Hydrogen separation filter and method for manufacturing hydrogen separation filter

Abstract

To provide a hydrogen separation filter having a high hydrogen permeation rate and a method for manufacturing the same. The hydrogen separation filter includes: a porous substrate; and a palladium layer provided on the porous substrate. A lattice constant a of palladium, which is calculated from a face interval of a crystal plane parallel to a thickness direction of the palladium layer, satisfies the following formula (1), in which a0 represents a lattice constant of completely relaxed palladium, that is, 0.38898 nm.

Description

Technical Field

[0001] This invention relates to a hydrogen separation filter and a method for manufacturing the hydrogen separation filter. Background Technology

[0002] As a method for purifying hydrogen, membrane separation using metal membranes is known. Patent Document 1 describes a porous filter and a hydrogen separation membrane in which a palladium thin film or a palladium alloy thin film is formed on one side of the porous filter. In the porous filter, only defects larger than the micropores that open on one side of the porous ceramic membrane are sealed by the metal, while the micropores in the porous ceramic membrane are not sealed by the metal.

[0003] Patent Document 1: Japanese Patent No. 5891512 Specification Summary of the Invention

[0004] Hydrogen separation filters preferably have a high hydrogen permeation rate. This invention provides a hydrogen separation filter with a high hydrogen permeation rate and a method for manufacturing the same.

[0005] The present invention includes the following methods.

[0006] [Method 1]

[0007] A hydrogen separation filter comprising:

[0008] Porous substrates; and

[0009] A palladium layer is disposed on the porous substrate.

[0010] In the hydrogen separation filter

[0011] The lattice constant α of palladium, determined by the interplanar spacing of the crystal planes parallel to the thickness direction of the palladium layer, satisfies the following equation (1):

[0012]

[0013] (In the formula, a0 represents the lattice constant of fully relaxed palladium, which is 0.38898 nm).

[0014] [Method 2]

[0015] According to the hydrogen separation filter of method 1, wherein,

[0016] The palladium layer has a thickness of 50–200 nm.

[0017] [Method 3]

[0018] The hydrogen separation filter according to method 1 or 2 has a concentration of 5 mmol·s⁻¹. -1 ·m -2 ·Pa-0.5 The above refers to the hydrogen permeation rate.

[0019] [Method 4]

[0020] A method for manufacturing a hydrogen separation filter, comprising the following steps:

[0021] A palladium layer was formed on a porous substrate by sputtering at a gas pressure of 0.4–8.0 μTorr.

[0022] [Method 5]

[0023] The method according to method 4 is used to manufacture a hydrogen separation filter according to any one of methods 1 to 3.

[0024] Invention Effects

[0025] The hydrogen separation filter of the present invention and the hydrogen separation filter manufactured by the manufacturing method of the present invention have a high hydrogen permeation rate. Attached Figure Description

[0026] Figure 1 This is a schematic cross-sectional view of the hydrogen separation filter involved in the embodiment. Detailed Implementation

[0027] Hereinafter, embodiments will be described with appropriate reference to the accompanying drawings, but the present invention is not limited to the embodiments described below. Various modifications, alterations, additions, omissions and / or combinations of the embodiments described below can be made without departing from the technical scope set forth in the claims.

[0028] In the accompanying drawings referenced in the following description, the dimensions and shapes of the parts are exaggerated for ease of explanation and may sometimes differ from the actual dimensions and shapes.

[0029] In this application, unless otherwise specified, the numerical range represented by the symbol "~" includes the values ​​before and after the symbol "~" as the lower limit and upper limit, respectively. The upper and lower limits described in this application can be used individually or in any combination.

[0030] In this application, unless otherwise specified, "comprising" and "containing" mean that it can include additional components or elements, and include "essentially composed of" and "composed of". "Essentially composed of" means that it can include additional components or elements that will not substantially cause adverse effects. "Composed of" means that it includes only the described materials or elements, but does not exclude the inclusion of unavoidable impurities.

[0031] In this application, "perpendicular" includes not only precise perpendicularity but also substantial perpendicularity, and "parallel" includes not only precise parallelism but also substantial parallelism.

[0032] Furthermore, unless otherwise specified in this application, "on" includes both "directly on" and "indirectly on".

[0033] (1) Hydrogen separation filter

[0034] Figure 1 The hydrogen separation filter 1 shown in the embodiment includes a porous substrate 10 and a palladium layer 60 disposed on the porous substrate 10. The palladium layer 60 can be formed directly on the porous substrate 10.

[0035] The porous substrate 10 comprises an oxide material (e.g., a metal oxide, a half-metal oxide, or a mixture thereof), preferably composed of an oxide material in nature, and more preferably composed of an oxide material. Examples of oxide materials include alumina, zirconium oxide, titanium oxide, and mixtures thereof.

