Method for operating an electrochemical reactor and electrochemical reactor

Abstract

This suppresses the performance degradation of the electrochemical reactor caused by startup and shutdown operations. [Solution] The method of operating the electrochemical reactor involves controlling the electrolysis unit so that, in each of the startup, operation, and shutdown processes, the first time-averaged pressure at a first position in the cathode chamber that is closer to the inlet than the outlet of the cathode chamber is equal to or greater than the second time-averaged pressure at a second position in the anode chamber that is opposite the first position across the diaphragm, and the third time-averaged pressure at a third position in the cathode chamber that is closer to the outlet than the inlet is equal to or greater than the fourth time-averaged pressure at a fourth position in the anode chamber that is opposite the third position across the diaphragm.

Description

[Technical Field]

[0001] Embodiments of the present invention relate to a method for operating an electrochemical reactor and an electrochemical reactor. [Background technology]

[0002] In recent years, concerns about the depletion of fossil fuels such as oil and coal have led to increased expectations for renewable energy sources that can be used sustainably. Examples of renewable energy sources include solar cells and wind power. However, these sources have the challenge of not being able to provide a stable power supply because their output depends on weather and natural conditions. Therefore, attempts are being made to stabilize the power supply by storing electricity generated from renewable energy sources in batteries. However, storing electricity presents problems such as the cost of batteries and losses that occur during storage.

[0003] In response to these issues, technologies that convert electrical energy into chemical substances (chemical energy) are attracting attention. These technologies include using electricity generated from renewable energy sources to electrolyze water and produce hydrogen from water, or electrochemically reducing carbon dioxide to produce carbon monoxide, formic acid, methanol, methane, acetic acid, ethanol, ethane, ethylene, and other carbon compounds, or electrochemically reducing nitrogen to produce ammonia. Storing these chemical substances in cylinders or tanks has the advantage of reducing energy storage costs and minimizing storage losses compared to storing electricity (electrical energy) in batteries.

[0004] Such electrochemical reactions are typically carried out in apparatus equipped with electrolytic cells or cell stacks. The operating modes of electrochemical reactors can vary depending on the type of reaction and the purpose of use. For example, they may be operated continuously for long periods, or they may be started and stopped frequently. Continuous operation and start-and-stop operations can cause a degradation in the performance of the electrolytic cell stack, such as an increase in cell voltage or a decrease in product selectivity. For example, methods are known to restore the performance of an electrolytic cell stack once it has deteriorated, and to protect the electrolytic cell from adverse effects of unexpected events such as power outages. On the other hand, in order to further improve the reliability of electrochemical reactors, it is important to sufficiently minimize the degradation of the electrolytic cell stack's performance caused by continuous operation and start-and-stop operations in normal operating modes. Therefore, there is a need for start-and-stop operation methods for electrochemical reactors that can suppress the degradation of the electrolytic cell stack's performance. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2022 / 183190 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] The problem that the embodiments of the present invention aim to solve is to suppress the performance degradation of an electrochemical reactor associated with start-up and stop-down operations. [Means for solving the problem]

[0007] A method for operating an electrochemical reactor according to an embodiment, the electrochemical reactor comprising an electrolytic section having a cathode, an anode, a cathode chamber facing the cathode, an anode chamber facing the anode, and a diaphragm provided between the cathode chamber and the anode chamber, the method comprising a start-up process in which at least one parameter selected from a group of multiple parameters including temperature, pressure, current density, voltage, composition of a first fluid containing a substance to be reduced supplied to the cathode chamber, flow rate of the first fluid, composition of a second fluid containing a substance to be oxidized supplied to the anode chamber, and flow rate of the second fluid is adjusted to satisfy the start-up conditions, and operating the electrolytic section within an operating condition range including the start-up conditions, and reducing the substance to be reduced at the cathode to produce a reduction product The electrolytic unit comprises an operating process, a shutdown process in which at least one parameter selected from a group of multiple parameters is adjusted to satisfy the storage start conditions, and a storage process in which the electrolytic unit is operated within a range of storage conditions including the storage start conditions. In each of the startup process, operating process, and shutdown process, the electrolytic unit is controlled such that the first time-averaged pressure at a first position in the cathode chamber, which is closer to the inlet of the cathode chamber than to the outlet of the cathode chamber, is equal to or greater than the second time-averaged pressure at a second position in the anode chamber, which is opposite the first position across a diaphragm, and the third time-averaged pressure at a third position in the cathode chamber, which is closer to the outlet than to the inlet, is equal to or greater than the fourth time-averaged pressure at a fourth position in the anode chamber, which is opposite the third position across a diaphragm. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic diagram showing an example of the configuration of an electrochemical reaction apparatus. [Figure 2] This is a schematic diagram showing other configuration examples of the electrolytic unit. [Figure 3] This is a schematic diagram showing other configuration examples of the electrolytic unit. [Figure 4] This is a schematic diagram illustrating an example of how to operate an electrochemical reactor. [Figure 5] This is a schematic diagram showing the relationship between the location of the flow path and the pressure. [Figure 6]It is a schematic diagram showing the relationship between the position and pressure of the flow path. [Figure 7] It is a schematic diagram showing the relationship between the position and pressure of the flow path. [Figure 8] It is a schematic diagram showing another configuration example of the electrochemical reaction device. [Figure 9] It is a schematic diagram showing another configuration example of the electrochemical reaction device. [Figure 10] It is a diagram showing the experimental results of Examples 9 to 13. [Figure 11] It is a diagram showing the experimental results of Examples 14 and 15.

Mode for Carrying Out the Invention

[0009] Figure 1 is a schematic diagram showing a configuration example of the electrochemical reaction device according to the embodiment. Figure 1 shows a configuration example of the electrochemical reaction device 1. The electrochemical reaction device 1 includes an electrolysis unit 10, a flow path P1, a flow path P2, a flow path P3, a flow path P4, a cathode supply unit 21, and an anode supply unit 22.

[0010] The electrolysis unit 10 can perform, for example, at least one electrolysis reaction. The electrolysis unit 10 includes a cathode 11, an anode 12, a diaphragm 13, a cathode chamber 140, and an anode chamber 150.

[0011] The electrolysis unit 10 may have, for example, a membrane electrode assembly. Figure 2 is a schematic diagram showing another configuration example of the electrolysis unit 10. As shown in Figure 2, the electrolysis unit 10 may include a cathode 11, an anode 12, a diaphragm 13, a flow path plate 14, a flow path plate 15, a current collector 16, and a current collector 17. Figure 2 shows the X-axis, the Y-axis, and the Z-axis. The X-axis, Y-axis, and Z-axis intersect perpendicularly to each other. The Z-axis is along the thickness direction of the electrolysis unit 10. Figure 2 shows a part of the X-Z cross-section including the X-axis and the Z-axis. The cathode 11, the anode 12, and the diaphragm 13 may be laminated to form an electrolytic cell 100 having a membrane electrode assembly MEA.

[0012] Cathode 11 is a reduction electrode for, for example, carrying out a reduction reaction of at least one substance to be reduced to produce a reduction product. The at least one substance to be reduced includes, for example, carbon dioxide or nitrogen. Cathode 11 reduces carbon dioxide to produce a carbon compound, or reduces nitrogen to produce a nitrogen compound such as ammonia. Examples of carbon compounds include carbon monoxide, formic acid, methanol, methane, ethanol, ethane, ethylene, formaldehyde, ethylene glycol, acetic acid, propanol, etc. Cathode 11 may produce a side reaction in which hydrogen is generated by the reduction of water, along with the reduction reaction of carbon dioxide or nitrogen.

[0013] The cathode 11 has, for example, a cathode catalyst that promotes a reduction reaction to reduce at least one target substance. The cathode catalyst can be formed using, for example, a material that reduces the activation energy required to reduce at least one target substance. In other words, the cathode catalyst can be formed using, for example, a material that lowers the overpotential when a reduction product is generated by the reduction reaction of at least one target substance.

[0014] The cathode 11 may have a first surface in contact with the diaphragm 13 and a second surface facing the cathode chamber 140. The cathode 11 may also have, for example, a gas diffusion layer and a cathode catalyst layer. The cathode 11 may have a porous layer between the gas diffusion layer and the cathode catalyst layer that is denser than the gas diffusion layer. The gas diffusion layer is located on the cathode chamber 140 side, and the cathode catalyst layer is located on the diaphragm 13 side. The cathode catalyst layer may be embedded within the gas diffusion layer. The cathode catalyst layer preferably has catalyst nanoparticles or catalyst nanostructures. The gas diffusion layer is made of, for example, carbon paper or carbon cloth and is treated with a water-repellent finish. An electrolytic solution or ions are supplied to the cathode catalyst layer from the anode 12 side via the diaphragm 13. In the gas diffusion layer, a cathode supply fluid is supplied from the cathode chamber 140, and the products of the reduction reaction are discharged. The reduction reaction occurs near the boundary between the gas diffusion layer and the cathode catalyst layer, and the gaseous product is discharged outside the electrolytic cell 100 through the cathode channel via the gas diffusion layer.

[0015] Examples of cathode catalysts include metals such as gold (Au), silver (Ag), copper (Cu), platinum (Pt), palladium (Pd), nickel (Ni), cobalt (Co), iron (Fe), manganese (Mn), titanium (Ti), cadmium (Cd), zinc (Zn), indium (In), gallium (Ga), lead (Pb), and tin (Sn), as well as alloys and intermetallic compounds containing at least one of these metals; carbon materials such as carbon (C), graphene, carbon nanotubes (CNTs), fullerenes, and Ketjenblack; and metal complexes such as Ru complexes and Re complexes. Various shapes can be applied to the cathode catalyst layer, including plate-like, mesh-like, wire-like, particulate, porous, thin-film-like, and island-like forms.

[0016] Anode 12 is an oxidation electrode for producing oxidation products by carrying out an oxidation reaction of at least one oxidizing agent (substance to be oxidized). The at least one oxidizing agent includes, for example, water. Anode 12 oxidizes, for example, substances or ions in the electrolyte (anodic solution) to produce oxygen.

[0017] The anode 12 may have a first surface in contact with the diaphragm 13 and a second surface facing the anode chamber 150. The anode 12 has, for example, an anode catalyst that promotes an oxidation reaction that oxidizes water to produce oxygen. The anode catalyst can be formed using, for example, a material that reduces the activation energy when oxidizing the oxidizer, in other words, a material that lowers the reaction overpotential. Examples of oxidation reactions at the anode 12 include the oxidation of water to produce oxygen or hydrogen peroxide, and the oxidation of chloride ions (Cl - This includes reactions that oxidize ) to produce chlorine, and reactions that oxidize carbonate ions or bicarbonate ions to produce carbon dioxide.

[0018] Examples of anode catalysts include metals such as platinum (Pt), palladium (Pd), iridium (Ir), and nickel (Ni), alloys and intermetallic compounds containing these metals, binary metal oxides such as 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), lithium oxide (Li-O), and lanthanum oxide (La-O), ternary metal oxides such as Ni-Co-O, Ni-Fe-O, La-Co-O, Ni-La-O, Sr-Fe-O, and Ru-Co-O, quaternary metal oxides such as Pb-Ru-Ir-O, La-Sr-Co-O, and Ru-Co-Sn-O, and metal complexes such as Ru complexes and Fe complexes.

[0019] The anode 12 may have a structure that allows anode supply fluid and ions to move between the diaphragm 13 and the anode chamber 150, for example, a substrate having a porous structure such as a mesh material, a punching material, a porous body, or a metal fiber sintered body. The substrate may be made of a metallic material such as titanium (Ti), nickel (Ni), iron (Fe), or an alloy containing at least one of these metals (for example, SUS), or it may be made of the anode catalyst described above. When an oxide is used as the anode catalyst, it is preferable to attach or laminate the anode catalyst to the surface of the substrate made of the above-mentioned metallic material to form a catalyst layer. The anode catalyst may have nanoparticles, nanostructures, nanowires, etc. to enhance the oxidation reaction. A nanostructure is a structure in which nanoscale irregularities are formed on the surface of the catalyst material.

