Manufacturing method of air separation membrane

Abstract

To provide a manufacturing method of an air separation membrane having high separability under a low temperature environment.SOLUTION: A manufacturing method of an air separation membrane includes applying sol containing organoalkoxysilane onto a support layer, firing the sol at 450 to 550°C under an air atmosphere to form gel, and forming an active separation layer. The manufacturing method of an air separation membrane includes repeating the application of the sol and the firing of the sol to form the gel, and forming the active separation layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing an air separation membrane. [Background technology]

[0002] The three main components of air (nitrogen, oxygen, and argon) are mainly separated by adsorption separation, cryogenic separation, and membrane separation.

[0003] Adsorption separation utilizes physical or chemical action to capture specific components at the sites of an adsorbent, thereby separating them from other components. For example, in a nitrogen / oxygen system using a molecular sieve as the adsorbent, nitrogen exhibits strong adsorption properties, resulting in the other component, oxygen, becoming the product. Furthermore, adsorption and desorption operations require pressure or temperature swings, and both operations are performed at room temperature or above. Desorption operations are particularly difficult at low temperatures.

[0004] Cryogenic separation separates air-based components through distillation using vapor-liquid equilibrium. Because cryogenic separation must be operated under conditions where gas and liquid coexist, the operating temperature is near the dew point (-196°C to -100°C), which means it is carried out at extremely low temperatures. Furthermore, cryogenic separation requires the application of energy to liquefy and separate the air, which requires multiple compression and expansion processes, necessitating the use of tray columns and packed columns for distillation. Furthermore, due to the constraints of vapor-liquid equilibrium, it is difficult to separate argon / oxygen systems, requiring multiple distillation processes.

[0005] Membrane separation separates mixtures using the sieve of membrane pores. Therefore, it is not subject to the constraints of gas-liquid equilibrium such as relative volatility. In membrane separation, it is generally advantageous for the kinetic energy of the molecules to be high in order for the mixture to pass through the barrier inside the pores, so it is carried out at very high temperatures (for example, 500°C to 800°C).

[0006] Patent Document 1 discloses a separation device that combines distillation and membrane separation. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] US Patent Application Publication No. 2010 / 0077796 Summary of the Invention [Problem to be solved by the invention]

[0008] In low-temperature separation, Knudsen diffusion occurring at pinholes cannot be ignored, so it is necessary to precisely control the pore size and create a pinhole-free membrane. However, when membrane separation is performed in the same phase (e.g., gas phase and gas phase), it is a mechanism that utilizes differences in molecular diffusivity, and because of the pore size distribution, no separation membranes applicable to commercial operation, for example, in nitrogen / oxygen systems, have been obtained. Furthermore, the separation device disclosed in Patent Document 1 uses a separation membrane made of an organic polymer membrane for membrane separation, and therefore has an operating temperature limit of approximately -90°C. Therefore, in low-temperature environments below the dew point of mixed gases containing air-based components (-196°C to -100°C), Knudsen diffusion occurring in pinholes cannot be ignored. In order to separate mixed gases containing air-based components in low-temperature environments, it is necessary to create a membrane without pinholes while precisely controlling the pore size.

[0009] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing an air separation membrane that has high separation ability in a low-temperature environment. [Means for solving the problem]

[0010] In order to solve the above problems, the present invention has the following configuration. [1] A sol containing an organoalkoxysilane is applied onto a support layer; A method for producing an air separation membrane, comprising: calcining the sol at 450 to 550°C in an air atmosphere to form a gel, thereby forming an active separation layer. [2] The method for producing an air separation membrane according to [1], comprising repeating the application of the sol and the calcination of the sol to form a gel, thereby forming the active separation layer. [3] The method for producing an air separation membrane according to [1] or [2], further comprising forming an intermediate layer made of a hydrophobic material between the support layer and the active separation layer. [4] The method for producing an air separation membrane according to any one of [1] to [3], wherein the support layer is hollow and tubular. [Effects of the Invention]

[0011] According to the method for producing an air separation membrane of the present invention, an air separation membrane having high separation ability in a low-temperature environment can be produced. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a cross-sectional view schematically showing the configuration of a membrane module that can be used in an air separation unit according to an embodiment of the present invention. [Figure 2] 1 is a cross-sectional view showing an example of the configuration of a separation unit that can be applied to a membrane module that can be applied to an air separation unit that is an embodiment to which the present invention is applied. [Figure 3] 1 is an enlarged cross-sectional photograph showing a separation membrane applicable to an air separation unit according to an embodiment of the present invention. [Figure 4] 1A and 1B are schematic diagrams showing examples of inorganic materials having a crosslinked structure of siloxane bonds, where (a) shows the structure of a bridged organosilica, and (b) shows the structure of a side-chain organosilica. [Figure 5] 1 is a system diagram showing an example of the configuration of an air separation unit according to an embodiment of the present invention. [Figure 6] FIG. 1 is a system diagram showing a modified configuration of an air separation unit according to an embodiment of the present invention. [Figure 7] FIG. 1 is a system diagram showing a modified configuration of an air separation unit according to an embodiment of the present invention. [Figure 8]FIG. 1 is a system diagram showing a modified configuration of an air separation unit according to an embodiment of the present invention. [Figure 9] FIG. 1 is a graph showing the permeability (Permeance) of various gases when they pass through separation units (air separation membranes) of Examples and Comparative Examples relative to the kinetic molecular diameters of the gases. [Figure 10] FIG. 1 is a graph showing the permeance of various gases relative to their kinetic molecular diameters in a separation unit (air separation membrane) of a comparative example. [Figure 11] 1 shows the adsorption isotherms of oxygen, argon, and nitrogen for the gels of the examples and comparative examples. [Figure 12] 1 shows the adsorption isotherms of oxygen, argon and nitrogen for comparative gels. [Figure 13] FIG. 1 is a graph showing the ratio of oxygen / argon permeability to nitrogen / methane permeability when separation units of an example and a comparative example are used. DETAILED DESCRIPTION OF THE INVENTION

[0013] The method for producing an air separation membrane of the present invention, the air separation membrane produced by this method, the membrane module, and the air separation unit will be described in detail below with reference to the drawings. Note that the drawings used in the following description may show characteristic parts enlarged for convenience in order to make the characteristics easier to understand, and the dimensional proportions of the components may not necessarily be the same as those in reality.

[0014] Furthermore, when a numerical range is indicated using "to" in this specification, the numerical values ​​before and after "to" are included as the lower limit and upper limit.

