Method for producing gas separation membrane and gas separation membrane

Abstract

To provide a method for manufacturing a gas separation membrane which is excellent in gas separation selectivity and durability, and a gas separation membrane which is excellent in gas separation selectivity and durability.SOLUTION: A method for manufacturing a gas separation membrane includes the steps of: preparing a composite metal sol containing silane alkoxide or aluminum alkoxide, titanium alkoxide, a β-diketone ligand, a hydroxy ether catalyst and water; molding and heating the composite metal sol and thereby preparing a composite metal gel membrane; and baking the composite metal gel membrane and thereby manufacturing a gas separation membrane.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a gas separation membrane excellent in gas separation selectivity and durability, and a gas separation membrane excellent in gas separation selectivity and durability.

Background Art

[0002] As an energy, hydrogen, unlike fossil fuels such as coal, oil, and natural gas, does not generate carbon dioxide even when burned. In addition to the electrolysis of water vapor, hydrogen can be produced from various resources such as fossil fuels such as oil and natural gas, methanol and ethanol, sewage sludge, and waste plastics. Furthermore, hydrogen may also be generated secondarily in the process in ironworks, chemical factories, etc. Therefore, hydrogen is attracting attention as a next-generation energy.

[0003] However, one of the drawbacks of hydrogen is that it is difficult to purify. For example, since hydrogen has a lower adsorptivity to activated carbon etc. than other gases, purification by the adsorption method is being studied. However, for the purification of hydrogen by the adsorption method, a pressure of several atmospheres to several tens of atmospheres is required, so there are problems in energy efficiency and safety. On the other hand, purification of hydrogen by a gas separation membrane is highly energy-efficient and safe.

[0004] As a material for the gas separation membrane, silica which is amorphous, has fine pores, and has high permeability can be considered, but silica has a drawback of being inferior in durability. On the other hand, zirconia etc. have high durability, but have high crystallinity, and the pores are the voids between crystal grains, so it is difficult to form the fine pores necessary for gas separation. Therefore, Non-Patent Document 1 discloses a zirconia-titania composite membrane made amorphous by suppressing the reactivity of the precursor using diethanolamine. The present inventors have also produced a zirconia-titania composite membrane using organic chelating agents such as diethanolamine, isoeugenol, 2,3-dihydroxynaphthalene, and ethyl acetoacetate (Non-Patent Documents 2 to 4).

Prior Art Documents

Non-Patent Literature

[0005]

Non-Patent Literature 1

Non-Patent Literature 2

Non-Patent Literature 3

Non-Patent Literature 4

Summary of the Invention

Problems to be Solved by the Invention

[0006] As described above, a zirconia - titania composite membrane intended for use as a gas separation membrane has been produced. However, compared with a silica membrane, it has a larger pore diameter and insufficient gas separation selectivity, and its gas permeability has never been high. On the other hand, the silica membrane has a problem of durability. Therefore, an object of the present invention is to provide a method for manufacturing a gas separation membrane excellent in gas separation selectivity and durability, and a gas separation membrane excellent in gas separation selectivity and durability.

Means for Solving the Problems

[0007] The inventors of the present invention have conducted intensive studies to solve the above problems. As a result, it has been found that a more homogeneous composite metal oxide can be produced by controlling the reactivity of a metal alkoxide, which is a precursor of a metal oxide, using a specific organic chelating agent and an organic solvent. As a result, the inventors of the present invention have combined the characteristics of specific metal oxides to produce a gas separation membrane excellent in both gas separation selectivity and durability, and completed the present invention. The present invention is shown below.

[0008] [1] A method for manufacturing a gas separation membrane, comprising: a step of preparing a composite metal sol containing a silane alkoxide or an aluminum alkoxide, a titanium alkoxide, a β-diketone ligand represented by the following formula (I), a catalyst, a hydroxyether solvent represented by the following formula (II), and water; [Chemical formula] [In the formula, R 1 ~R 3 each independently represents H or a C 1-6 alkyl group which may have a substituent α; R 4 represents a C 1-2 alkyl group; R 5 represents a C 1-4 alkanediyl group; The substituent α represents one or more substituents selected from a halogeno group, a C 1-6 alkoxy group, and a C 1-6 alkoxy-[-R 6 -O-] n - group (wherein R 6 represents a C 1-4 alkanediyl group, and n represents an integer of 1 or more and 5 or less).) a step of preparing a composite metal gel membrane by forming and heating the composite metal sol; and a step of manufacturing a gas separation membrane by firing the composite metal gel membrane.

[0009] [2] The method according to [1], wherein R 1 and R 3 are C 1-4 alkyl groups, and R 2 is H. [3] The method according to [1] or [2], wherein the catalyst is hydrogen chloride. [4] The method according to any one of [1] to [3] above, wherein the hydroxyether solvent is one or more hydroxyether solvents selected from methoxymethanol, ethoxymethanol, 2-methoxyethanol, and 2-ethoxyethanol. [5] The method according to any one of [1] to [4] above, wherein the molar ratio of the silane alkoxide or aluminum alkoxide to the titanium alkoxide is 0.2 or more and 1.2 or less. [6] The method according to any one of [1] to [5] above, wherein the molar ratio of water to the total of the titanium alkoxide and the silane alkoxide or aluminum alkoxide is 0.05 or more and 500 or less. [7] The method according to any one of [1] to [5] above, wherein the proportion of the hydroxyether solvent to the total of the silane alkoxide or aluminum alkoxide, the titanium alkoxide, the β-diketone ligand, the catalyst, the hydroxyether solvent, and the water is 20% by mass or more and 99.5% by mass or less.

