from the actual ones.

[0035] (First Embodiment)

[0036] Figure 1 is a view showing a carbon dioxide electrolysis device 1 (1A) according to the first embodiment. Figure 1 The carbon dioxide electrolysis device 1A shown in the figure is provided with: an electrolytic cell 4 (4A) of carbon dioxide (CO2) having a cathode section 2 and an anode section 3; a first power source control section 6 connected to a first power source (external power source) 5 that supplies electric power to the electrolytic cell 4A; a second power source control section 8 connected to a second power source (external power source or internal power source) 7 that supplies electric power to the electrolytic cell 4A; a detection section 9 that detects the reaction amount of the electrolytic cell 4A; a gas control section 10 that controls the supply amount of a gas containing carbon dioxide (CO2) supplied to the cathode section 2 of the electrolytic cell 4A, and the like; and a comprehensive control section 11 that comprehensively controls each of the control sections 6, 8, 10, and the detection section 9, and the like. Hereinafter, each of the sections will be described in detail.

[0037] As shown in Figure 2 , the electrolytic cell 4A of CO2 is provided with:

[0038] the cathode section 2 having a first housing section (housing groove) 13 for housing a first electrolyte 12 containing CO2 and a reduction electrode (cathode) 14 disposed in the first housing section 13;

[0039] the anode section 3 having a second housing section (housing groove) 16 for housing a second electrolyte 15 containing water and an oxidation electrode (anode) 17 disposed in the first housing section 16; and

[0040] a separator 18 disposed between the first housing section 13 and the second housing section 16.

[0041] The first housing section 13, the second housing section 16, and the separator 18 constitute a reaction groove 19.

[0042] The two chambers of the first housing section 13 and the second housing section 16 in the reaction groove 19 are made permeable to hydrogen ions (H + ), hydroxide ions (OH - ), bicarbonate ions (HCO3 - ), and carbonate ions (CO3 2-The diaphragm 18 is separated by plasma movement. The reaction tank 19 can be formed of, for example, quartz white plate glass, acrylic resin (PMMA), polystyrene (PS), or the like. A part of the reaction tank 5 can use a light-transmissive material, and the remaining part can use a resin material. Examples of the resin material include, for example, polyether ether ketone (PEEK), polyamide (PA), polyvinylidene fluoride (PVDF), polyoxymethylene (POM) (copolymer), polyphenylene ether (PPE), acrylonitrile-butadiene-styrene copolymer (ABS), polypropylene (PP), polyethylene (PE), or the like.

[0043] The reduction electrode 14 is arranged in the first housing portion 13, and CO2 is further housed therein. The CO2 is housed in the first housing portion 13 in the form of the first electrolyte solution 12 containing the CO2, for example. The first electrolyte solution 12 functions as a reduction electrode solution (cathode solution), and contains carbon dioxide (CO2) as a substance to be reduced. Here, the form of the CO2 present in the first electrolyte solution 12 is not limited to a gaseous state, and can be dissolved CO2 or carbonate ions (CO3 2- ), bicarbonate ions (HCO3 - ), or the like. The first electrolyte solution 12 can contain hydrogen ions, and is preferably an aqueous solution. The oxidation electrode 17 is arranged in the second housing portion 16, and the second electrolyte solution 15 containing water is further housed therein. The second electrolyte solution 15 functions as an oxidation electrode solution (anode solution), and contains, for example, water (H2O), chloride ions (Cl - ), carbonate ions (CO3 2- ), bicarbonate ions (HCO3 - ), or the like, as a substance to be oxidized. The second electrolyte solution 15 can be an aqueous alcohol solution, an aqueous amine solution, or the like.

[0044] By changing the amount of water and the electrolyte components contained in the first and second electrolyte solutions 12 and 15, the reactivity, the selectivity of the reduced substance, and the ratio of the generated chemical substances can be changed. The first and second electrolyte solutions 12 and 15 can contain redox couples as needed. Examples of the redox couples include, for example, Fe 3+ / Fe 2+ or IO 3- / I - . The first housing portion 13 is connected to a gas supply flow path 20 for supplying a raw material gas containing CO2 and a first liquid supply flow path 21 for supplying the first electrolyte solution 12, and is further connected to a first gas and liquid discharge flow path 22 for discharging a reaction gas and the first electrolyte solution 12. The second housing portion 16 is connected to a second liquid supply flow path 23 for supplying the second electrolyte solution 15, and is further connected to a second gas and liquid discharge flow path 24. The first and second housing portions 13 and 16 can further have a space portion for housing a gas contained in a reactant and a product.

[0045] A flow rate adjusting section 25 that adjusts the amount of the CO2-containing raw material gas supplied to the first housing section 13 is provided in the gas supply flow path 20. As the flow rate adjusting section 25, for example, a variable throttle valve or a flow rate regulating valve is used. A flow meter 26 is also provided in the gas supply flow path 20. That is, the flow rate of the raw material gas flowing in the gas supply flow path 20 can be adjusted by the flow rate adjusting section 25, and the flow rate of the adjusted raw material gas can be measured. A pump 27 that delivers the first electrolyte 12 to the first housing section 13 is provided in the first liquid supply flow path 21. A pump 28 that delivers the second electrolyte 15 to the second housing section 16 is provided in the second liquid supply flow path 23. The first gas and liquid discharge flow path 22 has a generated gas flow path 22A and an exhaust flow path 22B, which are configured to be switched by on-off valves VI, V2. A gas-liquid separator that separates the generated gas from the electrolyte or the like can also be connected to the first and second gas and liquid discharge flow paths 22, 24.

[0046] The pressure in the first and second housing sections 13, 16 is preferably set to a pressure at which CO2 is not liquefied, and specifically, is preferably adjusted to a range of 0.1 MPa or higher and 6.4 MPa or lower. If the pressure in the housing sections 13, 16 is less than 0.1 MPa, the reduction reaction efficiency of CO2 can decrease. If the pressure in the housing sections 13, 16 exceeds 6.4 MPa, CO2 is liquefied, and the reduction reaction efficiency of CO2 can decrease. Sometimes, damage to the separator 18 or the like occurs due to the pressure difference between the first housing section 13 and the second housing section 16. Therefore, the difference (pressure difference) between the pressure of the first housing section 13 and the pressure of the second housing section 16 is preferably 1 MPa or lower.

[0047] The lower the temperature of the electrolytes 12, 15, the higher the solubility of CO2, but from the viewpoint of carbon dioxide electrolysis, the solution resistance becomes high at low temperatures, and the theoretical voltage of the reaction becomes high, and thus it is not favorable. On the other hand, when the temperature of the electrolytes 12, 15 is high, the amount of dissolved CO2 becomes low, but it is favorable for carbon dioxide electrolysis. Therefore, the operating temperature condition of the electrolytic cell 4A is preferably in a moderate temperature range, for example, a range of atmospheric temperature or higher and the boiling point of the electrolytes 12, 15 or lower. When the electrolytes 12, 15 are aqueous solutions, it is preferable that the temperature be 10°C or higher and 100°C or lower, and more preferably 25°C or higher and 80°C or lower. When the CO2-containing raw material gas is filled in the first housing section 13 and water vapor is filled in the second housing section 16, it is possible to operate at a higher temperature. At this time, the operating temperature is determined in consideration of the heat resistance of the components such as the separator 18. In the case where the separator 18 is an ion exchange membrane or the like, the operating temperature is at most 180°C, and in the case where a high polymer porous membrane such as Teflon (registered trademark) is used, the maximum temperature is 300°C.

[0048] The first electrolyte 12 and the second electrolyte 15 can be electrolytes containing different substances, or they can be the same electrolyte containing the same substances. If the first electrolyte 12 and the second electrolyte 15 contain the same substances and the same solvent, they can be considered as one electrolyte. Furthermore, the pH of the second electrolyte 12 can be higher than the pH of the first electrolyte 15. This allows hydrogen ions, hydroxide ions, and other ions to easily move through the membrane 18. Additionally, the potential difference between the liquids caused by the pH difference enables efficient redox reactions.

