WO2024232396A1 - Method for producing ammonia-based compound and apparatus for producing ammonia-based compound - Google Patents

Abstract

The disclosed production method is for producing an ammonia-based compound. The production method includes a step (X) for applying a voltage between a positive electrode (121) and a negative electrode (122) in the liquid L containing dissolved nitrogen.

Description

Method and apparatus for producing ammonia-based compounds

The present invention relates to a method for producing ammonia-based compounds and an apparatus for producing ammonia-based compounds.

The Haber-Bosch process is known as a method for synthesizing ammonia. The Haber-Bosch process requires the use of fossil resources such as coal and natural gas, and also requires the reaction to take place in a high-temperature, high-pressure environment. As a result, the Haber-Bosch process has had issues such as its high environmental impact and low production efficiency.

On the other hand, synthesis of ammonia by electrolysis has also been proposed. Claim 1 of Patent Document 1 (Patent No. 5127385) states:
"An apparatus for electrolytically synthesizing ammonia from water and nitrogen, the apparatus comprising:
(1) An apparatus for synthesizing ammonia by supplying finely divided water vapor and nitrogen gas to a molten salt that is an electrolytic bath,
(2) an anode that oxidizes O ^2- and/or ^OH- produced by the reaction of the water vapor to generate oxygen gas;
(3) a cathode that reduces nitrogen gas to generate ^N3- ;
(4) a means for supplying the finely divided water vapor;
(5) A means for supplying a gas that generates a gas lift to the molten salt to generate an upward flow in the molten salt, thereby circulating the molten salt in a loop having a supply port of the anode, the cathode, and the means for supplying water vapor in a part of the loop,
(6) A supply port for a means for supplying a gas that generates the gas lift is provided at or near the bottom of the electrolytic cell.
The document describes an ammonia electrolytic synthesis apparatus characterized by the above-mentioned.

Patent No. 5127385

Currently, there is a demand for new methods for producing ammonia-based compounds. One of the objects of the present invention is to provide a new method for producing ammonia-based compounds.

One aspect of the present invention relates to a method for producing an ammonia-based compound. The method includes a step (X) of applying a voltage between an anode and a cathode in a liquid containing dissolved nitrogen.

Another aspect of the present invention relates to an apparatus for producing an ammonia-based compound. The apparatus includes a tank in which a liquid containing dissolved nitrogen is placed, and an anode and a cathode placed in the tank.

According to the present invention, an ammonia-based compound can be produced by a new method.
The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings.

FIG. 1 is a diagram showing a schematic configuration of an example of a manufacturing apparatus according to the present embodiment. FIG. 2 is a diagram showing a schematic configuration of another example of the manufacturing apparatus according to this embodiment. FIG. 3 is a diagram showing a schematic configuration of another example of the manufacturing apparatus of this embodiment. FIG. 4 is a diagram showing a schematic configuration of another example of the manufacturing apparatus of this embodiment. FIG. 5 is a diagram showing a schematic configuration of another example of the manufacturing apparatus of this embodiment. FIG. 6 is a diagram showing a schematic configuration of another example of the manufacturing apparatus of this embodiment. FIG. 7 is a diagram showing a schematic configuration of another example of the manufacturing apparatus of this embodiment. FIG. 8 is a diagram showing a schematic configuration of another example of the manufacturing apparatus of this embodiment. FIG. 9 is a diagram showing a schematic configuration of another example of the manufacturing apparatus of this embodiment.

Below, the embodiment of the present invention will be described with examples, but the present invention is not limited to the examples described below. In the following description, specific numerical values and materials may be exemplified, but other numerical values and other materials may be applied as long as the effects of the present invention are obtained. In this specification, the expression "numerical value A to numerical value B" includes numerical value A and numerical value B and can be read as "numerical value A or more and numerical value B or less." In the following description, when a lower limit and an upper limit of a numerical value related to a specific physical property or condition are exemplified, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined, as long as the lower limit is not equal to or greater than the upper limit. In the following description, when examples of components or methods are listed, only one of the listed examples may be used, or multiple of the listed examples may be used in combination, unless otherwise specified.

(Method for producing ammonia-based compounds)
The production method according to this embodiment may be referred to as production method (M) below. The production method (M) is a method for producing an ammonia-based compound. The production method (M) includes a step (X) of applying a voltage between an anode and a cathode in a liquid containing dissolved nitrogen. Hereinafter, the liquid may be referred to as "liquid (L)" or "liquid L".

In step (X), electrolysis occurs by applying a voltage between the anode and the cathode while they are immersed in the liquid (L). The reaction caused by the electrolysis in step (X) is not clear at present. However, a reduction reaction of dissolved nitrogen may occur at the cathode. Specifically, the dissolved nitrogen in the liquid (L) may be electrolyzed to generate nitride ions (N ³⁻ ) as shown in the following formula. The generated nitride ions may react with water to generate ammonia.
N ₂ +6e ^- →2N ^3-

It is believed that N ^3- produced by the above reaction reacts with hydrogen ions (H ⁺ ) or water molecules in the liquid (L) to become ammonia or ammonium ions. The reaction at the anode depends on the type of liquid (L) and the anode. When the anode is an electrode containing activated carbon, an electrolytic reaction (oxidation reaction) and/or adsorption of anions may occur at the anode. When the anode is a metal electrode, an electrolytic reaction (oxidation reaction) may occur at the anode, and oxygen gas, for example, may be produced.

