Method for producing MOF membrane composite, and MOF membrane composite

Abstract

This method for producing an MOF membrane composite involves: adhering a seed crystal of a CAU-10-type MOF onto a support (step S12); preparing an Al source solution, which is an aqueous solution containing an Al ion source (step S13a); preparing a ligand solution in which an organic ligand used for the synthesis of the CAU-10 type MOF is dissolved in a solvent (step S13b); preparing a raw material solution by mixing, at a speed at which turbidity is not generated, the ligand solution with the Al source solution (step S14); and forming an MOF film, that is, a CAU-10-type MOF, on the support through solvothermal synthesis by immersing the support in the raw material solution (step S15).

Description

Method for producing MOF membrane composite and MOF membrane composite

[0001] The present invention relates to a method for producing a MOF membrane composite and a MOF membrane composite. [Reference to Related Applications] This application claims the benefit of priority from Japanese Patent Application JP2023-144625, filed on September 6, 2023, the entire disclosure of which is incorporated herein by reference.

[0002] In recent years, active research has been conducted on metal-organic frameworks (MOFs), which are crystalline porous materials constructed through coordination bonds between metal ions and organic ligands. MOFs are porous materials with high surface areas, and are expected to be used for gas and liquid separation when formed on porous supports, similar to zeolite membranes.

[0003] One type of MOF known is called "CAU-10". CAU-10 type MOFs are composed of Al(OH)(C ８ H ３ O ４ X), which has an aluminum ion as a metal ion and an organic ligand in which a functional group X (including the case where X is a hydrogen atom) is bonded to the carbon atom at position 5 of the aromatic ring of isophthalic acid. ８ H ３ O ４X) is expressed as "CAU-10-X", and Da-Shiuan Chiou and seven others, "Highly CO2 Selective Meta-Organic Framework Membranes with Favorable Coulombic Effect", Advanced Functional Materials. 2021, 31, 2006-924, Wiley-VCH GmbH (Reference 1) reports the formation of a CAU-10-H film on a flat plate. Helge Reinsch and six others, "Structures, Sorption Characteristics, and Nonlinear Optical Properties of a New Series of Highly Stable Aluminum MOFs", Chemistry of Materials, 2013, 25, 17-26, American Chemical Society (Reference 2) reports the formation of a CAU-10-NH ２ The present invention relates to a powder of the formula (I), where X is H, CH ３ , OCH ３ , NO ２ , N.H. ２ or OH.

[0004] Incidentally, the only known membrane of a MOF represented by CAU-10-X (hereinafter referred to as a "CAU-10-type MOF") is CAU-10-H, as described in Reference 1. Other CAU-10-type MOFs are known only in powder form.

[0005] On the other hand, when various raw materials are mixed at the blending ratios described in known documents such as Literature 1 and Literature 2, a cloudy solution is obtained. In this state, the concentrations of the various raw materials vary in the solution, making it unsuitable for forming a CAU-10 MOF membrane. Even if a CAU-10 MOF membrane can be formed, there will be areas where the membrane is not formed, and the membrane thickness will be uneven. In particular, when forming a MOF membrane by immersing a support having a certain size in a deep container, it is not possible to form a membrane of uniform thickness.

[0006] An object of the present invention is to provide a method for producing a MOF membrane composite having a CAU-10 MOF membrane with small thickness variation, and also to provide MOF membrane composites having membranes of various types of CAU-10 MOFs.

[0007] A first aspect of the present invention is a method for producing a MOF membrane composite, comprising the steps of: a) attaching seed crystals of a CAU-10 MOF to a support; b) preparing an Al source solution, which is an aqueous solution containing an Al ion source; c) preparing a ligand solution in which an organic ligand used in the synthesis of the CAU-10 MOF is dissolved in a solvent; d) mixing the Al source solution and the ligand solution at a rate that does not cause turbidity to prepare a raw material solution; and e) immersing the support in the raw material solution and forming a MOF membrane, which is a CAU-10 MOF, on the support by solvothermal synthesis.

[0008] According to Aspect 1 of the present invention, it is possible to obtain a MOF membrane composite having a CAU-10 MOF membrane with small thickness variation.Moreover, it is possible to obtain MOF membrane composites having membranes of various types of CAU-10 MOFs.

[0009] A second aspect of the present invention is the method for producing the MOF membrane composite of the first aspect, wherein in the step d), stirring is performed while the ligand solution is added dropwise to the Al source solution.

[0010] Aspect 3 of the present invention is the method for producing the MOF membrane composite according to Aspect 1 (or Aspect 1 or 2), wherein in the step d), the pH of the raw material solution during production is maintained at 2.5 or higher and 3.5 or lower.

[0011] A fourth aspect of the present invention is the method for producing the MOF membrane composite according to the first aspect (which may be any one of the first to third aspects), wherein the molar ratio of the solvent to the organic ligand in the ligand solution is 40 or more and 500 or less.

[0012] A fifth aspect of the present invention is the method for producing the MOF membrane composite of the first aspect (which may be any one of the first to fourth aspects), wherein the organic ligand is any one selected from isophthalic acid, 5-aminoisophthalic acid, 5-methylisophthalic acid, 5-methoxyisophthalic acid, 5-nitroisophthalic acid, and 5-hydroxyisophthalic acid.

[0013] A sixth aspect of the present invention is the method for producing an MOF membrane composite according to any one of the first to fifth aspects, wherein the support has through-holes, and in the step e), the support is immersed in the raw material solution with the extension direction of the through-holes parallel to the vertical direction.

[0014] A seventh aspect of the present invention is a MOF membrane composite comprising a support having through holes and an MOF membrane, which is a CAU-10 MOF, formed on the inner surface of the through holes or on the outer surface of the support, wherein the support is divided into three equal parts in the longitudinal direction along which the through holes extend, and three film thicknesses of the MOF membrane at the center of the three parts in the longitudinal direction are obtained, and the maximum difference between the average intra-pore film thickness, which is the average of the three film thicknesses, and the three film thicknesses is 30% or less of the average intra-pore film thickness.

