JP5736669B2 - Ammonia synthesizer - Google Patents

Description

  The present invention relates to an ammonia synthesizer, and more particularly to an ammonia synthesizer that enables efficient ammonia synthesis under mild reaction conditions.

Conventionally, a plant for synthesizing ammonia has been constructed, and the produced ammonia (NH ₃ ) has been used as a raw material for fertilizers and various chemical products. In the past, the Haber-Bosch method was used for the synthesis of ammonia, and the direct synthesis reaction of ammonia as shown in the reaction formula 1 is also used in recent years.

[Chemical 1]
N ₂ + 3H ₂ → 2NH ₃ (1)

The Harbor Bosch method was a reaction under high-temperature and high-pressure conditions, but studies have been made to cause the reaction of Reaction Formula 1 under mild conditions in order to save energy and increase reaction efficiency. Yes. For example, according to the method described in Patent Document 1, a method for reducing the reaction temperature of the ammonia synthesis reaction to about 50 ° C. to 250 ° C. by devising a method for supplying hydrogen (H ₂ ) as a raw material is proposed. Has been.

JP 2000-247632 A

  In the ammonia synthesis represented by the above formula, industrially, hydrogen is obtained by various chemical methods. Typically, hydrogen is synthesized at low cost by a catalytic reaction (reaction formula 2) using a hydrocarbon such as naphtha or natural gas and water vapor.

[Chemical 2]
CH ₄ + H ₂ O → 3H ₂ + CO (2)

In order to obtain hydrogen using, for example, natural gas mainly containing methane (CH ₄ ), for example, by the steam reforming (steam reforming) reaction represented by the reaction formula 2, the reaction system is heated to about 800 ° C. It is necessary to heat up to a large amount, and a large amount of energy is required.

However, since there is no description about how to supply how the Patent Document 1, H _2, when applied to the method of Patent Document 1 to the industrial process requires a lot of energy to the supply of H _2. For this reason, in the overall reaction up to obtaining ammonia, the study for energy saving is insufficient, leaving much room for study.

  The present invention has been made in view of such circumstances, and an ammonia synthesizer capable of efficiently performing ammonia synthesis under mild reaction conditions by reducing the reaction temperature of an addition reaction using steam. The purpose is to provide.

  In order to solve the above-described problems, an ammonia synthesizer according to the present invention has a hollow base and an inner wall material that divides the inside of the base into two spaces, and the ammonia synthesizer is provided in one of the two spaces. Is provided with a reforming catalyst for steam-reforming hydrocarbons to generate hydrogen, and at least a part of the inner wall material is a hydrogen separation membrane capable of separating the hydrogen from the one space to the other space And the other space is provided with a synthesis catalyst for synthesizing ammonia using the hydrogen and nitrogen in the reaction.

  First, the steam reforming reaction of hydrocarbons is an equilibrium reaction, and the hydrogen generation reaction is an endothermic reaction. Therefore, it is usually necessary to heat to about 800 ° C. in order to promote the reaction. On the other hand, in the ammonia synthesizer of the present invention, the produced hydrogen moves to the other space outside the system through the hydrogen separation membrane, so that the equilibrium reaction can be promoted to the hydrogen production side.

  Further, it is known that the hydrogen permeation amount in the hydrogen separation membrane can be expressed by the following mathematical formula 1.

Here, Q: hydrogen permeation amount, A ₁ , B: coefficient, R: gas constant, T: thermodynamic temperature of permeating hydrogen, A: area of hydrogen separation membrane, t: film thickness of hydrogen separation membrane, P ₁ : Hydrogen partial pressure in one space, P ₂ : Hydrogen partial pressure in the other space.

Since the hydrogen that has moved to the other space is consumed in the synthesis reaction in the other space, the value of P _{2 in} Equation 1 is always a low value or substantially zero. Therefore, the hydrogen permeation amount increases as shown in Equation 1, and the equilibrium reaction is further promoted to the hydrogen production side in the steam reforming reaction.

  That is, according to the structure of this invention, compared with the case where steam reforming and ammonia synthesis are performed by separate apparatuses, the steam reforming reaction is promoted. Thereby, in the normal steam reforming reaction, heating at about 800 ° C. is necessary, but the reaction temperature can be lowered. Therefore, it is possible to provide an ammonia synthesizer that enables efficient ammonia synthesis under mild reaction conditions as a whole apparatus.

