WO2021065892A1

WO2021065892A1 - Ammonia synthesis catalyst

Info

Publication number: WO2021065892A1
Application number: PCT/JP2020/036850
Authority: WO
Inventors: 難波　哲哉; 工藤田; 和寛八木田
Original assignee: 国立研究開発法人産業技術総合研究所; Ntn株式会社
Priority date: 2019-10-02
Filing date: 2020-09-29
Publication date: 2021-04-08
Also published as: JP2021053606A; JP7385863B2

Abstract

An ammonia synthesis catalyst that is for synthesizing ammonia from nitrogen and hydrogen. The ammonia synthesis catalyst comprises an iron-based alloy piece that contains vanadium.

Description

Ammonia synthesis catalyst

The present invention relates to an ammonia synthesis catalyst.

Ammonia is an important raw material for chemical fertilizers that are indispensable for food production, and at the same time, it is also a major raw material for a huge amount of nitrogen-based chemicals, and the production of ammonia continues to increase. The Haber-Bosch method, which synthesizes ammonia by reacting nitrogen in the air with hydrogen, was industrialized about 100 years ago, but it is still indispensable for supporting human society by producing ammonia. It has become.

The Haber-Bosch method uses nitrogen in the presence of a doubly promoted iron catalyst in which several mass% _{of Al 2} O ₃ and K ₂ O are added as co-catalysts to _{Fe 3} O ₄ , which is a catalyst component. This is a method for producing ammonia by directly reacting hydrogen with hydrogen under high temperature and high pressure conditions of 400 ° C. to 600 ° C. and 200 to 400 atm.

So far, a ruthenium catalyst has been developed as an alternative ammonia synthesis catalyst for the Haber-Bosch method catalyst. However, the ruthenium catalyst has a problem that the activity decreases as the hydrogen pressure increases, and sufficient catalytic activity cannot be obtained. In addition, ruthenium catalysts are expensive. Therefore, it is desired to develop a highly catalytically active and inexpensive ammonia synthesis catalyst that can replace the Haber-Bosch catalyst.

An object of the present invention is to provide an inexpensive ammonia synthesis catalyst capable of efficiently synthesizing ammonia from nitrogen and hydrogen.

The present inventors have made diligent studies to solve the above problems. As a result, they found that the iron-based alloy piece containing vanadium functions as an ammonia synthesis catalyst, and completed the present invention.
That is, the present invention is as follows.

[1]
Ammonia synthesis catalyst for synthesizing ammonia from nitrogen and hydrogen, which is composed of vanadium-containing iron-based alloy pieces.
[2]
The ammonia synthesis catalyst according to [1], wherein the content of vanadium with respect to the entire iron-based alloy piece containing vanadium is 0.1% by mass or more and 5.2% by mass or less.
[3]
The ammonia synthesis catalyst according to [1] or [2], wherein the vanadium-containing iron-based alloy piece has a vanadium-containing triiron tetroxide layer on the surface.
[4]
The ammonia synthesis catalyst according to any one of [1] to [3], wherein the vanadium-containing iron-based alloy piece has a spherical shape.
[5]
The ammonia synthesis catalyst according to [4], wherein the diameter of the sphere is 0.2 mm or more and 1.0 cm or less.
[6]
The ammonia synthesis catalyst according to any one of [1] to [5], wherein the specific surface area of the vanadium-containing iron-based alloy piece is ^{more than 0 m 2} / g and 1.0 m ^{2 / g or less.}
[7]
The ammonia synthesis catalyst according to any one of [1] to [6], wherein the vanadium-containing iron-based alloy piece is a vanadium-containing steel piece.
[8]
Includes an ammonia synthesis step in which nitrogen and hydrogen are reacted in the presence of a catalyst to synthesize ammonia.
A method for producing ammonia, wherein the catalyst is the ammonia synthesis catalyst according to any one of [1] to [7].
[9]
The method for producing ammonia according to [8], wherein the reaction temperature in the ammonia synthesis step is 350 ° C. or higher and 600 ° C. or lower.
[10]
The method for producing ammonia according to [8] or [9], wherein the reaction pressure in the ammonia synthesis step is 1.0 bar or more and 100 bar or less.
[11]
Equipped with a reaction vessel that synthesizes ammonia from nitrogen and hydrogen inside
An ammonia production system in which the ammonia synthesis catalyst according to any one of [1] to [7] is arranged inside the reaction vessel.