[0015] Aspect 8 of the present invention is the MOF membrane composite of Aspect 7, wherein the support has two parallel through holes including the through hole, and the maximum value of the difference between an average inter-pore thickness, which is the average of the average intra-pore thicknesses of the two through holes, and the average intra-pore thickness of the two through holes is 30% or less of the average inter-pore thickness.

[0016] A ninth aspect of the present invention is the MOF membrane composite of the seventh aspect (which may be either the seventh or eighth aspect), wherein the length of the through-hole is 10 cm or more and 200 cm or less.

[0017] Aspect 10 of the present invention is the MOF membrane composite of Aspect 7 (which may be any one of Aspects 7 to 9), wherein the maximum width of the through hole in a cross section perpendicular to the longitudinal direction is 1 mm or more and 20 mm or less, and the length of the through hole is 10 times or more and 100 times or less the maximum width of the through hole.

[0018] An eleventh aspect of the present invention is a MOF membrane composite comprising a support and a MOF membrane that is a CAU-10 MOF formed on the support, wherein the organic ligand used in forming the MOF membrane is any one selected from the group consisting of 5-methylisophthalic acid, 5-aminoisophthalic acid, and 5-nitroisophthalic acid.

[0019] 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.

[0020] 1 is a cross-sectional view of a separation membrane composite (MOF membrane composite); 2 is an enlarged cross-sectional view of a portion of the separation membrane composite; 3 is a view showing the X-ray diffraction pattern of CAU-10-H; and 4 is a view showing the X-ray diffraction pattern of CAU-10-NH. ２ 1 shows the X-ray diffraction pattern of CAU-10-CH ３ 1 shows the X-ray diffraction pattern of CAU-10-NO ２ 1 shows the X-ray diffraction pattern of CAU-10-OCH ３ FIG. 1 is a diagram showing an X-ray diffraction pattern of CAU-10-OH. FIG. 2 is a diagram showing the flow of production of a separation membrane composite. FIG. 3 is a diagram showing the state of solvothermal synthesis. FIG. 4 is a diagram showing a separation device. FIG. 5 is a diagram showing the flow of separation of a mixed substance by a separation device.

[0021] FIG. 1 is a cross-sectional view of a MOF membrane composite 1 having a metal-organic framework (MOF) membrane (hereinafter also referred to as a "MOF membrane"). In this embodiment, the MOF membrane composite 1 is used for separating a specific fluid, and therefore will be referred to as a "separation membrane composite 1" hereinafter. However, the use of the MOF membrane composite 1 is not limited to separating a specific fluid. 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, which is a MOF membrane, provided on the support 11. A MOF membrane is at least a membrane of MOFs formed on the surface of the support 11, and does not include a membrane in which MOF particles are simply dispersed in an organic film. In FIG. 1, the separation membrane 12 is emphasized by a thick line. In FIG. 2, the separation membrane 12 is indicated by hatching. Furthermore, in FIG. 2, the thickness of the separation membrane 12 is depicted as being thicker than it actually is.

[0022] The support 11 is a porous member that is permeable to gas and liquid. 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, and a plurality of through-holes 111 extending in the longitudinal direction (i.e., the left-right direction in FIG. 1 ). In the example shown in FIG. 1 , the support 11 is substantially cylindrical. The cross section perpendicular to the longitudinal direction of each through-hole 111 (i.e., cell) is, for example, substantially circular. In FIG. 1 , the diameter of the through-hole 111 is drawn larger than in reality, and the number of through-holes 111 is drawn smaller than in reality. The 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.

[0023] 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.

[0024] The support 11 is made of 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.

[0025] 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.

[0026] 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, 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. Note that when the support 11 has a multilayer structure, the average pore size of the support 11 refers to the average pore size of the surface layer, including the surface on which the separation membrane 12 is formed.

[0027] The separation membrane 12 is a CAU-10 type MOF membrane, and is a porous membrane having fine pores (micropores). The separation membrane 12 is capable of separating a specific substance from a mixture of multiple types of substances by utilizing molecular sieving action 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 lower than the permeation rate of the specific substance.

[0028] The average thickness of the separation membrane 12 is 10 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) are observed using an SEM. The SEM magnification 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.

[0029] The average pore diameter of the MOF membrane constituting the separation membrane 12 is 0.3 nm or more and 0.7 nm or less. The "average pore diameter of the MOF" is the arithmetic mean of the long and short diameters of the pore openings theoretically derived from the skeletal structure of the MOF. Alternatively, the long and short diameters of the pore openings may be obtained by observation using a TEM (transmission electron microscope) to determine the average pore diameter. More precisely, the long and short diameters of the pore openings refer to the interstitial spacing of a 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. Here, the pore diameter refers to the pore diameter of the channel. The long diameter is the maximum diameter in the cross section of the channel, the short diameter is the diameter of the cross section in a direction approximately perpendicular to the long diameter, and the arithmetic mean of the short diameter and the long diameter is the average pore diameter. The average pore size is smaller than the average pore size of the support 11 in the vicinity of the surface on which the separation membrane 12 is formed.

[0030] 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 MOF in this embodiment is the arithmetic mean of the maximum 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.

[0031] At the interface between the separation membrane 12 and the support 11, a composite layer 13 is formed in which crystals of the MOF penetrate into the pores of the support 11. In FIG. 2 , the composite layer 13 is shown by drawing parallel diagonal lines over 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 necessarily have to be present, and the lower limit of the thickness of the composite layer 13 is 0.

[0032] 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 farthest from the separation membrane 12 in the depth direction. 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.

[0033] Not only when the composite layer 13 is not present, but also when the composite layer 13 is present, there is no separately formed intermediate layer 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. In other words, there is no intermediate layer formed in a step other than the step of forming the MOF membrane between the support 11 and the separation membrane 12. This structure is merely one example, and for example, the support 11 may include an intermediate layer separately formed on a basic portion, and the separation membrane 12 may be provided on this intermediate layer.