The liquid (L) may be a liquid containing water. The water content in the liquid (L) may be 50% by mass or more, 80% by mass or more, or 90% by mass or more. The water content in the solvent in the liquid (L) may be 50% by mass or more, 80% by mass or more, or 90% by mass or more, but is 100% by mass or less. The solvent for the liquid (L) may be water. That is, the liquid (L) may be an aqueous solution. The solvent for the liquid (L) may be a mixture of water and another liquid (e.g., an organic solvent) as long as it does not inhibit the production of ammonia-based compounds.

The liquid (L) may be an acidic aqueous solution. The pH of the liquid (L) may be 6 or less, 4 or less, or 3 or less. The pH of the liquid (L) may be 1 or more, or 2 or more. The pH of the liquid (L) may be in the range of 1.04 to 4 (for example, in the range of 2 to 3). By having the liquid (L) have a low pH, it is possible to suppress the generation of hydrogen at the cathode and increase the rate of production of nitride ions (N ³⁻ ).

Examples of the liquid (L) that is an acidic aqueous solution include water in which an acid is dissolved. As the acid, an acid containing an anion that is difficult to be electrolyzed at the anode may be used. Examples of anions that are difficult to be decomposed at the anode include sulfate ions, phosphate ions, and organic acid ions (acetate ions, etc.). An acid containing a chloride ion (Cl ⁻ ) as an anion may be used. Examples of acids dissolved in the liquid (L) include hydrogen chloride, phosphoric acid compounds, sulfuric acid, and acetic acid. Examples of phosphoric acid compounds include phosphoric acid, potassium hydrogen phosphate, and sodium hydrogen phosphate. The liquid (L) may be hydrochloric acid (hydrogen chloride aqueous solution). Only one of these acids may be dissolved in the liquid (L), or a plurality of these acids may be dissolved. The liquid (L) may contain other solutes (e.g., salts) in addition to the above acids.

The manufacturing method (M) may include a step (a) of dissolving a gas containing nitrogen gas in a liquid (L). In a step (X), a voltage is applied between an anode and a cathode in the liquid (L) prepared in the step (a). The step (X) may be carried out after the step (a). However, when an ammonia-based compound is produced continuously, the step (a) and the step (X) may be carried out simultaneously.

The method for dissolving nitrogen-gas-containing gas (gas containing nitrogen gas) in liquid is not particularly limited, and known methods may be used. Examples of methods for dissolving nitrogen-gas-containing gas in liquid include bubbling the nitrogen-gas-containing gas, stirring the liquid in an atmosphere in which the nitrogen-gas-containing gas is present, and passing the liquid through an atmosphere in which the nitrogen-gas-containing gas is present. These methods may be used in combination. For example, the liquid being bubbled with the nitrogen-gas-containing gas may be stirred.

Examples of liquids that dissolve the nitrogen-gas-containing gas include the liquids mentioned above (e.g., acidic aqueous solutions). The nitrogen-gas-containing gas may be nitrogen gas or a mixture of nitrogen gas and another gas. For example, the nitrogen-gas-containing gas may be air. Air is preferable because it is easily available anywhere and can reduce manufacturing costs.

In this specification, examples of electrodes (anode, cathode) having any substance A (element or compound) on their surface include electrodes whose surfaces are coated with substance A and electrodes made of substance A. There are no particular limitations on the substrate to be coated with substance A, and conductors such as metals (e.g., titanium, copper, iron, and alloys thereof) can be used.

There are no particular limitations on the cathode, so long as it is possible to produce an ammonia-based compound. The cathode is preferably an electrode with a large hydrogen overvoltage. By using a cathode with a large hydrogen overvoltage, the voltage applied between the anode and cathode can be increased, and as a result, the rate at which ammonia-based compounds are produced can be increased.

The cathode may have a substance (metal, compound, or element other than a metal) on its surface that has a hydrogen overvoltage equal to or higher than the hydrogen overvoltage of copper. Examples of metals that have a hydrogen overvoltage equal to or higher than the hydrogen overvoltage of copper include copper, palladium, tin, lead, zinc, mercury, and tantalum. Lead (Pb), tin (Sn), and zinc (Zn) are preferred because they have a large hydrogen overvoltage. The cathode may have at least one selected from the group consisting of activated carbon, lead, tin, and copper, or an alloy thereof, on its surface. The cathode may have at least one selected from the group consisting of lead and tin, on its surface. The cathode may be an electrode having lead or an alloy thereof on its surface, an electrode having tin or an alloy thereof on its surface, or an electrode having copper or an alloy thereof on its surface. The cathode may have stainless steel on its surface, or may contain stainless steel fibers. The cathode may have at least one selected from the group consisting of activated carbon, lead, tin, stainless steel, and tantalum on its surface. However, it is preferable to use a substance that is difficult to dissolve in the liquid (L) on the surface of the cathode.

The cathode may be an electrode using activated carbon. An electrode using activated carbon is preferable because it has a large surface area. The cathode may include a sheet containing activated carbon. Examples of sheets containing activated carbon include nonwoven fabrics made of activated carbon fibers and porous sheets carrying activated carbon. The cathode may be a sheet containing activated carbon used in electricity storage devices such as capacitors. The cathode may include a sheet containing activated carbon and a current collector in contact with the sheet. The current collector is not particularly limited, and a current collector made of metal can be used. It is preferable to use a metal (such as titanium) that is not easily dissolved in the liquid (L) for the current collector.

The activated carbon may be activated carbon that has been heat-treated at a high temperature (e.g., 900° C. or higher). The BET specific surface area of the activated carbon before the heat treatment may be 1000 m ² /g or more, 1500 m ² /g or more, or 2000 m ² /g or more. There is no particular upper limit to the BET specific surface area of the activated carbon, and it may be, for example, 3000 m ² /g or less.

