Separation membrane composite and method for producing separation membrane composite

Abstract

A separation membrane composite (1) comprises: a porous support (11); a first separation layer (13) that is in contact with the surface of the support (11) and is a membrane composed of zeolite; and a second separation layer (14) that is in contact with the surface of the first separation layer (13) on the side opposite the support (11) and that is an amorphous membrane in which zeolite fine particles (141) are mixed. Due to this configuration, it is possible to prevent a decrease in separation performance when the separation membrane composite (1) is used under high pressure.

Description

Separation membrane composite and method for producing the separation membrane composite

[0001] The present invention relates to a separation membrane composite and a method for manufacturing a separation membrane composite. [Reference to Related Applications] This application claims the benefit of priority from Japanese Patent Application JP2024-10863, filed on January 29, 2024, the entire disclosure of which is incorporated herein by reference.

[0002] Zeolite membranes have traditionally been used as separation membranes that utilize molecular sieving. Zeolite membranes are typically provided on a porous support and treated as separation membrane composites. For example, Japanese Patent Application Laid-Open No. 2020-163369 (Reference 1) discloses a zeolite membrane composite in which a zeolite membrane made of a 6-membered ring zeolite is provided on a support. In this zeolite membrane, among a plurality of zeolite crystal grains located on the surface, zeolite crystal grains having a minor axis of 300 nm or less occupy 85% or more of the surface area, thereby enabling easy removal of an organic structure-directing agent (hereinafter referred to as "organic SDA") from the zeolite membrane. Furthermore, Japanese Patent Laid-Open Publication No. 2007-320819 (Document 2) discloses a method for producing SOD-type zeolite, in which a reaction solution is heated to 80° C. to 200° C. to synthesize an organic SDA-containing zeolite, and then the organic SDA is removed by heat treatment at 500° C. to 1200° C. Japanese Patent Laid-Open Publication No. 2012-246207 (Document 3) discloses a method for synthesizing an SOD-type zeolite membrane that does not contain organic SDA.

[0003] International Publication No. 2023 / 140335 (Document 4) discloses a composite separation structure having a zeolite layer arranged in contact with a substrate and an amorphous silica layer arranged in contact with the zeolite layer. Japanese Patent Publication No. 6622714 (Document 5) discloses a zeolite membrane structure in which a first zeolite membrane is formed on a support and a second zeolite membrane is formed on the first zeolite membrane. International Publication No. 2017 / 169591 (Document 6) discloses a method for preparing a porous support and a method for synthesizing a DDR-type zeolite membrane.

[0004] Incidentally, microcracks may occur in the zeolite membrane when the zeolite membrane is calcined to remove the organic SDA as described in References 1 and 2. In this case, when the separation membrane composite is used under high pressure, cracks may propagate from the microcracks in the zeolite membrane, resulting in a decrease in separation performance.

[0005] An object of the present invention is to prevent a decrease in separation performance when a separation membrane composite is used at high pressure.

[0006] A first aspect of the invention is a separation membrane composite comprising: a porous support; a first separation layer that is in contact with the surface of the support and is a membrane made of zeolite; and a second separation layer that is in contact with the surface of the first separation layer opposite the support and is an amorphous membrane containing zeolite microparticles.

[0007] According to the present invention, it is possible to suppress a decrease in separation performance when the separation membrane composite is used at high pressure.

[0008] A second aspect of the present invention is the separation membrane composite of the first aspect, wherein the second separation layer has a thickness of 5 nm or more and 200 nm or less.

[0009] A third aspect of the present invention is the separation membrane composite of the first or second aspect, wherein the average particle size of the zeolite fine particles contained in the second separation layer is 1 nm or more and 100 nm or less.

[0010] A fourth aspect of the present invention is the separation membrane composite of any one of the first to third aspects, wherein the proportion of the zeolite fine particles in the second separation layer is 20% or more in a cross section perpendicular to the surface of the support.

[0011] A fifth aspect of the invention is a method for producing a separation membrane composite, comprising: a) preparing a porous support; b) forming a first separation layer, which is a membrane made of zeolite, on the surface of the support; and c) forming a second separation layer, which is an amorphous membrane containing zeolite microparticles, on the surface of the first separation layer opposite the support, wherein the c) step comprises: c1) immersing the support on which the first separation layer has been formed in a pretreatment liquid containing oxides of constituent elements to be used to form the zeolite microparticles for a predetermined period of time; c2) removing the support from the pretreatment liquid and drying it; c3) immersing the support in a raw material solution containing the constituent elements and an organic structure-directing agent to perform hydrothermal synthesis, thereby forming the second separation layer on the support; and c4) removing the organic structure-directing agent from the second separation layer on the support.

[0012] A sixth aspect of the invention is the method for producing a separation membrane composite according to the fifth aspect, further comprising, between the steps c3) and c4), a step of immersing the support on which the second separation layer has been formed in a post-treatment liquid adjusted to a pH of 9 or higher for one day or more.

[0013] The above and other objects, features, aspects and advantages will become more apparent from the following detailed description of the invention which proceeds with reference to the accompanying drawings.

[0014] Fig. 1 is a cross-sectional view of a separation membrane composite; Fig. 2 is a cross-sectional view showing an enlarged portion of the separation membrane composite; Fig. 3 is a view for explaining the structure of a second separation layer; Fig. 4 is a view showing the flow of manufacturing a separation membrane composite; Fig. 5 is a view showing a separation device; Fig. 6 is a view showing the flow of separation of a mixed substance.

[0015] FIG. 1 is a cross-sectional view of a separation membrane composite 1. FIG. 2 is a cross-sectional view showing an enlarged portion of the separation membrane composite 1. The separation membrane composite 1 includes a porous support 11 and a laminated membrane 12 provided on the support 11. In FIG. 1, the laminated membrane 12 is depicted with a thick line. The laminated membrane 12 includes a first separation layer 13 and a second separation layer 14. The first separation layer 13 is provided on the support 11, and the second separation layer 14 is provided on the first separation layer 13. In FIG. 2, the first separation layer 13 and the second separation layer 14 are depicted with parallel oblique lines at different intervals. Furthermore, in FIG. 2, the first separation layer 13 and the second separation layer 14 are depicted as being thicker than they actually are.

[0016] The support 11 is a porous member that is permeable to gases and liquids. In the example shown in FIG. 1 , the support 11 is a monolithic support having a single, continuous columnar body formed integrally with the support 11, and a plurality of through-holes 111 extending in the longitudinal direction (i.e., the left-right direction in FIG. 1 ). In the example shown in FIG. 1 , the support 11 is substantially cylindrical. The cross section perpendicular to the longitudinal direction of each through-hole 111 (i.e., cell) is, for example, substantially circular. In FIG. 1 , the diameter of the through-hole 111 is drawn larger than in reality, and the number of through-holes 111 is drawn smaller than in reality. The laminated film 12 is formed on the inner circumferential surface of the through-hole 111, covering the inner circumferential surface of the through-hole 111 over substantially the entire surface.

[0017] The length of the support 11 (i.e., the length in the left-right direction in FIG. 1 ) is, for example, 10 cm to 200 cm (the symbol "to" means greater than or equal to the value before it and less than or equal to the value after it). The outer diameter of the support 11 is, for example, 0.5 cm to 30 cm. The distance between the central axes of adjacent through holes 111 is, for example, 0.3 mm to 10 mm. The surface roughness (Ra) of the support 11 is, for example, 0.1 μm to 5.0 μm, and preferably 0.2 μm to 2.0 μm. The shape of the support 11 may be, for example, a honeycomb shape, a flat plate shape, a tubular shape, a cylindrical shape, a columnar shape, or a polygonal pillar shape. When the shape of the support 11 is tubular or cylindrical, the thickness of the support 11 is, for example, 0.1 mm to 10 mm.

[0018] The material of the support 11 can be various substances (for example, ceramic or metal) as long as they are chemically stable in the process of forming the laminated film 12 on the surface. In this embodiment, the support 11 is formed of a ceramic sintered body. Examples of ceramic sintered bodies selected as the material of the support 11 include alumina, silica, mullite, zirconia, titania, yttria, silicon nitride, and silicon carbide. In this embodiment, the support 11 includes at least one of alumina, silica, and mullite.

