MOF membrane complex and MOF membrane complex manufacturing method

Abstract

An MOF membrane complex (1) is provided with a porous support (11) and an MOF membrane (12) that is formed of an MOF and that is provided on the support (11). MOF crystal particles (121) in the MOF membrane (12) each have a shape having a polygonal column part (122) and two polygonal pyramid parts (123) of which the bottom surfaces are the two end faces of the polygonal column part (122). Lateral surfaces of the polygonal column part (122) have a striped pattern (P1) that extends in a direction along the two end faces. The standard deviation of the particle sizes of the MOF crystal particles (121) is 2.0-15.0 µm, and the value obtained by dividing the standard deviation of the particle sizes with the average of the particle sizes is 5.0-20.0.

Description

MOF membrane composite and method for producing MOF membrane composite

[0001] The present invention relates to a MOF membrane composite and a method for producing the MOF membrane composite. [Reference to Related Applications] This application claims the benefit of priority from Japanese Patent Application JP2024-042829, filed on March 18, 2024, the entire disclosure of which is incorporated herein by reference.

[0002] Metal-organic frameworks (MOFs) have high surface areas and high adsorption capacities, and research is underway to develop them as alternatives to conventional porous materials such as zeolites. MOFs are typically synthesized by reacting organic and metal-containing raw materials in water and organic solvents. Furthermore, MOF membranes can be formed on porous supports using synthesis methods similar to those used for zeolite membranes, including solvothermal synthesis and secondary growth methods. For example, Da-Shiuan Chiou and seven others, in "Highly CO2 Selective Metal-Organic Framework Membranes with Favorable Coulombic Effect" (Advanced Functional Materials, 2021, Vol. 31, 2006924) (Reference 1), disclose a MOF called "CAU-10-H." A CAU-10-H MOF membrane is formed on a support by attaching seed crystals to the support and growing crystal particles from the seed crystals.

[0003] When forming a MOF membrane on a support to produce a MOF membrane composite, it is desirable to uniformly disperse seed crystals, which are the starting points for crystal particle growth, in order to obtain a dense MOF membrane. However, it is difficult to attach seed crystals completely uniformly to the support, and if there are relatively large areas where no seed crystals are attached, crystal particles will not be generated in those areas, which may result in defects in the MOF membrane.

[0004] An object of the present invention is to provide a MOF membrane composite in which defects in the MOF membrane are reduced.

[0005] A first aspect of the invention is a MOF membrane composite comprising a porous support and a MOF membrane formed on the support and composed of MOFs, wherein crystal particles of the MOF in the MOF membrane have a shape having a polygonal pillar portion and two polygonal pyramid portions, each having both end faces of the polygonal pillar portion as bases, and the side surfaces of the polygonal pillar portion have a striped pattern extending in a direction along the both end faces, and the standard deviation of particle diameters of the crystal particles is 2.0 μm or more and 15.0 μm or less, and the value obtained by dividing the standard deviation of the particle diameters by the average particle diameter is 5.0 or more and 20.0 or less.

[0006] According to the present invention, it is possible to provide a MOF membrane composite in which defects in the MOF membrane are reduced.

[0007] A second aspect of the present invention is the MOF membrane composite of the first aspect, wherein the polygonal pillar portion is a square pillar.

[0008] A third aspect of the present invention is the MOF membrane composite of the second aspect, wherein the polygonal pyramidal portion is a square pyramid.

[0009] A fourth aspect of the invention is the MOF membrane composite of any one of the first to third aspects, wherein the MOF comprises aluminum ions and ligands coordinated to the aluminum ions, and an X-ray diffraction pattern obtained by irradiating the surface of the MOF membrane with X-rays has peaks at diffraction angles 2θ listed in the table below.

[0010]

[0011] A fifth aspect of the invention is the MOF membrane complex according to any one of the first to fourth aspects, wherein the ligand of the MOF is 1H-pyrrole-2,5-dicarboxylic acid.

[0012] A sixth aspect of the present invention is the MOF membrane composite of any one of the first to fifth aspects, ４ The ideal separation factor for HCl / He is 0.3 or less.

[0013] A seventh aspect of the present invention is the MOF membrane composite according to any one of the first to sixth aspects, ２ / N ２ The permeation rate ratio is 2 or more.

[0014] Aspect 8 of the invention is a method for producing a MOF membrane composite, comprising the steps of: a) attaching seed crystals of a MOF onto a porous support; b) preparing a raw material solution of a MOF; and c) immersing the support in the raw material solution and forming a membrane of the MOF on the support by solvothermal synthesis, wherein the step a) comprises the steps of: a1) preparing first seed crystals having a first average particle size and second seed crystals having a second average particle size smaller than the first average particle size; and a2) attaching the first seed crystals and the second seed crystals onto the support using a dispersion liquid in which the first seed crystals and the second seed crystals are mixed.

[0015] A ninth aspect of the invention is the method for producing the MOF membrane composite of the eighth aspect, wherein in the step a1), the first seed crystals and the second seed crystals are prepared by changing the grinding time of the MOF powder.

[0016] 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.

[0017] FIG. 1 is a cross-sectional view of a MOF membrane composite. FIG. 2 is a cross-sectional view showing an enlarged portion of the MOF membrane composite. FIG. 3 is a schematic view of MOF crystal particles. FIG. 4 is a perspective view showing MOF crystal particles. FIG. 5 is a diagram showing the flow of production of a MOF membrane composite. FIG. 6 is a diagram for explaining the treatment of a first comparative example. FIG. 7 is a diagram for explaining the treatment of a second comparative example. FIG. 8 is a diagram for schematically showing first and second seed crystals on a support. FIG. 9 is a diagram showing a separation device. FIG. 10 is a diagram showing the flow of separation of a mixed substance.

[0018] FIG. 1 is a cross-sectional view of a MOF membrane composite 1. FIG. 2 is an enlarged cross-sectional view of a portion of the MOF membrane composite 1. The MOF membrane composite 1 includes a porous support 11 and a metal-organic framework (MOF) membrane 12 (hereinafter referred to as the "MOF membrane 12") disposed 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 this embodiment, the MOF membrane composite 1 is used to separate specific fluids, and the MOF membrane composite 1 and the MOF membrane 12 are considered to be a separation membrane composite and a separation membrane, respectively. In FIG. 1, the MOF membrane 12 is emphasized with a thick line. In FIG. 2, the MOF membrane 12 is shaded with parallel diagonal lines. In FIG. 2, the thickness of the MOF membrane 12 is depicted thicker than it actually is.

