Ammonia production method and ammonia production device

Abstract

Provided are a method for producing ammonia by an electrolytic synthesis reaction using a molded body containing an MOF, and an ammonia production device.　This ammonia production method uses a molded body that contains a metal-organic framework and has a proton conductivity of 1.0 × 10−9 S / cm or more, and a positive electrode and a negative electrode. The molded body is disposed so as to be in contact with at least one of the positive electrode and the negative electrode, so that ammonia is produced by an electrolytic synthesis reaction.　

Description

Method for producing ammonia and ammonia production apparatus

[0001] The present invention relates to a method for producing ammonia and an ammonia production apparatus.

[0002] Ammonia (NH １－ｘ ) is used in industrial processes as a raw material for chemical fertilizers, nitric acid, and other organic compounds such as nylon fibers. NH ３ does not generate carbon dioxide (CO ２ ), which is a greenhouse gas, even when burned, and can be easily stored and transported by liquefaction. Therefore, it is also expected as an energy source for thermal power generation and the like.

[0003] NH ３ is produced by an industrial synthesis process in which nitrogen (N ２ ) and hydrogen (H ２ ) are reacted using a catalyst mainly composed of iron (Fe). However, the conventional industrial synthesis process requires severe reaction conditions of a high temperature of 400°C to 600°C and a high pressure of 100 atmospheres or more (for example, 20 MPa), resulting in high energy consumption and a problem of generating a large amount of CO ２ during the production process.

[0004] As a new ammonia synthesis method alternative to the Haber - Bosch method, an electrolytic synthesis method using a proton - conductive electrolyte has been attracting attention. Examples of proton - conductive electrolytes include organic polymers or inorganic oxides. For example, Non - Patent Document 1 discloses that proton - conductive perovskite - type oxides represented by BaZr ３ Y ｘ O ３－δ and BaCe １－ｘ Y ｘ O ３－δ are used as electrolytes in the electrolytic synthesis method of NH ３ . Further, Non - Patent Document 2 discloses an electrolytic synthesis method of NH ０．９ using a proton - conductive solid electrolyte and a nickel (Ni) cermet electrode, regarding BaCe ０．１ O <00​​It has been disclosed that (BCY) is used as an electrolyte.

[0005] Naohiro Shimoda et.al., "Ammonia synthesis over yttrium-doped barium zirconate and cerate-based perovskite-type oxide supported ruthenium catalysts" International Journal of hydrogen energy, 42(2017)29745-29755 Naohiro Shimoda et.al., "Electrochemical synthesis of ammonia using a proton conducting solid electrolyte and nickel cermet electrode" Journal of the Ceramic Society of Japan 125(4)252-256 2017

[0006] NH ３ When an inorganic oxide is used as an electrolyte in the electrolytic synthesis method of, since the reaction is carried out in a high temperature range of exceeding 300 ° C and about 400 ° C to 600 ° C, the decomposition reaction of the generated NH ３ may be promoted. On the other hand, when an organic polymer is used as an electrolyte in the electrolytic synthesis method of NH ３ , since the reaction is carried out in a low temperature range of less than 100 ° C, the problem is that the catalytic activity is low.

[0007] Therefore, as a method for producing ammonia that solves the above problems, the present invention provides a method for producing ammonia by an electrolytic synthesis reaction and an apparatus for producing ammonia, using a molded body containing a metal-organic framework (hereinafter also referred to as "MOF") having a polymer structure, which is a combination of a metal ion and a crosslinkable ligand that links the metal ions.

[0008] The first aspect of the present invention includes a metal-organic framework and has a proton conductivity of 1.0×10 －９We propose a method for producing ammonia by an electrolytic synthesis reaction, using a molded body with a density of S / cm or higher, a positive electrode, and a negative electrode, wherein the molded body is arranged in contact with at least one of the positive electrode and the negative electrode.

[0009] A second aspect of the present invention includes a metal-organic structure having a proton conductivity of 1.0 × 10 －９ We propose an ammonia production apparatus for producing ammonia by an electrolytic synthesis reaction, comprising a molded body with a density of S / cm or higher, a positive electrode and a negative electrode, wherein the molded body is arranged to be in contact with at least one of the positive electrode and the negative electrode.

[0010] This invention uses a molded article containing MOF to efficiently produce (specifically 4.0 × 10) through an electrolytic synthesis reaction. －１２ mol / s / cm ２ A method for producing ammonia (at the above production rate) can be provided.

[0011] This is a schematic diagram of an electrochemical cell used for the electrolytic synthesis reaction of ammonia, comprising a positive electrode, a negative electrode, and a molded body containing MOF.

[0012] Next, the present invention will be described based on examples of embodiments. However, the present invention is not limited to the embodiments described below.

[0013] Embodiments of the present invention include a metal-organic structure having a proton conductivity of 1.0 × 10⁻⁶ －９ We propose a method for producing ammonia by an electrolytic synthesis reaction, using a molded body with a density of S / cm or higher, a positive electrode, and a negative electrode, wherein the molded body is arranged in contact with at least one of the positive electrode and the negative electrode.

[0014] The proton conductivity (S / cm) of a molded body containing a metal-organic structure is measured under the following measurement condition 1. Measurement condition 1 A Pt paste is applied to one side of a test specimen made of the molded body, and an Ag / Pd paste is applied to the other side, both by screen printing to an area of ​​10 mm in length and 10 mm in width, respectively. After drying, electrodes are formed on both sides of the test specimen. An AC current of 100 mV is applied between the two electrodes at 170°C in an atmosphere of dry nitrogen gas flowing at 100 mL / min. Complex impedance analysis is performed in the frequency range of 0.1 Hz to 0.5 MHz, and the proton conductivity (S / cm) is determined from the total resistance component of the test specimen.

