Separation membrane composite and method for producing separation membrane composite

Abstract

A separation membrane composite (1) is provided with: a porous support (11) formed from a ceramic; and a separation membrane (12) that is provided on the support body (11) and is formed of a metal organic structure. The average film thickness of the separation film (12) is 2 [mu] m or less. The metal organic structure is composed of aluminum ions and ligands coordinated with the aluminum ions. A powder X-ray diffraction pattern of the metal organic structure has a peak at a predetermined diffraction angle 2 [theta]. In the separation membrane composite (1), the SF6 / He permeation rate ratio is 0.020 or less. The separation membrane composite (1) can have both a high separation coefficient and a high transmission rate.

Description

Technical Field

[0001] The present invention relates to a separation membrane complex and a method for producing the separation membrane complex.

[0002] [Reference to related applications]

[0003] This application claims the benefit of priority from Japanese patent application JP2023-37303 filed on March 10, 2023, the disclosure of which is incorporated herein in its entirety. Background Art

[0004] There is a growing social demand for technologies to separate and recover CO₂ contained in industrial waste gases emitted from factories and other sources as part of the global carbon neutral stream (CO₂ / N₂ separation). Molecular sieve separation using high-silica zeolite DDR or CHA zeolite membranes is difficult to achieve a high CO₂ / N₂ separation factor. Therefore, there is a demand for membranes that achieve a high separation factor by imparting not only molecular sieve properties but also affinity for CO₂.

[0005] Metal organic frameworks (MOFs) are porous materials with high surface areas and can be used in a variety of applications, including gas adsorption. Furthermore, by forming membranes on porous supports, similar to zeolite membranes, applications in gas or liquid separation are anticipated. Using MOFs with small pore sizes and ligands with a high affinity for CO2 can potentially achieve high CO2 / N2 separation coefficients. For example, "Multivariate Polycrystalline Metal-Organic Framework Membranes for CO2 / CH4Separation" (J.Am.Chem.Soc., 2021, Vol. 143, pp. 17716-17723) (Document 1) written by Weidong Fan et al. and "Conformational-change-induced selectivity enhancement of CAU-10-PDC membrane for H2 / CH4 and CO2 / CH4 separation" (Journal of Membrane Science Letters, 2021, Vol. 1, 100005) (Document 2) written by Chung-Kai Chang et al. discloses a structure in which a MOF membrane is formed on a ceramic support, which shows a relatively high value in terms of the CO2 / N2 or CO2 / CH4 permeation rate ratio.

[0006] However, regarding the performance of the separation membrane, not only the separation coefficient but also the permeation rate (the ease of permeation of highly permeable substances) is very important. By increasing the permeation rate, the number of separation membrane complexes required to form a separation device can be reduced, thereby reducing the manufacturing cost of the separation device and making the separation device compact. However, in the MOF membranes of non-patent documents 1 and 2, the permeation rate is reduced due to the large thickness. In order to increase the permeation rate in the MOF membrane, thin filming is also considered. However, the effects of grain boundary defects that usually form excessive gaps between MOF crystals and coordination defects that constitute part of the ligands of the MOF are significant, and a high separation coefficient cannot be obtained. Therefore, a separation membrane complex having both a high separation coefficient and a permeation rate is required. Summary of the Invention

[0007] An object of the present invention is to provide a separation membrane complex having a high separation coefficient and a high permeation rate.

[0008] The invention of Scheme 1 is a separation membrane complex comprising: a porous support body formed of ceramic; and a separation membrane, which is arranged on the support body and is formed of a metal organic structure, the average membrane thickness of the separation membrane is less than 2 μm, the metal organic structure is composed of aluminum ions and ligands coordinated with the aluminum ions, the powder X-ray diffraction pattern of the metal organic structure has a peak at the diffraction angle 2θ listed in the table below, and the transmission rate ratio of SF6 / He is less than 0.020.

[0009] Table 1

[0010]

[0011] According to the present invention, a separation membrane complex having a high separation coefficient and a high permeation rate can be provided.

[0012] The invention according to claim 2 is the separation membrane complex according to claim 1, wherein the average particle size of the metal-organic structure is 0.1 μm to 2 μm.

[0013] The invention according to claim 3 is the separation membrane complex according to claim 1 or 2, wherein the ligand of the metal-organic structure includes any one of 1H-pyrrole-2,5-dicarboxylic acid, 2,5-furandicarboxylic acid, and 3,5-pyridinedicarboxylic acid.

[0014] The invention according to claim 4 is the separation membrane complex according to any one of claims 1 to 3, wherein the thickness of the composite layer of the support and the metal-organic structure is 2 μm or less.

[0015] The invention according to claim 5 is the separation membrane complex according to any one of claims 1 to 4, wherein the permeation rate of CO 2 gas is 1000 GPU or higher.

[0016] The invention of Scheme 6 is a method for manufacturing a separation membrane complex, which includes the following steps: a) attaching a seed crystal formed by a metal organic structure to a porous support; b) preparing a synthesis solution; and c) immersing the support in the synthesis solution, using hydrothermal synthesis to grow the metal organic structure from the seed crystal to form a separation membrane on the support, the b) step includes a heating and stirring treatment of heating a solution obtained by mixing water, a monocarboxylate and a ligand while stirring, in the b) step, an aluminum source is mixed into the solution after the heating and stirring treatment, and an organic solvent is mixed into the solution at any time, in the separation membrane complex in which the separation membrane is formed on the support, the SF6 / He permeation rate ratio is less than 0.020.

[0017] The invention of claim 7 is the method for producing a separation membrane complex according to claim 6, wherein the organic solvent is an organic compound having a carbonyl group, and in the synthetic solution, the ratio of the amount of the organic solvent to the amount of the ligand is 0.1 to 10.

[0018] The invention according to claim 8 is the method for producing a separation membrane complex according to claim 6 or 7, wherein in the synthesis solution, the ratio of the amount of the monocarboxylate to the amount of the ligand is 0.5 to 1.8.

[0019] The above-mentioned objects and other objects, features, aspects and advantages will become more apparent from the following detailed description of the present invention with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a cross-sectional view of the separation membrane complex.

[0021] Figure 2 This is an enlarged cross-sectional view showing a portion of the separation membrane complex.

[0022] Figure 3 It is a diagram showing the production flow of the separation membrane complex.

[0023] Figure 4 It is a diagram showing a separation device.

[0024] Figure 5 This is a diagram showing the flow of separation of mixed substances using a separation device.

[0025] Figure 6A This is a diagram for explaining the synthesis of a separation membrane of a comparative example.

[0026] Figure 6B This is a diagram for explaining the synthesis of a separation membrane of a comparative example.

[0027] Figure 7AThis is a diagram for explaining the synthesis of a separation membrane.

[0028] Figure 7B This is a diagram for explaining the synthesis of a separation membrane. DETAILED DESCRIPTION

[0029] Figure 1 It is a cross-sectional view of the separation membrane complex 1 . Figure 2 This is an enlarged cross-sectional view of a portion of a separation membrane complex 1. The separation membrane complex 1 comprises a porous support 11 and a separation membrane 12 disposed on the support 11. As described later, the separation membrane 12 is a metal-organic structure (hereinafter referred to as "MOF") membrane, and the separation membrane complex 1 is a MOF membrane complex. The term "MOF membrane" refers to a MOF membrane formed at least on the surface of the support 11, and does not include a case where MOF particles are simply dispersed within an organic membrane. Figure 1 In FIG, the separation membrane 12 is drawn with a thick line. Figure 2 In FIG, parallel oblique lines are drawn on the separation membrane 12. Figure 2 In FIG, the thickness of the separation membrane 12 is drawn thicker than the actual thickness.

