Zeolite membrane composite and separation method

Abstract

A zeolite membrane composite (1) comprises a porous support (11) and a zeolite membrane (12) provided on the support (11). The zeolite membrane (12) comprises a low-density layer (13) covering the support (11) and a dense layer (14) covering the low-density layer (13). The dense layer (14) has a higher content of zeolite crystals (141) than the low-density layer (13). In a cross-section of the zeolite membrane composite (1) that is perpendicular to a surface of the support (11), the average aspect ratio of the zeolite crystals (141) contained in the dense layer (14) is 2-4 inclusive. When the surface of the zeolite membrane (12), which is a surface of the dense layer (14), is observed from a direction perpendicular to the surface, 20% or more of the zeolite crystals (141) positioned in the surface have triangular shapes. Accordingly, the zeolite membrane composite (1) with a high water permeation flux and hydrothermal resistance can be provided.

Description

[Technical Field]

[0001] The present invention relates to a zeolite membrane composite and a separation method. [Reference to Related Applications] This application claims the benefit of priority from Japanese Patent Application JP2022-029615, filed on February 28, 2022, the entire disclosure of which is incorporated herein by reference. [Background technology]

[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 zeolite membrane composites. For example, in the zeolite membrane composite of International Publication No. 2020 / 179432 (Reference 1), the zeolite membrane has a low-density layer covering the support and a dense layer covering the low-density layer, with the dense layer having a higher zeolite crystalline phase content than the low-density layer. This zeolite membrane composite achieves high permeability and separation performance. Furthermore, in the zeolite membrane composite of International Publication No. 2019 / 187640 (Reference 2), the zeolite membrane has a zeolite crystalline phase composed of multiple zeolite crystals and a dense grain boundary phase, which is the region between the multiple zeolite crystals. In this zeolite membrane, the density of at least a part of the grain boundary phase is made smaller than the density of the zeolite crystalline phase, and the width of the grain boundary phase is made 2 nm or more and 10 nm or less, thereby realizing high permeability, separation performance, and high durability. Note that JP 2004-83375 A (Reference 3) discloses a method for producing DDR-type zeolite.

[0003] The hydrothermal resistance of a zeolite membrane can be evaluated by the degree of decrease in the degree of vacuum before and after immersion in high-temperature water. Zeolite is known to dissolve in high-temperature water, and the hydrothermal resistance of a zeolite membrane generally decreases. Increasing the thickness of the zeolite membrane can improve the hydrothermal resistance, but this results in a decrease in the water permeation flux. Therefore, there is a demand for a zeolite membrane composite with high water permeation flux and hydrothermal resistance. Summary of the Invention

[0004] The present invention is directed to a zeolite membrane composite, and an object of the present invention is to provide a zeolite membrane composite having high water permeation flux and hydrothermal resistance.

[0005] A first aspect of the invention is a zeolite membrane composite comprising a porous support and a zeolite membrane provided on the support. The zeolite membrane comprises a low-density layer covering the support and a dense layer covering the low-density layer and having a higher zeolite crystal content than the low-density layer. In a cross section of the zeolite membrane composite perpendicular to the surface of the support, the zeolite crystals contained in the dense layer have an average aspect ratio of 2 or more and 4 or less. When the surface of the zeolite membrane, which is the surface of the dense layer, is observed from a direction perpendicular to the surface, 20% or more of the zeolite crystals located on the surface have a triangular shape.

[0006] According to the present invention, a zeolite composite membrane having high water permeation flux and high hydrothermal resistance can be provided.

[0007] A second aspect of the invention is the zeolite membrane composite of the first aspect, wherein, in the cross section of the zeolite membrane composite, the proportion of zeolite crystals contained in the dense layer having an aspect ratio of 3 or more is 10% or more.

[0008] A third aspect of the invention is the zeolite membrane composite of the first or second aspect, wherein, in the cross section of the zeolite membrane composite, the average inclination angle of the longitudinal direction of the zeolite crystals contained in the dense layer relative to the surface of the support is 60 degrees or more and 90 degrees or less.

[0009] A fourth aspect of the invention is the zeolite membrane composite of any one of the first to third aspects, wherein, in the cross section of the zeolite membrane composite, the length of the ridge line of the surface between two points spaced apart on the surface of the zeolite membrane is 1.2 times or more the distance between the two points.

[0010] A fifth aspect of the invention is the zeolite composite membrane of any one of the first to fourth aspects, wherein the zeolite contained in the dense layer has an Si / Al ratio of 3 or more.

[0011] A sixth aspect of the invention is the zeolite composite membrane of any one of the first to fifth aspects, wherein the zeolite contained in the dense layer is an eight-membered ring zeolite.

[0012] A seventh aspect of the present invention is directed to a separation method, comprising the steps of: (a) preparing the zeolite membrane composite of any one of the first to sixth aspects; and (b) supplying a mixed substance containing multiple types of gases or liquids to the zeolite membrane composite, and separating highly permeable substances in the mixed substance from other substances by permeating the zeolite membrane composite.

[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. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a cross-sectional view of a zeolite membrane composite. [Figure 2] FIG. 2 is an enlarged cross-sectional view showing a part of the zeolite composite membrane. [Figure 3] FIG. 2 is a cross-sectional view showing the vicinity of a zeolite membrane. [Figure 4] FIG. 2 is a schematic diagram showing a dense layer and a low-density layer. [Figure 5] FIG. 1 is a diagram showing the surface of a zeolite membrane. [Figure 6] FIG. 1 is a diagram showing a flow of manufacturing a zeolite membrane composite. [Figure 7A] FIG. 2 is a diagram illustrating the formation of a zeolite membrane. [Figure 7B] FIG. 2 is a diagram illustrating the formation of a zeolite membrane. [Figure 7C] FIG. 2 is a diagram illustrating the formation of a zeolite membrane. [Figure 8]FIG. 2 is a diagram showing the change in temperature of a raw material solution during hydrothermal synthesis. [Figure 9] FIG. [Figure 10] FIG. 1 is a diagram showing the flow of separation of a mixed substance. [Figure 11] FIG. 2 is a diagram for explaining measurement of the degree of vacuum. [Figure 12] FIG. 2 is a diagram showing the surface of a zeolite membrane of a comparative example. [Figure 13] FIG. 2 is a schematic diagram showing zeolite crystals contained in a dense layer. DETAILED DESCRIPTION OF THE INVENTION

[0015] FIG. 1 is a cross-sectional view of a zeolite membrane composite 1. FIG. 2 is an enlarged cross-sectional view of a portion of the zeolite membrane composite 1. The zeolite membrane composite 1 includes a porous support 11 and a zeolite membrane 12 provided on the support 11. The zeolite membrane refers to at least a zeolite membrane 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. In FIG. 1, the zeolite membrane 12 is depicted with a thick line. In FIG. 2, the zeolite membrane 12 is depicted with parallel diagonal lines. Furthermore, in FIG. 2, the thickness of the zeolite membrane 12 is depicted thicker than it actually is.

