JP5127385B2 - Ammonia electrosynthesis system - Google Patents

Description

  The present invention relates to an ammonia electrosynthesis apparatus.

Conventionally, ammonia has been widely produced at the industrial level by the Harbor Bosch process. The Harbor Bosch method is a method of synthesizing ammonia from hydrogen gas and nitrogen gas, and in the presence of an iron-based ternary catalyst containing Al ₂ O ₃ and K ₂ O in Fe, FeO, Fe ₃ O _{4 and the} like. Then, ammonia is produced by reacting hydrogen gas and nitrogen gas.

However, since the Harbor Bosch method is a synthesis at a high temperature and a high pressure, energy consumption and equipment scale are enormous. Moreover, there is a problem that a large amount of CO ₂ is discharged when hydrogen gas is obtained by steam reforming of hydrocarbons.

As a method for improving the above problem, development of a method that does not use hydrogen gas can be mentioned. For example, Non-Patent Document 1 describes a method for electrolytic synthesis of ammonia from water and nitrogen under normal pressure. In this method, nitride ions (N ³⁻ ) are generated from the cathode and reacted with water (water vapor) to electrosynthesize ammonia. Specifically, a molten salt is used as the electrolytic bath. At the cathode, nitrogen gas is reduced and N ³⁻ is supplied to the electrolytic bath. The electrolytic bath is supplied with water vapor and reacts with N ³⁻ to produce ammonia. At the anode, oxide ions (O ²⁻ ) by-produced by electrolytic synthesis and hydroxide ions (OH ⁻ ) generated by the equilibrium reaction of water vapor are oxidized to generate oxygen gas. Each reaction is exemplified as follows.

Anodic reaction: 3O ²⁻ → 3 / 2O ₂ + 6e ⁻
In molten salt: 3H ₂ O + 2N ^{3 −} → 2NH ₃ + 3O ²⁻
Cathodic reaction: N ₂ + 6e ⁻ → 2N ³⁻
Total reaction: N ₂ + 3H ₂ O → 2NH ₃ + 3 / 2O ₂
Ito, Y., Molten salt and high temperature chemistry, Vol. 46, no. 2. (August 2003) "Normal pressure ammonia electrosynthesis-Fundamental technology of ammonia economy-"

The ammonia electrosynthesis method described in Non-Patent Document 1 can electrolyze ammonia from water and nitrogen under conditions that are milder and consume less energy than the Harbor Bosch method. Further, since no hydrogen gas is used, there is no problem of discharging a large amount of CO ₂ .

  However, the electrolytic synthesis apparatus specifically disclosed in Non-Patent Document 1 has insufficient ammonia synthesis efficiency, and there is room for further improvement. Accordingly, an object of the present invention is to provide an apparatus for electrosynthesis of ammonia from water and nitrogen, and an ammonia electrosynthesis apparatus with improved ammonia synthesis efficiency.

  As a result of intensive studies to achieve the above object, the present inventor has found that the above object can be achieved by devising the type of water vapor supplied to the electrolytic bath and the means for stirring the electrolytic bath. It came to be completed.

