JPH11114388A - Hydrogen separating material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydrogen separating material prepared by forming a thin hydrogen permeable metal film on a porous metal base body. SOLUTION: This hydrogen separating material has a hydrogen permeable metal thin film applied on a porous metal base body with a silica thin film interposed. In this case the hydrogen permeable metal thin film is formed on the porous metal base body with the silica thin film interposed, and further another silica thin film is formed on the metal thin film. Both of the silica thin films have pores having <=10 Å average pore diameter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrogen separation material that selectively permeates hydrogen.

[0002]

2. Description of the Related Art There is known a hydrogen separation material having a structure in which a porous metal substrate is used as a support and a hydrogen permeable metal membrane is formed thereon. In the hydrogen separation material having such a structure, the thickness of the metal film is preferably as thin as possible.
The hydrogen permeability of the hydrogen separation material obtained by reducing the thickness of the metal film can be increased. When a porous metal substrate is used as a support, the pore size of the porous metal substrate is usually as large as several μm or more, so that it is necessary to increase the thickness of a metal film formed thereon. Usually required to be several tens of μm.
Therefore, such a thick metal film has low hydrogen separation performance. According to JP-A-4-349926, silica gel, alumina gel or silica-alumina gel is filled in the pores of the inorganic porous material to reduce the pore diameter of the porous substrate, and to smooth the surface, A hydrogen separation material having a thin metal film formed thereon has been proposed. However, in the case of this hydrogen separation material, since the gel is filled in the pores of the porous substrate, it has a high internal stress in the substrate, and the substrate is easily damaged when a thermal cycle is applied. There is a problem.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a hydrogen separation material having a thin hydrogen-permeable metal membrane formed on a porous metal substrate.

[0004]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, have completed the present invention. That is, according to the present invention, there is provided a hydrogen separation material (first hydrogen separation material) having a hydrogen permeable metal thin film on a porous metal substrate via a silica thin film. Further, according to the present invention, a porous metal substrate has a hydrogen-permeable metal thin film via a siliceous thin film, and further has a siliceous thin film on the metal thin film. A hydrogen separation material (second hydrogen separation material) characterized by containing pores having a pore diameter of 10 ° or less is provided.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The porous metal substrate used in the present invention is conventionally known. Such a porous metal substrate includes a porous metal such as porous stainless steel and porous nickel, and the like. Metals having a large number of fine through-holes, sintered metal fine particles, and the like can be given. The shape of the porous metal substrate includes various shapes such as a sheet shape, a plate shape, a tubular shape, and a container shape. The shape of the porous metal substrate is appropriately selected depending on the use of the hydrogen separation material. In the porous metal substrate used in the present invention, the average pore diameter is 1 to 1
00 μm, preferably 1 to 5 μm. The porosity is not particularly limited, but is usually 20 to 50%, preferably 30 to 40%.

The first hydrogen separation material of the present invention has a structure in which a siliceous thin film is formed on one or both surfaces of a porous metal substrate, and a hydrogen-permeable metal thin film is formed thereon. In this case, the siliceous thin film has a porous structure, and the average pore diameter is 10 ° or less, preferably 7 ° or less, and the lower limit is usually 2 °. The porosity is 20 to
It is 50%, preferably 30 to 40%. The thickness of the silica thin film is 10 μm or less, preferably 5 μm or less, and its lower limit is about 0.1 μm. In the case of the present invention, it is preferable to define the thickness of the thin film in the range of 1 to 2 μm.

