Separation membrane composite and method for producing separation membrane composite

Abstract

A separation membrane composite (1) is provided with: a porous support body (11); and a separation membrane (12) that is provided on the support body (11) and comprises a metal-organic structure. The separation membrane (12) constitutes a layer in contact with the support body (11), and is provided with: a particle-containing layer (16) in which granular particles (161) of the metal organic structure are scattered; and a dense layer (17) that is in contact with the particle-containing layer (16) on the side thereof opposite from the support body (11) and that does not contain the granular particles (161). In a cross section perpendicular to the surface of the separation membrane (12), the area ratio of the granular particles (161) in the particle-containing layer (16) is 5-90%. As a result of this configuration, the occurrence of cracks in the separation membrane (12) can be suppressed.

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 JP2024-030483, filed on February 29, 2024, the entire disclosure of which is incorporated herein by reference.

[0002] In recent years, efforts to become carbon neutral have been underway worldwide, and carbon dioxide (CO ) contained in industrial exhaust gases emitted from factories and other facilities has become a major issue. ２ ) and capture technology (CO ２ / N ２ There is a growing need for metal-organic frameworks (MOFs), which are porous materials with high surface areas. By forming membranes on porous supports, similar to zeolite membranes, MOFs are expected to be used in a variety of applications, including gas and liquid separation. For example, "Highly CO2 Selective Metal-Organic Framework Membranes with Favorable Coulombic Effect" (Advanced Functional Materials, 2021, Vol. 31, 2006924) (Reference 1) by Da-Shiuan Chiou and seven others discloses a MOF called "CAU-10-H." A CAU-10-H MOF membrane is formed on a support by attaching seed crystals to the support and growing crystal particles from the seed crystals. In addition, Japanese Patent Laid-Open No. 10-57784 (Document 2) describes that a zeolite membrane having an internal bridge structure (voids) has poor pressure resistance due to the weak strength of the bridge structure portion.

[0003] Meanwhile, a separation membrane composite in which a separation membrane is formed on a support is subjected to a heat treatment to dry and remove the solvent that has entered the pores of the separation membrane during cleaning. At this time, stress caused by the difference in thermal expansion coefficient between the support and the separation membrane makes the separation membrane more susceptible to cracking. When the separation membrane is made of MOF, cracking is particularly likely to occur due to the low strength of the grain boundaries of the MOF. In Literature 1, after the formation and cleaning of the MOF membrane, drying is carried out at 70°C for one day, which is considered to be highly likely to cause cracking in the MOF membrane. Furthermore, even at heating temperatures below 70°C, durability problems may arise during long-term use depending on the usage environment, etc.

[0004] An object of the present invention is to suppress the occurrence of cracks in a separation membrane made of an MOF.

[0005] A first aspect of the invention is a separation membrane composite comprising: a porous support; and a separation membrane provided on the support and made of a metal-organic framework; the separation membrane comprising: a particle-containing layer in contact with the support, the particle-containing layer being dotted with granular particles of the metal-organic framework; and a dense layer in contact with the particle-containing layer on the opposite side from the support, the dense layer not containing the granular particles; and the particle-containing layer having an area ratio of 5 to 90% in a cross section perpendicular to a surface of the separation membrane.

[0006] According to the present invention, it is possible to suppress the occurrence of cracks in a separation membrane made of a metal organic framework.

[0007] A second aspect of the present invention is the separation membrane composite of the first aspect, wherein the granular particles include aggregates of fine particles.

[0008] A third aspect of the present invention is the separation membrane composite of the first or second aspect, wherein the average particle size of the granular particles is 10 to 500 nm.

[0009] A fourth aspect of the present invention is the separation membrane composite of any one of the first to third aspects, wherein the particle-containing layer has a thickness of 1 μm or less.

[0010] A fifth aspect of the present invention is the separation membrane composite of any one of the first to fourth aspects, wherein the average thickness of the separation membrane is 1.1 to 20 times the thickness of the particle-containing layer.

[0011] The present invention is also directed to a method for producing a separation membrane composite.

[0012] A sixth aspect of the invention is a method for producing a separation membrane composite, comprising: a) preparing fine particles of a metal-organic framework; b) preparing a dispersion containing an organic solvent and water as a solvent, the fine particles, and a pH adjuster, and in which aggregates of the fine particles are dispersed as seed crystals; c) using the dispersion, attaching the seed crystals to a porous support; and d) immersing the support in a raw material solution and forming a separation membrane made of a metal-organic framework on the support by solvothermal synthesis.

[0013] A seventh aspect of the invention is the method for producing a separation membrane composite according to the sixth aspect, wherein the ratio of the organic solvent in the solvent of the dispersion is 90% by volume or more, and the ratio of the water is 10% by volume or less.

[0014] An eighth aspect of the invention is the method for producing a separation membrane composite according to the sixth or seventh aspect, wherein the average particle size of the aggregates in the dispersion is 10 to 500 nm.

[0015] 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.

[0016] 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 cross-sectional view showing the vicinity of a separation membrane. FIG. 4 is a diagram showing the flow of manufacturing a separation membrane composite. FIG. 5 is a diagram showing seed crystals attached to a support. FIG. 6 is a diagram for explaining the process of a comparative example. FIG. 7 is a diagram showing a separation device. FIG. 8 is a diagram showing the flow of separation of a mixed substance.

[0017] 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 membrane made of a metal-organic framework (MOF) (hereinafter also referred to as a "MOF membrane"), and the separation membrane composite 1 is a MOF membrane composite. An MOF membrane is at least a membrane of MOFs formed on the surface of the support 11, and does not include membranes in which MOF particles are simply dispersed in an organic film. In FIG. 1, the separation membrane 12 is emphasized with a thick line. In FIG. 2, the separation membrane 12 is indicated by parallel diagonal lines. Furthermore, in FIG. 2, the thickness of the separation membrane 12 is depicted as being thicker than it actually is.

[0018] The support 11 is a porous member that is permeable to gas and liquid. In the example shown in FIG. 1 , the support 11 is a so-called monolithic support in which a plurality of through holes 111 extending in the longitudinal direction (i.e., the left-right direction in FIG. 1 ) are provided in an integrally molded, continuous columnar body. In the example shown in FIG. 1 , the support 11 is substantially cylindrical. A 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 holes 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 holes 111 and covers the inner circumferential surface of the through holes 111 over substantially the entire surface.

[0019] The length of the support 11 (i.e., the length in the left-right direction in FIG. 1 ) is, for example, 10 cm to 200 cm (the symbol "to" means greater than or equal to the value before it and less than or equal to the value after it). The outer diameter of the support 11 is, for example, 0.5 cm to 30 cm. The distance between the central axes of adjacent through holes 111 is, for example, 0.3 mm to 10 mm. The surface roughness (Ra) of the support 11 is, for example, 0.1 μm to 5.0 μm, and preferably 0.2 μm to 2.0 μm. The shape of the support 11 may be, for example, a honeycomb shape, a flat plate shape, a tubular shape, a cylindrical shape, a columnar shape, or a polygonal pillar shape. When the shape of the support 11 is tubular or cylindrical, the thickness of the support 11 is, for example, 0.1 mm to 10 mm.

