JP2014172012A - Hydrogen separation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydrogen separation method capable of efficiently separating hydrogen at a comparatively low temperature.SOLUTION: In a hydrogen separation method to separate hydrogen by a Pd-Ag alloy film,: Ag content in the Pd-Ag alloy film is 15-30 mass%; and a temperature at separation treatment is lower than 300°C and is the temperature where the hydrogen transmission flux of the Pd-Ag alloy film becomes 80% or more of the hydrogen transmission flux of hydrogen at 400°C. It is preferable that the primary side pressure Pof the Pd-Ag alloy film at the separation treatment is 100-1,000 kPa and P/Pis 1.4-10.

Description

  The present invention relates to a method for separating hydrogen by a hydrogen separation membrane.

  As a hydrogen separation membrane that selectively permeates and separates hydrogen from a hydrogen-containing gas, there is a Pd-based alloy membrane, particularly a Pd-Ag alloy membrane. It is known that the permeation performance of a hydrogen separation membrane of this Pd-based alloy improves with increasing temperature and also with increasing difference in hydrogen partial pressure on both sides of the membrane.

  The alloy composition, operating temperature, and pressure can be set arbitrarily, but it must be used at a high temperature to ensure the required hydrogen permeation performance, and sufficient hydrogen permeation cannot be obtained at temperatures below 300 ° C. It is said that. This is because the hydrogen permeability of the Pd—Ag alloy film decreases monotonously (almost linearly) as the temperature decreases (Patent Documents 1 to 4). In paragraph 0002 of Patent Document 4, it is described that a typical operating temperature of the palladium alloy film is 300 to 600 ° C., and practically in a temperature range of 350 ° C. to 450 ° C. (center temperature around 400 ° C.). At present, hydrogen separation treatment is performed.

Patent 2651610 Patent No. 4917787 JP-A-2005-254191 JP2002-153737

  As described in Patent Documents 1 to 4, the Pd-based hydrogen separation membrane is improved in hydrogen permeation performance by performing a hydrogen separation treatment at a high temperature (300 ° C. to 600 ° C.). In addition to the large amount of energy consumption, it is necessary to make the constituent members of the hydrogen separation membrane and other hydrogen separation devices highly heat resistant, resulting in high member costs. Moreover, the higher the temperature, the faster the member will deteriorate. Furthermore, when the operating temperature of the hydrogen separation membrane is higher than 450 ° C., pinholes that cause gas leakage are easily formed, and there is a problem that the durability of the membrane is significantly reduced. For this reason, from the viewpoint of the hydrogen permeation performance and durability of the membrane, the heat resistance and cost of the constituent members, the hydrogen separation treatment is practically performed in a temperature range of 350 ° C. to 450 ° C. (around 400 ° C. central temperature). Yes.

  The present invention provides a hydrogen separation method that can efficiently separate hydrogen at a low temperature of less than 300 ° C., which has been considered that a practical hydrogen permeation rate cannot be obtained for a Pd-based alloy film. Objective.

  The hydrogen separation method of the present invention is a hydrogen separation method in which hydrogen is separated by a Pd—Ag alloy membrane, wherein the Ag content of the Pd—Ag alloy membrane is 15 to 30% by mass, and the temperature during the separation treatment is 300 ° C. And a temperature at which the hydrogen permeation flux of the Pd—Ag alloy film is 80% or more of the hydrogen permeation flux at 400 ° C.

In the present invention, the pressure _{P 1} on the primary side of the Pd-Ag alloy membrane during separation 50～1100KPa, it is preferable that the pressure of the secondary side from the vacuum 900kPa or less. Further, it is preferable that the ratio P ₁ / P ₂ between the primary pressure P ₁ and the secondary pressure P ₂ is 1.1 or more. In the present invention, it is particularly preferable that P ₁ is 100 to 1000 kPa, P ₁ / P ₂ is 1.4 to 10, and the temperature during the separation treatment is 100 ° C. or more and less than 300 ° C.

  The Ag content of the Pd—Ag alloy film is preferably 15 to 30% by mass.

  In the present invention, it is preferable to separate hydrogen around a temperature at which the hydrogen permeation flux reaches a maximum value in the temperature-hydrogen permeation flux curve.

