JP2001137673A - Hydrogen separating composite - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydrogen separating composite which does not internally contain cracks and pinholes, has excellent heat resistance and adhesion property and has high hydrogen permeability. SOLUTION: The hydrogen separating composite consists of a hydrogen permselective membrane (1) of which the thickness t1 ranges from 0.05 to 10 μm and the thicknesses t2 in the portions thereof riding on the front ends of porous supporting bodies (2) are <=5 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a hydrogen separation composite in which a hydrogen selective permeable membrane for selectively permeating hydrogen is formed on the surface of a porous support.

[0002]

2. Description of the Related Art A hydrogen separation complex has a hydrogen selective permeable membrane on the surface of a porous support for selectively permeating hydrogen, and is used for separating and purifying hydrogen. In the method for forming the hydrogen selective permeable membrane, usually, a combination of electroless plating and electrolytic plating is used. That is, an intervening layer is first formed on the surface of the porous support by electroless plating. This intervening layer only narrows the pores on the surface of the porous support and does not block the pores. Further, a dense hydrogen selective permeable film such as Pd is formed thereon by electrolytic plating so as to completely cover the pores narrowed by the electroless plating. When a gaseous mixture containing hydrogen at a constant pressure is brought into contact with the dense hydrogen permselective membrane, hydrogen molecules become dense Pd.
It is adsorbed on a hydrogen selective permeable membrane such as a membrane, emits electrons, and penetrates as a proton into a hydrogen selective permeable membrane such as Pd. The protons that have entered the hydrogen permselective membrane diffuse toward the side where the hydrogen concentration is lower, and pass through the hydrogen permselective membrane. Elements larger than hydrogen cannot penetrate into Pd or the like. On the rear surface of the dense hydrogen permselective membrane formed by electrolytic plating, protons and electrons combine to form hydrogen molecules. After that, it passes through the holes of the electroless plating and the porous support toward the side where the hydrogen partial pressure is lower. By recovering this hydrogen, high-purity hydrogen gas can be recovered by separating it from other gas components.

[0003] As can be seen from the above description, the following four items are important for increasing the hydrogen permeability. (A) The thickness of the hydrogen selective permeable membrane is reduced. This is for shortening the time required for proton diffusion. (B) The porosity of the porous support is increased, and the thickness of the porous support is reduced. This is for reducing the flow resistance of the separated hydrogen gas. (C) The temperature is increased to increase the diffusion rate of hydrogen in the hydrogen selective permeable membrane. (D) Increasing the hydrogen partial pressure difference between the inlet and the outlet of the hydrogen separation complex.

[0004] Of the above four items, the items that can be implemented in the hydrogen separation complex are the two items (a) and (b) described above. In particular, it is very preferable to reduce the thickness of the hydrogen selective permeable membrane in (a) because it not only increases the hydrogen permeability but also reduces the amount of expensive materials such as Pd. Here, the hydrogen permeability refers to a hydrogen permeation amount (mol) per unit time (s), unit membrane area (m ² ), and unit transmembrane pressure (Pa). However, if the thickness of Pd or the like is too thin, Pd or the like cannot maintain its own solid shape. For this reason, conventionally, as described above, by a porous support such as porous ceramics,
It supports a thin film of Pd or the like. Further, if the electrolytic plating layer of Pd or the like is too thin, it is not possible to completely close the pores of the porous support with the electrolytic plating layer alone. As described above, in the conventional technique, an electroless plating layer is provided as an intervening layer, and after reducing the pore diameter of the porous support, a complete hydrogen-selective permeable membrane without pores is formed by the electrolytic plating layer. ing.

[0005] The hydrogen selective permeable membrane is formed on a porous support by a wet process called plating. In order to form a thin hydrogen selectively permeable film without pollution, it is desirable to form the film by a dry process such as a vacuum evaporation method. As a result of studying film formation processes by various dry processes, a proposal has been made to form a hydrogen selective permeable membrane on a porous support by an ion plating method (Japanese Patent Application Laid-Open No. 11-267777).

[0006] In recent years, studies have been made to mount the above-mentioned hydrogen separation composite in an automobile for use in a fuel cell. When a hydrogen separation composite is used in a fuel cell for an automobile, the hydrogen separation composite undergoes a thermal cycle in which the hydrogen separation composite is alternately exposed to a normal temperature and a high temperature. Cracks may occur in the permeable membrane. For this reason, a hydrogen separation composite which can withstand the above-mentioned thermal cycle has been proposed (JP-A-10-28).
No. 850). According to this proposal, as the intervening layer of the hydrogen permselective membrane, a material having a coefficient of thermal expansion between the porous support and the hydrogen permselective membrane is used, and the intervening layer is formed on the surface of the porous support. It is formed so as to fill a part of the hole. A hydrogen selective permeable membrane is laminated on the intervening layer so as to completely fill the holes. The intermediate layer having an intermediate coefficient of thermal expansion is expected to improve the heat resistance of the hydrogen separation composite.

