Separation functional layer and separation membrane

Abstract

To provide a new separation functional layer that is suitable for separating acidic gas from a mixed gas containing acidic gas.SOLUTION: A separation functional layer 1 of the present invention contains a polyimide P and porous particles. The polyimide P includes a structural unit A1 derived from a tetracarboxylic dianhydride having a six-membered acid anhydride structure. A separation membrane 10 of the present invention includes the separation functional layer 1 and a porous support 3 supporting the separation functional layer 1.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a separation functional layer and a separation membrane. [Background technology]

[0002] Membrane separation has been developed as a method for separating acidic gases such as carbon dioxide from mixed gases. Compared to absorption methods, which separate acidic gases contained in mixed gases by absorbing them into an absorbent, membrane separation methods can efficiently separate acidic gases while reducing operating costs.

[0003] Separation membranes used in membrane separation methods include composite membranes in which a separation functional layer is formed on a porous support. Materials for the separation functional layer include resins such as polyimide resins and polyether block amide resins. For example, Patent Document 1 discloses a separation membrane containing a polyimide resin. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-184424 Summary of the Invention [Problem to be solved by the invention]

[0005] There is a need for a new separation functional layer that is suitable for separating acid gases from a gas mixture containing acid gases. [Means for solving the problem]

[0006] The present invention provides A separation functional layer containing polyimide and porous particles, The polyimide provides a separation functional layer containing a structural unit A1 derived from a tetracarboxylic dianhydride having a six-membered ring acid anhydride structure.

[0007] Furthermore, the present invention provides a film-forming device comprising the above-mentioned separation functional layer and a porous support supporting the separation functional layer; A separation membrane comprising: [Effects of the Invention]

[0008] According to the present invention, a new separation functional layer suitable for separating an acid gas from a gas mixture containing the acid gas can be provided. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a cross-sectional view schematically showing a separation functional layer according to one embodiment of the present invention. [Figure 2] 1 is a cross-sectional view schematically showing a separation membrane according to one embodiment of the present invention. [Figure 3] 1 is a schematic cross-sectional view of a membrane separation device equipped with a separation membrane of the present invention. [Figure 4] FIG. 10 is a perspective view schematically showing a modified example of a membrane separation device provided with a separation membrane of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] The separation functional layer according to the first aspect of the present invention is A separation functional layer containing polyimide and porous particles, The polyimide contains a structural unit A1 derived from a tetracarboxylic dianhydride having a six-membered ring acid anhydride structure.

[0011] In a second aspect of the present invention, for example, in the separation functional layer according to the first aspect, the porous particles contain an organic polymer.

[0012] In a third aspect of the present invention, for example, in the separation functional layer according to the second aspect, the organic polymer contains an aromatic ring.

[0013] In a fourth aspect of the present invention, for example, in the separation functional layer according to the second or third aspect, the organic polymer is a porous polymer.

[0014] In a fifth aspect of the present invention, for example, in the separation functional layer according to any one of the first to fourth aspects, the porous particles are surface-modified.

[0015] In a sixth aspect of the present invention, for example, in the separation functional layer according to any one of the first to fifth aspects, the content of the porous particles is 5% by weight or more and 50% by weight or less with respect to the polyimide.

[0016] In the seventh aspect of the present invention, for example, in the separation functional layer according to any one of the first to sixth aspects, the structural unit A1 is represented by the following formula (A1). [ka] In the formula (A1), R 1a ~R 4a are each independently a hydrogen atom or an optional substituent.

[0017] In an eighth aspect of the present invention, for example, the separation functional layer according to any one of the first to seventh aspects is used to separate an acidic gas from a mixed gas containing the acidic gas.

[0018] The separation membrane according to the ninth aspect of the present invention is A separation functional layer according to any one of the first to eighth aspects; a porous support supporting the separation functional layer; Equipped with.

[0019] The present invention will be described in detail below, but the following description is not intended to limit the present invention to a specific embodiment.

[0020] <Embodiments of Separation Functional Layer> FIG. 1 is a cross-sectional view schematically showing a separation functional layer 1 of this embodiment. The separation functional layer 1 of FIG. 1 can function as a free-standing membrane (single-layer membrane). The separation functional layer 1 preferably allows acidic gases contained in a mixed gas to pass preferentially through it. The separation functional layer 1 is typically a dense layer (non-porous layer) in which no pores are visible when observed at a magnification of 5000 times using a scanning electron microscope (SEM).

[0021] The separation functional layer 1 contains a polyimide and porous particles. The polyimide is a polyimide P containing a structural unit A1 derived from a tetracarboxylic dianhydride a1 having a six-membered ring acid anhydride structure S. The polyimide P preferably further contains a structural unit B derived from a diamine. In some cases, the separation functional layer 1 may contain a polyimide other than the polyimide P.

[0022] The structural unit A1 derived from the tetracarboxylic dianhydride a1 is a structural unit suitable for improving the permeability coefficient and permeation rate of acidic gases that permeate the separation functional layer 1. The tetracarboxylic dianhydride a1 has, for example, one or more, preferably two, acid anhydride structures S. The six-membered ring acid anhydride structure S is typically a glutaric anhydride structure represented by the following formula (1). [ka]

[0023] The tetracarboxylic dianhydride a1 may have a fused ring, and the fused ring may contain an acid anhydride structure S. The fused ring may contain an aromatic ring together with the acid anhydride structure S. The aromatic ring contained in the fused ring may be composed only of carbon atoms and hydrogen atoms, or may be a heteroaromatic ring containing a heteroatom such as an oxygen atom, a nitrogen atom, or a sulfur atom. The aromatic ring may be polycyclic or monocyclic. The number of carbon atoms in the aromatic ring is not particularly limited and is, for example, 4 to 14. Specific examples of the aromatic ring include a benzene ring, a naphthalene ring, an anthracene ring, a phenanthrene ring, a fluorene ring, a furan ring, a pyrrole ring, a pyridine ring, and a thiophene ring.