[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 multiple through-holes 111 extending in the longitudinal direction (i.e., the left-right direction in FIG. 1) are provided in the support 11. 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-holes 111 is drawn larger than in reality, and the number of through-holes 111 is drawn smaller than in reality. The zeolite membrane 12 is formed on the inner circumferential surfaces of the through-holes 111, covering the inner circumferential surfaces of the through-holes 111 over substantially the entire surfaces.

[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 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 zeolite membrane 12 on the surface. In this embodiment, the support 11 is formed of a ceramic sintered body. Examples of ceramic sintered bodies that can be 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 contains 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 size of the support 11 is, for example, 0.01 μm to 70 μm, and preferably 0.05 μm to 25 μm. The average pore size of the support 11 near the surface on which the zeolite membrane 12 is formed is 0.01 μm to 1 μm, and preferably 0.05 μm to 0.5 μm. The average pore size can be measured, for example, by a mercury porosimeter, a perm porometer, or a nanoperm porometer. Regarding the pore size 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 zeolite membrane 12 is formed is, for example, 25% to 50%.

[0021] The support 11 has, for example, a multilayer structure in which multiple layers with different average pore sizes are stacked in the thickness direction. The average pore size and sintered particle size in the surface layer, including the surface on which the zeolite membrane 12 is formed, are smaller than the average pore size and sintered particle size in the layers other than the surface layer. The average pore size in 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] The zeolite membrane 12 is a porous membrane having pores. The zeolite membrane 12 can be used as a separation membrane that separates a specific substance from a mixture of multiple substances by utilizing molecular sieving action. The zeolite membrane 12 is less permeable to other substances than to the specific substance. In other words, the amount of the other substances that permeates the zeolite membrane 12 is smaller than the amount of the specific substance that permeates the zeolite membrane 12.

[0023] The thickness of the zeolite membrane 12 is, for example, 0.05 μm to 30 μm, preferably 0.1 μm to 20 μm, and more preferably 0.5 μm to 10 μm. Increasing the thickness of the zeolite membrane 12 improves separation performance. Increasing the thickness of the zeolite membrane 12 increases the permeation rate. The surface roughness (Ra) of the zeolite membrane 12 is, for example, 5 μm or less, preferably 2 μm or less, more preferably 1 μm or less, and even more preferably 0.5 μm or less.

[0024] The average pore diameter of the zeolite membrane 12 is, for example, 1 nm or less. The average pore diameter of the zeolite membrane 12 is preferably 0.2 nm or more and 0.8 nm or less, more preferably 0.3 nm or more and 0.7 nm or less, and even more preferably 0.3 nm or more and 0.6 nm or less. If the average pore diameter is larger than 1 nm, the separation performance may decrease. If the average pore diameter is smaller than 0.2 nm, the permeation rate may decrease. The average pore diameter of the zeolite membrane 12 is smaller than the average pore diameter of the support 11 near the surface on which the zeolite membrane 12 is formed.

[0025] When the maximum number of rings in the zeolite constituting the zeolite membrane 12 is n, the average pore size is the arithmetic mean of the minor and major axes of the n-ring pores. An n-ring pore is a pore in which the number of oxygen atoms in the portion where an oxygen atom is bonded to a T atom (described later) to form a ring structure is n. When a zeolite has multiple types of n-ring pores with the same n, the arithmetic mean of the minor and major axes of all types of n-ring pores is the average pore size of the zeolite. In this way, the average pore size of a zeolite membrane is uniquely determined by the skeletal structure of the zeolite, and is listed in the "Database of Zeolite Structures" [online] of the International Zeolite Society, the Internet, and other sources.<URL:http: / / www.iza-structure.org / databases / > The values ​​can be obtained from the values ​​disclosed in

[0026] The type of zeolite constituting the zeolite membrane 12 is not particularly limited, but 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, MFI type, MOR type, PAU type, RHO type, SAT type, SOD type, or other zeolite.

[0027] The zeolite membrane 12 contains, for example, silicon (Si). The zeolite membrane 12 may contain, for example, any two or more of Si, aluminum (Al), and phosphorus (P). In this case, the zeolite constituting the zeolite membrane 12 may be a zeolite in which the atom (T atom) located at the center of the oxygen tetrahedron (TO4) constituting the zeolite is only Si or is composed of Si and Al; an AlPO-type zeolite in which the T atom is composed of Al and P; a SAPO-type zeolite in which the T atom is composed of Si, Al, and P; a MAPSO-type zeolite in which the T atom is composed of magnesium (Mg), Si, Al, and P; or a ZnAPSO-type zeolite in which the T atom is composed of zinc (Zn), Si, Al, and P. Some of the T atoms may be substituted with other elements.

[0028] When the zeolite membrane 12 contains Si atoms and Al atoms, the Si / Al ratio (molar ratio) in the zeolite membrane 12 is, for example, 1 or more and 100,000 or less. The Si / Al ratio is preferably 3 or more, more preferably 5 or more, and even more preferably 20 or more. The Si / Al ratio in the zeolite membrane 12 can be adjusted by adjusting the blending ratio of the Si source and the Al source in the raw material solution, which will be described later. The zeolite membrane 12 may contain an alkali metal. The alkali metal is, for example, sodium (Na) or potassium (K).

[0029] From the viewpoint of improving separation performance, the maximum number of rings in the zeolite constituting the zeolite membrane 12 is preferably 8. That is, the zeolite is preferably an 8-ring zeolite. The zeolite membrane 12 is, for example, a DDR-type zeolite. In other words, the zeolite membrane 12 is a zeolite membrane composed of a zeolite whose structure code is "DDR" as defined by the International Zeolite Association. In this case, the intrinsic pore diameter of the zeolite constituting the zeolite membrane 12 is 0.36 nm × 0.44 nm, and the average pore diameter is 0.40 nm.

[0030] Fig. 3 is a diagram showing a cross section of the zeolite membrane composite 1 perpendicular to the surface of the support 11. Fig. 3 shows an image (i.e., a TEM image) of the vicinity of the zeolite membrane 12 in a sample prepared for measurement, taken with a transmission electron microscope (TEM). In the following description, the image shown in Fig. 3 will be simply referred to as a "cross-sectional image."

[0031] The zeolite membrane 12 includes a low-density layer 13 and a dense layer 14. The low-density layer 13 is in direct contact with and covers the surface of the support 11. The dense layer 14 is in direct contact with and covers the surface of the low-density layer 13. The dense layer 14 is not in direct contact with the surface of the support 11, but indirectly contacts the surface of the support 11 via the low-density layer 13. For example, the thickness of the dense layer 14 is greater than the thickness of the low-density layer 13. The thickness of the dense layer 14 may be equal to or less than the thickness of the low-density layer 13. Each of the low-density layer 13 and the dense layer 14 includes zeolite crystals and grain boundaries. The grain boundaries are regions between adjacent zeolite crystals. The grain boundaries include, for example, amorphous (i.e., amorphous), crystals other than zeolite crystals, and / or voids. Typically, the density of the grain boundaries is lower than the density of the zeolite crystals.

[0032] The content of zeolite crystals 141 in the dense layer 14 is higher than the content of zeolite crystals 131 (see FIG. 4 described later) in the low-density layer 13. The content of zeolite crystals 141 in the dense layer 14 is preferably 95% or more, and more preferably 96% or more. The content of zeolite crystals 131 in the low-density layer 13 is preferably 5% or more and less than 95%, and more preferably 20% or more and 90% or less.