[0007]

However, the above-mentioned hydrogen separation complex has the following problems. 1. The hydrogen permeability of the hydrogen permselective membrane is low.

[0008] The causes of the low hydrogen permeability are (1) insufficient reduction of the thickness of the hydrogen selective permeable membrane, (2) thick porous support, and (3) pores of the porous support. It is possible that the rate is small. To improve this, the thickness of the hydrogen selective permeable membrane may be further reduced. However, simply reducing the thickness of the hydrogen selective permeable membrane causes the following problem. 2. Cracks and pinholes are inherent in the hydrogen selective permeable membrane.

[0009] Cracks and pinholes are more likely to occur as the hydrogen selective permeable membrane is made thinner. Further, pores on the surface of the porous support are hardly closed by the hydrogen selective permeable membrane. Further, if the hydrogen permselective membrane is made thin, the conformity between the hydrogen permselective membrane and the porous support becomes poor, and the following problem is likely to occur. 3. The adhesion strength between the hydrogen selective permeable membrane and the porous support decreases.

[0010] Since the thickness of the hydrogen permselective membrane tends to decrease more and more, the affinity between the hydrogen permselective membrane and the porous support becomes poor, and the above-mentioned adhesion strength decreases. In addition, since the interface structure between the hydrogen selective permeable membrane and the porous support is too flat, the above-mentioned adhesion strength is further reduced. Although the heat resistance of the hydrogen permselective membrane has been improved by the above proposal of providing an intermediate layer having an intermediate coefficient of thermal expansion, cracks and cracks occur in the porous support itself when used for a long time in a fuel cell of an automobile. The problem is clear. 4. That is, the heat resistance of the porous support is insufficient.

In order to sufficiently increase the heat resistance, the bending strength, pressure resistance and heat resistance of the porous support must be increased. In particular, it is necessary to increase the heat resistance to withstand a thermal cycle of reciprocating between room temperature and 500 ° C.

If the above properties are not sufficiently satisfactory, the thickness of the porous support must be increased to secure the strength, or the area of the hydrogen film must be increased to secure the required amount of hydrogen. As a result, there arises a problem that the volume of the hydrogen separation complex increases. However, this problem of increasing the volume is a problem that is naturally solved by improving the above-described various performances.

Accordingly, an object of the present invention is to provide a hydrogen separation composite which is excellent in heat resistance and adhesion and has a large hydrogen permeability without cracks or pinholes.

[0014]

In the hydrogen separation complex according to the first aspect of the present invention, a hydrogen selective permeable membrane for selectively permeating hydrogen is formed on the surface of a porous support. The thickness t ₁ of the hydrogen selective permeable membrane is in the range of 0.05 μm to ₁₀ μm, and the thickness t ₁ of the portion of the hydrogen selective permeable membrane placed on the tip constituting the outermost surface of the porous support is ₂ is 5 μm or less.

According to the above configuration, the hydrogen gas and other components can be separated and purified. The lower limit of the distance t ₁ is set to 0.05 μm because if it is less than 0.05 μm, it is difficult to completely close the pores of the porous support. The upper limit of the above-mentioned t ₁ is set to 10 μm because if it exceeds 10 μm, the hydrogen permeability is greatly reduced. On the other hand, if t ₁ exceeds 10 μm, the thickness t ₂ of the hydrogen selective permeable membrane placed on the tip of the porous support which is not effective for hydrogen separation increases, and the production cost increases. To a 5μm upper limit of the above t ₂ is because t ₁ described above when the thickness exceeds a 5μm is lowered thicker becomes hydrogen permeability exceed 10 [mu] m. Another reason is to prevent an increase in the number of hydrogen selective permeable membranes in a portion that is not effective for hydrogen separation, and to reduce the amount of expensive hydrogen selective permeable membranes used. Although there is no particular lower limit for t ₂ , if there is no hydrogen selective permeable membrane at this portion, other gas flows along the interface between the side surface of the projecting portion particles of the porous support and the side of the hydrogen selective permeable membrane. Since there is a possibility that component leakage may occur, it is desirable that the thickness be such that this interface leakage does not occur.

The thickness t ₁ of the hydrogen selective permeable membrane and the thickness t _{2 of the} portion of the porous support at the tip portion constituting the outermost surface are determined by the selective hydrogen permeation of the hydrogen separation complex. (A) Scanning electron microscope (S
It may be measured by EM: Scanning Electron Microscope photograph, or (b) EPMA (Electron Probe Micro Analys).
is) or by analyzing the element distribution using an analytical SEM or the like. A detailed method of measuring t ₁ and t ₂ will be described in an embodiment.

In the hydrogen separation complex of the first aspect, for example, as in the hydrogen separation complex of the second aspect, the above-mentioned t ₁
Is in the range of 0.05 μm to 3 μm, and t ₂ is 2
It is desirable that it is not more than μm.