According to the production method of the present invention, it is possible to provide an inexpensive ammonia synthesis catalyst capable of efficiently synthesizing ammonia from nitrogen and hydrogen.

It is a graph which shows the relationship between the reaction temperature in Experimental Example 1 and Experimental Example 2 and the ammonia concentration in a product gas.

In explaining the details of the present invention, specific examples will be given, but the contents are not limited to the following as long as they do not deviate from the gist of the present invention, and they can be modified as appropriate.

<Ammonia synthesis catalyst>
The ammonia synthesis catalyst according to the first embodiment of the present invention is a catalyst for synthesizing ammonia from nitrogen and hydrogen, and is composed of a vanadium-containing iron-based alloy piece. The ammonia synthesis catalyst composed of vanadium-containing iron-based alloy pieces does not mean that it does not contain any components other than vanadium-containing iron-based alloy pieces, and contains, for example, impurities of about several mass%. It may be, and may have an oxide layer on the surface. In addition, "vanadium", which is a necessary component for exhibiting catalytic performance, is not only vanadium itself (that is, vanadium atom), but also vanadium compounds such as vanadium oxide, vanadium nitride, vanadium carbide, and vanadium carbonitride. It may be contained in the iron-based alloy piece in the above embodiment.

The ammonia synthesis catalyst according to this embodiment has high catalytic activity per unit surface area and is cheaper than the ruthenium catalyst.

In the present specification, the catalytic activity per unit surface area shall be evaluated by the value obtained by dividing the ammonia yield by the total surface area of the ammonia synthesis catalyst and the reaction time as shown in the following formula (I). The total surface area of the ammonia synthesis catalyst can be calculated by multiplying the BET specific surface area (m ² / g) by the mass of the ammonia synthesis catalyst. As will be described later, the ammonia synthesis catalyst in this embodiment may not be able to measure the specific surface area by the BET specific surface area measuring method. In this case, the total surface area of the ammonia synthesis catalyst may be obtained from a geometric calculation formula.

Catalytic activity per unit surface area (mmol / m ² / hour) =
Ammonia yield (mmol) / total surface area of ammonia synthesis catalyst (m ² ) / reaction time (hour) (I)

(Iron-based alloy containing vanadium)
In the present embodiment, the vanadium-containing iron-based alloy constituting the vanadium-containing iron-based alloy piece means an alloy containing 50% by mass or more of iron, and in addition to vanadium and iron, manganese, chromium, molybdenum, etc. It may contain other elements such as nickel, silicon and carbon. The content, content ratio, etc. of the other element are not particularly limited.

The content of vanadium with respect to the entire vanadium-containing iron-based alloy is not particularly limited as long as it does not adversely affect the hardness, strength, toughness, abrasion resistance, and heat resistance of the vanadium-containing iron-based alloy piece, but is usually limited. It is 0.1% by mass or more and 5.2% by mass or less. The lower limit of the vanadium content is preferably 1.0% by mass or more, 1.5% by mass or more, 2.0% by mass or more, or 2.5% by mass or more. The upper limit of the vanadium content is preferably 5.0% by mass or less, or 4.5% by mass or less. When the vanadium content is in the above range, the reaction rate and the reaction yield are increased, and ammonia can be produced with high production efficiency. When vanadium is contained in the vanadium compound in the form of a vanadium compound, the content of the vanadium is an atomic conversion content.