That is, the present invention relates to the following ammonia electrosynthesis apparatus.
1. An apparatus for electrosynthesis of ammonia from water and nitrogen, the apparatus comprising:
(1) An apparatus for synthesizing the ammonia by supplying refined water vapor and nitrogen gas to a molten salt that is an electrolytic bath,
(2) an anode that generates oxygen gas by oxidizing O ²⁻ and / or OH ⁻ generated by the reaction of the water vapor;
(3) a cathode that reduces nitrogen gas to generate N ³⁻ ;
(4) means for supplying the refined water vapor;
(5) the supply gas to produce a gas lift in the molten salt, Ri by the causing the pre-Symbol upward flow in the molten salt, the molten salt, the anode, the means for supplying the cathode and the steam the gas causes the gas lift to circulate in a loop with a supply port to a portion to have a means for supplying,
(6) In the bottom of the electrolytic cell or in the vicinity of the bottom, a supply port of a means for supplying the gas that causes the gas lift is provided.
An ammonia electrosynthesis apparatus characterized by that.
2. An apparatus for electrosynthesis of ammonia from water and nitrogen, the apparatus comprising:
(1) An apparatus for synthesizing the ammonia by supplying refined water vapor and nitrogen gas to a molten salt that is an electrolytic bath,
(2) An electrolytic cell A and an electrolytic cell B having the molten salt, wherein the electrolytic cell A and the electrolytic cell B are separated from each other by a hydrogen permeable metal film,
(3) an anode provided in the electrolytic cell A that generates oxygen gas by oxidizing O ²⁻ and / or OH ⁻ generated by the reaction of the water vapor ;
(4) a cathode provided in the electrolytic cell B that reduces nitrogen gas to generate N ³⁻ ;
(5) means for supplying the refined water vapor;
(6) A gas that causes a gas lift to the molten salt in the electrolytic cell A is supplied, and an upward flow is generated in the molten salt, whereby the molten salt in the electrolytic cell A is converted into the anode and the hydrogen permeability. Means for supplying a gas for generating the gas lift so as to be circulated in a loop having a supply port of a means for supplying the metal film and the water vapor in part.
(7) At the bottom of the electrolytic cell A or in the vicinity of the bottom, a supply port for supplying gas for generating the gas lift is provided.
An ammonia electrosynthesis apparatus characterized by that.
3 . The ammonia electrolytic synthesis apparatus according to Item 1, wherein the molten salt is at least one selected from the group consisting of alkali metal halides and alkaline earth metal halides.
4). The molten salt in the electrolytic cell A is at least one selected from the group consisting of an alkali metal halide, an alkaline earth metal halide, and a molten hydroxide,
The molten salt in the electrolytic cell B is at least one selected from the group consisting of alkali metal halides and alkaline earth metal halides,
Item 3. The ammonia electrosynthesis apparatus according to Item 2.
5. Item 5. The ammonia electrolytic synthesis apparatus according to any one of Items 1 to 4, wherein the means for supplying water vapor supplies the refined water vapor having a bubble diameter of 100 nm to 1 mm.
6). Item 5. The ammonia according to any one of Items 1 to 4 , wherein the means for supplying water vapor supplies the fine water vapor so that 10 to 10 million bubbles are contained per 1 cm ^{3 of the} molten salt. Electrosynthesis device.
7). Item 7. The ammonia electrolytic synthesis apparatus according to any one of Items 1 to 6, wherein the means for supplying the gas for generating the gas lift supplies the gas for generating the gas lift including an inert gas.
8 . Item 8. The ammonia electrolytic synthesis apparatus according to any one of Items 1 to 7 , further comprising trap means for removing impurities from the ammonia-containing gas obtained by the electrolytic synthesis.

The ammonia electrosynthesis apparatus of the present invention supplies the refined water vapor to the molten salt. Further, the gas component is supplied to the molten salt, and the molten salt is stirred by the upward flow of the molten salt containing the gas component. Thereby, N ³⁻ and water vapor are efficiently brought into contact with each other, and O ²⁻ can be efficiently oxidized and removed, so that ammonia synthesis efficiency is improved.

  The ammonia electrosynthesis apparatus of the present invention includes a trap means for removing impurities contained in the ammonia-containing gas obtained by electrolytic synthesis (for example, a trap means for removing impurities such as molten salt vapor, unreacted water vapor, inert gas). By providing, higher purity ammonia can be obtained.

The ammonia electrosynthesis apparatus (invention apparatus) of the present invention is an apparatus for electrosynthesis of ammonia from water and nitrogen, and the apparatus comprises:
(1) An apparatus for synthesizing the ammonia by supplying refined water vapor and N ^3- to a molten salt that is an electrolytic bath,
(2) means for supplying a gas component to the molten salt and stirring the molten salt by an upward flow of the molten salt containing the gas component;
(3) an anode that oxidizes O ²⁻ generated by the reaction of the water vapor to generate oxygen gas;
(4) a cathode that reduces nitrogen gas to generate N ³⁻ ,
It is characterized by having.

An outline of ammonia electrolytic synthesis using the electrolytic synthesis apparatus of the present invention is shown below. That is, nitrogen gas is reduced at the cathode and N ^{3 −} is supplied to the electrolytic bath (molten salt). Water vapor is supplied to the molten salt, and water vapor and N ³⁻ are reacted to generate ammonia and O ²⁻ . At the anode, O ²⁻ is oxidized to generate oxygen gas. That is, in principle, ammonia and oxygen are synthesized from water and nitrogen.