[0030] The support 11 is a porous member through which gas and liquid can pass. Figure 1 In the example shown, the support body 11 is an integrally formed columnar main body provided with a plurality of Figure 1 An integral support body having multiple through holes 111 extending respectively in the left and right directions. Figure 1 In the example shown, the support body 11 is substantially cylindrical, and each through hole 111 (ie, cell) has a substantially circular cross section perpendicular to the longitudinal direction. Figure 1 In FIG. 1 , the diameter of the through-holes 111 is drawn larger than the actual diameter, and the number of the through-holes 111 is drawn smaller than the actual number. The separation membrane 12 is formed on the inner peripheral surface of the through-hole 111, covering the substantially entire inner peripheral surface of the through-hole 111.

[0031] The length of the support 11 (ie, Figure 1 The length in the left-right direction of the support body 11 is, for example, 10 cm to 200 cm. The outer diameter of the support body 11 is, for example, 0.5 cm to 30 cm. The distance between the center axes of adjacent through holes 111 is, for example, 0.3 mm to 10 mm. The surface roughness (Ra) of the support body 11 is, for example, 0.1 μm to 5.0 μm, preferably 0.2 μm to 2.0 μm. In addition, the shape of the support body 11 can be, for example, a honeycomb, a flat plate, a tubular, a cylindrical, a columnar or a polygonal columnar shape. When the shape of the support body 11 is tubular or cylindrical, the thickness of the support body 11 is, for example, 0.1 mm to 10 mm.

[0032] The support body 11 is formed of ceramic. Examples of ceramic sintered bodies selected as the material for the support body 11 include alumina, silica, mullite, zirconia, titania, yttrium oxide, silicon nitride, and silicon carbide. In the present embodiment, the support body 11 includes at least one of alumina, silica, and mullite. The support body 11 may include an inorganic bonding material. As the inorganic bonding material, at least one of titania, mullite, easily sintered alumina, silica, glass frit, clay mineral, and easily sintered cordierite may be used.

[0033] 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 to be formed is, for example, 0.01 μm to 1 μm, preferably 0.05 μm to 0.5 μm. For example, the average pore diameter can be measured using a mercury porosimeter, a pore size distribution meter, or a nano-size pore size distribution meter. Regarding the overall pore size distribution of 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 to be formed is, for example, 20% to 60%.

[0034] The support body 11 has, for example, a multilayer structure in which a plurality of layers having different average pore diameters are stacked in the thickness direction. The average pore diameter and sintered particle size of the surface layer including the surface to be formed into the separation membrane 12 are smaller than the average pore diameter and sintered particle size of the layers other than the surface layer. The average pore diameter of the surface layer of the support body 11 is, for example, 0.01 μm to 1 μm, preferably 0.05 μm to 0.5 μm. In the case where the support body 11 has a multilayer structure, the materials of each layer can use the above-mentioned materials. The materials of the multiple layers forming the multilayer structure may be the same or different. It should be noted that, in the case where the support body 11 has a multilayer structure, the average pore diameter of the support body 11 refers to the average pore diameter of the surface layer including the surface to be formed into the separation membrane 12.

[0035] The separation membrane 12 is a porous membrane having micropores. The separation membrane 12 can separate a specific substance from a mixture of multiple substances by utilizing molecular sieving or other effects. Other substances are less likely to permeate the separation membrane 12 than the specific substance. In other words, the permeation rate of the other substance through the separation membrane 12 is lower than that of the specific substance.

[0036] The average film thickness of the separation membrane 12 is 2 μm or less. Thus, a high permeation rate can be achieved. The lower limit of the average film thickness of the separation membrane 12 is not particularly limited. From the viewpoint of improving separation performance, it is, for example, 0.2 μm, preferably 0.5 μm, and more preferably 0.7 μm. In the determination of the average film thickness of the separation membrane 12, a cross section perpendicular to the surface of the separation membrane 12 is exposed by, for example, cross-section grinding. In this cross section, a plurality of randomly determined fields of view (for example, 7 fields of view) are observed using a scanning electron microscope (SEM). The magnification of the SEM is, for example, 5000 times. The average film thickness of the separation membrane 12 in each field of view (field of view average film thickness) is determined, and the arithmetic average of the field of view average film thickness of the remaining fields of view except for the fields of view with the largest and smallest values ​​of the field of view average film thickness is obtained as the average film 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.

[0037] As described above, the separation membrane 12 is composed of MOF. That is, the separation membrane 12 is a MOF membrane. The separation membrane 12 is typically composed solely of MOF. However, depending on the manufacturing method, the separation membrane 12 may contain a small amount (e.g., 1% by mass or less) of substances other than MOF. The pore diameter of the MOF constituting the separation membrane 12 is, for example, 1 nm or less. This pore diameter can be calculated based on the skeleton structure of the MOF crystals. This pore diameter is smaller than the average pore diameter of the support 11 near the surface on which the separation membrane 12 is to be formed.

[0038] The average particle size of the MOF constituting the separation membrane 12 is, for example, 0.1 μm to 2 μm. The average particle size is preferably 1 μm or less, more preferably 0.5 μm or less. In the separation membrane 12 having a smaller average particle size of MOF, the grain boundary defects that form excessive gaps between the crystals of MOF can be reduced, thereby improving the separation performance. The average particle size of the MOF in this embodiment is the arithmetic average of the maximum diameters of a plurality of particles (e.g., 30 particles) obtained by cross-sectional observation using an SEM. The plurality of particles to be measured can be randomly selected on the SEM image.

[0039] A composite layer 13 in which MOF crystals have entered the pores of the support 11 is formed at the interface between the separation membrane 12 and the support 11 . Figure 2 In the figure, composite layer 13 is indicated by parallel oblique lines overlapping a portion of support 11. Composite layer 13 is a portion of support 11. The thickness of composite layer 13 is, for example, 2 μm or less. This can suppress a decrease in the transmission rate caused by the presence of composite layer 13. Composite layer 13 may not be present; the lower limit of the thickness of composite layer 13 is 0.

[0040] 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 (hereinafter referred to as the "depth direction") is determined near a measurement position along the direction of the interface between the support body 11 and the separation membrane 12. In detail, 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 body 11. The boundary position on the side opposite to the separation membrane 12 in the composite layer 13 is the edge of the MOF farthest from the separation membrane 12 in the depth direction among the MOFs present in the pores of the support body 11. The distance in the depth direction between the boundary position on the separation membrane 12 side of the composite layer 13 and the boundary position on the side opposite to the separation membrane 12 is obtained as the thickness of the composite layer 13 at the measurement position. In addition, the average of the thicknesses 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 separation membrane complex 1.

