Hydrogen Separation Filter

Abstract

To provide a hydrogen separation filter which can perform hydrogen purification at low temperature relative to the conventional ones.SOLUTION: A hydrogen separation filter comprises: a porous base material; and a superlattice layer which is formed on the porous base material. The superlattice layer includes: at least one layer of lattice expansion layer with a first material; and at least two layers of hydrogen dissociation permeable layers with a second material selected from the group of Pd, V, Ta, Ti, Nb, and alloy of them. At least one layer of the lattice expansion layer and at least two layers of hydrogen dissociation permeable layers are alternatively laminated. The first material has the same crystal structure as that of the second material, and a lattice constant a1,bulk of a first bulk material having the same composition and the same crystal structure as the first material and a lattice constant a2,bulk of a second bulk material having the same composition and the same crystal structure as the second material satisfy the following expression (1): 1.03a2,bulk≤a1,bulk≤1.15a2,bulk (1).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a hydrogen separation filter. [Background technology]

[0002] A membrane separation method using a metal membrane is known as a method for purifying hydrogen. Patent Document 1 describes a porous filter in which defects opening on one side of a porous ceramic membrane are blocked with a metal, and a hydrogen separation membrane in which a thin palladium or palladium alloy thin film is formed on one side of the porous filter. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2011 / 122414 Summary of the Invention [Problem to be solved by the invention]

[0004] Metals that can selectively allow hydrogen to permeate include palladium (Pd), vanadium (V), tantalum (Ta), titanium (Ti), and niobium (Nb). These metals are easily embrittled in a hydrogen atmosphere. To prevent these metals from becoming embrittled, hydrogen separation membranes are generally used at high temperatures (e.g., about 400°C). However, hydrogen purification at high temperatures requires a large amount of energy.

[0005] Therefore, a hydrogen separation filter is provided that enables hydrogen purification at lower temperatures than conventional methods. [Means for solving the problem]

[0006] Aspects of the present disclosure include the following. [1] A porous substrate; a superlattice layer formed on the porous substrate; A hydrogen separation filter comprising: The superlattice layer is at least one lattice extension layer comprising a first material; At least two hydrogen dissociation permeation layers containing a second material selected from the group consisting of Pd, V, Ta, Ti, Nb, and alloys thereof; Including, the at least one lattice-extending layer and the at least two hydrogen dissociation permeation layers are alternately stacked; the first material and the second material have the same crystal structure; a lattice constant a of a first bulk material having the same composition and the same crystal structure as the first material; 1,バルク and a lattice constant a of a second bulk material having the same composition and the same crystal structure as the second material. 2,バルク However, the following formula (1): 1.03a 2,バルク ≦a 1,バルク ≦1.15a 2,バルク (1) A hydrogen separation filter that satisfies the above requirements. [2] 2. The hydrogen separation filter according to claim 1, wherein the uppermost layer of the superlattice layer that is farthest from the porous substrate and the lowermost layer that is closest to the porous substrate are both the hydrogen dissociation permeation layer. [3] The average lattice constant a2 of the second material calculated from the interplanar spacing of crystal planes perpendicular to the interface between the lattice expansion layer and the hydrogen dissociation permeation layer is expressed by the following formula (2): a 2,バルク <a2(2) 3. The hydrogen separation filter according to claim 1, wherein the above condition is satisfied. [4] The average lattice constant a2 of the second material calculated from the spacing of crystal planes perpendicular to the interface between the lattice expansion layer and the hydrogen dissociation permeation layer is expressed by the following formula (3): 1.5≦[(a2-a 2,バルク ) / a 2,バルク ]×100≦5 (3) 4. The hydrogen separation filter according to any one of aspects 1 to 3, which satisfies the above. [5] A hydrogen separation filter according to any one of aspects 1 to 4, wherein the lattice extension layer and the hydrogen dissociation permeation layer each have a thickness within a range of 1 to 10 nm. [6] the first material is Ag, Au, or Al; Aspect 6. The hydrogen separation filter according to any one of aspects 1 to 5, wherein the second material is Pd. [7] 7. The hydrogen separation filter of embodiment 6, wherein the first material is Ag. [8] A hydrogen separation filter according to any one of aspects 1 to 7, wherein the superlattice layer has a total thickness that is more than 7 times the average pore size of the porous substrate. [Effects of the Invention]

