WO2015005649A1

WO2015005649A1 - Separation membrane, hydrogen separation membrane including separation membrane, and device including hydrogen separation membrane

Info

Publication number: WO2015005649A1
Application number: PCT/KR2014/006115
Authority: WO
Inventors: Kwang Hee Kim; Hyeon Cheol Park; Kyoung-Seok Moon; Jae-Ho Lee; Keunwoo CHO; Eun Seog Cho
Original assignee: Samsung Electronics Co., Ltd.
Priority date: 2013-07-08
Filing date: 2014-07-08
Publication date: 2015-01-15
Also published as: KR20150007364A

Abstract

A separation membrane including an alloy of a Group 5 element, a transition metal being capable of forming a body-centered cubic (bcc) structure with the Group 5 element, and a metal having hydrogen dissociation capability, wherein the alloy has a crystalline bcc structure, a hydrogen separation membrane including the separation membrane, and a hydrogen separation device including the hydrogen separation membrane are disclosed.

Description

[DESCRIPTION]

[Invention Title]

SEPARATION MEMBRANE, HYDROGEN SEPARATION MEMBRANE INCLUDING SEPARATION MEMBRANE, AND DEVICE INCLUDING HYDROGEN SEPARATION MEMBRANE

[Technical Field]

A separation membrane, a hydrogen separation membrane including the same, and a hydrogen separation device including the hydrogen separation membrane are disclosed.

[Background Art]

Recently, hydrogen has been in the spotlight as a clean energy source. As a separation membrane for selectively separating hydrogen from hydrogen- containing gases, various metal/metal alloys, silica/zeolite ceramics, metal ceramic composites (cermet), carbon-based polymer separation membranes, and the like are known. Among them, representatively, a Pd-based alloy separation membrane is commercially used (Chemical Reviews, 107, 4078- 4110, 2007). However, in the case of a Pd-based alloy, Pd itself is a noble metal and is expensive, and hydrogen separation performance of the alloy is improved by only about 2 to 3 times. Representative Pd-based alloys include Pd-Ag23, Pd-Cu40, and the like (Platinum Metals Rev., 21 , 44-50, 1977).

Accordingly, there is increasing demand for a hydrogen separation membrane that has excellent hydrogen permeability that is similar to a Pd- based metal and has a competitive price. [Disclosure]

[Technical Problem]

One embodiment of the present invention provides a separation membrane having excellent hydrogen permeability without an additional catalyst layer, being capable of suppressing hydrogen embrittlement fractures, and being manufactured at a low cost.

Another embodiment of the present invention provides a hydrogen separation membrane including the separation membrane.

Yet another embodiment of the present invention provides a hydrogen separation device including the hydrogen separation membrane.

[Technical Solution]

According to one embodiment, a separation membrane includes an alloy of a Group 5 element, a transition metal being capable of forming a body- centered cubic (bcc) structure with the Group 5 element, and a metal having hydrogen dissociation capability, wherein the alloy has a crystalline structure of a body-centered cubic (bcc) structure.

The Group 5 element may include V (vanadium), Nb (niobium), or Ta (tantalum).

The transition metal being capable of forming a body-centered cubic (bcc) structure with the Group 5 element may be one of Ti (titanium), Zr (zirconium), and Hf (hafnium).

The metal having hydrogen dissociation capability may be Pd (palladium), Pt (platinum), Ni (nickel), or Fe (iron). The alloy may include about 10 atom% to about 59 atom% of the Group 5 element, about 40 atom% to about 89 atom% of the transition metal being capable of forming a bcc structure with the Group 5 element, and about 1 atom% to about 40 atom% of the metal having hydrogen dissociation capability.

The separation membrane including the alloy may have a non-porous dense layer structure having porosity of less than about 1 volume%.

The separation membrane may have a non-porous dense layer structure having porosity of about 0 volume%.

The separation membrane may have a thickness of about 5 to about 1000 pm.

For example, the Group 5 element may be Nb, the transition metal may be Ti, and the metal having hydrogen dissociation capability may be Pd.

According to another embodiment of the present invention, a hydrogen separation membrane including the separation membrane is provided.

The hydrogen separation membrane may have hydrogen solubility (a mole ratio of H/M, wherein H denotes hydrogen atoms and M denotes alloy atoms) of about 0.05 to about 0.25, measured under conditions of about a 0.1 to about 1 MPa hydrogen pressure and at about 300 °C to about 500 °C.

The hydrogen separation membrane may have hydrogen solubility (a mole ratio of H/M, wherein H denotes hydrogen atoms and M denotes alloy atoms) of about 0.1 to about 0.2, measured under conditions of about a 0.7 to about 1 MPa hydrogen pressure and at about 400 °C.

The hydrogen separation membrane may have hydrogen permeability of about 1.0 x 10^"° to about 1.0 x 10^"7 mol/m*s*Pa^1/2 at about 300 °C to about 500 °C.

The hydrogen separation membrane may not include a catalyst layer on the separation membrane.

According to another embodiment of the present invention, a hydrogen separation device includes the hydrogen separation membrane according to the embodiment, a chamber equipped with a supplier for a mixed gas including hydrogen gas, and a discharge chamber equipped with a discharger for separated hydrogen gas, wherein the hydrogen separation membrane is disposed between the chamber, and the discharge chamber.

