Electrolytic apparatus and electrolysis method

Abstract

To provide an electrolytic apparatus capable of improving recovery efficiency and production efficiency of: a water-soluble gas such as ammonia, which is a reduction product; and a water-soluble gas product which is an aqueous solution thereof.SOLUTION: An electrolytic apparatus 1 according to an embodiment includes: a first electrolytic cell 5 comprising a first reaction tank 2 in which a reduction electrode 10 is disposed and which generates a water-soluble gas as a reduction product, a second reaction tank 3 in which an oxidation electrode 11 is disposed, and a diaphragm 4; a gas-liquid contact device 7 which brings at least one of the water-soluble gas generated in the first reaction tank 2 and the aqueous solution thereof into contact with a liquefied recovery agent containing at least a part of components of an electrolytic solution to generate a liquefied substance of the water-soluble gas; a first gas-liquid separator 8 which separates a gas-liquid mixture containing the liquefied substance of the water-soluble gas into a liquid containing the liquefied substance of the water-soluble gas and a gas; a distiller 9 which separates the liquid from the first gas-liquid separator into the liquefied substance of the water-soluble gas and an electrolytic solution component; and a pipe which returns the electrolytic solution component from the distiller 9 to a storage part of the electrolytic solution.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] FIELD OF THE INVENTION An embodiment of the present invention relates to an electrolysis apparatus and an electrolysis method. [Background technology]

[0002] Ammonia production worldwide is approximately 140 million tons per year, and this production volume continues to rise. Approximately 80% of the production is used as a raw material for fertilizer and is converted into other nitrogen compounds, mainly urea, nitric acid, ammonium nitrate, and ammonium sulfate. Meanwhile, the remaining 20% ​​is used in the production of synthetic resins and fibers. Demand for ammonia is increasing to address food shortages due to global population growth, a lack of arable land, and increasingly sophisticated diets, particularly in emerging countries. Furthermore, ammonia is attracting attention for its use as an energy carrier due to its ease of handling, high energy density, and the fact that it contains no carbon and does not emit carbon dioxide when used.

[0003] Currently, ammonia is industrially synthesized from hydrogen and nitrogen gases derived from fossil fuels such as petroleum, coal, and natural gas using a method known as the Haber-Bosch process, which was invented about 100 years ago. This synthesis reaction requires harsh conditions, including high temperatures (400-650°C) and high pressures (200-400 atmospheres), and consumes 1.2% of the world's total energy, resulting in significant carbon dioxide emissions. To create a sustainable society for the future, there is a need to develop alternative processes that are less dependent on fossil fuels.

[0004] In response to these issues, catalysts for generating ammonia from nitrogen at room temperature and pressure have been developed for electrolysis methods and electrolysis devices that produce ammonia (NH3) by electrolyzing and reducing nitrogen (NH3). For example, it has been reported that a solution containing a molybdenum iodide complex with a PNP (2,6-bis(di-tert-butylphosphinomethyl)pyridine) ligand as the catalyst, alcohol or water as the proton source, and a lanthanoid metal halide (II), such as samarium (II) iodide, as the reducing agent, was stirred in the presence of nitrogen gas at room temperature to produce up to 4,350 equivalents of ammonia per catalyst. Other reported methods use a molybdenum iodide complex with a PNP ligand as the catalyst and the solution used in the cathode cell, or both the electrolyte membrane and the solution used in the cathode cell, as the proton source.

[0005] In the electrolysis device that produces ammonia (NH) by reducing nitrogen (N), the production and recovery efficiencies of the electrolysis product, ammonia, are low in the reduction chamber (cathode chamber) where nitrogen is reduced to produce ammonia. For example, because ammonia (NH) gas produced in the reduction chamber (cathode chamber) is water-soluble, at least a portion of the ammonia discharged from the reduction chamber is discharged in an aqueous solution dissolved in the electrolyte. Therefore, there is a need to efficiently recover ammonia from the aqueous ammonia discharged from the reduction chamber, thereby improving the recovery and production efficiencies of ammonia. This is not limited to the production of ammonia; similar issues arise when the electrolysis product is a water-soluble gas and the water-soluble gas product is recovered. That is, there is a need to improve the recovery and production efficiencies of the water-soluble gas product in an electrolysis device that produces a water-soluble gas by reducing a target substance such as nitrogen. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 3-265513 [Patent Document 2] Japanese Patent Application Laid-Open No. 2018-153735 [Patent Document 3] Japanese Patent Publication No. 2022-137607 [Patent Document 4] International Publication No. 2019 / 168093 [Patent Document 5] International Publication No. 2021 / 045206 [Patent Document 6] International Publication No. 2021 / 124616 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide an electrolysis apparatus and an electrolysis method that enable improvement in the recovery efficiency and production efficiency of water-soluble gases such as ammonia, which are reduction products, and water-soluble gas products, which are their aqueous solutions. [Means for solving the problem]

