JP2017124364A - Porous filter, hydrogen separation film with porous filter as support, hydrogen separation method, and manufacturing method of porous filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous filter which can be easily joined to a metallic device and further manufactured at low cost and does not include pores exceeding e.g., 2 μm on its surface, and a manufacturing method of the porous filter, to provide a hydrogen separation film which uses the porous filter as a support, thereby forming a palladium membrane or a palladium alloy membrane with high availability as a hydrogen separation film on the porous filter without defect, reduces the usage of expensive palladium and simultaneously makes a high hydrogen permeation speed compatible with high hydrogen selectivity, and to provide a hydrogen separation method for efficiently separating hydrogen while using the hydrogen separation film.SOLUTION: The present invention relates to a porous filter comprising a porous metal base material and a ceramic porous body that is provided on any one side of the porous metal base material. The ceramic porous body is infiltrated into pores on the one side of the porous metal base material and continuously covers exposed surfaces of constituent materials of the porous metal base material constituting the pores, and its outer surface includes a recess based on an uneven surface of the porous metal base material.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a porous filter, a hydrogen separation membrane using the filter as a support, a hydrogen separation method, and a method for producing the porous filter.

  Porous ceramic substrates and porous metal substrates can be used as a porous filter for gas or liquid filtration, and can also be used as a hydrogen separation membrane by forming a palladium or palladium alloy thin film on it. A porous inorganic thin film is formed and used as a molecular separation membrane.

  Although the pore diameter of the surface of the porous ceramic substrate varies depending on the application, it is preferably a fine pore of 2 μm or less, for example, preferably 1 μm or less, depending on the impurity particles in a filter application for removing impurities. It is more preferable that Even when a palladium or palladium alloy thin film for hydrogen separation is formed on a porous ceramic substrate, or when a porous inorganic thin film is formed to form a molecular separation film, it is porous to make a thin film of 10 μm or less. The maximum pore diameter on the surface of the ceramic substrate is preferably 2 μm or less, and more preferably 1 μm or less.

  In any application, it is necessary to reduce the permeation resistance and suppress the pressure loss in order to increase the permeation speed of the fluid to be treated such as gas or liquid passing through the porous ceramic substrate. However, miniaturization of pores causes an increase in pressure loss, and the thickness of the structure must be reduced. However, such reduction in thickness results in the loss of the necessary strength as a structural material.

  Therefore, it is usual to laminate a porous ceramic film having fine pores on the surface of a rough porous ceramic substrate. However, since the ceramic film is very fragile and easily damaged by handling, the burden on the operator is great, and the manufacturing cost is increased and a special process is required. Further, as a basic problem of ceramic materials, there is a bondability to metal materials. Especially when used at high temperatures, bonding of ceramics to a metal device is a big problem.

  On the other hand, in the case of a porous metal substrate such as a sintered metal body obtained by sintering metal particles or a metal mesh obtained by sintering a metal wire in a net shape, the maximum pore diameter of pores opened on the surface of the substrate is 2 μm. In general, the permeation rate of gas or liquid is high, but only relatively large impurities can be removed, and it is not suitable for removing fine impurities such as a ceramic porous body. When a thin film for hydrogen separation made of palladium or palladium alloy is formed on the surface, the surface layer is provided with relatively large pores in the surface of the porous metal substrate. If the thin film for hydrogen separation to be arranged is thin, for example, having a film thickness of 10 μm or less, damage and cracks are easily formed due to the unevenness of the pores, and selective hydrogen separation cannot be obtained.

  In order to solve this problem, there is one in which a porous ceramic film having a smooth surface having fine pores is formed on the surface of the porous metal substrate (see Patent Documents 1 and 2 below). In this case, there is an advantage that the attachment to the metal device is performed through the porous metal substrate.

Japanese Patent Laid-Open No. 2003-135943 JP 2006-346621 A

  However, as in the case of forming on the surface of a rough ceramic porous body, the production cost of forming a porous ceramic film with a smooth surface on the surface of the porous metal substrate increases, and the surface state is not smooth. However, sufficient adhesion of the thin film material for hydrogen permeation separation formed on the surface cannot be obtained, and it is difficult to obtain good results.

  The present invention was made in view of the current state of the prior art described above, and can be easily joined to a metal device and manufactured at low cost, for example, a porous filter having no pores exceeding 2 μm on the surface, It aims at providing the manufacturing method.

  In addition, the present invention uses the porous filter as a support to form a palladium thin film or a palladium alloy thin film, which is highly useful as a hydrogen separation membrane, on the porous filter without defects, thereby reducing the amount of expensive palladium used. An object of the present invention is to provide a hydrogen separation membrane that simultaneously achieves a high hydrogen permeation rate and high hydrogen selectivity, and to provide a hydrogen separation method that efficiently separates hydrogen using the hydrogen separation membrane. To do.