[0024] The fused ring may or may not have a substituent. The substituent of the fused ring is not particularly limited, and examples thereof include a halogen group and a hydrocarbon group. Examples of the halogen group include a fluoro group, a chloro group, a bromo group, and an iodo group. The number of carbon atoms in the hydrocarbon group is not particularly limited, and is, for example, 1 to 15. Examples of the hydrocarbon group include an alkyl group such as a methyl group, an ethyl group, and a propyl group. The hydrocarbon group may be a halogenated hydrocarbon group in which a hydrogen atom is substituted with a halogen group. When the fused ring has multiple substituents, the multiple substituents may be the same or different.

[0025] The tetracarboxylic dianhydride a1 is preferably represented by the following formula (a1). [ka]

[0026] In formula (a1), R 1a ~R 4a are each independently a hydrogen atom or an arbitrary substituent. The arbitrary substituent is not particularly limited, and examples thereof include a halogen group and a hydrocarbon group. Examples of the halogen group and the hydrocarbon group include those described above.

[0027] In the polyimide P, the structural unit A1 derived from the tetracarboxylic dianhydride a1 is preferably represented by the following formula (A1): The structural unit A1 represented by formula (A1) is derived from the tetracarboxylic dianhydride a1 represented by the above formula (a1). In formula (A1), the nitrogen atom contained in the imide group is derived from the diamine that has reacted with the tetracarboxylic dianhydride a1. [ka]

[0028] In formula (A1), R 1a ~R 4aare the same as in formula (a1) and are each independently a hydrogen atom or an arbitrary substituent. Specific examples of the structural unit A1 represented by formula (A1) include the following formula (A1-1). [ka]

[0029] In polyimide P, the ratio p1 of the amount of the structural unit A1 to the amount of all structural units A derived from tetracarboxylic dianhydride is, for example, 50 mol% or more, and may be 70 mol% or more, 90 mol% or more, 95 mol% or more, or even 99 mol% or more. Polyimide P may contain only the structural unit A1 as the structural unit A derived from tetracarboxylic dianhydride. However, polyimide P may further contain, in addition to structural unit A1, a structural unit A2 derived from tetracarboxylic dianhydride a2 having a five-membered ring acid anhydride structure. The tetracarboxylic dianhydride a2 is not particularly limited, and examples thereof include pyromellitic dianhydride and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride.

[0030] As described above, the polyimide P further contains a structural unit B derived from a diamine. A diamine is a compound having two primary amino groups. The diamine may or may not contain functional groups other than the primary amino groups. Examples of other substituents include a carboxyl group, a hydroxyl group, a thiol group, and a sulfonyl group. The diamine may have at least one functional group f selected from the group consisting of a carboxyl group, a hydroxyl group, and a thiol group.

[0031] The diamine may further have an aromatic ring. Examples of the aromatic ring include those described above for the tetracarboxylic dianhydride a1. In the diamine, the substituent on the aromatic ring includes, for example, a primary amino group. The aromatic ring may have a substituent other than the substituent including the primary amino group, or may not have any other substituent. The other substituent is not particularly limited, and examples include a group including the functional group f, a halogen group, a hydrocarbon group, and the like. Examples of the halogen group and the hydrocarbon group include those described above for the tetracarboxylic dianhydride a1. In the diamine, the other substituent may include a photopolymerizable functional group (for example, a vinyl group).

[0032] The diamine is represented by, for example, the following formula (b1), formula (b2), formula (b3), formula (b4) or formula (b5). [ka]

[0033] In formulas (b1) to (b5), R 1b ~R 30b are each independently a hydrogen atom or an arbitrary substituent. The arbitrary substituent is, for example, a group containing the functional group f, a halogen group, a hydrocarbon group, etc. Examples of the halogen group and the hydrocarbon group include those described above for the tetracarboxylic dianhydride a1.

[0034] In formulas (b3) and (b4), X 1 and X 2 is a single bond or an arbitrary linking group. The arbitrary linking group is, for example, a divalent hydrocarbon group. Examples of the divalent hydrocarbon group include alkylene groups such as methylene, ethylene, propane-1,3-diyl, and propane-2,2-diyl. The divalent hydrocarbon group may be a halogenated hydrocarbon group in which a hydrogen atom is substituted with a halogen group. The divalent hydrocarbon group may further have an aromatic ring. Examples of the aromatic ring include those described above for tetracarboxylic dianhydride a1. The divalent hydrocarbon group may be a fluorenediyl group. X 1 and X2 may contain a functional group such as an ether group or an ester group in addition to or instead of the divalent hydrocarbon group.

