Hydrogen-permeable membrane made of PdCu alloy and method for purifying hydrogen using the hydrogen-permeable membrane

Abstract

To provide a hydrogen permeable membrane used for hydrogen purification, which is more excellent in hydrogen permeability than a conventional PdCu alloy membrane.SOLUTION: The present invention relates to a hydrogen-permeable membrane made of a PdCu alloy. The hydrogen-permeable membrane is a PdCu alloy composed of 38.75 mass% or more and 39.5 mass% or less of Cu, the balance being Pd and unavoidable impurities, and an area ratio of a β phase in an arbitrary cross section is 95% or more. The hydrogen-permeable membrane according to the present invention has a hydrogen permeation coefficient φ of 2.0×10-8 mol / m S Pa1 / 2 or more at any temperature in the temperature range of 150°C or higher and 350°C or lower. The hydrogen permeation coefficient is a value that exceeds that of a PdCu alloy film having a Cu40 mass, which has been considered optimal.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a hydrogen-permeable membrane that selectively allows hydrogen to permeate from a hydrogen-containing gas, and in particular to a hydrogen-permeable membrane that has improved hydrogen permeability compared to conventionally known PdCu alloys. [Background technology]

[0002] Hydrogen gas is widely used in various fields, such as as a hydrogenation source and a reducing agent in the synthesis of various compounds. In recent years, in response to increasingly serious environmental and energy problems, there are high expectations for the use of hydrogen as a new renewable energy source. For example, hydrogen engines that run directly on hydrogen as fuel and fuel cells that generate electricity using hydrogen as fuel are being developed and put into practical use. However, in order to effectively use hydrogen as an energy source, it is necessary to produce and supply it efficiently and safely.

[0003] Various methods for industrially producing hydrogen gas are known, but all require purification of the produced hydrogen gas. For example, in the steam reforming method of organic fuels such as hydrocarbons, which has attracted attention as a method for producing hydrogen gas for fuel cells, the reformed gas produced contains, in addition to hydrogen as the main component, carbon monoxide, carbon dioxide, and other impurities. Because these impurities can cause deterioration of the catalysts that make up the fuel cell electrodes, it is necessary to purify the reformed gas before use to produce high-purity hydrogen. One hydrogen purification method that has been put into practical use is the hydrogen-permeable membrane method, which uses a hydrogen-permeable membrane made of a hydrogen-permeable alloy. Hydrogen purification using an alloy membrane can refine, for example, 99% pure hydrogen to a purity of 99.99% or higher, making it suitable for purifying high-purity hydrogen for fuel cells and other applications.

[0004] Known alloy membranes that make up hydrogen-permeable membranes include Pd alloy membranes made of PdAg-based alloys, PdCu-based alloys, etc., which utilize the selective hydrogen permeability of Pd (palladium). In particular, hydrogen-permeable membranes made of PdCu-based alloys are becoming increasingly popular because they have fewer problems with hydrogen embrittlement and corrosion resistance (Patent Documents 1 and 2, Non-Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-262252 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-12495 [Non-patent literature]

[0006] [Non-Patent Document 1] James Raphael Warren, “The Effect of Hydrogen on Palladium-Copper Based Membranes for Hydrogen Purification”, THE UNIVERSITY OF BIRMINGHAM, P22-29, 37-80. Summary of the Invention [Problem to be solved by the invention]

[0007] The hydrogen permeability of PdCu alloy membranes is exhibited in the β-phase state of the B2 structure based on bcc. In the above Pd-based alloys, additive elements such as Cu have the effect of promoting the phase transformation of the Pd alloy from the α-phase to the β-phase. Additive elements such as Cu are also necessary to prevent the strength of the alloy membrane from decreasing due to hydrogen embrittlement. The above-mentioned prior art documents disclose PdCu-based alloys with a wide range of Cu concentrations, but Non-Patent Document 1 states that a hydrogen-permeable membrane made of a PdCu alloy with a Cu concentration of 40 mass% has the highest hydrogen permeability.

[0008] However, based on the studies of the present inventors, it is believed that there is room for improvement in the hydrogen permeability of hydrogen-permeable membranes made of PdCu-based alloys. As mentioned above, the use of hydrogen is expected to expand as a variety of energy sources, and further improvements in purification capabilities are desired for its effective use. The present invention was made against this background, and its object is to provide a hydrogen-permeable membrane for hydrogen production and purification that has better hydrogen permeability than existing PdCu alloy membranes. [Means for solving the problem]

[0009] In order to find a hydrogen-permeable membrane with higher hydrogen permeability, the inventors decided to optimize the composition and cross-sectional structure of the alloy membrane based on a PdCu alloy. As mentioned above, in a PdCu alloy, the phase transformation to the β phase is promoted with increasing Cu concentration. However, since the hydrogen permeability of a Pd alloy is determined by Pd, it is considered preferable to increase the Pd concentration in the β phase as much as possible if hydrogen permeability is important. In other words, it is considered that there is an optimal range for improving the composition of a PdCu alloy, balancing the possibility of phase transformation to the β phase with ensuring hydrogen permeability.

