Method for producing ammonia

Abstract

This method for producing ammonia includes: a step for reacting an alkali metal with an aromatic hydrocarbon compound that has an unsubstituted aromatic ring or an aromatic ring substituted with a hydrocarbon group or an alkoxy group in at least one organic solvent that is selected from the group consisting of a cyclic ether solvent and an alkyl ether solvent so as to obtain a compound (A) that is composed of an alkali metal cation and a radical anion of the aromatic hydrocarbon compound; a step for reacting nitrogen with the compound (A) so as to obtain a metal nitride; and a step for reacting the metal nitride with water or an acidic aqueous solution so as to obtain ammonia or ammonium ions.

Description

Ammonia production method

[0001] This invention relates to a method for producing ammonia, and more specifically, to a method for producing ammonia using nitrogen gas.

[0002] Ammonia has traditionally been used as a raw material for fertilizers, melamine resin, and polyamide resin. Furthermore, ammonia is a substance composed of nitrogen atoms (N) and hydrogen atoms (H), and when burned, it produces CO2. ２ Because it does not emit CO2, it has attracted attention in recent years as a carbon-free energy source. For example, by co-firing ammonia in coal-fired power plants, CO2 is reduced. ２ It is attracting attention as an energy source that can reduce emissions.

[0003] Conventionally, the Haber-Bosch process, which synthesizes ammonia from hydrogen and nitrogen gas, has been known as a method for producing ammonia (for example, Non-Patent Document 1). However, in order to produce the hydrogen gas used as a raw material in the Haber-Bosch process, a large amount of carbon dioxide, which causes global warming, is emitted through the thermal decomposition of methane, and conditions of high temperature (400-500°C) and high pressure (100-300 atmospheres) are required, which consumes a large amount of energy and necessitates huge facilities for commercial viability. For this reason, alternative methods for producing ammonia to the conventional Haber-Bosch process have been proposed.

[0004] For example, Japanese Patent Publication No. 2012-219285 (Patent Document 1) describes a method for reducing nitrogen that can be used in nitrogen-involved processes such as atmospheric pressure electrolytic synthesis of ammonia, in which an anode and a cathode are placed in a molten salt of an alkali halide containing lithium, nitrogen is supplied to the cathode, and Li is placed between the anode and the cathode at the cathode. ＋ A nitrogen reduction method is described that involves applying a voltage to generate nitrogen. However, this method requires heating the molten alkali halide salt containing lithium to 450°C, which results in high manufacturing costs.

[0005] Furthermore, Japanese Patent Publication No. 2023-118104 (Patent Document 2) describes a method for producing ammonia by passing a gas containing nitrogen gas through an aqueous solution containing an alkali metal or alkaline earth metal, or a salt containing both an alkali metal and an alkaline earth metal. However, this method has the problem of low production efficiency and high manufacturing costs because it uses hydrogen gas obtained by the electrolysis of water as a hydrogen source.

[0006] Furthermore, Nature, 2019, Vol. 568, pp. 536-540 (Non-Patent Literature 2) describes a method for producing ammonia using samarium iodide as a reducing agent, by mixing samarium iodide in a solvent with a molybdenum catalyst, water, and nitrogen gas. However, this method has the problem of using a special material for the molybdenum catalyst, and also the short lifespan of the catalyst.

[0007] Japanese Patent Publication No. 2012-219285 Japanese Patent Publication No. 2023-118104

[0008] Agency for Natural Resources and Energy, "Can Ammonia Become a 'Fuel'?! (Part 1) - Uses of Ammonia That Are Familiar but You Don't Really Know About," [online], [Accessed September 19, 2024], Internet <URL: https: / / www.enecho.meti.go.jp / about / special / johoteikyo / ammonia_01.html> Ashida, Y. et al., Nature, 2019, Vol. 568, pp. 536-540

[0009] This invention has been made in view of the problems of the prior art described above, and aims to provide a method for easily producing ammonia under mild conditions using nitrogen gas.

[0010] As a result of intensive research to achieve the above object, the present inventors have prepared a compound composed of an alkali metal cation and a radical anion of the aromatic hydrocarbon compound by reacting a specific aromatic hydrocarbon compound with an alkali metal in a specific organic solvent, synthesized a metal nitride by reacting this compound with nitrogen, and found that ammonia or ammonium ions can be easily produced at normal temperature and pressure by reacting this metal nitride with water or an acidic aqueous solution, thus completing the present invention.