[0010] [8] A gas separation membrane comprising a composite metal oxide containing SiO2 or Al2O3 and TiO2. [9] The gas separation membrane according to [8] above, wherein the molar ratio of Si or Al to Ti contained in the composite metal oxide is 0.2 or more and 1.2 or less.

[10] The gas separation membrane according to [8] or [9] above, having a pore diameter of 0.6 nm or less measured by the Normalized Knudsen-based Permeance method.

[11] The BET specific surface area is 300 m 2 The gas separation membrane according to any one of [8] to

[10] above. [Advantages of the Invention]

[0011] Generally, when preparing a composite metal oxide from a metal alkoxide by the sol-gel method, due to the difference in reactivity of the metal alkoxides, aggregates of each metal oxide are sequentially formed, and it has been difficult to produce a homogeneous composite metal oxide. In particular, the hydrolysis rate of zirconium alkoxide is fast, and the hydrolysis rate of titanium alkoxide is also relatively fast. In contrast, in the present invention, by using a specific combination of metal alkoxides, namely silane alkoxide or aluminum alkoxide, and titanium alkoxide, together with a specific organic chelating agent and an organic solvent, a homogeneous composite metal oxide was successfully produced. Such a composite metal oxide has silica and fine pores, a high porosity, a large specific surface area, and excellent durability. Therefore, the present invention is extremely excellent industrially as it can contribute to the practical application of efficient gas separation by a metal oxide film.

Brief Description of the Drawings

[0012]

Figure 1

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Figure 7

Mode for Carrying Out the Invention

[0013] First, the method for manufacturing the gas separation membrane according to the present invention will be described below. However, the present invention is not limited to the following specific examples and the like.

[0014] 1. Preparation Step of Composite Metal Sol In this step, a composite metal sol containing a silane alkoxide or an aluminum alkoxide, a titanium alkoxide, a β-diketone ligand represented by formula (I), a catalyst, a hydroxyether solvent represented by formula (II), and water is prepared. Hereinafter, "the compound represented by formula (X)" may be abbreviated as "compound (X)".

[0015]

Chemical Formula

[0016] In the present disclosure, "C 1-6"Alkyl group" refers to a linear or branched monovalent saturated aliphatic hydrocarbon group having 1 to 6 carbon atoms. For example, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, s-butyl, t-butyl, n-pentyl, n-hexyl, etc. Preferably, it is a C 1-4 alkyl group, more preferably a C 1-2 alkyl group, and even more preferably methyl.

[0017] "C 1-4 alkanediyl group" refers to a linear or branched divalent saturated aliphatic hydrocarbon group having 1 to 6 carbon atoms. For example, methylene, ethylene, methylmethylene, n-propylene, methylethylene, n-butylene, methylpropylene, dimethylethylene, n-pentylene, n-hexylene, etc. Preferably, it is a C 1-4 alkylene, more preferably a C 1-2 alkylene, and even more preferably ethylene.

[0018] Examples of the "halogeno group" include fluoro, chloro, bromo, and iodo. Fluoro, chloro, or bromo is preferred, fluoro or chloro is more preferred, and fluoro is even more preferred.

[0019] "C 1-6 alkoxy group" refers to a linear or branched saturated aliphatic hydrocarbon oxy group having 1 to 6 carbon atoms. For example, methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, t-butoxy, n-pentoxy, n-hexoxy, etc. Preferably, it is a C 1-4 alkoxy group, more preferably a C 1-2 alkoxy group, and even more preferably methoxy.

[0020] R 1 ~R 3 which is a C 1-6When the alkyl group has the substituent α, the number of substituents is not particularly limited as long as it is substitutable. For example, it can be 1 or more and 10 or less. Also, the number of substituents can be appropriately adjusted according to the type of the substituent α. When the substituent α is a halogeno group, perhalogeno C 1-6 may be an alkyl group. When the substituent α is C 1-6 an alkoxy group or C 1-6 an alkoxy-[-R 6 -O-] n - group, the number of substituents is preferably 1 or more and 5 or less, more preferably 3 or less, and even more preferably 2 or less or 1.

[0021] In the alkoxy-[-R 6 -O-] n - group, n is preferably 3 or less, more preferably 2 or less, and even more preferably 1.

[0022] R 1 and R 3 are preferably C 1-6 alkyl groups which may have the substituent α, more preferably C 1-4 alkyl groups, and R 2 is preferably H.

[0023] The metal alkoxide is generally represented by M 1 (OR 10 ) m (wherein M 1 represents a metal, R 10 represents a C 1-4 alkyl group, and m represents the valence of the metal M 1 .). For example, the valence of silicon and titanium is 4, and the valence of aluminum is 3.

[0024] Metal alkoxides can be appropriately selected, for example, based on the hydrolysis rate. Generally, the hydrolysis rate of metal alkoxides is faster for lower alkoxides and faster when the alkyl group has a branch or a large steric hindrance. Specifically, the hydrolysis rate of metal alkoxides with a tertiary alkyl group is faster, and the hydrolysis rate of metal alkoxides with a primary alkyl group is slower. Also, since the hydrolysis rate of titanium alkoxides is faster than that of silane alkoxides and aluminum alkoxides, it is preferable to select a silane alkoxide or an aluminum alkoxide with a faster hydrolysis rate and a titanium alkoxide with a slower hydrolysis rate.