  The present inventor has intensively studied to achieve the above-described object. As a result, the metal alkoxide is filled in the pores that open to the surface of the porous metal substrate, and the metal alkoxide is hydrolyzed in the pores, so that the metal hydroxide and / or oxide pores are contained in the pores. When the body is formed, the maximum pore diameter of the pores opened on the surface can be miniaturized to 2 μm or less, and a porous filter that can be easily bonded to a metal device and can be manufactured at a low cost is obtained. It was found that forming a palladium thin film or a palladium alloy thin film on the surface of the porous filter formed as described above as a support provides a good hydrogen separation membrane, and the present invention was completed here.

That is, the object of the present invention includes a porous metal substrate and a ceramic porous body provided on one side of the porous metal substrate, and the ceramic porous body includes the porous metal substrate. Intrusion into the pores on one side, and continuously covering the exposed surface of the constituent material of the porous metal substrate constituting the pores,
The outer surface is provided with a recess based on the undulating surface of the porous metal substrate, which is achieved by the porous filter according to the invention of claim 1.

  The invention of claim 2 of the present application is such that the porous metal substrate is covered with an oxide film having a specific color different from the metal color inherent to the metal, and the invention of claim 3 is characterized in that the oxide film is: The specific color is composed of an oxide having any one of orange, brown, brown, red and gold colors.

  Furthermore, in the invention of claim 4, the ceramic porous body is composed of zirconium hydroxide and / or zirconia, the invention of claim 5 further contains yttrium, and the invention of claim 6 The porous metal substrate is composed of a laminated sintered body of a support portion having coarse pores and a fine layer forming finer pores laminated on one side thereof, and the ceramic porous body Is the porous filter provided in the fine layer.

  In the invention according to claim 7, the fine layer of the porous metal base material has a random distribution of straight metal short fibers having a predetermined fiber diameter d and an average length L equal to or larger than the fiber diameter d. The outer surface is characterized by comprising the non-smooth undulating surface.

  The object of the present invention is achieved by a hydrogen separation membrane according to the invention of claim 8 comprising a palladium thin film or a palladium alloy thin film for hydrogen separation on the undulating surface of any one of the porous filters. The object of the present invention is to reduce the hydrogen partial pressure on the downstream side to the hydrogen partial pressure on the upstream side when separating the hydrogen-containing mixed gas located on the upstream side of the hydrogen separation membrane by hydrogen permeation to the downstream side. This is achieved by the method for separating hydrogen from the hydrogen-containing mixed gas according to the invention of claim 9.

The object of the present invention is to
(A) a preparation stage for preparing a porous metal substrate having predetermined pore characteristics;
(B) An oxide film having a specific color other than the intrinsic metal color is formed on the surface of the metal base material by heat treatment in an oxidizing atmosphere at a temperature of 400 to 850 ° C. or immersion treatment in an alkaline solution. A surface oxidation treatment stage,
(C) Continuously covering the exposed surface of the constituent material of the porous metal base material that penetrates into any surface side of the metal base material provided with the oxide film and constitutes the pores, and the outer surface thereof A step of composite processing comprising forming a ceramic porous body having a recess and a finer pore than the porous metal substrate;
(D) It is achieved by the invention of claim 10 according to the method for producing a porous filter, comprising a drying step of drying after the combined treatment.

  The invention of claim 11 is characterized in that the ceramic porous body of the invention of claim 10 is obtained by hydrolysis of a metal alkoxide.

  According to the present invention, it is possible to obtain a porous filter in which pores opened on the surface of a porous metal substrate are covered with a ceramic porous body by a relatively simple method. This porous filter is used as a support. In the hydrogen separation membrane, a good lamination state without defects can be formed even if the thin film material for hydrogen separation formed on the surface is thin.

  The porous filter includes a ceramic porous body that penetrates into pores on the surface of the porous metal substrate and covers the exposed surface of the constituent material, and includes the concave portion on the outer surface thereof. From the above, it is possible to improve the efficiency of collecting foreign matter as a filter, and even when a thin film material for hydrogen separation is laminated on the surface, the film material of palladium or palladium alloy that does not have the defects and can be thinned is good. In addition, the recesses can greatly improve the adhesion with the thin film material for hydrogen separation.

  In addition, since the structure is based on the porous metal substrate, it has the advantage that it can be easily assembled and assembled as a mechanical device, and is durable as a filter device or a hydrogen separation module. It can be used effectively for systematization.

It is an expanded sectional view of the important section of the porous metal substrate which the porous filter concerning the present invention has. It is a principal part expansion schematic sectional drawing of the porous filter which concerns on this invention. It is a principal part expansion schematic sectional drawing of the hydrogen separation membrane which concerns on this invention. 2 is an image obtained by observing the surface of a porous filter manufactured in Example 1 with a scanning electron microscope. It is the image which observed the surface of the stainless steel sintered metal filter (porous metal base material) used in Example 1 with the scanning electron microscope.

  Hereinafter, the porous filter and the manufacturing method thereof according to the present invention will be described. The porous filter 1 includes a porous metal substrate 2 and a ceramic porous layer 3 provided on one side of the porous metal substrate 2.

