Separation membrane composite body and method for producing separation membrane composite body

Abstract

This separation membrane composite body (1) comprises: a porous support (11) which is formed of a ceramic; and a separation membrane (12) which is provided on the support (11) and is composed of a metal organic structure. The average film thickness of the separation membrane (12) is 2 μm or less. The metal organic structure is composed of an aluminum ion and a ligand that is coordinated to the aluminum ion. The powder X-ray diffraction pattern of the metal organic structure has a peak at a specific diffraction angle 2θ. With respect to this separation membrane composite body (1), the permeation rate ratio of SF6 / He is 0.020 or less. This separation membrane composite body (1) is capable of achieving both a high separation coefficient and a high permeation rate.

Description

Separation membrane composite and method for producing the separation membrane composite

[0001] The present invention relates to a separation membrane composite and a method for manufacturing a separation membrane composite. [Reference to Related Applications] This application claims the benefit of priority from Japanese Patent Application JP2023-37303, filed on March 10, 2023, the entire disclosure of which is incorporated herein by reference.

[0002] In the global trend toward carbon neutrality, CO contained in industrial exhaust gases emitted from factories, etc. ２ Technology to separate and recover CO ２ / N ２ There is a growing social need for separation of CO2. Separation by molecular sieving mechanism using high silica zeolite DDR type zeolite membrane or CHA type zeolite membrane has a high CO2 content. ２ / N ２ Since it is difficult to obtain a separation factor, in addition to the molecular sieve mechanism, CO ２ There is a demand for a separation membrane that can achieve a high separation factor by imparting affinity to the membrane.

[0003] Metal organic frameworks (MOFs) are porous materials with a large surface area, and are applicable to a variety of applications, including gas adsorption. Furthermore, by forming a membrane on a porous support, similar to a zeolite membrane, MOFs are expected to be used in gas and liquid separation. MOFs have small pore diameters and are suitable for CO ２ By using MOFs with ligands that have high affinity for CO ２ / N ２For example, in "Multivariate Polycrystalline Metal-Organic Framework Membranes for CO2 / CH4 Separation" (J. Am. Chem. Soc., 2021, Vol. 143, pp. 17716-17723) (Reference 1) by Weidong Fan and nine others 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, pp. 100005) (Reference 2) by Chung-Kai Chang and seven others, a structure in which an MOF membrane is formed on a ceramic support is disclosed, and CO ２ / N ２ or CO ２ / CH ４ The permeation rate ratio of 100% to 100% is relatively high.

[0004] Incidentally, when it comes to the performance of a separation membrane, not only the separation factor but also the permeation rate (ease of permeation of highly permeable substances) is important. Increasing the permeation rate can reduce the number of separation membrane composites required to construct a separation device, thereby reducing the manufacturing cost of the separation device and making it more compact. However, the MOF membranes of Non-Patent Documents 1 and 2 have a large thickness, resulting in a low permeation rate. While reducing the thickness of the MOF membrane is considered to increase the permeation rate, the effects of grain boundary defects, which form excessively large gaps between MOF crystals, and coordination defects, which are the absence of some of the ligands that make up the MOF, are usually significant, making it impossible to achieve a high separation factor. Therefore, there is a need for a separation membrane composite that achieves both a high separation factor and a high permeation rate.

[0005] An object of the present invention is to provide a separation membrane composite having a high separation factor and a high permeation rate.

[0006] A first aspect of the present invention is a separation membrane composite, comprising: a porous support formed of ceramic; and a separation membrane provided on the support and made of a metal-organic framework, wherein the separation membrane has an average thickness of 2 μm or less; the metal-organic framework comprises aluminum ions and ligands coordinated to the aluminum ions; and the powder X-ray diffraction pattern of the metal-organic framework has peaks at diffraction angles 2θ listed in the table below, and the metal-organic framework is SF ６ The permeation rate ratio of HCl / He is 0.020 or less.

[0007]

[0008] According to the present invention, a separation membrane composite having a high separation factor and a high permeation rate can be provided.

[0009] A second aspect of the present invention is the separation membrane composite of the first aspect, wherein the average particle size of the metal organic framework is 0.1 μm to 2 μm.

[0010] A third aspect of the present invention is the separation membrane composite of the first or second aspect, wherein the ligand of the metal organic framework includes any one of 1H-pyrrole-2,5-dicarboxylic acid, 2,5-furandicarboxylic acid, and 3,5-pyridinedicarboxylic acid.

[0011] A fourth aspect of the present invention is the separation membrane composite of any one of the first to third aspects, wherein the thickness of the composite layer of the support and the metal organic framework is 2 μm or less.

[0012] A fifth aspect of the present invention is the separation membrane composite of any one of the first to fourth aspects, ２ The gas permeation rate is 1000 GPU or more.

[0013] A sixth aspect of the invention is a method for producing a separation membrane composite, comprising: a) a step of attaching seed crystals made of a metal-organic framework onto a porous support; b) a step of preparing a synthesis solution; and c) a step of immersing the support in the synthesis solution and growing a metal-organic framework from the seed crystals by hydrothermal synthesis to form a separation membrane on the support, wherein the b) step includes a heating and stirring treatment in which a solution obtained by mixing water, a monocarboxylate, and a ligand is heated and stirred, and 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 timing, and the separation membrane composite in which the separation membrane is formed on the support is a separation membrane composite comprising: SF ６ The permeation rate ratio of HCl / He is 0.020 or less.

[0014] A seventh aspect of the invention is the method for producing a separation membrane composite according to the sixth aspect, wherein the organic solvent is an organic compound having a carbonyl group, and the ratio of the amount of substance of the organic solvent to the amount of substance of the ligand in the synthesis solution is 0.1 to 10.

[0015] An eighth aspect of the present invention is the method for producing a separation membrane composite according to the sixth or seventh aspect, wherein in the synthesis solution, the ratio of the amount of substance of the monocarboxylate to the amount of substance of the ligand is 0.5 to 1.8.