[0020] The support 11 is formed of, for example, ceramic. Examples of ceramic sintered bodies selected as the material of the support 11 include alumina, silica, mullite, zirconia, titania, yttria, silicon nitride, and silicon carbide. In this embodiment, the support 11 contains at least one of alumina, silica, and mullite. The support 11 may contain an inorganic binder. As the inorganic binder, at least one of titania, mullite, sinterable alumina, silica, glass frit, clay minerals, and sinterable cordierite can be used.

[0021] The average pore diameter of the support 11 is, for example, 0.01 μm to 70 μm, preferably 0.05 μm to 25 μm. The average pore diameter of the support 11 near the surface where the separation membrane 12 is formed is 0.01 μm to 1 μm, preferably 0.05 μm to 0.5 μm. The average pore diameter can be measured, for example, by a mercury porosimeter, a perm porometer, or a nanoperm porometer. With regard to the pore size distribution throughout the support 11, including the surface and interior, D5 is, for example, 0.01 μm to 50 μm, D50 is, for example, 0.05 μm to 70 μm, and D95 ​​is, for example, 0.1 μm to 2000 μm. The porosity of the support 11 near the surface where the separation membrane 12 is formed is, for example, 20% to 60%. The porosity can be determined as the percentage of the area where voids exist in an SEM (scanning electron microscope) image of a cross section of the support 11.

[0022] 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, and preferably 0.05 μm to 0.5 μm. When the support 11 has a multilayer structure, the materials described above can be used for each layer. The materials of the multiple layers forming the multilayer structure may be the same or different.

[0023] 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.

[0024] The average thickness of the separation membrane 12 is, for example, 5 μm or less, and preferably 2 μm or less. This makes it possible to achieve a high permeation rate. There is no particular limitation on the lower limit of the average thickness of the separation membrane 12, but from the viewpoint of improving separation performance, it is preferably 0.5 μm, and more preferably 0.7 μm. A method for measuring the average thickness of the separation membrane 12 will be described later. 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.

[0025] The MOF membrane constituting the separation membrane 12 is a polycrystalline membrane mainly composed of numerous MOF crystals formed on the surface of the support 11. Near the interface between the separation membrane 12 and the support 11, a composite layer 13 is formed in which the MOF crystals penetrate into the pores of the support 11. In FIG. 2 , the composite layer 13 is shown by drawing parallel diagonal lines overlaid on a portion of the support 11. The composite layer 13 is part of the support 11. The thickness of the composite layer 13 is, for example, 2 μm or less. This makes it possible to suppress a decrease in permeation rate due to the presence of the composite layer 13. The composite layer 13 does not have to be present, and the lower limit of the thickness of the composite layer 13 is 0.

[0026] In measuring the thickness of the composite layer 13, a cross section (longitudinal cross section) perpendicular to the surface of the separation membrane 12 is exposed, for example, by cross-sectional polishing. When observing the cross section using an SEM, the boundary position of the composite layer 13 in the direction perpendicular to the surface (hereinafter referred to as the "depth direction") is identified near one measurement position along the surface of the support 11 (the interface between the support 11 and the separation membrane 12). Specifically, the boundary position on the separation membrane 12 side of the composite layer 13 is the position closest to the support 11 at the interface between the separation membrane 12 and the support 11 (the lower end of the particle-containing layer 16 described below). 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 a plurality of different measurement positions (for example, 10 measurement positions) is determined as the thickness of the composite layer 13 in the separation membrane composite 1 .

[0027] Not only when the composite layer 13 is not present, but also when the composite layer 13 is present, there is no intermediate layer formed separately between the support 11 and the separation membrane 12 in the separation membrane composite 1, so the support 11 and the separation membrane 12 are in direct contact with each other. In other words, there is no intermediate layer formed between the support 11 and the separation membrane 12 in a step other than the step of forming the MOF membrane.

[0028] The average pore diameter of the MOF membrane constituting the separation membrane 12 is not particularly limited, but, for example, is 0.40 nm or more and 0.90 nm or less. The "average pore diameter of the MOF" is the average value of the long and short diameters of the pore openings theoretically derived from the skeletal structure of the MOF. The long and short diameters of the pore openings, more precisely, refer to the interlattice spacing of the highly regular lattice structure formed by metal ions and organic ligands. MOFs have a unique pore structure consisting of channels (pores) and cages (internal spaces) depending on the structural type. The pore diameter here refers to the pore diameter of the channel, with the maximum diameter in the cross section of the channel being the long diameter and the diameter of the cross section in a direction approximately perpendicular to the long diameter being the short diameter, and the arithmetic mean of the short diameter and the long diameter being the average pore diameter. This average pore diameter is smaller than the average pore diameter of the support 11 near the surface on which the separation membrane 12 is formed.

[0029] The average particle size of the MOFs constituting the surface of the separation membrane 12 (the surface opposite the support 11, the surface of the dense layer 17 described below), i.e., the average diameter of the crystal grains, is, for example, 0.1 μm to 2 μm. The average particle size is preferably 1 μm or less, and more preferably 0.5 μm or less. In a separation membrane 12 having a small average particle size of MOFs on the surface, grain boundary defects caused by the formation of excessively large gaps between MOF crystals are reduced, making it possible to improve separation performance. The average particle size of the MOFs on the surface of the separation membrane 12 is the arithmetic mean of the maximum Feret diameters of multiple MOF particles (e.g., 30 particles) measured by observing the membrane surface using an SEM. The multiple particles to be measured may be randomly selected on an SEM image.

[0030] The MOF constituting the separation membrane 12 is composed of metal ions and organic ligands (hereinafter simply referred to as "ligands") coordinated to the metal ions. The metal ions constituting the MOF are not particularly limited, but in practical terms, Al ３＋ , Co ３＋ , Co ２＋ , Ni ２＋ , Ni ＋ , Cu ２＋ , Cu ＋ , Zn ２＋ , Fe ３＋ , Fe２＋ , Ti ３＋ and Zr ４＋ More preferably, the metal ion comprises at least one selected from the group consisting of Al ３＋ , Zn ２＋ , Ti ３＋ and Zr ４＋ Preferably, the number of types of metal ions contained in the MOF is one, but may be multiple.