[0041] The MOF constituting the separation membrane 12 is composed of aluminum ions (Al 3+ ) and a ligand (organic ligand) coordinated to the aluminum ion. The ligand preferably has a high affinity for CO2 and includes, for example, 1H-pyrrole-2,5-dicarboxylic acid, 2,5-furandicarboxylic acid, or 3,5-pyridinedicarboxylic acid. Other ligands may be used depending on the type of substance to be separated. The powder X-ray diffraction (XRD) pattern of the MOF of separation membrane 12 exhibits peaks at all diffraction angles 2θ listed in Table 2.

[0042] Table 2

[0043]

[0044] Powder X-ray diffraction patterns were obtained using CuKα radiation as the radiation source in an X-ray diffraction apparatus. For example, a Rigaku Corporation X-ray diffraction apparatus (MiniFlex600) was used, with a tube voltage of 40 kV, a tube current of 15 mA, a scan rate of 0.5° / min, and a scan step of 0.02°. Furthermore, the divergence slit was set at 1.25°, the scattering slit was set at 1.25°, the receiving slit was set at 0.3 mm, the incident Soller slit was set at 5.0°, and the receiving Soller slit was set at 5.0°. A monochromator was not used, and a 0.015 mm thick nickel foil was used as a CuKβ filter.

[0045] Next, refer to Figure 3, an example of a manufacturing process for the separation membrane complex 1 is described. When manufacturing the separation membrane complex 1, first, seed crystals for manufacturing the separation membrane 12 are prepared (step S11). For example, MOF powder is generated by hydrothermal synthesis (solvothermal synthesis), and seed crystals are obtained from the MOF powder. The MOF powder can be generated by any or known manufacturing methods. The MOF powder can be used directly as seed crystals, or the powder can be processed by pulverization or the like to obtain seed crystals.

[0046] The average particle size (D50) of the seed crystals is preferably 0.5 μm or less. This can suppress the generation of grain boundary defects in the separation membrane 12 due to an excessively large average particle size of the MOF. The lower limit of the average particle size of the seed crystals is not particularly limited; 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 of the seed crystals can be measured, for example, by laser scattering.

[0047] Next, the porous support 11 is immersed in the dispersion obtained by dispersing the seed crystals, and the seed crystals are attached to the support 11 (step S12). Alternatively, the seed crystals are attached to the support 11 by bringing the dispersion obtained by dispersing the seed crystals into contact with the portion of the support 11 where the separation membrane 12 is to be formed. In this manner, a seed crystal-attached support is produced. The seed crystals may also be attached to the support 11 using other methods.

[0048] In addition, a synthetic solution (also called synthetic sol or raw material solution) for forming the separation membrane 12 is prepared and set aside (step S13). The preparation of the synthetic solution can be carried out before step S12 or at the same time as step S12. In the preparation of the synthetic solution, first, water, a monocarboxylate, a ligand and an organic solvent are mixed. Examples of monocarboxylates include formates such as sodium formate, lithium formate, potassium formate, and acetates such as sodium acetate. Monocarboxylic acids act as modulators in MOF synthesis and help improve crystallinity. Therefore, amino acids containing monocarboxylic acids (such as glycine, arginine, etc.) can be used. Regarding the ligand, a powder X-ray diffraction pattern having a peak at the diffraction angle 2θ described in Table 2 is obtained in the MOF synthesized using the ligand, and various organic compounds can be used. Preferred ligands are organic compounds with a high affinity for CO2, such as 1H-pyrrole-2,5-dicarboxylic acid, 2,5-furandicarboxylic acid or 3,5-pyridinedicarboxylic acid. Preferred organic solvents are organic compounds having a carbonyl group (carboxyl group, etc.), for example, N,N-dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), N-methylformamide, etc. Organic solvents not having a carbonyl group may also be used.

[0049] In the synthetic solution, the ratio of the amount of monocarboxylate to the amount of ligand (hereinafter also referred to as the "monocarboxylate / ligand ratio") is preferably 0.5 to 1.8. Without the addition of monocarboxylate, even if the heating and stirring treatment described later is carried out, the synthetic solution will become turbid, resulting in impaired uniformity and difficulty in generating MOF. On the other hand, if the monocarboxylate is added in excess, coordination defects in which a part of the ligand constituting MOF is missing will be easily formed as described later. In addition, the ratio of the amount of organic solvent to the amount of ligand (hereinafter also referred to as the "organic solvent / ligand ratio") is preferably 0.1 to 10. Without the addition of an organic solvent, the crystallinity of MOF decreases. On the other hand, if the organic solvent is added in excess, coordination defects will be easily formed as described later.

[0050] After obtaining a solution obtained by mixing water, a monocarboxylate, a ligand and an organic solvent, a heating and stirring treatment (aging) is performed in which the solution is heated and stirred. The heating temperature in the heating and stirring treatment is, for example, 20 to 100° C., preferably 40 to 80° C. The treatment time is, for example, 1 to 100 hours, preferably 1 to 12 hours. After the heating and stirring treatment is completed, an aluminum source (Al source) is mixed into the solution. Al sources are, for example, aluminum sulfate, aluminum chloride, aluminum nitrate, aluminum hydroxide, boehmite, and the like. Through the above operations, a synthetic solution for forming the separation membrane 12 is obtained. It should be noted that the mixing of the organic solvent into the solution does not necessarily need to be before the heating and stirring treatment, and can be during or after the heating and stirring treatment. That is, the organic solvent can be mixed into the above-mentioned solution at any time.

[0051] After the synthesis solution is prepared, the support 11 with the seed crystal attached is immersed in the synthesis solution. Thereafter, the synthesis solution is heated to start the hydrothermal synthesis. During the hydrothermal synthesis, MOF grows with the seed crystal as the nucleus, and a dense MOF membrane, i.e., the separation membrane 12, is formed on the support 11 (step S14). The synthesis temperature during the hydrothermal synthesis (the heating temperature of the synthesis solution) is, for example, 40 to 200°C, preferably 70 to 150°C. The hydrothermal synthesis time is, for example, 1 to 100 hours, preferably 1 to 50 hours.

[0052] After the hydrothermal synthesis is completed, the support 11 and separation membrane 12 are washed with pure water and then with ethanol, etc. Preferably, the washing with water and ethanol, etc., is repeated multiple times. The washed support 11 and separation membrane 12 are dried at, for example, 100°C. Through the above-described treatment, the separation membrane complex 1 described above is obtained.

[0053] Next, refer to Figure 4 and Figure 5 , separation of mixed substances using the separation membrane complex 1 will be described. Figure 4 It is a diagram showing the separation device 2. Figure 51 is a diagram showing a flow of separation of mixed substances by the separation device 2 .

[0054] In the separation device 2, a mixture containing multiple fluids (i.e., gases or liquids) is supplied to the separation membrane complex 1, and the highly permeable substance in the mixture is allowed to permeate through the separation membrane complex 1, thereby separating it from the mixture. Separation in the separation device 2 can be performed, for example, to extract the highly permeable substance from the mixture or to concentrate the less permeable substance.

[0055] The mixed substance (ie, mixed fluid) may be a mixed gas containing multiple gases, a mixed liquid containing multiple liquids, or a gas-liquid two-phase fluid containing both gas and liquid.

[0056] The mixed substance includes, for example, one or more substances selected from hydrogen (H2), helium (He), nitrogen (N2), oxygen (O2), water (H2O), carbon monoxide (CO), carbon dioxide (CO2), nitrogen oxides, ammonia (NH3), sulfur oxides, hydrogen sulfide (H2S), sulfur fluoride, mercury (Hg), arsine (AsH3), hydrogen cyanide (HCN), carbonyl sulfide (COS), C1-C8 hydrocarbons, organic acids, alcohols, thiols, esters, ethers, ketones and aldehydes.