[0033] The content of zeolite crystals 141 in the dense layer 14 is determined using the cross-sectional image. Specifically, one arbitrary zeolite crystal 141 is selected in the cross-sectional image, and a region including grain boundaries between all zeolite crystals 141 adjacent to the selected zeolite crystal 141 is selected. Next, the region is binarized using a predetermined threshold. The threshold is appropriately determined so that the selected zeolite crystal 141 can be distinguished from the grain boundaries. Next, based on the binarized image of the region, the area of ​​a portion having a concentration below the threshold (e.g., zeolite crystals 141) and the area of ​​a portion having a concentration equal to or greater than the threshold (e.g., grain boundaries) are determined. The area of ​​the zeolite crystal 141 is then divided by the total area of ​​the zeolite crystals 141 and the grain boundaries to determine the content of zeolite crystals 141 in the region. In this embodiment, the content of zeolite crystals 141 is calculated for each of ten regions in the dense layer 14 on the cross-sectional image, and the average of these content rates is taken as the content of zeolite crystals 141 in the dense layer 14. 131 The content of is also determined in the same manner as in the dense layer 14.

[0034] In the example shown in FIG. 3 , the dense layer 14 and the low-density layer 13 each primarily contain one type of zeolite. To easily form the zeolite membrane 12, it is preferable that the type of zeolite contained in the dense layer 14 is the same as the type of zeolite contained in the low-density layer 13. The zeolite contained in the dense layer 14 and the low-density layer 13 is preferably an 8-membered ring zeolite, more preferably a DDR-type zeolite. The Si / Al ratio of the zeolite contained in the dense layer 14 and the low-density layer 13 is preferably 3 or more, more preferably 5 or more, and even more preferably 20 or more. The type of zeolite contained in the dense layer 14 may be different from the type of zeolite contained in the low-density layer 13.

[0035] FIG. 4 is a schematic diagram showing the dense layer 14 and the low-density layer 13 in the zeolite membrane 12. As shown in FIG. 4, in the low-density layer 13, a plurality of zeolite crystals 131 are stacked in the thickness direction of the zeolite membrane 12 (the vertical direction in FIG. 4). In other words, the low-density layer 13 is formed by stacking two or more layers of zeolite crystals 131. On the other hand, in the dense layer 14, a plurality of zeolite crystals 141, each extending in the thickness direction, are densely arranged along the boundary surface between the dense layer 14 and the low-density layer 13. In other words, the dense layer 14 is formed by approximately one layer of zeolite crystals 141. In FIG. 4, the plurality of zeolite crystals 131 contained in the low-density layer 13 are depicted as having the same shape and size; however, in reality, the shapes and sizes of the plurality of zeolite crystals 131 vary widely. Similarly, although the multiple zeolite crystals 141 contained in the dense layer 14 are depicted as having the same shape and size, in reality, the multiple zeolite crystals 141 vary in shape and size (see FIG. 3).

[0036] In the cross-sectional image of FIG. 3 , i.e., in a cross section of the zeolite membrane composite 1 perpendicular to the surface of the support 11, the average aspect ratio of the zeolite crystals 141 contained in the dense layer 14 is preferably 2 or more and 4 or less, more preferably 2 or more and 3.8 or less. This achieves a high water permeation flux and high hydrothermal resistance, as described below. Furthermore, the proportion of zeolite crystals 141 having an aspect ratio of 3 or more among the zeolite crystals 141 contained in the dense layer 14 is preferably 10% or more, more preferably 20% or more. In the cross-sectional image, the average inclination angle of the longitudinal direction of the zeolite crystals 141 relative to the surface of the support 11 is preferably 60 degrees or more, more preferably 70 degrees or more, and even more preferably 80 degrees or more. This can suppress the generation of large gaps between the crystals that occur when the inclination angle is small, thereby achieving high separation performance. The average inclination angle is 90 degrees or less.

[0037] The aspect ratio and tilt angle of the zeolite crystals 141 contained in the dense layer 14 are determined using the cross-sectional image. Specifically, one arbitrary zeolite crystal 141 is selected in the cross-sectional image, and an approximate rectangle 140 that approximates the outer shape (outline) of the zeolite crystal 141 is set. The approximate rectangle 140 is, for example, the smallest circumscribing rectangle for the outer shape of the zeolite crystal 141. In FIG. 3, the approximate rectangle 140 of the zeolite crystal 141 is indicated by a thick dashed line. Furthermore, an approximate surface 110 of the support 11 is set in the cross-sectional image. The approximate surface 110 is determined by linearly approximating the surface of the support 11 in the cross-sectional image using the least squares method. In FIG. 3, the approximate surface 110 of the support 11 is indicated by a two-dot chain line.

[0038] In the cross-sectional image, the angle formed between the direction parallel to the long side of the approximate rectangle 140, i.e., the longitudinal direction of the approximate rectangle 140, and the approximate surface 110 of the support 11 is determined as the tilt angle of the zeolite crystal 141. When the tilt angle of the zeolite crystal 141 is 45 degrees or more, the aspect ratio of the zeolite crystal 141 is determined as the value obtained by dividing the length of the long side of the approximate rectangle 140 by the length of the short side. When the tilt angle of the zeolite crystal 141 is less than 45 degrees, the aspect ratio of the zeolite crystal 141 is determined as the value obtained by dividing the length of the short side of the approximate rectangle 140 by the length of the long side. In this embodiment, the aspect ratios and tilt angles are determined for 30 zeolite crystals 141 on the cross-sectional image, and the average of these aspect ratios is determined as the average aspect ratio of the zeolite crystal 141, and the average of these tilt angles is determined as the average tilt angle of the zeolite crystal 141. The proportion of zeolite crystals 141 having an aspect ratio of 3 or more can also be determined from these aspect ratios.

[0039] Fig. 5 is a diagram showing the surface of the zeolite membrane 12. Fig. 5 shows an image (i.e., an SEM image) of the surface of the zeolite membrane 12, which is the surface of the dense layer 14, captured by a scanning electron microscope (SEM) from a direction perpendicular to the surface. In the following description, the image shown in Fig. 5 will simply be referred to as a "surface image."

[0040] As shown in FIG. 5 , most of the zeolite crystals 141 on the surface of the zeolite membrane 12 have a triangular shape. When observed from a direction perpendicular to the surface of the zeolite membrane 12, the proportion of zeolite crystals 141 that are triangular among the zeolite crystals 141 located on the surface of the zeolite membrane 12 (hereinafter simply referred to as the “proportion of triangular crystals”) is 20% or more, preferably 30% or more, and more preferably 40% or more. This achieves a high water permeation flux, as described below. The triangular shape is not limited to a strict triangle formed by only three sides (line segments), but may have rounded corners, slightly notched edges, or slightly rounded sides. As described above, the zeolite crystals 141 contained in the dense layer 14 extend in the thickness direction. Therefore, depending on the tilt angle, the side surfaces of the zeolite crystals 141 may be reflected in the surface image. In this case, the shape of the region excluding the side surfaces is the shape of the zeolite crystals 141.

