JP2012201974A - Hydrogen permeable copper alloy, hydrogen permeable film, and steam reformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a Cu-Pd alloy excellent in hydrogen permeability in high-temperature and high-pressure conditions, strength, and stress relaxation resistance.SOLUTION: The hydrogen permeable copper alloy is represented by composition formula: PdCuX(X: at least one among Al, Ga and In; a: 41-50 at%; b: 1-a-c, c: 0.2-2 at%). In the hydrogen permeable copper alloy, the ratio of β-phase at 600°C is 5% or higher.

Description

  The present invention relates to a hydrogen permeable copper alloy, a hydrogen permeable membrane, and a steam reformer using the same, and more particularly to a hydrogen permeable Cu-Pd alloy, a hydrogen permeable membrane, and a steam reformer using the same. .

  Hydrogen is widely used, for example, as a desulfurization agent in the petroleum refining field, as a raw material for various chemicals including ammonia and methanol in the chemical industry field, as a reducing atmosphere gas in the semiconductor field, and as a fuel in the fuel cell field. Yes.

  As a hydrogen production technique, a steam reforming method for producing hydrogen from hydrocarbons or coal is known. For example, steam is reacted with methane at a high temperature of 700 to 800 ° C. under a metal catalyst to produce carbon monoxide and hydrogen. It is a method of getting. Carbon monoxide is further converted to carbon dioxide by a shift reaction. As a method for separating and purifying hydrogen from a mixed gas containing hydrogen and by-products, a method using a hydrogen permeable membrane is known. The hydrogen permeable membrane has a characteristic of selectively permeating only hydrogen. When one side (primary side) of the hydrogen permeable membrane is pressurized with a mixed gas, only hydrogen is dissolved into the hydrogen permeable membrane. It can diffuse and reach the opposite surface (secondary side). By separating hydrogen from the mixed gas in this way, hydrogen can be purified with high purity.

  Recently, development of a membrane reformer technology that simultaneously performs a hydrogen generation reaction and hydrogen separation and purification by combining a hydrogen permeable membrane and a reformer is in progress. This is a technology that is expected as a new hydrogen production method because it does not require a shift reactor or selective removal of carbon monoxide. Compared to the conventional technology of about 550 to 650 ° C. using a reforming catalyst. There is an advantage that the reforming reaction can proceed at a low temperature and with high reforming efficiency.

  Since palladium has hydrogen permselectivity, alloys mainly composed of palladium are used as a material for the hydrogen permeable membrane, and among these, Pd—Cu alloys are known. Japanese Patent Application Laid-Open No. 2001-262252 (Patent Document 1) describes that hydrogen embrittlement is suppressed by adding 0 to 20 at% of Cu containing Pd as a main component. In JP-A-2004-174373 (Patent Document 2), Cu has an effect of alloying Pd to improve strength and suppress hydrogen embrittlement, and a hydrogen gas purification / separation apparatus in which hydrogen gas can be 400 ° C. or higher. For example, it is preferable to use an alloy composition containing Pd as a main component and Cu in an amount of 1 to 40 at% so that high temperature strength can be maintained.

JP 2001-262252 A JP 2004-174373 A

  As described above, the hydrogen permeable membrane is used for hydrogen separation. However, since hydrogen separation proceeds by using a pressure difference, one side of the hydrogen permeable membrane (primary side) is used to increase the hydrogen separation rate. ) It is necessary to increase the pressure of the mixed gas. In particular, when a hydrogen permeable membrane is used as a membrane reformer in hydrogen production in a steam reforming reaction, the pressure may be set to 1 to 2 MPa. For this reason, the hydrogen permeable membrane is required to have such strength that can withstand such high pressures. However, if the film thickness is increased in order to obtain strength, the hydrogen separation rate of the hydrogen permeable membrane decreases. Moreover, about Pd-Cu alloy which is promising as a material for a hydrogen permeable film, since expensive Pd which is a noble metal is used, increasing the film thickness is disadvantageous in terms of cost. Furthermore, the Pd—Cu alloy has a problem that the hydrogen permeability at a high temperature is extremely lowered. Further, since stress is continuously applied to the hydrogen permeable membrane at a high temperature, it is required to have a good stress relaxation resistance property at a high temperature.

