JP4226009B2 - Hydrogen separation membrane and method for producing the same - Google Patents

Description

  The present invention relates to a porous hydrogen separation membrane, and more specifically, the problems of the low hydrogen permeation amount and the hydrogen embrittlement (HE) of a stainless metal support, which existing palladium-based dense separation membranes have. The present invention relates to a hydrogen separation membrane and a method for manufacturing the same.

  Many researches on the process of producing hydrogen by reforming hydrocarbons are in progress, and active research is still in progress. Looking at the process of producing synthesis gas from hydrocarbons, polymer electrolyte membrane fuel cells through steam reforming and water gas shift as shown in the following reaction formulas (1) and (2) Produces hydrogen, which is a raw material gas for (PEMFC). For example, see Non-Patent Document 1.

The hydrogen produced in the reactor undergoes a reverse aqueous reaction in accordance with the concentrations of carbon monoxide and hydrogen, so that the methane regeneration process can proceed. In addition, since the conversion rate of methane is determined according to the temperature, and the conversion rate of methane can be further increased by removing hydrogen from the product, the operating temperature of the reactor can be further reduced.
Currently, as shown in Non-Patent Documents 2 and 3, various researches are being made with the aim of developing a porous separation membrane using a palladium-based dense separation membrane, zeolite, or gamma alumina.

  In the case of a palladium-based dense separation membrane, separation by conduction of hydrogen ions proceeds, so that high selectivity can be obtained. On the other hand, the permeation amount of hydrogen per unit area is small, and the manufacturing process is very complicated. In particular, when a stainless steel metal support is used, a problem of hydrogen brittleness is caused. Therefore, in related fields, research and efforts have been devoted to ensuring durability. For example, see Non-Patent Document 4.

On the other hand, in the case of a porous separation membrane, a high hydrogen permeability can be obtained, so that it can be applied to a system capable of configuring a process even with a low selectivity such as a process for producing hydrogen as a gas source for a fuel cell. There is expected.
However, most porous separation membranes studied or developed to date use ceramic (gamma alumina, zeolite) supports. For example, see Non-Patent Document 5.

A. Basile, L. Paturzo, An experimental study of multilayered composite palladium membrane reactors for partial oxidation of methane to syngas, Catalysis Today 67 (2001) 55 R. Checchetto, N. Bazzanella, B. Parron, A. Miotello, Palladium membranes prepared by r. f. . magnetron sputtering for hydrogen purification, Surface and Coatings Technology 177-178 (2004) 73 T. Tomita, K. Nakayama, H. Sakai, Gas separation characteristics of DDR type zeolite membrane, Microporous and Mesoporous Materials, 68 (2004) 71 D. Lee, Y. Lee, S. Nam, B. Sea, K. Lee, Preparation and characterization of SiO2 composite membrane for purification of hydrogen from methanol steam reforming as an energy carrier system for PEMFC, Separation and Purification Technology 32 (2003) 45 D. Lee, L. Zang, S. T Oyama, S. Niu, R .; F. Saraf, Synthesis, Characterization, and gas permeation properties of a hydrogen permeable silica membrane supported on porous alumina, J. Membrane Science 231 (2004) 117

However, the biggest problem with this is the difficulty in the process of systemizing the completed separation membrane. That is, for the multi-layer structure of the separation membrane, the system configuration by sealing and welding is indispensable, but until now, the development of technology for this is still incomplete.
The present invention has been made in view of the problems of the prior art, and the first object of the present invention is to reduce the hydrogen permeation amount of the existing palladium-based dense separation membrane and the hydrogen of the stainless metal support. Provided is a hydrogen separation membrane that simultaneously solves the problem of brittleness (hydrogen embrittlement).
The second object of the present invention is to provide a hydrogen separation membrane having further improved thermal stability over the hydrogen separation membrane provided for the first object.
The third object of the present invention is to provide a method for producing a hydrogen separation membrane that is simple in process and suitable for mass production at low cost.