[0010] Furthermore, hydrogen-permeable membranes selectively extract hydrogen by allowing the hydrogen-mixed gas to be treated to permeate from one side to the other. Considering this mechanism of action, it is also necessary to consider the cross-sectional structure of the membrane. If the hydrogen permeability of PdCu alloys is due to the β phase, it is necessary to increase the occupancy rate of the β phase in the cross section of the hydrogen-permeable membrane.

[0011] Based on these considerations, the inventors reviewed both the alloy composition of PdCu alloy membranes and the treatments for effectively inducing phase transformation in the cross section. As a result, they found that by applying a PdCu alloy with a different composition range than the PdCu alloy with a Cu concentration of 40 mass%, which was previously considered optimal, and by performing a heat treatment at a low temperature under a pressurized hydrogen atmosphere, which was not found in the prior art, it is possible to obtain a PdCu alloy membrane that exhibits favorable hydrogen permeability. This new PdCu alloy membrane can clearly exhibit favorable hydrogen permeability compared to the previously optimized PdCu alloy with a Cu concentration of 40 mass%.

[0012] That is, the present invention, which solves the above problems, is a hydrogen-permeable membrane made of a PdCu alloy, characterized in that the PdCu alloy contains 38.75 mass % to 39.50 mass % Cu, the balance being Pd and unavoidable impurities, and the area ratio of the β phase in any cross section is 95% or more. The configuration and manufacturing method of the hydrogen-permeable membrane according to the present invention will be described in detail below.

[0013] (A) Structure of the hydrogen-permeable membrane according to the present invention (A-1) Alloy composition The hydrogen-permeable membrane of the present invention is composed of a binary PdCu alloy consisting of Pd and Cu, excluding inevitable impurities, as described below. As with the prior art, alloy membranes containing additive elements other than Cu are known as hydrogen-permeable PdCu alloy membranes. In this invention, a binary alloy is employed to prevent the intentional addition of additive elements other than Cu, which may result in a decrease in hydrogen permeability due to a decrease in Pd concentration. The present invention employs a PdCu alloy membrane with a Cu concentration of 38.75% by mass or more and 39.50% by mass or less. The PdCu alloy membrane of the present invention has a Pd concentration approximately 1% higher by mass than the conventionally considered optimal PdCu alloy membrane (Cu concentration 40% by mass).

[0014] The Cu concentration is set to 38.75% by mass or more and 39.50% by mass or less to enable the PdCu alloy to transform into the β phase and ensure favorable hydrogen permeability. At a Cu concentration of less than 38.75% by mass, it becomes difficult to develop the β phase, and even the heat treatment described below makes it difficult to develop a sufficient amount of β phase. On the other hand, at a Cu concentration exceeding 39.50% by mass, hydrogen permeability decreases, resulting in performance that is little different from that of conventional technology. In other words, if the Cu concentration is outside the above range, the alloy membrane will have insufficient hydrogen permeability. It is particularly preferable that the Cu concentration be set to 38.80% by mass or more and 39.20% by mass or less.

[0015] The PdCu alloy film of the present invention is composed of Pd and Cu and does not contain any other intentionally added elements, but the inclusion of unavoidable impurities is permitted. Examples of unavoidable impurities include Al, Fe, and Pt. The total content of these impurities is preferably 500 ppm or less.

[0016] (A-2) Cross-sectional structure of alloy film In the present invention, the area ratio of the β phase in any cross section of an alloy membrane made of a PdCu alloy is 95% or more. As described above, the hydrogen permeability of a PdCu alloy is manifested in the β phase state, so a high proportion of the β phase in the cross-sectional direction is necessary to ensure the hydrogen permeability of the alloy membrane. In the present invention, the hydrogen permeability is ensured by strictly specifying the proportion of the β phase in the alloy membrane cross section. In addition, in the present invention, an alloy membrane with suitable hydrogen permeability has an area ratio of the β phase in any cross section of 95% or more. "Arbitrary cross section" means that the above condition is met in any cross section selected arbitrarily, regardless of the direction of the PdCu alloy membrane. The area ratio should be calculated by observing a cross section in an area where both sides of the PdCu alloy membrane (both front and back ends) can be seen, and then calculating the area of ​​the β phase relative to the total area of ​​the observation region. The observation region is preferably set to a range that includes both front and back ends of the PdCu alloy membrane and has a width that is at least 10 times the thickness of the PdCu alloy membrane. The area ratio of the β phase in any cross section is more preferably 98% or more, and the upper limit of the area ratio of the β phase is preferably 100%.

