Separation membrane composite and method for producing separation membrane composite

Abstract

This separation membrane composite (1) comprises: a porous support body (11); a seal part (16) that covers a prescribed seal area (A1) on a target surface of the support body (11); and a separation membrane (12) that covers the non-seal area (A2) that is not covered by the seal part (16) on the target surface, and also covers the seal part (16) in the vicinity of the boundary (P) between the non-seal area (A2) and the seal area (A1). In a region of interest (R1) in a range of 10 mm from the edge (121) of the separation membrane (12) positioned on the seal part (16) toward the non-seal-area (A2) side, the separation membrane (12) has a non-penetrating crack (C1) that opens to the surface on the side opposite from the support body (11) and does not reach the support body (11). In a 50-μm-square region within the region of interest (R1), the total crack length of the non-penetrating crack (C1) is 50-1000 μm.

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 JP2024-042828, filed on March 18, 2024, the entire disclosure of which is incorporated herein by reference.

[0002] Conventionally, various separation membranes have been used for separating gases and liquids. Because separation membranes themselves generally have low strength, separation membrane composites are manufactured by forming a separation membrane on a porous support such as a metal or ceramic support, and the separation membrane composites are used for gas separation and the like. A seal portion that blocks the passage of fluids is provided at the end of the support in the separation membrane composite. For example, International Publication No. 2016 / 093192 (Reference 1) discloses a separation membrane structure having a glass seal. The glass seal has a seal main body portion disposed on the end face of the support and an extension portion disposed on the inner surface of the through-hole of the support. The separation membrane is formed on the inner surface of the through-hole and partially overlaps with the extension portion of the glass seal. In the separation membrane composite disclosed in Japanese Patent Laid-Open No. 2009-214075 (Reference 2), a separation membrane and a membrane-like seal portion disposed so as to contact the separation membrane are provided on the surface of the porous support, and the boundary portion between the separation membrane and the seal portion is covered with a coating zeolite.

[0003] As described above, in a separation membrane composite in which a separation membrane and a seal portion are provided on a support, when used for a long period of time under high-temperature conditions, cracks penetrating the separation membrane (hereinafter referred to as "penetrating cracks") may occur near the boundary between the seal portion and the separation membrane due to the difference in thermal expansion coefficients between the support, the seal portion, and the separation membrane. When penetrating cracks occur, the separation performance of the separation membrane composite decreases. Therefore, the separation membrane composite cannot be used for a long period of time under high-temperature conditions.

[0004] An object of the present invention is to prevent through cracks from occurring in a separation membrane when the separation membrane composite is used under high temperature conditions.

[0005] A first aspect of the invention is a separation membrane composite comprising a porous support, a sealing portion covering a predetermined sealing area on a target surface of the support, and a separation membrane covering a non-sealed area on the target surface that is not covered by the sealing portion and covering the sealing portion near the boundary between the non-sealed area and the sealed area, wherein in a region of interest ranging from an edge of the separation membrane located on the sealing portion to a region of interest that is 10 mm toward the non-sealed area, the separation membrane has non-penetrating cracks that open onto the surface opposite the support and do not reach the support, and the total crack length of the non-penetrating cracks in a 50 μm square region within the region of interest is 50 μm or more and 1000 μm or less.

[0006] According to the present invention, the occurrence of through cracks in the separation membrane due to use of the separation membrane composite under high temperature conditions can be suppressed.

[0007] A second aspect of the present invention is the separation membrane composite of the first aspect, wherein the separation membrane is a zeolite membrane or an MOF membrane.

[0008] A third aspect of the present invention is the separation membrane composite of the first or second aspect, wherein the support is made of a porous inorganic material.

[0009] A fourth aspect of the invention is a method for producing a separation membrane composite, comprising: a) preparing a porous support having a predetermined sealing region on a target surface covered with a sealing portion; b) contacting a first dispersion liquid having first seed crystals dispersed therein with the target surface to adhere the first seed crystals; c) contacting a second dispersion liquid having second seed crystals dispersed therein with a region on the target surface near the boundary between the sealing region and a non-sealed region not covered with the sealing portion to adhere the second seed crystals; and d) immersing the support in a raw material solution to perform solvothermal synthesis, thereby forming a separation membrane on the target surface.

[0010] A fifth aspect of the invention is the method for producing a separation membrane composite according to the fourth aspect, wherein in the step d), the temperature of the raw material solution is increased at a rate of 15 to 200° C. / h.

[0011] A sixth aspect of the invention is the method for producing a separation membrane composite according to the fourth or fifth aspect, further comprising a step of drying the support between the step b) and the step c).

[0012] 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.

[0013] 1 is a cross-sectional view of a separation membrane composite. FIG. 1 is a cross-sectional view showing an enlarged view of a portion of the separation membrane composite. FIG. 1 is a cross-sectional view showing an enlarged view of the vicinity of one end of the separation membrane composite. FIG. 1 is a cross-sectional view showing an enlarged view of the vicinity of the seal boundary. FIG. 2 is a view showing the surface of the separation membrane in a region of interest. FIG. 3 is a view showing a separation membrane composite of a comparative example. FIG. 4 is a view showing a separation membrane composite of a comparative example. FIG. 5 is a view showing a separation membrane composite of a comparative example. FIG. 6 is a view showing a flow of manufacturing a separation membrane composite. FIG. 7 is a view showing the state of a seed crystal attachment treatment near the seal boundary. FIG. 8 is a view for explaining the relationship between the rate of temperature rise of a raw material solution and the growth of a MOF membrane. FIG. 9 is a view for explaining the relationship between the rate of temperature rise of a raw material solution and the growth of a MOF membrane. FIG. 10 is a view showing the relationship between the rate of temperature rise of a raw material solution and the growth of a MOF membrane. FIG. 11 is a view showing the state of a dyeing test using a rhodamine solution. FIG. 12 is a view showing a separation apparatus. FIG. 13 is a view showing the flow of separation of mixed substances by a separation apparatus.

[0014] 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 separation membrane 12 provided on the support 11. An example of the separation membrane 12 is a metal-organic framework (MOF) membrane (hereinafter also referred to as a "MOF membrane"). In this case, the separation membrane composite 1 is a MOF membrane composite. A MOF membrane is at least a membrane of MOFs formed on the surface of a support 11, and does not include membranes in which MOF particles are simply dispersed in an organic film. In the following description, the separation membrane 12 is assumed to be a MOF membrane, but the separation membrane 12 may also be a zeolite membrane or a membrane made of another material. When the separation membrane 12 is a zeolite membrane or a MOF membrane, it becomes easy to create non-penetrating cracks in the separation membrane 12 by the attachment of seed crystals and solvothermal synthesis, as described below. In FIG. 2, the separation membrane 12 is shown with hatched lines and is drawn to appear thicker than it actually is.

[0015] 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 so-called monolithic support having a single, continuous columnar body formed integrally with the support 11. The single, continuous columnar body has 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 larger than the actual diameter, and the number of through-holes 111 is smaller than the actual number. The separation membrane 12 is formed on the inner circumferential surface of the through-hole 111 and covers the inner circumferential surface of the through-hole 111 over substantially the entire surface. In the separation membrane composite 1 shown in FIG. 1 , the inner circumferential surface of the through-hole 111 is the surface on which the separation membrane 12 is formed. The separation membrane 12 may also be formed on the outer circumferential surface of the support 11.