[0007] The hydrogen separation filter of the present invention makes it possible to purify hydrogen at lower temperatures than conventionally possible. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic cross-sectional view of a hydrogen separation filter according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments will be described with reference to the drawings as appropriate. In the drawings referred to in the following description, identical components or components having similar functions are designated by the same reference numerals, and repeated description may be omitted. For convenience of explanation, the dimensional ratios and shapes of each part in the drawings may be exaggerated and may differ from the actual dimensional ratios and shapes. Furthermore, in this application, a numerical range expressed using the symbol "to" includes the numerical values ​​written before and after the symbol "to" as the lower and upper limits, respectively. The upper and lower limits of the numerical ranges described in this application can be used alone or in any combination to define a preferred range.

[0010] As used herein, "comprising" and "containing" mean that additional components may be included, and encompass "consisting essentially of" and "consisting of." "Consisting essentially of" means that additional components may be included that do not have a substantial adverse effect. "Consisting of" means that the material contains only the listed materials, but does not exclude the inclusion of unavoidable impurities.

[0011] In this application, "vertical" includes not only exact vertical but also substantially vertical, and "parallel" includes not only exact parallel but also substantially parallel. Furthermore, in this application, "on" includes both "directly on" and "indirectly on" unless otherwise specified in the context.

[0012] 1 includes a porous substrate 20 and a superlattice layer 90 formed on the porous substrate 20. The superlattice layer 90 includes at least one lattice extension layer 40 and at least two hydrogen dissociation permeation layers 60, with the lattice extension layers 40 and the hydrogen dissociation permeation layers 60 stacked alternately. In this embodiment, the superlattice layer 90 may be formed directly on the porous substrate 20.

[0013] The porous substrate 20 may be formed from, for example, a metal, a metal oxide, or a resin, and may be formed from a metal oxide due to its high durability. Examples of metal oxides include aluminum oxide, zirconium oxide, and zeolite. Aluminum oxide is particularly preferred because it is inexpensive. The porous substrate 20 may have any shape, such as a flat plate or a cylindrical shape.

[0014] The porous substrate 20 has pores through which hydrogen can pass. The pores are blocked by the superlattice layer 90. The porous substrate 20 may have an average pore diameter, for example, within a range of 1 to 100 nm, preferably 1 to 10 nm. Having an average pore diameter within the above range ensures that the porous substrate 20 has sufficient hydrogen permeability, and the pores can be easily blocked by the superlattice layer 90 without making the superlattice layer 90 excessively thick. The average pore diameter may be less than 1 / 7 the thickness of the superlattice layer 90. The average pore diameter of the porous substrate 20 is determined based on a pore size distribution determined by mercury intrusion porosimetry in accordance with JIS R 1655:2003. Mercury intrusion porosimetry involves applying pressure to cause mercury to penetrate open pores, determining the relationship between the volume of mercury that penetrates the open pores and the pressure value applied at that time, and then calculating the diameter of the open pores using the Washburn equation, assuming that the open pores are cylindrical.

[0015] The porous substrate 20 may have a porosity in the range of 30 to 50%, which allows the porous substrate 20 to have sufficient mechanical strength and sufficient hydrogen permeability.

[0016] The superlattice layer 90 has a total of three or more lattice extension layers 40 and hydrogen dissociation permeation layers 60. From the viewpoints of ease of manufacture and hydrogen separation performance, the total number of lattice extension layers 40 and hydrogen dissociation permeation layers 60 is preferably 3 to 21 layers, more preferably 5 to 11 layers, and even more preferably 5 to 9 layers. In this embodiment, the uppermost layer 92 of the superlattice layer 90 (i.e., the layer farthest from the porous substrate 20) is a hydrogen dissociation permeation layer 60, and the lowermost layer 94 of the superlattice layer 90 (i.e., the layer closest to the porous substrate 20) is also a hydrogen dissociation permeation layer 60.