[0049] The first electrolyte 12 is preferably a solution with a high CO2 absorption rate. The form in which CO2 exists in the first electrolyte 12 is not limited to a dissolved state; CO2 in a bubbly state may also be present in the first electrolyte 12. Examples of electrolytes containing CO2 include aqueous solutions of bicarbonates or carbonates such as lithium bicarbonate (LiHCO3), sodium bicarbonate (NaHCO3), potassium bicarbonate (KHCO3), cesium bicarbonate (CsHCO3), sodium carbonate (Na2CO3), and potassium carbonate (K2CO3), as well as phosphoric acid and boric acid. The CO2-containing electrolyte may contain alcohols such as methanol, ethanol, and acetone, or may be an alcohol solution. The first electrolyte 12 may also be an electrolyte containing a CO2 absorbent that lowers the reduction potential of CO2, has high ionic conductivity, and absorbs CO2.

[0050] The second electrolyte 15 can be a solution using water (H2O), such as an aqueous solution containing any electrolyte. This solution is preferably an aqueous solution that promotes the oxidation reaction of water. Examples of aqueous solutions containing electrolytes include those containing phosphate ions (PO42O). 2- ), borate ions (BO3) 3- Sodium ions (Na) + ), potassium ions (K) + ), calcium ions (Ca 2+ Lithium ion (Li) + ), cesium ions (Cs) + ), magnesium ions (Mg 2+ ), chloride ions (Cl) - ), bicarbonate ions (HCO3) - ), carbonate ions (CO3) 2- ), hydroxide ions (OH-) - Aqueous solutions of , etc.

[0051] For example, electrolytes 12 and 15 can be used containing imidazole. Ions or pyridine Ions and cations with BF4 - or PF6 -ionic liquids which are salts formed of anions and are liquid at a wide temperature range or aqueous solutions thereof. Further, as other electrolytes, amine solutions or aqueous solutions thereof such as ethanolamine, imidazole, pyridine, etc. can be given. As the amines, primary amines, secondary amines and tertiary amines can be given. These electrolytes have high ionic conductivity, a property of absorbing carbon dioxide, and can have a characteristic of reducing reduction energy.

[0052] As the primary amines, methylamine, ethylamine, propylamine, butylamine, amylamine, hexylamine, etc. can be given. The hydrocarbon of the amine can be substituted with alcohol or halogen, etc. As the amine-substituted hydrocarbon, methanolamine, ethanolamine, chloromethylamine, etc. can be given. Further, unsaturated bonds can be present. These hydrocarbons are equally applicable to secondary amines and tertiary amines.

[0053] As the secondary amines, dimethylamine, diethylamine, dipropylamine, dibutylamine, diamylamine, dihexylamine, dimethanolamine, diethanolamine and dipropanolamine can be given. The substituted hydrocarbons can be different. This is equally applicable to tertiary amines. For example, as the hydrocarbon-different substances, methyl ethylamine, methyl propylamine, etc. can be given.

[0054] As the tertiary amines, trimethylamine, triethylamine, tripropylamine, tributylamine, trihexylamine, trimethanolamine, triethanolamine, tripropanolamine, tributanolamine, triamylolamine, trihexanolamine, methyl diethylamine, methyl dipropylamine, etc. can be given.

[0055] As the cations of the ionic liquids, 1-ethyl-3-methylimidazolium ion, 1-methyl-3-propylimidazolium ion, 1-butyl-3-methylimidazolium ion, 1-methyl-3-pentylimidazolium ion, 1-hexyl-3-methylimidazolium ion, etc. can be given.

[0056] As the imidazolium ion, 2-position of the imidazolium ion can be substituted. As the cations in which 2-position of the imidazolium ion is substituted, 1-ethyl-2,3-dimethylimidazolium ion, 1,2-dimethyl-3-propylimidazolium ion, 1-butyl-2,3-dimethylimidazolium ion, 1,2-dimethyl-3-pentylimidazolium ion, 1-hexyl-2,3-dimethylimidazolium

[0057] As the pyridinium ion, methylpyridinium ion, ethylpyridinium ion, propylpyridinium ion, butylpyridinium ion, pentylpyridinium ion, hexylpyridinium ion, imidazolium ion, and pyridinium Both the ion and the pyridine can be substituted with an alkyl group, and an unsaturated bond can be present.

[0058] As the anion, there can be mentioned fluoride ion (F - ), chloride ion (Cl - ), bromide ion (Br - ), iodide ion (I - ), BF4 - , PF6 - , CF3COO - , CF3SO3 - , NO3 - , SCN - , (CF3SO2)3C - , bis(trifluoromethyloxysulfonyl)imide, bis(perfluoroethylsulfonyl)imide, and the like. It can also be a dication in which a cation and an anion of an ionic liquid are connected with a hydrocarbon. Note that a buffer solution such as potassium phosphate solution can be supplied to the housing portions 13 and 16.

[0059] The separator 18 uses a film that selectively allows the passage of anions or cations. Thereby, the electrolytes 12 and 15 in contact with the reduction electrode 14 and the oxidation electrode 17, respectively, can be set to electrolytes containing different substances, and further, by the difference in ionic strength, the difference in pH, and the like, the reduction reaction and the oxidation reaction can be promoted. The use of the separator 18 enables the separation of the first electrolyte 12 and the second electrolyte 15. The separator 18 can have a function of allowing a part of the ions contained in the electrolytes 12 and 15 impregnating the two electrodes 14 and 17 to pass therethrough, i.e., a function of shielding one or more kinds of ions contained in the electrolytes 12 and 15. Thereby, for example, the pH and the like can be made different between the two electrolytes 12 and 15.

[0060] As the separator 18, for example, an ion exchange membrane such as Neoceptor (registered trademark) of Astom Co., Ltd., Selemion (registered trademark), Aciplex (registered trademark) of Asahi Glass Co., Ltd., Fumasep (registered trademark), fumapem (registered trademark) of Fumatech Co., Ltd., a fluororesin Nafion (registered trademark) obtained by sulfonating and polymerizing tetrafluoroethylene of DuPont Co., Lewabrane (registered trademark) of LANXESS Co., IONSEP (registered trademark) of IONTech Co., Mustang (registered trademark) of PALL Co., ralex (registered trademark) of Mega Co., GORE-TEX (registered trademark) of GORE-TEX Co., and the like can be used. In addition, the ion exchange membrane can be configured using a membrane having a hydrocarbon as a basic skeleton or a membrane having an amine group in an anion exchange. When there is a difference in pH between the first electrolyte 12 and the second electrolyte 15, by using a bipolar membrane in which a cation exchange membrane and an anion exchange membrane are stacked, it is possible to use while stably maintaining the pH of each electrolyte.

[0061] The separator 18 can use, in addition to the ion exchange membrane, for example, a silicone resin, a perfluoroalkoxy alkane (PFA), a perfluoroethylene propylene copolymer (FEP), a polytetrafluoroethylene (PTFE), an ethylene-tetrafluoroethylene copolymer (ETFE), a polyvinylidene fluoride (PVDF), a polychlorotrifluoroethylene (PCTFE), an ethylene-chlorotrifluoroethylene copolymer (ECTFE), or the like, a fluorine-based resin, a polyester sulfone (PES), a porous membrane of ceramic, a filler filled with a glass filter or agar, or the like, an insulating porous body such as zeolite or an oxide, and the like. It is particularly preferable to use a hydrophilic porous membrane as the separator 18 because clogging due to air bubbles does not occur.

[0062] The reduction electrode 14 is an electrode (cathode) that generates a carbon compound by reducing carbon dioxide (CO2). The reduction electrode 14 is disposed inside the first housing portion 2 and is immersed in the first electrolyte 13. The reduction electrode 14 includes, for example, a reduction catalyst for generating a carbon compound by a reduction reaction of carbon dioxide. As the reduction catalyst, a material that reduces the activation energy for reducing carbon dioxide can be given. In other words, a material that reduces the overvoltage when a carbon compound is generated by a reduction reaction of carbon dioxide can be given.