The vanadium-containing iron-based alloy is preferably vanadium-containing steel in that it is excellent in hardness, strength, toughness, wear resistance, and the like. Examples of the vanadium-containing steel include chrome steel, chrome molybdenum steel, nickel chrome steel, nickel chrome molybdenum steel, manganese steel, manganese chrome steel and the like with vanadium added. The content of each constituent element in the vanadium-containing steel can be in the range of a general content in the above-mentioned various steels.

Specific compositions of vanadium-containing steel include, for example, the following compositions.
Composition A
Vanadium: 0.1% by mass or more and 5.2% by mass or less Manganese: 0.3% by mass or more and 2.0% by mass or less Chromium: 0% by mass or more and 30% by mass or less Molybdenum: 0% by mass or more and 7.0% by mass or less Nickel: 30% by mass or less Silicon: 0.15% by mass or more and 5.0% by mass or less Carbon: 2.2% by mass or less Iron and unavoidable impurities: balance

Specific examples of the vanadium-containing steel are disclosed in, for example, AMS (Aerospace Material Standard; USA) 6278; AMS6491; JP2012-237062, JP2014-58729, or JP2015-151621. Such as steel obtained by adding vanadium to JIS standard SUJ2; and the like.

In this embodiment, the distribution state of vanadium in the vanadium-containing iron-based alloy is not particularly limited. That is, vanadium may be uniformly distributed in the base material of the iron-based alloy, or may be locally distributed. Examples of the mode in which vanadium is locally distributed in the iron-based alloy include a mode in which vanadium is present in a part, surface, etc. of the base material of the iron-based alloy at a higher abundance ratio than other parts. .. Of these, vanadium is preferably distributed so as to be present at least on a part of the surface of the iron-based alloy piece. The presence of vanadium, which is a catalytically active component, on the surface of the iron-based alloy piece promotes the reaction between nitrogen and hydrogen in contact with the catalytically active component, and ammonia can be produced at a high reaction rate and reaction yield. This is because it is presumed.

(Vanadium-containing triiron tetroxide layer)
The vanadium-containing iron-based alloy piece according to this embodiment preferably has a vanadium-containing ferric tetraoxide (Fe ₃ O ₄ ) layer on its surface. Since the vanadium-containing triiron tetraoxide layer is formed on the surface of the vanadium-containing iron-based alloy piece, the frequency of contact between nitrogen and hydrogen with the catalytically active component increases, so that the reaction rate and reaction yield are increased. Can be improved. In addition, the vanadium-containing triiron tetroxide layer is also effective in preventing rust on the vanadium-containing iron-based alloy.

The vanadium-containing triiron tetroxide layer can be formed by oxidizing the surface of a vanadium-containing iron-based alloy piece in which the triiron tetroxide layer is not formed on the surface. As the vanadium-containing iron-based alloy piece on which the triiron tetroxide layer is not formed on the surface, those mentioned as specific examples of vanadium-containing steel can be adopted. The oxidation treatment can be carried out by heating in the atmosphere. The heating temperature is usually 500 ° C. or higher, preferably 600 ° C. or higher, 650 ° C. or higher, or 800 ° C. or higher, and usually less than the transformation point of the iron-based alloy containing vanadium. The heating time is usually 0.5 hours or more, preferably 1.0 hours or more, and usually 10 hours or less, preferably 5 hours or less. As such an oxidation treatment, for example, the method of oxidation treatment of a steel member disclosed in Japanese Patent Application Laid-Open No. 2012-237062 or Japanese Patent Application Laid-Open No. 2014-58729 may be adopted.

(shape)
The shape of the iron-based alloy piece containing vanadium is not particularly limited. As described above, the ammonia synthesis catalyst according to this embodiment has high catalytic activity per unit surface area, and is therefore less susceptible to shape restrictions, that is, has a high degree of freedom in shape. Therefore, as the shape of the iron-based alloy piece containing vanadium, various shapes can be adopted depending on the reaction vessel, the process, the ammonia production system, and the like.
Specific shapes include a sphere; a polyhedron such as a cube, a hexagonal column, and a triangular pyramid; a needle shape; a plate shape; and the like. Of these, a sphere is preferable because it has excellent strength. The term "sphere" is not limited to a true sphere, but means a three-dimensional shape having a circular, elliptical, substantially circular, or substantially elliptical cross-sectional shape. The shape of the catalyst is not limited to one type, and two or more types can be combined.

