JPH06304457A - Hydrogen separating membrane - Google Patents

Abstract

PURPOSE:To separate hydrogen with a high concn. from a mixture contg. hydrogen even at high temp. by forming a thin film of a heat-resistant oxide and a thin film with a specified value of film thickness and contg. vanadium and palladium on the surface of a metal porous body having fine holes with a specified dimension. CONSTITUTION:This hydrogen separating film is the one prepd. by forming a thin film of a heat-resistant oxide and a thin film with a film thickness of at most 50mum and contg. vanadium and palladium on a metal porous body with holes of 0.1-20mum. As the thin film contg. vanadium and palladium is supported by the metal porous body, this film exhibits high strength and is rich in processability and it is easy to make a module and there is no need to use a large amt. of expensive palladium. In addition, as there exists the thin film of a heat-resistant oxide between the metal porous body and the vanadium and palladium-contg. thin film, thermal diffusion reaction between the metal component of the metal porous body and vanadium and palladium at high temp. can be prevented from occurring and the hydrogen transmitting characteristics can 14 also be prevented from decreasing.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a hydrogen separation membrane for separating hydrogen in a mixed gas.

[0002]

2. Description of the Related Art Recently, as an energy-saving separation technology,
Membrane separation methods for gas are drawing attention. As a method of separating hydrogen from a hydrogen-containing gas to obtain high-purity hydrogen of 99.99% or more, there is a method of using a film mainly containing Pd (palladium) (called a Pd film) (called a Pd film method). Known {Journal of Japan Petroleum Institute Vol. 15, No. 1 (1
972) p. 64}. Conventionally, a Pd film was produced by stretching Pd or an alloy mainly composed of Pd into a thin film, and this film was used while being supported by a support frame. There is a limit to the lower limit of the thickness of the film obtained by the distraction method, and since this film is used by being supported by a supporting frame, it is necessary to impart mechanical strength sufficient to withstand such a supporting method. If a thin film is used, the film is easily damaged during use.

As one means for separating a specific gas from a mixed gas by a gas diffusion method, Knudsen which uses a porous gas separation membrane having a pore size smaller than the mean free path of gas molecules, for example, several tens of Å to several hundred Å. A separation method by diffusion is known. For example, such a separation method is effective for separating H ₂ gas in a mixed gas such as hydrogen (H ₂ ), nitrogen (N ₂ ), and carbon monoxide (CO) having a relatively large molecular ratio, and is generally a gas separation membrane. An organic polymer film has been adopted as. However, such an organic polymer film has heat resistance,
Due to the defect of poor durability such as chemical resistance, it has been attempted to use a porous gas separation membrane made of an inorganic material such as a ceramic porous body, and JP-A-59-592.
No. 23, proposes a porous gas separation membrane made of such an inorganic material and is shown as a conventional example.

As a method for solving the above problems,
A method of using a hydrogen separation membrane in which a thin film containing Pd is formed on a porous support made of an inorganic material is disclosed in Japanese Patent Laid-Open No. 62-
No. 121616.

Furthermore, the present inventor has previously proposed a hydrogen separation membrane in which a thin film containing vanadium and palladium is formed on a porous metal body. (Japanese Patent Application No. 4-83669)
issue)

[0006]

The above-mentioned conventional methods have the following problems, respectively. (1) Since the ratio of the permeation coefficient of the mixed gas in the separation method by Knudsen diffusion is theoretically equal to the square root of the reciprocal of the molecular weight of each gas, it is difficult to obtain a hydrogen gas with a considerably small concentration. (2) In the Pd film method, a relatively thick film of about 60 to 150 μm has to be used, and the amount of expensive Pd used increases,
Further, the permeation rate of hydrogen is low. (3) A hydrogen separation membrane formed by forming a thin film containing Pd on a porous support made of an inorganic material, which is disclosed in JP-A-62-121616, is liable to be damaged due to its low strength. Difficult to seal with the tube sheet. (4) A hydrogen separation membrane, in which a thin film containing vanadium and palladium is formed on a porous metal body proposed in Japanese Patent Application No. 4-083669, is used at a high temperature of 600 ° C. or higher, the metal component of the porous metal body and vanadium, There is a problem that a hydrogen diffusion performance is deteriorated by causing a thermal diffusion reaction with palladium.