[0063] As the reduction electrode 14, for example, a metal material or a carbon material can be used. As the metal material, for example, gold, aluminum, copper, silver, platinum, palladium, zinc, mercury, indium, nickel, titanium, and the like, an alloy containing the metal, and the like can be used. As the carbon material, for example, graphene, a carbon nanotube (CNT), fullerene, Ketjen black, and the like can be used. Note that, not limited thereto, as the reduction catalyst, for example, a metal complex such as a Ru complex or a Re complex, an organic molecule having an imidazole skeleton or a pyridine skeleton can be used. The reduction catalyst can be a mixture of a plurality of materials. The reduction electrode 14 can have a structure in which a thin film-shaped, lattice-shaped, granular, linear, or the like reduction catalyst is provided on a conductive substrate, for example.

[0064] As the carbon compound generated by the reduction reaction in the reduction electrode 14, depending on the kind of the reduction catalyst and the like, for example, carbon monoxide (CO), formic acid (HCOOH), methane (CH4), methanol (CH3OH), ethane (C2H6), ethylene (C2H4), ethanol (C2H5OH), formaldehyde (HCHO), ethylene glycol (C2H6O2), and the like can be given. In addition, in the reduction electrode 14, simultaneously with the reduction reaction of carbon dioxide (CO2), a side reaction in which hydrogen (H2) is generated due to the reduction reaction of water (H2O) is sometimes caused.

[0065] The oxidation electrode 17 is an electrode (anode) in which a substance or an ion and the like in the second electrolytic solution 14 is oxidized. For example, water (H2O) is oxidized into oxygen or hydrogen peroxide water, or a chloride ion (Cl - ) is oxidized into chlorine. The oxidation electrode 17 is disposed inside the second housing portion 16 and is immersed in the second electrolytic solution 15. The oxidation electrode 17 contains an oxidation catalyst of the oxidized substance. As the oxidation catalyst, a material that reduces the activation energy at the time of oxidation of the oxidized substance, in other words, a material that reduces the reaction overvoltage is used.

[0066] As such an oxidation catalyst material, for example, a metal such as ruthenium, iridium, platinum, cobalt, nickel, iron, manganese, or the like can be given. In addition, a binary metal oxide, a ternary metal oxide, a quaternary metal oxide, or the like can be used. As the binary metal oxide, for example, 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), ruthenium oxide (Ru-O), or the like can be given. As the ternary metal oxide, for example, Ni-Fe-O, Ni-Co-O, La-Co-O, Ni-La-O, Sr-Fe-O, or the like can be given. As the quaternary metal oxide, for example, Pb-Ru-Ir-O, La-Sr-Co-O, or the like can be given. Note that, without being limited thereto, as the oxidation catalyst, a metal hydroxide containing cobalt, nickel, iron, manganese, or the like, a metal complex such as a Ru complex or a Fe complex, or the like can also be used. In addition, a plurality of materials can be used in mixture.

[0067] In addition, the oxidation electrode 17 can be a composite material containing both an oxidation catalyst and a conductive material. As the conductive material, for example, a carbon material such as carbon black, activated carbon, fullerene, a carbon nanotube, graphene, Ketjen black, diamond, a transparent conductive oxide such as indium tin oxide (ITO), zinc oxide (ZnO), Fluorine-doped Tin Oxide (FTO), Aluminum-doped Zinc Oxide (AZO), Antimony-doped Tin Oxide (ATO), a metal such as Cu, Al, Ti, Ni, Ag, W, Co, Au, or the like, and an alloy containing at least one of these metals can be given. The oxidation electrode 17 can have, for example, a structure in which a thin film, a lattice, a particle, a wire, or the like of an oxidation catalyst is provided on a conductive substrate. As the conductive substrate, for example, a metal material containing titanium, a titanium alloy, or stainless steel can be used.

[0068] The flow rate adjustment section 25 provided in the gas supply flow path 20 adjusts the amount of the raw material gas containing CO2 supplied to the first housing section 13. By increasing or decreasing the amount of CO2 supplied to the first housing section 13 using the flow rate adjustment section 25, the concentration of unreacted CO2 in the gas discharged from the first housing section 13, that is, the utilization rate of CO2 gas, can be adjusted. As described in detail below, when the electric power supplied from the first power supply 5 connected via the first power supply control section 6 to the electrolytic cell 4A varies or the warm-up operation of the second power supply 7 connected via the second power supply control section 8, even when the amount of CO2 consumed in the reduction reaction of CO2 varies, the amount of CO2 supplied to the first housing section 13 can be increased or decreased by the flow rate adjustment section 25, whereby the concentration of CO2 in the generated gas can be stabilized. Thus, the mechanism and the process for adjusting the concentration of CO2 in the generated gas discharged from the first housing section 13 can be simplified or eliminated, and the carbon dioxide electrolysis device 1A and the valuable substance manufacturing system can be made low cost.

[0069] The first power supply control section 6 and the first power supply 5 supply electric power in which oxidation-reduction reactions occur to the electrolytic cell 4A, and are electrically connected to the reduction electrode 14 and the oxidation electrode 17 of the electrolytic cell 4A. Using the electric energy supplied from the first power supply 5, the reduction reaction of the reduction electrode 14 and the oxidation reaction of the oxidation electrode 17 are performed. The first power supply control section 6 and the first power supply 5 and the reduction electrode 14, and the first power supply control section 6 and the first power supply 6 and the oxidation electrode 17 are connected, for example, by wiring. In the first power supply control section 6, electrical devices such as a DC / AC converter, a DC / DC converter, an AC / DC converter, an inverter, a converter, and a switch are provided. The driving mode of the electrolytic cell 4A can be a constant voltage mode or a constant current mode.

[0070] A detection section 9 including a current detection section that detects the current flowing through the electrolytic cell 4A and / or a voltage detection section that detects the voltage or potential applied to the electrolytic cell 4A is provided between the first power supply control section 6 and the electrolytic cell 4A. The detection section 9 includes at least one of the current detection section and the voltage detection section. The detection section 9 can have a mechanism for separately measuring the voltage and the current applied to the electrolytic cell 4A by wiring not shown and electrodes arranged in the electrolytic cell 4A. The detection signal of the detection section 9 is transmitted to the integrated control section 11. In the integrated control section 11, calculations are performed based on the current flowing through the electrolytic cell 4A and the voltage applied to the electrolytic cell 4A. Control signals are transmitted from the integrated control section 11 to the first power supply control section 6, the second power supply control section 8, and the gas control section 10.

[0071] The first power supply 5 can be a variable power supply, i.e., a power supply that converts a renewable energy into electric energy to be supplied. As examples of such a power supply, there are a power supply that converts kinetic or potential energy such as wind power, water power, geothermal power, tidal power, etc. into electric energy, a power supply such as a solar cell having a photoelectric conversion element that converts light energy into electric energy, a power supply such as a fuel cell or a storage battery that converts chemical energy into electric energy, a power supply that converts vibration energy such as sound into electric energy, and the like. The photoelectric conversion element has a function of performing charge separation using light energy such as sunlight. As examples of the photoelectric conversion element, there are a pin junction type solar cell, a pn junction type solar cell, an amorphous silicon solar cell, a multi-junction type solar cell, a single-crystal silicon solar cell, a polycrystalline silicon solar cell, a dye-sensitized type solar cell, an organic thin-film solar cell, and the like. The photoelectric conversion element can be layered with at least one of the reduction electrode 14 and the oxidation electrode 17 inside the reaction tank 19. Alternatively, it can be a general commercial power supply or a battery, etc.