[0019] 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, and multiple 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 MOF 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.

[0020] 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.

[0021] The support 11 is formed of, for example, 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.

[0022] The average pore diameter of the support 11 is, for example, 0.01 μm to 70 μm, preferably 0.05 μm to 25 μm. The average pore diameter of the support 11 near the surface on which the MOF 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, using 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 on which the MOF membrane 12 is formed is, for example, 20% to 60%. The porosity can be determined as the percentage of the area containing voids in an SEM (scanning electron microscope) image of a cross section of the support 11.

[0023] 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 MOF 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.

[0024] The MOF membrane 12 is a porous membrane having fine pores (micropores). The MOF 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 MOF membrane 12 than the specific substance. In other words, the permeation rate of the other substances through the MOF membrane 12 is lower than the permeation rate of the specific substance.

[0025] The average membrane thickness of the MOF membrane 12 is, for example, 5 μm or less, preferably 2 μm or less. This enables a high permeation rate to be achieved. The lower limit of the average membrane thickness of the MOF 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 membrane thickness of the MOF membrane 12, a cross section (longitudinal cross section) perpendicular to the surface of the MOF membrane 12 is exposed, for example, by cross-sectional polishing. In this cross section, multiple randomly selected fields (for example, seven fields) are observed using an SEM. The magnification of the SEM is, for example, 20,000 times. The average membrane thickness of the MOF membrane 12 in each field (field-average membrane thickness) is calculated as the average of the membrane thicknesses at five appropriately selected locations, and the arithmetic mean of the field-average membrane thicknesses of the remaining fields, excluding the fields with the maximum and minimum field-average membrane thickness values, is obtained as the average membrane thickness of the MOF membrane 12. The surface roughness (Ra) of the MOF membrane 12 is, for example, 2 μm or less, preferably 1 μm or less, and more preferably 0.5 μm or less.

[0026] The MOF membrane 12 is a polycrystalline membrane mainly composed of numerous MOF crystals (MOF crystal particles 121 in FIG. 3 , which will be described later) formed on the surface of the support 11. At the interface between the MOF 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 indicated by parallel diagonal lines superimposed 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 necessarily have to be present, and the lower limit of the thickness of the composite layer 13 is 0.

[0027] 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 the direction perpendicular to the interface between the support 11 and the MOF membrane 12 (hereinafter referred to as the "depth direction") is identified near one measurement position in the direction along the interface. Specifically, the boundary position on the MOF membrane 12 side of the composite layer 13 is the interface between the MOF membrane 12 and the support 11. The boundary position on the opposite side of the composite layer 13 from the MOF membrane 12 is the edge of the MOF present in the pores of the support 11 that is substantially continuous with the MOF membrane 12 in the depth direction but is farthest from the MOF membrane 12. The depth-wise distance between the boundary position on the MOF membrane 12 side of the composite layer 13 and the boundary position on the opposite side of the MOF membrane 12 is obtained as the thickness of the composite layer 13 at that measurement position. Then, the average thickness of the composite layer 13 at a plurality of different measurement positions (for example, 10 measurement positions) is determined as the thickness of the composite layer 13 in the MOF membrane composite 1.

[0028] 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 MOF membrane 12 in the MOF membrane composite 1, so the support 11 and the MOF membrane 12 are in direct contact with each other. In other words, there is no intermediate layer formed between the support 11 and the MOF membrane 12 in a step other than the step of forming the MOF membrane.

[0029] The average pore diameter of the MOF membrane 12 is, for example, 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 interstitial spacing of a highly regular lattice structure formed by metal ions (e.g., aluminum ions) and organic ligands. MOFs have a unique pore structure consisting of channels (pores) and cages (internal spaces) depending on their structural type. The pore diameter here refers to the pore diameter of the channel, with the long diameter being the maximum diameter in the cross section of the channel, and the short diameter being the diameter of the cross section in a direction approximately perpendicular to the long diameter. The arithmetic mean of the short diameter and the long diameter is 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 MOF membrane 12 is formed.

[0030] The MOFs constituting the MOF membrane 12 are, for example, aluminum ions (Al ３＋ ) and an organic ligand (hereinafter simply referred to as "ligand") coordinated to the aluminum ion. The metal ions constituting the MOF may contain small amounts of ions other than aluminum ions. The metal ions constituting the MOF may be other than aluminum ions. The ligands that are components of the MOF 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 are more permeable to certain gases 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, the ligand may have a ligand such as a pyridine group or a pyrrole group that can coordinate to a metal ion instead of a carboxy group.

[0031] The X-ray diffraction pattern obtained by irradiating the surface of the MOF membrane 12 (the surface opposite the support 11) with X-rays has peaks at all diffraction angles 2θ listed in Table 2, for example. The X-ray diffraction pattern is obtained using CuKα radiation as the radiation source of the X-ray diffraction device. For example, an X-ray diffraction device manufactured by Rigaku Corporation (device name: MiniFlex 600) is used, with a tube voltage of 40 kV, a tube current of 15 mA, a scanning speed of 0.5° / min, and a scanning step of 0.02°. The divergence slit is 1.25°, the scattering slit is 1.25°, the receiving slit is 0.3 mm, the incident Soller slit is 5.0°, and the receiving Soller slit is 5.0°. No monochromator is used, and 0.015 mm thick nickel foil is used as a CuKβ ray filter. The X-ray diffraction pattern may not have peaks at some or all of the diffraction angles 2θ listed in Table 2.

[0032]

[0033] 3 is a diagram schematically illustrating the MOF crystal particles 121 that constitute the MOF membrane 12, with the MOF crystal particles 121 on the support 11 indicated by rectangles. A large number of MOF crystal particles 121 are densely formed on the surface of the support 11. For reasons described below, defects in the MOF membrane 12 are reduced in the MOF membrane composite 1. Here, defects in the MOF membrane 12 are excessively large gaps between adjacent MOF crystal particles 121, and are spaces that allow the passage of molecules with a kinetic molecular diameter larger than the average pore size of the MOF.