[0041] The proportion of triangular crystals in the surface image is determined using the surface image. Specifically, 50 or more zeolite crystals 141 whose shapes can be confirmed are selected from the surface image, and it is determined whether each zeolite crystal 141 has a triangular shape. Then, the proportion of zeolite crystals 141 whose shapes have been determined to be triangular is determined as the proportion of triangular crystals.

[0042] In the zeolite membrane 12, where most of the zeolite crystals 141 contained in the dense layer 14 have a triangular shape, unevenness occurs on the surface. The unevenness on the surface of the zeolite membrane 12 can be quantified using the cross-sectional image of FIG. 3. Specifically, two points P1 and P2 that are separated from each other (e.g., 1 to 5 μm apart) on the surface of the zeolite membrane 12 are arbitrarily determined in the cross-sectional image. Next, the length of the ridge line C1 on the surface of the zeolite membrane 12 between the two points P1 and P2 and the distance (shortest distance) between the points P1 and P2 are determined. In FIG. 3, the ridge line C1 on the surface of the zeolite membrane 12 is indicated by a thick solid line. In the zeolite membrane composite 1, the value obtained by dividing the length of the ridge line C1 between the two points P1 and P2 by the distance between the two points P1 and P2 is preferably 1.2 or more, more preferably 1.3 or more. The upper limit of this value is not particularly limited, but is, for example, 2.0.

[0043] Next, with reference to FIG. 6, an example of a manufacturing flow of the zeolite membrane composite 1 will be described. When the zeolite membrane composite 1 is manufactured, first, membrane-forming seed crystals to be used in manufacturing the zeolite membrane 12 are prepared (step S11). For example, DDR-type zeolite powder is produced by hydrothermal synthesis, and membrane-forming seed crystals are obtained from the zeolite powder. DDR-type zeolite powder can be obtained, for example, by the manufacturing method described in Japanese Patent Application Laid-Open No. 2004-83375 (reference 3 mentioned above). In this manufacturing method, DDR-type zeolite powder is added as seed crystals to a raw material solution having a predetermined composition containing 1-adamantanamine dissolved in ethylenediamine, and dispersed therein. The raw material solution is then heated. At this time, membrane-forming seed crystals having a preferred crystal shape can be obtained by setting the heating temperature of the raw material solution to, for example, 150 to 180°C. The shape of the membrane-forming seed crystals is preferably rhombohedral or octahedral. The heating time of the raw material solution is, for example, 1 to 5 days.

[0044] Next, the membrane-forming seed crystals are attached onto the support 11 (step S12). FIGS. 7A to 7C are diagrams for explaining the formation of the zeolite membrane 12, and schematically show the membrane-forming seed crystals and the like on the support 11. In step S12, as shown in FIG. 7A, a seed crystal stack 125 is formed on the surface of the support 11, in which two or more layers of membrane-forming seed crystals are stacked. The seed crystal stack 125 has a plurality of seed crystal layers stacked on top of each other. It is preferable that the thickness of the seed crystal stack 125 is approximately uniform.

[0045] The formation of the seed crystal stack 125 in step S12 is carried out, for example, by immersing the porous support 11 in a solution in which membrane-forming seed crystals are dispersed. In this case, in order to form the seed crystal stack 125 on the support 11, the support 11 may be immersed in the solution and dried multiple times. The formation of the seed crystal stack 125 on the support 11 may also be carried out by bringing a solution in which membrane-forming seed crystals are dispersed into contact with the surface of the support 11. The seed crystal stack 125 may also be formed on the support 11 by other methods.

[0046] The support 11 to which the seed crystal stack 125 is attached is immersed in a raw material solution. The raw material solution is prepared by dissolving, for example, a Si source (silica source), an Al source (alumina source), and a structure-directing agent (hereinafter also referred to as "SDA") in a solvent. The composition of the raw material solution is, for example, 1.00SiO2:0.01Al2O3:0.015SDA:100H2O. Examples of the Si source include colloidal silica, fumed silica, tetraethoxysilane, and sodium silicate. Examples of the Al source include sodium aluminate, aluminum isopropoxide, aluminum hydroxide, boehmite, sodium aluminate, and alumina sol. The SDA is, for example, an organic substance. For example, 1-adamantanamine is used as the SDA. In addition to water, alcohol (e.g., ethanol) may also be used as the solvent for the raw material solution. When water is used as the solvent for the raw material solution, the molar ratio of SDA to water contained in the raw material solution is preferably 0.01 or less, and the molar ratio of SDA to water contained in the raw material solution is preferably 0.00001 or more.

[0047] Thereafter, DDR-type zeolite is grown by hydrothermal synthesis using the seed crystals of the seed crystal stack 125 as nuclei, thereby forming a DDR-type zeolite membrane 12 on the support 11 (step S13). Fig. 8 is a diagram showing the change in temperature of the raw material solution during hydrothermal synthesis. In Fig. 8, the change in temperature of the raw material solution is shown by a solid line L1, and the change in silica concentration in the raw material solution is shown by a dashed line L2. The silica concentration is shown as a ratio to the initial value, with the silica concentration at the start of hydrothermal synthesis being 100%.

[0048] As shown in Figure 8, in hydrothermal synthesis, the raw material solution is heated in two stages. In this processing example, the raw material solution is heated from an initial temperature T0 (e.g., room temperature) to a first synthesis temperature T1, and then maintained at the first synthesis temperature T1. After a predetermined time has passed since the raw material solution reached the first synthesis temperature T1, the raw material solution is heated from the first synthesis temperature T1 to a second synthesis temperature T2, which is higher than the first synthesis temperature T1, and then maintained at the second synthesis temperature T2. After a predetermined time has passed since the raw material solution reached the second synthesis temperature T2, the temperature of the raw material solution is returned to near the initial temperature T0.

[0049] During the period in which the raw material solution is maintained at the relatively low first synthesis temperature T1, the silica concentration is relatively high, and zeolite grows in various directions from the seed crystals of the seed crystal stack 125. As a result, a low-density layer 13 is formed, as shown in FIG. 7B. During the period in which the raw material solution is maintained at the relatively high second synthesis temperature T2, the silica concentration is relatively low, and zeolite grows in the thickness direction from the zeolite crystals contained in the low-density layer 13. As a result, a dense layer 14 is formed, as shown in FIG. 7C. As described above, in the dense layer 14, a plurality of zeolite crystals 141, each extending in the thickness direction, are densely arranged along the surface of the low-density layer 13.

[0050] 8, in hydrothermal synthesis, the silica concentration (Si amount) in the raw material solution during synthesis at the second synthesis temperature T2 can be adjusted by changing the first synthesis temperature T1 and the holding time at the first synthesis temperature T1. In practice, the average aspect ratio of the zeolite crystals 141 contained in the dense layer 14 can be adjusted by the silica concentration in the raw material solution during synthesis at the second synthesis temperature T2.