[0020] The diaphragm 13 is provided between the cathode 11 and the anode 12. The diaphragm 13 can separate the cathode chamber 140 and the anode chamber 150. The diaphragm 13 contains hydrogen ions (H + ) and hydroxide ions (OH - ), bicarbonate ions (HCO3) - ), carbonate ions (CO3 2- Ions such as ) can be moved. The diaphragm 13 allows for the formation of an electrolytic cell 100 having a two-chamber structure. The diaphragm 13 may be provided in contact with the cathode 11 and the anode 12.

[0021] The diaphragm 13 is composed of an ion exchange membrane or the like that can move ions and electrolyte between the cathode 11 and the anode 12, and can separate the cathode chamber 140 and the anode chamber 150. Examples of ion exchange membranes include Neosepta (registered trademark) from Astom, Celemion (registered trademark) from AGC, Aciplex (registered trademark) from Asahi Kasei, Fumasep (registered trademark) and Fumapem (registered trademark) from Fumatech, Nafion (registered trademark), a fluororesin produced by sulfonating and polymerizing tetrafluoroethylene from DuPont, Lewabrane (registered trademark) from LANXESS, IONSEP (registered trademark) from IONTECH, Mustang (registered trademark) from PALL, RALEX (registered trademark) from mega, and GORE-TEX (registered trademark) from GORE-TEX. However, other materials that can move ions between the anode 12 and the cathode 11, such as glass filters, porous polymer membranes, and porous insulating materials, may also be applied to the diaphragm 13.

[0022] In addition to ion exchange membranes, other materials can be used, such as silicone resins, fluororesins (perfluoroalkoxyalkanes (PFA), perfluoroethylene propene copolymers (FEP), polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene copolymers (ETFE), polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymers (ECTFE), etc.), polyethersulfone (PES), porous ceramic membranes, packing materials filled with glass filters or agar, and insulating porous materials such as zeolites and oxides. Hydrophilic porous membranes are particularly preferred as the diaphragm 13 because they do not become clogged with air bubbles.

[0023] The cathode chamber 140 is provided, for example, facing the cathode 11 and can form a cathode flow path. The cathode 11 may be located inside the cathode chamber 140, as shown in Figure 1. The cathode chamber 140 has an inlet for supplying cathode supply fluid to the cathode chamber 140 and an outlet for discharging cathode discharge fluid from the cathode chamber 140.

[0024] The cathode supply fluid undergoes a change in composition after passing through the cathode chamber 140 and is discharged outside the electrolytic unit 10. The fluid discharged from the electrolytic unit 10 is called the cathode discharge fluid. The cathode discharge fluid contains the target product, which is separated and recovered as needed. The cathode discharge fluid may be separated into gas and liquid phases, and a portion of the gas phase may be merged with the cathode supply fluid. This method is effective in increasing the conversion rate of reactants in the cathode supply fluid. Alternatively, the cathode discharge fluid may be separated into gas and liquid phases, and a portion or all of the liquid phase may be merged with the anode supply fluid.

[0025] The anode chamber 150 is provided, for example, facing the anode 12, and can form an anode flow path. As shown in Figure 1, the anode chamber 150 has an inlet for supplying anode supply fluid to the anode chamber 150 and an outlet for discharging anode discharge fluid from the anode chamber 150.

[0026] The anode supply fluid changes composition as it passes through the anode chamber 150 and is discharged outside the electrolytic unit 10. The fluid discharged from the anode chamber 150 is called the anode discharge fluid. The anode discharge fluid contains gases such as oxygen generated at the anode 12. The anode discharge fluid may be separated into gas and liquid phases, and part or all of the liquid phase may be merged with the anode supply fluid. The anode supply fluid can be circulated by treating the liquid phase portion of the anode discharge fluid as the anode supply fluid and supplying it to the anode chamber 150 without supplying anode supply fluid from outside the system.

[0027] The flow channel plate 14 forms, for example, a cathode chamber 140. The cathode chamber 140 is provided on the surface of the flow channel plate 14 facing the cathode 11, and can form a cathode flow channel.

[0028] The flow channel plate 15 forms, for example, an anode chamber 150. The anode chamber 150 is provided on the surface of the flow channel plate 15 facing the anode 12, and can form an anode flow channel.

[0029] Preferably, at least one of the flow channel plates 14 and 15 has at least one land (protrusion) 141 and land 151. The lands 141 and 151 are provided for mechanical retention and electrical conductivity. Land 141 is provided in contact with the cathode 11. Land 151 is provided in contact with the anode 12. Preferably, the lands 141 and 151 are provided alternately to homogenize the fluid flow. With such lands 141 and 151, the cathode flow channel and anode flow channel have a meandering shape along the surface.

[0030] The channel plates 14 and 15 are preferably formed from materials that have low chemical reactivity and high conductivity. Examples of such materials include metallic materials such as titanium and SUS, and carbon materials. In addition, components such as packing (not shown) may be sandwiched between each channel plate and adjacent components as needed.

[0031] The current collector 16 is stacked on the opposite side of the cathode 11 of the flow channel plate 14 and electrically connected to the cathode 11. The current collector 17 is stacked on the opposite side of the anode 12 of the flow channel plate 15 and electrically connected to the anode 12. The current collectors 16 and 17 are electrically connected to the power supply 40, for example, via wiring. It is preferable that the current collectors 16 and 17 are formed using materials with high conductivity.

[0032] The power supply 40 can be powered, for example, by supplying current or voltage to the electrolytic unit 10. The power supply 40 is electrically connected to the cathode 11 and anode 12 via, for example, the flow path plate 14, the flow path plate 15, the current collector 16, and the current collector 17. The power supply 40 can supply power to the electrolytic unit 10 to cause electrolytic reactions such as oxidation and reduction reactions, and is electrically connected to the cathode 11 and anode 12. The reduction reaction at the cathode 11 and the oxidation reaction at the anode 12 are carried out using the electrical energy supplied from the power supply 40. The power supply 40 and the current collector 16, and the power supply 40 and the current collector 17 are connected, for example, by wiring. Electrical equipment such as an inverter, converter, and battery may be installed between the electrolytic unit 10 and the power supply 40 as needed. The driving method for the electrolytic unit 10 may be a constant voltage method or a constant current method.

[0033] The power source 40 may be a normal commercial power source or a battery, or it may be a power source that converts renewable energy into electrical energy and supplies it. Examples of such power sources include power sources that convert kinetic energy or potential energy such as wind power, hydropower, geothermal energy, and tidal power into electrical energy; power sources such as solar cells that have a photoelectric conversion element that converts light energy into electrical energy; power sources such as fuel cells and storage batteries that convert chemical energy into electrical energy; and power sources such as devices that convert vibration energy such as sound into electrical energy. The photoelectric conversion element has the function of separating charges using the energy of light such as irradiated sunlight. Examples of photoelectric conversion elements include pin junction solar cells, pn junction solar cells, amorphous silicon solar cells, multi-junction solar cells, monocrystalline silicon solar cells, polycrystalline silicon solar cells, dye-sensitized solar cells, and organic thin-film solar cells. The photoelectric conversion element may also be stacked with at least one of the cathode 11 and anode 12 inside the electrolytic unit 10.

[0034] The electrolytic cell 100 is sandwiched between a pair of support plates (not shown) and further secured with bolts or the like. The electrolytic cell 100 may be positioned so that the membrane electrode assembly MEA is horizontal or vertical. When the membrane electrode assembly MEA is horizontal, it does not matter whether the cathode 11 or the anode 12 is on top.

[0035] The electrolytic unit 10 may have a cell stack formed by stacking multiple electrolytic cells 100. Figure 3 is a schematic diagram showing another configuration example of the electrolytic unit 10. Figure 3 shows a portion of the XZ cross-section including the X and Z axes. As shown in Figure 3, the electrolytic unit 10 may have multiple membrane electrode assemblies MEA, a flow channel plate 14, a flow channel plate 15, a current collector 16, a current collector 17, and a flow channel plate 18. Figure 3 shows multiple cathodes 11, multiple anodes 12, multiple diaphragms 13, multiple cathode chambers 140, and multiple anode chambers 150. Multiple membrane electrode assemblies MEA are provided between the current collector 16 and the current collector 17 to form a cell stack. By forming a cell stack, for example, the amount of reaction of the substance to be reduced per unit area increases, thus increasing the amount of reduction product produced. The number of stacked electrolytic cells 100 is preferably, for example, 10 or more and 150 or less.

[0036] If the electrolytic unit 10 has multiple electrolytic cells 100, the cathode supply fluid and anode supply fluid supplied to each cell can be distributed to each cell from a number of pipes less than the number of electrolytic cells 100. Also, the cathode discharge fluid and anode discharge fluid discharged from each cell can be combined into a number of pipes less than the number of electrolytic cells 100. The distribution of the cathode supply fluid and anode supply fluid, and the merging of the cathode discharge fluid and anode discharge fluid may be performed outside the electrolytic unit 10 or inside the electrolytic unit 10. Here, the inside of the electrolytic unit 10 refers to the area in which multiple electrolytic cells 100 are sandwiched between a pair of support plates and further tightened with bolts or the like.

[0037] The flow channel plate 18 is, for example, a bipolar plate having a cathode chamber 140 and an anode chamber 150. The flow channel plate 18 is provided between a plurality of membrane electrode assemblies (MEAs) and separates a plurality of electrolytic cells 100. Adjacent cathodes 11 and anodes 12 may be electrically connected via the flow channel plate 18. The plurality of electrolytic cells 100 are stacked, sandwiched between a pair of support plates, and further secured by tightening with bolts or the like. The cell stack may be installed with the membrane electrode assemblies (MEAs) in a horizontal or vertical configuration. When the membrane electrode assemblies (MEAs) are horizontal, the cathode 11 or anode 12 may be placed on the uppermost surface of the cell stack.

[0038] The cathode chamber 140 of the flow channel plate 18 is provided, for example, on the first surface of a bipolar plate and faces the cathode 11 of one of the multiple MEAs. The inlet of the cathode chamber 140 of the flow channel plate 18 is connected to flow channel P1. The outlet of the cathode chamber 140 of the flow channel plate 18 is connected to flow channel P3. Flow channels P1 and P2 are formed, for example, by piping.

[0039] The anode chamber 150 of the flow channel plate 18 is provided, for example, on a second surface opposite to the first surface of the bipolar plate and faces one of the other anodes 12 of the multiple MEAs. The inlet of the anode chamber 150 of the flow channel plate 18 is connected to flow channel P2. The outlet of the anode chamber 150 of the flow channel plate 18 is connected to flow channel P4. Flow channels P2 and P4 are formed, for example, by piping.

[0040] The cathode supply fluid is, for example, a cathode supply gas, or a two-phase flow (gas-liquid two-phase flow) of a cathode supply gas and a cathode supply liquid. The cathode supply gas includes, for example, at least one of the following gases: carbon dioxide, nitrogen, argon, and water vapor. The cathode supply gas may also be a mixture of at least two gases selected from carbon dioxide, nitrogen, argon, and water vapor. The cathode supply liquid may include, for example, water.

[0041] The cathode supply fluid is prepared, for example, by the cathode supply unit 21 and supplied to the electrolysis unit 10. The cathode supply unit 21 includes a humidifier 201. The cathode supply unit 21 may be provided with a bypass pipe that can bypass the humidifier 201 and allow the fluid to flow when the humidifier 201 is not used. The cathode supply fluid supply system including the cathode supply unit 21 may have a gas cylinder, a flow control unit, a pressure control unit, etc.