[0034] 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 that are components of the CAU-10 type MOF are Al ３＋ (aluminum ions). The ligand, which is a component of the CAU-10 MOF, is, for example, any one selected from isophthalic acid (benzene-1,3-dicarboxylic acid), 5-aminoisophthalic acid, 5-methylisophthalic acid, 5-methoxyisophthalic acid, 5-nitroisophthalic acid, and 5-hydroxyisophthalic acid. The ligand does not necessarily have to be of one type, and multiple types may be used.

[0035] 3A, 3B, 3C, 3D, 3E, and 3F show CAU-10-H, CAU-10-NH, ２ , CAU-10-CH ３ , CAU-10-NO ２ , CAU-10-OCH ３ 1 shows the X-ray diffraction patterns of MOFs of CAU-10-OH by X-ray diffractometry. The horizontal axis represents the diffraction angle (2θ / deg.), and the vertical axis represents the intensity (Intensity au). The X-ray diffraction pattern of the CAU-10 MOF has peaks at least near 2θ = 8.1°, 14.8°, and 22.4°.

[0036] Next, the manufacturing flow of the separation membrane composite 1 will be described with reference to FIG. 4. When the separation membrane composite 1 is manufactured, first, seed crystals to be used in forming the separation membrane 12 are prepared (step S11). The seed crystals are CAU-10 type MOFs, the same type as the MOF membrane to be formed. Specifically, first, an aluminum ion source (Al ion source) and a ligand are mixed with a solution containing water and an organic solvent such as dimethylformamide (DMF), and the mixture is stirred. After solvothermal synthesis by heating this solution, the product is separated from the solution by centrifugation and washed with water and ethanol, yielding a powder of MOF. The powder is dissolved in ethanol and zirconia (ZrO ２ Seed crystals are obtained by grinding (ball milling) MOFs with beads (such as PEG-1000). MOF powders may be produced by other known production methods. The MOF powders may also be used as seed crystals directly.

[0037] The average particle size (D50) of the seed crystals is preferably 0.5 μm or less. This makes it possible to suppress the occurrence of grain boundary defects in the MOF membrane, which would otherwise be caused by the average particle size of the MOFs becoming excessively large. There is no particular limitation on the lower limit of the average particle size of the seed crystals, but, for example, by setting the average particle size to 0.1 μm or more, it is possible to suppress a decrease in the crystallinity of the seed crystals. The average particle size (D50) of the seed crystals can be measured, for example, by a laser scattering method.

[0038] Next, the seed crystals are dispersed in a solvent (water and / or an organic solvent) to prepare a 0.01 wt % to 1 wt % dispersion. A porous support 11 is immersed in the dispersion to attach the seed crystals to the support 11 (dip coating method) (step S12). Alternatively, the dispersion in which the seed crystals are dispersed in a solvent is brought into contact with the portion of the support 11 where the separation membrane 12 is to be formed, thereby attaching the seed crystals to the support 11. The solvent is then removed by drying to prepare a seed crystal-attached support. The seed crystals may also be attached to the support 11 by other methods.

[0039] Next, a raw material solution (also called a synthesis sol or synthesis solution) to be used in forming the MOF membrane is prepared (steps S13a and S13b). The preparation of the raw material solution may be performed before step S12 or in parallel with step S12. In preparing the raw material solution, a solvent (water and / or an organic solvent), a ligand, a metal ion source, and other raw materials as needed are mixed, and these are mixed in a certain order.

[0040] Specifically, an Al ion source is dissolved in water (i.e., ion-exchanged water) to generate a solution (hereinafter referred to as the "Al source solution") (step S13a). This prepares the Al source solution. Examples of Al ion sources that can be used include aluminum nitrate nonahydrate, aluminum chloride hexahydrate, aluminum sulfate 14-18 hydrate, and aluminum hydroxide. Next, a solution (hereinafter referred to as the "ligand solution") is prepared by dissolving a ligand in an organic solvent (step S13b). This prepares the ligand solution. The ligand corresponds to the type of CAU-10 MOF, and examples of the ligands that can be used include isophthalic acid (benzene-1,3-dicarboxylic acid), 5-aminoisophthalic acid, 5-methylisophthalic acid, 5-methoxyisophthalic acid, 5-nitroisophthalic acid, and 5-hydroxyisophthalic acid. Examples of the organic solvent that can be used include DMF, diethylformamide (DEF), and methanol. Step S13a and step S13b may be performed in any order, and may be performed in parallel.

[0041] Next, while stirring the Al source solution, the ligand solution is gradually added to the Al source solution (step S14). Adding the ligand solution to the Al source solution all at once would cause the mixed solution to become cloudy. Therefore, the ligand solution is mixed with the Al source solution at a rate that does not cause cloudiness, thereby producing a raw solution that is not cloudy. In this manner, a clear raw solution is prepared. Preferably, in step S14, the ligand solution is added dropwise to the Al source solution while stirring. The drop rate is preferably between 0.01 g / sec and 0.5 g / sec, which more reliably produces a transparent raw solution. The phenomenon of the mixed solution becoming cloudy when the ligand solution is added all at once to the Al source solution is believed to be due to the ligand not dissolving in water and precipitating, resulting in an incomplete mixture. Furthermore, such an incomplete raw solution will settle downward over time once stirring is stopped. In other words, in this description, "no cloudiness" refers to a state in which no sediment is generated at the bottom even after stirring is stopped, and does not depend on the transparency of the solution.