As described above, by setting the upper limit of t ₁ to 3 μm and the upper limit of t ₂ to 2 μm, the pores of the porous support are completely closed, the hydrogen permeability is increased, and the cost is increased. The use amount of the hydrogen selective permeable membrane can be reduced.

In the hydrogen separation complex according to the third aspect, the first aspect is as follows.
In the hydrogen separation composite of the above, the hydrogen selective permeable membrane covers the porous support such that the above-mentioned t ₂ is 0.001 μm or more.

By forming the hydrogen permselective membrane so as to have a thickness of 0.001 μm or more as in this configuration, the interface between the side surface of the protrusion particles of the porous support and the side of the hydrogen permselective film is formed. , The interface leak of other gas components can be prevented. In order to prevent this interface leak, the hydrogen selectively permeable membrane should be 0.001 μm or more, that is, several atomic layers or more. However, if the thickness is less than 0.001 μm, the interface leak cannot be completely prevented. In order to completely stop the interfacial leakage even when the pressure applied to the hydrogen selective permeable membrane becomes extremely large, it is desirable that the above-mentioned t ₂ is 0.002 μm or more.

[0021] In the hydrogen separation complex according to the fourth aspect, the first aspect is as follows.
In each of the hydrogen separation complexes of any one of (1) to (3), each of the tip particles constituting the outermost surface of the porous support is separated from the surface side so that the diameter of the pores on the surface of the porous support becomes smaller. An overlying, intervening layer is formed.

According to this structure, the intervening layer narrows the pores of the porous support, so that even if the thickness of the hydrogen selective permeable membrane formed thereon is reduced, the hydrogen selective permeable membrane completely fills the pores. Can be closed. Further, even if the above-mentioned t ₂ is made extremely thin or even zero in an extreme case, gas components other than the hydrogen gas are prevented from being mixed into the hydrogen gas separated by the interface leak. Furthermore, due to this intervening layer,
Familiarity between the hydrogen selective permeable membrane and the porous support is improved,
The adhesion strength between the hydrogen selective permeable membrane and the porous support can be increased. In addition, since the familiarity is improved as described above, cracks and pinholes are less likely to occur in the hydrogen selective permeable membrane.

In the hydrogen separation complex according to claim 5, claim 4
In the hydrogen separation complex, the surface of the hydrogen separation complex is
Including a portion where the porous support covered with the intervening layer is exposed, the hydrogen permselective membrane includes pores at the surface of the porous support covered with the intervening layer between the exposed portions. Is sealed.

According to this configuration, the hydrogen selective permeable membrane does not have its membrane surface resting on all protrusions of the porous support. Generally, at a portion where the membrane surface of the hydrogen selective permeable membrane is placed on the protruding portion of the porous support, the hydrogen permeation amount is significantly reduced. This is because the passage through which hydrogen that has passed through the hydrogen selective permeable membrane passes is locally closed. Therefore, it can be said that such a portion of the hydrogen permselective membrane is an ineffective portion where the efficiency is greatly reduced in terms of hydrogen permeation. According to the hydrogen separation complex of the fifth aspect, the number of ineffective portions is reduced, so that an expensive hydrogen selective permeable membrane can be suppressed to a necessary minimum, and the production cost can be reduced. Further, since there is no place where a large stress concentration occurs so as to directly pierce the membrane of the hydrogen selective permeable membrane due to the tip of the projecting portion of the porous support, cracks are less likely to occur in the hydrogen selective permeable membrane. Further, since the hydrogen selective permeable membrane is supported at a position deeper than the surface of the porous support, the support by the anchor effect becomes stronger, and the heat resistance in a heat cycle or the like can be improved.

In the hydrogen separation complex according to claim 6, claim 1 is
In any one of the hydrogen separation composites according to any one of Items 1 to 5, the porous support is formed of silicon nitride.

The porous silicon nitride can secure high strength in spite of its high porosity. Therefore, both the porosity and the thickness of the porous support can be reduced. As a result, hydrogen permeating the hydrogen permselective membrane can pass through the porous support without receiving a large resistance, so that the amount of permeated hydrogen per unit area can be increased. In addition, since porous silicon nitride has good compatibility with the hydrogen selective permeable membrane, the adhesion strength between them can be increased. As a result,
The heat resistance that withstands a heat cycle between room temperature and a high temperature of about 500 ° C. is also improved. Furthermore, since silicon nitride is excellent in bending strength, compressive strength, and thermal shock resistance, it is possible to solve the problem that the porous support itself is cracked or cracked during use in which the porous support itself is subjected to a thermal cycle.

[0027] In the hydrogen separation complex according to the seventh aspect,
In the hydrogen separation composite of the above, the silicon nitride contains columnar β-type silicon nitride.