[0042] The anode supply fluid includes, for example, water. The form of water may be liquid water or water vapor. In particular, when the anode supply fluid does not contain a gas phase and is only in a liquid phase, hereinafter it is also referred to as an anode aqueous solution. Examples of the anode aqueous solution include an aqueous solution containing any electrolyte. Examples of the aqueous solution containing an electrolyte include, for example, hydroxide ions (OH - ), hydrogen ions (H + ), potassium ions (K + ), sodium ions (Na + ), lithium ions (Li + ), chloride ions (Cl - ), bromide ions (Br - ), iodide ions (I - ), nitrate ions (NO3 - ), sulfate ions (SO4[[ID=(...)]] 2- ), phosphate ions (PO4 2- ), borate ions (BO3 3- ), carbonate ions (CO3 2- ), and an aqueous solution containing at least one selected from hydrogen carbonate ions (HCO3 - ). In order to reduce the electrical resistance of the liquid, an alkaline solution in which an electrolyte such as potassium hydroxide or sodium hydroxide is dissolved at a high concentration may be used as the anode aqueous solution.

[0043] The anode supply fluid is supplied to the electrolysis unit 10 via the anode supply unit 22. The anode supply fluid supply system on the inlet side of the anode chamber 150, including the anode supply unit 22, includes, for example, a pressure control unit, an anode aqueous solution tank, a flow rate control unit (pump), a reference electrode, a pressure gauge, a temperature control mechanism, etc., when the anode supply fluid is an anode aqueous solution. The anode aqueous solution is supplied to the anode chamber 150 in the anode supply fluid supply system with its flow rate, pressure, and temperature controlled.

[0044] The humidifier 201 can humidify the cathode supply fluid supplied from a cathode supply fluid source, such as a gas cylinder. The humidifier 201 is installed in the middle of the flow path P1. It is preferable that the cathode supply fluid upstream of the humidifier 201 is only in the gas phase. The humidifier 201 can mix water vapor with the cathode supply fluid supplied upstream of the humidifier 201. Examples of humidification methods using the humidifier 201 include, but are not limited to, methods such as bubbling gas in liquid water, installing a vaporizer in the gas flow path and injecting liquid water into it for evaporation, or spraying liquid water in the gas for evaporation.

[0045] It is preferable that the humidifier 201 can adjust the amount of water vapor mixed with the cathode supply fluid supplied from the upstream stage of the humidifier 201. Examples of methods for adjusting the amount of water vapor include, but are not limited to, methods such as specifying the temperature of the liquid water used for bubbling, specifying the total amount and rate of liquid water injected into the vaporizer, or specifying the total amount and rate of liquid water discharged from the atomizer. It is preferable that the humidified cathode supply fluid discharged from the humidifier 201 consists only of the gas phase, but may also contain a liquid phase.

[0046] Next, an example of the operation method of the electrochemical reactor according to the embodiment will be described. Figure 4 is a schematic diagram illustrating an example of the operation method of the electrochemical reactor according to the embodiment. Figure 4 shows a horizontal axis representing time and a vertical axis representing the controlled parameter value.

[0047] The method for operating electrochemical reactor 1 broadly includes the following four processes: (1) Startup process: At least one of several parameters in the electrolytic unit 10, including temperature, pressure, current density, voltage, composition of the cathode supply fluid supplied to the cathode chamber 140, flow rate of the cathode supply fluid, composition of the anode supply fluid supplied to the anode chamber 150, and flow rate of the anode supply fluid, is adjusted to satisfy the start-up conditions. (2) Operating process: The electrolytic unit 10 is operated within the operating conditions range including the above operating start conditions, and reduction products are generated by reducing the raw material (substance to be reduced) supplied to the cathode chamber 140 at the cathode 11, and oxidation products are generated by oxidizing the raw material (substance to be oxidized) supplied to the anode chamber 150 at the anode 12. (3) Shutdown process: At least one of several parameters in the electrolytic unit 10, including temperature, pressure, current density, voltage, composition of the cathode supply fluid supplied to the cathode chamber 140, flow rate of the cathode supply fluid, composition of the anode supply fluid supplied to the anode chamber 150, and flow rate of the anode supply fluid, is adjusted to satisfy the storage start conditions. (4) Storage process: The electrolytic unit 10 is operated (stored) within the range of storage conditions, including the storage start conditions.

[0048] The startup process, operation process, shutdown process, and storage process may be performed in the order listed above. That is, the operation process may be performed after the startup process, the shutdown process after the operation process, and the storage process after the shutdown process. Alternatively, the startup process may be performed again after the storage process, and the sequence consisting of the startup process, operation process, shutdown process, and storage process may be repeated multiple times. In this case, the operation start conditions, operating condition range, storage start conditions, and storage condition range may differ in each iteration. The operations performed in each process may also differ in each iteration.

[0049] The startup, operation, shutdown, and storage phases can be distinguished by the amount of change in the parameters being adjusted.

[0050] In the transition from the startup process to the operation process, when all of the controllable parameters (controllable parameter values) among several parameters, including temperature, pressure, current density, voltage, composition of the cathode supply fluid supplied to the cathode chamber 140, flow rate of the cathode supply fluid, composition of the anode supply fluid supplied to the anode chamber 150, and flow rate of the anode supply fluid in the electrolytic unit 10, are continuously controlled within a predetermined range (operation start condition tolerance range) added to a predetermined setting value for the operation start condition (operation start condition setting value) for a predetermined duration, it can be determined that the transition from the startup process to the operation process has occurred. The same applies to the transition from the shutdown process to the storage process. When all of the controllable parameters among the adjustable parameters are continuously controlled within a predetermined range (operation start condition tolerance range) added to a predetermined setting value for the storage start condition for a predetermined duration, it can be determined that the transition from the shutdown process to the storage process has occurred.

[0051] When switching from the operating process to the shutdown process, it can be determined that a switch has occurred when at least one of the controllable parameters (controllable parameter value) among several parameters, including temperature, pressure, current density, voltage, composition of the cathode supply fluid supplied to the cathode chamber 140, flow rate of the cathode supply fluid, composition of the anode supply fluid supplied to the anode chamber 150, and flow rate of the anode supply fluid in the electrolytic unit 10, changes outside the range obtained by adding a predetermined tolerance to a predetermined boundary value of the operating condition range (operating condition range boundary value) (operating condition range boundary value tolerance range). Similarly, when switching from the storage process back to the startup process, it can be determined that a switch has occurred when at least one of the controllable parameters among the adjustable parameters changes outside the range obtained by adding a predetermined tolerance to a predetermined boundary value of the storage condition range (storage condition range boundary value) (storage condition range boundary value tolerance range).

[0052] As an example, we will describe a case where temperature, pressure, and current density in the electrolytic unit 10 are the parameters to be controlled during the startup process. A predetermined tolerance range and a predetermined duration may be set for each individual parameter.

[0053] Regarding the temperature of the electrolytic unit 10, for example, if it is continuously controlled within a range of ±5°C from the set value of the predetermined start-up conditions for a predetermined duration or longer, it can be determined that the conditions for switching from the startup process to the operation process are met. A tolerance range of ±3°C is more preferable. If it is difficult to directly measure the internal temperature of the electrolytic unit 10, the temperature of each fluid may be measured in the flow paths P1, P2, P3, and P4, and any of the measured temperatures may be used as an indicator instead of the temperature of the electrolytic unit 10.

[0054] Regarding the pressure in the electrolytic unit 10, for example, if it is continuously controlled within a range of ±10 kPa from the set value of the predetermined start-up conditions for a predetermined duration or longer, it can be determined that the conditions for switching from the startup process to the operation process are met. A tolerance range of ±5 kPa is more preferable. If it is difficult to directly measure the internal pressure of the electrolytic unit 10, for example, the pressure of the cathode supply fluid measured in the flow path P1 connected to the inlet of the cathode chamber 140, the pressure of the anode supply fluid measured in the flow path P2 connected to the inlet of the anode chamber 150, or the differential pressure calculated as the difference between them may be set as an indicator.

[0055] Regarding current density, for example, it can be ±10 mA / cm² relative to the set value for the predetermined operating start conditions. 2 When the control is maintained continuously within this range for a predetermined duration or longer, it can be determined that the conditions for switching from the startup process to the operation process have been met. The allowable range is ±5mA / cm 2 It is preferable if it is.

[0056] The predetermined duration can be appropriately set to a time such as 1 minute, 2 minutes, 3 minutes, 5 minutes, 10 minutes, or 15 minutes, depending on the performance of the electrochemical reaction apparatus of the embodiment.

[0057] During the startup process, operations such as supplying cathode fluid to the cathode chamber 140, supplying anode fluid to the anode chamber 150, preheating the electrolytic unit 10, boosting the pressure to adjust the inter-electrode differential pressure (described later), starting current application, and increasing the current density may be performed.

[0058] During the operation process, operations such as constant current operation, constant voltage operation, and fine-tuning of operating conditions due to performance degradation of the electrolytic unit 10 may be performed.

[0059] During the shutdown process, operations (actions) such as reducing the current density, stopping the application of current, stopping the flow of cathode supply fluid to the cathode chamber 140, stopping the flow of anode supply fluid to the anode chamber 150, purging by flowing gas through the cathode chamber 140 and the anode chamber 150, depressurization to adjust the differential pressure between electrodes, and cooling the electrolytic unit 10 may be performed.

[0060] During the storage process, for example, the electrolytic unit 10 may be sealed by operating valves provided in the flow paths P1, P2, P3, and P4, and the electrochemical reactor 1 may be left to stand. Alternatively, the cathode chamber 140 may be supplied with a constant flow rate of cathode supply fluid, and the anode chamber 150 may be supplied with a constant flow rate of anode supply fluid, while maintaining the pressure difference (inter-electrode differential pressure) between the cathode chamber 140 and the anode chamber 150.

[0061] Here, we focus on the pressure inside the electrolytic unit 10 as a factor that affects the performance of the electrolytic cell, specifically the selectivity of the product and the cell voltage.

[0062] The pressure inside the cathode chamber 140 varies depending on the location. In particular, when the cathode chamber 140 forms a cathode flow path, pressure loss occurs between the upstream part (for example, the part closer to the inlet than the outlet) and the downstream part (for example, the part closer to the outlet than the inlet) of the cathode flow path, so the pressure is higher upstream than downstream. The magnitude of the pressure loss in the cathode chamber 140 varies depending on the shape of the cathode chamber 140 and also on the operating conditions of the electrolytic unit 10. For example, the larger the flow rate of the cathode supply fluid supplied to the cathode chamber 140, the greater the value of the pressure loss. Similarly, the pressure inside the anode chamber 150 varies depending on the location. In particular, when the anode chamber 150 forms an anode flow path, pressure loss occurs between the upstream part (for example, the part closer to the inlet than the outlet) and the downstream part (for example, the part closer to the outlet than the inlet) of the anode flow path, so the pressure is higher upstream than downstream. The magnitude of the pressure loss in the anode chamber 150 varies depending on the shape of the anode chamber 150 and also on the operating conditions of the electrolytic unit 10. For example, the larger the flow rate of the anode supply fluid supplied to the anode chamber 150, the greater the pressure loss. Also, when an aqueous solution (anode aqueous solution) is supplied to the anode chamber 150, gases such as oxygen are generated in the anode 12 as the electrolytic unit 10 operates, forming a gas-liquid two-phase flow within the anode chamber 150, which increases the pressure loss in the anode chamber 150. The value of the pressure loss in the anode chamber 150 is affected by the amount of gas generated in the anode 12. In other words, the value of the pressure loss in the anode chamber 150 is affected by the current density.

[0063] It is preferable to control the electrolytic unit 10 such that, during the startup process, operation process, and shutdown process, the first time-averaged pressure at a first position in the cathode chamber 140 that is closer to the inlet of the cathode chamber 140 than to the outlet of the cathode chamber 140 is greater than or equal to the second time-averaged pressure at a second position in the anode chamber 150 that is opposite to the first position across the diaphragm 13, and the third time-averaged pressure at a third position in the cathode chamber 140 that is closer to the outlet than to the inlet is greater than or equal to the fourth time-averaged pressure at a fourth position in the anode chamber 150 that is opposite to the third position across the diaphragm 13. Furthermore, it is preferable that, similarly during the storage process, the first time-averaged pressure is greater than or equal to the second time-averaged pressure, and the third time-averaged pressure is greater than or equal to the fourth time-averaged pressure.