[0011] That is, the present invention provides the following aspects. [1] A step of reacting an aromatic hydrocarbon compound having an unsubstituted aromatic ring or an aromatic ring substituted with a hydrocarbon group or an alkoxy group with an alkali metal in at least one organic solvent selected from the group consisting of a cyclic ether-based solvent and an alkyl ether-based solvent to obtain a compound (A) composed of an alkali metal cation and a radical anion of the aromatic hydrocarbon compound; a step of reacting nitrogen with the compound (A) to obtain a metal nitride; and a step of reacting the metal nitride with water or an acidic aqueous solution to obtain ammonia or ammonium ions. A method for producing ammonia, comprising the above steps. [2] The method for producing ammonia according to [1], further comprising a step of separating and recovering the aromatic hydrocarbon compound in the organic solvent phase and ammonia or ammonium ions in the aqueous phase. [3] The aromatic hydrocarbon compound is represented by the following formula (1):

[0012]

[0013] (In formula (1), n1 is an integer of 1 to 6, and each R independently represents a hydrogen atom, a hydrocarbon group or an alkoxy group.) A linked polycyclic aromatic hydrocarbon compound represented by the formula and the following formula (2):

[0014]

[0015] A method for producing ammonia according to [1] or [2], wherein at least one compound is selected from the group consisting of condensed polycyclic aromatic hydrocarbon compounds represented by formula (2), where n2 is an integer from 1 to 7, and R independently represents a hydrogen atom, a hydrocarbon group, or an alkoxy group. [4] A method for producing ammonia according to [3], wherein in formula (1), n1 is an integer from 1 to 3, and R is a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, and in formula (2), n2 is an integer from 1 to 3, and R is a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms. [5] A method for producing ammonia according to [3] or [4], wherein the aromatic hydrocarbon compound is a linked polycyclic aromatic hydrocarbon compound represented by formula (1). [6] A method for producing ammonia according to any one of [1] to [5], wherein the organic solvent is a cyclic ether solvent. [7] The method for producing ammonia according to any one of [1] to [5], wherein the organic solvent is at least one selected from the group consisting of tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl ether, diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether. [8] The method for producing ammonia according to any one of [1] to [7], wherein the alkali metal is at least one selected from the group consisting of lithium, sodium, and potassium. [9] The method for producing ammonia according to any one of [1] to [8], wherein the concentration of the alkali metal in the organic solvent is 0.5 mol / L or higher than the concentration of the aromatic hydrocarbon compound in the organic solvent.

[0016] Note that although the reason why ammonia or ammonium ions can be easily produced at normal temperature and pressure by the present invention is not necessarily clear, the present inventors presume as follows. That is, when an aromatic hydrocarbon compound and an alkali metal are reacted in a non-aqueous organic solvent, even under normal temperature and pressure, a radical anion of a reduced aromatic hydrocarbon compound is formed, and the aromatic hydrocarbon compound is imparted with electron-donating properties. At this time, the reduction ability (reduction potential) can be controlled depending on the skeleton of the aromatic hydrocarbon compound and the type of the non-aqueous organic solvent. By using a cyclic ether-based solvent or an alkyl ether-based solvent as the non-aqueous organic solvent and using an aromatic hydrocarbon compound having an unsubstituted aromatic ring or an aromatic ring substituted with a hydrocarbon group or an alkoxy group as the aromatic hydrocarbon compound, a radical anion of a reduced aromatic hydrocarbon compound having a high reduction ability can be formed.

[0017] When nitrogen gas is supplied to a non-aqueous organic solvent containing a radical anion of a reduced aromatic hydrocarbon compound having a high reduction ability, electrons are donated from the radical anion of the aromatic hydrocarbon compound to nitrogen, and even under normal temperature and pressure, nitrogen is reduced and reacts with the alkali metal to generate a metal nitride (nitride of the alkali metal).

[0018] And when water or an acidic aqueous solution is added to the non-aqueous organic solvent containing the metal nitride, even under normal temperature and pressure, the metal nitride reacts with a proton (H ＋ ), and ammonia or ammonium ions are generated.

[0019] The following formula shows these series of reactions by taking the case where biphenyl is used as the aromatic hydrocarbon compound and lithium is used as the alkali metal as an example.

[0020]

[0021] Furthermore, the system after adding water or an acidic aqueous solution to a non-aqueous organic solvent containing metal nitride is a two-phase system consisting of an organic phase made of the non-aqueous organic solvent and an aqueous phase. The generated ammonia and ammonium ions move to the aqueous phase, while the hydrophobic aromatic hydrocarbon compounds are retained in the organic phase. Therefore, by separating the aqueous phase from the organic phase, the aromatic hydrocarbon compounds and ammonia and ammonium ions can be easily separated and recovered.

[0022] According to the present invention, it is possible to easily produce ammonia at room temperature and atmospheric pressure using nitrogen gas.

[0023] This is a schematic diagram showing the reaction vessels used in the examples and comparative examples.

[0024] The present invention will be described in detail below with reference to its preferred embodiments.