[0031] The ligands that are components of MOFs are not particularly limited, but one example is a bidentate ligand, which is an ion of an organic molecule having two carboxy groups. This makes it possible to easily form pores that allow a specific gas to pass through more easily than other specific gases. The structure other than the two carboxy groups is not particularly limited, but one suitable example is a ligand having a heterocycle. Furthermore, instead of a carboxy group, the ligand may have a ligand such as a pyridine group or a pyrrole group that can coordinate to a metal ion.

[0032] FIG. 3 is a diagram showing a cross section of the separation membrane composite 1 perpendicular to the surface of the separation membrane 12. FIG. 3 shows an image of the area around the separation membrane 12 in the cross section (longitudinal cross section) captured by an ultra-low voltage scanning electron microscope (ULV-SEM). In the following description, the image shown in FIG. 3 will be simply referred to as a "cross-sectional image." In addition, in the cross-sectional image, the separation membrane 12 side in the depth direction is referred to as the upper side, and the support 11 side is referred to as the lower side. The upper and lower sides in the cross-sectional image are unrelated to the direction of gravity.

[0033] The separation membrane 12 includes a particle-containing layer 16 and a dense layer 17. The particle-containing layer 16 contacts and covers the surface of the support 11. The dense layer 17 contacts and covers the surface of the particle-containing layer 16 on the side opposite the support 11. The dense layer 17 is not in contact with the surface of the support 11. Thus, the particle-containing layer 16 is located above the support 11 and below the dense layer 17, and is directly sandwiched between them. Each of the particle-containing layer 16 and the dense layer 17 includes MOF crystals and grain boundaries. The grain boundaries are regions between adjacent MOF crystals. The grain boundaries include, for example, non-crystalline (i.e., amorphous), crystals other than MOF crystals, and / or voids.

[0034] The particle-containing layer 16 further contains granular particles 161 of MOF. The granular particles 161 are present within the particle-containing layer 16 along the interface with the support 11. The granular particles 161 are scattered within the particle-containing layer 16. The outer shape of the granular particles 161 in the cross-sectional image is, for example, slightly rounded. The particle-containing layer 16 is a layer containing the granular particles 161, and the dense layer 17 is a layer not containing the granular particles 161. The content of MOF crystals in the dense layer 17 not containing the granular particles 161 is higher than the content of MOF crystals in the particle-containing layer 16. In other words, the dense layer 17 is a layer in which the MOF crystals are arranged more densely than in the particle-containing layer 16. Typically, the type of MOF contained in the dense layer 17 is the same as the type of MOF contained in the particle-containing layer 16. This makes it possible to easily form the separation membrane 12.

[0035] In the synthesis of the separation membrane 12 described below, aggregates (secondary particles) of MOF fine particles are used as seed crystals. The granular particles 161 are considered to be seed crystals remaining after the synthesis of the separation membrane 12, and the particle-containing layer 16 can be considered a seed crystal-containing layer. Typically, the granular particles 161 include aggregates of fine particles, and particles resulting from the fine particles are observed in the granular particles 161 in a cross-sectional image. The average particle diameter of the MOF fine particles, which are primary particles, is, for example, 2 to 100 nm, and preferably 3 to 50 nm. In cases where the particle diameter of the MOF fine particles is relatively large and one aggregate is composed of several fine particles, it is not necessary to observe particles in the granular particles 161 in a cross-sectional image.

[0036] The average particle diameter of the granular particles 161 (i.e., the average particle diameter of the granular particles 161 as secondary particles) is, for example, 10 to 500 nm, preferably 50 to 300 nm. In measuring the average particle diameter of the granular particles 161, first, the particle diameter of the granular particles 161 is determined by the arithmetic mean of the major axis and minor axis (the maximum diameter and the diameter in a direction approximately perpendicular to the maximum diameter) of the granular particles 161 in the cross-sectional image. Then, the arithmetic mean of the particle diameters of a predetermined number (e.g., 30) of granular particles 161 is determined as the average particle diameter of the granular particles 161. The granular particles 161 to be measured may be selected randomly on the cross-sectional image. Depending on the thickness of the separation membrane 12 and the like, the average particle diameter of the granular particles 161 (and the seed crystals described below) may be outside the range of 10 to 500 nm.

[0037] Of the granular particles 161 in the cross-sectional image of Fig. 3, the line perpendicular to the depth direction at the upper end of granular particle 161a, whose upper end is located at the top, is the upper end of particle-containing layer 16. Of the particles 110 forming the surface of support 11 (i.e., the particles 110 of support 11 located at the topmost position along the surface), the line perpendicular to the depth direction at the upper end of particle 110a, whose upper end is located at the bottom, is the lower end of particle-containing layer 16. In Fig. 3, the region of particle-containing layer 16 is enclosed by a thick rectangle, and the thickness of particle-containing layer 16 is indicated by arrow T1.

[0038] In the cross-sectional image, the area ratio of the granular particles 161 in the particle-containing layer 16 (i.e., the ratio of the sum of the areas of the granular particles 161 to the area of ​​the particle-containing layer 16; hereinafter, simply referred to as the "area ratio of the granular particles 161") is 5 to 90%. This suppresses the occurrence of cracks in the separation membrane 12, as will be described later. The lower limit of the area ratio of the granular particles 161 in the particle-containing layer 16 is preferably 10%, more preferably 20%, and even more preferably 30%. The upper limit of the area ratio of the granular particles 161 may be 85% or 80%. In measuring the area ratio of the granular particles 161, cross-sectional images (30,000x magnification) of five fields of view of the separation membrane composite 1 are obtained using an ULV-SEM, and the arithmetic average of the area ratios of the granular particles 161 in the cross-sectional images of the five fields of view is determined as the area ratio of the granular particles 161 in the separation membrane composite 1.

[0039] The thickness T1 of the particle-containing layer 16 is the depthwise distance between the upper and lower ends of the particle-containing layer 16. The thickness T1 of the particle-containing layer 16 is, for example, 1 μm or less, and preferably 0.8 μm or less. If the particle-containing layer 16 is excessively thick, defects may occur when high pressure is applied. To more reliably suppress the occurrence of cracks in the separation membrane 12, the thickness of the particle-containing layer 16 is, for example, 0.1 μm or more, and preferably 0.2 μm or more. As with the area ratio of the granular particles 161, the arithmetic mean of the thicknesses of the particle-containing layer 16 in the cross-sectional images of five fields of view is determined as the thickness T1 of the particle-containing layer 16 in the separation membrane composite 1.

[0040] Preferably, the average thickness of the separation membrane 12 is 1.1 to 20 times the thickness of the particle-containing layer 16. This prevents the particle-containing layer 16 in the separation membrane 12 from becoming excessively thin or thick. The thickness of the separation membrane 12 is the depth-wise distance between the lower end of the particle-containing layer 16 and the upper end of the dense layer 17. The upper end of the dense layer 17 is the uppermost position on the surface of the dense layer 17 (the surface opposite the support 11) in the cross-sectional image. As with the area ratio of the granular particles 161, the arithmetic mean of the thicknesses of the separation membrane 12 in the cross-sectional images of five fields of view is determined as the average thickness of the separation membrane 12 in the separation membrane composite 1. Depending on the design of the separation membrane composite 1, the thickness of the particle-containing layer 16 may be greater than 1 μm, and the average thickness of the separation membrane 12 may be greater than 20 times the thickness of the particle-containing layer 16.

