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

Abstract

Provided are a separation membrane capable of efficiently separating ammonia from ammonia mixed gas even in high-temperature environments, and a method for producing the separation membrane. The separation membrane comprises a silica network structure in which the substituent -R1-SO3X (where R1 represents an alkylene group or an aromatic group, and X represents a hydrogen atom or an alkali metal atom) is bound to some or all of the silicon (Si) atoms contained in a siloxane bond (SiOSi).

Description

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

[0001] The present invention relates to a separation membrane for separating ammonia from a mixed gas containing ammonia, a composite membrane, and a method for producing the separation membrane.

[0002] Ammonia is widely used worldwide as a raw material for fertilizer. Furthermore, because ammonia does not emit carbon dioxide when burned, it is expected to be utilized as one of the next-generation energy sources. Accordingly, various technologies have been developed, such as ammonia recovery technologies from exhaust gases related to melamine resin manufacturing and semiconductor manufacturing, and ammonia synthesis technologies.

[0003] For example, Patent Document 1 proposes a technology in which exhaust gas containing ammonia, hydrogen, and nitrogen discharged from a vapor phase growth apparatus in which a gallium nitride compound semiconductor manufacturing process is carried out is pressurized, and the ammonia contained in the exhaust gas is liquefied using a heat pump type cooler, and the ammonia is separated from the hydrogen and nitrogen and recovered.

[0004] In addition, nitrogen (N ２ ) and hydrogen (H ２ ) to ammonia (NH ３ The Haber-Bosch process is used as a method for synthesizing ammonia. In a typical ammonia synthesis process using the Haber-Bosch process, an iron-based catalyst is used to carry out a reaction at a high temperature and pressure of about 450°C and about 20 to 50 MPa, and the reaction is then cooled to about 38°C in a cooler to concentrate the ammonia. In recent years, various catalysts have been developed to alleviate the reaction conditions of the Haber-Bosch process (for example, Patent Document 2).

[0005] JP 2014-154792 A JP 2022-61257 A

[0006] In the ammonia recovery method of Patent Document 1, in order to separate the ammonia contained in high-temperature exhaust gas, the exhaust gas is pressurized and cooled to liquefy the ammonia, so a large amount of energy is required to recover the ammonia.

[0007] In addition, in the Haber-Bosch process using an active catalyst as described in Non-Patent Document 2, the reaction conditions are relaxed and can be carried out at 300 to 500°C and 1 to 10 MPa. However, to recover ammonia, it is still necessary to cool the high-temperature reaction gas and liquefy the ammonia. Therefore, a large amount of energy is required to recover ammonia.

[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a separation membrane, a composite membrane, and a method for manufacturing a separation membrane that can efficiently separate ammonia from an ammonia mixed gas even in a high-temperature environment, so as to enable separation of ammonia with less energy.

[0009] In order to achieve the above object, a separation membrane according to a first aspect of the present invention comprises: a siloxane bond (SiOSi) in which all or part of silicon (Si) is substituted with a substituent -R １ -SO ３ X (R １ represents an alkylene group or an aromatic group. X represents a hydrogen atom or an alkali metal atom.) is bonded to the silica network structure.

[0010] In the separation membrane of the above aspect, a substituent group -R ２ -PO ３ H (R ２ represents an alkylene group or an aromatic group) and -R ３ -COOH(R ３ represents an alkylene group or an aromatic group). １ -SO ３ At least one of an alkyl group and an aromatic group may be bonded to all or part of the silicon (Si) that is not bonded to H. A metal-containing compound having any of silicon, titanium, zirconium, and aluminum may be mixed with the silica network structure. A part of the silicon (Si) in the siloxane bond may be substituted with at least one of titanium, zirconium, and aluminum.

[0011] A composite membrane according to a second aspect of the present invention comprises a support made of a porous substrate, an intermediate layer provided on one main surface of the support and made of a porous substrate having an average pore size smaller than that of the support, and the separation membrane according to claim 1 or 2 provided on the main surface of the intermediate layer opposite to the support.

[0012] A method for producing a separation membrane according to a third aspect of the present invention includes: a precursor preparation step of preparing a precursor by diluting, with a solvent, a hydroxysilyl compound in which a sulfonic acid group is bonded to silicon (Si) via an alkylene group or an aromatic group; and a separation layer formation step of applying the precursor prepared in the precursor preparation step onto a porous substrate and heat-treating the precursor to form a separation layer. This separation membrane production method may also include an intermediate layer formation step of forming, on the porous substrate, an intermediate layer having pores that are smaller than the pores of the porous substrate and have an average pore diameter of 1 nm or more and 10 nm or less, in which the separation layer formation step involves applying the precursor prepared in the precursor preparation step onto the intermediate layer and heat-treating the precursor to form a separation layer.