  As shown in the enlarged schematic view (cross-sectional view) of FIG. 1, the porous metal substrate 2 is composed of a porous sintered structure having a complicated flow channel that is communicated between both surfaces, and a plurality of porous metal substrates 2 are formed on the surface. The pores 21 are provided. Further, the layer 3 of the ceramic porous body has a finer and finer porous structure than the pores 21 of the porous metal substrate 2, and in this embodiment, the upper surface side of the metal substrate 2 as shown in FIG. Shows a composite formed so as to form a layer having a predetermined thickness.

  The state of formation is continuous, including the exposed surface of the component 2A of the porous metal substrate that penetrates into the pores 21 at least on the surface side of the metal substrate 2 and constitutes the pores 21. And the outer surface thereof is provided with a recess 31 based on the undulating surface of the metal substrate 2. 1 and 2 are examples of a more preferable form for facilitating understanding of the configuration, and are not enlarged but partially enlarged or reduced, but the present invention is not limited to this. Gradient distribution including the layer 3 of the ceramic porous body formed, for example, over a certain depth of the metal substrate 2, and gradually reducing the distribution density from the one surface side toward the other surface side. It can also be.

  Examples of the porous metal base material 2 include a metal mesh and the like in addition to a sintered metal body formed by using, for example, a metal powder or a short metal fiber as a constituent material 2A so as to have predetermined pore characteristics. Can do. Examples of the metal material include stainless steel, hastelloy alloy, inconel alloy, nickel, nickel alloy, titanium, and titanium alloy. The constituent material of the present embodiment enhances the undulation state of the outer surface by the distribution in the random direction of the straight short metal fibers having a predetermined fiber diameter d and an average length L equal to or greater than the fiber diameter d. By making the surface rough, the more effective concave portion can be provided. Moreover, the molded body is used as the porous metal substrate 2 by sintering and molding so as to have predetermined pore characteristics.

  The pore diameter of the pore 21 is not particularly limited and should be appropriately selected depending on the application. For example, the maximum pore diameter is 10 μm or less, preferably 5 μm or less, and the measurement can be determined by, for example, a bubble point test.

  In addition, the porous metal substrate 2 can be constituted by one having the above-mentioned characteristics throughout, and for example, a support having relatively coarse pore characteristics is used as the first porous metal substrate 2a. Further, it is also preferable to use a composite structure in which the second porous metal base material 2b formed relatively thin with the pore diameter having fine pore characteristics on the upper surface side is superposed and integrated. In such a composite structure, the thickness of the second metal substrate 2b can be reduced to the minimum necessary, and as a metal substrate having a porous structure, it is low while having fine pore characteristics. There is an advantage of providing a necessary and sufficient structural strength with pressure loss.

  More specifically, the first metal substrate 2a is composed of, for example, a support made of a powder material of relatively coarse particles having a particle diameter of several tens to several hundreds of μm, and the first metal substrate 2a having the above structure on the surface thereof. A bimetallic substrate 2b is provided. This second porous metal substrate 2b has a non-smooth undulation surface on the outer surface due to a random distribution of short metal fibers having a predetermined fiber diameter d and an average length L equal to or greater than the fiber diameter d. For example, the short metal fibers are randomly distributed with an average diameter d of 10 μm or less (preferably 0.01 to 5 μm) and an average length L in the range of 1 to 20 times the diameter. It is recommended to use a ligation. These particle diameters, average diameters, and average lengths are not uniform and vary within the lot. For example, the average diameter of the short metal fibers is the average of the dimensions of the transverse and longitudinal directions of each short fiber, and the average length is also the same for each arbitrary short fiber. It is shown in the dimension which is statistically processed for the thickness.

  Such a composite-structured metal substrate is suitable as a surface filtration filter for filtering with the fine surface layer of the second metal substrate 2b, and its structure, type and molding thickness are not limited. Can be held stably. For example, the porous metal substrate 2 has a thickness of 0.3 to 3 mm, and in the composite structure, the second metal substrate 2b preferably has a thickness of about 0.05 to 0.5 mm. Moreover, the shape of the shape is exemplified by various shapes such as a plate shape, a hollow tubular shape, and a bottomed tubular shape, but is not limited thereto.

  The ceramic porous body 3A constituting the layer 3 of the ceramic porous body is, for example, an oxide selected from one or more of zirconium hydroxide, zirconia, yttrium, cerium, titanium, aluminum, and silicon, and / or hydroxylated. And porous structures such as mixtures and mixed oxides thereof. Among them, in particular, those mainly composed of zirconium hydroxide and / or zirconia can be easily sintered to form a good ceramic porous body, and since the coefficient of thermal expansion is close to that of metal, it has an affinity for metal. There are high features. In that case, the ceramic porous body preferably contains, for example, 60% or more of zirconium hydroxide and / or zirconia in the solidified state. Further, those containing yttrium are more preferred because they have the effect of stabilizing the crystal structure and improving the heat resistance. In that case, the content of the yttrium is recommended to be, for example, 1 to 30 wt%, preferably 2 to 15 wt%. The ceramic porous body with these compositions is suitable for the present invention.