When the columnar β-type silicon nitride is formed on the surface, the diameter of the pores on the surface of the porous support can be reduced, and the pores can be distributed at a high density. Therefore, the size of the supported particles constituting the hydrogen selective permeable membrane can be reduced when the hydrogen selective permeable membrane is formed, so that the thickness of the hydrogen selective permeable membrane can be reduced. Further, the porous support containing columnar β-type silicon nitride bonded to each other has both high porosity and high strength. Since the porous support has high strength, the thickness of the porous support can be reduced, and the resistance to the passage of the separated hydrogen gas can be reduced.
Further, since the porosity of the porous support is high, the resistance to the passage of the separated hydrogen gas is further reduced. By combining the above effects, it is possible to obtain a hydrogen separation complex having a significantly higher hydrogen permeability.

Further, the above-mentioned columnar β-type silicon nitride is
Since the columnar particles are formed to extend in random directions, if a hydrogen selective permeable membrane is formed thereon, the columnar particles exert an anchoring effect on the hydrogen selective permeable membrane. Therefore, the adhesion between the columnar β-type silicon nitride and the hydrogen selective permeable membrane is improved, and peeling is less likely to occur even in a thermal cycle between room temperature and 500 ° C.

In the hydrogen separation composite according to the seventh aspect, for example, as in the hydrogen separation composite according to the eighth aspect, the columnar β-type silicon nitride occupies 50% by volume or more in the porous support. It is desirable.

As described above, by setting the volume% of the columnar β-type silicon nitride in the porous support to 50% or more, the porous support is substantially formed of β-type silicon nitride. The same effect can be obtained. That is,
By setting the volume% of the columnar β-type silicon nitride to 50% or more, the thickness of the hydrogen selective permeable membrane can be reduced,
Due to the effect of a higher porosity and the like, an extremely large hydrogen permeability can be obtained.

In the hydrogen separation complex according to claim 7 or 8, for example, as in the hydrogen separation body according to claim 9, columnar β-type silicon nitride has a porosity of 30% to 80%. The average pore diameter is desirably 0.05 μm to 5 μm.

When the porosity of the columnar β-type silicon nitride is less than 30%, the resistance of the separated hydrogen gas to the passage through the porous support increases, and as a result, the hydrogen permeability decreases. On the other hand, when the porosity of the columnar β-type silicon nitride exceeds 80%, the strength required for the porous support cannot be secured, and the thickness must be increased.
The resistance to the passage of the separated hydrogen gas through the porous support is increased. Further, the lower limit of the average pore diameter of the columnar β-type silicon nitride is set to 0.05 μm, the thickness t ₂ of the hydrogen selective permeable membrane on the columnar β-type silicon nitride protrusion is less than 0.05 μm, This is because the thickness becomes too large compared to the above-mentioned t ₁ . As a result, the ratio of the hydrogen selective permeable membrane at the ineffective portion increases, and the manufacturing cost increases. On the other hand, the columnar β
The upper limit of the average pore diameter of the silicon nitride is 5 μm,
If the thickness exceeds 5 μm, the strength is reduced, and the size of the supported particles constituting the hydrogen selective permeable membrane cannot be reduced when the hydrogen selective permeable membrane is formed, and the thickness of the hydrogen selective permeable membrane cannot be reduced.

In the hydrogen separation complex according to any one of the first to ninth aspects, as in the hydrogen separation complex according to the tenth aspect, the hydrogen selective permeable membrane includes Pd, Ru, Pt, Rh, Ir, O, and O.
It is desirable that the metal film contains at least one selected from s, Au and Ag.

The above Pd, Ru, Pt, Rh, Ir, O
Since s, Au, and Ag all form a membrane that selectively allows only hydrogen, hydrogen can be separated and purified efficiently.

The hydrogen selective permeable membrane according to claim 11
Like hydrogen separation complex, silica, silica-based glass,
It may include at least one kind of porous membrane selected from ZrO ₂ , zeolite and carbon. In silica, an amorphous silica film formed by a sol-gel method, and in silica-based glass, a Vycor-based porous glass film has an action of separating hydrogen. For zeolites, Y-type zeolites, MFI-type, NaA-type, F-type
It is known that AU-type zeolites can separate hydrogen. In carbon, carbon nanotubes have a hydrogen separating effect.

The above-mentioned porous membrane is also known to selectively permeate only hydrogen, and has a characteristic that it is hardly corroded in a corrosive environment.

In all hydrogen separation composites having an intervening layer, the intervening layer is made of Mo, W, Ti, TiN, SiO ₂ , Ni and S
It is desirable to include at least one selected from i.

By forming the intervening layer containing the above substance on the surface of the protruding portion of the porous support, the affinity between the hydrogen selective permeable membrane and the porous support is improved, the adhesion strength is improved, and Cracks and pinholes are less likely to occur in the hydrogen selective permeable membrane. Further, it is possible to prevent a gas of a component other than the hydrogen gas from being mixed into the hydrogen gas due to an interface leak.