In particular, the apparatus of the present invention uses water vapor refined as water vapor. Therefore, a large surface area of water vapor involved in the ammonia synthesis reaction can be secured. Further, since the apparatus of the present invention supplies the gas component to the molten salt and stirs the molten salt by the upward flow, the supply of N ³⁻ to the molten salt and the removal of O ²⁻ from the molten salt are promoted to reduce the ammonia. Synthesis efficiency is improved.

  Hereafter, each structure of this invention apparatus is demonstrated.

(Electrolytic bath)
A molten salt is used as the electrolytic bath.

The molten salt is not particularly limited as long as N ³⁻ can stably exist, and examples thereof include at least one of an alkali metal halide and an alkaline earth metal halide.

  Examples of the alkali metal halide include LiF, NaF, KF, RbF, CsF, LiCl, NaCl, KCl, RbCl, CsCl, LiBr, NaBr, KBr, RbBr, CsBr, LiI, NaI, KI, RbI, CsI, and the like. Can be mentioned.

Examples of the alkaline earth metal halides, _{e.g., MgF 2, CaF 2, SrF} 2, BaF 2, MgCl 2, CaCl 2, SrCl 2, BaCl 2, MgBr 2, CaBr 2, SrBr 2, BaBr 2, MgI 2, CaI _{2, SrI 2,} BaI _2, and the like.

  These compounds can be used individually or in combination of 2 or more types. The combination and mixing ratio of the compounds are not limited, and are appropriately set according to the desired operating temperature of the molten salt.

  Although the temperature of the molten salt is not limited, 200 to 450 ° C. is preferable and 250 to 400 ° C. is more preferable in that ammonia is easily decomposed into nitrogen gas and hydrogen gas in a high temperature range, so that decomposition of ammonia is suppressed. .

In the present invention, at least one of the following (1) to (4) is preferable as the molten salt.
(1) LiCl-KCl
[Composition ratio: LiCl: KCl = 35-100 mol%: 65-0 mol% is preferable, and 55-65 mol%: 45-35 mol% is more preferable. ]
(2) LiCl-KCl-CsCl
[Composition ratio: LiCl: KCl: CsCl = 57.5: 13.3: 29.2 mol% is preferred. However, the composition ratio may be changed by about 20%. ]
(3) LiBr-KBr
[Composition ratio: LiBr: KBr = 35-100 mol%: 65-0 mol% is preferable, and 60-70 mol%: 40-30 mol% is more preferable. ]
(4) LiBr-KBr-CsBr
[Composition ratio: LiBr: KBr: CsBr = 56.1: 18.9: 25.0 mol% is preferred. However, the composition ratio may be changed by about 20%. ]
In addition, at least one of the following (5) to (19) can be used as the molten salt.
(5) LiCl-CsCl
[Composition ratio: 35 to 65 mol%: 65 to 35 mol% is preferable. (Eutectic melting point: 306 ° C)
(6) LiCl-NaCl-KCl
[Composition ratio: 45-60 mol%: 5-15 mol%: 30-40 mol% is preferable. (Eutectic point: 346 ° C)
(7) LiCl-NaCl-KCl-RbCl
[Composition ratio: 45 to 55 mol%: 5 to 15 mol%: 15 to 25 mol%: 20 to 30 mol% is preferable. (Eutectic melting point: 297 ° C)
(8) LiCl-NaCl-KCl-LiF
[Composition ratio: 45 to 55 mol%: 5 to 15 mol%: 30 to 40 mol%: 1 to 10 mol% is preferable. (Eutectic melting point: 332 ° C)
(9) LiCl-KBr
[Composition ratio: 55 to 65 mol%: 45 to 35 mol% is preferable. (Eutectic melting point: 360 ° C)
(10) LiCl-NaCl-KBr
[Composition ratio: 50 to 65 mol%: 5 to 15 mol%: 30 to 40 mol% is preferable. (Eutectic melting point: 340 ° C)
(11) LiCl-KCl-LiBr-KBr
[Composition ratio: 5 to 20 mol%: 5 to 40 mol%: 30 to 50 mol%: 20 to 35 mol% is preferable. (Eutectic melting point: 310 ° C)
(12) LiBr-KCl
[Composition ratio: 55 to 65 mol%: 45 to 35 mol% is preferable. (Eutectic melting point: 327 ° C)
(13) LiBr-NaBr-KCl
[Composition ratio: 50-60 mol%: 5-15 mol%: 30-40 mol% is preferred. (Eutectic melting point: 320 ° C)
(14) LiBr-CsBr
[Composition ratio: 45 to 70 mol%: 55 to 30 mol% is preferable. (Eutectic melting point: 230 ° C)
(15) LiBr-RbBr
[Composition ratio: 50 to 65 mol%: 50 to 35 mol% is preferable. Eutectic point 259 ° C)
(16) LiBr-NaBr-KBr
[Composition ratio: 50 to 65 mol%: 5 to 15 mol%: 30 to 40 mol% is preferable. Eutectic point 324 ° C)
(17) LiBr-KBr-RbBr
[Composition ratio: 50-60 mol%: 5-15 mol%: 30-40 mol% is preferred. (Eutectic point 268 ° C)
(18) LiI-KI
[Composition ratio: 60 to 70 mol%: 40 to 30 mol% is preferable. (Eutectic point 260 ° C)
(19) CsCl-CsF-CsI
[Composition ratio: 30 to 40 mol%: 30 to 40 mol%: 30 to 40 mol% is preferable. (Eutectic melting point: 365 ° C)
(cathode)
As the cathode, a cathode that reduces nitrogen gas and supplies N ³⁻ to the molten salt is used. The cathodic reaction is as follows.

