Hydrogen separation membrane and method for separating hydrogen

US 8 728 199B2

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Provided is a novel hydrogen separation membrane formed of a NbWMo-based alloy. A method for separating hydrogen using the hydrogen separation membrane and hydrogen separation conditions are selected by a particular procedure. A hydrogen separation membrane formed of the NbWMo-based alloy membrane. A method for separating hydrogen using the NbWMo-based alloy membrane and the conditions for separating hydrogen using the NbWMo-based alloy membrane are set by measuring the hydrogen pressure P of a hydrogen atmosphere for the NbWMo-based alloy membrane and the dissolved hydrogen content C of the NbWMo-based alloy membrane at a temperature T; generating a PCT curve associating the temperature T, the hydrogen pressure P, and the dissolved hydrogen content C on the basis of actual measurement data about the three requirements; and setting operating temperature and primary and secondary hydrogen pressure conditions by determining the relationship between the dissolved hydrogen content C and the brittle fracture of the NbWMo-based alloy membrane on the basis of the PCT curve to evaluate critical dissolved hydrogen content related to hydrogen embrittlement resistance.

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Claims

1. A hydrogen separation membrane, comprising:
a NbWMo alloy membrane containing Nb, W, and Mo,
wherein the alloy comprises 5 to 15 mol % of W and 5 to 15 mol % of Mo, and the balance comprises Nb.

Show 3 dependent claims

5. A method for setting conditions for separating hydrogen from a hydrogen-containing gas using a hydrogen separation membrane comprising a NbWMo alloy membrane, comprising the steps of:
measuring a hydrogen pressure P of a hydrogen atmosphere for the NbWMo alloy membrane and a dissolved hydrogen content C of the NbWMo alloy membrane at a temperature T;
generating a PCT curve associating the temperature T, the hydrogen pressure P, and the dissolved hydrogen content C on the basis of actual measurement data of the temperature, the pressure and the content; and
setting an operating temperature of the hydrogen separation membrane comprising the NbWMo alloy membrane and primary and secondary hydrogen pressure conditions by determining a relationship between the dissolved hydrogen content C and a brittle fracture of the NbWMo alloy membrane on the basis of the PCT curve to evaluate critical dissolved hydrogen content related to hydrogen embrittlement resistance,
wherein the alloy comprises 5 to 15 mol % of W and 5 to 15 mol % of Mo, and the balance comprises Nb.

Show 3 dependent claims

Description

FIELD OF INVENTION

The present invention relates to a hydrogen separation membrane formed of NbWMo-based alloy membrane and having superior hydrogen permeation performance and hydrogen embrittlement resistance, a method for separating hydrogen using the hydrogen separation membrane, and a method for setting conditions for separating hydrogen using the hydrogen separation membrane.

BACKGROUND OF INVENTION

There are known hydrogen separation membranes for separating hydrogen from a hydrogen-containing gas by selective permeation. Materials for forming a hydrogen separation membrane include various materials such as various metals, alloys, and ceramics and molecular sieve carbon, a typical example of which is Pd-based alloys (Patent Document 1). A hydrogen separation membrane formed of Pd-based alloy, however, shows only two to three times higher hydrogen separation performance even if a rare earth element, such as Y or Gd, having a great performance-improving effect is added and also has a disadvantage of high cost because Pd itself is a precious metal.

As an alternative to Pd-based alloy membranes, Patent Document 2 discloses a Nb-based-alloy hydrogen separation membrane mainly containing Nb and alloyed with one or more elements selected from the group consisting of V, Ta, Ni, Ti, Mo, and Zr. Patent Document 3 discloses, as a hydrogen separation membrane formed of a Nb alloy, a hydrogen separation membrane formed of a Nb alloy containing 5% to 25% by mass of at least one element selected from the group consisting of Pd, Ru, Re, Pt, Au, and Rh. Patent Document 4 discloses that a Nb foil covered with a Pd membrane on each side has the largest amount of hydrogen permeated as compared with Ta and V foils similarly covered with a Pd membrane on each side.

Patent Document 2 discloses a Nb-based-alloy hydrogen separation membrane formed of an alloy of Nb with one or more of the six elements including V, Ta, Ni, Ti, Mo, and Zr, and Patent Document 3 discloses a hydrogen separation membrane formed of an alloy of Nb with one or more of the six elements including Pd, Ru, Re, Pt, Au, and Rh, although they do not disclose that an alloy membrane of Nb and W or an alloy membrane of Nb, W, and Ta is effective as a hydrogen separation membrane.