[0034] When the MOF film 12 is observed from the surface using an ULV-SEM (Ultra Low Voltage Scanning Electron Microscope) (accelerating voltage 1 kV, magnification 30,000x, 50,000x), the MOF crystal particle 121 has the shape shown in the upper right of FIG. 3 . Specifically, the MOF crystal particle 121 has a shape including a polygonal prism portion 122 and two polygonal pyramid portions 123, each of which has both end faces of the polygonal prism portion 122 as its base. The polygonal prism portion 122 is an n-sided prism (n is an integer of 3 or greater), and the polygonal pyramid portion 123 is an n-sided pyramid. The polygonal prism portion 122 may be a regular n-sided prism, and the polygonal pyramid portion 123 may be a regular n-sided pyramid. The two polygonal pyramid portions 123 are continuous from both ends of the polygonal prism portion 122, and the side surface of each polygonal pyramid portion 123 shares a vertex with the side surface of the polygonal prism portion 122. The two polygonal pyramidal portions 123 have approximately the same shape. In reality, each MOF crystal particle 121 faces in various (random) directions, and only some of the MOF crystal particles 121 can be observed on the surface of the MOF membrane 12 as the shape shown in the upper right of Fig. 3. In other words, when the shape shown in the upper right of Fig. 3 is confirmed in at least a portion of the surface during observation, it can be said that the MOF crystal particle 121 has a shape including a polygonal column portion 122 and two polygonal pyramidal portions 123.

[0035] From observation of various surfaces of the MOF membrane 12, it is believed that in a typical MOF crystal particle 121, the polygonal columnar portion 122 is a square columnar portion and the polygonal pyramidal portion 123 is a square pyramid, as shown in FIG. 4 . In the MOF constituting the MOF membrane 12 in this embodiment, the basic crystal structure is believed to be a rectangular parallelepiped, and in the MOF crystal particle 121 in which the polygonal columnar portion 122 is a square columnar portion, it can be said that a crystal structure with a preferable shape is formed without excessive crystal chipping. Depending on the manufacturing conditions of the MOF, etc., the polygonal columnar portion 122 may be a triangular column, a pentagonal column, a hexagonal column, etc., and the polygonal pyramidal portion 123 may be a triangular pyramid, a pentagonal pyramid, a hexagonal pyramid, etc. It is believed that the shape of the MOF crystal particle 121 having the polygonal columnar portion 122 makes it easier to form a dense membrane compared to when the MOF crystal particle 121 has a thin plate-like shape, etc.

[0036] Each side surface of the polygonal prism 122 has a striped pattern P1. The striped pattern P1 extends in a direction along both end faces of the polygonal prism 122 (i.e., in a direction approximately perpendicular to the generatrix of the polygonal prism 122). Each line of the striped pattern P1 is continuous on all side surfaces of the polygonal prism 122 and goes around the entire polygonal prism 122. The surface of each side surface of the polygonal prism 122 having the striped pattern P1 is slightly rough, increasing the surface area of ​​the side surface. Therefore, compared to a case where the striped pattern P1 is not present, the area available for adsorbing gases and the like is increased, improving the permeation performance of the MOF membrane composite 1. Each side surface of the polygonal prism 123 is typically a smooth crystal plane, and the striped pattern P1 is not observed. The side surface of the polygonal prism 123 may have the striped pattern P1.

[0037] The average particle size of the MOF crystal particles 121 is, for example, 0.1 μm or more and 2 μm or less. The average particle size is preferably 1 μm or less, and more preferably 0.7 μm or less. The average particle size is preferably 0.3 μm or more. The standard deviation of the particle sizes of the MOF crystal particles 121 is 2.0 μm or more and 15.0 μm or less. As will be described later, if the standard deviation of the particle sizes is excessively small or excessively large, defects in the MOF membrane 12 may be more likely to occur. The standard deviation of the particle sizes may be 10.0 μm or less, or may be 8.0 μm or less. In the MOF membrane 12, the value obtained by dividing the standard deviation of the particle sizes by the average particle size (hereinafter referred to as the "coefficient of variation of particle size") is 5.0 or more and 20.0 or less, preferably 15.0 or less, and more preferably 10.0 or less. As will be described later, defects in the MOF membrane 12 are reduced by having the coefficient of variation of the particle diameter within the above range.

[0038] In measuring the particle diameter of the MOF crystal particles 121, three straight lines are drawn at arbitrary positions on an observation image (e.g., 20,000x magnification) of the surface of the MOF membrane 12 using an SEM, and the length of each MOF crystal particle 121 on the lines (i.e., the distance between two points on the outer edge of the particle where the lines intersect) is obtained as the particle diameter. The arithmetic mean and standard deviation of the particle diameters of a predetermined number (e.g., 60) of MOF crystal particles 121 are then determined as the mean and standard deviation of the particle diameters of the MOF crystal particles 121 in the MOF membrane composite 1.

[0039] Next, the production of the MOF membrane composite 1 will be described with reference to FIG. 5 . When the MOF membrane composite 1 is produced, first, first and second seed crystals to be used in the production of the MOF membrane 12 are prepared (step S11). The first and second seed crystals are produced, for example, from MOF precursor crystals. The precursor crystals are produced as MOF powder, for example, by solvothermal synthesis using water and / or an organic solvent (also called hydrothermal synthesis when the solvent is water). The precursor crystals contain, for example, aluminum ions. The precursor crystals may be produced by any or known production method. The precursor crystals may contain metal ions other than aluminum ions.

[0040] Next, a portion of the raw crystals is dispersed in an organic solvent (ethanol, etc.) and then placed in a bead mill (or ball mill) or the like, where the raw crystals are pulverized for a predetermined first pulverization time. This results in first seed crystals having a first average particle size. The first average particle size (D50) is, for example, 0.30 μm to 0.50 μm, preferably 0.35 μm to 0.40 μm. Regarding the particle size distribution of the first seed crystals, D5 is, for example, 0.20 μm to 0.38 μm, and D95 ​​is, for example, 0.38 μm to 0.80 μm. The particle size of the first seed crystals can be measured by a laser scattering method (the same applies to the particle size of the second seed crystals described below).