[0017] The function of the superlattice layer 90 will now be described. Hydrogen molecules are dissociated and adsorbed to generate hydrogen atoms on the surface 93 of the top layer 92 of the superlattice layer 90. The hydrogen atoms diffuse within the superlattice layer 90 and recombine at the interface 95 between the superlattice layer 90 and the porous substrate 20 to form hydrogen molecules, which are then released from the superlattice layer 90. The released hydrogen molecules pass through the porous substrate 20 and are discharged from the hydrogen separation filter 1. In this way, the hydrogen separation filter 1 can selectively allow hydrogen to pass through.

[0018] The superlattice layer 90 may have a thickness that is more than seven times the average pore diameter of the porous substrate 20. This allows the superlattice layer 90 to reliably block the pores, thereby providing good hydrogen separation performance for the hydrogen separation filter 1. From the standpoint of reducing the raw material costs and manufacturing time for the hydrogen separation filter 1, the total thickness of the superlattice layer 90 may be 100 nm or less.

[0019] The lattice extension layer 40 comprises a first material, and the hydrogen dissociation permeable layer 60 comprises a second material.

[0020] The second material is selected from the group consisting of Pd, V, Ta, Ti, Nb, and alloys thereof. Pd is particularly suitable as the second material because it has high hydrogen dissociation permeability even at low temperatures of 300°C or less.

[0021] The first material in the lattice extension layer 40 has the same crystal structure as the second material in the hydrogen dissociation permeation layer 60. The first material in the lattice extension layer 40 may also have the same crystal orientation as the second material in the hydrogen dissociation permeation layer 60.

[0022] The first bulk material has the same composition and the same crystal structure as the first material, and has a lattice constant a 1,バルク and a second bulk material having the same composition and the same crystal structure as the second material, with a lattice constant a 2,バルク and has a lattice constant a 1,バルク and lattice constant a 2,バルク is expressed by the following formula (1): 1.03a 2,バルク ≦a 1,バルク ≦1.15a 2,バルク (1) It should be noted that when the first material and the second material have a crystal structure other than a cubic crystal, the lattice constants of the same crystal axis of the first bulk material and the second bulk material satisfy formula (1). Here, a bulk material means a self-standing, i.e., completely relaxed material that is not supported by other members. When the first material and the second material have the same crystal structure and a composition that satisfies formula (1), the average lattice constant a2 of the second material in the hydrogen dissociation permeation layer 60 can be set to a value equal to the lattice constant a of the second bulk material. 2,バルク can be larger than

[0023] For example, if the second material is Pd having a face-centered cubic lattice (fcc) structure, the first material may be Al, Au, or Ag having an fcc structure, with Ag being particularly preferred because it is relatively inexpensive and resistant to oxidation. If the second material is V having a body-centered cubic lattice (bcc) structure, the first material may be Mo, W, or Nb having a bcc structure. If the second material is Ta having a bcc structure, the first material may be V, Mo, W, or Nb having a bcc structure. The lattice constants of the bulk materials of these metals are shown in Table 1.

[0024] [Table 1]

[0025] The average lattice constant a2 of the second material in the hydrogen dissociation permeation layer 60 is expressed by the following formula (2): a 2,バルク <a2(2) The average lattice constant a2 of the second material preferably satisfies the following formula (3): 1.5≦[(a2-a 2,バルク ) / a 2,バルク ]×100≦5 (3) and more preferably, the following formula (4): 3≦[(a2-a 2,バルク ) / a 2,バルク ]×100≦5 (4) More preferably, the following formula (5): 3.5≦[(a2-a 2,バルク ) / a 2,バルク ]×100≦4.5 (5) may be satisfied.