The cathode may include a sheet or a porous body made of conductive fibers. For example, the cathode may include a cloth (woven or nonwoven) of conductive fibers. The conductive fibers may be metal fibers. Preferred examples of metal fibers include metal fibers having the above-mentioned metals (metals with high hydrogen overvoltage) on the surface, and stainless steel fibers. The diameter of the metal fibers (e.g., stainless steel fibers) is not particularly limited, and may be 1 μm or more, 5 μm or more, or 8 μm or more, or may be 50 μm or less, 20 μm or less, 15 μm or less, or 10 μm or less. The type of stainless steel constituting the stainless steel fibers is not limited, and may be SUS304, SUS316L, or the like.

Stainless steel has a high hydrogen overvoltage. Furthermore, stainless steel fibers have a large surface area. Furthermore, the surface of stainless steel fibers has moderate hydrophilicity. Therefore, by using a cloth made of stainless steel fibers, it is possible to increase the current that flows during electrolysis, and to increase the rate at which ammonia-based compounds are produced.

There are no particular limitations on the anode, so long as it is possible to produce an ammonia-based compound. The anode is preferably an electrode with a low oxygen overvoltage. By using an anode with a low oxygen overvoltage, the anode potential can be lowered, and unwanted electrolysis reactions (e.g., oxidation of chloride ions) can be suppressed.

An example of an anode with a low oxygen overvoltage is an anode having iridium oxide on its surface. An example of an anode is an electrode whose surface is coated with iridium oxide. For example, a metal (e.g., titanium, niobium, tantalum, etc.) whose surface is coated with iridium oxide may be used as the anode. Other examples of anodes include electrodes with a large electric double layer capacity. The anode may be an electrode using activated carbon. Examples of electrodes using activated carbon include the electrodes using activated carbon described as examples of the cathode. In an anode using activated carbon, an electrolysis reaction (oxidation reaction) and/or adsorption of anions may occur. An anode using activated carbon can also be used as an electrode for removing dissolved oxygen in a liquid (L).

The combination of the anode and the cathode may be any of the following combinations (1) to (4).
(1) Anode: Anode using activated carbon. Cathode: Cathode using activated carbon.
(2) Anode: an anode having iridium oxide on the surface. Cathode: a cathode using activated carbon.
(3) Anode: an anode having iridium oxide on its surface. Cathode: a cathode having a metal with a large hydrogen overvoltage on its surface.
(4) Anode: An anode having iridium oxide on its surface. Cathode: A cathode comprising a porous body (e.g., cloth) containing stainless steel fibers.

In step (X), a voltage (DC voltage) is applied between the anode and cathode while they are immersed in the solution (S). A voltage required for electrolyzing dissolved nitrogen is applied between the anode and cathode. The magnitude of the applied voltage is affected by the liquid (L), the oxygen overvoltage of the anode, and the hydrogen overvoltage of the cathode. Therefore, the magnitude of the applied voltage may be selected according to the liquid (L), the anode, and the cathode. For example, a voltage may be applied so that the potential of the cathode is equal to or lower than the potential at which dissolved nitrogen is reduced. More specifically, a voltage may be applied so that the potential of the cathode is equal to or lower than the potential at which dissolved nitrogen is reduced, and the potential of the anode is equal to or higher than the oxygen generation potential. The potential of the electrodes may be controlled using a potentiostat.

When a cathode containing activated carbon and an anode having iridium oxide on its surface are used, the applied voltage may be in the range of 1.6 V to 2.0 V per unit cell. When a cathode having tin (Sn) on its surface and an anode having iridium oxide (IrO ₂ ) on its surface are used, the applied voltage may be in the range of 2.1 V to 2.5 V per unit cell. When a cathode including a stainless steel fiber cloth and an anode having iridium oxide on its surface are used, the applied voltage may be in the range of 2.1 V to 5 V per unit cell.

When an anode using activated carbon is used, charge may accumulate on the surface of the activated carbon of the anode during electrolysis at the cathode. Therefore, after step (X) has been performed to a certain extent, a step of releasing the charge accumulated on the surface of the activated carbon may be performed. For example, after performing step (X), a step of passing a current through the anode (anode using activated carbon) in step (X) as a cathode may be performed. For example, step (Z) may be performed in which a voltage is applied in the opposite direction to the voltage application direction in step (X). That is, in step (Z), a current may be passed between the anode (anode using activated carbon) in step (X) as a cathode and the cathode in step (X) as an anode. The activated carbon can be regenerated by step (Z).

In addition, instead of applying a voltage between the anode and cathode used in step (X), the activated carbon may be regenerated using a regeneration electrode for regenerating the activated carbon. For example, a voltage (DC voltage) may be applied between the regeneration electrode and the anode (activated carbon electrode) in step (X) so that the regeneration electrode serves as the anode and the activated carbon electrode serves as the cathode. The regeneration electrode is not particularly limited, but it is preferable that it is an electrode such as an iridium oxide electrode that has a low oxygen overvoltage and does not dissolve at the oxygen generation potential. The regeneration electrode may have platinum on its surface.

The cathode may have a void through which the liquid (L) flows. Then, step (X) may be performed in a state in which the liquid (L) flows through the void in the cathode. This configuration can increase the production rate of ammonia-based compounds. Examples of cathodes having voids include porous cathodes, cathodes having through holes, and cathodes including a cloth made of conductive fibers (e.g., stainless steel fibers). One example of a cathode having voids is a sheet containing activated carbon (e.g., a nonwoven fabric containing activated carbon). Another example of a cathode having voids is a metal electrode having voids. Examples of metal electrodes having voids include electrodes using foamed metal, electrodes using punched metal, electrodes using expanded metal, and electrodes composed of linear electrodes. The cathode may include at least one sheet-like electrode having voids. The cathode may include a laminate in which multiple sheet-like electrodes having voids are stacked. As described above, these electrodes may have a substance with a high hydrogen overvoltage on the surface. For example, these electrodes may have a surface made of a metal (such as lead, tin, or tantalum) that has a high hydrogen overvoltage.