[0015] Ammonia is produced by electrolytic synthesis by electrolyzing water and reacting it with nitrogen. Figure 1 is a schematic diagram of an electrochemical cell used for the electrolytic synthesis of ammonia, comprising a positive electrode, a negative electrode, and a molded body containing MOF. The electrochemical cell can be used in the ammonia production apparatus described later.

[0016] The production of ammonia by electrolytic synthesis involves water (H ２ O), or water (H ２ O) and nitrogen (N) ２ ) is supplied from the positive electrode side inlet 4 to the positive electrode 2, and water (H) is supplied to the positive electrode 2. ２ O) is electrolyzed to produce protons (H ＋ ) is generated. Protons (H) generated at positive electrode 2 ＋ ) is supplied to the negative electrode 3 through the molded body 1 containing MOF. Nitrogen (N) is supplied to the negative electrode 3 from the negative electrode inlet 5. ２ ) is supplied to the negative electrode 3. Protons (H) supplied from the positive electrode 2 to the negative electrode 3 through the molded body 1 containing MOF are supplied to the negative electrode 3. ＋ ) is nitrogen (N) supplied from the negative electrode inlet 5 to the negative electrode 3. ２ ) reacts with ammonia (NH ３ ) is synthesized. Nitrogen (N) is released from the positive electrode outlet 6. ２ ), oxygen (O ２ ) and water (H ２ O) flows out, and nitrogen (N) exits from the negative electrode outlet 7. ２ ) and ammonia (NH) produced by synthesis ３) flows out. The positive and negative electrodes may have catalysts on their electrode surfaces, or the electrodes themselves may function as catalysts. Furthermore, the electrolytic synthesis reaction of ammonia is represented by the following reaction equation (I). N ２ +3H ２ O→2NH ３ +3 / 2O ２ (I) If the molded body 1 containing the MOF contains a nitrogen-containing compound, in addition to the above reaction, ammonia (NH4) may be produced by an electrolytic synthesis reaction using the nitrogen-containing compound contained in the molded body 1 containing the MOF as a reaction source. ３ ) may be manufactured. For example, if the molded body 1 containing MOF contains polyamide-imide, the water (H) supplied from the positive electrode side inlet 4 to the positive electrode 2 ２ O) promotes the hydrolysis reaction of polyamide-imide, generating an amine compound, which then promotes electrochemical oxidation and hydrolysis, resulting in ammonia (NH₄). ３ ) may leak out. Examples of nitrogen-containing compounds included in the molded body 1 containing MOF include amide compounds, amino compounds, and nitrogen-containing heteroaromatic compounds.

[0017] The molded body in contact with at least one of the positive and negative electrodes includes a MOF. Preferably, the MOF is proton conductive. The molded body may further contain a proton conductive material. In this specification, "proton conductive" means conducting protons or oxonium ions when a potential gradient is applied.

[0018] MOFs have a polymer structure that combines metal ions with crosslinking ligands that link the metal ions. If the molded article is made of, for example, a proton-conducting organic polymer, it is not suitable for practical use at temperatures above 100°C because the heat resistance of the organic polymer is relatively low. If ammonia is produced by electrolytic synthesis at temperatures below 100°C, the activity of the catalyst may be low, and ammonia may not be produced efficiently. If the molded article is made of a proton-conducting inorganic oxide, as described in Non-Patent Documents 1 and 2 above, the proton conductivity increases at temperatures above 300°C, for example, above 350°C. If ammonia is produced by electrolytic synthesis at temperatures above 300°C, the decomposition reaction of the generated ammonia is accelerated due to the high temperature, and ammonia may not be produced efficiently. If the molded article contains an MOF, it functions as a proton conductor at a higher temperature than when the molded article is a proton-conducting organic polymer, and the proton conductivity increases at a lower temperature than when the molded article is a proton-conducting inorganic oxide. Therefore, electrolytic synthesis of ammonia can be carried out at a temperature where catalytic activity is high and the generated ammonia does not decompose, allowing for efficient ammonia production.

[0019] The electrolytic synthesis reaction is preferably carried out at a temperature between 100°C and 300°C. Specifically, the temperature at which the electrolytic synthesis reaction is carried out may be the temperature of the electrochemical cell. It contains MOF and has a proton conductivity of 1.0 × 10⁻⁶. －９ Molded articles with a density of S / cm or higher can produce ammonia by electrolytic synthesis in a temperature range of 100°C to 300°C, activating the electrode catalyst and efficiently producing ammonia at a temperature that does not decompose the generated ammonia. The electrolytic synthesis reaction is more preferably carried out at 105°C to 280°C, even more preferably at 110°C to 250°C, even more preferably at 130°C to 220°C, and particularly preferably at 150°C to 200°C.

[0020] The molded article of the present invention has a proton conductivity of 1.0 × 10 as measured under the above-described measurement condition 1. －９ It is S / cm or higher. From the viewpoint of promoting the electrolytic synthesis of ammonia, 1.0 × 10－８ It is preferable that the ratio is S / cm or higher, and 2.0 × 10 －８ It is more preferable that the ratio be S / cm or higher, and 3.0 × 10 －８ It is even more preferable that the ratio be S / cm or higher, and 1.0 × 10 －７ It is particularly preferable that the proton conductivity of the molded body measured under the aforementioned measurement condition 1 is 1.0 × 10⁻⁶. －９ When the proton conductivity is 1.0 × 10⁻⁶ or higher, the electrolytic synthesis reaction of ammonia can be promoted at a lower temperature than when the proton conductor is an inorganic oxide. There is no particular upper limit on the proton conductivity of the molded body. For example, the proton conductivity of the molded body is 1.0 × 10⁻⁶. －２ The effects of the present invention are fully realized when the proton conductivity is 1.0 × 10⁻⁶ or less. －４ A value of S / cm or less is also acceptable. The proton conductivity of the molded body can be set to the desired value by adjusting the combination and content of substances contained in the molded body, such as MOF, binder polymers, and dispersants.