In order to achieve the above object, the present invention provides a hydrogen separation membrane manufactured by press-molding metal fine particles having an adsorption property for hydrogen, wherein the metal fine particles include first metal powder 0.5 to 50. The second metal powder is 50 to 99.5% by weight and the average particle diameter is relatively larger than that of the first metal powder, and the first metal powder and the second metal powder are nickel powder, The first metal powder is selected from fine particles having an average particle diameter of 0.01 to 0.5 μm, and the second metal powder is selected from fine particles having an average particle diameter of 0.8 to 10 μm. In addition, a hydrogen separation membrane is provided in which the first metal powder and the second metal powder are mixed and compression-molded .
The surface of the first metal powder is preferably coated with at least one metal selected from the group consisting of Al, Si, Pt, Pd, Ru, Rh, Au, and Ag.
The second metal powder is preferably reduced in a hydrogen atmosphere at 200 to 500 ° C. as a pretreatment .

Furthermore, the present invention relates to a method for producing a hydrogen separation membrane including metal fine particles having adsorption characteristics for hydrogen, wherein the first metal powder has an average particle size of 0.5 to 50% by weight and a relative average particle diameter than the first metal powder. A hydrogen separation membrane comprising a step of mixing 50 to 99.5% by weight of a large second metal powder, a step of pressure-molding the mixed powder with a predetermined pressure, and a step of firing the compact in a hydrogen atmosphere. The first metal powder and the second metal powder are nickel powders, and the first metal powder is selected from fine particles having an average particle diameter of 0.01 to 0.5 μm, and The second metal powder is selected from fine particles having an average particle size of 0.8 to 10 μm .
In the production method of the present invention, preferably, the pressure-bonding is performed under a pressure of 1 to ²⁰ tons / cm ² .
In the production method of the present invention, the surface of the first metal powder is preferably coated with at least one metal selected from the group consisting of Al, Si, Pt, Pd, Ru, Rh, Au, and Ag. And
In the production method of the present invention, preferably in the step of mixing the first metal powder and the second metal powder, a step of simultaneously mixing Al oxide powder and / or Si oxide powder as a sintering inhibitor. It is desirable to include.
In the production method of the present invention, the second metal powder is preferably reduced in a hydrogen atmosphere at 200 to 500 ° C. as a pretreatment .

The hydrogen separation membrane according to the present invention can simultaneously solve the problems of the small hydrogen permeation amount and the hydrogen brittleness of the stainless steel metal support that the conventional palladium-based dense separation membrane has.
In addition, the hydrogen separation membrane according to the present invention can further improve the thermal stability by coating a metal powder with a metal component having an effect of suppressing sintering, and the production process of the separation membrane is simple and cost-effective. It also has the advantage of being suitable for low volume production.

Furthermore, the present invention will be described in more detail.
In the present invention, the metal fine particles having an adsorption characteristic for hydrogen are selected from a group of metal powders having different average particle sizes.
The smaller the particle size of the powder used when producing a porous medium by compressing the fine powder, the higher the probability of the presence of fine pores in the medium, so that the separation efficiency for hydrogen is also kept higher. It is generally considered to expect to be. This can be confirmed through Comparative Examples 1 and 2 described later.
That is, in the case of the hydrogen separation membrane of Comparative Example 2 manufactured using fine powder having an average particle size of 0.15 μm, the hydrogen / nitrogen selectivity at the lowest pressure difference is as high as 23.3 (see Table 6). On the other hand, in the case of the hydrogen separation membrane of Comparative Example 1 in which a powder having an average particle size of 5 μm was used, the selectivity of hydrogen / nitrogen at the minimum pressure difference was 14 (see Table 5). Can be confirmed.