[0017] Electron backscattered diffraction (EBSD) analysis is an effective method for detecting the β phase in any cross section of a PdCu alloy film. EBSD can obtain information on each crystal grain in the cross section of the alloy film, allowing the distribution and area ratio of the β phase in the cross section of the alloy film to be measured and calculated.

[0018] (A-2) Thickness and hydrogen permeability of alloy membrane The thickness of the PdCu alloy membrane constituting the hydrogen-permeable membrane of the present invention is preferably 1 μm or more and 250 μm or less. If it is less than 1 μm, the mechanical strength is insufficient and handling is difficult. If the membrane thickness exceeds 250 μm, the amount of hydrogen permeated is reduced, resulting in a decrease in purification efficiency. There are no particular restrictions on the shape of the PdCu membrane of the present invention.

[0019] The hydrogen-permeable film of the present invention has superior hydrogen permeability compared to conventional techniques. Specifically, it has a hydrogen permeability of 2.0×10 at any temperature in the temperature range of 150°C to 350°C. -8 mol / m S Pa 1 / 2 The above hydrogen permeability coefficient φ can be shown. This hydrogen permeability coefficient φ is more than 1.2 times the hydrogen permeability coefficient measured under the same conditions for a previously optimized PdCu alloy membrane with a Cu concentration of 40 mass%. The hydrogen permeability coefficient φ is calculated using the following formula.

[0020]

number

[0021] (B) Method for manufacturing a hydrogen-permeable membrane according to the present invention The hydrogen-permeable film according to the present invention can be produced by preparing a PdCu alloy film of the above composition and heat-treating it under predetermined conditions. The method for producing the PdCu alloy film is not particularly limited and can be appropriately selected depending on the film thickness, dimensions, etc. Thin-film PdCu alloy films can be produced using various thin-film formation processes, such as sputtering, vacuum deposition, chemical vapor deposition, and plating. Furthermore, plate- or foil-shaped PdCu alloy films can be produced by rolling an alloy ingot.

[0022] In the production of PdCu alloy films by the rolling method, a PdCu alloy ingot is produced by a melting and casting method, and then processed into an alloy film of a predetermined thickness by an appropriate combination of hot forging, hot rolling, cold rolling, etc. There are no particular restrictions on the processing steps from the ingot to the alloy film. However, since the introduction of processing strain in the PdCu alloy can promote the phase transformation to the β phase, it is preferable to produce a PdCu alloy film by cold processing at a processing rate of 65% to 85% as the final processing step.

[0023] Furthermore, PdCu alloy films with a Cu concentration of 38.75% by mass or more and 39.5% by mass or less produced by various manufacturing methods undergo a β-phase transformation when heat-treated within a predetermined temperature range. The heat-treatment temperature is 275°C or more and 350°C or less. The phase transformation temperature (α phase to β phase) within this composition range is estimated to be approximately 300°C. Heat treatment at temperatures below 275°C either does not cause a β-phase transformation or makes it difficult to achieve a β-phase area ratio of 95% or more in the film cross section. On the other hand, it is known that the β-phase decomposes to the α-phase at high temperatures. In the PdCu alloy of the present invention, β-phase decomposition tends to occur at temperatures above 350°C. In the present invention, it is necessary to achieve a β-phase area ratio of 95% or more in any cross section of the alloy film, and heat treatment at 350°C or less is required to ensure this area ratio without causing β-phase decomposition.

[0024] The atmosphere for the heat treatment for the phase transformation to the β phase is preferably a pressurized hydrogen-containing atmosphere, more preferably an atmosphere with a hydrogen partial pressure of 0.05 MPaG or more and 1.0 MPaG or less.

[0025] The heat treatment time is adjusted depending on the film thickness of the PdCu alloy film. The generation of the β phase by heat treatment proceeds from both surfaces of the PdCu alloy film, and the phase transformation progresses inside the film as the treatment time increases. In the present invention, it is necessary to increase the area ratio of the β phase in the cross section of the PdCu alloy film, so a sufficient heat treatment time is ensured so that the phase transformation occurs to the inside while taking the film thickness into consideration. For PdCu alloy films with a film thickness within the above-mentioned preferred range, a treatment time of 5 hours or more is preferable. Note that, since decomposition of the β phase is unlikely to occur if the heat treatment is performed within the above-mentioned temperature range, there is no problem with extending the treatment time.