[0051] The first synthesis temperature T1 is, for example, 100 to 130°C, preferably 110 to 120°C. The second synthesis temperature T2 is, for example, 130 to 160°C, preferably 140 to 150°C. The holding time at the first synthesis temperature T1 is, for example, 10 to 20 hours, preferably 10 to 15 hours. The holding time at the second synthesis temperature T2 is, for example, 20 to 30 hours, preferably 25 to 30 hours. The first synthesis temperature T1 and the second synthesis temperature T2 The total holding time is preferably 4 to 100 hours, for example, 40 hours. In the synthesis of the zeolite membrane 12, it is not necessarily required to provide a period during which the temperature is held at a constant temperature. For example, the formation of the low-density layer 13 and the dense layer 14 may be achieved by temporarily slowing down the rate of temperature change during heating.

[0052] After the hydrothermal synthesis is completed, the support 11 and the zeolite membrane 12 are washed with pure water. The washed support 11 and the zeolite membrane 12 are dried, for example, at 80°C. After the support 11 and the zeolite membrane 12 are dried, the zeolite membrane 12 is subjected to a heat treatment, whereby the SDA in the zeolite membrane 12 is almost completely burned off and penetrated into the micropores in the zeolite membrane 12. This gives the above-mentioned zeolite membrane composite 1.

[0053] Next, separation of a mixed substance using the zeolite membrane composite 1 will be described with reference to Fig. 9 and Fig. 10. Fig. 9 is a diagram showing a separation device 2. Fig. 10 is a diagram showing a flow of separation of a mixed substance by the separation device 2.

[0054] In the separation device 2, a mixed substance containing multiple types of fluids (i.e., gases or liquids) is supplied to the zeolite membrane composite 1, and highly permeable substances in the mixed substance (hereinafter also referred to as "highly permeable substances") are separated from the mixed substance by permeating through the zeolite 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 (hereinafter also referred to as "lowly permeable substances").

[0055] 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.

[0056] The mixture may include one or more of hydrogen (H), helium (He), nitrogen (N), oxygen (O), water (H), carbon monoxide (CO), carbon dioxide (CO), nitrogen oxides, ammonia (NH), sulfur oxides, hydrogen sulfide (H), sulfur fluoride, mercury (Hg), arsine (AsH), hydrogen cyanide (HCN), carbonyl sulfide (COS), C to C hydrocarbons, organic acids, alcohols, mercaptans, esters, ethers, ketones, and aldehydes. The highly permeable substance may be one or more of H, He, N, O, CO, NH, and H, preferably H.

[0057] Nitrogen oxides are compounds of nitrogen and oxygen. Examples of the nitrogen oxides include nitric oxide (NO), nitrogen dioxide (NO2), nitrous oxide (also called dinitrogen monoxide) (N2O), dinitrogen trioxide (N2O3), dinitrogen tetroxide (N2O4), dinitrogen pentoxide (N2O5), etc. X It is a gas called NOX.

[0058] Sulfur oxides are compounds of sulfur and oxygen. Examples of sulfur oxides include sulfur dioxide (SO2), sulfur trioxide (SO3), and other sulfur compounds. X It is a gas called SOX.

[0059] Sulfur fluoride is a compound of fluorine and sulfur. The sulfur fluoride may be, for example, disulfur difluoride (FSSF, S=SF), sulfur difluoride (SF), sulfur tetrafluoride (SF), sulfur hexafluoride (SF), or disulfur decafluoride (SF). 10 ) etc.

[0060] 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 saturated hydrocarbons (i.e., those without double or triple bonds in the molecule) or unsaturated hydrocarbons (i.e., those with double and / or triple bonds in the molecule). Examples of C1-C4 hydrocarbons include methane (CH4), ethane (C2H6), ethylene (C2H4), propane (C3H8), propylene (C3H6), normal butane (CH3(CH2)2CH3), isobutane (CH(CH3)3), 1-butene (CH2=CHCH2CH3), 2-butene (CH3CH=CHCH3), and isobutene (CH2=C(CH3)2).

[0061] The organic acid may be a carboxylic acid or a sulfonic acid. Examples of the carboxylic acid include formic acid (CHO), acetic acid (CHO), oxalic acid (CHO), acrylic acid (CHO), or benzoic acid (CHCOOH). Examples of the sulfonic acid include ethanesulfonic acid (CHOS). The organic acid may be a chain compound or a cyclic compound.

[0062] The alcohols mentioned above are, for example, methanol (CH3OH), ethanol (C2H5OH), isopropanol (2-propanol) (CH3CH(OH)CH3), ethylene glycol (CH2(OH)CH2(OH)) or butanol (C4H9OH).

[0063] Mercaptans are organic compounds with hydrogenated sulfur (SH) at the end, also known as thiols or thioalcohols. Examples of the mercaptans include methyl mercaptan (CHSH), ethyl mercaptan (CHSH), and 1-propanethiol (CHSH).

[0064] The esters mentioned above are, for example, formates or acetates.

[0065] The ethers mentioned above are, for example, dimethyl ether ((CH3)2O), methyl ethyl ether (C2H5OCH3), diethyl ether ((C2H5)2O) or tetrahydrofuran ((CH2)4O).

[0066] The ketone may be, for example, acetone ((CH3)2CO), methyl ethyl ketone (C2H5COCH3), or diethyl ketone ((C2H5)2CO).

[0067] The aldehydes mentioned above are, for example, acetaldehyde (CH3CHO), propionaldehyde (C2H5CHO) or butanal (butyraldehyde) (C3H7CHO).

[0068] In the following description, it is assumed that the mixed substance separated by the separation device 2 is a mixed liquid containing a plurality of types of liquid, and that separation is performed by pervaporation.

[0069] The separation device 2 includes a zeolite membrane composite 1, a plugging section 21, a housing 22, two seal members 23, a supply section 26, a first recovery section 27, and a second recovery section 28. The zeolite membrane composite 1, the plugging section 21, and the seal members 23 are housed in the housing 22. The supply section 26, the first recovery section 27, and the second recovery section 28 are disposed outside the housing 22 and connected to the housing 22.

[0070] The sealing portion 21 is attached to both ends of the support 11 in the longitudinal direction (i.e., the left-right direction in FIG. 9 ) and is a member that covers and seals both longitudinal end faces of the support 11 and the outer peripheral surfaces near these end faces. The sealing portion 21 prevents liquid from flowing in or out from these end faces of the support 11. The sealing portion 21 is, for example, a plate-like member made of glass or resin. The material and shape of the sealing portion 21 may be changed as appropriate. Note that the sealing portion 21 has 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 portion 21. Therefore, liquid and the like can flow in and out of the through holes 111 from these ends.

[0071] The shape of the housing 22 is not particularly limited, and may be, for example, a substantially cylindrical tubular member. The housing 22 is formed of, for example, stainless steel or carbon steel. The longitudinal direction of the housing 22 is substantially parallel to the longitudinal direction of the zeolite membrane composite 1. A supply port 221 is provided at one longitudinal end of the housing 22 (i.e., the left end in FIG. 9 ), and a first discharge port 222 is provided at the other end. A second discharge port 223 is provided on a side surface 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 a sealed space isolated from the space around the housing 22.