[0019] The support 11 may contain an inorganic binder, which may be at least one of titania, mullite, sinterable alumina, silica, glass frit, clay minerals, and sinterable cordierite.

[0020] The average pore diameter of the support 11 is, for example, 0.01 μm to 70 μm, preferably 0.05 μm to 25 μm. The average pore diameter of the support 11 near the surface on which the laminated film 12 is formed is 0.01 μm to 1 μm, preferably 0.05 μm to 0.5 μm. The average pore diameter can be measured, for example, by a mercury porosimeter, a perm porometer, or a nanoperm porometer. Regarding the pore diameter distribution throughout the support 11, including the surface and interior, D5 is, for example, 0.01 μm to 50 μm, D50 is, for example, 0.05 μm to 70 μm, and D95 ​​is, for example, 0.1 μm to 2000 μm. The porosity of the support 11 near the surface on which the laminated film 12 is formed is, for example, 20% to 60%.

[0021] The support 11 has, for example, a multilayer structure in which multiple layers with different average pore diameters are stacked in the thickness direction. The average pore diameter and sintered grain size in the surface layer, including the surface on which the laminated film 12 is formed, are smaller than the average pore diameter and sintered grain size in the layers other than the surface layer. The average pore diameter of the surface layer of the support 11 is, for example, 0.01 μm to 1 μm, and preferably 0.05 μm to 0.5 μm. When the support 11 has a multilayer structure, the materials described above can be used for each layer. The materials of the multiple layers forming the multilayer structure may be the same or different.

[0022] As described above, a laminated film 12 is provided on the surface of the support 11. The laminated film 12 can be used as a membrane that separates a specific substance from a mixture containing multiple types of substances by utilizing molecular sieving action. Other substances are less likely to permeate the laminated film 12 than the specific substance. In other words, the permeation rate of the other substances through the laminated film 12 is lower than the permeation rate of the specific substance. The laminated film 12 includes a first separation layer 13 in contact with the surface of the support 11 and a second separation layer 14 in contact with the surface of the first separation layer 13 opposite the support 11. The first separation layer 13 is a membrane made of zeolite. A membrane made of zeolite is at least a membrane of zeolite formed on the surface of the support 11, and does not include a membrane in which zeolite particles are simply dispersed in an organic film.

[0023] The thickness of the first separation layer 13 is, for example, 0.05 μm to 30 μm. The thickness of the first separation layer 13 is preferably 5 μm or less, more preferably 4 μm or less, and even more preferably 3 μm or less. The thickness of the first separation layer 13 is preferably 0.1 μm or more, and more preferably 0.5 μm or more. The thickness of the first separation layer 13 can be measured, for example, by imaging a cross section of the first separation layer 13 perpendicular to the surface of the support 11 using a scanning electron microscope (SEM) or the like.

[0024] The average pore diameter of the first separation layer 13 is preferably 1.0 nm or less, more preferably 0.8 nm or less, and even more preferably 0.6 nm or less. The average pore diameter of the first separation layer 13 is preferably 0.1 nm or more, more preferably 0.2 nm or more, and even more preferably 0.3 nm or more. The average pore diameter of the first separation layer 13 is smaller than the average pore diameter of the support 11 near the surface on which the first separation layer 13 is formed.

[0025] When the maximum number of rings in the zeolite constituting the first separation layer 13 is n, the average pore size is the arithmetic mean of the minor and major axes of the n-membered ring pores. An n-membered ring pore is a pore in which the number of oxygen atoms in the ring structure formed by bonding an oxygen atom to a T atom is n. When the zeolite has multiple types of n-membered ring pores with the same n, the average pore size of the zeolite is the arithmetic mean of the minor and major axes of all types of n-membered ring pores. Thus, the average pore size of a zeolite membrane is uniquely determined by the skeletal structure of the zeolite and can be determined from the values ​​disclosed in the International Zeolite Association's "Database of Zeolite Structures" [online] on the Internet at http: / / www.iza-structure.org / databases / .

[0026] The type of zeolite constituting the first separation layer 13 is not particularly limited, and may be, for example, AEI type, AEN type, AFN type, AFV type, AFX type, BEA type, CHA type, DDR type, ERI type, ETL type, FAU type (X type, Y type), GIS type, LEV type, LTA type, MEL type, MER type, MFI type, MOR type, MTN type, PAU type, RHO type, SAT type, SOD type, SZR type, or other zeolite. The maximum number of rings in the zeolite constituting the first separation layer 13 is preferably 8 or more. The first separation layer 13 is, for example, a DDR type zeolite. In other words, the first separation layer 13 is a zeolite membrane composed of a zeolite whose structure code is "DDR" as defined by the International Zeolite Association. In this case, the zeolite constituting the first separation layer 13 has an intrinsic pore size of 0.36 nm×0.44 nm and an average pore size of 0.40 nm.

[0027] The first separation layer 13, which is a zeolite membrane, contains, for example, silicon (Si). The first separation layer 13 may contain, for example, any two or more of Si, aluminum (Al), and phosphorus (P). In this case, the zeolite constituting the first separation layer 13 may be an oxygen tetrahedron (TO) constituting zeolite. ４Zeolites in which the atom (T atom) located at the center of the zeolite (T atom) is composed of only Si or Si and Al, AlPO zeolites in which the T atoms are composed of Al and P, SAPO zeolites in which the T atoms are composed of Si, Al, and P, MAPSO zeolites in which the T atoms are composed of magnesium (Mg), Si, Al, and P, and ZnAPSO zeolites in which the T atoms are composed of zinc (Zn), Si, Al, and P can be used. Some of the T atoms may be substituted with other elements.

[0028] When the first separation layer 13 contains Si atoms and Al atoms, the Si / Al ratio in the first separation layer 13 is, for example, 1 or more and 100,000 or less. The Si / Al ratio is preferably 5 or more, more preferably 20 or more, and even more preferably 100 or more, and the higher the Si / Al ratio, the better. The Si / Al ratio in the first separation layer 13 can be adjusted by adjusting the compounding ratio of the Si source and the Al source in the raw material solution, which will be described later. The first separation layer 13 may contain an alkali metal. The alkali metal is, for example, sodium (Na) or potassium (K).

[0029] FIG. 3 is a diagram illustrating the structure of the second separation layer 14, and schematically illustrates a cross section perpendicular to the surface of the support 11 on which the laminated membrane 12 is provided. The second separation layer 14 is an amorphous membrane containing zeolite fine particles 141. In the second separation layer 14, an amorphous material is formed into a membrane, and the zeolite fine particles 141 are present in the membrane. As will be described later, a separation membrane composite 1 having such a second separation layer 14 formed therein is prevented from experiencing a decrease in separation performance when used at high pressure. The amorphous material is, for example, an oxide, and is typically an oxide of the constituent elements that make up the zeolite fine particles. In this embodiment, the amorphous material is amorphous silica. The second separation layer 14, which is an amorphous silica membrane, has pores of various sizes and a wide pore size distribution.

[0030] The average particle diameter of the zeolite fine particles 141 is, for example, 200 nm or less, and preferably 150 nm or less. The average particle diameter of the zeolite fine particles 141 is more preferably 1 nm or more and 100 nm or less. When the average particle diameter of the zeolite fine particles 141 is within the above range, it becomes possible to remove a large amount of organic SDA from the zeolite fine particles 141 in the production of the separation membrane composite 1 described below, thereby improving the permeation rate. The lower limit of the average particle diameter may be 3 nm or 5 nm. The upper limit of the average particle diameter may be 90 nm or 80 nm.