[0041] Next, with reference to FIG. 4 , the production of the separation membrane composite 1 will be described. When the separation membrane composite 1 is produced, MOF microparticles are first prepared (step S11). To produce the MOF microparticles, for example, MOF powder is produced by solvothermal synthesis using water and / or an organic solvent (also known as hydrothermal synthesis when the solvent is water). The MOF powder may be produced by any known production method. The MOF powder is then pulverized using a ball mill or the like to obtain the MOF microparticles. The average particle diameter (D50) of the MOF microparticles is, for example, 200 nm or less, preferably 2 to 100 nm. When a MOF powder with a small particle diameter is produced by solvothermal synthesis, the pulverization of the MOF powder may be omitted, and the MOF powder may be treated as is as the MOF microparticles. The average particle diameter of the MOF microparticles can be measured by a laser scattering method (the same applies to the particle diameter of the seed crystals described below).

[0042] Next, a dispersion containing an organic solvent and water as solvents, MOF fine particles, and a pH adjuster is prepared (step S12). For example, when the MOF powder is milled in an organic solvent, the dispersion may be prepared by adding an aqueous solution of a pH adjuster to the organic solvent containing the milled MOF fine particles. Typically, the pH adjuster is a basic or acidic chemical, such as sodium hydroxide (NaOH), hydrogen chloride (HCl), or nitric acid (HNO).３ ) and the like. The aqueous solution of the pH adjuster is a basic aqueous solution or an acidic aqueous solution. By stirring the dispersion, the MOF fine particles (primary particles) aggregate, and a dispersion is obtained in which aggregates of the MOF fine particles (secondary particles) are dispersed as seed crystals. The average particle diameter (D50) of the aggregates in the dispersion is, for example, 10 to 500 nm, preferably 50 to 300 nm.

[0043] As long as aggregates having a desired average particle size are formed, the pH of the dispersion and the ratio of organic solvent to water in the dispersion solvent may be determined arbitrarily. In this processing example, the ratio of organic solvent is 90% by volume or more and less than 100% by volume. The ratio of organic solvent may be 80% by volume or more. The component other than the organic solvent in the dispersion solvent is water, and the ratio of water in the solvent is greater than 0% by volume and less than 10% by volume. When the dispersion contains water, the formation of aggregates by pH adjustment becomes easier. Furthermore, when the ratio of water is 10% by volume or less, dissolution of the fine particles is suppressed. The concentration of MOF fine particles (solid) in the dispersion is, for example, 0.01 to 1% by weight.

[0044] Next, a dispersion liquid in which the seed crystals are dispersed in a solvent is brought into contact with a portion of the support 11 where the separation membrane 12 is to be formed, thereby attaching (supporting) the seed crystals to the support 11 (step S13). For example, a dip coating method can be used in which the porous support 11 is immersed in the dispersion liquid to attach the seed crystals to the support 11. As shown in FIG. 5 , the seed crystals 81 are attached to the support 11 as aggregates (secondary particles) of MOF fine particles. Thereafter, the solvent is removed by drying to produce a seed crystal-attached support. The seed crystals may also be attached to the support 11 by other methods.

[0045] Next, a raw material solution (also called a synthetic sol or a synthetic solution) to be used in forming the separation membrane 12 is prepared. The raw material solution may be prepared in advance. In preparing the raw material solution, a solvent (water and / or an organic solvent), a ligand, a metal ion source, and the like are mixed. For example, the ligand is added to the solvent, and the ligand is dissolved by ultrasonic treatment or heating in a thermostatic bath. Then, metal ions are added to obtain the raw material solution.

[0046] Once the raw material solution is prepared, a support 11 with seed crystals attached is immersed in the raw material solution. The raw material solution is then heated to initiate solvothermal synthesis, including hydrothermal synthesis (hereinafter collectively referred to as "solvothermal synthesis"). In solvothermal synthesis, MOFs grow from the seed crystals, forming a separation membrane 12, which is an MOF membrane, on the support 11 (step S14). In FIG. 5, the separation membrane 12 is indicated by a two-dot chain line. In the separation membrane 12, all or part of the many seed crystals 81 remain as granular particles 161 (see FIG. 3). The synthesis temperature during solvothermal synthesis (the heating temperature of the raw material solution) is, for example, 40 to 200°C, preferably 70 to 150°C. The solvothermal synthesis time is, for example, 1 to 100 hours, preferably 1 to 50 hours.

[0047] A preferred raw material solution for solvothermal synthesis has a composition that makes it difficult for an MOF membrane to form on the support 11, i.e., makes it difficult for MOF nucleation to occur, when solvothermal synthesis is performed without attaching seed crystals 81 to the support 11. Such a raw material solution is prepared by diluting the original raw material solution or by changing the composition of the metal ion source and ligand. Use of such a raw material solution makes it possible to grow MOFs from the seed crystals 81 while maintaining the voids between the fine particles in the seed crystals 81, and more reliably form the separation membrane 12 in which the seed crystals 81 remain as granular particles 161.

[0048] After the solvothermal synthesis is complete, the support 11 and separation membrane 12 are washed with pure water, and then washed with ethanol or the like. Preferably, washing with water and ethanol or the like is repeated multiple times. After washing, the support 11 and separation membrane 12 are dried, for example, at 100°C. "Drying" means removing molecules of the substance used for washing, such as water or ethanol, from the pores of the separation membrane 12. Through the above processes, the separation membrane composite 1 is completed.

[0049] Here, a comparative example of a process for forming a separation membrane will be described. FIG. 6 is a diagram illustrating the process of the comparative example. In the process of the comparative example, the seed crystals dispersed in the dispersion are in the form of primary particles, and the seed crystals 91, which are primary particles, adhere to the support 11. In this case, although the reason is unclear, in the separation membrane 92 formed by solvothermal synthesis, only a small amount of seed crystals remain as granular particles. That is, in the separation membrane 92, a particle-containing layer is substantially absent, or, even if present, the area ratio of granular particles in the particle-containing layer is less than 5%. Furthermore, in a separation membrane composite having such a separation membrane 92, the separation performance is significantly reduced after heating the separation membrane composite, as in Comparative Examples 1 to 3 described below. The reason for the reduction in separation performance is thought to be that cracks occur in the separation membrane 92 due to stress caused by the difference in thermal expansion coefficient between the support 11 and the separation membrane 92 when the separation membrane composite is heated.