In one embodiment, the hydrogen separation membrane may be formed in a tubular shape, a cylindrical chamber barrier rib having a larger diameter than that of the tubular hydrogen separation membrane may be formed at the outside of the hydrogen separation membrane, a space between the chamber barrier rib and the hydrogen separation membrane may be formed as the chamber, and the inside of the tubular hydrogen separation membrane may be formed as the discharge chamber where hydrogen is discharged.

[Advantageous Effects]

The separation membrane according to an embodiment does not include any additional catalytic layer, thus, any additional process for preparing an additional catalystic layer is not required, which leads to the cost effectiveness. Further, the separation membrane does not suffer from performance deterioration or hydrogen embrittlement fracture due to the intermetallic layer resulting from the mutual diffusion of the metals in the catalystic layer and the separation layer. .

[Description of Drawings]

FIG. 1 is a schematic view showing a crystalline lattice of an alloy included in a separation membrane according to one embodiment of the present invention.

FIG. 2 is a schematic view showing a mechanism through which hydrogen gas is separated with a conventional separation membrane including a catalyst layer in both surfaces of the separation membrane.

FIG. 3 is a schematic view showing a mechanism through which hydrogen gas is separated with a separation membrane including no catalyst layer according to one embodiment of the present invention.

FIG. 4 is a schematic view showing a hydrogen separation device according to one embodiment.

FIG. 5 is a schematic view showing a hydrogen separation device including a tubular shape separation membrane according to another embodiment of the present invention.

FIG. 6 is an XRD analysis graph showing a crystalline structure of a pure Nb membrane, a pure Ti membrane, and a membrane including an alloy of Nb and Ti in different ratios.

FIG. 7 is a XRD analysis graph showing a crystalline structure of a pure Nb membrane, a membrane of an alloy of 40 atom% of Nb and 60 atom% of Ti, and a membrane of an alloy of Ti, Nb, and Pd.

FIG. 8 is a graph showing Vickers hardness of an alloy in which Ti is added to Nb in different contents.

FIG. 9 is a graph showing an elasticity coefficient (Young's modulus) when V (a), Nb (b), Ta (c), Mo (d), and W (e) are added to Ti in different ratios, respectively.

FIG. 10 is a graph showing Vickers hardness of an alloy in which Pd is added in different contents to pure Nb, or to an alloy of Ti and Nb in different ratios.

FIG. 11 is a photograph showing results of examining whether pure Nb, an alloy of Nb-Ti^'20 (Nb 80 atom% + Ti 20 atom%), or Nb-Ti40 (Nb 60 atom% + Ti 40 atom%) is cracked or not under a hydrogen pressure condition.

FIG. 12 shows the results of hydrogen permeability when the surface is not polished without coating Pd on the pure V membrane. Herein, the upper graph shows a pressure change at the back end of a separation membrane, and the lower graph shows hydrogen flow at the back end of the separation membrane.

FIG. 13 shows the results of hydrogen permeability when the surface is polished without coating Pd on the V-Pd10 alloy. Herein, the upper graph shows a temperature change at the top and bottom of a separation membrane, and the lower graph shows a pressure change at the back end of the separation membrane. FIG. 14 is a graph showing the results of hydrogen permeability when the surface is not polished without coating Pd on the TiNb40 alloy. Herein, the upper graph shows a temperature change at the front and back ends of a separation membrane, and the lower graph shows a pressure change at the back end of the separation membrane.

FIG. 15 is a graph showing the results of hydrogen permeability when · the surface is polished without coating Pd on the TiNb40 alloy. Herein, the upper graph shows a temperature change at the front and back ends of a separation membrane, and the lower graph shows a pressure change at the back end of the separation membrane.

FIG. 16 is a graph showing the results of temperature change (a), pressure change (b), and hydrogen flow (c) at the front and back ends of a membrane when the membrane of TiNb40 alloy coated with Pd having a thickness of 10 nm receives pressure from hydrogen.

FIG. 17A and FIG. 17B show the results of measuring hydrogen permeability of a Ti-Nb36-Pd10 alloy.

FIG. 17A is a graph showing a temperature change (upper) and the pressure change (lower) of a TiNb36Pd10 membrane at the front end and the back end of a membrane.

FIG. 17B is a graph enlarging the temperature change and the pressure change at the front and back ends of the membrane from the rectangle-marked region in the lower graph of FIG. 17A.

FIG. 18 is a graph showing the results of hydrogen embrittlement fractures when cooling a separation membrane of a Ti-Nb36-Pd10 alloy.

FIG. 19 shows photographs of the results of hydrogen embrittlement fractures when cooling a separation membrane sample of a Ti-Nb36-Pd10 alloy.

[Best Mode]

This disclosure will be described more fully hereinafter in the following detailed description, in which some but not all embodiments of this disclosure are described. However, this disclosure may be embodied in many different forms and is not construed as limited to the exemplary embodiments set forth herein.

As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of this disclosure. The size and thickness of each constituent element as shown in the drawings are randomly indicated for better understanding and ease of description, and this disclosure is not necessarily limited to as shown. The size and thickness of each constituent element as shown in the drawings are exaggeratedly indicated for better understanding and ease of description, and this disclosure is not necessarily limited to as shown.

The Group 5 element may include V (vanadium), Nb (niobium), or Ta

(tantalum).

The transition metal being capable of forming a body-centered cubic (bcc) structure with the Group 5 element may be one of Ti (titanium), Zr (zirconium), or Hf (hafnium).