[0021] The metal ions contained in the MOF are not particularly limited, but it is preferable that they be one or more selected from the group consisting of alkali metals, alkaline earth metals, transition metals, group 12 metal elements, and group 13 metal elements; more preferably that they be one or more selected from the group consisting of zinc ions, chromium ions, aluminum ions, magnesium ions, calcium ions, potassium ions, manganese ions, iron ions, cobalt ions, nickel ions, copper ions, yttrium ions, and zirconium ions; and even more preferably that they be one or more selected from the group consisting of zinc ions, chromium ions, aluminum ions, iron ions, cobalt ions, nickel ions, copper ions, and zirconium ions. By using such metal ions, an MOF with excellent stability at temperatures above 100°C can be obtained.

[0022] The crosslinking ligands included in the MOF are not particularly limited, but from the viewpoint of further enhancing the chemical stability of the MOF, it is preferable that the crosslinking ligands include polydentate ligands having two or more coordination sites capable of coordinating to metal ions. Examples of crosslinking ligands include phosphoric acid, polycarboxylic acids, amino acids, polyamines, nitrogen-containing heteroaromatic compounds and their anions, as well as oxide ions (O ２－ Preferably, one or more selected from the group consisting of ) can be used. The term "these anions" refers to the anions produced when the acidic functional group in the crosslinkable ligand exemplified above is deprotonated, and if there are multiple acidic protons in the ligand, it includes anions produced when only some of them are deprotonated and anions produced when all of them are deprotonated. For example, the phosphoric acid anion refers to the phosphate ion, hydrogen phosphate ion, and dihydrogen phosphate ion.

[0023] Polycarboxylic acids are compounds having two or more carboxyl groups, and examples include dicarboxylic acids, tricarboxylic acids, and tetracarboxylic acids. Examples of dicarboxylic acids include oxalic acid, butanediic acid, (E)-butenioic acid, benzene-1,4-dicarboxylic acid, benzene-1,3-dicarboxylic acid, 2-bromo-1,4-benzenedicarboxylic acid, biphenyl-4,4'-dicarboxylic acid, 2,5-dihydroxy-1,4-benzenedicarboxylic acid, (2E,4E)-hexa-2,4-dienediic acid, 1,4-naphthalenedicarboxylic acid, 2,5-naphthalenedicarboxylic acid, 1,4-anthracenedicarboxylic acid, 9,10-anthracenedicarboxylic acid, pyrene-2,7-dicarboxylic acid, 4,5,9,10-tetrahydropyrene-2,7-dicarboxylic acid, and 1H-pyrazole-3,5-dicarboxylic acid. Examples of tricarboxylic acids include benzene-1,3,5-tricarboxylic acid, biphenyl-3,4',5-tricarboxylic acid, and 1,3,5-tris(4-carboxyphenyl)benzene. An example of a tetracarboxylic acid is biphenyl-3,3',5,5'-tetracarboxylic acid.

[0024] An amino acid is a compound that contains at least one amino group and at least one carboxyl group in its molecule. In this specification, "amino group" refers to a primary amino group (-NH ２ ), secondary amino group (-NHR １ ) and tertiary amino group (-NR １ R ２ This refers to amino acids. Examples of amino acids include 2-amino-1,4-benzenedicarboxylic acid, aspartic acid, and glutamic acid.

[0025] Polyamines are compounds having two or more amino groups, and examples include diamines, triamines, and tetraamines. Examples of diamines include piperazine and 1,4-diazabicyclo[2.2.2]octane. Examples of triamines include biphenyl-3,4',5-triamine and 1,3,5-tris(4-aminophenyl)benzene. An example of a tetracarboxylic acid is biphenyl-3,3',5,5'-tetraamine.

[0026] A nitrogen-containing heteroaromatic compound is a compound having at least one nitrogen atom on its heteroaromatic ring, wherein the nitrogen atom can coordinate to a metal ion via its lone pair of electrons. Examples of nitrogen-containing heteroaromatic compounds include (i) a compound having two or more nitrogen atoms on its heteroaromatic ring, or (ii) a compound having one or more nitrogen atoms on its heteroaromatic ring and having one or more functional groups that can coordinate to a metal ion, such as a carboxyl group or an amino group. Furthermore, the two or more nitrogen atoms contained in the compound in (i) may be present on a single heteroaromatic ring, or they may be separated and present on two or more different heteroaromatic rings. Examples of compounds having two or more nitrogen atoms on a heteroaromatic ring in (i) include adenine, 4,4'-bipyridine, pyrimidine, pyrazine, 1,2,4-triazole, 1,3,5-triazine, imidazole, 5,6-dimethylbenzimidazole, 1H-benzimidazole, and 2-methylimidazole. Examples of compounds having one or more nitrogen atoms on a heteroaromatic ring and one or more functional groups capable of coordinating with metal ions, such as a carboxyl group and an amino group, include pyridine-4-carboxylic acid and pyridine-3-carboxylic acid.

[0027] The crosslinking ligands are not limited to those exemplified above. For example, the crosslinking ligand may be a derivative of the compounds exemplified above. In this specification, "derivative" means a compound in which part of the chemical structure is replaced with other atoms or groups of atoms, for example, a compound in which one or more hydrogen atoms in the chemical structure are replaced with a hydrocarbon group having 1 to 4 carbon atoms. Specific examples of derivatives of imidazole include 2-methylimidazole, 2-ethylimidazole, histamine, histidine, etc.