  As estimated from the above facts, it can be said that a finer powder is required to obtain a more improved result, but there is a difficulty in this because there is a limit to the production process of fine powder. . However, such limitations can greatly improve the density and selectivity by mixing and pressing metal powders having different particle sizes. This is due to the fact that the hydrogen separation membrane obtained in Example 1 described later has a markedly improved surface density compared to the hydrogen separation membranes in Comparative Examples 1 and 2, as shown in FIG. Can be confirmed.

The difference in the average particle size between the first metal powder and the second metal powder is not particularly limited, but is preferably a material having a difference of at least 0.3 μm or more, more preferably, the first metal powder has an average particle size of 0. It is preferable to use a powder selected from 0.01 to 0.5 [mu] m and an average particle size of the second metal powder selected from 0.8 to 10 [mu] m.
In order to improve the density and selectivity, the mixing ratio of the first metal powder and the second metal powder is 0.5 to 50% by weight of the first metal powder and 50 to 99.5 of the second metal powder. It is preferable that it is composed of% by weight.

The metal used as the first metal powder and the second metal powder has an adsorption characteristic for hydrogen, and any metal powder used as a component constituting a conventional hydrogen separation membrane may be used. This corresponds to nickel powder.
The first metal powder may be used as it is, but it is preferable to perform a special treatment on the outer surface in order to ensure stability at high temperatures. Such treatment is performed by coating a specific metal component on the outer surface of the first metal powder. Examples of the metal component that can coat the outer surface of the first metal powder are metals having a sintering suppressing effect, and are selected from the group of Al, Si, Pt, Pd, Ru, Rh, Au, and Ag. There may be mentioned at least one metal.

As described later, the hydrogen separation membrane of Example 2 obtained without coating with a metal having a sintering suppressing effect (sintering inhibitor) and the metal having a sintering suppressing effect were obtained. According to the results of the experiment obtained for the hydrogen separation membrane of Example 3, the selectivity for hydrogen / nitrogen was 11.5 and 21.5 at the lowest pressure difference, respectively. The role can be confirmed. With reference to FIG. 2 according to Example 2 and FIG. 3 according to Example 3, it can be confirmed that such a phenomenon brings about the stability of the structure as the sintering inhibitor is added. In addition, referring to the cross-sectional photograph of the hydrogen separation membrane shown in FIG. 3, the fine particles of the first metal powder having a relatively small average particle diameter when the sintering inhibitor is used are in a complete state. In order to ensure stability at a high temperature in view of the progress of the sintering in the relatively large second metal powder having an average particle size of 5 μm, a sintering inhibitor is added to all the particles used. It is recognized that coating is preferred.
Moreover, such a coating of the sintering inhibitor also serves to further strengthen the adsorption force for hydrogen.

The coating step of the sintering inhibitor is performed by firing the first metal powder in an air atmosphere at 200 to 400 ° C. for 1 to 5 hours, and using the liquid solution containing the sintering inhibitor. It is performed by a step of supporting a sintering inhibitor on the powder by an initial wet method and a step of fixing the supported metal by firing in an air atmosphere at 300 to 400 ° C.
As a simpler method, it is also possible to apply a sintering inhibitor directly to the outer surface of the first metal powder using a reducing agent (eg, NaBH ₄ ). However, in this case, it is necessary to perform careful washing to remove the residue (NaBO _{2 in the} above example) used as the reducing agent.

  In addition, although the sintering inhibitor in the present invention is preferably coated on metal powder, it can be replaced by mixing Al or / and Si oxide powder in order to simplify the manufacturing process. is there.

The mixed powder of the first metal powder and the second metal powder is pressure-molded into a certain shape and manufactured as a molded body. The pressurization (or pressure bonding) molding is preferably performed using a mixed metal powder mold, preferably under a pressure of 1 to ²⁰ tons / cm ² .
In order to make the pressure forming proceed more smoothly, the second metal powder having a relatively large average particle size can be reduced in a hydrogen atmosphere at 200 to 500 ° C.
Although the molded object obtained through the said process is not specifically limited, Preferably it is preferable to bake in 500-900 degreeC hydrogen atmosphere. More details will be supplemented in the description of the preferred embodiment.

