Ammonia production apparatus and ammonia production method

Abstract

To provide an ammonia production apparatus capable of producing ammonia with high efficiency.SOLUTION: An ammonia production apparatus 1 in an embodiment has an electrochemical reaction cell comprising a first reaction tank 2 in which a reduction electrode is arranged and gaseous nitrogen is supplied, a second reaction tank 3 in which an oxidation electrode is arranged and an electrolytic solution containing water or steam is supplied, and a diaphragm 4 provided between the first reaction tank 2 and the second reaction tank 3. In the ammonia production apparatus in an embodiment, the reduction electrode comprises a reduction catalyst for producing ammonia by reducing nitrogen, a porous carbon material for supporting the reduction catalyst, and an organic polymer material for binding the porous carbon material, and the porous carbon material has pores having a BET average pore diameter of 1 nm or more and 15 nm or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] An embodiment of the present invention relates to an ammonia manufacturing apparatus and an ammonia manufacturing 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 producing ammonia from nitrogen at room temperature and pressure have been developed. For example, it has been reported that a maximum of 4,350 equivalents of ammonia per catalyst was produced by stirring a solution containing a molybdenum iodide complex bearing 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, in the presence of nitrogen gas at room temperature. Other reported methods use a molybdenum iodide complex bearing 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] However, the above-mentioned ammonia production reaction requires the use of a stoichiometric amount of expensive samarium(II) iodide as a reducing agent. Furthermore, the reaction can only be controlled by the amount of the reducing agent. Therefore, from an industrial perspective, there is a need for a production method that allows for more inexpensive reaction control and efficient production and recovery of ammonia. For these reasons, there is a need for the development of an ammonia production apparatus and production method that can produce ammonia with high efficiency and efficiently recover the produced ammonia. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2019 / 168093 [Patent Document 2] International Publication No. 2021 / 045206 [Non-patent literature]

[0007] [Non-Patent Document 1] Nature Communications 8:14874 doi:10.1038 / ncomms 14874 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide an ammonia production apparatus and an ammonia production method that enable ammonia to be produced with high efficiency. [Means for solving the problem]

[0009] An embodiment of an ammonia manufacturing apparatus is an ammonia manufacturing apparatus comprising an electrochemical reaction cell including: a first reaction tank in which a reduction electrode is disposed and to which gaseous nitrogen is supplied; a second reaction tank in which an oxidation electrode is disposed and to which a water-containing electrolytic solution or water vapor is supplied; and a diaphragm provided between the first reaction tank and the second reaction tank, wherein the reduction electrode comprises a reduction catalyst that reduces nitrogen to produce ammonia, a porous carbon material that supports the reduction catalyst, and an organic polymer material that binds the porous carbon material, and the porous carbon material has pores with a BET average pore diameter of 1 nm or more and 15 nm or less. The reduction catalyst comprises a molybdenum complex. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a diagram showing an ammonia production apparatus according to an embodiment. [Figure 2] FIG. 2 is a diagram showing a first example of an electrochemical reaction unit of the ammonia manufacturing apparatus shown in FIG. [Figure 3] 1. FIG. 4 is a diagram showing a second example of the electrochemical reaction unit of the ammonia manufacturing apparatus shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an ammonia manufacturing apparatus and an ammonia manufacturing method according to embodiments will be described with reference to the drawings. In each embodiment shown below, substantially identical components are denoted by the same reference numerals, and some of the description thereof may be omitted. The drawings are schematic, and the relationship between thickness and planar dimensions, the thickness ratio of each part, etc. may differ from the actual ones.

[0012] FIG. 1 is a diagram illustrating an embodiment of an ammonia production apparatus 1. The ammonia production apparatus 1 shown in FIG. 1 includes an electrochemical reaction unit (electrolytic cell) 5 including a first reaction tank (electrolytic tank for reduction reaction) 2 to which gaseous nitrogen is supplied, a second reaction tank (electrolytic tank for oxidation reaction) 3 to which a water-containing electrolytic solution or water vapor is supplied, and a diaphragm 4; a nitrogen supply unit 7 including a nitrogen supply section (supply device) 6 for supplying nitrogen to the first reaction tank 2; an ammonia capture unit 9 including a capture section (capture device) 8 for capturing ammonia contained in the gas discharged from the first reaction tank 2; and an ammonia separation unit 11 including an ammonia separation section (separator) 10 for separating ammonia contained in the electrolytic solution discharged from the second reaction tank 3. The ammonia production apparatus 1 further includes an electrolyte circulation unit 13 including a circulation pipe 12 for circulating the second electrolyte contained in the second reaction tank 3 outside the second reaction tank 3. Each section will be described in detail below.

[0013] FIG. 2 shows a first example of an electrochemical reaction unit 5. The electrochemical reaction unit 5 shown in FIG. 2 includes a first reaction tank (electrolytic tank for reduction reaction) 2, a second reaction tank (electrolytic tank for oxidation reaction) 3, a diaphragm 4 provided between the first reaction tank 2 and the second reaction tank 3, a reduction electrode 14 disposed in the first reaction tank 2 and used for an electrochemical reduction reaction, and an oxidation electrode 15 disposed in the second reaction tank 3 and used for an electrochemical oxidation reaction, which together form an electrochemical reaction cell (electrolysis cell). The electrochemical reaction cell 5 converts hydrogen ions (H + ) and hydroxide ions (OH - The first reaction vessel 2 and the second reaction vessel 3 are separated by a diaphragm 4 that allows the movement of ions such as hydrogen and nitrogen. Gaseous nitrogen (N2) is supplied to the first reaction vessel 2 through a pipe. An electrolyte solution containing water (H2O) or water vapor (H2O) is supplied to the second reaction vessel 3 through a circulation pipe 12.

[0014] The electrochemical reaction unit 5 may have a configuration as shown in FIG. 3. FIG. 3 shows a second example of the electrochemical reaction unit 5. The electrochemical reaction unit 5 shown in FIG. 3 includes a first reaction tank 2, which is supplied with gaseous nitrogen (N), and a third reaction tank 16, which is supplied with an aqueous electrolyte (cathode solution), and which is disposed between the first reaction tank 2 and a diaphragm 4. The first reaction tank 2 and the third reaction tank 17 are connected via a porous reduction electrode 14, constituting a cathode chamber. The cathode chamber, which includes the first reaction tank 2 and the third reaction tank 16, is connected to the second reaction tank 3, which serves as an anode chamber, via the diaphragm 4 and a porous oxidation electrode 15. According to the electrochemical reaction unit 5 shown in FIG. 3, ammonia (NH) produced by reducing gaseous nitrogen (N) supplied to the first reaction tank 2 can be dissolved in the electrolyte (cathode solution) supplied to the third reaction tank 16 and extracted to the outside of the electrochemical reaction cell (electrolysis cell) 5. This makes it possible to increase the efficiency of ammonia recovery.