[0035] The diamine-derived structural unit B may have at least one functional group F selected from the group consisting of a carboxyl group, a hydroxyl group, a thiol group, and metal salts thereof. The metal contained in the metal salt as the functional group F is not particularly limited, and examples thereof include Li, Na, K, Be, Mg, Ca, Ba, Sc, Y, Ti, Zr, V, Cr, Mo, Mn, Fe, Co, Ni, Cu, Ag, Zn, B, Al, Ga, In, and Pb. In the metal salt as the functional group F, the metal is specifically present as a cation. The valence of this metal cation is, for example, 1 or more, preferably 2 or more, and more preferably 3 or more.

[0036] When the structural unit B contains a metal salt as the functional group F, multiple polyimides P can coordinate to the metal cation contained in the metal salt via a functional group such as a carboxyl group. This allows multiple polyimides P to crosslink with each other via the metal cation. The formation of such a crosslinked structure tends to suppress physical aging of the polyimide P, thereby preventing the separation performance of the separation functional layer 1 from deteriorating over time. When the polyimide P contains a metal salt as the functional group F, the separation performance of the separation functional layer 1 also tends to improve. The metal salt as the functional group F can be formed, for example, by exchanging a dissociable proton with a metal cation in the functional group f contained in the polyimide P obtained from a monomer group containing a tetracarboxylic dianhydride a1 and a diamine.

[0037] The structural unit B derived from a diamine is represented, for example, by the following formula (B1), (B2), (B3), (B4) or (B5): The structural units B represented by formulas (B1) to (B5) are derived from the diamines represented by the above formulas (b1) to (b5), respectively. [ka]

[0038] In formula (B1), R 1b ~R 4b are each independently a hydrogen atom or an arbitrary substituent. In formula (B1), the arbitrary substituent is, for example, a group containing the above-mentioned functional group F, a halogen group, a hydrocarbon group, etc. Examples of the halogen group and the hydrocarbon group include those described above for the tetracarboxylic dianhydride a1.

[0039] Specific examples of the structural unit B represented by formula (B1) include the following formulae (B1-1) to (B1-7): In these formulae, M represents any metal cation. [ka]

[0040] In formula (B2), R 5b ~R 8b are each independently a hydrogen atom or an arbitrary substituent. In formula (B2), the arbitrary substituent is, for example, a group containing a functional group F, a halogen group, a hydrocarbon group, etc. Examples of the halogen group and the hydrocarbon group include those described above for the tetracarboxylic dianhydride a1. Specific examples of the structural unit B represented by formula (B2) include the following formula (B2-1). [ka]

[0041] In formula (B3), R 9b ~R 16b are each independently a hydrogen atom or an arbitrary substituent, and X 1 is a single bond or an arbitrary linking group. In formula (B3), the arbitrary substituent is, for example, a group containing a functional group F, a halogen group, a hydrocarbon group, etc. Examples of the halogen group and the hydrocarbon group include those described above for the tetracarboxylic dianhydride a1.

[0042] X in formula (B3) 1In the formula (I), the optional linking group is, for example, a divalent hydrocarbon group. Examples of the divalent hydrocarbon group include those mentioned above. X 1 may contain a functional group such as an ether group or an ester group in addition to or instead of the divalent hydrocarbon group.

[0043] Specific examples of the structural unit B represented by formula (B3) include the following formulae (B3-1) to (B3-21): In these formulae, M represents any metal cation. [ka] [ka]

[0044] In formula (B4), R 17b ~R 24b are each independently a hydrogen atom or an arbitrary substituent, and X 2 is a single bond or an arbitrary linking group. In formula (B4), the arbitrary substituent is, for example, a group containing a functional group F, a halogen group, a hydrocarbon group, etc. Examples of the halogen group and the hydrocarbon group include those described above for the tetracarboxylic dianhydride a1.

[0045] X in formula (B4) 2 In the formula (I), the optional linking group is, for example, a divalent hydrocarbon group. Examples of the divalent hydrocarbon group include those mentioned above. X 2 may contain a functional group such as an ether group or an ester group in addition to or instead of the divalent hydrocarbon group.

[0046] Specific examples of the structural unit B represented by formula (B4) include the following formulae (B4-1) to (B4-6): In these formulae, M represents any metal cation. [ka]

[0047] In formula (B5), R 25b ~R 30b are each independently a hydrogen atom or an arbitrary substituent. In formula (B5), the arbitrary substituent is, for example, a group containing the functional group F, a halogen group, a hydrocarbon group, etc. Examples of the halogen group and the hydrocarbon group include those described above for the tetracarboxylic dianhydride a1. The structural unit B represented by formula (B5) is suitable for improving the rigidity of the polyimide P. A polyimide P with excellent rigidity tends to be able to suppress plasticization of the separation functional layer 1 even when the pressure of the mixed gas to be separated is high.

[0048] Specific examples of the structural unit B represented by formula (B5) include the following formulae (B5-1) and (B5-2). [ka]

[0049] In polyimide P, structural units A derived from tetracarboxylic dianhydride and structural units B derived from diamine are arranged alternately. Examples of combinations of adjacent structural units A and B in polyimide P include those represented by the following formulae (A1-B1), (A1-B3), and (A1-B5). In these formulae, R 1a ~R 4a , R 1b ~R 4b , R 9b ~R 16b , and R 25b ~R 30b is the same as described above for formula (A1), formula (B1), formula (B3) and formula (B5). [ka]

[0050] The weight-average molecular weight (Mw) of the polyimide P is, for example, 30,000 or more, preferably 50,000 or more, and more preferably 75,000 or more, from the viewpoint of the mechanical strength of the separation functional layer 1. The upper limit of the weight-average molecular weight of the polyimide P is not particularly limited and is, for example, 1,000,000. The weight-average molecular weight of the polyimide P can be calculated, for example, by measuring the molecular weight distribution of the polyimide P using a gel permeation chromatograph (GPC) equipped with a refractive index detector (RID) and using a calibration curve based on standard polystyrene from the obtained chromatogram (chart).