  Hereinafter, the contents of the present invention will be described in more detail with reference to examples. However, these examples are examples provided for understanding of the present invention, and the scope of rights of the present invention should not be construed to be limited to these examples.

20% by weight of nickel powder having an average particle diameter of 0.15 μm as the first metal powder and 80% by weight of nickel powder having an average particle diameter of 5 μm as the second metal powder were uniformly mixed for 30 minutes using a mortar. A porous separation membrane was manufactured using 1.3 g of the mixed powder using a circular mold having a diameter of 12.7 mm. The press pressure at this time was 9.97 tons / cm ² , and this pressure was maintained for 1 minute.
The permeabilities of the produced porous separation membrane with respect to hydrogen and nitrogen were measured using a gas permeation measuring device manufactured as shown in FIG.
Hydrogen and nitrogen were respectively supplied, and the flow rate of the gas that permeated through the porous separation membrane was measured with the pressure difference maintained at 2.2 psi between the front and rear ends of the separation membrane. The measuring apparatus includes a gas flow rate control unit 1 (mass flow control valve, pressure control valve) for supplying each gas, and an analysis unit 9 (gas chromatography) for measuring the flow rate of the gas that has passed through the separation membrane. Consists of. Reference numeral 2 is a gas mixer, 3 is an electric heating furnace, 4 is a unit separation membrane, 5 is a temperature sensor, 6 is a temperature controller, 7 is a pressure sensor and controller set, and 8 is a soap bubble flow meter. Yes. The portion where the unit separation membrane 4 was mounted was installed in an electric heating furnace 3 capable of adjusting the temperature, and the temperature of the permeable membrane was kept constant at 200 ° C. Further, the amount of permeation due to each pressure variable was measured by providing a pressure control valve in the discharge line of the supplied non-permeated gas and obtaining the pressure difference between both ends of the separation membrane.

The perm-selectivity was determined by the following equation (3) using the data of the permeation amounts for hydrogen and nitrogen measured as described above. At this time, the permeation amount of each gas (ML, L represents liters, the same applies hereinafter) was converted to the same separation membrane area (cm ² ), measurement time (min), and pressure difference (psi). It means the amount of transmission of a single component in the state. In addition, argon (Ar) was supplied as a transfer gas for discharging the separation membrane permeating gas from the lower end of the separation membrane.

As shown in Table 1 below, the hydrogen permeation amount is 33.6 to 10.5 ML / cm ² in the pressure variable range of 2.2 to 14.7 psi. min. atm, nitrogen 1.0-1.7 ML / cm ² . min. Atm, the hydrogen / nitrogen selectivity is 32.0-6.0.

The separation membrane produced in Example 1 was baked for 5 hours in a hydrogen atmosphere at 600 ° C., and then the permeability to hydrogen and nitrogen was measured. Other separation membrane production conditions and gas flow rate conditions were the same as in Example 1.
As shown in Table 2, the gas permeation amount measurement results are as follows: hydrogen permeation amount is 181 to 84 ML / cm ² . min. atm, nitrogen permeation is 15-26 ML / cm ² . min. Atm, hydrogen / nitrogen selectivity is at a level of 11.5-3.2.
Compared with Example 1, while the permeation amount of each gas was increased by 6 times or more, the selectivity decreased to about 1/2 to 1/3, and the phenomenon of increase in pore diameter in the separation membrane was observed. You can see that it occurred.