[0015] The reduction electrode 14 and the oxidation electrode 15 are connected to an external electrode 17. When power is supplied from the external electrode 17 to the reduction electrode 14 and the oxidation electrode 15, a reduction reaction occurs at the reduction electrode 14, and an oxidation reaction occurs at the oxidation electrode 15. In the second reaction vessel 3, for example, water (HO) in the electrolyte is oxidized at the oxidation electrode 15 to produce oxygen (O) and hydrogen ions (H + ) and electrons (e - ) is produced. The produced oxygen is discharged from the second reaction tank 3 via the circulation pipe 12 together with water. In the first reaction tank 2, nitrogen (N2) is reduced by the ammonia production catalyst to produce ammonia (NH3). The nitrogen containing ammonia is discharged to the outside of the first reaction tank 2 via the pipe and is continuously sent to the ammonia capture unit 9. Furthermore, a portion of the ammonia produced in the first reaction tank 2 passes through the diaphragm 4 and moves to the second reaction tank 3. The electrolyte solution or water vapor containing water mixed with ammonia in the second reaction tank 3 is discharged to the outside of the second reaction tank 3 via the circulation pipe 12 and is continuously or intermittently sent to the ammonia separation unit 11.

[0016] As described above, an electrolytic solution containing water (HO) or water vapor is supplied to the second reaction vessel 3. The electrolytic solution may be an aqueous solution containing an electrolyte. It is preferable that the electrolytic solution has high ionic conductivity and that the electrolyte itself does not undergo any reaction. Examples of electrolytes contained in such a first electrolyte solution include lithium hydroxide (LiOH), sodium hydroxide (NaOH), potassium hydroxide (KOH), lithium chloride (LiCl), sodium chloride (NaCl), potassium chloride (KCl), lithium bromide (LiBr), sodium bromide (NaBr), potassium bromide (KBr), lithium iodide (LiI), sodium iodide (NaI), potassium iodide (KI), lithium nitrate (LiNO3), sodium nitrate (NaNO3), potassium nitrate (KNO3), lithium sulfate (Li2SO4), sodium sulfate (Na2SO4), potassium sulfate (K2SO4), lithium hydrogen sulfate (LiHSO4), sodium hydrogen sulfate (NaHSO4), potassium hydrogen sulfate (KHSO4), lithium peroxodisulfate (Li2S2O8), sodium peroxodisulfate (Na 2S2O8), potassium peroxodisulfate (K2S2O8), lithium phosphate (Li3PO4), sodium phosphate (Na3PO4), potassium phosphate (K3PO4), dilithium hydrogen phosphate (Li2HPO4), disodium hydrogen phosphate (Na2HPO4), dipotassium hydrogen phosphate (K2HPO4), lithium dihydrogen phosphate (LiH2PO4), sodium dihydrogen phosphate (NaH2PO4), potassium dihydrogen phosphate (KH2PO4), lithium bicarbonate (LiHCO3), sodium bicarbonate (NaHCO3), potassium bicarbonate (KHCO3), lithium carbonate (Li2CO3), sodium carbonate (Na2CO3), potassium carbonate (K2CO3), lithium tetraborate (Li2BO7), sodium tetraborate (Na2BO7), potassium tetraborate (K2BO7), ionic liquids, etc. Water is preferably used as the solvent. The electrolyte concentration in the electrolytic solution is preferably in the range of, for example, 0.001 to 1 mol / L. Furthermore, the pH of the electrolytic solution contained in the second reaction tank is preferably greater than 7 and equal to or less than 14, as this is advantageous for increasing the amount of ammonia produced and improving the efficiency of recovery.

[0017] Examples of cations used in ionic liquids include imidazolium ions, pyridinium ions, pyrrolidinium ions, and piperidinium ions. Examples of imidazolium ions include 1-ethyl-3-methylimidazolium, 1-methyl-3-propylimidazolium, 1-butyl-3-methylimidazolium, 1-methyl-3-pentylimidazolium, and 1-hexyl-3-methylimidazolium. The imidazolium ion may be substituted at the 2-position. Examples include 1-ethyl-2,3-dimethylimidazolium, 1,2-dimethyl-3-propylimidazolium, 1-butyl-2,3-dimethylimidazolium, 1,2-dimethyl-3-pentylimidazolium, and 1-hexyl-2,3-dimethylimidazolium. Examples of pyridinium ions include methylpyridinium, ethylpyridinium, propylpyridinium, butylpyridinium, pentylpyridinium, and hexylpyridinium. Examples of pyrrolidinium ions include ethyl-methylpyrrolidinium, methyl-propylpyrrolidinium, butyl-methylpyrrolidinium, methyl-pentylpyrrolidinium, and hexyl-methylpyrrolidinium. Examples of piperidinium ions include ethyl-methylpiperidinium, methyl-propylpiperidinium, butyl-methylpiperidinium, methyl-pentylpiperidinium, and hexyl-methylpiperidinium. The imidazolium ion, pyridinium ion, pyrrolidinium ion, and piperidinium ion may each be substituted with an alkyl group or may contain an unsaturated bond. As the cation of the ionic liquid, a single cation or a combination of multiple cations may be used.

[0018] The anions of ionic liquids include fluoride ions, chloride ions, bromide ions, iodide ions, acetate ions, nitrate ions, hydrogen sulfate ions, phosphate ions, dicyanamide ions, and BF4 - , PF6 - , CF3COO - , CF3SO3 - , SCN - , (CF3SO2)3C -Examples of the ionic liquid include bis(trifluoromethoxysulfonyl)imide ion, bis(trifluoromethoxysulfonyl)imide ion, and bis(perfluoroethylsulfonyl)imide ion. As the anion of the ionic liquid, a single anion or a combination of multiple anions is used. Also, a zwitterion in which the cation and anion of the ionic liquid are linked by a hydrocarbon may be used. The above-mentioned ionic liquids may be used alone or in combination of two or more types.

[0019] An oxidation electrode 15 is placed in the second reaction vessel 3, and an electrolyte is further supplied to the oxidation electrode 15. When the hydrogen ion concentration of the electrolyte is 7 or less (pH≦7), H2O is oxidized to O2 and H + On the other hand, when the hydrogen ion concentration of the electrolyte is greater than 7 (pH>7), OH - is oxidized to produce O and H. The oxidation electrode 15 is made of a material that reduces the activation energy for the oxidation reaction. In other words, the oxidation electrode 15 is - The oxidation electrode 15 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 15 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.