  In the present invention, the substrate supplies the hydrocarbon and water vapor to the one space, and discharges at least a part of a reaction product of the reforming catalyst, and the one It is desirable to have turbulent flow generating means for generating turbulent flow in the one space.

  In one space, hydrogen in the vicinity of the hydrogen separation membrane easily contacts the hydrogen separation membrane and easily permeates the other space, while hydrogen at a position away from the hydrogen separation membrane does not easily contact the hydrogen separation membrane. There is a difference that it is difficult to transmit to the other space. Therefore, in one space, a concentration distribution is likely to occur, in which the hydrogen partial pressure decreases near the hydrogen separation membrane and the hydrogen partial pressure does not decrease so much at a position away from the hydrogen separation membrane. When the concentration distribution is generated, the hydrogen partial pressure on one space side is lowered, so that the hydrogen permeation amount is reduced.

  However, according to this configuration, by providing the turbulent flow generation means, the gas component flowing in one space is stirred and the concentration distribution becomes uniform. Therefore, it is difficult for the hydrogen permeation amount to decrease due to the concentration distribution of hydrogen in one space, and it is possible to supply the hydrogen produced in the reaction to the other space well, and the steam reforming reaction. Can be promoted.

In the present invention, it is desirable that the turbulent flow generating means is disposed apart from the hydrogen separation membrane.
According to this configuration, the area of the hydrogen separation membrane that is effective for permeating hydrogen through the hydrogen separation membrane does not decrease due to the installation of the turbulent flow generation means. Furthermore, since there is no physical contact between the turbulent flow generation means and the hydrogen separation membrane, the hydrogen separation membrane is hardly damaged (pinhole), and leakage due to the pinhole is also unlikely to occur. Therefore, the concentration of hydrogen separated through the hydrogen separation membrane increases, leading to improved performance.

In the present invention, the base is provided with two openings connected to the other space, and a sweep gas flowing from one second opening to the other second opening is supplied. Is desirable.
According to this configuration, since the hydrogen partial pressure in the other space can be reduced, hydrogen transfer through the hydrogen separation membrane can be promoted, and the reaction temperature of the addition reaction using water vapor can be reduced. It becomes possible.

In the present invention, the sweep gas is preferably the nitrogen.
According to this configuration, both the source gas and the sweep gas can be used, and an efficient reaction can be performed.

In the present invention, it is desirable that the inner wall material has a porous base material that supports the hydrogen separation membrane.
According to this configuration, it is possible to suppress the breakage of a very thin hydrogen separation membrane, and to form the hydrogen separation membrane by plating the porous substrate on the porous substrate, thereby facilitating the formation of the reactor.

In the present invention, the synthesis catalyst is formed on an iron compound as a forming material, and the hydrogen separation membrane is supported on one surface of the porous substrate using palladium or a palladium compound as a forming material. It is desirable that the substrate is disposed so as to face the other space.
According to the inventor's study, it has been found that if a palladium compound and an iron compound are in contact in a reactor heated to several hundred degrees, an alloy is formed and pinholes may be formed in the hydrogen separation membrane. Yes. Therefore, in the case of a configuration in which the material for forming the hydrogen separation membrane or the synthesis catalyst is a combination of these materials, a porous substrate can be arranged between the two so that they do not come into contact with each other. Deterioration due to generation can be suppressed.

  According to the present invention, it is possible to provide an ammonia synthesizer that can reduce the reaction temperature of an addition reaction using steam and efficiently perform ammonia synthesis under mild reaction conditions.

It is explanatory drawing which shows a part of manufacturing plant which has the ammonia synthesizer of this invention. It is a schematic perspective view which shows the principal part of the ammonia synthesizer of 1st Embodiment. It is sectional drawing which concerns on the ammonia synthesizer of 1st Embodiment. It is sectional drawing which concerns on the ammonia synthesizer of 2nd Embodiment.

[First Embodiment]
The ammonia synthesizer according to the first embodiment of the present invention will be described below with reference to FIGS. In all the drawings below, the dimensions and ratios of the constituent elements are appropriately changed in order to make the drawings easy to see.