[0057] Nitrogen oxides are compounds of nitrogen and oxygen. Examples of nitrogen oxides include nitric oxide (NO), nitrogen dioxide (NO2), nitrous oxide (also known as dinitrogen monoxide) (N2O), dinitrogen trioxide (N2O3), dinitrogen tetroxide (N2O4), and dinitrogen pentoxide (N2O5). X (Nox) gas.

[0058] Sulfur oxides are compounds of sulfur and oxygen. Examples of these sulfur oxides are sulfur dioxide (SO2) and sulfur trioxide (SO3), which are called SO X (Sox) gas.

[0059] Sulfur fluoride refers to a compound of fluorine and sulfur. Examples of the sulfur fluoride include sulfur difluoride (F-S-S-F, S=SF2), sulfur difluoride (SF2), sulfur tetrafluoride (SF4), sulfur hexafluoride (SF6) or sulfur decafluoride (SF6). 10 )wait.

[0060] C1 to C8 hydrocarbons refer to hydrocarbons with 1 or more and 8 or less carbon atoms. C3 to C8 hydrocarbons may be any of linear compounds, side chain compounds, and cyclic compounds. In addition, C2 to C8 hydrocarbons may be any of saturated hydrocarbons (i.e., hydrocarbons without double bonds and triple bonds in the molecule) and unsaturated hydrocarbons (i.e., hydrocarbons with double bonds and / or triple bonds in the molecule). Examples of C1 to C4 hydrocarbons include methane (CH4), ethane (C2H6), ethylene (C2H4), propane (C3H8), propylene (C3H6), n-butane (CH3(CH2)2CH3), isobutane (CH(CH3)3), 1-butene (CH2=CHCH2CH3), 2-butene (CH3CH=CHCH3), or isobutene (CH2=C(CH3)2).

[0061] The organic acid is a carboxylic acid or a sulfonic acid. Examples of carboxylic acids include formic acid (CH2O2), acetic acid (C2H4O2), oxalic acid (C2H2O4), acrylic acid (C3H4O2), or benzoic acid (C6H5COOH). Examples of sulfonic acids include ethanesulfonic acid (C2H6O3S). The organic acid may be a chain compound or a cyclic compound.

[0062] Examples of the alcohol include methanol (CH3OH), ethanol (C2H5OH), isopropyl alcohol (2-propanol) (CH3CH(OH)CH3), ethylene glycol (CH2(OH)CH2(OH)), and butanol (C4H9OH).

[0063] Thiols are organic compounds with hydrogenated sulfur (SH) at the end, and are also called thiol or thioalcohol. Examples of these thiols include methyl mercaptan (CH3SH), ethyl mercaptan (C2H5SH), and 1-propanethiol (C3H7SH).

[0064] The above-mentioned esters include formates and acetates, for example.

[0065] The above-mentioned ether is, for example, dimethyl ether ((CH3)2O), methyl ethyl ether (C2H5OCH3) or diethyl ether ((C2H5)2O).

[0066] The above-mentioned ketone is, for example, acetone ((CH3)2CO), methyl ethyl ketone (C2H5COCH3) or diethyl ketone ((C2H5)2CO).

[0067] The aldehyde mentioned above is, for example, acetaldehyde (CH3CHO), propionaldehyde (C2H5CHO), or butyraldehyde (C3H7CHO).

[0068] In the following description, an example is given in which the mixed substance separated by the separation device 2 is a mixed gas containing a plurality of gases.

[0069] The separation device 2 includes a separation membrane complex 1, a sealing portion 21, a housing 22, two sealing members 23, a supply unit 26, a first recovery unit 27, and a second recovery unit 28. The separation membrane complex 1, the sealing portion 21, and the sealing member 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 thereto.

[0070] The sealing portion 21 is installed in the longitudinal direction of the support body 11 (ie, Figure 4 The sealing portion 21 is a component that seals the two end portions on the longitudinal direction of the support body 11 and covers the two end faces in the longitudinal direction of the support body 11 and the outer peripheral surface near the two end faces. The sealing portion 21 prevents gas from flowing in and out relative to the two end faces of the support body 11. The sealing portion 21 is, for example, a plate-shaped component formed of glass or resin. The material and shape of the sealing portion 21 can be appropriately changed. It should be noted that the sealing portion 21 is provided with a plurality of openings that overlap with the plurality of through holes 111 of the support body 11, and therefore, the two ends in the longitudinal direction of each through hole 111 of the support body 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 the two ends.

[0071] The shape of the housing 22 is not limited, and it can be, for example, a substantially cylindrical member. The housing 22 is formed of, for example, stainless steel or carbon steel. The longitudinal direction of the housing 22 is substantially parallel to the longitudinal direction of the separation membrane complex 1. At one end of the longitudinal direction of the housing 22 (i.e., Figure 4 A supply port 221 is provided at the left end of the housing 22, 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. The supply port 221 is connected to the supply unit 26. The first discharge port 222 is connected to the first recovery unit 27. The second discharge port 223 is connected to the second recovery unit 28. The interior space of the housing 22 is a sealed space isolated from the space surrounding the housing 22.

[0072] Two sealing members 23 are disposed along the entire circumference of the separation membrane complex 1, near both ends in the longitudinal direction thereof, between the outer circumferential surface of the separation membrane complex 1 and the inner circumferential surface of the housing 22. Each sealing member 23 is a substantially annular member formed of a gas-impermeable material. For example, the sealing member 23 is an O-ring formed of a flexible resin. The sealing member 23 is in close contact with the outer circumferential surface of the separation membrane complex 1 and the inner circumferential surface of the housing 22 over its entire circumference. Figure 4 In the example shown, the sealing member 23 is in close contact with the outer peripheral surface of the sealing portion 21 and is indirectly in close contact with the outer peripheral surface of the separation membrane complex 1 via the sealing portion 21. The sealing member 23 and the outer peripheral surface of the separation membrane complex 1, as well as the sealing member 23 and the inner peripheral surface of the housing 22, are sealed, and gas is hardly or not allowed to pass through.

[0073] The supply unit 26 supplies the mixed gas to the interior space of the housing 22 through the supply port 221. The supply unit 26 is, for example, a blower or a pump that pressurizes the mixed gas toward the housing 22. The blower or pump includes a pressure regulating unit that regulates the pressure of the mixed gas supplied to the housing 22. The first recovery unit 27 and the second recovery unit 28 are, for example, storage containers that store the gas discharged from the housing 22 or blowers or pumps that transfer the gas.

[0074] When performing mixed gas separation, the separation membrane complex 1 is prepared by preparing the above-mentioned separation device 2 (step S21). Next, a mixed gas containing a plurality of gases having different permeabilities to the separation membrane 12 is supplied to the internal space of the housing 22 using the supply unit 26. For example, the main components of the mixed gas are CO2 and N2. The mixed gas may contain gases other than CO2 and N2. 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 for performing mixed gas separation is, for example, 10°C to 150°C.