[0031] To measure the average particle diameter of the zeolite microparticles 141, for example, a cross section of the second separation layer 14 perpendicular to the surface of the support 11 is captured using a transmission electron microscope (TEM) (hereinafter referred to as a "TEM image") to obtain the image. The magnification is, for example, 300,000 times. In the TEM image, areas without lattice fringes (interference fringes) are identified as amorphous portions, and areas with lattice fringes are identified as zeolite microparticles 141. The length between both ends of each zeolite microparticle 141 (e.g., the major axis and the length perpendicular to the major axis) is measured in each of two mutually perpendicular directions, and the average of the lengths in these two directions is calculated as the particle diameter of the zeolite microparticle 141. The average particle diameter is then calculated by averaging the particle diameters of a predetermined number (e.g., 10) of randomly selected zeolite microparticles 141. When the particle size distribution of the zeolite fine particles 141 can be obtained, the median value of the particle size distribution may be treated as the average particle size.

[0032] The type of zeolite constituting the zeolite microparticles 141 is not particularly limited, and for example, the above-mentioned types of zeolite can be used. Typically, the type of zeolite of the zeolite microparticles 141 is different from the type of zeolite of the first separation layer 13. Preferably, the maximum number of rings of the zeolite of the zeolite microparticles 141 is smaller than the maximum number of rings of the zeolite of the first separation layer 13. That is, the average pore size of the zeolite of the zeolite microparticles 141 is smaller than the average pore size of the zeolite of the first separation layer 13. A preferred example of the zeolite of the zeolite microparticles 141 is a six-ring zeolite, the maximum number of rings of which is six. Depending on the properties required of the separation membrane composite 1, the maximum number of rings of the zeolite of the zeolite microparticles 141 may be equal to or greater than the maximum number of rings of the zeolite of the first separation layer 13. Alternatively, the type of zeolite of the zeolite microparticles 141 may be the same as the type of zeolite of the first separation layer 13.

[0033] The crystal structure of the zeolite microparticles 141 can be analyzed by obtaining an FFT pattern of the zeolite microparticles 141 in a high-magnification TEM image. The crystal structure can also be analyzed by micro-area XRD or thin-film XRD. Furthermore, the crystal structure can also be analyzed by analyzing the ring structure of the zeolite using AFM-IR or UV-Raman spectroscopy. When analyzing the crystal structure of the zeolite microparticles 141, an appropriate analysis method can be selected depending on the size of the microparticles, the shape of the support, and the like.

[0034] In the example of FIG. 3 , the zeolite microparticles 141 are present inside the second separation layer 14 along the interface with the first separation layer 13. In other words, most of the zeolite microparticles 141 contained in the second separation layer 14 are in contact with or close to the first separation layer 13. Inside the second separation layer 14, the zeolite microparticles 141 may be present at a position away from the first separation layer 13. Also, inside the first separation layer 13, the zeolite microparticles 141 may be present at the grain boundaries of the zeolite crystals that make up the first separation layer 13. The grain boundaries are the grain boundaries of the zeolite crystals in the low-density layer and the dense layer described below, for example, the amorphous portion of the first separation layer 13. In FIG. 3 , the zeolite microparticles 141 present inside the first separation layer 13 are indicated by a two-dot chain line. If zeolite microparticles 141 with small average pore diameters are also present inside the first separation layer 13, the number of paths containing small pores can be increased in the gas permeation paths of the separation membrane composite 1, thereby improving separation accuracy.

[0035] Typically, the thickness of the second separation layer 14 is smaller than the thickness of the first separation layer 13. The thickness of the second separation layer 14 may be equal to or greater than the thickness of the first separation layer 13. The thickness of the second separation layer 14 is, for example, 500 nm or less, preferably 250 nm or less, and more preferably 200 nm or less. Reducing the thickness of the second separation layer 14 increases the permeation rate of substances with high permeability through the second separation layer 14. The thickness of the second separation layer 14 is, for example, 3 nm or more, preferably 5 nm or more. Increasing the thickness of the second separation layer 14 improves separation performance. The thickness of the second separation layer 14 can be measured, for example, using the TEM image described above.

[0036] As shown in Figure 3, in a cross section perpendicular to the surface of the support 11, the proportion of zeolite microparticles 141 in the second separation layer 14 is, for example, 5% or more, preferably 15% or more, and more preferably 20% or more. A higher proportion of zeolite microparticles 141 improves separation performance. If the proportion of zeolite microparticles 141 in the second separation layer 14 is excessively high, microcracks are likely to occur in the zeolite microparticles 141 during the production of the separation membrane composite 1 described below. Therefore, the proportion of zeolite microparticles 141 is, for example, 60% or less, preferably 50% or less, and more preferably 40% or less. The proportion of zeolite microparticles 141 in the second separation layer 14 can be determined, for example, as the proportion of the area of ​​the zeolite microparticles 141 to the entire second separation layer 14 in the TEM image. That is, in a cross section perpendicular to the surface of the support 11, a TEM image is obtained in a field of view that includes from the surface of the second separation layer 14 to the interface between the second separation layer 14 and the first separation layer 13, and the proportion of the area of ​​the zeolite microparticles 141 in that field of view to the entire area of ​​the second separation layer 14 is determined as the abundance ratio. Preferably, such measurements are performed at a total of 10 locations by randomly changing the field of view, and the average of the 10 values ​​(abundance ratios in each field of view) is treated as the abundance ratio of the zeolite microparticles 141 in the second separation layer 14.

[0037] Next, an example of a manufacturing flow of the separation membrane composite 1 will be described with reference to Figure 4. In the manufacturing of the separation membrane composite 1, first, a porous support 11 is prepared (step S11). Also, seed crystals to be used in manufacturing the first separation layer 13 are prepared. In one example of forming a DDR-type zeolite membrane as the first separation layer 13, DDR-type zeolite powder is produced by hydrothermal synthesis, and seed crystals are obtained from the zeolite powder. The zeolite powder may be used as the seed crystals as is, or the seed crystals may be obtained by processing the powder by pulverization or the like.

[0038] Subsequently, the support 11 is immersed in a dispersion liquid in which the seed crystals are dispersed, and the seed crystals are attached to the support 11. Alternatively, the dispersion liquid in which the seed crystals are dispersed is brought into contact with a portion of the support 11 where the first separation layer 13 is to be formed, thereby attaching the seed crystals to the support 11. In this way, a seed crystal-attached support is produced. The seed crystals may also be attached to the support 11 by other techniques.

[0039] The support 11 with the seed crystals attached is immersed in a raw material solution (synthetic sol) for the first separation layer. The raw material solution is prepared, for example, by dissolving and dispersing a Si source, an organic SDA, and the like in a solvent. The Si source is, for example, colloidal silica, sodium silicate, fumed silica, or an alkoxide. The organic SDA is, for example, 1-adamantanamine. The solvent is, for example, water. Then, a DDR-type zeolite membrane is formed on the support 11 by growing the DDR-type zeolite using the seed crystals as nuclei through hydrothermal synthesis. The zeolite membrane is the first separation layer 13. The temperature during the hydrothermal synthesis is, for example, 80 to 200°C. The hydrothermal synthesis time is, for example, 3 to 100 hours.

[0040] After the hydrothermal synthesis is completed, the support 11 and the first separation layer 13 are washed with pure water. The washed support 11 (and the first separation layer 13) are dried, for example, at 80°C. After the support 11 is dried, the organic SDA in the first separation layer 13 is burned and removed by heat treatment in an oxidizing gas atmosphere. This penetrates the micropores in the zeolite membrane. Preferably, the organic SDA is almost completely removed. The heating temperature for removing the organic SDA is, for example, 400 to 1200°C. The heating time is, for example, 5 to 200 hours. The oxidizing gas atmosphere is an atmosphere containing oxygen, for example, air. Through the above process, a first separation layer 13 having penetrating pores is obtained (step S12).

[0041] In the first separation layer 13 of this embodiment, a low-density layer in contact with the support 11 and a dense layer covering the low-density layer without contacting the support 11 are formed. The low-density layer is a layer of seed crystals attached to the support 11 and its vicinity, and the dense layer is a layer formed of zeolite crystals grown from the seed crystals. The low-density layer and the dense layer each contain zeolite crystals and grain boundaries. The grain boundaries are regions between adjacent zeolite crystals. The grain boundaries include, for example, amorphous regions, crystals other than zeolite crystals, and / or voids. The zeolite crystal content in the dense layer is higher than the zeolite crystal content in the low-density layer. Note that, in the formation of the zeolite membrane, the process of attaching seed crystals to the support 11 may be omitted, in which case the zeolite membrane is formed directly on the support 11. Of course, a zeolite membrane of a type other than a DDR type may be formed as the first separation layer 13.

