JP2006346621A - Hydrogen separation membrane and hydrogen separation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin film of palladium or a palladium alloy highly useful as a hydrogen separation membrane formed on a sintered metal support body, having no defect even with a thin film thickness. <P>SOLUTION: This hydrogen separation membrane comprises the support body comprising a porous sintered metal; a porous layer comprising a polycrystal sintered body of yttrium stabilized zirconia formed on the support body; and the thin film of palladium or a palladium alloy formed on the porous layer comprising the yttrium stabilized zirconia by plating. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a hydrogen separation membrane and a hydrogen separation method.

  A thin film of palladium or palladium alloy has a selective hydrogen permeability, and is used as a hydrogen separation membrane by utilizing this characteristic.

  When a palladium thin film or a palladium alloy thin film is used as a hydrogen separation membrane, the thinner the film thickness, the higher the permeation rate of hydrogen and the less the amount of expensive noble metal such as palladium used. For this reason, a porous ceramic such as alumina is usually used as a support, and a palladium thin film or a palladium alloy thin film is formed on the surface thereof by plating or other methods and used as a hydrogen separation membrane (for example, patent documents) 1).

However, porous ceramics such as alumina have poor bondability with metal, and when a hydrogen separation membrane is to be incorporated into the device, a special joint to the metal is required, resulting in problems such as sealing and strength of that part. It has become an obstacle to practical use. In order to improve this, a porous sintered metal may be used as a support for a hydrogen separation membrane such as palladium. In this case, although the bonding property to the apparatus is very good, the porous sintered metal has a rough surface, and the exposed gas permeation holes are sometimes several μm or more, and directly on it, palladium or palladium alloy Even if it is going to form a thin film, in order to seal the gas permeation hole of several micrometers or more, the film thickness of 20 micrometers or more is usually required, and even then, the defect cannot be completely eliminated. In addition, a base material such as stainless steel is used as the sintered metal, but it is known that the components such as iron and nickel diffuse into the palladium-based hydrogen separation membrane and deteriorate the performance as a hydrogen separation membrane. ing. Therefore, there is a method in which a ceramic such as silica, alumina, ceria, zirconia is coated on a sintered metal and a palladium film or a palladium alloy film is formed thereon. However, in the case of silica, alumina, or the like, the coefficient of thermal expansion is significantly different from that of palladium. In that respect, ceria and zirconia are advantageous in that they have a thermal expansion coefficient close to that of palladium, but they have poor sinterability and do not form a dense porous film even when coated on a sintered metal substrate. Even if the palladium membrane is formed by this method, there are many defects, and high hydrogen separation selectivity cannot be obtained when the palladium film thickness is 5 μm or less (for example, see Non-Patent Documents 1 and 2).
JP-A-5-137799 Dan Wang, Jianhua Tong, Hengyong Xu and Yasuyuki Matsumura, "Preparation of Palladium Membrane over Porous Stainless Steel Tube Modified with Zirconium Oxide", Catal. Today, 93-95, 689-693 (2004). Jianhua Tong, Hengyong Xu, Dan Wang and Yasuyuki Matsumura, "Preparation of Thin Palladium Membrane on Porous Stainless Steel Support Modified with Cerium Hydroxide", J. Jpn. Petrol. Inst., 47, 64-65 (2004).

  The present invention has been made in view of the current state of the prior art described above, and its main purpose is to use a palladium or palladium alloy thin film having a selective hydrogen permeability and to be highly practical and excellent. It is to provide a hydrogen separation membrane having performance.

  The present inventor has intensively studied to achieve the above-described object. As a result, a porous sintered metal body was used as a support, a porous layer made of a polycrystalline sintered body of yttrium-stabilized zirconia was formed thereon, and a palladium or palladium alloy thin film was formed thereon by plating. According to the multilayer structure composite formed by forming a defect-free thin film even when the film thickness of the palladium or palladium alloy thin film is 5 μm or less, it has been found that the durability is dramatically improved. The present invention has been completed.