[0015] <Membrane module> First, the configuration of a membrane module using an air separation membrane manufactured by an air separation membrane manufacturing method according to one embodiment of the present invention will be described. Figure 1 is a cross-sectional view schematically showing the configuration of the membrane module. As shown in FIG. 1, the membrane module 1 is generally configured to include a membrane module body 2, a separation unit 3, a raw material introduction section 4, a permeated component discharge section 5, and a non-permeated component discharge section 6.

[0016] The membrane module body 2 is a cylindrical container having a sealed space 2A inside. The membrane module body 2 is provided with a raw material introduction section 4 at one end and a permeated component discharge section 5 at the other end. The membrane module body 2 also has a non-permeated component discharge section 6 in its cylindrical trunk. Furthermore, a separation unit 3 is located in the space 2A inside the membrane module body 2.

[0017] FIG. 2 is a cross-sectional view showing an example of the configuration of the separation unit 3 of the membrane module 1. As shown in FIG. 1 and 2, the separation unit 3 is a hollow cylindrical member that extends in the axial direction of the membrane module main body 2 and has a closed end on the raw material introduction section 4 side and an open end on the permeated component discharge section 5 side. The separation unit 3 has a separation section 3A and a support section 3B.

[0018] Separation section 3A is located near the end of separation unit 3 on the raw material introduction section 4 side. Separation section 3A also has an air separation membrane 10 that separates air-based components on support layer 7. Air separation membrane 10 can be produced by the air separation membrane manufacturing method of the present invention.

[0019] The support layer 7 is a hollow cylindrical member that supports the air separation membrane 10. By supporting the air separation membrane 10 on the support layer 7, the mechanical strength of the separation section 3A can be increased.

[0020] The material of the support layer 7 is not particularly limited as long as it is a porous substrate that allows the air-based components used as raw materials to pass through. The porous substrate may be either an inorganic porous material or an organic porous material, and preferably has a strength sufficient for industrial use. Furthermore, to enhance the permeability of the air separation membrane 10, the larger the pore size and porosity of the porous substrate, the better. The average pore size of the porous substrate is preferably approximately 0.05 μm to 10 μm. If the pore size is too large, the difference with the pore size of the separation membrane becomes too great, making it difficult to form a separation layer, while if the pore size is too small, the permeability decreases. It is more preferably 0.1 μm to 5 μm, and particularly preferably 0.5 μm to 3 μm.

[0021] Examples of porous substrates include ceramics made of alumina (α-Al2O3 (α-alumina), γ-Al2O3 (γ-alumina)), mullite, zirconia, titania, or composites of these. Among these, ceramics containing α-alumina as the main component are preferred because they are inexpensive, easily available, and have excellent chemical resistance, heat resistance, and strength.

[0022] The shape of the support layer 7 is not particularly limited, but is preferably cylindrical or plate-like. More specifically, the support layer 7 may be a porous alumina tube (average pore diameter: 1 μm, porosity: approximately 50%).

[0023] The support section 3B is a hollow cylindrical member. The space inside the support section 3B, together with the space inside the support layer 7 that constitutes the separation section 3A, serves as a flow path for the component (permeating gas) that permeates the separation section 3A.

[0024] The material of the support portion 3B is not particularly limited as long as it is impermeable to the air-based components of the raw material. Examples of such materials include a non-porous alumina tube and a Pyrex glass tube. Among these, a non-porous alumina tube is preferred in view of the pressure resistance at the operating pressure (0.5 MPa) of the air separation unit and use at extremely low temperatures.

[0025] The separation unit 3 is configured such that the separation section 3A and the support section 3B are fixed to each other with an intermediate material (not shown) sandwiched therebetween. The material of the intermediate material is not particularly limited as long as it reduces the difference in thermal expansion coefficient between the separation section (support layer 7) 3A and the support section 3B. An example of such a material is glass frit.

[0026] The shape of the separation unit 3 is not particularly limited as long as it has a cylindrical space inside, and can be appropriately selected depending on the area and application of the air separation membrane 10. Examples of the shape of the separation unit 3 include a cylindrical shape and a square prism shape.

[0027] 1, the raw material introduction part 4 is located at one end of the membrane module main body 2. The raw material introduction part 4 is a gas component inlet that introduces a raw material containing air-based components into the inner space 2A of the membrane module main body 2.

[0028] The feedstock is air itself, or a mixed gas containing at least one of the three major components of air: nitrogen, oxygen, and argon, and also containing two or more components as a whole. Examples of gas components other than air-based components include carbon dioxide, neon, hydrogen, helium, krypton, and xenon. When the feedstock is a mixed gas containing air-based components, the ratio of each component in the feedstock is not particularly limited. Furthermore, since the membrane module 1 is used under operating conditions within the temperature range of an air separation unit (-196°C to 0°C), it is preferable that the mixed gas used as the feedstock does not contain components that solidify within this temperature range, such as water or carbon dioxide. In particular, the moisture content in the mixed gas to be separated may be such that its dew point is -50°C or lower, preferably -70°C or lower, and more preferably -100°C or lower.

[0029] The permeate component outlet 5 is located at the other end of the membrane module main body 2. The permeate component outlet 5 is a gas component outlet that discharges from the membrane module main body 2 the component (permeate gas) that permeates the separation section 3A of the separation unit 3 (i.e., the separation membrane 10).

[0030] The permeate component discharge section 5 is connected in a sealed state to the open end of the separation unit 3, and is in communication with the space inside the support section 3 that constitutes the separation unit 3. This allows the components that permeate through the separation section 3A of the separation unit 3 (i.e., permeated gas) to be discharged from the permeate component discharge section 5 to the outside of the membrane module body 2.

[0031] The non-permeating component discharge section 6 is located in the trunk of the membrane module main body 2. The non-permeating component discharge section 6 is a gas component discharge port that discharges components (i.e., non-permeating gases) that do not permeate the separation section 3A of the separation unit 3 (i.e., the air separation membrane 10) from the space 2A inside the membrane module main body 2.

[0032] The membrane module 1 selectively separates any component from a mixed gas containing air-based components under operating conditions within the temperature range of an air separation unit (-196°C to 0°C). That is, the feed air or a mixed gas containing air-based components is cooled to the above temperature range in advance. Furthermore, the membrane module 1 is placed inside a thermostatic chamber (cold box) to block heat from entering from the outside during operation of the air separation unit, and is maintained at approximately the same temperature as the feed gas.

[0033] <Separation membrane> Next, the configuration of an air separation membrane manufactured by the air separation membrane manufacturing method of the present invention will be described using an example in which it is applied to the above-mentioned membrane module 1. Figure 3 is an enlarged cross-sectional photograph showing an air separation membrane 10, which is one embodiment to which the present invention is applied.

