JP2009291742A - Hydrogen permeation member and hydrogen generating reactor using the same - Google Patents

Abstract

A hydrogen permeable member having good hydrogen permeation efficiency and capable of maintaining sufficient mechanical strength is obtained at low cost.
In this hydrogen permeable member, a polyimide resin layer having a thickness of 0.5 μm or more is formed on the surface of a hydrogen permeable metal layer. The hydrogen permeable member 10 is arranged so that the lower side in FIG. 1 is a low-purity gas having a high pressure (hydrogen partial pressure P ₁ ) and a low hydrogen concentration, and the upper side is a high-purity gas having a low pressure (hydrogen partial pressure P ₂ ) and a high hydrogen concentration. Is done. The hydrogen permeable metal layer 11 is a metal layer that is permeable to hydrogen, that is, has a high hydrogen permeability coefficient. In the hydrogen permeable metal layer 11 in the hydrogen permeable member 10 having the above structure, the hydrogen permeability coefficient φ can be made larger than that of the Pd alloy. In the hydrogen permeable member 10, even if the hydrogen permeable metal layer 11 becomes brittle, the mechanical strength of the entire hydrogen permeable member 10 is maintained by the thick polyimide resin layer 12.
[Selection] Figure 1

Description

  The present invention relates to a structure of a hydrogen permeable member used when purifying pure hydrogen from natural gas, for example. The present invention also relates to a hydrogen generation reactor in which this hydrogen permeable member is used.

  In recent years, hydrogen gas is often used as an energy source, including fuel cells. For this reason, technology for producing and storing pure hydrogen gas is important.

There are various methods for producing and storing pure hydrogen gas. For example, a method is known in which hydrogen is stored in an organic fuel, and hydrogen is extracted by performing a decomposition reaction as necessary. As an example, a hydrogen generation reaction by methylcyclohexane, which is one of a group of compounds called organic hydride, is shown in the following formula. Here, toluene is produced simultaneously with the production of hydrogen.

  Toluene in hydrogen is an impurity, and is preferably removed, for example, as high-purity hydrogen gas used in fuel cells. In addition, since the above reaction is restricted by chemical equilibrium, it is difficult to obtain hydrogen gas with an efficiency close to 100% from the charged methylcyclohexane.

For this reason, as a technique for solving the above two problems, hydrogen purification is performed in the hydrogen generation reaction field to obtain high purity hydrogen gas, and further, the chemical equilibrium is moved to achieve high reaction efficiency. A production reactor is used. FIG. 3 shows a schematic diagram of the simplest hydrogen generation reactor. In this hydrogen generation reactor 50, methylcyclohexane and a catalyst are introduced into a high temperature reaction furnace 51, and the above reaction occurs. Here, a purification unit 52 formed of a hydrogen permeable membrane is installed in the reaction furnace 51, and the pressure in the purification unit 52 is set lower than that outside (inside the reaction furnace 51). The purification unit 52 is formed of a hydrogen permeable membrane, and the hydrogen permeable membrane has the property of not allowing permeation of methylcyclohexane and toluene out of the gas present in the reaction furnace 51 but permeating only H ₂ . Accordingly, only hydrogen gas selectively permeates the hydrogen permeable membrane, enters the purification unit 52, and is taken out to the outside.

The principle of hydrogen permeating through a hydrogen permeable membrane generally formed of an alloy is as schematically shown in FIG. That is, the hydrogen molecules (H ₂ ) 71 adsorbed on the surface of the hydrogen permeable membrane 60 on the high pressure (hydrogen partial pressure P1) side are dissociated by the catalytic action of the hydrogen permeable membrane 60, and the form of a single hydrogen atom (H) 72 is obtained. Become. The hydrogen atoms 72 pass through the alloy as hydrogen ions (H ⁺ ) 73 and reach the surface on the low pressure (hydrogen partial pressure P ₂ ) side. Here, electrons are transferred again and again to form a hydrogen atom 72, recombined on the surface, and again become hydrogen molecules (H ₂ ) 71 and released to the low pressure side. In particular, this catalytic action acts strongly on the hydrogen molecule 71 and does not act on other impurity molecules (such as methylcyclohexane).