That is, the present invention provides the following hydrogen separation membrane and hydrogen separation method.
1. A support made of a porous sintered metal,
A porous layer made of a polycrystalline sintered body of yttrium-stabilized zirconia formed on the support, and a palladium or palladium alloy thin film formed by plating on the porous layer of yttria-stabilized zirconia Hydrogen separation membrane.
2. Item 2. The hydrogen separation membrane according to Item 1, wherein the yttrium-stabilized zirconia has a porous structure having an average pore diameter of 0.01 to 0.5 µm.
3. Item 3. The hydrogen separation membrane according to Item 1 or 2, wherein the palladium or palladium alloy thin film comprises one layer or two or more layers, and the total film thickness is 0.5 to 10 µm.
4). The hydrogen-containing mixed gas is positioned on one side separated by the hydrogen separation membrane according to any one of the above items 1 to 3, and the hydrogen partial pressure on the other side of the hydrogen separation membrane is set on the hydrogen-containing mixed gas side. A method for separating hydrogen from a hydrogen-containing mixed gas, characterized by having a partial pressure of hydrogen or lower.

  Hereinafter, the hydrogen separation membrane of the present invention will be specifically described.

Hydrogen separation membrane and production method thereof The hydrogen separation membrane of the present invention comprises a support made of a porous sintered metal, a porous layer made of a polycrystalline sintered body of yttrium-stabilized zirconia formed on the support, and It consists of a palladium or palladium alloy thin film formed by a plating method on the yttria-stabilized zirconia porous layer.

  According to the hydrogen separation membrane having such a structure, by having a porous layer made of a polycrystalline sintered body of yttrium-stabilized zirconia on a support made of a porous sintered metal, a palladium or palladium alloy thin film can be formed. The affinity is improved, the adhesion of the palladium or palladium alloy film is improved, and a thin film having no defect can be formed even when the film thickness is thin. In addition, the polycrystalline sintered body layer of yttrium-stabilized zirconia has high toughness and sinterability, and has a stable crystal structure. Therefore, a hydrogen separation membrane having a palladium or palladium alloy thin film formed thereon has a high temperature. The durability at is very good.

(1) Support body There is no limitation in particular about the material of the porous sintered metal used as a support body, For example, stainless steel, a Hastelloy alloy, an Inconel alloy, nickel, a nickel alloy, titanium, a titanium alloy etc. can be used. The shape of the sintered metal is not particularly limited, and may be appropriately determined according to the usage form as the hydrogen separation membrane, but is usually used as a plate shape, a hollow tubular shape, or the like. The porous sintered metal only needs to have a thickness that can maintain stability as a hydrogen separation membrane. For example, the porous sintered metal can have a thickness of about 0.2 to 2 mm.

  The pore diameter of the porous sintered metal is not particularly limited as long as the yttrium-stabilized zirconia layer formed thereon can be stably held. Usually, the average pore diameter may be about 1 to 50 μm. The average pore diameter in this case is a value measured by a mercury intrusion method.

(2) Yttrium-stabilized zirconia layer The yttrium-stabilized zirconia layer formed on the porous sintered metal is made of a polycrystalline sintered body. In this case, the amount of yttrium in the yttrium-stabilized zirconia is preferably about 0.3 to 15 mol%, more preferably about 1 to 8 mol% with respect to the total number of moles of yttrium and zirconium.

  The yttrium-stabilized zirconia layer may be composed of a substantially uniform sintered body as a whole. For example, in order to make the outer surface smooth, the zirconia particle size in the vicinity of the outer surface is set inside. It may be smaller than the grain size. The crystal grain size of yttrium-stabilized zirconia is obtained by observing the outer surface with a scanning electron microscope, and when the average value of the lengths of the long sides measured for any 100 crystals is defined as the average crystal grain size. The value is preferably about 0.1 to 3 μm, and more preferably about 0.2 to 1 μm.