  Therefore, an object of the present invention is to provide a Cu—Pd alloy that is excellent in hydrogen permeability, strength, and stress relaxation resistance under high temperature and high pressure. Another object of the present invention is to provide a hydrogen permeable membrane made of such a Cu—Pd alloy. Another object of the present invention is to provide a steam reforming apparatus using such a hydrogen permeable membrane.

  As a result of intensive studies to solve the above problems, the present inventor has included a predetermined amount of at least one of Al, Ga and In in a Cu-Pd alloy having a predetermined composition, and the proportion of β phase in the alloy. It was found that the hydrogen permeability, strength, and stress relaxation resistance at high temperature and high pressure were significantly improved by controlling.

In one aspect, the present invention completed on the basis of the above knowledge has a composition formula: Pd _a Cu _b X _c
(X: at least one of Al, Ga and In, a: 41-50 at%, b: 1-ac, c: 0.2-2 at%)
This is a hydrogen permeable copper alloy having a β-phase ratio of 5% or more at 600 ° C.

  In one embodiment, the hydrogen permeable copper alloy according to the present invention is such that X is Al and c is 0.5 to 2 at%.

  In another embodiment of the hydrogen permeable copper alloy according to the present invention, the proportion of β phase at 600 ° C. is 10% or more.

  In another aspect, the present invention is a hydrogen permeable membrane made of the copper alloy according to the present invention.

  In one embodiment, the hydrogen permeable membrane according to the present invention has a thickness of 1 to 200 μm.

  In still another aspect, the present invention is a steam reformer using the hydrogen permeable membrane according to the present invention.

  According to the present invention, a hydrogen permeable membrane excellent in hydrogen permeability and strength under high temperature and high pressure can be obtained. Further, Pd is a noble metal and is expensive, and since the ratio of Pd in the composition of the hydrogen permeable membrane according to the present invention is small, it can be manufactured at a lower cost than in the prior art.

The schematic of the measurement system which calculated | required the hydrogen permeability coefficient in the Example is shown.

  Hereinafter, embodiments of the present invention will be described in detail.

The copper alloy according to the present invention has a composition formula: Pd _a Cu _b X _c
(X: at least one of Al, Ga and In, a: 41-50 at%, b: 1-ac, c: 0.2-2 at%)
It is represented by
A Cu—Pd alloy composed of Cu and Pd has a reduced hydrogen separation rate and strength at a high temperature of 600 ° C. or higher. On the other hand, since the copper alloy according to the present invention has at least one of Al, Ga, and In added to the Cu—Pd alloy as described above, the hydrogen permeability and strength at high temperatures are improved. There is an effect. If at least one of Al, Ga, and In is contained in an alloy composition in an amount of 0.2 at% or more, the effect appears significantly. However, if the ratio of at least one of Al, Ga, and In exceeds 2 at% in the alloy composition, the effect of improving the hydrogen permeability is reduced this time, and in some cases, it deteriorates. Also, pinholes tend to be easily generated in the film. Therefore, in the copper alloy according to the present invention, the ratio of at least one of Al, Ga and In is defined as 0.2 to 2 at%. Further, the ratio of at least one of Al, Ga and In is more preferably 0.5 to 1.2 at%.
The X component is more preferably composed only of Al, and in that case, the proportion of Al is more preferably 0.5 to 2 at%. This is because Al has a higher effect of improving hydrogen permeability at a high temperature (600 ° C. or higher) than Ga and In.

  In a system in which at least one of Pd, Al, Ga and In does not exist, the hydrogen permeability at a high temperature near 600 ° C. tends to be improved when the ratio of Pd to Cu + Pd is set to a concentration of 50 at% or more. However, according to the examination results of the present inventors, in a system containing at least one of Al, Ga and In, the above 41 to 50 at% range obtains a high hydrogen permeability at a high temperature around 600 ° C. From the viewpoint, it is preferable, and when it exceeds 50 at%, the hydrogen permeability tends to decrease. Further, the ratio of Pd is more preferably 42 to 46 at%.