In the same manner as in Example 2, a separation membrane was produced and subjected to heat treatment. However, the outer surface of the powder having an average particle diameter of 0.15 μm was coated with aluminum. The coating method was performed as follows.
Aluminum nitrate is dissolved in distilled water, nickel powder is added and stirred for 10 minutes, then 0.1 mol% NaBH ₄ aqueous solution is gradually added dropwise to increase the pH of the solution to 8, and the aluminum component is added to the outer surface of the nickel powder. Coated. The coated nickel powder was washed 3 times with distilled water and then dried before use.
The measurement results of the gas permeation amount are as shown in Table 3, and the hydrogen permeation amount is 45.1 to 15.8 ML / cm ² . min. The amount of permeation of atm and nitrogen is 2.1 to 3.4 ML / cm ² . min. Atm, the hydrogen / nitrogen selectivity is at a level of 21.5 to 4.6.

  When compared with Example 1, the permeation amount of each gas was increased by 1.5 times or more, but the gas selectivity was reduced to about 2/3, indicating that the separation membrane was stable against sintering. Although it is impossible to secure 100%, it can be seen that the range of decrease in selectivity appears very small when compared with Example 2. Therefore, in view of such facts, the method of coating the outer surface of the nickel powder with aluminum is evaluated as a technique for imparting thermal stability to the nickel-based porous separation membrane.

The permeation amount for carbon dioxide, propane, and methane was measured for the separation membrane of Example 3.
As shown in Table 4, the permeation amount of each gas was measured and the selectivity for hydrogen was calculated. As shown in Table 4, the selectivity for carbon dioxide was 43 to 6.7, while the methane having the smallest molecular weight was selected. The lowest degree is 8.6 to 3.4.
Here, it should be noted that even when the pressure difference between both sides of the separation membrane was high at 14.7 psi, it was possible to obtain performance far exceeding the range of Knudsen diffusion for all the measured gases. It is a result.

[Comparative Example 1]
A porous separation membrane was produced as in Example 1, and the permeation amount for hydrogen and nitrogen was measured. However, a porous separation membrane was produced by changing the nickel powder to a powder having a single particle diameter of 5 μm (see FIG. 4).
As shown in Table 5, the gas permeation amount measurement results are as follows. Hydrogen permeation amount is 58.8 to 24.8 ML / cm ² . min. The amount of permeation of atm and nitrogen is 4.2 to 6.7 ML / cm ² . min. At atm, the hydrogen / nitrogen selectivity is at a low level of 14.0-3.6. In particular, the nitrogen permeation amount shows a very large permeation amount even in a low pressure state (2.2 psi) when compared with Example 1, so that it can be confirmed that the distribution of average pores is very large. Therefore, the limit is confirmed in the production of a porous separation membrane by pressure bonding of nickel powder having a micron-size single particle size.

[Comparative Example 2]
A porous separation membrane was produced as in Comparative Example 1, and the permeation amount for hydrogen and nitrogen was measured. However, a porous separation membrane was produced using a single component of nickel powder having an average particle size of 0.15 μm (see FIG. 5).
As shown in Table 6, the gas permeation amount measurement results are as follows. Hydrogen permeation amount is 73.5 to 17.9 ML / cm ² . min. The amount of permeation of atm and nitrogen is 3.1 to 3.7 ML / cm ² . min. At atm, the hydrogen / nitrogen selectivity is at a low level of 23.3 to 4.7.
Compared to the separation membrane produced using the mixed powder of Example 1 despite the use of ultrafine powder having an average particle size of 1/33 level compared to the nickel powder used in Comparative Example 1. Represents low selectivity. Therefore, as in the present invention, in the manufacturing process of the hydrogen separation membrane by pressure bonding, it is an absolute condition to obtain the required selectivity to use a powder having a multi-particle size distribution. It is evaluated as the result shown.

  As described above, the present invention has been described with reference to the preferred embodiments. However, those skilled in the art will recognize that the present invention is within the spirit and scope of the present invention described in the appended claims. It will be readily understood that various modifications and changes can be made.