1 / 2N ₂ + 3e ⁻ → N ^{3 −}
The material of the cathode may be any metal or alloy that can reduce nitrogen gas. For example, those containing nickel or iron are preferable, and those containing nickel are particularly preferable. The shape of the cathode is preferably porous, wire mesh, or mesh used for Raney catalysts or MCFC electrodes, and a catalyst such as Pt, Ir, or Ru may be supported on the surface of the cathode.

  Porous nickel has good wettability to molten salt, so that simply by contacting the molten salt, the inside of the porous layer is completely immersed and a solid-gas-liquid three-phase interface that facilitates the reduction reaction of nitrogen gas is sufficiently formed. Therefore, the electrode surface may not be used effectively. Therefore, by treating the surface of the porous nickel to control the wettability (coexisting wet and hard-to-wet areas) and blowing nitrogen gas into the porous nickel, etc. It is preferable to devise to generate a phase interface. For example, it is preferable to always generate a fresh solid-gas-liquid three-phase interface by blowing nitrogen gas into the cathode using a porous gas diffusion electrode.

Further, since the generated N ³⁻ stays inside the porous electrode is an obstacle to sustaining the reduction reaction of nitrogen gas, when the porous electrode is used, N ³⁻ is quickly removed from the porous electrode. It is preferable to remove outside. For example, it is preferable to devise a technique for constantly flowing (passing) the molten salt through the porous electrode or a technique for constantly flowing (stirring) the molten salt inside the porous gas by blowing nitrogen gas into the porous electrode.

(anode)
As the anode, an anode that generates oxygen gas by oxidizing O ²⁻ generated by the reaction of water vapor is used. The anodic reaction is as follows.

O ²⁻ → 1 / 2O ₂ + 2e ⁻
The above anodic reaction is a main reaction. In addition, a reaction (* 1) in which OH ⁻ generated by an equilibrium reaction of H ₂ O in molten salt is oxidized to generate oxygen gas, and a very small amount of molten salt. It is considered that a reaction (* 2) for generating oxygen gas from H ₂ O remaining therein also occurs.

H ₂ O + O ²⁻ →→ 2OH ⁻ , 2OH ⁻ → _1/2 O ₂ + H ₂ O + 2e (* 1)
H ₂ O → 1 / 2O ₂ + 2H ⁺ + 2e (* 2)
As the anode, an electrode material commercially available as an insoluble anode or an oxygen generating anode can be used. Among these, conductive ceramics such as nickel ferrite and conductive diamond electrodes are preferable. Especially for nickel ferrite consisting of a solid solution of Ni oxide and Fe _oxide, preferably has a _{Ni X Fe 3-X O 4} (X = 0.1~2.0), X = 0.3~1. More preferably, it is 5.