[0034] As shown in FIG. 3, the air separation membrane 10 of this embodiment is a laminated membrane of an intermediate layer 8 supported on a support layer 7 and an active separation layer 9.

[0035] Intermediate layer 8 is located on support layer 7 and supports active separation layer 9. By providing intermediate layer 8 between support layer 7 and active separation layer 9, the difference in average pore diameter between adjacent layers can be reduced. In this case, intermediate layer 8 has an average pore diameter smaller than that of support layer 7 and larger than that of active separation layer 9.

[0036] The intermediate layer 8 is a layer made of a hydrophobic material. Examples of hydrophobic materials include inorganic materials having a siloxane bond (-Si-O-Si-), carbon materials made of carbon, etc. Among these, it is preferable to use inorganic materials having a siloxane bond from the viewpoint of low-temperature resistance.

[0037] Here, when a hydrophilic material is used for the intermediate layer 8, even when high-temperature baking is performed using an inert gas, moisture that cannot be completely removed remains in the membrane pores. Therefore, at temperatures as low as 0°C or below, the moisture remaining in the membrane pores freezes, causing physical blockage and inhibiting gas permeation. In contrast, with the separation membrane 10 of this embodiment, the intermediate layer 8 is a layer made of a hydrophobic material, so moisture does not remain in the membrane pores after high-temperature baking. Therefore, even at temperatures as low as 0°C or below, blockage due to freezing of the remaining moisture does not occur, and gas permeation is not inhibited.

[0038] Examples of inorganic materials having siloxane bonds include sols prepared from organoalkoxysilanes, sols prepared from tetraethoxysilanes, etc. Among these, it is preferable to use sols prepared from organoalkoxysilanes from the viewpoint of pore size control.

[0039] Examples of organoalkoxysilanes include one or more precursors selected from 1,2-bis(triethoxysilyl)methane (BTESM), 1,2-bis(triethoxysilyl)ethane (BTESE), 1,2-bis(triethoxysilyl)propane (BTESP), and 1,2-bis(triethoxysilyl)benzene (BTESB), and one or more sols obtained from their hydrolyzates. Among these, BTESM or BTESE crosslinked with at least a C3 component, preferably a C2 or lower component, is preferred, from the viewpoint of exhibiting properties similar to those of inorganic materials, and BTESM is more preferred.

[0040] Examples of the gel structure formed by firing a sol prepared from an organoalkoxysilane include a bridged organosilica represented by the following general formula (1) and a side-chain organosilica represented by the following general formula (2).

[0041] [ka]

[0042] [ka]

[0043] In the general formula (1), the linking group X located between silicon atoms (Si) is a saturated hydrocarbon or an unsaturated hydrocarbon having an unsaturated bond between carbon atoms. The hydrocarbon has 1 to 6 carbon atoms, preferably 1 to 3 carbon atoms. The above-mentioned linking group X also includes a structure in which some of the hydrogen atoms are substituted with a simple metal ion or a compound such as a metal oxide. Examples of metal species constituting the metal ions or metal oxides include Ag, Cu, Fe, Ni, Co, Al, Ti, Zr, etc. Note that the metal species listed here are merely examples and are not limited to these metals.

[0044] In the general formula (1), the organic group R is a hydrogen atom, a saturated hydrocarbon having 1 to 10 carbon atoms, or an unsaturated hydrocarbon having an unsaturated bond between carbon atoms. The organic group R also includes a structure in which some of the hydrogen atoms are substituted with a simple metal ion or a compound such as a metal oxide. Examples of metal species constituting the metal ions or metal oxides include Ag, Cu, Fe, Ni, Co, Al, Ti, Zr, etc. Note that the metal species listed here are merely examples and are not limited to these metals.

[0045] In the general formula (2), the organic group R can be the same as in the general formula (1). In the general formula (2), OR' is a side chain (pendant) hanging from a siloxane bond, and examples of the organic group R' include CH3 and C2H5.

[0046] Examples of the side chain organosilica represented by the above general formula (2) include methyltriethoxysilane (MTES) and methyltrimethoxysilane (MTMS).

[0047] An example of a carbon material made of carbon is a carbon film.

[0048] The average pore diameter of the intermediate layer 8 is not particularly limited as long as it is smaller than the average pore diameter of the support layer 7 and larger than the average pore diameter of the active separation layer 9. It is particularly preferable that the average pore diameter of the intermediate layer 8 is about 2 nm or less. If the average pore diameter of the intermediate layer 8 is too large, the selectivity during gas separation decreases. If the average pore diameter of the intermediate layer 8 is too small, the gas permeability decreases.

[0049] The thickness of intermediate layer 8 is not particularly limited as long as it is thick enough to cover the irregularities on the upper surface of support layer 7 and flatten active separation layer 9. Such a thickness may be 10 to 500 nm, preferably 50 to 400 nm, and more preferably 100 to 300 nm.

[0050] The active separation layer 9 is located on the intermediate layer 8 and is a layer that selectively separates any component from the raw material gas mixture containing air-based components. The material of the active separation layer 9 is an inorganic material having a crosslinked structure of siloxane bonds, which is made of organoalkoxysilane as a precursor.

[0051] An example of an inorganic material having a crosslinked structure of siloxane bonds is a gel obtained by calcining a sol prepared from an organoalkoxysilane. The air separation membrane produced by the air separation membrane production method of the present invention includes an active separation layer in which the pore size is precisely controlled and pinholes are reduced. By controlling the pore size of the active separation layer in this way, an air separation membrane with high separation ability can be realized in a low-temperature environment.

[0052] Examples of organoalkoxysilanes include one or more precursors selected from 1,2-bis(triethoxysilyl)methane (BTESM), 1,2-bis(triethoxysilyl)ethane (BTESE), 1,2-bis(triethoxysilyl)propane (BTESP), and 1,2-bis(triethoxysilyl)benzene (BTESB), and one or more sols obtained from their hydrolyzates. Among these, from the viewpoint of exhibiting properties similar to those of inorganic materials, those in which the carbon number of the organic group R is 3 or less (BTESM, BTESE, BTESP) are preferred, and BTESM is more preferred. This reflects the conventional knowledge that as the carbon number of the organic group R increases, it begins to exhibit the properties of organic materials.

[0053] Examples of the gel structure formed by firing a sol prepared from an organoalkoxysilane include a bridged organosilica represented by the following general formula (3) and a side-chain organosilica represented by the following general formula (4).