  Similarly, the pore diameter of the yttrium-stabilized zirconia layer may be substantially uniform as a whole, or the internal pore diameter may be large and the pore diameter near the outer surface may be small. However, in any case, the average pore diameter measured by the mercury intrusion method for the entire yttrium-stabilized zirconia layer is preferably about 0.01 to 0.5 μm, and about 0.05 to 0.3 μm. More preferably.

  The thickness of the yttrium-stabilized zirconia layer is not particularly limited, but if it is too thick, gas diffusion is inhibited, and if it is too thin, the surface of the sintered metal body cannot be completely covered. For this reason, it is preferable that it is about 5-100 micrometers normally, and it is more preferable that it is about 10-50 micrometers.

  A method for forming the yttrium-stabilized zirconia layer is not particularly limited, and the yttrium-stabilized zirconia layer composed of a polycrystalline sintered body that satisfies the above-described conditions can be formed by appropriately using a known method for forming a ceramic thin film. That's fine.

  For example, yttrium-stabilized zirconia having the same composition as the target yttrium-stabilized zirconia layer is synthesized in advance, and pulverized to obtain a powder having an appropriate particle size. Then, if necessary, water, alcohol, Add a solvent such as ethylene glycol or dimethylformamide, a polymer such as styrene, vinyl acetate, ethylene, acrylate ester, or vinyl chloride, and apply it on the porous sintered metal as a kneaded product or slurry. And calcination to form a porous layer of yttrium-stabilized zirconia. The firing conditions in this case may be appropriately determined so that an yttrium-stabilized zirconia layer that satisfies the above-described conditions is formed in a temperature range that does not adversely affect the porous sintered metal used as the support.

  As another method, fine particles of yttrium-stabilized zirconia are prepared by a hydrothermal synthesis method using zirconium and yttrium hydroxide as a precursor, etc., and if necessary, water, alcohol, ethylene glycol, dimethylformamide, etc. A solvent such as styrene, vinyl acetate, ethylene, acrylic acid ester, vinyl chloride, etc., and added to a porous sintered metal as a kneaded product, slurry, etc., fired, yttrium A porous layer of stabilized zirconia may be formed. In addition, as a raw material of yttrium-stabilized zirconia, for example, hydroxide, solvent such as water, alcohol, ethylene glycol, dimethylformamide, styrene, vinyl acetate, ethylene, acrylate, vinyl chloride, etc. It is also possible to add a polymer or the like and apply it as a kneaded product or slurry on the porous sintered metal, and then calcinate it to obtain a polycrystalline sintered body of yttrium-stabilized zirconium.

(3) Palladium or palladium alloy thin film The hydrogen permeable membrane of the present invention is obtained by forming a palladium or palladium alloy thin film on the yttria-stabilized zirconia layer by plating.

  The above-mentioned yttria-stabilized zirconia layer made of a polycrystalline sintered body has good affinity with a palladium or palladium alloy thin film, and is excellent in adhesion by forming a palladium or palladium alloy thin film by a plating method. Even in the case of a thin film thickness of about or less, a good thin film without defects can be formed.

  The thickness of the palladium or palladium alloy thin film is not particularly limited, but is usually preferably about 0.5 to 10 μm, and more preferably about 1 to 5 μm. If the film thickness is too thin, the selectivity and durability of hydrogen are lowered, and if the film thickness is too thick, the hydrogen permeation rate is lowered and the economy is lost.

  The palladium alloy is preferably an alloy of palladium and one or more kinds of noble metals selected from the group consisting of silver, gold, copper, platinum, rhodium and ruthenium. The proportion of palladium in such a palladium alloy is preferably 50% by weight or more.

  The palladium or palladium alloy thin film is formed by the electroless plating method. After forming the palladium or palladium alloy thin film by the electroless plating method, if necessary, the palladium or palladium alloy thin film is formed by the electroplating method or the electroless plating method. May be formed. In addition, when forming two or more layers of palladium or palladium alloy thin films, it is preferable that the total thickness is about 0.5 to 10 μm.

  Specific plating conditions are not particularly limited, and plating may be performed according to known conditions using a known plating bath capable of forming a target palladium or palladium alloy thin film.