[0025] Silane alkoxides and aluminum alkoxides may be used in combination, or either one may be selected and used.

[0026] The usage ratio of silane alkoxide or aluminum alkoxide to titanium alkoxide may be appropriately adjusted according to the characteristics of each metal oxide, etc. For example, the crystallinity of silica (silane oxide, SiO2) and alumina (aluminum oxide, Al2O3) is relatively low, and it is possible to form a metal oxide having fine pores, a high porosity, and a large specific surface area. Titania (titanium oxide, TiO2) has high durability. In the present invention, the characteristics of both are utilized, but the ratio of silane alkoxide or aluminum alkoxide is preferably set relatively low. For example, the molar ratio of silane alkoxide or aluminum alkoxide to titanium alkoxide can be 0.2 or more and 1.2 or more. As the molar ratio, 0.5 or more is preferable, 1.1 or less is preferable, and 1.05 or less is more preferable.

[0027] The β-diketone ligand represented by formula (I) (β-diketone ligand (I)) probably coordinates with a more reactive titanium alkoxide to suppress its hydrolysis, and allows the hydrolysis of the silane alkoxide or aluminum alkoxide and the hydrolysis of the titanium alkoxide to proceed simultaneously. As a result, it is considered that the hydrolysis and polycondensation of the titanium alkoxide do not proceed first and crystallize, and a polymer containing both silicon or aluminum and titanium can be obtained.

[0028] The amount of the β-diketone ligand (I) used may be appropriately adjusted within a range where a homogeneous gas separation membrane can be obtained. However, in order to sufficiently reduce the reactivity of the titanium alkoxide, for example, the molar ratio of the β-diketone ligand (I) to 1 mol of the titanium alkoxide can be set to 0.5 or more and 5 or less. As the molar ratio, 0.8 or more is preferable, 0.9 or more is more preferable, 3 or less is preferable, and 2.5 or less is preferable. Further, since the β-diketone ligand (I) may also coordinate with the silane alkoxide or aluminum alkoxide, the β-diketone ligand (I) relative to the total molar number of the metal alkoxides can be set to 0.2 or more and 2 or less. As the molar ratio, 0.4 or more is preferable, 0.5 or less is preferable, 1.5 or less is preferable, and 1.2 or less is preferable.

[0029] The catalyst is not particularly limited as long as it can promote the hydrolysis and polycondensation of the metal alkoxide. Examples thereof include inorganic acids such as hydrogen chloride, hydrogen bromide, phosphoric acid, and nitric acid, and organic acids such as trifluoroacetic acid, methanesulfonic acid, benzenesulfonic acid, and toluenesulfonic acid. Inorganic acids are preferable, and hydrogen chloride is more preferable.

[0030] The amount of the catalyst used may be appropriately adjusted within a range where the hydrolysis and polycondensation of the metal alkoxide can be sufficiently promoted. For example, the molar ratio of the catalyst to the total molar number of the metal alkoxides can be set to 0.001 or more and 0.1 or less. As the molar ratio, 0.005 or more is preferable, 0.01 or more is more preferable, 0.05 or less is preferable, and 0.02 or less is more preferable.

[0031] The hydroxyether solvent (II) probably acts on the more reactive titanium alkoxide to suppress its hydrolysis, similarly to the β-diketone ligand (I), and is considered to cause the hydrolysis of the silane alkoxide or aluminum alkoxide and the hydrolysis of the titanium alkoxide to proceed simultaneously. Further, according to the experimental findings of the present inventors, the hydroxyether solvent (II) also has an effect of enhancing the stability of the precursor sol of the composite oxide.

[0032] Examples of the hydroxyether solvent (II) include alkoxymethanol such as methoxymethanol and ethoxymethanol; alkoxyethanol such as 2-methoxyethanol and 2-ethoxyethanol; alkoxypropanol such as 1-methoxy-2-propanol; and alkoxyethanol such as 3-methoxy-1-butanol. Alkoxymethanol or alkoxyethanol is preferable, one or more hydroxyether solvents selected from methoxymethanol, ethoxymethanol, 2-methoxyethanol, and 2-ethoxyethanol are more preferable, and alkoxyethanol is even more preferable.

[0033] The amount of the hydroxyether solvent (II) used may be appropriately adjusted within the range in which a homogeneous gas separation membrane can be obtained. However, in order to sufficiently reduce the reactivity of the titanium alkoxide, for example, the ratio of the hydroxyether solvent to the total of the silane alkoxide or aluminum alkoxide, titanium alkoxide, β-diketone ligand, catalyst, hydroxyether solvent, and water is preferably adjusted to 80% by mass or more and 99.5% by mass or less. As the ratio, 85% by mass or more or 90% by mass or more is preferable, and 95% by mass or more is more preferable.

[0034] Water is a component necessary for the hydrolysis of metal alkoxides. As the amount of water used, for example, it is preferable that the molar ratio of water to the total of titanium alkoxide and silane alkoxide or aluminum alkoxide is 0.05 or more and 500 or less. As the molar ratio, 0.1 or more is preferable, 0.2 or more is more preferable, and 400 or less or 300 or less is preferable, and 250 or less is more preferable.