The shape of the anode is not particularly limited, and may be any of the shapes exemplified for the cathode, or may be plate-shaped. The anode and cathode may each have a flat shape overall. The flat electrodes (anode, cathode) may be arranged parallel or nearly parallel to the surface of the liquid (L), or may be arranged perpendicular or nearly perpendicular to the surface of the liquid (L). When the electrode is considered to be a flat plate-shaped electrode, the angle between the main surface of the electrode and the surface of the liquid (L) may be in the range of 60 to 90° (e.g., in the range of 75 to 90°) or in the range of 0 to 30° (e.g., in the range of 0 to 15°).

An ammonia-based compound can be produced by the step (X). Examples of the ammonia-based compound include ammonia and a compound derived from ammonia. Examples of the compound derived from ammonia include ammonium salts. The ammonia-based compound may be at least one selected from the group consisting of ammonia and ammonium salts. Examples of the ammonium salt include ammonium chloride (NH ₄ Cl), ammonium sulfate ((NH ₄ ) ₂ SO ₄ ), ammonium phosphate ((NH ₄ ) ₃ PO ₄ ), and the like. The compound derived from ammonia may be a compound generated by the reaction of the ammonia generated by the step (X) with a component in the liquid (L).

The ammonia produced in step (X) may exist in the liquid (L) in the form of ions (e.g., NH4 ⁺ ). Therefore, the production method (M) can also be considered as a method for producing an ammonia-based atomic group. In this specification, an ammonia-based compound may be read as an ammonia-based atomic group. Examples of an ammonia-based atomic group include an ammonia-based compound and an ion derived from ammonia. Examples of an ion derived from ammonia include an ammonium ion (NH4 ⁺ ). The ammonia-based compound may be at least one selected from the group consisting of ammonia and ammonium chloride.

The liquid (L) containing the ammonia-based compound obtained in step (X) may be used for a predetermined purpose as it is. Alternatively, the manufacturing method (M) may include a step (Z) of separating the ammonia-based compound produced in step (X) from the liquid (L). Step (Z) is selected according to the type of ammonia-based compound produced in step (X) and the liquid (L). For example, ammonia may be selectively extracted by heating the liquid (L) containing the ammonia-based compound.

When the ammonia-based compounds in the liquid (L) are in an equilibrium state that changes depending on the pH of the liquid (L), the concentration of the ammonia-based compounds may be increased or the ammonia-based compounds may be made easier to separate from the liquid (L) by changing the pH of the liquid (L). For example, when the liquid (L) contains ammonium ions, it is possible to convert some of the ammonium ions into ammonia by making the liquid (L) alkaline, and to separate the ammonia gas from the liquid (L). At this time, the liquid (L) may be heated as necessary. The ammonia separated from the liquid (L) can be made into a liquid by applying pressure.

Dissolved oxygen present in the liquid (L) can be electrolyzed at the cathode to produce hydroxide ions (OH ⁻ ). Therefore, when dissolved oxygen is present in the liquid (L), the input power may be consumed for electrolysis of the dissolved oxygen. In order to reduce such losses, in the manufacturing method (M), a gas obtained by removing oxygen from air may be dissolved in the liquid (L). Alternatively, the manufacturing method (M) may include a step (b) of reducing the dissolved oxygen concentration in the liquid (L). The step (b) may be performed before or after the step (a) of dissolving a nitrogen-containing gas in the liquid (L). In a preferred example, the step (b) is performed after the step (a).

In the manufacturing method (M), nitrogen may be separated from air and used as a nitrogen-containing gas. The method and device for separating nitrogen from air are not particularly limited. For example, a nitrogen gas separator using hollow fibers made of polyimide (manufactured by UBE Co., Ltd.) may be used.

Step (b) may be performed by applying a DC voltage between the electrodes for removing dissolved oxygen in a range in which ammonia-based compounds are not produced. An activated carbon electrode may be used as the cathode for removing dissolved oxygen. An anode exemplified as an anode used in the production of ammonia-based compounds may be used as the anode for removing dissolved oxygen.

When an anode using activated carbon is used, dissolved oxygen may be electrolyzed at the anode in step (X). In that case, no power loss occurs due to dissolved oxygen.

In order to increase the concentration of dissolved nitrogen in the liquid (L), the nitrogen gas-containing gas may be dissolved in the liquid (L) while the liquid (L) and/or the nitrogen gas-containing gas (nitrogen gas-containing gas dissolved in the liquid (L)) are pressurized. For example, the entire system in which the liquid (L) is present may be pressurized. Alternatively, when dissolving the nitrogen gas-containing gas in the liquid (L), a high-pressure nitrogen gas-containing gas may be dissolved. As the high-pressure nitrogen gas-containing gas, a high-pressure nitrogen gas-containing gas stored in a gas cylinder or the like may be used.

When dissolving high-pressure nitrogen-containing gas in liquid (L), the tank in which step (X) is performed and the separation section in which ammonia-based compounds are separated may be separated and connected via a pressure regulating valve.

In the manufacturing method (M), a plurality of cells (electrolytic cells) in which the step (X) is performed may be used. The plurality of electrolytic cells may be connected in series or in parallel. One cell may have one or more electrode sets, each of which is made up of an anode and a cathode, arranged therein. The plurality of electrode sets may be connected in series or in parallel.