[0050] In contrast, in the separation membrane composite 1 of Figure 3, the separation membrane 12 comprises a particle-containing layer 16, which is a layer in contact with the support 11 and is dotted with MOF granular particles 161, and a dense layer 17, which is a layer in contact with the particle-containing layer 16 on the side opposite the support 11 and does not contain granular particles 161. In a cross section of the separation membrane composite 1 perpendicular to the surface of the separation membrane 12, the area ratio of the granular particles 161 in the particle-containing layer 16 is 5 to 90%. In such a separation membrane composite 1, as in Examples 1 to 10 described below, there is almost no deterioration in separation performance after heating the separation membrane composite 1. Therefore, it is believed that the presence of a certain amount of granular particles 161 relieves stress generated in the separation membrane 12 during heating, thereby suppressing the occurrence of cracks in the separation membrane 12.

[0051] Preferably, the granular particles 161 include an aggregate of MOF fine particles. In this case, the presence of voids between the MOF fine particles (primary particles) within the granular particles 161 can more reliably relieve stress that occurs when the separation membrane composite 1 is heated, making it possible to further suppress the occurrence of cracks in the separation membrane 12. As described above, it is not necessarily necessary to confirm the aggregates (grains) of fine particles in the granular particles 161 in the cross-sectional image.

[0052] The method for producing the separation membrane composite 1 includes the steps of preparing MOF microparticles, preparing a dispersion containing an organic solvent and water as a solvent, as well as microparticles and a pH adjuster, in which aggregates of the microparticles are dispersed as seed crystals, attaching the seed crystals to a porous support 11 using the dispersion, and immersing the support 11 in a raw material solution to form a separation membrane 12 made of MOF on the support 11 by solvothermal synthesis. This allows for easy production of the separation membrane composite 1, which can suppress the occurrence of cracks in the separation membrane 12.

[0053] Next, examples and comparative examples of separation membrane composites will be described. Table 1 shows the types of MOFs in the examples and comparative examples, as well as various measurement results.

[0054]

[0055] First, we describe the preparation of seed crystals for three types of MOFs, called "Al Fumarate," "KMF-1," and "UiO-66-NH2." In each example and comparative example, one of the three types of seed crystals was used.

[0056] <Preparation of Al Fumarate Seed Crystals> First, 0.28 g of fumaric acid (as a ligand) and 0.34 g of sodium formate were added to 30 mL of deionized water to prepare a mixed solution. Subsequently, 0.83 g of aluminum sulfate hexahydrate was added to the mixed solution as a metal ion source. Next, this solution was kept in an autoclave at 120°C for 12 hours to perform solvothermal synthesis. The precipitate was separated using a centrifuge and washed three times with deionized water and ethanol. The mixture was then dried at 100°C for 24 hours to obtain Al Fumarate powder.

[0057] 1 g of the above powder, φ1 mm ZrO ２ 30 g of balls and 9 mL of ethanol were placed in a 25 mL glass vial, and the vial was placed on a ball mill stand and milled at 200 rpm for 20 hours. Laser diffraction / scattering particle size distribution measurement revealed that the particle size (D50) of the resulting microparticles was 40 nm. 1 mL of 0.01 mol / L NaOH aqueous solution was added to the ethanol containing the microparticles, and the mixture was stirred with a stirrer for 10 minutes to aggregate the microparticles. This resulted in a dispersion in which aggregates of Al Fumarate microparticles were dispersed as seed crystals. Laser diffraction / scattering particle size distribution measurement revealed that the particle size (D50) of the seed crystals (aggregates) was 250 nm.

[0058] <Preparation of KMF-1 seed crystals> First, 1.551 g of 1H-pyrrole-2,5-dicarboxylic acid (as a ligand) and 1.36 g of sodium formate were added to 30 mL of deionized water to prepare a mixed solution. Subsequently, 3.333 g of aluminum sulfate hexahydrate was added to the mixed solution as a metal ion source. Next, this solution was kept in an autoclave at 120°C for 12 hours to perform solvothermal synthesis. The precipitate was separated using a centrifuge and washed three times with deionized water and ethanol. The mixture was then dried at 100°C for 24 hours to obtain KMF-1 powder.

[0059] 1 g of the above powder, φ1 mm ZrO ２ 30 g of balls and 9 mL of ethanol were placed in a 25 mL glass vial, and the vial was placed on a ball mill stand and milled at 200 rpm for 15 hours. Laser diffraction / scattering particle size distribution measurement revealed that the particle diameter (D50) of the resulting microparticles was 20 nm. 0.5 mL of a 0.01 mol / L NaOH aqueous solution was added to the ethanol containing the microparticles, and the mixture was stirred with a stirrer for 10 minutes to aggregate the microparticles. This resulted in a dispersion in which aggregates of KMF-1 microparticles were dispersed as seed crystals. Laser diffraction / scattering particle size distribution measurement revealed that the particle diameter (D50) of the seed crystals (aggregates) was 250 nm.

[0060] <Preparation of UiO-66-NH2 Seed Crystals> First, 0.233 g of zirconium chloride (metal ion source) and 0.166 g of 2-aminoterephthalic acid (ligand) were added to a mixed solvent of 3 mL of acetic acid and 30 mL of dimethylformamide (DMF) to prepare a mixed solution. The mixed solution was sonicated at room temperature for 30 minutes to obtain a homogeneous solution. Next, this solution was subjected to solvothermal synthesis by maintaining it in an autoclave at 120°C for 24 hours. The precipitate was separated using a centrifuge and washed three times with deionized water and ethanol. The mixture was then dried at 100°C for 24 hours to obtain UiO-66-NH2 powder.

[0061] The powder was not pulverized but dispersed in 9 mL of DMF. Laser diffraction / scattering particle size distribution measurement revealed that the particle size (D50) of the microparticles (powder) was 90 nm. 0.5 mL of a 0.01 mol / L HCl aqueous solution was added to the DMF containing the microparticles, and the mixture was stirred with a stirrer for 10 minutes to aggregate the microparticles. This resulted in a dispersion in which aggregates of UiO-66-NH2 microparticles were dispersed as seed crystals. Laser diffraction / scattering particle size distribution measurement revealed that the particle size (D50) of the seed crystals (aggregates) was 350 nm.

[0062] Example 1 Ethanol was added to a dispersion of Al Fumarate seed crystals to prepare 200 mL of a dispersion (dispersion for supporting seed crystals) with a solid content of MOF (Al Fumarate) of 0.1 wt %. The dispersion was brought into contact with a ceramic (alumina) support, and the adhering solvent was dried by blowing air to support the seed crystals on the support.