[0025] The present invention provides a method for producing ammonia, comprising: a step of reacting an aromatic hydrocarbon compound having an unsubstituted aromatic ring or an aromatic ring substituted with a hydrocarbon group or an alkoxy group with an alkali metal in at least one organic solvent selected from the group consisting of cyclic ether solvents and alkyl ether solvents to obtain a compound (A) consisting of an alkali metal cation and a radical anion of the aromatic hydrocarbon compound [step for preparing compound (A)]; a step of reacting compound (A) with nitrogen to obtain a metal nitride [step for synthesizing metal nitride]; and a step of reacting the metal nitride with water or an acidic aqueous solution to obtain ammonia or ammonium ions [step for producing ammonia components].

[0026] (Organic solvent) The organic solvent used in the present invention is at least one selected from the group consisting of cyclic ether solvents and alkyl ether solvents. By using these organic solvents, it is possible to easily produce ammonia from nitrogen gas at room temperature and atmospheric pressure. Among these organic solvents, cyclic ether solvents are preferred from the viewpoint of increasing the amount of ammonia component (ammonia or ammonium ions) produced.

[0027] Examples of cyclic ether solvents include tetrahydrofuran, 2-methyltetrahydrofuran, 3-methyltetrahydrofuran, and 2,5-dimethyltetrahydrofuran. These cyclic ether solvents may be used individually or in combination of two or more. Among these cyclic ether solvents, tetrahydrofuran and 2-methyltetrahydrofuran are preferred, and 2-methyltetrahydrofuran is more preferred, from the viewpoint of increasing the amount of ammonia component produced.

[0028] Examples of alkyl ether solvents include dimethyl ether, diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether. These alkyl ether solvents may be used individually or in combination of two or more. Among these alkyl ether solvents, tetraethylene glycol dimethyl ether, dimethyl ether, and diethyl ether are preferred from the viewpoint of increasing the amount of ammonia component produced, and tetraethylene glycol dimethyl ether is more preferred.

[0029] (Aromatic hydrocarbon compounds) The aromatic hydrocarbon compounds used in the present invention are aromatic hydrocarbon compounds having an unsubstituted aromatic ring or an aromatic ring substituted with a hydrocarbon group or an alkoxy group. By using such aromatic hydrocarbon compounds, it becomes possible to easily produce ammonia from nitrogen gas at room temperature and atmospheric pressure.

[0030] Examples of the aromatic hydrocarbon compound include the following formula (1):

[0031]

[0032] A linked polycyclic aromatic hydrocarbon compound represented by the following formula (2):

[0033]

[0034] Examples include condensed polycyclic aromatic hydrocarbon compounds represented by [formula]. These aromatic hydrocarbon compounds may be used individually or in combination of two or more. Among these aromatic hydrocarbon compounds, linked polycyclic aromatic hydrocarbon compounds are preferred from the viewpoint of increasing the amount of ammonia component produced.

[0035] In formula (1) above, n1 is an integer from 1 to 6, and from the viewpoint of increasing the amount of ammonia component produced, it is preferably an integer from 1 to 3, and more preferably an integer from 1 to 2.

[0036] Furthermore, in formula (1), R independently represents a hydrogen atom, a hydrocarbon group, and an alkoxy group. From the viewpoint of increasing the amount of ammonia component produced, the number of carbon atoms in the hydrocarbon group and alkoxy group is preferably 1 to 3, more preferably 1 to 2, and even more preferably 1. Among these, from the viewpoint of increasing the amount of ammonia component produced, R in formula (1) is preferably a hydrogen atom, a hydrocarbon group having 1 to 3 carbon atoms, more preferably a hydrocarbon group having 1 to 3 carbon atoms, and even more preferably a methyl group.

[0037] Examples of such linked polycyclic aromatic hydrocarbon compounds include biphenyl, 2-methylbiphenyl, 2,2'-dimethylbiphenyl, and 3,3',4,4'-tetramethylbiphenyl. These linked polycyclic aromatic hydrocarbon compounds may be used individually or in combination of two or more. Among these linked polycyclic aromatic hydrocarbon compounds, biphenyl, 2-methylbiphenyl, and 2,2'-dimethylbiphenyl are preferred from the viewpoint of increasing the amount of ammonia component produced, 2-methylbiphenyl and 2,2'-dimethylbiphenyl are more preferred, and 2-methylbiphenyl is even more preferred.

[0038] In formula (2) above, n2 is an integer from 1 to 7, and from the viewpoint of increasing the amount of ammonia component produced, it is preferably an integer from 1 to 3, and more preferably an integer from 1 to 2.

[0039] Furthermore, in formula (2), R independently represents a hydrogen atom, a hydrocarbon group, and an alkoxy group. From the viewpoint of increasing the amount of ammonia component produced, the number of carbon atoms in the hydrocarbon group and alkoxy group is preferably 1 to 3, more preferably 1 to 2, and even more preferably 1. Among these, from the viewpoint of increasing the amount of ammonia component produced, R in formula (2) is preferably a hydrogen atom, a hydrocarbon group having 1 to 3 carbon atoms, more preferably a hydrocarbon group having 1 to 3 carbon atoms, and even more preferably a methyl group.