[0016] 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.

[0017] The support 11 is formed, for example, from a porous inorganic material, preferably from ceramic. 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 contains at least one of alumina, silica, and mullite. The support 11 may contain an inorganic binder. As the inorganic binder, at least one of titania, mullite, sinterable alumina, silica, glass frit, clay minerals, and sinterable cordierite can be used. The support 11 may also be formed from a metal.

[0018] 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 where the separation membrane 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. With regard to 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 where the separation membrane 12 is formed is, for example, 20% to 60%. The porosity can be determined as the percentage of the area where voids exist in an SEM (scanning electron microscope) image of a cross section of the support 11.

[0019] 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 grain size in the surface layer, including the surface on which the separation membrane 12 is formed, are smaller than the average pore size and sintered grain 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.

[0020] The separation membrane 12 is a porous membrane having fine pores (micropores). The separation membrane 12 can separate a specific substance from a mixture of multiple substances by utilizing molecular sieving or the like. Other substances are less likely to permeate the separation membrane 12 than the specific substance. In other words, the permeation rate of the other substances through the separation membrane 12 is slower than the permeation rate of the specific substance.

[0021] The average thickness of the separation membrane 12 is, for example, 5 μm or less, preferably 3 μm or less. This enables a high permeation rate to be achieved. The lower limit of the average thickness of the separation membrane 12 is not particularly limited, but from the viewpoint of improving separation performance, it is preferably 0.5 μm, more preferably 0.7 μm. To measure the average thickness of the separation membrane 12, a cross section perpendicular to the surface of the separation membrane 12 is exposed, for example, by cross-sectional polishing. In the cross section, multiple randomly selected fields (e.g., seven fields) in an area excluding the vicinity of the seal boundary P described below (see FIG. 4) are observed using an SEM. The magnification of the SEM is, for example, 5000x. The average thickness of the separation membrane 12 in each field (field-average thickness) is calculated as the average of the thicknesses at five appropriately selected locations, and the arithmetic mean of the field-average thicknesses of the remaining fields excluding the fields with the maximum and minimum field-average thickness values ​​is obtained as the average thickness of the separation membrane 12. The surface roughness (Ra) of the separation membrane 12 is, for example, 2 μm or less, preferably 1 μm or less, and more preferably 0.5 μm or less.

[0022] The MOF membrane constituting the separation membrane 12 is a polycrystalline membrane mainly composed of numerous MOF crystals formed on the surface of the support 11. At the interface between the separation membrane 12 and the support 11, a composite layer 13 is formed in which the MOF crystals penetrate into the pores of the support 11. In FIG. 2 , the composite layer 13 is shown by drawing parallel diagonal lines overlaid on a portion of the support 11. The composite layer 13 is part of the support 11. The thickness of the composite layer 13 is, for example, 2 μm or less. This makes it possible to suppress a decrease in permeation rate due to the presence of the composite layer 13. The composite layer 13 does not have to be present, and the lower limit of the thickness of the composite layer 13 is 0.

[0023] In measuring the thickness of the composite layer 13, in cross-sectional observation using an SEM, the boundary position of the composite layer 13 in a direction perpendicular to the interface between the support 11 and the separation membrane 12 (hereinafter referred to as the "depth direction") is identified near one measurement position along the interface. Specifically, the boundary position on the separation membrane 12 side of the composite layer 13 is the interface between the separation membrane 12 and the support 11. The boundary position on the opposite side of the composite layer 13 from the separation membrane 12 is the edge of the MOF present in the pores of the support 11 that is substantially continuous with the separation membrane 12 in the depth direction but is farthest from the separation membrane 12. The depth-wise distance between the boundary position on the separation membrane 12 side of the composite layer 13 and the boundary position on the opposite side of the separation membrane 12 is obtained as the thickness of the composite layer 13 at that measurement position. Then, the average of the thicknesses of the composite layer 13 at multiple different measurement positions (e.g., 10 measurement positions) is determined as the thickness of the composite layer 13 in the separation membrane composite 1.

[0024] Not only when the composite layer 13 is not present, but also when the composite layer 13 is present, there is no intermediate layer formed separately between the support 11 and the separation membrane 12 in the separation membrane composite 1, so the support 11 and the separation membrane 12 are in direct contact with each other. In other words, there is no intermediate layer formed between the support 11 and the separation membrane 12 in a step other than the step of forming the MOF membrane.

[0025] The average pore diameter of the MOF membrane constituting the separation membrane 12 is not particularly limited, but, for example, is 0.40 nm or more and 0.90 nm or less. The "average pore diameter of the MOF" is the average value of the long and short diameters of the pore openings theoretically derived from the skeletal structure of the MOF. The long and short diameters of the pore openings, more precisely, refer to the interlattice spacing of the highly regular lattice structure formed by metal ions and organic ligands. MOFs have a unique pore structure consisting of channels (pores) and cages (internal spaces) depending on the structural type. The pore diameter here refers to the pore diameter of the channel, with the maximum diameter in the cross section of the channel being the long diameter and the diameter of the cross section in a direction approximately perpendicular to the long diameter being the short diameter, and the arithmetic mean of the short diameter and the long diameter being the average pore diameter. This average pore diameter is smaller than the average pore diameter of the support 11 near the surface on which the separation membrane 12 is formed.

[0026] The average particle size of the MOFs constituting the separation membrane 12, i.e., the average size of the crystal grains, is, for example, 0.1 μm to 2 μm. The average particle size is preferably 1 μm or less, and more preferably 0.5 μm or less. In a separation membrane 12 having a small average MOF particle size, grain boundary defects caused by excessively large gaps formed between MOF crystals are reduced, making it possible to improve separation performance. The average particle size of the MOFs in this embodiment is the arithmetic mean of the maximum Feret diameters of multiple MOF particles (e.g., 30 particles) measured by observing the membrane surface using an SEM. The multiple particles to be measured may be randomly selected on an SEM image.

[0027] The MOF constituting the separation membrane 12 is composed of metal ions and organic ligands (hereinafter simply referred to as "ligands") coordinated to the metal ions. The metal ions constituting the MOF are not particularly limited, but in practical terms, Al ３＋ , Co ３＋ , Co ２＋ , Ni ２＋ , Ni ＋ , Cu ２＋ , Cu ＋ , Zn ２＋ , Fe ３＋ , Fe ２＋ , Ti ３＋ and Zr ４＋ More preferably, the metal ion comprises at least one selected from the group consisting of Al ３＋ , Zn ２＋ , Ti ３＋ and Zr ４＋ Preferably, the number of types of metal ions contained in the MOF is one, but may be multiple.

[0028] The ligands that are components of MOFs are not particularly limited, but one example is a bidentate ligand, which is an ion of an organic molecule having two carboxy groups. This makes it possible to easily form pores that allow a specific gas to pass through more easily than other specific gases. The structure other than the two carboxy groups is not particularly limited, but one suitable example is a ligand having a heterocycle. Furthermore, instead of a carboxy group, the ligand may have a ligand such as a pyridine group or a pyrrole group that can coordinate to a metal ion.