[0063] A mixed solution was prepared by adding 0.39 g of fumaric acid and 0.45 g of sodium formate to 200 mL of deionized water. The mixed solution was heated to 40°C and stirred for 1 hour. After confirming that the mixed solution had become transparent, it was cooled to room temperature. Then, 1.10 g of aluminum sulfate 18-hydrate was added to the mixed solution to prepare a raw material solution.

[0064] Next, the seed crystal-carrying ceramic support and the raw material solution were loaded into a Teflon (registered trademark) container and held at 100°C for 20 hours to perform solvothermal synthesis. The resulting separation membrane composite was washed three times with deionized water and ethanol. The separation membrane composite was then left in the air for 12 hours or more to dry. Through these processes, the separation membrane composite of Example 1, which had a separation membrane made of Al Fumarate, was obtained.

[0065] Example 2 A mixed solution was prepared by adding 0.13 g of fumaric acid and 0.15 g of sodium formate to 200 mL of deionized water. The mixed solution was stirred for 1 hour while being heated to 40°C. After confirming that the mixed solution had become transparent, it was cooled to room temperature. Then, 0.37 g of aluminum sulfate 18-hydrate was added to the mixed solution to prepare a raw material solution. The rest of the procedure was the same as in Example 1.

[0066] Example 3 A mixed solution was prepared by adding 0.78 g of fumaric acid and 0.90 g of sodium formate to 200 mL of deionized water. The mixed solution was stirred for 1 hour while being heated to 40°C. After confirming that the mixed solution had become transparent, it was cooled to room temperature. Then, 2.20 g of aluminum sulfate 18-hydrate was added to the mixed solution to prepare a raw material solution. The rest of the procedure was the same as in Example 1.

[0067] Example 4 A dispersion for supporting seed crystals was prepared in which the solid content of MOF was 0.2 wt %. The rest of the procedure was the same as in Example 1.

[0068] Example 5 The procedure was the same as in Example 1, except that the temperature and time of the solvothermal synthesis were 80° C. and 10 hours.

[0069] Example 6 A dispersion for supporting seed crystals was prepared in which the solid content of MOF was 0.05 wt %. The rest of the procedure was the same as in Example 1.

[0070] Example 7 Ethanol was added to a dispersion of KMF-1 seed crystals to prepare 200 mL of a dispersion (dispersion for supporting seed crystals) with a solid content of 0.1 wt% MOF (KMF-1). The dispersion was brought into contact with a ceramic support, and the adhering solvent was dried by blowing air to support the seed crystals on the support.

[0071] A mixed solution was prepared by mixing 1.551 g of 1H-pyrrole-2,5-dicarboxylic acid and 1.36 g of sodium formate in 200 mL of deionized water, followed by adding 3.333 g of aluminum sulfate 18-hydrate to prepare a raw material solution.

[0072] Next, the seed crystal-carrying ceramic support and the raw material solution were loaded into a Teflon (registered trademark) container and held at 100°C for 20 hours to perform solvothermal synthesis. The resulting separation membrane composite was washed three times with deionized water and ethanol. The separation membrane composite was then left in the air for at least 12 hours and dried. Through these processes, the separation membrane composite of Example 7, which had a separation membrane made of KMF-1, was obtained.

[0073] Example 8 A dispersion for supporting seed crystals was prepared in which the solid content of MOF was 0.2 wt %. The rest of the procedure was the same as in Example 7.

[0074] Example 9 DMF was added to a dispersion of UiO-66-NH2 seed crystals to prepare 200 mL of a dispersion (dispersion for supporting seed crystals) with a solid content of MOF (UiO-66-NH2) of 0.1 wt %. The dispersion was brought into contact with a ceramic support, and the adhering solvent was dried by heated air blowing, thereby supporting the seed crystals on the support.

[0075] A mixed solution was prepared by adding 0.233 g of zirconium chloride and 0.166 g of 2-aminoterephthalic acid to a mixed solvent of 3 mL of acetic acid and 30 mL of DMF. The mixed solution was subjected to ultrasonic treatment at room temperature for 30 minutes to obtain a homogeneous solution (raw material solution).

[0076] Next, the seed crystal-carrying ceramic support and the raw material solution were loaded into a Teflon (registered trademark) container and maintained at 120°C for 20 hours to perform solvothermal synthesis. The resulting separation membrane composite was washed three times with deionized water and ethanol. The separation membrane composite was then left in the air for at least 12 hours to dry. Through these processes, the separation membrane composite of Example 9, which had a separation membrane made of UiO-66-NH2, was obtained.

[0077] Example 10 A dispersion for supporting seed crystals was prepared in which the solid content of MOF was 0.2 wt %. The rest of the procedure was the same as in Example 9.

[0078] Comparative Example 1: A mixed solution was prepared by adding 0.28 g of fumaric acid and 0.34 g of sodium formate to 30 mL of deionized water. Subsequently, 0.83 g of aluminum sulfate 18-hydrate was added to the mixed solution. This solution was then stored in an autoclave at 120°C for 12 hours to perform solvothermal synthesis. The precipitate was separated using a centrifuge and washed three times with deionized water and ethanol. The mixture was then dried at 100°C for 24 hours to obtain Al Fumarate powder as seed crystals. Laser diffraction / scattering particle size distribution measurement revealed that the particle size (D50) of the seed crystals was 1,200 nm.

[0079] The seed crystals were mixed with ethanol to prepare 200 mL of a dispersion (dispersion for supporting seed crystals) with a solid content of 0.1 wt % of MOF (Al Fumarate). The dispersion was brought into contact with a ceramic support, and the adhering solvent was dried by blowing air, thereby supporting the seed crystals on the support. Unlike in Examples 1 to 10, the seed crystals supported on the support were unpulverized, and the dispersion did not contain a pH adjuster.

[0080] A mixed solution was prepared by adding 0.39 g of fumaric acid and 0.45 g of sodium formate to 200 mL of deionized water. The mixed solution was heated to 40°C and stirred for 1 hour. After confirming that the mixed solution had become transparent, it was cooled to room temperature. Then, 1.10 g of aluminum sulfate 18-hydrate was added to the mixed solution to prepare a raw material solution.

[0081] Next, the seed crystal-carrying ceramic support and the raw material solution were loaded into a Teflon (registered trademark) container and held at 100°C for 20 hours to perform solvothermal synthesis. The resulting separation membrane composite was washed three times with deionized water and ethanol. The separation membrane composite was then left in the air for 12 hours or more to dry. Through the above treatment, a separation membrane composite of Comparative Example 1 having a separation membrane made of Al Fumarate was obtained.

[0082] Comparative Example 2: A mixed solution was prepared by adding 0.28 g of fumaric acid and 0.34 g of sodium formate to 30 mL of deionized water. Subsequently, 0.83 g of aluminum sulfate 18-hydrate was added to the mixed solution. This solution was then stored in an autoclave at 120°C for 12 hours to perform solvothermal synthesis. The precipitate was separated using a centrifuge and washed three times with deionized water and ethanol. The mixture was then dried at 100°C for 24 hours to obtain Al Fumarate powder as seed crystals.