When O ²⁻ and OH ⁻ cannot be sufficiently removed by the anodic reaction, these anions accumulate in the molten salt, which may hinder the ammonia generation reaction or the nitrogen gas reduction reaction at the cathode. Therefore, (1) a device for promptly leading O ²⁻ generated by the ammonia production reaction to the vicinity of the anode, (2) a device for effectively contacting the anode with the electrolytic bath containing O ²⁻ , and (3) generation. It is preferable to devise a method in which oxygen gas to be discharged is quickly discharged out of the electrolytic bath.

As for the above (1), it is preferable to guide O ²⁻ from the ammonia generation part (reaction field of N ³⁻ and water vapor) to the vicinity of the anode using the convection of the electrolytic bath. As for the above (2), in order to increase the contact area of the anode with respect to the flow rate of the molten salt moving by convection, the anode surface is provided with a molten salt flow path or irregularities, or a porous or meshed anode. Regarding (3) above, it is preferable that the molten salt flow inside, and it is preferable to discharge oxygen gas from the molten salt by blowing an inert gas such as argon or helium.

(Miniaturized water vapor)
The apparatus of the present invention uses water vapor that has been refined as water vapor to be supplied to the molten salt.

Since the ammonia generation reaction between water vapor and N ³⁻ mainly proceeds as a gas-liquid reaction, the reaction proceeds more efficiently when the bubble size (bubble diameter) of the water vapor is smaller.

The bubble diameter of water vapor depends on the temperature of the molten salt, the N ³ -concentration, the number of water vapor bubbles, and the like. Therefore, the bubble diameter of the water vapor is determined according to the scale of the ammonia generation unit and the N ³⁻ generation rate at the cathode. Although the bubble diameter of water vapor is not exact, it is preferably about 100 nm to 1 mm, more preferably about 1 μm to 1 mm. Incidentally, the bubble size is the bubble diameter during supply to the molten salt steam (or immediately after the supply), the bubble diameter as the reaction with N ^3- progresses decreases.

Further, the number of bubbles of water vapor contained per unit volume, the temperature of the molten salt, N ^3- concentration, may be determined by the bubble diameter of the steam, during the steam supply (or immediately after the supply), molten salt 1 cm ³ It is preferable that 10 to 10 million pieces are contained per one, and more preferably 100 to 5 million pieces are contained.

  For measuring the bubble diameter and its distribution, a general method for measuring the bubble diameter and the number of bubbles in a liquid can be used. For example, for relatively large bubbles of several μm to several tens of μm, a transparent window made of Pyrex (registered trademark) glass or quartz glass is provided in the vicinity of the bubble supply unit, and adheres to the bubbles or windows in the molten salt. The bubbles can be observed directly with a microscope or the like, or the Coulter counter method (a method for determining the bubble size distribution by measuring the change in the electrical resistance of the molten salt containing bubbles) as long as it does not hinder the ammonia electrosynthesis reaction. The bubble diameter distribution may be measured by In the case of very fine bubbles of nanometer size, use the light scattering method (a method of obtaining the distribution of bubbles that passed through the scattered light by irradiating a semiconductor laser or the like into the molten salt per unit time). Thus, the bubble diameter distribution can be measured.

  The method for generating fine water vapor is not particularly limited. For example, in the case of micron-order bubbles, a method of passing through a porous member made of Pyrex (registered trademark) or high-purity alumina can be mentioned. In order to obtain fine bubbles of submicron order or less, the water vapor bubbles may be further refined by applying ultrasonic waves or the like.

Temperature of miniaturized steam is not limited, compared with the heat of reaction it is preferred to keep heated preliminarily to a temperature close to the molten salt in order not to lower the temperature of the molten salt, water vapor and N ^3- and Even when steam at a low temperature is blown, the decrease in bath temperature can be suppressed. The water vapor may be heated separately by a heater or the like, or may be heated by the molten salt bath by installing a flow path of the water vapor in the molten salt bath.

(Means for stirring molten salt)
The apparatus of the present invention has means for supplying a gas component to the molten salt and stirring the molten salt by an upward flow of the molten salt containing the gas component. This means supplies the gas component to the molten salt, and the molten salt in the gas supply unit has a smaller apparent density than the surrounding molten salt, thereby generating buoyancy, and an upward flow is generated in the molten salt in the gas supply unit. Stir the molten salt by gas lift. As a method of causing the molten salt to flow, there is a method of providing a driving unit such as a propeller, and the device of the present invention can also use the driving unit in combination.