[0042] Once the raw material solution is prepared, the support 11 with the seed crystals attached thereto is immersed in the raw material solution 51 in a container 52, as shown in FIG. 5 . In the raw material solution 51, the support 11 is supported by a support frame (not shown) and does not contact the bottom of the container 52. When the support 11 is a so-called monolithic type having a plurality of parallel through-holes 111, the support 11 is immersed in the raw material solution 51 with the extension direction of the through-holes 111 parallel to the vertical direction in order to reduce the difference in conditions among the plurality of through-holes 111. If a turbid raw material solution is used here, the turbidity concentration will be higher in the lower part of the container 52 storing the raw material solution 51, and therefore, in the subsequent solvothermal synthesis, the MOF production conditions will differ between the lower and upper parts of the through-holes 111. As a result, even if an MOF membrane of appropriate thickness is formed in the lower part of the through-holes 111, an insufficient MOF membrane may be formed in the upper part of the through-holes 111.

[0043] In contrast, when the unclouded raw material solution 51 produced by steps S13a, S13b, and S14 is used, the difference in MOF production requirements between the upper and lower portions of each through-hole 111 is small, so that it is possible to form an MOF membrane of uniform thickness throughout each through-hole 111 and throughout all through-holes 111. In other words, it is possible to form a CAU-10 MOF membrane with small thickness variation among each through-hole 111 and among multiple through-holes. Note that the same effect can be obtained even when the support 11 has a shape other than a monolithic shape.

[0044] Then, the raw material solution is heated to initiate solvothermal synthesis (also called hydrothermal synthesis when the solvent is water). In solvothermal synthesis, CAU-10 type MOFs grow using the seed crystals as nuclei, and a dense MOF membrane is formed on the support 11 as a separation membrane 12 (step S15). The MOF membrane is composed of CAU-10-H, CAU-10-NH, ２ , CAU-10-CH ３ , CAU-10-OCH ３ , CAU-10-NO ２ or CAU-10-OH (see Background Art). The synthesis temperature during solvothermal synthesis (heating temperature of the raw material solution) is, for example, 80°C to 180°C, and preferably 110°C to 140°C. The solvothermal synthesis time is, for example, 2 hours to 72 hours, and preferably 10 hours to 35 hours.

[0045] After the solvothermal synthesis is completed, the support 11 and the MOF membrane are washed with ion-exchanged water, and then washed with ethanol, methanol, or the like. Preferably, washing with water, ethanol, methanol, or the like is repeated multiple times. After washing, the support 11 and the MOF membrane are dried, for example, at 60°C to 100°C (step S16). "Drying" refers to removing molecules of the substances used for washing, such as water, ethanol, or methanol, from the pores of the MOF membrane. The separation membrane composite 1 is completed by drying.

[0046] The above-described method for producing separation membrane composite 1 can produce a transparent solution as a raw material solution for the MOF membrane, thereby enabling the production of MOF membrane composites having CAU-10 MOF membranes with little variation in thickness. Furthermore, MOF membrane composites having various types of CAU-10 MOF membranes can be produced.

[0047] Next, separation of a mixed substance using the separation membrane composite 1 will be described with reference to Figures 6 and 7. Figure 6 is a diagram showing the separation device 2. Figure 7 is a diagram showing the flow of separation of a mixed substance using the separation device 2.

[0048] 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.

[0049] 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.

[0050] The mixture may include, for example, hydrogen (H ２ ), helium (He), nitrogen (N ２ ), oxygen (O ２ ), water (H ２ O), carbon monoxide (CO), carbon dioxide (CO ２ ), nitrogen oxides, ammonia (NH ３ ), sulfur oxides, hydrogen sulfide (H ２ S), sulfur fluoride, mercury (Hg), arsine (AsH ３ ), hydrogen cyanide (HCN), carbonyl sulfide (COS), C1-C8 hydrocarbons, organic acids, alcohols, mercaptans, esters, ethers, ketones, and aldehydes.

[0051] 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.

[0052] 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 SOXX.

[0053] 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.

[0054] 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 )

[0055] 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 ３ S) and the like. The organic acid may be a chain compound or a cyclic compound.

[0056] 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.

[0057] 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 (C２ H ５ SH) or 1-propanethiol (C ３ H ７ SH), etc.

[0058] The esters mentioned above are, for example, formates or acetates.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] The separation device 2 includes a separation membrane composite 1, a sealing unit 21, a housing 22, two seal members 23, a supply unit 26, a first recovery unit 27, and a second recovery unit 28. The separation membrane composite 1, the sealing unit 21, and the seal members 23 are housed within the housing 22. The supply unit 26, the first recovery unit 27, and the second recovery unit 28 are disposed outside the housing 22 and connected to the housing 22.

[0064] The sealing portion 21 is attached to both longitudinal end portions of the support 11 (i.e., the left-right direction in FIG. 6 ) 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 gas from flowing in and out from these end faces of the support 11. The sealing portion 21 is, for example, a plate-like member formed 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, gas and the like can flow in and out of the through holes 111 from these ends.

[0065] 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. 6 ), 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 a sealed space isolated from the space surrounding the housing 22.

[0066] The two seal members 23 are disposed around the entire circumference between the outer peripheral surface of the separation membrane composite 1 and the inner peripheral surface of the housing 22 near both longitudinal ends of the separation membrane composite 1. Each seal member 23 is a substantially annular member made of a gas-impermeable material. The seal members 23 are, for example, O-rings made of a flexible resin. The seal members 23 are in close contact with the outer peripheral surface of the separation membrane composite 1 and the inner peripheral surface of the housing 22 around the entire circumference. In the example shown in FIG. 6 , the seal member 23 is in close contact with the outer peripheral surface of the sealing portion 21 and indirectly in close contact with the outer peripheral surface of the separation membrane composite 1 via the sealing portion 21. A seal is formed between the seal member 23 and the outer peripheral surface of the separation membrane composite 1, and between the seal member 23 and the inner peripheral surface of the housing 22, so that gas hardly or completely passes through.

[0067] 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.

[0068] 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.

[0069] 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, about 1 atmosphere (0.101 MPa).

[0070] 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.

[0071] Next, examples and comparative examples of separation membrane composites will be described. Table 1 shows the manufacturing conditions and measurement results of the examples and comparative examples.