[0064] The first time-averaged pressure can be defined by the average value of the first pressure at the first location over the duration of each process. The second time-averaged pressure can be defined by the average value of the second pressure at the second location over the duration of each process. The third time-averaged pressure can be defined by the average value of the third pressure at the third location over the duration of each process. The fourth time-averaged pressure can be defined by the average value of the fourth pressure at the fourth location over the duration of each process.

[0065] Furthermore, the pressure difference between the cathode chamber 140 and the anode chamber 150 is referred to as the inter-electrode differential pressure. As mentioned above, the pressure inside the cathode chamber 140 and the anode chamber 150 differs depending on the location. Therefore, the inter-electrode differential pressure also differs depending on the location. In the following, we will focus on the difference between the pressure at an arbitrary location (location A) inside the cathode chamber 140 and the pressure at a location (location B) opposite location A across the diaphragm 13 inside the anode chamber 150, and define the difference between the pressure at location A and the pressure at location B (inter-electrode differential pressure) as the value obtained by subtracting the pressure on the anode 12 side from the pressure on the cathode 11 side.

[0066] For example, when performing an electrochemical reaction by supplying a cathode supply fluid (gas) to the cathode chamber 140 and an anode supply fluid (liquid) to the anode chamber 150, it is preferable to operate the system with the inter-electrode differential pressure at each position being zero or greater, i.e., the pressure on the cathode 11 side (pressure in the cathode chamber 140) being greater than or equal to the pressure on the anode 12 side (pressure in the anode chamber 150), at least during the start-up process, the operation process, and the shutdown process. Maintaining an inter-electrode differential pressure of zero kPa or greater suppresses the excessive movement of the liquid on the anode 12 side to the cathode 11 side through the diaphragm 13. While the movement of the liquid on the anode 12 side to the cathode 11 side is necessary to some extent to form a reaction field inside the cathode 11, excessive movement of liquid can have adverse effects. Excessively moved liquid can enter pores in the cathode catalyst layer and gas diffusion layer of the cathode 11 and block the pores. Pore ​​blockage hinders the supply of reactant gases to the reaction field near the cathode catalyst surface, leading to a decrease in the performance of the electrolytic unit 10, such as increased cell resistance and reduced product selectivity for the target product. Maintaining an inter-electrode differential pressure of zero or greater suppresses excessive liquid movement, thereby preventing a decrease in the performance of the electrolytic cell. By maintaining an inter-electrode differential pressure of zero or greater not only during operation but also during the startup and shutdown phases, it is possible to suppress a decrease in the performance of the electrolytic unit 10 during the second and subsequent operation phases when multiple startups and shutdowns are performed.

[0067] Figures 5, 6, and 7 are schematic diagrams showing the relationship between the position of the flow path and the pressure. Figures 5, 6, and 7 have a horizontal axis representing the position of the flow path and a vertical axis representing the pressure in the flow path. As mentioned above, the differential pressure between the electrodes differs depending on the position, so it is preferable that the minimum value of the differential pressure between the electrodes is zero or greater. It is even more preferable that the minimum value of the differential pressure between the electrodes is positive. When supplying a cathode supply fluid (gas) to the cathode chamber 140 and an anode supply fluid (liquid) to the anode chamber 150, the pressure loss is often greater in the anode chamber 150 than in the cathode chamber 140. For example, when the cathode channel inlet (cathode inlet) and the anode channel inlet (anode inlet) are located opposite each other across the diaphragm 13, and the cathode channel outlet (cathode outlet) and the anode channel outlet (anode outlet) are located opposite each other across the diaphragm 13, and the cathode fluid and anode fluid are flowing in the same direction, the inter-electrode differential pressure at the outlet side of each channel is greater than the inter-electrode differential pressure at the inlet side of each channel (Figure 5). Also, as shown in Figure 6, the pressure at the outlet of the cathode channel may be lower than the pressure at the inlet of the anode channel. In this case as well, the inter-electrode differential pressure at each position within the channel is always greater than or equal to zero. When the cathode fluid and anode fluid are flowing in opposite directions, the inter-electrode differential pressure at the position where the outlet of the cathode channel and the inlet of the anode channel are opposite each other across the diaphragm 13 is the smallest within the electrolytic unit 10 (Figure 7).

[0068] Since it is difficult to measure the pressure and inter-electrode pressure at various locations inside the electrolytic unit 10, it is useful to estimate them from the pressure measurements at the inlets and outlets of both electrodes of the cell. We will explain using an example where the cathode chamber 140 forms the cathode flow path and the anode chamber 150 forms the anode flow path, with the cathode flow path inlet and anode flow path inlet located opposite each other across a diaphragm 13, and the cathode flow path outlet and anode flow path outlet located opposite each other across the diaphragm 13, and the cathode fluid and anode fluid flow in the same direction. For example, pressure gauges are installed in flow paths P1, P2, P3, and P4 connected to the inlets and outlets of the cathode and anode flow paths, and the pressure is measured. It is preferable that the pressure gauges be installed as close as possible to the cathode chamber 140 and anode chamber 150. From the pressure measured in this way, the pressure loss of the cathode flow path and anode flow path can be obtained. Furthermore, the inter-electrode pressure at the channel inlet can be determined by subtracting the pressure at the anode channel inlet from the pressure at the cathode channel inlet, and the inter-electrode pressure at the channel outlet can be determined by subtracting the pressure at the anode channel outlet from the pressure at the cathode channel outlet. For example, assuming that the inter-electrode pressure inside the electrolytic unit 10 changes along the channel, and that the inter-electrode pressure at the channel inlet and the inter-electrode pressure at the channel outlet can be approximated by a linear function with endpoints, the inter-electrode pressure at each position can be estimated as the value obtained by dividing the endpoint value by the length of the channel. In addition, the spatial average value of the inter-electrode pressure can be estimated, for example, by the simple average value of the inter-electrode pressure at the channel inlet and the inter-electrode pressure at the channel outlet.

[0069] The pressure in the cathode chamber 140, the pressure in the anode chamber 150, and the inter-electrode differential pressure change over time during each process. Therefore, during at least the startup process, the operation process, and the shutdown process, the spatial minimum value of the inter-electrode differential pressure is averaged over the duration of each process, and the operation can be performed such that the resulting time-averaged value (time-averaged inter-electrode differential pressure) is zero or greater. It is more preferable if the time-averaged inter-electrode differential pressure is positive.

[0070] For example, when controlling the electrochemical reactor 1 so that the spatial minimum value of the inter-electrode differential pressure is a positive value close to zero, depending on the precision of the control, there may be times when the spatial minimum value of the inter-electrode differential pressure becomes negative. Even in such cases, if the time average value of the spatial minimum value of the inter-electrode differential pressure throughout each process is greater than or equal to zero, the effect of suppressing the performance degradation described above can be expected.

[0071] During the storage process, the electrolytic unit 10 may be operated with the minimum value of the inter-electrode differential pressure set to zero or greater. During the storage process, the pressure in the cathode chamber 140, the pressure in the anode chamber 150, and the inter-electrode differential pressure change over time. Therefore, the spatial minimum value of the inter-electrode differential pressure is averaged over the time required for the storage process, and the electrolytic unit 10 can be operated so that the resulting time-averaged value (time-averaged inter-electrode differential pressure) is zero or greater. It is more preferable if the time-averaged value is positive. This prevents excessive movement of the liquid from the anode 12 side to the cathode 11 side through the diaphragm 13, and suppresses the deterioration of the performance of the electrolytic unit 10 during subsequent operating processes.

[0072] The inter-electrode differential pressure during operation may be set to be greater than or equal to the inter-electrode differential pressure during storage. The inter-electrode differential pressure varies with position and also depends on time. Therefore, the spatial minimum value of the inter-electrode differential pressure may be taken into consideration and set so that this value is less than or equal to the operating value during storage. Alternatively, the spatial average value of the inter-electrode differential pressure within the electrolytic unit 10 may be taken into consideration and set so that this value is less than or equal to the operating value during storage. Furthermore, it is preferable that the first and second time-averaged inter-electrode differential pressures during storage are set to be less than or equal to the first and second time-averaged inter-electrode differential pressures during operation, respectively, for the first time-averaged inter-electrode differential pressure between the first pressure at the first position and the second pressure at the second position, and the second time-averaged inter-electrode differential pressure between the third pressure at the third position and the fourth pressure at the fourth position.

[0073] During the startup process, supplying humidifying gas of the cathode supply fluid to the cathode chamber 140 is effective in suppressing performance degradation of the electrolytic unit 10. In particular, when starting and stopping are repeated, it is preferable to supply humidifying gas to the cathode chamber 140 during the second and subsequent startup processes. For example, when electrolysis is performed by supplying the cathode supply fluid gas to the cathode chamber 140 and an aqueous solution of the anode supply fluid to the anode chamber 150, during the second and subsequent startup processes, the aqueous solution that has moved from the anode chamber 150 to the cathode chamber 140 during previous operations is present in the cathode chamber 140. If drying gas is supplied to the cathode in this state, water may evaporate from the aqueous solution in the cathode chamber 140, increasing its concentration, or solid salts may precipitate. The high-concentration aqueous solution and solid salts in the cathode chamber 140 can promote the movement of the aqueous solution from the anode chamber 150 to the cathode chamber 140. In addition, solid salts themselves inhibit the diffusion of gases, which are reactants. These effects can lead to a decrease in the performance of the electrolytic unit 10 during subsequent operation. By supplying humidifying gas to the cathode chamber 140 during the startup process, the relative humidity inside the cathode chamber 140 becomes higher compared to when dry gas is supplied. This prevents the electrolyte from becoming highly concentrated and solid salts from precipitation inside the cathode chamber 140, thus contributing to maintaining the performance of the electrolytic unit 10.

[0074] During the startup process, the dew point of the humidifying gas supplied to the cathode chamber 140 is preferably 0°C or higher, and more preferably room temperature (25°C) or higher. It is even more preferable if it is 40°C or higher. On the other hand, if the dew point of the supplied gas is higher than the temperature of the piping (flow path P1) connected to the inlet of the cathode chamber 140 or the temperature of the cathode chamber 140, water vapor in the supplied gas may condense to form liquid water, which may hinder the diffusion of the reactant gas. Therefore, the temperature of the flow path P1 and the temperature of the cathode chamber 140 may be measured, and the dew point of the supplied gas may be controlled to be below these temperatures.

[0075] During the startup process, the electrolytic unit 10 may be preheated. During the startup, operation, shutdown, and storage processes, if the dew point of the gas supplied to the cathode chamber 140 is higher than the temperature of the flow path P1 or the temperature of the cathode chamber 140, condensate may be formed. This condensate can enter the cathode chamber 140, particularly the porous structure of the cathode catalyst layer and gas diffusion layer, inhibiting the diffusion of reactant gases and product gases, potentially causing a decrease in the performance of the electrolytic unit 10. In contrast, preheating the electrolytic unit 10 during the startup process can suppress the condensation of water vapor in the gas supplied to the cathode chamber 140. Furthermore, preheating not only the electrolytic unit 10 but also the various pipes, including the flow path P1, can suppress the condensation of water vapor within the various pipes. Preheating can be performed, for example, by connecting a heater or temperature controller to the electrolytic unit 10.