[0029] FIG. 3 is an enlarged view of the vicinity of one end of the separation membrane composite 1 of FIG. 1 . In one example of the separation membrane composite 1, a seal portion 16 is provided at each longitudinal end of the support 11. The seal portion 16 is formed of a dense sealing material such as glass or resin. The seal portion 16 continuously covers the area on the end face of the support 11 other than the through holes 111, the area on the outer circumferential surface of the support 11 near the end face (see FIG. 1 ), and the area on the inner circumferential surface of each through hole 111 near the end face. The seal portion 16 seals these areas on the surface of the support 11. The seal portion 16 is a sealing portion that prevents fluid from flowing in and out of these areas. Note that both longitudinal ends of each through hole 111 are not covered by the seal portion 16, and fluid can flow in and out of the through hole 111 from these ends.

[0030] In the seal portion 16, the length (longitudinal length) of the portion on the outer peripheral surface of the support 11 and the length of the portion on the inner peripheral surface of each through-hole 111 are, for example, 0.1 to 5.0 cm. In the seal portion 16 of this embodiment, the length of the portion on the inner peripheral surface of the through-hole 111 is shorter than the length of the portion on the outer peripheral surface of the support 11. Depending on the design of the separation membrane composite 1, in the seal portion 16, the length of the portion on the inner peripheral surface of the through-hole 111 may be equal to or longer than the length of the portion on the outer peripheral surface of the support 11.

[0031] On the inner circumferential surface of each through hole 111, a seal boundary P (shown by a black dot in FIG. 3 ) is set near each end face of the support body 11, and the seal portion 16 covers the inner circumferential surface from the seal boundary P toward the end face in the longitudinal direction. The seal boundary P is the tip position of the seal portion 16 inside the through hole 111. Typically, the position of the seal boundary P in the longitudinal direction is approximately the same around the entire circumference of the inner circumferential surface, but may vary to some extent along the circumferential direction. For multiple through holes 111, the position of the seal boundary P in the longitudinal direction is preferably approximately the same, but may vary to some extent. In the following description, the area A1 on the inner circumferential surface of each through hole 111 that is covered by the seal portion 16 is referred to as the "sealed area A1," and the area not covered by the seal portion 16 is referred to as the "non-sealed area A2." The sealed area A1 and the non-sealed area A2 are adjacent to each other, and the seal boundary P is the boundary between the sealed area A1 and the non-sealed area A2.

[0032] The separation membrane 12 described above covers substantially the entire area between the seal portions 16 provided at both ends of the support 11 on the inner circumferential surface of each through hole 111, i.e., the non-sealed area A2. That is, a portion of the inner circumferential surface of the through hole 111 is covered by the seal portion 16, and the entire remainder is covered by the separation membrane 12. The separation membrane 12 also partially covers the seal portion 16 near the seal boundary P. A composite portion where the seal portion 16 and the separation membrane 12 overlap is provided near the seal boundary P. The length of the portion where the seal portion 16 and the separation membrane 12 overlap (composite portion) in the longitudinal direction is, for example, 0.1 μm to 100 μm, and preferably 0.1 μm to 10 μm. The thickness of the separation membrane 12 near the seal boundary P is greater than the average film thickness of the separation membrane 12. The thickness of the separation membrane 12 in the vicinity of the seal boundary P can be measured in an SEM image, as can the average membrane thickness (the same applies to the thicknesses of the seed crystal-containing layer and the dense layer described below).

[0033] FIG. 4 is an enlarged view of the vicinity of the seal boundary P. Like FIGS. 1 and 3, FIG. 4 shows a cross section along the longitudinal direction and perpendicular to the inner circumferential surface of the through hole 111. As shown in FIGS. 3 and 4, on the inner circumferential surface of the through hole 111, the thickness of the seal portion 16 gradually increases from the seal boundary P toward the end face of the support body 11. In reality, the surface of the seal portion 16 has a gentle slope near the seal boundary P. Furthermore, the surface roughness (irregularities) of the seal portion 16 is small, i.e., the surface of the seal portion 16 is smooth. As described above, the seal portion 16 is covered by the separation membrane 12 near the seal boundary P.

[0034] Here, attention is focused on a region R1 (hereinafter referred to as the "region of interest R1") extending 10 mm from the edge 121 of the separation membrane 12 located on the seal portion 16 toward the non-sealed region A2. The region of interest R1 is a region that includes the seal boundary P (or overlaps with the seal boundary P). As shown in FIG. 4 , in the region of interest R1, the separation membrane 12 has a crack C1. The crack C1 is a linear groove that opens on the surface of the separation membrane 12 opposite the support 11 (hereinafter simply referred to as the "surface of the separation membrane 12") and has a width of 50 nm or more on the surface of the separation membrane 12. The upper limit of the width of the crack C1 is not particularly limited, but is, for example, 300 nm. The crack C1 occurs, for example, along the grain boundaries between the MOF crystals. The crack C1 may also occur within the MOF crystals. Cracks may or may not be present in the separation membrane 12 outside the region of interest R1.

[0035] In the production of the separation membrane composite 1 described below, many seed crystals adhere near the seal boundary P. As a result, in the region of interest R1 near the seal boundary P, the thickness of the separation membrane 12 is greater than in other regions, as described above. During the production of the separation membrane composite 1, cracks are more likely to occur in the separation membrane 12 in the region of interest R1. Furthermore, in the separation membrane 12 in the region of interest R1, a seed crystal-containing layer containing seed crystals and a dense layer not containing seed crystals are formed. As described below, by performing a seed crystal adhesion process only near the seal boundary P using a second dispersion liquid in which second seed crystals are dispersed, the surface of the seed crystals near the seal boundary P after adhesion of the second seed crystals becomes flatter than other portions due to the surface tension of the second dispersion liquid, making it possible to produce a separation membrane having a seed crystal-containing layer with little thickness variation. As a result, the seed crystal-containing layer of the membrane after synthesis has a relatively uniform thickness, which can suppress the occurrence of through-cracks. The seed crystal-containing layer is a layer that comes into contact with the support 11. The dense layer is a layer that is in contact with the seed crystal-containing layer on the side opposite to the support 11, and the MOF crystal grains are more densely present in the dense layer than in the seed crystal-containing layer. In Figure 4, the boundary between the dense layer and the seed crystal-containing layer is indicated by a dashed line L1.