Patent Document 1: U.S. Pat. No. 2,773,561

Patent Document 2: Japanese Unexamined Patent Application Publication No. 2000-159503

Patent Document 3: Japanese Unexamined Patent Application Publication No. 2002-206135

Patent Document 4: U.S. Pat. No. 3,350,846

OBJECT AND SUMMARY OF INVENTION
Object of Invention

An object of the present invention is to provide a hydrogen separation membrane formed of a NbWMo-based alloy membrane, a method for separating hydrogen using a hydrogen separation membrane formed of a NbWMo-based alloy membrane, and a method for setting conditions for separating hydrogen using a hydrogen separation membrane formed of a NbWMo-based alloy membrane.

SUMMARY OF INVENTION

A first aspect of the present invention provides a hydrogen separation membrane which is formed of a NbWMo alloy membrane containing Nb alloyed with W and Mo.

A second aspect of the present invention provides a method for selectively separating hydrogen from a hydrogen-containing gas using a hydrogen separation membrane formed of a NbWMo alloy membrane containing Nb alloyed with W and Mo.

A third aspect of the present invention provides a method for selectively separating hydrogen from a hydrogen-containing gas using a hydrogen separation membrane formed of a NbWMo alloy membrane containing Nb alloyed with W and Mo, which includes the steps of:

measuring a hydrogen pressure P of a hydrogen atmosphere for the NbWMo alloy membrane and a dissolved hydrogen content C of the NbWMo alloy membrane at a temperature T;

generating a PCT curve associating the temperature T, the hydrogen pressure P, and the dissolved hydrogen content C on the basis of actual measurement data of the temperature, the pressure and the content;

setting an operating temperature of the hydrogen separation membrane and primary and secondary hydrogen pressure conditions by determining a relationship between the dissolved hydrogen content C and a brittle fracture of the NbWMo alloy membrane on the basis of the PCT curve to evaluate critical dissolved hydrogen content related to hydrogen embrittlement resistance; and

separating hydrogen from the hydrogen-containing gas using the NbWMo alloy membrane under the set conditions.

A fourth aspect of the present invention provides a method for setting conditions for separating hydrogen from a hydrogen-containing gas using a hydrogen separation membrane formed of a NbWMo alloy membrane, which includes the steps of:

measuring a hydrogen pressure P of a hydrogen atmosphere for the NbWMo alloy membrane and a dissolved hydrogen content C of the NbWMo alloy membrane at a temperature T;

generating a PCT curve associating the temperature T, the hydrogen pressure P, and the dissolved hydrogen content C on the basis of actual measurement data of the temperature, the pressure and the content; and

setting an operating temperature of the hydrogen separation membrane formed of the NbWMo alloy membrane and primary and secondary hydrogen pressure conditions by determining a relationship between the dissolved hydrogen content C and the brittle fracture of the NbWMo alloy membrane on the basis of the PCT curve to evaluate critical dissolved hydrogen content related to hydrogen embrittlement resistance.

Advantageous Effects of Invention

The present invention provides the following effects a) to e):

a) The hydrogen separation membrane formed of the NbWMo alloy membrane can be used as a separation membrane for selective hydrogen permeation at high pressure.

b) The hydrogen separation membrane formed of the NbWMo alloy membrane has high strength and good hydrogen permeation performance.

c) The NbWMo alloy membrane is useful in practical use because it is inexpensive.

d) The operating conditions of the hydrogen separation membrane formed of the NbWMo alloy membrane, including the operating temperature and the primary and secondary hydrogen pressure conditions, can be optimized using the PCT curve.

e) Because the operating conditions of the hydrogen separation membrane formed of the NbWMo alloy membrane can be optimized using the PCT (pressure-dissolved hydrogen content-temperature) curve, the range of hydrogen separation from a hydrogen-containing gas using the hydrogen separation membrane can be extended.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a longitudinal sectional view illustrating the structure of a small punch test apparatus and the method for operating the apparatus.

FIG. 2 is an enlarged view of a portion of the apparatus in FIG. 1 around a membrane sample.

FIG. 3 is a plot of the relationship between the hydrogen pressure P of an atmosphere and dissolved hydrogen content C at a temperature of 500° C. for Nb-based alloy membranes.

FIG. 4 is a plot of the relationship between the hydrogen pressure P of an atmosphere and dissolved hydrogen content C at a temperature of 400° C. for Nb-based alloy membranes.

FIG. 5 is a graph showing the relationship between the equilibrium hydrogen pressure and Mo content of NbWMo alloys.

FIG. 6 is a plot of the relationship between the hydrogen pressure P of an atmosphere and dissolved hydrogen content C at temperatures of 500° C., 450° C., and 400° C. for a Nb-5 mol % W-5 mol % Mo alloy membrane.

FIG. 7 is a graph showing the deformability (load-deflection curve) of pure Nb, a Nb-5 mol % W alloy, and a Nb-5 mol % W-5 mol % Mo alloy determined by a small punch test.

FIG. 8 is a graph showing the test conditions and results of a hydrogen permeation test at 500° C. for Pd-26 mol % Ag alloy, Nb-5 mol % W alloy, and Nb-5 mol % W-5 mol % Mo alloy.