[0075] The mixed gas supplied to the housing 22 from the supply unit 26 is introduced into each through hole 111 of the support body 11 from the left end of the separation membrane complex 1 in the figure as shown by arrow 251. The gas with high permeability in the mixed gas (for example, CO2, hereinafter referred to as "high permeability substance") passes through the separation membrane 12 and the support body 11 provided on the inner peripheral surface of each through hole 111 and is discharged from the outer peripheral surface of the support body 11. Thus, the high permeability substance is separated from the gas with low permeability (for example, N2, hereinafter referred to as "low permeability substance") in the mixed gas (step S22). The gas discharged from the outer peripheral surface of the support body 11 (hereinafter referred to as "permeated substance") 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).

[0076] Furthermore, the gas in the mixed gas other than the gas that has permeated the separation membrane 12 and the support 11 (hereinafter referred to as "non-permeable substances") passes through the through-holes 111 of the support 11 from the left to the right in the figure, as indicated by arrow 252, and is recovered by the first recovery unit 27 via the first discharge port 222. The pressure of the gas recovered by the first recovery unit 27 via the first discharge port 222 is, for example, substantially the same as the introduction pressure. The non-permeable substances may include, in addition to the low-permeability substances described above, high-permeability substances that do not permeate the separation membrane 12.

[0077] Next, separation membrane composites Examples 1 to 21 and Comparative Examples 1 to 7 are described. Table 3 shows the ligand type, seed crystal D50 value (average particle size), monocarboxylate / ligand ratio, organic solvent / ligand ratio, and heating and stirring conditions in Examples 1 to 21 and Comparative Examples 1 to 7.

[0078] Table 3

[0079]

[0080] <Preparation of Seed Crystals (1H-Pyrrole-2,5-dicarboxylic Acid)>

[0081] Mix 1.551 g of 1H-pyrrole-2,5-dicarboxylic acid and 1.36 g of sodium formate in 50 mL of deionized water to create a mixed solution. Stir the mixed solution at 50°C for 3 hours, cool it to room temperature, and add 3.333 g of aluminum sulfate octahydrate. Next, maintain the solution at 120°C for 12 hours. Separate the precipitate using a centrifuge and wash it three times with deionized water and ethanol. This procedure yields a powder of a MOF containing 1H-pyrrole-2,5-dicarboxylic acid as a ligand, which serves as a seed crystal.

[0082] <Preparation of Seed Crystals (2,5-Furandicarboxylic Acid)>

[0083] Mix 1.562 g of 2,5-furandicarboxylic acid and 1.36 g of sodium formate in 50 mL of deionized water to create a mixed solution. Stir the mixed solution at 50°C for 3 hours, cool it to room temperature, and add 2.413 g of aluminum chloride hexahydrate. Next, maintain the solution at 100°C for 12 hours. Separate the precipitate using a centrifuge and wash it three times with deionized water and ethanol. This procedure yields a powder of a MOF containing 2,5-furandicarboxylic acid as a ligand, which serves as a seed crystal.

[0084] <Preparation of Seed Crystals (3,5-Pyridinedicarboxylic Acid)>

[0085] Mix 1.67 g of 3,5-pyridinedicarboxylic acid and 1.36 g of sodium formate in 50 mL of deionized water to create a mixed solution. Stir the mixed solution at 50°C for 3 hours, cool it to room temperature, and add 3.333 g of aluminum sulfate octahydrate. Next, maintain the solution at 120°C for 12 hours. Separate the precipitate using a centrifuge and wash it three times with deionized water and ethanol. This procedure yields a powder of a MOF containing 3,5-pyridinedicarboxylic acid as a ligand, which serves as a seed crystal.

[0086] <Supporting Seed Crystals on Ceramic Support>

[0087] Place 1 g of the resulting seed crystals into a glass vial containing zirconia balls, and then add 9 g of water. The glass vial is secured to a ball mill stand, and the seed crystals are pulverized at 60 rpm for 5 to 24 hours to obtain seed crystals with an average particle size (D50) of 0.33 to 0.50 μm. These seed crystals are then supported on a ceramic support.

[0088] (Example 1)

[0089] To 150 mL of deionized water, 1.551 g of 1H-pyrrole-2,5-dicarboxylic acid, 1.22 g of sodium formate, and 0.58 g of N,N-dimethylformamide (an organic solvent) were added to prepare a mixed solution. The mixed solution was heated to 60°C and stirred for 2 hours (heat-stirring treatment). After confirming that the mixed solution had become transparent, it was cooled to room temperature. Then, 3.333 g of aluminum sulfate octahydrate was added to the mixed solution to prepare a synthesis solution. The monocarboxylate / ligand ratio (mol ratio, the same below) in the synthesis solution was 1.8, and the organic solvent / ligand ratio (mol ratio, the same below) was 0.8. Next, a ceramic support carrying seed crystals containing 1H-pyrrole-2,5-dicarboxylic acid (average particle size 0.33 μm) and the synthesis solution were placed in a Teflon (registered trademark) container and hydrothermal synthesis was carried out at 100°C for 20 hours. The obtained separation membrane complex was washed three times with deionized water and ethanol, and then dried.

[0090] (Example 2)

[0091] The procedure was the same as in Example 1 except that the temperature of the hydrothermal synthesis was changed to 80°C.

[0092] (Example 3)

[0093] The same procedures as in Example 1 were followed except that the ratio of monocarboxylate / ligand was changed to 1.

[0094] (Example 4)

[0095] The same procedures as in Example 1 were followed except that the ratio of monocarboxylate salt to ligand was changed to 0.6.

[0096] (Example 5)

[0097] The same procedures as in Example 1 were followed except that the heating temperature in the heating and stirring treatment of the mixed solution was changed to 40° C. and the stirring time was changed to 5 hours.

[0098] (Example 6)

[0099] The same procedures as in Example 1 were followed except that the heating temperature in the heating and stirring treatment of the mixed solution was changed to 80° C. and the stirring time was changed to 12 hours.

[0100] (Example 7)

[0101] The same procedures as in Example 1 were followed except that the ratio of organic solvent to ligand was changed to 0.1.

[0102] (Example 8)

[0103] The same procedures as in Example 1 were followed except that the ratio of organic solvent to ligand was changed to 8.

[0104] (Example 9)

[0105] The procedure was the same as in Example 1 except that the hydrothermal synthesis time was changed to 10 hours and the organic solvent was changed to N-methylformamide.

[0106] (Example 10)

[0107] The same procedures as in Example 1 were followed except that the average particle size of the seed crystals supported on the ceramic support was changed to 0.50 μm.

[0108] (Example 11)

[0109] 1.562 g of 2,5-furandicarboxylic acid, 1.22 g of sodium formate, and 0.58 g of N,N-dimethylformamide as an organic solvent were added to 150 mL of deionized water to prepare a mixed solution. The mixed solution was heated to 60°C and stirred for 2 hours (heat-stirring treatment). After confirming that the mixed solution had become transparent, it was cooled to room temperature. Then, 2.413 g of aluminum chloride hexahydrate was added to the mixed solution to prepare a synthetic solution. The ratio of monocarboxylate / ligand in the synthetic solution was 1.8, and the ratio of organic solvent / ligand was 0.8. Next, a ceramic support carrying seed crystals containing 2,5-furandicarboxylic acid (average particle size 0.25 μm) and the synthetic solution were placed in a Teflon container and hydrothermal synthesis was carried out at 80°C for 20 hours. The resulting separation membrane complex was washed three times with deionized water and ethanol, and then dried.

