Separation membrane complex and method for producing a separation membrane complex

Abstract

A separation membrane complex (1) comprises a porous ceramic support (11) and a separation membrane (12) formed on the support (11) and composed of a metal-organic framework. The average thickness of the separation membrane (12) is no greater than 2 µm. The metal-organic framework consists of aluminum ions and ligands coordinated to the aluminum ions. A powder X-ray diffraction pattern of the metal-organic framework exhibits peaks at predetermined diffraction angles 2θ. In the separation membrane complex (1), the SF6 / He permeance ratio is no higher than 0.020. The separation membrane complex (1) enables the achievement of both a high separation factor and a high permeance.

Description

TECHNICAL AREA

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

[0002] The present application enjoys priority over Japanese patent application No. 2023-37303, filed on March 10, 2023, the contents of which are hereby incorporated in their entirety by this notice. TECHNICAL BACKGROUND

[0003] Within the context of the global trend towards CO2 neutrality, the societal need for a technology (CO2 / N2 separation) for separating and collecting CO2 contained in industrial emissions from plants or similar sources has increased. Since a high CO2 / N2 separation factor is difficult to achieve using a molecular sieve mechanism with a DDR-type or CHA-type zeolite membrane (high-silicate zeolite), a separation membrane is required that, in addition to the molecular sieve mechanism, can achieve a high separation factor through its affinity for CO2.

[0004] Metal-organic framework (MOF) is a porous material with a large surface area and can be used for various purposes such as gas adsorption. Furthermore, similar to a zeolite membrane, forming a membrane on a porous support allows for gas or liquid separation. Using MOF with a small pore diameter and incorporating ligands with a high affinity for CO2, a high CO2 / N2 separation coefficient can be achieved. In “Multivariate Polycrystalline Metal-Organic Framework Membranes for CO2 / CH4 Separation” by Weidong Fan and nine others (J. Am. Chem. Soc., 2021, Vol. 143, pp. 17716 to 17723) (Document 1) and “Conformational-change-induced selectivity enhancement of CAU-10-PDC membrane for H2 / CH4 and CO2 / CH4 separation” by Chung-Kai Chang and seven others (Journal of Membrane Science Letters, 2021, Vol. 1, p.100005) (Document 2) discloses, for example, a structure in which a MOF membrane is formed on a ceramic support and a permeance ratio of CO2 / N2 or that of CO2 / CH4 has a relatively high value.

[0005] For the performance of a separation membrane, in addition to the separation factor, the permeance (permeability to highly permeable substances) is also important. Increasing the permeance makes it possible to reduce the number of separation membrane complexes required for the construction of a separation device, thereby lowering the manufacturing costs and miniaturizing the device. However, the permeance of the MOF membrane disclosed in non-patent documents 1 and 2 is low due to its large thickness.While reducing the membrane thickness is a possible method to increase the permeance in the MOF membrane, this typically leads to effects such as grain boundary defects (resulting in the formation of excessively large gaps between MOF crystals), coordination defects (related to the absence of some MOF ligands), and / or similar issues, making it impossible to achieve a high separation factor. Therefore, a separation membrane complex exhibiting both a high separation factor and high permeance is required. BRIEF SUMMARY OF THE INVENTION

[0006] It is an object of the present invention to provide a separation membrane complex which has both a high separation factor and a high permeance.

[0007] A first aspect of the present invention relates to a separation membrane complex, and the separation membrane complex according to the first aspect comprises a porous support formed from ceramic and a separation membrane formed on the support and composed of a metal-organic framework, wherein in the separation membrane complex according to the first aspect the average thickness of the separation membrane is not greater than 2 µm, the metal-organic framework is composed of aluminium ions and ligands coordinated to the aluminium ions, a powder X-ray diffraction pattern of the metal-organic framework exhibits peaks at the diffraction angles 2θ specified in the table below, and a permeance ratio of SF6 / He is not greater than 0.020. (Table 1) 2θ [°] (1) 8,2-8,4 (2) 9,1-9,3 (3) 11,8-12,0 (4) 12,4-12,6 (5) 14,9-15,1 (6) 16,7-16,9 (7) 17,1-17,3 (8) 18,4-18,6 (9) 19,1-19,3 (10) 22,5-22,7 (11) 24,3-24,5 (12) 25,1-25,3 (13) 26,9-27,1

[0008] According to the present invention, it is possible to provide a separation membrane complex that has both a high separation factor and a high permeance.

[0009] A second aspect of the present invention is provided for the separation membrane complex according to the first aspect and in the separation membrane complex according to the second aspect the average particle diameter of the metal-organic framework is 0.1 µm to 2 µm.

[0010] A third aspect of the present invention is provided for the separation membrane complex according to the first or second aspect, wherein in the separation membrane complex according to the third aspect the ligands of the metal-organic framework comprise one of 1H-pyrrole-2,5-dicarboxylic acid, 2,5-furandicarboxylic acid and 3,5-pyridindicarboxylic acid.

[0011] A fourth aspect of the present invention is provided for the separation membrane complex according to one of the first to third aspects and in the separation membrane complex according to the fourth aspect a thickness of a composite layer of the support and the metal-organic framework is not greater than 2 µm.

[0012] A fifth aspect of the present invention is provided for the separation membrane complex according to one of the first to fourth aspects, wherein in the separation membrane complex according to the fifth aspect the permeance for CO2 gas is not less than 1000 GPU.

[0013] A sixth aspect of the present invention is provided for a method for producing a separation membrane complex, and the method for producing a separation membrane complex according to the sixth aspect comprises a) applying seed crystals built from a metal-organic framework to a porous support, b) preparing a synthesis solution, and c) forming a separation membrane on the support by immersing the support in the synthesis solution and carrying out a hydrothermal synthesis to grow a metal-organic framework from the seed crystals, and wherein in the method for producing a separation membrane complex according to the sixth aspect, embodiment b) comprises a heating and stirring method for heating and stirring a solution in which water, monocarboxylic acid salt, and ligands are mixed.wherein an aluminum source is mixed into the solution according to the heating and stirring process and an organic solvent is mixed into the solution at any time during embodiment b), and wherein in a separation membrane complex in which the separation membrane is formed on the support, the permeance ratio of SF6 / He in the separation membrane complex, in which the separation membrane is formed on the support, does not exceed 0.020.

[0014] A seventh aspect of the present invention is provided for the process for producing a separation membrane complex according to the sixth aspect, wherein in the process for producing a separation membrane complex according to the seventh aspect the organic solvent is an organic compound with a carbonyl group and the ratio of the amount of substance of the organic solvent to that of the ligands in the synthesis solution is 0.1 to 10.

[0015] An eighth aspect of the present invention is provided for the process for producing a monocarboxylic acid salt separation membrane complex according to the sixth or seventh aspect, wherein in the process for producing a separation membrane complex according to the eighth aspect the ratio of the amount of substance of the monocarboxylic acid to that of the ligands in the synthesis solution is 0.5 to 1.8.

[0016] These and other tasks, features, aspects and advantages of the present invention will become clearer from the following detailed description of the present invention in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a cross-sectional view of a separation membrane complex; Fig. Figure 2 is an enlarged cross-sectional view showing part of the separating membrane complex; Fig.Figure 3 is a flowchart showing a process for producing the separation membrane complex; Fig. 4 is a view showing a separating device; Fig. Figure 5 is a flowchart showing a process for separating a mixed substance using the separation device; Fig. 6A is a view to illustrate the synthesis of a separation membrane in a comparative example; Fig. 6B is a view used to illustrate the synthesis of the separating membrane in the comparative example; Fig. 7A is a view used to illustrate the synthesis of a separation membrane; and Fig. Figure 7B is a view used to illustrate the synthesis of the separating membrane. DESCRIPTION OF EXECUTION FORMS

[0017] Fig. Figure 1 is a cross-sectional view of a separation membrane complex 1. Fig.Figure 2 is an enlarged cross-sectional view showing part of the separation membrane complex 1. The separation membrane complex 1 comprises a porous support 11 and a separation membrane 12 formed on the support 11. As described later, the separation membrane 12 is a MOF membrane formed from a metal-organic framework (hereinafter referred to as "MOF"), and the separation membrane complex 1 is an MOF membrane complex. The MOF membrane is obtained at least by forming MOF on a surface of the support 11 in a membrane shape and does not include a membrane obtained by simply dispersing MOF particles in an organic membrane. Fig. In Figure 1, the separating membrane 12 is represented by a thick line. Fig. 2 is the separating membrane 12 hatched. In addition, in Fig. 2. The thickness of the separating membrane is 12 times greater than actually depicted.