[0040] Examples of such condensed polycyclic aromatic hydrocarbon compounds include naphthalene, anthracene, tetracene, pentane, hexacene, heptacene, and octacene. These condensed polycyclic aromatic hydrocarbon compounds may be used individually or in combination of two or more. Among these condensed polycyclic aromatic hydrocarbon compounds, naphthalene, anthracene, tetracene, and pentanene are preferred from the viewpoint of increasing the amount of ammonia component produced, naphthalene, anthracene, and tetracene are more preferred, and naphthalene and anthracene are even more preferred.

[0041] (Alkali Metals) There are no particular restrictions on the alkali metals used in the present invention, but from the viewpoint of increasing the amount of ammonia component produced, lithium, sodium, potassium, rubidium, cesium, and calcium are preferred, lithium, sodium, potassium, and rubidium are more preferred, and lithium, sodium, and potassium are even more preferred. These alkali metals may be used individually or in combination of two or more.

[0042] [Preparation step for compound (A)] The preparation step for compound (A) is a step of reacting the aromatic hydrocarbon compound with the alkali metal in the organic solvent to obtain compound (A) consisting of an alkali metal cation and a radical anion of the aromatic hydrocarbon compound.

[0043] There are no particular restrictions on the combination of the organic solvent and the aromatic hydrocarbon compound used in the preparation step of compound (A), but from the viewpoint of increasing the amount of ammonia component produced, a combination of the linked polycyclic aromatic hydrocarbon compound or the condensed polycyclic aromatic hydrocarbon compound and the cyclic ether solvent is preferred, a combination of the linked polycyclic aromatic hydrocarbon compound and the cyclic ether solvent is more preferred, a combination of biphenyl or 2-methylbiphenyl and tetrahydrofuran or 2-methyltetrahydrofuran is even more preferred, and a combination of biphenyl and 2-methyltetrahydrofuran and a combination of 2-methylbiphenyl and tetrahydrofuran are particularly preferred.

[0044] There are no particular restrictions on the concentration of the aromatic hydrocarbon compound in the organic solvent, but from the viewpoint of increasing the amount of ammonia component produced, 0.5 to 3.0 mol / L is preferred, 1.0 to 3.0 mol / L is more preferred, and 1.0 to 2.0 mol / L is even more preferred. Similarly, there are no particular restrictions on the concentration of the alkali metal in the organic solvent, but from the viewpoint of increasing the amount of ammonia component produced, 0.5 to 3.0 mol / L is preferred, 1.0 to 3.0 mol / L is more preferred, and 1.0 to 2.0 mol / L is even more preferred. Furthermore, the concentration of the aromatic hydrocarbon compound and the concentration of the alkali metal may be the same, or the concentration of the alkali metal may be 0.5 mol / L or more higher than the concentration of the aromatic hydrocarbon compound.

[0045] In the preparation step of compound (A), compound (A) is synthesized by reacting the aromatic hydrocarbon compound with the alkali metal in the organic solvent, thereby forming an alkali metal cation and a radical anion of the aromatic hydrocarbon compound. The conditions for this reaction are not particularly limited, and the reaction can be carried out at room temperature and atmospheric pressure. In the present invention, compound (A) can be easily obtained under such mild conditions.

[0046] As for the compound (A) obtained in this way, for example, when a linked polycyclic aromatic hydrocarbon compound represented by formula (1) is reacted with an alkali metal M, the following formula (1A) is obtained:

[0047]

[0048] A compound (1A) is obtained, which consists of an alkali metal cation and the radical anion of the linked polycyclic aromatic hydrocarbon compound, represented by formula (2). Furthermore, when the condensed polycyclic aromatic hydrocarbon compound represented by formula (2) is reacted with an alkali metal M, the following formula (2A) is obtained:

[0049]

[0050] A compound (2A) is obtained, which consists of an alkali metal cation and the radical anion of the condensed polycyclic aromatic hydrocarbon compound.

[0051] In formula (1A), n1 is an integer from 1 to 6, and from the viewpoint of increasing the amount of ammonia component produced, it is preferably an integer from 1 to 3, and more preferably an integer from 1 to 2.

[0052] Furthermore, in formula (1A), R independently represents a hydrogen atom, a hydrocarbon group, and an alkoxy group. From the viewpoint of increasing the amount of ammonia component produced, the number of carbon atoms in the hydrocarbon group and alkoxy group is preferably 1 to 3, more preferably 1 to 2, and even more preferably 1. Among these, from the viewpoint of increasing the amount of ammonia component produced, R in formula (1A) is preferably a hydrogen atom, a hydrocarbon group having 1 to 3 carbon atoms, more preferably a hydrocarbon group having 1 to 3 carbon atoms, and even more preferably a methyl group.