The present invention is intended to solve the above-mentioned problems of the prior art, and paying attention to the absorbability and permeability of vanadium and palladium for H ₂ , the characteristics of vanadium and palladium. The present invention intends to provide a membrane for separating a high concentration of hydrogen from a mixed gas containing hydrogen by effectively utilizing the above as a metal porous body.

[0008]

The present invention has a range of 0.1 to 20 μm.
A hydrogen separation membrane, which is formed by forming a thin film of a heat-resistant oxide and a thin film containing vanadium and palladium having a thickness of 50 μm or less on at least one surface of a metal porous body having m pores.

In the present invention, the metal porous body having pores has heat resistance to withstand temperatures of 300 ° C. or higher, has no reactivity with the gas to be treated, and has a thickness of 0.1 to 20 μm.
It is suitable to use a metal porous body having pores which are as uniform as possible within the range. The pore diameter is set to 0.1 μm or more so as not to interfere with gas diffusion, and 20 μm or less is used when a thin film containing vanadium and palladium is coated to a film thickness of 50 μm or less. This is because it tends to occur. It is appropriate to use a cylindrical or plate-shaped metal porous body, and a metal porous body having a thickness of 0.1 to 2 mm is preferable from the viewpoint of strength and workability as a support.

In the present invention, examples of the metal porous body are as follows. (1) A foamed (porous) metal that is press-molded to control the pore size, and that has a smaller pore size obtained by thermal spraying or plating. (2) Molded metal fine powder (50 μm or less) having a small particle size. (3) Powders that can be removed by a chemical reaction (for example, graphite that can be removed by combustion) are added to a metal mixed or melted with a metal powder, and then the powder is removed by a chemical reaction to generate pores. (4) Rolled metal fiber nonwoven fabric with a fiber diameter of 1 to 20 μm
Sintered.

In the present invention, the thin film containing vanadium and palladium means one containing vanadium and palladium in an amount of 1% by weight or more and the total amount of vanadium and palladium in an amount of 50% by weight or more. The thickness of the thin film is preferably 50 μm or less, particularly 2 to 20 μm. The thin film containing vanadium and palladium means Pt, Rh, Ru, Ir, in addition to vanadium and palladium.
Group VIII elements such as Fe, Ni, Co, Cu, Ag, Au
And the like, and those containing alloys of these alloys or alloys and single metals.

Examples include vanadium-palladium alloys, vanadium-palladium alloys containing other metals, or vanadium alloys compounded with palladium or palladium alloys.

In the present invention, the heat-resistant oxide thin film means SiO ₂ , Al ₂ O ₃ , ZrO ₂ , TiO ₂ , La ₂ O.
Periodic Table IIIa melting point of more than 1000 ° C., such as _3, III
b, IVa and IVb oxides are contained and the film thickness is 50
Refers to those of less than μm.

The following method is used as an example of a method for forming a thin film of a heat-resistant oxide and a thin film containing vanadium and palladium having a thickness of 50 μm or less on at least one surface of the porous metal body.

(1) Method for forming a thin film of a heat-resistant oxide on the surface of a porous metal body A sol or gel of a heat-resistant oxide, a hydroxide or a slurry containing these is applied or dipped in the porous metal body and baked. What I did. Thermally resistant oxide or hydroxide sprayed on a porous metal. Vapor phase methods such as vacuum deposition, ion plating, and vapor phase chemical reaction (CVD).