The gas component supply port is preferably provided at or near the bottom of the electrolytic bath. Thus, efficient stirring can be achieved by securing a large distance for the gas component to rise in the molten salt. Such agitation of the electrolytic bath efficiently moves N ³⁻ generated at the cathode to the ammonia generation part, increases the efficiency of contacting N ³⁻ with water vapor, and O ² generated as a by-product by electrolytic synthesis. ^- the preferred because of enhancing the efficiency of exhaust as the oxygen gas is moved in the anode.

  As the gas component used for the gas lift, for example, the water vapor can be used. That is, the molten salt may be stirred by using water vapor used for ammonia synthesis for gas lift. However, since fine bubbles generally have a very low ascent rate in the liquid, if unreacted fine water vapor bubbles remain in the molten salt, they are not easily detached from the bath and circulate in the convection bath. However, there is a high possibility that the cathode reaction becomes an obstacle. In addition, water vapor is often consumed by the ammonia production reaction, and the bubble diameter is often gradually reduced. Excess supply of water vapor may interfere with the ammonia production reaction. Therefore, in order to increase the flow rate of the molten salt, it is preferable to perform gas lift with an inert gas such as argon gas, helium gas, nitrogen gas. Such an inert gas can be mixed with water vapor or supplied separately from water vapor.

  Since ammonia generated by electrolytic synthesis is easily dissolved in the molten salt, it is preferable that ammonia be actively expelled from the molten salt by blowing an inert gas. Such inert gas bubbles do not need to be fine bubbles like the water vapor bubbles. Although the bubble diameter of the bubble of an inert gas is not limited, 1 micrometer-300 mm are preferable and 30 micrometers-100 mm are more preferable.

The ratio of water vapor to inert gas when using inert gas is not limited. And flow rate of the molten salt by gas lift, may be appropriately set according to N ^3- feed rate of the cathode. The flow rate of the molten salt by the gas lift is preferably a rate suitable for discharging most of O ²⁻ as oxygen gas out of the system at the anode. Further, N ^3- feed rate of from the cathode to the ammonia generator, N ^3- production rate at the cathode which is dependent on the flow rate of the N ^3- production rate and the molten salt at the cathode is obtained from the cathode current value From this, it is preferable to set the water vapor flow rate and the inert gas flow rate based on the H ₂ O supply amount required per unit time.

  Embodiment 1 and Embodiment 2 will be exemplified below to specifically describe the device of the present invention.

(Embodiment 1)
An example (FIG. 1) of the apparatus of the present invention will be described as Embodiment 1.

In Embodiment 1, the molten salt circulates in the loop, and the driving force is a gas lift by supplying an inert gas. N ³⁻ generated by the porous cathode rides on the flow of the molten salt that passes through the porous cathode due to the flow of the molten salt generated by the gas lift, and enters the ammonia generating section that is the same location as the molten salt driving section by the gas lift. Carried. In this ammonia generation part, fine water vapor bubbles are supplied, and almost all of the water vapor reacts with N ³⁻ to generate ammonia before reaching the upper part of the bath. The produced ammonia is discharged together with unreacted fine water vapor bubbles into the gas phase by the inert gas that has become the driving force of the gas lift, and is carried to the ammonia purification step described later. On the other hand, O ²⁻ by-produced by the ammonia generation reaction is carried to the anode along the flow of the molten salt. In this anode part, the ratio of the cathode area to the molten salt flow rate is increased by the unevenness on the anode, and the oxygen gas generated on the anode is gasified by making the molten salt thickness a thin liquid film of about several mm. It is quickly discharged into the phase. The molten salt that has passed through the anode is subsequently sent into the porous cathode.

  By performing electrolysis using the above apparatus, the following reaction proceeds in the electrolytic bath.

_{^{N 3- + 3 / 2H 2 O}} → NH 3 + 3 / 2O 2-
That is, the overall reaction of ammonia electrosynthesis is as follows.