[0018] The support 11 is a porous component that can be permeated by gas and liquid. In the Fig. In the exemplary case shown in 1, the support 11 is a monolithic type support with a one-piece and continuously formed column-shaped main body, which is provided with a plurality of through holes 111 extending in the longitudinal direction (i.e. in Fig. 1 in the left and right directions). In the Fig. In the example shown in Figure 1, the support 11 has an essentially circular column shape. A cross-section perpendicular to the longitudinal direction of each of the through holes 111 (i.e., cells) is, for example, essentially circular. Fig.1. The diameter of each through-hole 111 is larger than the actual diameter, and the number of through-holes 111 is smaller than the actual number. The separating membrane 12 is formed on an inner surface of each through-hole 111, substantially covering the entire inner surface of the through-hole 111.

[0019] The length of the support 11 (i.e. the length in the left and right directions of 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 center 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. Furthermore, the shape of the support 11 can be, for example, honeycomb-like, flat-plate-like, tubular, cylindrical, columnar, polygonal-prismatic, or the like. If the support 11 has a tubular or cylindrical shape, the thickness of the support 11 is, for example, 0.1 mm to 10 mm.

[0020] The support 11 is made of ceramic. Examples of a ceramic sintered body selected as the material for the support 11 include aluminum oxide, silicon dioxide, mullite, zirconium oxide, titanium dioxide, yttrium oxide, silicon nitride, silicon carbide, and the like. In the present preferred embodiment, the support 11 contains at least one type of aluminum oxide, silicon dioxide, and mullite. The support 11 may contain an inorganic binder. At least one of the following may be used as the inorganic binder: titanium dioxide, mullite, readily sinterable aluminum oxide, silicon dioxide, glass frit, a clay mineral, and readily sinterable cordierite.

[0021] The average pore diameter of the support 11 is, for example, 0.01 µm to 70 µm, and 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, and preferably 0.05 µm to 0.5 µm. The average pore diameter can be measured, for example, using a mercury porosimeter, a permeability porometer, or a nanopermeability porometer. Regarding the pore diameter distribution of the entire support 11, including its surface and interior, D5 is, for example, 0.01 µm to 50 µm, D50, for example, 0.05 µm to 70 µm, and D95, for example, 0.1 µm to 2000 µm. The porosity of the support 11 near the surface on which the separating membrane 12 is formed is, for example, 20% to 60%.

[0022] The support 11, for example, has a multilayer structure in which a plurality of layers with different average pore diameters are stacked in one thickness direction. The average pore diameter and the sintered particle diameter in a surface layer, including the surface on which the separation membrane 12 is formed, are smaller than in layers other than the surface layer. The average pore diameter in the surface layer of the support 11 is, for example, 0.01 µm to 1 µm and preferably 0.05 µm to 0.5 µm. If the support 11 has a multilayer structure, the materials for the respective layers can be those described above. The materials for the plurality of layers that form the multilayer structure can be the same or different from one another.If the support 11 has a multilayer structure, the average pore diameter of the support 11 refers to the average pore diameter in the surface layer including the surface on which the separation membranes 12 are formed.

[0023] The separation membrane 12 is a porous membrane with micropores. The separation membrane 12 can separate a specific substance from a mixture containing a multitude of different substances, using a molecular sieve function or similar mechanism. Compared to the specific substance, each of the other substances penetrates the separation membrane 12 less readily. In other words, the permeance of each other substance through the separation membrane 12 is lower than that of the specific substance described above.

[0024] The average thickness of the separation membrane 12 is no greater than 2 µm. This allows for high permeance. A lower limit for the average thickness of the separation membrane 12 is not particularly restrictive, but with a view to increasing the separation efficiency, the lower limit for the average thickness of the separation membrane 12 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 a surface of the separation membrane 12 is exposed, for example, by cross-sectional polishing. A plurality of randomly selected viewing fields (e.g., seven viewing fields) are observed in the cross-section using a scanning electron microscope (SEM). The SEM magnification is, for example, 5000x.The average thickness (viewing field average thickness) of the separating membrane 12 in each viewing field is determined, and the arithmetic mean of the viewing field average thicknesses in the remaining viewing fields, obtained by excluding the viewing fields with the largest and smallest viewing field average thickness values, is determined as the average thickness of the separating membrane 12. The surface roughness (Ra) of the separating membrane 12 is, for example, 2 µm or less, preferably 1 µm or less, and more preferably 0.5 µm or less.

[0025] As described above, the separation membrane 12 is formed from MOF. In other words, the separation membrane 12 is an MOF membrane. Although the separation membrane 12 is typically composed only of MOF, it may also contain small amounts (e.g., 1% by mass or less) of other substances besides MOF, depending on the manufacturing process or similar factors. The pore diameter of the MOF from which the separation membrane 12 is constructed is, for example, 1 nm or less. The pore diameter can be calculated from the framework structure of the MOF crystals. 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.

[0026] The average particle diameter of the MOF from which the separation membrane 12 is constructed is, for example, 0.1 µm to 2 µm. The average particle diameter is preferably 1 µm or less and more preferably 0.5 µm or less. In the separation membrane 12, which is constructed from the MOF with a small average particle diameter, it is possible to reduce grain boundary defects, which relate to the formation of an excessively large gap between the crystals of the MOF, and thereby increase the separation efficiency. The average particle diameter of the MOF in the present preferred embodiment is the arithmetic mean of the respective largest diameters of a plurality of particles (e.g., 30 particles), measured by cross-sectional observation using SEM. The plurality of particles to be measured can be randomly selected from an image obtained by SEM.

[0027] At an interface between the separating membrane 12 and the support 11, a composite layer 13 is formed, in which the MOF crystals enter the interior of the pores of the support 11. Fig. Figure 2 shows the composite layer 13 by overlapping hatching of the carrier 11. The composite layer 13 is part of the carrier 11. The thickness of the composite layer 13 is, for example, no more than 2 µm. This makes it possible to suppress a reduction in permeability due to the presence of the composite layer 13. The composite layer 13 does not have to be present, and a lower limit for the thickness of the composite layer 13 is 0.

[0028] When measuring the thickness of the composite layer 13, the boundary positions of the composite layer 13 are determined during cross-sectional analysis using SEM. These boundary positions are defined in one direction (hereinafter referred to as the "depth direction") perpendicular to the interface between the support 11 and the separating membrane 12, near a measurement position along the interface. More precisely, the boundary position of the composite layer 13 on the side of the separating membrane 12 is the interface between the separating membrane 12 and the support 11. The boundary position of the composite layer 13 on the other side, opposite the separating membrane 12, is an edge of the MOF that is furthest away from the separating membrane 12 in the depth direction, among the MOFs present in the pores of the support 11.The distance between the boundary position of the composite layer 13 on the side of the separation membrane 12 and that on the other side opposite the separation membrane 12 in the depth direction is determined as the thickness of the composite layer 13 at the measurement position. Then, an average of the thicknesses of the composite layer 13 at a large number of different measurement positions (e.g., 10 measurement positions) is determined as the thickness of the composite layer 13 in the separation membrane complex 1.

[0029] The MOF forming the separating membrane 12 is made of aluminum ions (Al 3+The membrane is constructed from 1H-pyrrole-2,5-dicarboxylic acid and ligands (organic ligands) coordinated to the aluminum ions. It is preferred that the ligands have a high affinity for CO₂ and contain, for example, 1H-pyrrole-2,5-dicarboxylic acid, 2,5-furandicarboxylic acid, or 3,5-pyridinedicarboxylic acid. Depending on the type of substance to be separated, other ligands can also be used. A powder X-ray diffraction (XRD) pattern of the MOF of the separation membrane 12 shows 2θ peaks at all diffraction angles listed in Table 2. (Table 2) 2θ [°] (1) 8,2-8,4 (2) 9,1-9,3 (3) 11,8-12,0 (4) 12,4-12,6 (5) 14,9-15,1 (6) 16,7-16,9 (7) 17,1-17,3 (8) 18,4-18,6 (9) 19,1-19,3 (10) 22,5-22,7 (11) 24,3-24,5 (12) 25,1-25,3 (13) 26,9-27,1

[0030] The powder X-ray diffraction pattern is recorded using CuKα rays as the radiation source of an X-ray diffraction apparatus. For example, an X-ray diffraction apparatus from Rigaku Corporation (apparatus name: MiniFlex 600) is used under the following conditions: tube voltage 40 kV, tube current 15 mA, scanning rate 0.5° / min, and scanning step 0.02°. Further conditions are: divergence slit 1.25°, scattering slit 1.25°, receiving slit 0.3 mm, incidence angle 5.0°, and light-receiving solar slit 5.0°. No monochromator is used, and a nickel foil with a thickness of 0.015 mm is used as the CuKβ beam filter.