  FIG. 1 is an explanatory diagram showing a part of a manufacturing plant having an ammonia synthesizer 1A of the present embodiment.

  The ammonia production plant shown in FIG. 1 includes an ammonia synthesizer 1A that synthesizes ammonia by a catalytic reaction, a first pipe 4 and a second pipe 5 that supply raw materials to the ammonia synthesizer 1A, and a first pipe that discharges the synthesized ammonia. 3 piping 6, a cooling device 7 that cools and liquefies ammonia, a fourth piping 8 through which liquefied ammonia flows, and a fifth piping 9 that discharges gas from the cooling device 7. In addition, it has a heating device (not shown) for heating the ammonia synthesizer 1A.

To the ammonia synthesizer 1A, natural gas and water vapor are supplied from a supply pipe 41 constituting the first pipe 4, and nitrogen (N ₂ ) is supplied from the second pipe 5, and ammonia is synthesized using these as raw materials. . Substances other than ammonia, specifically hydrogen and carbon monoxide (CO), generated in the process of synthesis, are discharged from the discharge pipe 42. The discharged hydrogen and carbon monoxide are used as fuel for a heating device (not shown). The synthesized ammonia is discharged to the cooling device 7 through the third pipe 6 and is liquefied by the cooling device 7. In addition, the opening part provided in the connection part of the supply piping 41 and the discharge piping 42, and the base | substrate 2 corresponds to the 1st opening part of this invention.

  The liquefied ammonia is discharged through the fourth pipe 8, and the gas components (ammonia and unreacted gas) in the gas phase that have not been liquefied are taken out through the fifth pipe 9. A pipe 91 constituting the fifth pipe 9 is connected to the second pipe 5 for supplying nitrogen to the ammonia synthesizer 1A. As a result, the ammonia that has not been liquefied is supplied again to the cooling device 7 via the ammonia synthesizer 1A, and is recovered without waste. The unreacted gas component is used again as a raw material for ammonia synthesis in the ammonia synthesizer 1A. In addition, the opening part of the both ends of the cylindrical inner wall material 3 connected with the 2nd piping 5 and the 3rd piping 6 corresponds to the 2nd opening part of this invention.

  Further, the pipe 91 is provided with a pipe 92 for releasing (purging) gas components in the gas phase portion of the cooling device 7 and a valve 93 for opening and closing the pipe 92.

  FIG. 2 is a schematic perspective view showing the main part of the ammonia synthesizer 1A, and FIG. 3 is a cross-sectional view taken along line AA in FIG.

  As shown in the figure, an ammonia synthesizer 1A of the present invention comprises a hollow cylindrical base 2 and a hollow cylindrical inner wall material 3 disposed in the base 2 and extending in the same direction as the base 2. Have. A space surrounded by the base 2 and the inner wall material 3 constitutes a first flow path (one space) 10, and a space inside the inner wall material 3 constitutes a second flow path (the other space) 20. .

  Here, the base body 2 and the inner wall material 3 are shown as extending in one direction, but the present invention is not limited to this and may be curved. Further, the cross-sectional shape is not limited to a circle, and any shape can be adopted.

  A supply pipe 41 shown in FIG. 1 is connected to the base 2, and natural gas and water vapor indicated by reference numeral G <b> 1 are supplied into the first flow path 10. 1 is connected to the inner wall member 3, and nitrogen indicated by reference numeral G2 in the second flow path 20 and gas components from the gas phase portion of the cooling device 7 shown in FIG. Supplied.

  The first flow path 10 is filled with a steam reforming catalyst that catalyzes the reaction of the following reaction formula 3 and generates hydrogen using natural gas and steam. Reaction formula 3 describes the reaction formula for methane, which is the main component of natural gas.

[Chemical formula 3]
CH ₄ + H ₂ O → 3H ₂ + CO (3)

  As such a catalyst, generally known nickel (Ni) -based, ruthenium (Ru) -based, and platinum (Pt) -based catalysts can be used.

  The inner wall material 3 includes a hydrogen separation membrane 31 and a porous substrate 32 such as a ceramic or metal porous material that supports the hydrogen separation membrane 31. In the inner wall material 3 of the present embodiment, a hydrogen separation membrane 31 is disposed on the porous substrate 32 on the side facing the first flow path 10.