[0053] Furthermore, in formula (1A), M represents an alkali metal, y represents the valence of the alkali metal ion, x1 represents the number of alkali metals in one molecule of compound (1A), x1y represents the valence of the radical anion of the linked polycyclic aromatic hydrocarbon compound, and x1y = x1 × y.

[0054] Furthermore, in formula (2A), n2 is an integer from 1 to 7, and from the viewpoint of increasing the amount of ammonia component produced, it is preferably an integer from 1 to 3, and more preferably an integer from 1 to 2.

[0055] In the formula (2A), each R independently represents a hydrogen atom, a hydrocarbon group, or an alkoxy group. From the perspective of increasing the production amount of the ammonia component, the number of carbon atoms in the hydrocarbon group and the alkoxy group is preferably 1 to 3, more preferably 1 to 2, and even more preferably 1. Among these, from the perspective of increasing the production amount of the ammonia component, R in the formula (2A) is preferably a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, more preferably a hydrocarbon group having 1 to 3 carbon atoms, and even more preferably a methyl group.

[0056] Furthermore, M in the formula (2A) represents an alkali metal, y represents the valence of the alkali metal ion, x2 represents the number of alkali metals in one molecule of the compound (2A), x2y represents the valence of the radical anion of the condensed polycyclic aromatic hydrocarbon compound, and x2y = x2 × y.

[0057] 〔Metal nitride synthesis step〕The metal nitride synthesis step is a step of reacting nitrogen with the compound (A) obtained in the preparation step of the compound (A) to synthesize a metal nitride (alkali metal nitride).

[0058] The method of reacting nitrogen with the compound (A) is not particularly limited, but from the perspective of simplicity, a method of passing nitrogen gas through a solution containing the compound (A) obtained in the preparation step of the compound (A) can be mentioned. The conditions of this reaction are not particularly limited, and the reaction can be carried out under normal temperature and pressure. In the present invention, a metal nitride can be easily obtained by such a simple method under such mild conditions.

[0059] Among the metal nitrides thus obtained, from the perspective of increasing the production amount of the ammonia component, lithium nitride (Li ３ N), sodium nitride (Na ３ N), potassium nitride (K ３ N), rubidium nitride (Rb ３ N), and cesium nitride (Cs ３ N) are preferred, and lithium nitride (Li ３ N), sodium nitride (Na ３ N), rubidium nitride (Rb ３ N), and cesium nitride (Cs ３ N) are more preferred.

[0060] [Ammonia component generation process] The ammonia component generation process is a process in which the metal nitride obtained in the metal nitride synthesis process is reacted with water or an acidic aqueous solution to obtain an ammonia component (ammonia or ammonium ions).

[0061] There are no particular restrictions on the method of reacting metal nitride with water or an acidic aqueous solution, but the reaction can be carried out by adding water or an acidic aqueous solution to a solution containing metal nitride.

[0062] Examples of the acidic aqueous solutions include aqueous solutions of acids such as sulfuric acid, hydrochloric acid, acetic acid, boric acid, and oxalic acid. Among these acidic aqueous solutions, from the viewpoint of increasing the amount of ammonia component produced, aqueous sulfuric acid, hydrochloric acid, acetic acid, and boric acid are preferred, aqueous sulfuric acid, hydrochloric acid, and acetic acid are more preferred, and aqueous sulfuric acid and hydrochloric acid are even more preferred.

[0063] [Separation and Recovery Step] In the method for producing ammonia according to the present invention, it is preferable to further include a step of separating and recovering the aromatic hydrocarbon compound in the organic solvent phase and the ammonia component (ammonia or ammonium ions) in the aqueous phase after the ammonia component generation step.

[0064] The solution obtained by the ammonia component generation step is separated into two phases by adding water or an acidic aqueous solution to the metal nitride-containing solution in the ammonia component generation step. The upper phase is an organic solvent phase consisting of the organic solvent containing the aromatic hydrocarbon compound, and the lower phase is an aqueous phase containing ammonia components generated in the ammonia component generation step and alkali metals or alkali metal ions, with a portion of the organic solvent. Due to the polarity-nonpolarity interaction between the organic solvent phase and the aqueous phase, and the salting-out effect where solutes such as low molecular weight organic compounds do not dissolve in high-concentration salt solutions, the phase separation effect between the organic solvent phase and the aqueous phase is significant. Therefore, in the separation and recovery step, the organic solvent phase and the aqueous phase can be easily separated, and as a result, the aromatic hydrocarbon compound contained in the organic solvent phase and the ammonia component contained in the aqueous phase can be easily separated and recovered.