The metal having hydrogen dissociation capability may be Pd

(palladium), Pt (platinum), Ni (nickel), or Fe (iron).

Recently, as candidates for substituting for the separation membrane of a Pd-based alloy, Group 5 metals (vanadium (V), niobium (Nb), and tantalum (Ta)) have been actively researched. These Group 5 metals have higher affinity for hydrogen than Pd so have excellent hydrogen-containing properties, and the Group 5 metals generally have excellent hydrogen diffusion characteristics through a small lattice of the body-centered cubic structure to provide higher hydrogen permeation performance of about 10-100 times that of Pd (J. Membr. Sci., 362, 12-28 (2010)). However, these Group 5 metals have no hydrogen dissociation characteristics by themselves, so one surface or both surfaces need to be coated with a Pd catalyst layer having a thickness of about 100-500 nm. In this case, for providing the catalyst layer, a sputter deposition or liquid deposition process is required on the separation membrane, so the cost of the separation membrane is increased.

One embodiment of the present invention provides a separation membrane that does not require a Pd catalyst layer.

For this, the separation membrane according to one embodiment may be accomplished by alloying a metal capable of suppressing hydrogen embrittlement fractures of the Group 5 element while forming the body-centered cubic (bcc) crystalline structure with the Group 5 element and a metal having hydrogen dissociation capability to provide the separation membrane itself with the hydrogen dissociation capability while having no catalyst layer, based on a metal of the Group 5 element having bcc structure, so as to provide the alloy with the bcc crystalline structure .

Specifically, when the Group 5 element includes V, Nb, or Ta, an element capable of forming the bcc crystalline structure together with the Group 5 metal may be selected from Ti, Zr, or Hf. The Ti, Zr, or Hf may form the bcc crystalline structure by itself, or may form the bcc structure together with the Group 5 element. In this case, it is assumed that a more stable bcc crystalline structure may be formed when using a Group 5 metal along with Ti, Zr, or Hf, having a similar crystalline lattice size to that of the Group 5 metal.

On the other hand, it is confirmed that Ti, Zr, and Hf have a characteristic of maintaining alloy ductility when alloyed with other metals.

Since Group 5 elements have the bcc crystalline structure they have high affinity for hydrogen, but the hydrogen affinity is too high to prevent the hydrogen embrittlement fractures due to hydrogen solidification.

In order to solve this problem, it is required to maintain the alloy ductility.

It is known that the hydrogen embrittlement fractures more easily occur as the metal hardness is increased, and that the hardness and the ductility generally have an inversely proportional relationship. Accordingly, it is understood that the hydrogen embrittlement fractures are suppressed when the ductility is maintained by decreasing the alloy hardness.

As understood from the following examples, when adding Ti to the Group 5 metals at greater than or equal to a predetermined content, the alloy hardness is decreased and the ductility is further increased. In addition, the alloy of the Group 5 metal and Ti maintains the bcc crystalline structure in all composition ratios.

On the other hand, even if maintaining the bcc crystalline structure and the ductility for suppressing the hydrogen embrittlement fractures, it is understood that the hydrogen permeability is not obtained when not adding a metal having hydrogen dissociation capability.

Accordingly, the separation membrane according to one embodiment requires a metal capable of maintaining the hydrogen permeability and suppressing the hydrogen embrittlement fractures and also having the hydrogen dissociation capability, wherein the metal may be one such as Pd, Pt, Ni, and Fe which is mainly used as a catalyst layer in the conventional separation membrane.

As mentioned above, the alloy for the separation membrane may include a metal capable of maintaining the alloy ductility by being alloyed with the Group 5 element at greater than or equal to the predetermined content, for example, the alloy may. include Ti, Zr, or Hf at greater than or equal to about 40 atom%, specifically, at greater than or equal to about 50 atom%, and more specifically, at greater than or equal to about 60 atom%.

On the other hand, the metal having the hydrogen dissociation capability may be included in the alloy in a sufficient amount to provide the hydrogen dissociation capability, and for example, the metal may be included at greater than or equal to about 1 atom%, specifically, at greater than or equal to about 3 atom%, more specifically, at greater than or equal to about 5 atom%, and even more specifically, at greater than or equal to about 8 atom%.

The metal having the hydrogen dissociation capability is generally an expensive metal such as Pd, so the metal may be included in a content sufficient to provide an appropriate hydrogen separating property by being included in the alloy, for example, the metal may be included at less than or equal to about 20 atom%, specifically, at less than or equal to about 15 atom%, and more specifically, at less than or equal to about 10 atom% considering the economical aspect. The Group 5 element may be included in the alloy in the remaining content after adjusting the contents of the metal capable of maintaining the bcc crystalline structure together with the Group 5 element and also maintaining the alloy ductility and the metal having the hydrogen dissociation capability within the range. Generally, the elements such as Ti, Zr, and Hf are cheaper than Group 5 elements, so the elements may be included in a higher amount than the Group 5 element. Even though these elements are included at greater than or equal to about 80 atom%, for example, at greater than or equal to about 85 atom%, and specifically, up to about 89 atom%, these elements may not be harmful to the hydrogen permeability of the Group 5 element and maintain the alloy ductility to suppress the hydrogen embrittlement fractures.