[0035] The composite metal sol is obtained by hydrolysis and polycondensation of metal alkoxides. When the hydrolysis rate and polycondensation rate of metal alkoxides are slow, chain polymers tend to be obtained. When they are fast, polycondensation proceeds in two-dimensional or three-dimensional directions, and spherical polymers tend to be obtained. When producing a gas separation membrane with a smaller pore diameter and a larger specific surface area, it is preferable to form a chain polymer with a smaller molecular weight at this stage. When producing a gas separation membrane with a relatively large pore diameter and a relatively small specific surface area, it is preferable to form a spherical polymer with a larger molecular weight. Also, in order to laminate a layer with a relatively large pore diameter and a relatively small specific surface area and a layer with a smaller pore diameter and a larger specific surface area, both spherical polymer sol and chain polymer sol may be prepared.

[0036] In order to slow down the hydrolysis rate and polycondensation rate of metal alkoxides, in addition to adjusting the concentration of metal alkoxides in the reaction solution to be low or the concentration of water to be high, the reaction temperature is adjusted to be low. As the reaction temperature, for example, it can be 10°C or more and 40°C or less, and as the reaction time, it can be 10 minutes or more and 4 hours or less. The reaction temperature can also be normal temperature. Also, as the reaction temperature for accelerating the hydrolysis rate and polycondensation rate of metal alkoxides, it can be 60°C or more and 120°C or less, and as the reaction time, it can be 5 hours or more and 50 hours or less. The reaction may be carried out under heating reflux conditions.

[0037] 2. Preparation process of composite metal gel film In this process, the composite metal sol obtained in the previous process is molded and heated to distill off the solvent and water to prepare a composite metal gel film.

[0038] The forming method of the composite metal sol is not particularly limited, and a conventional method may be used. For example, the composite metal sol can be applied, sprayed, or spin-coated on a porous substrate. Also, the porous substrate can be immersed in the composite metal sol. Further, it is also possible to form a thin film by pre-heating the porous substrate and applying etc. while evaporating the solvent or water in the composite metal sol. When applying the composite metal sol etc. without heating the porous substrate, since the composite metal sol penetrates into the pores of the porous substrate, a relatively thick film can be formed, and in the case of dip coating, an even thicker film can be formed.

[0039] Also, the coating etc. of the composite metal sol and drying can be repeated to increase the film thickness. Further, when producing a multilayer gas separation membrane by forming a layer with a relatively large pore diameter and a relatively small specific surface area on a porous substrate and then forming a layer with a small pore diameter and a large specific surface area, two or more composite metal sols with different molecular weights are used.

[0040] As the substrate on which the composite metal gel film is to be formed, those having through-holes are preferable. The composite metal gel film may be peeled off from the substrate, but when integrated with the substrate, the substrate imparts mechanical strength to the composite metal gel film or the gas separation membrane.

[0041] The material of the substrate is not particularly limited, and examples include porous bodies such as alumina, silica, cordierite, zirconia, titania, magnesia, zeolite, bicore glass, and sintered metal.

[0042] The average pore diameter of the substrate is preferably 1 nm or more and 5 μm or less. If the average pore diameter is 1 nm or more, gas permeability can be more reliably ensured, and if it is 5 μm or less, a composite metal gel film can be well formed on its surface. The average pore diameter is more preferably 10 nm or more and 1 μm or less.

[0043] The structure of the substrate may be a flat film or a hollow tube, and is not particularly limited, but a hollow tube structure is preferred. The outer diameter of such a hollow tube is preferably 1 mm or more and 10 cm or less. If the outer diameter is 1 mm or more, the pressure loss of the permeated gas is sufficiently small, and the energy consumption can be sufficiently suppressed. If it is 10 cm or less, the manufacturing cost of the gas separation system can be sufficiently suppressed. The outer diameter is more preferably 2 mm or more and 5 cm or less.

[0044] The drying temperature of the composite metal sol can be, for example, 30°C or more and 200°C or less, and the drying time can be 5 minutes or more and 50 hours or less.

[0045] 3. Manufacturing process of the gas separation membrane In this step, a gas separation membrane is manufactured by firing the composite metal gel membrane obtained in the previous step.

[0046] The firing conditions may be appropriately adjusted within the range in which the composite metal gel membrane can be obtained and are not particularly limited. For example, the firing temperature can be 300°C or more and 1000°C or less, and the firing time can be 5 minutes or more and 10 hours or less.

[0047] The gas separation membrane according to the present invention contains a composite metal oxide containing SiO2 or Al2O3 and TiO2. In the present disclosure, "composite metal oxide" means that most of it is -M 2 -O-Ti- (wherein M 2 represents Si or Al, two bonds from Si and Ti are omitted, and one bond from Al is omitted.) and is composed of a structure containing the same. That is, the composite metal oxide according to the present invention is not simply a separate inclusion of SiO2 or Al2O3 and TiO2, but is composed of a polymer containing Si or Al and Ti in its chemical structure.

[0048] Since the composite metal oxide included in the gas separation membrane according to the present invention utilizes the characteristics of both silica or alumina and titania, for example, the molar ratio of silica or alumina to titania in the composite metal oxide can be 0.2 or more and 1.2 or less. As the molar ratio, 0.5 or more is preferable, 1.1 or less is preferable, and 1.05 or less is more preferable.