(2) Method for forming thin film containing vanadium and palladium Liquid phase method such as plating Surface activation treatment (alternately dipping in tin chloride solution and palladium chloride solution), electroless plating (palladium) (Dipped in a liquid containing the compound of (1), a reducing agent, and vanadium powder) Further, electroless plating followed by electroplating, or electroplating followed by electroless plating. Vapor phase methods such as vacuum deposition, ion plating, and vapor phase chemical reaction (CVD).

The metal porous body on which the thin film containing vanadium and palladium is formed as described above can be used as a hydrogen separation membrane which selectively permeates only hydrogen.

When a mixed gas containing hydrogen is supplied to one side of the hydrogen separation membrane, the hydrogen separation membrane selectively permeates only hydrogen, and pure hydrogen flows out from the other side of the hydrogen separation membrane. The hydrogen permeation rate increases as the temperature increases, and the hydrogen pressure difference on both sides of the hydrogen separation membrane increases. The preferred operating temperature range of the hydrogen separation membrane of the present invention is 8
The temperature is not higher than 00 ° C., and the preferable range of the hydrogen pressure difference between the both sides of the hydrogen separation membrane is 0.5 to 10 kg / cm ² .

The permeation rate of hydrogen is extremely high, 400
15 to 60 cm ³ / c at a pressure difference of 2 kg / cm ²
m ² · min, which is 3 times that of the conventional Pd film method.
It reaches ~ 15 times.

The bleed gas is taken out in a state where the hydrogen partial pressure is equal to the pressure of hydrogen inside. Therefore, by controlling the internal hydrogen pressure to be taken out, the composition of the bleed gas,
It becomes possible to control the fractionation rate of hydrogen.

[0021]

In the hydrogen separation membrane of the present invention, since the thin film containing vanadium and palladium is supported by the metal porous body, it has high strength and is excellent in workability, is easily modularized, and is expensive. There is an advantage that the usage amount of is small. Furthermore, between the metal porous body and the thin film containing vanadium and palladium, since a thin film of a heat-resistant oxide is present, the metal diffusion of the metal component of the metal porous body under high temperature and vanadium and palladium is prevented, It is possible to prevent deterioration of hydrogen permeation performance.

[0022]

【Example】

(Example 1) A metal fiber non-woven fabric made of SUS316 having a fiber diameter of 8 μm and a wire mesh (SUS316) of 200 mesh, 100 mesh and 40 mesh stacked on each other was heated at 1100 ° C. for 3 hours to wind a laminated porous metal body. Processed,
A pipe having a diameter of 20 and a length of 300 mm was manufactured by welding.
The total thickness of this pipe was about 0.6 mm, and the thickness of the porous metal thin film having a pore size of about 10 μm was 0.05 mm.

On the outer surface of this pipe, a sample in which zirconia was deposited (zirconia film thickness 10 μm) and a sample in which alumina was deposited (alumina film thickness 20 μm) were prepared. As shown in Table 1, samples 1 to 3 were prepared by depositing vanadium and palladium at different ratios on the surface of the sample on which zirconia was deposited. Further, as shown in Table 1, Samples 4 to 6 were prepared by simultaneously vapor-depositing nickel, cobalt or molybdenum in addition to vanadium and palladium on the surface of the alumina vapor-deposited sample.

A hydrogen permeation test was carried out using a test apparatus shown in FIG. 1 using a porous metal pipe (Samples 1 to 6) coated with vanadium and palladium as a hydrogen separation membrane. The hydrogen separation membrane 1 is fixed to the stainless steel outer tube 3 with an O-ring 2, and the outside is heated in an electric furnace. The temperature was measured at the center of the inner tube using Thermocouple 8.

A mixed gas of H ₂ / N ₂ = 1 (mol) is continuously supplied from the supply hole 4, bleed gas is discharged from the discharge hole 5, and 99.99% or more of pure gas is discharged from the lower discharge hole 6. Hydrogen (pressure: 1 kg / cm ² abs.) Could be obtained. In FIG. 1, 7 indicates a sweep gas supply port.