The siliceous thin film formed on the porous metal substrate in the present invention may be composed of SiO bonds or may contain SiH bonds and SiN bonds in addition to SiO bonds. In this case, the ratio of the SiO bond contained in the siliceous thin film is determined by the total silicon (S) contained in the siliceous thin film.
i) 65 to 99.5 atom%, preferably 95 to 95 atom%, in the ratio of the number of Si atoms forming SiO bonds to the number of atoms.
It is 99 atomic%. If the ratio of SiO bonds is less than the above range, the heat resistance and stability of the siliceous thin film deteriorate. When the SiH thin film contains SiH bonds,
The ratio of the SiH bonds is determined by the number of S atoms forming SiH bonds with respect to the total number of Si atoms contained in the siliceous thin film.
The number of i atoms is preferably in the range of 30 atomic% or less, more preferably 5 atomic% or less. The lower limit is about 0.5 atomic%. Further, when the SiH bond is contained in the siliceous thin film, the ratio of the SiN bond is preferably in the range of 30 at% or less, more preferably 5 at% or less. The lower limit is about 0.5 atomic%.

As the material of the hydrogen-permeable metal thin film in the present invention (hereinafter, also simply referred to as a metal film), conventionally known metals, for example, palladium, palladium metal, (Pd
-Ag, Pd-Cu, Pd-Pt, Pd-Ag-Cu,
Pd-Ag-X) (X: oxide such as Al, Mg, Be), Pd-V, Pd-V-Co, Ni, Ti, LaN
₅ , Fe-Ti and the like.

The first hydrogen separation material of the present invention can be produced by forming a polysilazane film on one or both sides of a porous metal substrate, firing the polysilazane film, and forming a metal film thereon. it can. The formation of the polysilazane film on the surface of the porous metal substrate can be carried out by applying a solution containing polysilazane to the surface of the porous metal body and drying. Various kinds of conventionally known polysilazanes can be used. The polysilazane used in the present invention also includes various modified products. Such a modified polysilazane is described in detail in, for example, JP-A-9-31333.
The ratio of the SiH bonds contained in the polysilazane is 30 atom% or less, preferably 5 atom% or less, which is the ratio of the number of Si atoms forming SiH to the total number of Si atoms contained in the polysilazane. The polysilazane preferably used in the present invention may be, for example, one represented by the following formula.

Embedded image In the above formula, R represents a hydrogen or hydrocarbon group, and n is 0.3
The above numbers are shown, and m represents a number of 0 or more. The ratio m / n between m and n is 0-2, preferably 0-1. The hydrocarbon group represented by R includes an aliphatic hydrocarbon group and an aromatic hydrocarbon group. Specific examples thereof include, for example, methyl, ethyl, propyl, phenyl, tolyl and the like. The number average molecular weight of polysilazane is 50 to 50.
000, preferably 100 to 100,000.

Solvents for dissolving polysilazane include aromatic hydrocarbon solvents such as benzene, toluene, xylene, ethylbenzene, diethylbenzene, trimethylbenzene, triethylbenzene; cyclohexane, cyclohexene, ethylcyclohexane, methylcyclohexane, decahydronaphthalene. , P-menthane and other alicyclic hydrocarbon solvents; dipentene, n-pentane,
i-pentane, n-hexane, i-hexane, n-heptane, i-heptane, n-octane, i-octane, n
Saturated hydrocarbon solvents such as -nonane, i-nonane, n-decane and i-decane; ether solvents such as dipropyl ether and dibutyl ether; ketone solvents such as methyl isobutyl ketone. The concentration of polysilazane contained in the solution is 0.1 to 30% by weight, preferably 0.1 to 30% by weight.
-20% by weight.

The application of the solution containing polysilazane to the surface of the porous metal substrate can be performed by a conventionally known method such as a dipping method or a roll coating method. Also, the application can be a multiple application over multiple applications. The thickness of the polysilazane film formed on the porous metal substrate is appropriately selected according to the desired thickness of the siliceous film, but is usually 0.5 to 10 μm, preferably 1 to 2 μm.