[0049] Since most of the gas separation membrane according to the present invention is composed of amorphous rather than crystal and has very fine through-holes, it exhibits excellent gas separation selectivity. The through-hole is a hole that extends from the front surface to the back surface of the membrane, and is a hole through which gas molecules smaller than the pore diameter can pass. Specifically, it is preferable that the pore diameter measured by the Normalized Knudsen-based Permeance method (NKP method) is 0.6 nm or less. As the pore diameter, 0.55 nm or less is more preferable, and 0.5 nm or less is even more preferable. As the pore diameter, since it is desired to allow H2 molecules to pass, 0.3 nm or more is preferable. The "NKP method" is a method for evaluating sub-nano-sized pore diameters by utilizing the fact that the permeability deviates from Knudsen diffusion based on the mass of molecules due to the influence of the size of molecules passing through the membrane. Generally, for example, the gas permeation rates (unit: mol / (m 2 ·s·Pa)) of gases such as He, H2, CO2, N2, SF6 are measured, the Normalized Knudsen-based Permeance (NKP) is calculated from the measured values, and the NKP values are plotted against the diameter d i of each molecule, and the molecular size d p when the NKP value becomes zero is determined as the average pore size.

[0050] The surface area of the gas molecular membrane according to the present invention is preferably large. If the surface area of the membrane is large, it is considered to have many fine pores necessary for gas separation selectivity. As the surface area of the membrane, the BET specific surface area obtained from the nitrogen adsorption isotherm can be used as an index. Specifically, as the BET specific surface area of the gas separation membrane according to the present invention, 300 m 2The above is preferable. The surface area of the TiO2-SiO2 composite oxide according to the present invention tends to be larger. As the BET specific surface area according to the present invention, 400 m 2 or more is preferable.

[0051] The gas separation membrane according to the present invention has excellent gas separation selectivity. Specifically, for example, the permeability to hydrogen is 5×10 -7 mol / m 2 ·s·Pa or more, while the permeability to sulfur hexafluoride, which is a relatively large gas molecule, is 1×10 -8 mol / m 2 ·s·Pa or more, and it is preferable that the ratio of the permeability to hydrogen to the permeability to sulfur hexafluoride (permeability to hydrogen / permeability to sulfur hexafluoride) is 500 or more.

[0052] As the film thickness of the gas separation membrane, particularly the composite metal oxide layer, 5 nm or more and 20 μm or less are preferable. If the film thickness is 5 nm or more, gas separation selectivity can be more reliably ensured, and if it is 20 μm or less, sufficient permeability can be more reliably ensured.

[0053] The composite metal material constituting the gas separation membrane according to the present invention has fine pores, a high porosity, a large specific surface area, and excellent durability. Therefore, the gas separation membrane according to the present invention is promising as a very practical gas separation membrane.

Examples

[0054] Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, and it is of course possible to appropriately modify and implement it within the scope that conforms to the gist of the foregoing and following descriptions, and all of them are included in the technical scope of the present invention.

[0055] Example 1: Preparation of TiO2-SiO2 Composite Oxide (1) TiO2-SiO2-ACA Polymer Sol 2-Methoxyethanol (4.04 g), H2O (14.6 g), and 36% concentrated hydrochloric acid (1.07 g) were added into a vial and stirred well. Separately, 2-methoxyethanol (4.04 g), titanium(IV) tetrapropoxide (TiTP, 0.59 g, 2.03 mmol), tetraethyl orthosilicate (TEOS, 0.43 g, 2.03 mmol), and acetylacetone (ACA, 0.21 g, 2.03 mmol) were added into a Erlenmeyer flask and stirred for 5 minutes. Then, using a microtube pump, the solution in the vial was dropped into the stirred solution in the Erlenmeyer flask at a rate of 1 mL / min. After the addition was completed, the mixture was further stirred at room temperature for 1 hour to prepare a 4 mass% TiO2-SiO2-ACA polymer sol. In the reaction solution, Ti:Si:ACA = 1:1:1 (molar ratio), the HCl concentration was 1.5 mass%, and H2O / (TiTP + TEOS) = 200 (molar ratio). Also, since the ratio of H2O to metal alkoxide was relatively low and the reaction temperature was set at room temperature, the hydrolysis reaction rate and polycondensation rate of the metal alkoxide were slow, and the polycondensate was considered to be a linear polymer.

[0056] (2) TiO2-SiO2-ACA colloidal sol 2-Methoxyethanol (71.8 g) and 36% concentrated hydrochloric acid (3.21 g) were mixed, and the resulting solution was added to the TiO2-SiO2-ACA polymer sol (25 g) obtained in (1) above, and stirred at 80 °C for 12 hours to prepare a 1 mass% TiO2-SiO2-ACA colloidal sol (100 g). The mass ratio of the additional HCl to the total of TiTP and TEOS was 1.16. It is considered that due to the reaction at high temperature for a long time in the presence of the added HCl catalyst, the linear polymer underwent polycondensation in the two-dimensional direction to obtain a spherical colloidal sol.

[0057] (3) TiO2-SiO2 composite oxide The TiO2-SiO2-ACA colloidal sol was placed in a petri dish and gelled by standing on a hot plate at 40 °C for 1 day. Then, a powder sample was obtained by firing in air at 500 °C.