[0083] 1 g of the above powder, φ1 mm ZrO ２ 30 g of balls and 9 mL of ethanol were placed in a 25 mL glass vial, and the powder was milled at 200 rpm for 20 hours. Laser diffraction / scattering particle size distribution measurement revealed that the particle size (D50) of the resulting microparticles was 40 nm. Ethanol and water were added to the ethanol containing the microparticles to prepare a 200 mL dispersion (seed crystal support dispersion) with a MOF solids content of 0.1 wt %, an organic solvent ratio of 80 vol %, and a water ratio of 20%. Unlike Examples 1 to 10 above, the dispersion did not contain a pH adjuster. Other than the above, the same procedures were followed as in Comparative Example 1.

[0084] Comparative Example 3: A mixed solution was prepared by adding 1.551 g of 1H-pyrrole-2,5-dicarboxylic acid and 1.36 g of sodium formate to 30 mL of deionized water. Subsequently, 3.333 g of aluminum sulfate hexahydrate was added to the mixed solution. This solution was then maintained in an autoclave at 120°C for 12 hours to carry out solvothermal synthesis. The precipitate was separated using a centrifuge and washed three times with deionized water and ethanol. The mixture was then dried at 100°C for 24 hours to obtain KMF-1 powder as seed crystals. Laser diffraction / scattering particle size distribution measurement revealed that the particle size (D50) of the seed crystals was 20,000 nm.

[0085] The seed crystals were mixed with ethanol to prepare 200 mL of a dispersion (dispersion for supporting seed crystals) with a solids content of 0.1 wt % of MOF (KMF-1). The dispersion was brought into contact with a ceramic support, and the adhering solvent was dried by blowing air, thereby supporting the seed crystals on the support. Unlike in Examples 1 to 10, the seed crystals supported on the support were unpulverized, and the dispersion did not contain a pH adjuster.

[0086] A mixed solution was prepared by mixing 1.551 g of 1H-pyrrole-2,5-dicarboxylic acid and 1.36 g of sodium formate in 200 mL of deionized water, followed by adding 3.333 g of aluminum sulfate 18-hydrate to prepare a raw material solution.

[0087] Next, the seed crystal-carrying ceramic support and the raw material solution were loaded into a Teflon (registered trademark) container and held at 100°C for 20 hours to perform solvothermal synthesis. The resulting separation membrane composite was washed three times with deionized water and ethanol. The separation membrane composite was then left in the air for 12 hours or more to dry. Through these processes, a separation membrane composite of Comparative Example 3 was obtained, which had a separation membrane made of KMF-1.

[0088] <Various Measurements of Separation Membrane> In each of the separation membrane composites of Examples 1 to 10 and Comparative Examples 1 to 3, cross-sectional images showing the longitudinal cross section of the separation membrane were taken using an ULV-SEM (ultra-low accelerating voltage scanning electron microscope). A ZEISS Gemini SEM 460 was used as the ULV-SEM, with an accelerating voltage of 1 kV and a display magnification of 30,000 times to acquire in-lens secondary electron images. As described with reference to FIG. 3 , the line perpendicular to the depth direction at the top end of the granular particle whose top end is located at the topmost position among the granular particles in the cross-sectional image was taken as the top end of the particle-containing layer. The line perpendicular to the depth direction at the top end of the particle whose top end is located at the bottommost position among the particles (alumina particles) forming the surface of the support was taken as the bottom end of the particle-containing layer.

[0089] For each separation membrane composite, cross-sectional images were obtained from five fields of view, and the area ratio of granular particles in the particle-containing layer in each cross-sectional image was determined. The arithmetic average of the area ratios of granular particles in the cross-sectional images from the five fields of view was defined as the area ratio of granular particles for that separation membrane composite. The arithmetic average of the thicknesses (depth-direction distance between the upper and lower ends) of the particle-containing layer in the cross-sectional images from the five fields of view was defined as the thickness of the particle-containing layer for that separation membrane composite. The measurement results for the area ratio of granular particles and the thickness of the particle-containing layer are shown in the "Area ratio of granular particles" and "Thickness of particle-containing layer" columns in Table 1. The cross-sectional images confirmed that the granular particles contained aggregates of fine particles, and the particle diameters of the granular particles were in the range of 10 to 500 nm.

[0090] The thickness of the separation membrane was defined as the depth distance between the lower end of the particle-containing layer and the upper end of the dense layer. The upper end of the dense layer was defined as the uppermost position on the surface of the dense layer in the cross-sectional image. As above, the arithmetic mean of the thicknesses of the separation membranes in the cross-sectional images of five fields of view was defined as the average thickness of the separation membrane in the separation membrane composite. In Table 1, the average thickness of the separation membrane is shown in the "Separation membrane thickness" column, and the ratio of the thickness of the separation membrane to the thickness of the particle-containing layer (separation membrane thickness / particle-containing layer thickness) is shown in the "Thickness ratio" column.

[0091] <CO ２ / N ２ Measurement of the rate of change in the permeation rate ratio ２ 50% by volume, N ２ A mixed gas with a composition of 50% by volume of CO was introduced onto the surface of the separation membrane at 25°C and a pressure of 0.3 MPa. ２ and N ２ The permeation rate of CO was measured (see separation device 2 in FIG. 7 described later). The permeation rate (permeance) is the rate at which a gas passes through a unit membrane area and a unit pressure difference. ２ The permeation rate is N ２ By dividing by the permeation rate, the CO ２ Permeation rate and N ２ The ratio of the CO ２ / N ２ The permeation rate ratio was obtained.

[0092] Next, the mixed gas was introduced onto the surface of the separation membrane at 100°C and a pressure of 0.3 MPa, and the high-temperature operating condition was maintained for 12 hours. Subsequently, the mixed gas was again introduced onto the surface of the separation membrane at 25°C and a pressure of 0.3 MPa, and after confirming that the temperature of the separation membrane composite had dropped, CO ２ and N ２ The permeation rate of CO after high temperature use was measured. ２ / N ２ The CO permeation rate ratio after high temperature use was obtained. ２ / N ２ The permeation rate ratio was calculated using the CO ２ / N ２ By dividing by the transmission rate ratio, the CO ２ / N ２ The rate of change in the transmission rate ratio was calculated. ２ / N ２ The rate of change in the transmission rate ratio is shown in Table 1 as "CO ２ / N ２ The results are shown in the "Rate of change in transmission rate ratio" column.