(size)
The size of the vanadium-containing iron-based alloy piece is not particularly limited as long as it can be arranged in the reaction vessel, and can be appropriately selected depending on the catalytic activity, the amount of ammonia produced, the scale of the reaction apparatus, and the like.
As described above, the ammonia synthesis catalyst according to the present embodiment has high catalytic activity per unit surface area, and it is not necessary to increase the surface area of the catalyst in order to improve the catalytic activity. Therefore, the major axis of the iron-based alloy piece containing vanadium is about 0.2 mm, 1.0 mm, 2.0 mm, 4.0 mm, 5.0 mm, 6.0 mm, 8.0 mm, or 1.0 cm. Good. By setting the vanadium-containing iron-based alloy piece to this size, workability is improved and ammonia can be easily produced. Further, as a matter of course, since the ammonia synthesis reaction can be promoted even if the surface area of the catalyst is large, the major axis of the iron-based alloy piece containing vanadium may be about several nm to several hundred μm.

For example, when the shape of the iron-based alloy piece containing vanadium is spherical, its diameter is usually 0.05 mm or more and 5.0 cm or less. The lower limit of the diameter is preferably 0.2 mm or more, 0.3 mm or more, 1.0 mm or more, 2.0 mm or more, 2.5 mm or more, or 3.0 mm or more. The upper limit of the diameter is preferably 3.0 cm or less, 1.0 cm or less, 8.0 mm or less, 6.0 mm or less, or 4.0 mm or less. By setting the diameter of the sphere within the above range, the ease of handling the catalyst is improved.

(Specific surface area)
Conventionally, the double-accelerated iron catalyst used industrially has a specific surface area ^{adjusted to several tens of m 2} / g in order to obtain a high reaction rate, a reaction yield, and the like. On the other hand, since the ammonia synthesis catalyst according to this embodiment has high catalytic activity per unit surface area, it is not necessary to increase the specific surface area as in the conventional double-accelerated iron catalyst. Therefore, the specific surface area of the ammonia synthesis catalyst according to this embodiment is not particularly limited, and can be appropriately selected depending on the shape of the catalyst, the size of the catalyst, the amount of ammonia to be produced, the scale of the reaction apparatus, and the like.

In this embodiment, the specific surface area of the vanadium-containing iron-based alloy piece (that is, the specific surface area of the ammonia synthesis catalyst) is determined by the shape, size, etc. described above, and is usually ^{more than 0 m 2} / g and 1.0 m ^2. It is less than / g. The lower limit of the surface area of the vanadium-containing iron-based alloy piece is preferably 1.0 × 10 ^-7 m ² / g or more, or 1.0 × 10 ^-6 m ² / g or more. The upper limit of the surface area of the vanadium-containing iron-based alloy piece is preferably 1.0 × 10 ^-3 m ² / g or less, 1.0 × 10 ^-4 m ² / g or less, or 1.0 × 10 ^{It is -5} m ² / g or less.

The specific surface area of the ammonia synthesis catalyst is the surface area per unit mass determined by the BET specific surface area measurement method by _{N 2 adsorption.} However, since the surface of the iron-based alloy piece containing vanadium is smooth, it is less than the measurement limit of the device by the BET specific surface area measurement method, and the specific surface area cannot be measured (that is, the measurement result is 0 m ² / g). ) May be. In such a case, considering that the surface of the vanadium-containing iron-based alloy piece is smooth, the surface area of the vanadium-containing iron-based alloy piece obtained from the geometric calculation formula is the vanadium-containing iron. The value divided by the mass of the base alloy piece is taken as the specific surface area of the iron base alloy piece containing vanadium. For example, the specific surface area of the vanadium-containing iron-based alloy piece is calculated by the formula (II) when the shape of the vanadium-containing iron-based alloy piece is spherical, and the shape of the vanadium-containing iron-based alloy piece. When is a cube, it is calculated by equation (III).