  As the hydrogen separation membrane 31, a known material can be used as a forming material. Examples of the forming material include Pd-based materials such as palladium (Pd) or Pd-silver (Ag) alloy, Pd-copper (Cu) alloy, vanadium (V) or vanadium alloy, zirconium (Zr) -nickel. (Ni) amorphous alloy etc. can be mentioned. By providing these metals on the porous substrate 32 as a thin film having a thickness of 1 μm to 100 μm by a method such as plating or sticking, the hydrogen separation membrane 31 is formed.

  Hydrogen generated in the first flow path 10 is supplied to the second flow path 20 via the hydrogen separation membrane 31 and the porous substrate 32. Further, the gas component G3 (carbon monoxide, unreacted natural gas, water vapor, and hydrogen that did not permeate the hydrogen separation membrane 31) that did not permeate the hydrogen separation membrane 31 is exhausted from the exhaust pipe 42 shown in FIG. The

  The second flow path 20 is filled with an ammonia synthesis catalyst that catalyzes the reaction of the following reaction formula 4 and generates ammonia using nitrogen and hydrogen. In the ammonia synthesis catalyst, ammonia is synthesized from hydrogen supplied to the second flow path 20 through the hydrogen separation membrane 31 and nitrogen supplied to the second flow path 20 from the second pipe 5 shown in FIG. The

[Chemical formula 4]
N ₂ + 3H ₂ → 2NH ₃ (4)

  As such a catalyst, a generally known iron-based catalyst or the like can be used, and examples thereof include AS-4 manufactured by Zude Chemie Catalysts.

  As the catalyst filled in the first flow path 10 and the second flow path 20, a catalyst having a particle size such that a gap through which a gas flows after filling can be used. For example, it may have a cylindrical (pellet) shape, a spherical shape, a flake shape, or the like, and some or all of them may be connected to each other.

  Nitrogen supplied to the second flow path 20 also has a function as a sweep gas for flowing the synthesized ammonia. Therefore, the mixed gas G4 of ammonia and nitrogen is discharged from the second flow path 20 and introduced into the cooling device 7 shown in FIG.

  Here, the effect of the above-described ammonia synthesizer 1A will be described in more detail. The ammonia synthesizer 1A of the present invention can lower the reaction temperature of the steam reforming reaction (hydrogen synthesis reaction) shown in the reaction formula 3 in the first flow path 10 for the following reasons, and thus the reaction as a whole reaction system The energy used for can be reduced.

  First, the steam reforming reaction of natural gas is an equilibrium reaction, and the reaction indicated by the right-pointing arrow shown in Reaction Formula 3 is an endothermic reaction. Therefore, it is usually necessary to heat to about 800 ° C. in order to promote the reaction. On the other hand, in the ammonia synthesizer 1A of the present embodiment, hydrogen generated on the right side of the reaction formula 3 moves to the second flow path 20 outside the system via the hydrogen separation membrane 31, so that the equilibrium reaction is performed as hydrogen. It can be promoted to the production side.

  Further, it is known that the hydrogen permeation amount in the hydrogen separation membrane 31 can be expressed by the following formula 1.

Here, Q: hydrogen permeation amount, A ₁ , B: coefficient, R: gas constant, T: thermodynamic temperature of permeating hydrogen, A: area of hydrogen separation membrane, t: film thickness of hydrogen separation membrane, P ₁ : Hydrogen partial pressure on the first flow path 10 side, P ₂ : hydrogen partial pressure on the second flow path 20 side.

As shown in Reaction Formula 4, since hydrogen is consumed in the second flow path 20, the value of P _{2 in} Formula 1 is always a low value or substantially zero. Therefore, the hydrogen permeation amount is increased as shown in Equation 1, and the equilibrium reaction is further promoted to the hydrogen generation side in the steam reforming reaction.

  Thus, compared with the case where steam reforming and ammonia synthesis are performed by separate apparatuses, the reaction of the reaction formula 3 is promoted in the ammonia synthesizer 1A of the present embodiment. As a result, in a normal steam reforming reaction, heating at about 800 ° C. is necessary, but in the ammonia synthesizer 1A of the present embodiment, the steam reforming step can be performed at a reaction temperature of about 350 ° C. to 550 ° C. Become.