Accordingly, a separation membrane according to the embodiment includes an alloy that includes about 10 atom% to about 59 atom% of the Group 5 element, about 40 atom% to about 89 atom% of the transition metal being capable of forming a bcc structure with the Group 5 element, and about 1 atom% to about 40 atom% of the metal having hydrogen dissociation capability.

In an exemplary embodiment, the separation membrane may include an alloy of Nb, Ti, and Pd.

The separation membrane including the alloy of Nb, Ti, and Pd shows excellent hydrogen permeability even when having a monolayer structure including no additional Pd catalyst layer, and also the separation membrane is not cracked during a hydrogen embrittlement fracture test according to cooling the same after a hydrogen separation process at a high temperature, so it is understood that the hydrogen embrittlement fractures do not occur. In the case of the alloy, particularly, Nb and Ti have similar lattice sizes, so it is assumed that the bcc crystalline structure is more easily formed to further improve the hydrogen permeability.

On the other hand, Nb and Ti have too high affinity for hydrogen to prevent the fractures of the separation membrane when applying hydrogen pressure at about 7 bar for only about 5 minutes when alloying only Nb and Ti and coating the additional Pd catalyst layer as in the conventional case.

Accordingly, by providing an alloy including Nb, Ti, and Pd in the content ratio according to another embodiment of the present invention, the obtained separation membrane may suppress the hydrogen embrittlement fractures and accomplish excellent hydrogen permeability and reduce the number of processes and the cost by omitting the additional catalyst layer.

The alloy may include the bcc crystalline structure at greater than or equal to about 80 %, for example, at greater than or equal to about 85 %, and specifically, at greater than or equal to about 90 %.

From XRD (X-ray diffraction) results, it is understood that the obtained alloy maintains the bcc structure when the elements are included in the content ratio. In other words, as shown in FIG. 6 and FIG. 7, it is understood that the alloy of Nb and Ti or the alloy including Nb, Ti, and Pd shows the bcc crystalline structure in all composition ranges as in pure Ti and pure Nb.

Thereby, it is understood that these alloys maintain the bcc crystal structure and also maintain the ductility, so as to provide excellent hydrogen permeability and provide resistance to the hydrogen embrittlement fractures.

The separation membrane may have a thickness of about 5 to about 1000 pm.

The hydrogen separation membrane is a separation membrane that selectively separates only hydrogen gas from a gas mixture containing hydrogen gas, and it has high hydrogen permeability because it has a crystalline structure of a body-centered cubic structure, which may easily diffuse hydrogen. As the result, the hydrogen separation membrane may separate hydrogen with high purity. A separation membrane having a crystalline structure of a high degree of greater than or equal to about 80 volume% of the alloy may be useful as a hydrogen separation membrane.

The hydrogen separation membrane may be applied in a technical field for selectively permeating and separating only H₂ gas among a gas including H2, CO2, and CO, which is produced through steam reforming, coal gasification, WGS (water gas shift) reaction, and the like. For example, it may be applied for a high purity hydrogen generator, a hydrogen regenerator for a fuel cell, a separation membrane for hydrogen separation of a mixed gas for a gasification combined thermal power plant, a separation membrane for H2/CO2 separation, and the like.

The separated hydrogen may be used for electric power generation by combustion of clean energy source hydrogen, or it may be used as a chemical raw material (NH₄, olefin, and the like) or for purification of petroleum. Meanwhile, since remaining gas after hydrogen removal includes a CO₂ component at a high concentration, the CO₂ rich gas may be selectively collected and stored for use.

As shown in FIG. 2, a conventional hydrogen separation membrane 11 adsorbs hydrogen gas (H₂) first among various gases including hydrogen, the adsorbed hydrogen gas (H₂) is dissociated into hydrogen atoms (H) on the surface 12 of the hydrogen separation membrane, and the dissociated hydrogen atoms (H) are permeated through the separation membrane 1 . The hydrogen atoms (H) are dissolved and diffused through the tetrahedral or octahedral interstitial sites of the bcc unit cells of the separation membrane, thus achieving permeation (M.D. Dolan, J. Membr. Sci. 362, 12-28, 2010). The hydrogen atoms (H) permeated through the membrane are recombined again to form hydrogen gas (H₂), which is then desorbed from the hydrogen separation membrane and separated.

FIG. 1 is a schematic view showing the crystalline lattice of a body- centered cubic structure that may be formed when the separation membrane is formed of the alloy of the Group 5 element (Nb) 2, Ti atoms 1 , and Pd atoms 3 according to one embodiment of the present invention.

As shown in FIG. 1 , the three components may form a crystalline structure of a body-centered cubic structure together. The body-centered cubic structure may secure many tetrahedral or octahedral spaces, which are favorable for dissolution or diffusion of hydrogen atoms (H), and increase hydrogen permeability.

In the separation membrane, the Group 5 element, and Ti, Zr, or Hf, form a body-centered cubic structure, and it is required to properly maintain the body-centered cubic structure while alloying. Further, these elements may maintain a lattice constant similar to the lattice constant of the body-centered cubic structure of a pure Group 5 element. Accordingly, for example, in the separation membrane, a body-centered cubic structure of the 3-component alloy may have a lattice constant of about 3.2 to about 3.4 A, which is similar to those of pure Nb and bcc beta-titanium.