[0036] The porous substrate 10 can have any shape for the first surface 12 and the second surface 14, such as a plate, sheet, or cylinder. The porous substrate 10 has micropores that allow hydrogen to pass through, which are connected from the first surface 12 to the second surface 14. The micropores are sealed by a palladium layer 60.

[0037] The average diameter (average pore size) of the pores in the porous substrate 10 is preferably 5 to 20 nm, more preferably 5 nm or more but less than 20 nm, and particularly preferably 5 to 15 nm. With an average pore size within the above range, the porous substrate 10 has sufficient hydrogen permeability and the pores can be sealed with a palladium layer 60 having a thickness of 50 to 200 nm. In this application, the average pore size of the porous substrate 10 is determined according to the pore size distribution obtained by mercury intrusion porosimetry in accordance with JIS R 1655:2003. Mercury intrusion porosimetry is a method in which pressure is applied to immerse mercury into an open pore, the relationship between the volume of mercury immersed in the open pore and the applied pressure is determined, and based on the result, assuming the open pore is cylindrical, the diameter of the open pore is calculated using the Washburn equation.

[0038] The porous substrate 10 can have a porosity of 30% to 70%. With a porosity within this range, the porous substrate 10 has sufficient hydrogen permeability and the fine pores can be sealed by a palladium layer 60 with a thickness of 50 to 200 nm. In this application, the porosity of the porous substrate 10 is the open porosity determined according to JIS R 1634:1998 and using the Archimedes method.

[0039] The first surface 12 of the porous substrate 10 may have a surface roughness of 0.1 to 2 μm. In this application, the surface roughness refers to the arithmetic mean roughness Ra according to JIS B 0601:2013, which is determined by optical interferometry.

[0040] A palladium layer 60 is formed on the first surface 12 of the porous substrate 10. Typically, the palladium layer 60 has a higher hydrogen permeation rate compared to a palladium alloy layer of the same thickness, such as a palladium-silver alloy.

[0041] The palladium layer 60 can have a thickness of 50–200 nm. This is a smaller value compared to the thickness of conventional palladium layers used for hydrogen separation. If the thickness of the palladium layer 60 is small, the hydrogen permeation rate per unit area (mmol·s) of the palladium layer 60 will be higher. -1 ·m -2 ·Pa -0.5 The hydrogen permeation rate (mmol·s⁻¹) is improved, thus enabling the target hydrogen permeation rate (mmol·s⁻¹) to be achieved over a smaller area than existing technologies. -1 ·Pa -0.5 Therefore, the amount of palladium required for the manufacture of hydrogen separation filter 1 can be reduced, thereby reducing raw material costs.

[0042] The lattice constant α of palladium in palladium layer 60 satisfies the following equation (1):

[0043]

[0044] (In the formula, a0 represents the lattice constant of fully relaxed palladium, which is 0.38898 nm).

[0045] The lattice constant α of palladium in palladium layer 60 is determined based on the interplanar spacing of the crystal planes parallel to the thickness direction of palladium layer 60. Specifically, the electron beam diffraction pattern of palladium layer 60 is obtained using a transmission electron microscope (TEM), the interplanar spacing of the crystal planes parallel to the thickness direction of palladium layer 60 is determined based on the electron beam diffraction pattern, and the lattice constant α of palladium in palladium layer 60 is determined using the value of the interplanar spacing. Equation (1) above indicates that, compared to the fully relaxed state, the palladium lattice in palladium layer 60 expands in the direction perpendicular to the thickness direction of palladium layer 60. If the palladium lattice expands in palladium layer 60, the hydrogen diffusion path changes from octahedral sites to tetrahedral sites, thereby making it easier for hydrogen to diffuse in palladium layer 60 due to the quantum effect of atomic nuclei, thus increasing the hydrogen diffusion coefficient of palladium layer 60. As a result, the hydrogen separation filter 1 can have a high hydrogen permeation rate.

[0046] (2) Manufacturing method of hydrogen separation filter

[0047] The method for manufacturing the hydrogen separation filter according to the embodiments includes the following steps: setting the gas pressure to 0.4 to 8.0 μTorr and forming a palladium layer on a porous substrate by sputtering. Argon (Ar) can be used as the sputtering gas.

[0048] By setting the gas pressure to 0.4–8.0 μTorr and forming a palladium layer by sputtering, a palladium layer satisfying the above formula (1) can be formed, and the resulting hydrogen separation filter can have a high hydrogen permeation rate. When the gas pressure exceeds 8.0 μTorr, the collision frequency between sputtered particles and gas molecules is high, and the mean free path of the sputtered particles becomes shorter. As a result, the energy of the sputtered particles colliding with the substrate is lower, and the expansion of the palladium lattice in the formed palladium layer is insufficient. When the gas pressure is less than 0.4 μTorr, the sputtering equipment and the cost of operating it become expensive.