[0031] Next, with reference to Fig.Section 3 describes an exemplary procedure for the preparation of the separation membrane complex 1. In the preparation of the separation membrane complex 1, the seed crystals to be used for the production of the separation membrane 12 are first prepared (step S11). For example, MOF powder is synthesized as seed crystals by hydrothermal synthesis (solvothermal synthesis), and the seed crystals are obtained from the MOF powder. The MOF powder can be synthesized by any known manufacturing process. The MOF powder can be used as seed crystals or processed by pulverization or the like to obtain the seed crystals.

[0032] The average particle diameter (D50) of the seed crystals is preferably no greater than 0.5 µm. This makes it possible to suppress the occurrence of grain boundary defects due to an excessive increase in the average particle diameter of the MOF. A lower limit for the average particle diameter of the seed crystals is not particularly important, but by setting the average particle diameter to, for example, no less than 0.1 µm, a reduction in the crystallinity of the seed crystals can be suppressed. The average particle diameter of the seed crystals can be measured, for example, by a laser scattering method.

[0033] The porous support 11 is then immersed in a dispersion liquid containing the seed crystals, and the seed crystals are thereby deposited onto the support 11 (step S12). Alternatively, the dispersion liquid containing the seed crystals can be brought into contact with a section of the support 11 where the separation membrane 12 is to be formed, thereby depositing the seed crystals onto the support 11. In this way, a support with seed crystals deposited on it is produced. The seed crystals can be deposited onto the support 11 by any other method.

[0034] Next, a synthesis solution (also called synthetic sol or starting material solution) is prepared and used to form the separation membrane 12 (step S13). The synthesis solution can be prepared before or simultaneously with step S12. To prepare the synthesis solution, water, a monocarboxylic acid salt, the ligands, and an organic solvent are first mixed. A monocarboxylic acid salt is, for example, a formate such as sodium formate, lithium formate, potassium formate, or the like, or an acetate such as sodium acetate or the like. The monocarboxylic acid acts as a modulator in MOF synthesis and contributes to increased crystallinity. Therefore, an amino acid (e.g., glycine, arginine, or the like) containing a monocarboxylic acid can be used.Regarding the ligands, various organic compounds can be used in the MOF synthesized using these ligands, provided that a powder X-ray diffraction pattern with peaks at the diffraction angles 2θ specified in Table 2 is obtained. Preferred ligands are organic compounds with a high affinity for CO₂ and include, for example, 1H-pyrrole-2,5-dicarboxylic acid, 2,5-furandicarboxylic acid, 3,5-pyridinedicarboxylic acid, or the like. A preferred organic solvent is an organic compound containing a carbonyl group (carboxyl group or the like) and includes, for example, N,N-dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), N-methylformamide, or the like. An organic solvent without a carbonyl group may also be used.

[0035] In the synthesis solution, the ratio of the amount of monocarboxylic acid salt to that of the ligands (hereinafter also referred to as the "monocarboxylic acid salt / ligand ratio") is preferably 0.5 to 1.8. If no monocarboxylic acid salt is added, the synthesis solution becomes cloudy even when the heating and stirring process described later is carried out, the uniformity decreases, and the formation of the MOF is hindered. On the other hand, as described later, excessive addition of monocarboxylic acid salt can more easily lead to a coordination defect, which involves the absence of some of the ligands from which the MOF is built. Furthermore, the ratio of the amount of organic solvent to that of the ligands (hereinafter also referred to as the "organic solvent / ligand ratio") is preferably 0.1 to 10. If no organic solvent is added, the crystallinity of the MOF decreases.On the other hand, as described later, adding too much organic solvent can more easily lead to coordination errors.

[0036] After obtaining a solution in which water, monocarboxylic acid salt, the ligands, and the organic solvent are mixed, a heating and stirring process (aging) is carried out. The heating temperature in the heating and stirring process is, for example, 20 to 100°C and preferably 40 to 80°C. The processing time is, for example, 1 to 100 hours and preferably 1 to 12 hours. After completion of the heating and stirring process, an aluminum source (Al source) is mixed into the solution. The Al source is, for example, aluminum sulfate, aluminum chloride, aluminum nitrate, aluminum hydroxide, boehmite, or the like. In this way, the synthesis solution used to form the separation membrane 12 is obtained. The mixing of the organic solvent into the solution does not necessarily have to take place before the heating and stirring process, but can also take place during or after the heating and stirring process.In other words, the organic solvent can be mixed into the solution described above at any time.

[0037] After preparation of the synthesis solution, the support 11, on which the seed crystals are deposited, is immersed in the synthesis solution. The hydrothermal synthesis is then initiated by heating the synthesis solution. During the hydrothermal synthesis, the MOF is grown from the seed crystals as nuclei to form the separation membrane 12, which is a dense MOF membrane on the support 11 (step S14). The synthesis temperature (the heating temperature of the synthesis solution) during the hydrothermal synthesis is, for example, 40°C to 200°C and preferably 70°C to 150°C. The hydrothermal synthesis time is, for example, 1 to 100 hours and preferably 1 to 50 hours.

[0038] After completion of the hydrothermal synthesis, the support 11 and the separation membrane 12 are washed with pure water and subsequently with ethanol or the like. Preferably, the washing with water and ethanol or the like is repeated several times. After washing, the support 11 and the separation membrane 12 are dried, for example, at 100°C. The separation membrane complex 1 described above is obtained by the above process.

[0039] Next, with reference to the Fig. 4 and Fig. 5 the separation of a mixed substance using the separation membrane complex 1 is described. Fig. Figure 4 is a view showing a separating device 2. Fig. Figure 5 is a flowchart showing the process of separating the mixed substance through the separation device 2.

[0040] In the separation device 2, a mixed substance containing a variety of fluid types (i.e., gases or liquids) is fed to the separation membrane complex 1, and a substance with high permeability in the mixed substance is caused to permeate the separation membrane complex 1, thereby being separated from the mixed substance. The separation in the separation device 2 can be carried out, for example, to extract a substance with high permeability from a mixed substance or to concentrate a substance with low permeability.

[0041] The mixed substance (i.e., the mixed fluid) can be a mixed gas containing a variety of gases, a mixed liquid containing a variety of liquids, or a gas-liquid biphase fluid containing both a gas and a liquid.

[0042] The mixed substance contains at least one type of, for example, hydrogen (H2), helium (He), nitrogen (N2), oxygen (O2), water (H2O), carbon monoxide (CO), carbon dioxide (CO2), nitrogen oxide, ammonia (NH3), sulfur oxide, hydrogen sulfide (H2S), sulfur fluoride, mercury (Hg), arsine (AsH3), hydrogen cyanide (HCN), carbonyl sulfide (COS), C1 to C8 hydrocarbons, organic acids, alcohol, mercaptans, esters, ethers, ketones and aldehydes.

[0043] Nitrogenous oxide is a compound of nitrogen and oxygen. The nitrogen oxide described above is, for example, a gas called NO₂. X such as nitric oxide (NO), nitrogen dioxide (NO2), dinitrogen monoxide (also known as dinitrogen monoxide) (N2O), dinitrogen trioxide (N2O3), dinitrogen tetroxide (N2O4), dinitrogen pentoxide (N2O5) or the like.

[0044] Sulfur oxide is a compound of sulfur and oxygen. The sulfur oxide described above is, for example, a gas called SO₂. X such as sulfur dioxide (SO2), sulfur trioxide (SO3) or the like.