The separation membrane including the alloy may have a non-porous dense layer structure having porosity of less than about 1 volume% to about 0 volume%. Thus, it is formed as a dense layer structure to selectively permeate and separate only a material to be separated. If the separation membrane is applied to a hydrogen separation membrane, it is formed as a dense layer structure so as to pass decomposed hydrogen atoms through the metal interstitial sites and selectively separate hydrogen.

As the thickness of the separation membrane becomes thinner, permeability of the material to be separated may increase. Accordingly, the separation membrane may have a thickness of about 5 to about 1000 μιτι.

As described above, by alloying the Group 5 element with Ti, Zr, or Hf, the separation membrane has improved ductility compared to a separation membrane including only the Group 5 element. When the ductility is ensured at room temperature by increasing the ductility, the membrane may be manufactured by cold rolling, so mass production thereof is possible at a low cost. Even if the Group 5 element is alloyed with Ti, Zr, or Hf, the body- centered cubic structure may be well maintained, and the ductility may also be maintained.

The layer consisting of a pure Group 5 element forms a metal hydride compound during the hydrogen permeation, so hydrogen embrittlement may occur. In this case, when the embrittled region is applied with stress, the hydrogen embrittlement fracture may occur.

As described above, the ductility of the separation membrane is increased by adding Ti, Zr, or Hf, and the increased ductility may compensate the hydrogen embrittlement problem. In addition, the alloy of the Group 5 element and Ti, Zr, or Hf decreases the threshold temperature at which the metal hydride compound is formed compared to the pure Group 5 element, so as to suppress the formation of the metal hydride compound under the same conditions.

The ductility of the separation membrane may be evaluated according to the ASTM E8M standard micro-tensile test. According to one embodiment, the separation membrane may have an elongation percentage of about 5 to about 25 % according to the evaluation of ASTM E8M standard micro-tensile test. According to another embodiment, the separation membrane may have a maximum load of about 200 to about 600 MPa (measured at about 300 °C) according to the evaluation of the ASTM E8M standard micro-tensile test.

The separation membrane has excellent hydrogen permeability, so as to provide low hydrogen solid solubility, and specifically, the hydrogen solid solubility (H/M unit) may be about 0.05 to about 0.25 when measured under the conditions of hydrogen pressure of about 0.1 to about 1 MPa and at about 300 to about 500 °C. More specifically, the hydrogen solid solubility may be about 0.1 to about 0.2 when measured under the conditions of hydrogen pressure of about 0.7 to about 1 MPa and at about 400 °C.

In addition, the hydrogen separation membrane fabricated by using the obtained separation membrane has excellent hydrogen permeability. The hydrogen permeability may be calculated by the following Equation 1.

[Equation 1]

Permeability = solubility (S) ^χ diffusion coefficient (D)

The hydrogen separation membrane may have hydrogen permeability of about 1.0 x 10^"8 to about 1.0 x 10^"7 mol/m*s*Pa^1/2 at about 300 °C to about 500 °C.

The hydrogen separation membrane may have a thickness of about 5 pm to about 1000 pm, and specifically about 20 to about 200 pm. When the separation membrane has the ranged thickness, the separation membrane may have suitable permeability for application as a separation membrane.

The separation membrane may be fabricated according to a known method of manufacturing an alloy, but is not limited to the method. For example, each metal may be uniformly melted by arc melting, induction melting, spark plasma sintering, mechanical milling, or the like, and may undergo hot rolling/cold rolling to provide the separation membrane in a desirable thickness.

As described above, the separation membrane according to one embodiment does not need to include the additional catalyst layer on one surface of both surfaces thereof. Accordingly, as shown in FIG. 3, in the hydrogen separation membrane 10 according to the present invention, hydrogen atoms are dissociated and absorbed through the separation membrane 11 , and as only hydrogen atoms are separated, hydrogen gas (H2) is again provided. In other words, the catalyst layer for dissociating hydrogen molecules (H₂) into hydrogen atoms (H) is not required on one surface or both surfaces of the hydrogen separation membrane, unlike in the conventional separation membrane.

In another embodiment of the present invention, a hydrogen separation device that includes the hydrogen separation membrane, a chamber equipped with a supplier for a mixed gas including hydrogen gas, and a discharge chamber equipped with a discharger for separated hydrogen gas is provided.

The hydrogen separation membrane is disposed between the chamber and the discharge chamber in the hydrogen separation device.

FIG. 4 is a schematic view showing the hydrogen separation device 20 according to one embodiment. When a mixed gas including hydrogen gas is introduced into a chamber 22 through a supplier 21 of the mixed gas including hydrogen gas, only hydrogen gas of the mixed gas is selectively separated into a discharge chamber 24 through a hydrogen separation membrane 23. The separated hydrogen gas may be recovered through a discharge unit 25. The hydrogen separation device 20 may further include a means 26 for recovering the remaining gas from which the hydrogen gas is separated. The hydrogen separation device 20 is shown in a simplified form for better comprehension and ease of description, and may further include additional constitutional components according to its use. FIG. 5 is a schematic view showing another embodiment in which the hydrogen separation device 30 is formed in a tubular shape. The hydrogen separation device 30 includes a tubular shaped hydrogen separation membrane 33, and a large cylindrical chamber barrier 36 having a larger diameter than the tubular shaped hydrogen separation membrane is formed outside of the hydrogen separation membrane 33. A space between the chamber barrier rib 36 and the hydrogen separation membrane is provided as a chamber 32, and the inside of the tubular shaped hydrogen separation membrane 33 is provided as a discharge chamber 34 for discharging hydrogen. The chamber 32 may further include a supply unit (not shown) for a mixed gas including hydrogen gas and a recovery unit (not shown) for recovering the remaining gas from which hydrogen gas is separated. In addition, a discharge unit (not shown) may be further included for discharging the hydrogen gas separated into the discharge chamber 34.