[0072]

[0073] Example 1-1: CAU-10-H (Preparation of Seed Crystals) A mixed solution was prepared by adding 1.43 g of aluminum sulfate 14-18 hydrate, which serves as an Al ion source, and 0.71 g of isophthalic acid, which serves as a ligand, to a mixed solvent of 14 g of ion-exchanged water and 3.5 g of N,N-dimethylformamide (DMF). The mixed solution was then subjected to solvothermal synthesis at 120°C for 12 hours. The precipitate was separated using a centrifuge and washed three times with ion-exchanged water and ethanol to obtain seed crystals of CAU-10-H.

[0074] (Supporting of seed crystals) 1 g of CAU-10-H seed crystals was dispersed in 10 mL of ethanol and pulverized in a ball mill for 24 hours to obtain a dispersion of seed crystals having an average particle size (D50) of 250 nm. Ethanol was then added so that the concentration of the dispersion became 0.01%. A porous alumina support was immersed in the dispersion to adhere the dispersion to the support, and the solvent was evaporated in a dryer to support the seed crystals on the support surface. The support used had an average pore size of approximately 100 nm.

[0075] (MOF Membrane Formation) First, a solution of isophthalic acid (a ligand) in DMF (ligand solution) was slowly added dropwise to a solution of aluminum sulfate 14-18 hydrate (an Al ion source) and sodium formate in ion-exchanged water (an Al source solution) while stirring, to prepare a raw material solution. The molar ratio of aluminum sulfate 14-18 hydrate, isophthalic acid, sodium formate, ion-exchanged water, and DMF was 1:1:2:6394:394. The pH of the Al source solution before mixing was 3.4, and the pH of the raw material solution after mixing was 3.5. The raw material solution was transparent.

[0076] Next, the raw material solution and the support coated with the seed crystals were placed in a Teflon (registered trademark) container, and solvothermal synthesis was carried out at 130°C for 12 hours to obtain a MOF membrane composite in which a CAU-10-H membrane was formed on the support. This MOF membrane composite was washed three times with ion-exchanged water and ethanol. Thereafter, the MOF membrane composite was dried at 80°C for 12 hours.

[0077] (Film Thickness Measurement Results) The longitudinal cross section of the MOF membrane was observed at seven randomly selected visual fields using a SEM (scanning electron microscope), and as already described, the average film thickness of the MOF membrane in each visual field image (visual field average film thickness) was determined. The arithmetic mean of the visual field average film thicknesses of five visual fields excluding the visual fields with the maximum and minimum visual field average film thickness values ​​was taken as the average film thickness of the MOF membrane. The same applies to the following Examples and Comparative Examples.

[0078] The average thickness of the MOF membrane in Example 1-1 was measured by the above method and found to be 0.5 μm.

[0079] (Measurement results of intrapore evaluation value) The support was divided into three equal parts in the longitudinal direction along which the through-holes extended, and an image of the longitudinal cross section of the MOF membrane in one through-hole was obtained using an SEM at the longitudinal center of each part (approximately the center, but not necessarily the exact center). The thickness of the MOF membrane in each image was determined by measuring the distance between an arbitrary point on the membrane surface in the three images obtained and a point at the interface between the MOF membrane and the support perpendicular to the arbitrary point on the membrane surface. The average value of the three membrane thicknesses was calculated as the "average intrapore membrane thickness," and the difference between each of the three membrane thicknesses and the average intrapore membrane thickness (more precisely, the absolute value of the difference) was calculated. The ratio of the maximum value of this difference to the average intrapore membrane thickness was calculated as the intrapore evaluation value. The same applies to the following examples and comparative examples. By calculating the average intrapore membrane thickness from the three membrane thicknesses, the average membrane thickness can be obtained from as few images as possible, while taking into account membrane thicknesses other than the longitudinal center.

[0080] The hole evaluation value in Example 1-1 was 14%.

[0081] (Measurement results of inter-hole evaluation value) Another through hole was selected, and the average intra-hole film thickness was also calculated using the above method for this through hole, and the average of the two average intra-hole film thicknesses was calculated as the average inter-hole film thickness. The difference between the average intra-hole film thickness and the average inter-hole film thickness for each of the two through holes (more precisely, the absolute value of the difference) was calculated, and the ratio of the maximum value of this difference to the average inter-hole film thickness was calculated as the inter-hole evaluation value. The same applies to the following examples and comparative examples.

[0082] The hole spacing evaluation value in Example 1-1 was 10%.

[0083] Example 1-2: CAU-10-H An MOF membrane composite was obtained in the same manner as in Example 1-1, except that the molar ratio of aluminum sulfate 14-18 hydrate, isophthalic acid, sodium formate, ion-exchanged water, and DMF in the raw material solution for MOF membrane formation was 1:1:2:12788:788. The pH of the Al source solution before mixing was 3.6, and the pH of the raw material solution after mixing was 3.7. The raw material solution was transparent. The average membrane thickness of the MOF membrane in Example 1-2 was 0.3 μm. The intrapore evaluation value was 29%. The interpore evaluation value was 28%.

[0084] Example 2-1: CAU-10-NH ２ > (Preparation of seed crystals) 0.16 g of aluminum chloride hexahydrate, which is an Al ion source, and 0.24 g of 5-aminoisophthalic acid, which is a ligand, were added to a mixed solvent of 16 g of ion-exchanged water and 4 g of N,N-dimethylformamide (DMF) to prepare a mixed solution. Next, the mixed solution was subjected to solvothermal synthesis at 120°C for 12 hours. The precipitate was separated using a centrifuge, washed three times with ion-exchanged water and ethanol, and CAU-10-NH ２ Seed crystals of

[0085] (Supporting of seed crystals) CAU-10-NH ２ A support carrying seed crystals was obtained in the same manner as in Example 1-1, except that the following was used.