[0041] Furthermore, another portion of the raw crystals is dispersed in an organic solvent and then introduced into a bead mill or the like, where the raw crystals are pulverized for a second pulverization time longer than the first pulverization time. This results in second seed crystals having a second average particle size smaller than the first average particle size. The second average particle size (D50) is, for example, 0.10 μm to 0.30 μm, preferably 0.18 μm to 0.22 μm. Regarding the particle size distribution of the second seed crystals, D5 is, for example, 0.05 μm to 0.20 μm, and D95 ​​is, for example, 0.20 μm to 0.60 μm. The value obtained by dividing the first average particle size by the second average particle size (first average particle size / second average particle size) is, for example, 1.1 to 6, preferably 1.5 to 5. Alternatively, the first seed crystal and the second seed crystal may be obtained by grinding the raw crystal for a first grinding time, removing a portion thereof, and further grinding the remainder thereof so that the total grinding time is a second grinding time.

[0042] Next, the first and second seed crystals are dispersed in a solvent (water and / or organic solvent) to prepare a dispersion having a seed crystal (total of the first and second seed crystals) concentration of, for example, 0.01 to 1 wt %. In the dispersion, the ratio of the weight of the first seed crystals to the weight of the second seed crystals (weight of the first seed crystals / weight of the second seed crystals) is, for example, 0.1 to 99, preferably 2 to 40. The dispersion containing the first and second seed crystals is brought into contact with the portion of the support 11 where the MOF membrane 12 is to be formed, thereby adhering the first and second seed crystals to the support 11 (step S12). For example, a dip coating method can be used in which the porous support 11 is immersed in the dispersion to adhere the first and second seed crystals to the support 11. The solvent is then removed by drying to prepare a seed crystal-adhered support. The amount of seed crystals attached to the surface of the support 11 (the total amount of the first and second seed crystals) is, for example, 0.01 to 0.60 g / m ２ and preferably 0.10 to 0.30 g / m ２ The first and second seed crystals may be attached to the support 11 by other methods.

[0043] Next, a raw material solution (also referred to as a synthesis sol or synthesis solution) used to form the MOF membrane 12 is prepared (step S13). 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, and a metal ion source are mixed. In one 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. The metal ions are, for example, aluminum ions. The metal ions may be other than aluminum ions.

[0044] After all the raw materials are added, the raw material solution is stirred for a certain period of time. The stirring time is, for example, 0.5 to 10 hours, preferably 2 to 5 hours. Using a sol that has been stirred for a certain period of time makes it possible to synthesize crystals with a striped pattern. MOF membranes can also be synthesized using a sol immediately after the raw materials have been confirmed to be dissolved, but in this case, crystals with smooth crystal faces without striped patterns are produced.

[0045] 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 using the seed crystals as nuclei, forming an MOF film 12 on the support 11 (step S14). 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.

[0046] After the solvothermal synthesis is complete, the support 11 and the MOF 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 MOF membrane are dried, for example, at 100°C. "Drying" means removing molecules of the substances used for washing, such as water and ethanol, from the pores of the MOF membrane. The MOF membrane composite 1 is obtained by the above treatment.

[0047] Here, the processes of the first and second comparative examples for forming an MOF membrane will be described. FIGS. 6A and 6B are diagrams illustrating the processes of the first and second comparative examples, respectively. In the process of the first comparative example, seed crystals with an excessively small particle size distribution are prepared and attached to the support 11. At this time, it is not easy to attach the seed crystals uniformly and at approximately equal intervals, and relatively large areas where no seed crystals are attached may occur. As a result, as shown in FIG. 6A , gaps are generated between adjacent MOF crystal particles 91 (grain boundaries) in the formed MOF membrane 92, resulting in defects D1 in the MOF membrane. While it is possible to eliminate these gaps by growing the MOF crystal particles 91 larger, the thickness of the MOF membrane 92 would become excessively large, resulting in a membrane prone to cracking.

[0048] In the process of the second comparative example, seed crystals with an excessively large particle size distribution are prepared and attached to the support 11. In this case, as shown in Figure 6B, in the formed MOF membrane 92, the difference in particle size between adjacent MOF crystal particles 91 becomes large, resulting in variations in the size of the contact area between the MOF crystal particles 91. In the portion D2 where the contact area is excessively small, cracks are likely to occur due to the influence of stress caused by the difference in the thermal expansion coefficient between the MOF membrane 92 and the support 11 when the MOF membrane composite is heated or dried.

[0049] In contrast, in the production of the MOF membrane composite 1 shown in FIG. 5 , first seed crystals having a first average particle size and second seed crystals having a second average particle size smaller than the first average particle size are prepared and attached to the support 11. In this case, as shown in FIG. 7 , first seed crystals 81 and second seed crystals 82 coexist on the support 11, and the gaps between the MOF crystal particles 121 (shown by the two-dot chain line in FIG. 7 ) grown from the relatively larger first seed crystals 81 are filled with the MOF crystal particles 121 grown from the relatively smaller second seed crystals 82, forming a dense MOF membrane 12. Furthermore, by ensuring that the particle size distribution is neither too large nor too small, excessively small contact areas between adjacent MOF crystal particles 91 are less likely to occur, as shown in FIG. 6B , and a MOF membrane 12 with reduced defects can be formed. As a result, the separation performance of the MOF membrane composite 1 is improved.

[0050] Next, examples and comparative examples of MOF membrane composites will be described. Table 3 shows various measurement results for the examples and comparative examples. In Examples 1 to 8 and Comparative Example 1, MOF membranes called KMF-1 were synthesized. In Examples 9 to 12, MIL-160, CAU-10-H, and CAU-10-NH were synthesized, respectively. ２ , CAU-10-CH ３ We synthesized a MOF membrane called

[0051]

[0052] Example 1 Synthesis of Seed Crystals Aluminum sulfate 14-18 hydrate, 1H-pyrrole-2,5-dicarboxylic acid, and sodium formate were added to ion-exchanged water and mixed by ultrasonic treatment and stirring. After heating the mixed solution at 100°C for 12 hours (solvothermal synthesis), the product was separated from the solution by centrifugation, washed with ion-exchanged water and ethanol, and dried at 25°C. As a result, KMF-1 powder was obtained as raw crystals. The raw crystals were added to ethanol, and ZrO ２ The first seed crystals were obtained by pulverizing for 20 hours using beads (diameter 1 mm). The same operation was performed to obtain second seed crystals, except that the pulverization time was changed to 30 hours. Regarding the particle size distribution of the first seed crystals, D5 was 0.25 μm, D50 (first average particle size) was 0.38 μm, and D95 ​​was 0.70 μm. Regarding the particle size distribution of the second seed crystals, D5 was 0.18 μm, D50 (second average particle size) was 0.28 μm, and D95 ​​was 0.40 μm. The particle size of the seed crystals was measured by a laser scattering method.

