Hydrogen separation membrane

Abstract

To provide a hydrogen separation membrane that is superior in durability.SOLUTION: A hydrogen separation membrane comprises: a porous body containing metal oxide; and a palladium layer arranged inside the porous body. The porous body includes: small pores each having a pore diameter of 10 nm or smaller; and large pores each having a pore diameter of 50 nm or larger. In the hydrogen separation membrane, an average pore diameter of the large pores is 100 nm-500 nm.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to hydrogen separation membranes. [Background technology]

[0002] One method for separating hydrogen gas from a gas containing hydrogen is to use a hydrogen separation membrane with a palladium layer. This method utilizes the hydrogen dissolution-diffusion mechanism of palladium. Specifically, hydrogen molecules (H2) contained in gas that comes into contact with one side of the palladium layer dissociate into hydrogen atoms (H), which then pass through the gaps between the palladium atoms in the hydrogen atom state. The hydrogen atoms that pass through the palladium layer recombine on the other side of the palladium layer to form hydrogen molecules, which are then recovered as hydrogen gas.

[0003] Because atoms other than hydrogen atoms cannot permeate a palladium layer, a method using a hydrogen separation membrane with a palladium layer can separate extremely high-purity hydrogen gas. However, because palladium is a rare metal, it is desirable to reduce the amount of palladium used in hydrogen separation membranes. Therefore, hydrogen separation membranes have been proposed in which a thin palladium film is formed on a porous ceramic substrate by plating, CVD, or other techniques (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2017-124364 Summary of the Invention [Problem to be solved by the invention]

[0005] The durability of hydrogen separation membranes comprising a thin palladium film formed on a substrate made of porous ceramics leaves room for improvement. In view of the above circumstances, an object of the present disclosure is to provide a hydrogen separation membrane that is excellent in durability. [Means for solving the problem]

[0006] The means for solving the above problems include the following embodiments. <1> A hydrogen separation membrane comprising a porous body containing a metal oxide and a palladium layer disposed inside the porous body, wherein the porous body has small pores with a pore diameter of 10 nm or less and large pores with a pore diameter of 50 nm or more, and the large pores have an average pore diameter of 100 nm to 500 nm. <2> The coefficient of variation of the pore size of small pores is within 10%. <1> The hydrogen separation membrane according to claim 1. <3> The coefficient of variation of the pore size of the large pores is within 5%. <1> or <2> The hydrogen separation membrane according to claim 1. <4> The palladium layer is in a state where palladium and a porous body are mixed together. <1> ~ <3> The hydrogen separation membrane according to any one of claims 1 to 10. [Effects of the Invention]

[0007] According to the present disclosure, a hydrogen separation membrane with excellent durability is provided. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view conceptually showing an example of the configuration of a hydrogen separation membrane. [Figure 2] FIG. 2 is a partially enlarged view of a cross section of the hydrogen separation membrane shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments. In this specification, numerical ranges indicated using "to" include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the present specification, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range. In addition, in the present specification, the upper or lower limit of a numerical range may be replaced with a value shown in the examples.

[0010] One embodiment of the present disclosure comprises: The hydrogen separation membrane comprises a porous body containing a metal oxide and a palladium layer disposed inside the porous body, the porous body having small pores with a pore diameter of 10 nm or less and large pores with a pore diameter of 50 nm or more, and the large pores have an average pore diameter of 100 nm to 500 nm.

[0011] The hydrogen separation membrane of the present disclosure has a palladium layer disposed inside a porous body containing a metal oxide. That is, layers made of porous bodies are disposed on both sides of the palladium layer. As a result, the palladium layer is physically protected by the porous bodies disposed on both sides, and deterioration of the palladium layer due to thermal stress and hydrogen embrittlement (a phenomenon in which palladium becomes embrittled due to the absorption of hydrogen atoms) applied during use of the hydrogen separation membrane is effectively suppressed.

[0012] In this disclosure, the palladium layer refers to the middle region when the hydrogen separation membrane is divided into three regions in the thickness direction, where palladium is present. The boundaries between the region corresponding to the palladium layer and the regions on both sides of it (regions made of porous material where palladium is not present) can be determined by observing a cross section obtained by cutting the hydrogen separation membrane in the thickness direction. The palladium layer may contain a metal oxide that constitutes the porous body together with palladium, or may contain a palladium alloy. The palladium layer is preferably in a state where palladium and a porous body are mixed together, and more preferably in a state where palladium is present in the pores of the porous body.

[0013] The configuration of the hydrogen separation membrane of the present disclosure will be described with reference to the drawings. FIG. 1 is a cross-sectional view conceptually showing an example of the structure of a hydrogen separation membrane. 1 includes a porous body 12 containing a metal oxide and a palladium layer 14 disposed inside the porous body 12. When a gas containing hydrogen gas (Gas) is supplied to one side of the hydrogen separation membrane 10, only hydrogen gas (H2) is recovered from the other side of the hydrogen separation membrane 10.