Accordingly, the hydrogen permeation rate J in this case is given by the following equation.

Here, D, K, and L are the hydrogen diffusion coefficient, hydrogen solid solution coefficient, and film thickness in the hydrogen permeable membrane, respectively. P ₁ is the hydrogen partial pressure on the high pressure side (low purity gas with low hydrogen purity), and P ₂ is the hydrogen partial pressure on the low pressure side (high purity gas with high hydrogen purity). Here, D · K is defined as a hydrogen permeation coefficient φ. Therefore, in order to increase the hydrogen permeation rate, it is necessary that the hydrogen permeation coefficient φ is large, the difference (pressure difference) between P ₁ and P ₂ is large, and the film thickness L is small.

  Therefore, in addition to a large hydrogen permeability coefficient φ, the hydrogen permeable membrane is required to have a mechanical strength that can withstand this pressure difference even when it is thin. However, it is generally known that a metal that has adsorbed hydrogen becomes brittle. Therefore, it is required that not only the mechanical strength is high but also the degree of embrittlement is small.

  For example, a palladium (Pd) -based alloy is known as a material that meets these requirements, and a hydrogen permeable membrane using this alloy has been put into practical use. Accordingly, many hydrogen generation reactors using a Pd-based alloy as a hydrogen permeable membrane are known, including Patent Document 1.

JP 2007-268404 A

  However, Pd is a kind of rare metal and is extremely expensive. Therefore, it is desirable to use an alloy containing no Pd instead. However, although there are many materials other than Pd-based alloys having a hydrogen permeability coefficient larger than Pd, all of them are embrittled due to hydrogen absorption, particularly when hydrogen generation reaction is performed at a low temperature such as organic hydride. It was remarkable and it was difficult to obtain a hydrogen permeable membrane that could withstand practical use.

  Therefore, it has been difficult to obtain a hydrogen permeable membrane having good hydrogen permeation efficiency and maintaining sufficient mechanical strength at low cost.

  The present invention has been made in view of such problems, and an object thereof is to provide an invention that solves the above problems.

  The present inventors have found that the above problem can be solved by forming a structure in which the hydrogen permeable membrane and the polyimide resin layer are laminated.

  The hydrogen-permeable member of the present invention is characterized by comprising a laminated structure of a hydrogen-permeable metal layer that is permeable to hydrogen molecules and a polyimide resin layer having a thickness of 0.5 μm or more.

  The hydrogen permeable metal layer of the present invention is preferably composed of a two-phase alloy having a phase having hydrogen permeability and a phase having hydrogen embrittlement resistance.

  The hydrogen permeable metal layer used in the hydrogen permeable member of the present invention is characterized in that an alloy of niobium (Nb), titanium (Ti), or nickel (Ni) is used. This alloy is suitable because its hydrogen permeability is comparable to that of Pd and has excellent hydrogen embrittlement resistance.

  Moreover, Pd or a Pd alloy layer is formed as a catalyst layer for promoting dissociation and recombination of hydrogen molecules on the surface of the hydrogen permeable metal phase used in the hydrogen permeable member of the present invention.

  The hydrogen generation reactor of the present invention is characterized in that a hydrogen permeable member is disposed between a low purity gas having a high hydrogen partial pressure and low hydrogen purity and a high purity gas having a low hydrogen partial pressure and high hydrogen purity. To do.

The temperature of the low purity gas used in the hydrogen generation reactor of the present invention is between 100 and 350 ° C.

In the hydrogen production reactor of the present invention, a hydrogen partial pressure difference between the low purity gas and the high purity gas is 1.0 MPa or less.

The hydrogen generation reactor according to the present invention has a structure in which the hydrogen-permeable members according to the present invention are laminated.

  Since the present invention is configured as described above, a hydrogen permeable member having good hydrogen permeation efficiency and capable of maintaining sufficient mechanical strength even at low temperatures can be obtained at low cost. Using this hydrogen permeable member, a high-performance hydrogen production reactor can be obtained at low cost.

  The best mode for carrying out the present invention will be described below.