[0028] Examples of MOFs include MOF-303, DMAS_Znox, ZnPIm, MIL-101, MIL(20)-1, and MIP-202(Zr). MOF-303 contains Al ions. DMAS_Znox contains Zn ions. ZnPIm contains Zn ions. MIL-101 contains Cr ions. MIL(20)-1 contains Cr ions. MIP-202(Zr) contains Zr ions. The proton conductivity of the molded body containing the metal-organic structure, measured under the aforementioned measurement condition 1, is 1.0 × 10⁻⁶. －９ To achieve a ratio of S / cm or higher, it is preferable to use one or more MOFs selected from the group consisting of DMAS_Znox, ZnPIm, and MIL(20)·1, and two or more may be used. When one or more MOFs selected from the group consisting of DMAS_Znox, ZnPIm, and MIL(20)·1 are included in the molded article, these MOFs have sufficient proton conductivity and are mixed substantially uniformly in the mixture used in the manufacture of the molded article, and can be distributed substantially uniformly in the molded article, resulting in a ratio of 1.0 × 10⁻⁶. －９ Having a proton conductivity of S / cm or higher, it can efficiently produce ammonia by electrolytic synthesis at a temperature between 100°C and 300°C, which is higher than the temperature when using proton-conducting organic polymers and lower than the temperature when using proton-conducting inorganic oxides.

[0029] The molded body is preferably an electrolyte membrane containing MOF and a binder polymer. When the molded body is an electrolyte membrane containing MOF and a binder polymer, its heat resistance and flexibility are increased, improving handling. As a result, it becomes easier to position the molded body in contact with at least one of the positive and negative electrodes, facilitating the electrolysis of water at the positive electrode and facilitating the conduction of protons generated by electrolysis to the negative electrode. This allows the molded body to maintain a stable state even when placed in a humidified condition.

[0030] When the molded article is an electrolyte membrane containing MOF and a binder polymer, it is preferable that the binder polymer be contained in a range of 5% to 90% by mass, more preferably in a range of 15% to 80% by mass, and even more preferably in a range of 25% to 70% by mass, when the total of MOF and the binder polymer is 100% by mass. When the electrolyte membrane contains the binder polymer in a range of 5% to 90% by mass, when the total of MOF and the binder polymer is 100% by mass, the heat resistance and flexibility of the molded article are increased, improving its handling. As a result, it becomes easier to position the molded article in contact with at least one of the positive and negative electrodes, making it easier to electrolyze water at the positive electrode and conduct protons generated by electrolysis to the negative electrode, thus maintaining a stable state of the molded article even when it is placed in a humidified state.

[0031] The polymer used as a binder has the effect of improving the heat resistance of the molded article. There are no particular restrictions on the polymer used as a binder that can be used in the present invention, but it is preferable that it does not substantially decompose at the ammonia electrolytic synthesis reaction temperature. From the viewpoint of more reliably obtaining the above-mentioned effects, it is more preferable that the polymer used as a binder does not substantially decompose above 300°C, and even more preferable that it does not substantially decompose above 350°C. Furthermore, it is preferable that the polymer used as a binder is a polymer having proton conductivity. Based on the above, examples of preferred polymers include one or more selected from the group consisting of polyamide-imide, polysulfone, polyphenylsulfone, polyvinylidene fluoride, polyimide, polyvinyl butyral, and cellulose ester.

[0032] The molded article of the present invention is preferably an electrolyte membrane containing MOF, a binder polymer, and a dispersant. When the molded article is an electrolyte membrane containing MOF, a binder polymer, and a dispersant, the dispersant can suppress the aggregation of MOF and the binder polymer, allowing them to be mixed substantially uniformly, and an electrolyte membrane having a desired proton conductivity can be formed as a molded article. The resulting molded article has improved handling due to increased heat resistance and flexibility. As a result, it becomes easier to position the molded article in contact with at least one of the positive and negative electrodes, making it easier to electrolyze water at the positive electrode and conduct protons generated by electrolysis to the negative electrode. Even when the molded article is placed in a humidified state, it can maintain a stable state.

[0033] When a molded article containing a proton conductor is an electrolyte membrane comprising an MOF, a binder polymer, and a dispersant, it is preferable that the electrolyte membrane is composed of a composition comprising the MOF, the binder polymer, and the dispersant. In the composition forming the electrolyte membrane, the content of the dispersant is preferably in the range of 1 to 35 parts by mass, more preferably in the range of 2 to 25 parts by mass, and even more preferably in the range of 4 to 15 parts by mass, based on 100 parts by mass of the total of the MOF and the binder polymer. When the content of the dispersant in the composition forming the electrolyte membrane is in the range of 1 to 35 parts by mass per 100 parts by mass of the total of the MOF and the binder polymer, the dispersant suppresses aggregation of the MOF and the binder polymer, making it easier to mix them substantially uniformly without impairing the proton conductivity of the molded article, and making it easier to obtain a molded article that is an electrolyte membrane having the desired proton conductivity.

[0034] Commercially available dispersants can be used. Examples include Marialim FA-1150AM-08 (manufactured by NOF Corporation), Marialim AKM-0531 (manufactured by NOF Corporation), Esream AD-3172M (manufactured by NOF Corporation), Esream C-20951 (manufactured by NOF Corporation), Esream C-20931 (manufactured by NOF Corporation), Esream 221P (manufactured by NOF Corporation), Hinoact T-9100 (manufactured by Kawaken Fine Chemicals), Hinoact KF-1300M (manufactured by Kawaken Fine Chemicals), Ajisper PN411 (manufactured by Ajinomoto Fine Techno Co., Ltd.), and Ajisper PN111 (manufactured by Ajinomoto Fine Techno Co., Ltd.).

[0035] A method for manufacturing a molded article will be described. When the molded article is an electrolyte membrane containing an MOF and a polymer that acts as a binder, the method for manufacturing the molded article preferably has the following steps: (A) A step of preparing a mixed solution containing the polymer that acts as a binder, the MOF, and a solvent. (B) A step of casting the mixed solution to form a wet film and removing the solvent from the wet film.