[0026]

[Table 1] The samples 1 to 6 were subjected to an aging test at 500 ° C. for 1000 hours, and as a result, the hydrogen permeation performance was constant.

Table 2 shows the results of testing the sample 4 by changing the pressure and temperature of the mixed gas.

[0028]

[Table 2]

(Example 2) SUS316 having a fiber diameter of 2 μm
A metal fiber non-woven fabric and a layer of 200 mesh, 100 mesh and 40 mesh wire mesh (SUS316) are heated at 1200 ° C. for 3 hours, and the laminated and sintered metal porous body is wound and welded to a diameter of 20 × length. A metal porous body having a thickness of 300 mm was produced. The total thickness of this pipe is about 0.6 mm, and the thickness of the porous metal thin film having a pore size of 5 to 7 μm is 0.05 mm.

To a nitric acid aqueous solution prepared by adding 100 g of water to 2 g of concentrated nitric acid, 100 g of tetraethoxysilane was added and heated to 80 ° C. with rapid stirring to prepare a silica sol. The operation of applying the silica sol to the surface of the metal porous body and firing it at 500 ° C. was repeated to form a silica thin film of 10 μm on the surface of the metal porous body.

V-Ni alloy (85:15) of 10 μm or less
(% By weight) Powder for suspension of electroless palladium (Pd
The compound, hydrazine, and ammonia water) are immersed in the metal porous pipe, and V: Pd: Ni = 60: 3.
A thin film of 20 μm having a composition of 4: 6 (% by weight) was coated on the metal porous body. The same test as in Example 1 (mixed gas pressure 3 kg / cm ² G, flow rate 20 Nl / min,
As a result of carrying out 400 ° C.), 99.99% or more of hydrogen was obtained at 9.6 Nl / min. As a result of conducting an aging test on the above pipe at 500 ° C. for 1000 hours, the hydrogen permeation performance was constant.

(Example 3) Using a metal porous pipe on which the same thin silica film as in Example 2 was formed to a thickness of 10 µm, the outside of this pipe was vapor-deposited to first make 90:10 (wt%) nickel on vanadium. Sample 8 was prepared by vapor deposition so as to have a film thickness of 15 μm, and further 2 μ of palladium was vapor deposited, and sample 9 was prepared by vapor deposition of 5 μ having a composition of palladium and silver of 77:23 (wt%).

Test similar to Example 1 (mixed gas pressure 3 k
g / cm ² G, flow rate 20 Nl / min, 400 ° C.), and as a result, 99.99% or more of hydrogen was 10.8 Nl / min in sample 8 and 10.5 in sample 9.
Nl / min was obtained.

(Comparative Example) Vanadium and palladium were directly added to the porous metal pipe of Example 1 at a ratio of 10: 9 in the same manner as in Example 1 except that a thin film of zirconia was not formed.
As a result of vapor deposition at a ratio of 0 wt% and a hydrogen permeation test,
Similar to Example 1, 99.99% or more of hydrogen was 2.6 Nl /
got min. For the above sample, 500
As a result of performing an aging test at 1000 ° C. for 1000 hours, the hydrogen flow rate was reduced to 1.2 Nl / min.

[0035]

As is apparent from the above examples, the hydrogen separation membrane of the present invention can be used as a hydrogen separation membrane that selectively permeates only hydrogen for a long time even at high temperature.

[Brief description of drawings]

FIG. 1 is a schematic view of a test apparatus used for demonstrating the hydrogen separation effect of the hydrogen separation membrane of the present invention.

Claims (1)

[Claims] 1. A heat-resistant oxide thin film and a thin film containing vanadium and palladium having a thickness of 50 μm or less are formed on at least one surface of a metal porous body having pores of 0.1 to 20 μm. A hydrogen separation membrane characterized by the above.