[0076] Preferably, the temperatures of the cathode chamber 140 and the flow path P1 are raised to above the dew point of the gas supplied to the cathode chamber 140 during operation by preheating during the startup process. Furthermore, it is preferable that the temperatures of the cathode chamber 140 and the flow path P1 remain above the dew point of the supplied gas even during the startup process. For example, if the temperatures of the cathode chamber 140 and the flow path P1 are low before the start of preheating, the dew point of the cathode supply gas can be lowered, and then, after waiting for the temperatures of the cathode chamber 140 and the flow path P1 to rise by the preheating process, the dew point of the cathode supply gas can be raised. The dew point of the cathode supply gas may also be continuously changed in response to the rise in the temperatures of the cathode chamber 140 and the flow path P1.

[0077] Furthermore, the preheating operation may be performed before applying current to the electrolytic unit 10 during the startup process. The startup process includes an operation (current application operation) in which current is applied and the current value is increased to a value specified in the operating start conditions. The preheating operation can be performed first, and in conjunction with this, the dew point of the gas supplied to the cathode 11 can be raised to a predetermined value in the operating start conditions while suppressing the formation of condensate water in the flow path P1 and cathode chamber 140, and then the current application operation can be performed. In this way, the electrolytic reaction during the current application operation can be carried out under conditions close to the operating start conditions, and unintended adverse effects on the electrolytic unit 10 can be prevented.

[0078] Methods for preheating the electrolytic unit 10 include, but are not limited to, circulating an aqueous solution at a temperature higher than the temperature of the electrolytic unit 10 into the anode chamber 150, or operating a heater attached to the electrolytic unit 10. Furthermore, regarding the preheating time, methods include ending preheating after a predetermined time, or measuring the temperature at a specific point within the electrolytic unit 10 and continuing preheating until that temperature exceeds a specified value, but are not limited to these.

[0079] During the shutdown process, a purge operation can be performed to change the composition of the fluid in the cathode chamber 140 and the fluid in the anode chamber 150. For example, if electrolysis is performed by supplying a humidified gas containing carbon dioxide to the cathode chamber 140 and an aqueous solution to the anode chamber 150, during the operation process, a mixed gas of the target product, by-product hydrogen, and unreacted humidified carbon dioxide exists in the cathode chamber 140, and a gas-liquid two-phase flow of the aqueous solution and the generated gas exists in the anode chamber 150. During the shutdown process, if the humidified carbon dioxide is continued to be supplied to the cathode chamber 140 after the current is stopped, the fluid in the cathode chamber 140 will be replaced with only humidified carbon dioxide. Similarly, in the anode chamber 150, if the supply of the aqueous solution is stopped after the current is stopped and an inert gas such as argon gas is circulated instead, the fluid containing the gas-liquid two-phase flow that was present in the anode chamber 150 will be discharged outside the anode chamber 150, and the anode chamber 150 will be replaced with argon gas.

[0080] If liquid is present in the anode chamber 150 during storage, some of the liquid may move from the anode chamber 150 to the cathode chamber 140 via the diaphragm 13 and enter the porous structure of the cathode catalyst layer and gas diffusion layer. This could then hinder the diffusion of reactant gases and product gases during the next startup, potentially causing a decrease in the performance of the electrolytic unit 10. By draining the liquid from the anode chamber 150, it is expected that this phenomenon will be suppressed and the performance of the electrolytic unit 10 will be maintained.

[0081] In the purging operation, the gas supplied to the cathode chamber 140 is preferably a humidified gas. The dew point of the gas is preferably 0°C or higher, and more preferably room temperature or higher. It is even more preferably 40°C or higher. On the other hand, if the dew point of the gas supplied to the cathode chamber 140 for purging is higher than the temperature of the flow path P1 or the temperature of the cathode chamber 140, water vapor in the gas will condense to form liquid water, which may hinder the diffusion of the reactant gas during the next startup. Therefore, the temperature of the flow path P1 and the temperature of the cathode chamber 140 may be measured, and the dew point of the supplied gas may be controlled to be below these temperatures.

[0082] During operation, the flow rate of the substance to be reduced supplied to the cathode chamber 140 and the flow rate of the substance to be oxidized supplied to the anode chamber 150 may always be controlled to be greater than or equal to a theoretical amount calculated from the current applied to the electrolytic unit 10.

[0083] Here, the theoretical quantity calculated from the current applied to the electrolytic unit 10 is defined as follows. Considering the reduction reaction in the cathode chamber, if the current applied to the electrolytic unit 10 is I[A], the Faraday constant is F[C / mol], the number of electrons required to produce one molecule of reduction product is k, and the number of molecules of the substance to be reduced required to produce one molecule of reduction product is m, then the theoretical quantity of the substance to be reduced N[mol / s] can be found as N=(mI) / (kF). The theoretical quantity N is converted to other units such as volumetric flow rate as appropriate. For the oxidation reaction in the anode chamber 150, the theoretical quantity of the substance to be oxidized N can be found using a similar formula by setting the number of electrons required to produce one molecule of oxidation product to k and the number of molecules of the substance to be oxidized to m.

[0084] If the supply flow rate of the substance to be reduced / oxidized is less than the theoretical amount, some of the current will be used for side reactions, reducing the selectivity of the desired reduction / oxidation product. Therefore, in order to efficiently produce the desired reduction / oxidation product or produce it at a high concentration, the flow rate of the substance to be reduced / oxidized may be set to a value greater than the theoretical amount. From the viewpoint of suppressing side reactions, it is more preferable that the flow rate of the substance to be reduced / oxidized is 105% or more of the theoretical amount, and even more preferable that it is 110% or more of the theoretical amount.

[0085] During the startup and shutdown processes, the flow rate of the substance to be reduced supplied to the cathode chamber 140 and the flow rate of the substance to be oxidized supplied to the anode chamber 150 may always be controlled to be greater than or equal to the theoretical amount calculated from the current applied to the electrolytic unit 10. During the startup and shutdown processes, for example, if side reaction products adversely affect the performance and durability of the electrolytic unit 10, it is necessary to suppress side reactions during the startup and shutdown processes as well. For this reason, the flow rate of the substances to be reduced / oxidized may be set to greater than or equal to the theoretical amount. From the viewpoint of suppressing side reactions, it is more preferable that the flow rate of the substances to be reduced / oxidized is 105% or more of the theoretical amount, and even more preferable that it is 110% or more of the theoretical amount.

[0086] During the startup, operation, shutdown, and storage phases, the current flowing through the electrolytic unit 10 is basically in the direction of flowing from the cathode 11 through the external circuit including the power supply 40 to the anode 12. In other words, current flows from the positive electrode of the power supply 40 to the anode 12 of the electrolytic unit 10, and current flows from the cathode 11 of the electrolytic unit 10 to the negative electrode of the power supply 40. Taking this direction as positive, the current density is always -5 mA / cm². 2 It can be operated as described above. Even if a reverse current flows, its magnitude is 5 mA / cm². 2This corresponds to the following: In particular, when stopping the current during the shutdown process, a reverse current may flow. If the value of the reverse current is large, unintended reactions may occur in the cathode and anode, such as corrosion of the electrode material, which may lead to a decrease in the performance of the electrolytic unit 10. It is more preferable that the current density is always zero or greater during the startup process, the operation process, the shutdown process, and the storage process.

[0087] As described above, reverse current can cause electrode corrosion and other issues, potentially degrading the performance of the electrolytic unit 10. On the other hand, reverse current also plays a role in refreshing the electrolytic unit 10. Therefore, in at least one of the startup and shutdown processes, the current density flowing through the electrolytic unit 10 may be controlled to include a period in which the current density is less than zero, with the direction of current flowing from the cathode 11 through the external circuit including the power supply 40 to the anode being considered positive.

[0088] For example, when electrolysis is performed by flowing carbon dioxide into the cathode chamber 140 and an aqueous solution into the anode chamber 150, the phenomenon of the aqueous solution moving from the anode chamber 150 to the cathode chamber 140 via the diaphragm 13 is accelerated by the positive current described above. If the aqueous solution moves in excess, it will inhibit the diffusion of reactant gases and product gases, leading to a decrease in the performance of the electrolysis unit 10. By flowing a reverse current through the electrolysis unit 10, it is possible to return some of the electrolyte that has moved to the cathode chamber 140 back to the diaphragm 13 and the anode chamber 150.

[0089] During the startup, operation, shutdown, and storage processes, the cathode 11 may be operated so that its potential relative to the standard hydrogen electrode is always +1.5V or less. Preferably, the potential of the cathode 11 is +1.0V or less, more preferably +0.5V or less, and even more preferably 0V or less. For example, when metal nanoparticles supported on carbon are used as the cathode catalyst, if the potential of the cathode 11 becomes high, oxidation of the carbon support and elution / reprecipitation of metal components may progress, which can reduce catalytic activity due to changes in the catalyst structure and an increase in metal particle size. To suppress these phenomena, it is preferable to control the potential of the cathode 11 to a low level. The phenomenon of the potential of the cathode 11 fluctuating in a spike-like manner in the noble direction is likely to occur when the current is stopped during the shutdown process, so controlling the potential of the cathode 11 during the shutdown process is particularly effective.

[0090] During the storage process, the current may be set to zero. This makes it possible to set the rate of product formation during storage to zero, which is suitable for operating the electrochemical reactor. On the other hand, during the storage process, the current may be set to a value greater than zero. This can suppress phenomena such as spike-like fluctuations in electrode potential and reverse current that may occur when the current is set to zero, and is expected to suppress the performance degradation of the electrolytic unit 10 when it is repeatedly started and stopped.

[0091] During the startup process, the rate of increase in current density is up to 1 mA / cm² per second. 2 It is preferable to control the current density as follows: If the current density is increased rapidly, an overshoot of the cell voltage in the electrolytic unit 10 may occur, and the electrode potential may take an unintended value. Also, when electrolysis is performed by supplying electrolyte to the anode chamber 150, if a current is applied rapidly, a large amount of gas will be generated all at once in the anode 12, causing a rapid increase in pressure inside the anode chamber 150, making it difficult to control the differential pressure between electrodes. To suppress such situations, it is preferable to increase the current density gradually during the startup process.

[0092] Figure 8 is a schematic diagram showing another configuration example of the electrochemical reactor of the embodiment. In addition to the electrolytic unit 10, the electrochemical reactor 1 may further include a power supply 40, a temperature controller 50, a pressure controller 60, and a control device 70.

[0093] The power supply 40 can supply voltage or current to the electrolytic unit 10. The power supply 40 may be connected to the current collectors 16 and 17, for example, via wiring. Further details of the power supply 40 can be found in the description of the power supply 40 shown in Figure 2.

[0094] The temperature controller 50 can adjust the temperature of the electrolytic unit 10. The temperature controller 50 may have, for example, a heater or a cooler. The electrolytic unit 10 may be preheated by heating it with the temperature controller 50.

[0095] The pressure regulator 60 can adjust the pressure in the electrolytic section 10. The pressure regulator 60 may, for example, control the differential pressure between electrodes by appropriately adjusting the pressures in the flow paths P1, P2, P3, and P4, and adjusting the pressure between the cathode chamber 140 and the anode chamber 150.

[0096] The control device 70 controls the operation of the electrochemical reaction apparatus according to the various operating methods described above by controlling the electrolytic unit 10, the power supply 40, the temperature controller 50, and the pressure controller 60.

[0097] The electrochemical reactor of the embodiment may further include at least one detector. Examples of detectors include, but are not limited to, thermometers, pressure gauges, dew point meters, ammeters, voltmeters, gas flow meters, gas composition analyzers, etc. Figure 9 is a schematic diagram showing another configuration example of the electrochemical reactor of the embodiment. The electrochemical reactor 1 may further include detector D1, detector D2, detector D3, and detector D4, as shown in Figure 9.

[0098] The detector D1 is located in the middle of the flow path P1, for example, before the electrolytic unit 10. The detector D1 can detect, for example, at least one parameter of the cathode supply fluid. Examples of at least one parameter include temperature, pressure, dew point, current, voltage, flow rate, composition, etc. Examples of detector D1 include, but are not limited to, thermometers, pressure gauges, dew point meters, ammeters, voltmeters, gas flow meters, gas composition analyzers, etc.