[0026] Here, the average lattice constant a2 of the second material is determined from the interplanar spacing of crystal planes perpendicular to the interface 62 between the lattice expansion layer 40 and the hydrogen dissociation permeation layer 60. Specifically, electron diffraction patterns of the second material are obtained using a transmission electron microscope (TEM) at three locations: near both surfaces (top and bottom) of each hydrogen dissociation permeation layer 60 and at intermediate positions between them. Based on each electron diffraction pattern, the lattice constant is calculated from the interplanar spacing of crystal planes perpendicular to the interface 62 between the lattice expansion layer 40 and the hydrogen dissociation permeation layer 60, and the average of the obtained values ​​is calculated to determine the average lattice constant a2 of the second material. The above formula (2) indicates that the crystal lattice of the second material in the hydrogen dissociation permeation layer 60 is expanded at least in a direction parallel to the interface 62 compared to a fully relaxed state. The crystal lattice of the second material in the hydrogen dissociation permeation layer 60 may also be expanded in a direction perpendicular to the interface 62. In conventional hydrogen separation filters such as that described in Patent Document 1, when hydrogen diffuses through the hydrogen dissociation permeation layer at low temperatures, the crystal lattice of the hydrogen dissociation permeation layer repeatedly expands and contracts, resulting in embrittlement. However, in the hydrogen separation filter 1 of this embodiment, the crystal lattice of the hydrogen dissociation permeation layer 60 is expanded in advance, which suppresses the expansion and contraction of the crystal lattice due to hydrogen diffusion and thereby suppresses embrittlement of the hydrogen dissociation permeation layer 60 at low temperatures. Therefore, the hydrogen separation filter 1 of this embodiment enables hydrogen purification at lower temperatures than conventional filters.

[0027] The lattice expansion layer 40 and the hydrogen dissociation permeation layer 60 may each have a thickness in the range of 1 to 10 nm, preferably 2 to 8 nm, and more preferably 4 to 6 nm, which prevents or reduces the formation of an alloy between the first material and the second material and sufficiently expands the crystal lattice of the hydrogen dissociation permeation layer 60.

[0028] An example of a method for manufacturing the hydrogen separation filter 1 according to this embodiment will be described. The second material and the first material are alternately deposited on the porous substrate 20 by sputtering. As a result, a superlattice layer 90 consisting of alternately stacked hydrogen dissociation permeation layers 60 and lattice extension layers 40 is formed on the porous substrate 10. In this way, the hydrogen separation filter 1 according to this embodiment is obtained.

[0029] The present invention is not limited to the above-described embodiment, and various design modifications can be made without departing from the spirit of the present invention as defined in the claims. [Example]

[0030] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0031] (1) Preparation of hydrogen separation filter Example 1 A ceramic membrane filter (NGK Insulators, Ltd. "Cefilt," ultrafiltration membrane, molecular weight cutoff 20,000, average pore size 5 nm, hereinafter simply referred to as "substrate") was placed in the deposition chamber of a sputtering apparatus equipped with a pure Ag target and a pure Pd target. After cleaning the surface of the substrate by Ar ion etching, a 5 nm thick Pd layer was formed on the substrate by sputtering, followed by a 5 nm thick Ag layer. In the same manner, the formation of Pd layers and Ag layers was alternately repeated to form a superlattice layer consisting of four Pd layers and three Ag layers on the substrate. The total thickness of the superlattice layer was approximately 35 nm. In this way, a hydrogen separation filter (hereinafter simply referred to as "filter") was produced.

[0032] Comparative Example 1 The surface of the substrate was cleaned by Ar ion etching in the same manner as in Example 1, and then a Pd layer with a thickness of 35 nm was formed on the substrate by sputtering, thereby producing a hydrogen separation filter (hereinafter simply referred to as "filter").

[0033] (2) Measurement of lattice constant Using a TEM, electron diffraction patterns of the Pd layers were obtained at three locations, near both sides of each Pd layer and at the intermediate position between them, for the filter of Example 1. Based on each of the 12 electron diffraction patterns obtained, the lattice constant of Pd was calculated from the spacing of the crystal planes perpendicular to the interface between the Pd layer and the Ag layer, and the average value a pd The average lattice constant a pd is the lattice constant a of bulk Pd pd,バルク (0.38898nm), which was approximately 1.04 times the wavelength.

[0034] Similarly, electron diffraction patterns of the Pd layer were obtained at three locations, near both sides of the Pd layer of the filter of Comparative Example 1 and at an intermediate position between them. Based on the obtained electron diffraction patterns, the lattice constant of Pd was calculated from the spacing of the crystal planes perpendicular to the surface of the Pd layer, and the average value a pd The average lattice constant a pd is the lattice constant a of bulk Pd pd,バルク (0.38898nm) was approximately 1.00 times.