  In the case of forming a palladium alloy thin film, the alloy thin film may be formed by an electroless plating method according to known conditions using an electroless plating solution containing a palladium compound and a compound containing other alloy components. A palladium alloy thin film may be formed by performing an alloying process after forming a plating film of two or more layers containing one or two or more of each metal constituting the palladium alloy by an electroless plating method or an electroplating method. In this method, the palladium alloy thin film can be formed more stably. Alloying can be performed by heating in a non-oxidizing atmosphere, usually in a reducing gas atmosphere or an inert gas atmosphere. As the reducing gas, for example, a reducing gas such as hydrogen, carbon monoxide, or methanol can be used. Examples of the inert gas include helium, nitrogen, and argon. Alternatively, it may be performed under vacuum. The heating temperature for alloying can be appropriately set according to the type of alloy and the like, but is preferably about 300 to 800 ° C, more preferably about 400 to 700 ° C. The upper limit temperature for alloying may be appropriately determined in consideration of the heat resistance of the sintered metal serving as the base material.

  The plating film made of palladium or a palladium alloy thin film may be formed on the entire surface of the support, but usually, depending on the shape of the support, on the surface in contact with the hydrogen-containing gas when used as a hydrogen separation membrane. What is necessary is just to form. For example, when a plate-like support is used, a plating film may be formed on the surface in contact with the hydrogen-containing gas. When a hollow tubular support is used, for example, a plating film is formed on the outer surface. do it.

  Also, when forming the plating film, a method of pressing the plating solution into the pores from one side of the porous body, contacting one side of the porous body with the plating solution, and reducing the pressure on the other side If a method of sucking the plating solution or the like is adopted, the adhesion of the formed plating film can be improved, and further, sealing of defects on the surface of the support is accelerated.

Prior to electroless plating, a catalyst for electroless plating is applied to the yttrium-stabilized zirconia layer on the support. The method for applying the electroless plating catalyst is not particularly limited, and a known catalyst applying method such as a method of immersing in a colloidal solution containing a catalyst component can be adopted. However, the palladium compound is converted into yttrium-stabilized zirconia by chemical vapor deposition. A catalyst for electroless plating may be applied by a method of reducing the temperature after vapor deposition on the surface of the layer and thermally decomposing it. Also, during chemical vapor deposition, if palladium compound vapor is sucked from the sintered metal side or pressurized from the yttrium stabilized zirconium side, palladium deposits on the pores of the yttrium stabilized zirconium and seals the pores. A stop effect can also be obtained, and a defect-free metal film can be formed by electroless plating. Palladium compounds used for chemical vapor deposition include bis (acetylacetonato) palladium (II), bis (hexafluoroacetylacetonato) palladium (II), palladium acetate, potassium bis (oxalato) palladate, bis (dithiooxalato) palladium acid Potassium, tetraamminepalladium chloride, bis (ethylenediamine) palladium chloride, bis (2,2′-bipyridine) palladium perchlorate, bis (1,10-phenanthroline) palladium perchlorate, bis (dimethylglyoximato ) Palladium (II), [Pd (PCH ₃ ) ₄ ], [Pd (PPh ₂ C ₂ H ₃ PPh ₂ ) ₂ ] (wherein Ph represents a phenyl group), dichlorobis (η-ethylene) palladium (II ), Tetrachlorodi (η-ethylene) palladium (II) Carbonyl dichloropalladium (II), can be exemplified dicarbonyl dichloropalladium (II) and the like.

  The vaporization temperature of the palladium compound at the time of chemical vapor deposition is not particularly limited as long as it is a temperature at which the palladium compound to be used is vaporized, and can be appropriately set according to the kind of the palladium compound. The temperature is usually about 40 to 250 ° C, preferably about 50 to 200 ° C. The vaporized palladium compound may be introduced onto the yttrium-stabilized zirconia layer in association with a carrier gas. As the carrier gas, for example, an inert gas such as nitrogen, helium, or argon can be used, but in some cases, a reactive gas such as hydrogen or oxygen may be used as the carrier gas. The deposition temperature on the yttrium-stabilized zirconium may be equal to or higher than the vaporization temperature of the palladium compound, and is usually about 40 to 600 ° C., preferably about 50 to 400 ° C. When the palladium compound is thermally decomposed immediately after vapor deposition, the vapor deposition temperature is preferably about 200 to 600 ° C, more preferably about 250 to 400 ° C.