[0072] The second power supply control section 8 and the second power supply 7 supply electric power for generating a redox reaction to the electrolytic cell 4A and are electrically connected to the reduction electrode 14 and the oxidation electrode 17 of the electrolytic cell 4A. Using electric energy supplied from the second power supply 7, a reduction reaction of the reduction electrode 14 and an oxidation reaction of the oxidation electrode 17 are performed. The second power supply control section 8 and the second power supply 7 are connected to the reduction electrode 14 and the oxidation electrode 17, for example, by wiring. In the second power supply control section 8, an electrical device such as a DC / AC converter, a DC / DC converter, an AC / DC converter, an inverter, a converter, a switch, and the like is provided. The driving mode of the electrolytic cell 4A can be a constant voltage mode or a constant current mode. The second power supply 7 can be a storage battery, a commercial power supply, a fuel cell, or the like. The second power supply 7 is preferably a power supply having a rated voltage and / or a rated current.

[0073] The integrated control section 11, which is constituted by a computer such as a PC or a microcomputer, for example, performs arithmetic processing on the detection signal output from the detection section 9. A control signal from the integrated control section 11 is transmitted to the first power supply control section 6, the second power supply control section 8, the gas control section 10, and the like. The first power supply control section 6, the second power supply control section 8, the gas control section 10, and the integrated control section 11 can be constituted independently of each other or can be constituted by integrating them by a computer such as a PC or a microcomputer.

[0074] Next, the operation of the electrolytic cell 4A will be described with reference to FIG. 2. Figure 3The operation method of the carbon dioxide electrolysis device 1 driven by the first power source 5 and the second power source 7 will be described. As the operation method of the carbon dioxide electrolysis device 1A as the first power source 5 and the second power source 7, a normal operation (ordinary operation) and a warm-up operation can be cited. When the first power source 5 uses a variable power source, in a state where the power supply from the first power source 5 is stopped, that is, in a state where the current flowing through the electrolytic cell 4A is zero, after the state continues, when the power supply, that is, the electric current, is resumed quickly, the phenomenon that the voltage of the electrolytic cell 4A is sharply increased and it is difficult to start the electrolytic cell 4A is sometimes observed. In order to follow the operation variation caused by the rapid start of the electrolytic cell 4A, for example, the warm-up operation described below is implemented using the second power source 7.

[0075] In the normal operation, the power is supplied from the first power source 6 to the electrolytic cell 4A (S101). In the normal operation, in order to adjust the concentration of the unreacted CO2 output from the electrolytic cell 4A, the flow rate of the CO2 can be controlled (S102). In the normal operation, the current or the voltage flowing through the electrolytic cell 4A is detected by the detection section 9 (S103). When the detected current or voltage flowing through the electrolytic cell 4A is, for example, lower than a prescribed time, a prescribed value (S104), the warm-up operation generated by the second power source 7 is introduced by the second power source control section 8 (S105). At this time, either the first power source 5 can be disconnected by the first power source control section 6, or the parallel operation of the first power source 5 and the second power source 7 can be performed. The determination of whether the current or the voltage flowing through the electrolytic cell 4A is lower than the prescribed time, the prescribed value is performed in the integrated control section 11, the control signal from the integrated control section 11 is sent to the first and second power source control sections 6, 8, the switching control of the first power source 5 and the second power source 7 is performed, and in addition, the supply amount of the CO2 is controlled by the gas control section 10 (S106).

[0076] In the warm-up operation, the current smaller than the rated current is supplied from the second power source 7 to the electrolytic cell 4A by the second power source control section 8. The amount of the CO2 consumed in the reduction reaction of the CO2 in the warm-up operation is smaller than that in the normal operation. Therefore, in order to adjust the concentration of the unreacted CO2 output from the electrolytic cell 4A, the control signal is sent from the integrated control section 11 to the gas control section 10, and the operation of the flow rate adjustment section 25 is controlled by the gas control section 10. At this time, in order to improve the accuracy of the flow rate adjustment, as shown in FIG. 6, the feedback mechanism that measures the flow rate of the raw material gas supplied to the first housing section 13 by the flow meter 26 and sends the measured data to the gas control section 10 can be provided. Figure 1 Figure 1 ​The flow rate adjusting section 25 and the flow meter 26 shown are not limited to separate functions and arrangements, and a mass flow controller or the like in which the functions of measuring and adjusting the flow rate of gas or liquid are integrated can be used. The CO2 flow rate can also not be adjusted during warm-up operation, and instead the exhaust flow path 22B can be switched to by operating the valves V1 and V2 to exhaust the gas output from the electrolytic cell 4A. The switching of the operation from normal operation to warm-up operation, the control of the first power source 5 and the second power source 7 in parallel operation, the adjustment of the CO2 flow rate introduced into the electrolytic cell 4A, and the exhaust operation are linked.

[0077] Next, the integrated control section 11 predicts the power generation amount of the solar cell, wind power generator, or the like as the first power source 5 based on the weather forecast, and when it is predicted that a state in which the current or voltage flowing through the electrolytic cell 4A exceeds a prescribed value for a prescribed time (S107), the warm-up operation by the second power source 7 is returned to the normal operation of the first power source 5. With regard to the return from the second power source 7 to the first power source 5, for example, when the current or voltage flowing from the first power source 5 measured by the first power source control section 6 exceeds a prescribed value for a prescribed time (S107), the warm-up operation can be ended and returned to the normal operation. By introducing such a warm-up operation, the electrolytic cell 4A can be rapidly started, the followability to fluctuating current can be ensured, and furthermore, the fluctuation in the CO2 concentration in the gas output from the electrolytic cell 4A can also be suppressed.

[0078] As another operation method other than the warm-up operation, an operation method called low-speed start described below can be applied. During normal operation, the power generation amount of the solar cell, wind power generator, or the like as the first power source 5 is predicted based on the weather forecast, and when it is predicted that a state in which the current or voltage flowing through the electrolytic cell 4A is lower than a prescribed value for a prescribed time, the first power source 5 is cut off by the first power source control section 6, and the electrolytic cell 4A is placed in a stopped state. At this time, the supply of CO2 and electrolyte is also preferably stopped. Next, when it is predicted that a state in which the current or voltage flowing through the electrolytic cell 4A exceeds a prescribed value for a prescribed time based on the power generation amount of the first power source 5, low-speed start of the electrolytic cell 4A based on a ramp-up wave is performed by the second power source control section 8 and the second power source 7.

[0079] Low-speed start based on a ramp-up wave refers to an operation method in which the current rising time Δt is applied, and the current flowing through the electrolytic cell 4A is increased from zero to the rated current. If Δt is too short, the cell voltage excessively rises, and the electrolytic cell 4A cannot be started, so Δt is preferably 5 minutes or more, more preferably 10 minutes or more, and further preferably 30 minutes or more. After the rated current is reached by low-speed start, the normal operation based on the first power source control section 6 and the first power source 5 is switched to. Since the concentration of CO2 in the gas output from the electrolytic cell 4A is unstable during low-speed start, the gas output from the electrolytic cell 4A can be switched to the exhaust flow path 22B by valve operation to be exhausted.

[0080] Next, the operation of the carbon dioxide electrolysis device 1A will be described. Here, a case will be described in which the water solution containing carbon dioxide and the potassium bicarbonate aqueous solution are used as the electrolytes 12, 15, carbon dioxide (CO2) is mainly reduced to carbon monoxide (CO), and water or hydroxyl ions are oxidized to oxygen. The reduction reaction of CO2 is not limited to the generation reaction of CO, and can be the generation reaction of ethanol (C2H5OH), ethylene (C2H4), ethane (C2H6), methane (CH4), methanol (CH3OH), acetic acid (CH3COOH), propanol (C3H7OH), or the like.