[0110] (Example 12)

[0111] The same procedures as in Example 11 were carried out except that the heating temperature in the heating and stirring treatment of the mixed solution was changed to 40°C.

[0112] (Example 13)

[0113] The same procedures as in Example 11 were carried out except that the ratio of monocarboxylate / ligand was changed to 1.

[0114] (Example 14)

[0115] The same procedures as in Example 11 were carried out except that the ratio of organic solvent to ligand was changed to 2.

[0116] (Example 15)

[0117] To 150 mL of deionized water, 1.67 g of 3,5-pyridinedicarboxylic acid, 1.22 g of sodium formate, and 0.58 g of N,N-dimethylformamide (an organic solvent) were added to prepare a mixed solution. The mixed solution was heated to 60°C and stirred for 2 hours (heat-stirring treatment). After confirming that the mixed solution had become transparent, it was cooled to room temperature. Then, 3.333 g of aluminum sulfate octahydrate was added to the mixed solution to prepare a synthesis solution. The ratio of monocarboxylate / ligand in the synthesis solution was 1.8, and the ratio of organic solvent / ligand was 0.8. Next, a ceramic support carrying seed crystals containing 3,5-pyridinedicarboxylic acid (average particle size 0.35 μm) and the synthesis solution were placed in a Teflon container and hydrothermal synthesis was carried out at 100°C for 20 hours. The resulting separation membrane complex was washed three times with deionized water and ethanol, and then dried.

[0118] (Example 16)

[0119] The same procedures as in Example 15 were carried out except that the heating temperature in the heating and stirring treatment of the mixed solution was changed to 40°C.

[0120] (Example 17)

[0121] The same procedures as in Example 15 were carried out except that the ratio of monocarboxylate / ligand was changed to 1.

[0122] (Example 18)

[0123] The same procedures as in Example 15 were carried out except that the ratio of organic solvent to ligand was changed to 2.

[0124] (Example 19)

[0125] To 150 mL of deionized water, 0.775 g of 1H-pyrrole-2,5-dicarboxylic acid, 0.781 g of 2,5-furandicarboxylic acid, 1.26 g of lithium formate monohydrate, and 0.36 g of N,N-dimethylformamide as an organic solvent were added to prepare a mixed solution. The mixed solution was heated to 60°C and stirred for 2 hours (heat-stirring treatment). After confirming that the mixed solution had become transparent, it was cooled to room temperature. Then, 3.333 g of aluminum sulfate octahydrate was added to the mixed solution to prepare a synthesis solution. The ratio of monocarboxylate / ligand in the synthesis solution was 1.5, and the ratio of organic solvent / ligand was 0.5. Next, a ceramic support carrying the same seed crystals as in Example 1 (including 1H-pyrrole-2,5-dicarboxylic acid seed crystals) and the above synthesis solution were placed in a Teflon container and hydrothermal synthesis was carried out at 100°C for 10 hours. The resulting separation membrane composite was washed three times with deionized water and ethanol, and then dried.

[0126] (Example 20)

[0127] To 150 mL of deionized water, 0.775 g of 1H-pyrrole-2,5-dicarboxylic acid, 0.835 g of 3,5-pyridinedicarboxylic acid, 1.51 g of sodium acetate, and 0.36 g of N,N-dimethylformamide (organic solvent) were added to prepare a mixed solution. The mixed solution was heated to 60°C and stirred for 2 hours (heat-stirring treatment). After confirming that the mixed solution had become transparent, it was cooled to room temperature. Then, 3.333 g of aluminum sulfate octahydrate was added to the mixed solution to prepare a synthesis solution. The ratio of monocarboxylate / ligand in the synthesis solution was 1.5, and the ratio of organic solvent / ligand was 0.5. Next, a ceramic support carrying the same seed crystals as in Example 1 (including 1H-pyrrole-2,5-dicarboxylic acid seed crystals) and the above synthesis solution were placed in a Teflon container and hydrothermal synthesis was carried out at 100°C for 20 hours. The resulting separation membrane complex was washed three times with deionized water and ethanol, and then dried.

[0128] (Example 21)

[0129] To 150 mL of deionized water, 0.781 g of 2,5-furandicarboxylic acid, 0.781 g of 3,5-pyridinedicarboxylic acid, 1.47 g of potassium formate, and 0.58 g of N,N-dimethylformamide as an organic solvent were added to prepare a mixed solution. The mixed solution was heated to 60°C and stirred for 2 hours (heat-stirring treatment). After confirming that the mixed solution had become transparent, it was cooled to room temperature. Then, 3.333 g of aluminum sulfate octahydrate was added to the mixed solution to prepare a synthetic solution. The ratio of monocarboxylate / ligand in the synthetic solution was 1.5, and the ratio of organic solvent / ligand was 0.8. Next, a ceramic support carrying the same seed crystals as in Example 11 (including 2,5-furandicarboxylic acid seed crystals) and the synthetic solution were placed in a Teflon container and hydrothermal synthesis was carried out at 100°C for 20 hours. The resulting separation membrane complex was washed three times with deionized water and ethanol, and then dried.

[0130] (Comparative Example 1)

[0131] The same procedures as in Example 1 were followed except that the heating and stirring treatment was not performed.

[0132] (Comparative Example 2)

[0133] The procedure was the same as in Comparative Example 1, except that the ratio of monocarboxylate / ligand was changed to 0 (ie, no monocarboxylate was added). In Comparative Example 2, no separation membrane was formed on the support.

[0134] (Comparative Example 3)

[0135] The same procedures as in Example 1 were followed except that the ratio of organic solvent to ligand was changed to 12.

[0136] (Comparative Example 4)

[0137] The procedure was the same as in Example 1 except that the ratio of organic solvent to ligand was changed to 0 (ie, no organic solvent was added).

[0138] (Comparative Example 5)

[0139] A synthetic solution was prepared using the method and composition described in "Multivariate Polycrystalline Metal-Organic Framework Membranes for CO2 / CH4 Separation" by Weidong Fan et al. (J. Am. Chem. Soc., 2021, Vol. 143, pp. 17716-17723) (reference 1), and film formation was performed without using a seed crystal in the same manner as in reference 1. In Comparative Example 5, the entire surface of the support on which the film was to be formed was not covered with the separation membrane.

[0140] (Comparative Example 6)

[0141] The same procedure as in Comparative Example 5 was repeated except that the same seed crystals as in Example 11 (seed crystals containing 2,5-furandicarboxylic acid) were used.

[0142] (Comparative Example 7)

[0143] The same procedures as in Example 15 were carried out except that the heating and stirring treatment was not performed.

[0144] <Measurement and evaluation of separation membrane complexes>

[0145] Various measurements were performed on the separation membrane composites of Examples 1 to 21 and Comparative Examples 1 to 7. Table 4 shows the average membrane thickness of the separation membrane, the thickness of the composite layer, the average particle size of the separation membrane, the CO2 permeation rate, and the SF6 / He permeation rate ratio.