  When the inventor conducted various studies, the hydrogen permeation flux of the Pd—Ag alloy film does not decrease monotonously (almost linearly) as the temperature decreases in a temperature range of 500 ° C. or lower. It has been found that in the range of about 130 ° C. to 350 ° C., the hydrogen permeation flux does not differ greatly from the hydrogen permeation flux at 350 ° C. even if the temperature decreases, or conversely increases (takes a maximum value).

  The present invention is based on such knowledge. According to the present invention, hydrogen can be efficiently separated at a considerably lower temperature than in the prior art, for example, around 300 ° C. or lower, without sacrificing the hydrogen permeation flux. For this reason, energy consumption for heating is reduced, heat resistance characteristics required for the member are alleviated, and member cost can be reduced. Moreover, the thermal deterioration of a member can be suppressed.

It is a graph which shows the hydrogen permeation flux of a hydrogen separation membrane. It is a graph which shows the hydrogen permeation flux of a hydrogen separation membrane. It is a graph which shows the hydrogen permeation flux of a hydrogen separation membrane. It is a graph which shows the hydrogen permeation flux of a hydrogen separation membrane. It is a graph which shows the hydrogen permeation flux of a hydrogen separation membrane. It is a graph which shows the hydrogen permeation flux of a hydrogen separation membrane. It is a graph which shows the hydrogen permeation flux of a hydrogen separation membrane. This is the relationship between the temperature at which the hydrogen permeation flux becomes maximum and the primary gas pressure. It is a graph which shows the hydrogen permeation flux of a hydrogen separation membrane. It is a graph which shows the relationship between the minimum temperature which shows a flux equivalent to 80% of hydrogen permeation flux in 400 degreeC, and Ag density | concentration, and the critical temperature of Ag-alpha 'transformation, and Ag density | concentration. It is sectional drawing of the module for hydrogen permeation tests.

  The hydrogen separation membrane used in the present invention is preferably a Pd—Ag alloy membrane (Ag 15-30% by mass, particularly 20-30% by mass).

  The alloy film can be obtained by melting an alloy having the above composition and rolling it to a thickness of preferably 1 to 500 μm, particularly preferably 10 to 50 μm. In addition, you may employ | adopt means other than rolling for thin film formation. The hydrogen separation membrane is formed on the surface of a support material such as a breathable metal or ceramic by a film formation method such as sputtering, CVD, or plating, and has a thickness of 1 to 500 μm, particularly about 1 to 20 μm. Also good.

  As a hydrogen production apparatus equipped with a hydrogen separation membrane, the hydrogen separation membrane is installed in a container called a housing, casing, vessel or the like, and has a primary chamber and a secondary chamber separated by a hydrogen separation membrane. The structure is not particularly limited as long as it further has heating means as required. The form of the film may be any form such as a flat film type and a cylindrical type. The hydrogen separation membrane may be overlaid on a porous support or a support plate having grooves on the surface. As a porous body, any of a metal material, a ceramic material, etc. may be sufficient.

  The source gas (hydrogen-containing gas) supplied to the primary chamber of the hydrogen production apparatus may be any gas containing hydrogen, such as a hydrocarbon steam reformed gas, a fuel cell fuel off-gas, a biogas containing hydrogen, The gas generated from the biomass gasification furnace is exemplified, but it is not limited thereto.

  The operating temperature of the apparatus (specifically, the gas temperature on the primary side) depends on the composition of the film and the pressure on the primary side and the secondary side, but when a Pd—Ag alloy film of 15 to 30% by mass of Ag is used. It is preferable that the temperature is 100 to less than 300 ° C, particularly 100 to 295 ° C, particularly 130 ° C to 295 ° C.

  In the present invention, in the graph of temperature-hydrogen permeation flux, hydrogen is separated at a temperature that is not higher than 300 ° C. and has a maximum hydrogen permeation flux (for example, 165 ° C. in the case of FIG. 1). Specifically, it is preferable to separate hydrogen at a temperature at which the hydrogen permeation flux reaches a maximum value ± 10 ° C. or at a temperature at which the hydrogen permeation flux reaches 80% or more of the maximum value. .