[0036] <Step (A)> In Step (A), there are no restrictions on the order in which the polymer, MOF, and solvent are mixed. For example, the MOF and polymer may be mixed first, and then the solvent may be added to prepare the mixture, or the polymer and solvent may be mixed beforehand, and then the MOF may be added to prepare the mixture. Three or more components may also be mixed simultaneously. If the molded article contains a dispersant, a mixture with the dispersant added may be produced in this step. There are no restrictions on the order in which the polymer, MOF, solvent, and dispersant are mixed.

[0037] The solvent used to prepare the mixture can be appropriately selected considering the solubility of the polymer in the solvent, but from the viewpoint of polymer solubility, aprotic polar solvents can be preferably used. Examples of aprotic polar solvents include N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), acetone, and cyclopentanone. These solvents can be used individually or in combination of two or more.

[0038] While there are no particular restrictions on the solvent content, appropriately adjusting the solvent content can improve the fluidity of the mixture, thereby enhancing its moldability, and increase its viscosity, making it easier to control the thickness of the electrolyte membrane.

[0039] The resulting mixture may be subjected to defoaming under reduced pressure as needed. In this case, the defoaming pressure is preferably 0.2 kPa to 80 kPa, and more preferably 5 kPa to 30 kPa. The defoaming can be carried out, for example, at room temperature. The defoaming time is preferably 15 minutes to 2 hours, and more preferably 30 minutes to 1 hour.

[0040] <Step (B)> Once the mixture is obtained, the mixture is then cast onto the substrate to form a wet film. For example, glass plates, metal plates, resin plates, and resin sheets can be used as the substrate. There are no particular restrictions on the method of casting the mixture; for example, a wet film with a uniform thickness can be easily obtained by using an applicator. Alternatively, a wet film can be obtained by dropping the mixture onto the substrate.

[0041] Next, the solvent is removed from the wet film by drying to obtain an electrolyte film. Drying can be carried out under atmospheric pressure or under reduced pressure. Drying is preferably carried out at a temperature below the decomposition temperature of the MOF and the polymer binder, and if the MOF has a melting point, it is preferable to carry out drying at a temperature below that melting point. More specifically, when drying is carried out under atmospheric pressure, the drying temperature is preferably 100°C to 200°C, more preferably 120°C to 180°C, and even more preferably 130°C to 150°C. The drying time is preferably 15 minutes to 24 hours, more preferably 30 minutes to 12 hours, and even more preferably 1 hour to 8 hours. When drying is carried out under atmospheric pressure, drying can be carried out in an inert gas atmosphere or in the atmosphere. There are no particular restrictions on the heating means. For example, heating means such as blowing hot air, irradiating with infrared rays, or heating in a heating furnace can be used.

[0042] The film thickness of the electrolyte membrane can be adjusted, for example, by the following methods: When using an applicator to form a wet film by casting the mixed solution, the film thickness can be adjusted by appropriately selecting the gap of the applicator. When obtaining a wet film by dropping the mixed solution onto a substrate, the film thickness can be adjusted by appropriately selecting the amount dropped per unit area. The electrolyte membrane obtained in this way can be peeled off the substrate if necessary and then used for various purposes.

[0043] The thickness of the electrolyte membrane is preferably 10 μm to 500 μm, more preferably 20 μm to 300 μm, even more preferably 40 μm to 200 μm, and particularly preferably 50 μm to 100 μm. By having the electrolyte membrane thickness within the range of 10 μm to 500 μm, it is possible to achieve high proton conductivity while ensuring ease of handling.

[0044] The positive and negative electrodes used in the electrolytic synthesis of ammonia may consist solely of electrode materials, or they may be compositions containing electrode materials and catalysts. As positive and negative electrode materials, those commonly used in this field can be used without particular limitations, as long as they are electrically conductive. For example, carbon paper (JNT30, manufactured by JNTG Co., LTD), Pt paste (TR-7905, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.), Ag / Pd paste (TR-9020, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.), etc., can be used. As positive electrode catalysts, those commonly used in this field can be used without particular limitations, as long as they have the activity to electrolyze water. For example, Pt paste (TR-7905, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.), Ag / Pd paste (TR-9020, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.), carbon paper with Pt deposited on it, etc., can be used. As negative electrode catalysts, those commonly used in this field can be used without particular limitations, as long as they exhibit the activity for the electrolytic synthesis reaction of ammonia. For example, Pt paste (TR-7905, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.), Ag / Pd paste (TR-9020, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.), or carbon paper with Ru deposited on it can be used.

[0045] The molded body of the present invention is positioned to be in contact with at least one of the positive electrode and the negative electrode. By positioning the molded body to be in contact with at least one of the positive electrode and the negative electrode, protons (H) generated at the positive electrode by electrolysis are formed. ＋ This facilitates the supply of the positive electrode to the negative electrode through the molded body. If the molded body contains amorphous material in part, the amorphous portion may be in contact with at least one of the positive electrode and the negative electrode.

[0046] The method for manufacturing an electrochemical cell includes an MOF, and the proton conductivity measured under the aforementioned measurement condition 1 is 1.0 × 10⁻⁶. －９ The structure may be formed by placing a composition containing electrode material and catalyst in contact with at least one surface of a molded body with a density of S / cm or greater. For example, it may be formed by coating the surface of the molded body with a composition containing electrode material and catalyst.

[0047] The electrolytic synthesis reaction of ammonia may be carried out in a humidified state by supplying a humidifying medium to the molded body. If the temperature during the electrolytic synthesis reaction of ammonia is high, the relative humidity will be low, and the protons (H) generated at the positive electrode will be low. ＋ When the protons are supplied to the negative electrode via a proton conductor contained in the molded body, the proton conductivity of the molded body may decrease.

