Silica membrane

Abstract

To provide a silica membrane that can efficiently separate specific components from a mixed solution containing components with different molecular sizes and physical properties, and whose performance (separation ability) is difficult to decrease even when repeatedly used.SOLUTION: The silica membrane of the present disclosure has a central pore size of 0.5 to 5.0 nm and has amino and / or ammonium groups. The silica membrane preferably contains a structure derived from a silane coupling agent having the amino group and / or the ammonium group. The silane coupling agent contains alkoxy groups and monovalent organic groups respectively attached to silicon atoms, and at least one of the monovalent organic groups preferably has an amino group and / or an ammonium group in and / or at the end of the chain.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to silica membranes. [Background technology]

[0002] In recent years, nanoporous separation membranes such as silica membranes are capable of separating substances at the molecular level, and are therefore expected to be applied to separation membranes, membrane reactors, chemical sensors, etc. Among these, separation membranes that utilize the molecular sieving function of nanoporous separation membranes and the physical properties of the membrane surface (e.g., hydrophilicity or hydrophobicity) to separate a specific component from a mixture containing two or more components are known.

[0003] For example, the methanol carbonylation process is known as an industrial method for producing acetic acid. In this process, acetaldehyde is by-produced during the reaction, and this acetaldehyde causes a decrease in the quality of the product acetic acid. In addition, this process uses methyl iodide as a promoter for the metal catalyst. However, because methyl iodide is expensive, it is separated from the mixture with acetaldehyde and reused. However, because acetaldehyde and methyl iodide have similar boiling points, it has been difficult to completely separate acetaldehyde and methyl iodide. For this reason, methods disclosed in Patent Documents 1 to 4 are known as methods for separating acetaldehyde and methyl iodide. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2017 / 057142 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-94764 [Patent Document 3] Japanese Patent Application Publication No. 9-40590 [Patent Document 4] Japanese Patent Application Publication No. 9-77697 Summary of the Invention [Problem to be solved by the invention]

[0005] However, it has not been possible to completely separate acetaldehyde and methyl iodide even with the methods disclosed in Patent Documents 1 to 4. Furthermore, although the use of a silica membrane (nanoporous separation membrane) for separating acetaldehyde and methyl iodide has been considered, even with the use of a conventional silica membrane, it has not been possible to completely separate acetaldehyde and methyl iodide, and there has been a problem in that the performance (separation ability) of the membrane decreases with repeated use.

[0006] Therefore, an object of the present disclosure is to provide a silica membrane that can efficiently separate a specific component from a mixed solution containing components with different molecular sizes and physical properties, and whose performance (separation ability) is not easily reduced even with repeated use. [Means for solving the problem]

[0007] As a result of intensive research to achieve the above object, the inventors of the present disclosure have found that by performing separation using a silica membrane having a specific structure, it is possible to efficiently separate a mixed solution of acetaldehyde and methyl iodide, which is a mixed solution containing components with different molecular sizes and physical properties, and that the performance (separation ability) is not likely to deteriorate even after repeated use.The present disclosure relates to a product that was completed based on these findings and through further research.

[0008] That is, the present disclosure provides a silica membrane having a median pore diameter of 0.5 to 5.0 nm and having amino groups and / or ammonium groups.

[0009] The silica film preferably has a structure derived from a silane coupling agent having the amino group and / or the ammonium group.

[0010] In the silica film, the silane coupling agent preferably contains an alkoxy group and a monovalent organic group, each bonded to a silicon atom, and at least one of the monovalent organic groups has an amino group and / or an ammonium group in the chain and / or at the end.

[0011] In the silica film, the number of atoms in the main chain between the silicon atom and the nitrogen atom in the amino group and / or the ammonium group is preferably 2 to 4.

[0012] The silica membrane preferably has a central pore size of 0.8 to 4.0 nm.

[0013] The silica membrane preferably has a central pore size of 1.0 to 3.0 nm.

[0014] The silica film preferably has a surface water contact angle of 0 to 70°.