[0040]

Embodiments of the present invention will now be described with reference to the drawings.

(Embodiment 1) FIG. 1 is a schematic cross section of a surface portion of a hydrogen separation complex in which a columnar β-type silicon nitride 2 is used as a porous support and a hydrogen selective permeable membrane 1 is formed on the surface thereof. FIG. Here, a method for measuring t ₁ and t ₂ will be described in detail.

First, (a) the measurement method based on the SEM photograph
explain about. (1) First, hydrogen in the hydrogen separation complex
The surface cross section including the permselective membrane 1 is mirrored by lapping.
Finish on the surface. (2) RIE (Reactive Ion Etching) method
Etching lightly with the porous support particles 2 and water
The boundary with the element selectively permeable membrane 1 is clearly brought out.
(3) SEM of the surface cross section at a magnification of 2000 times or more
Take a photo. (4) As shown in FIG.
As t₁₁~ T_Fifteen, T_{twenty one}~ T_{twenty five}Is measured. t ₁₁~
t_FifteenIs the position of water at five points while the horizontal axis of the photograph is divided into six equal parts.
Measure the distance from the outermost surface to the deepest part of the elemental selective permeable membrane.
You. The average of the measured values is t₁And However, extremely
Exclude thick and thin locations. example
If the distance at that position is
It is desirable to exclude cases that are more than twice or less than half
New Further, the surface of the hydrogen selective permeable membrane described in Embodiment 3
Unless the position can be predicted, the porous support
It is desirable to exclude the case where a surface is formed. exclude
Even if there is a position, the average value is obtained by measuring three or more points.
If there are less than 3 points, it is hoped that no
Good. t_{twenty one}~ T_{twenty five}Indicates the outermost surface of the porous support in the photograph
Hydrogen permselective membrane resting on the tip of the particles that make up the surface
Is measured at five points at arbitrary locations. t_TwoIs its average
And

Next, (b) an element distribution mapping method using EPMA or analytical SEM will be described. (1)
As in the case of the SEM photograph, the surface section including the hydrogen selective permeable membrane 1 of the hydrogen separation complex is mirror-finished by lapping. (2) At a magnification of 2,000 or more, the surface cross-section is subjected to in-plane mapping of constituent elements by EPMA or analytical SEM, etc., and the boundary between the porous support particles and the hydrogen selective permeable membrane and the existing position are clearly defined. I do. (3) In the element mapping photograph, as shown in FIG. 1, t ₁₁ to t ₁₅ and t ₂₁ to
to measure the t _25. From t _{11 to} t ₁₅ , the distance from the outermost surface to the deepest part of the hydrogen selective permeable membrane is measured at five points while the horizontal axis of the photograph is equally divided into six. The average value of the measured values is defined as t ₁ . However, extremely thick or thin portions are excluded. For example, it is desirable to exclude the case where the distance at that position is twice or more or half or less of the distance at another position. Further, except for the case where the surface position of the hydrogen selective permeable membrane shown in Embodiment 3 can be predicted,
It is desirable to exclude the case where the porous support forms the outermost surface. Even if there is a position to be excluded, it is desirable that the average value is obtained by measurement of three or more points, and that if it is less than three points, no measurement is performed on the photograph. t ₂₁ ~t ₂₅ measures 5 points thickness at any point of the hydrogen-permselective membrane resting on tip of the particles constituting the outermost surface of the porous support in the photograph. t ₂ is the average value.

The thickness t ₁ of the hydrogen selective permeable membrane 1 measured in the above manner is 0.05 to ₁₀ μm, preferably 0.05 to ₁₀ μm.
The range is 3 μm. Further, t ₂ is set to 5 μm or less, preferably 2 μm or less. Further, the thickness is desirably 0.001 μm or more. The overall shape of the porous support made of columnar β-type silicon nitride is a disk, cylinder, monolith,
Any shape such as a bundle of honeycomb-shaped elements may be used.

The columnar β-type silicon nitride has a high porosity but a high strength. Therefore, the porous support having a high porosity can be thinned. As a result, the hydrogen permeability per unit area of the hydrogen selective permeable membrane can be increased. In addition, the hydrogen selective permeable membrane and the columnar β-type silicon nitride are well compatible, and the anchoring effect of the projection of the columnar β-type silicon nitride is added, so that the peeling resistance of the hydrogen selective permeable membrane is improved. Furthermore, since the columnar β-type silicon nitride itself has high high-temperature strength and high heat resistance, it can withstand a heating cycle between room temperature and 500 ° C.