1 / 2N ₂ + 3 / 2H ₂ O → NH ₃ + 3 / 4O ₂
The theoretical decomposition voltage calculated from the above reaction equation is 1.17 V at 600K. For example, in the case of the LiCl-KCl system, the anode is in a potential region that is nobler than about 2.8V (notation for Li ⁺ / Li potential, the same applies hereinafter), and the cathode is in a potential region that is less than about 0.6V. Should be set. In this case, the synthesis reaction proceeds at an inter-electrode voltage of 2.2 V or higher, which is about 1.0 V higher than the theoretical decomposition voltage. This is because the ammonia generation reaction from H ₂ O and N ³⁻ is spontaneously proceeding in the molten salt, and the electrolysis voltage is generated by electrochemically generating this ammonia generation reaction. Can be made much closer to the theoretical decomposition voltage.

(Embodiment 2)
An example (FIG. 2) of the device of the present invention will be described as Embodiment 2.

  Embodiment 2 uses two electrolytic cells, electrolytic cell A and electrolytic cell B, and the cells are separated by a hydrogen permeable metal film.

  By performing electrolysis using the apparatus of FIG. 2, the following reaction proceeds on the electrolytic cell A side.

Anodic reaction: 3O ²⁻ → 3 / 2O ₂ + 6e ⁻
Cathodic reaction: 3H ₂ O + 6e ⁻ → 3O ² + 6H (a)
Total reaction A: 3H ₂ O → 3 / 2O ₂ + 6H
That is, on the electrolytic cell A side of the hydrogen permeable metal film, atomic hydrogen is occluded into the metal film by water electrolysis and diffuses in the metal film to the electrolytic cell B side. On the other hand, the following reaction proceeds on the electrolytic cell B side.

Anodic reaction: 6H + 2N ^{3 −} → 2NH ₃ + 6e ⁻
Cathodic reaction: N ₂ + 6e ⁻ → 2N ³⁻ (b)
Total reaction B: N ₂ + 6H → 2NH ₃
That is, the hydrogen atoms that have diffused into the electrolytic cell B side in the metal film electrochemically react with N ^{3− in} the bath of the electrolytic cell B to generate NH ₃ . In this case, the electrolysis voltage required for both electrolytic cells is about 1.2V. This proceeds spontaneously in the molten salt,
H ₂ O + N ³⁻ → NH ₃ + O ²⁻
This is equivalent to the fact that a voltage of about 1.0 V can be recovered by causing the reaction to proceed electrochemically by the above-described cathodic reaction (a) and anodic reaction (b). In this case, as the molten salt of the electrolytic cell A, in addition to the above-described molten salt, a molten hydroxide or a molten hydroxide-H ₂ O type can be used. As such a metal hydroxide, an alkali metal hydroxide is preferable, and NaOH and KOH are particularly preferable. In the electrolytic cell A, a proton conductive solid electrolyte can also be used.

(Ammonia purification means)
Ammonia is obtained by electrolytic synthesis, but since the recovered gas usually contains impurities other than ammonia, it is preferable to obtain high-purity ammonia by purification.

Impurities that may be contained in the recovered gas are (a) molten salt vapor, (b) unreacted water vapor, and (c) inert gas (including nitrogen gas used at the cathode). In addition, when removing said (A)-(C) by refinement | purification, it is preferable to remove in order of (I)->(B)-> (C).
(A) Removal of molten salt vapor The molten salt vapor begins to condense and solidify when it reaches the melting point of the molten salt or less, and when it reaches the gas recovery line, it is in a state of solidification in the form of fine particles. Therefore, it can be easily removed with a dust filter or the like maintained at room temperature to about 150 ° C. In addition, when dew condensation occurs in the gas recovery line, the generated ammonia is absorbed by the dew condensation, which may cause a decrease in ammonia yield and deterioration of the piping. Therefore, at least about 80 ° C. between the electrolytic cell and the electrolyte recovery unit. It is preferable to hold the above to prevent condensation.
(B) Removal of unreacted water vapor Unreacted water vapor is preferably solidified quickly using a cooler kept at 0 ° C. or lower (preferably −5 ° C. or lower). This is to prevent the molten salt from dissolving in the condensed water droplets and lowering the solidification rate due to the lowering of the freezing point, and also to prevent the generated ammonia from being absorbed into the condensed water droplets to prevent a decrease in yield and deterioration of the cooling machine. Because of that. As a cooling method, it is possible to use a general gas fluid cooling method such as using heat of vaporization or using the Peltier effect. For example, ammonia gas containing water vapor may be sprayed onto a cooled structure and recovered as an ice film on the structure, or may be recovered as ice particles by spraying a cooled inert gas.
(C) Removal of inert gas (including nitrogen gas used at the cathode) The inert gas is preferably removed at the end of the purification means. Since ammonia is liquefied at −33 ° C. even under normal pressure, liquid ammonia and inert gas can be separated by using this feature, for example, by exposing to about −40 ° C. or lower. In consideration of temporarily storing purified ammonia in a container such as a cylinder, if it is pressurized to about several atmospheres, ammonia will be liquefied at a higher temperature (if it is about 8-9 atmospheres, it will be liquefied even at room temperature). It becomes easy.