[0036] During the production of the separation membrane composite 1, cracks C1 that occur on the surface of the separation membrane 12 are prevented from reaching the surface of the support 11 due to the presence of the seed crystal-containing layer. As a result, almost all of the cracks C1 in the region of interest R1 become non-penetrating cracks that do not reach the surface of the support 11. Whether almost all of the cracks C1 are non-penetrating cracks can be confirmed, for example, by a dyeing test using a rhodamine solution. In the dyeing test, a rhodamine solution is prepared by dissolving powdered rhodamine in a solvent in which rhodamine is soluble (e.g., water or ethanol). The rhodamine solution is allowed to come into contact with the surfaces of the separation membrane 12 and the seal portion 16 for a predetermined period of time (see Figure 10 described below), and then a cross section along the longitudinal direction and perpendicular to the inner circumferential surface of the through hole 111 is observed visually and with an optical microscope. If the support 11 is not dyed in the region of interest R1, almost all of the cracks C1 in the region of interest R1 are determined to be non-penetrating cracks. The surface of the separation membrane 12 may or may not be dyed. In the following description, the crack C1 in the separation membrane 12 in the region of interest R1 will be referred to as a "non-penetrating crack C1."

[0037] FIG. 5 is a diagram showing the surface of the separation membrane 12 in the region of interest R1, and for convenience of illustration, the lead lines of the symbols C1 and R2 are shown as dashed lines. As shown in FIG. 5, a typical non-penetrating crack C1 spreads in a mesh-like pattern on the surface of the separation membrane 12. In the following description, on the surface of the separation membrane 12, each branch point of a line representing a crack is considered to be an end point (for a portion that reaches the edge 121 of the separation membrane 12, the intersection with the edge 121 is considered to be the end point, and if the line is interrupted, the point of interruption is considered to be the end point; the same applies below), and the portion of the line between two adjacent end points on the line is considered to be one non-penetrating crack C1. Typically, each non-penetrating crack C1 is connected to another non-penetrating crack C1.

[0038] In the separation membrane composite 1, the total length of the non-penetrating cracks C1 in a 50-μm square region within the region of interest R1 (hereinafter simply referred to as the "total length of the non-penetrating cracks C1") is 50 μm or more and 1000 μm or less. The total length of the non-penetrating cracks C1 is preferably 50 μm or more and 500 μm or less, and more preferably 50 μm or more and 200 μm or less.

[0039] To measure the total length of the non-penetrating cracks C1, the surface of the separation membrane 12 is observed using an SEM. The magnification of the SEM is, for example, 5000x. In a 50 μm square region R2 (the region surrounded by a thick line in Figure 5) randomly selected in the region of interest R1, the straight-line distance between both ends of each non-penetrating crack C1 (each of which is an intersection with other non-penetrating cracks C1) is obtained as the crack length of the non-penetrating crack C1. In this way, the crack length is a length obtained by linearly approximating the crack. When a non-penetrating crack C1 intersects with the border line of region R2, the intersection point is considered to be the endpoint of the non-penetrating crack C1. The sum of the crack lengths of all non-penetrating cracks C1 included in the region R2 is obtained as the total length of the non-penetrating cracks C1 in the region R2. Then, the arithmetic mean of the total lengths of the non-penetrating cracks C1 in a plurality of different regions R2 (here, 10 regions R2) is determined as the total length of the non-penetrating cracks C1 in the separation membrane composite 1.

[0040] Here, comparative separation membrane composites will be described. Figures 6A to 6D show comparative separation membrane composites 9a to 9d, and, like Figure 4, show cross sections of the separation membrane composites 9a to 9d near the region of interest R1. In the region of interest R1 of the separation membrane composite 9a shown in Figure 6A, the separation membrane 92 does not have any cracks. When the separation membrane composite 9a is used under high-temperature conditions, stress (e.g., compressive stress) occurs in each location due to differences in the thermal expansion coefficients of the support 91, the seal portion 96, and the separation membrane 92. In Figure 6A, the stress generated in the separation membrane 92 is indicated by arrow W (similar to Figures 4 and 6B to 6D). In a separation membrane 92 with relatively low strength, cracks C3 (shown by the two-dot chain line in Figure 6A) that penetrate to the support 91 are generated due to the influence of stress, resulting in a decrease in the separation performance of the separation membrane composite 9a.

[0041] In the noted region R1 of the separation membrane composite 9b shown in Figure 6B, the separation membrane 92 has a through crack C2 that penetrates all the way to the support 91. In the separation membrane composite 9b, the through crack C2 can reduce the stress that occurs in the separation membrane 92 when used under high-temperature conditions, thereby suppressing the occurrence of further cracks. On the other hand, the presence of the through crack C2 that penetrates all the way to the support 91 reduces the separation performance of the separation membrane composite 9b even before use under high-temperature conditions.

[0042] In the region of interest R1 of separation membrane composite 9c shown in Figure 6C, separation membrane 92 has non-penetrating cracks C1 that do not penetrate all the way to support 91. However, because the number of non-penetrating cracks C1 is excessively small (for example, the total length of non-penetrating cracks C1 is less than 50 µm), when separation membrane composite 9c is used under high temperature conditions, the non-penetrating cracks C1 are unable to sufficiently reduce the stress generated in separation membrane 92, and cracks C3 (shown by two-dot chain lines in Figure 6C) that penetrate all the way to support 91 are generated.

[0043] 6D , the separation membrane 92 also has non-penetrating cracks C1 that do not penetrate all the way to the support 91. However, because there are an excessive number of non-penetrating cracks C1 (for example, the total length of the non-penetrating cracks C1 is greater than 1000 μm), when the separation membrane composite 9c is used under high-temperature conditions, the non-penetrating cracks C1 may easily connect to each other, resulting in a large crack C3 (shown by a two-dot chain line in FIG. 6D ) that penetrates all the way to the support 91.

[0044] On the other hand, in the separation membrane composite 1 shown in Figures 4 and 5, in the region of interest R1, the separation membrane 12 has non-penetrating cracks C1 that open on the surface opposite the support 11 and do not reach the support 11. Furthermore, the total crack length of the non-penetrating cracks C1 in a 50 μm square area within the region of interest R1 (i.e., the total length of the non-penetrating cracks C1) is 50 μm or more and 1000 μm or less. This allows the non-penetrating cracks C1 to sufficiently reduce the stress generated in the separation membrane 12 when the separation membrane composite 1 is used under high-temperature conditions. As a result, the occurrence of penetrating cracks and a decrease in separation performance due to use under high-temperature conditions can be suppressed. In other words, the separation membrane composite 1 can be used for long periods of time under high-temperature conditions.

[0045] Next, with reference to FIG. 7 , the manufacture of the separation membrane composite 1 will be described. When the separation membrane composite 1 is manufactured, a porous support 11 is first prepared (step S11). On the target surface of the support 11 where the separation membrane 12 is to be formed, a sealed region A1 covered by a sealed portion 16 and a non-sealed region A2 not covered by the sealed portion 16 are provided adjacent to each other (see FIG. 3 ). In this processing example, the support 11 is monolithic, and the target surface is the inner circumferential surface of each through-hole 111. On this inner circumferential surface, sealed regions A1 are provided at both longitudinal ends, and the region between the sealed regions A1 at both ends is the non-sealed region A2. The support 11 and the sealed portion 16 are formed by known methods.