[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 separation membrane composite; FIG. 2 is a cross-sectional view showing an enlarged portion of the separation membrane composite; FIG. 3 is a diagram showing the flow of manufacturing a separation membrane composite; FIG. 4 is a diagram showing a separation device; FIG. 5 is a diagram showing the flow of separation of mixed substances by a separation device; FIG. 6 is a diagram for explaining the synthesis of a separation membrane of a comparative example; FIG. 7 is a diagram for explaining the synthesis of a separation membrane; FIG. 8 is a diagram for explaining the synthesis of a separation membrane; FIG. 9 is a diagram for explaining the synthesis of a separation membrane.

[0018] FIG. 1 is a cross-sectional view of a separation membrane composite 1. FIG. 2 is a cross-sectional view showing an enlarged portion of the separation membrane composite 1. The separation membrane composite 1 includes a porous support 11 and a separation membrane 12 provided on the support 11. As described below, the separation membrane 12 is a MOF membrane made of a metal-organic framework (hereinafter referred to as "MOF"), and the separation membrane composite 1 is a MOF membrane composite. A MOF membrane is at least a membrane of MOFs formed on the surface of a support 11, and does not include a membrane in which MOF particles are simply dispersed in an organic film. In FIG. 1, the separation membrane 12 is depicted with a thick line. In FIG. 2, the separation membrane 12 is depicted with parallel diagonal lines. Furthermore, in FIG. 2, the thickness of the separation membrane 12 is depicted thicker than it actually is.

[0019] The support 11 is a porous member that is permeable to gas and liquid. In the example shown in FIG. 1 , the support 11 is a monolithic support having a single, continuous columnar body formed integrally with the support 11, and a plurality of through-holes 111 extending in the longitudinal direction (i.e., the left-right direction in FIG. 1 ). In the example shown in FIG. 1 , the support 11 is substantially cylindrical. The cross section perpendicular to the longitudinal direction of each through-hole 111 (i.e., cell) is, for example, substantially circular. In FIG. 1 , the diameter of the through-hole 111 is drawn larger than in reality, and the number of through-holes 111 is drawn smaller than in reality. The separation membrane 12 is formed on the inner circumferential surface of the through-hole 111 and covers the inner circumferential surface of the through-hole 111 over substantially the entire surface.

[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 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 columnar 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 made of ceramic. Examples of ceramic sintered bodies selected as the material of the support 11 include alumina, silica, mullite, zirconia, titania, yttria, silicon nitride, and silicon carbide. In this embodiment, the support 11 contains at least one of alumina, silica, and mullite. The support 11 may contain an inorganic binder. As the inorganic binder, at least one of titania, mullite, sinterable alumina, silica, glass frit, clay minerals, and sinterable cordierite can be used.

[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 separation membrane 12 is formed is 0.01 μm to 1 μm, preferably 0.05 μm to 0.5 μm. The average pore diameter can be measured, for example, by a mercury porosimeter, a perm porometer, or a nanoperm porometer. With regard to the pore diameter 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 separation membrane 12 is formed is, for example, 20% to 60%.

[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 separation membrane 12 is formed, are smaller than the average pore size and sintered grain size in the layers other than the surface layer. The average pore size in the surface layer of the support 11 is, for example, 0.01 μm to 1 μm, preferably 0.05 μm to 0.5 μm. When the support 11 has a multilayer structure, the materials described above can be used for each layer. The materials of the multiple layers forming the multilayer structure may be the same or different. Note that when the support 11 has a multilayer structure, the average pore size of the support 11 refers to the average pore size of the surface layer, including the surface on which the separation membrane 12 is formed.

[0024] The separation membrane 12 is a porous membrane having fine pores (micropores). The separation membrane 12 can separate a specific substance from a mixture of multiple substances by utilizing molecular sieving or the like. Other substances are less likely to permeate the separation membrane 12 than the specific substance. In other words, the permeation rate of the other substances through the separation membrane 12 is slower than the permeation rate of the specific substance.

[0025] The average thickness of the separation membrane 12 is 2 μm or less. This enables a high permeation rate to be achieved. The lower limit of the average thickness of the separation membrane 12 is not particularly limited, but from the viewpoint of improving separation performance, it is, for example, 0.2 μm, preferably 0.5 μm, and more preferably 0.7 μm. To measure the average thickness of the separation membrane 12, a cross section perpendicular to the surface of the separation membrane 12 is exposed, for example, by cross-sectional polishing. In the cross section, multiple randomly selected fields (e.g., seven fields) are observed using a scanning electron microscope (SEM). The magnification of the SEM is, for example, 5000x. The average thickness of the separation membrane 12 in each field (field-average thickness) is determined, and the arithmetic mean of the field-average thicknesses of the remaining fields, excluding the fields with the maximum and minimum field-average thickness values, is obtained as the average thickness of the separation membrane 12. The surface roughness (Ra) of the separation membrane 12 is, for example, 2 μm or less, preferably 1 μm or less, and more preferably 0.5 μm or less.

[0026] As described above, the separation membrane 12 is composed of MOFs. That is, the separation membrane 12 is a MOF membrane. The separation membrane 12 is typically composed only of MOFs, but depending on the production method, the separation membrane 12 may contain a small amount (e.g., 1 mass % or less) of substances other than MOFs. The pore diameter of the MOFs that constitute the separation membrane 12 is, for example, 1 nm or less. The pore diameter can be calculated from the skeletal structure of the MOF crystal. The pore diameter is smaller than the average pore diameter of the support 11 near the surface on which the separation membrane 12 is formed.

[0027] The average particle size of the MOFs constituting the separation membrane 12 is, for example, 0.1 μm to 2 μm. The average particle size is preferably 1 μm or less, and more preferably 0.5 μm or less. A separation membrane 12 with a small average MOF particle size can reduce grain boundary defects, which form excessively large gaps between MOF crystals, and improve separation performance. The average particle size of the MOF in this embodiment is the arithmetic mean of the maximum diameters of multiple particles (e.g., 30 particles) measured by cross-sectional observation using an SEM. The multiple particles to be measured may be randomly selected on an SEM image.