In this case, the pressure P ₁ on the primary side of the apparatus is preferably as high as possible. However, if the pressure P ₁ exceeds 1100 kPa, the required value of the pressure strength of the apparatus becomes extremely high and there are also legal regulations. It is preferably 50 to 1100 kPa, particularly 100 to 1100 kPa. Secondary pressure _{P 2} of the apparatus, is preferably low, 200 kPa or less, for example vacuum ~200kPa are preferred. In the case the secondary side pressure is atmospheric or higher, since the pump for depressurizing the secondary side is not required, it is preferable that the secondary side pressure P ₂ atmospheric pressure (100 kPa) or more. The larger the ratio P ₁ / P ₂ between the primary pressure P ₁ and the secondary pressure P ₂ , the higher the hydrogen permeation flux, and therefore the higher the ratio P ₁ / P _2. About 4 to 10 is preferable.

  Examples will be described below.

[Example 1]
An ingot was obtained from a molten alloy having a composition of 80 mass% Pd and 20 mass% Ag, and this was rolled to produce a Pd-20 mass% Ag hydrogen separation membrane having a thickness of 25 µm and a diameter of 12 mm. This hydrogen separation membrane was set in the test module 1 shown in FIG. 4, and the hydrogen permeation flux was measured.

  In this hydrogen permeation test module 1, a hydrogen separation membrane 4 is disposed between a rear end face of a gas introduction pipe 2 and a front end face of a gas extraction pipe 6 via gaskets 3 and 5. A nut 7 is fitted on the introduction pipe 2, and a cap nut 8 is engaged with a flange portion 6 a at the tip of the extraction pipe 6.

  The cap nut 8 is extended to the introduction tube 2 side, and a male screw on the outer peripheral surface of the nut 7 is screwed into a female screw on the inner peripheral surface. The leading end of the nut 7 comes into contact with the flange portion 2 a at the rear end of the introduction pipe 2, whereby the extraction pipe 6 is attracted to the introduction pipe 2 side through the cap nut 8, and the rear end surface of the introduction pipe 2 and the extraction pipe 6 are The hydrogen separation membrane 4 is sandwiched between the front end face via the gaskets 3 and 5.

  The gaskets 3 and 5 have an annular shape of the same size, and the area of the inner hole is the membrane permeation area A of the hydrogen separation membrane 4. The cap nut 8 is provided with a small hole 8a for a gas leak test.

The inner hole of the gasket is 5.6 mm, but the diameter of the contact portion between the gasket and the membrane sample when tightened with the cap nut 8 is 7.1 mm, and the effective membrane permeation area A is 39.6 mm ² (3 96 × 10 ⁻⁵ m ² ).

  The hydrogen permeation test module 1 is installed in an electric furnace, the raw material gas is supplied to the introduction pipe 2, and the hydrogen gas is taken out from the extraction pipe 6.

The gas pressure _{P 1} of the introduction tube 2 and 100 kPa, the gas pressure _{P 2} of the take-out tube 6 was 10 kPa. As the source gas, high purity hydrogen having a purity of 99.99999% or more was used. The hydrogen gas that permeated the hydrogen separation membrane 4 was recovered in a recovery container (not shown). The operation was performed by changing the temperature of the electric furnace between 100 and 500 ° C. The hydrogen permeation flux was measured and the result is shown in FIG. As shown in FIG. 1, the hydrogen permeation flux tends to decrease as the temperature decreases between 500 ° C. and 250 ° C., but the hydrogen permeation flux increases as the temperature decreases between 250 ° C. and 165 ° C. After tending to reach a maximum at about 165 ° C., the hydrogen permeation flux decreased again. It can be seen that the hydrogen permeation flux at 300 ° C. is approximately 80% of the hydrogen permeation flux at 400 ° C., and an equivalent hydrogen permeation flux is obtained at about 130 ° C. Further, the hydrogen permeation flux at 165 ° C., which showed the maximum, is a value equivalent to the hydrogen permeation flux at 450 ° C. That is, by operating at 130 to 165 ° C., a hydrogen permeation flux equivalent to 300 to 450 ° C. is obtained, and the operating temperature can be lowered by 285 to 170 ° C. without sacrificing the hydrogen permeation flux. is there. For this reason, it is possible to reduce the operating cost (heating cost) and the cost by reducing the heat resistance of the members constituting the apparatus. Moreover, the thermal deterioration of a structural member can be suppressed.