[0046] Also, seed crystals to be used in the production of the separation membrane 12 are prepared. The seed crystals are produced as MOF powders, for example, by solvothermal synthesis using water and / or an organic solvent (also called hydrothermal synthesis when the solvent is water). The MOF powder may be produced by any known production method. The MOF powder may be used as the seed crystals as is, or more preferable seed crystals may be obtained by processing the powder by pulverization or the like. The average particle diameter (D50) of the seed crystals (first seed crystals described below) is, for example, 10 to 1,000 nm, preferably 50 to 500 nm, and more preferably 100 to 200 nm. The average particle diameter (D50) of the seed crystals can be measured, for example, by a laser scattering method.

[0047] The obtained seed crystals are dispersed in a solvent (water and / or an organic solvent) to prepare, for example, a 0.01 wt % to 1 wt % dispersion. The seed crystals are then attached to substantially the entire inner circumferential surface of each through-hole 111 by contacting the dispersion with the dispersed seed crystals (step S12). For example, a dip coating method can be used in which the porous support 11 is immersed in the dispersion to attach the seed crystals to the support 11. In step S12, the seed crystals are primarily attached to the non-sealed region A2, but they may also be attached to the surface of the sealed portion 16 (the same applies to step S14 described below). As will be described later, a seed crystal attachment process (step S14 described below) separate from step S12 is also performed. Therefore, in the following description, the dispersion used in step S12 will be referred to as the "first dispersion," and the dispersion used in the separate seed crystal attachment process will be referred to as the "second dispersion." The first dispersion is a liquid in which first seed crystals are dispersed in a solvent, and in step S12, the first seed crystals are attached to the inner circumferential surfaces of the through holes 111. The first seed crystals may be attached to the support 11 by other methods.

[0048] Next, the support 11 is dried (step S13). In this processing example, "drying" refers to substantially removing the solvent of the first dispersion from the support 11. The support 11 may be dried in a dryer or may be naturally dried. Depending on the types of the first dispersion and the second dispersion described below, the drying process in step S13 may be omitted.

[0049] Once the drying of the support 11 is complete, an additional seed crystal attachment process is performed near the seal boundary P (step S14). In the seed crystal attachment process near the seal boundary P, a second dispersion in which second seed crystals are dispersed in a solvent is used. The type of MOF and / or the average particle size (D50) of the second seed crystals may be the same as or different from that of the first seed crystals. The concentration of the second seed crystals in the second dispersion may be the same as or different from the concentration of the first seed crystals in the first dispersion.

[0050] FIG. 8 is a diagram illustrating the seed crystal attachment process near the seal boundary P. In this seed crystal attachment process, for example, a container 81 containing a second dispersion 82 is prepared, and the support 11 is placed in the container 81 with the through-holes 111 oriented approximately parallel to the direction of gravity. At this time, the liquid level of the second dispersion 82 in the container 81 is at a height that immerses only the lower end of the support 11. Specifically, the liquid level of the second dispersion 82 is located slightly (for example, 0.1 to 10 mm) above the seal boundary P (the upper end of the seal portion 16) on the inner circumferential surface of the through-holes 111 at the lower end of the support 11. In this manner, the second dispersion 82 in which the second seed crystals are dispersed is brought into contact with a portion near the seal boundary P in the non-sealed region A2, thereby attaching the second seed crystals to that portion. Thereafter, the support 11 is turned upside down, and the same process is performed. This completes the seed crystal attachment process near the seal boundary P at both ends of the support 11.

[0051] Next, a raw material solution (also referred to as a synthetic sol or a synthetic solution) to be used in forming the separation membrane 12 (here, a MOF membrane) is prepared. The raw material solution may be prepared in advance. In preparing the raw material solution, a solvent (water and / or an organic solvent), a ligand, a metal ion source, and the like are mixed. For example, the ligand is added to the solvent, and the ligand is dissolved by ultrasonic treatment or heating in a thermostatic bath. Then, metal ions are added to obtain the raw material solution.

[0052] Once the raw material solution is prepared, a support 11 with seed crystals attached is immersed in the raw material solution. The raw material solution is then heated to initiate solvothermal synthesis, including hydrothermal synthesis (hereinafter collectively referred to as "solvothermal synthesis"). In the solvothermal synthesis, MOFs grow from the seed crystals as starting points, and a separation membrane 12, which is an MOF membrane, is formed on the support 11 (step S15). The synthesis temperature (heating temperature of the raw material solution) during the solvothermal synthesis is, for example, 40 to 200°C, preferably 70 to 150°C. The solvothermal synthesis time is, for example, 1 to 100 hours, preferably 1 to 50 hours.

[0053] Here, the relationship between the temperature rise rate in solvothermal synthesis and the growth of an MOF film will be described. Figures 9A to 9C are diagrams illustrating the relationship between the temperature rise rate of the raw material solution and the growth of an MOF film. As shown in Figure 9A, a seed crystal 83 is attached to the support 11 immediately before solvothermal synthesis. If the temperature rise rate of the raw material solution during solvothermal synthesis is excessively slow (e.g., the temperature rise rate of the raw material solution per hour is less than 15°C, i.e., the temperature rise rate of the raw material solution is less than 15°C / h), the seed crystal 83 dissolves in the raw material solution 71, as shown by the dashed line in Figure 9B. As a result, the seed crystal-containing layer described with reference to Figure 4 cannot be properly formed. Furthermore, if the temperature rise rate of the raw material solution during solvothermal synthesis is excessively fast (e.g., greater than 200°C / h), nucleation occurs predominantly in the raw material solution 71, as shown in Figure 9C, suppressing the growth of the MOF film. As a result, a dense layer cannot be properly formed.

[0054] Therefore, to properly form a separation membrane 12 including a seed crystal-containing layer and a dense layer, the temperature increase rate during solvothermal synthesis is preferably 15 to 200°C / h, more preferably 30 to 100°C / h. In the separation membrane 12 formed in step S15, the thickness increases near the seal boundary P where the first seed crystals and the second seed crystals are attached, making cracks more likely to occur. Furthermore, the presence of the seed crystal-containing layer prevents the cracks from reaching the support 11 and they remain in the dense layer. That is, non-penetrating cracks C1 are formed in the separation membrane 12. Note that, as long as the non-penetrating cracks C1 are properly formed, the temperature increase rate during solvothermal synthesis may be outside the range of 15 to 200°C / h.

[0055] After the solvothermal synthesis is complete, the support 11 and the separation membrane 12 are washed with pure water, and then washed with ethanol or the like. Preferably, washing with water and ethanol or the like is repeated multiple times. After washing, the support 11 and the separation membrane 12 are dried, for example, at 100°C. "Drying" means removing molecules of the substance used for washing, such as water or ethanol, from the pores of the separation membrane 12. In this way, the separation membrane composite 1 is completed.

[0056] As described above, the manufacturing method of the separation membrane composite 1 of FIG. 7 includes the steps of: preparing a porous support 11 in which a predetermined sealing area A1 on a target surface (in the above example, the inner peripheral surface of the through hole 111) is covered with a sealing portion 16 (step S11); contacting a first dispersion liquid containing dispersed first crystals with the target surface to adhere the first crystals (step S12); contacting a second dispersion liquid containing dispersed second crystals with the target surface near the boundary (seal boundary P) between the non-sealed area A2 and the sealed area A1, which is not covered by the sealing portion 16, to adhere the second crystals (step S14); and immersing the support 11 in a raw material solution and performing solvothermal synthesis to form a separation membrane 12 on the target surface (step S15). This facilitates the formation of a separation membrane 12 with a moderate number of non-penetrating cracks C1 near the seal boundary P. As a result, the occurrence of penetrating cracks in the separation membrane 12 can be suppressed when the separation membrane composite 1 is used under high-temperature conditions.