(Embodiment 2) FIGS. 2 and 3 are schematic sectional views of a surface portion of a hydrogen separation complex according to Embodiment 2. FIG. In the second embodiment, the intervening layer 3 is interposed between the hydrogen selective permeable membrane 1 and the columnar β-type silicon nitride 2. FIG. 2 shows that the intervening layer 3 is deeply inserted into the columnar β-type silicon nitride projecting portion, so that the hydrogen selective permeable membrane 1 is almost formed on the intervening layer. On the other hand, in the case of FIG. 3, the intervening layer 3 is formed only on the surface side of the protrusion, and the hydrogen selective permeable membrane 1 directly contacts the protrusion at a position deep in the protrusion. ing. The method of measuring t ₁ and t ₂ when there is an intervening layer is as shown in FIGS. Basically, the measurement is performed in the same manner as described with reference to FIG. However, since the diameter of the pores of the porous support becomes smaller by the amount of the intervening layer 3, the portion of the intervening layer is treated as an enlarged porous support.

Due to the above-mentioned intervening layer, the diameter of the pores on the surface becomes small, and even if the thickness of the hydrogen selective permeable membrane is reduced, the hydrogen selective permeable membrane can completely close the pores. . Further, even if the above-mentioned t ₂ is less than 0.001 μm or even zero, it is possible to prevent substances other than the hydrogen gas from being mixed into the hydrogen gas due to interfacial leakage. Further, the intervening layer improves the conformity between the hydrogen selective permeable membrane and the porous support, and can increase the adhesion strength between the hydrogen selective permeable membrane and the porous support. Further, since the affinity between the hydrogen selective permeable membrane and the porous support is improved, cracks and pinholes are less likely to occur in the hydrogen selective permeable membrane.

(Embodiment 3) FIG. 4 is a schematic sectional view of a surface portion of a hydrogen separation complex according to Embodiment 3. In the third embodiment, the hydrogen selective permeable membrane 1 does not completely cover the surface, but the columnar β-type silicon nitride 2 covered by the intervening layer 3 is exposed on the surface. The method of measuring t ₁ and t ₂ when there is an intervening layer is as shown in FIG. Basically, the measurement is performed in the same manner as described with reference to FIGS. According to this configuration, the number of ineffective portions is reduced, so that an expensive hydrogen selectively permeable membrane can be minimized. Further, since stress concentration does not occur so as to pierce the hydrogen selective permeable membrane at the projecting portion covered with the intervening layer, cracks are less likely to occur in the hydrogen selective permeable membrane.

[0049]

EXAMPLE Next, a hydrogen separation complex of the present invention was prepared,
The results of investigations on various properties such as hydrogen permeability will be described. As the hydrogen selective permeable membrane, a Pd alloy film composed of 10 wt% of Ag and the balance substantially composed of Pd was used. As a porous support, silicon nitride (Si) containing 80% by volume of columnar β-type silicon nitride (Si ₃ N ₄ ) was used. ₃ N ₄₎ was used. The porosity of this porous support was 50%, and the average pore diameter was 0.4 μm.

(Production Method of Porous Support) To a powder containing α-type silicon nitride having an average particle diameter of 0.3 μm as a main component, 10 wt% of yttrium oxide powder having an average particle diameter of 1 μm was added. For 72 hours.
After drying, a molding aid was added, and a width of 100 mm and a thickness of 1.
Extruded into a 5 mm sheet, then 23 mm in diameter
And cut out into disks. The disc is placed in the atmosphere for 50
The molding aid was removed by heating at 0 ° C. × 1 hour.
A baking treatment was performed at 1800 ° C. × 1 hour in nitrogen. The disk of the obtained silicon nitride sintered body has a diameter of 21 mm, a thickness of 1 mm, a β-type silicon nitride ratio of 80%, a porosity of 50%, and an average fineness measured by a mercury intrusion method. The pore size was 0.4 μm.

(Method of Forming Intervening Layer) An intervening layer was formed on the surface of the above silicon nitride sintered body by RF magnetron sputtering. W, Mo, or the like was used as the target, depending on the type of the intervening layer to be formed. The atmosphere is argon gas containing 5% by volume of hydrogen gas, and the pressure is 5%.
mTorr. The input power was 450 W, and the average deposition rate was about 0.02 μm / min. The above-mentioned porous support was not heated, and the support holder was cooled with water, but since the surface of the porous support was exposed to plasma,
There was some temperature rise. By measurement with radiation thermometer,
The temperature was estimated to have reached 100 ° C. or higher. Immediately after the start of film formation for opening the shutter, it is considered that the temperature was almost around room temperature. The film thickness was controlled by the film formation time, that is, the time from opening to closing of the shutter.