[0065] The present invention will be described more specifically below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0066] (Example 1) In a glove box, 2-methylbiphenyl (2-Me-bPh), an aromatic hydrocarbon compound, was dissolved in tetrahydrofuran (THF), an organic solvent, to a concentration of 1.0 mol / L to prepare a 20 ml solution. Then, metallic lithium (Li) was added to further increase the concentration to 1.0 mol / L, and the mixture was stirred at room temperature to react 2-methylbiphenyl with metallic lithium, thereby producing lithium ions (Li). ＋ ) and the radical anion of 2-methylbiphenyl ([2-Me-bPh]) － A solution containing a compound consisting of ) was obtained.

[0067] This solution is placed in the glass reaction vessel 1 shown in Figure 1, and nitrogen gas is supplied at a flow rate of 0.5 L / min from the gas inlet 2 at room temperature to form lithium nitride (Li ３ N) was synthesized. 24 hours after the start of gas introduction, 10 ml of a 2.0 mol / L sulfuric acid aqueous solution was added to the solution in the reaction vessel, and the solution in the reaction vessel separated into two phases. The upper phase was an organic solvent phase consisting of THF containing 2-Me-bPh, and the lower phase was an organic solvent phase consisting of ammonium ions (NH) containing THF, which were proton-exchanged by nitrogen reduction and acid treatment. ４ ＋ ) and lithium ion (Li ＋ It is an aqueous phase that includes ).

[0068] The aqueous phase of the lower stage was separated and recovered, and the resulting aqueous solution was subjected to quantitative analysis of ammonium ions using the following method to determine the amount of ammonium ions produced. The results are shown in Table 1.

[0069] <Quantitative Analysis of Ammonium Ions> The obtained aqueous solution was filtered through a syringe filter with a pore size of 0.2 μm, and the resulting filtrate was diluted 100 times with water to prepare a sample solution. This sample solution was then subjected to ion chromatography (Dionex ICS-5000, manufactured by Thermo Fisher Scientific Co., Ltd.) ＋ Quantitative analysis of ammonium ions was performed using the following method:

[0070] (Example 2) The same procedure as in Example 1 was followed, except that the concentration of 2-methylbiphenyl (2-Me-bPh) was changed to 2.0 mol / L and the concentration of metallic lithium (Li) was changed to 2.0 mol / L. ＋ ) and the radical anion of 2-methylbiphenyl ([2-Me-bPh]) － A solution containing a compound consisting of ) was prepared, and further nitrogen reduction and acid treatment were performed. The aqueous phase was separated and recovered, and quantitative analysis of ammonium ions was performed to determine the amount of ammonium ions produced. The results are shown in Table 1.

[0071] (Example 3) Lithium ion (Li) was prepared in the same manner as in Example 1, except that biphenyl (bPh) was used as the aromatic hydrocarbon compound. ＋ ) and the biphenyl radical anion ([bPh] － A solution containing a compound consisting of ) was prepared, and further nitrogen reduction and acid treatment were performed. The aqueous phase was separated and recovered, and quantitative analysis of ammonium ions was performed to determine the amount of ammonium ions produced. The results are shown in Table 1.

[0072] (Example 4) The same procedure as in Example 1 was followed except that naphthalene (Naph) was used as the aromatic hydrocarbon compound, and lithium ions (Li ＋ ) and the radical anion of naphthalene ([Naph]) － A solution containing a compound consisting of ) was prepared, and further nitrogen reduction and acid treatment were performed. The aqueous phase was separated and recovered, and quantitative analysis of ammonium ions was performed to determine the amount of ammonium ions produced. The results are shown in Table 1.

[0073] (Example 5) Lithium ions (Li) were prepared in the same manner as in Example 1, except that tetraethylene glycol dimethyl ether (G4) was used as the organic solvent. ＋ ) and the radical anion of 2-methylbiphenyl ([2-Me-bPh]) － A solution containing a compound consisting of ) was prepared, and further nitrogen reduction and acid treatment were performed. The aqueous phase was separated and recovered, and quantitative analysis of ammonium ions was performed to determine the amount of ammonium ions produced. The results are shown in Table 1.

[0074] (Example 6) As an aromatic hydrocarbon compound, 2,2'-dimethylbiphenyl (2,2'-Me ２ Except for using -bPh), the same procedure as in Example 5 was used for lithium ions (Li ＋ ) and the radical anion of 2,2'-dimethylbiphenyl ([2,2'-Me ２ -bPh] － A solution containing a compound consisting of ) was prepared, and further nitrogen reduction and acid treatment were performed. The aqueous phase was separated and recovered, and quantitative analysis of ammonium ions was performed to determine the amount of ammonium ions produced. The results are shown in Table 1.

[0075] (Example 7) As an aromatic hydrocarbon compound, 3,3',4,4'-tetramethylbiphenyl (3,3',4,4'-Me ４ Except for using -bPh), the same procedure as in Example 5 was used for lithium ions (Li ＋ ) and the radical anion of 3,3',4,4'-tetramethylbiphenyl ([3,3',4,4'-Me ４ -bPh] － A solution containing a compound consisting of ) was prepared, and further nitrogen reduction and acid treatment were performed. The aqueous phase was separated and recovered, and quantitative analysis of ammonium ions was performed to determine the amount of ammonium ions produced. The results are shown in Table 1.