[0072] Two seal members 23 are disposed around the entire circumference between the outer circumferential surface of the zeolite membrane composite 1 and the inner circumferential surface of the housing 22 near both longitudinal ends of the zeolite membrane composite 1. Each seal member 23 is a substantially annular member made of a liquid-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 circumferential surface of the zeolite membrane composite 1 and the inner circumferential surface of the housing 22 around the entire circumference. In the example shown in FIG. 9 , the seal member 23 is in close contact with the outer circumferential surface of the sealing portion 21 and indirectly with the outer circumferential surface of the zeolite membrane composite 1 via the sealing portion 21. A seal is formed between the seal member 23 and the outer circumferential surface of the zeolite membrane composite 1 and between the seal member 23 and the inner circumferential surface of the housing 22, so that liquids can hardly or completely pass through.

[0073] The supply unit 26 supplies the mixed liquid to the internal space of the housing 22 through the supply port 221. The supply unit 26 includes, for example, a pump that pressure-feeds the mixed liquid toward the housing 22. The pump includes a temperature regulator and a pressure regulator that regulate the temperature and pressure, respectively, of the mixed liquid supplied to the housing 22. The first recovery unit 27 includes, for example, a storage container that stores the liquid discharged from the housing 22, or a pump that transfers the liquid. The second recovery unit 28 includes, for example, a vacuum pump that reduces the pressure of the space outside the outer circumferential surface of the zeolite membrane composite 1 in the housing 22 (i.e., the space sandwiched between the two seal members 23), and a cooling chiller trap that cools and liquefies the gas that has vaporized and permeated the zeolite membrane composite 1.

[0074] When separating a mixed liquid, the above-described separation device 2 is provided, thereby preparing a zeolite membrane composite 1 (FIG. 10: step S21). Subsequently, a mixed liquid containing a plurality of liquids having different permeabilities to the zeolite membrane 12 is supplied by the supply unit 26 to the internal space of the housing 22. For example, the main components of the mixed liquid are water (H2O) and ethanol (C2H5OH). The mixed liquid may contain liquids other than water and ethanol. The pressure of the mixed liquid 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 2 MPa, and the temperature of the mixed liquid is, for example, 10°C to 200°C.

[0075] The mixed liquid 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 zeolite membrane composite 1 in the drawing, as indicated by arrow 251. A highly permeable substance, which is a liquid with high permeability in the mixed liquid, vaporizes and permeates through the zeolite membrane 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. In this way, the highly permeable substance (e.g., water) is separated from a less permeable substance (e.g., ethanol), which is a liquid with low permeability in the mixed liquid (step S22).

[0076] The gas (hereinafter referred to as "permeate") discharged from the outer peripheral surface of the support 11 is led to the second collection section 28 via the second discharge port 223 as shown by the arrow 253, where it is cooled and collected as a liquid. The pressure of the gas collected by the second collection section 28 via the second discharge port 223 (i.e., permeate pressure) is, for example, about 6.67 kPa (about 50 Torr). The permeate may include low-permeate substances that have permeated the zeolite membrane 12 in addition to the high-permeate substances described above.

[0077] Furthermore, the liquid in the mixed liquid excluding the substances that have permeated the zeolite membrane 12 and the support 11 (hereinafter referred to as "impermeable substances") passes through each through-hole 111 of the support 11 from left to right in the figure and is recovered by the first recovery unit 27 via the first discharge port 222, as indicated by arrow 252. The pressure of the liquid 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 low-permeability substances described above, the impermeable substances may also include highly permeable substances that did not permeate the zeolite membrane 12. The impermeable substances recovered by the first recovery unit 27 may be circulated to the supply unit 26 and supplied again into the housing 22, for example.

[0078] Next, with reference to Table 1, Examples 1 to 3 and Comparative Examples 1 to 5 of the zeolite membrane composite will be explained.

[0079] [Table 1]

[0080] (Seed crystal production) Similar to the manufacturing method described in JP 2004-83375 A (reference 3), seed crystals were added to a raw material solution, dispersed, and then the raw material solution was heated. This produced membrane-forming seed crystals, which were DDR-type zeolite crystal powders. In Examples 1 to 3 and Comparative Examples 2 to 5, the raw material solution was heated to 150°C and synthesis was carried out for three days to obtain rhombohedral membrane-forming seed crystals. In Comparative Example 1, the raw material solution was heated to 120°C and synthesis was carried out for three days to obtain spherical membrane-forming seed crystals.

[0081] (Seed crystal attachment) A support was brought into contact with a solution in which film-forming seed crystals were dispersed, and the seed crystals were attached to the support. In Examples 1 to 3 and Comparative Examples 1 to 3 and 5, a seed crystal laminate (i.e., a composite layer) in which two or more film-forming seed crystals were laminated was formed, as described with reference to FIG. 7A. In Comparative Example 4, a seed crystal monolayer was formed in which there was one film-forming seed crystal layer.

[0082] (Synthesis of DDR-type zeolite) The support with the seed crystals attached was immersed in a raw material solution (synthesis sol) placed in a sealed container. The raw material solution was prepared by dissolving a Si source, an Al source, SDA, and other ingredients in a solvent. The composition of the raw material solution was 1.00SiO2:0.01Al2O3:0.015SDA:100HO. 1-Adamantaneamine was used as the SDA contained in the raw material solution. DDR-type zeolite was grown using the seed crystals as nuclei by hydrothermal synthesis, thereby forming a DDR-type zeolite membrane on the support. In the hydrothermal synthesis, the raw material solution was heated in two stages, as described with reference to FIG. 8. The first synthesis temperature T1 was 100°C, and the second synthesis temperature T2 was 140°C. In Examples 1 to 3 and Comparative Examples 1 to 3, the retention time at the first synthesis temperature T1 was the time listed under "Low Temperature" in Table 1, and the retention time at the second synthesis temperature T2 was the time listed under "High Temperature" in Table 1. In Comparative Examples 4 and 5, the raw material solution was heated at 140°C in one step.

[0083] (DDR type zeolite cleaning and SDA removal) After the hydrothermal synthesis, the support and the zeolite membrane were thoroughly washed with pure water and then dried at 80°C. The zeolite membrane was then heat-treated to burn off the SDA. Through the above treatments, zeolite membrane composites of Examples 1 to 3 and Comparative Examples 1 to 5, each having a DDR type zeolite membrane, were obtained.

[0084] (Measuring the average aspect ratio) Samples prepared from the zeolite membrane composite for measurement were observed with a transmission electron microscope (TEM) to obtain cross-sectional images. The presence of a low-density layer and a dense layer was confirmed in the zeolite membrane composites of Examples 1 to 3 and Comparative Examples 1 to 3 and 5. The thicknesses of the zeolite membranes including the low-density layer and the dense layer were almost the same. On the other hand, in Comparative Example 4, the absence of a low-density layer and only the dense layer was confirmed.

[0085] In the cross-sectional image, one arbitrary zeolite crystal contained in the dense layer was selected, and an approximate rectangle was set as the smallest circumscribing rectangle for the outer shape of the zeolite crystal. When the inclination angle of the longitudinal direction of the approximate rectangle with respect to the approximate surface of the support was 45 degrees or more, the value obtained by dividing the length of the long side of the approximate rectangle by the length of the short side was taken as the aspect ratio of the zeolite crystal. When the inclination angle was less than 45 degrees, the value obtained by dividing the length of the short side of the approximate rectangle by the length of the long side was taken as the aspect ratio of the zeolite crystal. The above aspect ratios were calculated for 30 zeolite crystals in the cross-sectional image, and the average of these aspect ratios was taken as the average aspect ratio of the zeolite crystals contained in the dense layer.