[0042] After the first separation layer 13 is formed on the support 11, an aqueous solution containing a predetermined oxide is prepared as a pretreatment liquid. The oxide is an oxide of a constituent element to be used to form the zeolite microparticles 141 of the second separation layer 14, and includes, for example, silica. The oxide may further include alumina. The constituent element preferably includes a major constituent element having the largest amount of substance, excluding oxygen, among the elements that form the zeolite microparticles 141, and the major constituent element is, for example, silicon. The concentration of the constituent element in the pretreatment liquid is, for example, 1 to 60 mass %, and preferably 3 to 50 mass %.

[0043] When the oxides of the constituent elements are silica and alumina, the mass ratio of silica to alumina in the pretreatment liquid is, for example, the same as that of the raw material solution for the second separation layer described below. The pretreatment liquid may contain only silica. Typically, the pretreatment liquid does not contain an organic SDA. The solvent of the pretreatment liquid may be a solvent other than water. The support 11 on which the first separation layer 13 has been formed is immersed in the pretreatment liquid for a predetermined time to perform pretreatment for forming the second separation layer 14 (step S13). As a result, oxides of the constituent elements are attached to the surface of the first separation layer 13 (the surface opposite to the support 11). The temperature of the pretreatment liquid is, for example, 0 to 80°C, preferably 40 to 60°C. The immersion time is, for example, 1 to 480 minutes, preferably 5 to 30 minutes.

[0044] The support 11 is then removed from the pretreatment solution, and the support 11 and the first separation layer 13 are dried (step S14). The drying temperature is, for example, 50 to 150°C, and the drying time is, for example, 30 to 480 minutes. Next, the support 11 and the first separation layer 13 are immersed in a raw material solution for the second separation layer. The raw material solution is prepared, for example, by dissolving and dispersing oxides of the above-mentioned constituent elements and an organic SDA in a solvent. The oxide includes, for example, silica. The oxide may further include alumina. The organic SDA is, for example, tetramethylammonium hydroxide. The solvent is, for example, water. Then, by performing hydrothermal synthesis, an amorphous film containing zeolite microparticles 141, i.e., the second separation layer 14, is formed on the first separation layer 13 (step S15). The temperature during hydrothermal synthesis is, for example, 80 to 230°C. The hydrothermal synthesis time is, for example, 2 to 60 hours.

[0045] The reason why the above treatment results in the formation of an amorphous film containing zeolite microparticles 141 is not entirely clear, but it may be thought that the following applies: As a result of the pretreatment described above, oxides of the constituent elements of the zeolite microparticles 141 adhere to the surface of the first separation layer 13. During hydrothermal synthesis, these oxides slowly dissolve in the raw material solution, increasing the concentration of these oxides near the surface of the first separation layer 13 and forming an amorphous layer. If hydrothermal synthesis is continued in this state, the amorphous layer inhibits the crystal growth of the zeolite, and the zeolite microparticles 141 are formed in a dispersed state. As a result, an amorphous film containing zeolite microparticles 141 is formed.

[0046] In one example, the zeolite fine particles 141 are formed along the surface of the first separation layer 13 within the second separation layer 14, but the zeolite fine particles 141 may also be formed at positions within the second separation layer 14 away from the first separation layer 13 or at grain boundaries within the first separation layer 13. As described above, in step S14, the support 11 and the first separation layer 13 are thoroughly dried before being immersed in the raw material solution for the second separation layer, thereby preventing the oxides of the above-mentioned constituent elements attached to the surface of the first separation layer 13 from easily (in a short time) dissolving into the raw material solution. This prevents the composition of the raw material solution from changing significantly from the intended one during hydrothermal synthesis (i.e., the occurrence of a large compositional deviation).

[0047] After the hydrothermal synthesis is completed, the support 11 on which the first separation layer 13 and the second separation layer 14 (i.e., the laminated film 12) are formed is washed with pure water. The support 11 is then immersed in a post-treatment liquid for post-treatment (step S16). The post-treatment liquid is, for example, a liquid whose pH is adjusted to 9 or higher by mixing sodium hydroxide or the like with pure water. The solvent of the post-treatment liquid may be a liquid other than water. Note that, in the cleaning after the formation of the second separation layer 14, the cleaning liquid (e.g., pure water) in which the support 11 is immersed may be used as the post-treatment liquid if the pH of the cleaning liquid gradually increases to 9 or higher. In this way, the post-treatment liquid may be prepared by various methods. Furthermore, this post-treatment may be performed consecutively with the cleaning after the formation of the second separation layer 14, or the cleaning and post-treatment may be repeated multiple times.

[0048] In the second separation layer 14, the amorphous portion is less stable than the zeolite fine particles 141 and is more easily dissolved in the alkaline post-treatment liquid. Therefore, the post-treatment in step S16 makes the density of the amorphous portion in the second separation layer 14 less dense than before the post-treatment. The temperature of the post-treatment liquid is, for example, 0 to 50°C. The support 11 is immersed in the post-treatment liquid for one day or more. From the perspective of efficiently producing the separation membrane composite 1, the upper limit of the immersion time is, for example, 10 days. Thereafter, the support 11 is removed from the post-treatment liquid and washed with pure water. After washing, the support 11 and laminated membrane 12 are dried, for example, at 80°C.

[0049] Next, the support 11 is heat-treated in an oxidizing gas atmosphere, thereby burning and removing the organic SDA in the zeolite fine particles 141 of the second separation layer 14 (step S17). This penetrates the micropores of the zeolite fine particles 141, completing the separation membrane composite 1. Preferably, the organic SDA is almost completely removed. The heating time for removing the organic SDA is, for example, 30 to 100 hours. The heating temperature is, for example, 400 to 700°C, preferably 500°C or less. During this process, stress is generated in the first separation layer 13 and the second separation layer 14 due to the difference in thermal expansion with the support 11. However, in the second separation layer 14, the effect of this stress is mitigated by the amorphous portion, reducing the occurrence of microcracks in the zeolite fine particles 141. As a result, when the separation membrane composite 1 is used at high pressure, a decrease in separation performance due to the propagation of cracks from the microcracks in the zeolite fine particles 141 is suppressed. The organic SDA may be removed simultaneously from the first separation layer 13 and the second separation layer 14. That is, in step S12 of forming the first separation layer 13, the process may proceed to step S13 without removing the organic SDA of the zeolite of the first separation layer 13, and then in the organic SDA removal step of step S17, the organic SDA of the zeolite of the first separation layer 13 and the second separation layer 14 may be removed simultaneously.

[0050] Next, examples of separation membrane composites will be described. Table 1 shows the types of zeolites used in the first and second separation layers and the manufacturing conditions for the second separation layers in Examples 1 to 12 and Comparative Examples 1 and 2. Table 2 shows the results of various measurements of the second separation layer and the performance evaluation results of the separation membrane composites.

[0051]

[0052]

[0053] <Preparation of Separation Membrane Composites of Examples 1 to 12> (Preparation of Support and Formation of First Separation Layer) A porous alumina support having a multilayer structure was prepared in the same manner as the preparation method described in International Publication No. 2017 / 169591 (the above-mentioned Document 6). After attaching seed crystals to the alumina support, the alumina support was immersed in a raw material solution for the zeolite membrane to perform hydrothermal synthesis, thereby forming a zeolite membrane as the first separation layer. The zeolite membrane was then heated in an electric furnace to burn off the organic SDA in the zeolite membrane. Here, for Examples 1 to 9, a DDR type zeolite membrane was formed as the first separation layer in the same manner as the preparation method for a DDR type zeolite membrane described in the above-mentioned Document 6.