[0076] (Example 8) The same procedure as in Example 1 was followed, except that 2-methyltetrahydrofuran (2-Me-THF) was used as the organic solvent, biphenyl (bPh) was used as the aromatic hydrocarbon compound, and the concentration of metallic lithium (Li) was changed to 1.5 mol / L. ＋ ) and the biphenyl radical anion ([bPh] － A solution containing a compound consisting of ) was prepared, and further nitrogen reduction and acid treatment were performed. The aqueous phase was separated and recovered, and quantitative analysis of ammonium ions was performed to determine the amount of ammonium ions produced. The results are shown in Table 1.

[0077] (Example 9) The same procedure as in Example 8 was followed, except that the concentration of metallic lithium (Li) was changed to 2.0 mol / L. ＋ ) and the biphenyl radical anion ([bPh] －A solution containing a compound consisting of ) was prepared, and further nitrogen reduction and acid treatment were performed. The aqueous phase was separated and recovered, and quantitative analysis of ammonium ions was performed to determine the amount of ammonium ions produced. The results are shown in Table 1.

[0078] (Example 10) The same procedure as in Example 8 was followed, except that the concentration of metallic lithium (Li) was changed to 1.0 mol / L. ＋ ) and the biphenyl radical anion ([bPh] － A solution containing a compound consisting of ) was prepared, and further nitrogen reduction and acid treatment were performed. The aqueous phase was separated and recovered, and quantitative analysis of ammonium ions was performed to determine the amount of ammonium ions produced. The results are shown in Table 1.

[0079] (Example 11) Lithium ions (Li) were used in the same manner as in Example 8, except that naphthalene (Naph) was used as the aromatic hydrocarbon compound. ＋ ) and the radical anion of naphthalene ([Naph]) － A solution containing a compound consisting of ) was prepared, and further nitrogen reduction and acid treatment were performed. The aqueous phase was separated and recovered, and quantitative analysis of ammonium ions was performed to determine the amount of ammonium ions produced. The results are shown in Table 1.

[0080] (Example 12) Lithium ions (Li) were prepared in the same manner as in Example 8, except that 2-methylbiphenyl (2-Me-bPh) was used as the aromatic hydrocarbon compound. ＋ ) and the radical anion of 2-methylbiphenyl ([2-Me-bPh]) － A solution containing a compound consisting of ) was prepared, and further nitrogen reduction and acid treatment were performed. The aqueous phase was separated and recovered, and quantitative analysis of ammonium ions was performed to determine the amount of ammonium ions produced. The results are shown in Table 1.

[0081] (Example 13) The same procedure as in Example 11 was followed except that the concentration of metallic lithium (Li) was changed to 1.0 mol / L. ＋ ) and the radical anion of naphthalene ([Naph]) －A solution containing a compound consisting of ) was prepared, and further nitrogen reduction and acid treatment were performed. The aqueous phase was separated and recovered, and quantitative analysis of ammonium ions was performed to determine the amount of ammonium ions produced. The results are shown in Table 1.

[0082] (Example 14) Lithium ions (Li) were used in the same manner as in Example 5, except that naphthalene (Naph) was used as the aromatic hydrocarbon compound. ＋ ) and the radical anion of naphthalene ([Naph]) － A solution containing a compound consisting of ) was prepared, and further nitrogen reduction and acid treatment were performed. The aqueous phase was separated and recovered, and quantitative analysis of ammonium ions was performed to determine the amount of ammonium ions produced. The results are shown in Table 1.

[0083] (Example 15) Lithium ion (Li) was prepared in the same manner as in Example 5, except that biphenyl (bPh) was used as the aromatic hydrocarbon compound. ＋ ) and the biphenyl radical anion ([bPh] － A solution containing a compound consisting of ) was prepared, and further nitrogen reduction and acid treatment were performed. The aqueous phase was separated and recovered, and quantitative analysis of ammonium ions was performed to determine the amount of ammonium ions produced. The results are shown in Table 1.

[0084] (Comparative Example 1) Lithium ions (Li) were prepared in the same manner as in Example 4, except that a mixed solvent of 30 vol% ethylene carbonate (EC), 40 vol% dimethyl carbonate (DMC), and 30 vol% ethyl methyl carbonate (EMC) was used as the organic solvent. ＋ ) and the radical anion of naphthalene ([Naph]) － Attempts were made to prepare a compound consisting of ), but the target compound could not be obtained.