[0015] The silica membrane is preferably provided on at least one surface of the porous substrate.

[0016] The present disclosure also provides a composite membrane comprising a porous substrate and the above-described silica membrane provided on at least one surface of the porous substrate. [Effects of the Invention]

[0017] The silica membrane can efficiently separate a mixed solution containing components with different molecular sizes and physical properties (e.g., a mixed solution of acetaldehyde and methyl iodide), and its performance (separation ability) is unlikely to deteriorate even after repeated use. [Brief explanation of the drawings]

[0018] [Figure 1] 1 shows the transition of transmittance ratio in Examples and Comparative Examples. [Figure 2] 1 shows the transition of acetaldehyde permeability in Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0019] The silica membrane of the present disclosure is a porous membrane formed primarily from an inorganic compound containing silica, has a median pore size of 0.5 to 5.0 nm, and contains amino groups and / or ammonium groups (hereinafter sometimes referred to as "amino groups, etc."). In a mixed solution containing hydrophilic and hydrophobic low molecules, the silica membrane allows the hydrophilic low molecules to permeate while blocking the hydrophobic low molecules, concentrating them. Hereinafter, a mixed solution containing acetaldehyde as a hydrophilic low molecule and methyl iodide as a hydrophobic low molecule will be used as an example. Since the median pore size of the silica membrane is within the above range, the silica membrane allows acetaldehyde to permeate due to its molecular sieving function. On the other hand, while methyl iodide would also permeate if the silica membrane only had the molecular sieving function, the presence of amino groups, etc., gives the membrane surface moderate hydrophilicity, presumably making it difficult for methyl iodide to permeate. This silica membrane's performance allows efficient separation of acetaldehyde and methyl iodide.

[0020] Furthermore, conventional silica membranes, for example, silica membranes that do not have amino groups or the like on their surface but have hydroxyl groups, have molecular sieve function and hydrophilic surface properties similar to the silica membrane of the present disclosure, but tend to have reduced acetaldehyde permeability with repeated use. On the other hand, the silica membrane of the present disclosure has the characteristic of high performance stability and less reduction in acetaldehyde permeability even with repeated use. The reason for this is unclear, but it is believed that the mixed solution containing acetaldehyde and methyl iodide to be separated may contain components that are highly reactive with hydroxyl groups. In conventional silica membranes, the hydrophilicity of the membrane surface is reduced due to the reaction of these components with hydroxyl groups, resulting in reduced acetaldehyde permeability. On the other hand, the amino groups and the like in the silica membrane of the present disclosure have low reactivity with these components, which is likely why the membrane has high performance stability and less reduction in acetaldehyde permeability even with repeated use.

[0021] The silica membrane of the present disclosure preferably has a monovalent organic group having an amino group or an ammonium group in the chain and / or at the end. The monovalent organic group having an amino group or an ammonium group is not particularly limited, but examples thereof include alkyl groups such as cyclic alkyl groups, linear alkyl groups, and branched alkyl groups, and groups in which two or more alkyl groups are bonded via heteroatoms such as oxygen atoms and sulfur atoms. Among these, alkyl groups are preferred, more preferably linear or branched alkyl groups, and even more preferably linear alkyl groups. The number of carbon atoms in the monovalent organic group is not particularly limited, but is preferably 1 to 20, more preferably 1 to 10, and even more preferably 1 to 7. The above phrase "having an amino group or an ammonium group in the chain and / or at the end" means, more specifically, that a secondary amino group or an ammonium group, a tertiary amino group or an ammonium group, or a quaternary ammonium group is present in the chain of the monovalent organic group, that an amino group or an ammonium group is bonded to a secondary or tertiary carbon atom in the chain of the monovalent organic group, or that an amino group (-NH2; primary amino group) or an ammonium group (-NH3 + ; primary ammonium group) is bonded.