Specific surface area of vanadium-containing iron-based alloy pieces (m ² / g)
= Surface area of iron-based alloy piece containing vanadium 4πr ² (m ² ) / Mass of iron-based alloy piece containing vanadium (g) (II)
(In the formula, r represents the radius of the sphere.)

^{Specific surface area (m 2} / g) of iron-based alloy pieces containing vanadium =
Surface area of vanadium-containing iron-based alloy piece 6a ² (m ² ) / Mass of vanadium-containing iron-based alloy piece (g) (III)
(In the formula, a represents the length of one side of the cube.)

<Ammonia production method>
The method for producing ammonia according to the second embodiment of the present invention includes an ammonia synthesis step of reacting nitrogen with hydrogen in the presence of the ammonia synthesis catalyst according to the first embodiment of the present invention to synthesize ammonia. ..
The specific production method is not particularly limited as long as it is a method of synthesizing ammonia by contacting nitrogen and hydrogen with the ammonia synthesis catalyst according to the first embodiment of the present invention, and any known production method may be used as appropriate. A similar method can be adopted.

(Catalyst amount)
The amount of the ammonia synthesis catalyst used in the ammonia synthesis reaction is not particularly limited, and is appropriately selected according to the shape of the ammonia synthesis catalyst, the size of the ammonia synthesis catalyst, the amount of ammonia to be produced, the capacity of the reaction vessel, the scale of the reaction apparatus, and the like. can do.

(Reaction temperature)
The reaction temperature in the ammonia synthesis step is usually 350 ° C. or higher and 600 ° C. or lower, although it depends on the reaction conditions such as reaction pressure and reaction time. The lower limit of the reaction temperature is preferably 400 ° C. or higher or 450 ° C. or higher. The upper limit of the reaction temperature is preferably 550 ° C. or lower. By setting the reaction temperature in the above range, a high ammonia production rate and an ammonia yield can be obtained.

(Reaction pressure)
The reaction pressure in the ammonia synthesis step can be appropriately selected depending on the reaction conditions such as the amount of catalyst and the reaction temperature, but is usually 0.1 bar or more and 100 bar or less. The lower limit of the reaction pressure is preferably 1.0 bar or more or 2.0 bar or more. The upper limit of the reaction pressure is preferably 10 bar or less or 5.0 bar or less. In the present specification, the reaction pressure in the ammonia synthesis step is a gauge pressure.

(Reaction time)
The reaction time of the ammonia synthesis reaction is not particularly limited and can be appropriately selected depending on the reaction temperature, scale and the like. Since the ammonia synthesis catalyst composed of vanadium-containing iron-based alloy pieces exhibits high catalytic activity, ammonia can be efficiently produced even if the reaction time is short. Further, as described above, the ammonia synthesis catalyst according to the first embodiment of the present invention is excellent in hardness, strength, toughness, abrasion resistance, and heat resistance, and therefore is continuously used as an ammonia synthesis catalyst for a long period of time. Is possible. The specific reaction time may be 1 hour or more, 12 hours or more, 24 hours or more, or 36 hours or more, and may be 60 hours or more, or 48 hours or less. Of these, the reaction time is preferably 24 hours or more.

(Reactor)
The reactor used in the ammonia synthesis step is not particularly limited, and a known reactor used for ammonia synthesis can be used. Examples of the known reaction device include a batch type reaction device, a closed circulation type reaction device, a distribution type reaction device, and the like. Of these, from a practical point of view, a distribution type reaction device, for example, a normal pressure fixed bed flow reaction device, a high pressure fixed bed flow reaction device, or the like is preferable. Further, any one type of reactor filled with a catalyst, a reactor in which a plurality of reactors filled with a catalyst are connected, and a reactor having a plurality of reaction layers in the same reactor can be used. it can.