[0051] The content of polyimide P in the separation functional layer 1 is, for example, 50 wt% or more, and may be 60 wt% or more, 70 wt% or more, 80 wt% or more, 90 wt% or more, or even 95 wt% or more, or may be less than 100 wt%.

[0052] As described above, the separation functional layer 1 contains porous particles. The porous particles are dispersed in a matrix containing polyimide P. The porous particles may be separated from one another within the matrix, or may be partially aggregated.

[0053] The porous particles typically contain an organic material. Preferably, the porous particles contain an organic polymer. Preferably, the porous particles do not contain metal elements. Preferably, the porous particles are made of only an organic polymer. The molecular weight of the organic polymer is, for example, 10,000 or more.

[0054] Typically, the bonds contained in the organic polymer consist solely of covalent bonds, and the porous particles preferably do not contain coordinate or ionic bonds.

[0055] The organic polymer may contain an aromatic ring. The aromatic ring may be composed only of carbon atoms and hydrogen atoms, or may be a heteroaromatic ring containing a heteroatom such as an oxygen atom, a nitrogen atom, or a sulfur atom. The aromatic ring may be polycyclic or monocyclic. The number of carbon atoms in the aromatic ring is not particularly limited and is, for example, 4 to 14. Specific examples of the aromatic ring include a benzene ring, a naphthalene ring, an anthracene ring, a phenanthrene ring, a fluorene ring, a furan ring, a pyrrole ring, a pyridine ring, and a thiophene ring. The organic polymer preferably contains a benzene ring.

[0056] The organic polymer may contain an aromatic ring and a linking group connecting two or more aromatic rings. The linking group may be, for example, a chain hydrocarbon group or a quaternary carbon atom. The chain hydrocarbon group may be, for example, a divalent hydrocarbon group. Examples of the divalent hydrocarbon group include alkylene groups such as a methylene group, an ethylene group, a propane-1,3-diyl group, and a propane-2,2-diyl group, with a methylene group being preferred.

[0057] The organic polymer may have a functional group, such as an amino group or a hydroxyl group, which may be bonded to an aromatic ring.

[0058] The organic polymer is typically a porous polymer. Therefore, the porous particle is typically a porous organic polymer particle. The porous particle may be a porous polymer microparticle.

[0059] The porous polymer is preferably at least one selected from the group consisting of porous aromatic frameworks (PAFs) and hypercrosslinked polymers (HCPs). PAFs are porous structures formed by linking aromatic ring connectors, and have a regular structure in which multiple aromatic ring connectors are linked by direct carbon-carbon covalent bonds. HCPs are porous polymers formed by crosslinking multiple aromatic rings with hydrocarbon linking groups such as -CH-.

[0060] PAF is typically obtained by polymerizing a monomer that is an aromatic ring linker having a reactive group. The number of reactive groups in the monomer may be, for example, 1 to 6, 2 to 5, or 3 to 4, and preferably 4. The reactive group is preferably a halogen group. Examples of the halogen group include a fluoro group, a chloro group, a bromo group, and an iodo group.

[0061] The monomers used in the synthesis of PAF include, for example, tetrakis(4-bromophenyl)methane, tetrakis(4-chlorophenyl)methane, and derivatives thereof. For example, PAF (hereinafter referred to as "PAF-1") obtained by homopolymerizing or copolymerizing at least one selected from the group consisting of tetrakis(4-bromophenyl)methane and tetrakis(4-chlorophenyl)methane has a structural unit represented by the following formula (1). PAF can be synthesized, for example, by subjecting the above-mentioned monomers to a coupling reaction. [ka]

[0062] HCPs are typically obtained by polymerizing aromatic hydrocarbon monomers having reactive groups. The number of reactive groups may be, for example, 1 to 6, 2 to 4, or 2 to 3, and preferably 2. The reactive groups are preferably halogen groups. Examples of halogen groups include fluoro, chloro, bromo, and iodo groups. The aromatic hydrocarbon may further have other substituents in addition to the reactive groups. Examples of other substituents include hydrocarbon groups, amino groups, and hydroxyl groups. The number of carbon atoms in the hydrocarbon group is not particularly limited and is, for example, 1 to 15. Examples of the hydrocarbon group include alkyl groups such as methyl, ethyl, propyl, and butyl groups. The number of other substituents is not particularly limited and is, for example, 1 to 3.

[0063] Examples of the monomers used in the synthesis of HCPs include α,α'-dichloro-p-xylene, α,α'-dichloro-m-xylene, α,α'-dibromo-p-xylene, α,α'-dibromo-m-xylene, benzyl chloride, and derivatives thereof. Derivatives are typically compounds in which at least one hydrogen atom on the benzene ring of the above-mentioned monomers is substituted with a substituent. Examples of such substituents include those mentioned above. Examples of derivatives include 2,4-bis(chloromethyl)-1,3,5-trimethylbenzene, 4-tert-butylbenzyl chloride, and 4-(chloromethyl)benzyl alcohol. The HCP may be a homopolymer of one of the above-mentioned monomers, or a copolymer of two or more of them.