  The copper alloy according to the present invention is composed of Cu, Pd, and at least one of Al, Ga, and In, and does not actively contain other elements, but is inevitably mixed in during the manufacturing process. Since other elements such as impurities may be contained in a very small amount, such a case is also included in the scope of the present invention. The allowable values of other elements cannot be determined in general, but when the hydrogen permeation coefficient is not significantly adversely affected near 600 ° C. (eg, the rate of decrease of the hydrogen permeation coefficient is 5% or less), for example, Cu, Pd , And when it is mixed at a concentration of 0.1 at% or less with respect to the total of at least one of Al, Ga and In, it is considered that there is no significant adverse effect. Other elements include, but are not limited to, Pt, Rh, Ir, Ru, Ni, Co, Ti, Nb, Ta, Ag, B, Y, La, Ce, which are known as additive elements to the hydrogen permeable film. Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

  The β phase of the copper alloy has a very high hydrogen permeability compared to the α phase. Further, if the proportion of the β phase is large in the copper alloy, the strength is improved accordingly. Normally, the β phase in the copper alloy disappears at a high temperature of 600 ° C. or higher, but the Cu—Pd alloy according to the present invention contains at least one of Al, Ga, and In at a predetermined concentration. Even at a high temperature of ℃ or higher, the β phase is present in an amount of 5% or more, and has good hydrogen permeability and strength. The proportion of β phase is preferably 10% or more, and typically 20 to 100%.

  Since stress is continuously applied to the hydrogen permeable membrane at a high temperature, it is required to have a good stress relaxation resistance property at a high temperature. In the copper alloy according to the present invention, the proportion of β phase in the alloy is controlled as described above, and the amount of deformation (elongation ε) after a stress (σ) of 40 MPa is continuously applied at 600 ° C. for 100 hours. ) Is 3 to 25 (%), which is superior in stress relaxation resistance at high temperatures as compared with conventional hydrogen permeable membranes.

  The copper alloy according to the present invention is a Cu—Pd alloy to which a predetermined amount of at least one of Al, Ga, and In is added as described above, and has a hydrogen permeability, strength, and stress relaxation resistance near 600 ° C. of Al, Ga. And at least one of In is significantly higher than when not added. For this reason, it can use especially suitably as a hydrogen permeable membrane used when it is requested | required to isolate | separate hydrogen from hydrogen containing gas in the vicinity of the said temperature and under high pressures, such as 1-2 MPa.

Although the copper alloy which concerns on this invention is not limited, after melt-casting the ingot adjusted to the predetermined component, it can manufacture by repeating annealing and rolling suitably. Specifically, an ingot heated at 800 ° C. or higher is hot-rolled, and after removing the black skin, it is thinned to a predetermined thickness by cold rolling. It has been found that by rolling down the oil film thickness during cold rolling and reducing oil pits, shear deformation is reduced and pinholes are less likely to occur even if the plate thickness is reduced.
The oil film thickness at the time of rolling is represented by the following formula (1).
h = 3η (μ1 + μR) / (pθ) (1)
(H is theoretical oil film thickness (m); η is oil film viscosity [(N / m ² ) s]; μ1 is material speed (m / s); μR is roll peripheral speed (m / s); p is material yield Stress (N / m ² ); θ is the biting angle (rad)
When manufacturing the hydrogen permeable membrane of the present invention, when η, μ1, μR, p, θ is controlled so as to satisfy 0.1 × 10 ⁻⁶ (m) ≦ h ≦ 0.5 × 10 ⁻⁶ (m) It is preferable because shear deformation is reduced and pinholes are hardly generated.
Further, after the heat treatment, the higher the degree of workability during rolling, the higher the strength. Therefore, it is preferable to cold-roll at a workability of 98% or more. Annealing is performed as necessary. It can also be produced by wet plating or sputtering.

  When the copper alloy according to the present invention is used as a hydrogen permeable membrane, the hydrogen permeation amount is inversely proportional to the film thickness, so that the permeation amount per unit area increases as the film thickness decreases. Moreover, since the material to be used is reduced when the film thickness is small even in the same area, it is very effective to reduce the film thickness when used as a hydrogen permeable film. However, if it is too thin, the mechanical strength cannot be maintained, and an impurity gas other than hydrogen reaches the secondary side due to pinholes or the like, so that it is necessary to have a certain thickness or more. On the other hand, if the film thickness is too thick, the amount of hydrogen that reaches the secondary side is reduced and productivity is deteriorated. Therefore, the film thickness is preferably 1 to 200 μm, and more preferably 5 to 50 μm. The film thickness can be adjusted by controlling the rolling reduction during rolling.