Conventionally, for example, a dispersion slurry of ceramic fine particles or a sol-like or gel-like ceramic fine particle precursor is coated on a porous metal substrate by a method such as spraying, screen printing, dipping, electrophoretic electrodeposition or gas deposition. A ceramic film material has been formed by using such a method. However, in the case of such a method, in order to close the relatively large surface pores 21 of the porous metal substrate 2, the surface of the porous metal substrate 2 is completely covered with a ceramic layer until the surface becomes smooth. It is necessary and requires a great deal of cost and labor.

  Therefore, in the present invention, a metal alkoxide is selected to form such a fine porous portion, and a solution (metal alkoxide solution) dissolved in a solvent is applied onto the surface of the porous metal substrate 2. And forming a metal hydroxide and / or oxide by hydrolyzing the metal alkoxide in the pores 21 on the surface of the porous metal substrate 2 by placing it under conditions where water vapor and / or water are present. And confirming that the layer 3 of the predetermined ceramic porous body can be satisfactorily formed by the method of removing the alcohol or metal alkoxide solvent as one of the reaction products. It is configured by continuously covering the pores 21 that open upward and the exposed surfaces of the constituent material 2A of the metal substrate 1 that constitutes the pores 21.

  In order to increase the affinity of the ceramic porous body 3A for the porous metal substrate 2, it is preferable to form a predetermined oxide film on the surface of the porous metal substrate 2 in advance. The oxide film has, for example, a specific color other than the original intrinsic metal color of the metal material. As an optimal oxidation treatment method, for example, the metal substrate 2 is made of sodium hydroxide, potassium hydroxide or the like. It can be easily formed by a chemical reaction caused by immersion or application in an alkaline solution or other various oxidation treatment liquids, or a thermal reaction by heat treatment in an oxidizing atmosphere such as air. . The unique metal color of the metal material is confirmed as a color in a state in which the metal material is crushed, cut, or surface-cleaned, for example.

  Such an oxide film improves the compatibility with the processing fluid at the time of forming the ceramic porous body, and the surface state can be roughened to a dull finish state, thereby improving the bonding property between the two. Further, when the latter is a heat treatment in an oxidizing atmosphere and the metal substrate 2 is made of stainless steel, for example, 1 minute by heating at 400 to 850 ° C. in air, preferably 500 to 700 ° C. Hold for ~ 5 hours. By the treatment, an oxide film having a temper color of, for example, orange, brown, brown, red, or gold is formed on the metal base 2. Such a color change is a phenomenon that is also observed in the case of the chemical reaction, and a similar oxide film is formed.

  The color changes variously depending on the type of metal material constituting the metal substrate, its processing conditions, and the degree of oxidation, and at the same time changes the thickness of the oxide film. For example, in the heat treatment of the stainless steel, the temper color is darkened with increasing heating conditions, such as orange to gold to red at 500 ° C., brown to reddish brown at 600 ° C., purple brown at 700 ° C., Along with this, the amount of oxidation also increases, but on the other hand, the colors may be difficult to be converted into specific numerical values, and therefore include intermediate colors thereof. In addition to improving the compatibility with the ceramic porous body, this oxide film also has advantages such as surface protection and process identification management.

  Examples of the metal alkoxide include zirconium propoxide, zirconium isopropoxide, zirconium butoxide, zirconium t-butoxide, yttrium isopropoxide, titanium isopropoxide, aluminum ethoxide, aluminum isopropoxide, aluminum butoxide, and methyl silicate. These compounds are exemplified, but other metal alkoxides may be used. The metal alkoxide solvent may be any one that is not reactive with the metal alkoxide, and preferably has a low water content. Examples of such a solvent include alcohol dehydrates such as methanol, ethanol, and propanol, but other solvents may be used.

  Further, a metal salt or complex such as yttrium, cerium, or zirconium may be dissolved in a solvent. Examples of such compounds include yttrium nitrate, cerium nitrate, yttrium acetylacetonate, and zirconium acetylacetonate. These compounds may contain water of crystallization. In such a case, after dissolving in a solvent, the solvent may be dehydrated with a dehydrating agent such as molecular sieves. Here, the concentration of the metal alkoxide in the metal alkoxide solution in which the metal alkoxide is dissolved in the solvent and the conditions for applying the metal alkoxide will affect the penetration depth when the metal alkoxide is formed on the metal substrate. It is preferable to set in the range of%.

  The introduction of the metal alkoxide solution into the pores 21 opened on the surface of the porous metal substrate 2 can be achieved, for example, by immersing the porous metal substrate 2 in the metal alkoxide solution and then pulling it up in the air. In addition to the immersion method in the solution, the ceramic porous body 3A is provided on the one surface side by, for example, coating or spraying, for example, by the capillary phenomenon or further by vacuum suction from the other surface side, to a predetermined depth ( It is possible to infiltrate into H) or to provide a concentration gradient that gradually reduces the distribution amount from the surface side.