It is a schematic diagram which shows an example of the ammonia electrosynthesis apparatus of this invention. It is a schematic diagram which shows an example of the ammonia electrosynthesis apparatus of this invention.

Claims (8)

An apparatus for electrosynthesis of ammonia from water and nitrogen, the apparatus comprising:
(1) An apparatus for synthesizing the ammonia by supplying refined water vapor and nitrogen gas to a molten salt that is an electrolytic bath,
(2) an anode that generates oxygen gas by oxidizing O ²⁻ and / or OH ⁻ generated by the reaction of the water vapor;
(3) a cathode that reduces nitrogen gas to generate N ³⁻ ;
(4) means for supplying the refined water vapor;
(5) the supply gas to produce a gas lift in the molten salt, Ri by the causing the pre-Symbol upward flow in the molten salt, the molten salt, the anode, the means for supplying the cathode and the steam the gas causes the gas lift to circulate in a loop with a supply port to a portion to have a means for supplying,
(6) In the bottom of the electrolytic cell or in the vicinity of the bottom, a supply port of a means for supplying the gas that causes the gas lift is provided.
An ammonia electrosynthesis apparatus characterized by that.   An apparatus for electrosynthesis of ammonia from water and nitrogen, the apparatus comprising:
(1) An apparatus for synthesizing the ammonia by supplying refined water vapor and nitrogen gas to a molten salt that is an electrolytic bath,
(2) An electrolytic cell A and an electrolytic cell B having the molten salt, wherein the electrolytic cell A and the electrolytic cell B are separated from each other by a hydrogen permeable metal film,
(3) O generated by the reaction of the water vapor ^2- And / or OH ⁻ An anode provided in the electrolytic cell A for generating oxygen gas by oxidizing
(4) Reduce nitrogen gas to N ^3- A cathode provided in the electrolytic cell B,
(5) means for supplying the refined water vapor;
(6) A gas that causes a gas lift to the molten salt in the electrolytic cell A is supplied, and an upward flow is generated in the molten salt, whereby the molten salt in the electrolytic cell A is converted into the anode and the hydrogen permeability. Means for supplying a gas for generating the gas lift so as to be circulated in a loop having a supply port of a means for supplying the metal film and the water vapor in part.
(7) At the bottom of the electrolytic cell A or in the vicinity of the bottom, a supply port for supplying gas for generating the gas lift is provided.
An ammonia electrosynthesis apparatus characterized by that.   The ammonia electrolytic synthesis apparatus according to claim 1, wherein the molten salt is at least one selected from the group consisting of an alkali metal halide and an alkaline earth metal halide.   The molten salt in the electrolytic cell A is at least one selected from the group consisting of an alkali metal halide, an alkaline earth metal halide, and a molten hydroxide,
  The molten salt in the electrolytic cell B is at least one selected from the group consisting of alkali metal halides and alkaline earth metal halides,
The ammonia electrosynthesis apparatus according to claim 2.   The ammonia electrosynthesis apparatus according to any one of claims 1 to 4, wherein the means for supplying water vapor supplies the refined water vapor having a bubble diameter of 100 nm to 1 mm.   The means for supplying water vapor is 1 cm of the molten salt. ³ The ammonia electrolytic synthesizer according to any one of claims 1 to 4, wherein the atomized water vapor is supplied so that 10 to 10 million bubbles are included.   The ammonia electrolytic synthesis apparatus according to any one of claims 1 to 6, wherein the means for supplying the gas for generating the gas lift supplies the gas for generating the gas lift including an inert gas. The ammonia electrosynthesis apparatus according to any one of claims 1 to 7 , further comprising trap means for removing impurities from the ammonia-containing gas obtained by the electrolytic synthesis.

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