  In this temperature range, the ammonia synthesis reaction in the second flow path 20 is also sufficiently generated, so that the reaction temperature can be lowered as a whole reaction system.

  Therefore, according to the ammonia synthesizer 1A configured as described above, it is possible to efficiently synthesize ammonia under mild reaction conditions.

  In the present embodiment, the porous base material 32 is disposed on the side facing the second flow path 20, but the porous base material 32 is configured on the first flow path 10 side. It doesn't matter.

  For example, when a palladium-based thin film is used as the hydrogen separation membrane 31, iron contained in the ammonia synthesis catalyst and palladium contained in the hydrogen separation membrane 31 form an alloy at the operating temperature of the ammonia synthesizer 1, and the hydrogen separation membrane There is a possibility that scratches (pinholes) may occur in 31. Therefore, it is preferable that a ceramic porous substrate 32 is disposed between the hydrogen separation membrane 31 and the second flow path 20 filled with the ammonia synthesis catalyst so as not to contact them.

  However, when the metal contained in the material for forming the hydrogen separation membrane 31 and the ammonia synthesis catalyst are not a combination that forms an alloy at the operating temperature (for example, the material for forming the hydrogen separation membrane 31 is not Pd-based). The hydrogen separation membrane 31 and the ammonia synthesis catalyst may be in contact with each other. In that case, the porous substrate 32 may be disposed on the first flow path 10 side.

  Also in the relationship between the hydrogen separation membrane 31 and the steam reforming catalyst, the arrangement position of the porous substrate 32 can be set by the same concept.

  In the present embodiment, the gas flowing through the first flow path 10 and the second flow path 20 is shown as a parallel flow, but it may be a counter flow.

  Further, in the present embodiment, the base body 2 and the inner wall material 3 are shown as extending in the same direction, but the present invention is not limited to this and may be curved.

  In the present embodiment, the inner wall material 3 is cylindrical and has been shown as being inserted into the internal space of the base body 2. However, the present invention is not limited thereto, and for example, the inner wall material 3 has a flat plate shape. As long as the first flow path 10 and the second flow path 20 are adjacent to each other through a hydrogen separation membrane provided on the inner wall material 3, such as a structure that divides the internal space of the two, various structures are adopted. can do.

[Second Embodiment]
FIG. 4 is an explanatory diagram of an ammonia synthesizer 1B according to the second embodiment of the present invention. The ammonia synthesizer 1B of this embodiment is partly in common with the ammonia synthesizer 1A of the first embodiment. The difference is that a plurality of baffle plates (turbulent flow generation means) 21 are provided in the first flow path 10. Therefore, in this embodiment, the same code | symbol is attached | subjected about the component which is common in 1st Embodiment, and detailed description is abbreviate | omitted.

  The baffle plate 21 employs, for example, a donut-shaped disk, and is disposed on the inner side wall of the base 2 in the first flow path 10 so as not to contact the surface of the inner wall material 3. That is, the baffle plate 21 is disposed away from the hydrogen separation membrane 31 provided on the surface of the inner wall material 3.

  Although the figure shows a state in which the baffle plates 21 are provided at three locations in the first flow path 10, the number of the baffle plates 21 can be changed as appropriate. Further, the size of the baffle plate 21 such as the length of the baffle plate 21 provided at three locations from the base 2 and the width in the flow path extending direction may be the same or different from each other.

  In order for hydrogen to pass through the hydrogen separation membrane 31, it is first necessary for hydrogen to come into contact with the hydrogen separation membrane 31. In the first flow path 10, hydrogen in the vicinity of the hydrogen separation membrane 31 is transferred to the hydrogen separation membrane 31. However, hydrogen at a position away from the hydrogen separation membrane 31 is less likely to contact the hydrogen separation membrane 31 and difficult to permeate the second channel 20. Therefore, in the first flow path 10, a concentration distribution is likely to occur in which the hydrogen partial pressure decreases in the vicinity of the hydrogen separation membrane 31 and the hydrogen partial pressure does not decrease much at a position away from the hydrogen separation membrane 31.