[0099] Detector D2 is located in the middle of the flow path P2, for example, before the electrolytic unit 10. Detector D2 can detect, for example, at least one parameter of the anode supply fluid. Examples of at least one parameter include temperature, pressure, dew point, current, voltage, flow rate, composition, etc. Examples of detector D2 include, but are not limited to, thermometers, pressure gauges, dew point meters, ammeters, voltmeters, gas flow meters, gas composition analyzers, etc.

[0100] Detector D3 is located in the middle of the flow path P3, for example, downstream of the electrolytic unit 10. Detector D3 can detect at least one parameter of the cathode discharge fluid from the electrolytic unit 10. Examples of at least one parameter include temperature, pressure, dew point, current, voltage, flow rate, composition, etc. Examples of detector D3 include, but are not limited to, thermometers, pressure gauges, dew point meters, ammeters, voltmeters, flow meters, composition analyzers, etc.

[0101] The detector D4 is located in the middle of the flow path P4, for example, downstream of the electrolytic unit 10. The detector D4 can detect at least one parameter of the anode discharge fluid from the electrolytic unit 10. Examples of at least one parameter include temperature, pressure, dew point, current, voltage, flow rate, composition, etc. Examples of detector D4 include, but are not limited to, thermometers, pressure gauges, dew point meters, ammeters, voltmeters, flow meters, composition analyzers, etc.

[0102] The electrochemical reactor 1 may have a detector in the electrolysis unit 10. The detector in the electrolysis unit 10 can detect, for example, at least one parameter related to the operating state of the electrolysis unit 10, or at least one parameter related to the state of the cathode supply fluid, cathode discharge fluid, anode supply fluid, and anode discharge fluid flowing through any of the above components. Examples of these at least one parameters include temperature, pressure, dew point, current, voltage, flow rate, composition, etc. Examples of these detectors include, but are not limited to, thermometers, pressure gauges, dew point meters, ammeters, voltmeters, flow meters, composition analyzers, etc. These parameters are each sent to the receiving unit 71 as detection signals (data signals).

[0103] The control device 70 includes a receiving unit 71 that receives detection signals from at least one of the following: detector D1, detector D2, detector D3, detector D4, detectors provided in the electrolytic unit 10, power supply 40, temperature controller 50, and pressure controller 60; a calculation unit 72 that performs calculation processing based on the detection signals; and a control unit 73 that generates control signals to control the operation of the electrolytic unit 10, power supply 40, temperature controller 50, and pressure controller 60 based on the results of the calculation processing. The control device 70 may be configured using hardware such as a processor. Alternatively, each operation may be stored as an operation program on a computer-readable recording medium such as memory, and each operation may be executed by appropriately reading the operation program stored on the recording medium using hardware.

[0104] The receiving unit 71 receives detection signals from at least one of the detectors D1, D2, D3, D4, the detector of the electrolytic unit 10, the power supply 40, the temperature controller 50, and the pressure controller 60, and transmits them to the calculation unit 72. The calculation unit 72 includes, for example, a computer on which a calculation algorithm is implemented. The calculation unit 72 performs calculation processing based on the information of the received detection signals and determines how to operate the electrolytic unit 10. It then transmits the result of this determination to the control unit 73. The control unit 73 may transmit control signals to the electrolytic unit 10, the power supply 40, the temperature controller 50, and the pressure controller 60 based on the determination result (calculation result) received from the calculation unit 72, and control them to reach a desired operating state.

[0105] The receiving unit 71, the calculation unit 72, and the control unit 73 may be implemented on separate computers or on a single computer. The calculations in the calculation unit 72 may be performed automatically or may include judgment by an operator. For example, a portion of the results of the signal analysis by the calculation unit 72 may be displayed to the operator via a user interface, the operator may see this and input instructions to the calculation unit 72, and the calculation unit 72 may perform additional calculations based on those instructions, or based on both the received signal and the input instructions, and the results may be output to the control unit 73.

[0106] The calculation algorithm implemented in the arithmetic unit 72 can be created based on knowledge gained from preliminary experiments, etc. Furthermore, the algorithm may be updated based on accumulated operating data, similar to a machine learning model.

[0107] A refresh process may be performed during the operation process. The refresh process can be performed to restore performance when the cell performance in the electrolytic unit 10 deteriorates, or to prevent deterioration of cell performance. The refresh process is not included in the operation process, nor is it included in the start-up process, shut-down process, or storage process. The transition from the operation process to the refresh process can be determined when at least one of the controllable parameters changes outside the range obtained by adding a predetermined tolerance to the boundary value of a predetermined operating condition range. Furthermore, the return from the refresh process to the operation process can be determined when all of the controllable parameters are continuously controlled within the range obtained by adding a predetermined tolerance to the set value of a predetermined operation start condition for a predetermined duration.

[0108] Examples of operations in the refresh process include, but are not limited to, reducing the current density, making the current density zero, applying a reverse current, reducing the potential difference between the cathode 11 and the anode 12, making the potential difference zero, reversing the potentials of the cathode and anode, flowing rinse fluid into the cathode chamber 140, and drying the cathode chamber 140. During the refresh process, it is acceptable for the temporal and spatial average value of the inter-electrode differential pressure to become negative, that is, for the pressure in the anode chamber 150 to be higher than the pressure in the cathode chamber 140. [Examples]

[0109] (Examples 1-8, Comparative Examples 1 and 2) The following describes examples and comparative examples of electrochemical reactors for the reduction reaction of carbon dioxide. The experiment uses an electrode area of ​​400 cm². 2 A single cell was used. A gold-supported carbon catalyst was used for the cathode 11, an iridium oxide catalyst for the anode 12, and a porous polymer membrane for the diaphragm 13. The cathode chamber 140 formed the cathode channel, and the anode chamber 150 formed the anode channel, with fluid flowing in the same direction through both channels. Carbon dioxide gas was supplied to the cathode channel, and humidification was controlled by a humidifier 201. In Examples 1, 2, 5-8, and Comparative Examples 1 and 2, the carbon dioxide gas was dry gas. In Examples 3 and 4, the carbon dioxide gas was humidified gas. An aqueous potassium bicarbonate solution was supplied as the electrolyte to the anode channel. A DC stabilized power supply was used for the power supply 40.

[0110] In each example, the parameters to be controlled were evaluated, and the CO selectivity retention rate (retention rate of the amount of CO produced) during the 10th operation was evaluated as an indicator for comparing the performance of each example. This is defined as the ratio obtained by dividing the CO selectivity during the 10th operation, when the startup, operation, shutdown, and storage processes are repeated, by the CO selectivity during the first operation. Table 1 shows the values ​​of each parameter and the CO selectivity retention rate for each process. CO selectivity represents the ratio of the amount of CO produced in the reduction product. The maximum rate of increase of the current supplied to the cell is 1 mA / cm² / second. 2The results were as follows: The current density during the operating process was 1.25 in Examples 5-8, compared to 1 (arbitrary unit (au)) in Examples 1-4 and Comparative Examples 1 and 2. In Examples 1-8 and Comparative Examples 1 and 2, the inter-electrode differential pressure in each process is the time-averaged inter-electrode differential pressure in each process. In each example, the current density during the storage process was 0 mA / cm². 2 That's what I decided.

[0111] In Examples 1-4 and Comparative Examples 1 and 2, the CO2 flow rate during the startup and shutdown processes were 125% or more of the theoretical amount calculated from the current density. In Examples 5-7, the CO2 flow rate during the startup and shutdown processes were 150% or more of the theoretical amount calculated from the current density. Furthermore, in Example 8, the CO2 flow rate during the startup and shutdown processes varied within a range of 0% to 150% of the theoretical amount calculated from the current density.

[0112] In Examples 1-4, 6-8, and Comparative Examples 1 and 2, the electrolytic unit 10 was preheated. Preheating of the electrolytic unit 10 was carried out by circulating heated electrolyte through the anode channel.

[0113] During the fall-off process, the current density flowing through the electrolytic section 10 is -5 mA / cm², with the direction of current flow from the cathode 11 to the anode 12 being considered positive. 2 That concludes the findings. During the shutdown process, the potential of cathode 11 relative to the standard hydrogen electrode (cathode potential vs SHE) was always +1.5V or less.

[0114] Furthermore, in the down-cycle processes of Examples 1-3, 5-8, and Comparative Examples 1 and 2, CO2 gas was supplied to both electrode channels for purging. In Example 4, however, no purging operation was performed during the down-cycle process. The CO2 gas supplied to the cathode channel during the purging operation was humidified gas in Examples 1-3, 5, 6, and 8, and Comparative Examples 1 and 2, while it was dry gas in Example 7.

[0115] In Example 1, during the startup process, the time-averaged value of the inter-electrode differential pressure at the channel inlet, calculated using the fluid pressure measured in channels P1 and P2, was 0 kPa or higher. Gas flows through the cathode channel and liquid flows through the anode channel, and since the pressure loss is greater in the anode channel, if the time-averaged value of the inter-electrode differential pressure at the channel inlet is 0 kPa or higher, the inter-electrode differential pressure will be even greater downstream, and the time-averaged value of the inter-electrode differential pressure for the entire cell will also be 0 kPa or higher. During the operation process, the time-averaged value of the inter-electrode differential pressure was approximately 90 kPa at the channel inlet and approximately 130 kPa at the channel outlet. During the shutdown process, similar to the startup process, the time-averaged value of the inter-electrode differential pressure at the channel inlet was 0 kPa or higher, and therefore it was also 0 kPa or higher for the entire cell. In Example 1, the CO selectivity maintenance rate during the 10th operation process was 90%.

[0116] In contrast, in Comparative Example 1, the time-averaged value of the inter-electrode differential pressure at the flow channel inlet during the startup process was less than zero. Other conditions were the same as in Example 1. The CO selectivity maintenance rate in Comparative Example 1 during the 10th operation was 78%, which was lower than in Example 1. As mentioned above, the inter-electrode differential pressure increases along the flow channel, so even in Comparative Example 1, the inter-electrode differential pressure at the flow channel outlet during the startup process was 0 kPa or higher. However, it is thought that the electrolyte movement from anode 12 to cathode 11 progressed due to the negative inter-electrode differential pressure near the flow channel inlet, inhibiting gas diffusion in the cathode catalyst layer and reducing CO selectivity.

[0117] In Comparative Example 2, the time-averaged differential pressure between electrodes at the flow path inlet was less than zero during the shutdown process. In this case as well, the CO selectivity maintenance rate during the 10th operation was 76%, which was lower than in Example 1. This is thought to be due to the movement of electrolyte from the anode flow path to the cathode flow path near the flow path inlet.

[0118] In Example 2, the average value of the inter-electrode differential pressure time during the storage process was less than zero. Other conditions were the same as in Example 1. In this case, the CO selectivity maintenance rate during the 10th operation was 82%, which was also lower than in Example 1.

[0119] In Example 3, the gas supplied to the cathode flow path during the startup process was changed from dry gas to humidified gas. Other conditions were the same as in Example 1. By changing to humidified gas, the CO selectivity maintenance rate during the 10th operation process was 97%, an improvement from 90% in Example 1.

[0120] In Example 4, after stopping the application of current during the down-cycle process, the cell was stored while maintaining the differential pressure between electrodes without purging the bipolar fluids, and with humidified carbon dioxide gas flowing through the cathode and potassium bicarbonate aqueous solution flowing through the anode. Other conditions were the same as in Example 1. As a result, the CO selectivity maintenance rate during the 10th operation cycle was 100%, and no degradation was observed within the range of significant figures.

[0121] The difference between Example 5 and Example 6 is whether or not the cell was preheated during the startup process. Compared to Example 5, where the cell was not preheated, Example 6, where the cell was preheated, showed a slightly higher CO selectivity maintenance rate during the 10th operation cycle.