[0014] FIG. 2 is a partially enlarged view of the cross section of the hydrogen separation membrane 10 shown in FIG. 2, the porous body 12 has small pores with relatively small diameters and large pores with relatively large diameters. The palladium layer 14 is in a state in which nano-sized palladium particles 16 are arranged inside the small pores and large pores of the porous body 12.

[0015] Palladium particles 16 are densely packed inside the large pores of the palladium layer 14. Hydrogen molecules contained in the gas that reaches the palladium layer 14 through the large pores dissociate into hydrogen atoms on the surface of the palladium layer 14, and the hydrogen atoms permeate the palladium layer 14. The hydrogen atoms that permeate the palladium layer 14 recombine to form hydrogen molecules, which are recovered as hydrogen gas (H2).

[0016] In the present disclosure, pores contained in a porous body having a pore diameter of 10 nm or less are referred to as small pores, and pores having a pore diameter of 50 nm or more are referred to as large pores. In the present disclosure, the pore diameter of small pores or large pores refers to the diameter of the opening of the pore observed on the surface of the porous body. In the present disclosure, the average pore size of small pores or large pores is the arithmetic mean value of the pore sizes measured for 100 small pores or large pores arbitrarily selected from the pores observed on the surface of the porous body.

[0017] In the hydrogen separation membrane of the present disclosure, the large pores in the porous body have an average pore size of 100 nm to 500 nm. The porous body has large pores with an average pore size of 100 nm to 500 nm, which ensures sufficient contact between the gas supplied to the hydrogen separation membrane and the palladium layer, maintaining good hydrogen gas separation efficiency. Furthermore, the large pores act as a buffer against expansion, contraction, and deformation of the porous body, improving its physical strength.

[0018] In the hydrogen separation membrane of the present disclosure, the average pore size of the small pores in the porous body is preferably 2 nm to 4 nm. It is believed that when the porous body has small pores and the average pore diameter of the small pores is 2 nm to 4 nm, the size of the palladium particles arranged in the small pores is controlled to be small, thereby further improving the resistance of the palladium layer to hydrogen embrittlement.

[0019] From the viewpoint of increasing the durability of the palladium layer and achieving uniform hydrogen dissolution and diffusion, it is preferable that the pore sizes of the small pores and large pores contained in the porous body vary little. Specifically, the coefficient of variation of the pore diameter of the small pores is preferably within 10%, and the coefficient of variation of the pore diameter of the large pores is preferably within 5%. In the present disclosure, the coefficient of variation of the pore diameter of small pores or large pores is a value expressed as a percentage obtained by dividing the standard deviation of the pore diameters measured for 100 small pores or large pores arbitrarily selected from the pores observed on the surface of the porous body by the arithmetic mean value of the pore diameters (see the formula below). Coefficient of variation = (standard deviation / mean value) x 100

[0020] From the viewpoint of increasing the durability of the palladium layer and making the dissolution and diffusion of hydrogen uniform, the number of large pores contained in the porous body is 1 per 100 μm. 2 It is preferable that the number of particles is 5 or more per 100 μm. 2 More preferably, 10 particles / 100 μm or more 2 It is more preferable that the number of large pores contained in the porous body is 100 / 100 μm or more. 2 It may be the following: In the present disclosure, the number of macropores refers to the number of macropores observed on the surface of the porous body.

[0021] From the viewpoint of increasing the durability of the palladium layer and achieving uniform dissolution and diffusion of hydrogen gas, the thickness of the palladium layer is preferably 0.1 μm to 5.0 μm, more preferably 0.1 μm to 1.5 μm, and even more preferably 0.3 μm to 0.7 μm. From the viewpoint of increasing the durability of the palladium layer and achieving uniform dissolution and diffusion of hydrogen gas, it is preferable that the thickness of the palladium layer varies little. Specifically, the coefficient of variation in the thickness of the palladium layer is preferably within 10%. In the present disclosure, the coefficient of variation of the thickness of the palladium layer is a value expressed as a percentage obtained by dividing the standard deviation of the thickness of the palladium layer measured at any 10 locations by the average thickness. The thickness of the palladium layer is measured by cutting the hydrogen separation membrane in the thickness direction and examining the cut surface using an electron microscope or the like.

[0022] From the viewpoint of increasing the durability of the palladium layer and achieving uniform dissolution and diffusion of hydrogen gas, the thickness of the hydrogen separation membrane is preferably 1 μm to 50 μm, more preferably 1 μm to 15 μm, and even more preferably 3 μm to 7 μm. From the viewpoint of increasing the durability of the palladium layer and achieving uniform dissolution and diffusibility of hydrogen gas, it is preferable that the thickness of the hydrogen separation membrane varies little. Specifically, it is preferable that the coefficient of variation of the thickness of the hydrogen separation membrane is within 10%. In the present disclosure, the coefficient of variation of the thickness of a hydrogen separation membrane is a value expressed as a percentage obtained by dividing the standard deviation of the thickness of the hydrogen separation membrane measured at any 10 locations by the average thickness. The thickness of the hydrogen separation membrane is measured by cutting the hydrogen separation membrane in the thickness direction and examining the cut surface using an electron microscope or the like. In the present disclosure, the thickness of the hydrogen separation membrane is defined as the total thickness of the palladium layer and the porous layers disposed on both sides of the palladium layer.