[0013] Furthermore, a method for producing a separation membrane according to a fourth aspect includes a precursor preparation step of mixing an oxidizing agent into a sol solution containing an alkoxysilane in which a mercapto group is bonded to silicon (Si) via an alkylene group or an aromatic group, a catalyst for promoting the reaction, and a solvent, to oxidize the sol solution, thereby preparing a precursor in which the mercapto group is substituted with a sulfonic acid group, and a separation layer formation step of applying the precursor prepared in the precursor preparation step onto a porous substrate and heat-treating the precursor to form a separation layer. The separation membrane production method may also include an intermediate layer formation step of forming an intermediate layer on the porous substrate, the intermediate layer having pores smaller than the pores of the porous substrate and having an average pore diameter of 1 nm to 10 nm, in which the separation layer formation step involves applying the precursor prepared in the precursor preparation step onto the intermediate layer and heat-treating the precursor to form a separation layer.

[0014] The separation membrane according to the present invention can efficiently separate ammonia in a high temperature range.

[0015] 1 is a schematic diagram of a separation membrane according to a first embodiment of the present invention; 2 is a flowchart showing the flow of a manufacturing method for a separation membrane according to the first embodiment; 3 is a graph showing an example of the measurement results of the particle size of TPS diluted with a solvent, (A) is a graph when diluted with ethanol, and (B) is a graph when diluted with water; 4 is an SEM photograph of a cross section of a separation membrane according to the first embodiment, and (B) is an enlarged view of (A); 5 is a flowchart showing the flow of a manufacturing method for a separation membrane according to a second embodiment; 6 is an SEM photograph of a cross section of a separation membrane according to the second embodiment, (A) is a diagram when oxidation was not performed, and (B) is a diagram when oxidation with hydrogen peroxide was performed; 7 is a graph showing the relationship between the molecular size and permeability of permeating gases at 200°C for TPS separation membranes and MPTMS separation membranes, and (B) is a graph showing the relationship between the molecular size of permeating gases and dimensionless permeability normalized by helium permeability for MPTMS separation membranes; ３ , H ２ , N ２ 1 shows the permeability and selectivity of NH for single and two-component gas permeation at 300°C for the TPS separation membrane. ３ , H ２ , N ２ 1A and 1B are graphs showing the separation characteristics of an ammonia separation membrane, in which (A) shows the characteristics at 50° C. or less, and (B) shows the characteristics at 200° C.

[0016] (Embodiment 1) Hereinafter, a separation membrane 10 which is a separation membrane for ammonia according to this embodiment will be described. As shown in the schematic diagram of Figure 1, the separation membrane 10 according to this embodiment includes a support 11, an intermediate layer 12, and a separation layer 13.

[0017] (Support) The support 11 is a porous substrate having a plurality of pores. In order to perform ammonia separation on a high-temperature mixed gas, it is preferable to use a support 11 having high heat resistance, and therefore the support 11 is preferably an inorganic porous body.

[0018] Examples of inorganic porous bodies that can serve as the support 11 include alumina (α-Al ２ O ３ , γ-Al ２ O ３ ), silicon dioxide (SiO２ ), mullite (3Al ２ O ３ 2SiO ２ ~2Al2O ３ SiO ２ ), titanium dioxide (TiO ２ Examples of suitable ceramics include ceramics made of metal oxides such as α-alumina and zirconia, or composites thereof, and stainless steel porous bodies. The support 11 according to this embodiment is a ceramic porous support that is inexpensive, easily available, and has excellent heat resistance and strength, and is mainly composed of α-alumina.

[0019] The shape of the support 11 is not particularly limited, but a cylindrical or plate shape is preferred. Furthermore, if the pore diameter of the support 11 is too large, the coating liquid (precursor solution) for forming the separation layer 13 will enter the pores of the support 11, causing defects in the separation layer 13. Therefore, it is preferable to select a support 11 with an appropriate pore diameter taking into consideration the viscosity of the precursor solution. The average pore diameter of the support 11 is preferably about 100 nm to 2000 nm.

[0020] (Intermediate Layer) The intermediate layer 12 is provided on one main surface of the support 11. The intermediate layer 12 is made of a porous substrate having an average pore size smaller than that of the support 11. If the pore size of the support 11 is excessively large compared to the particle size of the precursor material constituting the separation layer 13, the precursor of the separation layer 13 will penetrate into the pores of the support 11 when the separation layer 13 is formed on the support 11, resulting in an increase in the thickness of the separation layer 13. As the thickness of the separation layer 13 increases, the permeation resistance increases and the ammonia permeability decreases. Therefore, it is preferable to provide the intermediate layer 12 between the support 11 and the separation layer 13 to reduce the difference in pore size between adjacent layers and adjust the pore size of the surface underlying the separation layer 13.