[0008] The electrolytic device of the embodiment includes a first electrolytic cell including a first reaction tank in which a reduction electrode is disposed and a substance to be reduced is supplied and a water-soluble gas is produced as a reduction product, a second reaction tank in which an oxidation electrode is disposed and an electrolyte is supplied, and a diaphragm provided between the first reaction tank and the second reaction tank, a substance to be reduced supplying section that supplies the substance to be reduced to the first reaction tank, an electrolyte circulation unit including a circulation pipe for circulating the electrolyte outside the first electrolytic cell and a tank for storing the electrolyte so as to supply the electrolyte to the second reaction tank, and a water-soluble gas produced in the first reaction tank and a small amount of the water-soluble gas and the water-soluble substance. the gas-liquid contactor, which is supplied with at least one of the water-soluble gas and its aqueous solution, and which brings a liquefied recovery agent containing at least a portion of the components of the electrolyte into contact with at least one of the water-soluble gas and its aqueous solution, and discharges a gas-liquid mixture containing a liquefied product of the water-soluble gas; a first gas-liquid separator, which is supplied with the gas-liquid mixture discharged from the gas-liquid contactor and which separates the gas-liquid mixture into a liquid component containing the liquefied product of the water-soluble gas and a gas component; a distiller, which separates the liquefied product of the water-soluble gas and the electrolyte component from the liquid component discharged from the first gas-liquid separator; and a return pipe, which returns the electrolyte component discharged from the distiller to the storage section for the electrolyte. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram showing an electrolysis device according to a first embodiment. [Figure 2] FIG. 2 is a diagram showing an electrolysis device according to a second embodiment. [Figure 3] FIG. 3 is a diagram showing a first example of a second electrolytic cell in the electrolytic apparatus shown in FIG. 2. [Figure 4] FIG. 3 is a diagram showing a second example of the second electrolytic cell in the electrolytic apparatus shown in FIG. 2. [Figure 5] FIG. 3 is a diagram showing a third example of the second electrolytic cell in the electrolytic apparatus shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, electrolysis devices and electrolysis methods according to embodiments will be described with reference to the drawings. In each of the following embodiments, substantially identical components are denoted by the same reference numerals, and some of their descriptions may be omitted. The drawings are schematic, and the relationship between thickness and planar dimensions, the thickness ratio of each component, etc. may differ from the actual ones.

[0011] FIG. 1 is a diagram showing an electrolysis device 1 as an ammonia production device according to an embodiment. The electrolysis device 1 shown in Figure 1 mainly includes a first electrolysis cell 5 including a first reaction tank (cathode tank / reduction chamber) 2 to which nitrogen (N) is supplied as a gaseous product to be reduced, a second reaction tank (anode tank / oxidation chamber) 3 to which an aqueous electrolyte is supplied, and a diaphragm 4; a nitrogen supply unit (reduced product supply section) 6 to supply nitrogen to the first reaction tank 2; a gas-liquid contactor 7 that contacts at least one of ammonia (NH) and its aqueous solution contained in the gas discharged from the first reaction tank 2 with a liquefied recovery agent containing at least a portion of the electrolyte to produce a gas-liquid mixture containing a liquefied water-soluble gas; a first gas-liquid separator 8 to which the gas-liquid mixture produced in the gas-liquid contactor 7 is supplied and which separates the mixture into a liquid component containing the liquefied water-soluble gas and a gas component; and a distiller 9 to which the liquid component containing the liquefied water-soluble gas is supplied from the first gas-liquid separator 8 and which separates the liquid component into a liquefied water-soluble gas and an electrolyte component. Each component will be described in detail below.

[0012] In the first electrolysis cell 5, a reduction electrode (cathode) 10 used in an electrochemical reduction reaction is disposed in the first reaction tank 2. An oxidation electrode (anode) 11 used in an electrochemical oxidation reaction is disposed in the second reaction tank 3. Between the first reaction tank 2 and the second reaction tank 3, a hydrogen ion (H + ) and hydroxide ions (OH -A diaphragm 4 capable of transferring ions such as ions (O) is disposed in the first electrolytic cell 5. The first electrolytic cell 5 is separated into a first reaction tank 2 and a second reaction tank 3 by the diaphragm 4. Gaseous nitrogen (N) is supplied to the first reaction tank 2 from a nitrogen supply device 6. Alternatively, an electrolytic solution (second electrolytic solution) in which nitrogen (N) is dissolved may be supplied to the first reaction tank 2. An electrolytic solution (first electrolytic solution) containing water (HO) is supplied to the second reaction tank 3 by an electrolytic solution circulation unit 12. The electrolytic solution circulation unit 12 includes a second gas-liquid separator 14 to which the electrolytic solution containing gaseous oxidation products (e.g., O) generated by the oxidation electrode 11 and discharged from the second reaction tank 3 is supplied via a first circulation pipe 13, and a circulation pump 16 and an electrolytic solution storage tank 17 provided in a second circulation pipe 15.