In the electrolysis in step (X), the potential of the cathode may be a potential at which hydrogen gas is generated at the cathode. By setting the potential of the cathode to a potential at which hydrogen gas is generated, it may be possible to increase the power used in the electrolysis of dissolved nitrogen. The current used in the electrolysis of dissolved nitrogen at the cathode is current In, and the current used in the production of hydrogen gas at the cathode is current Ih. In this case, the potential of the cathode in step (X) may be a potential at which the ratio Ih/In of the current Ih to the current In is 0.01 or more (e.g., 0.03 or more). The potential of the cathode in step (X) may be a potential at which the ratio Ih/In is 0.20 or less, or 0.10 or less.

(Ammonia-based compound manufacturing equipment)
The manufacturing apparatus according to this embodiment may be referred to as "manufacturing apparatus (D)" below. The manufacturing apparatus (D) is an apparatus for manufacturing an ammonia-based compound. The manufacturing apparatus (D) allows the manufacturing method (M) to be easily implemented. The manufacturing method (M) may be implemented using an apparatus other than the manufacturing apparatus (D). The matters described for the manufacturing method (M) may be applied to the manufacturing apparatus (D), and therefore duplicated explanations may be omitted. The matters described for the manufacturing apparatus (D) may be applied to the manufacturing method (M).

The manufacturing apparatus (D) includes a tank in which a liquid (L) containing dissolved nitrogen is placed, and an anode and a cathode placed in the tank. The liquid (L), anode, and cathode have been described above, so redundant description will be omitted.

The power supply for carrying out step (X) may be prepared separately from the manufacturing equipment (D). Alternatively, the manufacturing equipment (D) may include a power supply (DC power supply) for applying a voltage (DC voltage) between the anode and the cathode. The power supply may be a solar cell or a secondary battery. Alternatively, the power supply may be an AC-DC converter that converts externally supplied AC to DC. The power supply supplies power for causing electrolysis in step (X). The manufacturing equipment (D) may include a potentiostat for controlling the potential of the electrodes (anode, cathode).

The tank in which the liquid (L) is placed is not particularly limited, and may be any tank in which the liquid (L) can be stably placed. The tank may be a tank that is not open to the atmosphere.

The manufacturing apparatus (D) may further include a gas dissolving section that dissolves the nitrogen gas-containing gas in the liquid (L). The gas dissolving section includes equipment for carrying out the above-mentioned method for dissolving the nitrogen gas-containing gas in the liquid. For example, the gas dissolving section may include equipment for bubbling the nitrogen gas-containing gas, equipment for stirring the liquid, and equipment for spraying the liquid in the nitrogen gas-containing gas. The nitrogen gas-containing gas may be air or nitrogen gas.

As described above, the cathode may have a gap through which the liquid (L) flows. In this case, the manufacturing apparatus (D) may further include a liquid delivery mechanism that delivers the liquid (L) so that it flows through the gap of the cathode. The liquid delivery mechanism is not particularly limited, and a known liquid delivery mechanism may be used. Examples of the liquid delivery mechanism include a screw-shaped liquid delivery mechanism and a pump.

The manufacturing apparatus (D) may include a dissolved oxygen removal unit for carrying out the above-mentioned step (b). The dissolved oxygen removal unit includes a cathode for removing dissolved oxygen and an anode for removing dissolved oxygen, and includes a power source for applying a voltage thereto as necessary. The power source is not particularly limited, and may be any of the power sources exemplified as the power source for carrying out step (X).

When pressurizing the liquid (L) and/or the nitrogen-containing gas in order to increase the concentration of dissolved nitrogen in the liquid (L), the manufacturing apparatus (D) may include a pressurizing mechanism for that purpose. There are no particular limitations on the pressurizing mechanism, and a pump or the like may be used.

When dissolving high-pressure nitrogen-containing gas in the liquid (L), the manufacturing equipment (D) may include a tank (electrolytic tank) for carrying out the step (X) and a separation section (e.g., a separation tank) for separating the ammonia-based compounds. The electrolytic tank and the separation section may be connected via a pressure regulating valve.

In the manufacturing equipment (D), nitrogen may be separated from air and used as a nitrogen-containing gas. In that case, the manufacturing equipment (D) may include a device that separates nitrogen from air. The device that separates nitrogen is not limited, and a nitrogen gas separator (manufactured by UBE Co., Ltd.) using hollow fibers made of polyimide may be used.

The manufacturing equipment (D) may include a plurality of cells (electrolytic cells) in which the step (X) is carried out. The plurality of electrolytic cells may be connected in series or in parallel. One cell may have one or more electrode sets, each of which is made up of an anode and a cathode, arranged therein. The plurality of electrode sets may be connected in series or in parallel.

The manufacturing apparatus (D) may include a separator disposed between the cathode and anode. The separator can separate a tank in which the liquid (L) is disposed. The separator may be a sheet that allows ions to pass through but inhibits the passage of liquid to some extent. For example, the separator may be a porous membrane made of a resin (e.g., polyolefin) that is used in lithium ion secondary batteries. For example, a separator for lithium ion secondary batteries manufactured by Celgard may be used.

Below, examples of embodiments according to the present disclosure will be specifically described with reference to the drawings. The above description can be applied to the embodiments described below, and the embodiments described below may be modified based on the above description. Among the components of the embodiments described below, components that are not essential to the manufacturing method and manufacturing apparatus according to the present disclosure and can be omitted may be omitted. In addition, the matters described below may be applied to the above embodiments.

(Embodiment 1)
In the first embodiment, an example of a manufacturing method (M) and a manufacturing apparatus (D) will be described. The configuration of a manufacturing apparatus 100 of the first embodiment is shown in FIG. 1. The manufacturing apparatus 100 of an ammonia-based compound includes a tank 110, an anode 121 and a cathode 122 disposed in the tank 110, and a power source (DC power source) 130. A liquid L containing dissolved nitrogen is disposed in the tank 110. The power source 130 applies a predetermined DC voltage between the anode 121 and the cathode 122. This causes a current to flow between the anode 121 and the cathode 122, causing electrolysis. As a result, an ammonia-based compound is produced in the liquid L.