[0028] At the interface between the separation membrane 12 and the support 11, a composite layer 13 is formed in which crystals of the MOF penetrate into the pores of the support 11. In FIG. 2 , the composite layer 13 is shown by drawing parallel diagonal lines over a portion of the support 11. The composite layer 13 is part of the support 11. The thickness of the composite layer 13 is, for example, 2 μm or less. This makes it possible to suppress a decrease in permeation rate due to the presence of the composite layer 13. The composite layer 13 does not necessarily have to be present, and the lower limit of the thickness of the composite layer 13 is 0.

[0029] In measuring the thickness of the composite layer 13, in cross-sectional observation using an SEM, the boundary position of the composite layer 13 in a direction perpendicular to the interface between the support 11 and the separation membrane 12 (hereinafter referred to as the "depth direction") is identified near one measurement position along the interface. Specifically, the boundary position on the separation membrane 12 side of the composite layer 13 is the interface between the separation membrane 12 and the support 11. The boundary position on the opposite side of the composite layer 13 from the separation membrane 12 is the edge of the MOF present in the pores of the support 11 that is farthest from the separation membrane 12 in the depth direction. The depth-wise distance between the boundary position on the separation membrane 12 side of the composite layer 13 and the boundary position on the opposite side of the separation membrane 12 is obtained as the thickness of the composite layer 13 at that measurement position. Then, the average of the thicknesses of the composite layer 13 at multiple different measurement positions (e.g., 10 measurement positions) is determined as the thickness of the composite layer 13 in the separation membrane composite 1.

[0030] The MOF constituting the separation membrane 12 contains aluminum ions (Al ３＋) and a ligand (organic ligand) coordinated to the aluminum ion. ２ Preferably, the ligand has a high affinity with the MOF, and examples thereof include 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 the separation membrane 12 has peaks at all diffraction angles 2θ listed in Table 2.

[0031]

[0032] Powder X-ray diffraction patterns are obtained using CuKα radiation as the radiation source of an X-ray diffractometer. For example, an X-ray diffractometer 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°. A monochromator is not used, and 0.015 mm thick nickel foil is used as a CuKβ radiation filter.

[0033] Next, an example of a manufacturing flow of the separation membrane composite 1 will be described with reference to FIG. 3 . When the separation membrane composite 1 is manufactured, first, seed crystals to be used in manufacturing the separation membrane 12 are prepared (step S11). The seed crystals are obtained from MOF powder, which is produced, for example, by hydrothermal synthesis (solvothermal synthesis). The MOF powder may be produced by any or known manufacturing method. The MOF powder may be used as the seed crystals directly, or the seed crystals may be obtained by processing the MOF powder by pulverization or the like.

[0034] The average particle size (D50) of the seed crystals is preferably 0.5 μm or less. This makes it possible to suppress the occurrence of grain boundary defects in the separation membrane 12, which would otherwise be caused by the average particle size of the MOFs becoming excessively large. There is no particular limitation on the lower limit of the average particle size of the seed crystals, but, for example, by setting the average particle size to 0.1 μm or more, it is possible to suppress a decrease in the crystallinity of the seed crystals. The average particle size of the seed crystals can be measured, for example, by a laser scattering method.

[0035] Next, the porous support 11 is immersed in the dispersion liquid in which the seed crystals are dispersed, and the seed crystals are attached to the support 11 (step S12). Alternatively, the dispersion liquid in which the seed crystals are dispersed is brought into contact with the portion of the support 11 where the separation membrane 12 is to be formed, thereby attaching the seed crystals to the support 11. In this way, a seed crystal-attached support is produced. The seed crystals may also be attached to the support 11 by other methods.

[0036] A synthesis solution (also referred to as a synthesis sol or raw material solution) used to form the separation membrane 12 is prepared (step S13). The synthesis solution may be prepared before step S12 or in parallel with step S12. In preparing the synthesis solution, water, a monocarboxylate, a ligand, and an organic solvent are first mixed. Examples of the monocarboxylate include formates such as sodium formate, lithium formate, and potassium formate, and acetates such as sodium acetate. Monocarboxylic acids act as modulators in MOF synthesis and contribute to improving crystallinity. Therefore, amino acids containing monocarboxylic acids (e.g., glycine, arginine, etc.) may be used. Regarding the ligand, various organic compounds can be used as long as the MOF synthesized using the ligand provides a powder X-ray diffraction pattern with peaks at the diffraction angles 2θ listed in Table 2. A preferred ligand is CO ２The organic solvent is an organic compound having a high affinity with the solvent, 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 (such as a carboxyl group), such as N,N-dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), and N-methylformamide. Organic solvents without a carbonyl group may also be used.

[0037] In the synthesis 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. If a monocarboxylate is not added, the synthesis solution becomes cloudy and loses homogeneity, even when the heating and stirring treatment described below is performed, making it difficult to produce an MOF. On the other hand, if an excessive amount of monocarboxylate is added, coordination defects, in which some of the ligands constituting the MOF are missing, are likely to occur, as described below. Furthermore, 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. If an organic solvent is not added, the crystallinity of the MOF decreases. On the other hand, if an excessive amount of organic solvent is added, coordination defects are likely to occur, as described below.

[0038] Once a solution containing water, a monocarboxylate, a ligand, and an organic solvent is obtained, 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 with the solution. Examples of the Al source include aluminum sulfate, aluminum chloride, aluminum nitrate, aluminum hydroxide, and boehmite. This results in a synthesis solution used to form the separation membrane 12. Note that the organic solvent does not necessarily need to be mixed with the solution before the heating and stirring treatment; it may be mixed during or after the heating and stirring treatment. In other words, the organic solvent may be mixed with the solution at any time.