(Method of forming hydrogen selective permeable film) Pd as a hydrogen selective permeable film was formed by RF magnetron sputtering.
-An Ag film was formed. A Pd-Ag alloy was used as a target. The atmosphere was an argon gas containing 5% by volume of hydrogen gas, and the pressure was 5 mTorr. The input power was 450 W, and the average deposition rate was about 0.02 μm / min. The heating of the porous support was not performed, and the support holder was cooled with water. However, since the surface of the porous support was exposed to plasma, there was a slight rise in temperature. Temperature measured by radiation thermometer is 100 ℃
It was estimated that this had been reached. Immediately after the start of film formation for opening the shutter, it is considered that the temperature was almost around room temperature. The film thickness was controlled by the film formation time, that is, the time from opening to closing of the shutter. Thickness t for hydrogen permselective membrane
₁ and t ₂ were determined by measuring t ₁ and t ₂ of the formed Pd—Ag alloy film by a method based on an SEM photograph.

The method for forming the intervening layer and the Pd-Ag film is as follows.
In addition to RF magnetron sputtering, unbalanced
Magnetron (UBM) sputtering, ion plating, arc ion plating, vapor deposition, electroless plating, chemical vapor deposition (CVD), electrochemical vapor deposition (E-CVD) And the like, and the desired performance can be obtained. In particular, E-CVD
According to the method, acetic acid Pd, acetylacetonato Pd complex,
Using Pd chloride or the like, the Pd salt and the Ag salt are supplied to the surface of the porous support with argon gas. In addition to this, by supplying hydrogen gas from the back side of the porous support utilizing the fact that it is porous, and adjusting the two so that they are in contact near the surface of the substrate, very dense Pd -Ag alloy film can be obtained. The temperature of the porous support varies somewhat depending on the type of salt used, but a temperature range of about 200 ° C to 550 ° C is usually applied.
The pressure of the atmosphere is less than 1 atm and 1 mTorr
The above-described reduced pressure conditions are generally used.

(Evaluation Method of Hydrogen Permeability, etc.) A mixed gas of carbon monoxide (CO) and hydrogen was supplied, and hydrogen gas was separated and purified by the above-described hydrogen separation complex. The device used for this measurement is shown in FIG. A hydrogen separation complex 10 having a hydrogen selective permeable membrane 1 formed on a silicon nitride support 2 having a diameter of 21 mm and a thickness of 1 mm via an intervening layer is attached to the tip of a cylindrical support tube 6 and a seal 5 is provided. Was given. This support tube 6 is stored in an electric furnace 7. 1: 1 molar ratio
A mixed gas of carbon monoxide and hydrogen is supplied to the hydrogen separation complex, and the flow rate and purity of the hydrogen gas permeating the complex 10 are measured by a flow meter and a gas chromatography analyzer to select hydrogen. Rate and transmittance were obtained. The transmembrane pressure was 0.1 MPa, and the test temperature was 500 ° C. In addition, the adhesion was evaluated as follows: a cell tape was attached to the surface of the hydrogen selective permeable membrane, and when the hydrogen selective permeable membrane adhered to the tape when peeled off, it was evaluated as “poor”.
And

(Evaluation results)

[0056]

[Table 1]

Table 1 shows the results. In Table 1, t ₁ ,
t ₂ etc. are average values. No. 1 as a comparative example,
In No. 2, leak occurred because t ₁ was less than the lower limit, and the hydrogen selectivity also became a low value before practical use. In No5, t ₂ is 0.0005 μm,
Since the lower limit of 0.001 μm was not reached, an interface leak occurred, and the penetration between the hydrogen selective permeable membrane and the silicon nitride support became poor. As a result, the selectivity of hydrogen gas became 0%. Further, the No10, because t ₂ is zero, as with No5, hydrogen gas selectivity resulting leakage 0
%Met. Comparative Example N in which the hydrogen permselective membrane is too thick
In o17 and No18, the compatibility with the silicon nitride support was poor due to the excessive thickness, and the hydrogen selectivity was 55% and 48%, respectively. Further, due to the excessive thickness, the hydrogen permeability became 1/1000 to 1/100 of the hydrogen permeability of the hydrogen separation composite of the present invention.

On the other hand, in the present invention, for example,
In No. 3 and No. 4, since the thickness of the hydrogen permselective membrane is in the thin range within the range of the present invention, the hydrogen permeability is 6.
High values of 3 × 10 ^-4 and 2.8 × 10 ^-4 mol / (m ² · s · Pa) were obtained. No7, the No8, leakage and adhesion is good, by an amount t ₁ becomes thicker No3,
The hydrogen permeability was lower than that of No. 4. Also, No
In No. 6 and No. 9, t ₂ was too small or zero, but since there was provided a W film or a Mo film as an intervening layer, there was no leakage and good adhesion was obtained. In No. 11 to No. 16, there is no leak and the adhesion is good.
The hydrogen permeability tends to decrease as t ₁ and t ₂ increase.

Although the embodiments and examples of the present invention have been described above, the embodiments and examples of the present invention disclosed above are merely examples, and the scope of the present invention is not limited to these. The present invention is not limited to the embodiments and examples of the present invention. The scope of the present invention is shown by the description of the claims, and further includes all modifications within the meaning and scope equivalent to the description of the claims.