The polysilazane film formed on the porous metal substrate is heated at 150 to 500 ° C., preferably at 150 ° C.
Heat to ~ 400 ° C to form a siliceous film. By this heating, conversion of SiH, SiR (R: hydrogen or hydrocarbon group) and SiN in the polysilazane to SiO occurs, and the polysilazane film is converted to a siliceous film having a porous structure. In the case of the present invention, this siliceous film is made of SiH
It may contain a bond and a SiN bond. As the atmosphere for heating the polysilazane film, various atmospheres such as air, an inert gas, and a water vapor-containing gas are employed, but an air atmosphere is preferable. A metal film is formed on the silica thin film formed as described above. The formation of the metal film in this case can be performed by various conventionally known methods. Examples of such a method include an electroless plating method, a method combining an electroless plating method and an electroplating method, a vacuum evaporation method, a sputtering method, a gas phase chemical reaction method (CVD method), and the like. The thickness of the metal film formed on the siliceous film surface is
The range of the thin film is 5 μm or less. The lower limit of the film thickness is usually about 1 μm. In the case of the present invention, it is preferable to form a thin film in the range of 1 to 5 μm.

The first hydrogen-separating material of the present invention obtained as described above is a dense one in which the siliceous thin film has excellent mechanical strength and durability and does not have pinholes or cracks of 10 mm or more. Therefore, it has good handleability and usability. Further, since the siliceous film is a thin film, it exhibits high hydrogen permeability.

The second hydrogen separation material of the present invention has a structure in which a siliceous thin film is formed on a porous metal substrate, a metal film is formed thereon, and a siliceous thin film is further formed on the metal film. Have. To produce the second hydrogen separation material having such a structure, a first siliceous thin film is formed on one or both surfaces of a porous metal substrate. As the method for forming the siliceous membrane, the above-described method described for the first hydrogen separation material can be employed. The average pore diameter of the siliceous membrane is 10 ° or less, preferably 7 ° or less, and the porosity is 20 to 50%, preferably 30 to 40%.
%. The thickness of the siliceous film formed on the surface of the porous metal substrate is 10 μm or less, preferably 5 μm or less,
The lower limit is about 0.1 μm. In the case of the present invention, it is particularly preferable that the thickness be in the range of 1 to 2 μm. Next, a metal film is formed on the surface of the first siliceous film. In this case, as the method of forming the metal film, the various methods described above for the first hydrogen separation material can be employed. The thickness of this metal film is set to a thin range of 5 μm or less. The lower limit of the film thickness is usually about 1 μm. In the case of the present invention, the thickness is preferably in the range of 1 to 5 μm.

Next, a second siliceous thin film is formed on the surface of the metal film. In this case, as the method for forming the siliceous film, the above-described method described for the first hydrogen separation material can be employed. The average pore diameter of the siliceous membrane is 10 ° or less, preferably 7 ° or less,
Its lower limit is about 2 °. The porosity is 20
５０50%, preferably 30-40%. The thickness of the siliceous film formed on the metal film surface is not particularly limited,
Usually, it is 0.05 μm or more, preferably 0.1 μm or more, and its upper limit is about 1 μm. In the case of the present invention,
In particular, the thickness is preferably in the range of 0.1 to 0.5 μm.
Further, the siliceous film formed on the surface of the metal film does not necessarily need to be formed on the entire metal film, and may be a part of the film in some cases.

Since the surface of the metal film of the second hydrogen separation material is covered and protected by the above-mentioned ceramic film, it is hardly damaged during handling and use. Also, since the metal film does not come into direct contact with the gas atmosphere during its use,
The function of the metal film as a carbonization catalyst is greatly suppressed, and even if the metal film is brought into contact with a gas atmosphere containing a hydrocarbon such as an olefin, the olefin is hardly carbonized.