(4) Post-treatment The hydrogen separation membrane obtained by the above-described method may be used as it is, but the performance as a hydrogen separation membrane can be stabilized by performing a heat treatment. The heat treatment may be performed in a non-oxidizing atmosphere, and can usually be performed by heating in a reducing gas atmosphere or an inert gas atmosphere. As the reducing gas, for example, a reducing gas such as hydrogen or methanol can be used. Examples of the inert gas include helium, nitrogen, argon, water vapor, and the like. Alternatively, it may be performed under vacuum. The treatment temperature can be appropriately set according to the thickness of the hydrogen separation membrane, the type of alloy, etc., but is preferably about 200 to 800 ° C., particularly preferably about 300 to 600 ° C. The treatment time may normally be about 1 to 100 hours. In order to remove organic substances adhering to the surface of the hydrogen separation membrane during the treatment, it may be brought into contact with oxygen or a gas containing oxygen.

Hydrogen Separation Method The hydrogen separation membrane of the present invention can be used for separating only hydrogen from a mixed gas containing hydrogen according to a conventional method. For example, a hydrogen-containing mixed gas is positioned on one side separated by the hydrogen separation membrane, one surface of the hydrogen separation membrane is brought into contact with the hydrogen-containing gas, and the hydrogen partial pressure on the other surface side is mixed with the hydrogen-containing mixture. What is necessary is just to be below the hydrogen partial pressure on the gas side. Thereby, hydrogen selectively permeates through the hydrogen separation membrane, and only hydrogen on the hydrogen-containing mixed gas side can be moved to the opposite side for separation. The temperature of the hydrogen separation membrane in this case is usually about 150 ° C. to 700 ° C., preferably about 300 ° C. to 600 ° C. If the temperature is too low, embrittlement of the palladium or palladium alloy thin film tends to occur, and if the temperature is too high, the film tends to deteriorate.

  According to the present invention, a palladium or palladium alloy thin film having no defect can be formed by a relatively simple method even when the film thickness is thin. This method does not require a large-scale manufacturing facility, and is extremely useful because it is free from strict control of processes and poor yield and facilitates mass production.

  The resulting hydrogen separation membrane has a defect-free palladium or palladium alloy thin film so that it can completely prevent the permeation of gases other than hydrogen, has excellent hydrogen selective permeability, and contains hydrogen. It can be effectively used as a hydrogen separation membrane for separating only hydrogen from a mixed gas.

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

Example 1
Cylindrical stainless steel sintered metal filter with a layer thickness of 30 μm, an average pore diameter of 0.1 μm, an yttrium content of 2 mol%, and an average crystal grain size of 0.5 μm and coated on the outside with a sintered stainless steel metal filter (filter length: 3 cm, filter 1 cm in diameter and 0.5 mm in thickness) was washed with hexane and degreased. Next, the filter was immersed in a commercially available alkaline electroless plating catalyst application solution at 40 ° C. to attach palladium nuclei to the surface. This was reduced with a commercially available reducing agent and subsequently immersed in a commercially available electroless palladium plating solution at 60 ° C. to form a 1.7 μm-thick palladium thin film on the surface of the filter by an electroless plating method.

  Next, this was heated to 400 ° C. under an argon stream, and subsequently heat-treated at 400 ° C. for 24 hours under a hydrogen stream.

  As a result of conducting a hydrogen permeation test on the hydrogen separation membrane obtained by the above method, a hydrogen permeation flow rate of 970 ml / min was obtained at 500 ° C. and a hydrogen differential pressure of 0.5 atm. Further, a similar test was performed for argon, but no argon permeation was detected at a differential pressure of 2 atm, and it was confirmed that the amount of argon permeation was 0.01 ml / min or less.