[0022] The amino group may be a primary amino group, a secondary amino group, or a tertiary amino group. The ammonium group may be a primary ammonium group, a secondary ammonium group, a tertiary ammonium group, or a quaternary ammonium group. The amino group may be a substituted amino group substituted with an organic group. Alternatively, the amino group may be an unsubstituted amino group, which can be converted into a substituted amino group by subjecting a silica membrane having an unsubstituted amino group to organic matter treatment or by using the membrane for separating organic matter. The amino group may be of only one type, or may be of two or more types.

[0023] The substituent possessed by the substituted amino group or the like is a monovalent organic group, and examples thereof include an alkyl group (preferably an alkyl group having 1 to 8 carbon atoms, more preferably an alkyl group having 1 to 6 carbon atoms, and even more preferably an alkyl group having 1 to 4 carbon atoms), an aryl group (preferably an aryl group having 6 to 14 carbon atoms, and more preferably an aryl group having 6 to 10 carbon atoms), or a group formed by combining these. When the substituted amino group or the like possesses multiple substituents, the multiple substituents may be the same or different.

[0024] The silica membrane may contain a monovalent organic group that does not have an amino group or the like. Examples of the monovalent organic group that does not have an amino group or the like include alkyl groups; groups having a carboxy group, a hydroxyl group, or a mercapto group at the alkyl group terminal; and groups having an ether bond or a thioether bond in the alkyl chain. The alkyl group is not particularly limited, but may be, for example, a cyclic alkyl group, a linear alkyl group, or a branched alkyl group. The number of carbon atoms in the alkyl group is also not particularly limited, but is preferably 1 to 20, more preferably 1 to 10, and even more preferably 1 to 7. Hereinafter, the amino group or the like contained in the silica membrane and the monovalent organic group that does not have an amino group or the like may be collectively referred to as a monovalent organic group.

[0025] The silica membrane may contain a metal oxide as an inorganic compound forming the membrane. Examples of the metal oxide include alumina, zirconia, titania, and magnesia. The pore size of the silica membrane and surface properties of the silica membrane, such as the hydrophilicity or hydrophobicity of the surface and the water contact angle, can be adjusted by adjusting the type and ratio of the metal oxide used in combination with silica, plasma treatment of the silica membrane, introduction of monovalent organic groups onto the surface, and the type and amount of the monovalent organic groups.

[0026] The central pore diameter of the silica membrane is not particularly limited as long as it is 0.5 to 5.0 nm, but is preferably 0.8 to 4.0 nm, and more preferably 1.0 to 3.0 nm. The central pore diameter is the median diameter (D50) and can be measured by a single-component gas permeation test (H2, CO2, N2, CH4, CF4, SF6) or nanoperm porometry. The central pore diameter is preferably in a range suitable for separating mixed liquids rather than mixed gases. In addition, the central pore diameter of the silica membrane before the introduction of a silane coupling agent is preferably within the above range.

[0027] The water contact angle of the silica film surface is not particularly limited, but is preferably 0 to 70°, more preferably 15 to 70°, and even more preferably 30 to 70°. When the water contact angle is within the above range, the surface exhibits appropriate hydrophilicity, making it difficult for hydrophobic low molecules to permeate, and enabling efficient separation of a mixed solution containing components with different molecular sizes and physical properties (hydrophilicity).

[0028] The silica film preferably has a structure derived from a silane coupling agent having an amino group and / or an ammonium group. That is, the silica film preferably has an amino group or the like introduced therein by the silane coupling agent. In other words, the silica film preferably has an amino group or the like derived from the silane coupling agent. The silane coupling agent may be one type or two or more types.

[0029] When the silica membrane has a structure derived from the silane coupling agent, when the silane coupling agent is introduced into the silica membrane, the hydroxyl groups present on the surface of the silica membrane undergo dehydration condensation with the alkoxy groups of the silane coupling agent. This reduces the amount of hydroxyl groups on the silica membrane surface, reducing the reaction between the hydroxyl groups and components highly reactive with hydroxyl groups in a mixed solution containing acetaldehyde and methyl iodide. On the other hand, the amount of amino groups derived from the silane coupling agent increases, allowing the surface of the silica membrane to maintain appropriate hydrophilicity, allowing efficient separation of acetaldehyde and methyl iodide. In addition, the performance is highly stable, and the permeability of acetaldehyde is less likely to decrease even after repeated use.