[0054] [ka]

[0055] [ka]

[0056] In the general formula (3), the linking group X located between silicon atoms (Si) is a saturated hydrocarbon or an unsaturated hydrocarbon having an unsaturated bond between carbon atoms. The number of carbon atoms in the hydrocarbon is 1 to 6, preferably 1 to 3. The above-mentioned linking group X also includes a structure in which some of the hydrogen atoms are substituted with a simple metal ion or a compound such as a metal oxide. Examples of metal species constituting the metal ions or metal oxides include Ag, Cu, Fe, Ni, Co, Al, Ti, Zr, etc. Note that the metal species listed here are merely examples and are not limited to these metals.

[0057] In the general formula (3), the organic group R is a hydrogen atom, a saturated hydrocarbon having 1 to 10 carbon atoms, or an unsaturated hydrocarbon having an unsaturated bond between carbon atoms. The organic group R also includes a structure in which some of the hydrogen atoms are substituted with a simple metal ion or a compound such as a metal oxide. Examples of metal species constituting the metal ions or metal oxides include Ag, Cu, Fe, Ni, Co, Al, Ti, Zr, etc. Note that the metal species listed here are merely examples and are not limited to these metals.

[0058] In the general formula (4), the organic group R can be the same as in the general formula (3). In the general formula (4), OR' is a side chain (pendant) hanging from a siloxane bond, and examples of the organic group R' include CH3 and C2H5.

[0059] Examples of the side chain organosilica represented by the general formula (4) include methyltriethoxysilane (MTES) and methyltrimethoxysilane (MTMS).

[0060] FIG. 4 is a schematic diagram showing an example of an inorganic material having a crosslinked structure of siloxane bonds, where (a) shows the structure of a bridged organosilica, and (b) shows the structure of a side-chain organosilica. As the active separation layer 9, it is preferable to use a gel in which the siloxane bond is substituted with a linking group X, as shown in FIG. 4(a). The linking group X is not particularly limited and can be appropriately selected depending on the type of gas to be separated, etc. Examples of the linking group X include saturated hydrocarbons having 1 to 8 carbon atoms and unsaturated hydrocarbons having an unsaturated bond between carbon atoms, as well as aromatic groups such as a phenyl group.

[0061] The average pore size of the active separation layer 9 is preferably 1 nm or less. When the average pore size is within this range, oxygen can be selectively separated from a mixed gas containing air-based components.

[0062] Specifically, for example, when the average pore diameter of the active separation layer 9 is 1 nm or less, oxygen can be selectively separated from a mixed gas containing air-based components. When selectively separating oxygen from a mixed gas containing air-based components, the average pore diameter of the active separation layer 9 is more preferably 0.1 nm to 0.8 nm, and particularly preferably 0.2 nm to 0.6 nm.

[0063] The thickness of the active separation layer 9 is not particularly limited as long as it can selectively separate any component from a mixed gas containing air-based components. Such a thickness may be 10 to 500 nm, preferably 30 to 400 nm, and more preferably 50 to 300 nm.

[0064] Air separation membrane 10 selectively separates any component from a mixed gas containing air-based components under operating conditions within the temperature range of an air separation unit (-196°C to 0°C). Here, "permeance," which is an index of the performance of an air separation membrane, is defined as the molar flow rate that permeates the membrane divided by the external surface area of ​​the membrane and the gas partial pressure.

[0065] For example, when a gel obtained from BTESM is used as the active separation layer 9 and a gel prepared from BTESE is used as the intermediate layer 8, the air separation membrane 10 becomes an oxygen separation membrane that allows oxygen to permeate from a mixed gas containing air-based components. In this case, the performance of the separation membrane 10 of this embodiment is such that the oxygen permeability is at least 1×10 under the operating conditions of −196° C. to 0° C. -8 [mol / (m 2 ·s·Pa)] or more, and 1×10 -6 [mol / (m 2 ·s·Pa)] or more is preferable.

[0066] Furthermore, when air separation membrane 10 is an oxygen separation membrane, the performance of air separation membrane 10 is preferably such that the oxygen / argon permeability ratio is at least 8 or more, more preferably 10 or more, and even more preferably 12 or more. With such performance, air separation membrane 10 can be used to separate oxygen and argon from a mixed gas containing oxygen and argon. By producing an air separation membrane using the air separation membrane production method of the present invention, the oxygen / argon permeability ratio can be adjusted to 8 or more.

[0067] <Air separation membrane manufacturing method> In one embodiment of the present invention, a method for manufacturing an air separation membrane includes applying a sol containing an organoalkoxysilane onto a support layer, and baking the sol at 450 to 550°C in an air atmosphere to form a gel, thereby forming an active separation layer.

[0068] As an example, a method for manufacturing an air separation membrane 10 as shown in FIGS. 2 and 3 will be specifically described, but the present invention is not limited to this.

[0069] First, it is preferable to form intermediate layer 8 on the surface of support layer 7. It is preferable to form intermediate layer 8 after first homogenizing the surface of support layer 7. The material used for homogenization is preferably fine particles of the same material as the porous substrate used for support layer 7. For example, when alumina is used as the porous substrate, it is preferable to support alumina fine particles of the same material on the surface of the porous substrate and then homogenize it. The alumina particles can be supported on the porous substrate by using a sol of the same material as that used to form the intermediate layer 8 (for example, a sol obtained from organoalkoxysilane) as the binder, dispersing the alumina particles in the binder, applying the binder to the surface of the porous substrate, drying, and firing. It is also preferable to perform the above process multiple times to homogenize the surface of the porous substrate, and in this case, it is advisable to gradually reduce the size of the alumina particles dispersed in the binder.

[0070] An intermediate layer 8 is formed on the homogenized support layer 7. The intermediate layer 8 may be formed by a hot coating method as follows. In the hot coating method, the porous substrate is preheated to about 170°C to 180°C, and a dilute solution of a sol obtained from an organoalkoxysilane is applied to the surface of the porous substrate, followed by baking to form the intermediate layer 8. Note that the above process may be repeated multiple times to obtain an intermediate layer 8 of the desired thickness.

[0071] Next, an active separation layer 9 is formed on the surface of the intermediate layer 8. The active separation layer 9 is formed by gelling and supporting an organoalkoxysilane sol. For example, hydrochloric acid or nitric acid is added as an acid to a 50°C ethanol solution with an adjusted water / silica ratio, and the mixture is stirred for about an hour. The resulting sol is then applied to a preheated intermediate layer to form a thin film, and sintered.

[0072] The applied gel is then baked. Baking is carried out in an air atmosphere at 450 to 550°C. An atmosphere containing 5 to 30% by volume of oxygen may be used instead of the air atmosphere. The baking temperature is preferably 470 to 530°C, and more preferably 480 to 520°C. The application of the sol and baking of the sol may be repeated several times, for example, 1 to 5 times, to form a gel, and an active separation layer may be formed.