[0081] If a voltage of the electrolysis voltage or more is applied between the reduction electrode 14 and the oxidation electrode 17, a reduction reaction of carbon dioxide (CO2) occurs in the vicinity of the reduction electrode 14 connected to the first electrolyte 12. As shown in the following formula (1), CO2 contained in the first electrolyte 12 is reduced by electrons (e - ) supplied from the power supply, and carbon monoxide (CO) and hydroxyl ions (OH - ) are generated. As shown in formula (2) or formula (3), a part of the generated hydroxyl ions (OH - ) reacts with CO2, and bicarbonate ions (HCO3 - ) and carbonate ions (CO3 2- ) are generated. By the voltage between the reduction electrode 14 and the oxidation electrode 17, a part of the hydroxyl ions (OH - ), the bicarbonate ions (HCO3 - ), and the carbonate ions (CO3 2- ) are moved to the second electrolyte 15 via the separator 18.

[0082] 2CO2+2H2O+4e - →2CO+4OH - …(1)

[0083] 2CO2+2OH - →2HCO3 - …(2)

[0084] 2HCO3 - +2OH - →CO3 2- +H2O …(3)

[0085] An oxidation reaction of water (H2O) occurs in the vicinity of the oxidation electrode 17 connected to the second electrolyte 15. As shown in the following formula (4), an oxidation reaction of H2O contained in the second electrolyte 15 occurs, and electrons disappear, and oxygen (O2) and hydrogen ions (H + ) are generated.

[0086] 2H2O→4H + +O2+4e - …(4)

[0087] As shown in equations (5) to (7), a part of the generated hydrogen ions (H + ) reacts with a part of the hydroxide ions (OH - ), bicarbonate ions (HCO3 - ), carbonate ions (CO3 2- ) that have moved via the separator 18, to generate water (H2O) and carbon dioxide (CO2).

[0088] 2H + +CO3 2- →H2O+CO2 …(5)

[0089] 2H + +2HCO3 - →2H2O+2CO2 …(6)

[0090] H + +OH - →H2O …(7)

[0091] Among the above, the operation by the generation of OH - in the reduction electrode 14 is explained, but the operation can also be performed by the generation and movement of H + in the oxidation electrode 17, as described below. If a voltage of the electrolysis voltage or more is applied between the reduction electrode 14 and the oxidation electrode 17, an oxidation reaction of water (H2O) occurs in the vicinity of the oxidation electrode 17 connected to the second electrolyte 15. As shown in equation (8) below, the oxidation reaction of H2O contained in the second electrolyte 15 occurs, electrons disappear, and oxygen (O2) and hydrogen ions (H + ) are generated. A part of the generated hydrogen ions (H + ) move to the first electrolyte 12 via the separator 18.

[0092] 2H2O→4H + +O2+4e - …(8)

[0093] When the hydrogen ions (H + ) generated on the oxidation electrode 17 side reach the vicinity of the reduction electrode 14 and electrons (e - ) are supplied from the power source 5 to the reduction electrode 14, a reduction reaction of carbon dioxide (CO2) occurs. As shown in equation (9) below, the hydrogen ions (H + ) that have moved to the vicinity of the reduction electrode 14 and the electrons (e -), CO2 contained in the first electrolyte 12 is reduced to generate carbon monoxide (CO).

[0094] 2CO2+ 4H + + 4e - → 2CO + 2H2O … (9)

[0095] As described above, the reduction reaction of carbon dioxide requires movement of ions to the reduction electrode 14 and the oxidation electrode 17. If the current or voltage flowing through the electrolytic cell 4A is lower than a prescribed time or prescribed value, the movement of these ions decreases, resulting in a problem of inability to quickly start up to a rated current and inability to follow a varying current. When the current or voltage flowing through the electrolytic cell 4A is lower than a prescribed time or prescribed value, or when it is predicted that it will be lower than a prescribed time or prescribed value, the movement of ions can be continued and the quick start up to a rated current and the followability to a varying current can be improved by the warm-up operation by the introduction of the second power source 7. Therefore, for example, even when a varying power source is used as the first power source 5, the operation of the carbon dioxide electrolysis device 1A can be stabilized and the variation in the CO2 gas concentration in the generated gas can be suppressed. Furthermore, by suppressing the temporal change in the concentration of unreacted CO2, the availability and the utilization value of the generated gas in a subsequent process can be improved.

[0096] (Second Embodiment)

[0097] Referring to Figure 4 and Figure 5 A carbon dioxide electrolysis device 1B of a second embodiment will be described. Figure 4 The contact mode of the carbon dioxide electrolysis device 1B with the reduction electrode 14 of a gas containing CO2 (sometimes referred to as CO2 gas) and the contact mode of the oxidation electrode 17 with the second electrolyte (anode solution) containing water are different from those of the carbon dioxide electrolysis device 1A of the first embodiment. That is, the electrolytic cell 4B in the carbon dioxide electrolysis device 1B of the second embodiment is different in configuration from the electrolytic cell 4A of the first embodiment. The configurations of the other parts, for example, the reduction electrode 14, the oxidation electrode 17, the separator 18, the second electrolyte, the power sources 5, 7, and the like are the same as those of the first embodiment.

[0098] In the second embodiment, a first electrolyte containing CO2 can be used instead of a gas containing CO2. In addition, a flow path (omitted from illustration) can be provided between the reduction electrode 14 and the separator 18, and a gas containing CO2 can be circulated in the first flow path 31, or the first electrolyte can be circulated in the flow path between the reduction electrode 14 and the separator 18. The first electrolyte used in this case can contain CO2 or can not contain CO2. Furthermore, a gas containing water vapor can be used instead of the second electrolyte containing water.

[0099] AsFigure 5 As shown in FIG. 2, the electrolytic cell 4B of the second embodiment has a reduction electrode 14, an oxidation electrode 17, a separator 18, a first flow path 31 through which a gas containing CO2(or a first electrolyte solution containing CO2) flows, a second flow path 32 through which a second electrolyte solution containing water (an anode solution) flows, a first current collector 33 electrically connected to the reduction electrode 14, and a second current collector 34 electrically connected to the oxidation electrode 17. The first flow path 31 constitutes a first housing portion, and the second flow path 32 constitutes a second housing portion. The first and second current collectors 33 and 34 of the electrolytic cell 4B are connected to the detection portion 9, the first power supply control portion 6, the first power supply 5, the second power supply control portion 8, and the second power supply 7 via wiring. Figure 4 The detection portion 9, the first power supply control portion 6, the first power supply 5, the second power supply control portion 8, and the second power supply 7 are connected to each other.

[0100] In the operation of the electrolytic cell 4B, the first flow path 31 can be clogged or the supply of the gas containing CO2 can be stopped due to the deposition of the reduction product of CO2 or the components of the second electrolyte solution moving to the reduction electrode 14 side in the first flow path 31. Therefore, in order to suppress the deposition, it is preferable that moisture be present in the gas containing CO2. On the other hand, when the amount of moisture in the gas containing CO2 is too large, a large amount of moisture is supplied to the catalyst surface in the reduction electrode 14, and hydrogen is easily generated, and thus it is not preferable. Therefore, as the amount of moisture in the gas containing CO2, the relative humidity is preferably 20 to 90%, and more preferably 30 to 70%.

[0101] The first flow path 31 is connected to the first supply flow path 20 through which the gas containing CO2 is supplied and the first discharge flow path 22 through which the generated gas is discharged. The second flow path 32 is connected to the second supply flow path 23 through which the electrolyte solution containing water is supplied and the second discharge flow path 24. The configurations of the detection portion 9, the first power supply control portion 6, the first power supply 5, the second power supply control portion 8, the second power supply 7, the gas control portion 10, the integrated control portion 11, the flow rate adjustment portion 25, and the flow meter 26, and the like can be the same as those of the first embodiment, and are electrically or mechanically connected in the same manner as in the first embodiment.