[0030] The silane coupling agent contains an alkoxy group and a monovalent organic group, each bonded to a silicon atom, and at least one of the monovalent organic groups has an amino group and / or an ammonium group in the chain and / or at the end. That is, the silane coupling agent contains an alkoxy group and a monovalent organic group having an amino group or the like, both bonded to a silicon atom, and may further contain a monovalent organic group not having an amino group or the like.

[0031] In the monovalent organic group having an amino group or the like, the monovalent organic group is not particularly limited, but examples thereof include alkyl groups such as cyclic alkyl groups, linear alkyl groups, and branched alkyl groups, and groups in which two or more alkyl groups are bonded via heteroatoms such as oxygen atoms and sulfur atoms. Among these, alkyl groups are preferred, more preferably linear or branched alkyl groups, and even more preferably linear alkyl groups. In addition, the number of carbon atoms in the monovalent organic group is not particularly limited, but is preferably 1 to 20, more preferably 1 to 10, and even more preferably 1 to 7.

[0032] In the silane coupling agent, the number of atoms in the main chain between the silicon atom in the silane coupling agent and the nitrogen atom in the amino group and / or the ammonium group is preferably 1 to 8, more preferably 2 to 4. When the number of atoms in the main chain is 8 or less (particularly 4 or less), the pores are prevented from becoming small, the hydrophilicity of the silica film surface is moderate, and permeability is improved. For example, when the main chain is a divalent linear hydrocarbon group, the number of atoms in the main chain is the same as the number of carbon atoms.

[0033] In the monovalent organic group having an amino group or the like, the amino group may be any of a primary amino group, a secondary amino group, and a tertiary amino group. The ammonium group may be any of a primary ammonium group, a secondary ammonium group, a tertiary ammonium group, and a quaternary ammonium group. The amino group or the like may be a substituted amino group substituted with an organic group. Alternatively, the amino group or the like may be an unsubstituted amino group, which can be converted into a substituted amino group or the like by subjecting a silica membrane having an unsubstituted amino group or the like to organic matter treatment or by using it for separating organic matter. For example, when a methyl iodide (MeI) solution is passed through a monovalent organic group having a primary amino group, a secondary amino group or a primary ammonium group may be generated from the primary amino group, and other amino groups or ammonium groups may also be generated. The amino group may be of only one type, or two or more types.

[0034] The silane coupling agent may contain a monovalent organic group that does not have an amino group or the like. Examples of the monovalent organic group that does not have an amino group or the like include alkyl groups; groups having a carboxy group, a hydroxyl group, or a mercapto group at the alkyl group terminal; and groups having an ether bond or a thioether bond in the alkyl group chain. The alkyl group is not particularly limited, but may be, for example, a cyclic alkyl group, a straight-chain alkyl group, or a branched-chain alkyl group. The number of carbon atoms in the alkyl group is also not particularly limited, but is preferably 1 to 20, more preferably 1 to 10, and even more preferably 1 to 7.

[0035] The alkoxy group contained in the silane coupling agent is represented by the general formula RO- (R represents an alkyl group). The alkyl group represented by R is preferably a linear or branched alkyl group, and more preferably a linear alkyl group. The number of carbon atoms in the alkyl group represented by R (i.e., the number of carbon atoms in the alkoxy group) is not particularly limited, but is preferably 1 to 10, more preferably 1 to 5, even more preferably 1 to 4, and particularly preferably 1 or 2. Specific examples of the alkoxy group contained in the silane coupling agent include a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, a butoxy group, a sec-butoxy group, and a t-butoxy group.

[0036] The silane coupling agent is preferably represented by the following formula: R x -Si-R 1 m (OR 2 ) 3-m (R 1 R represents an alkyl group having 1 to 3 carbon atoms which may have a substituent. 2 R represents an alkyl group having 1 to 3 carbon atoms which may have a substituent. X represents an alkyl group having an amino group and / or the above ammonium group in the chain and / or at the end, and m represents an integer of 1 to 3.