[0064] For example, an HCP (hereinafter referred to as "pDCX") obtained by homopolymerizing or copolymerizing at least one selected from the group consisting of α,α'-dichloro-p-xylene, α,α'-dichloro-m-xylene, α,α'-dibromo-p-xylene, and α,α'-dibromo-m-xylene has a structural unit represented by the following formula (2). An HCP (hereinafter referred to as "p(DCX-co-TMDCX)") obtained by copolymerizing at least one selected from the group consisting of α,α'-dichloro-p-xylene, α,α'-dichloro-m-xylene, α,α'-dibromo-p-xylene, and α,α'-dibromo-m-xylene with 2,4-bis(chloromethyl)-1,3,5-trimethylbenzene has a structural unit represented by the following formula (3). An HCP obtained by copolymerizing at least one selected from the group consisting of α,α'-dichloro-p-xylene, α,α'-dichloro-m-xylene, α,α'-dibromo-p-xylene, and α,α'-dibromo-m-xylene with 4-tert-butylbenzyl chloride (hereinafter referred to as "p(DCX-co-tBuBnC)") has a structural unit represented by the following formula (4): [ka]

[0065] In formula (2), although not shown, CH in the benzene ring may be linked to another structural unit represented by formula (2). That is, the carbon atom constituting CH may be bonded to a linker (typically a methylene group) that links the structural units represented by formula (2). Similarly, in formula (3), CH in the benzene ring may be linked to another structural unit represented by formula (3). In formula (4), CH in the benzene ring may be linked to another structural unit represented by formula (4).

[0066] The above-mentioned HCPs can be synthesized, for example, by subjecting the above-mentioned monomers to a Friedel-Crafts alkylation reaction.

[0067] The porous particles may be surface-modified. That is, the porous particles may have a surface modified with a modifying group. Examples of the modifying group include an amino group and a hydroxyl group. The porous particles may contain an HCP having a structural unit represented by the following formulas (5) to (6). Typically, the structural unit represented by the following formulas (5) to (6) is contained near the surface of the porous particles. [ka]

[0068] In this specification, an HCP having a constitutional unit represented by formula (5) is referred to as pDCX-OH, and an HCP having a constitutional unit represented by formula (6) is referred to as pDCX-NH2. pDCX-OH may have a constitutional unit represented by formula (2), a constitutional unit represented by formula (3), or a constitutional unit represented by formula (4), and a constitutional unit represented by formula (5). pDCX-NH2 may have a constitutional unit represented by formula (2), a constitutional unit represented by formula (3), or a constitutional unit represented by formula (4), and a constitutional unit represented by formula (6).

[0069] The average particle size of the porous particles is, for example, 1000 nm or less, preferably 500 nm or less, and more preferably 200 nm or less. The lower limit of the average particle size of the porous particles is, for example, 1 nm. The average particle size of the porous particles can be determined by the following method. First, the cross section of the separation functional layer 1 is observed with a scanning electron microscope. In the obtained electron microscope image, the area of ​​a specific porous particle is calculated by image processing. The diameter of a circle having the same area as the calculated area is regarded as the particle size (particle diameter) of the specific porous particle. The particle sizes of an arbitrary number (at least 50) of porous particles are calculated, and the average of the calculated values ​​is regarded as the average particle size of the nanoparticles.

[0070] The specific surface area of ​​porous particles is, for example, 10 m 2 / g or more, preferably 100m 2 / g or more, more preferably 500m 2 / g or more, more preferably 1000m 2 The upper limit of the specific surface area of ​​the porous particles is, for example, 100,000 m 2 The specific surface area of ​​the porous particles can be measured, for example, by the BET adsorption method using nitrogen gas adsorption.

[0071] The shape of the porous particles is not particularly limited, and may be spherical, ellipsoidal, scaly, or fibrous.

[0072] In the separation functional layer 1, the content of the porous particles relative to the polyimide P may be 1 wt % to 50 wt %, 5 wt % to 50 wt %, or even 5 wt % to 20 wt %.

[0073] The total content of polyimide P and porous particles in the separation functional layer 1 is, for example, 50 wt% or more, and may be 60 wt% or more, 70 wt% or more, 80 wt% or more, 90 wt% or more, or even 95 wt% or more, or may be 100 wt% or less. The separation functional layer 1 may be composed essentially of polyimide P and porous particles only.

[0074] The separation functional layer 1 may further contain other components in addition to polyimide P and porous particles. Examples of such other components include nanoparticles. Examples of nanoparticles include those exemplified for the intermediate layer 2 described below. In the separation functional layer 1, the nanoparticles are dispersed in a matrix containing polyimide P, for example. The nanoparticles may be spaced apart from one another within the matrix, or may be partially aggregated.

[0075] The thickness of the separation functional layer 1 is, for example, 500 μm or less, and may be 300 μm or less, 100 μm or less, 50 μm or less, 25 μm or less, 20 μm or less, or even 10 μm or less. The thickness of the separation functional layer 1 may be 0.05 μm or more, or may be 0.1 μm or more. The thickness of the separation functional layer 1 can be measured, for example, by observing a cross section of the separation functional layer 1 with a scanning electron microscope.

[0076] (Method of manufacturing the separation functional layer) In this embodiment, the manufacturing method of the separation functional layer 1 preferably includes, for example, applying a coating liquid containing polyimide P and porous particles onto a substrate to form a coating film, and drying the coating film to form the separation functional layer 1.