In the reactor, an ammonia synthesis catalyst is placed in the reaction vessel where ammonia synthesis is performed. The method of arranging the ammonia synthesis catalyst in the reaction vessel is not particularly limited, and can be appropriately selected depending on the amount, shape, etc. of the catalyst.

From the viewpoint of arranging the ammonia synthesis catalyst at a position suitable for contact with nitrogen and hydrogen inside the reaction vessel, it is preferable to fix the catalyst inside the reaction vessel with a catalyst support. For example, the ammonia synthesis catalyst may be placed inside the reaction vessel in a state of being sandwiched or wrapped in the catalyst support.
The catalyst support is not particularly limited as long as the ammonia synthesis catalyst can be fixed in the reaction vessel and the catalytic reaction is not adversely affected. Specific examples of the catalyst support include quartz wool; glass wool; a plate having holes for the flow of reaction gas, such as alumina, zirconia, and magnesia. These catalyst supports are not limited to one type, and two or more types can be used in combination.

The reaction apparatus is preferably provided with heat removing means. This is because the reaction for synthesizing ammonia from nitrogen and hydrogen is an equilibrium reaction and an exothermic reaction accompanied by volume shrinkage. Therefore, from the viewpoint of improving the ammonia yield, it is preferable to remove the heat of reaction.
As the heat removing means, a known heat removing means such as an intercooler can be used. Therefore, for example, by connecting a plurality of reaction vessels in which an ammonia synthesis catalyst is arranged in series and installing an intercooler as a heat removing means at the outlet of each reaction vessel, the ammonia yield can be improved.

<Ammonia production system>
The ammonia production system according to the third embodiment of the present invention includes a reaction vessel for synthesizing ammonia from nitrogen and hydrogen, and the inside of the reaction vessel is the ammonia according to the first embodiment of the present invention. A synthetic catalyst is arranged.
The ammonia production system according to the present embodiment is not particularly limited in other configurations as long as the ammonia synthesis catalyst according to the first embodiment of the present invention is provided inside the reaction vessel, and may include any configuration. it can. Preferably, the ammonia production system according to the present embodiment includes a reaction apparatus used in the method for producing ammonia according to the second embodiment of the present invention.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention can be appropriately modified as long as it does not deviate from the gist of the present invention. Therefore, the scope of the present invention should not be construed as limited by the specific examples shown below.
The method for measuring the BET specific surface area of the catalyst in the examples is as follows.

<Measurement method of BET specific surface area>
Nitrogen gas was adsorbed on the surface of the catalyst at the temperature of liquid nitrogen, and the amount of nitrogen adsorbed in the monolayer was measured. The measurement conditions are as follows.
(Measurement condition)
Specific surface area measuring device: BELSORP-mini II manufactured by Microtrac Bell
Adsorbed gas: Nitrogen (99.999% by volume)
Adsorption temperature: Liquid nitrogen temperature (-196 ° C)

<Experimental example 1>
(Manufacturing of steel pieces containing vanadium)
AMS6419 was heated at 950 ° C. for 1 hour in an air atmosphere to obtain vanadium-containing steel pieces as an ammonia synthesis catalyst. The obtained vanadium-containing steel piece was a sphere having a diameter of 3.0 mm, and the mass per sphere was 2.0 g. The vanadium content in the obtained vanadium-containing steel piece was 2.0% by mass.
As a result of measuring the BET specific surface area of the obtained ammonia synthesis catalyst by the above-mentioned method, the measured value was 0 m ² / g, and it was found that the BET specific surface area of the ammonia synthesis catalyst was less than the measurement limit. Since the ammonia synthesis catalyst is a sphere, the specific surface area of the ammonia synthesis catalyst was calculated by the above formula (II) and found to be 5.7 × ^10-5 m ² / g.