[0013] A power supply (external or internal) 18 is electrically connected to the reduction electrode (cathode) 10 and the oxidation electrode (anode) 11. By supplying power from the power supply 18 to the reduction electrode 10 and the oxidation electrode 11, a reduction reaction occurs at the reduction electrode 10, and an oxidation reaction occurs at the oxidation electrode 11. In the second reaction vessel 3, for example, water (HO) in the electrolyte is oxidized at the oxidation electrode 11 to produce oxygen (O) and hydrogen ions (H + ) and electrons (e - The generated oxygen is discharged from the second reaction tank 3 together with the electrolytic solution via the first circulation pipe 13, and is separated into the electrolytic solution and oxygen in the second gas-liquid separator 14. In the first reaction tank 2, nitrogen (N2) is reduced by, for example, an ammonia generation catalyst, and ammonia (NH3) is generated.

[0014] Ammonia is a water-soluble gas, and the electrolyte may transfer from the second reaction tank 3 to the first reaction tank 2 through the diaphragm 4. When the electrolyte transfers from the second reaction tank 3 to the first reaction tank 2, it is thought that at least a portion of the water-soluble gas ammonia will be dissolved in the electrolyte present in the first reaction tank 2. Because at least a portion of the water-soluble gas ammonia is thought to exist in the electrolyte as a water-soluble substance (water-soluble gas product), ammonia cannot be efficiently recovered simply by subjecting the discharge from the first reaction tank 2 to gas-liquid separation. For this reason, in the electrolysis device 1 of this embodiment, the discharge from the first reaction tank 2, i.e., the discharge containing gas components including ammonia (NH3) as a reduction product, unreacted nitrogen (N2), hydrogen (H2) produced by co-electrolysis, etc., and liquid components including aqueous ammonia, electrolyte, etc., is sent to the gas-liquid contactor 7, where it is contacted with a liquefaction recovery agent, and a liquefied product is obtained by liquefying the water-soluble gas ammonia (NH3) using the liquefaction recovery agent. The liquefied recovery agent is supplied to the gas-liquid contactor 7 by a liquefied recovery agent supply device 19 .

[0015] The liquefied recovery agent is a liquid containing at least some of the components of the electrolyte. When the reduction product is ammonia (NH), the ammonia reacts with sulfuric acid or a sulfate to produce ammonium sulfate ((NH)SO) according to the following formula (1) or (2). Ammonium sulfate is easily soluble in water and easily becomes a liquid. Therefore, it is preferable to use sulfuric acid or a sulfate as the liquefied recovery agent.

[0016] 2NH3 + H2SO4 → (NH4)2SO4…(1) 2NH4OH+H2SO4→ (NH4)2SO4+2H2O …(2) On the other hand, it is preferable to use sulfates such as potassium sulfate (K2SO4), calcium sulfate (CaSO4), sodium sulfate (Na2SO4), etc. as the electrolyte, which allows ammonia to be recovered from the ammonium salt liquefied by the liquefaction recovery agent, and the base portion of the ammonium salt to be reused as the electrolyte.

[0017] The gas-liquid contactor 7 discharges a gas-liquid mixture, which is a mixture of a liquid component containing a liquefied water-soluble gas, such as ammonium sulfate ((NH4)2SO4), and a liquefaction recovery agent, such as sulfuric acid, and a gas component containing unreacted nitrogen (N2) and hydrogen (H2) produced by a side reaction. The gas-liquid mixture discharged from the gas-liquid contactor 7 is sent to a first gas-liquid separator 8, where it is separated into a liquid component containing a liquefied water-soluble gas, such as liquefied water-soluble gas, and a liquefaction recovery agent, such as sulfuric acid, and a gas component containing nitrogen (N2), hydrogen (H2), and the like. The separated gas components are separated into nitrogen (N2) and hydrogen (H2) as necessary, and the separated nitrogen is reused as a raw material.

[0018] The liquid component separated in the first gas-liquid separator 8 is sent to a distiller 9, where it is separated into a liquefied water-soluble gas, such as ammonium sulfate ((NH)SO), and a liquefied recovery agent, such as sulfuric acid. The distillate containing the water-soluble gas, such as ammonium sulfate ((NH)SO), separated by the distiller 9, is sent to a device that performs at least one of cooling and compression and is liquefied. Ammonium (NH) can be obtained by, for example, heating the ammonium sulfate ((NH)SO) obtained by distillation. In addition, sulfates, such as sulfuric acid (HSO), potassium sulfate (KSO), calcium sulfate (CaSO), and sodium sulfate (NaSO), obtained by distillation, are returned to the electrolyte storage tank 17 of the electrolyte circulation unit 12 via a re-transmission pipe 20 for reuse as electrolyte.