[0077] Polyimide P can be prepared by the following method: First, a diamine is dissolved in a solvent to obtain a solution. Examples of the solvent include polar organic solvents such as N-methyl-2-pyrrolidone and 1,3-dioxolane.

[0078] Next, tetracarboxylic dianhydrides including the tetracarboxylic dianhydride a1 are gradually added to the resulting solution. This causes the tetracarboxylic dianhydride a1 to react with the diamine-containing monomers to form polyamic acid. The addition of the tetracarboxylic dianhydrides is carried out, for example, under stirring conditions for 3 to 20 hours in a heated environment at 140°C or higher.

[0079] Next, polyamic acid is imidized to obtain polyimide P. Examples of imidization methods include chemical imidization and thermal imidization. Chemical imidization is a method in which polyamic acid is imidized, for example, at room temperature using a dehydration condensation agent. Examples of dehydration condensation agents include acetic anhydride, pyridine, and triethylamine. Thermal imidization is a method in which polyamic acid is imidized by heat treatment. The heat treatment temperature is, for example, 180°C or higher.

[0080] The content of polyimide P in the coating liquid can be adjusted appropriately depending on the solubility of polyimide P, and is, for example, 1 wt % to 30 wt %.

[0081] The content of the porous particles in the coating liquid can be adjusted as appropriate and is, for example, 1 wt % to 50 wt % relative to the polyimide P, preferably 5 wt % to 50 wt %, and more preferably 5 wt % to 20 wt %.

[0082] The coating liquid preferably further contains a solvent. The solvent is typically a good solvent capable of dissolving polyimide P. The solvent preferably contains at least one selected from the group consisting of amide compounds and lactone compounds, and more preferably contains an amide compound. Examples of amide compounds include N,N-dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), and N,N-dimethylacetamide (DMAc). Examples of lactone compounds include γ-butyrolactone.

[0083] The content of the solvent in the coating liquid is not particularly limited, and is, for example, 30 wt % to 99 wt %.

[0084] The coating liquid may further contain a surfactant (leveling agent) to improve coating properties. However, according to the investigations of the present inventors, when the coating liquid contains a surfactant, the separation performance of the produced separation functional layer 1 tends to decrease. Therefore, it is preferable that the coating liquid does not contain a surfactant.

[0085] The coating liquid may further contain a compound containing a metal cation. This compound allows the dissociative proton of the functional group f contained in the polyimide P to be exchanged with the metal cation in the coating liquid, thereby forming a polyimide P having a metal salt as the functional group F. Examples of the metal cation include those metals contained in the metal salt as the functional group F. Specific examples of the compound containing a metal cation include Al(acac)3, Fe(acac)2, Ga(acac)3, and Mg(acac)2.

[0086] The substrate to which the coating liquid containing polyimide P and porous particles is applied is typically a release liner. Examples of the substrate include films containing resin; paper; and sheets containing metal materials such as aluminum and stainless steel. Sheets containing metal materials tend to have high heat resistance. The substrate is preferably a film containing resin because of its excellent surface smoothness. In the substrate, examples of the polymer contained in the resin include polyolefins such as polyethylene, polypropylene, polybutene, polybutadiene, and polymethylpentene; polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; polyvinyl chloride, vinyl chloride copolymers; polyurethanes; ethylene-vinyl acetate copolymers; and polyimides, with polyimides being preferred.

[0087] The surface of the substrate may be subjected to a release treatment. The release treatment can be carried out by applying a release treatment agent to the surface of the substrate. Examples of the release treatment agent include silicone-based release treatment agents, long-chain alkyl-based release treatment agents, fluorine-based release treatment agents, and molybdenum sulfide-based release treatment agents. The release treatment agents may be used alone or in combination of two or more. The substrate may be a polyimide film that has been subjected to a release treatment.

[0088] The thickness of the substrate is not particularly limited and is, for example, 5 to 100 μm, and preferably 10 to 50 μm.

[0089] Before applying the coating liquid, the substrate may be subjected to a surface modification treatment. When the substrate has been subjected to a release treatment, the surface modification treatment may be performed on the surface of the substrate that has been subjected to the release treatment. Examples of the surface modification treatment include corona treatment, plasma treatment, excimer treatment, and flame treatment, and corona treatment is preferred.

[0090] Surface modification treatment can be carried out by irradiating the surface of the substrate with active energy rays. Specific examples of active energy rays include electron beams, ion beams, plasma beams, and ultraviolet rays. When corona treatment is performed as the surface modification treatment, the discharge rate is, for example, 0.1 kW·min / m 2 The upper limit of the discharge amount is not particularly limited, and may be, for example, 10 kW min / m 2 is.

[0091] The method for applying the coating liquid to the substrate is not particularly limited, and for example, spin coating, dip coating, slot die coating, etc. may be used. The coating liquid may be applied to the substrate using an applicator, a wire bar, etc. The coating liquid may be applied to the surface of a substrate that has been subjected to a release treatment or a surface modification treatment.

[0092] A coating film is formed by applying the coating liquid to the substrate. The thickness of the coating film can be adjusted appropriately depending on the desired thickness of the separation functional layer 1, and is, for example, 1 μm to 100 μm.

[0093] The drying conditions for the coating film are not particularly limited, and for example, the drying temperature is 50°C to 200°C and the drying time is 1 minute to 10 hours. The coating film can be dried using a heater or the like. As an example, the coating film may be dried by passing it through a heating unit equipped with a heater. The coating film may be dried by passing it through multiple heating units. The set temperatures of the multiple heating units may be the same or different.