The manufacturing apparatus 100 may further include a gas dissolution section that dissolves the nitrogen-containing gas in the liquid L. FIG. 2 shows a schematic configuration of an example of a manufacturing apparatus (D) including such a gas dissolution section. The manufacturing apparatus 100 shown in FIG. 2 includes a gas dissolution section 140. The gas dissolution section 140 includes a gas dissolution tank 141, a gas dissolution mechanism 142 arranged in the gas dissolution tank 141, a first flow path 143, a second flow path 144, and a pump 145.

In FIG. 2, an example is shown in which the pump 145 is disposed in the first flow path 143, but the pump 145 may be disposed in the second flow path 144. In FIG. 2, the flow direction of the liquid L is indicated by an arrow. The liquid L in the gas dissolution tank 141 is sent from the gas dissolution tank 141 to the tank 110 through the first flow path 143 by the pump 145. The liquid L in the tank 110 is sent to the gas dissolution tank 141 through the second flow path 144. That is, the liquid L in the tank 110 circulates through a circulation path including the tank 110 and the gas dissolution tank 141.

2 shows an example in which a bubbling device for bubbling (e.g., air) is used as the gas dissolution mechanism 142 in the membrane 111b. A flow path (not shown) for supplying nitrogen-gas-containing gas is connected to the gas dissolution mechanism 142. Of the bubbled nitrogen-gas-containing gas, gas that has not dissolved in the liquid L is released from a gas outlet 141a at the top of the gas dissolution tank 141. The gas dissolution mechanism 142 may be a stirring device that stirs the liquid L in the presence of nitrogen-gas-containing gas. Nitrogen gas is dissolved in the liquid L by the gas dissolution mechanism 142, becoming dissolved nitrogen. The dissolved nitrogen concentration of the liquid L in the gas dissolution tank 141 is increased by the gas dissolution mechanism 142. On the other hand, the dissolved nitrogen concentration of the liquid L in the tank 110 is decreased by electrolysis.

As described above, the cathode 122 may have a gap through which the liquid L flows. FIG. 3 shows a schematic configuration of an example of a manufacturing apparatus (D) in this case. In FIG. 3, the direction in which the liquid L flows is indicated by an arrow. In the manufacturing apparatus 100 shown in FIG. 3, a first flow path 143 and a second flow path 144 are arranged so that the liquid L in the tank 110 passes through the gap in the cathode 122. Specifically, an inlet 143a through which the liquid L in the gas dissolution tank 141 flows into the tank 110 and an outlet 144a through which the liquid L flows out of the tank 110 toward the gas dissolution tank 141 are arranged to sandwich the cathode 122. The cathode 122 is arranged to separate the tank 110.

As described above, the manufacturing apparatus (D) may include a dissolved oxygen removal section for removing dissolved oxygen. The manufacturing apparatus (D) may also include a mechanism for pressurizing the liquid L and/or the nitrogen gas-containing gas.

One example of a manufacturing apparatus (D) including a pump for pressurizing the liquid L and the nitrogen-gas-containing gas is shown in FIG. 4, and another example is shown in FIG. 5. The manufacturing apparatus 100 in FIGS. 4 and 5 includes a pump 151 for pressurizing the nitrogen-gas-containing gas and sending it to the tank 110. In the manufacturing apparatus 100 in FIGS. 4 and 5, the nitrogen-gas-containing gas is pressurized and sent to the tank 110. This makes it possible to increase the concentration of dissolved nitrogen in the liquid L and to increase the rate of production of ammonia-based compounds. The area in which the liquid L is pressurized may be sealed to maintain the pressure.

The manufacturing apparatus in FIG. 5 is a modified version of the manufacturing apparatus in FIG. 3, so a duplicated description will be omitted. In the manufacturing apparatus 100 in FIG. 5, bubbling is performed using pressurized nitrogen-containing gas. The manufacturing apparatus 100 in FIG. 5 includes a gas outlet 141a for releasing gas in the gas dissolution tank 141, and a pressure adjustment valve 152 arranged in a flow path between the gas outlet 141a and the gas dissolution tank 141. The pressure adjustment valve 152 is a valve for maintaining the pressure in the gas dissolution tank 141.

FIG. 6 shows another example of a manufacturing apparatus (D) including a pump for pressurizing the liquid L and the nitrogen-gas-containing gas. Note that the power source is not shown in FIGS. 6 and 7. The manufacturing apparatus 100 in FIG. 6 includes a pump 151 for pressurizing the nitrogen-gas-containing gas and sending it to the tank 110. In the manufacturing apparatus 100 in FIG. 6, the nitrogen-gas-containing gas is pressurized and sent to the tank 110. This makes it possible to increase the concentration of dissolved nitrogen in the liquid L and to increase the rate of production of ammonia-based compounds.

The manufacturing apparatus 100 in FIG. 6 includes a separation tank 161 as a separation section for separating ammonia-based compounds. The separation tank 161 and the tank 110 are connected by flow paths 162 and 163. A pump 164 is disposed in the flow path 162. A pressure regulating valve (pressure reducing valve) 165 is disposed in the flow path 163. The pump 164 circulates the liquid L in the direction of the arrow through a circulation path formed by the tank 110, the flow path 163, the separation tank 161, and the flow path 162. In the manufacturing apparatus in FIG. 6, the flow path 162 downstream of the pump 164, the tank 110, and the flow path 163 upstream of the pressure regulating valve 165 are high-pressure regions. On the other hand, the flow path 163 downstream of the pressure regulating valve 165, the separation tank 161, and the flow path 162 upstream of the pump 164 can be low-pressure (for example, about atmospheric pressure).