FIG. 9 is a graph showing the test conditions and results of a hydrogen permeation test at 450° C. for Nb-5 mol % W-5 mol % Mo alloy.

FIG. 10 is a graph showing the test conditions and results of a hydrogen permeation test at 400° C. for Pd-26 mol % Ag alloy and Nb-5 mol % W-5 mol % Mo alloy.

DESCRIPTION OF EMBODIMENTS

The present invention, including the process of achieving the present invention, will now be detailed.

To increase the permeation rate of hydrogen through a hydrogen separation membrane based on alloys such as Pd-based alloys, the dissolved hydrogen content of the membrane material and the diffusion rate of hydrogen need to be increased. It is known, however, that a high hydrogen dissolution may result in significant hydrogen embrittlement, depending on the type of membrane material. To achieve a membrane material having both high hydrogen permeation rate and hydrogen embrittlement resistance, therefore, it is necessary to examine and grasp the conditions for avoiding embrittlement due to hydrogen as well as to ensure a sufficient hydrogen dissolution of the membrane material.

Nb has a higher hydrogen permeability coefficient than Pd-based alloys such as PdAg alloy, although it is believed that it is difficult to use a Nb-based alloy as a hydrogen separation membrane because hydrogen embrittlement occurs. As disclosed in Patent Documents 2 and 3, for example, a method for inhibiting hydrogen embrittlement by addition of alloying element has been proposed, although there is no proposal as to the conditions where a Nb-based alloy can be used without causing embrittlement by addition of other element.

For Nb alloys, it is difficult to ensure both hydrogen embrittlement resistance and high hydrogen permeation rate, which is industrially important, simply by achieving high solubility or hydrogen permeability coefficient Φ by simple condition setting or control, such as by specifying the percentage of material added (as often seen in the claims section of patent literature); it is necessary to select an appropriate operating temperature and operating pressure (on the primary and secondary sides) in addition to an appropriate type and amount of material added.

The inventors have developed a technique of determining the optimum conditions for achieving a high hydrogen concentration difference between primary and secondary sides of the membrane using a PCT curve (pressure-composition-temperature curve) while reducing the dissolved hydrogen content by adding another component and have found that that a Nb-based alloy shows ductility in the range of H/M=0.2 or less and can be used at low dissolved hydrogen concentration.

The performance of a hydrogen separation membrane based on an alloy such as a Pd alloy has conventionally been evaluated using the hydrogen permeability coefficient Φ alone. For Nb alloys, however, the dissolution reaction of hydrogen does not follow Sievert's law (C=K×P1/2); in this case, it is inappropriate to evaluate the hydrogen permeability using the hydrogen permeability coefficient Φ (=DK).

The hydrogen permeability coefficient Φ is proportional to the hydrogen permeation rate J as far as Sievert's law holds; however, Patent Document 2 describes the relationship as hydrogen permeability coefficient Φ=hydrogen permeation performance, and Patent Document 3 only discloses that the hydrogen solubility increased as compared with PdAg alloy, which does not necessarily contribute to an increased hydrogen permeation rate J, which is industrially important.

According to the present invention, however, it has turned out that the hydrogen embrittlement resistance of a NbWMo alloy membrane can be improved by reducing the dissolved hydrogen content within the operating temperature range of the hydrogen separation membrane.

The NbWMo alloy membrane of the present invention preferably has the following composition:

W: 30 mol % or less, particularly 0.1 to 30 mol %, more particularly 5 to 15 mol %

Mo: 30 mol % or less, particularly 0.1 to 30 mol %, more particularly 5 to 15 mol %

Nb: balance

where the total content of Nb, W, and Mo is 100 mol %. W is preferably added in an amount of 30 mol % or less, particularly 0.1 to 30 mol %, which improves the hydrogen embrittlement resistance as compared with a membrane formed of pure Nb. Mo is preferably added in an amount of 30 mol % or less, particularly 0.1 to 30 mol %, which improves the hydrogen embrittlement resistance as compared with a membrane formed of NbW. The NbWMo alloy membrane of the present invention may contain incidental impurities such as Ta.

This application is based on Japanese Patent Application No. 2009-212357 filed on Sep. 14, 2009, the entire contents of which are incorporated herein by reference.

Citations

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US 2008 284,337 A1 - Ceramic Metal Halide Discharge Lamp
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US 2007 248,874 A1 - Hydrogen Separation Membrane and Fuel Cell, and Manufacturing Method Therefor
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US 2013 243,660 A1 - SEPARATION MEMBRANE, HYDROGEN SEPARATION MEMBRANE INCLUDING THE SEPARATION MEMBRANE, AND DEVICE INCLUDING THE HYDROGEN SEPARATION MEMBRANE
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