[0020] As described above, the first reaction vessel 2 is provided with a reduction electrode 14, to which nitrogen gas is further supplied. To carry out the reduction reaction, the reduction electrode 14 is preferably made of an electrically conductive electrode material. Furthermore, since the gas diffusion property allows the reaction area to be increased, the electrode preferably has a porous structure. Specifically, the reduction electrode 14 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 a porous carbon material (particles) serving as a catalyst support and a polymer material that binds the porous carbon material serving as the catalyst support.

[0021] The reduction catalyst (ammonia production catalyst) used in the reduction electrode 14 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).

[0022] 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).

[0023] 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).

[0024] 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).

[0025] 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).

[0026] 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.

[0027] The molybdenum complex (A) may be, for example, a molybdenum complex represented by the following formula (A1).

[0028] [ka] 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.

[0029] 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.

[0030] Examples of the molybdenum complex (B) include molybdenum complexes represented by the following formulae (B1), (B2) and (B3).

[0031] [ka] 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.

[0032] 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.

[0033] The molybdenum complex (C) may be, for example, a molybdenum complex represented by the following formula (C1).

[0034] [ka] 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.

[0035] 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.

[0036] Examples of the molybdenum complex (D) include molybdenum complexes represented by the following formulae (D1) and (D2).

[0037] [ka] 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.

[0038] 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.

[0039] 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).

[0040] [ka] 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.

[0041] 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.

[0042] 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 used. 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 makes it possible to realize a three-phase interface-controlled reduction electrode 14 capable of directly reacting nitrogen (N). This significantly increases the efficiency of gas-phase ammonia production.

[0043] If the BET average pore diameter of the porous carbon material exceeds 15 nm, the pores are too large to efficiently retain molecular catalysts such as molybdenum complexes. On the other hand, if the BET average pore diameter of the porous carbon material is less than 1 nm, the pores are too small to efficiently retain molecular catalysts such as molybdenum complexes. In either case, the function of the ammonia production catalyst (reduction catalyst) in the reduction electrode 14 cannot be sufficiently enhanced, and gaseous N2 cannot be efficiently reduced. It is more preferable that the BET average pore diameter of the porous carbon material be 2 nm or more and 10 nm or less.

[0044] 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.

[0045] Among the various carbon materials mentioned above, activated carbon has a developed pore structure, a large specific surface area, and adsorption performance, and is a preferred material as a support for an ammonia production catalyst because it easily satisfies the above-mentioned BET average pore diameter. Activated carbon is produced by carbonizing plant-based raw materials (wood, charcoal, coconut shells, etc.) or mineral-based raw materials (coke, coal tar, coal pitch, etc.), followed by activation treatment with water vapor or an alkaline solution such as potassium hydroxide.

[0046] The characteristics of activated carbon can be evaluated using the gas adsorption method with a specific surface area and pore size distribution measurement device. To measure specific surface area and pore size distribution, a reversibly adsorbable inert gas (adsorbate) such as nitrogen, argon, or krypton is used. The measurement procedure involves placing a sample in a sample tube of known volume, removing any adhering matter from the sample by heating and vacuum drying, and then introducing a fixed amount of adsorbate into the sample tube, bringing the adsorbate into contact with the sample surface. The amount of adsorption increases over time, eventually reaching a plateau. This state is called the adsorption equilibrium state, the amount of adsorption is called the equilibrium adsorption amount, and the pressure is called the equilibrium pressure. The amount of adsorption is determined by measuring the pressure change until the adsorption equilibrium state is reached.

[0047] The specific surface area is calculated by using BET theory to calculate the amount of the first adsorption layer from the amount of adsorbate adsorbed on the sample surface, and the area occupied by one molecule of adsorbate is used to determine the specific surface area. Pore volume and pore distribution are analyzed by dividing the region into micropores (pore diameters of 2.0 nm or less) and mesopores (pore diameters of more than 2.0 nm and less than 50 nm). The micropore region is analyzed using the t method, while the mesopore region is analyzed using the BJH method. The t method analyzes the volume and pore diameter of the micropore region by converting the amount of adsorbate adsorbed on a nonporous sample and the amount of adsorbate adsorbed on a measurement sample into the thickness of the adsorption layer (t) and comparing them. In the mesopore region, the liquefaction phenomenon (capillary condensation) of adsorbate molecules within the pores occurs at a certain relative pressure. The BJH method analyzes the amount of liquefied adsorbate within the pores from the change in pressure and adsorption amount. In the BJH method, pressure can be converted to pore diameter using the Kelvin equation, so the pore volume and pore distribution can be determined.

[0048] The solubility of a molecular catalyst, such as a molybdenum complex, in a solvent affects the ease of adsorption into the pores of activated carbon. Examples of solvents that can be used to dissolve a molybdenum complex include methanol, ethanol, 1-propanol, 2-propanol, hexafluoro-2-propanol, tetrahydrofuran, acetone, acetonitrile, and chloroform. Among these, methanol is preferred due to its low boiling point and high solubility. The temperature at which the molybdenum complex is adsorbed onto activated carbon is preferably 0 to 90°C, more preferably 5 to 40°C, taking into account the decomposition temperature of the molybdenum complex and the boiling point of the solvent. If the adsorption time for the molybdenum complex onto activated carbon is too short, adsorption may not be complete. On the other hand, if the adsorption time is too long, workability may be impaired. Therefore, the time for adsorbing the molybdenum complex onto activated carbon is preferably 30 minutes to 48 hours, more preferably 1 to 24 hours.

[0049] The polymeric material used to bond the catalyst support is preferably a water-insoluble polymeric material that can maintain the catalyst layer structure even in a humid environment. Examples of such polymeric materials include fluororesins such as perfluoroalkoxyalkane (PFA), perfluoroethylenepropene copolymer (FEP), polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene copolymer (ETFE), polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTFE), and ethylene-chlorotrifluoroethylene copolymer (ECTFE), as well as polystyrene, polyvinyl butyral, and poly(4-vinylpyridine). Examples of ion-conductive polymeric materials include DuPont's Nafion®, a fluororesin made by sulfonating and polymerizing tetrafluoroethylene; Dioxide Materials' Sustainion®; and Versogen's PiperION®.