[0049] Example

[0050] The present invention will be specifically described below through embodiments, but the present invention is not limited to these embodiments.

[0051] (1) Fabrication of hydrogen separation filter

[0052] A porous substrate was created by coating a porous alumina substrate ("Precision Filter Membrane MF0.1" manufactured by NGK INSULATORS, LTD.) with alumina particles.

[0053] In the film-forming chamber of a sputtering apparatus equipped with a pure Pd target, a porous substrate was placed opposite the pure Pd target. An Ar gas environment with the gas pressures listed in Table 1 was established within the film-forming chamber, and a Pd layer was formed on the porous substrate by sputtering. Specifically, a high voltage was applied to the pure Pd target as the cathode, generating a glow discharge that cationized Ar. The Ar cations collided with the target, sputtering Pd atoms from the target and attaching them to the porous substrate. In Examples 1-4 and Comparative Example 1, a Pd layer with a thickness of 100 nm was formed. In Comparative Example 2, a Pd layer with a sufficient thickness could not be formed, therefore the hydrogen permeation velocity measurement described later could not be performed. The thickness of the Pd layer was measured using a cross-sectional reflectance electron image of the fabricated hydrogen separation filter.

[0054] (2) Determination of lattice constant

[0055] Electron beam diffraction patterns of the Pd layers of the filters in Examples 1-4 and Comparative Examples 1 and 2 were obtained using TEM. Based on the electron beam diffraction patterns, the interplanar spacing of the crystal planes parallel to the thickness direction of the Pd layer (i.e., perpendicular to the surface of the Pd layer) was determined. The lattice constant a of the Pd layer was calculated using the values ​​of the interplanar spacing. The ratio of the lattice constant a to the lattice constant a0 (0.38898 nm) of fully relaxed Pd (a / a0) is shown in Table 1.

[0056] (3) Determination of hydrogen permeation rate

[0057] In accordance with JIS K7126:2006 (Plastics—Films and sheets—Test methods for gas permeability—Part 1: Differential pressure method), the hydrogen permeation rate per unit area (unit: mmol·s) of the hydrogen separation filters of Examples 1-4 and Comparative Example 1 at 400°C was determined by gas chromatography. -1 ·m -2 ·Pa -0.5 The results are shown in Table 1. The hydrogen separation filters of Examples 1–4 all exhibited a hydrogen content of 5 mmol·s⁻¹. -1 ·m -2 ·Pa -0.5 The above-mentioned high hydrogen permeation rate. The hydrogen separation filter of Comparative Example 1 has a hydrogen permeation rate of less than 5 mmol·s⁻¹. -1 ·m -2 ·Pa -0.5 The performance is insufficient.

[0058] Based on the above evaluation results, it is shown that when the lattice constant 'a' of the Pd layer satisfies 1.006 ≤ a / a0 ≤ 1.043, the hydrogen separation filter can have a high hydrogen permeation rate. Furthermore, it is shown that a hydrogen separation filter with this high hydrogen permeation rate can be manufactured by setting the gas pressure to 0.4–8.0 μTorr and forming the Pd layer by sputtering.

[0059] [Table 1]

[0060]

[0061] Symbol Explanation

[0062] 1-Hydrogen separation filter, 10-Porous substrate, 12-First surface, 14-Second surface, 60-Palladium layer.

Claims

1. A hydrogen separation filter, comprising: Porous substrate; and A palladium layer is disposed on the porous substrate. The hydrogen separation filter is characterized in that... The lattice constant α of palladium, determined by the interplanar spacing of the crystal planes parallel to the thickness direction of the palladium layer, satisfies the following equation (1): In the formula, a0 represents the lattice constant of fully relaxed palladium, which is 0.38898 nm.

2. The hydrogen separation filter according to claim 1, characterized in that, The palladium layer has a thickness of 50–200 nm.

3. The hydrogen separation filter according to claim 1 or 2, characterized in that, With 5 mmol·s -1 ·m -2 ·Pa -0.5 The above refers to the hydrogen permeation rate.

4. A method for manufacturing a hydrogen separation filter, characterized in that, Includes the following steps: A palladium layer was formed on a porous substrate by sputtering at a gas pressure of 0.4–8.0 μTorr.

5. The method for manufacturing a hydrogen separation filter according to claim 4, characterized in that, Used to manufacture the hydrogen separation filter as described in claim 1 or 2.

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