In addition, according to another embodiment, when including the tubular shaped hydrogen separation membrane 33, the mixed gas is supplied to the inside of the tubular shaped hydrogen separation membrane 33, and hydrogen from the mixed gas is passed through the tubular shaped hydrogen separation membrane 33 and separated to the outside of the tubular shaped hydrogen separation membrane 33 to discharge hydrogen, contrary to the case shown in FIG. 5. In other words, the inside of the hydrogen separation membrane 33 is provided as a chamber for supplying the mixed gas, and the outside of the hydrogen separation membrane 33 is provided as a discharge chamber for discharging hydrogen. Hereinafter, the embodiments are illustrated in more detail with reference to examples. However, they are exemplary examples of the present invention, and this disclosure is not limited thereto.

[Mode for Invention]

(Examples)

Preparation Example 1 : Preparation of Ti-Nb alloy, Ti-Nb-Pd alloy, V-Pd alloy, and Nb-Pd alloy

An alloy is prepared by including Ti and Nb in various content ratios. Also, an alloy is prepared by including Ti, Nb, and Pd in various content ratios.

In addition, a V-Pd alloy is prepared.

Furthermore, a Nb-Pd alloy is prepared.

Specifically, the component elements for each alloy are mixed in the various content ratios and uniformly melted using arc melting and alloyed to provide a separation membrane having a thickness of 400 μητι. For the control group, only Ti or Nb is melted in accordance with the same procedure to provide a separation membrane.

Specifically, each element is weighed and added into an arc melter, and then the material is evaporated under a high vacuum (less than or equal to 2x10^"5 torr) to complete remove oxygen. Then Ar gas is injected to provide an anti-oxidation condition, and the current is increased to melt the material and then naturally cool it in an arc melter. An obtained ingot is provided in a thickness of 400 pm and heat-treated in a high vacuum furnace to remove defects such as surface pollutants, internal stress, and dislocation. Then both surfaces thereof are coated with Pd at a thickness of 150 nm to provide a hydrogen separation membrane for measuring hydrogen permeability.

Experimental Example 1 : Confirmation of crystalline structures of Ti-Nb alloy and Ti-Nb-Pd alloy

The Ti-Nb alloys obtained from Preparation Example 1 are examined to determine whether they maintain the bcc crystal structure as in pure Ti or pure Nb.

In other words, the Ti-Nb alloys obtained from Preparation Example 1 containing Ti at 20, 40, 60, and 80 atom%, the pure Ti, and the pure Nb are measured regarding crystalline structure using XRD, and the results are shown in FIG. 6.

As shown in FIG. 6, it is understood that an alloy of Nb and Ti maintains the bcc crystalline structure of Nb or Ti itself in all composition ranges.

In addition, the alloy of Ti, Nb, and Pd obtained from Preparation Example 1 is measured regarding alloy crystal structure by XRD, and the results are shown in FIG. 7.

As shown in FIG. 7, it is understood that alloys including Ti-Nb and further including 5 atom% and 10 atom% of Pd, respectively, also maintain the bcc crystalline structure as in the pure Nb or Ti-Nb alloy.

From the results, the alloy of the Nb-Ti metal and the alloy in which Pd is added thereto also maintain the stable bcc crystalline structure, so it may be assumed to provide excellent hydrogen permeability.

Experimental Example 2: Confirmation of effects of maintaining alloy ductility of Ti In order to measure the hardness of an alloy, differing from the case of Preparation Example 1 , one surface of the water drop-shaped alloy sample obtained by arc melting is polished using sandpaper. The surface is polished smooth with No. 600 fine sandpaper, and the hardness thereof is measured using a hardness tester capable of loading 1 kg.

Vickers hardness of the Nb-Ti alloy is measured, and the results are shown in FIG. 8.

As shown in FIG. 8, it is understood that the Vickers hardness of the alloy is decreased when adding Ti at greater than or equal to 40 atom% to Nb, and the ductility of the alloy is still maintained even when adding at greater than or equal to 60 atom%. Generally, it is known that a metal becomes more brittle and the ductility is reduced when the hardness is increased.

In addition, according to the same procedure as in Preparation Example 1 , Ti is mixed with V, Ta, Mo, and W in various content ratios to provide an alloy, the elasticity coefficient (Young's modulus) of the alloy of Ti with another metal is measured, and the results are shown in FIG. 9.

As shown in FIG. 9, it is understood that the alloy of Ti with another metal also decreases the elasticity coefficient of the alloy when increasing the content of Ti.

Thereby, it is understood that the ductility of the alloy is maintained, and the elasticity coefficient is decreased when Ti is alloyed with another metal. Accordingly, it is expected that the hydrogen separation membrane using a Ti- added alloy may have resistance to hydrogen embrittlement fractures since the ductility is increased. Experimental Example 3: Measurement of ductility of Nb-Ti-Pd alloy

In addition to the results of Experimental Example 2, the Vickers hardness of the Ti-Nb-Pd alloy added with Pd in the various content ratios is measured, and the results are shown in FIG. 10.