[0045] Sulfur fluoride is a compound of fluorine and sulfur. Examples of the sulfur fluoride described above include disulfur difluoride (SFSF, S=SF2), sulfur difluoride (SF2), sulfur tetrafluoride (SF4), sulfur hexafluoride (SF6), and disulfur decafluoride (SF2F). 10 ) or the like.

[0046] C1 to C8 hydrocarbons are hydrocarbons with no fewer than 1 and no more than 8 carbon atoms. C3 to C8 hydrocarbons can be linear chain compounds, side chain compounds, or ring compounds. Furthermore, C2 to C8 hydrocarbons can be either saturated hydrocarbons (i.e., in which no double or triple bonds are present in the molecule) or unsaturated hydrocarbons (i.e., in which one double and / or one triple bond is present in the molecule). Examples of C1 to C4 hydrocarbons are methane (CH4), ethane (C2H6), ethylene (C2H4), propane (C3H8), propylene (C3H6), normal butane (CH3(CH2)2CH3), isobutane (CH(CH3)3), 1-butene (CH2=CHCH2CH3), 2-butene (CH3CH=CHCH3) or isobutylene (CH2=C(CH3)2).

[0047] The organic acid described above is a carboxylic acid, a sulfonic acid, or the like. Examples of carboxylic acids include formic acid (CH₂O₂), acetic acid (C₂H₄O₂), oxalic acid (C₂H₂O₄), acrylic acid (C₃H₄O₂), benzoic acid (C₆H₅COOH), and the like. Examples of sulfonic acids include ethanesulfonic acid (C₂H₆O₃S) and the like. The organic acid can be either a chain compound or a ring compound.

[0048] The alcohol described above is, for example, methanol (CH3OH), ethanol (C2H5OH), isopropanol (2-propanol) (CH3CH(OH)CH3), ethylene glycol (CH2(OH)CH2(OH)), butanol (C4H9OH) or the like.

[0049] Mercaptans are organic compounds with hydrogenated sulfur (SH) at their terminal end and are also known as thiols or thioalcohols. Examples of mercaptans described above include methyl mercaptan (CH3SH), ethyl mercaptan (C2H5SH), 1-propanethiol (C3H7SH), and similar compounds.

[0050] The ester described above is, for example, formic acid ester, acetic acid ester, or the like.

[0051] The ether described above is, for example, dimethyl ether ((CH3)2O), methyl ethyl ether (C2H5OCH3), diethyl ether ((C2H5)2O) or the like.

[0052] The ketone described above is, for example, acetone ((CH3)2CO), methyl ethyl ketone (C2H5COCH3), diethyl ketone ((C2H5)2CO) or the like.

[0053] The aldehyde described above is, for example, acetaldehyde (CH3CHO), propionaldehyde (C2H5CHO), butanal (butyraldehyde) (C3H7CHO) or the like.

[0054] The following description assumes that the mixed substance to be separated by the separation device 2 is a mixed gas containing several types of gases.

[0055] The separating device 2 comprises the separating membrane complex 1, sealing elements 21, a housing 22, two sealing components 23, a feed section 26, a first collecting section 27, and a second collecting section 28. The separating membrane complex 1, the sealing elements 21, and the sealing components 23 are located inside the housing 22. The feed section 26, the first collecting section 27, and the second collecting section 28 are located outside the housing 22 and connected to the housing 22.

[0056] The sealing parts 21 are components that are located at both end sections in the longitudinal direction (i.e. in the left and right direction of Fig.4) of the support 11 and cover and seal both end surfaces in the longitudinal direction of the support 11 and outer surfaces near the end surfaces. The sealing elements 21 prevent gas from entering or escaping both end surfaces of the support 11. The sealing element 21 is, for example, a plate-shaped component made of glass or plastic. The material and shape of the sealing element 21 can be modified accordingly. Since the sealing element 21 is provided with a plurality of openings that correspond to the plurality of through-holes 111 of the support 11, both ends of each through-hole 111 of the support 11 are not covered in the longitudinal direction by the sealing elements 21. Therefore, gas or the like can enter and exit from both ends of the through-hole 111.

[0057] The shape of the housing 22 is not particularly restricted; for example, it is a tubular component with a substantially cylindrical shape. The housing 22 is made of, for example, stainless steel or carbon steel. The longitudinal direction of the housing 22 runs substantially parallel to the longitudinal direction of the separating membrane complex 1. A feed opening 221 is located at an end section on one side in the longitudinal direction of the housing 22 (i.e., at an end section on the left side). Fig.4) provided, and a first outlet opening 222 is provided at another end section on the other side. A second outlet opening 223 is provided on a side surface of the housing 22. The feed section 26 is connected to the feed opening 221. The first collecting section 27 is connected to the first outlet opening 222. The second collecting section 28 is connected to the second outlet opening 223. An interior of the housing 22 is a sealed space that is isolated from the space surrounding the housing 22.

[0058] The two sealing components 23 are arranged longitudinally around the entire circumference between an outer surface of the separating membrane complex 1 and an inner surface of the housing 22, near both end sections of the separating membrane complex 1. Each of the sealing components 23 is an essentially ring-shaped component made of a material that is impermeable to gas. For example, the sealing component 23 is an O-ring made of a flexible resin. The sealing components 23 are in close contact with the outer surface of the separating membrane complex 1 and the inner surface of the housing 22 around their entire circumference. In the exemplary case of Fig.4. The sealing components 23 come into close contact with the outer surfaces of the sealing components 21 and indirectly into close contact with the outer surface of the separating membrane complex 1, with the sealing components 21 being arranged between them. The sections between the sealing components 23 and the outer surface of the separating membrane complex 1, as well as between the sealing components 23 and the inner surface of the housing 22, are sealed, thus preventing the gas from passing through these sections, either largely or completely.

[0059] The supply section 26 guides the mixed gas through the supply opening 221 into the interior of the housing 22. The supply section 26 includes, for example, a blower or a pump for pumping the mixed gas towards the housing 22. The blower or pump includes a pressure control unit for controlling the pressure of the mixed gas supplied to the housing 22. The first collecting section 27 and the second collecting section 28 each include, for example, a storage container for storing the gas discharged from the housing 22, or a blower or a pump for transporting the gas.

[0060] When the separation of the mixed gas is performed, the separation device 2 described above is manufactured, thereby producing the separation membrane complex 1 (step S21). Subsequently, the feed section 26 introduces a mixed gas, containing a variety of gases with different permeances for the separation membrane 12, into the interior of the housing 22. For example, the main component of the mixed gas is CO2 and N2. The mixed gas can contain any gas other than CO2 or N2. The pressure (i.e., the feed pressure) of the mixed gas supplied from the feed section 26 into the interior of the housing 22 is, for example, 0.1 MPa to 20.0 MPa. The temperature for the separation of the mixed gas is, for example, 10°C to 150°C.

[0061] The mixed gas supplied from the feed section 26 into the housing 22 is fed from the left end of the separating membrane complex 1 in this figure into the interior of each through-hole 111 of the support 11, as indicated by arrow 251. High-permeability gas (e.g., CO2, hereinafter referred to as the "high-permeability substance") in the mixed gas permeates the separating membrane 12, which is formed on the inner surface of each through-hole 111 and the support 11, and is drawn out of the outer surface of the support 11. The high-permeability substance is thereby separated from low-permeability gas (e.g., N2, hereinafter referred to as the "low-permeability substance") in the mixed gas (step S22). The gas discharged from the outer surface of the support 11 (hereinafter referred to as the “permeate substance”) is collected by the second collecting section 28 through the second outlet opening 223, as indicated by arrow 253. The pressure (i.e.The permeate pressure of the gas collected through the second collecting part 28 via the second outlet opening 223 is, for example, about 1 atmospheric pressure (0.101 MPa).

[0062] Furthermore, the mixed gas contains a gas (hereinafter referred to as the “non-permeate substance”) that is not the gas that has permeated the separating membrane 12 and the support 11. This non-permeate substance flows through each through-hole 111 of the support 11 from left to right in this figure and is collected through the first collecting section 27 via the first outlet opening 222, as indicated by arrow 252. The pressure of the gas collected through the first outlet opening 222 of the first collecting section 27 is, for example, essentially equal to the supply pressure. In addition to the low-permeability substance described above, the non-permeate substance may also include a high-permeability substance that has not permeated the separating membrane 12.