In the separation tank 161, the ammonia-based compounds are separated. The separation of the ammonia-based compounds may be performed by adjusting the pH, or the like. Alternatively, the ammonia-based compounds may be separated by utilizing the difference in physical properties between the ammonia-based compounds and the liquid L (e.g., the difference in vapor pressure or the difference in boiling point). When utilizing the difference between the boiling point of the ammonia-based compounds and the boiling point of the liquid L, the liquid L in the separation tank 161 may be heated. The separation tank 161 is provided with an outlet for removing the ammonia-based compounds as necessary.

In the devices of Figures 4 and 6, the flat cathode is placed approximately parallel to the surface of liquid L. In this case, the cathode 122 may be placed near the surface of liquid L. For example, a part of the cathode 122 may be exposed above the surface of liquid L. Alternatively, the cathode 122 may be placed so that the distance between the surface of liquid L and the cathode 122 immersed in liquid L is within 1 cm. By placing the cathode 122 near the surface of liquid L, the dissolved nitrogen in liquid L can be electrolyzed quickly.

As shown in FIG. 5, in the manufacturing apparatus (D), bubbling may be performed using a high-pressure nitrogen-containing gas. FIG. 7 shows an example of bubbling using a high-pressure nitrogen-containing gas in the apparatus of FIG. 6. The manufacturing apparatus 100 of FIG. 7 includes a gas dissolving mechanism 142 and a pump 151. The pump 151 sends high-pressure nitrogen-containing gas to the gas dissolving mechanism 142. In the gas dissolving mechanism 142, the nitrogen-containing gas is released into the liquid L in the form of bubbles. The manufacturing apparatus 100 of FIG. 7 may include a gas outlet for releasing gas in the tank 110, and a pressure regulating valve arranged in a flow path between the gas outlet and the tank 110.

In addition, devices other than that shown in FIG. 6 may also include a separation section for separating ammonia-based compounds, similar to that shown in FIG. 6.

Another example of the manufacturing apparatus (D) is shown in FIG. 8. The manufacturing apparatus 100 in FIG. 8 includes a tank 110, an anode 121 and a cathode 122 disposed in the tank 110, a power source (not shown), and a separator 181. The tank 110 is divided by the separator 181 into an anode tank 111 and a cathode tank 112. The separator 181 may be any of the separators described above.

A gas discharge pipe 111a is connected to the top of the anode chamber 111. A membrane 111b that does not allow liquid to pass but allows gas to pass is arranged midway through the gas discharge pipe 111a. A known membrane may be used for the membrane 111b, or a microporous membrane made of fluororesin may be used. For example, Temish (registered trademark) manufactured by Nitto Denko Corporation may be used for the membrane 111b.

The cathode chamber 112 is divided into cathode chamber 112a and cathode chamber 112b by the cathode 122. The cathode chamber 112a is located on the anode 121 side. A supply path 188 for liquid L is connected to the bottom of the cathode chamber 112a (the area between the separator 181 and the cathode 122). A discharge path 189 for liquid is connected to the top of the cathode chamber 112b. The supply path 188 and the discharge path 189 are connected to the gas dissolving section 140 (not shown).

The flow of liquid in the manufacturing apparatus 100 in FIG. 8 is indicated by arrows. Liquid L (e.g., an acidic aqueous solution) in which the dissolved nitrogen concentration has increased in the gas dissolving section 140 is supplied from the supply path 188 to the cathode chamber 112a. The liquid L moves to the cathode chamber 112b through the gap in the cathode 122. Liquid L is distributed throughout the chamber 110. By applying a DC voltage between the anode 121 and the cathode 122, an ammonia-based compound is generated in the cathode chamber 112. Meanwhile, oxygen gas is generated in the anode 121. The generated oxygen gas is discharged to the outside of the manufacturing apparatus 100 through the gas discharge pipe 111a and the membrane 111b. Liquid L containing the ammonia-based compound is discharged from the discharge path 189. In this manner, an ammonia-based compound is generated.

As shown in FIG. 9, two anode chambers 111 may be arranged to sandwich the cathode chamber 112.

The above description discloses the following manufacturing apparatus and method.
(1) A method for producing an ammonia-based compound, comprising the steps of:
A method for producing an ammonia-based compound, comprising: a step (X) of applying a voltage between an anode and a cathode in a liquid containing dissolved nitrogen.
(2) The manufacturing method described in (1), wherein the liquid is an acidic aqueous solution.
(3) The method according to (1) or (2), further comprising the step (a) of dissolving a gas containing nitrogen gas in the liquid.
(4) The manufacturing method described in (3), wherein the gas is air.
(5) The method according to any one of (1) to (4), wherein the anode has iridium oxide on a surface thereof.
(6) The method according to any one of (1) to (5), wherein the cathode has at least one selected from the group consisting of activated carbon, lead, tin, and tantalum on a surface thereof.
(7) The method according to any one of (1) to (6), wherein the ammonia-based compound is at least one selected from the group consisting of ammonia and ammonium salts.
(8) The cathode has a gap through which the liquid flows,
The method according to any one of (1) to (7), wherein the step (X) is performed in a state in which the liquid is flowing through the gap.
(9) An apparatus for producing an ammonia-based compound, comprising:
A tank in which a liquid containing dissolved nitrogen is placed;
and an anode and a cathode disposed in the tank.
(10) The manufacturing apparatus according to (9), wherein the liquid is an acidic aqueous solution.
(11) The manufacturing apparatus according to (9) or (10), further comprising a gas dissolving section for dissolving a gas containing nitrogen gas in the liquid.
(12) The manufacturing apparatus according to (11), wherein the gas is air.
(13) The manufacturing apparatus according to any one of (9) to (12), wherein the anode has iridium oxide on a surface thereof.
(14) The manufacturing apparatus according to any one of (9) to (13), wherein the cathode has at least one selected from the group consisting of activated carbon, lead, tin, and tantalum on a surface thereof.
(15) The production apparatus according to any one of (9) to (14), wherein the ammonia-based compound is at least one selected from the group consisting of ammonia and ammonium salts.
(16) The manufacturing apparatus according to any one of (9) to (15), wherein the cathode has a gap through which the liquid flows.