[0053] [Seeding] The first seed crystal and the second seed crystal were dispersed in ethanol in a weight ratio of 4:1 to prepare a dispersion. The concentration of the seed crystals (the total of the first seed crystal and the second seed crystal) in the dispersion was set to 0.10 wt %. The dispersion was used to attach the first seed crystal and the second seed crystal to an alumina support.

[0054] [MOF membrane synthesis] Aluminum sulfate 14-18 hydrate, 1H-pyrrole-2,5-dicarboxylic acid, sodium formate, and ion-exchanged water were mixed in a molar ratio of 0.5:1:2:12000 to prepare a raw material solution (synthetic sol) for membrane synthesis. The support with attached seed crystals and the raw material solution were placed in a Teflon (registered trademark) container and heated at 100°C for 10 hours (solvothermal synthesis). This resulted in a MOF membrane composite with a KMF-1 MOF membrane formed on the support. The MOF membrane composite was washed with ion-exchanged water and ethanol at room temperature and then dried at 80°C. The MOF membrane composite was further washed once with methanol and dried at room temperature.

[0055] [XRD Measurement] X-rays were irradiated onto the surface of the MOF membrane to obtain an X-ray diffraction pattern. The measurement conditions for the X-ray diffraction pattern were the same as those described above. The X-ray diffraction pattern had peaks at all diffraction angles 2θ listed in Table 2. This also applies to the following Examples and Comparative Examples.

[0056] [Surface Observation] When the surface of the MOF membrane was observed using ULV-SEM (accelerating voltage 1 kV, magnification 30,000x, 50,000x), the MOF crystal particles in the MOF membrane were found to have a shape comprising a polygonal pillar and two polygonal pyramids, each of which had its base at both end faces of the polygonal pillar. Furthermore, the side surfaces of the polygonal pillars had striped patterns extending in the direction along the end faces. This also applies to the following examples and comparative examples.

[0057] [Measurement of particle size] Three straight lines were drawn at arbitrary positions on an image (magnification 20,000x) of the MOF membrane surface observed using an SEM, and the length of each MOF crystal particle on the lines was obtained as the particle size. The arithmetic mean and standard deviation of the particle sizes of 60 MOF crystal particles were calculated as the mean and standard deviation of the particle sizes of the MOF crystal particles in the MOF membrane composite. The coefficient of variation of the particle size was obtained by dividing the standard deviation of the particle sizes by the mean particle size. The standard deviation and coefficient of variation of the particle sizes of the MOF crystal particles in the MOF membrane composite of Example 1 are shown in Table 3. In the following examples and comparative examples, the standard deviation and coefficient of variation of the particle size were obtained in a similar manner.

[0058] [CF ４ / He Ideal Separation Factor Measurement] CF ４ The permeation rates of CF and He were measured by introducing the gas to be measured (single gas) onto the surface of the MOF membrane at 25°C and a pressure of 0.2 MPa. The permeation pressure was atmospheric pressure (0.10 MPa). The permeation rate (permeance) is the gas permeation rate per unit membrane area and unit pressure difference. ４ / He ideal separation factor is CF ４ The CF was obtained by dividing the permeation rate by the He permeation rate. ４ The kinetic molecular diameter of CF in the MOF membrane composite of Example 1 is slightly larger than the pore diameter of the MOF of KMF-1, and the kinetic molecular diameter of He is smaller than the pore diameter of the MOF of KMF-1.４ The ideal separation factors for CF / He are shown in Table 3. In the following examples and comparative examples, the same method was used. ４ The ideal separation factor for HCl / He was obtained.

[0059] [CO ２ / N ２ Measurement of Permeation Rate Ratio] CO ２ and N ２ The permeation rate of CO ２ 50% by volume, N ２ A mixed gas with a composition of 50% by volume of CO was introduced onto the surface of the MOF membrane at 25°C and a pressure of 0.2 MPa. The permeation pressure was atmospheric pressure (0.10 MPa). ２ / N ２ The permeation rate ratio is ２ The permeation rate is N ２ The CO permeation rate in the MOF membrane composite of Example 1 was calculated by dividing the CO permeation rate by the ２ / N ２ The permeation rate ratio is as shown in Table 3. In the following examples and comparative examples, the CO ２ / N ２ The permeation rate ratio was obtained.

[0060] Example 2 The same procedure as in Example 1 was carried out, except that the synthesis temperature of the MOF membrane was changed to 80°C.

[0061] Example 3 The same procedure as in Example 1 was carried out, except that the molar ratio of aluminum sulfate 14-18 hydrate, 1H-pyrrole-2,5-dicarboxylic acid, sodium formate, and ion-exchanged water in the raw material solution was changed to 1:1:2:12000.

[0062] Example 4 The same procedure as in Example 1 was carried out, except that the molar ratio of aluminum sulfate 14-18 hydrate, 1H-pyrrole-2,5-dicarboxylic acid, sodium formate, and ion-exchanged water in the raw material solution was changed to 0.5:1:2:16000.

[0063] Example 5 The same procedure as in Example 1 was carried out, except that the molar ratio of aluminum sulfate 14-18 hydrate, 1H-pyrrole-2,5-dicarboxylic acid, sodium formate, and ion-exchanged water in the raw material solution was changed to 0.5:1:2:10000.

[0064] Example 6 The same procedure as in Example 1 was carried out, except that the molar ratio of aluminum sulfate 14-18 hydrate, 1H-pyrrole-2,5-dicarboxylic acid, sodium formate, and ion-exchanged water in the raw material solution was changed to 0.5:1:2:8000.