[0039] Once the synthesis solution is prepared, a support 11 with seed crystals attached is immersed in the synthesis solution. The synthesis solution is then heated to initiate hydrothermal synthesis. In the hydrothermal synthesis, MOFs grow using the seed crystals as nuclei, and a separation membrane 12, which is a dense MOF membrane, is formed on the support 11 (step S14). The synthesis temperature during hydrothermal synthesis (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.

[0040] After the hydrothermal synthesis is completed, the support 11 and the separation membrane 12 are washed with pure water and then with ethanol or the like. Preferably, washing with water and ethanol or the like is repeated multiple times. After washing, the support 11 and the separation membrane 12 are dried, for example, at 100°C. By the above-mentioned treatment, the above-mentioned separation membrane composite 1 is obtained.

[0041] Next, separation of a mixed substance using the separation membrane composite 1 will be described with reference to Figures 4 and 5. Figure 4 is a diagram showing the separation device 2. Figure 5 is a diagram showing the flow of separation of a mixed substance by the separation device 2.

[0042] In the separation device 2, a mixed substance containing multiple types of fluids (i.e., gases or liquids) is supplied to the separation membrane composite 1, and highly permeable substances in the mixed substance are separated from the mixed substance by permeating through the separation membrane composite 1. Separation in the separation device 2 may be performed, for example, for the purpose of extracting highly permeable substances from the mixed substance, or for the purpose of concentrating less permeable substances.

[0043] 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.

[0044] 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 (NH３ ), 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.

[0045] 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.

[0046] Sulfur oxides are compounds of sulfur and oxygen. Examples of the sulfur oxides include sulfur dioxide (SO ２ ), sulfur trioxide (SO ３ ) and other SOs Ｘ It is a gas called SOXX.

[0047] 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.

[0048] 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 )

[0049] The organic acid is a carboxylic acid or a sulfonic acid. The carboxylic acid is, for example, formic acid (CH ２ O ２ ), acetic acid (C ２ H ４ O ２ ), oxalic acid (C ２ H ２ O ４ ), acrylic acid (C ３ H ４ O ２ ) or benzoic acid (C ６ H ５ COOH), etc. Sulfonic acids include, for example, ethanesulfonic acid (C ２ H ６ O ３S) and the like. The organic acid may be a chain compound or a cyclic compound.

[0050] 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.

[0051] 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.

[0052] The esters mentioned above are, for example, formates or acetates.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] The separation device 2 includes a separation membrane composite 1, a sealing unit 21, a housing 22, two seal members 23, a supply unit 26, a first recovery unit 27, and a second recovery unit 28. The separation membrane composite 1, the sealing unit 21, and the seal members 23 are housed within the housing 22. The supply unit 26, the first recovery unit 27, and the second recovery unit 28 are disposed outside the housing 22 and connected to the housing 22.

[0058] The sealing portion 21 is attached to both longitudinal end portions of the support 11 (i.e., the left-right direction in FIG. 4 ) 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.

[0059] The shape of the housing 22 is not limited, but may be, for example, a substantially cylindrical tubular member. The housing 22 is formed, for example, from stainless steel or carbon steel. The longitudinal direction of the housing 22 is substantially parallel to the longitudinal direction of the separation membrane composite 1. A supply port 221 is provided at one longitudinal end of the housing 22 (i.e., the left end in FIG. 4 ), 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.

[0060] The two seal members 23 are disposed around the entire circumference between the outer circumferential surface of the separation membrane composite 1 and the inner circumferential surface of the housing 22 near both longitudinal ends of the separation membrane composite 1. Each seal member 23 is a substantially annular member made of a gas-impermeable material. The seal members 23 are, for example, O-rings made of a flexible resin. The seal members 23 are in close contact with the outer circumferential surface of the separation membrane composite 1 and the inner circumferential surface of the housing 22 around the entire circumference. In the example shown in FIG. 4 , the seal member 23 is in close contact with the outer circumferential surface of the sealing portion 21 and indirectly in close contact with the outer circumferential surface of the separation membrane composite 1 via the sealing portion 21. A seal is formed between the seal member 23 and the outer circumferential surface of the separation membrane composite 1, and between the seal member 23 and the inner circumferential surface of the housing 22, so that gas hardly or completely passes through.

[0061] 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.

[0062] When separating a mixed gas, the separation device 2 is prepared, thereby preparing the separation membrane composite 1 (step S21). Next, a mixed gas containing multiple types of gases with different permeabilities through the separation membrane 12 is supplied by the supply unit 26 to the internal space of the housing 22. For example, the main components of the mixed gas are CO ２ and N ２ The mixed gas contains CO ２ and N ２ The pressure of the mixed gas supplied from the supply unit 26 to the internal space of the housing 22 (i.e., the introduction pressure) is, for example, 0.1 MPa to 20.0 MPa. The temperature at which the mixed gas is separated is, for example, 10°C to 150°C.

[0063] The mixed gas supplied from the supply unit 26 to the housing 22 is introduced into each of the through-holes 111 of the support 11 from the left end of the separation membrane composite 1 in the drawing, as indicated by arrow 251. A gas with high permeability in the mixed gas (for example, CO ２ The highly permeable substance (hereinafter referred to as "highly permeable substance") passes through the separation membrane 12 provided on the inner circumferential surface of each through-hole 111 and the support 11, and is discharged from the outer circumferential surface of the support 11. As a result, the highly permeable substance is able to separate the low permeable gas (e.g., N ２ (hereinafter referred to as "low-permeability material") is separated from the low-permeability material (step S22). The gas (hereinafter referred to as "permeation material") discharged from the outer peripheral surface of the support 11 is recovered by the second recovery unit 28 via the second discharge port 223, as shown by arrow 253. The pressure of the gas recovered by the second recovery unit 28 via the second discharge port 223 (i.e., permeation pressure) is, for example, about 1 atmosphere (0.101 MPa).