[0073] The sol baking time can be 5 to 120 minutes, and preferably 10 to 80 minutes. The baking time means the time from when the set baking temperature is reached until the baking temperature falls below the set temperature or until the object to be baked is removed from the baking device.

[0074] As described above, the air separation membrane manufactured by the method of the present invention includes an active separation layer with precisely controlled pore size and reduced pinholes. By controlling the pore size of the active separation layer in this manner, an air separation membrane with high separation ability can be realized in a low-temperature environment.

[0075] <Air separation unit> Next, the configuration of an air separation unit employing the present invention, an air separation membrane manufactured by the method for manufacturing an air separation membrane of the present invention, will be described using an example in which the unit is applied to the above-mentioned membrane module 1. Figure 5 is a system diagram showing an example of the configuration of an air separation unit that is an embodiment to which the present invention is applied.

[0076] 5, the air separation unit 101 of this embodiment is generally configured to include a cold box (constant temperature bath) 20, a membrane module 1, a main heat exchanger 30, a feedstock introduction path L1, a permeated component discharge path L2, and a non-permeated component discharge path L3. The air separation unit 101 separates any component from feed air by membrane separation using the membrane module 1.

[0077] The cold box (constant temperature bath) 20 keeps the internal space warm to block heat from entering from the outside so that the air separation unit can operate. In the internal space of the cold box 20, a main heat exchanger 30 and a membrane module 1 are arranged.

[0078] The main heat exchanger 30 is located within the cold box 20 and performs heat exchange between one or more hot fluids and one or more cold fluids, cooling the hot fluids and heating the cold fluids. In the air separation unit 101 of this embodiment, the feedstock introduction path L1 carries a hot fluid, and the permeated component extraction path L2 and the non-permeated component extraction path L3 carry cold fluids, and heat exchange is performed between them. That is, the main heat exchanger 30 cools the feed air flowing through the feedstock introduction path L1 to a temperature near the dew point (for example, around −196 to −100° C.). The main heat exchanger 30 may further include a hot fluid and a cold fluid (not shown).

[0079] The membrane module 1 is located within the cold box 20, and separates the introduced raw air into components that permeate (hereinafter referred to as "permeating components") and components that do not permeate (hereinafter referred to as "non-permeating components") using a separation section 3A having an air separation membrane.

[0080] The raw material introduction path L1 is a flow path for introducing a raw material gas to be subjected to membrane separation into the membrane module 1. The raw material introduction path L1 is connected to the raw material introduction section 4 of the membrane module 1 (see FIG. 1).

[0081] In the raw material introduction path L1, there are arranged, in this order, a compression block 40 that compresses the raw material air to a required pressure, a pretreatment block 50 that removes impurities such as moisture and hydrocarbons contained in the raw material air, and a main heat exchanger 30. That is, in the raw material air supply path, the membrane module 1 is located on the secondary side of the main heat exchanger 30. As a result, the raw material air from which impurities have been removed and whose temperature and pressure have been increased to the required temperature and pressure is introduced into the membrane module 1.

[0082] The permeate component discharge path L2 is a flow path that discharges, from the membrane module 1, components of the raw gas that permeate through the separation section 3A having an air separation membrane. The permeate component discharge path L2 is connected to the permeate component discharge section 5 of the membrane module 1 (see FIG. 1).

[0083] The non-permeated component discharge path L3 is a flow path that discharges, from the membrane module 1, components of the raw gas introduced into the membrane module 1 that do not permeate through the separation section 3A having an air separation membrane. The non-permeated component discharge path L3 is connected to the non-permeated component discharge section 6 of the membrane module 1 (see FIG. 1).

[0084] In this air separation unit 101, feed air introduced into membrane module 1 is separated into a permeated component and a non-permeated component by separation section 3A having an air separation membrane, and each component is discharged from membrane module 1. The permeated component and non-permeated component discharged from membrane module 1 have their cold energy recovered by main heat exchanger 30, and then each component is recovered as a product.

[0085] Specifically, in the membrane module 1 used in the air separation unit 101, by using an air separation membrane including an active separation layer in which the pore size is precisely controlled and pinholes are reduced, which is manufactured by the air separation membrane manufacturing method of the present invention, it is possible to separate, for example, raw air into oxygen and nitrogen.

[0086] (Variation 1) Next, a first modified example of an air separation unit that is an embodiment to which the present invention is applied will be described. Figure 6 is a system diagram showing a modified example of the configuration of an air separation unit that is an embodiment to which the present invention is applied.

[0087] 6, an air separation apparatus 201 according to Modification 1 of this embodiment is generally configured to include a cold box (constant temperature bath) 20, a membrane module 1, a main heat exchanger 30, a distillation column 60, a raw material introduction path L1, a permeated component discharge path L2, a non-permeated component discharge path L3, and a product discharge path L4. That is, the air separation apparatus 201 according to Modification 1 differs in configuration from the above-described air separation apparatus 101 in that it includes a distillation column 60 on the secondary side of the membrane module 1. Therefore, the components shown in the above-described air separation apparatus 101 are denoted by the same reference numerals, and their description will be omitted.

[0088] Distillation column 60 is located within cold box 20 and separates the introduced feed containing two or more air-based components into a low-boiling component and a high-boiling component. The distillation column 60 is connected to a non-permeated component discharge path L3 and a product discharge path L4.

[0089] The non-permeated component discharge path L3 is located between the membrane module 1 and the distillation column 60, and is connected to any position in the distillation column 60. This allows the non-permeated component discharged from the membrane module 1 to be introduced into the distillation column 60 as a raw material.

[0090] Product discharge line L4 is connected to any position in the height of distillation column 60. As a result, components with a composition ratio according to the position in the height of distillation column 60 are discharged from distillation column 60 as a product.

[0091] According to the air separation apparatus 201 of the first modification, the feed air introduced into the membrane module 1 is separated into a permeated component and a non-permeated component by the separation section 3A having an air separation membrane, and the components are discharged from the membrane module 1, respectively. The permeated component discharged from the membrane module 1 is recovered as a product after the cold energy is recovered by the main heat exchanger 30. The non-permeated component discharged from the membrane module 1 is introduced into the distillation column 60, where it is separated into a low boiling point component and a high boiling point component, and the separated components are discharged from the product discharge line L4. The components discharged from the distillation column 60 are recovered as products or residue after the cold heat is recovered by the main heat exchanger 30 .

[0092] Specifically, in the membrane module 1 used in the air separation device 201 of variant 1, by using an air separation membrane including an active separation layer in which the pore size is precisely controlled and pinholes are reduced, which is manufactured by the air separation membrane manufacturing method of the present invention, it is possible to separate the feed air into oxygen, which is a permeable component, and nitrogen and argon, which are non-permeable components. In the distillation column 60, for example, nitrogen and argon can be easily separated.