[0102] The first flow path 31 is arranged so as to face the reduction electrode 14. The first flow path 31 is connected to the first supply flow path 20, and supplies the gas containing CO2 from the first supply flow path 20. A pump (not shown), a flow rate adjusting section 25, and a flow meter 26 are arranged in the first supply flow path 20. Although not shown, the first supply flow path 20 is connected to a tank containing CO2 gas. It is configured so that the CO2 gas and the cathode solution flow in the first flow path 31 while being connected to the reduction electrode 14. The CO2 gas and the CO2 in the cathode solution that have passed through the reduction electrode 14 are reduced by the reduction electrode 14. The gas or solution containing the reduction reaction product of CO2 is discharged from the first discharge flow path 22. A product detecting section (not shown) or the like can also be provided in the first discharge flow path 22. Further, the first discharge flow path 22 is connected to a product separation section or a storage tank (not shown) or the like.

[0103] The second flow path 32 is arranged so as to face the oxidation electrode 17. The second flow path 32 is connected to a solution tank (not shown) or the like, and is configured so that the anode solution flows in the second flow path 32 while being connected to the oxidation electrode 17. The H2O in the anode solution that has passed through the oxidation electrode 17 is oxidized by the oxidation electrode 17. The solution containing the oxidation reaction product of H2O is sent to a product separation section or a storage tank (not shown) or the like.

[0104] In the carbon dioxide electrolysis device 1B of the second embodiment, as in the first embodiment, power is supplied from the first power supply 5 via the first power supply control section 6, and the current or voltage flowing through the electrolytic cell 4B is monitored by the detecting section 9. When the current or voltage flowing through the electrolytic cell 4B is lower than a prescribed value for a prescribed time, the warm-up operation of the second power supply control section 8 and the second power supply 7 is initiated. The operation method of the warm-up operation and the switching method between the warm-up operation and the normal operation are the same as in the first embodiment. By initiating the warm-up operation, the rapid start of the electrolytic cell 4B and the followability to the fluctuating current can be ensured. In addition, when the warm-up operation is initiated, the control of the gas control section 10 and the flow rate adjusting section 25 is linked so as to make the CO2 concentration in the gas discharged from the first flow path 31 a desired value. Thus, the CO2 concentration in the gas discharged from the first flow path 31 is adjusted to the desired value. Therefore, the temporal fluctuation of the CO2 gas concentration in the generated gas can be suppressed, and the availability and the utilization value of the reduction reaction product can be improved.

[0105] (Third Embodiment)

[0106] Reference Figure 6 A carbon dioxide electrolysis device 1C of a third embodiment will be described. Figure 6The carbon dioxide electrolysis device 1C shown differs from the carbon dioxide electrolysis device 1B of the second embodiment in that the electrochemical reaction cell 41, which is different from the electrolytic cell 4B, is connected to the first power source 5 and the first power source control section 6 by wiring. The configurations of the other parts are the same as those of the carbon dioxide electrolysis device 1B of the second embodiment.

[0107] During normal operation, power is supplied to the electrolytic cell 4B by the first power source control section 6 and the first power source 5, and the current or voltage flowing through the electrolytic cell 4B is monitored by the detection section 9. When the current or voltage flowing through the electrolytic cell 4B is lower than a prescribed value for a prescribed time, the first power source 5 is cut off by the first power source control section 6, and the warm-up operation of the second power source control section 8 and the second power source 7 is introduced to the electrolytic cell 4B. The normal operation and the warm-up operation up to this point are performed in the same manner as in the second embodiment.

[0108] During the warm-up operation, the first power source 5 is disconnected from the electrolytic cell 4B. The power of the first power source 5 that is disconnected from the electrolytic cell 4B is supplied to the electrochemical reaction cell 41 by the first power source control section 6. As the electrochemical reaction cell 41, a water electrolytic cell, a chemical cell such as a lithium ion cell, a double-layer capacitor, or the like, which does not cause a malfunction even if the voltage fluctuates, can be cited. By adopting such a configuration, the power of the first power source 5 during the warm-up operation can be effectively utilized.

[0109] (4th Embodiment)

[0110] Reference Figure 7 The carbon dioxide electrolysis device 1D of the fourth embodiment will be described. Figure 7 The carbon dioxide electrolysis device 1D shown differs from the carbon dioxide electrolysis device 1B of the second embodiment in that the electrolytic cell 4B and the capacitor 42 are connected in parallel by wiring. The configurations of the other parts are the same as those of the carbon dioxide electrolysis device 1B of the second embodiment.

[0111] As the first power source 5, when a variable power source whose output fluctuates depending on the weather, such as a solar cell or a wind power generator, is used, in order to suppress the fluctuation of the CO2 concentration output from the electrolytic cell 4B, it is preferable to adjust the CO2 flow rate input to the electrolytic cell 4B in synchronization with the fluctuation of the current. However, due to the length of the piping and the like, the response time of the CO2 flow rate supplied to the electrolytic cell 4B is longer than the fluctuation period of the current, and takes one second to several tens of seconds, and there is a problem in that it is difficult to synchronize with the fluctuation of the current. In the fourth embodiment, the capacitor 42 is connected in parallel to the electrolytic cell 4A, and the current introduced to the electrolytic cell 4B is smoothed. Thereby, it is possible to adjust the flow rate of CO2 in synchronization.

[0112] The larger the capacitance of capacitor 42, the better the effect of suppressing fluctuating current. On the other hand, if the capacitance of capacitor 42 is too large, charging the capacitor will take a long time, and there is a problem that it will take a long time for the current introduced into electrolytic cell 4B to reach the desired value. Therefore, the capacitance of capacitor 42 is preferably 0.1F or more and 1000F or less, more preferably 1F or more and 100F or less. As capacitor 42, a double-layer capacitor that can increase capacitance is preferred.

[0113] (Fifth Embodiment)

[0114] Reference Figure 8 and Figure 9 The carbon dioxide electrolysis apparatus 1E of the fifth embodiment is described. Figure 8 The difference between the carbon dioxide electrolysis device 1E shown and the carbon dioxide electrolysis device 1B of the second embodiment is that, in addition to the electrolysis cell 4C having a cooling water flow path, it also has a cooling water control unit 51, a cooling water flow rate adjustment unit 52, an electrolyte control unit 53, and an electrolyte flow rate adjustment unit 54 for controlling the cooling water flowing in the cooling water flow path. The configuration of all other parts is the same as that of the carbon dioxide electrolysis device 1B of the second embodiment.

[0115] like Figure 9 As shown, the cathode section 2 of the electrolytic cell 4C has a cooling water flow path 55 different from the first flow path 31 through which CO2-containing gas flows, and the anode section 3 has a cooling water flow path 55 different from the second flow path 32 through which electrolyte flows. The cooling water flow path 55 is connected to a cooling water supply flow path 56 that supplies cooling water. A cooling water flow rate adjustment unit 52 is provided in the cooling water supply flow path 56. An electrolyte flow rate adjustment unit 54 is provided in the electrolyte supply flow path 23. The cooling water flow rate adjustment unit 52 and the electrolyte flow rate adjustment unit 54 are, for example, diaphragm pumps, tubular pumps, plunger pumps, or other liquid delivery pumps.

[0116] Control signals are sent from the integrated control unit 11 to the cooling water control unit 51 and the electrolyte control unit 53. The control signal from the cooling water control unit 51 is sent to the cooling water flow adjustment unit 52, and the control signal from the electrolyte control unit 53 is sent to the electrolyte flow adjustment unit 54. Additionally, a heater (not shown) can be installed in the electrolytic cell 4C. Based on the calculation results of the integrated control unit 11, the electrolyte flow rate, cooling water flow rate, and the amount of power supplied to the heater are adjusted, thereby adjusting the temperature of the electrolytic cell 4C.