[0064] Furthermore, gases (hereinafter referred to as "impermeable substances") excluding the gas that has permeated the separation membrane 12 and the support 11 of the mixed gas pass through each through-hole 111 of the support 11 from left to right in the figure, and are recovered by the first recovery unit 27 via the first discharge port 222, as shown by arrow 252. The pressure of the gas recovered by the first recovery unit 27 via the first discharge port 222 is, for example, approximately the same as the introduction pressure. In addition to the above-mentioned low-permeable substances, the impermeable substances may also include highly permeable substances that did not permeate the separation membrane 12.

[0065] Next, separation membrane composites of Examples 1 to 21 and Comparative Examples 1 to 7 will be described. Table 3 shows the type of ligand, the D50 value (average particle size) of the seed crystals, the ratio of monocarboxylate salt to ligand, the ratio of organic solvent to ligand, and the conditions of the heating and stirring treatment in Examples 1 to 21 and Comparative Examples 1 to 7.

[0066]

[0067] <Preparation of Seed Crystals (1H-Pyrrole-2,5-Dicarboxylic Acid)> A mixed solution was prepared by mixing 1.551 g of 1H-pyrrole-2,5-dicarboxylic acid and 1.36 g of sodium formate with 50 mL of deionized water. The mixed solution was stirred at 50°C for 3 hours, cooled to room temperature, and 3.333 g of aluminum sulfate 18-hydrate was added. Next, this solution was maintained at 120°C for 12 hours. The precipitate was separated using a centrifuge and washed three times with deionized water and ethanol. As a result, a powder of MOF containing 1H-pyrrole-2,5-dicarboxylic acid as a ligand was obtained as seed crystals.

[0068] <Preparation of Seed Crystals (2,5-Furandicarboxylic Acid)> 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 deionized 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 maintained at 100°C for 12 hours. The precipitate was separated using a centrifuge and washed three times with deionized water and ethanol. As a result, a powder of MOF containing 2,5-furandicarboxylic acid as a ligand was obtained as seed crystals.

[0069] <Preparation of Seed Crystals (3,5-Pyridinedicarboxylic Acid)> A mixed solution was prepared by mixing 1.67 g of 3,5-pyridinedicarboxylic acid and 1.36 g of sodium formate with 50 mL of deionized water. The mixed solution was stirred at 50°C for 3 hours, then cooled to room temperature, and 3.333 g of aluminum sulfate 18-hydrate was added. Next, this solution was maintained at 120°C for 12 hours. The precipitate was separated using a centrifuge and washed three times with deionized water and ethanol. As a result, a powder of MOF containing 3,5-pyridinedicarboxylic acid as a ligand was obtained as seed crystals.

[0070] <Supporting of seed crystals on ceramic support> 1 g of the obtained seed crystals was placed in a glass vial containing zirconia balls, and 9 g of water was added. The glass vial was set on a ball mill stand, and the seed crystals were 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. The seed crystals were then supported on a ceramic support.

[0071] Example 1: 1.551 g of 1H-pyrrole-2,5-dicarboxylic acid, 1.22 g of sodium formate, and 0.58 g of N,N-dimethylformamide (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 (heating and stirring treatment). After confirming that the mixed solution had become transparent, it was cooled to room temperature. 3.333 g of aluminum sulfate hexahydrate was then added to the mixed solution to prepare a synthesis solution. The monocarboxylate / ligand ratio (molar ratio; the same applies hereinafter) in the synthesis solution was 1.8, and the organic solvent / ligand ratio (molar ratio; the same applies hereinafter) was 0.8. Next, a ceramic support carrying seed crystals (average particle size 0.33 μm) containing 1H-pyrrole-2,5-dicarboxylic acid and the synthesis solution were placed in a Teflon (registered trademark) container, and hydrothermal synthesis was performed at 100°C for 20 hours. The resulting separation membrane composite was washed three times with deionized water and ethanol, and then dried.

[0072] Example 2 The procedure was the same as Example 1, except that the temperature of the hydrothermal synthesis was changed to 80°C.

[0073] Example 3 The same procedure as in Example 1 was carried out except that the ratio of monocarboxylate to ligand was changed to 1.

[0074] Example 4 The procedure was the same as Example 1, except that the monocarboxylate / ligand ratio was changed to 0.6.

[0075] Example 5 The procedure was the same as in Example 1, 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.

[0076] Example 6 The procedure was the same as in Example 1, 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.

[0077] Example 7 The same procedure as in Example 1 was carried out except that the organic solvent / ligand ratio was changed to 0.1.

[0078] Example 8 The same procedure as in Example 1 was carried out except that the organic solvent / ligand ratio was changed to 8.

[0079] Example 9 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.

[0080] Example 10 The procedure was the same as in Example 1, except that the average particle size of the seed crystals supported on the ceramic support was changed to 0.50 μm.

[0081] Example 11: 1.562 g of 2,5-furandicarboxylic acid, 1.22 g of sodium formate, and 0.58 g of N,N-dimethylformamide (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 (heating and stirring treatment). After confirming that the mixed solution was transparent, it was cooled to room temperature. 2.413 g of aluminum chloride hexahydrate was then added to the mixed solution to prepare a synthesis solution. The synthesis solution had a monocarboxylate / ligand ratio of 1.8 and an organic solvent / ligand ratio of 0.8. Next, a ceramic support carrying seed crystals (average particle size 0.25 μm) containing 2,5-furandicarboxylic acid and the synthesis solution were placed in a Teflon container and subjected to hydrothermal synthesis at 80°C for 20 hours. The resulting separation membrane composite was washed three times with deionized water and ethanol and then dried.

[0082] Example 12 The procedure was the same as in Example 11, except that the heating temperature in the heating and stirring treatment of the mixed solution was changed to 40°C.

[0083] Example 13 The same procedure as in Example 11 was carried out except that the ratio of monocarboxylate to ligand was changed to 1.

[0084] Example 14 The same procedure as in Example 11 was carried out except that the organic solvent / ligand was changed to 2.