  The formation thickness is, for example, 0.5 to 50 μm, preferably 1 to 20 μm or less by adjusting the concentration, and the formation thickness H is, for example, as shown in FIG. 2 when the cross section in the thickness direction is enlarged. The average dimension between the virtual upper surface obtained by averaging the convex portions and the concave portions (valley portions) on the surface side and the lowermost surface of the layer 3 of the ceramic porous body is shown, and the measurement width is, for example, 2 mm.

  Thus, the metal alkoxide solution that has entered the pores 21 reacts with moisture in the air and starts to solidify. The time for placing in the air may be appropriately adjusted depending on the reactivity, concentration, air humidity, and temperature of the metal alkoxide solution, but it is usually preferably 30 minutes or longer. If it is shorter than this, solidification of the metal alkoxide solution may be insufficient. Further, in order to complete the solidification, it may be placed in the air for a long time. However, in order to proceed the hydrolysis more completely, it can be brought into contact with steam or immersed in water. Removal of the alcohol or metal alkoxide solvent, which is one of the reaction products, may be performed by degassing by heating and / or decompression.

  Furthermore, in order to make the ceramic porous body 3A formed here stronger and dry, it is possible to further perform heating (sintering) at a relatively low temperature of, for example, 400 ° C. or lower. What is necessary is just to adjust a heating temperature and a heating time suitably according to the physical property calculated | required by the porous filter 1 obtained. Moreover, the ceramic porous body 3A penetrates into the pores 21 opened on the surface side of the porous metal substrate 2 and covers the exposed surface of the constituent material 2A. Concave portions 31 corresponding to the surface state of the pores 21 and the undulating surface of the porous metal substrate are formed.

  In order to reduce the size of the concave portion 31, a series of steps subsequent to the immersion in the metal alkoxide may be repeated. At this time, the introduction of the metal alkoxide solution into the pores 21 may be promoted by reducing the pressure from the other surface side of the porous metal substrate 2.

  Here, for the concave portion 31, for example, an average maximum diameter when a predetermined concave portion is observed (maximum diameter of the concave portion 31 when the porous filter 1 is viewed in a plan view; a maximum dimension in the left-right direction shown in FIG. 2) The maximum depth (the maximum dimension in the vertical direction shown in FIG. 2) of the concave portion is determined. The verification is performed by, for example, observing the observation field arbitrarily extracted with respect to the porous filter by the presence or absence of the concave portion confirmed in the field of view. The number of visual fields is, for example, about 3 to 10 points, and is measured using a laser microscope, SEM, or the like. As a simple method, for example, the surface roughness of the surface having the concave portion can be verified.

  The maximum diameter of the recess 31 is, for example, 0.5 times or more the diameter of the metal powder or short fiber material constituting the porous metal member, and for hydrogen separation disposed on the surface thereof. From the viewpoint of forming a thin film material, the thickness is set to 20 μm or less, and the maximum depth is, for example, in the range of 1 to 20 μm, preferably 10 μm or less.

This concave portion is formed based on the undulating surface including the pores 21 of the porous metal base 2 of the base. As shown in, for example, an arbitrary enlarged cross-sectional view as shown in FIG. Since the pores 21 opened on the surface of the material 2 are mixed with deep and shallow ones, in the ceramic porous body 3A encapsulating the porous metal substrate 2, the depth is small. On the shallow pore 21, there may be a case where the concave portion 31 corresponding to the pore 21 is not formed. Therefore, the number of the recesses 31 in the ceramic porous body 3A based on the pores 21 opened on the surface of the porous metal substrate 2 is larger than the number of the pores 21 opened on the surface of the porous metal substrate 2. If the ratio is too small, there is a concern that it is difficult to ensure high adhesion when a hydrogen separation membrane such as palladium or palladium alloy is further formed on the surface of the porous filter 1. The number of the recesses 31 formed based on the pores 21 opened on the surface of the substrate 2 is, for example, 30% with respect to the number of the pores 21 opened on the surface of the porous metal substrate 2. It is preferable to configure so that the number becomes the above. More preferably, for example, by providing 50 / mm ² or more of the concave portions 31, it is possible to improve the adhesion when the hydrogen separation membrane is formed on the porous filter 1.

  As a result, the porous filter 1 thus obtained has the exposed surfaces of the pores 21 and the constituent material 2A thereof over the entire surface layer of the porous metal substrate 2 immersed in the metal alkoxide solution. The ceramic porous body 3A is continuously encapsulated. The coating thickness on the exposed surface of the constituent material is, for example, 5 μm or less, preferably 3 μm or less, more preferably 1 μm or less. The coating thickness means the coating thickness that covers the outermost surface of the constituent material 2A (short fiber) of the porous metal substrate 2.