[0063] Next, Examples 1 to 21 and Comparative Examples 1 to 7 of the separation membrane complex are described. Table 3 shows the type of ligands, the D50 value (average particle diameter) of the seed crystals, the monocarboxylic acid salt / ligand ratio, the organic solvent / ligand ratio, and the heating and stirring conditions in Examples 1 to 21 and Comparative Examples 1 to 7. (Table 3) Ligands D50 value of seed crystals (µm) Monocarboxylic acid salt / ligands (molar ratio) Organic solvent / ligands (molar ratio) Heating and stirring conditions Example 1 1H-Pyrrole-2,5-dicarboxylic acid 0,33 1,8 0,8 60°C x 2 h Example 2 1H-Pyrrole-2,5-dicarboxylic acid 0,33 1,8 0,8 60°C x 2 h Example 3 1H-Pyrrole-2,5-dicarboxylic acid 0,33 1 0,8 60°C x 2 h Example 4 1H-Pyrrole-2,5-dicarboxylic acid 0,33 0,6 0,8 60°C x 2 h Example 5 1H-Pyrrole-2,5-dicarboxylic acid 0,33 1,8 0,8 40°C x 5 h Example 6 1H-Pyrrole-2,5-dicarboxylic acid 0,33 1,8 0,8 80°C x 12 h Example 7 1H-Pyrrole-2,5-dicarboxylic acid 0,33 1,8 0,1 60°C x 2 h Example 8 1H-Pyrrole-2,5-dicarboxylic acid 0,33 1,8 8 60°C x 2 h Example 9 1H-Pyrrole-2,5-dicarboxylic acid 0,33 1,8 0,8 60°C x 2 h Example 10 1H-Pyrrole-2,5-dicarboxylic acid 0,50 1,8 0,8 60°C x 2 h Example 11 2,5-Furandicarboxylic acid 0,25 1,8 0,8 60°C x 2 h Example 12 2,5-Furandicarboxylic acid 0,25 1,8 0,8 40°C x 2 h Example 13 2,5-Furandicarboxylic acid 0,25 1 0,8 60°C x 2 h Example 14 2,5-Furandicarboxylic acid 0,25 1,8 2 60°C x 2 h Example 15 3,5-Pyridinedicarboxylic acid 0,35 1,8 0,8 60°C x 2 h Example 16 3,5-Pyridinedicarboxylic acid 0,35 1,8 0,8 40°C x 2 h Example 17 3,5-Pyridinedicarboxylic acid 0,35 1 0,8 60°C x 2 h Example 18 3,5-Pyridinedicarboxylic acid 0,35 1,8 2 60°C x 2 h Example 19 1H-Pyrrole-2,5-dicarboxylic acid 2,5-Furandicarboxylic acid 0,33 1,5 0,5 60°C x 2 h Example 20 1H-Pyrrole-2,5-dicarboxylic acid 3,5-Pyridinedicarboxylic acid 0,33 1,5 0,5 60°C x 2 h Example 21 2,5-Furandicarboxylic acid 3,5-Pyridindicarboxylic acid 0,25 1,5 0,8 60°C x 2 h Comparative example 1 1H-Pyrrole-2,5-dicarboxylic acid 0,33 1,8 0,8 No Comparative example 2 1H-Pyrrole-2,5-dicarboxylic acid 0,33 0 0,8 No Comparative example 3 1H-Pyrrole-2,5-dicarboxylic acid 0,33 1,8 12 60°C x 2 h Comparative example 4 1H-Pyrrole-2,5-dicarboxylic acid 0,33 1,8 0 60°C x 2 h Comparative example 5 2,5-Furandicarboxylic acid - 2 0 No Comparative example 6 2,5-Furandicarboxylic acid 0,25 2 0 No Comparative example 7 3,5-Pyridinedicarboxylic acid 0,35 1,8 0,8 No <Herstellung von Impfkristallen (1H-Pyrrol-2,5-dicarbonsäure)>

[0064] 1.551 g of 1H-pyrrole-2,5-dicarboxylic acid and 1.36 g of sodium formate are mixed in 50 ml of deionized water to prepare a solution. After stirring the solution at 50°C for 3 hours, it is cooled to room temperature and 3.333 g of aluminum sulfate 18-hydrate (octadecahydrate) is added. This solution is then kept at 120°C for 12 hours. A sediment is separated using a centrifuge and washed three times with deionized water and ethanol. This yields MOF powder containing 1H-pyrrole-2,5-dicarboxylic acid as a ligand, in the form of seed crystals. <Herstellung von Impfkristallen (2,5-Furandicarbonsäure)>

[0065] 1.562 g of 2,5-furandicarboxylic acid and 1.36 g of sodium formate are mixed in 50 ml of deionized water to prepare a solution. After stirring the solution at 50°C for 3 hours, it is cooled to room temperature and 2.413 g of aluminum chloride hexahydrate are added. This solution is then kept at 100°C for 12 hours. A precipitate is separated using centrifugation and washed three times with deionized water and ethanol. This yields MOF powder containing 2,5-furandicarboxylic acid as a ligand, in the form of seed crystals. <Herstellung von Impfkristallen (3,5-Pyridindicarbonsäure)>

[0066] 1.67 g of 3,5-pyridinedicarboxylic acid and 1.36 g of sodium formate are mixed in 50 ml of deionized water to prepare a solution. After stirring the solution at 50°C for 3 hours, it is cooled to room temperature and 3.333 g of aluminum sulfate 18-hydrate (octadecahydrate) is added. This solution is then kept at 120°C for 12 hours. A sediment is separated using a centrifuge and washed three times with deionized water and ethanol. This yields MOF powder containing 3,5-pyridinedicarboxylic acid as a ligand, in the form of seed crystals. <Aufbringen der Impfkristalle auf einen Keramikträger>

[0067] The resulting 1 g of seed crystals are placed in a glass bottle containing zirconia pebbles and then mixed with 9 g of water. The bottle is placed on 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 diameter (D50) of 0.33 to 0.50 µm. The seed crystals are then applied to the ceramic substrate. (Example 1)

[0068] 1.551 g of 1H-pyrrole-2,5-dicarboxylic acid, 1.22 g of sodium formate, and 0.58 g of N,N-dimethylformamide as an organic solvent are added to 150 ml of deionized water to prepare a mixed solution. The mixed solution is stirred for 2 hours while heated to 60°C (heating and stirring method). After verifying that the mixed solution has become transparent, it is cooled to room temperature. Then, 3.333 g of aluminum sulfate 18-hydrate (octadecahydrate) are added to the mixed solution to prepare a synthesis solution. In the synthesis solution, the ratio of monocarboxylic acid salt to ligand (in molar ratio, the same applies to the following values) is 1.8, and the ratio of organic solvent to ligand (in molar ratio, the same applies to the following values) is 0.8.Next, the ceramic support, on which the seed crystals (with an average particle diameter of 0.33 µm) are applied with 1H-pyrrole-2,5-dicarboxylic acid, and the synthesis solution described above are placed in a Teflon container (registered trademark), and the hydrothermal synthesis is carried out at 100°C for 20 hours. The resulting separation membrane complex is washed three times with deionized water and ethanol and then dried. (Example 2)

[0069] Example 2 is the same as Example 1, except that the temperature of the hydrothermal synthesis was changed to 80°C. (Example 3)

[0070] Example 3 is the same as Example 1, except that the ratio of monocarboxylic acid salt to ligands has been changed to 1. (Example 4)

[0071] Example 4 is the same as Example 1, except that the ratio of monocarboxylic acid salt to ligands has been changed to 0.6. (Example 5)

[0072] Example 5 is the same as Example 1, except that the heating temperature in the heating and stirring process of the mixed solution has been changed to 40°C and the stirring time has been changed to 5 hours. (Example 6)

[0073] Example 6 is the same as Example 1, except that the heating temperature in the heating and stirring process of the mixed solution has been changed to 80°C and the stirring time has been changed to 12 hours. (Example 7)

[0074] Example 7 is the same as Example 1, except that the ratio of organic solvent to ligand has been changed to 0.1. (Example 8)

[0075] Example 8 is the same as Example 1, except that the ratio of organic solvent to ligand has been changed to 8. (Example 9)

[0076] Example 9 is the same as Example 1, except that the processing time of the hydrothermal synthesis has been changed to 10 hours and the organic solvent has been changed to N-methylformamide. (Example 10)