[0019] As described above, in the electrolysis device 1 of the embodiment, when the reduction product is a water-soluble gas such as ammonia, the water-soluble gas can be liquefied using a liquefaction recovery agent containing at least a portion of the electrolyte component, and the gas is converted into a liquefied product that can be separated from the electrolyte by distillation and recovered. This makes it possible to efficiently recover water-soluble gases such as ammonia and to improve the production efficiency of ammonia. As a result, it is possible to provide an electrolysis device 1 and an electrolysis method that improve the recovery and production efficiency of water-soluble gases such as ammonia. Note that, in the above embodiment, the production and recovery of ammonia, a water-soluble gas, as the reduction product has been described. However, the reduction product is not limited to ammonia. The electrolysis device 1 of the embodiment can also be applied when the reduction product is a water-soluble gas. In this case, the electrolyte and a liquefaction recovery agent containing at least a portion of the electrolyte component can be selected and used depending on the water-soluble gas as the reduction product.

[0020] The components constituting each part of the electrolysis device 1 and the materials used in each part will be described below. However, the materials described below are merely examples and are not limited to these. For example, the oxidation electrode 11 uses a material that reduces the activation energy required to cause an oxidation reaction. In other words, the oxidation electrode 11 is used to convert HO or OH - The oxidation electrode 11 is made of a material that reduces the overvoltage that occurs when a reaction of oxidizing the metal oxide (Pt) and extracting electrons occurs. Examples of materials that can be used to form the oxidation electrode 11 include binary metal oxides such as platinum (Pt), manganese oxide (Mn-O), iridium oxide (Ir-O), nickel oxide (Ni-O), cobalt oxide (Co-O), iron oxide (Fe-O), tin oxide (Sn-O), indium oxide (In-O), and ruthenium oxide (Ru-O), ternary metal oxides such as Ni-Co-O, La-Co-O, Ni-La-O, and Sr-Fe-O, quaternary metal oxides such as Pb-Ru-Ir-O and La-Sr-Co-O, and metal complexes such as Ru complexes and Fe complexes.

[0021] To carry out the reduction reaction, the reduction electrode 10 is preferably made of an electrically conductive electrode material. Furthermore, it is preferable that the electrode have a porous structure, since the reaction area can be increased by gas diffusion. Specifically, the reduction electrode 10 preferably has a gas diffusion layer and a catalyst layer. For example, carbon paper, carbon cloth, carbon felt, or the like is used for the gas diffusion layer. The catalyst layer contains a reduction catalyst that reduces nitrogen to produce ammonia, as well as porous carbon material (particles) as a catalyst support and a polymer material that binds the porous carbon material as a catalyst support.

[0022] The reduction catalyst (ammonia production catalyst) used in the reduction electrode 10 promotes the production of ammonia from nitrogen, and is, for example, a molybdenum complex, but is not limited to this. Examples of the ammonia production catalyst include the following molybdenum complexes (A) to (D).

[0023] A first example is a molybdenum complex having, as a PCP ligand (A), N,N-bis(dialkylphosphinomethyl)dihydrobenzimidazolidene (wherein the two alkyl groups may be the same or different, and at least one hydrogen atom on the benzene ring may be substituted with an alkyl group, an alkoxy group, or a halogen atom).

[0024] A second example is a molybdenum complex having, as a PNP ligand (B), 2,6-bis(dialkylphosphinomethyl)pyridine (wherein the two alkyl groups may be the same or different, and at least one hydrogen atom on the pyridine ring may be substituted with an alkyl group, an alkoxy group, or a halogen atom).

[0025] A third example is a molybdenum complex having, as the (C)PPP ligand, a bis(dialkylphosphinomethyl)arylphosphine (wherein the two alkyl groups may be the same or different).

[0026] A fourth example is a molybdenum complex represented by (D) trans-Mo(N2)2(R1R2R3P)4 (wherein R1, R2, and R3 are alkyl or aryl groups which may be the same or different, and two R3s may be bonded to each other to form an alkylene chain).

[0027] In the molybdenum complexes described above, the alkyl group may be, for example, a methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, or the like; a linear or branched alkyl group such as a structural isomer thereof; or a cyclic alkyl group such as a cyclopropyl group, cyclobutyl group, cyclopentyl group, or cyclohexyl group. The alkyl group preferably has 1 to 12 carbon atoms, more preferably 1 to 6 carbon atoms. The alkoxy group may be, for example, a methoxy group, ethoxy group, propoxy group, butoxy group, pentoxy group, hexyloxy group, or the like; a linear or branched alkoxy group such as a structural isomer thereof; or a cyclic alkoxy group such as a cyclopropoxy group, cyclobutoxy group, cyclopentoxy group, or cyclohexyloxy group. The alkoxy group preferably has 1 to 12 carbon atoms, more preferably 1 to 6 carbon atoms. Examples of halogen atoms include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

[0028] The molybdenum complex (A) may be, for example, a molybdenum complex represented by the following formula (A1).

[0029] [ka]

[0030] In the formula, R1 and R2 are alkyl groups which may be the same or different, X is an iodine atom, a bromine atom, or a chlorine atom, and at least one hydrogen atom on the benzene ring may be substituted with an alkyl group, an alkoxy group, or a halogen atom.