[0085] (Comparative Example 2) Lithium ions (Li) were prepared in the same manner as in Example 1, except that 2-bromoviphenyl (2-Br-bPh) was used as the aromatic hydrocarbon compound. ＋ ) and the radical anion of 2-bromoviphenyl ([2-Br-bPh]) －We attempted to prepare a solution containing a compound consisting of ), but gelation occurred. Furthermore, nitrogen reduction and acid treatment were performed on this gelled product, but no ammonium ions were generated.

[0086] (Comparative Example 3) Lithium ions (Li) were prepared in the same manner as in Example 1, except that 1-bromonaphthalene (1-Br-Naph) was used as the aromatic hydrocarbon compound. ＋ ) and the radical anion of 1-bromonaphthalene ([1-Br-Naph]) － We attempted to prepare a solution containing a compound consisting of ), but gelation occurred. Furthermore, nitrogen reduction and acid treatment were performed on this gelled product, but no ammonium ions were generated.

[0087]

[0088] As shown in Table 1, it was confirmed that compound (A), consisting of an alkali metal cation and a radical anion of the aromatic hydrocarbon compound, can be prepared by reacting an alkali metal with an unsubstituted aromatic ring or an aromatic ring substituted with a hydrocarbon group or an alkoxy group in at least one organic solvent selected from the group consisting of cyclic ether solvents and alkyl ether solvents, and then reacting the obtained compound (A) with nitrogen to synthesize an alkali metal nitride, and finally reacting the obtained alkali metal nitride with an acidic aqueous solution to obtain an ammonium ion.

[0089] More specifically, it was found that when tetrahydrofuran is used as the organic solvent, ammonia can be produced by using biphenyl, naphthalene, or biphenyl having one methyl group as a substituent as the aromatic hydrocarbon compound, and when tetraethylene glycol dimethyl ether is used as the organic solvent, ammonia can be produced by using biphenyl having multiple methyl groups as substituents.

[0090] Furthermore, it was found that when 2-methyltetrahydrofuran was used as the organic solvent, ammonia could be produced by reacting an excess of lithium with the aromatic hydrocarbon compound, using biphenyl, naphthalene, or biphenyl having one methyl group as a substituent. This result suggests that the reducing ability is enhanced by forming a diradical anion from a monoradical anion.

[0091] As described above, according to the present invention, it is possible to easily produce ammonia at room temperature and atmospheric pressure using nitrogen gas. Therefore, the ammonia production method of the present invention is useful as a method that offers excellent workability and enables the production of ammonia at low cost.

[0092] 1: Reaction vessel 2: Gas inlet 3: Gas outlet 4: Solution containing a compound consisting of an alkali metal cation and a radical anion of an aromatic hydrocarbon compound

Claims

A step of reacting an aromatic hydrocarbon compound having an unsubstituted aromatic ring or an aromatic ring substituted with a hydrocarbon group or an alkoxy group with an alkali metal in at least one organic solvent selected from the group consisting of cyclic ether solvents and alkyl ether solvents to obtain a compound (A) consisting of an alkali metal cation and a radical anion of the aromatic hydrocarbon compound, A step of reacting the compound (A) with nitrogen to obtain a metal nitride, A step of reacting the aforementioned metal nitride with water or an acidic aqueous solution to obtain ammonia or ammonium ions, A method for producing ammonia, including the following: 　 A method for producing ammonia according to claim 1, further comprising the step of separating and recovering the aromatic hydrocarbon compound in the organic solvent phase from ammonia or ammonium ions in the aqueous phase. 　 The aforementioned aromatic hydrocarbon compound is defined by the following formula (1): (In formula (1), n1 is an integer from 1 to 6, and R independently represents a hydrogen atom, a hydrocarbon group, or an alkoxy group.) Linked polycyclic aromatic hydrocarbon compounds represented by the following formula (2): (In formula (2), n² is an integer from 1 to 7, and R independently represents a hydrogen atom, a hydrocarbon group, or an alkoxy group.) A method for producing ammonia according to claim 1, wherein the compound is at least one selected from the group consisting of condensed polycyclic aromatic hydrocarbon compounds represented by . 　 In formula (1) above, n1 is an integer from 1 to 3, and R is a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms. In formula (2) above, n2 is an integer from 1 to 3, and R is a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms. The method for producing ammonia according to claim 3. 　 The method for producing ammonia according to claim 3, wherein the aromatic hydrocarbon compound is a linked polycyclic aromatic hydrocarbon compound represented by formula (1). 　 The method for producing ammonia according to claim 1, wherein the organic solvent is a cyclic ether solvent. 　 The method for producing ammonia according to claim 1, wherein the organic solvent is at least one selected from the group consisting of tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl ether, diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether. 　 The method for producing ammonia according to claim 1, wherein the alkali metal is at least one selected from the group consisting of lithium, sodium, and potassium. 　 The method for producing ammonia according to claim 1, wherein the concentration of the alkali metal in the organic solvent is 0.5 mol / L or higher than the concentration of the aromatic hydrocarbon compound in the organic solvent.

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