[0021] The inorganic porous material for the intermediate layer 12 is, for example, alumina (α-Al ２ O ３ , γ-Al ２ O ３ ), silicon dioxide (SiO ２ ), mullite (3Al ２ O ３ 2SiO ２ ~2Al２ O ３ SiO ２ ), titanium dioxide (TiO ２ The material of the intermediate layer 12 according to the present embodiment is silica-zirconia (SiO ), which is easy to control the pore size and is easy to form the intermediate layer 12 by a sol-gel method. ２ -ZrO ２ )

[0022] (Separation Layer) The separation layer 13 is provided on the main surface of the intermediate layer 12 opposite to the support 11. The separation layer 13 is formed of a silicon-based material having sulfonic acid groups that have a high affinity for ammonia. By using a silicon-based material, it is possible to increase the degree of cross-linking and improve the molecular sieving properties. Furthermore, since the separation layer 13 has siloxane (SiO) bonds with high bond energy, the heat resistance of the network structure is increased, and therefore the heat resistance of the separation layer 13 can be improved. Furthermore, since the separation layer 13 has sulfonic acid groups, it is possible to increase the selectivity for ammonia. In other words, the separation layer 13 has a substituent -R on all or part of the silicon (Si) contained in the siloxane bonds (SiOSi). １ -SO ３ X (R １ represents an alkylene group or an aromatic group having 1 to 8 carbon atoms. X represents a hydrogen atom or an alkali metal atom. Examples of alkali metals include sodium, potassium, and cesium. The separation layer 13 is formed by a silica network structure to which ) are bonded. The following structural formula shows the network structure of the separation layer 13. As shown in the structural formula above, in the network structure of the separation layer 13, oxygen is bonded to two to four bonds of Si to form a ring structure, forming pores effective for permeation. Actual amorphous silica is said to consist of 3- to 8-membered oxygen rings, and pores effective for permeation are 5- to 7-membered rings.

[0023] In this embodiment, the separation layer 13 is formed using a hydroxysilyl compound in which a sulfonic acid group is bonded to silicon (Si) via an alkylene group or an aromatic group (hereinafter, sometimes simply referred to as a hydroxysilyl compound having a sulfonic acid group). Examples of the hydroxysilyl compound having a sulfonic acid group that can be used include alkylsulfonic acid type silicon monomers such as 3-(trihydroxysilyl)-1-propanesulfonic acid (TPS), and aromatic sulfonic acid type silicon monomers such as trihydroxysilylethylphenylsulfonic acid. The following structural formula shows the structure of a hydroxysilyl compound having a sulfonic acid group. In the above structural formula, R １ represents an alkylene group or aromatic group having 1 to 8 carbon atoms. As shown in the structural formula above, in TPS, R is -C ３ H ６ -, and in the aromatic sulfonic acid type silicon monomer, R １ In Example 1 described later, TPS is used as the precursor material of the separation layer 13.

[0024] In addition, a substituent group -R is attached to a part of the silicon (Si) of the siloxane bond. ２ -PO ３ H (R ２ represents an alkylene group having 1 to 8 carbon atoms or an aromatic group), and -R ３ -COOH(R ３ represents an alkylene group having 1 to 8 carbon atoms or an aromatic group) may be bonded to the alkyl group.

[0025] The separation layer 13 can function as a separation membrane by itself. The separation membrane 10 is also called a composite membrane. The thickness of the separation layer 13 is preferably 100 to 500 nm from the viewpoints of permeability and durability. In other words, even a thin separation layer 13 having a thickness of 100 to 500 nm can exhibit sufficient ammonia separation performance.

[0026] (Method for manufacturing separation membrane) Hereinafter, a method for manufacturing separation membrane 10 according to this embodiment will be described with reference to the flowchart in Figure 2. The method for manufacturing separation membrane 10 according to this embodiment includes a precursor preparation step of preparing a precursor for forming separation layer 13, an intermediate layer formation step of forming intermediate layer 12 on support 11, and a separation layer formation step of forming separation layer 13 on intermediate layer 12 using the precursor prepared in the precursor preparation step.

[0027] First, in the precursor preparation step, a hydroxysilyl compound having a sulfonic acid group is diluted with a solvent to prepare a precursor (step S11). The solvent is preferably a good solvent for the silyl compound, and examples of the solvent include protic polar solvents such as methanol, ethanol, and propanol, and aprotic solvents such as acetone, tetrahydrofuran, and dimethylformamide.