[0085] Example 15: 1.67 g of 3,5-pyridinedicarboxylic acid, 1.22 g of sodium formate, and 0.58 g of N,N-dimethylformamide (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 (heating and stirring treatment). After confirming that the mixed solution was transparent, it was cooled to room temperature. 3.333 g of aluminum sulfate hexahydrate was then added to the mixed solution to prepare a synthesis solution. The synthesis solution had a monocarboxylate / ligand ratio of 1.8 and an organic solvent / ligand ratio of 0.8. Next, a ceramic support carrying seed crystals (average particle size 0.35 μm) containing 3,5-pyridinedicarboxylic acid and the synthesis solution were placed in a Teflon container and subjected to hydrothermal synthesis at 100°C for 20 hours. The resulting separation membrane composite was washed three times with deionized water and ethanol and then dried.

[0086] Example 16 The same procedure as in Example 15 was carried out except that the heating temperature in the heating and stirring treatment of the mixed solution was changed to 40°C.

[0087] Example 17 The same procedure as in Example 15 was carried out except that the ratio of monocarboxylate to ligand was changed to 1.

[0088] Example 18 The same procedure as in Example 15 was carried out except that the organic solvent / ligand ratio was changed to 2.

[0089] Example 19: 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 (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 (heating and stirring treatment). After confirming that the mixed solution was transparent, it was cooled to room temperature. 3.333 g of aluminum sulfate hexahydrate was then added to the mixed solution to prepare a synthesis solution. The monocarboxylate / ligand ratio in the synthesis solution was 1.5, and the organic solvent / ligand ratio was 0.5. Next, a ceramic support carrying the same seed crystals (seed crystals containing 1H-pyrrole-2,5-dicarboxylic acid) as in Example 1 and the synthesis solution were placed in a Teflon container, and hydrothermal synthesis was performed at 100°C for 10 hours. The resulting separation membrane composite was washed three times with deionized water and ethanol, and then dried.

[0090] Example 20: 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 150 mL of deionized water to prepare a mixed solution. The mixed solution was heated to 60°C and stirred for 2 hours (heating and stirring treatment). After confirming that the mixed solution was transparent, it was cooled to room temperature. 3.333 g of aluminum sulfate hexahydrate was then added to the mixed solution to prepare a synthesis solution. The monocarboxylate / ligand ratio in the synthesis solution was 1.5, and the organic solvent / ligand ratio was 0.5. Next, a ceramic support carrying the same seed crystals (seed crystals containing 1H-pyrrole-2,5-dicarboxylic acid) as in Example 1 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 composite was washed three times with deionized water and ethanol, and then dried.

[0091] Example 21: 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 (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 (heating and stirring treatment). After confirming that the mixed solution was transparent, it was cooled to room temperature. 3.333 g of aluminum sulfate hexahydrate was then added to the mixed solution to prepare a synthesis solution. The synthesis solution had a monocarboxylate / ligand ratio of 1.5 and an organic solvent / ligand ratio of 0.8. Next, a ceramic support carrying the same seed crystals (seed crystals containing 2,5-furandicarboxylic acid) as in Example 11 and the synthesis solution were placed in a Teflon container and subjected to hydrothermal synthesis at 100°C for 20 hours. The resulting separation membrane composite was washed three times with deionized water and ethanol and then dried.

[0092] Comparative Example 1 The procedure was the same as in Example 1, except that the heating and stirring treatment was not carried out.

[0093] Comparative Example 2 was the same as Comparative Example 1, except that the monocarboxylate / ligand ratio was changed to 0 (i.e., no monocarboxylate was added). In Comparative Example 2, no separation membrane was formed on the support.

[0094] Comparative Example 3 The same procedure as in Example 1 was carried out except that the organic solvent / ligand ratio was changed to 12.

[0095] Comparative Example 4 The procedure was the same as in Example 1, except that the organic solvent / ligand ratio was changed to 0 (that is, no organic solvent was added).

[0096] (Comparative Example 5) A synthesis solution was prepared using the method and composition described in Weidong Fan et al., "Multivariate Polycrystalline Metal-Organic Framework Membranes for CO2 / CH4 Separation" (J. Am. Chem. Soc., 2021, Vol. 143, pp. 17716-17723) (above-mentioned Document 1), and membrane formation was carried out without using seed crystals, as in Document 1. In Comparative Example 5, it was not possible to coat the entire surface of the support on which the membrane was to be formed with the separation membrane.

[0097] Comparative Example 6 Comparative Example 5 was repeated except that the same seed crystals as in Example 11 (seed crystals containing 2,5-furandicarboxylic acid) were used.

[0098] Comparative Example 7 The same procedure as in Example 15 was carried out except that the heating and stirring treatment was not carried out.

[0099] <Measurements and Evaluation of Separation Membrane Composites> Various measurements were carried out 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 diameter of the separation membrane, and CO ２ Permeation rate and SF ６ The permeation rate ratio of HCl / He is shown.

[0100]

[0101] The average 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 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 and 3 to 7, the thickness of the composite layer was 2 μm or less, but the average thickness of the separation membrane was 2 μm or more. As described above, in Comparative Example 2, no separation membrane was formed 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 and 5 to 7, the average particle size of the separation membrane was greater than 2 μm. When powder X-ray diffraction measurements were performed on the MOFs constituting the separation membranes of Examples 1 to 21, the obtained powder X-ray diffraction patterns had peaks at the diffraction angles 2θ listed in Table 2 above.

[0102] Also, CO２ Gas, SF ６ The permeation rates of the individual gases, CO and He, were measured using the separation device 2. Note that the permeation rates were not measured in Comparative Examples 2 and 5, in which poor separation membrane formation occurred. ２ The permeation rate was 1000 GPU or more, and a high permeation rate was achieved. ２ The transmission rate was less than 1000 GPU. 1 GPU is 1 × 10 －６ cm ３ (STP) / (cm ２ In Examples 1 to 21, the SF relative to the permeation rate of He gas was ６ The ratio of gas permeation rates, i.e., SF ６ 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 SF ６ The permeation rate ratio of HCl / He was greater than 0.020.