[0065] Example 7 The same operation as in Example 1 was carried out, except that a solution A containing aluminum sulfate 14-18 hydrate and ion-exchanged water in a molar ratio of 0.5:2000 and a solution B containing 1H-pyrrole-2,5-dicarboxylic acid, sodium hydroxide, and ion-exchanged water in a molar ratio of 1:2:2000 were prepared, and solution A and solution B were mixed in a molar ratio of 1:1 to prepare a raw material solution.

[0066] Example 8 The same operation as in Example 7 was carried out, except that a solution A containing aluminum sulfate 14-18 hydrate and ion-exchanged water in a molar ratio of 0.5:4000 and a solution B containing 1H-pyrrole-2,5-dicarboxylic acid, sodium hydroxide, and ion-exchanged water in a molar ratio of 1:2:4000 were prepared, and solution A and solution B were mixed in a molar ratio of 1:1 to prepare a raw material solution.

[0067] Example 9 Synthesis of Seed Crystals A mixed solution was prepared by mixing 1.562 g of 2,5-furandicarboxylic acid and 1.36 g of sodium formate with 50 mL of ion-exchanged water. The mixed solution was stirred at 50°C for 3 hours, then cooled to room temperature, and 2.413 g of aluminum chloride hexahydrate was added. Next, this solution was kept at 100°C for 12 hours. The precipitate was separated using a centrifuge and washed three times with ion-exchanged water and ethanol. As a result, a powder of MIL-160 (raw crystals) containing 2,5-furandicarboxylic acid as a ligand was obtained. The raw crystals were added to ethanol, and ZrO ２ The first seed crystals were obtained by milling for 20 hours using beads (1 mm diameter). The same procedure was repeated except that the milling time was changed to 30 hours to obtain second seed crystals. Regarding the particle size distribution of the first seed crystals, D5 was 0.21 μm, D50 (first average particle size) was 0.37 μm, and D95 ​​was 0.71 μm. Regarding the particle size distribution of the second seed crystals, D5 was 0.19 μm, D50 (second average particle size) was 0.25 μm, and D95 ​​was 0.39 μm.

[0068] [Seeding] The same procedure as in Example 1 was carried out except that MIL-160 was used as the seed crystal.

[0069] [MOF Membrane Synthesis] A mixed solution was prepared by adding 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 to 150 mL of ion-exchanged water. The mixed solution was heated to 60°C and stirred for 2 hours. After confirming that the mixed solution had become transparent, it was cooled to room temperature. 2.413 g of aluminum chloride hexahydrate was then added to the mixed solution to prepare a raw material solution. The support with attached seed crystals and the raw material solution were placed in a Teflon (registered trademark) container and heated at 80°C for 20 hours (solvothermal synthesis). This resulted in a MOF membrane composite with a MIL-160 MOF membrane formed on the support. The MOF membrane composite was washed with ion-exchanged water and ethanol at room temperature and then dried at 80°C. The MOF membrane composite was further washed once with methanol and dried at room temperature.

[0070] Example 10 Synthesis of Seed Crystals A mixed solution was prepared by adding 1.43 g of aluminum sulfate 14-18 hydrate, which is an Al ion source, and 0.71 g of isophthalic acid, which is 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 (parent crystals) of CAU-10-H. The parent crystals were placed in ethanol, and ZrO ２ The first seed crystals were obtained by milling for 20 hours using beads (1 mm diameter). The same procedure was repeated except that the milling time was changed to 30 hours to obtain second seed crystals. Regarding the particle size distribution of the first seed crystals, D5 was 0.23 μm, D50 (first average particle size) was 0.35 μm, and D95 ​​was 0.69 μm. Regarding the particle size distribution of the second seed crystals, D5 was 0.18 μm, D50 (second average particle size) was 0.24 μm, and D95 ​​was 0.38 μm.

[0071] [Seeding] The same procedure as in Example 1 was carried out except that CAU-10-H was used as the seed crystal.

[0072] [MOF Membrane Synthesis] A solution of aluminum sulfate 14-18 hydrate and sodium formate, which are Al ion sources, in ion-exchanged water (Al source solution) was slowly mixed with a solution of isophthalic acid, which is a ligand, in DMF (ligand solution), by adding dropwise 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 support with attached seed crystals and the raw material solution were placed in a Teflon (registered trademark) container and heated at 130°C for 12 hours (solvothermal synthesis). This resulted in a MOF membrane composite in which a CAU-10-H MOF membrane was formed on the support. The MOF membrane composite was washed with ion-exchanged water and ethanol at room temperature and then dried at 80°C. The MOF membrane composite was further washed once with methanol and dried at room temperature.

[0073] Example 11 [Synthesis of seed crystals] A mixed solution was prepared by adding 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, to a mixed solvent of 16 g of ion-exchanged water and 4 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, washed three times with ion-exchanged water and ethanol, and CAU-10-NH ２ The seed crystals (raw crystals) were added to ethanol to obtain ZrO ２ The first seed crystals were obtained by milling for 20 hours using beads (1 mm diameter). The second seed crystals were obtained by the same procedure except that the milling time was changed to 30 hours. Regarding the particle size distribution of the first seed crystals, D5 was 0.23 μm, D50 (first average particle size) was 0.38 μm, and D95 ​​was 0.70 μm. Regarding the particle size distribution of the second seed crystals, D5 was 0.17 μm, D50 (second average particle size) was 0.25 μm, and D95 ​​was 0.40 μm.

[0074] [Seeding] CAU-10-NH as seed crystals ２ The same procedure as in Example 1 was carried out except that the following was used.

[0075] [Synthesis of MOF Membrane] 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 support with the seed crystals attached and the raw material solution were placed in a Teflon (registered trademark) container and heated at 130°C for 12 hours (solvothermal synthesis). This produced CAU-10-NH ２ A MOF membrane composite was obtained in which a MOF membrane of this size was formed on a support. The MOF membrane composite was washed with ion-exchanged water and ethanol at room temperature and then dried at 80°C. The MOF membrane composite was further washed once with methanol and dried at room temperature.

[0076] Example 12 [Synthesis of seed crystals] CAU-10-CH was synthesized in the same manner as in Example 10, except that 0.77 g of 5-methylisophthalic acid was used as the ligand. ３ The seed crystals (origin crystals) were obtained. Regarding the particle size distribution of the first seed crystals, D5 was 0.20 μm, D50 (first average particle size) was 0.37 μm, and D95 ​​was 0.70 μm. Regarding the particle size distribution of the second seed crystals, D5 was 0.19 μm, D50 (second average particle size) was 0.26 μm, and D95 ​​was 0.40 μm.