[0093] In the separation membrane composites of Examples 1 to 10, the area ratio of granular particles was 5% or more (actually, 30% or more). ２ / N ２ In Examples 1 to 10, the CO 2 permeation rate after high-temperature use was the same as that before high-temperature use. ２ / N ２ The permeation rate ratio (i.e., separation performance) was maintained, and the occurrence of cracks due to heating was suppressed. On the other hand, in the separation membrane composites of Comparative Examples 1 to 3, the area ratio of granular particles was less than 5%. ２ / N ２ The rate of change in the transmission rate ratio was 0.7 or less. ２ / N ２The permeation rate ratio was significantly reduced, and it is believed that cracks were generated by heating. In this example, a separation membrane composite in which the area ratio of granular particles exceeded 90% was not produced, but it is presumed that in such a separation membrane composite, large voids (bridge structures) are likely to form in the particle-containing layer (between the support and the dense layer), resulting in low durability against high introduction pressure.

[0094] Next, separation of a mixed substance using the separation membrane composite 1 will be described with reference to Figures 7 and 8. Figure 7 is a diagram showing the separation device 2. Figure 8 is a diagram showing the flow of separation of a mixed substance by the separation device 2.

[0095] 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.

[0096] 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.

[0097] The mixture may include, for example, hydrogen (H ２ ), helium (He), nitrogen (N ２ ), oxygen (O ２ ), water (H ２ O), carbon monoxide (CO), carbon dioxide (CO ２ ), nitrogen oxides, ammonia (NH ３ ), sulfur oxides, hydrogen sulfide (H ２ S), sulfur fluoride, mercury (Hg), arsine (AsH ３ ), hydrogen cyanide (HCN), carbonyl sulfide (COS), C1-C8 hydrocarbons, organic acids, alcohols, mercaptans, esters, ethers, ketones, and aldehydes.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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 )

[0102] The organic acid is a carboxylic acid or a sulfonic acid. The carboxylic acid is, for example, formic acid (CH ２ O ２ ), acetic acid (C ２ H ４ O ２ ), oxalic acid (C ２ H ２ O ４ ), acrylic acid (C ３ H ４ O ２ ) or benzoic acid (C ６ H ５ COOH), etc. Sulfonic acids include, for example, ethanesulfonic acid (C ２ H ６ O ３ S) and the like. The organic acid may be a chain compound or a cyclic compound.

[0103] 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.

[0104] 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.

[0105] The esters mentioned above are, for example, formates or acetates.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] 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.

[0111] The sealing portion 21 is attached to both longitudinal end portions of the support 11 (i.e., the left-right direction in FIG. 7 ) 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.

[0112] 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. 7 ), 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.

[0113] The two seal members 23 are disposed around the entire circumference between the outer peripheral surface of the separation membrane composite 1 and the inner peripheral surface of the housing 22 near both longitudinal ends of the separation membrane composite 1. Each seal member 23 is a substantially annular member made of a gas-impermeable material. The seal members 23 are, for example, O-rings made of a flexible resin. The seal members 23 are in close contact with the outer peripheral surface of the separation membrane composite 1 and the inner peripheral surface of the housing 22 around the entire circumference. In the example shown in FIG. 7 , the seal member 23 is in close contact with the outer peripheral surface of the sealing portion 21 and indirectly in close contact with the outer peripheral surface of the separation membrane composite 1 via the sealing portion 21. A seal is formed between the seal member 23 and the outer peripheral surface of the separation membrane composite 1, and between the seal member 23 and the inner peripheral surface of the housing 22, so that gas hardly or completely passes through.

[0114] 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.

[0115] 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.

[0116] 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, 0 MPa to 0.10 MPa (approximately 1 atmosphere).

[0117] 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.

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

[0119] 4, the support 11 is immersed in the raw material solution, but "immersion" here does not necessarily mean that the entire support 11 is immersed in the raw material solution, and includes a state in which only the portion of the surface of the support 11 where separation membrane 12 is to be formed is in contact with the raw material solution. In other words, the step of forming separation membrane 12 is a step of bringing the raw material solution into contact with the portion of the surface of the support 11 where separation membrane 12 is to be formed, and heating it.

[0120] In the production of the separation membrane composite 1, the type of MOF in the seed crystals and the type of MOF in the MOF membrane formed from the raw material solution do not have to be the same. That is, the type of MOF in the granular particles 161 in the separation membrane 12 may be different from the type of MOF in other portions. Furthermore, the separation membrane 12 may contain two or more types of ligands. The separation membrane composite 1 may also be produced by a method other than the above production method.

[0121] In the separation device 2, substances other than those exemplified in the above description may be separated from the mixed substance.

[0122] The configurations in the above-described embodiment and each modification may be combined as appropriate as long as they are not mutually contradictory.

[0123] While the invention has been particularly depicted and described, it should be understood that the foregoing description is illustrative and not restrictive, and that numerous modifications and variations are possible without departing from the scope of the invention.

[0124] The separation membrane composite of the present invention can be used in a variety of fields for separating various substances.

[0125] DESCRIPTION OF SYMBOLS 1 Separation membrane composite 11 Support 12 Separation membrane 16 Particle-containing layer 17 Dense layer 81 Seed crystals 161, 161a Granular particles S11 to S14, S21, S22 Steps

Claims

1. A separation membrane composite comprising: a porous support; and a separation membrane provided on the support and made of a metal-organic framework, wherein the separation membrane comprises: a particle-containing layer in contact with the support and dotted with granular particles of the metal-organic framework; and a dense layer in contact with the particle-containing layer on the side opposite the support and not containing the granular particles, wherein the granular particles account for 5 to 90% of the area of ​​the particle-containing layer in a cross section perpendicular to the surface of the separation membrane.

2. A separation membrane composite according to claim 1, wherein the granular particles comprise aggregates of fine particles.

3. A separation membrane composite according to claim 1, wherein the granular particles have an average particle size of 10 to 500 nm.

4. A separation membrane composite according to claim 1, wherein the particle-containing layer has a thickness of 1 μm or less.

5. A separation membrane composite according to any one of claims 1 to 4, wherein the average thickness of the separation membrane is 1.1 to 20 times the thickness of the particle-containing layer.

6. A method for producing a separation membrane composite, comprising: a) preparing fine particles of a metal-organic framework; b) preparing a dispersion containing an organic solvent and water as a solvent, the fine particles, and a pH adjuster, and in which aggregates of the fine particles are dispersed as seed crystals; c) using the dispersion to attach the seed crystals to a porous support; and d) immersing the support in a raw material solution and forming a separation membrane made of a metal-organic framework on the support by solvothermal synthesis.

7. A method for producing a separation membrane composite according to claim 6, wherein the ratio of the organic solvent in the solvent of the dispersion is 90% by volume or more, and the ratio of the water is 10% by volume or less.

8. The method for producing a separation membrane composite according to claim 6 or 7, wherein the average particle size of the aggregates in the dispersion is 10 to 500 nm.

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