Example 2
Layer thickness 30 μm, average pore diameter 0.1 μm, yttrium content coated on cylindrical stainless steel sintered metal filter (filter length 3 cm, filter diameter 1 cm, thickness 0.5 mm) in the same manner as in Example 1. A palladium thin film having a film thickness of 1.0 μm was formed on the surface of the yttrium-stabilized zirconia layer having a 2 mol% average grain size of 0.5 μm. Furthermore, it was placed in an electroplating bath of a palladium / silver ammine complex system, and a palladium / silver alloy film having a thickness of 2.0 μm containing 20% by weight of silver was formed by electroplating. This was heated to 400 ° C. under an argon stream, and then heat-treated at 400 ° C. for 24 hours under a hydrogen stream.

  As a result of conducting a hydrogen permeation test on the hydrogen separation membrane obtained by the above method, a hydrogen permeation flow rate of 360 ml / min was obtained at 350 ° C. and a hydrogen differential pressure of 1 atm. Further, a similar test was performed for argon, but no argon permeation was detected at a differential pressure of 2 atm, and it was confirmed that the amount of argon permeation was 0.01 ml / min or less.

Example 3
Cylindrical stainless steel sintered metal filter with a layer thickness of 30 μm, an average pore diameter of 0.1 μm, an yttrium content of 2 mol%, and an average crystal grain size of 0.5 μm and coated on the outside with a sintered stainless steel metal filter (filter length: 3 cm, filter 1 cm in diameter and 0.5 mm in thickness) was washed with hexane and degreased. Next, the filter was immersed in a commercially available alkaline electroless plating catalyst application solution at room temperature to attach palladium nuclei to the surface. This was reduced with a commercially available reducing agent, subsequently immersed in a commercially available electroless palladium plating solution at 60 ° C., and a palladium thin film was formed on the surface of the filter by an electroless plating method. The film thickness of the obtained palladium thin film was 2.7 μm.

  Next, the metal filter on which the palladium thin film was formed was placed in a copper ammine complex-based electroplating bath, and a copper film having a thickness of 2.5 μm was formed by electroplating. This was heated to 400 ° C. under an argon stream, and subsequently heat-treated at 400 ° C. for 24 hours under a hydrogen stream to alloy the film.

  As a result of performing a hydrogen permeation test on the hydrogen separation membrane obtained by the above method, a hydrogen permeation flow rate of 890 ml / min was obtained at 450 ° C. and a hydrogen differential pressure of 2 atm. Further, a similar test was performed for argon, but no argon permeation was detected at a differential pressure of 2 atm, and it was confirmed that the amount of argon permeation was 0.01 ml / min or less.

  Next, in order to confirm the durability of the hydrogen separation membrane, the alternate supply of hydrogen and argon was repeated at 450 ° C., and the hydrogen embrittlement was evaluated. Was not recognized.

Claims (4)

A support made of a porous sintered metal,
A porous layer formed of a polycrystalline sintered body of yttrium-stabilized zirconia formed on the support, and a palladium or palladium alloy thin film formed by plating on the porous layer of yttria-stabilized zirconia. Hydrogen separation membrane. The hydrogen separation membrane according to claim 1, wherein the yttrium-stabilized zirconia has a porous structure having an average pore diameter of 0.01 to 0.5 µm. The hydrogen separation membrane according to claim 1 or 2, wherein the palladium or palladium alloy thin film comprises one layer or two or more layers, and the total film thickness is 0.5 to 10 µm. A hydrogen-containing mixed gas is positioned on one side separated by the hydrogen separation membrane according to any one of claims 1 to 3, and the hydrogen partial pressure on the other surface side of the hydrogen separation membrane is set on the hydrogen-containing mixed gas side. A method for separating hydrogen from a hydrogen-containing mixed gas, characterized by having a partial pressure of hydrogen or lower.