[0037] R 1 and R 2 In the formula (I), the substituent that the alkyl group may have is not particularly limited as long as it does not interfere with the hydrolysis and dehydration condensation of the silane coupling agent, and examples thereof include an alkoxy group having 1 to 6 carbon atoms, an alkenyloxy group having 2 to 6 carbon atoms, an aliphatic acyl group having 2 to 6 carbon atoms, a benzoyl group, a nitro group, a nitroso group, a hydroxy group, a cyano group, a sulfonic acid group, an amino group such as a primary amino group, a carboxy group, a hydroxyl group, a mercapto group, and a halogen atom.

[0038] R XIn the alkyl group having an amino group or the like, the alkyl group is not particularly limited, but is preferably, for example, a cyclic alkyl group, a straight-chain alkyl group, or a branched-chain alkyl group, more preferably a straight-chain or branched-chain alkyl group, and even more preferably a straight-chain alkyl group. The number of carbon atoms in the alkyl group is not particularly limited, but is preferably 1 to 20, more preferably 1 to 10, and even more preferably 1 to 7.

[0039] Above R X In the alkyl group having an amino group or the like, the number of atoms in the main chain between the nitrogen atom in the amino group or the like and Si is preferably 1 to 8, more preferably 2 to 4. When the number of atoms in the main chain is 8 or less (particularly 4 or less), the pores are prevented from becoming small, and the hydrophilicity of the silica membrane surface is made appropriate, resulting in better permeability.

[0040] Specific examples of the silane coupling agent include 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropyltriethoxysilane, trimethoxy[3-(methylamino)propyl]silane, [3-(N,N-dimethylamino)propyl]trimethoxysilane, trimethoxy[3-(phenylamino)propyl]silane, and N-[2-(N-vinylbenzylamino)ethyl]-3-aminopropyl.

[0033] Examples of the silane coupling agent include N-[8-(trimethoxysilyl)octyl]ethane-1,2-diamine, N-[3-(trimethoxysilyl)propyl]-1-butanamine, [3-(diethylamino)propyl]trimethoxysilane, 3-[(1,3-dimethylbutylidene)amino]propyltriethoxysilane, (3-mercaptopropyl)trimethoxysilane, (3-mercaptopropyl)triethoxysilane, and N,N-bis[(diphenylphosphino)methyl]-3-(triethoxysilyl)propylamine. These silane coupling agents may be used alone or in combination.

[0041] In the silica film, the amino group and / or the ammonium group is bonded to a silicon atom constituting the silica film via, for example, a group represented by the following formula (1). -X-Si(-O-)3(1) [In formula (1), X represents a divalent organic group, the bond extending to the left of X is bonded to a nitrogen atom in the amino group or the ammonium group, and the bond extending to the right of O is bonded to a silicon atom constituting the silica film and / or a silicon atom in another group represented by formula (1)]

[0042] The number of atoms in the main chain in X is preferably 1 to 8, more preferably 2 to 4. When the number of atoms in the main chain is 8 or less (particularly 4 or less), the pores are prevented from becoming small, and the hydrophilicity of the silica membrane surface is made appropriate, resulting in better permeability.

[0043] The silica film can be prepared by subjecting a silane coupling agent having an amino group and / or an ammonium group to a dehydration condensation reaction with a silica film having a silanol group. The dehydration condensation reaction can be carried out, for example, by impregnating a cloth with a liquid containing the silane coupling agent, applying the liquid to the silica film having a silanol group, and allowing the reaction to proceed at 110°C for 0.5 to 1 hour. Furthermore, the silica film having a silanol group may be subjected to a treatment to increase the number of hydroxyl groups by introducing water vapor or irradiating the silica film with plasma before the reaction with the silane coupling agent.

[0044] The thickness of the silica film is, for example, 0.1 to 10 μm, and preferably 0.1 to 1 μm.