FIG. 1 is a cross-sectional view of a hydrogen permeable member 10 according to an embodiment of the present invention. In the hydrogen permeable member 10, a polyimide resin layer 12 is formed on the surface of the hydrogen permeable metal layer 11. The hydrogen permeable member 10 is arranged so that the lower side in FIG. 1 is a low-purity gas having a high pressure (hydrogen partial pressure P ₁ ) and a low hydrogen concentration, and the upper side is a high-purity gas having a low pressure (hydrogen partial pressure P ₂ ) and a high hydrogen concentration. Is done. Therefore, in FIG. 1, hydrogen permeates in the direction of the arrow.

The hydrogen permeable metal layer 11 is a metal layer that is permeable to hydrogen, that is, has a high hydrogen permeability coefficient. FIG. 2 shows the pressure dependence of the hydrogen permeability coefficient of various metals. From this result, the hydrogen permeable metal layer 11 is an alloy mainly composed of niobium (Nb), vanadium (V), tantalum (Ta), zirconium (Zr) or the like as a material having a hydrogen permeability coefficient higher than that of Pd. Preferably, it is configured. Further, as described in JP-A-2006-274297, for example, an alloy in which Ti and Ni are added to Nb and an alloy in which embrittlement during hydrogen absorption is reduced can be used. This alloy is preferably used because it has sufficient mechanical strength and is easy to use with a thin film thickness. The Nb-Ti-Ni alloy suitable as the hydrogen permeable alloy includes (a) a primary crystal phase containing 70 atomic% or more of Nb, and (b) a phase containing 60 atomic% or more of Ni and Ti in total. It is a two-phase alloy having a eutectic phase in which a phase containing a large amount of Nb other than the primary crystal is mixed. An Nb-Ti-Ni alloy has this two-phase alloy as long as the composition is expressed by Nb _100-xy Ti _x Ni _y (in atomic percent, 10 ≦ x ≦ 60, 10 ≦ y ≦ 50). It becomes a hydrogen permeable metal layer.

  The polyimide resin layer 12 is a layer made of polyimide, that is, a polymer containing an imide bond. Since this polyimide layer is composed of a polymer, hydrogen molecules having a small molecular weight easily pass through it. Therefore, even if a thick polyimide resin layer is used as the reinforcing member, sufficient hydrogen permeability can be secured. When the thickness of the polyimide resin layer 12 is less than 0.5 μm, the effect of maintaining the mechanical strength is insufficient. On the other hand, even if the thickness of the polyimide resin layer exceeds 300 μm, the effect of maintaining the mechanical strength does not change so much, which is not preferable because the material cost increases. For this reason, the thickness is preferably 0.5 to 300 μm, more preferably 1 to 200 μm.

  The hydrogen separation metal layer 11 preferably has a thickness of 0.1 μm or more and 1 mm or less. Since the hydrogen separation metal layer has a hydrogen separation rate that is inversely proportional to the thickness, if the thickness exceeds 1 mm, a sufficient hydrogen separation rate cannot be obtained. On the other hand, if the thickness is less than 0.1 μm, pinholes are likely to occur during the production of the film, resulting in a problem that it is difficult to obtain high-purity hydrogen. The preferred thickness is 0.3 μm or more and 500 μm or less, and more preferably 1 μm or more and 300 μm or less.

  The polyimide resin layer 12 in this film thickness range can be formed, for example, by performing spin coating (rotary coating) on the hydrogen permeable metal layer 11. For example, the polyimide resin layer 12 having a desired uniform thickness can be formed by performing a heat treatment after the polyamic acid solution is dropped onto the hydrogen permeable metal layer 11 and spin-coated.

The hydrogen permeable member 10 is used as a material constituting the purification unit 52 in the hydrogen generation reactor 50 having the structure of FIG. That is, the hydrogen permeable member 10 is used by being disposed between the high-pressure side low-purity gas and the low-pressure side low-purity gas. At that time, the temperature (particularly the temperature of the low-purity gas on the high pressure side) is preferably between 100 and 350 ° C. as the temperature range in which the reactions of the above formulas 1 to 3 occur efficiently. Further, the hydrogen partial pressure difference (P ₁ −P ₂ ) on both sides of the hydrogen permeable member 10 is preferably 1.0 MPa or less from the viewpoint of safety when handling hydrogen gas.