[0050] The catalyst layer may contain an ionic liquid. By disposing the ionic liquid on the catalyst-supported surface of the catalyst layer, the adhesion of excess moisture is suppressed, thereby reducing the generation of hydrogen due to the reduction of water and promoting the ammonia production reaction. The ionic liquid contained in the reduction catalyst 14 can be the same as that used in the above-mentioned electrolytic solution.

[0051] 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 Corporation, and PiperION (registered trademark) from Versogen. An anion exchange membrane is preferably used because it is advantageous for increasing the amount of ammonia produced.

[0052] 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.

[0053] In the ammonia production apparatus 1 shown in FIG. 1, the nitrogen supply unit 7 is a unit that supplies gaseous nitrogen to the first reaction vessel (electrolytic vessel for reduction reaction) 2 and includes a nitrogen supply device 6. The nitrogen supplied from the nitrogen supply device 6 can be, for example, nitrogen in the air, but is not limited thereto. Because air contains approximately 21% oxygen, it is preferable to extract nitrogen by first separating the oxygen. When nitrogen in the air is used, an oxygen separator that separates oxygen from the air and extracts nitrogen is used in the nitrogen supply device 6. The oxygen separation method for separating oxygen from air in the oxygen separator 6 can be, for example, a cryogenic separation method that utilizes differences in boiling points, an adsorption separation method that utilizes differences in the adsorption properties of zeolite adsorbents for gas molecules, or a membrane separation method that utilizes differences in the permeation rate of gas molecules through a membrane. The method can be selected appropriately depending on the cost and scale of the apparatus, and is not particularly limited. The nitrogen supply unit 7 further includes a humidifier 18 that humidifies the nitrogen extracted from the air. It is preferable to supply humidified nitrogen to the first reaction vessel 2.

[0054] Nitrogen gas containing ammonia is discharged from the first reaction tank 2. The discharge pipe of the first reaction tank 2 is connected to an ammonia capture unit 9. The ammonia capture unit 9 is a unit that captures ammonia contained in the gas discharged from the first reaction tank 2, and is equipped with an ammonia capture device 8. The ammonia capture device 8 is not particularly limited, and for example, a device that selectively captures ammonia by bringing the exhaust gas into contact with an aqueous solution (absorbent) having a pH of 0 to 7 for absorbing ammonia is used. Such an ammonia capture device 8 can simultaneously separate by-product hydrogen and unreacted nitrogen contained in the exhaust gas.

[0055] The ammonia captured by the ammonia capture device 8 is contained in the capture liquid and is sent to a first separator 19, which separates the ammonia from the capture liquid. The first ammonia separator 19 may be a distillation method or 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, or a membrane separation method that utilizes differences in the permeation rate of gas molecules through a membrane for separation. The first ammonia separator 19 may be selected appropriately depending on the cost, the scale of the device, and the like, and is not particularly limited. The first ammonia separator 19 is provided with a pipe for recovering the ammonia separated from the capture liquid.

[0056] When ammonia is separated from the collecting liquid by distillation, a distillation column is used as the first ammonia separation device 19. The distillation column is configured to separate ammonia, which has a boiling point lower than that of water used as at least a part of the collecting liquid. In the distillation column, ammonia is separated by distillation from the supplied collecting liquid using a conventional method. Specifically, the collecting liquid is distilled under reduced pressure of 10 to 120 Torr (1333 to 15999 Pa), and ammonia is discharged from a pipe at the top of the distillation column. The ammonia discharged from the pipe is recovered in a tank or the like (not shown).

[0057] Ammonia may be separated by a stripping method, in which the absorbent liquid is brought into contact with steam and the ammonia in the absorbent liquid is transferred to the steam for recovery. In this case, the first ammonia separation unit 19 includes a stripping tower whose interior is divided by perforated plates, and is configured so that the supplied absorbent liquid flows from the upper to the lower section of the stripping tower. The steam flows from the lower section to the upper section and rises through the liquid blocked by the perforated plates. When the absorbent liquid comes into contact with the steam, the ammonia in the absorbent liquid vaporizes and moves into the steam side, and is discharged from the piping at the top of the tower. Furthermore, when a carbonate aqueous solution is used as the absorbent, the ammonia in the absorbent liquid can be converted into ammonium bicarbonate, which can be thermally decomposed in a thermal decomposition unit to separate and recover ammonia and carbon dioxide.

[0058] The second reaction tank 3 is connected to an electrolyte circulation unit 13. The electrolyte circulation unit 13 is a unit that circulates the electrolyte through a circulation pipe 12 so as to extract the produced ammonia-containing electrolyte from the second reaction tank 3 to the outside and to resupply the electrolyte to the second reaction tank 3. The circulation pipe 12 is provided with a liquid feed pump 20 for circulating the electrolyte, and an electrolyte storage tank 21 for storing the electrolyte and adjusting the electrolyte concentration, pH, etc. The electrolyte circulation unit 13 is configured to circulate the electrolyte between the second reaction tank 3 and the electrolyte storage tank 21 by the liquid feed pump 20.

[0059] In FIG. 1, the liquid feed pump 20 is provided in the circulation pipe 12 that sends the electrolyte from the electrolyte storage tank 21 to the second reaction tank 3, but the liquid feed pump 20 may also be provided in the circulation pipe 12 that sends the electrolyte from the second reaction tank 3 to the electrolyte storage tank 21. The electrolyte circulation unit 13 preferably includes an exhaust unit that exhausts excess nitrogen that has not dissolved in the electrolyte and gas generated by the oxidation-reduction reaction. The exhaust unit may be, for example, a pipe equipped with a valve, and is provided, for example, in the electrolyte storage tank 21. The electrolyte storage tank 21 functions as a gas-liquid separation tank, in which oxygen (O2) generated by the oxidation reaction is separated from the electrolyte.

[0060] The ammonia separation unit 10 is a unit that recovers ammonia (NH), a nitrogen reduction product, from the electrolyte. The ammonia separation unit 10 includes a second separator 11 that separates ammonia from the electrolyte, a three-way valve 22 that extracts at least a portion of the electrolyte circulating in a circulation pipe 12, a pipe 23 that sends the electrolyte extracted from the three-way valve 22 to the second separator 10, and a pipe 24 that sends the electrolyte from which ammonia has been separated in the second separator 10 to an electrolyte storage tank 21. The three-way valve 22 is provided in the circulation pipe 12, and the ammonia separation unit 11 is connected to the electrolyte circulation unit 13 via the three-way valve 22. The electrolyte circulating in the circulation pipe 12 can be extracted not only by using the three-way valve 23 provided in the circulation pipe 12, but also by connecting a pipe having a valve to the electrolyte storage tank 21, and the configuration is not particularly limited. The second ammonia separator 8 is applied with the same separation method and has the same configuration as the first ammonia separator 19. The second ammonia separator 8 can have the same configuration as the first ammonia separator 19, except that ammonia is separated from the electrolytic solution instead of the absorbent solution.