[0045] The silica membrane is preferably provided on at least one surface of a porous substrate. The porous substrate acts as a substrate for supporting the silica membrane. The porous substrate has pores that allow acetaldehyde to pass through. Furthermore, by providing the silica membrane on at least one surface of the porous substrate, a composite membrane can be obtained.

[0046] The porous substrate may be any known or commonly used material, and examples of the material constituting the porous substrate include inorganic materials such as silica, alumina, mullite, zirconia, cordierite, titania, silicon nitride, silicon carbide, stainless steel, copper, aluminum, titanium, and ceramics.

[0047] The thickness of the porous substrate is, for example, 50 to 3000 μm, and preferably 500 to 2000 μm.

[0048] Each aspect disclosed in this specification can be combined with any other feature disclosed in this specification. Each configuration and combination thereof in each embodiment is an example, and addition, omission, substitution, and other modifications of configurations are possible as appropriate within the scope of the present disclosure. Furthermore, each invention according to this disclosure is not limited by the embodiments or the following examples, but is limited only by the scope of the claims. [Example]

[0049] Hereinafter, one embodiment of the present disclosure will be described in more detail based on examples.

[0050] Example 1 A commercially available nanoceramic porous substrate (model number: eSep-nano-Si-1.5-2, manufactured by E-Sep Corporation) was used as the porous layer, primarily composed of silica with through-pores of 1.5 to 2.0 nm. The silica porous layer was approximately 500 nm thick, and the underlying layer was supported by an α-alumina porous substrate formed with macropores. The outer shape was cylindrical, with a diameter of 12 mm, an inner diameter of 9 mm, and a length of 40 cm. Air at 25°C and a humidity of 50% or higher was introduced to the outside of the cylindrical membrane for at least 1 minute. During this time, the pressure inside the cylindrical membrane was reduced, and water vapor was forcibly introduced into the membrane pores. The membrane was left in a state where water vapor remained in the pores for at least 6 hours to promote the generation of OH groups in the silica layer. The silane coupling agent, 3-aminopropyltrimethoxysilane (APTMS), was diluted 100 times with water and left to stand at room temperature for at least 3 hours to allow the hydrolysis reaction to proceed sufficiently. The liquid was then soaked into a cloth, which was then used to apply the cylindrical composite membrane prepared above. The cloth was then dried at 110°C for 0.5 hours to fix the membrane, yielding a silica membrane.

[0051] Example 2 The silica membrane obtained in Example 1 was circulated with 99.5 wt % MeI (manufactured by Wako Pure Chemical Industries, Ltd.) at room temperature for 7 hours, and then left to stand for 16 hours to obtain a silica membrane.

[0052] (Comparative Example 1) A commercially available nanoceramic porous substrate (model number: eSep-nano-Si-0.5-1, manufactured by E-Sep Corporation) composed primarily of silica with through-pores of 0.5 to 1.0 nm was prepared and used as the silica membrane. Unlike Examples 1 and 2, the silica membrane did not contain amino groups because no silane coupling agent was introduced. The thickness of the silica porous layer in the substrate was approximately 500 nm, and the lower layer was supported by an α-alumina porous substrate formed with macropores. The outer shape was cylindrical, with a diameter of 12 mm, an inner diameter of 9 mm, and a length of 40 cm.

[0053] (Comparative Example 2) A commercially available nanoceramic porous substrate (model number: eSep-nano-Si-1-1.5, manufactured by E-Sep Corporation) composed primarily of silica with through-pores of 1.0 to 1.5 nm was prepared and used as the silica membrane. Unlike Examples 1 and 2, the silica membrane did not contain amino groups because a silane coupling agent was not introduced. The thickness of the silica porous layer in the substrate was approximately 500 nm, and the lower layer was supported by an α-alumina porous substrate formed with macropores. The outer shape was cylindrical, with a diameter of 12 mm, an inner diameter of 9 mm, and a length of 40 cm.