  The method for separating hydrogen from a hydrogen-containing gas using the hydrogen-permeable membrane according to the present invention includes a step of passing the hydrogen-containing gas through the hydrogen-permeable membrane. Generally, a method is adopted in which a mixed gas containing hydrogen is disposed on one side (primary side) of the membrane, and the pressure on the primary side is increased relative to the other side (secondary side) of the membrane. . Since the hydrogen permeable membrane according to the present invention is particularly excellent in hydrogen permeability at around 600 ° C., the hydrogen-containing gas preferably passes through the hydrogen permeable membrane at a temperature of 550 to 650 ° C. More preferably, the temperature passes through the hydrogen permeable membrane. In addition, the hydrogen permeable membrane according to the present invention also has good strength. For example, destruction of pinholes and the like can be satisfactorily suppressed by properly setting the support even under a high pressure of 1 to 2 MPa.

  The structure of the steam reformer that separates hydrogen from the hydrogen-containing gas using a hydrogen permeable membrane is known per se, and any known structure can be adopted as the steam reformer according to the present invention. There is no particular limitation. For example, the steam reformer according to the present invention includes a reforming catalyst layer in a gas-permeable porous alumina ceramics reaction tube in which the hydrogen permeable membrane according to the present invention is formed on the inner wall surface, and surrounds the reaction tube. Alternatively, a hydrogen recovery chamber may be provided.

  The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to these examples.

(Example)
Cu-Pd alloy composed of at least one of Cu, Pd, and Al, Ga, and In and adjusted to have a composition satisfying the atomic ratio shown in Table 1 after melting and casting, respectively, 800 ° C. or higher The ingot heated to 1 was hot-rolled, and after removing the black skin, it was cold-rolled into a film having a predetermined thickness. Here, about the rolling work degree, 90% or more was ensured from 1.5 mmt to 20, 25, and 150 μmt.
The film thickness refers to the average value of five locations measured with a micrometer.
The proportion of the β phase of the alloy was measured as follows. First, after degreasing and washing the rolled sample, it was heat-treated at 600 ° C. for 100 h in an Ar atmosphere, and then rapidly cooled to room temperature (water-cooled) to prepare a measurement sample that maintained the structure. Next, the crystal orientation of each sample was determined by EBSP. Specifically, JXA8500F manufactured by JEOL Ltd., acceleration voltage of 20 kV, WD23, current of 5 × 10 ⁻⁸ A, step width of 50 μm × 20 μm from sample tilt angle of 70 ° to sample after cleanup. Measurement was made at a total of 5 locations at 2 μm, the ratio of each body-centered cubic structure (BCC) was determined, and the average was taken as the proportion of β phase.

The hydrogen permeation coefficient was measured for each of the membranes thus obtained in the following manner.
A hydrogen gas cylinder (not shown), a heating furnace 11, a primary-side hydrogen pipe 12, a secondary-side hydrogen pipe 13, and a 1/2 VCR that is arranged in a tubular furnace and connects the primary-side hydrogen pipe and the secondary-side hydrogen pipe ( (Registered trademark) Hydrogen permeable membrane 14 (hydrogen permeable part diameter 11.2 mm) fixed with a gasket with a filter in the joint, a hydrogen measuring device (hydrogen mass flow controller (Yamatake, MQV9050)) connected to the secondary hydrogen pipe ) Was constructed (see FIG. 1). Hydrogen supplied through a pipe from a hydrogen gas cylinder enters the primary side of the VCR joint, passes through the hydrogen permeable membrane, and exits from the secondary side of the VCR joint. The tubular furnace containing the VCR joint to which the hydrogen permeable membrane is fixed can be heated to a predetermined temperature, and the temperature of the VCR joint portion of the hydrogen fixing portion is measured with a thermocouple. In the measurement test, the primary side pressure was set to 0.3 MPaG, the secondary side pressure was set to 0 MPaG, the hydrogen supply amount on the primary side was set to 50 sccm, and the hydrogen permeation amount was measured while supplying hydrogen at 600 ° C. for 24 hours, The hydrogen permeation coefficient q was measured by the following formula.
_{q = f M · d · S} -1 · (P 1/2 -p 1/2) -1
q: Hydrogen permeation coefficient (mol · m ^-1 · sec ^-1 · Pa ^-1/2 )
f _M : secondary hydrogen flow rate (mol · sec ⁻¹ )
d: Film thickness (m)
S: membrane area (m ² )
P: Primary pressure (Pa)
p: Secondary pressure (Pa)
When the amount of permeation increased rapidly during the hydrogen permeation test, the primary side was replaced with He, and it was examined whether leakage occurred on the secondary side. In principle, it is considered that a leak of He on the secondary side of the hydrogen permeable membrane that does not allow the permeation of He has a pinhole in the permeable membrane.