[0057] Preferably, in step S15, the temperature rising rate of the raw material solution is 15 to 200° C. / h. This makes it possible to more reliably form the seed crystal-containing layer and the dense layer in separation membrane 12, and to easily realize separation membrane 12 having non-penetrating cracks C1.

[0058] Preferably, the method for producing the separation membrane composite 1 further includes a step of drying the support 11 between steps S12 and S14. This allows the first and second seed crystals to be properly attached to the vicinity of the seal boundary P, and more reliably forms the separation membrane 12 having non-penetrating cracks C1. Note that if non-penetrating cracks C1 can be formed, the drying step may be omitted.

[0059] Next, examples and comparative examples of the separation membrane composite will be described. Table 1 shows the manufacturing conditions and measurement results of the examples and comparative examples.

[0060]

[0061] First, we will explain the preparation of seed crystals for four types of MOFs called "MIL-160," "Al Fumarate," "UiO-66," and "KMF-1." In each example and comparative example, one of the four types of seed crystals was used.

[0062] <Preparation of MIL-160 seed crystal powder> First, 1.562 g of 2,5-furandicarboxylic acid (as a ligand) and 1.36 g of sodium formate were added to 50 mL of deionized water to prepare a mixed solution. Subsequently, 2.413 g of aluminum chloride hexahydrate was added to the mixed solution as a metal ion source. Next, this solution was kept in an autoclave at 100°C for 12 hours to perform solvothermal synthesis. The precipitate was separated using a centrifuge and washed three times with deionized water and ethanol. The mixture was then dried at 100°C for 24 hours to obtain MIL-160 powder.

[0063] <Preparation of Al Fumarate Seed Crystal Powder> First, 0.28 g of fumaric acid (as a ligand) and 0.34 g of sodium formate were added to 30 mL of deionized water to prepare a mixed solution. Subsequently, 0.83 g of aluminum sulfate 18-hydrate was added to the mixed solution as a metal ion source. Next, this solution was kept in an autoclave at 120°C for 12 hours to perform solvothermal synthesis. The precipitate was separated using a centrifuge and washed three times with deionized water and ethanol. The mixture was then dried at 100°C for 24 hours to obtain Al Fumarate powder.

[0064] <Preparation of UiO-66 seed crystal powder> First, 0.233 g of zirconium chloride, which is a metal ion source, and 0.166 g of terephthalic acid, which is a ligand, were added to a mixed solvent of 3 mL of acetic acid and 30 mL of dimethylformamide (DMF) to prepare a mixed solution. The mixed solution was subjected to ultrasonic treatment at room temperature for 30 minutes to obtain a homogeneous solution. Next, this solution was kept in an autoclave at 120°C for 24 hours to perform solvothermal synthesis. The precipitate was separated using a centrifuge and washed three times with deionized water and ethanol. Then, it was dried at 100°C for 24 hours to obtain UiO-66-NH ２ A powder of 1000 ppm was obtained.

[0065] <Preparation of KMF-1 seed crystal powder> First, 1.551 g of 1H-pyrrole-2,5-dicarboxylic acid (ligand) and 1.36 g of sodium formate were added to 30 mL of deionized water to prepare a mixed solution. Subsequently, 3.333 g of aluminum sulfate 18-hydrate was added to the mixed solution as a metal ion source. Next, this solution was held in an autoclave at 120°C for 12 hours to perform solvothermal synthesis. The precipitate was separated using a centrifuge and washed three times with deionized water and ethanol. Subsequently, the mixture was dried at 100°C for 24 hours to obtain KMF-1 powder.

[0066] Example 1 1 g of MIL-160 powder prepared as above, ZrO ２ 30 g of balls and 9 mL of ethanol were placed in a 25 mL glass vial. The glass vial was placed on a ball mill stand and the seed crystals were milled at 60 rpm for 20 hours to obtain seed crystals with an average particle size (D50) of 0.25 μm. The obtained seed crystals were dispersed in an ethanol solvent to obtain a dispersion. The concentration of the seed crystals in the dispersion was 0.1 wt%.

[0067] Furthermore, a monolithic ceramic support was prepared with seal portions formed at both longitudinal ends. The above dispersion was brought into contact with the inner circumferential surface of each through-hole of the support, and seed crystals were attached to the inner circumferential surface. The ceramic support was then dried at 25°C. After drying, only the ends of the ceramic support were immersed in the dispersion (see Figure 8). That is, a seed crystal attachment treatment (referred to as "end immersion treatment" in Table 1) was performed near the seal boundary on the inner circumferential surface of the through-hole, and additional seed crystals were attached.

[0068] (Synthesis of MOF membrane) 1.562 g of 2,5-furandicarboxylic acid, 1.22 g of sodium formate, and 0.58 g of N,N-dimethylformamide as an organic solvent were added to 150 mL of deionized water to prepare a mixed solution. After confirming that the mixed solution was transparent, 2.413 g of aluminum chloride hexahydrate was added to prepare a raw material solution. Next, the ceramic support carrying the seed crystals and the raw material solution were placed in a Teflon (registered trademark) container and maintained at 80°C for 20 hours to perform solvothermal synthesis. The heating rate during this process was 100°C / h. The obtained separation membrane structure was washed successively with deionized water, a mixed solvent of deionized water and ethanol, and then dried. Through the above treatment, the separation membrane composite of Example 1 was obtained.

[0069] Example 2: 1 g of the Al Fumarate powder prepared as described above, 1 mm diameter ZrO ２ 30 g of balls and 9 mL of ethanol were placed in a 25 mL glass vial. The glass vial was placed on a ball mill stand and the seed crystals were milled at 60 rpm for 20 hours to obtain seed crystals with an average particle size (D50) of 0.25 μm. The obtained seed crystals were dispersed in an ethanol solvent to obtain a dispersion. The concentration of the seed crystals in the dispersion was 0.1 wt%.

[0070] A monolithic ceramic support was also prepared, with seal portions formed at both longitudinal ends. The dispersion liquid was brought into contact with the inner circumferential surface of each through-hole of the support, and seed crystals were attached to the inner circumferential surface. The ceramic support was then dried at 25°C. Only the ends of the dried ceramic support were immersed in the dispersion liquid (see Figure 8). That is, a seed crystal attachment process (end immersion process) was performed near the seal boundary on the inner circumferential surface of the through-hole, and additional seed crystals were attached.

[0071] (Synthesis of MOF membrane) 0.39 g of fumaric acid and 0.45 g of sodium formate were added to 150 mL of deionized water to prepare a mixed solution. After confirming that the mixed solution was transparent, 1.10 g of aluminum sulfate 18-hydrate was added to prepare a raw material solution. Next, the ceramic support carrying the seed crystals and the raw material solution were placed in a Teflon (registered trademark) container and held at 100°C for 20 hours to perform solvothermal synthesis. The heating rate during this process was 100°C / h. The obtained separation membrane structure was washed sequentially with deionized water, a mixed solvent of deionized water and ethanol, and then dried. Through the above treatment, the separation membrane composite of Example 2 was obtained.