[0058] Test Example 1: Analysis by X-ray Diffraction (XRD) The powder of the TiO2-SiO2 composite oxide obtained in Example 1 was analyzed by XRD. For comparison, TiO2 powder and SiO2 powder were also prepared using only TEOS or only TiTP, and the TiO2 powder and SiO2 powder were analyzed in the same manner. The results are shown in Fig. 1. As shown in the results of Fig. 1, no diffraction peak was observed in the SiO2 powder and it was amorphous, while diffraction peaks of mainly anatase-type TiO2 were observed in the TiO2 powder, confirming that it was crystalline. On the other hand, for the TiO2-SiO2 composite oxide of Example 1 produced using acetylacetone (ACA), almost no diffraction peak was observed, confirming that it was almost amorphous. The reason is considered that acetylacetone (ACA) preferentially coordinates to titanium ions in highly reactive TiTP and reduces its reaction rate, so that the hydrolysis and polycondensation of TiTP and TEOS proceed similarly, and the TiO2-SiO2 network is well formed while the crystallization of TiO2 is suppressed.

[0059] Comparative Example 1: Examination of Solvent In Example 1, a TiO2-SiO2-ACA colloidal sol was prepared in the same manner except that 1-propanol was used instead of 2-methoxyethanol. As a result, when the TiO2-SiO2-ACA polymer sol was diluted and started to be heated, it became cloudy instantly, and precipitation occurred after stirring (Fig. 2). It is considered that it cannot be uniformly applied to the substrate, etc., and a uniform TiO2-SiO2 composite oxide cannot be obtained.

[0060] Example 2: Preparation of TiO2-Al2O3 Composite Oxide (1) TiO2-Al2O3-ACA Polymer Sol 2-Methoxyethanol (24.4 g), H2O (0.011 g), and 36% concentrated hydrochloric acid (0.5 g) were added to the vial and stirred well. Separately, 2-methoxyethanol (24.4 g), titanium(IV) tetrapropoxide (TiTP, 0.174 g), and aluminum sec-butoxide (AISB, 0.151 g) were added to a Erlenmeyer flask and stirred for 5 minutes. Further, acetylacetone (ACA, 0.182 g) was added and mixed. Then, using a microtube pump, the solution in the vial was dropped into the stirred solution in the Erlenmeyer flask at a rate of 1 mL / min. After the addition was completed, the mixture was stirred at room temperature for an additional 1 hour to prepare a TiO2-Al2O3-ACA polymer sol. In the reaction solution, Ti:Al:ACA = 1:1:1 (molar ratio), the HCl concentration was 1.0 mass%, and H2O / (TiTP + AISB) = 0.5 (molar ratio).

[0061] (2) TiO2-Al2O3 composite oxide The TiO2-Al2O3-ACA polymer sol was placed in a petri dish and gelled by standing on a hot plate at 40 °C for 1 day. Then, a powder sample was obtained by firing in air at 250 °C.

[0062] (3) Analysis by X-ray diffraction (XRD) The powder of the TiO2-Al2O3 composite oxide obtained in Example 2(2) above was analyzed by XRD. For comparison, TiO2 powder and SiO2 powder were also prepared using only TEOS or only AISB, and the TiO2 powder and Al2O3 powder were analyzed in the same manner. The results are shown in Figure 3. As shown in the results of Figure 3, almost no diffraction peaks were observed for the Al2O3 powder and it was amorphous, while for the TiO2 powder, diffraction peaks of mainly anatase-type TiO2 were observed and it was confirmed to be crystalline. On the other hand, for the TiO2-Al2O3 composite oxide of Example 2 produced using acetylacetone (ACA), similar to the TiO2-SiO2 composite oxide of Example 1, almost no diffraction peaks were seen and it was confirmed to be almost amorphous.

[0063] Test Example 2: Nitrogen Adsorption-Desorption Test The TiO2-SiO2 composite oxide of Example 1 produced using acetylacetone (ACA), TiO2 powder, SiO2 powder, and a 1:1 (molar ratio) mixed powder of TiO2 powder and SiO2 powder were subjected to a nitrogen adsorption-desorption test. The results are shown in Fig. 4(1).

[0064] As shown in the results of Fig. 4(1), the adsorption isotherm of SiO2 powder was of type IV with hysteresis, that is, the adsorption amount obtained by sequentially increasing the adsorption equilibrium pressure (adsorption) was different from the adsorption amount obtained by sequentially decreasing the equilibrium pressure (desorption). Type IV indicates the presence of mesopores (pores with a diameter of 2.0 to 50 nm), and also agrees with the fact that the specific surface area of SiO2 powder is large due to the large amount of nitrogen adsorption. On the other hand, since the nitrogen adsorption amount of TiO2 powder is small, it can be seen that the specific surface area is small, and it has been shown that the mixed powder of TiO2 powder and SiO2 powder has properties intermediate between the two. In contrast, the adsorption isotherm of the TiO2-SiO2 composite oxide of Example 1 was of the Langmuir type in which the nitrogen adsorption amount was large at a low relative pressure p / p0 of nitrogen saturation vapor pressure and did not change significantly even when the relative pressure p / p0 increased. The Langmuir-type adsorption isotherm indicates the presence of a monomolecular layer having micropores (pores with a diameter of ~2.0 nm). Moreover, it was found that the nitrogen adsorption amount per relative pressure p / p0 of the TiO2-SiO2 composite oxide of Example 1 was almost the same as that of the mixed powder of TiO2 powder and SiO2 powder, and its specific surface area was larger than that of the mixed powder of TiO2 powder and SiO2 powder.