[0026] (C) Hydrogen purification method and hydrogen purification device using the hydrogen-permeable membrane according to the present invention The hydrogen-permeable membrane of the present invention can purify hydrogen by selectively allowing hydrogen to permeate from a hydrogen-containing gas (feed). That is, the hydrogen purification method of the present invention is a method for purifying hydrogen by allowing a hydrogen-containing gas to permeate through a hydrogen-permeable membrane, characterized in that the hydrogen-permeable membrane of the present invention is used as the hydrogen-permeable membrane and the gas is permeated through the hydrogen-permeable membrane at a treatment temperature of 100°C or higher and 375°C or lower.

[0027] Because the hydrogen permeability coefficient of a PdCu alloy membrane is temperature-dependent, it is necessary to appropriately select the treatment temperature (operating temperature) using the hydrogen-permeable membrane in hydrogen purification. In the hydrogen purification method of the present invention using a PdCu alloy membrane with a Cu concentration of 38.75 mass% to 39.5 mass%, the preferred treatment temperature is 100°C to 375°C. Within this temperature range, the PdCu alloy membrane of the present invention can exhibit a higher hydrogen permeability coefficient than the conventional technique (Cu concentration 40 mass%). Furthermore, the hydroelectric permeable membrane of the present invention can exhibit a hydrogen permeability coefficient equal to or higher than the conventional technique (Cu concentration 40 mass%) in the temperature range from above 375°C to approximately 450°C. However, because temperatures above 375°C may cause decomposition of the β-phase, resulting in a decrease in the hydrogen permeability coefficient, the preferred upper limit of the treatment temperature is 375°C. The treatment temperature refers to the temperature within the range where the hydrogen-containing gas to be purified contacts and permeates the hydrogen-permeable membrane. The treatment temperature is adjusted by adjusting at least one of the temperature of the hydrogen-containing gas, the temperature of the hydrogen-permeable membrane, and the ambient temperature in the hydrogen production (purification) device to fall within the above temperature range.

[0028] In the purification of gases containing hydrogen, the gas to be treated is supplied to one side (primary side) of a hydrogen-permeable membrane. At this time, the pressure on the primary side is made higher than that on the other side (secondary side) of the hydrogen-permeable membrane, and purified hydrogen that has permeated the hydrogen-permeable membrane is extracted. There are no particular restrictions on the pressure difference between the primary and secondary sides.

[0029] In the hydrogen purification process using a PdCu alloy membrane according to the present invention, the PdCu alloy membrane may be heat-treated to form the β phase as described above, or may be heat-treated immediately before the hydrogen purification process. That is, a PdCu alloy membrane containing 38.75 to 39.5 mass% Cu, the balance being Pd and unavoidable impurities, is prepared, and the PdCu alloy membrane is heat-treated in a hydrogen atmosphere at a temperature of 275 to 350°C to form a hydrogen-permeable membrane. The gas may then be permeated through the hydrogen-permeable membrane at a treatment temperature of 100 to 375°C.

[0030] The above hydrogen purification method is carried out by a hydrogen purification device that employs the hydrogen-permeable membrane of the present invention. The main components of this hydrogen purification device, other than the hydrogen-permeable membrane, can be the same as those of known hydrogen purification devices. When installing the hydrogen-permeable membrane in the hydrogen-permeable device, a gas-permeable support may be combined with the hydrogen-permeable membrane to supplement its mechanical strength. Examples of the support that can be used include metal mesh and porous sintered materials. However, a support is not essential, as the thickness of the hydrogen-permeable membrane may be sufficient to ensure mechanical strength. [Effects of the Invention]

[0031] As explained above, the hydrogen-permeable membrane made of a PdCu alloy according to the present invention has a composition range strictly defined as a Cu concentration of 38.75 mass% or more and 39.5 mass% or less, and the optimal β-phase area ratio in the cross section of the PdCu alloy membrane is clarified. The processing conditions for this β-phase formation cannot be applied to the previously considered optimal PdCu alloy membrane (Cu concentration 40 mass%), but were discovered in the PdCu alloy membrane of the alloy composition according to the present invention. The hydrogen-permeable membrane according to the present invention has a higher hydrogen permeability coefficient than conventional PdCu alloy membranes (Cu concentration 40 mass%). [Brief explanation of the drawings]