[0031] Examples of the alkyl group, alkoxy group, and halogen atom include those already exemplified. R1 and R2 are preferably bulky alkyl groups (e.g., tert-butyl or isopropyl). It is preferred that the hydrogen atoms on the benzene ring are unsubstituted or that the hydrogen atoms at the 5th and 6th positions are substituted with linear, cyclic, or branched alkyl groups having 1 to 12 carbon atoms.

[0032] Examples of the molybdenum complex (B) include molybdenum complexes represented by the following formulae (B1), (B2) and (B3).

[0033] [ka]

[0034] In the formula, R1 and R2 are alkyl groups which may be the same or different, X is an iodine atom, a bromine atom, or a chlorine atom, and at least one hydrogen atom on the pyridine ring may be substituted with an alkyl group, an alkoxy group, or a halogen atom.

[0035] Examples of the alkyl group, alkoxy group, and halogen atom include those already exemplified. R1 and R2 are preferably bulky alkyl groups (e.g., tert-butyl or isopropyl). It is preferred that the hydrogen atom on the pyridine ring is unsubstituted or that the hydrogen atom at position 4 is substituted with a linear, cyclic, or branched alkyl group having 1 to 12 carbon atoms.

[0036] The molybdenum complex (C) may be, for example, a molybdenum complex represented by the following formula (C1).

[0037] [ka]

[0038] In the formula, R1 and R2 are alkyl groups which may be the same or different, R3 is an aryl group, and X is an iodine atom, a bromine atom, or a chlorine atom.

[0039] Examples of the alkyl group include the same groups as those already exemplified. Examples of the aryl group include a phenyl group, a tolyl group, a xylyl group, a naphthyl group, and groups in which at least one of the cyclic hydrogen atoms is substituted with an alkyl group or a halogen atom. Examples of the alkyl group and the halogen atom include the same groups as those already exemplified. R1 and R2 are preferably bulky alkyl groups (e.g., tert-butyl group or isopropyl group). R3 is preferably, for example, a phenyl group.

[0040] Examples of the molybdenum complex (D) include molybdenum complexes represented by the following formulae (D1) and (D2).

[0041] [ka]

[0042] In the formula, R1, R2, and R3 are alkyl or aryl groups which may be the same or different; and n is 2 or 3.

[0043] Examples of the alkyl group and aryl group include those already exemplified. In formula (D1), it is preferred that R1 and R2 are aryl groups (e.g., phenyl groups) and R3 is an alkyl group having 1 to 4 carbon atoms (e.g., methyl group), or that R1 and R2 are alkyl groups having 1 to 4 carbon atoms (e.g., methyl group) and R3 is an aryl group (e.g., phenyl group). In formula (D2), it is preferred that R1 and R2 are aryl groups (e.g., phenyl groups) and n is 2.

[0044] The ammonia production catalyst (reduction catalyst) that promotes the production of ammonia from nitrogen may be, for example, a metallocene complex represented by the following formula (E1).

[0045] [ka]

[0046] In the formula, M is a tetravalent metal ion, which is either titanium, zirconium, or hafnium. X1 and X2 are the same or different anions with coordinating properties. The anion is Cl. - , Br - , I - , CH3 - , or OH - It is preferable that Cl - More preferably, metallocene complexes such as bis(cyclopentadienyl)titanium dichloride and bis(cyclopentadienyl)zirconium dichloride are used.

[0047] Furthermore, as the ammonia-producing catalyst (reduction catalyst), metal catalysts such as molybdenum, bismuth, iron, rhodium, ruthenium, titanium, zirconium, etc. may be used. These may be used alone or in combination of two or more.

[0048] The catalyst support supports an ammonia production catalyst (reduction catalyst) and is made of a porous carbon material. Examples of porous carbon materials (carbon particles) include channel black, furnace black, thermal black, acetylene black, activated carbon, natural graphite, artificial graphite, graphitized carbon, graphene, carbon nanotubes (CNTs), fullerenes, Ketjen black, and glassy carbon. Among these, porous carbon materials with pores having a BET average pore diameter of 1 nm to 15 nm are preferred. By using a porous carbon material with pores having a BET average pore diameter of 1 nm to 15 nm as the catalyst support, molecular catalysts such as the molybdenum complex described above can be immobilized to the electrode with high density and efficiency. This allows for the realization of a three-phase interface-controlled reduction electrode 10 capable of directly reacting nitrogen (N). This significantly increases the efficiency of ammonia production in the gas phase.

[0049] By adsorbing and retaining an ammonia production catalyst in the pores of a porous carbon material having the above-mentioned BET average pore diameter, it can be used as a catalyst support for nitrogen reduction reactions. For example, when the ammonia production catalyst is a molybdenum complex, by contacting porous carbon particles with a solution in which the molybdenum complex is dissolved, the molybdenum complex is attracted to the porous carbon particles by the attractive force (van der Waals force) from the porous carbon particles, and adsorption occurs in the pores of the porous carbon particles. The above-mentioned BET average pore diameter is an example of a property of a porous carbon material that can suitably retain an ammonia production catalyst. In order to increase the reaction area, the specific surface area of ​​the porous carbon material is set to 800 m 2 / g or more 2000m 2 Further, in order to increase the catalyst loading, the average pore volume of the porous carbon material is preferably 0.2 cm 3 / g or more 5cm 3 / g or less is preferable.