[0086] (MOF membrane formation) First, a solution of 5-aminoisophthalic acid (a ligand) in DMF (ligand solution) was slowly added dropwise to a solution of aluminum chloride hexahydrate (an Al ion source) in ion-exchanged water (Al source solution) while stirring, to prepare a raw material solution. The molar ratio of aluminum chloride hexahydrate, 5-aminoisophthalic acid, ion-exchanged water, and DMF was 1:1:670:41. The pH of the Al source solution before mixing was 2.8, and the pH of the raw material solution after mixing was 2.6. The raw material solution was transparent.

[0087] Next, the raw material solution and the support coated with the seed crystals were placed in a Teflon (registered trademark) container, and solvothermal synthesis was carried out at 130°C for 12 hours to form CAU-10-NH on the support. ２A MOF membrane structure was obtained with the membrane formed. This MOF membrane composite was washed three times with ion-exchanged water and ethanol. The MOF membrane composite was then dried at 80°C for three hours. The MOF membrane composite was then washed once with methanol and dried at room temperature.

[0088] (Measurement Results) The average thickness of the MOF membrane in Example 2-1 was 0.9 μm. The intrapore evaluation value was 11%. The interpore evaluation value was 10%.

[0089] Example 2-2: CAU-10-NH ２ An MOF membrane composite was obtained in the same manner as in Example 2-1, except that aluminum nitrate nonahydrate was used as the Al ion source. The pH of the Al source solution before mixing was 2.8, and the pH of the raw material solution after mixing was 2.5. The raw material solution was transparent. The average membrane thickness of the MOF membrane in Example 2-2 was 1.3 μm. The intrapore evaluation value was 14%. The interpore evaluation value was 15%.

[0090] Example 2-3: CAU-10-NH ２ An MOF membrane composite was obtained in the same manner as in Example 2-1, except that the solvothermal synthesis temperature for MOF membrane formation was 140°C. The average thickness of the MOF membrane in Example 2-3 was 1.2 μm. The intrapore evaluation value was 17%. The interpore evaluation value was 12%.

[0091] Example 2-4: CAU-10-NH ２ > An MOF membrane composite was obtained in the same manner as in Example 2-1, except that the molar ratio of aluminum chloride hexahydrate, 5-aminoisophthalic acid, ion-exchanged water, and DMF in the raw material solution for MOF membrane formation was 0.5:1:670:41. The pH of the Al source solution before mixing was 3.1, and the pH of the raw material solution after mixing was 2.8. The raw material solution was transparent. The average membrane thickness of the MOF membrane in Example 2-4 was 2.3 μm. The intrapore evaluation value was 14%. The interpore evaluation value was 25%.

[0092] Example 3: CAU-10-CH ３ (Preparation of seed crystals) CAU-10-CH was prepared in the same manner as in Example 1-1, except that 0.77 g of 5-methylisophthalic acid was used as the ligand.３ Seed crystals of

[0093] (Supporting of seed crystals) CAU-10-CH ３ A support carrying seed crystals was obtained in the same manner as in Example 1-1, except that the following was used.

[0094] (MOF membrane formation) A raw material solution was prepared in the same manner as in Example 1-1, except that 5-methylisophthalic acid was used as the ligand and sodium formate was not added to the Al source solution. The molar ratio of aluminum sulfate 14-18 hydrate, 5-methylisophthalic acid, ion-exchanged water, and DMF was 1:1:2000:123. The pH of the Al source solution before mixing was 3.1, and the pH of the raw material solution after mixing was 2.9. The raw material solution was transparent.

[0095] Next, the raw material solution and the support coated with the seed crystals were placed in a Teflon (registered trademark) container, and solvothermal synthesis was carried out at 130°C for 12 hours to form CAU-10-CH on the support. ３ A MOF membrane composite was obtained. The MOF membrane composite was washed three times with ion-exchanged water and ethanol. Then, the MOF membrane composite was dried in a dryer at 80°C for 3 hours.

[0096] The average thickness of the MOF membrane in Example 3 was 3.9 μm. The intrapore evaluation value was 22%. The interpore evaluation value was 20%.

[0097] Example 4: CAU-10-NO ２ (Preparation of seed crystals) CAU-10-NO was prepared in the same manner as in Example 1-1, except that 0.28 g of 5-nitroisophthalic acid was used as the ligand. ２ Seed crystals of

[0098] (Supporting of seed crystals) CAU-10-NO ２ A support carrying seed crystals was obtained in the same manner as in Example 1-1, except that the following was used.

[0099] (Formation of MOF membrane) A raw material solution was prepared in the same manner as in Example 2-1, except that 5-nitroisophthalic acid was used as the ligand. The molar ratio of aluminum chloride hexahydrate, 5-nitroisophthalic acid, ion-exchanged water, and DMF was 1:1:2352:193. The pH of the Al source solution before mixing was 3.3, and the pH of the raw material solution after mixing was 3.0. The raw material solution was transparent.

[0100] Next, the raw material solution and the support coated with the seed crystals were placed in a Teflon (registered trademark) container, and solvothermal synthesis was carried out at 130°C for 12 hours to form CAU-10-NO on the support. ２ A MOF membrane composite was obtained. The MOF membrane composite was washed three times with ion-exchanged water and ethanol. Then, the MOF membrane composite was dried in a dryer at 80°C for 3 hours.

[0101] The average thickness of the MOF membrane in Example 4 was 2.5 μm. The intrapore evaluation value was 15%. The interpore evaluation value was 10%.

[0102] Example 5: CAU-10-OCH ３ (Preparation of seed crystals) CAU-10-OCH was prepared in the same manner as in Example 1-1, except that 0.84 g of 5-methoxyisophthalic acid was used as the ligand. ３ Seed crystals of

[0103] (Supporting of seed crystals) CAU-10-OCH ３ A support carrying seed crystals was obtained in the same manner as in Example 1-1, except that the following was used.