[0028] FIG. 3 is a graph showing the results of particle size measurements by dynamic light scattering (DLS) when TPS is diluted with ethanol and water. The particle sizes of the TPS solution are mainly 2-3 nm when diluted with ethanol and mainly 1-2 nm when diluted with water. Since the average pore size of the intermediate layer 12 (described later) is approximately 1 nm, it is preferable to prepare the precursor solution by diluting with ethanol in order to form the separation layer 13 so as to cover all of the pores in the intermediate layer 12. In this embodiment, a TPS aqueous solution (35% aqueous solution, Oakwood Chemical Co.) is diluted with ethanol to prepare a 0.1 wt % TPS solution, which serves as the precursor solution.

[0029] The intermediate layer forming step is a step of forming an intermediate layer having pores smaller than the pores of the porous substrate and having an average pore diameter of 1 nm to 10 nm. In the separation layer forming step, the precursor prepared in the precursor preparing step is applied to the intermediate layer, and the precursor is heat-treated to form the separation layer. Specifically, in the intermediate layer forming step, the intermediate layer 12 is formed on the support 11. In this embodiment, before forming the intermediate layer 12, α-alumina particles are applied to the outer surface of the support 11, which is a porous α-alumina tube (manufactured by Nikkato Corporation, porosity 50%, outer diameter 10 mm, length 100 mm) with an average pore diameter of approximately 1 μm, to homogenize the outer surface of the porous α-alumina tube (step S12).

[0030] Specifically, silica-zirconia (SiO ２ -ZrO ２ Two types of α-alumina particles (Sumitomo Chemical Co., Ltd.) with average particle sizes of 0.2 μm and 2 μm were dispersed in 2 wt % silica-zirconia sol (Si / Zr = 1:1) colloidal sol to prepare a 10 wt % particle-sol mixture. The prepared particle-sol mixture was applied to the outer surface of an alumina tube using a nonwoven fabric (Bencott (registered trademark), Asahi Kasei Corporation). After drying at room temperature for 20 minutes and at high temperature (180°C) for 10 minutes, the mixture was heat-treated (fired) in air at 550°C for 15 minutes using an electric tubular furnace (EKR-29K, Isuzu Manufacturing Co., Ltd.). This procedure was repeated three or four times to cover the surface of the support 11, which has relatively large pores, and form a smoothed particle layer.

[0031] Next, an intermediate layer 12 is formed on the support 11 whose outer surface has been homogenized (step S13). Specifically, a 2 wt % silica-zirconia sol is diluted with water to obtain a 0.5 wt % silica-zirconia sol. The porous α-alumina tube serving as the support 11 is preheated to a high temperature (170-180°C), and a diluted solution of silica-zirconia colloidal sol is applied to the outer surface of the support 11 using a nonwoven fabric (hot coating method), followed by baking in air at 550°C for 15 minutes. This results in an intermediate layer 12 having an average pore diameter of approximately 1 nm formed on the outer surface of the support 11. In this embodiment, the average pore diameter of the intermediate layer 12 is approximately 1 nm, but this is not limited thereto. It is sufficient that the pore diameter of the support 11 is adjusted so as not to be excessively large compared to the particle diameter of the precursor material constituting the separation layer 13. Specifically, since the sol particle size of the coating sol (silica-zirconia colloidal sol) is about 1 nm to 10 nm, the pore size on the surface of the intermediate layer 12 is preferably 1 nm to 10 nm, and more preferably 1 nm to 2 nm.

[0032] The separation layer formation step is a step of applying the precursor prepared in the precursor preparation step described above onto the intermediate layer and heat-treating the precursor to form a separation layer. Specifically, in the separation layer formation step, a separation layer 13 is formed on the intermediate layer 12 (step S14). Specifically, a 0.1 wt % TPS solution, which is the precursor solution prepared in the precursor preparation step, is applied (cold coated) onto the intermediate layer using a nonwoven fabric at room temperature. Then, the resulting mixture is baked at 300°C in nitrogen for 20 to 30 minutes using an electric tubular furnace to form the separation layer 13 on the intermediate layer 12. Through these steps, the separation membrane 10 is manufactured.

[0033] The intermediate layer 12 is an optional layer, and when the intermediate layer 12 is not provided, the separation layer formation process is a process of applying the precursor prepared in the precursor preparation process described above onto a porous substrate and heat-treating the precursor to form a separation layer.

[0034] 4 shows the structure of a separation membrane 10 prepared using a TPS precursor solution diluted with ethanol. The prepared separation membrane 10 has a multilayer structure, but it can be seen that the layers are bonded without clear boundaries. As shown in FIG. 4, the thickness of the separation layer 13 is approximately 150 nm, and it can be seen that a thin separation layer 13 without defects such as cracks has been formed.