[0065] Also, a graph plotting the specific surface area against the TiO2 content of each powder is shown in Fig. 4(2). As shown in the results of Fig. 4(2), the TiO2-SiO2 composite oxide of Example 1 is located above the theoretical line obtained from the specific surface areas of TiO2 powder, SiO2 powder, and their mixed powder. Therefore, it was revealed that the TiO2-SiO2 composite oxide of Example 1 has fine pores and a large specific surface area exceeding the theoretical value.

[0066] Test Example 3: Nitrogen Adsorption-Desorption Test A TiO₂-Al₂O₃ composite oxide was prepared in the same manner as in Example 2 except that the molar ratio of H₂O to metal alkoxide (H₂O / (TiTP + AISB)) was changed to 0.5 or 1, the Ti:Al:ACA (molar ratio) was changed to 1:1:2, and the calcination temperature was changed to 250 °C. A nitrogen adsorption-desorption test was conducted in the same manner as in Test Example 2. The results are shown in Fig. 5(1).

[0067] As shown in the results of Fig. 5(1), the TiO₂-Al₂O₃ composite oxide produced using acetylacetone (ACA) showed a Langmuir-type adsorption isotherm and was found to have micropores. Also, when the amount of H₂O relative to the metal alkoxide was small, it was found that the number of micropores increased, presumably due to a decrease in the reactivity of the metal alkoxide.

[0068] In addition, the TiO₂ powder and Al₂O₃ powder were also subjected to a nitrogen adsorption-desorption test, and a graph plotting the specific surface area against the Al₂O₃ content is shown in Fig. 5(2). As shown in the results of Fig. 5(2), the specific surface area of the TiO₂-Al₂O₃ composite oxide produced using ACA is located above the theoretical line obtained from the specific surface areas of the TiO₂ powder and Al₂O₃ powder, suggesting that the specific surface area is large. Therefore, it was clarified that the TiO₂-Al₂O₃ composite oxide produced using ACA has fine pores and a large specific surface area exceeding the theoretical value.

[0069] Example 3: Preparation of TiO₂-SiO₂ Composite Oxide Film An alumina frit was applied to the joint between a 10φ alumina porous tube ("KU-A-2" manufactured by Nikkato Corporation) and an alumina non-porous tube, and they were joined using an oxygen burner. The obtained substrate was immersed in ethanol, and nitrogen gas was supplied from the inside of the substrate to confirm that no bubbles leaked from the joint. Next, the substrate was dried, and alumina frit with an average particle size of 2 μm was added to the TiO2-SiO2-ACA colloidal sol obtained in Example 1 so that the total mass was 10% by mass, and it was applied to the surface of the porous tube portion of the substrate using a benchtop. It was dried in air for 2 to 4 minutes, and the particles attached to the surface were rubbed off with a benchtop. Then, it was left standing at 180 °C for 10 minutes, fired in a tubular furnace at 500 °C for 15 minutes, left standing at 180 °C for 10 minutes again, and left standing at room temperature. The process from applying the sol to firing was repeated one more time. Separately, alumina frit with an average particle size of 0.2 μm was added to the TiO2-SiO2-ACA colloidal sol obtained in Example 1 so that the total mass was 10% by mass, and it was applied using a benchtop. It was dried in air for 2 to 4 minutes, and the particles attached to the surface were rubbed off with a benchtop. Then, it was left standing at 180 °C for 10 minutes, fired in a tubular furnace at 500 °C for 15 minutes, left standing at 180 °C for 10 minutes again, and left standing at room temperature. The coating and firing were repeated until it was confirmed that no bubbles came out from the side of the porous tube etc. when a pressure of 0.1 MPa was applied by the bubble point method, thereby forming a particle layer. The substrate with the formed particle layer was left standing in a constant temperature bath at 180 °C for 5 minutes. Next, using a benchtop folded in half, the TiO2-SiO2-ACA colloidal sol was applied while turning the substrate with a finger. The substrate was left standing in a constant temperature bath at 180 °C for 5 minutes, fired in a tubular furnace at 500 °C for 15 minutes, and left standing in a constant temperature bath at 180 °C for 10 minutes again. By repeating the above operations about 3 to 55 times, an intermediate layer was formed. The substrate with the formed intermediate layer was left standing in a constant temperature bath at 180 °C for 10 minutes, the TiO2-SiO2-ACA colloidal sol diluted to 0.5% by mass was applied in the same manner as in the case of the intermediate layer, left standing at 200 °C for 5 minutes in a tubular furnace under a nitrogen atmosphere, and then fired at 300 °C for 15 minutes. After firing, it was cooled to about 200 °C while maintaining the nitrogen atmosphere. By repeating the above operations about 4 times, a separation layer was formed.

[0070] Test Example 4: Gas Permeability Test The upstream side of the TiO2-SiO2 composite oxide film prepared in Example 3 was pressurized to 0.15 - 0.2 MPa, and the downstream side of the film was set at atmospheric pressure (0.1 MPa) to create a pressure difference, allowing each pure gas to permeate. The pressures on the upstream and downstream sides of the film were measured with pressure sensors respectively. The gas permeation flow rate of the film was measured with a fully automatic soap film flow meter placed on the downstream side. The temperature of the permeation cell was controlled at 200 °C using a temperature controller, a high-temperature compatible K thermocouple, and a mantle heater. The results are shown in Fig. 6, and the ratio of the gas permeability of He to N2 or SF6 is shown in Table 1.