[0048] When an electrolytic synthesis reaction of ammonia is carried out in a molded body humidified by supplying a humidifying medium, it is preferable that the atmospheric pressure dew point temperature of the supplied humidifying medium be 1°C or higher, more preferably 5°C or higher, even more preferably 10°C or higher, and particularly preferably 20°C or higher. When an electrolytic synthesis reaction of ammonia is carried out in a humidified state by supplying a humidifying medium with an atmospheric pressure dew point temperature of 1°C or higher, for example, when the temperature at which the electrolytic synthesis reaction is carried out is between 100°C and 300°C, even at a relatively high temperature of 150°C or higher, the proton conductivity does not decrease, and the protons (H) generated at the positive electrode are produced. ＋ The humidifier is supplied to the negative electrode via a molded body, allowing for efficient ammonia synthesis. There is no particular upper limit on the atmospheric pressure dew point temperature. For example, humidification may be carried out by supplying a humidifying medium with an atmospheric pressure dew point temperature of 100°C. Alternatively, humidification may be carried out by supplying a humidifying medium under pressurized conditions. The humidifying medium is preferably a humidifying gas, and more preferably humidified nitrogen or water vapor. Humidified nitrogen can be produced, for example, by humidifying dry nitrogen through a bubbling container containing water heated to a predetermined temperature. Dry nitrogen may include, for example, dry air, and the nitrogen content in the dry nitrogen may be 99.0% by volume or more, or 99.9% by volume or more.

[0049] A second embodiment of the present invention includes an MOF with a proton conductivity of 1.0 × 10 －９ This is an ammonia production apparatus for producing ammonia by an electrolytic synthesis reaction, comprising a molded body with a density of S / cm or higher, a positive electrode and a negative electrode, wherein the molded body is arranged to be in contact with at least one of the positive electrode and the negative electrode.

[0050] The ammonia production apparatus may be an ammonia production apparatus that includes an electrochemical cell 1, as shown in Figure 1 above, which has a positive electrode 2 and a negative electrode 3, and a molded body 1 containing an MOF arranged so as to be in contact with at least one of the positive electrode 2 and the negative electrode 3.

[0051] Embodiments of the present invention encompass the following technical concepts: [1] A metal-organic structure comprising a proton conductivity of 1.0 × 10 －９ A method for producing ammonia by an electrolytic synthesis reaction, wherein a molded body with a density of S / cm or higher, a positive electrode, and a negative electrode are used, and the molded body is arranged so that at least one of the positive electrode and the negative electrode is in contact with the molded body. [2] The method for producing ammonia according to [1], wherein the electrolytic synthesis reaction is carried out at a temperature of 100°C or higher and 300°C or lower. [3] The method for producing ammonia according to [1] or [2], wherein the molded body is an electrolyte membrane containing the metal-organic structure and a polymer that acts as a binder. [4] The method for producing ammonia according to any one of [1] to [3], wherein the metal-organic structure contains one or more metal ions selected from the group consisting of zinc ions, chromium ions, aluminum ions, magnesium ions, calcium ions, potassium ions, manganese ions, iron ions, cobalt ions, nickel ions, copper ions, yttrium ions, and zirconium ions. [5] The method for producing ammonia according to any one of [1] to [4], wherein the metal-organic structure comprises one or more crosslinking ligands selected from the group consisting of phosphoric acid, polycarboxylic acid, amino acids, polyamines, nitrogen-containing heteroaromatic compounds and their anions and oxide ions. [6] The method for producing ammonia according to any one of [1] to [5], wherein the molded article comprises the metal-organic structure, a polymer that serves as a binder, and a dispersant. [7] A metal-organic structure comprising a proton conductivity of 1.0 × 10 －９ An ammonia production apparatus for producing ammonia by an electrolytic synthesis reaction, comprising a molded body with a density of S / cm or more, a positive electrode and a negative electrode, wherein the molded body is arranged to be in contact with at least one of the positive electrode and the negative electrode.

[0052] The present invention will be described in further detail below based on examples and comparative examples. The present invention is not limited to these examples.

[0053] Synthesis of DMAS_Znox DMAS_Znox was synthesized as follows, according to the method described in Angew. Chem. 2014, 126, 2676. 0.143 g of zinc sulfate heptahydrate, 0.158 g of oxalic acid, and 6 mL of dimethylformamide were weighed and mixed, then placed in an autoclave and heated at 160°C for 4 days (96 hours). After that, it was cooled to room temperature over 24 hours. The resulting solid was filtered off, washed with DMF, and vacuum-dried at 120°C to obtain DMAS_Znox powder. DMAS_Znox contains zinc ions as metal ions, oxalate ions as crosslinking ligands, and dimethylaminium ions and sulfate ions as non-coordinating counterions.

[0054] Synthesis of ZnPIm ZnPIm was synthesized as follows, according to the method described in J. Am. Chem. Soc. 2012, 134, 7612-7615. 0.081 g of zinc oxide, 0.136 g of imidazole, 205 μL of 85% phosphoric acid, and 0.5 mL of ethanol were added to a mortar and mixed with a pestle for 15 minutes. The resulting white powder was then collected, washed with ethanol, and dried overnight (approximately 15 hours) in a 100°C oven to obtain ZnPIm powder. ZnPIm contains zinc ions as metal ions, hydrogen phosphate ions and dihydrogen phosphate ions as crosslinking ligands, and imidazolium ions as non-coordinating counterions.

[0055] Synthesis of MIL(20)·1 MIL(20)·1 was synthesized as follows according to the method described in RSC Adv. 2017, 7, 403-407. First, 15 mg of MIL-101(Cr) (manufactured by Atomis) was dried under reduced pressure at 180°C for 6 hours. Then, under a nitrogen atmosphere, it was mixed with 85 mg of imidazole trifluoromethanesulfonate in a mortar for 15 minutes. MIL-101(Cr) has a chromium ion as a metal ion and terephthalate (benzene-1,4-dicarboxylic acid anion) and oxide ions as crosslinking ligands. MIL(20)·1 is a compound in which imidazole trifluoromethanesulfonate is filled into the pores of MIL-101(Cr). MIL(20)·1 contains 27% by mass of imidazolium ions.