[0061] Next, the process for producing ammonia using the above-described ammonia production apparatus will be described. First, in the initial stage, humidified nitrogen gas is supplied to the first reaction tank 2. The electrolyte is supplied to the second reaction tank 3 via the circulation pipe 12. In this state, power is supplied from the external electrode 17 to the reduction electrode 14 and the oxidation electrode 15.

[0062] The external power source 17 may be a conventional commercial power source or a battery, or 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, hydroelectric, geothermal, and tidal energy, into electrical energy; power sources such as solar cells with photoelectric conversion elements that convert light energy into electrical energy; power sources such as fuel cells and storage batteries that convert chemical energy into electrical energy; and devices that convert vibrational energy, such as sound, into electrical energy. Photoelectric conversion elements have 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, single-crystalline silicon solar cells, polycrystalline silicon solar cells, dye-sensitized solar cells, and organic thin-film solar cells.

[0063] By applying power from the external electrode 17 to the reduction electrode 14 and the oxidation electrode 15, water (HO) or hydroxide ions (OH) in the electrolyte are electrochemically converted at the oxidation electrode 15. - For example, when the hydrogen ion concentration of the electrolyte is 7 or less (pH ≦ 7), H2O is oxidized to O2 and H2O according to the following formula (1): + When the hydrogen ion concentration of the electrolyte is greater than 7 (pH>7), OH is generated based on the following formula (2): - is oxidized to produce O2 and H2O 3H2O → 3 / 2O2+6H + +6e - …(1) 6OH - → 3 / 2O2+3H2O+6e - …(2)

[0064] In the first reaction vessel 2, nitrogen (N2) is reduced by the ammonia production catalyst to produce ammonia (NH3). The ammonia production catalyst is as described above. N2 is reduced by the conductive ion species of the diaphragm 4 according to the following formula (3) or formula (4), to produce ammonia (NH3). N2+6H2O+6e -→ 2NH3+6OH - …(3) N2+6H + +6e - → 2NH3…(4)

[0065] The gas containing NH3 produced by the N2 reduction described above is sent via piping to the trapping device 8, where, as described above, the exhaust gas is brought into contact with an aqueous solution (trapping liquid) with a pH of 0 to 7, thereby selectively trapping ammonia. At the same time, by-product hydrogen and unreacted nitrogen contained in the exhaust gas are separated. The trapping liquid containing ammonia is sent to the first ammonia separation device 19, where the ammonia is separated from the trapping liquid.

[0066] A portion of the NH3 produced by N2 reduction is sent to the second reaction tank 3 via the diaphragm 4 and dissolved in the electrolyte. The electrolyte containing NH3 is sent to the electrolyte storage tank 21 via the circulation pipe 12, where oxygen (O2) is separated, and then sent back to the second reaction tank 4. By circulating the electrolyte through the circulation pipe 12, the ammonia concentration in the electrolyte increases. At least a portion of the electrolyte with an increased ammonia concentration is sent to the second ammonia separation device 10 via the three-way valve 22, where the ammonia is separated from the electrolyte.

[0067] The supply of the ammonia-containing electrolyte to the second ammonia separator 10 may be continuous from the start of operation of the apparatus, but is preferably intermittent once the ammonia concentration in the electrolyte has reached a sufficient level. That is, when the ammonia concentration in the electrolyte is low, the energy input for recovering ammonia from the electrolyte becomes greater than the amount of energy stored in the ammonia, resulting in higher ammonia production costs. In response to this issue, an electrolyte containing a high concentration of ammonia can be obtained by circulating the electrolyte through the circulation pipe 12 via the second reaction tank 3 and the electrolyte storage tank 21. It is preferable to send the electrolyte containing a high concentration of ammonia to the second ammonia separator 10. This allows for efficient recovery of ammonia, which is a reduction product of N2. To improve ammonia recovery efficiency, it is preferable to send an electrolyte containing ammonia at a concentration of 0.01 to 50 mass% to the ammonia separator 10.

[0068] In the oxidation-reduction reaction in the electrolytic cell 5 described above, the electrolyte solution sent to the second reaction vessel 3 is preferably an alkaline solution having a pH of more than 7 and not more than 14, as described above. - can be used as carrier ions. This makes it possible to efficiently recover the generated ammonia.

[0069] Next, additional configuration examples and modified examples of the ammonia manufacturing apparatus 1 of the embodiment will be described. The second reaction tank 3 may be provided with a circulation mechanism such as a pump. By promoting the circulation of the electrolyte by the circulation mechanism, ions (H + OH -) can be improved. Furthermore, flow paths may be provided in the first and second reaction vessels 2 and 3, or multiple circulation mechanisms may be provided. Furthermore, multiple (three or more) reaction vessel flow paths may be provided to reduce ion diffusion and circulate ions more efficiently. By creating a liquid flow using a circulation mechanism, it is possible to prevent generated bubbles from remaining on the electrode surface or the reaction vessel surface, thereby promoting the reaction.

[0070] The first and second reaction vessels 2 and 3 may be provided with a temperature adjustment mechanism for adjusting the temperature of the electrolytic solution. By controlling the temperature using the temperature adjustment mechanism, it is possible to control the catalytic performance. For example, by making the temperature of the reaction system uniform, it is possible to stabilize the catalytic performance. It is also possible to prevent temperature rise in order to stabilize the system. The reaction temperature in the electrochemical reaction cell 5 can be appropriately selected in the range of 5 to 95°C, taking into consideration that the electrolytic solution is an aqueous solution, the reaction efficiency, and economic efficiency. Preferably, it is close to room temperature (10 to 40°C).

[0071] The electrochemical reaction cell 5 can increase the reaction area and obtain a larger reaction current by making the electrodes porous. The electrochemical reaction cell 5 may have an electrode structure in which a diaphragm is sandwiched between a porous oxidation electrode and a porous reduction electrode. That is, in the electrochemical reaction cell 5 shown in FIG. 2, the porous oxidation electrode and the porous reduction electrode are arranged in contact with both sides of the diaphragm. An electrolyte is supplied to the surface of the porous oxidation electrode opposite to the surface in contact with the diaphragm. An ammonia production catalyst is arranged on the surface of the porous reduction electrode in contact with the diaphragm, and nitrogen is supplied to the surface of the porous reduction electrode opposite to the surface in contact with the diaphragm. The electrochemical reaction cell 5 may have a porous reduction electrode and a nitrogen supply pipe that supplies nitrogen to the ammonia production catalyst via the porous oxidation electrode. A flow path may be provided in the path through which nitrogen flows. By providing multiple (three or more) gas flow paths, nitrogen can be distributed uniformly to the porous reduction electrode.