[0093] (Variation 2) Next, a second modified example of an air separation unit that is an embodiment to which the present invention is applied will be described. Figure 7 is a system diagram showing a modified example of the configuration of an air separation unit that is an embodiment to which the present invention is applied.

[0094] 7, an air separation unit 301 according to Modification 2 of this embodiment is generally configured to include a cold box (constant temperature bath) 20, a membrane module 1, a main heat exchanger 30, distillation columns 60 and 70, a feedstock introduction path L1, a permeant component discharge path L2, a non-permeant component discharge path L3, product discharge paths L4 and L6, and a feedstock air introduction path L5. That is, the air separation unit 301 according to Modification 2 differs in configuration from the air separation unit 201 according to Modification 1 described above in that it further includes a distillation column 70 on the primary side of the membrane module 1. Therefore, the components shown in the air separation unit 201 according to Modification 1 described above are denoted by the same reference numerals, and their description will be omitted.

[0095] Distillation column 70 is located within cold box 20 and separates the introduced feed containing two or more air-based components into a low-boiling component and a high-boiling component. The distillation column 70 is connected to a feed air introduction line L5, a feedstock introduction line L1, and a product discharge line L6.

[0096] The feed air introduction path L5 is a flow path for introducing the feed air into the distillation column 70. The feed air introduction path L5 is connected to the distillation column 70 at any position in the column height.

[0097] The feed air introduction path L5 is provided with, in this order, a compression block 40 that compresses the feed air to a required pressure, a pretreatment block 50 that removes impurities such as moisture and hydrocarbons contained in the feed air, and a main heat exchanger 30. As a result, the feed air from which impurities have been removed and whose temperature and pressure have been increased to the required temperature and pressure is introduced into the distillation column 70.

[0098] The raw material introduction path L1 is located between the distillation column 70 and the membrane module 1, and is connected to an arbitrary position in the height of the distillation column 70. As a result, components having a composition ratio according to the position in the height of the distillation column 70 are introduced into the membrane module 1 as raw materials.

[0099] Product discharge line L6 is connected to the bottom or top of distillation column 70. As a result, components with a composition ratio according to the position in the height of distillation column 70 are discharged from distillation column 70 as a product.

[0100] According to the air separation unit 301 of variant 2, the feed air introduced into the distillation column 70 is separated into low-boiling point components and high-boiling point components, and is introduced as a feed into the membrane module 1 via a feed introduction path L1 extracted from any position into the distillation column 70. Furthermore, the components discharged from the distillation column 70 to the product discharge line L6 have their cold energy recovered by the main heat exchanger 30, and are then recovered as products or residue. The raw material introduced into the membrane module 1 is separated into a permeated component and a non-permeated component by a separation section 3A having an air separation membrane, and the components are discharged from the membrane module 1, respectively. The permeated component discharged from the membrane module 1 is recovered as a product after the cold energy is recovered by the main heat exchanger 30. The non-permeated component discharged from the membrane module 1 is introduced into the distillation column 60, where it is separated into a low boiling point component and a high boiling point component, and the separated components are discharged from the product discharge line L4. The components discharged from the distillation column 60 are recovered as products or residue after the cold heat is recovered by the main heat exchanger 30 .

[0101] Specifically, in the membrane module 1 used in the air separation unit 301 of variant 2, by using an air separation membrane including an active separation layer in which the pore size is precisely controlled and pinholes are reduced, which is manufactured by the air separation membrane manufacturing method of the present invention, it is possible to separate a raw material containing oxygen and argon into oxygen, which is a permeable component, and argon, which is a non-permeable component. In the distillation column 70 located on the upstream side of the membrane module 1, nitrogen can be separated from oxygen and argon. In the distillation column 60 located on the secondary side of the membrane module 1, argon and oxygen can be separated.

[0102] (Variation 3) Next, a third modified example of an air separation unit that is an embodiment to which the present invention is applied will be described. Figure 8 is a system diagram showing a modified example of the configuration of an air separation unit that is an embodiment to which the present invention is applied.

[0103] 8, an air separation apparatus 401 according to Modification 3 of this embodiment is generally configured to include a cold box (constant temperature bath) 20, a membrane module 1, a main heat exchanger 30, a distillation column 70, a feedstock introduction path L1, a permeant component discharge path L2, a non-permeant component discharge path L3, and a feedstock air introduction path L5. That is, the air separation apparatus 401 according to Modification 3 differs in configuration from the air separation apparatus 301 according to Modification 2 described above in that the distillation column 60 on the secondary side of the membrane module 1 is omitted. Therefore, the components shown in the air separation apparatus 301 according to Modification 2 described above are denoted by the same reference numerals, and a description thereof will be omitted.

[0104] Distillation column 70 is located within cold box 20 and separates the introduced feed containing two or more air-based components into a low-boiling component and a high-boiling component. The distillation column 70 is connected to a feed air introduction line L5 and a feed material introduction line L1.

[0105] The feed air introduction path L5 is a flow path for introducing the feed air into the distillation column 70. The feed air introduction path L5 is connected to the distillation column 70 at a position at the bottom of the column height.

[0106] According to the air separation unit 401 of the third variant, the feed air introduced into the distillation column 70 is separated into low-boiling point components and high-boiling point components, and a portion of the components is introduced as feed into the membrane module 1 via the feed introduction path L1. The raw material introduced into the membrane module 1 is separated into a permeated component and a non-permeated component by a separation section 3A having an air separation membrane, and the components are discharged from the membrane module 1, respectively. The permeated component discharged from the membrane module 1 is recovered as a product after the cold energy is recovered by the main heat exchanger 30. The non-permeated component discharged from the membrane module 1 is recovered as a product or residue after the cold energy is recovered by the main heat exchanger 30.

[0107] Specifically, in the membrane module 1 used in the air separation unit 401 of variant example 3, by using an air separation membrane including an active separation layer in which the pore size is precisely controlled and pinholes are reduced, which is manufactured by the air separation membrane manufacturing method of the present invention, it is possible to separate a raw material containing oxygen and argon into oxygen, which is a permeable component, and argon, which is a non-permeable component. In the distillation column 70 located on the upstream side of the membrane module 1, nitrogen can be separated from oxygen and argon.