[0146] Table 4

[0147]

[0148] The average membrane thickness of the separation membrane, the thickness of the composite layer, and the average particle size of the separation membrane were measured by cross-sectional observation using an SEM as described above. In Examples 1 to 21, the average membrane thickness of the separation membrane was 2 μm or less, and the thickness of the composite layer was 2 μm or less. In Comparative Examples 1, 3 to 7, the thickness of the composite layer was 2 μm or less, but the average membrane thickness of the separation membrane reached 2 μm or more. As described above, in Comparative Example 2, no separation membrane was generated on the support. In Examples 1 to 21, the average particle size of the separation membrane was less than 0.5 μm, but in Comparative Examples 1, 5 to 7, the average particle size of the separation membrane was greater than 2 μm. It should be noted that the MOF constituting the separation membranes of Examples 1 to 21 was subjected to powder X-ray diffraction measurement, and the obtained powder X-ray diffraction pattern had a peak at the diffraction angle 2θ described in Table 2 above.

[0149] In addition, the permeation rate of each gas was measured using the above-mentioned separation device 2 for CO2 gas, SF6 gas, and He gas. It should be noted that the permeation rate was not measured in Comparative Examples 2 and 5, where poor separation membrane formation occurred. In Examples 1 to 21, the CO2 permeation rate was 1000 GPU or more, achieving a high permeation rate. On the other hand, in Comparative Examples 6 and 7, the CO2 permeation rate was less than 1000 GPU. It should be noted that 1 GPU is 1×10 －6 cm 3 (STP) / (cm 2 ·sec·cmHg). In addition, in Examples 1 to 21, the ratio of the permeation rate of SF6 gas to the permeation rate of He gas, i.e., the SF6 / He permeation rate ratio, was 0.020 or less. On the other hand, in all the comparative examples (Comparative Examples 1, 3, 4, 6, and 7) in which the permeation rate was measured, the SF6 / He permeation rate ratio was greater than 0.020.

[0150] However, if the separation membrane contains a large number of grain boundary defects (which create excessively large gaps between MOF crystals) or coordination defects (which cause a portion of the ligands that constitute the MOF to be missing), a high separation factor cannot be achieved. In the separation membrane described above, grain boundary defects and coordination defects are expected to have defect sizes of 0.5 nm or larger. Therefore, in this example, the defect content in the separation membrane was evaluated by the permeation rate ratio between SF6 gas, which has a dynamic molecular diameter of 0.56 nm, and He gas, which has a dynamic molecular diameter significantly smaller than SF6 gas. As described above, in Examples 1 to 21, the SF6 / He permeation rate ratio was below 0.020, indicating almost no SF6 gas permeation. Therefore, it can be said that the separation membrane composites of Examples 1 to 21 have reduced grain boundary defects and coordination defects, resulting in high separation factors. In contrast, in all comparative examples where permeation rates were measured, the SF6 / He permeation rate ratio exceeded 0.020, indicating significant permeation of SF6 gas. Therefore, in the separation membrane composites of the comparative examples, the separation factor was reduced due to the influence of grain boundary defects and coordination defects.

[0151] Here, the reasons why the SF 6 / He permeation rate ratio becomes smaller (the separation coefficient increases) in the separation membrane composites of Examples 1 to 21 are examined. Figure 6A and Figure 6B This is a diagram for explaining the synthesis of a separation membrane 92 of a comparative example having a relatively large average particle size. Figure 7A and Figure 7B This is a diagram for explaining the synthesis of the separation membranes 12 of Examples 1 to 21 having a relatively small average particle size. Figure 6A and Figure 7A Shows the state at the initial stage of membrane synthesis, Figure 6B and Figure 7B The state when the film synthesis is completed is shown.

[0152] It is believed that in the synthesis of the separation membrane 92 of the comparative example, Figure 6A As shown in FIG. 1 , in the early stage of film synthesis, the particle size of MOF crystals 91 becomes larger. In this case, the gaps between MOF crystals 91 also become larger, and grain boundary defects are easily generated. In order to fill the gaps between MOF crystals 91, as shown in FIG. Figure 6B As shown, it is necessary to grow MOF crystals 91 significantly, which increases the thickness of separation membrane 92. In other words, the separation coefficient decreases in a separation membrane having an average thickness of approximately 2 μm.

[0153] On the other hand, in Examples 1 to 21, since the separation membrane 12 is synthesized by the secondary growth method using seed crystals with a small average particle size (for example, 0.5 μm or less), Figure 7A As shown in FIG, in the initial stage of film synthesis, the particle size of MOF crystals 91 is small. Therefore, the gaps between MOF crystals 91 are also small, and grain boundary defects are less likely to occur. In addition, when the film synthesis is completed with an average film thickness of less than 2 μm, as shown in FIG. Figure 7BAs shown, the average particle size of the separation membrane 12 (the average particle size of the MOF crystals 91 ) is also maintained at a low level of 0.1 to 2 μm, and the generation of grain boundary defects is suppressed.

[0154] The reason why the average particle size of the separation membrane becomes smaller may not be clear, but in Comparative Examples 1, 6, and 7, which were not subjected to heating and stirring treatment, the average particle size was greater than 2μm, so it is believed that the heating and stirring treatment is helpful. It is believed that: during the heating and stirring treatment, the ligand used as the raw material of the synthetic solution is heated and dissolved, and the precursor of the MOF in the synthetic solution is adsorbed on the seed crystal and stabilized, which is speculated to affect the formation of the MOF membrane as described above. In the separation membrane composites of Examples 1 to 21, by reducing the average particle size, the average membrane thickness of the separation membrane can be made thinner (less than 2μm) and a high permeation rate can be easily achieved. In addition, the grain boundary defects can be reduced to make the SF6 / He permeation rate ratio less than 0.020, that is, a high separation factor is obtained. In fact, in this separation membrane composite, the thickness of the composite layer of the support body and MOF is also less than 2μm, and the permeation rate of CO2 gas is more than 1000GPU.

[0155] However, it is believed that in the synthesis of MOF membranes, the organic solvent (and monocarboxylic acid) competes with the ligand and repeatedly coordinates / dissociates with respect to the metal ions, slowing down the growth rate of the crystals and obtaining a highly crystalline MOF. Therefore, when no organic solvent is added, the crystallinity of the MOF decreases. On the other hand, it is believed that if an excessive amount of organic solvent is added, the MOF is formed in a state of organic solvent coordination, and coordination defects are easily formed (see Comparative Example 3). In Examples 1 to 21, by making the mol ratio of the organic solvent containing the carbonyl group to the ligand (the ratio of organic solvent to ligand) in the synthetic solution be 0.1 to 10, the coordination defects can be reduced, and a highly crystalline MOF can be obtained, thereby obtaining a high separation factor.

[0156] In addition, it is believed that if a monocarboxylate is not added to the synthetic solution, deprotonation of the ligand is less likely to occur, resulting in a turbid synthetic solution and impaired uniformity, making it difficult to form a separation membrane (see Comparative Example 2). On the other hand, it is believed that if an excessive amount of monocarboxylate is added, the MOF is formed in a state coordinated by the monocarboxylic acid, which easily forms coordination defects (see Comparative Example 6). In Examples 1 to 21, by setting the monocarboxylate / ligand ratio in the synthetic solution to 0.5 to 1.8, coordination defects can be reduced, and the uniformity of the synthetic solution can be ensured, thereby obtaining a suitable separation membrane.