  The porous filter 1 of the present invention smoothes the flow of the fluid to be treated by the layered composite structure in which the pores 21 opening on the surface of the porous metal substrate 2 are further refined by the ceramic porous body 3A. And contributes to the improvement of corrosion resistance. Also, when the hydrogen separation membrane is laminated on the surface thereof, the presence of the porous ceramic body 3A can provide a shielding effect for suppressing diffusion of adjacent metal materials, and can have durability.

  Next, a hydrogen separation membrane using the porous filter and a manufacturing method thereof will be described. As shown in FIG. 3, the hydrogen separation membrane 5 of the present invention has a palladium thin film or a palladium alloy thin film 4 formed on the undulating surface of the porous filter 1 as a support. Note that FIG. 3 is partially enlarged or reduced rather than the actual size ratio in order to facilitate understanding of the configuration.

  The palladium alloy thin film is preferably an alloy (palladium alloy) of palladium and one or more metals selected from the group consisting of silver, gold, copper, nickel, platinum, rhodium and ruthenium. The proportion of palladium in such a palladium alloy is preferably 40% by weight or more. The average film thickness of the palladium thin film or the palladium alloy thin film is set to, for example, 0.5 to 10 μm, preferably 1 to 7 μm. If the film thickness is smaller than this, the pinholes of the film increase and it is difficult to ensure hydrogen selectivity as a hydrogen separation membrane. If the film thickness is larger than this, the hydrogen permeation rate is reduced and the practicality is lost.

  The formation of the palladium thin film or the palladium alloy thin film directly on the surface of the porous filter 1 may be performed by a known method such as electroless plating, chemical vapor deposition, or magnetron sputtering. When forming a palladium alloy thin film, the metal thin films constituting the palladium alloy may be laminated and then alloyed by heating. After the formation of the first metal thin film on the porous filter 1, the electroplating method can be used for film formation because the surface has conductivity. The first metal thin film is preferably a thin film containing palladium. Even when the first metal thin film is a thin film containing no palladium, a palladium alloy thin film can be formed by alloying by subsequent heating if a thin film containing palladium is formed thereabove. .

  Here, as a pre-stage for forming the palladium thin film or the palladium alloy thin film on the surface of the porous filter 1, defects existing on the surface of the porous filter 1 may be sealed in advance with a metal such as palladium. A conventionally known method can be adopted as the sealing method. For example, first, after applying an electroless plating catalyst to the surface of the ceramic porous body layer 3 in the porous filter 1, the plating catalyst is reduced. Thereafter, an electroless plating solution containing metal ions such as palladium ions and a reducing agent is disposed on the porous metal substrate 2 side of the porous filter 1, and a concentrated solution such as glucose is applied to the layer 3 side of the ceramic porous body. Arranging and guiding the electroless plating solution to defects present on the surface of the layer 3 of the ceramic porous body, where the defects can be sealed by depositing metal (palladium or the like). When the porous filter 1 whose surface defects are sealed with a metal such as palladium is used as a support for the hydrogen separation membrane, pinhole generation in the palladium thin film or palladium alloy thin film formed on the support is suppressed. As a result, the film thickness can be reduced as compared with the prior art. When the porous filter 1 is used as a support for the hydrogen separation membrane, for example, as disclosed in Japanese Patent Application Laid-Open No. 2007-90294, it is generally performed to form a module in a bottomed cylindrical shape.

  The thus configured hydrogen separation membrane 5 constitutes a module as disclosed in the above publication, and can be used to separate only hydrogen from a mixed gas containing hydrogen. For example, a hydrogen-containing mixed gas is supplied to the upstream side separated by the hydrogen separation membrane and permeated to the downstream side through the hydrogen separation membrane, and the hydrogen partial pressure of the downstream hydrogen-containing mixed gas is reduced. This is achieved by setting it to be lower than the hydrogen partial pressure on the upstream side.

  Thus, hydrogen selectively permeates through the hydrogen separation membrane, and only hydrogen on the hydrogen-containing mixed gas side can be moved to the opposite side for separation. The temperature of the hydrogen separation membrane in this case is usually about 150 ° C. to 700 ° C., preferably about 300 ° C. to 600 ° C. If the temperature is too low, embrittlement of the palladium or palladium alloy thin film tends to occur, and if the temperature is too high, the film tends to deteriorate, which is not preferable.

  Hereinafter, the present invention will be described in more detail with reference to examples.