[0094] The manufacturing method of this embodiment may further include subjecting the obtained separation functional layer 1 to a heat treatment (annealing treatment). This step tends to improve the separation performance of the separation functional layer 1 and also suppress deterioration of the separation performance of the separation functional layer 1 over time. This step also makes it possible to obtain a separation functional layer 1 that contains almost no residual solvent by sufficiently volatilizing the solvent. The annealing treatment may be performed before or after removing the substrate from the laminate of the separation functional layer 1 and the substrate.

[0095] The temperature of the heat treatment may be, for example, higher than 100°C, 130°C or higher, or even 150°C or higher. The upper limit of the heat treatment temperature is not particularly limited and may be, for example, 350°C or lower, or 300°C or lower. The heat treatment time is, for example, 1 minute or longer, or may be 10 minutes or longer, or 30 minutes or longer. The upper limit of the heat treatment time is not particularly limited and may be, for example, 24 hours or shorter.

[0096] The manufacturing method of this embodiment preferably further includes removing the substrate from the laminate of the separation functional layer 1 and the substrate. By removing the substrate, a separation functional layer 1 that functions as a free-standing membrane can be obtained.

[0097] The manufacturing method of this embodiment is not limited to the above. A coating liquid containing polyamic acid, which is a precursor of polyimide P, may be used instead of the coating liquid containing polyimide P. The separation functional layer 1 may be produced by applying this coating liquid onto the substrate and imidizing the polyamic acid to form polyimide P.

[0098] (Characteristics of the separation functional layer) As described above, the separation functional layer 1 preferably allows acidic gases contained in a mixed gas to permeate preferentially. As an example, when a mixed gas consisting of carbon dioxide and nitrogen is supplied to a space adjacent to one side of the separation functional layer 1 using the separation functional layer 1 in an initial state, the permeability coefficient C1 of carbon dioxide permeating the separation functional layer 1 taking into consideration the thickness of the separation functional layer 1 is, for example, 500 Barrer or more, 600 Barrer or more, 700 Barrer or more, 1000 Barrer or more, or even 2000 Barrer or more. The upper limit of the permeability coefficient C1 is not particularly limited, and may be, for example, 5000 Barrer. Note that Barrer is 10 -10 ·cm 3 (STP)·cm / (sec·cm 2 cm 3 (STP) refers to the volume of carbon dioxide at 1 atmosphere and 0°C.

[0099] The permeability coefficient C1 can be determined by the following method. First, a mixed gas consisting of carbon dioxide and nitrogen is supplied to a space adjacent to one surface of the separation functional layer 1, and the space adjacent to the other surface of the separation functional layer 1 is depressurized. This results in a permeated fluid that has permeated through the separation functional layer 1. The weight of the permeated fluid, as well as the volume ratio of carbon dioxide and the volume ratio of nitrogen in the permeated fluid, are measured. The permeability coefficient C1 can be calculated from the measurement results. In the above operation, the carbon dioxide concentration in the mixed gas is 50 vol% under standard conditions (0°C, 101 kPa). The mixed gas supplied to the space adjacent to one surface of the separation functional layer 1 has a temperature of 30°C and a pressure of 0.1 MPa. The space adjacent to the other surface of the separation functional layer 1 is depressurized so that the pressure in the space is 0.1 MPa lower than the atmospheric pressure in the measurement environment.

[0100] Under the above conditions for measuring the permeability coefficient C1, the separation coefficient α1 of carbon dioxide relative to nitrogen of the separation functional layer 1 in the initial state is not particularly limited, and may be, for example, 8 or more, 15 or more, or even 20 or more. The upper limit of the separation coefficient α1 is not particularly limited, and may be, for example, 100 or 60. The separation coefficient α1 can be calculated from the following formula. In the following formula, the permeability coefficient C1 N2 is the permeability coefficient of nitrogen that permeates through the separating functional layer 1 under the measurement conditions for the permeability coefficient C1. Separation factor α1 = permeability coefficient C1 / permeability coefficient C1 N2

[0101] As described above, the separation functional layer 1 of this embodiment contains polyimide P and porous particles. In this separation functional layer 1, physical aging of the polyimide is suppressed, which can prevent the separation performance of the separation functional layer 1 from decreasing over time. In particular, the separation functional layer 1 of this embodiment can improve the separation performance (particularly the permeability coefficient of acidic gases) when used for a long period of time.

[0102] The separation performance of the separation functional layer 1 after long-term use can be evaluated by the following method. First, the separation functional layer 1 is stored in an environment of 85°C for 500 hours (durability test). After the durability test, the separation functional layer 1 is measured for the permeability coefficient C2 of carbon dioxide passing through the separation functional layer 1 when a mixed gas of carbon dioxide and nitrogen is supplied to a space adjacent to one side of the separation functional layer 1 using the same method as for the permeability coefficient C1.

[0103] The permeability coefficient C2 after the durability test is, for example, 500 Barrer or more, and may be 550 Barrer or more, 600 Barrer or more, 700 Barrer or more, or even 820 Barrer or more. The upper limit of the permeability coefficient C2 is not particularly limited and is, for example, 5000 Barrer. The separation functional layer 1 can improve the permeability coefficient C2 after the durability test.