[0072] Example 3: 1 g of UiO-66 powder prepared as above, 1 mm diameter ZrO ２ 30 g of balls and 9 mL of ethanol were placed in a 25 mL glass vial. The glass vial was placed on a ball mill stand and the seed crystals were milled at 60 rpm for 20 hours to obtain seed crystals with an average particle size (D50) of 0.28 μm. The obtained seed crystals were dispersed in an ethanol solvent to obtain a dispersion. The concentration of the seed crystals in the dispersion was 0.1 wt%.

[0073] A monolithic ceramic support was also prepared, with seal portions formed at both longitudinal ends. The dispersion liquid was brought into contact with the inner circumferential surface of each through-hole of the support, and seed crystals were attached to the inner circumferential surface. The ceramic support was then dried at 25°C. Only the ends of the dried ceramic support were immersed in the dispersion liquid (see Figure 8). That is, a seed crystal attachment process (end immersion process) was performed near the seal boundary on the inner circumferential surface of the through-hole, and additional seed crystals were attached.

[0074] (Synthesis of MOF membrane) 0.632 g of terephthalic acid and 15 mL of acetic acid were added to 135 mL of DMF to prepare a mixed solution. After confirming that the mixed solution was transparent, 0.814 g of zirconium chloride was added to prepare a raw material solution. Next, the ceramic support carrying the seed crystals and the raw material solution were placed in a Teflon (registered trademark) container and held at 120°C for 20 hours to perform solvothermal synthesis. The heating rate during this process was 100°C / h. The obtained separation membrane structure was washed sequentially with deionized water, a mixed solvent of deionized water and ethanol, and then dried. Through the above treatment, the separation membrane composite of Example 3 was obtained.

[0075] Example 4: 1 g of the KMF-1 powder prepared as above, φ1 mm ZrO ２ 30 g of balls and 9 mL of ethanol were placed in a 25 mL glass vial. The glass vial was placed on a ball mill stand and the seed crystals were milled at 60 rpm for 20 hours to obtain seed crystals with an average particle size (D50) of 0.38 μm. The obtained seed crystals were dispersed in an ethanol solvent to obtain a dispersion. The concentration of the seed crystals in the dispersion was 0.1 wt%.

[0076] A monolithic ceramic support was also prepared, with seal portions formed at both longitudinal ends. The dispersion liquid was brought into contact with the inner circumferential surface of each through-hole of the support, and seed crystals were attached to the inner circumferential surface. The ceramic support was then dried at 25°C. Only the ends of the dried ceramic support were immersed in the dispersion liquid (see Figure 8). That is, a seed crystal attachment process (end immersion process) was performed near the seal boundary on the inner circumferential surface of the through-hole, and additional seed crystals were attached.

[0077] (Synthesis of MOF membrane) 1.551 g of 1H-pyrrole-2,5-dicarboxylic acid and 1.22 g of sodium formate were added to 150 mL of deionized water to prepare a mixed solution. After confirming that the mixed solution was transparent, 3.333 g of aluminum sulfate 18-hydrate was added to prepare a raw material solution. Next, the ceramic support carrying the seed crystals and the raw material solution were placed in a Teflon (registered trademark) container and held at 100°C for 20 hours to perform solvothermal synthesis. The temperature increase rate during this process was 100°C / h. The obtained separation membrane structure was washed in turn with deionized water, a mixed solvent of deionized water and ethanol, and ethanol, and then dried. Through the above treatments, the separation membrane composite of Example 4 was obtained.

[0078] Example 5 The procedure was the same as Example 1, except that the temperature increase rate during synthesis of the MOF membrane was 15° C. / h.

[0079] Example 6 The procedure was the same as in Example 1, except that the temperature increase rate during synthesis of the MOF membrane was set to 200° C. / h.

[0080] Comparative Example 1 The procedure was the same as in Example 1, except that in supporting the seed crystals on the ceramic support, the treatment of attaching the seed crystals to the vicinity of the seal boundary (end immersion treatment) was omitted.

[0081] <Measurement of Total Crack Length> In each separation membrane composite of Examples 1-6 and Comparative Example 1, the surface of the separation membrane in the region of interest was observed using an SEM (5000x magnification). As described with reference to FIG. 5, grooves with a width of 50 nm or more were considered to be cracks, and the total crack length was obtained by summing the lengths (linear approximation lengths) of the cracks in each of 10 randomly selected 50 μm square regions in the region of interest. The arithmetic average of the total crack lengths in the 10 regions was taken as the total crack length in the separation membrane composite. In Examples 1-6, the total crack length was in the range of 50 μm or more and 1000 μm or less, but in Comparative Example 1, the total crack length was less than 50 μm.

[0082] <SF ６ Measurement of permeation rate> For each separation membrane composite, SF ６(sulfur hexafluoride) gas was introduced onto the surface of the separation membrane at a temperature of 25°C and a pressure of 0.3 MPa to form SF ６ The permeation rate of the separation membrane composite was measured (see separation device 2 in FIG. 10 described later). The permeation rate (permeance) is the rate at which gas permeates per unit membrane area and unit pressure difference. Next, the separation membrane composite was subjected to high-temperature conditions in which gas at 100°C was supplied for 3 hours. Subsequently, the SF ６ The permeation rate of SF after use under high temperature conditions was measured. ６ The permeation rate of SF before use under high temperature conditions ６ By dividing by the permeation rate of ６ The change in permeation rate (in Table 1, simply referred to as "SF ６ In Comparative Example 1, the SF before and after high-temperature use was measured. ６ The change in permeation rate was 2.4, whereas in Example 1-6, the SF ６ The change in permeation rate is 1, and even after use under high temperature conditions, SF ６ The permeation rate did not change.

[0083] <Dyeing Test> Powdered rhodamine was dissolved in a solvent to prepare a rhodamine solution. As shown in Figure 10, the support 11 of each separation membrane composite after use at high temperatures was positioned so that the through-hole 111 was approximately parallel to the direction of gravity, and silicone tubes 51 and 52 were connected to the upper and lower end faces of the support 11. The tubes 51 and 52 had bottoms. The tubes 51 and 52 were filled with a rhodamine solution 53, and the surfaces of the separation membrane 12 and the seal portion 16 were contacted with the rhodamine solution for 3 hours. After removing the tubes 51 and 52, the separation membrane composite was washed with running water and dried. A cross section along the longitudinal direction and perpendicular to the inner circumferential surface of the through-hole 111 was exposed, and the cross section was observed visually and with an optical microscope to confirm whether or not the support 11 was stained in the region of interest. In the "Rhodamine Staining After High-Temperature Use" column in Table 1, "None" indicates that the support 11 was not stained in the region of interest, and "Yes" indicates that the support 11 was stained.