  In the hydrogen permeable metal layer 11 in the hydrogen permeable member 10 having the above structure, the hydrogen permeability coefficient φ can be made larger than that of the Pd alloy. However, when hydrogen is adsorbed in this, a mechanically brittle metal hydride is formed. That is, embrittlement occurs and the mechanical strength decreases. Under the circumstances, the degree of embrittlement is greater than that of the Pd alloy as described above.

  However, when the polyimide resin layer 12 is sufficiently thick, its mechanical strength is sufficient. In addition, since polyimide is different from metal, embrittlement does not occur even when hydrogen is absorbed. Furthermore, it is known that polyimide does not decompose even at around 350 ° C. Therefore, sufficient mechanical strength is maintained even under the reaction of Formula 1.

  Therefore, in the hydrogen permeable member 10, even if the hydrogen permeable metal layer 11 is embrittled, the mechanical strength of the entire hydrogen permeable member 10 is maintained by the thick polyimide resin layer 12. Therefore, even if the pressure difference between the both sides of the hydrogen permeable member 10 is large, it is not destroyed.

On the other hand, hydrogen molecules permeate through the polyimide because small molecules are likely to penetrate between polymers. Accordingly, in addition to H ₂ , toluene that is purified simultaneously with hydrogen in the reaction of Formula 1 and methylcyclohexane, which is a raw material gas, pass through the polyimide, although the transmittance thereof is lower than that of H ₂ .

On the other hand, in the hydrogen permeable metal layer 11, as shown in FIG. 4, after H ₂ is adsorbed on its surface, it is dissociated by catalytic action with the metal on the surface. This dissociated hydrogen (H) becomes hydrogen ions and permeates through the hydrogen permeable metal layer 11 and reaches the opposite surface. On the opposite surface, the atomized hydrogen is recombined and released as hydrogen molecules (H ₂ ). This catalytic reaction works selectively with respect to hydrogen molecules. Therefore, in the hydrogen permeable metal layer 11, toluene and methylcyclohexane hardly permeate, and the selective permeability of H ₂ is particularly high. That is, the hydrogen permeable metal layer 11 has high selectivity for hydrogen molecules.

  Therefore, in this hydrogen permeable member 10 in which the polyimide resin layer 12 and the hydrogen permeable metal layer 11 are laminated, the hydrogen permeable metal layer 11 maintains high selective permeability to hydrogen molecules.

  At this time, since the rare metal Pd is not used, the hydrogen permeable metal layer 11 can be manufactured at a low cost.

  Therefore, the hydrogen permeable member 10 has good hydrogen permeation efficiency, can maintain sufficient mechanical strength, and can be obtained at low cost.

  In the structure of FIG. 1, the polyimide resin layer is formed on one side of the hydrogen permeable metal layer on the high pressure side, but the present invention is not limited to this, and the polyimide resin layer is formed on both sides of the hydrogen permeable metal layer. You can also In this case, the mechanical strength of the hydrogen permeable member can be further increased. Furthermore, it is also possible to laminate many layers of these. Also, the polyimide resin layer can be formed only on one side of the low pressure side.

  Further, the polyimide resin layer can be formed on the entire surface of the hydrogen permeable metal layer, or only the central portion of the hydrogen permeable metal phase can be formed and the hydrogen permeable metal layer can be left exposed. In the former case, when incorporating the hydrogen generation reactor into the hydrogen generation reactor, the polyimide resin layer functions as a sealing material by sandwiching the hydrogen permeable member between the frames of the hydrogen generation reactor, and good airtightness can be obtained. In the latter case, since the hydrogen permeable metal layer is exposed at the end of the hydrogen permeable member, when the frame of the hydrogen generation reactor is made of metal, good airtightness can be obtained by performing welding.