As shown in FIG. 10, it is confirmed that the hardness increase is suppressed in the Ti-Nb alloy added with Pd compared to the alloy in which Pd is added to the single Nb metal. In other words, it is understood that the ductility of Ti-Nb-Pd alloy is maintained higher than that of the Nb-Pd alloy. Furthermore, when increasing the content of Ti, it is confirmed that the hardness is further decreased, and the ductility is enhanced.

Experimental Example 4: Confirmation of suppression of hydrogen embrittlement fractures of Nb-Ti alloy

From the results of Experimental Examples 2 and 3, it is confirmed that the case of adding Ti may maintain the alloy ductility. It is examined whether the hydrogen embrittlement fractures may be suppressed when a separation membrane is fabricated by using these alloys.

That is, as shown in FIG. 11 , it is understood that the pure Nb is cracked on the metal surface, while a Nb-Ti20 alloy is somewhat cracked to decrease the crack occurrence, and a Nb-Ti40 alloy is not cracked, under the same hydrogen charging conditions.

In other words, when alloying the Ti metal, the alloy ductility is increased so as to provide effects on suppressing the hydrogen embrittlement fractures of the alloy.

Experimental Example 5: Evaluation of hydrogen permeability (1) Evaluation of hydrogen permeability of V-Pd alloy

A V-Pd alloy obtained from Preparation Example 1 is measured to determine hydrogen permeability.

V-Pd has much better ductility than Nb-Pd, so it is determined whether the alloys capable of maintaining the ductility and having a Group 5 metal and the hydrogen dissociation capability have hydrogen permeability or not.

As shown in FIG. 13, the alloy does not have hydrogen permeability.

Specifically, FIG. 12 shows the results of measuring the hydrogen permeability of the control group of which both ends of the metal Pd that is not coated with pure V and not polished on the surface are evaporated and subjected to hydrogen pressure. Although the upper graph of FIG. 12 shows a pressure increase of 1 kPa per hour, the pressure increase is caused by gas leakage at the back end, so substantial hydrogen permeation is not found. This may be confirmed from the lower graph of FIG. 12 (graph measuring hydrogen flow).

FIG. 13 shows the results of measuring the hydrogen permeability in a state in which only the surface is polished without coating Pd on the V-Pd 10 alloy.

From the above graph of FIG. 13, it is found that both the front end and the back end of the metal have no temperature change, but from the lower graph, it is found that only pressure of the back end is increased. However, the pressure increase is also caused by gas leakage at the back end like the upper graph of FIG. 12, and substantial hydrogen permeability is not found.

(2) Evaluation of hydrogen permeability of Ti-Nb alloy It is confirmed that the hydrogen permeability is not provided when Pd is not coated on the Ti-Nb alloy obtained from Preparation Example 1.

Specifically, FIG. 14 shows graph results of temperature and pressure changes at both ends of the separation membrane (500 μηη thickness) in which the alloy is not annealed and not polished on the surface in a state of not coating Pd on the surface after the hydrogen pressure.

From the above graph of FIG. 14, it is understood that the temperature is not changed at either end of the separation membrane after hydrogen pressure, and that the pressure is increased at the back end, but the difference is insignificant and is only within the error range caused by mechanical error.

FIG. 15 shows the results of measuring the hydrogen permeability of the separation membrane (thickness is decreased to 450 μητι) in which the alloy is not annealed and not coated with Pd, but the surface is polished.

From the results of the upper graph of FIG. 15, it is understood that the temperature is not changed at either end of the separation membrane and the pressure is slightly increased, but the change is only within the error range as in FIG. 14.

Accordingly, it is understood that the Ti-Nb alloy itself, which is not coated with Pd on the surface, does not have hydrogen permeability.

On the other hand, as shown in FIG. 16, it is understood that the sample is broken by pressure of only 7 bar for 5 minutes when Pd is coated at a thickness of 10 nm on the Ti-Nb alloy. In other words, it is shown that the separation membrane is broken by hydrogen embrittlement by supplying excessive hydrogen when Pd is present on the alloy surface in a layer form. In FIG. 16, (a) shows that the temperature is not changed at either end of the separation membrane; and (b) shows that the front end pressure is sharply increased and suddenly decreased by the hydrogen embrittlement fractures, and on the other hand, the back end pressure is suddenly increased due to the separation membrane fractures caused by oversupply of hydrogen. FIG. 16 (c) shows the flow of the back end, wherein the hydrogen flow is rapidly increased.

In other words, as the Nb-T^'i alloy itself is a metal having very high affinity for hydrogen, it is understood that a Pd catalyst layer or the like may not be coated thereon since the affinity for hydrogen is too high.

(3) Measurement of hydrogen permeability of Ti-Nb-Pd alloy

A Ti-Nb-Pd alloy is fabricated by adding 10 atom% of Pd to the alloy having a Ti:Nb composition ratio of 6:4, the hydrogen permeability thereof is measured, and the results are shown in FIG. 17.

The upper graph of FIG. 17A shows the temperature change of the alloy separation membrane according to time. It is understood that the temperature is increased and maintained according to the hydrogen pressure, and from the lower graph, it can be determined that the front end pressure is increased and maintained at a predetermined level and the back end pressure is slightly increased.