[0104] (MOF membrane formation) A raw material solution was prepared in the same manner as in Example 1-1, except that 5-methoxyisophthalic acid was used as the ligand and sodium formate was not added to the Al source solution. The molar ratio of aluminum sulfate 14-18 hydrate, 5-methoxyisophthalic acid, ion-exchanged water, and DMF was 1:1:2352:193. The pH of the Al source solution before mixing was 3.1, and the pH of the raw material solution after mixing was 2.9. The raw material solution was transparent.

[0105] Next, the raw material solution and the support coated with the seed crystals were placed in a Teflon (registered trademark) container, and solvothermal synthesis was carried out at 130°C for 12 hours to form CAU-10-OCH ３ A MOF membrane composite was obtained. The MOF membrane composite was washed three times with ion-exchanged water and ethanol. Then, the MOF membrane composite was dried in a dryer at 80°C for 3 hours.

[0106] The average thickness of the MOF membrane in Example 5 was 2.5 μm. The intrapore evaluation value was 10%. The interpore evaluation value was 12%.

[0107] Example 6 CAU-10-OH (Preparation of Seed Crystals) Seed crystals of CAU-10-OH were obtained in the same manner as in Example 1-1, except that 0.24 g of 5-hydroxyisophthalic acid was used as the ligand.

[0108] (Supporting of Seed Crystals) A support supporting seed crystals was obtained in the same manner as in Example 1-1, except that CAU-10-OH was used as the seed crystals.

[0109] (Formation of MOF membrane) A raw material solution was prepared in the same manner as in Example 2-1, except that 5-hydroxyisophthalic acid was used as the ligand. The molar ratio of aluminum chloride hexahydrate, 5-hydroxyisophthalic acid, ion-exchanged water, and DMF was 1:1:2352:193. The pH of the Al source solution before mixing was 3.2, and the pH of the raw material solution after mixing was 3.0. The raw material solution was transparent.

[0110] Next, the raw material solution and the support coated with the seed crystals were placed in a Teflon (registered trademark) container, and solvothermal synthesis was carried out at 130°C for 12 hours to obtain an MOF membrane composite in which a CAU-10-OH membrane was formed on the support. This MOF membrane composite was washed three times with ion-exchanged water and ethanol. The MOF membrane composite was then dried in a dryer at 80°C for 3 hours.

[0111] The average thickness of the MOF membrane in Example 6 was 2.3 μm. The intrapore evaluation value was 13%. The interpore evaluation value was 16%.

[0112] <Comparative Example 1: CAU-10-NH ２> An MOF membrane composite was obtained in the same manner as in Example 2-1, except that in preparing the raw material solution for MOF membrane formation, the ligand solution was added all at once to the Al source solution and mixed. The pH of the Al source solution before mixing was 2.8, and the pH of the raw material solution after mixing was 2.6. The raw material solution became turbid. The average thickness of the MOF membrane in Comparative Example 1 was 0.9 μm. The intrapore evaluation value was 40%. The interpore evaluation value was 31%.

[0113] <Comparative Example 2: CAU-10-NH ２ > An MOF membrane composite was obtained in the same manner as in Example 2-1, except that the molar ratio of aluminum chloride hexahydrate, 5-aminoisophthalic acid, ion-exchanged water, and DMF in the raw material solution for MOF membrane formation was 1:1:134:8. The pH of the Al source solution before mixing was 2.1, and the pH of the raw material solution after mixing was 1.8. Turbidity occurred in the raw material solution. The average thickness of the MOF membrane in Comparative Example 1 was 4.6 μm. The intrapore evaluation value was 35%. The interpore evaluation value was 30%.

[0114] In the above embodiment, the variation in film thickness in the through-hole 111 is suppressed, and the intra-hole evaluation value is set to 30% or less. Furthermore, the variation in film thickness between the through-holes 111 is also suppressed, and the inter-hole evaluation value is also set to 30% or less.

[0115] As an additional example, as shown in Table 2, CAU-10-NH ２ The ligand solutions for synthesis were prepared with a molar ratio of organic solvent to ligand in the range between Example 2-1 and Comparative Example 2, less than 40, and the degree of turbidity of the raw material solutions was confirmed. Other conditions were the same as those of Example 2-1 and Comparative Example 2. In Additional Example 1, where the molar ratio of organic solvent to ligand was 33, the pH of the Al source solution before the start of mixing was 2.7, and the pH of the raw material solution after the completion of mixing was 2.4. In Additional Example 2, where the molar ratio was 24, the pH of the Al source solution before the start of mixing was 2.6, and the pH of the raw material solution after the completion of mixing was 2.2. In Additional Example 3, where the molar ratio was 16, the pH of the Al source solution before the start of mixing was 2.4, and the pH of the raw material solution after the completion of mixing was 2.0. In all of Additional Examples 1 to 3, the raw material solutions became turbid.

[0116]

[0117] As an additional example, as shown in Table 3, CAU-10-CH ３ The ligand solutions for synthesis were prepared with a molar ratio of organic solvent to ligand in the range of approximately 40, and the degree of turbidity of the raw material solutions was confirmed. Other conditions were the same as in Example 3. In Additional Example 4, where the molar ratio of organic solvent to ligand was 42, the pH of the Al source solution before the start of mixing was 2.8, and the pH of the raw material solution after mixing was 2.5. In Additional Example 5, where the molar ratio was 33, the pH of the Al source solution before the start of mixing was 2.6, and the pH of the raw material solution after mixing was 2.4. In Additional Example 4, the raw material solution became transparent, while in Additional Example 5, the raw material solution became turbid.

[0118]

[0119] As shown in Tables 2 and 3, when the molar ratio was 33 or less, the raw material solution became cloudy even when the rate at which the ligand solution was dropped was slowed. Moreover, Examples 1-1, 1-2, 2-1 to 2-4, 3, 4, 5, and 6 and Comparative Example 2 show that in order to prevent the raw material solution from becoming cloudy, the molar ratio of the organic solvent to the ligand in the ligand solution is preferably 40 or more and 500 or less. Furthermore, Examples 1-1, 1-2, 2-1 to 2-4, 3, 4, 5, and 6 and Comparative Example 1 show that while the ligand solution is mixed with the Al source solution to generate the raw material solution, the pH during the generation is preferably maintained in the range of 2.5 or more and 3.5 or less.