[0103] However, if there are many grain boundary defects in the separation membrane, which form excessively large gaps between the MOF crystals, or many coordination defects, which are the absence of some of the ligands that make up the MOF, a high separation factor cannot be obtained. In the separation membrane, the grain boundary defects and coordination defects are expected to have a defect size of 0.5 nm or more. Therefore, in this example, SF with a dynamic molecular diameter of 0.56 nm was used. ６ Gas and SF ６ The defect amount in the separation membrane was evaluated based on the permeation rate ratio to He gas, which has a sufficiently smaller dynamic molecular diameter than the SF gas. ６ The permeation rate ratio of SF / He was 0.020 or less in all cases. ６ Therefore, it can be said that the separation membrane composites of Examples 1 to 21 have reduced grain boundary defects and coordination defects, and thus have high separation factors. In contrast, in all the comparative examples where the permeation rate was measured, the SF ６ The permeation rate ratio of SF / He is greater than 0.020. ６Therefore, the separation factor of the separation membrane composite of the comparative example is low due to the influence of the grain boundary defects and coordination defects.

[0104] Here, in the separation membrane composites of Examples 1 to 21, SF ６ The reason why the permeation rate ratio of HCl / He becomes smaller (the separation factor becomes higher) will be considered. Figures 6A and 6B are diagrams for explaining the synthesis of separation membrane 92 of a comparative example, in which the average particle size is relatively large. Figures 7A and 7B are diagrams for explaining the synthesis of separation membranes 12 of Examples 1 to 21, in which the average particle size is relatively small. Figures 6A and 7A show the initial state of membrane synthesis, and Figures 6B and 7B show the state at the completion of membrane synthesis.

[0105] In the synthesis of the separation membrane 92 of the comparative example, it is believed that the particle size of the MOF crystals 91 increases in the early stages of membrane synthesis, as shown in Figure 6A. In this case, the gaps between the MOF crystals 91 also increase, making grain boundary defects more likely to occur. To fill the gaps between the MOF crystals 91, the MOF crystals 91 must be grown large, as shown in Figure 6B, which increases the thickness of the separation membrane 92. In other words, a separation membrane with an average thickness of about 2 µm has a low separation factor.

[0106] On the other hand, in Examples 1 to 21, the separation membrane 12 was synthesized by the secondary growth method using seed crystals with a small average particle size (e.g., 0.5 μm or less). As a result, the particle size of the MOF crystals 91 was small at the beginning of membrane synthesis, as shown in FIG. 7A. Therefore, the gaps between the MOF crystals 91 were also small, making it less likely that grain boundary defects would occur. Furthermore, even at the completion of membrane synthesis, when the average membrane thickness was 2 μm or less, the average particle size of the separation membrane 12 (the average particle size of the MOF crystals 91) remained small, at 0.1 to 2 μm, as shown in FIG. 7B, thereby suppressing the occurrence of grain boundary defects.

[0107] The reason for the small average particle size of the separation membrane is not entirely clear, but since the average particle size was larger than 2 μm in all of Comparative Examples 1, 6, and 7, which were not subjected to the heating and stirring treatment, it is believed that the heating and stirring treatment contributed to this. In the heating and stirring treatment, the ligand used as a raw material for the synthesis solution is heated and dissolved, which is thought to cause the MOF precursor in the synthesis solution to be adsorbed onto the seed crystals and stabilized, and this is presumed 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 thin (2 μm or less), making it easy to achieve a high permeation rate. Furthermore, grain boundary defects can be reduced, and SF ６ In practice, the thickness of the composite layer of the support and MOF in this separation membrane composite is 2 μm or less, and the CO ２ The gas permeation rate is 1000 GPU or more.

[0108] In the synthesis of MOF membranes, the organic solvent (and monocarboxylic acid) competes with the ligands to repeatedly coordinate and dissociate with metal ions, slowing the crystal growth rate and resulting in highly crystalline MOFs. Therefore, if no organic solvent is added, the crystallinity of the MOF decreases. On the other hand, if an excess of organic solvent is added, the MOF is formed with the organic solvent still coordinated, which is thought to increase the likelihood of coordination defects (see Comparative Example 3). In Examples 1 to 21, by setting the molar ratio of the organic solvent containing a carbonyl group to the ligand (organic solvent / ligand ratio) in the synthesis solution to 0.1 to 10, highly crystalline MOFs were obtained while reducing coordination defects, resulting in a high separation factor.

[0109] Furthermore, if a monocarboxylate salt is not added to the synthesis solution, deprotonation of the ligand is unlikely to occur, the synthesis solution becomes cloudy, and uniformity is impaired, which is thought to make it difficult to produce a separation membrane (see Comparative Example 2). On the other hand, if an excess of monocarboxylate salt is added, an MOF is formed with the monocarboxylic acid remaining coordinated, which is thought to make coordination defects more likely to occur (see Comparative Example 6). In Examples 1 to 21, by setting the monocarboxylate salt / ligand ratio in the synthesis solution to 0.5 to 1.8, coordination defects were reduced and the uniformity of the synthesis solution was ensured, resulting in the production of an appropriate separation membrane.

[0110] As described above, the separation membrane composite 1 includes a porous support 11 made of ceramic and a separation membrane 12 made of MOF and disposed on the support 11. The separation membrane 12 has an average thickness of 2 μm or less. The MOF is composed of aluminum ions and ligands coordinated to the aluminum ions. The powder X-ray diffraction pattern of the MOF has peaks at the diffraction angles 2θ listed in Table 2 above. In the separation membrane composite 1, SF ６ The permeation rate ratio of HCl / He is 0.020 or less. Such a separation membrane composite 1 can achieve both a high separation factor and a high permeation rate.

[0111] Preferably, the average particle size of the MOF is 0.1 μm to 2 μm, which can reduce grain boundary defects in the thin separation membrane 12 and improve the separation factor.

[0112] Preferably, the ligand of the MOF comprises one of 1H-pyrrole-2,5-dicarboxylic acid, 2,5-furandicarboxylic acid, or 3,5-pyridinedicarboxylic acid. ２ By using a ligand with high affinity for CO ２ The gas permeation rate can be improved.