[0035] As described above, the separation layer 13 of the separation membrane 10 has sulfonic acid groups that have a high affinity for ammonia, making it possible to form a separation membrane 10 with high ammonia selectivity. Furthermore, by using a hydroxysilyl compound, which is a silicon-based material, the degree of cross-linking of the polymers that make up the separation layer 13 can be increased, thereby improving the molecular sieving properties. Furthermore, because the separation layer 13 has siloxane (SiO) bonds with high bond energy as its skeleton, the heat resistance of the network structure is increased, making it possible to improve the heat resistance of the separation layer 13. Therefore, the ammonia permeation selectivity of the separation membrane 10 can be improved in a high-temperature environment of 200°C or higher, making it possible to efficiently separate ammonia.

[0036] Furthermore, when separation membrane 10 according to the present embodiment includes intermediate layer 12, the pore size of intermediate layer 12 supporting separation layer 13 can be adjusted, thereby preventing the precursor solution from penetrating into the base layer when forming separation layer 13. This allows a thin separation layer 13 to be formed, thereby reducing the permeation resistance of ammonia, the gas to be separated, and improving the permeability.

[0037] (Embodiment 2) In the above-described embodiment 1, a hydroxysilyl compound having a sulfonic acid group is used as the material for the separation layer 13. However, the material for the separation layer 13 is not limited to this, and other materials configured so that the separation layer 13 has a siloxane (SiO) bond and a sulfonic acid group can be used. This embodiment differs from embodiment 1 in that an alkoxysilane in which a mercapto group is bonded to silicon (Si) via an alkylene group or an aromatic group (hereinafter, sometimes simply referred to as an alkoxysilane having a mercapto group) is used as the starting material for forming the separation layer 13'. The support 11 and intermediate layer 12 are the same as those in embodiment 1, so they are denoted by the same reference numerals and detailed description is omitted. The following formula is a conceptual diagram (reaction formula) of network formation when the starting material has a sulfonic acid group or a mercapto group. In the above conceptual diagram, R ４ represents an alkylene group or an aromatic group having 1 to 8 carbon atoms. In the above conceptual diagram, in (a), the sulfonic acid groups of the starting material remain after the network is formed, so that the separation layer 13 is configured to have sulfonic acid groups. On the other hand, in (b), the mercapto groups of the starting material remain after the network is formed, so that these mercapto groups are oxidized and substituted or converted into sulfonic acid groups, so that the separation layer 13' is configured to have sulfonic acid groups.

[0038] (Separation Layer) In this embodiment, the separation layer 13' is formed using an alkoxysilane having a mercapto group. Examples of alkoxysilane having a mercapto group that can be used include silicon-based monomers having a mercapto group such as (3-mercaptopropyl)trimethoxysilane (MPTMS), and silicon-based polymers having a mercapto group such as poly(dimethylsiloxane-co-methylphenylsiloxane) and mercapto-terminated polydimethylsiloxane. The following chemical formula shows an alkoxysilane having a mercapto group: In the above chemical formula, R ４ represents an alkylene group or an aromatic group having 1 to 8 carbon atoms. ４ Ga-C ３ H６ The starting material is not limited to this, and a compound in which the methoxy group of MPTMS is replaced with a methyl group or a phenyl group can also be used. In Example 2 described later, MPTMS is used as the precursor material of the separation layer 13'.

[0039] (Method for manufacturing separation membrane) Hereinafter, a method for manufacturing separation membrane 10' according to this embodiment will be described with reference to the flowchart in Figure 5. The method for manufacturing separation membrane 10' according to this embodiment includes a precursor preparation step of preparing a precursor for forming separation layer 13', an intermediate layer formation step of forming intermediate layer 12 on support 11, and a separation layer formation step of forming separation layer 13' on intermediate layer 12 using the precursor prepared in the precursor preparation step.

[0040] The precursor preparation step involves mixing an oxidizing agent into a sol solution containing a mixture of an alkoxysilane having a mercapto group, a catalyst for promoting the reaction, and a solvent, and oxidizing the mixture to prepare a precursor. Specifically, in the precursor preparation step, a precursor solution for forming the separation layer 13′ is prepared using an alkoxysilane having a mercapto group. Specifically, an MPTMS mixed solution is prepared by dissolving MPTMS (Thermo Fisher Scientific) in ethanol. Then, a mixture of hydrochloric acid (HCl) and water, which serves as a catalyst for promoting the reaction, is added to the MPTMS mixed solution under continuous stirring, and the mixture is allowed to react at room temperature for 12 hours (step S21). This hydrolyzes and condenses MPTMS in the ethanol, preparing a sol solution. The concentration of MPTMS in the sol solution is 5 wt %. The molar ratio of each component in the sol solution is MPTMS / H ２ O / HCl=1 / 50 / 0.1.