[0054] In Example 10, an FAU zeolite membrane was formed as the first separation layer. FAU zeolite was used as the seed crystals. To prepare a raw material solution for the FAU zeolite membrane, 25.3 g of sodium hydroxide (Sigma-Aldrich) and 1.5 g of sodium aluminate powder (Sigma-Aldrich) were mixed with 160 g of distilled water. Then, 25.3 g of approximately 30% by mass silica sol (trade name: Snowtex S, Nissan Chemical Industries, Ltd.) was added and stirred with a magnetic stirrer (room temperature, 30 minutes) to obtain a raw material solution. Although the raw material solution of Example 10 did not contain organic SDA, it was heated in the same manner as above to remove adsorbed water.

[0055] In Example 11, an LTA zeolite membrane was formed as the first separation layer. LTA zeolite was used as the seed crystals. To prepare a raw material solution for the LTA zeolite membrane, 5.0 g of sodium hydroxide (manufactured by Sigma-Aldrich) and 3.9 g of sodium aluminate powder (manufactured by Sigma-Aldrich) were mixed with 173 g of distilled water. Subsequently, 0.85 g of a tetramethylammonium hydroxide solution was further mixed. The mixed solution was stirred at room temperature for 1 hour, and then colloidal silica (trade name: Snowtex 50T, manufactured by Nissan Chemical Industries, Ltd.) was added to obtain a raw material solution.

[0056] In Example 12, an MFI zeolite membrane was formed as the first separation layer. MFI zeolite was used as the seed crystals. To prepare a raw material solution for the MFI zeolite membrane, 0.86 g of a 40 mass% tetrapropylammonium hydroxide solution (manufactured by SACHEM) and 0.45 g of tetrapropylammonium bromide (manufactured by Wako Pure Chemical Industries, Ltd.) were mixed. Then, 192.0 g of distilled water and 6.75 g of approximately 30 mass% silica sol (trade name: Snowtex S, manufactured by Nissan Chemical Industries, Ltd.) were added, and the mixture was stirred with a magnetic stirrer (room temperature, 30 minutes) to obtain a raw material solution.

[0057] (Formation of Second Separation Layer) An aqueous solution containing oxides of the constituent elements to form the second separation layer was prepared as a pretreatment liquid. In Examples 1 to 9, the oxide of the constituent element was silica, and in Examples 10 to 12, the oxides of the constituent elements were silica and alumina. In Table 1, the concentration of the oxide of the constituent element in the pretreatment liquid for each of Examples 1 to 12 is shown in the column "Concentration of Pretreatment Liquid." The alumina support on which the first separation layer had been formed was immersed in the pretreatment liquid and held at 50°C or higher for 1 hour, thereby carrying out pretreatment. Thereafter, the alumina support was removed from the pretreatment liquid and dried at 100°C.

[0058] The pretreated alumina support was placed in a fluororesin inner tube (internal volume 300 ml) of a stainless steel pressure vessel, and the raw material solution for the second separation layer was then added and subjected to a heat treatment (hydrothermal synthesis). This resulted in a second separation layer, which was an amorphous membrane containing zeolite microparticles. The hydrothermal synthesis time for each of Examples 1 to 12 is as shown in Table 1. The hydrothermal synthesis temperature was 180°C.

[0059] In forming the second separation layer, a raw material solution for MTN zeolite was used in Examples 1 to 9. The raw material solution was prepared by mixing 6.28 g of a 30% by mass tetramethylammonium hydroxide solution (manufactured by SACHEM) with 146.8 g of distilled water. Then, 14.8 g of an approximately 30% by mass silica sol (trade name: Snowtex S, manufactured by Nissan Chemical Industries, Ltd.) was added and stirred with a magnetic stirrer (room temperature, 30 minutes) to obtain a raw material solution.

[0060] In Examples 10 and 11, a raw material solution for SOD-type zeolite was used. The raw material solution was prepared by mixing 23.1 g of alumina sol (manufactured by Nissan Chemical Industries, Ltd.), 7.6 g of phosphoric acid (manufactured by Wako Pure Chemical Industries, Ltd.), 21.7 g of potassium hydroxide (manufactured by Wako Pure Chemical Industries, Ltd.), 125.5 g of distilled water, 48.8 g of tetramethylammonium hydroxide (manufactured by SACHEM), and 125.5 g of approximately 30% by mass silica sol (trade name: Snowtex S, manufactured by Nissan Chemical Industries, Ltd.). The mixture was then stirred with a magnetic stirrer (room temperature, 30 minutes) to obtain a raw material solution.

[0061] In Example 12, a raw material solution for ETL zeolite was used. This raw material solution was prepared by mixing 2.1 g of alumina sol (manufactured by Nissan Chemical Industries, Ltd.), 9.3 g of rubidium hydroxide (manufactured by Sigma-Aldrich), 0.6 g of sodium hydroxide (manufactured by Sigma-Aldrich), 18.8 g of tetramethylammonium hydroxide (manufactured by SACHEM), and 121.4 g of approximately 30% by mass silica sol (trade name: Snowtex S, manufactured by Nissan Chemical Industries, Ltd.). The mixture was then stirred with a magnetic stirrer (room temperature, 30 minutes) to obtain a raw material solution.

[0062] Next, a post-treatment liquid was prepared by mixing sodium hydroxide with distilled water to adjust the pH to 9 or higher. For Examples 1 to 3 and Examples 5 to 12, post-treatment was performed by immersing the alumina support after the formation of the second separation layer in the post-treatment liquid for one day or more. After the post-treatment, the alumina support was washed with distilled water and dried at 80°C for 12 hours or more. For Example 4, no post-treatment was performed. Thereafter, the alumina supports of Examples 1 to 12 were heated to 450°C in an electric furnace and held there for 50 hours to burn off the organic SDA. Through the above treatments, the separation membrane composites of Examples 1 to 12 were obtained.

[0063] <Preparation of Separation Membrane Composites of Comparative Examples 1 and 2> In preparing the separation membrane composites of Comparative Examples 1 and 2, an MTN zeolite membrane was formed as the first separation layer, and the formation of the second separation layer was omitted. The raw material solution used to form the MTN zeolite membrane was the same as that used to form the second separation layer in Examples 1 to 9. With regard to the combustion removal of the organic SDA from the MTN zeolite membrane serving as the first separation layer, the firing temperature in Comparative Example 1 was 700°C, and the firing temperature in Comparative Example 2 was 450°C. In Table 1, the values ​​for Comparative Examples 1 and 2 in the "Firing Temperature" column of "Second Separation Layer" indicate the firing temperatures during the combustion removal of the organic SDA in the first separation layer.

[0064] <Various Measurements of the Second Separation Layer> In the separation membrane composites of Examples 1 to 12 and Comparative Examples 1 and 2, a cross section of the second separation layer perpendicular to the surface of the alumina support was imaged using a transmission electron microscope at a magnification of 300,000 times to obtain a TEM image. To obtain the TEM image, a sample was prepared by the FIB method using an FIB device (Helios G4 manufactured by FEI Corporation), and images were taken using a multifunctional electron microscope (JEM-F200 manufactured by JEOL Corporation) at an acceleration voltage of 200 kV. In the TEM image, the distance from the boundary between the first separation layer and the second separation layer 14 to the surface of the second separation layer was determined as the thickness of the second separation layer. In Table 2, the thickness of the second separation layer is shown in the "Film Thickness" column.

[0065] In addition, in the TEM image, areas without lattice fringes were identified as amorphous portions, and areas with lattice fringes were identified as zeolite microparticles. The length between both ends of the zeolite microparticles was measured in each of two mutually perpendicular directions, and the average of the lengths in these two directions was calculated as the particle diameter of the zeolite microparticles. The average particle diameter was then determined as the average particle diameter of 10 zeolite microparticles. Furthermore, the proportion of the area of ​​the zeolite microparticles in the entire second separation layer in the TEM image was calculated as the proportion of the zeolite microparticles present in the second separation layer. In Table 2, the columns "Particle diameter of microparticles" and "Proportion of microparticles present" show the average particle diameter of the zeolite microparticles and the proportion of the zeolite microparticles present in the second separation layer.