The hydrogen separation material of the present invention has a function of selectively transmitting hydrogen gas from a mixed gas containing hydrogen gas. In order to separate the hydrogen gas in the mixed gas using the hydrogen separation material of the present invention, a mixed gas containing hydrogen is brought into contact with one side (supply side) of the hydrogen separation material. Thereby, the hydrogen gas in the mixed gas selectively permeates the hydrogen separation material, and a gas containing the hydrogen gas at an increased concentration can be obtained on the opposite side (permeation side) of the hydrogen separation material. . In the separation of hydrogen gas using this hydrogen separation material, the higher the separation temperature, the higher the hydrogen separation efficiency. In the case of the present invention, the separation temperature is 200-700.
° C, preferably 300-600 ° C. Further, as the hydrogen partial pressure on the supply side of the hydrogen separation material is larger than the hydrogen partial pressure on the permeation side, the permeation speed of the hydrogen gas becomes higher. When performing hydrogen separation from a mixed gas using the hydrogen separation material of the present invention, the hydrogen gas permeability is significantly higher than the permeability of other gases such as nitrogen and methane, and hydrogen is efficiently separated from the mixed gas. Can be separated.

[0018]

Next, the present invention will be described in more detail with reference to examples.

Example 1 A porous tube made of stainless steel was used as a porous metal substrate. In this metal porous tube, the inner diameter is 7 mm, the outer diameter is 10 mm, the length is 100 mm, and the outer surface has a pore diameter of 1 to 2 μm. In order to obtain a polysilazane solution A, polysilazane having a repeating structural unit represented by the following formula (2) and having a number average molecular weight of 1,000 was dissolved in cyclohexene as a solvent so that the concentration became 1.0 wt%.

Embedded image Next, the above-mentioned metal porous tube (hereinafter, also simply referred to as a porous tube) is immersed in the solution A, and then dried.
The process was repeated to form a polysilazane film on the outer surface of the porous tube. Next, the porous tube was fired in air at 450 ° C. for 1 hour. By this baking, the polysilazane film was converted into a porous silica film having a thickness of 0.2 μm. In the siliceous membrane, the average pore diameter was about 5 °, and the density was 2.2 g / cm ³ . The average pore diameter was determined by an argon adsorption method. Also, this siliceous film contains 98 atomic% of Si forming SiO,
It contained 1 atomic% of Si forming SiH and 1 atomic% of Si forming SiN. next,
Forming a Pd film on the silica film by electroless plating, and forming a Pd film on the Pd film by electrolytic plating;
A Pd film having a total thickness of 0.8 μm was formed. Next, after plating Ag thereon by an electroless plating method, it was baked at 800 ° C. for 2 hours in an argon atmosphere. In this way,
A hydrogen separation material A of the present invention having a Pd-Ag alloy film (thickness: 1 μm, Ag / Pd weight ratio = 1/4) on a porous tube via a siliceous film was obtained.

Example 2 In the same manner as in Example 1, a 0.2 μm thick
1 μm thick Pd through a siliceous membrane with an average pore diameter of 5 °
-An Ag alloy film was formed. Next, the porous tube obtained above is immersed in a polysilazane solution B obtained by dissolving the polysilazane in cyclohexane at a concentration of 0.2 wt%, and the coating operation of drying is performed five times to form a polysilazane film. Calcination was performed at 450 ° C. for 1 hour. In this way, a Pd-Ag film having a thickness of 1 μm is provided on a porous tube via a siliceous film having a thickness of 0.2 μm, and a silica material having a thickness of 0.1 μm and an average pore diameter of 5 ° A hydrogen separation material B of the present invention having a membrane was obtained.

Application Example 1 Using the tubular hydrogen separation material obtained in Example 1, a gas permeability measurement test was performed. As the measuring device, the device system shown in FIG. 1 was used. Table 2 shows the measurement results.

In FIG. 1, reference numeral 1 denotes a gas cylinder, 2 denotes a pressure reducing valve, 3 denotes a needle valve, 4 denotes a pressure gauge, 5 denotes a female nut, 6 denotes a union, 7 denotes a heater, 8 denotes a chamber, and 9 denotes an intermediate portion to be tested. Alumina tube having a tubular hydrogen separation material M as a material, 10 is a gas chromatograph,
Numeral 11 denotes a membrane flow meter. The gas chamber 8 is formed of an annular space formed between the outer wall surface of the inner tube and the inner wall surface of the outer tube of the double tube composed of the inner tube and the outer tube. The portion of the tube wall corresponding to the tubular hydrogen separation material M, which is an object, is deleted, and the gas in the chamber 8 comes into contact with the hydrogen separation material M. In this case, the axial length of the tube wall to be deleted is shorter than the length of the hydrogen separation material M.