[0077] [Seeding] CAU-10-CH ３ The same procedure as in Example 1 was carried out except that the following was used.

[0078] [Synthesis of MOF membrane] A raw material solution was prepared in the same manner as in Example 10, 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 support with the seed crystals attached and the raw material solution were placed in a Teflon (registered trademark) container and heated at 130°C for 12 hours (solvothermal synthesis). As a result, CAU-10-CH ３A MOF membrane composite was obtained in which a MOF membrane of this size was formed on a support. The MOF membrane composite was washed with ion-exchanged water and ethanol at room temperature and then dried at 80°C. The MOF membrane composite was further washed once with methanol and dried at room temperature.

[0079] Comparative Example 1 The same operation as in Example 1 was carried out, except that in seeding, only the second seed crystals were used as the seed crystals in the dispersion liquid.

[0080] Here, when Examples 1 to 12 are compared with Comparative Example 1, in Comparative Example 1, CF ４ In Examples 1 to 12, the ideal separation factor of CF / He was greater than 0.3. ４ In Comparative Example 1, the ideal separation factor for CO / He was 0.3 or less. ２ / N ２ The permeation rate ratio is 1, whereas in Examples 1 to 12, the CO ２ / N ２ The permeation rate ratio was equal to or greater than 2. Therefore, it can be said that the MOF membrane composites of Examples 1 to 12 had fewer defects in the MOF membrane than the MOF membrane composite of Comparative Example 1, and also achieved improved separation performance.

[0081] The reason why defects in the MOF membranes in Examples 1 to 12 are reduced compared to Comparative Example 1 is not entirely clear. However, in Comparative Example 1, only second seed crystals were attached to the support, and therefore, as explained with reference to FIG. 6A, defects in the MOF membrane are likely to occur in the relatively large regions where no seed crystals are attached. On the other hand, in Examples 1 to 12, as explained with reference to FIG. 7, the gaps between the MOF crystal particles grown from the relatively large first seed crystals are filled with the MOF crystal particles grown from the relatively small second seed crystals. Furthermore, there are no seed crystals with excessively small particle sizes, and the number of areas where the contact area between adjacent MOF crystal particles is excessively small is reduced, which is thought to have reduced defects.

[0082] In Comparative Example 1, the standard deviation of particle size was 1.2 μm and the coefficient of variation was 4.3, whereas in Examples 1 to 12, the standard deviation of particle size was 2.5 μm to 6.1 μm and the coefficient of variation was 6.5 to 14.0. Therefore, it is considered possible to reduce defects in the MOF membrane if the standard deviation of particle size is 2.0 μm or more and the coefficient of variation is 5.0 or more. Although the upper limits of the standard deviation and coefficient of variation of particle size are not necessarily clear, in Examples 1 to 12, the CF ４ The ideal separation factor of CO / He is sufficiently small, and ２ / N ２ Because the permeation rate ratio is sufficiently large, it is considered possible to reduce defects in the MOF membrane even if the standard deviation of the particle size is 15.0 μm and the coefficient of variation is 20.0. The standard deviation of the particle size is preferably 10.0 μm or less, more preferably 8.0 μm or less. The coefficient of variation of the particle size is preferably 15.0 or less, more preferably 10.0 or less.

[0083] As described above, the MOF membrane composite 1 includes a porous support 11 and a MOF membrane 12 formed on the support 11 and made of a MOF. Each MOF crystal particle 121 in the MOF membrane 12 has a shape including a polygonal columnar portion 122 and two polygonal pyramidal portions 123, each of which has a base at each end face of the polygonal columnar portion 122. The side surface of the polygonal columnar portion 122 has a striped pattern P1 extending in a direction along the end faces. Furthermore, the standard deviation of the particle diameters of the MOF crystal particles 121 is 2.0 μm or more and 15.0 μm or less, and the value obtained by dividing the standard deviation of the particle diameters by the average particle diameter is 5.0 or more and 20.0 or less. This allows for the provision of a MOF membrane composite 1 with reduced defects in the MOF membrane 12, as in Examples 1 to 12.

[0084] Preferably, the MOF is composed of aluminum ions and ligands coordinated to the aluminum ions. Furthermore, the X-ray diffraction pattern obtained by irradiating the surface of the MOF membrane 12 with X-rays has peaks at the diffraction angles 2θ shown in Table 2. This makes it possible to more reliably provide a MOF membrane composite 1 with reduced defects in the MOF membrane 12.

[0085] CF in MOF membrane composite 1４ The ideal separation factor of HCl / He is preferably 0.3 or less, more preferably 0.2 or less, and even more preferably 0.1 or less. This makes it possible to provide a MOF membrane composite 1 with further reduced defects in the MOF membrane 12.

[0086] CO in MOF membrane composite 1 ２ / N ２ is preferably 2 or more, more preferably 5 or more, and even more preferably 10 or more. This makes it possible to provide an MOF membrane composite 1 with improved separation performance.

[0087] The method for producing the MOF membrane composite 1 includes a seed crystal attachment step of attaching MOF seed crystals to a porous support 11, a raw material solution preparation step of preparing a MOF raw material solution, and a MOF membrane formation step of immersing the support 11 in the raw material solution and forming a MOF membrane 12 on the support 11 by solvothermal synthesis. The seed crystal attachment step includes a step of preparing first seed crystals 81 having a first average particle size and second seed crystals 82 having a second average particle size smaller than the first average particle size, and a step of attaching the first seed crystals 81 and the second seed crystals 82 to the support 11 using a dispersion liquid in which the first seed crystals 81 and the second seed crystals 82 are mixed. This makes it possible to easily provide a MOF membrane composite 1 with reduced defects in the MOF membrane 12.

[0088] Preferably, the first seed crystals 81 and the second seed crystals 82 are produced by changing the milling time of separately prepared MOF powder. This allows the first seed crystals 81 and the second seed crystals 82 to be easily prepared. Note that the first seed crystals 81 and the second seed crystals 82, which have different average particle sizes, may be directly produced by different synthesis methods, and milling of the MOF powder may be omitted.