[0066] The crystal structure of the zeolite microparticles was analyzed by obtaining an FFT pattern of the zeolite microparticles in a high-magnification TEM image. This confirmed that the type of zeolite microparticles shown in "Zeolite Type" in the "Second Separation Layer" in Table 1 was formed. The crystal structure of the zeolite microparticles may also be analyzed by other methods. In micro-XRD (wide-angle X-ray diffraction), for example, an X-ray diffractometer (D8 DISCOVER μHR Hybrid manufactured by Bruker AXS) is used, and the X-ray source is CuKα radiation, the output is 50 kV, 22 mA, the slit system is a 300 μmφ pinhole, and the detector is a two-dimensional detector. In micro-Raman spectroscopy, for example, an NRS-5100 manufactured by JASCO Corporation is used, with a laser wavelength of 532 nm and a measurement wavenumber range of 1200 to 200 cm. －１ It is possible to perform measurements as follows.

[0067] <Performance Evaluation of Separation Membrane Composite> A mixed gas consisting of hydrogen and methane mixed at a volume ratio of 20:80 was supplied to the separation membrane composite, and the hydrogen permeation rate and methane permeation rate were measured. In the separation membrane composite, the first and second separation layers were formed on the inner surfaces of multiple through-holes in a monolithic alumina support. Both ends of the alumina support, excluding the through-holes, were sealed with glass, and the alumina support was housed in a housing (see Figure 5 described below). That is, the separation membrane composite was placed in the housing. Furthermore, seal members were placed between both ends of the alumina support and the housing. In this state, the mixed gas was introduced into each through-hole of the alumina support, and gas that permeated the first and second separation layers and the alumina support was collected from an exhaust port provided in the housing. In measuring the permeation rate, the pressure of the introduced gas (mixed gas) was 0.6 MPa, and the pressure of the permeated gas was 0.1 MPa (approximately 1 atmosphere). The hydrogen permeation rate and the methane permeation rate were determined by measuring the amount of permeated gas and the hydrogen and methane concentrations in the permeated gas. In Table 2, the hydrogen permeation rate is shown in the "Hydrogen permeation rate" column, and the value obtained by dividing the hydrogen permeation rate by the methane permeation rate is shown in the "Hydrogen / Methane permeation rate ratio (0.6 MPa)" column.

[0068] In addition, instead of the above mixed gas, CF４ (carbon tetrafluoride) gas is supplied to the separation membrane composite, and CF ４ The permeation rate was measured. As in the case of the mixed gas, the pressure of the introduced gas was 0.3 MPa and the pressure of the permeated gas was 0.1 MPa. ４ CF in the "Permeation Rate (0.3 MPa)" column ４ The permeation rate is shown. ４ The purpose of measuring the permeation rate is to evaluate firing cracks. In the evaluation of firing cracks, it is preferable to measure the permeation rate of molecules having a kinetic molecular diameter 1.5 times or more the average pore diameter of the zeolite constituting the second separation layer (in the comparative example having a single separation layer, the separation layer). When the zeolite is an MTN type, the permeation rate is 1.5 times or more the average pore diameter of the zeolite constituting the second separation layer (in the comparative example having a single separation layer, the separation layer). ４ is preferred.

[0069] Furthermore, the mixed gas was supplied again to the separation membrane composite, and the hydrogen permeation rate and methane permeation rate were measured. At this time, the pressure of the inlet gas was 5 MPa, and the pressure of the permeated gas was 0.1 MPa. Subsequently, the hydrogen / methane permeation rate ratio at high pressure (5 MPa) was determined by dividing the hydrogen permeation rate by the methane permeation rate. The retention rate of the permeation rate ratio at high pressure relative to the permeation rate ratio at low pressure was determined by dividing the hydrogen / methane permeation rate ratio at high pressure (5 MPa) by the hydrogen / methane permeation rate ratio obtained when the pressure of the inlet gas was 0.6 MPa ("Hydrogen / methane permeation rate ratio (0.6 MPa)" in Table 2). In the column "Retention rate of high-pressure permeation rate ratio relative to low-pressure permeation rate ratio" in Table 2, a retention rate of 0.95 or higher was evaluated as "good," and a retention rate of less than 0.95 was evaluated as "poor."

[0070] As shown in Table 2, the separation membrane composites of Examples 1 to 12 exhibited good retention rates of the high-pressure permeation rate ratio relative to the low-pressure permeation rate ratio. In contrast, the separation membrane composites of Comparative Examples 1 and 2 exhibited poor retention rates due to a low hydrogen / methane permeation rate ratio at high pressure. The reason why the hydrogen / methane permeation rate ratio (i.e., separation performance) at high pressure in the separation membrane composites of Comparative Examples 1 and 2 is reduced is not entirely clear, but it may be thought that the following may be the case. In Comparative Examples 1 and 2, the second separation layer is omitted, and only the first separation layer made of zeolite is provided on the alumina support. During firing to burn off the organic SDA, stress caused by the difference in thermal expansion between the alumina support and the first separation layer causes microcracks in the zeolite particles of the first separation layer. When the separation membrane composite is used at high pressure, cracks propagate from these microcracks, resulting in a decrease in separation performance. Note that in Comparative Example 1, CF ４ The high permeation rate suggests that large cracks had occurred before use at high pressure.

[0071] On the other hand, in the separation membrane composites of Examples 1 to 12, the retention rate of the high-pressure permeation rate ratio relative to the low-pressure permeation rate ratio was good, and the separation performance degradation was suppressed when the separation membrane composites were used at high pressure. The reason for this is thought to be, for example, as follows: In the separation membrane composites of Examples 1 to 12, the second separation layer was an amorphous membrane containing zeolite fine particles. Therefore, during firing to burn off the organic SDA in the second separation layer, the amorphous portion mitigated the effects of stress caused by the difference in thermal expansion between the alumina support and the first and second separation layers. As a result, the occurrence of microcracks in the zeolite fine particles contained in the second separation layer was suppressed, and the separation performance degradation was suppressed when the separation membrane composites were used at high pressure.

[0072] In a separation membrane composite, it is possible to form the second separation layer solely from amorphous material; however, the pore size distribution of amorphous material is broad, resulting in poor separation performance in the separation membrane composite. In contrast, a separation membrane composite in which zeolite fine particles with a narrow pore size distribution are mixed in the second separation layer achieves high separation performance. To more reliably achieve high separation performance, it is preferable for a large number of zeolite fine particles to be present in the second separation layer. Comparing Examples 1 to 3 and 5 to 12, in which post-treatment of the separation membrane composite was performed, Examples 1 and 5 to 12, in which the proportion of zeolite fine particles in the second separation layer was 20% or more, achieved a high hydrogen / methane permeation rate ratio. Therefore, to more reliably improve separation performance, it is preferable for the proportion of zeolite fine particles in the second separation layer to be 20% or more.

[0073] Focusing on the film thickness of the second separation layer, in Example 1 where the film thickness is 250 nm, the hydrogen permeation rate is significantly reduced. In Example 2 where the film thickness is 4 nm, the hydrogen permeation rate is high but the hydrogen / methane permeation rate ratio is low. Therefore, to improve both the hydrogen / methane separation performance and the hydrogen permeation rate, it is preferable that the thickness of the second separation layer be 5 nm or more and 200 nm or less.

[0074] On the other hand, considering that a high hydrogen permeation rate was obtained in Example 9, where the second separation layer had a thickness of 180 nm, the significantly lower hydrogen permeation rate in Example 1, where the thickness was 250 nm, is thought to be due not only to the large thickness but also to the insufficient removal of organic SDA from the zeolite microparticles, i.e., the remaining organic SDA. The average particle diameter of the zeolite microparticles was 120 nm in Example 1 and 90 nm in Example 9. Generally, the smaller the particle diameter of the zeolite microparticles, the easier it is to remove the organic SDA by calcination. Therefore, in order to adequately remove the organic SDA from the zeolite microparticles in the second separation layer and improve the hydrogen permeation rate, it is preferable that the average particle diameter of the zeolite microparticles be 100 nm or less. In particular, when zeolite microparticles are formed from a 6-membered ring zeolite with a small maximum number of rings, from which the organic SDA is difficult to remove, the average particle diameter is preferably within the above range. To ensure a certain level of separation performance, the average particle diameter of the zeolite microparticles is preferably 1 nm or more.