[0056] Synthesis of MIP-202(Zr) MIP-202(Zr) was synthesized as follows according to the method described in Nat. Commun. 2018, 9, 4937. 2.8 g of L-aspartic acid and 5 mL of deionized water were placed in a 25 mL round-bottom beaker and stirred. Then 2.33 g of zirconium chloride and 5 mL of deionized water were added, and the mixture was heated under reflux at approximately 120°C for 1 hour. The resulting solid was filtered off, washed with water / ethanol, and dried to obtain MIP-202(Zr) powder. MIP-202(Zr) contains zirconium ions as metal ions.

[0057] Synthesis of MOF-303 MOF-303 was synthesized as follows, according to the method described in International Publication No. 2019 / 010102: 5.2 g of aluminum chloride hexahydrate, 3.75 g of 3,5-pyrazoledicarboxylic acid, and 360 g of deionized water were placed in a 500 mL glass container and stirred to prepare an aqueous solution. Next, an aqueous sodium hydroxide solution, prepared by dissolving 1.3 g of sodium hydroxide in 15.0 g of deionized water, was added dropwise to the aqueous solution. The container containing the obtained aqueous solution was sealed and heated at 100°C for 24 hours. The resulting solid was filtered off, washed with water, and dried to obtain MOF-303 powder. MOF-303 contains aluminum ions as metal ions.

[0058] Polymers and Dispersants The polymers and dispersants used in each of the examples and comparative examples described below are as follows: <Polymers> ・Polyamide-imide (PAI 4000 TF manufactured by Solvey, Inc., hereinafter also referred to as "PAI") ・Cellulose ester (L-20 manufactured by Daicel Corporation, hereinafter also referred to as "L-20") <Dispersants> ・Marialim FA-1150AM-08 (manufactured by NOF Corporation, a polymer polycarboxylic acid-based dispersant with a comb-like structure, aqueous solution of 50% active ingredient) ・Esream 221P (manufactured by NOF Corporation, a low molecular weight dispersant, 100% active ingredient) ・Marialim AKM-0531 (manufactured by NOF Corporation, a polymer polycarboxylic acid-based dispersant, 100% active ingredient) ・Hinoact KF-1300M (manufactured by Kawaken Fine Chemicals Co., Ltd., a basic dispersant, 100% active ingredient)

[0059] Manufacturing of Molded Body 1 2.00 g of DMAS_Znox, 1.00 g of PAI, 6.17 g of NMP, and 0.22 g of Esream 221P were weighed out and mixed in a mortar until a uniform paste was obtained (Step (A)). The mixture was transferred to a Teflon® beaker and placed in a vacuum desiccator, where it was reduced to 10 kPa and degassed for 30 minutes. Table 1 shows the polymer content (mass%) when the total of MOF and polymer is set to 100 mass%, and the dispersant content (parts by mass) per 100 parts by mass of the total of MOF and polymer. Next, the degassed mixture was dropped onto a glass plate and coated with an applicator to form a wet film. At this time, the gap of the applicator was adjusted so that the film thickness of the molded body was the value shown in Table 1. This wet film was dried in the atmosphere to obtain molded body 1 (Step (B)).

[0060] Manufacturing of molded articles 2 to 10 Molded articles were obtained in the same manner as molded article 1, except that the type and mass of MOF, the type and mass of polymer, the type and mass of dispersant, the type and mass of solvent, and the film thickness of the proton conductor were changed as shown in Table 1. In molded article 6, the MOF was DMAS_Znox / ZnPIm = 80 / 20 (mass ratio), and the dispersant used was Marialim AKM-0531 / Marialim FA-1150AM-08 = 80 / 20 (mass ratio).

[0061] Measurement of Molded Body Film Thickness The film thickness of the molded body was measured using a digital measuring instrument (Nikon DIGIMICRO STAND MS-1C). The arithmetic mean of the thicknesses at five points was taken as the film thickness of the proton conductor.

[0062] Measurement of Proton Conductivity of Molded Body A 30 mm x 30 mm test piece was cut from the molded body. Pt paste (TR-7905, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) was applied to one side of the test piece, and Ag / Pd paste (TR-9020, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) was applied to the other side, both sides, by screen printing to form electrodes. The electrodes were dried to form electrodes on both sides of the test piece. Next, an AC current of 100 mV was applied between the two electrodes under a dry nitrogen stream (100 mL / min) at 170°C. Complex impedance analysis was performed using a SOLARTRON SI 1260 IMPEDANCE / GAIN-PHASE ANALYZER (manufactured by Solartron Analytical) in the frequency range of 0.1 Hz to 0.5 MHz, and the proton conductivity (S / cm) was determined from the total resistance component. For molded bodies with high resistance that could not be subjected to complex impedance analysis, the description "unmeasurable" was used.

[0063] These evaluation results are shown in Table 1. In Table 1, "mass of dispersant" refers to the mass of the active ingredient of the dispersant, and does not include the mass of water, which is the solvent, when the dispersant is used in aqueous solution form. Also, "dispersant content" in the table refers to the parts by mass of the dispersant per 100 parts by mass of the total of the MOF and polymer. Also, in Table 1, "film thickness" refers to the film thickness of the molded article.

[0064]

[0065] Molded bodies 1 to 7 include a metal-organic structure, and the proton conductivity measured under the aforementioned measurement condition 1 is 1.0 × 10⁻⁶. －９ It is S / cm or higher.