[0113] Preferably, the thickness of the composite layer 13 of the support 11 and the MOF is 2 μm or less, which allows the separation membrane composite 1 to achieve a higher permeation rate.

[0114] Preferably, CO ２The gas permeation rate is 1000 GPU or more. ２ Depending on the application of the separation membrane composite 1, it is possible to perform gas separation in a suitable manner. ２ The gas transmission rate may be less than 1000 GPU.

[0115] The method for producing the separation membrane composite 1 includes a step of attaching seed crystals made of MOFs to a porous support 11 (step S12), a step of preparing a synthesis solution (step S13), and a step of immersing the support 11 in the synthesis solution and growing MOFs from the seed crystals by hydrothermal synthesis to form a separation membrane 12 on the support 11 (step S14). Step S13 includes a heating and stirring treatment in which a solution containing a mixture of water, a monocarboxylate, and a ligand is heated and stirred. In step S13, an Al source is mixed with the solution after the heating and stirring treatment, and an organic solvent is mixed with the solution at any timing. In the separation membrane composite 1 in which the separation membrane 12 is formed on the support 11, SF ６ The permeation rate ratio of HCl / He is 0.020 or less. This makes it possible to provide a separation membrane composite 1 having a high separation factor and permeation rate.

[0116] Conventional MOF synthesis requires the use of large amounts of organic solvents such as methanol, ethanol, and DMF, resulting in a high environmental impact. On the other hand, synthesis without the use of an organic solvent does not allow for the proper formation of an MOF membrane. In contrast, in a preferred method for producing the separation membrane composite 1, the organic solvent is an organic compound having 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 the proper formation of an MOF membrane while reducing the amount of organic solvent used and the environmental impact.

[0117] Preferably, the ratio of the molar amount of monocarboxylate to the molar amount of ligand in the synthesis solution is 0.5 to 1.8, which allows for the proper formation of an MOF membrane and reduces coordination defects to improve the separation factor.

[0118] The separation membrane composite 1 and the method for manufacturing the separation membrane composite 1 can be modified in various ways.

[0119] When a high separation factor and a high permeation rate are achieved in the separation membrane composite 1, the average particle size of the MOF may be outside the range of 0.1 μm to 2 μm, and the thickness of the composite layer 13 of the support 11 and the MOF may be greater than 2 μm. Similarly, in the synthesis solution, the organic solvent / ligand ratio may be outside the range of 0.1 to 10, and the monocarboxylate / ligand ratio may be outside the range of 0.5 to 1.8.

[0120] In the production of the separation membrane composite 1, when the synthesis solution contains two or more types of ligands (see Examples 19 to 21), the ligand contained in the MOF of the seed crystal may be different from the two or more types of ligands. Alternatively, powders of multiple types of MOFs with different ligands may be mixed and used as seed crystals. When the synthesis solution contains only one type of ligand, the ligand contained in the MOF of the seed crystal may be the same as or different from the one type of ligand.

[0121] In addition to the support 11 and the separation membrane 12, the separation membrane composite 1 may further include a functional membrane or a protective membrane 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 a silicone membrane. In addition, the functional membrane or protective membrane laminated on the separation membrane 12 may contain a CO ２ A substance that easily adsorbs specific molecules such as the above may be added.

[0122] The separation membrane composite 1 may be produced by a method other than the above-described production method.

[0123] In the separation device 2 and the separation method, substances other than those exemplified in the above description may be separated from the mixed substance.

[0124] The configurations in the above-described embodiment and each modification may be combined as appropriate as long as they are not mutually contradictory.

[0125] 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.

[0126] The separation membrane composite of the present invention can be used in a variety of fields as a separation membrane or adsorption membrane for various substances.

[0127] 1 Separation membrane composite 11 Support 12 Separation membrane 13 Composite layer S11 to S14, S21, S22 Steps

Claims

1. A separation membrane composite, comprising: a porous support formed of ceramic; and a separation membrane provided on the support and made of a metal-organic framework, wherein the separation membrane has an average thickness of 2 μm or less, the metal-organic framework is made of aluminum ions and ligands coordinated to the aluminum ions, and the powder X-ray diffraction pattern of the metal-organic framework has peaks at the diffraction angles 2θ shown in the table below, and SF ６ A separation membrane composite having a permeation rate ratio of 0.020 or less.

2. The separation membrane composite according to claim 1, wherein the average particle size of the metal-organic framework is 0.1 μm to 2 μm.

3. The separation membrane composite according to claim 1, wherein the ligand of the metal-organic framework comprises any one of 1H-pyrrole-2,5-dicarboxylic acid, 2,5-furandicarboxylic acid, and 3,5-pyridinedicarboxylic acid.

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

5. The separation membrane composite according to any one of claims 1 to 4, ２ A separation membrane composite having a gas permeation rate of 1000 GPU or more.

6. A method for producing a separation membrane composite, comprising: a) attaching seed crystals of a metal-organic framework onto a porous support; b) preparing a synthesis solution; and c) immersing the support into the synthesis solution and growing a metal-organic framework from the seed crystals by hydrothermal synthesis to form a separation membrane on the support, wherein the b) step includes a heating and stirring treatment in which a solution of a mixture of water, a monocarboxylate, and a ligand is heated and stirred, and 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 timing, and in a separation membrane composite in which the separation membrane is formed on the support, SF ６ A method for producing a separation membrane composite having a permeation rate ratio of 0.020 or less.

7. A method for producing a separation membrane composite according to claim 6, wherein the organic solvent is an organic compound having a carbonyl group, and the ratio of the amount of substance of the organic solvent to the amount of substance of the ligand in the synthesis solution is 0.1 to 10.

8. A method for producing a separation membrane composite according to claim 6 or 7, wherein the ratio of the amount of substance of the monocarboxylate to the amount of substance of the ligand in the synthesis solution is 0.5 to 1.8.