[0086] As shown in Table 1, in the zeolite membrane composites of Examples 1 to 3, the average aspect ratio of the zeolite crystals contained in the dense layer was 2 or more and 4 or less. On the other hand, in Comparative Example 2, the average aspect ratio was less than 2, and in Comparative Example 3, the average aspect ratio was greater than 4. In Examples 1 to 3, the proportion of zeolite crystals with an aspect ratio of 3 or more among the zeolite crystals contained in the dense layer was 10% or more, and the average tilt angle was 60 degrees or more and 90 degrees or less. In Comparative Examples 1, 4, and 5, measurement of the aspect ratio was omitted.

[0087] (Ratio of triangular crystals) The surface of the zeolite membrane, which is the surface of the dense layer, was observed perpendicularly to the surface using a scanning electron microscope (SEM) to obtain a surface image. From the surface image, 50 or more zeolite crystals were selected, and the proportion of zeolite crystals with a triangular shape among these zeolite crystals was calculated as the proportion of triangular crystals. In the zeolite membrane composites of Examples 1 to 3 and Comparative Examples 2 to 4, the proportion of triangular crystals was 20% or more. On the other hand, in Comparative Example 1, which used spherical membrane-forming seed crystals, the proportion of triangular crystals was less than 5%. In Comparative Example 5, the proportion of triangular crystals was less than 10%. In Comparative Example 5, similar to Examples 1 to 3, rhombohedral membrane-forming seed crystals were used. However, because the raw material solution was heated in only one stage at the second synthesis temperature T2 (high temperature), the crystal growth of the membrane occurred too rapidly, presumably preventing the crystal shape from becoming triangular.

[0088] (Membrane performance evaluation) Using the above-mentioned separation device 2, water and ethanol (50:50 [mass ratio]) were separated by pervaporation at a temperature of 60°C and a permeation side pressure of 50 torr, and the permeation amount of the liquid recovered in the second recovery section 28 was measured. The density of the liquid was determined using a density specific gravity meter, and the water / ethanol ratio was measured. The water permeation flux and separation factor were then calculated from the permeation amount of the liquid and the water / ethanol ratio. The separation factor is the value obtained by dividing the water concentration (mass %) by the ethanol concentration. In Table 1, the water permeation flux was 2.5 kg / m 2 h or more is evaluated as "◎", and 2 h and 2.0 kg / m 2 h or more was evaluated as "Good." 2 less than h and 1.5 kg / m 2 h or more is evaluated as "△", and 2 In the zeolite membrane composites of Examples 1 to 3 and Comparative Example 3, the water permeation flux was 1.5 kg / m 2 h or more, and a high water permeation flux was obtained. In Comparative Examples 1, 2, 4, and 5, the water permeation flux was 1.5 kg / m 2 was less than h.

[0089] (Hydrothermal resistance evaluation) In the evaluation of hydrothermal resistance, the degree of vacuum was measured using a housing 22 containing a zeolite membrane composite 1, as in FIG. 9 . For the measurement of the degree of vacuum, a vacuum pump 291 (manufactured by ULVAC KIKO Co., Ltd.: direct-coupled oil rotary vacuum pump, model number: G-20DA, pumping speed 24 L / min, ultimate pressure 1.3 Pa, two-stage) was connected to port 221 at one longitudinal end of the housing 22, as shown in FIG. 11 , and a vacuum was drawn. A vacuum gauge 292 (manufactured by GE Sensing: calibrator, model number: DPI800) was connected to port 222 at the other end of the housing 22, and the ultimate vacuum was measured. At this time, port 223 provided on the side of the housing 22 was open to the atmosphere. The zeolite membrane composite removed from the housing 22 was then immersed in high-temperature water (180°C) for 12 hours, washed with ion-exchanged water, and dried at room temperature for 12 hours or more. Thereafter, the degree of vacuum was measured again, and the ratio of the degree of vacuum after immersion to the degree of vacuum before immersion was used as an index of hydrothermal resistance. In Table 1, a ratio of 95% or more was evaluated as "Good," a ratio of less than 95% but 90% or more was evaluated as "Average," and a ratio of less than 90% was evaluated as "Poor." In the zeolite membrane composites of Examples 1 to 3, the ratio was 95% or more, and high hydrothermal resistance was obtained. In Comparative Example 3, the ratio was less than 90%, and hydrothermal resistance was low. Note that evaluation of hydrothermal resistance was not performed in Comparative Examples 1, 2, 4, and 5, which had low water permeation flux.

[0090] Here, we consider the reason why the zeolite membrane composites of Examples 1 to 3 have higher water permeation flux and hydrothermal resistance than those of Comparative Examples 1 to 5. Fig. 12 is a diagram showing the surface of the zeolite membrane in the zeolite membrane composite of Comparative Example 1, and corresponds to the surface image in Fig. 5.

[0091] As shown in Fig. 12, in the zeolite membrane composite of Comparative Example 1, many of the zeolite crystals 91 have a substantially circular shape. The same is true for the zeolite membrane composite of Comparative Example 5. On the other hand, in the zeolite membrane composites of Examples 1 to 3, many of the zeolite crystals 141 have a triangular shape, as shown in Fig. 5. Comparing the zeolite crystals 91 in Fig. 12 and the zeolite crystals 141 in Fig. 5, which have substantially the same area, the zeolite crystals 141 having a triangular shape have a longer perimeter than the zeolite crystals 91 having a substantially circular shape. This is thought to result in a higher water permeation flux in the zeolite membrane composites of Examples 1 to 3, as compared to Comparative Examples 1 and 5.

[0092] Fig. 13 is a schematic diagram showing zeolite crystals contained in dense layer 14. The upper part of Fig. 13 shows zeolite crystals 91 of a comparative example having an average aspect ratio of 1, the middle part shows zeolite crystals 141 of a comparative example having an average aspect ratio of 3, and the lower part shows zeolite crystals 91 of a comparative example having an average aspect ratio of 6. The dense layers 14 in the upper, middle, and lower parts of Fig. 13 have the same thickness.

[0093] As shown in the upper part of Figure 13, when the average aspect ratio of the zeolite crystals 91 is excessively small, the number of grain boundaries per unit area (shown by thick dashed lines in Figure 13) is smaller than that shown in the middle part of Figure 13. Therefore, it is believed that the zeolite membrane composite of Comparative Example 2, which has an excessively small average aspect ratio, has a reduced water permeation flux. As shown in the lower part of Figure 13, when the average aspect ratio of the zeolite crystals 91 is excessively large, the number of grain boundaries per unit area is greater than that shown in the middle part of Figure 13. Therefore, it is believed that the zeolite membrane composite of Comparative Example 3, which has an excessively large average aspect ratio, has a high water permeation flux but a reduced hydrothermal resistance because the grain boundaries are easily damaged. In other words, the zeolite membrane composites of Examples 1 to 3, which have an average aspect ratio of 2 or more and 4 or less, have both high water permeation flux and high hydrothermal resistance. In Comparative Example 4, in which only the dense layer was formed, it is believed that the length of the grain boundary through which water permeated was excessively long, resulting in a low water permeation flux.