[0072] The electrochemical reaction cell 5 may have an electrolyte between the porous reduction electrode and the diaphragm. That is, the electrochemical reaction cell 5 shown in Fig. 3 can be supplied with nitrogen from the side of the reduction electrode 14 opposite to the ammonia production catalyst. In this way, the structure of the electrochemical reaction cell 5 can be modified in various ways. [Example]

[0073] Next, examples and their evaluation results will be described.

[0074] Example 1 [Cathode fabrication] The cathode was fabricated by spraying catalytic ink onto carbon paper with a carbon particle layer (MPL layer). The catalytic ink used for the cathode contained activated carbon A (BET average pore diameter: 3.37 nm, specific surface area: 1300 m) as a carrier for the molybdenum complex. 2 / g, pore volume: 0.36 cm 2 The catalyst ink was prepared using a catalyst having a molecular weight of 1000 to 12000 kJ / g, Sustainion (registered trademark) from Dioxide Materials, which is an anion exchange resin, as the ionomer, and 2-propanol as the dispersion medium. Activated carbon, ionomer, and 2-propanol were mixed in a glass vial and dispersed for 20 minutes using an ultrasonic homogenizer to prepare a catalyst ink. The catalyst ink was then spray-coated onto carbon paper (MB-30 (trade name) manufactured by Avcarb) fixed to a metal plate and heated to 90°C, forming a catalyst layer. The catalyst layer was applied to the MPL layer side. At this time, the catalyst layer was applied to 1 cm of the coated surface. 2 The amount of activated carbon per electrode was 0.7 mg, and the amount of ionomer per electrode was 0.08 mg. Next, the electrode with the catalyst layer formed was immersed in a catalyst solution (1 mg of molybdenum complex dissolved in 10 mL of methanol) prepared by dissolving a molybdenum triiodo complex (ligand: 1,3-bis(ditertiarybutylphosphinomethylbenzimidazol-2-ylidene), a PCP ligand) in methanol at room temperature in an argon atmosphere for 1 hour. The electrode was then air-dried under an argon stream to form a cathode (20 mm x 20 mm square). 0.1 mg of the molybdenum complex was adsorbed onto the activated carbon of the cathode.

[0075] [Preparation of anode] The anode was made by etching titanium into a mesh structure, increasing the surface area, and forming iridium oxide as an oxidation catalyst on the wire mesh (20 mm x 20 mm square).

[0076] [Fabrication of membrane electrode assembly and N2 electrolysis cell] A membrane electrode assembly (catalyst area 400 mm) was stacked between the anode and cathode, sandwiching a Dioxide Materials Sustainion® membrane (25 mm x 25 mm square) as a separator. 2 ) was prepared. The cathode catalyst layer and the anion exchange membrane were arranged so as to be in contact with each other. The membrane electrode assembly was sandwiched between a titanium channel (serpentine, land width 0.4 mm, channel width 1.5 mm, channel depth 1 mm) via a Teflon (registered trademark) gasket, to assemble an N2 electrolysis cell.

[0077] [Controlled potential electrolysis measurement (ammonia production experiment)] A 0.1 M potassium sulfate solution was supplied to the anode channel of the N2 electrolysis cell at 1 mL / min as the electrolyte. The pH of the electrolyte was 7. Meanwhile, saturated humidified 100% N2 gas was supplied to the cathode channel at 40 mL / min at room temperature. A power supply (Solartron Cell Test System, Toyo Corporation) was connected to the outside of the cathode and anode channels, and a voltage of 3.0 V was applied for 1 hour. The reduction products generated at the cathode of the N2 electrolysis cell were analyzed. The liquid and gas discharged from the cathode channel were collected in a 10 mM aqueous sulfuric acid solution as an ammonia collection solution, and ammonia was quantified. Furthermore, the gas after ammonia collection was sampled, and hydrogen was quantified by gas chromatography (Varian Micro GC CP4900).

[0078] [Ammonia determination method (indophenol method)] Ammonia was quantified using the indophenol method. The analytical procedure for the indophenol method is as follows: 2.5 ml of the ammonia collection solution was mixed with 5 ml of coloring solution (1) (5 g of phenol and 25 mg of sodium nitroprusside (Na2[Fe(CN)5(NO)]·2H2O) in purified water to a final volume of 500 ml), followed by mixing. 5 ml of coloring solution (2) (2.5 g of sodium hydroxide and 4.2 ml of sodium hypochlorite in purified water to a final volume of 500 ml) was then added and mixed. The solution was allowed to stand at room temperature for at least 30 minutes. The absorbance of the indophenol derivative at around 640 nm was measured using a UV-visible absorption spectrophotometer (Shimadzu, UV-2500PC) to quantify ammonia.

[0079] The faradaic efficiency was calculated based on the current consumed in the reduction reaction at the cathode and quantitative analysis of the reduction products. The faradaic efficiency is expressed as the ratio of the amount of electricity required to produce the reduction product to the amount of electricity input. The faradaic efficiency of each analyzed reduction product was taken as the product selectivity (%). In the N2 electrolysis cell prepared by the above method, the ammonia selectivity was 0.15%.

[0080] Example 2 Activated carbon A used for the cathode was replaced with activated carbon B (BET average pore diameter: 1.57 nm, specific surface area: 1350 m 2 / g, pore volume: 0.35 cm 2 An N2 electrolytic cell was prepared in the same manner as in Example 1, except that the N2 electrolytic cell was changed to ammonia (CO₂ / g). Using this N2 electrolytic cell, an attempt was made to produce ammonia in the same manner as in Example 1. As a result, the ammonia selectivity was 0.08%.

[0081] Example 3 Activated carbon A used for the cathode was replaced with activated carbon C (BET average pore diameter: 9.1 nm, specific surface area: 1250 m 2 An N2 electrolytic cell was prepared in the same manner as in Example 1, except that the N2 electrolytic cell was changed to ammonia (ammonia gas: 0.33 cm2 / g, pore volume: 0.33 cm2 / g). Using this N2 electrolytic cell, an attempt was made to produce ammonia in the same manner as in Example 1. As a result, the ammonia selectivity was 0.12%.