[0041] Next, hydrogen peroxide (H ２ O ２ , 30 wt%) in a sol solution / H ２ O ２ The precursor solution is prepared by adding the mercapto groups to the sol solution dropwise so that the mass ratio of the mercapto groups to the sulfonic acid groups is 1 / 0.2 and oxidizing the mercapto groups by stirring for a predetermined time (step S22).

[0042] The intermediate layer forming step is a step of forming an intermediate layer on a porous substrate, the intermediate layer having pores smaller than the pores of the porous substrate and having an average pore diameter of 1 nm to 10 nm. In the separation layer forming step, the precursor prepared in the precursor preparation step is applied to the intermediate layer, and the precursor is heat-treated to form a separation layer. Steps S23 and S24 of the intermediate layer forming step are the same as steps S12 and S13 of the intermediate layer forming step according to the first embodiment. Steps S23 and S24 form an intermediate layer 12 having an average pore diameter of approximately 1 nm on the outer surface of the support 11.

[0043] The separation layer forming step is a step of applying the precursor prepared in the precursor preparation step onto the intermediate layer and heat-treating the precursor to form a separation layer. Specifically, a separation layer 13' is formed on the intermediate layer 12 (step S25). Specifically, the oxidized MPTMS sol solution, which is the precursor solution prepared in the precursor preparation step, is applied (cold coated) onto the intermediate layer using a nonwoven fabric at room temperature. Then, the mixture is baked at 300°C in a nitrogen atmosphere for 20 to 30 minutes using an electric tubular furnace to form a separation layer 13' on the intermediate layer 12. Through the above steps, the separation membrane 10' is manufactured.

[0044] The intermediate layer 12 is an optional layer, and when the intermediate layer 12 is not provided, the separation layer formation process is a process of applying the precursor prepared in the precursor preparation process described above onto a porous substrate and heat-treating the precursor to form a separation layer.

[0045] 6A and 6B are diagrams showing the structures of a separation membrane 10' prepared by oxidizing a precursor solution of MPTMS with hydrogen peroxide and without oxidation. In the separation membrane 10' prepared by oxidizing a precursor solution of MPTMS with hydrogen peroxide (FIG. 6B), a thicker separation layer 13' (up to 900 nm) is formed than in the separation membrane 10' prepared without oxidation with hydrogen peroxide (FIG. 6A). This is thought to be because the size of the sol increases due to oxidation, suppressing its penetration into the intermediate layer 12 and resulting in the accumulation of the oxidized sol on the silica-zirconia intermediate layer.

[0046] As described above, in this embodiment, by preparing a precursor by oxidizing an alkoxysilane having a mercapto group using hydrogen peroxide, it is possible to form a separation layer 13' having a sulfonic acid group with high affinity for ammonia and high ammonia selectivity. Furthermore, by using an alkoxysilane, the degree of cross-linking of the polymer constituting the separation layer 13' can be increased, thereby improving the molecular sieving properties. Furthermore, since the separation layer 13' has a siloxane (SiO) bond with high bond energy as its skeleton, the heat resistance of the network structure is increased, thereby improving the heat resistance of the separation layer 13'. Therefore, the ammonia permeation selectivity of the separation membrane 10' in a high-temperature environment of 200°C or higher can be improved, thereby enabling efficient ammonia separation.

[0047] Separation membrane 10' according to this embodiment also includes intermediate layer 12. This allows the pore size of intermediate layer 12 supporting separation layer 13' to be adjusted, thereby preventing the precursor solution from penetrating into the base layer when forming separation layer 13'. This allows a thin separation layer 13' to be formed, reducing the permeation resistance of ammonia, the gas to be separated, and improving the permeability.

[0048] (Separation Characteristics) Below, examples of measurement results of the separation characteristics of the separation membrane 10 according to Example 1 (hereinafter also referred to as the TPS separation membrane) and the separation membrane 10′ according to Example 2 (hereinafter also referred to as the MPTMS separation membrane) are described. Figures 7(A) and (B) show the relationship between the molecular size of the permeating gas in a 200°C environment and the single gas permeability and the dimensionless permeability normalized by the helium (He) permeability for the TPS separation membrane and the MPTMS separation membrane. The DLS size of the TPS precursor solution diluted with water is mainly distributed in the range of 1 to 2 nm, and it is thought that it is difficult to effectively cover the micropores (up to 1 nm) on the intermediate layer 12. Therefore, the TPS separation membrane prepared using the TPS precursor solution diluted with water exhibited a high gas permeability comparable to that of the membrane without the intermediate layer 12 alone, without forming the separation layer 13, and the permeation characteristics of non-adsorbable gases were comparable to the Knudsen diffusion shown in Figure 7(B).

[0049] MPTMS separation membranes are non-adsorbable gases, especially He and H ２ Higher NH ３ The reason why the MPTMS separation membrane exhibits selectivity for non-adsorbable gases comparable to that of Knudsen diffusion is thought to be because the MPTMS separation membrane of this example contains pores and pinholes between particles.