[0089] Next, separation of a mixed substance using the MOF membrane composite 1 will be described with reference to Figures 8 and 9. Figure 8 is a diagram showing a separation device 2. Figure 9 is a diagram showing the flow of separation of a mixed substance using the separation device 2.

[0090] In the separation device 2, a mixed substance containing multiple types of fluids (i.e., gases or liquids) is supplied to the MOF membrane composite 1, and highly permeable substances in the mixed substance are separated from the mixed substance by permeating through the MOF 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] Sulfur oxides are compounds of sulfur and oxygen. Examples of the sulfur oxides include sulfur dioxide (SO ２ ), sulfur trioxide (SO３ ) and other SOs Ｘ It is a gas called SOX.

[0095] 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.

[0096] 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 )

[0097] The organic acid is a carboxylic acid or a sulfonic acid. The carboxylic acid is, for example, formic acid (CH ２O 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.

[0098] 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.

[0099] 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.

[0100] The esters mentioned above are, for example, formates or acetates.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] 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.

[0105] The separation device 2 includes a MOF membrane composite 1, a plugging 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 MOF membrane composite 1, the plugging 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.

[0106] The sealing portion 21 is attached to both longitudinal end portions of the support 11 (i.e., the left-right direction in FIG. 8 ) 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.

[0107] 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 MOF membrane composite 1. A supply port 221 is provided at one longitudinal end of the housing 22 (i.e., the left end in FIG. 8 ), 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.

[0108] Two seal members 23 are disposed around the entire circumference of the MOF membrane composite 1 between the outer peripheral surface of the MOF membrane composite 1 and the inner peripheral surface of the housing 22 near both longitudinal ends of the MOF 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 MOF membrane composite 1 and the inner peripheral surface of the housing 22 around the entire circumference. In the example shown in Figure 8, the seal member 23 is in close contact with the outer peripheral surface of the sealing portion 21 and indirectly contacts the outer peripheral surface of the MOF membrane composite 1 via the sealing portion 21. A seal is formed between the seal member 23 and the outer peripheral surface of the MOF 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.

[0109] 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.

[0110] When separating a mixed gas, the above-mentioned separation device 2 is prepared, thereby preparing the MOF membrane composite 1 (step S21). Next, a mixed gas containing multiple types of gases with different permeabilities to the MOF 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.

[0111] 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 MOF membrane composite 1 in the drawing, as indicated by arrow 251. A gas with high permeability in the mixed gas (e.g., CO ２ The highly permeable substance (hereinafter referred to as "highly permeable substance") passes through the MOF 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 absorbed into the gas having low permeability (for example, 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).

[0112] Furthermore, gases (hereinafter referred to as "impermeable substances") excluding the gas that has permeated the MOF 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 MOF membrane 12.

[0113] The above-described MOF membrane composite 1 and the method for producing the MOF membrane composite 1 can be modified in various ways.

[0114] Depending on the separation performance required for the MOF membrane composite 1, ４ The ideal separation factor for CO / He may be greater than 0.3, ２ / N ２ The permeation rate ratio may be less than 2.

[0115] In the above embodiment, the support 11 is immersed in the raw material solution in step S14 of Fig. 5 . However, "immersion" here does not necessarily mean that the entire support 11 is immersed in the raw material solution, 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. In other words, the step of forming a MOF membrane is a step of bringing the raw material solution into contact with the portion of the surface of the support 11 where the MOF membrane is to be formed, and heating it.

[0116] The MOF membrane composite 1 may be produced by a method other than the above-described production method.

[0117] In the separation device 2, substances other than those exemplified in the above description may be separated from the mixed substance.

[0118] The configurations in the above-described embodiment and each modification may be combined as appropriate as long as they are not mutually contradictory.

[0119] 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.

[0120] The MOF membrane composite of the present invention can be used in a variety of fields for separating various substances.

[0121] REFERENCE SIGNS LIST 1 MOF membrane composite 11 support 12 MOF membrane 81 first seed crystal 82 second seed crystal 121 MOF crystal particle 122 polygonal column portion 123 polygonal pyramid portion P1 striped pattern S11 to S14, S21, S22 steps

Claims

1. A MOF membrane composite comprising: a porous support; and a MOF membrane formed on the support and made of a MOF, wherein crystal particles of the MOF in the MOF membrane have a shape having a polygonal pillar portion and two polygonal pyramid portions whose bases are opposite end faces of the polygonal pillar portion, and the side surfaces of the polygonal pillar portion have a striped pattern extending in a direction along the opposite end faces; the standard deviation of particle diameters of the crystal particles is 2.0 μm or more and 15.0 μm or less; and the value obtained by dividing the standard deviation of the particle diameters by the average of the particle diameters is 5.0 or more and 20.0 or less.

2. The MOF membrane composite according to claim 1, wherein the polygonal pillar portion is a square pillar.

3. The MOF membrane composite according to claim 2, wherein the polygonal pyramidal portion is a square pyramid.

4. A MOF membrane composite according to claim 1, wherein the MOF comprises aluminum ions and ligands coordinated to the aluminum ions, and the X-ray diffraction pattern obtained by irradiating the surface of the MOF membrane with X-rays has peaks at the diffraction angles 2θ shown in the table below.

5. The MOF membrane complex according to claim 1, wherein the ligand of the MOF is 1H-pyrrole-2,5-dicarboxylic acid.

6. The MOF membrane composite according to claim 1, ４ A MOF membrane composite having an ideal separation factor of 0.3 or less for CO / He.

7. The MOF membrane composite according to any one of claims 1 to 6, ２ / N ２ The MOF membrane composite has a permeation rate ratio of 2 or more.

8. A method for producing a MOF membrane composite, comprising: a) attaching seed crystals of a MOF onto a porous support; b) preparing a raw material solution of a MOF; and c) immersing the support in the raw material solution and forming a membrane of the MOF on the support by solvothermal synthesis, wherein the a) step comprises: a1) preparing first seed crystals having a first average particle size and second seed crystals having a second average particle size smaller than the first average particle size; and a2) attaching the first seed crystals and the second seed crystals onto the support using a dispersion liquid in which the first seed crystals and the second seed crystals are mixed.

9. The method for producing a MOF membrane composite according to claim 8, wherein in step a1), the first seed crystals and the second seed crystals are prepared by changing the grinding time of the MOF powder.

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