[0032] [Figure 1] XRD diffraction patterns of the surface of hydrogen-permeable membranes (PdCu alloy membranes (39 mass% Cu)) produced at various heat treatment temperatures. [Figure 2] EBSD profiles of the cross section of a hydrogen-permeable membrane (PdCu alloy membrane (39 mass% Cu)) produced at each heat treatment temperature. [Figure 3] 1 is a graph showing the relationship between the heat treatment temperature of a PdCu alloy film (39 mass % Cu) and the area ratio of the β phase in the cross section. [Figure 4] FIG. 2 is a diagram showing the configuration of a hydrogen permeability coefficient measuring device used in each embodiment. [Figure 5] 1 is a graph showing the measurement results of the hydrogen permeability coefficient of various PdCu alloy films (Cu concentration 37 mass % to 41 mass %, heat treatment temperature 400° C.). [Figure 6]1 is a graph showing the measurement results of the hydrogen permeability coefficient of various PdCu alloy films (Cu concentration 37 mass % to 41 mass %, heat treatment temperature 320° C.). [Figure 7] 1 is a graph showing the relationship between the area ratio of the β phase in a cross section of a PdCu alloy membrane having a Cu concentration of 39.0 mass % and the hydrogen permeability coefficient. [Figure 8] 1 is a graph showing the measurement results of hydrogen permeability coefficients at various treatment temperatures in hydrogen purification using a PdCu alloy membrane (Cu concentrations of 39 mass % and 40 mass %). DETAILED DESCRIPTION OF THE INVENTION

[0033] First embodiment Hereinafter, an embodiment of the present invention will be described. In this embodiment, a PdCu alloy membrane with a Cu concentration of 39.0 mass% (Pd concentration of 61.0 mass%) was manufactured and heat-treated to produce a hydrogen-permeable membrane. At this time, multiple hydrogen-permeable membranes were manufactured by varying the heat treatment temperature, and the area ratio of the β phase and the hydrogen permeability coefficient in the cross section were measured.

[0034] A PdCu alloy ingot manufactured by melt casting was prepared. The ingot surface was chamfered and cleaned, and then cold-rolled to produce a PdCu alloy film. In the processing step, intermediate annealing (600-900°C) was performed and multiple cold-rolling processes were carried out, resulting in a PdCu alloy film with a thickness of 15 μm, with a final rolling reduction rate of 85%. This PdCu alloy film was then heat-treated at temperatures of 275°C, 300°C, 350°C, and 375°C to promote the β-phase transformation. The heat treatment was carried out in hydrogen at 0.05 MPaG for 24 hours.

[0035] The surface of the heat-treated PdCu alloy film was subjected to XRD analysis using an XRD analyzer (MACScience M03XHF22) with Cu Kα radiation as the X-ray source.

[0036] Then, the PdCu alloy film manufactured in this embodiment was cut and the cross section was subjected to EBSD analysis, and the area ratio of the β phase in the cross section in the observation area was measured. As a pretreatment for EBSD analysis, the sample cross section was finish-polished using diamond paste to 0.25 μm, and the surface was further milled using an ion milling device (IM4000 manufactured by Hitachi High-Tech Corporation). The ion milling conditions were: stage control F2, acceleration 0.1 kV, discharge 1.5 kV, ion beam irradiation angle 70 degrees, eccentricity 4 mm, argon gas flow rate 0.07 cm 3 The surface was milled for 20 minutes under the conditions of 1 / min.

[0037] EBSD analysis was performed using an ultra-high-resolution analytical scanning electron microscope (SU-70, Hitachi High-Tech Corporation; NORDLYS-MAX3, Oxford Instruments). The analysis conditions were: pitch 0.2 μm, pinning mode 4x4, gain 0, exposure time auto, EBSD solver setting, number of bands 12, and Hough resolution 60. The analysis was performed using reflector 44 for the FCC phase (lattice constant 3.7653 Å) and reflector 43 for the B2 phase. The area fraction of the β phase (lattice constant 2.9662 Å) was measured using the image analysis software provided with the analyzer.

[0038] Figure 1 shows the XRD diffraction patterns of the hydrogen-permeable membrane (PdCu alloy membrane) surface treated at each heat treatment temperature, and Figure 2 shows the results of EBSD analysis of the cross section of each hydrogen-permeable membrane.

[0039] Referring to FIG. 1, based on the results of XRD analysis, it can be inferred that the PdCu alloy film is substantially composed of the β phase, with the phase transformation to the β phase completed at all heat treatment temperatures. However, EBSD analysis of the cross section of the PdCu alloy film confirms that the α phase is formed internally after heat treatment at 375°C. Considering that the β phase is formed internally after heat treatment at 275°C to 350°C, the α phase observed after heat treatment at 375°C is likely due to an untransformed residual α phase or a phase that was once transformed to the β phase and then retransformed to the α phase at high temperatures. FIG. 3 shows the relationship between the heat treatment temperature of the PdCu alloy film and the area ratio of the β phase in the cross section. In this embodiment, it was confirmed that the area ratio of the β phase in the film cross section was 98% or more after heat treatment at 275°C to 350°C.