[0120] The length of the support 11 used in the above examples in the direction in which the through-holes 111 extend is 16 cm. Generally, when a raw material solution becomes cloudy in solvothermal synthesis, a depth of 10 cm or more is thought to cause thickness variations that affect quality, and therefore the above-described method for producing a separation membrane composite 1 is suitable when the length of the through-holes 111 is 10 cm or more. Furthermore, in practice, the length of the through-holes 111 of the separation membrane composite 1, i.e., the length of the separation membrane composite 1, is 200 cm or less.

[0121] Since the maximum width of each through hole 111 in a cross section perpendicular to the penetration direction of the support 11 used in the above examples is 2 mm, it can be said that an MOF membrane with small variability can be formed if the maximum width is at least 1 mm or more. Note that, for practical use as a separation membrane composite 1, the maximum width of each through hole 111 is 20 mm or less. Furthermore, since the length of the support 11 used in the above examples is 16 cm, the above examples show that an MOF membrane with small variability can be formed if the length of the through hole 111 is 10 to 100 times the maximum width of the through hole 111.

[0122] The separation membrane composite 1 and the method for manufacturing the separation membrane composite 1 can be modified in various ways.

[0123] The separation membrane composite 1 may be produced by a method other than the above-described production method.

[0124] In the separation device 2, substances other than those exemplified above may be separated from the mixed substance. The MOF membrane composite, which is the separation membrane composite 1, is not limited to a permeation type separation membrane and may be an adsorption type separation membrane. Furthermore, the MOF membrane composite may be used for purposes other than fluid separation.

[0125] As already explained, the support 11 is not limited to a so-called monolith type. The number of through-holes 111 may be one. When fluid permeation through the MOF membrane is not required, the support 11 is not limited to a porous type.

[0126] In the above embodiment, in step S15 of Fig. 4, the support 11 is immersed in the raw material solution 51. However, "immersion" here does not necessarily mean that the entire support 11 is immersed in the raw material solution 51, but also includes a state in which only the portion of the surface of the support 11 where the MOF membrane is to be formed is in contact with the raw material solution 51. In other words, the step of forming the MOF membrane is a step of bringing the raw material solution 51 into contact with the portion of the surface of the support 11 where the MOF membrane is to be formed, and heating it.

[0127] The configurations in the above-described embodiment and each modification may be combined as appropriate as long as they are not mutually contradictory.

[0128] While the invention has been particularly depicted 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.

[0129] The MOF membrane composite of the present invention can be used in a variety of fields, for example, for separating various substances.

[0130] 1 Separation membrane composite (MOF membrane composite) 11 Support 12 Separation membrane (MOF membrane) 51 Raw material solution 111 Through-holes S11 to S16 Steps

Claims

1. A method for producing a MOF membrane composite, comprising: a) attaching seed crystals of a CAU-10 type MOF onto a support; b) preparing an Al source solution, which is an aqueous solution containing an Al ion source; c) preparing a ligand solution in which an organic ligand used in the synthesis of a CAU-10 type MOF is dissolved in a solvent; d) mixing the Al source solution and the ligand solution at a rate that does not cause turbidity to prepare a raw material solution; and e) immersing the support in the raw material solution and forming a MOF membrane, which is a CAU-10 type MOF, on the support by solvothermal synthesis.

2. A method for producing a MOF membrane composite according to claim 1, wherein in the step d), stirring is performed while the ligand solution is added dropwise to the Al source solution.

3. A method for producing a MOF membrane composite according to claim 1, wherein in the step d), the pH of the raw material solution during production is maintained at 2.5 or more and 3.5 or less.

4. A method for producing a MOF membrane complex according to claim 1, wherein the molar ratio of the solvent to the organic ligand in the ligand solution is 40 or more and 500 or less.

5. A method for producing a MOF membrane composite according to claim 1, wherein the organic ligand is any one selected from the group consisting of isophthalic acid, 5-aminoisophthalic acid, 5-methylisophthalic acid, 5-methoxyisophthalic acid, 5-nitroisophthalic acid, and 5-hydroxyisophthalic acid.

6. A method for producing a MOF membrane composite according to any one of claims 1 to 5, wherein the support has through holes, and in step e), the support is immersed in the raw material solution with the extension direction of the through holes parallel to the vertical direction.

7. A MOF membrane complex comprising: a support having through holes; and a MOF membrane which is a CAU-10 type MOF formed on the inner surface of the through holes or on the outer surface of the support, wherein when the support is divided into thirds in the longitudinal direction along which the through holes extend, and three thicknesses of the MOF membrane are obtained at the center of the longitudinal direction of the three portions, the maximum difference between the average inner-pore thickness value, which is the average of the three thicknesses, and the three thicknesses is 30% or less of the average inner-pore thickness value.

8. A MOF membrane composite according to claim 7, wherein the support has two parallel through holes including the through hole, and the maximum difference between an inter-pore thickness average, which is the average of the average inner-pore thicknesses of the two through holes, and the average inner-pore thickness of the two through holes, is 30% or less of the average inter-pore thickness.

9. The MOF membrane composite according to claim 7, wherein the length of the through-hole is 10 cm or more and 200 cm or less.

10. A MOF membrane composite according to claim 7, wherein the maximum width of the through hole in a cross section perpendicular to the longitudinal direction is 1 mm or more and 20 mm or less, and the length of the through hole is 10 times or more and 100 times or less the maximum width of the through hole.

11. A MOF membrane complex comprising: a support; and a MOF membrane which is a CAU-10 type MOF formed on the support, wherein an organic ligand used in forming the MOF membrane is any one selected from the group consisting of 5-methylisophthalic acid, 5-aminoisophthalic acid, and 5-nitroisophthalic acid.

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