(Synthesis of ammonia)
2.0 g of the ammonia synthesis catalyst was sandwiched between quartz wool and filled in the quartz reaction tube (inner diameter: 22 mm) of the atmospheric pressure fixed bed flow reactor.
Next, the ammonia synthesis catalyst was pretreated. Specifically, a raw material gas consisting _{of N 2} and H ₂ _{(N 2} : H ₂ = 1: 3 (volume ratio)) is distributed at 80 mL / min in a quartz reaction tube filled with an ammonia synthesis catalyst under normal pressure. The temperature was raised to 600 ° C. over 30 minutes, and the temperature was maintained at 600 ° C. for 30 minutes.

Subsequently, the raw material gas was passed through the quartz reaction tube at 80 mL / min to synthesize ammonia. In the synthesis of ammonia, the reaction temperature was 600 ° C., the reaction pressure was 1 bar, and the reaction time was 1 hour. The ammonia concentration in the produced gas was measured by an infrared spectroscope (manufactured by Thermo Fisher, iS50) equipped with a multi-reflective gas cell having an optical path length of 2.4 m. The catalytic activity per unit surface area of the ammonia synthesis catalyst was calculated by the formula (I) and found to be 514 mmol / m ² / hour.

As described above, after synthesizing ammonia at 600 ° C., the reaction temperature was lowered by about 50 ° C., and the cycle of synthesizing ammonia for 1 hour was performed 6 times. The reaction conditions in these cycles were the same as those for ammonia synthesis at 600 ° C., except for the reaction temperature. Further, in each cycle, the produced gas was constantly introduced into the gas cell, and the ammonia concentration in the produced gas was measured by the above-mentioned method.

The relationship between the reaction temperature and the measured ammonia concentration is shown in FIG. In FIG. 1, the thermodynamic equilibrium curve of the ammonia synthesis reaction at 1.0 bar is shown by a broken line. The catalytic activity per unit surface area of the ammonia synthesis catalyst at the reaction temperature of 490 ° C., which showed the highest ammonia concentration, was calculated by the formula (I) and found to be 815 mmol / m ² / hour.

<Experimental example 2>
Ammonia at each temperature by the same method as in Experimental Example 1 except that the ammonia synthesis catalyst was changed to 2.0 g of a spherical catalyst having a diameter of 3 mm made of vanadium-free steel pieces (SUJ2 steel pieces specified in JIS). Was synthesized and the ammonia concentration in the produced gas was measured. Since the specific surface area of the ammonia synthesis catalyst in this experimental example was less than the measurement limit in the BET specific surface area measurement method, it was 5.7 × 10 ^-5 m ² / g when calculated by the formula (II). ..

The relationship between the reaction temperature and the measured ammonia concentration is shown in FIG. The catalytic activity per unit surface area of the ammonia synthesis catalyst at the reaction temperature of 480 ° C., which showed the highest ammonia concentration, was calculated by the formula (I) and found to be 17 mmol / m ² / hour.

<Reference example>
The catalyst Cs-Ru / MgO obtained by co-supporting Ru and Cs on magnesium oxide was described in F. Rosowski, et al., Appl. Catal. A: Gen., 151 (2), 443-460 (1997). Prepared according to the described method. As a result of measurement by ICP-AES, the amount of Ru supported in the catalyst was 3% by mass. The BET specific surface area of the catalyst was 41 m ² / g.

Ammonia was synthesized in the same manner as in Experimental Example 1 except that the ammonia synthesis catalyst was changed to 0.1 g of Cs-Ru / MgO, and the ammonia concentration in the produced gas was measured. The catalytic activity per unit surface area of the ammonia synthesis catalyst at the reaction temperature of 380 ° C., which showed the highest ammonia concentration, was calculated by the formula (I) and found to be 0.07 mmol / m ² / hour.