[0071] [Table 1]

[0072] As shown in the results of Fig. 6 and Table 1, it was demonstrated that the TiO2-Al2O3 composite oxide produced using acetylacetone (ACA) has a large difference in gas permeability depending on the gas molecular diameter and is extremely excellent in gas separation selectivity. In addition, the permeation amounts of CF4 and SF6 through the TiO2-Al2O3 composite oxide film were very small and impossible to measure. From this point as well, it can be seen that the TiO2-Al2O3 composite oxide film according to the present invention is excellent in gas separation selectivity.

[0073] Test Example 5: Durability Test The durability was evaluated by exposing the metal oxide film to water vapor and comparing the gas permeability before and after that. Specifically, nitrogen gas was blown into water to generate 3 kPa of water vapor, which was continuously supplied to the TiO2-SiO2 composite oxide film of Example 3 maintained at 25 °C and the SiO2 film prepared in the same manner for comparison for 2 weeks. Then, after drying each film at 25 °C, the permeation rate of each gas was determined under the same conditions as in Test Example 4. The results are shown in Fig. 7.

[0074] As shown in the results of Fig. 7(1), although the permeabilities of He and H2 through the SiO2 film did not change before and after water vapor exposure, the permeability of relatively small molecules decreased while that of relatively large molecules increased due to water vapor exposure, resulting in a smaller difference in gas permeability according to the gas molecular diameter and a significant decrease in gas separation selectivity. The reason is considered to be that water vapor adsorbed on the SiO2 film decomposed and recombined the SiO2 network, creating pinholes. On the other hand, although the gas permeability of the TiO2-SiO2 composite oxide film according to the present invention decreased somewhat due to water vapor exposure, especially the gas permeability of relatively large molecules decreased, and the gas separation selectivity tended to increase instead. Separately, the pore diameter d p decreased from 0.47 nm to 0.40 nm according to the NKP (Normalized Knudsen-based Permeance) plot. Therefore, it was revealed that the TiO2-SiO2 composite oxide film according to the present invention densifies due to water vapor exposure, but the network for gas separation is maintained and it has excellent durability.

[0075] In addition, the relationship between the H2 permeability and the H2 / CH4 permeability ratio before and after water vapor exposure of the TiO2-Al2O3 composite oxide film and the SiO2 film is shown in Fig. 7(2). As shown in the results of Fig. 7(2), the permeability of H2 through the SiO2 film decreased due to water vapor exposure, and the gas separation selectivity also decreased significantly. The reason is considered to be that the network of the SiO2 film was destroyed by water vapor exposure. In contrast, the permeability of H2 through the TiO2-SiO2 composite oxide film according to the present invention also decreased due to water vapor exposure, but the gas separation selectivity improved instead. The reason is considered to be that the TiO2-SiO2 composite oxide film densified due to water vapor exposure.

Claims

1. A method for manufacturing a gas separation membrane, comprising: preparing a composite metal sol containing a silane alkoxide or an aluminum alkoxide, a titanium alkoxide, a β-diketone ligand represented by the following formula (I), a catalyst, a hydroxyether solvent represented by the following formula (II), and water; 【Chemical 1】 [wherein, R 1 to R 3 each independently represents H or a C 1-6 alkyl group which may have a substituent α, R 4 represents a C 1-2 alkyl group, R 5 represents a C 1-4 alkanediyl group, The substituent α is a halogeno group, C 1-6 alkoxy group, and C 1-6 alkoxy-[[-R 6 -O-]] n - group (wherein R 6 represents a C 1-4 alkanediyl group, and n represents an integer of 1 or more and 5 or less). It represents one or more substituents selected from these.] preparing a composite metal gel membrane by shaping and heating the composite metal sol; and manufacturing a gas separation membrane by firing the composite metal gel membrane, wherein the molar ratio of the silane alkoxide or aluminum alkoxide to the titanium alkoxide is 0.2 or more and 1.2 or less.

2. R 1 and R 3 is C 1-4 an alkyl group, and R 2 is H, the method according to claim 1.

3. The method according to claim 1 or 2, wherein the catalyst is hydrogen chloride.

4. The method according to any one of claims 1 to 3, wherein the hydroxyether solvent is at least one hydroxyether solvent selected from methoxymethanol, ethoxymethanol, 2-methoxyethanol, and 2-ethoxyethanol.

5. The method according to any one of claims 1 to 4, wherein the molar ratio of the catalyst to the total number of moles of the silane alkoxide, aluminum alkoxide, and titanium alkoxide is 0.01 or more.

6. The method according to any one of claims 1 to 5, wherein the molar ratio of water to the total of the titanium alkoxide and the silane alkoxide or aluminum alkoxide is 0.05 or more and 500 or less.

7. The method according to any one of claims 1 to 5, wherein the ratio of the hydroxyether solvent to the total of the silane alkoxide or aluminum alkoxide, the titanium alkoxide, the β-diketone ligand, the catalyst, the hydroxyether solvent, and the water is 20% by mass or more and 99.5% by mass or less.

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