As shown in Equation 1 above, the hydrogen permeation amount through the hydrogen separation membrane 31 is affected by the hydrogen partial pressures (P ₁ and P _{2 in} Equation 1) on both sides across the hydrogen separation membrane 31. Therefore, the density distribution as described above occurs, the hydrogen permeation to lower the hydrogen partial pressure P ₁ becomes the reducing.

  However, in the ammonia synthesizer 1B of the present embodiment, by providing the baffle plate 21, gas components in the first flow path 10 (natural gas, water vapor, and hydrogen generated by the reaction in the first flow path 10, Carbon monoxide) is stirred, and the concentration distribution of each gas component becomes uniform in the first flow path 10. Therefore, it is difficult for the hydrogen permeation amount to decrease due to the concentration distribution of hydrogen in the first flow path 10, and it is possible to supply the hydrogen generated in the reaction to the second flow path 20 satisfactorily. .

  The baffle plate 21 is disposed so as not to contact the surface of the inner wall material 3. Thereby, the area of the hydrogen separation membrane that is effective for permeating hydrogen through the hydrogen separation membrane 31 is not reduced by the installation of the baffle plate 21. Furthermore, since there is no physical contact between the baffle plate 21 and the hydrogen separation membrane 31, the hydrogen separation membrane 31 is not easily damaged (pinhole) and leaks due to the pinhole are also unlikely to occur. Therefore, the concentration of hydrogen separated through the hydrogen separation membrane 31 increases, leading to improved performance.

  Even in the ammonia synthesizer 1B configured as described above, ammonia synthesis can be efficiently performed under mild reaction conditions.

  In the present embodiment, the baffle plate 21 is a donut-shaped disk, but turbulence is generated in the airflow in the first flow path 10 to stir the gas components in the first flow path 10. Other configurations of the disc can be adopted as long as they can be configured. Based on the same concept, the baffle plate 21 may have a plate shape that does not transmit a gas component, or may have a mesh shape that allows a gas component to pass therethrough.

  The preferred embodiments of the present invention have been described above with reference to the accompanying drawings, but it goes without saying that the present invention is not limited to such examples. Various shapes, combinations, and the like of the constituent members shown in the above-described examples are examples, and various modifications can be made based on design requirements and the like without departing from the gist of the present invention.

DESCRIPTION OF SYMBOLS 1A, 1B ... Ammonia synthesizer, 2 ... Base | substrate, 3 ... Inner wall material, 10 ... 1st flow path (one space), 20 ... 2nd flow path (the other space), 21 ... Baffle plate (turbulent flow generation means) ), 31 ... hydrogen separation membrane, 32 ... porous substrate,

Claims (7)

A hollow substrate;
A hollow inner wall member disposed concentrically on the inside of the base body and extending in the same direction as the base body ,
In one space surrounded by the base body and the inner wall material, a reforming catalyst that generates hydrogen by steam reforming hydrocarbon is disposed,
At least a part of the inner wall material is formed with a hydrogen separation membrane capable of separating the hydrogen from the one space into the other space inside the inner wall material ,
A synthesis catalyst for synthesizing ammonia using the hydrogen and nitrogen in the reaction is disposed in the other space. The base body supplies the hydrocarbon and water vapor to the one space, and discharges at least a part of a reaction product of the reforming catalyst; and
2. The ammonia synthesizer according to claim 1, further comprising turbulent flow generating means for generating turbulent flow in the one space in the one space.   The ammonia synthesizer according to claim 2, wherein the turbulent flow generating means is disposed apart from the hydrogen separation membrane. The base is provided with two second openings connected to the other space,
4. The ammonia synthesizer according to claim 1, wherein a sweep gas flowing from one of the second openings to the other of the second openings is supplied. 5.   The ammonia synthesizer according to claim 4, wherein the sweep gas is the nitrogen.   6. The ammonia synthesizer according to claim 1, wherein the inner wall material has a porous base material that supports the hydrogen separation membrane. 7. The synthetic catalyst uses an iron compound as a forming material,
The hydrogen separation membrane is supported on one surface of the porous substrate using palladium or a palladium compound as a forming material,
The ammonia synthesizer according to claim 6, wherein the porous base material is disposed so as to face the other space.

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