[0157] As described above, the separation membrane complex 1 comprises: a porous support 11 formed of ceramic; and a separation membrane 12 provided on the support 11 and formed of a MOF. The average thickness of the separation membrane 12 is 2 μm or less. The MOF is composed of aluminum ions and ligands coordinated with the aluminum ions. The powder X-ray diffraction pattern of the MOF has a peak at the diffraction angle 2θ listed in Table 2 above. The separation membrane complex 1 has an SF6 / He permeation rate ratio of 0.020 or less. This separation membrane complex 1 can achieve both a high separation coefficient and a high permeation rate.

[0158] The average particle size of MOF is preferably 0.1 μm to 2 μm. This can reduce grain boundary defects in the thin separation membrane 12 and improve the separation coefficient.

[0159] Preferably, the ligand of the MOF contains any one of 1H-pyrrole-2,5-dicarboxylic acid, 2,5-furandicarboxylic acid, or 3,5-pyridinedicarboxylic acid. By using a ligand with high affinity for CO2, the permeation rate of CO2 gas can be increased.

[0160] The thickness of the composite layer 13 of the support 11 and MOF is preferably 2 μm or less. This allows a higher permeation rate to be achieved in the separation membrane complex 1 .

[0161] Preferably, the CO2 gas permeation rate is 1000 GPU or higher. This allows for good separation of CO2 gas. Depending on the application of the separation membrane complex 1, the CO2 gas permeation rate may be less than 1000 GPU.

[0162] The method for manufacturing the separation membrane complex 1 includes the following steps: attaching a seed crystal formed of MOF to a porous support 11 (step S12), preparing a synthesis solution (step S13), immersing the support 11 in the synthesis solution and using hydrothermal synthesis to grow MOF from the seed crystal to form a separation membrane 12 on the support 11 (step S14). Step S13 includes: heating and stirring a solution obtained by mixing water, a monocarboxylate and a ligand while stirring. In step S13, an Al source is mixed into the solution after the heating and stirring treatment, and an organic solvent is mixed into the solution at an arbitrary time. In the separation membrane complex 1 in which the separation membrane 12 is formed on the support 11, the permeation rate ratio of SF6 / He is less than 0.020. As a result, a separation membrane complex 1 with a high separation coefficient and permeation rate can be provided.

[0163] However, conventional MOF synthesis uses large amounts of organic solvents such as methanol, ethanol, and DMF, increasing the environmental burden. On the other hand, synthesis without an organic solvent fails to properly form a MOF membrane. In contrast, in a preferred method for producing the separation membrane complex 1, the organic solvent is an organic compound containing a carbonyl group, and the ratio of the amount of organic solvent to the amount of ligand in the synthesis solution is 0.1 to 10. This allows for proper MOF membrane formation while reducing the amount of organic solvent used and lowering the environmental burden.

[0164] Preferably, the ratio of the amount of the monocarboxylate to the amount of the ligand in the synthesis solution is 0.5 to 1.8. This allows for proper formation of the MOF membrane and reduces coordination defects, thereby improving the separation coefficient.

[0165] The above-mentioned separation membrane complex 1 and the method for producing the separation membrane complex 1 can be modified in various ways.

[0166] When the separation membrane complex 1 achieves a high separation coefficient and a high permeation rate, the average particle size of the MOF can be within the range of 0.1 μm to 2 μm, and the thickness of the composite layer 13 of the support 11 and MOF can be greater than 2 μm. Similarly, in the synthesis solution, the organic solvent / ligand ratio can be within the range of 0.1 to 10, and the monocarboxylate / ligand ratio can be within the range of 0.5 to 1.8.

[0167] In the production of the separation membrane complex 1, when the synthesis solution contains two or more ligands (see Examples 19-21), the ligand contained in the seed MOF may be different from the two or more ligands. Alternatively, powders of multiple MOFs with different ligands may be mixed and used as seed crystals. When the synthesis solution contains only one ligand, the ligand contained in the seed MOF may be the same as or different from the one ligand.

[0168] The separation membrane complex 1 may further include a functional membrane or a protective membrane in addition to the support 11 and the separation membrane 12, which is laminated on the separation membrane 12. Such a functional membrane or protective membrane may be an inorganic membrane such as a zeolite membrane, a silica membrane, or a carbon membrane, or an organic membrane such as a polyimide membrane or an organosilicon membrane. Furthermore, a substance that readily adsorbs specific molecules such as CO2 may be added to the functional membrane or protective membrane laminated on the separation membrane 12.

[0169] The separation membrane complex 1 can be produced by methods other than the above-mentioned production methods.

[0170] In the separation device 2 and the separation method, substances other than the substances exemplified in the above description can be separated from the mixed substance.

[0171] The configurations in the above-described embodiment and various modifications may be appropriately combined as long as they do not contradict each other.

[0172] While the invention has been described in detail, the above description is illustrative and not restrictive, and it is understood that numerous modifications and variations may be employed without departing from the scope of the invention.

[0173] Industrial applicability

[0174] The separation membrane complex of the present invention can be utilized in various fields as a separation membrane or adsorption membrane for various substances.

[0175] Explanation of symbols

[0176] 1 Separation membrane complex

[0177] 11 support body

[0178] 12 Separation membrane

[0179] 13 composite layers

[0180] Steps S11 to S14, S21, and S22

Claims

1. A separation membrane complex comprising: a porous support body formed of ceramics; and a separation membrane provided on the support and formed of a metal organic structure; The average thickness of the separation membrane is 2 μm or less. The metal organic structure is composed of aluminum ions and ligands coordinated with the aluminum ions, The powder X-ray diffraction pattern of the metal organic structure has a peak at the diffraction angle 2θ described in the following table. The transmission rate ratio of SF6 / He is less than 0.

020. Table 1 2. The separation membrane complex according to claim 1, wherein The average particle size of the metal organic structure is 0.1 μm to 2 μm.

3. The separation membrane complex according to claim 1, wherein The ligand of the metal organic structure includes any one of 1H-pyrrole-2,5-dicarboxylic acid, 2,5-furandicarboxylic acid or 3,5-pyridinedicarboxylic acid.

4. The separation membrane complex according to claim 1, wherein The thickness of the composite layer of the support and the metal-organic structure is less than 2 μm.

5. The separation membrane complex according to any one of claims 1 to 4, wherein The permeation rate of CO2 gas is above 1000 GPU.

6. A method for producing a separation membrane complex, comprising the following steps: a) attaching a seed crystal formed of a metal organic structure to a porous support; b) preparing a synthesis solution; and c) immersing the support in the synthesis solution, growing the metal organic structure from the seed crystal by hydrothermal synthesis, and forming a separation membrane on the support, The step b) includes heating and stirring a solution obtained by mixing water, a monocarboxylate and a ligand while heating the solution. In the step b), the aluminum source is mixed into the solution after the heating and stirring treatment, and the organic solvent is mixed into the solution at an arbitrary timing. In the separation membrane composite including the separation membrane formed on the support, a permeation rate ratio of SF6 / He is 0.020 or less.

7. The method for producing a separation membrane complex according to claim 6, wherein: The organic solvent is an organic compound having a carbonyl group, In the synthetic solution, the ratio of the amount of the organic solvent to the amount of the ligand is 0.1 to 10.

8. The method for producing a separation membrane complex according to claim 6 or 7, wherein In the synthetic solution, the ratio of the amount of the monocarboxylate to the amount of the ligand is 0.5 to 1.8.

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