[Experiment 2]
The hydrogen permeation coefficient was measured under the same conditions as in Example 1 except that the Pd—Ag alloy film was changed to Pd-23 mass% Ag, and the results are shown in FIG. As shown in FIG. 2, in Example 2 (Pd-23 mass% Ag), the hydrogen permeation flux becomes maximum at about 180 ° C., and this maximum hydrogen permeation flux at 180 ° C. is equivalent to the hydrogen permeation flux at about 385 ° C. It was confirmed that Therefore, in the case of this Pd-23 mass% Ag membrane, it is recognized that hydrogen can be efficiently separated at a low temperature of less than 300 ° C. as in Experimental Example 1. The broken line in the figure is obtained by extrapolating the temperature dependence of the hydrogen permeation flux at a high temperature of 350 ° C. or higher to a low temperature, in order to obtain a hydrogen permeation flux equivalent to 80% of the hydrogen permeation flux at 400 ° C. Is estimated to require a high temperature of 305 ° C. However, as shown in FIG. 2, it can be seen that a hydrogen permeation flux equivalent to 80% of the hydrogen permeation flux at 400 ° C. is obtained at about 155 ° C. That is, it can be seen that the hydrogen separation treatment can be efficiently performed at a temperature considerably lower than the temperature predicted from the extrapolation line.

[Experiment 3]
The hydrogen permeation coefficient was measured under the same conditions as in Examples 1 and 2 except that the Pd—Ag alloy film was changed to Pd-25 mass% Ag, and the results are shown in FIG. As shown in FIG. 3, in Example 3 (Pd-25 mass% Ag), the hydrogen permeation flux becomes maximum at about 190 ° C., and this maximum hydrogen permeation flux at 190 ° C. is equivalent to the hydrogen permeation flux at about 425 ° C. It was confirmed that Therefore, in the case of this Pd-25 mass% Ag membrane, it is recognized that hydrogen can be efficiently separated at a low temperature of less than 300 ° C. as in Experimental Examples 1 and 2. It can also be seen that a hydrogen permeation flux equivalent to 80% of the hydrogen permeation flux at 400 ° C. is obtained at about 140 ° C.

[Experimental Example 4]
The hydrogen permeation coefficient was measured under the same conditions as in Examples 1 to 3 except that the Pd-Ag alloy film was changed to Pd-27 mass% Ag, and the results are shown in FIG. As shown in FIG. 4, Experimental Example 4 (Pd-27 mass% Ag) has a maximum hydrogen permeation flux at about 175 ° C., and this maximum hydrogen permeation flux at 175 ° C. is equivalent to the hydrogen permeation flux at about 340 ° C. It was confirmed that Therefore, in the case of this Pd-27 mass% Ag membrane, it is recognized that hydrogen can be efficiently separated at a low temperature of less than 300 ° C. as in Experimental Examples 1 to 3. It can also be seen that a hydrogen permeation flux equivalent to 80% of the hydrogen permeation flux at 400 ° C. is obtained at about 160 ° C.

[Experimental Example 5]
The hydrogen permeation coefficient was measured under the same conditions as in Examples 1 to 4 except that the Pd—Ag alloy film was changed to Pd-30 mass% Ag, and the results are shown in FIG. As shown in FIG. 5, Experimental Example 5 (Pd-30 mass% Ag) has a maximum hydrogen permeation flux at about 220 ° C., and this maximum hydrogen permeation flux at 220 ° C. is equivalent to the hydrogen permeation flux at about 300 ° C. It was confirmed that Therefore, in the case of this Pd-30 mass% Ag membrane, it is recognized that hydrogen can be efficiently separated at a low temperature of less than 300 ° C. as in Experimental Examples 1 to 4. It can also be seen that a hydrogen permeation flux equivalent to 80% of the hydrogen permeation flux at 400 ° C. is obtained at about 180 ° C. FIG. 5 also shows the results when the Pd—Ag alloy film is Pd-40 mass% Ag. In the case of Pd-40 mass% Ag, the hydrogen permeation flux monotonously decreased as the temperature decreased.