[0040] Next, the hydrogen permeability coefficient was measured for the hydrogen-permeable membranes (PdCu alloy membranes) produced by heat treatment at each temperature. The produced hydrogen-permeable membranes were cut into discs with a diameter of 21.3 mm. Samples were prepared by sandwiching this hydrogen-permeable membrane and a stainless steel wire mesh (diameter 18.4 mm) between ICF34 flange gaskets (effective area 2.08 cm). 2 This sample was set in a sample holder. The sample holder is a vacuum chamber that has a space on the primary side (gas supply side) and a space on the secondary side (permeation gas side) for the sample (hydrogen-permeable membrane), and is equipped with nozzles for gas supply and gas discharge.

[0041] Figure 4 shows an outline of the hydrogen permeability coefficient measurement device. The sample holder constructed as described above was set in an electric furnace and connected to the vacuum pump and the piping of various gas flow meters. Before measurement, the primary and secondary sides of the sample holder were evacuated and then replaced with hydrogen. Next, the furnace was heated to a predetermined measurement temperature, and hydrogen at a predetermined pressure was introduced into the primary side of the hydrogen-permeable membrane. The flow rate of hydrogen that had permeated to the secondary side was then measured. The permeability coefficient was calculated from the measured flow rate of the permeated gas (hydrogen), the supply-side pressure, the permeation-side pressure, and the thickness of the hydrogen-permeable membrane. The measurement conditions in this embodiment were as follows: Test temperature: 320℃ Supply gas: Hydrogen (hydrogen concentration 99.99%) Primary pressure: 0.05 MPa G Secondary pressure: 0MPa G Exam duration: 2.5 hours

[0042] The hydrogen permeability coefficients (measured at 320°C) of the hydrogen-permeable films made of PdCu alloys manufactured in this embodiment (heat treatment temperatures: 275°C, 300°C, 350°C, 375°C) were as follows.

[0043] [Table 1]

[0044] From Table 1, it can be seen that the PdCu alloy membrane (heat treatment temperature 375°C) with a low area ratio of the β phase in the membrane cross section has a significantly inferior hydrogen permeability coefficient. In other words, to obtain a PdCu alloy membrane with excellent hydrogen permeability, it is necessary to transform the membrane into the β phase all the way to the inside.

[0045] Considering the results of the XRD and EBSD analyses described above, it can be said that XRD analysis is insufficient when examining the hydrogen permeability of hydrogen-permeable membranes made of PdCu alloy membranes. XRD analysis can grasp the structure of the object to a depth of about several micrometers from the surface, but it cannot measure the internal structure. In this regard, in previous studies such as Non-Patent Document 1, XRD analysis has mainly been used for structural analysis of hydrogen-permeable membranes. However, this method is considered to be insufficient for evaluating the true properties of PdCu alloy membranes.

[0046] Second embodiment In this embodiment, PdCu alloy membranes with different Cu concentrations were manufactured, and the relationship between the Cu concentration (Pd concentration) and the hydrogen permeability coefficient was investigated. Here, the membranes were compared with a conventional PdCu alloy membrane with a Cu concentration of 40.0 mass% (Pd concentration of 60.0 mass%), and the hydrogen permeability of this conventional membrane was also compared.

[0047] The PdCu alloy film was manufactured in the same manner as in the first embodiment, and the composition of the alloy ingot was adjusted to manufacture a PdCu alloy film with a Cu concentration of 37 mass % to 41 mass % (Pd concentration of 59 mass % to 63 mass %).

[0048] In this embodiment, a preliminary study was first conducted to confirm the hydrogen permeability when the optimum heat treatment temperature was applied to a PdCu alloy membrane with a Cu concentration of 40.0 mass% (Pd concentration of 60.0 mass%), which is a conventional technology. According to Non-Patent Document 1 and the like, a PdCu alloy membrane with a Cu concentration of 40.0 mass% exhibits optimum hydrogen permeability when heat treated at 400°C, so the heat treatment temperature was set to 400°C.

[0049] In this embodiment, the manufactured PdCu alloy membrane was processed into the same shape as in the first embodiment without heat treatment to prepare a sample, and then set in a hydrogen permeability measurement device. After the same pre-measurement setup as in the first embodiment, the electric furnace was heated to 400°C, the heat treatment temperature for β-phase transformation, and hydrogen gas was introduced (primary pressure 0.3 MPa) simultaneously with the start of the temperature increase. From the start of this temperature increase, the PdCu alloy membrane began to undergo a phase transformation to the β-phase. As the phase transformation to the β-phase progressed, the hydrogen flow rate measured by the permeation gas flow meter increased. Then, once the permeated hydrogen flow rate stabilized, the hydrogen permeability coefficient was measured. Other measurement conditions were the same as in the first embodiment.