[0082] (Comparative Example 1) Activated carbon A used for the cathode was replaced with activated carbon D (BET average pore diameter: 30 nm, specific surface area: 1100 m 2 / g, pore volume: 0.31 cm 2 An N2 electrolytic cell was prepared in the same manner as in Example 1, except that the N2 concentration was changed to 1 / g. 2 Using the electrolytic cell, an attempt was made to produce ammonia in the same manner as in Example 1. As a result, the selectivity for ammonia was 0.01%.

[0083] According to Examples 1 to 3 and Comparative Example 1, it is clear that the BET average pore size of activated carbon that can suitably retain a molybdenum complex is 1 to 15 nm, and more preferably 2 to 10 nm.

[0084] Example 4 An N2 electrolysis cell was prepared in the same manner as in Example 1, except that the diaphragm used in the membrane electrode assembly was changed to a porous membrane (a hydrophilically treated PTFE membrane manufactured by Sumitomo Electric Industries, Ltd., with a pore size of 0.1 μm and a thickness of 60 μm). Using this N2 electrolysis cell, ammonia production was attempted in the same manner as in Example 1. As a result, the ammonia selectivity was 0.21%.

[0085] Example 5 An N2 electrolytic cell was prepared in the same manner as in Example 1, except that the electrolyte supplied to the anode flow path of the N2 electrolytic cell was changed to 0.1 M 1-ethyl-3-methylimidazolium tetrafluoroborate. Using this N2 electrolytic cell, ammonia production was attempted in the same manner as in Example 1. As a result, the ammonia selectivity was 0.23%.

[0086] Example 6 The cathode prepared in Example 1 was immersed in a 50% methanol solution of 1-hexyl-3-methylimidazolium bis(trifluoromethoxysulfonyl)imide for 30 minutes and then air-dried in the air to impregnate the cathode with an ionic liquid. Ammonia production was attempted in the same manner as in Example 1, except for using this cathode. The result was ammonia selectivity of 0.33%.

[0087] Example 7 An N2 electrolysis cell was fabricated in the same manner as in Example 1, except that the electrolyte supplied to the anode flow channel of the N2 electrolysis cell was changed to 0.1 M potassium carbonate (pH = 10). Using this N2 electrolysis cell, ammonia production was attempted in the same manner as in Example 1. As a result, the ammonia selectivity was 0.17%.

[0088] Example 8 An N2 electrolysis cell was fabricated in the same manner as in Example 1, except that the electrolyte supplied to the anode flow channel of the N2 electrolysis cell was changed to 0.1 M potassium hydroxide (pH = 13). Using this N2 electrolysis cell, ammonia production was attempted in the same manner as in Example 1. As a result, the ammonia selectivity was 0.14%.

[0089] Example 9 An N2 electrolysis cell was fabricated in the same manner as in Example 1, except that the diaphragm used in the membrane electrode assembly was changed to a Nafion membrane (N117 membrane immersed in a 1 M KOH aqueous solution and exchanged with potassium ions). Using this N2 electrolysis cell, ammonia production was attempted in the same manner as in Example 1. As a result, the ammonia selectivity was 0.41%.

[0090] Example 10 An N2 electrolytic cell was prepared in the same manner as in Example 1, except that the ionomer used in the cathode was changed to PTFE and the electrode was baked at 340°C for 30 minutes. Using this N2 electrolytic cell, ammonia production was attempted in the same manner as in Example 1. As a result, the ammonia selectivity was 0.34%.

[0091] 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.

[0092] The technical solutions of the above-mentioned embodiments are as follows: (Technical proposal 1) An ammonia manufacturing apparatus comprising an electrochemical reaction cell including: a first reaction tank in which a reduction electrode is disposed and to which gaseous nitrogen is supplied; a second reaction tank in which an oxidation electrode is disposed and to which a water-containing electrolytic solution or water vapor is supplied; and a diaphragm provided between the first reaction tank and the second reaction tank, the reduction electrode comprises a reduction catalyst that reduces nitrogen to produce ammonia, a porous carbon material that supports the reduction catalyst, and an organic polymer material that binds the porous carbon material; The porous carbon material has pores with a BET average pore diameter of 1 nm or more and 15 nm or less. (Technical proposal 2) The ammonia production apparatus according to Technical Solution 1, wherein the reduction catalyst comprises a molybdenum complex. (Technical proposal 3) The ammonia production apparatus according to Technical Scheme 1 or 2, wherein the organic polymer comprises an anion exchange resin. (Technical proposal 4) The ammonia manufacturing apparatus according to any one of Technical Schemes 1 to 3, wherein the electrolytic solution supplied to the second reaction tank has a pH greater than 7 and less than or equal to 14. (Technical proposal 5) The specific surface area of ​​the porous carbon material is 800m 2 / g or more 2000m 2 / g or less. (Technical proposal 6) The porous carbon material has an average pore volume of 0.2 cm 3 / g or more 5cm 3 / g or less. (Technical proposal 7) a nitrogen supply unit including a nitrogen supply unit that introduces gaseous nitrogen into the first reaction tank; an ammonia capture unit including an ammonia capture section that captures ammonia contained in the discharge from the first reaction tank; an ammonia separation unit including an ammonia separation section that separates ammonia from the electrolytic solution discharged from the second reaction tank; The ammonia manufacturing apparatus according to any one of Technical Schemes 1 to 6, comprising: (Technical proposal 8) The ammonia manufacturing apparatus according to Technical Proposal 7 further comprises an electrolyte circulation unit including a circulation pipe for circulating the electrolyte contained in the second reaction tank outside the second reaction tank, and an electrolyte storage tank disposed in the circulation pipe for storing the electrolyte. (Technical proposal 9) The ammonia manufacturing apparatus according to Technical Scheme 7 or 8, wherein the nitrogen supply unit includes an oxygen separation device that separates oxygen in the air to extract nitrogen as the nitrogen supply section, and a humidification device that humidifies the separated nitrogen. (Technical proposal 10) The ammonia manufacturing apparatus according to any one of Technical Schemes 7 to 9, wherein the ammonia capture unit includes, as the ammonia capture section, a capture device that brings the gas discharged from the first reaction tank into contact with a capture liquid containing an aqueous solution having a pH of 1 or more and 7 or less to capture the ammonia. (Technical proposal 11) The ammonia production apparatus according to Technical Proposal 10, wherein the ammonia capture unit further comprises a separation device that applies a distillation method, a cryogenic separation method, an adsorption separation method, or a membrane separation method to separate ammonia from the capture liquid that has captured ammonia. (Technical proposal 12) an electrochemical reaction 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; supplying gaseous nitrogen into the first reaction tank and supplying a water-containing electrolytic solution or water vapor into the second reaction tank; supplying electric power to the reduction electrode and the oxidation electrode, reducing nitrogen in the first reaction tank by the reduction electrode to produce ammonia, and oxidizing the electrolytic solution or water vapor in the second reaction tank by the oxidation electrode; and separating ammonia from the effluent of the first reaction vessel to produce ammonia; the reduction electrode comprises a reduction catalyst that reduces nitrogen to produce ammonia, a porous carbon material that supports the reduction catalyst, and an organic polymer material that binds the porous carbon material; The method for producing ammonia, wherein the porous carbon material has pores with a BET average pore diameter of 1 nm or more and 15 nm or less. (Technical proposal 13) The method for producing ammonia according to Technical Scheme 12, wherein the electrolytic solution supplied to the second reaction vessel has a pH greater than 7 and less than or equal to 14. (Technical proposal 14) The method for producing ammonia according to Technical Scheme 12 or 13, further comprising the steps of circulating the electrolytic solution outside the second reaction tank, extracting at least a portion of the circulating electrolytic solution, separating ammonia from the extracted electrolytic solution, and sending the electrolytic solution from which ammonia has been separated to the second reaction tank. (Technical proposal 15) 15. The method for producing ammonia according to any one of Technical Schemes 12 to 14, wherein the reduction catalyst comprises a molybdenum complex. [Explanation of symbols]