[0050] The TPS precursor solution diluted with ethanol has an appropriate particle size, and the formed TPS separation membrane has excellent NH ３ The TPS membranes formed using the TPS precursor solution diluted with ethanol exhibit excellent molecular sieving and adsorption-diffusion properties.

[0051] FIG. 8 shows the NH ３ , H ２ , N ２ transmittance and NH ３ The MPTMS membrane exhibits high selectivity for single and binary gas permeation at 300°C. ３ , H ２ , N ２ The transmittance of NH ３ This indicates that the MPTMS membrane has a strong NH ３ Despite showing affinity, H ２ and N ２ NH permeation ３ This indicates that there was no inhibitory effect on the permeation of

[0052] Figure 9 shows the NH permeation rate of single and binary gases through a TPS separation membrane at 300 °C. ３ , H ２ , N ２ At high temperatures such as 300°C, the permeability and selectivity of NH ３ The adsorption of the molecules to the membrane surface weakens, so the adsorbed NH ３ H by ２ , N ２The permeability and selectivity of the two-component gas permeation were comparable to those of the single-component gas permeation.

[0053] 10(A) and (B) show the conventional NH ３ Separation membrane and NH according to each of the above embodiments ３ The separation characteristics of the separation membrane are summarized. ３ The permeability and selectivity of NH 2 in a high-temperature environment shown in FIG. ３ Transmittance vs. NH ３ / H ２ There is a significant negative correlation in selectivity. NH of PFSA (perfluorosulfonic acid) membrane and BTPA (bis[3-(trimethoxysilyl)propyl]amine) membrane ３ The transmittance is about 10 －６ mol・m －２ ・s －１ ・Pa －１ However, the NH ３ The selectivity is ３ The selectivity of the TPS and MPTMS separation membranes was lower than that of the 10 －７ mol・m －２ ・s －１ ・Pa －１ Such a high NH ３ This is believed to be due to the combined effects of excellent molecular sieving and adsorption / diffusion. Compared with the MPTMS separation membrane, the TPS separation membrane exhibited a moderate NH permeability. ３ / H ２ Selectivity and significantly higher NH ３ / N ２ This indicates that the pore size of the TPS separation membrane is H ２ and N ２ This is thought to be because the kinetic diameter is between 0.30-0.35 nm.

[0054] (Modification) In Example 1, a hydroxysilyl compound having a sulfonic acid group was used as the precursor material for the separation layer 13, and in Example 2, an alkoxysilane having a mercapto group was used as the precursor material for the separation layer 13′, but the precursor material is not limited to these materials alone. For example, in addition to these materials, a composite component material not having a sulfonic acid group may also be used. Examples of composite component materials not having a sulfonic acid group include various metal-containing materials such as silicon, titanium, zirconium, and aluminum. Alternatively, these metal alkoxides (tetraethoxysilane, methyltriethoxysilane, phenyltriethoxysilane, diethoxy(dimethyl)silane, etc. in the case of silicon, titanium tetraisopropoxide, titanium tetraisobutoxide, etc. in the case of titanium, zirconium tetra-n-butoxide (zirconium(IV) butoxide), etc.) can be used. This makes it possible to improve the heat resistance and mechanical strength of the separation layers 13, 13'. The above-mentioned various composite component materials are mixed with a hydroxysilyl compound having a sulfonic acid group or an alkoxysilane solution having a mercapto group to form the separation layers 13, 13' of the composite material. The metal alkoxide, which is a component of the composite material, may be added not only before the formation of the sol, but also after the formation of the sol to form the separation layers 13, 13' of the composite material. When the metal alkoxide is added before the formation of the sol, one or both of the metal constituting the metal alkoxide and the substituent other than the alkoxyl group are incorporated into a part of the silica network structure. That is, when a metal is incorporated, a part of the Si in the siloxane bond is replaced with at least one of titanium, zirconium, and aluminum. When a substituent other than an alkoxyl group is incorporated, the substituent -R in the siloxane bond is replaced with at least one of titanium, zirconium, and aluminum. １ -SO ３At least one of an alkyl group and an aromatic group is bonded to a portion of Si that is not bonded to H. On the other hand, when a metal alkoxide is added after sol formation, a separation layer 13, 13' of a composite material is formed in which a metal-containing compound is mixed with the sol of the silica network structure. Note that even when a metal alkoxide is added before sol formation, metal-containing compounds that remain without being incorporated into the silica network structure may be mixed into the separation layer. In addition, the heat resistance and mechanical strength of the separation layer can be improved by adding nanoparticles (titania, zirconia, carbon, silicon carbide, alumina, etc.).