[0108] <Air separation method> Next, an air separation method according to one embodiment of the present invention will be described. The air separation method according to this embodiment is carried out using an air separation apparatus 101 to which the above-described membrane module 1 is applied. Specifically, the air separation method of this embodiment selectively separates any component from a mixed gas containing air-based components using a membrane module 1 including an air separation membrane at a temperature near the dew point of the mixed gas containing air-based components. The air separation unit 101 applied to the air separation method of this embodiment is an example, and is not limited to this. For example, the air separation units 201, 301, and 401 described above may be applied to the air separation method of this embodiment.

[0109] As described above, according to the air separation apparatus 101 and air separation method of this embodiment, the membrane module 1 includes the air separation membrane 10, which includes an active separation layer with precisely controlled pore size and reduced pinholes, manufactured by the air separation membrane manufacturing method of the present invention, and can maintain membrane performance even at the extremely low temperatures at which air separation apparatuses are operated, allowing membrane separation to be used in low-temperature environments (-196°C to 0°C). Therefore, unlike adsorption, this is not a batch operation, and operating pressure and temperature swings are not required.

[0110] Furthermore, the air separation unit 101 and air separation method of this embodiment use membrane separation, which is not restricted by vapor-liquid equilibrium in distillation, and can promote separation in a system (e.g., argon / oxygen) with a relative volatility close to 1. Furthermore, because membrane separation is performed at a temperature near the dew point of the mixed gas, surface diffusion is likely to occur, which inhibits the diffusion of other components, thereby improving selectivity and permeability.

[0111] The technical scope of the present invention is not limited to the above-described embodiment, and includes designs within the scope that do not deviate from the gist of the present invention. For example, the air separation unit 101 of the above-described embodiment is a simplified representation of the configuration, and is not limited to this.

[0112] Furthermore, the above-described air separation unit 101 and the air separation units 201, 301, and 401 of Modifications 1 to 3 have been described as examples of configurations including one main heat exchanger 30, but two or more heat exchangers may be provided. Furthermore, in the above-described air separation unit 101, the membrane module 1 is located on the secondary side of the main heat exchanger 30, but the membrane module 1 may also be disposed on the secondary side of another heat exchanger.

[0113] Furthermore, the above-described air separation unit 101 and the air separation units 201, 301, and 401 of Modifications 1 to 3 have been described as examples of configurations in which one distillation column is provided on the primary or secondary side of the membrane module 1. However, the present invention is not limited to this. For example, two or more distillation columns may be provided on the primary or secondary side of the membrane module 1. [Example]

[0114] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following descriptions.

[0115] <Experimental Example 1> A separation unit (air separation membrane) having the configuration shown in Figure 2 was prepared under the following conditions, and the air separation membrane, more specifically, the molecular diameter dependency of the active separation layer on the firing atmosphere and firing temperature of the active separation layer, was evaluated.

[0116] (Example 1-1) (Materials used) Support: Non-porous alumina tube (length 200 mm) Support layer: porous alumina tube (outer diameter: 10 mm, length: 100 mm, average pore size: 1 μm, porosity: approximately 50%) Intermediate layer: BTESM gel is used as a hydrophobic material (thickness: 100-300 nm) Active separation layer: Supports BTESM polymer gel (thickness: 50-300nm)

[0117] (Preparation ratio) ·Middle layer ···BTESM:H2O:HCl=1:200:0.1 ·Active separation layer ···BTESM:H2O:HCl=1:200:0.1

[0118] (Film forming method) After supporting fine particles of Al2O3 dissolved in water on the support layer (α-Al2O3), the layer was sintered in air at 500°C for 15 minutes. This process was repeated several times. The intermediate layer was prepared by applying the BTESM sol prepared in the above-mentioned ratio to a preheated support layer and sintering it. The layer was then fired in air at 500°C for 15 minutes. This process was repeated several times. The active separation layer was prepared by applying the BTESM sol prepared in the above ratio onto a preheated support layer and sintering it. The layer was then fired at 500°C for 60 minutes in an air atmosphere. This process was repeated several times.

[0119] (evaluation) Various pure gases were supplied to the fabricated separation unit (air separation membrane) under the following conditions, and the permeability of each gas was measured. The results are shown in Figure 9. Gas types: Hydrogen (H2), Helium (He), Oxygen (O2), Argon (Ar), Nitrogen (N2), Methane (CH4), Carbon Tetrafluoride (CF4), Sulfur Hexafluoride (SF6) Gas temperature: 200℃ Flow rate through the membrane: 1L / min External surface area of ​​the membrane: 3.14×10 -3 m 2 Primary pressure: 200kPaG Secondary pressure: atmospheric pressure

[0120] (Comparative Example 1-1) A separation unit was produced under the same conditions as in Example 1-1, except that the firing temperature during film formation was changed to 600°C.

[0121] (Comparative Example 1-2) A separation unit was produced under the same conditions as in Example 1-1, except that the firing atmosphere during film formation was changed to a nitrogen atmosphere, the firing temperature was changed to 200° C., and the intermediate layer was changed to BTESE.

[0122] (Comparative Examples 1-3) A separation unit was produced under the same conditions as in Comparative Example 1-2, except that the baking temperature during film formation was changed to 300°C.

[0123] (Comparative Examples 1-4) A separation unit was produced under the same conditions as in Comparative Example 1-2, except that the firing temperature during film formation was changed to 400°C.

[0124] (Comparative Examples 1-5) A separation unit was produced under the same conditions as in Comparative Example 1-2, except that the firing temperature during film formation was changed to 600° C. and the intermediate layer was changed to BTESM.

[0125] Fig. 9 is a graph showing the permeance of various gases relative to their kinetic molecular diameters in the separation units (air separation membranes) of Example 1-1 and Comparative Example 1-1. Fig. 10 is a graph showing the permeance of various gases relative to their kinetic molecular diameters in the separation units (air separation membranes) of Comparative Examples 1-2 to 1-5. In Figs. 9 and 10, the X-axis represents the kinetic molecular diameter (nm) and the Y-axis represents the permeance.

[0126] 9, the separation unit (air separation membrane) of Example 1-1 was formed by firing the active separation layer in an air atmosphere at 500°C, and therefore had significantly different permeabilities for nitrogen and methane. In other words, the active separation layer of Example 1 was found to be a membrane with few pinholes that contribute to Knudsen diffusion and a narrow pore distribution.

[0127] On the other hand, in the separation unit of Comparative Example 1-1, the permeabilities of both nitrogen and methane were low, suggesting that the membrane was dense.

[0128] 10, in the cases of Comparative Examples 1-2 to 1-5 in which firing was performed under a nitrogen atmosphere, the permeabilities of nitrogen and methane were similar at all firing temperatures, indicating that the firing temperature had almost no effect on the pore distribution of the active separation layer.