[0077] Example 10 is the same as Example 1, except that the average particle diameter of the seed crystals applied to the ceramic support has been changed to 0.50 µm. (Example 11)

[0078] 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 are added to 150 ml of deionized water to prepare a mixed solution. The mixed solution is stirred for 2 hours while heated to 60°C (heating and stirring method). After verifying that the mixed solution has become transparent, it is cooled to room temperature. Then, 2.413 g of aluminum chloride hexahydrate are added to the mixed solution to prepare a synthesis solution. In the synthesis solution, the ratio of monocarboxylic acid salt to ligand is 1.8 and the ratio of organic solvent to ligand is 0.8.Next, the ceramic support, on which the seed crystals (with an average particle diameter of 0.25 µm) containing 2,5-furandicarboxylic acid are applied, and the synthesis solution described above are placed in the Teflon container, and the hydrothermal synthesis is carried out at 80°C for 20 hours. The resulting separation membrane complex is washed three times with deionized water and ethanol and then dried. (Example 12)

[0079] Example 12 is the same as Example 11, except that the heating temperature for the heating and stirring process of the mixed solution has been changed to 40°C. (Example 13)

[0080] Example 13 is the same as Example 11, except that the ratio of monocarboxylic acid salt to ligand has been changed to 1. (Example 14)

[0081] Example 14 is the same as Example 11, except that the organic solvent / ligand has been changed to 2. (Example 15)

[0082] 1.67 g of 3,5-pyridinedicarboxylic acid, 1.22 g of sodium formate, and 0.58 g of N,N-dimethylformamide as an organic solvent are added to 150 ml of deionized water to prepare a mixed solution. The mixed solution is stirred for 2 hours while heated to 60°C (heating and stirring method). After verifying that the mixed solution has become transparent, it is cooled to room temperature. Then, 3.333 g of aluminum sulfate 18-hydrate (octadecahydrate) are added to the mixed solution to prepare a synthesis solution. In the synthesis solution, the ratio of monocarboxylic acid salt to ligand is 1.8 and the ratio of organic solvent to ligand is 0.8.Next, the ceramic support, on which the seed crystals (with an average particle diameter of 0.35 µm) containing 3,5-pyridinedicarboxylic acid are applied, and the synthesis solution described above are placed in the Teflon container, and the hydrothermal synthesis is carried out at 100°C for 20 hours. The resulting separation membrane complex is washed three times with deionized water and ethanol and then dried. (Example 16)

[0083] Example 16 is the same as Example 15, except that the heating temperature for the heating and stirring process of the mixed solution has been changed to 40°C. (Example 17)

[0084] Example 17 is the same as Example 15, except that the ratio of monocarboxylic acid salt to ligand has been changed to 1. (Example 18)

[0085] Example 18 is the same as Example 15, except that the ratio of organic solvent to ligand has been changed to 2. (Example 19)

[0086] 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 are added to 150 ml of deionized water to prepare a mixed solution. The mixed solution is stirred for 2 hours while heated to 60°C (heat and stir method). After verifying that the mixed solution has become transparent, it is cooled to room temperature. Then, 3.333 g of aluminum sulfate 18-hydrate (octadecahydrate) are added to the mixed solution to prepare a synthesis solution. In the synthesis solution, the ratio of monocarboxylic acid salt to ligand is 1.5 and the ratio of organic solvent to ligand is 0.5.Next, the ceramic support, on which the same seed crystals (seed crystals containing 1H-pyrrole-2,5-dicarboxylic acid) as in Example 1 are applied, and the synthesis solution described above are placed in the Teflon container, and the hydrothermal synthesis is carried out at 100°C for 10 hours. The resulting separation membrane complex is washed three times with deionized water and ethanol and then dried. (Example 20)

[0087] 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 as an organic solvent are added to 150 ml of deionized water to prepare a mixed solution. The mixed solution is heated at 60°C for 2 hours with stirring (heating and stirring method). After verifying that the mixed solution has become transparent, it is cooled to room temperature. Then, 3.333 g of aluminum sulfate 18-hydrate (octadecahydrate) are added to the mixed solution to prepare a synthesis solution. In the synthesis solution, the ratio of monocarboxylic acid salt to ligand is 1.5 and the ratio of organic solvent to ligand is 0.5.Next, the ceramic support, on which the same seed crystals (seed crystals containing 1H-pyrrole-2,5-dicarboxylic acid) as in Example 1 are applied, and the synthesis solution described above are placed in the Teflon container, and the hydrothermal synthesis is carried out at 100°C for 20 hours. The resulting separation membrane complex is washed three times with deionized water and ethanol and then dried. (Example 21)

[0088] 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 are added to 150 ml of deionized water to prepare a mixed solution. The mixed solution is stirred for 2 hours while heated to 60°C (heating and stirring method). After verifying that the mixed solution has become transparent, it is cooled to room temperature. Then, 3.333 g of aluminum sulfate 18-hydrate (octadecahydrate) are added to the mixed solution to prepare a synthesis solution. In the synthesis solution, the ratio of monocarboxylic acid salt to ligand is 1.5 and the ratio of organic solvent to ligand is 0.8.Next, the ceramic support, on which the same seed crystals (seed crystals containing 2,5-furandicarboxylic acid) as in Example 11 are applied, and the synthesis solution described above are placed in the Teflon container, and the hydrothermal synthesis is carried out at 100°C for 20 hours. The resulting separation membrane complex is washed three times with deionized water and ethanol and then dried. (Comparative example 1)

[0089] Comparative example 1 is the same as example 1, except that the heating and stirring process is not carried out. (Comparative example 2)

[0090] Comparison Example 2 is identical to Comparison Example 1, except that the ratio of monocarboxylic acid salt to ligand has been changed to 0 (in other words, no monocarboxylic acid salt is added). Furthermore, no separation membrane is formed on the support in Comparison Example 2. (Comparative example 3)

[0091] Comparative example 3 is the same as example 1, except that the ratio of organic solvent to ligands has been changed to 12. (Comparative example 4)

[0092] Comparative example 4 is the same as example 1, except that the ratio of organic solvent to ligands was changed to 0 (in other words, no organic solvent was added). (Comparative example 5)

[0093] A synthesis solution is prepared according to the method and composition disclosed 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 to 17723) (document 1 described above), and as in document 1, membrane formation is carried out without the use of seed crystals. In Comparative Example 5, the entire surface of the support on which membrane formation is to be carried out cannot be covered with the separation membrane. (Comparative example 6)

[0094] Comparative example 6 is the same as comparative example 5, except that the same seed crystals (seed crystals containing 2,5-furandicarboxylic acid) are used as in example 11. (Comparative example 7)

[0095] Comparative example 7 is the same as example 15, except that the heating and stirring process is not carried out. <Messung und Bewertung des Trennmembrankomplexes>

[0096] Various measurements are performed on the separation membrane complex in Examples 1 to 21 and the comparison examples 1 to 7. Table 4 shows the average thickness of the separation membrane, the thickness of the composite layer, the average particle diameter of the separation membrane, the CO2 permeance, and the permeance ratio of SF6 / He. (Table 4) average thickness of the separating membrane (µm) Composite layer thickness (µm) average particle diameter of the separation membrane (µm) O2 permeance (GPU) Permeance ratio of SF6 / He Example 1 2 1,9 0,30 2000 0,015 Example 2 1,7 1,5 0,26 2100 0,016 Example 3 2 1,9 0,35 2000 0,008 Example 4 1,9 1,7 0,30 2400 0,009 Example 5 1,9 1,2 0,4U 2290 0,010 Example 6 1,8 1,2 0,10 2445 0,005 Example 7 2 1,5 0,31 2300 0,015 Example 8 2 1,9 0,25 2030 0,018 Example 9 1 1 0,20 4500 0,005 Example 10 1,5 1 0,30 3200 0,012 Example 11 2 1,9 0,30 1050 0,005 Example 12 1,7 1,5 0,26 1200 0,011 Example 13 1 1 0,20 2000 0,010 Example 14 1,7 1,3 0,30 1250 0,008 Example 15 2 1,9 0,30 1200 0,015 Example 16 2 1,9 0,30 1100 0,017 Example 17 2 1,9 0,40 1100 0,011 Example 18 1,9 1,8 0,28 1450 0,015 Example 19 1 1 0,2 3000 0,004 Example 20 1 1 0,25 2950 0,004 Example 21 2 1,3 0,40 1010 0,011 Comparative example 1 2,5 1,9 2,2 1900 0,05 Comparative example 2 - - - - No separation membrane is created. Comparative example 3 2 1,9 0,25 1900 0,061 Comparative example 4 2 1,5 0,31 2000 0,023 Comparative example 5 3 2 5 - Poor coverage with separating membrane Comparative example 6 2,5 2 2,3 750 0,101 Comparative example 7 2 1,8 3 950 0,029