[0075] As described above, the method for producing a separation membrane composite includes the steps of preparing a porous support (step S11), forming a first separation layer, which is a zeolite membrane, on the surface of the support (step S12), and forming a second separation layer, which is an amorphous membrane containing zeolite fine particles, on the surface of the first separation layer opposite the support. The step of forming the second separation layer also includes the steps of immersing the support on which the first separation layer has been formed in a pretreatment solution containing oxides of the constituent elements to be used to form the zeolite fine particles for a predetermined period of time (step S13), removing the support from the pretreatment solution and drying it (step S14), immersing the support in a raw material solution containing the constituent elements and an organic SDA for hydrothermal synthesis to form the second separation layer on the support (step S15), and removing the organic SDA from the second separation layer on the support (step S17). This allows an amorphous membrane (second separation layer) containing zeolite fine particles to be appropriately formed, and prevents the separation performance from decreasing when the separation membrane composite is used at high pressure.

[0076] Here, a six-membered ring zeolite powder with a particle size of 100 nm to 300 nm was synthesized in the same manner as in JP 2020-163369 A (reference 1 above), and the six-membered ring zeolite powder was subjected to thermogravimetric analysis. The results confirmed that, while almost 100% of the organic SDA was removed from the zeolite powder when fired at 700°C, a large amount of the organic SDA remained when fired at 500°C or below. Meanwhile, when firing at temperatures higher than 500°C in the production of a separation membrane composite, the difference in thermal expansion between the support, which may be composed of an alumina sintered body, mullite sintered body, titania sintered body, or the like, and the zeolite membrane becomes large, resulting in the generation of cracks.

[0077] In contrast, as described above, in a separation membrane composite in which the average particle diameter of the zeolite microparticles in the second separation layer is 1 nm or more and 100 nm or less, the firing temperature is set to 500°C or less, which suppresses the occurrence of cracks during firing while achieving appropriate removal of the organic SDA from the zeolite microparticles.

[0078] Preferably, the above-described manufacturing method further includes, between steps S15 and S17, a step (step S16) of immersing the support on which the second separation layer has been formed in a post-treatment solution adjusted to a pH of 9 or higher for one day or more. This reduces the amorphous density of the second separation layer. As a result, the organic SDA is more easily removed from the zeolite fine particles in the treatment of step S17, improving separation performance and also enabling an improvement in the hydrogen permeation rate.

[0079] Next, separation of a mixed substance using the separation membrane composite 1 will be described with reference to Figures 5 and 6. Figure 5 is a diagram showing the separation device 2. Figure 6 is a diagram showing the flow of separation of a mixed substance by the separation device 2.

[0080] In the separation device 2, a mixed substance containing multiple types of fluids (i.e., gases or liquids) is supplied to the separation membrane composite 1, and highly permeable substances in the mixed substance are separated from the mixed substance by permeating through the separation membrane composite 1. Separation in the separation device 2 may be performed, for example, for the purpose of extracting highly permeable substances from the mixed substance, or for the purpose of concentrating less permeable substances.

[0081] The mixed substance (i.e., mixed fluid) may be a mixed gas containing multiple types of gases, a mixed liquid containing multiple types of liquids, or a gas-liquid two-phase fluid containing both gas and liquid.

[0082] The mixture may include, for example, hydrogen (H ２ ), helium (He), nitrogen (N ２ ), oxygen (O ２ ), water (H ２ O), carbon monoxide (CO), carbon dioxide (CO ２ ), nitrogen oxides, ammonia (NH ３ ), sulfur oxides, hydrogen sulfide (H ２ S), sulfur fluoride, mercury (Hg), arsine (AsH ３ ), hydrogen cyanide (HCN), carbonyl sulfide (COS), C1-C8 hydrocarbons, organic acids, alcohols, mercaptans, esters, ethers, ketones, and aldehydes.

[0083] Nitrogen oxides are compounds of nitrogen and oxygen. Examples of the nitrogen oxides include nitric oxide (NO), nitrogen dioxide (NO ２ ), nitrous oxide (also called dinitrogen monoxide) (N ２ O), dinitrogen trioxide (N ２ O ３ ), dinitrogen tetroxide (N ２ O ４ ), dinitrogen pentoxide (N ２ O ５ ) etc. Ｘ It is a gas called NOX.

[0084] Sulfur oxides are compounds of sulfur and oxygen. Examples of the sulfur oxides include sulfur dioxide (SO ２ ), sulfur trioxide (SO ３ ) and other SOs Ｘ It is a gas called SOX.

[0085] Sulfur fluoride is a compound of fluorine and sulfur. The above-mentioned sulfur fluoride is, for example, disulfur difluoride (FS-SF, S=SF ２ ), sulfur difluoride (SF ２ ), sulfur tetrafluoride (SF４ ), sulfur hexafluoride (SF ６ ) or disulfur decafluoride (S ２ F １０ ) etc.

[0086] C1-C8 hydrocarbons are hydrocarbons with one or more carbon atoms and eight or less. C3-C8 hydrocarbons may be straight-chain compounds, branched-chain compounds, or cyclic compounds. C2-C8 hydrocarbons may be either saturated hydrocarbons (i.e., those without double and triple bonds in the molecule) or unsaturated hydrocarbons (i.e., those with double and / or triple bonds in the molecule). C1-C4 hydrocarbons include, for example, methane (CH ４ ), ethane (C ２ H ６ ), ethylene (C ２ H ４ ), propane (C ３ H ８ ), propylene (C ３ H ６ ), normal butane (CH ３ (CH ２ ) ２ CH ３ ), isobutane (CH(CH ３ ) ３ ), 1-butene (CH ２ =CHCH ２ CH ３ ), 2-butene (CH ３ CH=CHCH ３ ) or isobutene (CH ２ =C(CH ３ ) ２ )

[0087] The organic acid is a carboxylic acid or a sulfonic acid. The carboxylic acid is, for example, formic acid (CH ２ O ２ ), acetic acid (C ２ H ４ O ２ ), oxalic acid (C ２ H ２ O ４ ), acrylic acid (C ３ H ４ O ２ ) or benzoic acid (C６ H ５ COOH), etc. Sulfonic acids include, for example, ethanesulfonic acid (C ２ H ６ O ３ S) and the like. The organic acid may be a chain compound or a cyclic compound.

[0088] The alcohols mentioned above include, for example, methanol (CH ３ OH), ethanol (C ２ H ５ OH), isopropanol (2-propanol) (CH ３ CH(OH)CH ３ ), ethylene glycol (CH ２ (OH)CH ２ (OH)) or butanol (C ４ H ９ OH) and the like.

[0089] Mercaptans are organic compounds with hydrogenated sulfur (SH) at the end, and are also called thiols or thioalcohols. Examples of the above-mentioned mercaptans include methyl mercaptan (CH ３ SH), ethyl mercaptan (C ２ H ５ SH) or 1-propanethiol (C ３ H ７ SH), etc.

[0090] The esters mentioned above are, for example, formates or acetates.

[0091] The above-mentioned ethers include, for example, dimethyl ether ((CH ３ ) ２ O), methyl ethyl ether (C ２ H ５ OCH ３ ) or diethyl ether ((C ２ H ５ ) ２ O) etc.

[0092] The above-mentioned ketones can be, for example, acetone ((CH ３ ) ２ CO), methyl ethyl ketone (C ２ H ５COCH ３ ) or diethyl ketone ((C ２ H ５ ) ２ CO), etc.

[0093] The aldehydes mentioned above include, for example, acetaldehyde (CH ３ CHO), propionaldehyde (C ２ H ５ CHO) or butanal (butyraldehyde) (C ３ H ７ CHO) etc.

[0094] In the following description, it is assumed that the mixed substance separated by the separation device 2 is a mixed gas containing a plurality of types of gases.

[0095] The separation device 2 includes a separation membrane composite 1, a sealing unit 21, a housing 22, two seal members 23, a supply unit 26, a first recovery unit 27, and a second recovery unit 28. The separation membrane composite 1, the sealing unit 21, and the seal members 23 are housed within the housing 22. The supply unit 26, the first recovery unit 27, and the second recovery unit 28 are disposed outside the housing 22 and connected to the housing 22.