[0050] The measurement results of the hydrogen permeability coefficient of various PdCu alloy films (Cu concentration 37 mass% to 41 mass%) when the heat treatment temperature for β-phase transformation was set to 400°C are shown in Figure 5. From Figure 5, it was confirmed that the PdCu alloy film with a Cu concentration of 40.0 mass% (Pd concentration 60.0 mass%) exhibited the highest hydrogen permeability coefficient when heat treated at 400°C. This result is consistent with the results of previous reports.

[0051] On the other hand, in the case of the PdCu alloy membrane (first embodiment) with a Cu concentration of 39 mass % or less, the hydrogen permeability coefficient is extremely low when heat treated at 400° C. As confirmed in the first embodiment, in the PdCu alloy membrane with a Cu concentration of 39 mass %, it is considered that the untransformed α phase remains or the phase that has once transformed to the β phase retransforms to the α phase at high temperatures when heat treated at 400° C., and this can be said to correspond to this result.

[0052] Therefore, each PdCu alloy membrane was heat-treated at a heat treatment temperature of 320°C, and their hydrogen permeability coefficients were measured. In this study, a PdCu alloy membrane that had not been heat-treated was set in the measurement device and heat-treated in the same manner as above. First, the heating temperature was set to 320°C and the temperature was increased, and hydrogen gas was introduced. Heating at 320°C was continued until the permeated hydrogen flow rate stabilized. After confirming that the flow rate had stabilized, the temperature was increased to 400°C and the hydrogen permeability coefficient was measured. The results are shown in Figure 6.

[0053] From Figure 6, it can be seen that by setting the heat treatment temperature to 320°C, clear hydrogen permeability is exhibited in a PdCu alloy membrane with a Cu concentration of 39.0 mass% (Pd concentration of 61.0 mass%). Within the Cu concentration range of 41 mass% to 39 mass% (Pd concentration of 59 mass% to 61 mass%), the hydrogen permeability coefficient increases with increasing Pd concentration. The maximum hydrogen permeability coefficient is achieved in a PdCu alloy membrane with a Cu concentration of 39.0 mass% (Pd concentration of 61.0 mass%), which is 1.3 times higher than that of the prior art. The hydrogen permeability coefficient of this PdCu alloy membrane with a Cu concentration of 39.0 mass% is also high compared to the hydrogen permeability coefficient of the PdCu alloy membrane with a Cu concentration of 40.0 mass% heat-treated at 400°C.

[0054] Third embodimentIn this embodiment, PdCu alloy membranes with different β-phase area ratios were manufactured using the same PdCu alloy membrane (Cu concentration 39.0 mass%) as in the first embodiment, while adjusting the heat treatment temperature for β-phase generation, and their hydrogen permeability coefficients were measured. In this embodiment, as in the second embodiment, the PdCu alloy membrane was subjected to heat treatment (treatment temperature 275°C to 375°C) using a measuring device to transform into the β-phase, and then the hydrogen permeability coefficient was measured. The measurement temperature for the hydrogen permeation test was 300°C. After measuring the hydrogen permeability coefficient, the PdCu alloy membrane was removed and subjected to EBSD analysis to measure the β-phase area ratio of the cross section.

[0055] Figure 7 shows the test results, and is a graph showing the relationship between the area fraction of the β phase in the cross section of a PdCu alloy membrane with a Cu concentration of 39.0 mass% and the hydrogen permeability coefficient. It can be seen from Figure 7 that the hydrogen permeability coefficient increases as the area fraction of the β phase in the cross section of the PdCu alloy membrane increases. Based on the hydrogen permeability coefficient of the conventional PdCu alloy membrane with a Cu concentration of 40 mass% studied in the second embodiment, it was confirmed that in this embodiment, the area fraction of the β phase needs to be 95% or more, and preferably 98% or more.

[0056] Fourth embodiment In this embodiment, the relationship between the treatment temperature in hydrogen purification and the hydrogen permeability coefficient was confirmed. The PdCu alloy membrane (Cu concentration 39.0 mass%) of the first embodiment was set in a measuring device, and the hydrogen permeability coefficient was measured at test temperatures set to 180°C to 600°C. In this embodiment, as in the second embodiment, the PdCu alloy membrane was subjected to heat treatment using the measuring device to transform into the β phase, and then the hydrogen permeability coefficient was measured at each temperature. The heat treatment temperature was 300°C. For comparison, a similar measurement was also performed on a PdCu alloy membrane with a Cu concentration of 40.0 mass% (heat treatment temperature was 400°C).