In order to measure the gas permeability of a tubular hydrogen separation material M as a test object using the measuring apparatus system of FIG. 1, a predetermined gas is supplied from a cylinder 1 filled with hydrogen, nitrogen or methane. The hydrogen separation material M is introduced into the chamber 8 surrounding the hydrogen separation material M through the pressure reducing valve 2 and the needle valve 3, and the chamber 8 and the hydrogen separation material M are
Heat. Cooling water is circulated through the union 6 to maintain the temperature of the hydrogen separation material M at a predetermined temperature. Chamber 8
Of the gas introduced into the tube, the gas (permeated gas) that has passed through the tube wall of the hydrogen separation material M as the test object is sent from the rear end of the alumina tube 9 to the gas chromatography 10 where the gas is analyzed. Is done. The exhaust gas (non-permeated gas) from the rear end of the chamber 8 is also subjected to gas analysis by the gas chromatography 10. The flow rate of the non-permeate gas sent from the rear end of the chamber 8 to the gas chromatography is measured by the membrane flow meter 11. In the measurement of the gas permeability, the measurement temperature (the temperature of the hydrogen separation material M) was adjusted by the flow rate of the cooling water. As the measurement temperature, 300 ° C, 400 ° C, and 500 ° C were used. The gas pressure was adjusted with a needle valve, and the gas pressure was about 200 kPa.

[0024]

[Table 2]

Application Example 2 An experiment was conducted in the same manner as in Application Example 1, except that the material obtained in Example 2 was used as the hydrogen separation material. Table 3 shows the results.

[0026]

[Table 3] The gas transmission rates Q of N ₂ and CH ₄ shown in Tables 2 and 3 are all below the measurement limit. The unit of the gas permeability Q shown in Tables 2 and 3 is std m ³ / (m ² · sec
KPa) and is defined by the following equation: Q = F / A · △ P In the formula, Q indicates a gas permeability, and F is a gas permeation flow rate (st
dm ³ / sec), A represents the gas catalyst area (m ² ), and ΔP is the differential pressure (kPa) between the gas supply side and the gas supply side.

[0027]

According to the hydrogen separation material of the present invention, although the porous substrate is made of a metal having a large average pore diameter, its surface is very dense and has a small average pore diameter. A metal film formed through a thin film,
Even if the metal film is made as thin as 5 μm or less, a metal film free of pinholes and cracks can be obtained. Therefore, the hydrogen separation material of the present invention has excellent hydrogen separation performance. In addition, since the hydrogen separation material of the present invention does not have a structure in which the gel is filled in the porous substrate, no particular internal stress is generated, and the substrate may be damaged even if a heat cycle is applied. Nor.

[Brief description of the drawings]

FIG. 1 shows a system diagram for measuring gas permeability.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Gas cylinder 4 Pressure gauge 7 Heater 8 Chamber 9 Alumina tube 10 Gas chromatography 11 Membrane flow meter M Hydrogen separation material

Claims (4)

[Claims] 1. A hydrogen separation method comprising a hydrogen-permeable metal thin film on a porous metal substrate via a siliceous thin film, wherein the siliceous thin film contains pores having an average pore diameter of 10 ° or less. material. 2. A hydrogen-permeable metal thin film is provided on a porous metal substrate with a silica thin film interposed therebetween, and further a silica thin film is provided on the metal thin film, and each of the silica thin films has an average pore diameter. A hydrogen separation material comprising pores of 10 ° or less. 3. The hydrogen separation material according to claim 1, wherein the thickness of the siliceous thin film on the porous substrate is 10 μm or less. 4. The hydrogen separation material according to claim 1, wherein the siliceous thin film comprises a calcined product of a polysilazane film.