[0096] The sealing portions 21 are provided at both longitudinal ends of the support 11 (i.e., the left-right direction in FIG. 5 ) and are members that cover and seal both longitudinal end faces of the support 11 and the outer peripheral surfaces near these end faces. The sealing portions 21 prevent gas from flowing in or out from these end faces of the support 11. The sealing portions 21 are, for example, plate-like members formed of glass or resin. The material and shape of the sealing portions 21 may be changed as appropriate. Note that the sealing portions 21 have multiple openings that overlap with the multiple through holes 111 of the support 11, and therefore both longitudinal ends of each through hole 111 of the support 11 are not covered by the sealing portions 21. Therefore, gas and the like can flow in and out of the through holes 111 from these ends.

[0097] The shape of the housing 22 is not limited, but may be, for example, a substantially cylindrical tubular member. The housing 22 is formed, for example, from stainless steel or carbon steel. The longitudinal direction of the housing 22 is substantially parallel to the longitudinal direction of the separation membrane composite 1. A supply port 221 is provided at one longitudinal end of the housing 22 (i.e., the left end in FIG. 5 ), and a first discharge port 222 is provided at the other end. A second discharge port 223 is provided on the side of the housing 22. A supply unit 26 is connected to the supply port 221. A first collection unit 27 is connected to the first discharge port 222. A second collection unit 28 is connected to the second discharge port 223. The internal space of the housing 22 is an enclosed space isolated from the space surrounding the housing 22.

[0098] The two seal members 23 are disposed around the entire circumference between the outer peripheral surface of the separation membrane composite 1 and the inner peripheral surface of the housing 22 near both longitudinal ends of the separation membrane composite 1. Each seal member 23 is a substantially annular member made of a gas-impermeable material. The seal members 23 are, for example, O-rings made of a flexible resin. The seal members 23 are in close contact with the outer peripheral surface of the separation membrane composite 1 and the inner peripheral surface of the housing 22 around the entire circumference. In the example shown in FIG. 5 , the seal member 23 is in close contact with the outer peripheral surface of the sealing portion 21 and indirectly in close contact with the outer peripheral surface of the separation membrane composite 1 via the sealing portion 21. A seal is formed between the seal member 23 and the outer peripheral surface of the separation membrane composite 1, and between the seal member 23 and the inner peripheral surface of the housing 22, so that gas hardly or completely passes through.

[0099] Supply unit 26 supplies the mixed gas to the internal space of housing 22 via supply port 221. Supply unit 26 is, for example, a blower or a pump that pressure-feeds the mixed gas toward housing 22. The blower or pump includes a pressure adjustment unit that adjusts the pressure of the mixed gas supplied to housing 22. First recovery unit 27 and second recovery unit 28 are, for example, storage containers that store the gas drawn out from housing 22, or blowers or pumps that transport the gas.

[0100] When separating a mixed gas, the separation device 2 is prepared, thereby preparing the separation membrane composite 1 (step S21). Next, a mixed gas containing multiple types of gases with different permeabilities through the laminated membrane 12 is supplied by the supply unit 26 to the internal space of the housing 22. For example, the main component of the mixed gas is H ２ and C.H. ４ The mixed gas contains H ２ and C.H. ４ The pressure of the mixed gas supplied from the supply unit 26 to the internal space of the housing 22 (i.e., the introduction pressure) is, for example, 0.1 MPa to 20.0 MPa. The temperature at which the mixed gas is separated is, for example, 10°C to 150°C.

[0101] The mixed gas supplied from the supply unit 26 to the housing 22 is introduced into each of the through-holes 111 of the support 11 from the left end of the separation membrane composite 1 in the drawing, as indicated by arrow 251. A gas with high permeability in the mixed gas (for example, H ２ The highly permeable substance (hereinafter referred to as "highly permeable substance") passes through the laminated film 12 provided on the inner circumferential surface of each through-hole 111 and the support 11, and is discharged from the outer circumferential surface of the support 11. As a result, the highly permeable substance is able to disperse gases with low permeability (for example, CH ４ (hereinafter referred to as "low-permeability material") is separated from the low-permeability material (step S22). The gas (hereinafter referred to as "permeation material") discharged from the outer peripheral surface of the support 11 is recovered by the second recovery unit 28 via the second discharge port 223, as shown by arrow 253. The pressure of the gas recovered by the second recovery unit 28 via the second discharge port 223 (i.e., permeation pressure) is, for example, about 1 atmosphere (0.101 MPa).

[0102] Furthermore, gases (hereinafter referred to as "impermeable substances") excluding the gas that has permeated the laminated membrane 12 and the support 11 of the mixed gas pass through each through-hole 111 of the support 11 from left to right in the figure, and are recovered by the first recovery unit 27 via the first discharge port 222, as shown by arrow 252. The pressure of the gas recovered by the first recovery unit 27 via the first discharge port 222 is, for example, approximately the same as the introduction pressure. In addition to the above-mentioned low-permeability substances, the impermeable substances may also include highly permeable substances that did not permeate the laminated membrane 12.

[0103] The separation membrane composite 1 and the method for manufacturing the separation membrane composite 1 can be modified in various ways.

[0104] The thickness of the second separation layer 14 is not limited to the range of 5 nm to 200 nm, and the average particle size of the zeolite fine particles 141 contained in the second separation layer 14 is not limited to the range of 1 nm to 100 nm. The proportion of the zeolite fine particles 141 in the second separation layer 14 may be less than 20%.

[0105] The separation membrane composite 1 may be produced by a method other than the above-described production method.

[0106] In the separation device 2 and the separation method, substances other than those exemplified in the above description may be separated from the mixed substance.

[0107] The configurations in the above-described embodiment and each modification may be combined as appropriate as long as they are not mutually contradictory.

[0108] While the invention has been particularly illustrated and described, it should be understood that the foregoing description is illustrative and not restrictive, and that numerous modifications and variations are possible without departing from the scope of the invention.

[0109] The separation membrane composite of the present invention can be used, for example, as a hydrogen separation membrane, and further, can be used in a variety of fields as a separation membrane for various substances other than hydrogen, an adsorption membrane for various substances, and the like.

[0110] 1 Separation membrane composite 11 Support 13 First separation layer 14 Second separation layer 141 Zeolite fine particles S11 to S17, S21, S22 Steps

Claims

1. A separation membrane composite comprising: a porous support; a first separation layer that is in contact with the surface of the support and is a membrane made of zeolite; and a second separation layer that is in contact with the surface of the first separation layer opposite the support and is an amorphous membrane containing zeolite fine particles.

2. A separation membrane composite according to claim 1, wherein the thickness of the second separation layer is 5 nm or more and 200 nm or less.

3. A separation membrane composite according to claim 1, wherein the average particle size of the zeolite fine particles contained in the second separation layer is 1 nm or more and 100 nm or less.

4. A separation membrane composite according to any one of claims 1 to 3, wherein the proportion of zeolite fine particles in the second separation layer is 20% or more in a cross section perpendicular to the surface of the support.

5. A method for producing a separation membrane composite, comprising: a) preparing a porous support; b) forming a first separation layer, which is a membrane made of zeolite, on the surface of the support; and c) forming a second separation layer, which is an amorphous membrane containing zeolite fine particles, on the surface of the first separation layer opposite the support, wherein the c) step comprises: c1) immersing the support, on which the first separation layer has been formed, in a pretreatment liquid containing oxides of constituent elements to be used to form the zeolite fine particles, for a predetermined period of time; c2) removing the support from the pretreatment liquid and drying it; c3) immersing the support in a raw material solution containing the constituent elements and an organic structure-directing agent to perform hydrothermal synthesis, thereby forming the second separation layer on the support; and c4) removing the organic structure-directing agent from the second separation layer on the support.

6. The method for producing a separation membrane composite according to claim 5, further comprising, between step c3) and step c4), a step of immersing the support on which the second separation layer has been formed in a post-treatment liquid adjusted to a pH of 9 or higher for one day or more.

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