[Experimental Examples 6 to 8]
In Experimental Example 2 (Pd-23 mass% Ag), the hydrogen permeation coefficient was measured under the same conditions except that the gas pressures P ₁ and P ₂ were changed as follows, and the results are shown in FIG. The unit of P ₁ and P ₂ is kPa.
No. 6 P ₁ = 800, P ₂ = 100 (P ₁ / P ₂ = 800/100 = 8)
No. 7 P ₁ = 500, P ₂ = 100 (P ₁ / P ₂ = 500/100 = 5)
No. 8 P ₁ = 250, P ₂ = 100 (P ₁ / P ₂ = 250/100 = 2.5)

  As is clear from FIG. In the case of 6, the hydrogen permeation flux reached a maximum at about 280 ° C., and the maximum hydrogen permeation flux at 280 ° C. was found to be equivalent to the hydrogen permeation flux at about 480 ° C. It can also be seen that a hydrogen permeation flux equivalent to 80% of the hydrogen permeation flux at 400 ° C. is obtained at about 213 ° C. No. In the case of 7, the hydrogen permeation flux reached a maximum at about 250 ° C., and the maximum hydrogen permeation flux at 250 ° C. was found to be equivalent to the hydrogen permeation flux at about 485 ° C. It can also be seen that a hydrogen permeation flux equivalent to 80% of the hydrogen permeation flux at 400 ° C. is obtained at about 203 ° C. No. In the case of 8, the hydrogen permeation flux reached a maximum at about 230 ° C., and the maximum hydrogen permeation flux at 230 ° C. was found to be equivalent to the hydrogen permeation flux at about 490 ° C. It can also be seen that a hydrogen permeation flux equivalent to 80% of the hydrogen permeation flux at 400 ° C. is obtained at about 184 ° C. Thus, by setting the temperature at 184 ° C. or higher, particularly 203 ° C. or higher, especially 213 ° C. or higher and 300 ° C. or lower, particularly less than 300 ° C. It was found that hydrogen can be separated.

[Experimental Examples 9 to 11]
In Experimental Example 2 (Pd-23 mass% Ag), the hydrogen permeation coefficient was measured under the same conditions except that the gas pressures P ₁ and P ₂ were changed as follows, and the results are shown in FIG. The unit of P ₁ and P ₂ is kPa.
No. 9 P ₁ = 1000, P ₂ = 100 (P ₁ / P ₂ = 1000/100 = 10)
No. 10 P ₁ = 1000, P ₂ = 200 (P ₁ / P ₂ = 1000/200 = 20)
No. 11 P ₁ = 1000, P ₂ = 800 (P ₁ / P ₂ = 1000/800 = 1.25)

  As shown in FIG. 7, in all of Experimental Examples 9 to 11, the hydrogen permeation flux showed a minimum at around 400 ° C., then increased with a decrease in temperature, showed a maximum at around 300 ° C., and then decreased again. A hydrogen permeation flux equivalent to 80% of the hydrogen permeation flux at 400 ° C. In the case of No. 9, the temperature is about 226 ° C. No. 10 is about 239 ° C. In the case of 11, it can be seen that each can be obtained at a temperature of about 275 ° C. Thus, it was recognized that hydrogen can be separated at a low cost and with a high hydrogen permeation flux by setting the temperature to 226 ° C. or more and 300 ° C. or less, particularly less than 300 ° C.

From the results of Experimental Example 6-9 shows a case where the gas pressure P ₂ on the secondary side and 100 kPa, the temperature and the primary side of the relationship of the gas pressure P ₁ represents a hydrogen permeation flux maximum in FIG. The temperature at which the hydrogen permeation flux reaches a maximum decreases as the primary pressure P ₁ decreases, and the peak temperature is lower than 300 ° C. particularly at P ₁ = 1000 kPa or less.