[0054] The separation performance of acetaldehyde and methyl iodide for various silica membranes shown in Table 1 was evaluated by pervaporation under heated and pressurized conditions. Specifically, a membrane with a membrane area of ​​120.6 cm was first placed in a pervaporation device. 2 A separation membrane of 79.77% by mass was installed. Approximately 600 g of a mixture of 79.77% by mass of acetaldehyde, 7.78% by mass of methyl iodide, and 12.45% by mass of water was charged into the device as the feed liquid components. The mixture was heated to 50°C in a water bath, and while the pressure on the feed liquid side was maintained at 190 kPaG, it was fed to the separation membrane at 75 ml / min using a liquid feed pump. The pressure on the permeation side was set to normal pressure, and the mixture was allowed to permeate for 4 to 5 hours, after which it was collected in a cold trap. The permeability of acetaldehyde [mol / m 2 ·s·Pa] and the permeability ratio were calculated. The permeability ratio was calculated as [permeability of acetaldehyde / permeability of methyl iodide]. The results are shown in Table 1. In Table 1, "AD" indicates acetaldehyde. The same experiment was repeated six times for the silica membrane of Example 1, three times for the silica membrane of Example 2, four times for the silica membrane of Comparative Example 1, and five times for the silica membrane of Comparative Example 2, and evaluation was performed. Figure 1 shows the transition of the permeability ratio in the Examples and Comparative Examples. Figure 2 shows the transition of the permeability of acetaldehyde in the Examples and Comparative Examples.

[0055] The water contact angles of the silica films of Examples 1 and 2 were measured by dropping a drop of water onto the film surface using a contact angle meter "Drop Master 700" (manufactured by Kyowa Interface Science Co., Ltd.). For the silica film of Example 1, the water contact angle was measured before the experiment and after six experiments, and for the silica film of Example 2, the water contact angle was measured after three experiments. The results are shown in Table 2.

[0056] [Table 1]

[0057] [Table 2]

[0058] As can be seen from Table 1, when a silica membrane having a median pore size of 0.5 to 5.0 nm and having amino groups was used as a separation membrane (Examples 1 and 2), the permeability of acetaldehyde was high, and the permeability ratio did not change significantly over the number of experiments (Figures 1 and 2). On the other hand, when a silica membrane not having amino groups was used as a separation membrane (Comparative Examples 1 and 2), the permeability of acetaldehyde was low, and the permeability ratio decreased significantly over the number of experiments (Figures 1 and 2). This demonstrates that a silica membrane having a median pore size of 0.5 to 5.0 nm and having amino groups can efficiently separate a mixed solution containing components with different molecular sizes and / or physical properties, i.e., acetaldehyde and methyl iodide, and its performance (separation ability) is unlikely to deteriorate even after repeated use.

Claims

1. A silica membrane for separating acetaldehyde and methyl iodide, The central pore diameter is 0.5 to 5.0 nm and has an amino group and / or an ammonium group; The silica film has a thickness of 0.5 to 10 μm.

2. The silica film according to claim 1 , having a structure derived from a silane coupling agent having the amino group and / or the ammonium group.

3. 3. The silica film according to claim 2, wherein the silane coupling agent comprises an alkoxy group and a monovalent organic group, each bonded to a silicon atom, and at least one of the monovalent organic groups has an amino group and / or an ammonium group in the chain and / or at the end.

4. 4. The silica film according to claim 3, wherein the number of atoms in the main chain present between the silicon atom and the nitrogen atom in the amino group and / or the ammonium group is 2 to 4.

5. The silica membrane according to any one of claims 1 to 4, wherein the central pore diameter is 0.8 to 4.0 nm.

6. The silica membrane according to any one of claims 1 to 5, wherein the central pore diameter is 1.0 to 3.0 nm.

7. 7. The silica film according to claim 1, wherein the surface has a water contact angle of 0 to 70°.

8. The silica membrane according to any one of claims 1 to 7, which is provided on at least one surface of a porous substrate.

9. A composite membrane comprising a porous substrate and the silica membrane according to any one of claims 1 to 8 provided on at least one surface of the porous substrate.

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