SEM (scanning type) of a porous separation membrane produced by pressure-bonding a powder having a multi-particle size distribution in which 20% by weight of nickel powder having an average particle size of 0.15 μm and 80% by weight of nickel powder having an average particle size of 5 μm are mixed. It is an electron microscope photograph. A powder having a multi-particle size distribution in which 20% by weight of nickel powder having an average particle size of 0.15 μm and 80% by weight of nickel powder having an average particle size of 5 μm is pressed and manufactured, and then fired in a hydrogen atmosphere at 600 ° C. It is a SEM photograph of the made porous separation membrane. After pressure-bonding and producing a powder having a multi-particle size distribution in which an aluminum component is coated and nickel powder having an average particle size of 0.15 μm and 20% by weight of nickel powder and 80% by weight of nickel powder having an average particle size of 5 μm are mixed, It is a SEM photograph of the porous separation membrane baked in 600 degreeC hydrogen atmosphere. It is a SEM photograph of the porous separation membrane manufactured by press-bonding single particle size nickel powder having an average particle size of 5 μm. It is a SEM photograph of the porous separation membrane manufactured by press-bonding single particle size nickel powder having an average particle size of 0.15 μm. It is a block diagram of the performance evaluation apparatus of the porous separation membrane used in the Example of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Gas flow control part (mass flow control valve, pressure control valve), 2 ... Gas mixer, 3 ... Electric heating furnace, 4 ... Unit separation membrane, 5 ... Temperature sensor, 6 ... Temperature controller, 7 ... Pressure Sensor and controller set, 8 ... soap bubble flow meter, 9 ... analysis unit (gas chromatography)

Claims (8)

In hydrogen separation membranes produced by pressure forming metal fine particles with adsorption properties for hydrogen,
The fine metal particles are composed of 0.5 to 50% by weight of the first metal powder and 50 to 99.5% by weight of the second metal powder having an average particle size relatively larger than that of the first metal powder.
The first metal powder and the second metal powder are nickel powders,
The first metal powder is selected from fine particles having an average particle diameter of 0.01 to 0.5 μm, and the second metal powder is selected from fine particles having an average particle diameter of 0.8 to 10 μm. The hydrogen separation membrane is characterized in that the first metal powder and the second metal powder are mixed and compression-molded .   The surface of the first metal powder is coated with at least one metal selected from the group consisting of Al, Si, Pt, Pd, Ru, Rh, Au, and Ag. The hydrogen separation membrane as described.   The hydrogen separation membrane according to claim 1, wherein the second metal powder is reduced in a hydrogen atmosphere at 200 to 500 ° C. as a pretreatment. In a method for producing a hydrogen separation membrane including fine metal particles having adsorption characteristics for hydrogen,
Mixing 0.5 to 50% by weight of the first metal powder and 50 to 99.5% by weight of the second metal powder having a relatively larger average particle diameter than the first metal powder to obtain a mixed powder;
A method for producing a hydrogen separation membrane, comprising: a step of pressure-molding the mixed powder with a predetermined pressure to obtain a molded body; and a step of firing the molded body in a hydrogen atmosphere .
The first metal powder and the second metal powder are nickel powders,
The first metal powder is selected from fine particles having an average particle diameter of 0.01 to 0.5 μm, and the second metal powder is selected from fine particles having an average particle diameter of 0.8 to 10 μm. A method for producing a hydrogen separation membrane . The method for producing a hydrogen separation membrane according to claim 4 , wherein the compression molding is performed under a pressure of 1 to ²⁰ tons / cm ² . Wherein the first metal powder has a surface Al, Si, Pt, Pd, Ru, Rh, Au, to claim 4, characterized in that it is coated with at least one metal selected from the group of Ag The manufacturing method of the hydrogen separation membrane of description. The step of mixing the first metal powder and the second metal powder includes a step of simultaneously mixing Al oxide powder and / or Si oxide powder as a sintering inhibitor. 4. The method for producing a hydrogen separation membrane according to 4 . The method for producing a hydrogen separation membrane according to claim 4 , wherein the second metal powder is reduced in a hydrogen atmosphere at 200 to 500 ° C. as a pretreatment.

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