[0055] Furthermore, the precursor material may be composed primarily of a material having a sulfonic acid group according to the above-described embodiments, with a material having an acidic group as a secondary component. Examples of the secondary component having an acidic group include a material having a carboxyl group, such as carboxyethylsilanetriol, and a material having a phosphate group, such as 3-(trihydroxysilyl)propyl methylphosphonate. This allows the acidity of the separation layer 13, 13' to be adjusted to suit the separation target, thereby improving the separation characteristics of the separation membrane 10, 10'. The various secondary component materials described above are mixed with a hydroxysilyl compound having a sulfonic acid group or an alkoxysilane solution having a mercapto group to form the separation layer 13, 13' of a composite material.

[0056] In Example 2, hydrogen peroxide and a sol solution are mixed in the precursor preparation step to oxidize alkoxysilane having a mercapto group, thereby converting the mercapto group to a sulfonic acid group. However, this is not limited to this. For example, an unoxidized sol solution is applied to the intermediate layer 12 and baked to form the separation layer 13', thereby producing the separation membrane 10'. The produced separation membrane 10' may then be immersed in hydrogen peroxide water to oxidize the separation layer 13' and convert it to a sulfonic acid group.

[0057] The present invention is suitable for separating ammonia, particularly for separating ammonia in a high-temperature environment. CROSS-REFERENCE TO RELATED APPLICATIONS

[0058] This application claims priority based on Japanese Patent Application No. 2024-068026 filed with the Japan Patent Office on April 19, 2024, and Japanese Patent Application No. 2025-011740 filed with the Japan Patent Office on January 27, 2025, the entire disclosures of which are incorporated herein by reference in their entirety.

[0059] 10, 10' separation membrane, 11 support, 12 intermediate layer, 13, 13' separation layer

Claims

1. All or some of the silicon (Si) in the siloxane bond (SiOSi) have a substituent -R １ -SO ３ X (R １ represents an alkylene group or an aromatic group; and X represents a hydrogen atom or an alkali metal atom.

2. A substituent -R is attached to a part of the silicon (Si) of the siloxane bond. ２ -PO ３ H (R ２ represents an alkylene group or an aromatic group) and -R ３ -COOH(R ３ The separation membrane according to claim 1 , wherein at least one of the following is bonded:

3. The substituent -R of the siloxane bond １ -SO ３ 2. The separation membrane according to claim 1, wherein at least one of an alkyl group and an aromatic group is bonded to all or part of the silicon (Si) that is not bonded to H.

4. The separation membrane according to claim 1, wherein a metal-containing compound having any of silicon, titanium, zirconium, and aluminum is mixed with the silica network structure.

5. The separation membrane according to claim 1, wherein a portion of the silicon (Si) in the siloxane bond is substituted with at least one of titanium, zirconium, and aluminum.

6. A composite membrane comprising: a support made of a porous substrate; an intermediate layer made of a porous substrate and having an average pore size smaller than that of the support, provided on one main surface of the support; and the separation membrane according to claim 1 or 2 provided on the main surface of the intermediate layer opposite to the support.

7. A method for producing a separation membrane, comprising: a precursor preparation step of preparing a precursor by diluting in a solvent a hydroxysilyl compound in which a sulfonic acid group is bonded to silicon (Si) via an alkylene group or an aromatic group; and a separation layer formation step of applying the precursor prepared in the precursor preparation step onto a porous substrate and heat-treating the precursor to form a separation layer.

8. A method for producing a separation membrane according to claim 7, comprising an intermediate layer forming step of forming an intermediate layer on the porous substrate, the intermediate layer having pores smaller than the pores of the porous substrate and having an average pore size of 1 nm or more and 10 nm or less, and wherein in the separation layer forming step, the precursor prepared in the precursor preparation step is applied onto the intermediate layer and the precursor is heat-treated to form a separation layer.

9. A method for producing a separation membrane, comprising: a precursor preparation step of mixing an oxidizing agent into a sol solution obtained by mixing an alkoxysilane in which a mercapto group is bonded to silicon (Si) via an alkylene group or an aromatic group, a catalyst for promoting the reaction, and a solvent, to oxidize the solution, thereby preparing a precursor in which the mercapto group is substituted with a sulfonic acid group; and a separation layer formation step of applying the precursor prepared in the precursor preparation step onto a porous substrate and heat-treating the precursor to form a separation layer.

10. A method for producing a separation membrane according to claim 9, comprising an intermediate layer forming step of forming an intermediate layer on the porous substrate, the intermediate layer having pores smaller than the pores of the porous substrate and having an average pore diameter of 1 nm or more and 10 nm or less, and wherein in the separation layer forming step, the precursor prepared in the precursor preparation step is applied onto the intermediate layer and the precursor is heat-treated to form a separation layer.

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