The above (6) and (14) may be replaced with the following (6) and (14).
(6) The method according to any one of (1) to (5), wherein the cathode has at least one selected from the group consisting of activated carbon, lead, tin, stainless steel, and tantalum on a surface thereof.
(14) The manufacturing apparatus according to any one of (9) to (13), wherein the cathode has at least one selected from the group consisting of activated carbon, lead, tin, stainless steel, and tantalum on a surface thereof.

The manufacturing apparatus and manufacturing method disclosed herein will be explained in more detail using examples.

(Experiment 1)
In Experiment 1, an example of producing an ammonia-based compound will be described. An _IrO2 electrode was used as the anode. An activated carbon cloth (a cloth made of fibers containing activated carbon) was used as the cathode. An activated carbon cloth heat-treated at 900°C was used as the activated carbon cloth. A hydrochloric acid solution with a pH of 2 was used as the liquid (L). The dissolved nitrogen concentration in the liquid (L) was increased by bubbling air in the liquid (L).

While continuing to bubble air, a direct current of 1.8 V was applied between the anode and cathode immersed in liquid (L) for approximately 3 minutes, allowing a current to flow between the anode and cathode. After that, Nessler's reagent was used to check whether ammonia was being produced in liquid (L). As a result, it was confirmed that ammonia was being produced in liquid (L).

A comparison was made between the case where step (X) was performed using the apparatus shown in Figure 2 and the case where step (X) was performed using the apparatus shown in Figure 3. As a result, when the apparatus shown in Figure 3 was used, the current value flowing between the anode and cathode increased by 30 times compared to when the apparatus shown in Figure 2 was used. From this result, it is believed that ammonia-based compounds can be efficiently produced by using the apparatus shown in Figure 3.

In an experiment using a cloth made of stainless steel fibers as the cathode instead of the activated carbon cloth, the current flowing during electrolysis could be increased. In an experiment of synthesizing an ammonia-based compound using an activated carbon cloth, the current per unit area of the cathode was 0.0067 A/ ^cm2 . By replacing the activated carbon cloth with a cloth made of stainless steel fibers, the current per unit area of the cathode was significantly increased (20 times or more). This suggests that the use of a cloth made of stainless steel fibers increased the rate of production of ammonia-based compounds.

INDUSTRIAL APPLICABILITY The present invention can be used in a method for producing an ammonia-based compound and an apparatus for producing an ammonia-based compound.
Although the present invention has been described with respect to the presently preferred embodiments, such disclosure should not be interpreted as limiting. Various variations and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. Accordingly, the appended claims should be interpreted to cover all variations and modifications without departing from the true spirit and scope of the present invention.

100: Manufacturing apparatus 110: Tank 121: Anode 122: Cathode 130: Power source 140: Gas dissolving section 141: Gas dissolving tank 141a: Gas discharge port 142: Gas dissolving mechanism 143: First flow path 144: Second flow path 145: Pump L Liquid

Claims (16)

A method for producing an ammonia-based compound, comprising the steps of:
A method for producing an ammonia-based compound, comprising: a step (X) of applying a voltage between an anode and a cathode in a liquid containing dissolved nitrogen. The manufacturing method according to claim 1, wherein the liquid is an acidic aqueous solution. The method of claim 1 or 2, which includes step (a) of dissolving a gas containing nitrogen gas in the liquid. The manufacturing method of claim 3, wherein the gas is air. The manufacturing method according to claim 1 or 2, wherein the anode has iridium oxide on its surface. The manufacturing method according to claim 1 or 2, wherein the cathode has at least one material selected from the group consisting of activated carbon, lead, tin, stainless steel, and tantalum on its surface. The method according to claim 1 or 2, wherein the ammonia-based compound is at least one selected from the group consisting of ammonia and ammonium salts. The cathode has a gap through which the liquid flows,
The method according to claim 1 or 2, wherein the step (X) is carried out in a state in which the liquid is flowing through the gap. An apparatus for producing an ammonia-based compound, comprising:
A tank in which a liquid containing dissolved nitrogen is placed;
and an anode and a cathode disposed in the tank. The manufacturing apparatus according to claim 9, wherein the liquid is an acidic aqueous solution. The manufacturing apparatus according to claim 9 or 10, further comprising a gas dissolving section that dissolves a gas containing nitrogen gas in the liquid. The manufacturing apparatus of claim 11, wherein the gas is air. The manufacturing apparatus according to claim 9 or 10, wherein the anode has iridium oxide on its surface. The manufacturing apparatus according to claim 9 or 10, wherein the cathode has at least one material selected from the group consisting of activated carbon, lead, tin, stainless steel, and tantalum on its surface. The manufacturing apparatus according to claim 9 or 10, wherein the ammonia-based compound is at least one selected from the group consisting of ammonia and ammonium salts. The manufacturing apparatus according to claim 9 or 10, wherein the cathode has a gap through which the liquid flows.

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