[0094] As described above, the zeolite membrane composite 1 includes a porous support 11 and a zeolite membrane 12 provided on the support 11. The zeolite membrane 12 includes a low-density layer 13 covering the support 11 and a dense layer 14 covering the low-density layer 13. In a cross section of the zeolite membrane composite 1 perpendicular to the surface of the support 11, the zeolite crystals 141 contained in the dense layer 14 have an average aspect ratio of 2 or more and 4 or less. When the surface of the zeolite membrane 12, which is the surface of the dense layer 14, is observed from a direction perpendicular to the surface, 20% or more of the zeolite crystals 141 located on the surface have a triangular shape. This makes it possible to realize a zeolite membrane composite 1 having high water permeation flux and hydrothermal resistance, as in Examples 1 to 3 above. Furthermore, by forming a dense layer 14 having a higher zeolite crystal content than the low-density layer 13 on the low-density layer 13 covering the support 11, it is possible to easily form a thin, defect-free dense layer 14 compared to when the dense layer is formed directly on the support. As a result, it is possible to achieve both a high water permeation flux and high separation performance.

[0095] Preferably, in the cross section of the zeolite membrane composite 1, the proportion of zeolite crystals 141 having an aspect ratio of 3 or more among the zeolite crystals 141 contained in the dense layer 14 is 10% or more. By containing a large number of zeolite crystals 141 having aspect ratios within a preferred range, the water permeation flux and hydrothermal resistance can be more reliably improved.

[0096] Preferably, in the cross section of the zeolite composite membrane 1, the average inclination angle of the longitudinal direction of the zeolite crystals 141 contained in the dense layer 14 relative to the surface of the support 11 is 60 degrees or more and 90 degrees or less. In this way, the zeolite composite membrane 1 having a large average inclination angle can prevent large gaps from being generated between the crystals, thereby achieving high separation performance.

[0097] Preferably, in the cross section of the zeolite membrane composite 1, the length of the ridge C1 on the surface of the zeolite membrane 12 between two points P1 and P2 that are spaced apart from each other is at least 1.2 times the distance between the two points P1 and P2. In such a zeolite membrane 12, zeolite crystals 141 having a preferred shape are formed in the dense layer 14, and high water permeation flux and high hydrothermal resistance can be more reliably achieved.

[0098] Preferably, the Si / Al ratio of the zeolite contained in the dense layer 14 is 3 or more. This can further improve the hydrothermal resistance of the zeolite membrane composite 1. In addition, the zeolite contained in the dense layer 14 is preferably an 8-membered ring zeolite. This can suitably achieve selective permeation of target substances (particularly water) with relatively small molecular diameters through the zeolite membrane composite 1.

[0099] The above-described separation method includes a step of preparing a zeolite membrane composite 1 (step S21), and a step of supplying a mixed substance containing multiple types of gases or liquids to the zeolite membrane composite 1 and separating highly permeable substances in the mixed substance from other substances by permeating the zeolite membrane composite 1 (step S22). In this separation method, by using the zeolite membrane composite 1 having a high water permeation flux and high hydrothermal resistance, various mixed substances can be separated efficiently and stably. The separation method using the zeolite membrane composite 1 is particularly suitable for separating mixed substances containing water.

[0100] The above-described zeolite membrane composite 1 and separation method can be modified in various ways.

[0101] 3, the proportion of zeolite crystals 141 having an aspect ratio of 3 or more among the zeolite crystals 141 contained in the dense layer 14 may be less than 10%. The average tilt angle of the zeolite crystals 141 may be less than 60 degrees. Furthermore, the value obtained by dividing the length of the ridgeline C1 between two points P1 and P2 on the surface of the zeolite membrane 12 by the distance between the two points P1 and P2 may be less than 1.2.

[0102] The zeolite contained in the dense layer 14 may have a Si / Al ratio of less than 3, and the maximum number of rings in the zeolite may be less than eight or greater than eight.

[0103] In addition to the support 11 and the zeolite membrane 12, the zeolite membrane composite 1 may further include a functional membrane or a protective membrane laminated on the zeolite membrane 12. Such a functional membrane or protective membrane may be an inorganic membrane such as a zeolite membrane, a silica membrane, or a carbon membrane, or an organic membrane such as a polyimide membrane or a silicone membrane. Furthermore, a substance that easily adsorbs water may be added to the functional membrane or protective membrane laminated on the zeolite membrane 12.

[0104] In the separation method, the mixed substance may be separated by vapor permeation, reverse osmosis, gas permeation, etc., in addition to the pervaporation method exemplified in the above description. Furthermore, substances other than the substances exemplified in the above description may be separated from the mixed substance.

[0105] The configurations in the above-described embodiment and each modification may be combined as appropriate as long as they are not mutually contradictory.

[0106] 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. [Industrial Applicability]

[0107] The zeolite membrane composite of the present invention can be used, for example, as a dehydration membrane, and further, can be used in various fields in which zeolites are used, such as separation membranes for various substances other than water and adsorption membranes for various substances. [Explanation of symbols]

[0108] 1 Zeolite membrane composite 11 Support 12 Zeolite membrane 13 Low density layer 14 Layer compacta 141 Zeolite crystals (in the dense layer) S11~S13, S21, S22 steps

Claims

1. A zeolite membrane composite, a porous support; a zeolite membrane provided on the support; Equipped with The zeolite membrane is a low-density layer covering the support; a dense layer covering the low-density layer and having a higher zeolite crystal content than the low-density layer; Equipped with In a cross section of the zeolite membrane composite perpendicular to the surface of the support, the average aspect ratio of the zeolite crystals contained in the dense layer is 2 or more and 4 or less, When the surface of the zeolite membrane, which is the surface of the dense layer, is observed from a direction perpendicular to the surface, 20% or more of the zeolite crystals located on the surface have a triangular shape.

2. The zeolite membrane composite according to claim 1, In the cross section of the zeolite composite membrane, the proportion of zeolite crystals having an aspect ratio of 3 or more among the zeolite crystals contained in the dense layer is 10% or more.

3. The zeolite membrane composite according to claim 1, In the cross section of the zeolite membrane composite, the average inclination angle of the longitudinal direction of the zeolite crystals contained in the dense layer relative to the surface of the support is 60 degrees or more and 90 degrees or less.

4. The zeolite membrane composite according to claim 1, In the cross section of the zeolite membrane composite, the length of the ridge line on the surface between two points spaced apart from each other on the surface of the zeolite membrane is 1.2 times or more the distance between the two points.

5. The zeolite membrane composite according to claim 1, The zeolite contained in the dense layer has a Si / Al ratio of 3 or more.

6. The zeolite membrane composite according to claim 1, The zeolite contained in the dense layer is an eight-membered ring zeolite.

7. A separation method comprising: a) preparing a zeolite composite membrane according to any one of claims 1 to 6; b) supplying a mixed substance containing a plurality of types of gases or liquids to the zeolite membrane composite, and separating highly permeable substances in the mixed substance from other substances by permeating the highly permeable substances through the zeolite membrane composite; Equipped with.

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