<Discussion>
From FIG. 1, it was found that when a steel piece containing vanadium was used as an ammonia synthesis catalyst, the ammonia synthesis reaction was promoted at a reaction temperature of about 350 ° C. or higher, and ammonia could be produced in a high yield. It was also found that the yield of ammonia was highest at around 490 ° C. Further, from FIG. 1, it is shown that when a steel piece containing vanadium is used as an ammonia synthesis catalyst, the thermodynamic equilibrium curve of the ammonia synthesis reaction is reached at a reaction temperature of 550 ° C. or higher, and ammonia can be efficiently produced. It was. On the other hand, when a steel piece containing no vanadium was used as a catalyst, it was found that very little ammonia was obtained regardless of the reaction temperature.
That is, according to the results of Experimental Examples 1 and 2, the catalytic activity of the ammonia synthesis catalyst differs greatly depending on whether or not it contains vanadium, and the vanadium-containing steel pieces are significantly higher than the vanadium-free steel pieces. It was confirmed that it showed catalytic activity.

In addition, the maximum value of catalytic activity per unit surface area (815 mmol / m ² / hour) of the ammonia synthesis catalyst composed of steel pieces containing vanadium and the standard ammonium synthesis catalyst Cs-Ru / MgO per unit surface area. When compared with the maximum value of catalytic activity (0.07 mmol / m ² / hour), the former was about 12000 times that of the latter, indicating that the catalytic activity per unit surface area was extremely high.

Further, since the ammonia synthesis catalyst in Experimental Example 1 is a steel having high hardness, it was visually confirmed that the shape hardly changed before and after the ammonia synthesis reaction. That is, it can be said that the ammonia synthesis catalyst according to the present embodiment is excellent in hardness and strength, and problems are unlikely to occur even if the shape is changed according to the reaction vessel, process, and the like.

According to the present invention, ammonia can be easily and efficiently synthesized by reacting nitrogen and hydrogen in the presence of vanadium-containing iron-based alloy pieces. As the vanadium-containing iron-based alloy, an inexpensive iron-based alloy on the market can be adopted. Therefore, the ammonia synthesis catalyst according to the present invention is advantageous from the viewpoint of availability and manufacturing cost. .. Further, since the ammonia synthesis catalyst according to the present invention is an iron-based alloy having excellent hardness, strength and the like, it has a high degree of freedom in shape and can be shaped according to the reaction vessel, process and the like.
From the above, it is considered that the method for producing ammonia according to this embodiment is also useful as an alternative method to the Haber-Bosch method.

Claims

Ammonia synthesis catalyst for synthesizing ammonia from nitrogen and hydrogen, which is composed of vanadium-containing iron-based alloy pieces.
The ammonia synthesis catalyst according to claim 1, wherein the content of vanadium with respect to the entire iron-based alloy piece containing vanadium is 0.1% by mass or more and 5.2% by mass or less.
The ammonia synthesis catalyst according to claim 1 or 2, wherein the vanadium-containing iron-based alloy piece has a vanadium-containing triiron tetroxide layer on the surface.
The ammonia synthesis catalyst according to any one of claims 1 to 3, wherein the vanadium-containing iron-based alloy piece has a spherical shape.
The ammonia synthesis catalyst according to claim 4, wherein the diameter of the sphere is 0.2 mm or more and 1.0 cm or less.
The ammonia synthesis catalyst according to any one of claims 1 to 5, wherein the specific surface area of the vanadium-containing iron-based alloy piece is more than 0 m 2 / g and 1.0 m 2 / g or less.
The ammonia synthesis catalyst according to any one of claims 1 to 6, wherein the vanadium-containing iron-based alloy piece is a vanadium-containing steel piece.
Includes an ammonia synthesis step in which nitrogen and hydrogen are reacted in the presence of a catalyst to synthesize ammonia.
A method for producing ammonia, wherein the catalyst is the ammonia synthesis catalyst according to any one of claims 1 to 7.
The method for producing ammonia according to claim 8, wherein the reaction temperature in the ammonia synthesis step is 350 ° C. or higher and 600 ° C. or lower.
The method for producing ammonia according to claim 8 or 9, wherein the reaction pressure in the ammonia synthesis step is 1.0 bar or more and 100 bar or less.
Equipped with a reaction vessel that synthesizes ammonia from nitrogen and hydrogen inside
An ammonia production system in which the ammonia synthesis catalyst according to any one of claims 1 to 7 is arranged inside the reaction vessel.