[0050] A membrane that allows selective passage of anions or cations is used as the diaphragm 4. Examples of ion exchange membranes that can be used for the diaphragm 4 include Neosepta (registered trademark) from Astom Corporation, Selemion (registered trademark) from Asahi Glass Co., Ltd., Aciplex (registered trademark) from Asahi Kasei Corporation, Fumasep (registered trademark) and fumapem (registered trademark) from Fumatech Corporation, Nafion (registered trademark), a fluororesin obtained by sulfonating and polymerizing tetrafluoroethylene from DuPont Corporation, lewabrane (registered trademark) from LANXESS, IONSEP (registered trademark) from IONTECH, Mustang (registered trademark) from PALL Corporation, ralex (registered trademark) from mega Corporation, Gore-Tex (registered trademark) from Gore-Tex Corporation, Sustainion (registered trademark) from Dioxide Materials, and PiperION (registered trademark) from Versogen. Use of an anion exchange membrane is preferred because it is advantageous for increasing the amount of ammonia produced.

[0051] In addition to an ion exchange membrane, other materials that can be used for the diaphragm 4 include silicone resin, fluororesin such as perfluoroalkoxyalkane (PFA), perfluoroethylenepropene copolymer (FEP), polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene copolymer (ETFE), polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTFE), and ethylene-chlorotrifluoroethylene copolymer (ECTFE), ceramic porous membranes, glass filters, packings filled with agar, and insulating porous materials such as zeolites and oxides. Hydrophilic porous membranes are preferred for the diaphragm 4 because they are not clogged with air bubbles.

[0052] In the electrolysis device 1 shown in FIG. 1 , the nitrogen supply device 6 is a unit that supplies gaseous nitrogen to the first reaction tank (cathode tank / reduction chamber) 2. The nitrogen supplied from the nitrogen supply device 6 may be, for example, nitrogen in the air, but is not limited to this. Because air contains approximately 21% oxygen, it is preferable to extract nitrogen by separating the oxygen in advance. When nitrogen in the air is used, an oxygen separator that separates oxygen from the air to extract nitrogen is used in the nitrogen supply device 6. Methods for separating oxygen from air in the oxygen separator include, for example, a cryogenic separation method that utilizes differences in boiling points for separation, an adsorption separation method that utilizes differences in the adsorption properties of zeolite adsorbents for gas molecules, and a membrane separation method that utilizes differences in the permeation speed of gas molecules through a membrane for separation. These methods can be selected appropriately depending on the cost and scale of the device, and are not particularly limited.

[0053] (Second embodiment) Next, an electrolysis apparatus 1 of a second embodiment will be described with reference to Figures 2 to 5. The electrolysis apparatus 1 of the second embodiment shown in Figure 2 includes, in addition to the components of the electrolysis apparatus 1 of the first embodiment shown in Figure 1, a second electrolysis cell 21 that separates the electrolyte components (e.g., metal salts) separated in the distiller 9 into a portion containing a base and a portion containing a metal, and enables the separated portion containing the base to be reused as a liquefied recovery agent. Except for the second electrolysis cell 21 and the portion including it, the electrolysis apparatus 1 has the same configuration as the electrolysis apparatus 1 of the first embodiment.

[0054] A first example of the second electrolytic cell 21 is shown in Figures 2 and 3. The second electrolytic cell 21 of the first example includes a first reaction tank (cathode tank) 23 in which a reduction electrode 22 is disposed, a second reaction tank (anode tank) 25 in which an oxidation electrode 24 is disposed, and a liquid feed tank 28 disposed between the first reaction tank 23 and the second reaction tank 25, the liquid feed tank 28 having a first diaphragm 26 disposed on the first reaction tank 23 side and a second diaphragm 27 disposed on the second reaction tank 25 side. A cation exchange membrane is used for the first diaphragm 26 so that metal ions can be transferred to the first reaction tank 23. An anion exchange membrane is used for the second diaphragm 27 so that base ions such as sulfate ions can be transferred to the second reaction tank 25.

[0055] The electrolyte is sent to the liquid sending tank 28 through a liquid sending pipe 29 branched off from the second circulation pipe 15. A power supply 30 is connected to the reduction electrode 22 and the oxidation electrode 24. When power is supplied from the power supply 30 to the reduction electrode 22 and the oxidation electrode 24, metal ions, which are cations, move to the first reaction tank 23, and base ions, which are anions, move to the second reaction tank 25. For example, when potassium sulfate (K2SO4) is used as the electrolyte, the potassium sulfate sent to the liquid sending tank 28 converts potassium ions (K + ) and sulfate ions (SO4 2- ) and potassium ions (K + ) moves to the first reaction tank 23 and becomes potassium hydroxide (KOH), and sulfate ions (SO4 2- ) moves to the second reaction tank 25 and becomes sulfuric acid (H2SO4).