<Example 1>
Stainless steel sintered body having an average fiber diameter of 3 μm and an average length of 15 μm is formed on the outer peripheral surface of a stainless powder sintered body formed into a bottomed cylindrical shape having an outer diameter of 15 mm, a thickness of 2 mm, and a length of 45 mm. A porous metal substrate formed with a fine layer as a constituent material and integrally laminated and sintered was used. The fine layer of short fibers has a structure thickness of 0.2 mm and uniform fine pores of about 2.5 μm throughout the layer, and the short fibers are randomly distributed on the outer surface. It was what formed the undulating surface. And this metal base material was heated in air at 600 degreeC for 5 hours, and was equipped with the brown-brown oxide film on the surface. (Step 1)

  Next, this stainless steel sintered metal filter (porous metal base material) was immersed in a 1-propanol solution (metal alkoxide solution) containing 17% by weight of zirconium propoxide, which is a metal alkoxide, and then pulled up. The shaft was rotated at a rotational speed of 50 rpm for 5 minutes to uniformly disperse the adhered solution on the outer peripheral surface side of the metal substrate (Step 2). Then, it was left in the air at room temperature for 1 hour. This rotation treatment prevents excessive penetration of the metal base material into the pores and contributes to the formation of the concave portion on the surface side.

  Next, steam was sprayed onto the surface with a commercially available steam washer to clean the surface, and the hydrolysis of zirconium propoxide (metal alkoxide) was made more complete, then immersed in acetone and taken out into the air (step 3). ). And it dried for 1 h at 80 degreeC in the air. (Step 4).

  Next, the steps 2 to 4 were repeated, and the porous filter according to Example 1 was obtained by heating in air at 200 ° C. for 10 hours. By this repeated treatment, the ceramic porous body reliably closed the gap at the joint interface with the metal substrate, and the characteristics as a porous body could be improved. Here, the porous filter according to Example 1 has a structure in which the outer surface of a bottomed cylindrical stainless steel sintered metal filter (porous metal substrate) is covered with a layer of a ceramic porous body. .

<Example 2>
For the porous filter according to Example 1, Steps 2 to 4 were repeated twice. However, in this example, in the step 2, the sintered metal filter made of stainless steel is immersed in a 1-propanol solution (metal alkoxide solution) containing 13% by weight of zirconium propoxide (metal alkoxide), and the zirconium propoxide is hydrolyzed. After the ceramic porous body was formed by decomposition, it was heated in air at 200 ° C. for 10 hours and dried. And the process of steps 2-4 was once implemented twice with respect to this obtained molded article. However, in step 2 performed once again, the inside of the stainless steel sintered metal filter was immersed in a 1-propanol solution containing 6% by weight of zirconium propoxide while reducing the pressure. And the porous filter which concerns on Example 2 was obtained by heating at 200 degreeC for 10 hours in the air.

  As a result of observing the surface of the porous filter thus formed with a scanning electron microscope, as shown in FIG. 4, the exposed surface of the pores on the surface of the porous metal substrate is covered with a layered ceramic porous body. In spite of this, it was confirmed that a concave portion based on pores opened on the surface of the porous metal substrate was formed.

  Further, as seen in a scanning electron microscope image of the stainless sintered metal filter (porous metal substrate) before being covered with the ceramic porous body shown in FIG. 5, the stainless sintered metal filter (porous metal substrate) The thickness of the layered ceramic porous body on the stainless sintered metal filter (porous metal substrate) is 2 μm or less. Further, the maximum pore diameter of pores opening on the surface of this porous filter by the bubble point test was 0.7 μm.

<Example 3>
As the solution used in Step 2 of Example 1, a 1-propanol solution (metal alkoxide solution) containing 13% by weight of zirconium propoxide (metal alkoxide) was used, and Steps 1 to 4 shown in Example 1 were performed. Further, Steps 2 to 4 were performed once more. Then, after heating at 400 degreeC in the air for 10 hours, the process of step 2-4 was repeated twice again. However, in Step 2, the inside of the stainless steel sintered metal filter was immersed in a 1-propanol solution containing 7% by weight of zirconium propoxide while reducing the pressure. Further, after heating again in air at 400 ° C. for 10 hours, the steps 2 to 4 were repeated twice to obtain a porous filter according to Example 3. At this time, in Step 2, the stainless steel sintered metal filter was immersed in a 1-propanol solution containing 8% by weight of zirconium propoxide and 0.1% by weight of yttrium nitrate while reducing the pressure.

  Subsequently, in order to seal the defect which exists in the surface (surface of the ceramic porous body layer) of the formed porous filter, the following sealing processes were implemented. First, the bottomed cylindrical porous filter according to Example 3 was immersed in a commercially available alkaline catalyst solution (Okuno Pharmaceutical Co., Ltd., OPC-50 inducer) at 50 ° C., and its outer surface (ceramic porous body) Palladium ions were adhered to the surface of the layer. Subsequently, palladium was added to the outer surface by dipping in a reducing solution containing a commercially available dimethylaminoborane (Okuno Pharmaceutical Co., Ltd., OPC-150 Cryster MU) to reduce palladium ions. An electrolytic palladium plating solution (Okuno Pharmaceutical Co., Ltd., Paratop) is filled into the bottomed cylindrical porous filter, and the outer surface of the porous filter (the surface of the ceramic porous layer) has a glucose concentration of 4 mol / L. In an aqueous solution of 50 ° C, the electroless palladium plating solution is moved from the inside to the outside of the porous filter and flows out through the defective portion of the outer surface of the porous filter. Palladium metal was deposited, and defects opening on the outer surface were closed and / or covered with metal. This series of sealing steps was performed twice.