[Experimental Examples 12 to 16]
In Experimental Example 4 (Pd-27 mass% Ag), the hydrogen permeation coefficient was measured under the same conditions except that the gas pressures P ₁ and P ₂ were set as follows, and the results are shown in FIG. The unit of P ₁ and P ₂ is kPa.
No. 12 P ₁ = 1000, P ₂ = 10 (P ₁ / P ₂ = 1000/10 = 100)
No. 13 P ₁ = 1000, P ₂ = 100 (P ₁ / P ₂ = 1000/100 = 10)
No. 14 P ₁ = 260, P ₂ = 60 (P ₁ / P ₂ = 260/60 = 4.3)
No. 15 P ₁ = 100, P ₂ = 10 (P ₁ / P ₂ = 100/10 = 10)
No. 16 P ₁ = 50, P ₂ = 5 (P ₁ / P ₂ = 50/5 = 10)

  As is clear from FIG. 9, in the case of the Pd-27 mass% Ag film, the hydrogen permeation flux near 300 ° C. is as high as the hydrogen permeation flux at 400 ° C., which is 160 ° C. or more, particularly 175 It has been found that hydrogen can be separated at a low cost and a high hydrogen permeation flux by setting the temperature to not less than 300 ° C. and not more than 300 ° C., particularly less than 300 ° C., particularly 295 ° C.

Incidentally, the low primary pressure _{P 1} No. 14 to 16, it can be seen that it is preferable not only to increase P ₁ / P ₂ but also to increase P ₁ itself because the hydrogen permeation flux is small even when the secondary pressure P ₂ is low.

  FIG. 10 shows the relationship between the minimum temperature showing the permeability of 80% of the hydrogen permeation flux at 400 ° C. and the Ag concentration for each Pd—Ag alloy shown in FIGS. It can be seen that the temperature at which a hydrogen permeation flux equivalent to 80% of the hydrogen permeation flux at 400 ° C. tends to decrease as the Ag concentration decreases. FIG. 10 also shows the relationship between the critical temperature of the α-α ′ transformation and the Ag concentration. As shown in FIG. 10, it can be seen that the critical temperature of the α-α ′ transformation decreases as the Ag concentration increases. In the region below this linear relationship, the α-α ′ transformation occurs. In this case, a large distortion occurs in the metal film due to expansion and contraction caused by a difference in lattice constant between the α phase and the α ′ phase. For this reason, if the hydrogen separation treatment is performed at a temperature lower than the critical temperature of the α-α ′ transformation, the durability of the alloy film is significantly lowered. From the intersection of the two straight lines shown in FIG. 10, the lowest Ag concentration at which 80% hydrogen permeation flux at 400 ° C. is obtained without causing α-α ′ transformation can be estimated to be 15%. The temperature can be estimated to be about 100 ° C.

DESCRIPTION OF SYMBOLS 1 Hydrogen permeation test module 2 Gas introduction pipe 3,5 Gasket 4 Hydrogen separation membrane 6 Gas extraction pipe 7 Nut 8 Cap nut

Claims (7)

In a hydrogen separation method in which hydrogen is separated by a Pd—Ag alloy membrane,
A hydrogen separation method characterized in that the temperature during the separation treatment is lower than 300 ° C., and the hydrogen permeation flux of the Pd—Ag alloy membrane is 80% or more of the hydrogen permeation flux at 400 ° C. 2. The hydrogen separation method according to claim ₁ , wherein the pressure P1 on the primary side of the Pd—Ag alloy film during the separation treatment is set to 50 to 1100 kPa. According to claim 1 or 2, the hydrogen separation method characterized by the pressure _{P 2} on the secondary side of the PdAg alloy film than 900 kPa. 4. The ratio P ₁ / P ₂ between the primary pressure P ₁ and the secondary pressure P ₂ of the Pd—Ag alloy film according to claim 1 is 1.1 or more. The hydrogen separation method characterized by these. 5. The temperature at the time of separation treatment according to claim 1, wherein the primary side pressure P ₁ of the Pd—Ag alloy film is 100 to 1000 kPa, P ₁ / P ₂ is 1.4 to 10. Is performed at a temperature of 100 ° C. or higher and lower than 300 ° C.   6. The hydrogen separation method according to claim 1, wherein the Ag content of the Pd—Ag alloy film is 15 to 30% by mass.   The hydrogen separation method according to any one of claims 1 to 6, wherein hydrogen is separated near a temperature at which the hydrogen permeation flux reaches a maximum value in the temperature-hydrogen permeation flux curve.

Images