[0060]

The hydrogen separation composite according to the present invention, in which the hydrogen selective permeable membrane is divided into an effective portion and an ineffective portion and the thickness is limited at each portion, does not cause a leak or the like and has a high hydrogen permeability. Have. Further, in the hydrogen separation composite using columnar β-type silicon for the porous support, the thickness of the effective portion of the hydrogen selective permeable membrane can be further reduced, and an extremely high hydrogen permeability can be secured. Therefore, by using the hydrogen separation complex of the present invention, only hydrogen can be separated and purified very efficiently from a mixed gas containing hydrogen.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view illustrating a method for obtaining thicknesses t ₁ and t ₂ near the surface of a hydrogen separation composite according to Embodiment 1 of the present invention.

FIG. 2 is a schematic cross-sectional view illustrating a method for obtaining thicknesses t ₁ and t ₂ near the surface of a hydrogen separation complex according to Embodiment 2 of the present invention.

FIG. 3 is a schematic cross-sectional view illustrating a method for obtaining thicknesses t ₁ and t ₂ near the surface of a hydrogen separation complex different from that of FIG. 2 in the second embodiment.

FIG. 4 is a schematic cross-sectional view illustrating a method for obtaining thicknesses t ₁ and t ₂ near the surface of a hydrogen separation complex according to Embodiment 3 of the present invention.

FIG. 5 is a configuration diagram showing a measurement device for evaluating the performance of the hydrogen separation complex.

[Explanation of symbols]

1 hydrogen selective permeable membrane (Pd membrane or Pd-based alloy membrane), 2
Porous support (porous silicon nitride), 3 intervening layers, 5
Seal, 6 support (cylindrical), 7 electric furnace, 10
Hydrogen separation composite, t ₁₁ ~t ₁₅ Distance from the outermost surface of the deepest part of the selective hydrogen permeation membrane in 6 equal portions point of SEM photographs,
The average value of t ₁ t _{11 to} t ₁₅ , the thickness of the hydrogen selective permeable membrane on the tip of the porous support particles on the surface of the t _{21 to} t ₂₅ hydrogen separation composite, the thickness of t ₂ t _{21 to} t ₂₅ Average value.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D006 GA41 MA02 MA09 MA22 MA24 MA31 MB04 MB15 MC02 MC03 PB66 4G040 FA06 FB09 FC01 FD01 FD06 FE01

Claims (12)

[Claims] 1. A hydrogen separation composite selective hydrogen permeation membrane which selectively transmits hydrogen to the surface of the porous support is formed, the thickness t ₁ is 0.05μm of the selective hydrogen permeation membrane ~ 10μ
m, and a thickness t _{2 of a} portion of the hydrogen selective permeable membrane, which is placed on a tip portion constituting an outermost surface of the porous support, is 5 μm or less. 2. The hydrogen separation complex according to claim 1, wherein the t ₁ is in a range of 0.05 μm to 3 μm, and the t ₂ is 2 μm or less. 3. The hydrogen selective permeable membrane according to claim 1, wherein said t ₂ is in the range of 0.
2. The hydrogen separation composite according to claim 1, wherein the composite has a thickness of 001 μm or more. 4. An interposition wherein each of the tip particles constituting the outermost surface of the porous support is covered from the surface side such that the diameter of pores on the surface of the porous support is reduced. The hydrogen separation composite according to any one of claims 1 to 3, wherein a layer is formed. 5. The surface of the hydrogen separation complex includes a portion where the porous support covered with the intervening layer is exposed,
The hydrogen separation composite according to claim 4, wherein the hydrogen selective permeable membrane seals pores on a surface portion of the porous support covered with the intervening layer between the exposed portions. . 6. The porous support is silicon nitride.
The hydrogen separation composite according to claim 1. 7. The hydrogen separation composite according to claim 6, wherein the silicon nitride includes columnar β-type silicon nitride. 8. The hydrogen separation composite according to claim 7, wherein the columnar β-type silicon nitride occupies 50% by volume or more in the porous support. 9. The silicon nitride has a porosity of 30%.
８０80%, and the average pore diameter is from 0.05 μm to 5 μm.
The hydrogen separation complex according to claim 7, wherein m is m. 10. The hydrogen selective permeable membrane, wherein Pd, Ru,
A metal film containing at least one selected from Pt, Rh, Ir, Os, Au and Ag.
10. The hydrogen separation complex according to any one of 9. 11. The hydrogen selective permeable membrane is made of silica, silicon,
Power glass, ZrO _Two, Zeolite and carbon bleach
Claims comprising at least one kind of porous membrane selected from the group consisting of:
Item 11. The hydrogen separation complex according to any one of Items 1 to 10. 12. The intervening layer is made of Mo, W, Ti, Ti.
N, containing at least one selected from among SiO _2, Ni and Si, hydrogen separation composite according to any one of claims 4-11.