[0023] In the present disclosure, the method for producing the porous body is not particularly limited. For example, the porous body may be produced by a method in which a precursor of a metal oxide constituting the porous body is heated in an oxygen-containing atmosphere to convert the precursor into the metal oxide. Examples of the precursor of the metal oxide include alkoxides, chlorides, and hydroxides. The type of metal oxide constituting the porous body is not particularly limited as long as it does not interfere with the function of the hydrogen separation membrane. Specific examples of metal oxides include alumina, silica, zirconia, titania, etc. The metal oxide contained in the porous body may be one type or two or more types.

[0024] There are no particular limitations on the method for forming a porous body having pores of a desired size. The first method for forming a porous body with pores of the desired size involves mixing a pore template material with the precursor of the metal oxide that will form the porous body. Examples of pore template materials include materials that form rod-like micelles, such as surfactants. The pore size of the pores (especially large pores) contained in the porous body can be controlled by the length of the lipophilic group (carbon chain) of the surfactant. A second method for forming a porous body with pores of a desired size is to physically form pores in a metal oxide or its precursor, such as by stereolithography using a 3D printer.

[0025] The method for forming a palladium layer inside the porous body is not particularly limited. A first method for forming a palladium layer inside a porous body is to diffuse palladium ions into a membrane made of a porous body, and then bring the palladium ions that have reached a predetermined depth into contact with a reducing agent to precipitate palladium (counter membrane diffusion method). The diffusion of palladium ions may be carried out using a known plating bath composition containing palladium ions.

[0026] A second method for forming a palladium layer inside a porous body includes forming a palladium layer on the surface of a membrane made of a porous body by a known thin film formation technique, and then placing a separately prepared porous membrane on the formed palladium layer, or forming a membrane made of a porous body.

[0027] In one embodiment of the present disclosure, the porous body may be formed using a metal-organic framework (MOF). MOFs are porous complexes composed of metal ions and organic molecules, and it is known that their pore size can be controlled by the type of raw material and synthesis conditions. Furthermore, metal oxides obtained using MOFs as precursors are thought to have lower crystallinity and greater flexibility than common metal oxides, and therefore porous bodies made of metal oxides obtained using MOFs are less likely to break even when deformed by changes in gas pressure, etc., and are thought to have greater durability.

[0028] The type of MOF used in the present disclosure is not particularly limited. Specific examples of metal ions contained in MOFs include Cu, Zn, Co, In, Al, Fe, V, Mg, Mn, Ni, Ru, Mo, Cr, W, Rh, and Pd. Among these, Cu, Zn, Co, In, Al, Fe, and V are preferred, and Cu, Zn, and Co are more preferred. The organic molecules contained in the MOF are not particularly limited as long as they are organic ligands that can form coordinate bonds with metal ions. Specific examples of organic molecules include dicarboxylic acids, tricarboxylic acids, imidazoles, benzimidazoles, azabenzimidazoles, and derivatives thereof. Specific examples of MOFs include Cu-BTC, MOF-5, IRMOF-3, MIL-47, MIL-53, MIL-96, MMOF, SIM-1, ZIF-7, ZIF-8, ZIF-22, ZIF-69, and ZIF-90.

[0029] The hydrogen separation membrane of the present disclosure is suitable for use in a method for producing hydrogen gas. Because the hydrogen gas produced using the hydrogen separation membrane of the present disclosure has high purity, it is suitable for use in, for example, the production of semiconductor materials, pharmaceuticals, etc. The hydrogen separation membrane of the present disclosure has excellent durability, and therefore can reduce production costs compared to conventional methods of producing hydrogen gas using palladium. [Explanation of symbols]

[0030] 10 Hydrogen separation membrane 12 Porous materials 14 Palladium layer 16 Palladium particles

Claims

1. A hydrogen separation membrane comprising: a porous body containing a metal oxide; and a palladium layer disposed inside the porous body, wherein the porous body has small pores with a pore diameter of 10 nm or less and large pores with a pore diameter of 50 nm or more, and the large pores have an average pore diameter of 100 nm to 500 nm.

2. 2. The hydrogen separation membrane according to claim 1, wherein the coefficient of variation of the pore size of the small pores is within 10%.

3. 3. The hydrogen separation membrane according to claim 1, wherein the coefficient of variation of the pore size of the large pores is within 5%.

4. 3. The hydrogen separation membrane according to claim 1, wherein the palladium layer is a mixture of palladium and a porous material.

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