[0097] The average thickness of the separating membrane, the thickness of the bonding layer, and the average particle diameter of the separating membrane are measured by cross-sectional observation using SEM, as previously described. In Examples 1 to 21, the average thickness of the separating membrane is not greater than 2 µm, and the thickness of the bonding layer is not greater than 2 µm. In Comparative Examples 1 and 3 to 7, the thickness of the bonding layer is not greater than 2 µm, but the average thickness of the separating membrane is not less than 2 µm. In Comparative Example 2, as described above, no separating membrane is produced on the support. In Examples 1 to 21, the average particle diameter of the separating membrane is less than 0.5 µm, but in Comparative Examples 1 and 5 to 7, the average particle diameter of the separating membrane is greater than 2 µm.When the powder X-ray diffraction measurement is performed on the MOF that forms the separation membrane of Examples 1 to 21, the powder X-ray diffraction pattern obtained exhibits peaks at the diffraction angles 2θ specified in Table 2 described above.

[0098] Furthermore, the permeance of a single gas is measured for CO2 gas, SF6 gas, and He gas using the separation device 2 described above. In comparative examples 2 and 5, where poor formation of the separation membrane occurs, the permeance is not measured. In each of examples 1 to 21, the CO2 permeance is not lower than 1000 GPU, and a high permeance is achieved. On the other hand, in each of comparative examples 6 and 7, the CO2 permeance is lower than 1000 GPU. Additionally, 1 GPU corresponds to 1 × 10 -6 cm 3 (STP) / (cm 2·s·cmHg). Furthermore, in each of examples 1 to 21, the ratio of the permeance of SF6 gas to the permeance of He gas, i.e., the permeance ratio of SF6 / He, is not higher than 0.020. On the other hand, in all comparison examples (comparative examples 1, 3, 4, 6 and 7) where the permeance was measured, the permeance ratio of SF6 / He is higher than 0.020.

[0099] If the separation membrane contains many grain boundary defects, each denoting the formation of an excessively large gap between the MOF crystals, or many coordination defects, each denoting the absence of some of the ligands that make up the MOF, a high separation factor cannot be achieved. Since the grain boundary defect or the coordination defect in the separation membrane described above is expected to have a defect size of 0.5 nm or more, in the present preferred embodiment, the amount of defects in the separation membrane is evaluated based on the permeance ratio of SF6 gas, which has a dynamic molecular diameter of 0.56 nm, and He gas, which has a dynamic molecular diameter sufficiently smaller than that of SF6 gas. In each of Examples 1 to 21, as described above, the permeance ratio of SF6 / He is not higher than 0.020, and SF6 gas barely penetrates the separation membrane.Therefore, in the separation membrane complex of each of examples 1 to 21, the grain boundary errors and coordination errors are reduced, and a high separation factor can be achieved. On the other hand, in all comparison examples where permeance was measured, the permeance ratio of SF6 / He is higher than 0.020, and a significant amount of SF6 gas passes through the separation membrane. Therefore, in the separation membrane complex of each of the comparison examples, the separation factor is lower due to the effects of the grain boundary errors and coordination errors.

[0100] Here, the reasons why the permeance ratio of SF6 / He in the separation membrane complex of each of examples 1 to 21 is reduced (the separation factor increases) are investigated. Fig. 6A and Fig. Figure 6B shows views used to illustrate the synthesis of a separation membrane 92 in a comparative example where the average particle diameter is relatively large. Fig. 7A and Fig. Figure 7B are views used to explain the synthesis of the separation membrane 12 in Examples 1 to 21, where the average particle diameter is relatively small. Fig. 6A and Fig. Figures 7A each show an initial state of membrane synthesis and the Fig. 6B and Fig. Figures 7B each show a final state of membrane synthesis.

[0101] In the synthesis of the separating membrane 92 in the comparative example, as in Fig. As shown in Figure 6A, it is assumed that the particle diameter of the MOF crystals 91 is large in an initial state of membrane synthesis. In this case, the gap between the MOF crystals 91 becomes large, and grain boundary defects easily occur. To fill the gap between the MOF crystals 91, it is necessary, as shown in Fig.As shown in Figure 6B, it is necessary to allow the MOF crystals 91 to grow larger, thereby increasing the thickness of the separation membrane 92. In other words, in the separation membrane with an average thickness of about 2 µm, the separation factor decreases.

[0102] On the other hand, in Examples 1 to 21, since the separation membrane 12 was synthesized by the secondary growth method using seed crystals with a small average particle diameter (e.g., not larger than 0.5 µm), the particle diameter of the MOF crystals 91 in the initial state of membrane synthesis, as in Fig. 7A shows, small. Therefore, the gap between the MOF crystals 91 becomes smaller and grain boundary defects occur less frequently. Furthermore, even at the end of membrane synthesis, when the average thickness is no greater than 2 µm, as in Fig.Figure 7B shows that a state is maintained in which the average particle diameter of the separation membrane 12 (the average particle diameter of the MOF crystals 91) is small, in particular 0.1 to 2 µm, and the occurrence of the grain boundary error is suppressed.

[0103] Although the reason for the decrease in the average particle diameter of the separation membrane is not entirely clear, it is assumed that the heating and stirring procedure contributes to this, since the average particle diameter in comparative examples 1, 6, and 7, where no heating and stirring procedure is performed, is greater than 2 µm in each case. It is assumed that the heating and stirring procedure heats and melts the ligands used as starting material for the synthesis solution, thereby adsorbing and stabilizing a MOF precursor in the synthesis solution onto the seed crystals, and this is thought to influence the formation of the MOF membrane described above.In the separation membrane complex of each of Examples 1 to 21, reducing the average particle diameter makes it possible to decrease the average thickness of the separation membrane (to 2 µm or less) and easily achieve a high permeance. Furthermore, it becomes possible to reduce the grain boundary error, thereby lowering the SF6 / He permeance ratio to no more than 0.020, in other words, achieving a high separation factor. In the separation membrane complex, the thickness of the composite layer consisting of the support and the MOF is also no greater than 2 µm, and the permeance of CO2 gas is no less than 1000 GPU.

[0104] In the synthesis of the MOF membrane, it is assumed that the organic solvent (and the monocarboxylic acid) competes with the ligands, thereby repeating the coordination / dissociation with / of metal ions and reducing the crystal growth rate, resulting in a MOF with high crystallinity. Therefore, if no organic solvent is added, the crystallinity of the MOF will be lower. Conversely, if the organic solvent is added in excess, the MOF is assumed to form through coordination with the organic solvent, and coordination errors can easily occur (see comparative example 3).In examples 1 to 21, adjusting the molar ratio of the organic solvent containing the carbonyl group and the ligands (ratio of organic solvent / ligands) in the synthesis solution to 0.1 to 10 yields a MOF with high crystallinity, while reducing the coordination error and thereby achieving a high separation factor.

[0105] Furthermore, it is assumed that in the synthesis solution, if no monocarboxylic acid salt is added, ligand deprotonation is minimal, the synthesis solution becomes cloudy and its uniformity is reduced, and the separation membrane is more difficult to generate (see Comparative Example 2). Conversely, it is assumed that if an excess of monocarboxylic acid salt is added, the MOF is formed while the monocarboxylic acid is coordinated to it, and thus the coordination error can occur more easily (see Comparative Example 6). In Examples 1 to 21, adjusting the ratio of monocarboxylic acid salt to ligand in the synthesis solution to 0.5 to 1.8 reduces the coordination error and ensures the uniformity of the synthesis solution, thereby allowing a suitable separation membrane to be obtained.