[0084] In the separation membrane composite of Comparative Example 1, the dyeing test showed that the support was dyed in the noted region R1, confirming the presence of a penetrating crack in the separation membrane. ６ Taking into consideration the results of the permeation rate measurements, in Comparative Example 1, in which the total length of the cracks (which are assumed to have been non-penetrating cracks) was less than 50 μm, it is thought that the non-penetrating cracks were unable to sufficiently reduce the stress generated in the separation membrane when used under high-temperature conditions, resulting in the generation of penetrating cracks.

[0085] In contrast, in the separation membrane composite of Example 1-6, the support was not stained at any position as a result of the staining test. ６ The permeation rate also did not change before and after use under high-temperature conditions. Therefore, it is considered that almost all of the cracks in the noted region remained as non-penetrating cracks even after use under high-temperature conditions. Thus, in Example 1-6, in which the total length of the non-penetrating cracks was 50 μm or more and 1000 μm or less, it can be said that the occurrence of penetrating cracks in the separation membrane was suppressed when used under high-temperature conditions.

[0086] Next, separation of a mixed substance using the separation membrane composite 1 will be described with reference to Figures 11 and 12. Figure 11 is a diagram showing the separation device 2. Figure 12 is a diagram showing the flow of separation of a mixed substance by the separation device 2.

[0087] 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.

[0088] 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.

[0089] The mixture may include, for example, hydrogen (H ２ ), helium (He), nitrogen (N２ ), 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.

[0090] 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.

[0091] 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.

[0092] 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 (SF ４ ), sulfur hexafluoride (SF ６ ) or disulfur decafluoride (S ２ F １０ ) etc.

[0093] 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 )

[0094] 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 (C ６ H ５ COOH), etc. Sulfonic acids include, for example, ethanesulfonic acid (C ２ H ６ O ３S) and the like. The organic acid may be a chain compound or a cyclic compound.

[0095] 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.

[0096] 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.

[0097] The esters mentioned above are, for example, formates or acetates.

[0098] 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.

[0099] The above-mentioned ketones can be, for example, acetone ((CH ３ ) ２ CO), methyl ethyl ketone (C ２ H ５ COCH ３ ) or diethyl ketone ((C ２ H ５ ) ２ CO), etc.

[0100] 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.

[0101] 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.

[0102] The separation device 2 includes a separation membrane composite 1, a housing 22, two seal members 23, a supply section 26, a first recovery section 27, and a second recovery section 28. The separation membrane composite 1 and the seal members 23 are housed within 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.

[0103] 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. 11 ), 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.

[0104] The two seal members 23 are disposed around the entire circumference between the outer circumferential surface of the separation membrane composite 1 and the inner circumferential 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 circumferential surface of the separation membrane composite 1 and the inner circumferential surface of the housing 22 around the entire circumference. In the example shown in FIG. 11 , the seal member 23 is in close contact with the outer circumferential surface of the seal portion 16 and indirectly in close contact with the outer circumferential surface of the separation membrane composite 1 via the seal portion 16. A seal is formed between the seal member 23 and the outer circumferential surface of the separation membrane composite 1, and between the seal member 23 and the inner circumferential surface of the housing 22, so that gas hardly or completely passes through.

[0105] 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.

[0106] 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 separation 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 gas are CO ２ and N ２ The mixed gas contains CO ２ and N ２ 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.

[0107] 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, CO ２ The highly permeable substance (hereinafter referred to as "highly permeable substance") passes through the separation 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. As a result, the highly permeable substance is able to separate the low permeable gas (e.g., N ２ (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, 0 MPa to 0.10 MPa (approximately 1 atmosphere).

[0108] Furthermore, gases (hereinafter referred to as "impermeable substances") excluding the gas that has permeated the separation 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-permeable substances, the impermeable substances may also include highly permeable substances that did not permeate the separation membrane 12.

[0109] The separation membrane composite 1 and the method for manufacturing the separation membrane composite 1 can be modified in various ways.

[0110] 7, the support 11 is immersed in the raw material solution, but "immersion" here does not necessarily mean that the entire support 11 is immersed in the raw material solution, and includes a state in which only the target surface of the support 11 is in contact with the raw material solution. In other words, the step of forming the separation membrane 12 is a step of bringing the target surface of the support 11 into contact with the raw material solution and heating it.

[0111] The target surface of the support body 11 is not limited to the inner peripheral surface of the through hole 111, but may be the outer peripheral surface of the support body 11. It may also be one surface of the flat plate-shaped support body 11. The sealing area A1 on the target surface of the support body 11 may be provided in a position other than both ends of the support body 11 in the longitudinal direction.

[0112] In the production of the separation membrane composite 1, the type of MOF in the seed crystals and the type of MOF in the MOF membrane do not have to be the same. Furthermore, the raw material solution may contain two or more types of ligands. The separation membrane composite 1 may also be produced by a method other than the above-described production method.

[0113] In the separation device 2, substances other than those exemplified in the above description may be separated from the mixed substance.

[0114] The configurations in the above-described embodiment and each modification may be combined as appropriate as long as they are not mutually contradictory.

[0115] 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.

[0116] The separation membrane composite of the present invention can be used in a variety of fields for separating various substances.

[0117] DESCRIPTION OF SYMBOLS 1 Separation membrane composite 11 Support 12 Separation membrane 16 Seal portion 71 Raw material solution 82 Dispersion liquid 83 Seed crystal 121 Edge (of separation membrane) A1 Sealed area A2 Non-sealed area C1 Non-penetrating crack P Sealed boundary R1 Attention area R2 Area S11 to S15, S21, S22 Steps

Claims

1. A separation membrane composite comprising: a porous support; a sealing portion covering a predetermined sealing area on a target surface of the support; and a separation membrane covering a non-sealed area on the target surface not covered by the sealing portion and covering the sealing portion near the boundary between the non-sealed area and the sealed area, wherein in a region of interest ranging 10 mm from the edge of the separation membrane located on the sealing portion toward the non-sealed area, the separation membrane has non-penetrating cracks that open onto the surface opposite the support and do not reach the support, and the total crack length of the non-penetrating cracks in a 50 μm square region within the region of interest is 50 μm or more and 1000 μm or less.

2. The separation membrane composite according to claim 1, wherein the separation membrane is a zeolite membrane or an MOF membrane.

3. A separation membrane composite according to claim 1 or 2, wherein the support is formed from a porous inorganic material.

4. A method for producing a separation membrane composite, comprising: a) preparing a porous support having a predetermined sealing area on a target surface covered with a sealing portion; b) contacting a first dispersion liquid having first seed crystals dispersed therein with the target surface to adhere the first seed crystals; c) contacting a second dispersion liquid having second seed crystals dispersed therein with a portion of the target surface near the boundary between the sealing area and a non-sealed area not covered with the sealing portion to adhere the second seed crystals; and d) immersing the support in a raw material solution to perform solvothermal synthesis, thereby forming a separation membrane on the target surface.

5. The method for producing a separation membrane composite according to claim 4, wherein in step d), the temperature rise rate of the raw material solution is 15 to 200°C / h.

6. A method for producing a separation membrane composite according to claim 4 or 5, further comprising a step of drying the support between step b) and step c).

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