[0035] (3) Hydrogen separation performance evaluation The hydrogen gas permeability and nitrogen gas permeability (unit: mol m) of the filters of Example 1 and Comparative Example 1 were measured by gas chromatography in accordance with JIS K7126:2006 (Plastics and sheets - Gas permeability test method - Part 1: Differential pressure method). -2 ·s -1 Pa -1 ) were measured under the condition of 100°C. The ratio of hydrogen gas permeability to nitrogen gas permeability (i.e., hydrogen gas permeability / nitrogen gas permeability) of the filter of Example 1 was 3519. The ratio of hydrogen gas permeability to nitrogen gas permeability of the filter of Comparative Example 1 was 4. It was shown that the filter of Example 1 exhibited significantly higher hydrogen separation performance than the filter of Comparative Example 1 at a low temperature of 100°C. [Explanation of symbols]

[0036] 1: Hydrogen separation filter, 20: Porous substrate, 40: Lattice extension layer, 60: Hydrogen dissociation permeation layer, 62: Interface between the lattice extension layer and the hydrogen dissociation permeation layer, 90: Superlattice layer, 92: Top layer of the superlattice layer, 93: Surface of the top layer of the superlattice layer, 94: Bottom layer of the superlattice layer, 95: Interface between the superlattice layer and the porous substrate

Claims

1. A porous substrate; a superlattice layer formed on the porous substrate; A hydrogen separation filter comprising: The superlattice layer is at least one lattice-extending layer comprising a first material; At least two hydrogen dissociation permeation layers containing a second material selected from the group consisting of Pd, V, Ta, Ti, Nb, and alloys thereof; Including, the at least one lattice-expanding layer and the at least two hydrogen dissociation permeation layers are alternately stacked; the first material and the second material have the same crystal structure; a lattice constant a of a first bulk material having the same composition and the same crystal structure as the first material; １，バルク and a lattice constant a of a second bulk material having the same composition and the same crystal structure as the second material. ２，バルク is expressed by the following formula (1): <h2 style=";text-align:left;direction:ltr">11.03a<h2 style=";text-align:left;direction:ltr"> ２，バルク <h2 style=";text-align:left;direction:ltr"> ≦a<h2 style=";text-align:left;direction:ltr"> １，バルク <h2 style=";text-align:left;direction:ltr"> ≦1.15a<h2 style=";text-align:left;direction:ltr"> ２，バルク <h2 style=";text-align:left;direction:ltr"> (11) Fulfilling A hydrogen separation filter, wherein the lattice-extending layer and the hydrogen dissociation permeation layer each have a thickness in the range of 1 to 10 nm.

2. 2. The hydrogen separation filter according to claim 1, wherein the uppermost layer of the superlattice layer that is farthest from the porous substrate and the lowermost layer that is closest to the porous substrate are both the hydrogen dissociation permeation layer.

3. The average lattice constant a of the second material is calculated from the spacing of the crystal planes perpendicular to the interface between the lattice expansion layer and the hydrogen dissociation permeation layer. ２ is expressed by the following formula (2): a ２，バルク <a ２ (2) The hydrogen separation filter according to claim 1 or 2, which satisfies the above.

4. The average lattice constant a of the second material is calculated from the spacing of the crystal planes perpendicular to the interface between the lattice expansion layer and the hydrogen dissociation permeation layer. ２ is expressed by the following formula (3): 1.5≦[(a ２ -a ２，バルク ) / a ２，バルク ] × 100≦5 (3) The hydrogen separation filter according to claim 1 or 2, wherein the hydrogen separation filter satisfies the following condition.

5. the first material is Ag, Au, or Al; 3. The hydrogen separation filter according to claim 1, wherein the second material is Pd.

6. 6. The hydrogen separation filter according to claim 5, wherein the first material is Ag.

7. 3. The hydrogen separation filter according to claim 1, wherein the superlattice layer has a thickness that is more than seven times the average pore size of the porous substrate.

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