[0056] The sulfuric acid produced in the second reaction tank 25 is sent to the supply device 19 as a liquefied recovery agent and supplied to the gas-liquid contactor 7. The potassium hydroxide produced in the first reaction tank 23 is sent to the electrolyte storage tank 17 and used as a concentration adjuster for the electrolyte. Here, the case where potassium sulfate (K2SO4) is used as the electrolyte and sulfuric acid (H2SO4) is used as the liquefied recovery agent has been given as an example, but the present invention is not limited to this. The same applies when a different sulfate is used as the electrolyte; sulfuric acid is produced in the second reaction tank 25 and hydroxides are produced from metal ions of the sulfate in the first reaction tank 23, and these are respectively used in the same way as the liquefied recovery agent and the concentration adjuster for the electrolyte.

[0057] A second example of the second electrolytic cell 21 will be described with reference to Fig. 4. The second electrolytic cell 21 of the second example includes a first reaction tank 23 in which a reduction electrode 22 is disposed, a second reaction tank 25 in which an oxidation electrode 24 is disposed, and a diaphragm 31 disposed between the first reaction tank 23 and the second reaction tank 25. An electrolytic solution is delivered to the second reaction tank 25 via a liquid delivery pipe 29, and pure water (HO) is delivered to the first reaction tank 23 via a pipe 31. A cation exchange membrane is used for the diaphragm 31 so that metal ions can be transferred from the second reaction tank 25 to the first reaction tank 23.

[0058] According to the electrolytic cell 20 shown in Fig. 4, sulfuric acid is produced in the second reaction tank 25, and hydroxides (KOH, etc.) of metal ions of sulfate are produced in the first reaction tank 23. Therefore, the sulfuric acid produced in the second reaction tank 25 can be used as a liquefied recovery agent, and the hydroxides of metal ions produced in the first reaction tank 23 can be used as a concentration adjuster for the electrolytic solution. Note that while the electrolytic cell 20 shown in Fig. 4 makes it possible to easily extract hydroxides of metal ions such as KOH, the purity of the sulfuric acid tends to decrease slightly.

[0059] A third example of the second electrolytic cell 21 will be described with reference to Fig. 5. The second electrolytic cell 21 of the third example includes a first reaction tank 23 in which a reduction electrode 22 is disposed, a second reaction tank 25 in which an oxidation electrode 24 is disposed, and a diaphragm 31 disposed between the first reaction tank 23 and the second reaction tank 25. An electrolytic solution is delivered to the first reaction tank 23 via a liquid delivery pipe 29, and pure water (HO) is delivered to the second reaction tank 25 via a pipe 32. An anion exchange membrane is used for the diaphragm 31 so that sulfate ions can be transferred from the first reaction tank 23 to the second reaction tank 25.

[0060] According to the electrolytic cell 20 shown in Figure 5, sulfuric acid is produced in the second reaction tank 25, and hydroxides (e.g., KOH) of metal ions of sulfate are produced in the first reaction tank 23. Therefore, the sulfuric acid produced in the second reaction tank 25 can be used as a liquefied recovery agent, and the hydroxides of metal ions produced in the first reaction tank 23 can be used as a concentration adjuster for the electrolytic solution. Note that while the electrolytic cell 20 shown in Figure 5 allows for easy extraction of sulfuric acid, the purity of the hydroxides of metal ions such as KOH tends to decrease slightly. The second electrolytic cell 21 can be selected from the first to third examples as appropriate based on the intended use, required accuracy, etc.

[0061] The configurations of the above-described embodiments can be applied in combination with each other, and some of them can be replaced with other configurations. Although several embodiments of the present invention have been described herein, 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, modifications, etc. can be made without departing from the spirit of the invention. These embodiments and their modifications are intended to be included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as set forth in the claims. [Explanation of symbols]

[0062] 1...electrolysis device, 2, 23...first reaction tank (cathode tank), 3, 25...second reaction tank (anode tank), 4, 31...diaphragm, 5...first electrolytic cell, 6...nitrogen supply device, 7...gas-liquid contactor, 8...first gas-liquid separator, 9...distiller, 10, 22...reduction electrode, 11, 24...oxidation electrode, 12...electrolyte circulation unit, 13, 15...circulation piping, 14...second gas-liquid separator, 16...circulation pump, 17...electrolyte storage tank, 18, 30...power source, 21...second electrolytic cell, 26...first diaphragm, 27...second diaphragm, 28...liquid supply tank, 29...liquid supply piping.