[0057] The measurement results are shown in Figure 8. As a relationship between the treatment temperature and hydrogen permeability coefficient in hydrogen purification, the hydrogen permeability coefficient of the PdCu alloy membrane of this embodiment (Cu concentration 39.0 mass%) peaks at around 300°C to 350°C. In contrast, the PdCu alloy membrane of the conventional example (Cu concentration 40.0 mass%) has a peak hydrogen permeability coefficient at around 400°C. Comparing this embodiment with the conventional example, although the treatment temperatures at which the hydrogen permeability coefficient reaches its maximum value are different, it was confirmed that the PdCu alloy membrane of this embodiment exhibits a higher hydrogen permeability coefficient than the conventional example between 100°C and around 450°C. In particular, it was confirmed that a higher hydrogen permeability coefficient was exhibited in the temperature range up to around 350°C, making this a more preferable treatment temperature.

[0058] From the results of the second to fourth embodiments, it was confirmed that a PdCu alloy membrane with the highest hydrogen permeability coefficient can be obtained by setting the Cu concentration at approximately 39.0 mass%. It can be said that this PdCu alloy membrane can obtain a higher hydrogen permeability coefficient than the conventional PdCu alloy membrane with a Cu concentration of 40.0 mass% by appropriate heat treatment (phase transformation treatment to the β phase). [Industrial Applicability]

[0059] The hydrogen-permeable membrane made of a PdCu alloy according to the present invention has a Cu concentration of 38.75 mass% or more and 39.5 mass% or less, a composition range that is strictly defined. Furthermore, hydrogen permeability is ensured by increasing the β-phase occupancy rate in the cross section of the hydrogen-permeable membrane. The present invention has a higher hydrogen permeability coefficient than the PdCu alloy membrane (Cu concentration 40 mass%) that was previously considered optimal. In addition to its use in chemical synthesis, hydrogen is also expected to be utilized as a new renewable energy source in recent years. The present invention can contribute to the supply of high-purity hydrogen to such a wide range of fields.

Claims

1. In a hydrogen-permeable membrane made of a PdCu alloy, The PdCu alloy contains 38.75 mass% or more and 39.20 mass% or less of Cu, the remainder being Pd and unavoidable impurities, The hydrogen-permeable membrane has a thickness of 1 μm or more and 250 μm or less, A hydrogen-permeable film characterized in that, when the hydrogen-permeable film is cut and a cross section is subjected to EBSD analysis, the area ratio of the β phase in the cross section is 95% or more.

2. 2.0 × 10 at any temperature in the temperature range of 150 ° C or more and 350 ° C or less －８ mol / m・S・Pa １ / ２ 2. The hydrogen-permeable film according to claim 1, having a hydrogen permeability coefficient φ of at least 1000 kJ / cm.

3. 3. A method for manufacturing a hydrogen-permeable membrane according to claim 1 or 2, comprising: preparing a PdCu alloy film having a thickness of 1 μm to 250 μm, the film containing 38.75 mass % to 39.20 mass % Cu, the remainder being Pd and unavoidable impurities; The method comprises the step of heat treating the PdCu alloy film in a pressurized hydrogen-containing atmosphere at a temperature of 275° C. or higher and 350° C. or lower.

4. A method for purifying hydrogen by passing a hydrogen-containing gas through a hydrogen-permeable membrane, comprising: The hydrogen-permeable membrane according to claim 1 or 2 is used as the hydrogen-permeable membrane, A hydrogen purification method, characterized in that the gas is permeated through the hydrogen-permeable membrane at a treatment temperature of 100°C or higher and 375°C or lower.

5. A method for purifying hydrogen by passing a hydrogen-containing gas through a hydrogen-permeable membrane, comprising: A PdCu alloy film having a thickness of 1 μm or more and 250 μm or less and containing 38.75 mass % or more and 39.20 mass % or less of Cu, the remainder being Pd and inevitable impurities, is prepared; a hydrogen-permeable membrane according to claim 1 or 2, wherein the PdCu alloy membrane is heat-treated in a hydrogen atmosphere at a temperature of 275° C. or higher and 350° C. or lower before the hydrogen-containing gas is allowed to permeate therethrough; Thereafter, the treatment temperature is set to 100° C. or higher and 375° C. or lower to allow the gas to permeate through the hydrogen-permeable membrane.

6. A hydrogen generating device comprising: the hydrogen-permeable membrane according to claim 1 or 2; and a support for supporting the hydrogen-permeable membrane.

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