  Further, as described above, when hydrogen permeates through the hydrogen-permeable metal layer, a catalytic reaction that causes dissociation and recombination of hydrogen molecules occurs on the surface. A metal layer that easily generates this catalytic reaction may be formed only on the outermost surface of the hydrogen permeable metal layer. The metal layer is preferably a Pd or Pd alloy layer. As described above, Pd is a rare metal and expensive. However, in this structure, it is sufficient to form a thin layer of, for example, about 10 to 500 nm on the outermost surface. And the manufacturing cost will not increase significantly. When this Pd layer is thick, in addition to the high cost, the hydrogen permeation efficiency becomes worse than the result of FIG. The Pd or Pd alloy layer is also preferably formed on both sides of the hydrogen permeable metal layer, but may be formed only on one side.

The organic fuel used for the reaction is not particularly limited as long as it contains hydrogen and can perform a hydrogen generation reaction in a temperature range of 100 to 350 ° C. For example, alcohols such as methanol, ethanol, propanol, and butanol, and organic compounds such as organic hydride such as methylcyclohexane, decalin, and methyldecalin can be used.

  Since the hydrogen permeable member can be manufactured at low cost and has good hydrogen permeation efficiency and mechanical strength, a hydrogen generation reactor using the hydrogen permeable member also has high performance and low cost.

  EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited by these Examples.

(Examples 1-7, Comparative Examples 1-2)
First, Nb, Ti, and Ni raw materials were weighed so that the Nb _100-xy Ti _x Ni _y alloy composition was x = y = 30 (atomic%) in the composition formula. The raw material was put into a vacuum arc melting furnace and the atmosphere was evacuated. The atmospheric pressure at this time is 6.7 × 10 ^{−4 to} 6.7 × 10 ⁻³ Pa (5 × 10 ^{−6 to} 5 × 10 ⁻⁵ Torr). Further, Ar was introduced into the atmosphere, and then the getter agent Ti was dissolved to remove the impurity gas in the atmosphere. Next, each of these alloy samples was melted to form an alloy ingot. The operation of reversing the sample so as to make the alloy composition uniform for each ingot was melted five times to obtain an Nb—Ti—Ni-based hydrogen permeable alloy ingot. The obtained ingot was sliced to a thickness of 1 mm using a wire electric discharge machine. Further, after polishing the surface with abrasive paper, cold rolling was performed to obtain a hydrogen permeable alloy having a thickness of 10 to 900 μm. This hydrogen permeable alloy was subjected to heat treatment in Ar at 1100 ° C. for 96 hours.
Finally, the sample surface was mirror-polished and a Pd thin film was formed to 100 nm by sputtering to form a hydrogen permeable metal layer. A polyimide solution was applied to the obtained hydrogen permeable metal layer with varying thickness depending on the sample, dried, and subjected to heat treatment at 300 ° C. for 1 h to form a target polyimide layer. Table 1 shows the final thickness of the hydrogen-permeable metal layer of the manufactured hydrogen-permeable member and the thickness of the formed polyimide layer.

(Reference Examples 1 and 2)
A commercially available Pd film (thickness: 100 μm) was used, and a polyimide layer having a thickness of 10 μm was formed on the surface of the film by the same method as described above. A Pd film having a polyimide layer formed thereon was designated as Reference Example 1, and a Pd film having no polyimide layer formed thereon was designated as Reference Example 2.

  The evaluation method of the produced hydrogen permeable member will be described. The produced hydrogen permeable member was fixed to the hydrogen generation reactor shown in FIG. The catalyst used here is a commercially available Pt catalyst powder. Piping was connected to the hydrogen generation reactor with the configuration of an evaluation apparatus as shown in FIG. The hydrogen generation reactor was heated to 350 ° C. and methylcyclohexane was introduced as a fuel so that the pressure in the reaction furnace 51 became 0.3 MPa to perform a hydrogen generation reaction. The pressure of the refinement | purification part 52 at this time was 0.1 MPa. The amount of hydrogen obtained through the hydrogen permeable member was measured, and the hydrogen recovery rate was calculated from the theoretically generated hydrogen amount obtained from the amount of methylcyclohexane introduced and the actually obtained hydrogen amount. Table 1 shows the hydrogen recovery rate of each sample.

From the results in Table 1, it can be seen that if the thickness of the hydrogen permeable layer is the same, there is almost no difference in the hydrogen recovery rate even if the thickness of the polyimide layer changes. This means that the polyimide layer is not a factor that impedes hydrogen permeation.