Claims

1. a first electrolysis cell including: a first reaction tank in which a reduction electrode is disposed and to which a substance to be reduced is supplied and which produces a water-soluble gas as a reduction product; a second reaction tank in which an oxidation electrode is disposed and to which an electrolytic solution is supplied; and a diaphragm provided between the first reaction tank and the second reaction tank; a reduction product supply unit that supplies the reduction product to the first reaction tank; an electrolyte circulation unit including a circulation pipe for circulating the electrolyte outside the first electrolytic cell and a tank for storing the electrolyte so as to supply the electrolyte to the second reaction tank; a gas-liquid contactor to which at least one of the water-soluble gas and its aqueous solution produced in the first reaction tank is supplied, which contacts a liquefied recovery agent containing at least a portion of a component of the electrolytic solution with at least one of the water-soluble gas and its aqueous solution, and which discharges a gas-liquid mixture containing a liquefied product of the water-soluble gas; a first gas-liquid separator to which the gas-liquid mixture discharged from the gas-liquid contactor is supplied and which separates the gas-liquid mixture into a liquid component containing the liquefied water-soluble gas and a gas component; a distiller that separates the liquid component discharged from the first gas-liquid separator into a liquefied water-soluble gas and an electrolyte component; a return pipe for returning the electrolytic solution components discharged from the distiller to the storage section of the electrolytic solution; An electrolysis device comprising:

2. the substance to be reduced is nitrogen, the water-soluble gas is ammonia, the liquefaction recovery agent is sulfuric acid or a sulfate salt; 2. The electrolysis system of claim 1, wherein the ammonia is liquefied as ammonium sulfate in the gas-liquid contactor.

3. 3. The electrolysis apparatus according to claim 1, wherein the distillate obtained in the still is liquefied by a device that performs at least one of cooling and compression.

4. 3. The electrolysis device according to claim 1 or 2, wherein the electrolyte circulation unit comprises a second gas-liquid separator to which the electrolyte containing gas as an oxidation product produced in the second reaction tank is supplied and which separates the electrolyte from the gas as the oxidation product.

5. 2. The electrolysis apparatus according to claim 1, further comprising a second electrolytic cell comprising: a first reaction tank in which a reduction electrode is disposed; a second reaction tank in which an oxidation electrode is disposed; and a diaphragm provided between the first reaction tank and the second reaction tank, the second electrolytic cell being supplied with the electrolytic solution components separated in the distiller, separating a portion containing a base from the electrolytic solution components, and returning the separated portion containing the base to the gas-liquid contactor as the liquefied recovery agent.

6. the substance to be reduced is nitrogen, the water-soluble gas is ammonia, the liquefaction recovery agent is sulfuric acid or a sulfate salt; The ammonia is liquefied as ammonium sulfate in the gas-liquid contactor; 6. The electrolysis apparatus of claim 5, wherein the base-containing portion separated in the second electrolysis cell is sulfuric acid.

7. a step of reducing the material to be reduced to produce a water-soluble gas as a reduction product by using a first electrolysis cell including a first reaction tank in which a reduction electrode is disposed, a second reaction tank in which an oxidation electrode is disposed, and a diaphragm provided between the first reaction tank and the second reaction tank, by supplying a material to be reduced to the first reaction tank, supplying an electrolytic solution to the second reaction tank, and supplying electric power to the reduction electrode and the oxidation electrode; a step of contacting at least one of the water-soluble gas and its aqueous solution produced in the first reaction tank with a liquefaction recovery agent containing at least a portion of a component of the electrolytic solution to obtain a gas-liquid mixture containing a liquefied product of the water-soluble gas; separating the gas-liquid mixture into a liquid component containing the liquefied water-soluble gas and a gas component; distilling the liquid component containing the liquefied water-soluble gas to separate the liquefied water-soluble gas from an electrolyte component; returning the electrolyte component separated from the liquid component to the second reaction vessel; An electrolysis method comprising:

8. 8. The electrolysis method according to claim 7, wherein the electrolytic solution is circulated from the second reaction tank through a second gas-liquid separator and a tank for storing the electrolytic solution by a circulation pipe arranged outside the first electrolytic cell.

9. the substance to be reduced is nitrogen, the water-soluble gas is ammonia, the liquefaction recovery agent is sulfuric acid or a sulfate salt; 9. The electrolysis method according to claim 7 or 8, wherein the ammonia is liquefied as ammonium sulfate by the liquefaction recovery agent.

10. 9. The electrolysis method according to claim 7 or 8, wherein the distillate obtained by the distillation is liquefied by at least one of cooling and compression.

11. 9. The electrolysis method according to claim 7 or 8, further comprising: sending the electrolytic solution components obtained by the distillation to a second electrolytic cell; separating a portion of the electrolytic solution components containing a base; and using the separated portion containing the base as the liquefied recovery agent.

12. the substance to be reduced is nitrogen, the water-soluble gas is ammonia, the liquefaction recovery agent is sulfuric acid or a sulfate salt; The ammonia is liquefied as ammonium sulfate by the liquefaction recovery agent, 12. The electrolytic process of claim 11, wherein the base-containing moiety is sulfuric acid.

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