[0066] Although molded bodies 8 to 10 contain a metal-organic structure, under the aforementioned measurement condition 1, the resistance of the molded bodies was high, making it impossible to measure the proton conductivity.

[0067] Example 1 A 30 mm x 30 mm test piece was cut from molded body 1. Pt paste (TR-7905, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) was applied to one side of the test piece, and Ag / Pd paste (TR-9020, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) was applied to the other side, both measuring 10 mm x 10 mm, by screen printing. The pieces were then dried to create an electrochemical cell for the electrolytic synthesis reaction of ammonia, as shown in Figure 1, which included the molded body, a positive electrode, and a negative electrode. Dry nitrogen (100 mL / min) was supplied to the negative electrode side of this electrochemical cell, and humidified nitrogen with an atmospheric pressure dew point of 80°C (100 mL / min of dry nitrogen humidified through a bubbling container at 80°C) was supplied to the positive electrode side. A voltage of 2 V was applied between the two electrodes at a cell temperature of 170°C to synthesize ammonia. The generated ammonia was collected by bubbling the exhaust gas from the negative electrode side into a 5 mmol / L sulfuric acid aqueous solution. The temperature at which the electrolytic synthesis reaction is carried out may specifically be the temperature of the electrochemical cell (hereinafter also referred to as the "cell temperature").

[0068] Examples 2-11 and Comparative Examples 1-3: Ammonia synthesis was carried out in the same manner as in Example 1, except that the molded body, positive electrode, negative electrode, cell temperature, positive electrode gas dew point temperature, and electrolysis voltage were changed as shown in Table 2. The Pt sputter and Ru sputter were prepared by depositing Pt and Ru onto carbon paper (JNT30, manufactured by JNTG Co., LTD) by sputtering, and were placed in contact with the cut molded body.

[0069] Ammonia production rate conversion value (mol / s / cm) ２ The amount of ammonium in a 5 mmol / L sulfuric acid aqueous solution from which ammonia was collected was quantified using the indophenol blue method with a test reagent (WAK-NH4-4, Kyoritsu Chemical Co., Ltd.) and a detector (Digital Pack Test DPM2). By dividing this quantified value by the reaction time and electrode area, the ammonia production rate equivalent value (mol / s / cm²) was obtained. ２ The following was calculated. The results are shown in Table 2.

[0070]

[0071] Examples 1 to 11 include a metal-organic structure with a proton conductivity of 1.0 × 10⁻⁶. －９Using any of the molded bodies 1 to 7 with a S / cm or higher rating, along with a positive and negative electrode, ammonia could be produced by electrolytic synthesis at a temperature range of 100°C to 300°C.

[0072] In Comparative Examples 1 and 2, proton conductivity could not be measured, and the proton conductivity was 1.0 × 10⁻⁶. －９ Although molded bodies 8 and 9, which are presumed to have a conductivity of less than S / cm, were used, and the positive and negative electrodes were used, ammonia could not be produced by the electrolytic synthesis reaction. In Comparative Example 3, the proton conductivity could not be measured, but the proton conductivity was 1.0 × 10⁻⁶. －９ A molded body 10, estimated to have a S / cm or less ratio, was used along with the positive and negative electrodes. However, the film ruptured during the test, causing gas leakage, and evaluation could not be performed.

[0073] This disclosure provides a method for producing ammonia by electrolytic synthesis reaction using a molded article containing MOF. The ammonia produced by the manufacturing method of this disclosure (NH₄) ３ ) can be used as a raw material for chemical fertilizers, nitrates, and other organic compounds such as nylon fibers. The manufacturing method of the present disclosure efficiently produces ammonia (NH ３ It is possible to produce ammonia (NH) from which the ammonia produced is produced. ３ ) is a greenhouse gas (CO2) even when burned. ２ Because it does not generate fumes, is easily liquid, and is easy to store and transport, it can be used as an energy source for thermal power generation and other applications.

[0074] 1: Molded body, 2: Positive electrode, 3: Negative electrode, 4: Positive electrode inlet, 5: Negative electrode inlet, 6: Positive electrode outlet, 7: Negative electrode outlet

Claims

1. Contains a metal-organic structure and has a proton conductivity of 1.0 × 10⁻⁶ －９ A method for producing ammonia by an electrolytic synthesis reaction, comprising using a molded body with a density of S / cm or higher, a positive electrode, and a negative electrode, wherein the molded body is arranged in contact with at least one of the positive electrode and the negative electrode.

2. The method for producing ammonia according to claim 1, wherein the electrolytic synthesis reaction is carried out at a temperature of 100°C or higher and 300°C or lower.

3. The method for producing ammonia according to claim 1 or 2, wherein the molded body is an electrolyte membrane comprising the metal-organic structure and a polymer that serves as a binder.

4. The method for producing ammonia according to claim 1 or 2, wherein the metal-organic structure contains one or more metal ions selected from the group consisting of zinc ions, chromium ions, aluminum ions, magnesium ions, calcium ions, potassium ions, manganese ions, iron ions, cobalt ions, nickel ions, copper ions, yttrium ions, and zirconium ions.

5. The method for producing ammonia according to claim 1 or 2, wherein the metal-organic structure comprises one or more crosslinkable ligands selected from the group consisting of phosphoric acid, polycarboxylic acid, amino acid, polyamine, nitrogen-containing heteroaromatic compounds and their anions and oxide ions.

6. The method for producing ammonia according to claim 1 or 2, wherein the molded article comprises the metal-organic structure, a polymer acting as a binder, and a dispersant.

7. Contains a metal-organic structure and has a proton conductivity of 1.0 × 10⁻⁶ －９ An ammonia production apparatus for producing ammonia by an electrolytic synthesis reaction, comprising a molded body with a density of S / cm or higher, a positive electrode and a negative electrode, wherein the molded body is arranged to be in contact with at least one of the positive electrode and the negative electrode.

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