[0122] Examples 6 and 7 differ in whether or not the carbon dioxide flowing through the cathode channel was humidified during the bipolar fluid purging operation performed in the downstart process. Compared to Example 6, which used humidified gas, Example 7, which used dry gas, showed a lower CO selectivity maintenance rate during the 10th operation.

[0123] In Example 8, control was implemented so that during the start-up and shut-down processes, there were periods when the amount of carbon dioxide supplied to the cathode channel was less than the theoretical amount calculated from the current density. As a result, the CO selectivity maintenance rate during the 10th operation was 85%, which was lower than the 96% in Example 6, where the amount of carbon dioxide supplied during the start-up and shut-down processes was always greater than or equal to the theoretical amount.

[0124] [Table 1]

[0125] (Examples 9-15) The following describes another example of an electrochemical reactor for the reduction reaction of carbon dioxide. The experiment uses an electrode area of ​​400 cm². 2 A single cell was used. A gold-supported carbon catalyst was used for the cathode 11, an iridium oxide catalyst for the anode 12, and a porous polymer membrane for the diaphragm 13. The cathode chamber 140 formed the cathode channel, and the anode chamber 150 formed the anode channel, with fluid flowing in the same direction through both channels. Carbon dioxide gas was supplied to the cathode channel and humidified by a humidifier 201. A potassium bicarbonate aqueous solution was supplied to the anode channel as the electrolyte. A DC stabilized power supply 40 was used as the power supply.

[0126] In Examples 9-15 (also known as Experiment 9-15), during the initial startup process, the time-averaged differential pressure between electrodes at the channel inlet, calculated using the fluid pressure measured in channels P1 and P2, was 0 kPa or higher. Gas flows through the cathode channel and liquid through the anode channel, and since the anode channel has a greater pressure loss, if the time-averaged differential pressure between electrodes at the channel inlet is 0 kPa or higher, the differential pressure between electrodes will be even greater downstream, resulting in a time-averaged differential pressure of 0 kPa or higher for the entire cell. During the operation process, the time-averaged differential pressure between electrodes was approximately 100 kPa at the channel inlet and approximately 105 kPa at the channel outlet. During the shutdown process, after adjusting the current and voltage, the cell was stored while maintaining the differential pressure between electrodes without purging the bipolar fluids, and with humidified carbon dioxide gas flowing through cathode 11 and potassium bicarbonate aqueous solution flowing through anode 12. In subsequent startup processes, the cell transitioned from the storage process to the operation process while maintaining the differential pressure between electrodes. Therefore, except for the initial startup process, the inter-pole differential pressure was maintained at the same level as during normal operation.

[0127] In Examples 9-13, the CO2 flow rate during the startup, operation, shutdown, and storage processes was 125% or more of the theoretical amount calculated from the current density. In particular, it was 125% during the operation process. On the other hand, in Examples 14 and 15, the CO2 flow rate during the startup, operation, shutdown, and storage processes was 100% or more of the theoretical amount calculated from the current density. In particular, it was 100% during the operation process.

[0128] In Examples 9 to 15, the electrolytic unit 10 was preheated during the initial startup process. Preheating of the electrolytic unit 10 was performed by circulating heated electrolyte through the anode channel. In the second and subsequent startup processes, preheating was not performed because electrolyte had already circulated through the anode during the preceding storage process.

[0129] In Examples 9-15, the maximum value of the cathode potential was varied, and its effect on the characteristics of the electrochemical reactor during repeated start-up and shutdown was evaluated. Examples 9-13 were a series of tests in which the maximum cathode potential was varied at five levels under the condition that the CO2 supply during the operating process was 125% of the theoretical amount, while Examples 14 and 15 were a series of tests in which the maximum cathode potential was varied at two levels under the condition that the CO2 supply during the operating process was 100% of the theoretical amount. The maximum value of the cathode potential was changed by changing the set value of the current density or cell voltage during the storage process. The set value of the current density or cell voltage during the storage process was made smaller than the value during the operating process. During the shutdown process, the current density or cell voltage was changed from the value during the operating process to the set value during the storage process, and at this time the cathode potential fluctuated in the nomadic direction. In particular, the fluctuation of the cathode potential became significant when the current density or cell voltage reached the set value during the storage process. The closer the current density or cell voltage setting during the storage process was to the current density or cell voltage setting during the operation process, the smaller the fluctuation in cathode potential during shutdown, and consequently, the smaller the maximum value of the cathode potential tended to be. For each level of experimentation, the cell was reconfigured each time to avoid influence from experiments at other levels. Furthermore, the current density during the operation process was controlled to the same predetermined value in all levels of experimentation. The current density during the storage process was 0 mA / cm² in Examples 9 and 14. 2 In Examples 10 and 11, the values ​​were below the lower limit of measurement, and in Examples 12, 13, and 15, the value was 0 mA / cm². 2 The value was larger. In all cases, the current density flowing through the electrolytic section 10 during the fall-off process was -5 mA / cm², with the direction of current flow from cathode 11 to anode 12 being positive. 2 The above was the result. Furthermore, during the down-cycle process, the potential of cathode 11 relative to the standard hydrogen electrode (cathode potential vs SHE) was always +1.5V or less. During the up-cycle process, the maximum rate of increase of the current supplied to the cell was 1 mA / cm per second. 2 The following conditions were observed. Table 2 shows the main conditions and the maximum measured cathode potential (also called the maximum cathode potential) in each example. In Table 2, the current density during the storage process is shown as a relative value to the current density during the operation process.

[0130] [Table 2]

[0131] In Examples 9, 11, 12, and 13, the CO selectivity maintenance rate during the 10th operation was 100% in all cases. In all cases, no decrease in CO selectivity was observed compared to the first operation, and no influence due to differences in conditions was observed. In Example 10, the CO selectivity value during the 10th operation could not be obtained due to a temporary malfunction of the measuring equipment. Therefore, in Examples 9 to 13, the CO selectivity maintenance rate and cell voltage maintenance rate during the 100th operation were evaluated as indicators for comparing the performance of the electrochemical reactor. These are defined as the ratio obtained by dividing the CO selectivity and cell voltage during the 100th operation (after repeating the start-up, operation, shutdown, and storage processes) by the CO selectivity and cell voltage during the first operation, respectively. In addition, the value obtained by dividing the CO selectivity maintenance rate by the cell voltage maintenance rate (selectivity / voltage) was also evaluated. This value corresponds to the energy efficiency maintenance rate. Energy efficiency is the proportion of the input electrical energy that is effectively used for CO generation, and the maintenance rate of energy efficiency is the ratio of how much the energy efficiency changed between the 1st and 100th trials.

[0132] Figure 10 shows graphs plotting the CO selectivity maintenance rate, cell voltage maintenance rate, and their ratios at the 100th cycle for Examples 9-13 against the maximum cathode potential. The cathode potential (Vx) during the operation of Examples 9-13 was approximately -1.8V relative to a standard hydrogen electrode. A tendency was observed for the CO selectivity maintenance rate, cell voltage maintenance rate, and their ratios at the 100th cycle to approach 100% as the maximum cathode potential was closer to this value. In other words, a tendency was observed for the characteristics of the electrochemical reactor to be maintained as the maximum cathode potential recorded during shutdown was closer to the cathode potential value during the operation.

[0133] In Examples 14 and 15, the CO selectivity retention rates at the 10th operation cycle were 94% and 103%, respectively. While a decrease in CO selectivity was observed in Example 14, no decrease in CO selectivity was observed at the 10th cycle in Example 15. In Examples 14 and 15, the CO selectivity retention rate and cell voltage retention rate at the 50th operation cycle were further evaluated as indicators to compare the performance of the electrochemical reactor. These are defined as the ratio obtained by dividing the CO selectivity and cell voltage at the 50th operation cycle (after repeating the start-up, operation, shutdown, and storage processes) by the CO selectivity and cell voltage at the 1st operation cycle, respectively. In addition, the value obtained by dividing the CO selectivity retention rate by the cell voltage retention rate was also evaluated. This value corresponds to the energy efficiency retention rate and shows how much the energy efficiency changed between the 1st and 50th cycles.

[0134] Figure 11 shows graphs plotting the CO selectivity maintenance rate, cell voltage maintenance rate, and their ratios against the maximum cathode potential in Examples 14 and 15. The cathode potential (Vx) during the operation of Examples 14 and 15 changed during repeated starts and stops, but remained in the range of approximately -2.6V to approximately -1.9V relative to the standard hydrogen electrode. Here again, a tendency was observed where the smaller the maximum cathode potential, the closer the CO selectivity maintenance rate, cell voltage maintenance rate, and their ratios were to 100% at the 50th cycle.

[0135] Examples 9 to 15 show that, during the start-up, shut-down, and storage processes, the potential of the cathode 11 relative to the standard hydrogen electrode is preferably in the range of being greater than or equal to the value during the operation process and less than or equal to 0V, and more preferably in the range of being greater than or equal to the value during the operation process and less than or equal to -0.5V. It is even more preferable that it is in the range of being greater than or equal to the value during the operation process and less than or equal to -0.75V. However, in cases where the maximum value of the potential of the cathode 11 relative to the standard hydrogen electrode is kept low, the current density and cell voltage during the storage process become close to the values ​​during the operation process. As a result, power consumption during the storage process increases, and it also becomes necessary to properly process the electrolytic reaction products generated during the storage process. Therefore, it is preferable to determine the level to which the maximum value of the cathode potential is controlled from a wide range of perspectives, including not only resistance to repeated start-up and stop-down, but also the functions required of the electrochemical reactor, and constraints in terms of system and cost.

[0136] The configurations of each embodiment described above can be applied in combination, and can also be partially replaced. Although several embodiments of the present invention have been described here, these embodiments are presented as examples and are not intended to limit the scope of the invention. These 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 variations are included in the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as described in the claims.