[0093] 1...ammonia production apparatus, 2...first reaction tank (electrolytic tank for reduction reaction), 3...second reaction tank (electrolytic tank for oxidation reaction), 4...diaphragm, 5...electrochemical reaction unit (electrolytic cell), 6...nitrogen supply section (supply device), 7...nitrogen supply unit, 8...ammonia separation section (separator), 9...ammonia separation unit, 8...ammonia capture section (capture device), 9...ammonia capture unit, 10...ammonia separation section (separator), 11...ammonia separation unit, 12...circulation piping, 13...electrolyte circulation unit, 14...reduction electrode, 15...oxidation electrode, 16...third reaction tank, 18...humidifier, 19...ammonia separator, 20...liquid transfer pump, 21...electrolyte storage tank, 22...three-way valve, 23, 24...piping.

Claims

1. An ammonia manufacturing apparatus comprising an electrochemical reaction cell including: a first reaction tank in which a reduction electrode is disposed and to which gaseous nitrogen is supplied; a second reaction tank in which an oxidation electrode is disposed and to which a water-containing electrolytic solution or water vapor is supplied; and a diaphragm provided between the first reaction tank and the second reaction tank, the reduction electrode comprises a reduction catalyst that reduces nitrogen to produce ammonia, a porous carbon material that supports the reduction catalyst, and an organic polymer material that binds the porous carbon material; the porous carbon material has pores with a BET average pore diameter of 1 nm or more and 15 nm or less, The ammonia production apparatus, wherein the reduction catalyst comprises a molybdenum complex.

2. The ammonia production apparatus according to claim 1 , wherein the organic polymer material comprises an anion exchange resin.

3. 2. The ammonia manufacturing apparatus according to claim 1, wherein the electrolytic solution supplied to the second reaction tank has a pH greater than 7 and not greater than 14.

4. The specific surface area of ​​the porous carbon material is 800 m ２ / g or more 2000m ２ 2. The ammonia manufacturing apparatus according to claim 1, wherein the SiO2 content is 0.15 / g or less.

5. The average pore volume of the porous carbon material is 0.2 cm ３ / g or more 5cm ３ 2. The ammonia manufacturing apparatus according to claim 1, wherein the SiO2 content is 0.15 / g or less.

6. a nitrogen supply unit including a nitrogen supply section that introduces gaseous nitrogen into the first reaction tank; an ammonia capture unit including an ammonia capture section that captures ammonia contained in the discharge from the first reaction tank; an ammonia separation unit including an ammonia separation section that separates ammonia from the electrolytic solution discharged from the second reaction tank; The ammonia production apparatus according to claim 1, comprising:

7. 7. The ammonia manufacturing apparatus according to claim 6, further comprising: an electrolyte circulation unit including: a circulation pipe for circulating the electrolyte contained in the second reaction tank outside the second reaction tank; and an electrolyte storage tank disposed in the circulation pipe for storing the electrolyte.

8. 7. The ammonia manufacturing apparatus according to claim 6, wherein the nitrogen supply unit comprises, as the nitrogen supply section, an oxygen separation device that separates oxygen in air to extract nitrogen, and a humidification device that humidifies the separated nitrogen.

9. 7. The ammonia manufacturing apparatus according to claim 6, wherein the ammonia capture unit includes, as the ammonia capture section, a capture device that brings the gas discharged from the first reaction tank into contact with a capture liquid containing an aqueous solution having a pH of 1 or more and 7 or less to capture the ammonia.

10. The ammonia production apparatus according to claim 9, wherein the ammonia capture unit further comprises a separation device that applies a distillation method, a cryogenic separation method, an adsorption separation method, or a membrane separation method to separate ammonia from the capture liquid that has captured ammonia.

11. an electrochemical reaction 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; supplying gaseous nitrogen into the first reaction tank and supplying a water-containing electrolytic solution or water vapor into the second reaction tank; supplying electric power to the reduction electrode and the oxidation electrode, reducing nitrogen in the first reaction tank by the reduction electrode to produce ammonia, and oxidizing the electrolytic solution or water vapor in the second reaction tank by the oxidation electrode; and separating ammonia from the effluent of the first reaction vessel to produce ammonia; the reduction electrode comprises a reduction catalyst that reduces nitrogen to produce ammonia, a porous carbon material that supports the reduction catalyst, and an organic polymer material that binds the porous carbon material; the porous carbon material has pores with a BET average pore diameter of 1 nm or more and 15 nm or less, The method for producing ammonia, wherein the reduction catalyst comprises a molybdenum complex.

12. 12. The method for producing ammonia according to claim 11, wherein the electrolytic solution supplied to the second reaction vessel has a pH greater than 7 and not greater than 14.

13. 12. The method for producing ammonia according to claim 11, further comprising the steps of circulating the electrolytic solution outside the second reaction tank, withdrawing at least a portion of the circulating electrolytic solution, separating ammonia from the withdrawn electrolytic solution, and sending the electrolytic solution from which ammonia has been separated to the second reaction tank.

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