[0117] When the current or voltage flowing through the electrolytic cell 4C detected by the detection section 9 is lower than a prescribed value for a prescribed time during normal operation, warm-up operation is performed by the second power source control section 8 to introduce the second power source 7. At this time, either the first power source 5 can be cut off by the first power source control section 6 or the first power source 5 can be operated in parallel with the second power source 7. Since the electrolytic cell 4C is supplied with current at less than the rated current during warm-up operation, the Joule heat of the electrolytic cell 4C during warm-up operation is less than that during normal operation. In order to make the temperature of the electrolytic cell 4C the same as during normal operation, control is performed to reduce the flow rate of the electrolyte and the cooling water or to increase the amount of power supplied to the heater during warm-up operation. By setting the temperature of the electrolytic cell 4C during warm-up operation to be the same as during normal operation, it is possible to ensure rapid startup to the rated current and followability to fluctuating current.

[0118] (6th Embodiment)

[0119] Figure 10 A valuable substance manufacturing system 61 provided with the carbon dioxide electrolysis device 1B of the second embodiment is shown. The generated gas discharged from the cathode section 2 of the electrolytic cell 4B can be directly utilized or consumed, or a chemical synthesis device can be provided in the rear section of the electrolytic cell 4B to manufacture a valuable substance with high added value. Figure 10 The configuration of a valuable substance manufacturing system 60 connected to the carbon dioxide electrolysis device 1B and the chemical synthesis device 61 is shown.

[0120] The carbon dioxide electrolysis device 1B has a first product separator 29A provided in the first discharge flow path 22, a second product separator 29B provided in the second discharge flow path 24, and a tank 30. The generated gas discharged from the cathode section 2 of the electrolytic cell 4B is transported to the chemical synthesis section 63 via the first product separator 29A and the storage tank 62 to be converted into a valuable substance. In the first product separator 29A, processing to remove moisture in the generated gas or to remove remaining CO2 or the like is performed, and a gas of a desired composition is introduced to the chemical synthesis section 63. Note that in the carbon dioxide electrolysis device 1B of the embodiment, the first product separator 29A can be omitted when adjusting the CO2 concentration in the generated gas.

[0121] For example, when CO gas is generated in electrolytic cell 4B, methanol can be produced through methanol synthesis by mixing the generated CO gas and H2 gas as a raw material, or injectable fuel and light oil can be produced through Fischer-Tropsch synthesis. However, if a large amount of unreacted CO2 is present in the CO gas, problems such as side reactions during synthesis, adverse effects on the catalyst used in the synthesis, and reduced yield may occur. In this embodiment, by controlling the CO2 concentration in the CO gas, the availability and utilization value of the gas generated in the CO2 reduction reaction can be improved. In this embodiment, not only the CO2 concentration in the generated gas can be adjusted, but also the generation of H2, a side reaction of the CO2 reduction reaction, can be adjusted. This is because by increasing or decreasing the amount of CO2-containing gas supplied to the cathode 2, the amount of H2 generated also increases or decreases accordingly.

[0122] Example

[0123] Next, the implementation examples and their evaluation results are described in detail.

[0124] (Example 1)

[0125] manufacture Figure 11 The carbon dioxide electrolysis device 1E shown is configured as follows. Figure 11 The carbon dioxide electrolysis device 1E shown basically has the same characteristics as... Figure 8 The carbon dioxide electrolysis apparatus 1E shown has the same configuration, except that a humidifier 71, a gas-liquid separator 29A installed in the first discharge path 24, a gas-liquid separator 29B installed in the second discharge path 24, and an electrolyte tank 30 are added to the first supply path 20. A mass flow controller 72 is used as the gas flow adjustment unit. In addition, a potentiostat / galvanometer P / G is used for verification experiments simulating the operation of the first power supply 5 and the first power supply control unit 6, the second power supply 7 and the second power supply control unit 8, and the detection unit 9.

[0126] As the reduction electrode for a carbon dioxide electrolyzer, a carbon particle-loaded gold nanoparticle-coated electrode was used. The average particle size of the gold nanoparticles was 3 nm, and the loading was 10% by mass. As the oxidation electrode, an electrode coated with IrO2 nanoparticles on a Ti mesh was used. An anion exchange membrane was used as the separator. Note that both the reduction and oxidation electrodes were cut to have an electrode area of ​​16 cm². 2 To use. With Figure 9Similarly, the carbon dioxide electrolytic cell shown has the following components stacked sequentially from left to right: a first cooling water channel, a first insulating plate, a first current collector, a first flow channel, a reduction electrode, a diaphragm, an oxidation electrode, a second flow channel, a second current collector, a second insulating plate, and a second cooling water channel, all clamped together by a support plate (not shown) to form the carbon dioxide electrolytic cell. Furthermore, to measure the reduction electrode potential and the oxidation electrode potential, a Pt foil (not shown) serving as a reference electrode is brought into contact with the diaphragm on the reduction electrode side.

[0127] The aforementioned carbon dioxide electrolyzer is connected to both the solution and gas systems and operated under the following conditions: CO2 gas (purity: >99.9%) is introduced into the electrolyzer via a mass flow controller and a humidifier at a specified flow rate in the first flow path. The humidification temperature is set to 40°C. Furthermore, the cell temperature is controlled at 40°C by flowing cooling water at a flow rate of 10 mL / min in the cooling water path and by using a heater installed in the electrolyzer. A liquid collector, acting as a gas-liquid separator, is installed at the flow path outlet. Additionally, 1 L of a potassium bicarbonate aqueous solution (concentration 0.1 M KHCO3) is circulated in the second flow path at a flow rate of 10 mL / min.

[0128] Next, the potentiostat / galvanometer is connected to the reduction electrode, oxidation electrode, and reference electrode, so that various currents simulating the operation of the first power supply, the first power supply control unit, the second power supply, and the second power supply control unit flow between the reduction electrode and the oxidation electrode, thereby carrying out the CO2 reduction reaction, and the values ​​of the cell voltage, reduction electrode potential, and oxidation electrode potential are collected at this time.

[0129] like Figure 12 As shown in the time variation of the current, a simulation of the operation of the first power supply and the first power supply control unit is performed with the rated current J1 = 200mA / cm. 2 It becomes J2 = 0 mA / cm 2 And J2 = 0 mA / cm 2 After a duration of Δt1, the current increases to J1 = 200 mA / cm. 2 The current variation test. As an example, Figure 13 This represents the cell voltage, reduction electrode potential, and oxidation electrode potential when Δt is 1 minute and 3 minutes, respectively. It can be seen that when Δt1 = 1 minute, it can quickly start up to J1 = 200 mA / cm². 2 In contrast, when Δt1 = 3 minutes, the cell voltage becomes too high, making it difficult to quickly start up to J1 = 200mA / cm. 2 Will changing Δt1 enable rapid startup to J1 = 200mA / cm? 2 The survey results are summarized in Figure 14The table shows the criteria for determining whether a battery voltage of less than 6V at startup is considered a successful startup and is indicated by "○". Conversely, a battery voltage of 6V or higher is considered a failure to start quickly and is indicated by "×". Figure 14 As shown in the table, rapid startup is not possible when Δt1 = 3 minutes or more.

[0130] Next, as Figure 12 As shown, the operation of the first power supply and the first power supply control unit, and the second power supply and the second power supply control unit are simulated, with the current changing from the rated current J1 = 200mA / cm. 2 The change is to J2, and after a duration of Δt, it starts to change to J1 = 200 mA / cm. 2 Current variation test. Here, J1 simulates the normal operation of the first power supply and the first power supply control unit, and J2 simulates the warm-up operation of the second power supply and the second power supply control unit. The test will change whether J2 can quickly start up to J1 = 200mA / cm. 2 The survey results are summarized in Figure 15 The table shows the criteria for determining whether a cell voltage less than 6V at startup is sufficient for rapid startup, indicated by "○". A cell voltage greater than 6V is considered insufficient for rapid startup, indicated by "×". Measurements are stopped upon determining that a rapid startup is not possible, indicated by "-". When J2 = 50mA / cm 2 At that time, that is, when the rated current J1 = 200mA / cm 2 When the current is 1 / 4 of the rated current is used for warm-up operation, it can quickly start up to the rated current.