  After the porous filter according to Example 3 in which the sealing step was completed was washed with water, it was immersed in a commercially available alkaline catalyst solution at 50 ° C. to allow palladium ions to adhere to the outer surface, and subsequently in a commercially available reducing solution. Then, the outer surface of the support was immersed in a commercially available electroless palladium plating solution at 50 ° C. to deposit palladium on the outer surface of the porous filter.

  The average film thickness of the obtained palladium-containing thin film was 2.5 μm. And the porous filter in which the palladium containing thin film was formed in the outer surface was immersed in the electroplating liquid which consists of a copper ethylenediamine complex, the copper electroplating was performed, and the copper containing thin film was formed on the palladium thin film. After washing and drying, the temperature was raised to 400 ° C. under an argon stream, followed by heat treatment at 400 ° C. for 24 hours under a hydrogen stream to obtain a 5 μm-thick palladium / copper alloy thin film using a porous filter as a support. A hydrogen separation membrane 5 was obtained.

The hydrogen permeation rate (k) of a hydrogen separation membrane containing palladium as a main component generally follows the Sievert law. That is,
k = J / (p1 ^0.5 -p2 ^0.5 )
It becomes. Here, J is the hydrogen permeation flow rate (mmol / s / m ² ), p1 is the inlet-side hydrogen partial pressure (Pa), and p2 is the outlet-side hydrogen partial pressure (Pa).

Therefore, in order to evaluate the performance of the hydrogen separation membrane obtained by the above method, a hydrogen permeation test was performed in the range of a hydrogen differential pressure of 0 to 2 atm. As a result, 0.6 mmol / s / m ² / Pa ^{0 at} 400 ° C. A hydrogen permeation rate of ^.5 was obtained. In addition, when the permeation | transmission test of argon was done, there was no remarkable permeation | transmission of argon. Moreover, peeling of the palladium thin film or the like was not observed, and the film had good adhesion.

DESCRIPTION OF SYMBOLS 1 Porous filter 2 Porous metal base material 2A Constituent material 21 Pore 3A opened to the surface in a porous metal base material Ceramic porous body 3 Ceramic porous body layer 31 Recessed part 5 Hydrogen separation membrane

Claims (11)

A porous metal substrate, and a ceramic porous body provided on any one side of the porous metal substrate;
The ceramic porous body continuously covers the porous metal base material into the pores on the one surface side and the exposed surface of the porous metal base material constituting the pores. The outer surface has a recess based on the undulating surface of the porous metal substrate.   The porous filter according to claim 1, wherein the porous metal substrate is covered with an oxide film having a specific color different from a metal color unique to the metal.   The porous filter according to claim 2, wherein the oxide film is made of an oxide having a specific color of any one of orange, brown, brown, red, and gold.   The porous filter according to claim 1, wherein the ceramic porous body is composed of zirconium hydroxide and / or zirconia.   The porous filter according to claim 4, wherein the ceramic porous body further contains yttrium.   The porous metal substrate is composed of a laminated sintered body of a support portion having coarse pores and a fine layer having finer pores arranged and laminated on one side thereof, and the ceramic porous body is The porous filter according to claim 1, wherein the porous filter is provided in the fine layer.   The fine layer of the porous metal substrate has a predetermined fiber diameter d and a random distribution of straight metal short fibers having an average length L equal to or greater than the fiber diameter d, and the outer surface thereof is non-smooth. The porous filter according to claim 6, comprising a undulating surface.   A hydrogen separation membrane comprising a palladium thin film or a palladium alloy thin film for hydrogen separation on the undulating surface of the porous filter according to any one of claims 1 to 7.   The hydrogen partial pressure on the upstream side of the hydrogen separation membrane according to claim 8 is subjected to hydrogen permeation separation on the downstream side, and the hydrogen partial pressure on the downstream side is made lower than the hydrogen partial pressure on the upstream side. A method for separating hydrogen from a hydrogen-containing mixed gas. A) a preparation stage of preparing a porous metal substrate having predetermined pore characteristics;
B) Surface oxidation that forms an oxide film having a specific color other than the intrinsic metal color on the surface of the metal substrate by heat treatment in an oxidizing atmosphere at a temperature of 400 to 850 ° C. or immersion treatment in an alkaline solution. Processing stage,
C) The porous metal base material that penetrates into the pores on one side of the metal base material provided with the oxide film and continuously covers the exposed surface of the porous metal base material constituting the pores; A step of a composite treatment comprising a recess on the outer surface and forming a composite ceramic porous body having finer pores than the porous metal substrate;
D) providing a drying step for drying after the combined treatment;
A method for producing a porous filter characterized by the above. The method for producing a porous filter according to claim 10, wherein the ceramic porous body is obtained by hydrolysis of a metal alkoxide.