  Subsequently, the hydrogen embrittlement resistance of the hydrogen permeable member was evaluated. The produced hydrogen permeable member was fixed to the hydrogen generation reactor shown in FIG. The catalyst used here is a commercially available Pt catalyst powder. The piping shown in FIG. 5 was connected to the hydrogen generation reactor. The hydrogen generation reactor was heated to 100 ° C. or 350 ° C. and methylcyclohexane was introduced as a fuel so that the pressure in the reaction furnace 51 was 0.2, 0.5, and 0.9 MPa, and a hydrogen generation reaction was performed. The pressure of the refinement | purification part 52 at this time was all 0.1 MPa. The time required to break the film was measured, and the results are shown in Table 2.

  From the results in Table 2, it can be seen that as the thickness of the polyimide layer increases, the time until film breakage significantly increases at both 150 ° C. and 350 ° C. In particular, the results at 150 ° C. show that the present invention is very effective in suppressing hydrogen embrittlement at low temperatures. Also, as the thickness of the hydrogen separation metal membrane layer increases, the time it takes for the membrane to break down increases. However, increasing the thickness of the polyimide layer is more effective in suppressing hydrogen embrittlement at low temperatures. It is.

  Using the hydrogen permeable member of Example 1, a hydrogen production reactor in which the hydrogen permeable member was laminated was produced. First, a commercially available Pd catalyst powder was dispersed in ethanol, and the dispersion was impregnated with a metal porous body made of SUS316. After drying, a heat treatment was performed at 400 ° C. for 1 hour to prepare a metal porous body 91 supporting the catalyst. . The metal porous body 91 supporting the catalyst and the hydrogen permeable member of Example 1 were laminated as shown in FIG. 6 to produce a hydrogen generation reactor.

It is sectional drawing which shows the structure of the hydrogen permeable member used as embodiment of this invention. It is a figure which shows the temperature dependence of the hydrogen permeability coefficient of various metal materials. It is a figure which shows the outline of the structure of a hydrogen production | generation reactor. It is a figure which shows the principle which hydrogen permeate | transmits in a hydrogen permeable film. It is the schematic of the evaluation apparatus of a hydrogen permeable member. It is a figure which shows the outline of the hydrogen production | generation reactor which has a laminated structure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Hydrogen permeable member 11 Hydrogen permeable metal layer 12 Polyimide resin layer 50 Hydrogen generation reactor 51 Reactor 52 Purification unit 53 Catalyst 60 Hydrogen permeable membrane 71 Hydrogen molecule 72 Hydrogen atom 73 Hydrogen ion 74 Impurity molecule 81 Fuel supply pump 82 Hydrogen generation reaction Device 83 Mass flow meter 84 Four-way valve 85 Gas chromatograph 91 Metal porous body 92 Gas flow path

Claims (7)

  A hydrogen permeable member comprising a laminated structure of a hydrogen permeable metal layer that is permeable to hydrogen molecules and a polyimide resin layer having a thickness of 0.5 μm or more.   2. The hydrogen permeable member according to claim 1, wherein the hydrogen permeable metal layer is made of a two-phase alloy having a phase having hydrogen permeability and a phase having hydrogen embrittlement resistance.   The hydrogen permeable member according to claim 1 or 2, wherein an alloy of niobium (Nb), titanium (Ti), or nickel (Ni) is used for the hydrogen permeable metal layer.   The hydrogen-permeable member according to any one of claims 1 to 3, wherein a palladium (Pd) or Pd alloy layer is formed on a surface of the hydrogen-permeable metal layer.   The hydrogen permeation according to any one of claims 1 to 4, between a low-purity gas having a high hydrogen partial pressure and low hydrogen purity and a high-purity gas having a low hydrogen partial pressure and high hydrogen purity. A hydrogen generation reactor, wherein members are arranged.   The hydrogen generation reactor according to claim 5, wherein the temperature of the low purity gas is in a range of 100 to 350 ° C.   The hydrogen generation reactor according to claim 5 or 6, wherein a hydrogen partial pressure difference between the low purity gas and the high purity gas is 1.0 MPa or less.