FIG. 17B shows an enlarged region marked by the rectangular box of the lower graph of FIG. 17A. As shown in FIG. 17B, it is found that the temperature is not changed in the front and back ends of the separation membrane in that state, and the pressure is slowly increased at the back end to provide hydrogen permeability.

From the result, it is confirmed that a much greater amount of hydrogen is generated in the Nb-Ti-Pd alloy compared to the sample before adding Pd.

In addition, it is understood that in the case of the alloy separation membrane, even if a sample passing a small amount of hydrogen is cooled while maintaining the hydrogen pressure at greater than or equal to about 7 bar after one day, the hydrogen embrittlement fracture does not occur.

The hydrogen permeability result is shown in FIG. 18, and even in the case of investigating the sample by the naked eye after measuring the permeability, crack traces are not found in the coin-shaped sample (referring to FIG. 19).

It is found that the temperature is decreased according to cooling from the upper graph of FIG. 18, and it is found that the pressure of the front end is decreased according to a decrease of the temperature in the back end.

While this disclosure has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

1 : Ti atoms 2: Nb atoms

3: Pd atoms

4: tetrahedral site among which hydrogen is adsobed

10: hydrogen separation membrane 11 : separation membrane 12: catalyst layer 20, 30: hydrogen separation device

21 : supplier for a mixed gas including hydrogen gas

22, 32: chamber 23, 33: hydrogen separation membrane

24, 34: discharge chamber 26: recovery unit

25: discharge unit for the separated hydrogen gas

36: chamber barrier rib

Claims

[CLAIMS]

[Claim 1 ]

A separation membrane comprising:

an alloy including:

a Group 5 element;

a transition metal being capable of forming a body-centered cubic (bcc) structure with the Group 5 element; and

a metal having hydrogen dissociation capability,

wherein the alloy has a crystalline structure of a body-centered cubic (bcc) structure,

the Group 5 element is selected from V (vanadium), Nb (niobium), and Ta (tantalum),

the transition metal is selected from Ti (titanium), Zr (zirconium), and Hf (hafnium), and

the metal having hydrogen dissociation capability is Pd (palladium), Pt (platinum), Ni (nickel), or Fe (iron).

[Claim 2]

The separation membrane of claim 1 , wherein the alloy includes about 10 atom% to about 59 atom% of the Group 5 element, about 40 atom% to about 89 atom% of the transition metal being capable of forming a bcc structure with the Group 5 element, and about 1 atom% to about 40 atom% of the metal having hydrogen dissociation capability.

[Claim 3]

The separation membrane of claim 1 , wherein the alloy includes about 10 atom% to about 49 atom% of the Group 5 element, about 50 atom% to about 89 atom% of the transition metal being capable of forming a bcc structure with the Group 5 element, and about 1 atom% to about 30 atom% of the metal having hydrogen dissociation capability.

[Claim 4]

The separation membrane of claim 1 , wherein the alloy includes about 10 atom% to about 39 atom% of the Group 5 element, about 60 atom% to about 89 atom% of the transition metal being capable of forming a bcc structure with the Group 5 element, and about 1 atom% to about 20 atom% of the metal having hydrogen dissociation capability.

[Claim 5]

The separation membrane of claim 1 , wherein the alloy includes greater than or equal to about 80 volume% of a crystalline structure of a bcc structure.

[Claim 6]

The separation membrane of claim 1 , wherein its porosity is less than about 1 volume%.

[Claim 7]

The separation membrane of claim 1 , wherein its thickness is about 5 to about 1000 pm.

[Claim 8]

The separation membrane of claim 1 , wherein the Group 5 element is Nb, the transition metal is Ti, and the metal having hydrogen dissociation capability is Pd.

[Claim 9]

A hydrogen separation membrane comprising the separation membrane according to claim 1.

[Claim 10]

The hydrogen separation membrane of claim 9, which has hydrogen solubility of about 0.05 to about 0.25, measured under conditions of about a 0.1 to about 1 MPa hydrogen pressure and at about 300 °C to about 500 °C.

[Claim 1 1 ]

The hydrogen separation membrane of claim 9, which has hydrogen solubility of about 0.1 to about 0.2, measured under conditions of about a 0.7 to about 1 MPa hydrogen pressure and at about 400 °C.

[Claim 12]

The hydrogen separation membrane of claim 9, which has hydrogen permeability of about 1.0 x 10^"8 to about 1.0 x 10^"7 mol/m^*s^*Pa^1/2 at about 300 °C to about 500 °C.

[Claim 13]

The hydrogen separation membrane of claim 9, which does not comprise a catalyst layer.

[Claim 14]

A hydrogen separation device, comprising:

the hydrogen separation membrane of claim 9;

a chamber equipped with a supplier for a mixed gas including hydrogen gas; and

a discharge chamber equipped with a discharger for separated hydrogen gas,

wherein the hydrogen separation membrane is disposed between the chamber and the discharge chamber.

[Claim 15]

The hydrogen separation device of claim 14, wherein the hydrogen separation membrane is formed in a tubular shape,

a cylindrical chamber barrier rib having a larger diameter than that of the tubular hydrogen separation membrane is formed at the outside of the hydrogen separation membrane,

a space between the chamber barrier rib and the hydrogen separation membrane is formed as the chamber, and the inside of the tubular hydrogen separation membrane is formed as the discharge chamber where hydrogen is discharged.