  Furthermore, as an evaluation of the stress relaxation resistance, for Examples 1, 4, 7, 12, and 15, the amount of deformation (elongation ε) after continuously applying a stress (σ) of 40 MPa at 600 ° C. for 100 hours. Was measured.

(Comparative example)
Cu—Pd alloy, or Cu— that is a copper alloy composed of Cu, Pd, and at least one of Al, Ga, and In, whose components are adjusted to have a composition that satisfies the atomic ratios shown in Table 1. For the Pd alloy, ingots heated to 800 ° C. or higher were hot-rolled after melting and casting, respectively, and after the black skin was removed, the Pd alloy was cold-rolled into a film having a predetermined thickness.
The film thickness refers to the average value of five locations measured with a micrometer.
The proportion of the β phase of the alloy was measured using EBSP.

For each of the films thus obtained, the hydrogen permeation coefficient q was measured using the measurement system shown in FIG.
The presence / absence of a pinhole was also judged in the same manner (without pinhole: ○, with pinhole: ×).
For Comparative Examples 1 and 2, the stress relaxation resistance was similarly evaluated.

  The test results are shown in Table 1.

(Evaluation results)
Examples 1 to 19 all had a good hydrogen permeability coefficient (good hydrogen permeability), and no pinholes were generated.
Further, in Examples 1, 4, 7, 12, and 15, the amount of deformation (elongation ε) after applying a stress (σ) of 40 MPa at 600 ° C. for 100 hours is small, and the stress relaxation resistance is low. It was found to be good.
Comparative Examples 1, 5, and 6 do not contain any of Al, Ga, and In in the film, the ratio of β phase at 600 ° C. is less than 5%, and both the hydrogen permeability and strength are poor. Met. Further, in Comparative Example 1, it was found that the amount of deformation (elongation ε) after the stress (σ) of 40 MPa was continuously applied for 100 hours was large, and the stress relaxation resistance was poor.
Comparative Examples 2, 3, 4, 11, and 12 had poor strength because the concentrations of Al, Ga, and In were high.
In Comparative Examples 7 and 9, the hydrogen permeability was poor because the concentration of Pd in the film was less than 41 at%.
In Comparative Examples 8 and 10, the hydrogen permeability was poor because the Pd concentration in the film was more than 50 at%.

11 Heating furnace 12 Primary side hydrogen piping 13 Secondary side hydrogen piping 14 Hydrogen permeable membrane

Claims (6)

Composition formula: Pd _a Cu _b X _c
(X: at least one of Al, Ga and In, a: 41-50 at%, b: 1-ac, c: 0.2-2 at%)
Represented by
A hydrogen-permeable copper alloy having a β-phase ratio of 5% or more at 600 ° C.   The hydrogen permeable copper alloy according to claim 1, wherein X is Al and c is 0.5 to 2 at%.   A hydrogen-permeable copper alloy in which the proportion of the β phase at 600 ° C. is 10% or more.   A hydrogen permeable membrane made of the copper alloy according to claim 1.   The hydrogen permeable membrane according to claim 4, having a thickness of 1 to 200 μm.   A steam reformer using the hydrogen permeable membrane according to claim 4 or 5.

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