[0137] The above embodiments can be summarized in the following technical proposal. (Technical proposal 1) A method for operating an electrochemical reaction apparatus, The electrochemical reaction apparatus comprises an electrolytic section having a cathode, an anode, a cathode chamber facing the cathode, an anode chamber facing the anode, and a diaphragm provided between the cathode chamber and the anode chamber. The aforementioned method, A startup process is provided for adjusting at least one parameter selected from a group of parameters, including temperature, pressure, current density, voltage, the composition of a first fluid containing the substance to be reduced supplied to the cathode chamber, the flow rate of the first fluid, the composition of a second fluid containing the substance to be oxidized supplied to the anode chamber, and the flow rate of the second fluid, in the electrolytic unit to satisfy the startup conditions. The operation process involves operating the electrolytic unit within an operating condition range including the operation start conditions, and generating reduction products by reducing the target substance with the cathode. A shutdown process is performed to adjust at least one parameter selected from the group of multiple parameters to satisfy the storage start conditions. A storage process comprising operating the electrolytic unit within a range of storage conditions including the storage start conditions, It is equipped with, In each of the startup process, the operation process, and the shutdown process, the electrolytic unit is controlled such that the first time-averaged pressure at a first position in the cathode chamber, which is closer to the inlet of the cathode chamber than to the outlet of the cathode chamber, is equal to or greater than the second time-averaged pressure at a second position in the anode chamber, which is opposite the first position across the diaphragm, and the third time-averaged pressure at a third position in the cathode chamber, which is closer to the outlet than to the inlet, is equal to or greater than the fourth time-averaged pressure at a fourth position in the anode chamber, which is opposite the third position across the diaphragm. Operating procedures for electrochemical reactors. (Technical proposal 2) In each of the startup process, the operation process, and the shutdown process, the electrolytic unit is controlled such that the first time-averaged pressure is greater than the second time-averaged pressure and the third time-averaged pressure is greater than the fourth time-averaged pressure. The method described in Technical Proposal 1. (Technical proposal 3) The aforementioned operating process is performed after the aforementioned startup process. The aforementioned shutdown process is performed next in the aforementioned operation process, The aforementioned storage process is carried out after the aforementioned drop-off process. The method described in Technical Proposal 1 or Technical Proposal 2. (Technical proposal 4) The aforementioned startup process is performed again after the aforementioned storage process. The sequence consisting of the startup process, the operation process, the shutdown process, and the storage process is repeated multiple times. The method described in Technical Proposal 3. (Technical proposal 5) The aforementioned diaphragm is a porous membrane. The method described in any one of Technical Proposal 1 to Technical Proposal 4. (Technical proposal 6) A reduction reaction of carbon dioxide occurs in the cathode. The method described in any one of Technical Proposal 1 to Technical Proposal 5. (Technical proposal 7) In the startup process, a humidifying gas is supplied to the cathode chamber as the first fluid. The method described in any one of Technical Proposal 1 to Technical Proposal 6. (Technical proposal 8) In the aforementioned startup process, the electrolytic unit is preheated. The method described in any one of Technical Proposal 1 to Technical Proposal 7. (Technical proposal 9) During the aforementioned down-cycle process, a purging operation is performed on the anode chamber and the cathode chamber. The method described in any one of Technical Proposal 1 to Technical Proposal 8. (Technical proposal 10) In the purging operation, the fluid in the cathode chamber is replaced with a humidifying gas. The method described in Technical Proposal 9. (Technical proposal 11) In the aforementioned operating process, The flow rate of the substance to be reduced supplied to the cathode chamber is always greater than or equal to the theoretical amount of the substance to be reduced calculated from the current flowing through the electrolytic unit. The flow rate of the substance to be oxidized supplied to the anode chamber is always greater than or equal to the theoretical amount of the substance to be oxidized calculated from the current. The method described in any one of Technical Proposal 1 to Technical Proposal 10. (Technical proposal 12) In the aforementioned startup process and shutdown process, The flow rate of the substance to be reduced supplied to the cathode chamber is always greater than or equal to the theoretical amount of the substance to be reduced calculated from the current flowing through the electrolytic unit. The flow rate of the substance to be oxidized supplied to the anode chamber is always greater than or equal to the theoretical amount of the substance to be oxidized calculated from the current. The method described in any one of Technical Proposal 1 to Technical Proposal 10. (Technical proposal 13) In the aforementioned startup process, the aforementioned operation process, the aforementioned shutdown process, and the aforementioned storage process, The current density of the electrolytic section is always -5 mA / cm², with the direction of current flow from the cathode through the external circuit including the power supply to the anode being considered positive. 2 That's all. The method described in any one of Technical Proposal 1 to Technical Proposal 12. (Technical proposal 14) In at least one of the above-mentioned startup process and the above-mentioned shutdown process, The current density of the electrolytic unit includes a period during which the current density is less than zero, with the direction of current flow from the cathode through the external circuit including the power supply to the anode being considered positive. The method described in any one of Technical Proposal 1 to Technical Proposal 12. (Technical proposal 15) In the aforementioned startup process, the aforementioned operation process, the aforementioned shutdown process, and the aforementioned storage process, The potential of the cathode relative to the standard hydrogen electrode is always +1.5V or less. The method described in any one of Technical Proposal 1 to Technical Proposal 14. (Technical proposal 16) During the storage process, the current density of the electrolytic unit is zero. The method described in any one of Technical Proposal 1 to Technical Proposal 15. (Technical proposal 17) During the storage process, the current density of the electrolytic unit is greater than zero. The method described in any one of Technical Proposal 1 to Technical Proposal 15. (Technical proposal 18) In the aforementioned storage process, The electrolytic unit is controlled such that the first time-averaged pressure is equal to or greater than the second time-averaged pressure, and the third time-averaged pressure is equal to or greater than the fourth time-averaged pressure. The method described in any one of Technical Proposal 1 to Technical Proposal 17. (Technical proposal 19) In the aforementioned storage process, The electrolytic unit is controlled such that the first time-averaged pressure becomes greater than the second time-averaged pressure, and the third time-averaged pressure becomes greater than the fourth time-averaged pressure. The method described in any one of Technical Proposal 1 to Technical Proposal 17. (Technical proposal 20) With respect to the first time-averaged inter-electrode pressure between the first pressure at the first position and the second pressure at the second position, and the second time-averaged inter-electrode pressure between the third pressure at the third position and the fourth pressure at the fourth position, the electrolytic unit is controlled such that the first and second time-averaged inter-electrode pressures during the storage process are less than or equal to the first and second time-averaged inter-electrode pressures during the operation process, respectively. The method described in any one of Technical Proposal 1 to Technical Proposal 19. (Technical proposal 21) In the aforementioned startup process, The maximum rate of increase of the current supplied to the electrolytic unit is 1 mA / cm² per second. 2 The following is: The method described in any one of Technical Proposal 1 to Technical Proposal 20. (Technical proposal 22) An electrochemical reactor that can be operated by the method described in any one of Technical Proposal 1 to Technical Proposal 21, The electrolytic unit and, A power supply that supplies current or voltage to the electrolytic unit, A temperature controller for adjusting the temperature of the electrolytic unit, A pressure regulator for adjusting the pressure in the electrolytic section, A control device that controls the operation of the electrochemical reaction apparatus by controlling the electrolytic unit, the power supply, the temperature controller, and the pressure controller, An electrochemical reaction apparatus equipped with the following: [Explanation of Symbols]

[0138] 1...Electrochemical reactor, 10...Electrolytic section, 11...Cathode, 12...Anode, 13...Diaphragm, 14...Flow channel plate, 15...Flow channel plate, 16...Current collector, 17...Current collector, 18...Flow channel plate, 40...Power supply, 50...Temperature controller, 60...Pressure controller, 70...Control device, 71...Receiver, 72...Calculation unit, 73...Control unit, 100...Electrolytic cell, 140...Cathode chamber, 141...Land, 150...Anode chamber, 151...Land, 201...Humidifier, D1...Detector, D2...Detector, D3...Detector, D4...Detector, MEA...Membrane electrode assembly, P1...Flow channel, P2...Flow channel, P3...Flow channel, P4...Flow channel.

Claims

1. A method for operating an electrochemical reaction apparatus, The electrochemical reaction apparatus comprises an electrolytic section having a cathode, an anode, a cathode chamber facing the cathode, an anode chamber facing the anode, and a diaphragm provided between the cathode chamber and the anode chamber. The aforementioned method, A startup process involves adjusting at least one parameter selected from a group of parameters, including temperature, pressure, current density, voltage, the composition of a first fluid containing the substance to be reduced supplied to the cathode chamber, the flow rate of the first fluid, the composition of a second fluid containing the substance to be oxidized supplied to the anode chamber, and the flow rate of the second fluid, in the electrolytic unit to satisfy the operating start conditions. The operation process involves operating the electrolytic unit within an operating condition range including the operation start conditions, and generating reduction products by reducing the target substance with the cathode. A shutdown process is performed to adjust at least one parameter selected from the group of multiple parameters to satisfy the storage start conditions. A storage process comprising operating the electrolytic unit within a range of storage conditions including the storage start conditions, It is equipped with, In each of the startup process, the operation process, and the shutdown process, the electrolytic unit is controlled such that the first time-averaged pressure at a first position in the cathode chamber, which is closer to the inlet of the cathode chamber than to the outlet of the cathode chamber, is equal to or greater than the second time-averaged pressure at a second position in the anode chamber, which is opposite the first position across the diaphragm, and the third time-averaged pressure at a third position in the cathode chamber, which is closer to the outlet than to the inlet, is equal to or greater than the fourth time-averaged pressure at a fourth position in the anode chamber, which is opposite the third position across the diaphragm. Operating procedures for electrochemical reactors.

2. In each of the startup process, the operation process, and the shutdown process, the electrolytic unit is controlled such that the first time-averaged pressure becomes greater than the second time-averaged pressure and the third time-averaged pressure becomes greater than the fourth time-averaged pressure. The method according to claim 1.

3. The aforementioned operating process is performed after the aforementioned startup process. The aforementioned shutdown process is performed next in the aforementioned operation process, The aforementioned storage process is carried out after the aforementioned drop-off process. The method according to claim 1.

4. The aforementioned startup process is performed again after the aforementioned storage process. The sequence consisting of the startup process, the operation process, the shutdown process, and the storage process is repeated multiple times. The method according to claim 3.

5. The aforementioned diaphragm is a porous membrane. The method according to claim 1.

6. A reduction reaction of carbon dioxide occurs in the cathode. The method according to claim 1.

7. In the startup process, a humidifying gas is supplied to the cathode chamber as the first fluid. The method according to claim 1.

8. In the aforementioned startup process, the electrolytic unit is preheated. The method according to claim 1.

9. During the aforementioned down-cycle process, a purging operation is performed on the anode chamber and the cathode chamber. The method according to claim 1.

10. In the purging operation, the fluid in the cathode chamber is replaced with a humidifying gas. The method according to claim 9.

11. In the aforementioned operating process, The flow rate of the substance to be reduced supplied to the cathode chamber is always greater than or equal to the theoretical amount of the substance to be reduced calculated from the current flowing through the electrolytic unit. The flow rate of the substance to be oxidized supplied to the anode chamber is always greater than or equal to the theoretical amount of the substance to be oxidized calculated from the current. The method according to claim 1.

12. In the aforementioned startup process and shutdown process, The flow rate of the substance to be reduced supplied to the cathode chamber is always greater than or equal to the theoretical amount of the substance to be reduced calculated from the current flowing through the electrolytic unit. The flow rate of the substance to be oxidized supplied to the anode chamber is always greater than or equal to the theoretical amount of the substance to be oxidized calculated from the current. The method according to claim 1.

13. In the aforementioned startup process, the aforementioned operation process, the aforementioned shutdown process, and the aforementioned storage process, The current density of the electrolytic section is always -5 mA / cm², with the direction of current flow from the cathode through the external circuit including the power supply to the anode being considered positive. ２ That's all. The method according to claim 1.

14. In at least one of the above-mentioned startup process and the above-mentioned shutdown process, The current density of the electrolytic unit includes a period during which the current density is less than zero, with the direction of current flow from the cathode through the external circuit including the power supply to the anode being considered positive. The method according to claim 1.

15. In the aforementioned startup process, the aforementioned operation process, the aforementioned shutdown process, and the aforementioned storage process, The potential of the cathode relative to the standard hydrogen electrode is always +1.5V or less. The method according to claim 1.

16. During the storage process, the current density of the electrolytic unit is zero. The method according to claim 1.

17. During the storage process, the current density of the electrolytic unit is greater than zero. The method according to claim 1.

18. In the aforementioned storage process, The electrolytic unit is controlled such that the first time-averaged pressure is equal to or greater than the second time-averaged pressure, and the third time-averaged pressure is equal to or greater than the fourth time-averaged pressure. The method according to claim 1.

19. In the aforementioned storage process, The electrolytic unit is controlled such that the first time-averaged pressure becomes greater than the second time-averaged pressure, and the third time-averaged pressure becomes greater than the fourth time-averaged pressure. The method according to claim 1.

20. With respect to the first time-averaged inter-electrode pressure between the first pressure at the first position and the second pressure at the second position, and the second time-averaged inter-electrode pressure between the third pressure at the third position and the fourth pressure at the fourth position, the electrolytic unit is controlled such that the first and second time-averaged inter-electrode pressures during the storage process are less than or equal to the first and second time-averaged inter-electrode pressures during the operation process, respectively. The method according to claim 1.

21. In the aforementioned startup process, The maximum rate of increase of the current supplied to the electrolytic unit is 1 mA / cm² per second. ２ The following is: The method according to claim 1.

22. An electrochemical reactor that can be operated by the method described in any one of claims 1 to 21, The electrolytic unit and, A power supply that supplies current or voltage to the electrolytic unit, A temperature controller for adjusting the temperature of the electrolytic unit, A pressure regulator for adjusting the pressure in the electrolytic section, A control device that controls the operation of the electrochemical reaction apparatus by controlling the electrolytic unit, the power supply, the temperature controller, and the pressure controller, An electrochemical reaction apparatus equipped with the following:

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