[0129] This shows that firing in a nitrogen atmosphere has almost no effect on the pore size distribution regardless of the firing temperature, while in an air atmosphere, optimizing the firing temperature makes it possible to precisely control the pore size while suppressing pinholes.

[0130] <Experimental Example 2> The adsorption isotherms of the calcined gels were evaluated depending on the calcination atmosphere and temperature. Example 2-1 A BTESM sol was prepared in the same manner as in Example 1, and the solvent was evaporated in a container heated to 50°C to produce a gel powder. This gel powder was then calcined in an air atmosphere at 500°C for 60 minutes. Adsorption isotherms for oxygen, argon, and nitrogen were plotted for the resulting powder using a gas / vapor adsorption analyzer (Microtrack-Bel, BelsoapMax).

[0131] (Comparative Examples 2-1 to 2-3) Comparative Examples 2-1 to 2-3 were prepared by carrying out the same procedure as in Example 2-1, except that the gel powder was fired in an air atmosphere at 300°C, 400°C, and 600°C, respectively.

[0132] (Comparative Examples 2-4 to 2-9) Comparative Examples 2-4 to 2-9 were prepared by carrying out the same procedure as in Example 2-1, except that the gel powder was fired in a nitrogen atmosphere at 200°C, 300°C, 400°C, 500°C, and 600°C, respectively.

[0133] Figures 11(a) to 11(d) show the adsorption isotherms of oxygen, argon, and nitrogen for the gels of Example 2-1 and Comparative Examples 2-1 to 2-3, respectively. Figures 12(a) to 12(e) show the adsorption isotherms of oxygen, argon, and nitrogen for the gels of Comparative Examples 2-4 to 2-9, respectively.

[0134] In Example 2-1, the selectivity to oxygen was significantly increased. On the other hand, in Comparative Example 2-3, a dense membrane structure was formed that could not adsorb any molecules. This result indicates that when the firing temperature was increased from 500°C in an air atmosphere, the structure transitioned from an organosilica membrane to a silica membrane. The results of Example 2-1 showed that by firing the active separation layer in air at around 500°C, an active separation layer with pores that can separate oxygen and argon using a molecular sieve could be produced without forming pinholes.

[0135] On the other hand, when firing was performed in a nitrogen atmosphere, at high temperatures, i.e., 600°C, differences in the amount of adsorption of each gas were observed, but almost no difference in gas selectivity was observed.

[0136] The above results show that when the firing conditions are controlled so that the active separation layer is fired in an air atmosphere at around 500°C, molecular sieving performance is exhibited, which was not exhibited at any temperature when fired in a nitrogen atmosphere.

[0137] <Experimental Example 3> The influence of different firing atmospheres on gas separation ability at low temperature and at room temperature was investigated.

[0138] Example 3-1 The separation unit of Example 1-1 was used to carry out the following evaluations. Various pure gases were supplied to the separation unit under the following conditions, and the permeance of each gas was measured, and the oxygen / argon permeability ratio and nitrogen / methane permeability ratio were calculated. Gas types: Hydrogen (H2), Oxygen (O2), Argon (Ar), Nitrogen (N2), Methane (CH4) Gas temperature: 30℃ or -115℃ Flow rate through the membrane: 1L / min External surface area of ​​the membrane: 3.14×10 -3 m 2 Primary pressure: 200kPaG

[0139] (Comparative Example 3-1) (Materials used) Support: Non-porous alumina tube (length 200 mm) Support layer: porous alumina tube (outer diameter: 10 mm, length: 100 mm, average pore size: 1 μm, porosity: approximately 50%) Intermediate layer: BTESE gel is used as a hydrophobic material (thickness: 100-300 nm) Active separation layer: Supports BTESM polymer gel (thickness: 50-300nm)

[0140] (Preparation ratio) ·Middle layer ···BTESE:H2O:HCl=1:240:0.1 ·Active separation layer ···BTESM:H2O:HCl=1:200:0.1

[0141] (Film forming method) After supporting fine particles of Al2O3 dissolved in water on the support layer (α-Al2O3), the substrate was fired in a N2 atmosphere at 300°C for 15 minutes. This process was repeated several times. The intermediate layer was prepared by applying the BTESE sol prepared in the above ratio onto a preheated support layer and sintering it. The layer was then fired at 300°C in a N2 atmosphere. This process was repeated several times. The BTESM sol prepared according to the above-mentioned ratio was applied to a preheated support layer and sintered to form the active separation layer. It was then baked at 300°C for 60 minutes in a nitrogen atmosphere. This process was repeated several times to prepare a separation unit. Nine separation units were prepared under the same conditions.

[0142] FIG. 13 is a diagram showing the oxygen / argon permeability ratio relative to the nitrogen / methane permeability when the separation units of Example 3-1 and Comparative Example 3-1 are used. Squares indicate the gas permeability ratio at a gas temperature of 30°C, and circles indicate the gas permeability ratio at a gas temperature of -115°C. Data indicated by arrows are data from Example 3-1, and the rest are data from Comparative Example 3-1. The separation unit of Example 3-1 has a high nitrogen / methane permeability. This indicates that the membrane has few pinholes that would cause Knudsen diffusion. Furthermore, even at a low temperature of -115°C, the oxygen / argon permeability ratio was high, at about 12.

[0143] On the other hand, when the separation unit of Comparative Example 3-1 was used, the nitrogen / methane permeability ratio and the oxygen / argon permeability ratio at a gas temperature of -115°C were both low values. [Explanation of symbols]

[0144] 1...membrane module, 2...membrane module body, 2A...space, 3...separation unit, 3A...separation section, 3B...support section, 4...feedstock introduction section, 5...permeated component discharge section, 6...non-permeated component discharge section, 7...support layer, 8...intermediate layer, 9...active separation layer, 10...air separation membrane, 20...cold box (constant temperature bath), 30...main heat exchanger, 40...compression block, 50...pretreatment block, 60, 70...distillation column, 101, 201, 301, 401...air separation unit, L1...feedstock introduction path, L2...permeated component discharge path, L3...non-permeated component discharge path, L4, L6...product discharge path, L5...feedstock air introduction path

Claims

1. A sol containing an organoalkoxysilane is applied onto a support layer, and calcining the sol at 450 to 550° C. in an air atmosphere to form a gel, thereby forming an active separation layer.

2. 2. The method of claim 1, further comprising repeatedly applying the sol and baking the sol to form the gel and the active separating layer.

3. 3. The method for producing an air separation membrane according to claim 1, further comprising forming an intermediate layer made of a hydrophobic material between the support layer and the active separation layer.

4. The method for producing an air separation membrane according to claim 1 or 2, wherein the support layer is hollow tubular.

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