[0106] As described above, the separation membrane complex 1 comprises the porous ceramic support 11 and the separation membrane 12, which is formed on the support 11 and is composed of MOF. The average thickness of the separation membrane 12 is no more than 2 µm. The MOF is composed of aluminum ions and ligands coordinated to the aluminum ions. The powder X-ray diffraction pattern of the MOF exhibits peaks at the diffraction angles 2θ specified in Table 2 above. In the separation membrane complex 1, the permeance ratio of SF6 / He is no more than 0.020. In such a separation membrane complex 1, it is possible to achieve both a high separation factor and a high permeance.

[0107] Preferably, the average particle diameter of the MOF is 0.1 µm to 2 µm. This makes it possible to reduce the grain boundary error and increase the separation factor in the thin separation membrane 12.

[0108] Preferably, the ligands of the MOF contain one of the following compounds: 1H-pyrrole-2,5-dicarboxylic acid, 2,5-furandicarboxylic acid, and 3,5-pyridindicarboxylic acid. By using ligands with a high affinity for CO2, it is therefore possible to increase the permeance of CO2 gas.

[0109] Preferably, the thickness of the composite layer 13 consisting of the support 11 and the MOF is no more than 2 µm. This makes it possible to achieve a higher permeance in the separation membrane complex 1.

[0110] Preferably, the permeance of CO2 gas is not less than 1000 GPU. This makes it possible to carry out suitable separation of the CO2 gas. Depending on the intended use of the separation membrane complex 1, the permeance of CO2 gas can be less than 1000 GPU.

[0111] The process for producing the separation membrane complex 1 comprises a step for depositing the MOF-constructed seed crystals onto the porous support 11 (step S12), a step for preparing the synthesis solution (step S13), and a step for forming the separation membrane 12 on the support 11 by immersing the support 11 in the synthesis solution and performing the hydrothermal synthesis to grow the MOF from the seed crystals (step S14). Step S13 involves the heating and stirring procedure for heating and stirring the solution containing water, the monocarboxylic acid salt, and the ligands. In step S13, the aluminum source is mixed into the solution after the heating and stirring procedure, and the organic solvent is added to the solution at an arbitrary time point. In the separation membrane complex 1, in which the separation membrane 12 is formed on the support 11, the permeance ratio of SF6 / He is no more than 0.020.This makes it possible to provide the separation membrane complex 1 with both a high separation factor and a high permeance.

[0112] Conventional MOF synthesis increases environmental impact due to the use of large quantities of organic solvents such as methanol, ethanol, or DMF. Conversely, if the synthesis is performed without organic solvents, it is impossible to form the MOF membrane appropriately. In contrast, in a preferred method for preparing the separation membrane complex 1, the organic solvent described above is an organic compound with a carbonyl group, and the ratio of the amount of organic solvent to the amount of ligands in the synthesis solution is between 0.1 and 10. This makes it possible to form the MOF membrane appropriately and reduces the amount of organic solvent used, thereby decreasing environmental impact.

[0113] Preferably, the ratio of the amount of monocarboxylic acid salt to that of the ligands in the synthesis solution is 0.5 to 1.8. This makes it possible to form the MOF membrane in a suitable manner and to reduce the coordination error, thereby increasing the separation factor.

[0114] Various modifications can be made to the separation membrane complex 1 described above and to the method for producing the separation membrane complex 1 described above.

[0115] In the separation membrane complex 1, the average particle diameter of the MOF can only lie outside the range of 0.1 µm to 2 µm, or the thickness of the composite layer 13 of the support 11 and the MOF can only be greater than 2 µm, if both a high separation factor and a high permeance can be achieved. Similarly, in the synthesis solution, the ratio of organic solvent / ligand can lie outside the range of 0.1 to 10, or the ratio of monocarboxylic acid salt / ligand can lie outside the range of 0.5 to 1.8.

[0116] In the preparation of the separation membrane complex 1, if the synthesis solution contains two or more types of ligands (see Examples 19 to 21), the ligands contained in the MOFs of the seed crystals may differ from those two or more types of ligands. Furthermore, a mixture of several types of MOF powders containing different ligands may be used as seed crystals. If the synthesis solution contains only one type of ligand, the ligands contained in the MOFs of the seed crystals may be identical to or different from that single type of ligand.

[0117] The separation membrane complex 1 can, in addition to the support 11 and the separation membrane 12, include a functional layer or a protective layer laminated onto the separation membrane 12. Such a functional layer or protective layer can be an inorganic membrane such as a zeolite membrane, a silicon dioxide membrane, a carbon membrane, or the like, or an organic membrane such as a polyimide membrane, a silicone membrane, or the like. Furthermore, a substance that readily adsorbs a specific molecule, such as CO2, can be added to the functional layer or protective layer laminated onto the separation membrane 12.

[0118] The separation membrane complex 1 can be produced by any method other than the manufacturing process described above.

[0119] In the separation device 2 and the separation process, all substances other than those shown by way of example in the preceding description can be separated from the mixed substance.

[0120] The configurations in the preferred embodiment and the variations described above can only be combined appropriately if they do not conflict with each other.

[0121] Although the invention has been shown and described in detail, the foregoing description is in every respect explanatory and not limiting. It is therefore understood that numerous modifications and variations are possible without altering the scope of the invention. INDUSTRIAL APPLICABILITY

[0122] The separation membrane complex of the present invention can be used in various fields as a separation membrane, adsorption membrane or the like for various substances. Reference symbol list 1 Separation membrane complex 11 carriers 12 Separation membrane 13 Composite layer S11 to S14, S21, S22 step QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JP 2023-37303

[0002] Cited non-patent literature

[0000] J.Am. Chem. Soc., 2021, Volume 143, pp. 17716 to 17723 [0004, 0093] Journal of Membrane Science Letters, 2021, Volume 1, p. 100005

[0004]

Claims

[1] Separation membrane complex comprising: a porous support formed from ceramic; and a separating membrane formed on the support and composed of a metal-organic framework, where the average thickness of the separating membrane is no greater than 2 µm, wherein the metal-organic framework is composed of aluminium ions and ligands coordinated to the aluminium ions, a powder X-ray diffraction pattern of the metal-organic framework exhibits peaks at the diffraction angles 2θ specified in the table below and a permeance ratio of SF6 / He is not higher than 0.

020. (Table 1) 2θ [°] (1) 8,2-8,4 (2) 9,1-9,3 (3) 11,8-12,0 (4) 12,4-12,6 (5) 14,9-15,1 (6) 16,7-16,9 (7) 17,1-17,3 (8) 18,4-18,6 (9) 19,1-19,3 (10) 22,5-22,7 (11) 24,3-24,5 (12) 25,1-25,3 (13) 26,9-27,1 [2] Separation membrane complex according to claim 1, wherein the average particle diameter of the metal-organic framework is 0.1 µm to 2 µm. [3] Separation membrane complex according to claim 1, wherein the ligands of the metal-organic framework comprise one of 1H-pyrrole-2,5-dicarboxylic acid, 2,5-furandicarboxylic acid and 3,5-pyridindicarboxylic acid. [4] Separation membrane complex according to claim 1, wherein the thickness of a composite layer consisting of the support and the metal-organic framework is not greater than 2 µm. [5] Separation membrane complex according to any one of claims 1 to 4, wherein the permeance for CO2 gas is not less than 1000 GPU. [6] Method for the production of a separation membrane complex, comprising: a) Application of seed crystals composed of a metal-organic framework onto a porous support; b) Preparation of a synthesis solution; and c) Forming a separation membrane on the support by immersing the support in the synthesis solution and carrying out a hydrothermal synthesis to grow a metal-organic framework from the seed crystals, where embodiment b) includes a heating and stirring method for heating and stirring a solution in which water, monocarboxylic acid salt and ligands are mixed; an aluminum source is mixed into the solution using the heating and stirring method, and an organic solvent is mixed into the solution at any time during execution b), and a permeance ratio of SF6 / He is not higher than 0.020 in a separation membrane complex, the separation membrane being formed on the support. [7] Method for producing a separation membrane complex according to claim 6, wherein the organic solvent is an organic compound with a carbonyl group and The ratio of the amount of organic solvent to the amount of ligands in the synthesis solution is 0.1 to 10. [8] Method for producing a separation membrane complex according to claim 6 or 7, wherein the ratio of the amount of substance of the monocarboxylic acid salt to that of the ligands in the synthesis solution is 0.5 to 1.8.

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