[0131] The results above indicate that 40mA / cm is appropriate during normal operation. 2 When the following current is sustained for more than 120 seconds, a current of 50mA / cm is introduced. 2 The warm-up operation at 1 / 4 of the rated current ensures rapid start-up and current following.

[0132] (Example 2)

[0133] In Example 2, Figure 7 A low-speed start-up simulation test was conducted in the carbon dioxide electrolysis device 1E shown. Figure 16 As shown in the schematic diagram of current change, the current is made to start from zero, i.e., J2 = 0 mA / cm. 2 Up to rated current J1 = 200mA / cm 2 The current rise time Δt2 varies, and the cell voltage values ​​are collected. The maximum cell voltage for each Δt2 is shown in the figure. Figure 17As a criterion for the determination, the condition in which the cell voltage is less than 6 V is determined as the condition in which the cell can be started and is indicated by "0", and the condition in which the determination is made as the condition in which the cell cannot be started is indicated by "X", and the results are summarized in the table of Figure 18 From these results, it is known that, as a method of operation from the cell stop state in which the current is zero to the cell start in which the rated current is obtained, the low-speed start using the ramp-up wave in which the current rise time Δt2 = 5 minutes or more is effective. In addition, in order to further suppress the excessive cell voltage, the method of operation in which the low-speed start using the ramp-up wave in which Δt2 = 30 minutes or more is effective.

[0134] Note that the configurations of the above-described embodiments can be applied in combination of each other, or a part of them can be replaced. Although several embodiments of the present application are described here, these embodiments are only illustrative and are not intended to limit the scope of the present application. These embodiments can be implemented in various other ways, and various omissions, substitutions, modifications, and the like can be made without departing from the scope of the present application. These embodiments and modifications thereof are included in the scope and spirit of the present application, and are also included in the scope of the application described in the claims and equivalents thereof.

Claims

1. A carbon dioxide electrolysis device, which includes: An electrolytic cell includes: a first containment section for containing at least carbon dioxide; a second containment section for containing an electrolyte containing water or water vapor; a diaphragm disposed between the first containment section and the second containment section; a reduction electrode disposed in the first containment section; an oxidation electrode disposed in the second containment section; and a cooling water flow path, wherein... The cooling water flow path is different from that of the first and second receiving sections. The first power control unit is capable of being connected to a first power source, which is a variable power source, that supplies power to the electrolytic cell. The second power control unit is connected to a second power source that supplies power to the electrolytic cell. The cooling water supply unit supplies cooling water to the cooling water flow path. The cooling water control unit controls the amount of cooling water supplied to the cooling water flow path, and The integrated control unit controls the first power control unit and the second power control unit to switch the power supply from the first power source or the second power source to the electrolytic cell; in, When the power supplied to the electrolytic cell from the first power source is lower than a predetermined time or a predetermined value, or when it is predicted to be lower than a predetermined time or a predetermined value, the integrated control unit controls the first power source control unit and the second power source control unit to disconnect the first power source from the electrolytic cell and supply power to the electrolytic cell from the second power source. The integrated control unit controls the cooling water control unit so that the flow rate of cooling water supplied to the cooling water flow path during the period when the power is supplied from the second power source to the electrolytic cell is less than the flow rate of cooling water supplied to the cooling water flow path during the period when the power is supplied from the first power source to the electrolytic cell.

2. The carbon dioxide electrolysis apparatus according to claim 1, characterized in that, It also has: The detection unit detects the reaction amount in the electrolytic cell, and The gas control unit controls the amount of carbon dioxide supplied to the electrolytic cell based on the detection signal from the detection unit.

3. The carbon dioxide electrolysis apparatus according to claim 2, characterized in that, The detection unit is configured to detect at least one of the current and voltage of the electrolytic cell.

4. The carbon dioxide electrolysis apparatus according to any one of claims 1 to 3, characterized in that, It also has: The electrolyte supply unit supplies the electrolyte to the electrolytic cell, and An electrolyte control unit controls the amount of electrolyte supplied to the electrolytic cell.

5. The carbon dioxide electrolysis apparatus according to any one of claims 1 to 3, characterized in that, The first power source has a variable power source, which selects one of the following renewable energy sources—automotive energy, potential energy, light energy, chemical energy, and vibration energy—to convert into electrical energy for supply.

6. The carbon dioxide electrolysis apparatus according to any one of claims 1 to 3, characterized in that, The second power source includes a battery, a fuel cell, or an electrical system.

7. The carbon dioxide electrolysis apparatus according to any one of claims 1 to 3, characterized in that, The electrolytic cell has a discharge path for discharging products from the first containment section, the discharge path having a generating gas path and an exhaust gas path that can be switched by a valve.

8. The carbon dioxide electrolysis apparatus according to any one of claims 1 to 3, characterized in that, It also includes an electrochemical reaction cell, which is different from the electrolytic cell, connected to the first power control unit.

9. The carbon dioxide electrolysis apparatus according to any one of claims 1 to 3, characterized in that, It also includes a capacitor connected in parallel with the electrolytic cell.

10. A method for carbon dioxide electrolysis, characterized in that, The process includes the following steps: The process of supplying electricity to an electrolytic cell from a first power source (which is a variable power source) for normal operation, wherein the electrolytic cell comprises: a first containment section for containing at least carbon dioxide, a second containment section for containing an electrolyte containing water or water vapor, a diaphragm disposed between the first containment section and the second containment section, a reduction electrode disposed in the first containment section, an oxidation electrode disposed in the second containment section, and a cooling water flow path, wherein the cooling water flow path is different from the first containment section and the second containment section; and When the power supplied to the electrolytic cell from the first power source is lower than a specified time or a specified value, or when it is predicted to be lower than a specified time or a specified value, the first power source is disconnected from the electrolytic cell, and power is supplied to the electrolytic cell from the second power source to perform a warm-up operation. Specifically, control is performed such that the flow rate of cooling water supplied to the cooling water path during the period when the power is supplied from the second power source to the electrolytic cell is less than the flow rate of cooling water supplied to the cooling water path during the period when the power is supplied from the first power source to the electrolytic cell.

11. The carbon dioxide electrolysis method according to claim 10, wherein, The warm-up operation supplies a smaller current to the electrolytic cell from the second power source than the current supplied from the first power source.

12. The carbon dioxide electrolysis method according to claim 10, wherein, When the predicted current or voltage flowing through the electrolytic cell exceeds a predetermined value for a predetermined time, the warm-up operation increases the current flowing through the electrolytic cell from zero to a predetermined current through the second power source.

13. The carbon dioxide electrolysis method according to any one of claims 10 to 12, wherein, During the warm-up operation, the amount of carbon dioxide supplied to the electrolytic cell is controlled according to the amount of electricity supplied from the second power source to the electrolytic cell.

14. The carbon dioxide electrolysis method according to any one of claims 10 to 12, wherein, During the warm-up operation, the product discharged from the first containment section of the electrolytic cell is discarded.

15. The carbon dioxide electrolysis method according to any one of claims 10 to 12, wherein, During the warm-up operation, the first power source is disconnected from the electrolytic cell and connected to an electrochemical reaction cell that is different from the electrolytic cell.

16. The carbon dioxide electrolysis method according to any one of claims 10 to 12, characterized in that, The first power source has a variable power source, which selects one of the following renewable energy sources—automotive energy, potential energy, light energy, chemical energy, and vibration energy—to convert into electrical energy for supply.

17. The carbon dioxide electrolysis method according to any one of claims 10 to 12, characterized in that, The second power source includes a battery, a fuel cell, or an electrical system.

18. A valuable material manufacturing system, which possesses: The carbon dioxide electrolysis apparatus according to any one of claims 1 to 3, and A chemical synthesis apparatus connected to the first containment section of the carbon dioxide electrolysis apparatus, wherein at least a portion of the gas discharged from the first containment section is used as raw material to chemically synthesize valuable substances.

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