[0104] In the separation functional layer 1, the ratio C2 / C1 of the permeability coefficient C2 to the permeability coefficient C1 is, for example, 40% or more, and may be 45% or more, 50% or more, 55% or more, or even 60% or more. The upper limit of the ratio C2 / C1 is, for example, 110%.

[0105] The separation coefficient α2 of the separation functional layer 1 for carbon dioxide relative to nitrogen after the durability test is, for example, 20 or more, 30 or more, or even 35 or more. The upper limit of the separation coefficient α2 after the durability test is not particularly limited, and may be, for example, 100 or 60. The separation coefficient α2 after the durability test can be calculated using the following formula. In the following formula, the permeability coefficient C2 N2 is the permeability coefficient of nitrogen that permeates through the separating functional layer 1 after the durability test under the measurement conditions for the permeability coefficient C1 described above. Separation factor α2 = permeability coefficient C2 / permeability coefficient C2 N2

[0106] Furthermore, when a mixed gas of carbon dioxide and methane is supplied to a space adjacent to one surface of the separation functional layer 1 using the separation functional layer 1 in its initial state, the permeability coefficient C3 of carbon dioxide passing through the separation functional layer 1 taking into consideration the thickness of the separation functional layer 1 is, for example, 500 Barrer or more, and may be 600 Barrer or more, 700 Barrer or more, 900 Barrer or more, or even 1000 Barrer or more. The upper limit of the permeability coefficient C3 is not particularly limited and may be, for example, 5000 Barrer.

[0107] The permeability coefficient C3 can be determined in the same manner as the permeability coefficient C1, except that a gas mixture consisting of carbon dioxide and methane is used and the weight of the permeating fluid and the volume fraction of carbon dioxide and volume fraction of methane in the permeating fluid are measured.

[0108] Under the above conditions for measuring the permeability coefficient C3, the separation coefficient α3 of carbon dioxide relative to methane of the separation functional layer 1 in the initial state is not particularly limited, and may be, for example, 10 or more, 13 or more, or even 15 or more. The upper limit of the separation coefficient α3 is not particularly limited, and may be, for example, 100 or 60. The separation coefficient α3 can be calculated from the following formula. However, in the following formula, the permeability coefficient C3 CH4 is the permeability coefficient of methane that permeates through the separating functional layer 1 under the measurement conditions for the permeability coefficient C3. Separation factor α3 = permeability coefficient C3 / permeability coefficient C3 CH4

[0109] For the separation functional layer 1 after the durability test described above, when a mixed gas of carbon dioxide and methane is supplied to a space adjacent to one side of the separation functional layer 1 using the same method as for the permeability coefficient C3, the permeability coefficient C4 of carbon dioxide passing through the separation functional layer 1 is, for example, 500 Barrer or more, and may be 550 Barrer or more, 600 Barrer or more, or even 700 Barrer or more. The upper limit of the permeability coefficient C4 is not particularly limited, and may be, for example, 5000 Barrer. The separation functional layer 1 can improve the permeability coefficient C4 after the durability test.

[0110] In the separation functional layer 1, the ratio C4 / C3 of the permeability coefficient C4 to the permeability coefficient C3 is, for example, 40% or more, and may be 45% or more, 50% or more, 55% or more, or even 60% or more. The upper limit of the ratio C4 / C3 is, for example, 110%.

[0111] The separation coefficient α4 of the separation functional layer 1 for carbon dioxide relative to methane after the durability test is not particularly limited, and may be, for example, 10 or more, 13 or more, or even 15 or more. The upper limit of the separation coefficient α4 after the durability test is not particularly limited, and may be, for example, 100 or 60. The separation coefficient α4 after the durability test can be calculated using the following formula. In the following formula, the permeability coefficient C4 CH4 is the permeability coefficient of methane that permeates through the separating functional layer 1 after the durability test under the measurement conditions for the permeability coefficient C3 described above. Separation factor α4 = permeability coefficient C4 / permeability coefficient C4 CH4

[0112] (Use of separation functional layer) The separation functional layer 1 of this embodiment can be used to separate acidic gases from a gas mixture containing acidic gases. Examples of acidic gases in the gas mixture include carbon dioxide, hydrogen sulfide, carbonyl sulfide, sulfur oxides (SOx), hydrogen cyanide, and nitrogen oxides (NOx), with carbon dioxide being preferred. The gas mixture contains gases other than the acidic gas. Examples of other gases include nonpolar gases such as hydrogen, nitrogen, and methane, and inert gases such as helium, with nitrogen and methane being preferred. The separation functional layer 1 of this embodiment is particularly suitable for separating carbon dioxide from a gas mixture containing carbon dioxide and nitrogen. However, the use of the separation functional layer 1 is not limited to separating acidic gases from the above-mentioned gas mixture.

[0113] <Embodiments of separation membrane> As shown in Fig. 2, the separation membrane 10 of this embodiment includes the above-described separation functional layer 1, and further includes a porous support 3. As shown in Fig. 2, the separation membrane 10 preferably further includes an intermediate layer 2 disposed between the separation functional layer 1 and the porous support 3. The porous support 3 supports the separation functional layer 1. The intermediate layer 2 is in direct contact with both the separation functional layer 1 and the porous support 3.

[0114] (middle class) The intermediate layer 2 preferably contains a resin, and more preferably further contains nanoparticles dispersed in the resin (matrix). The nanoparticles may be separated from one another within the matrix, or may be partially aggregated. However, the intermediate layer 2 may not contain nanoparticles, and may be essentially composed of a resin.

[0115] The material of the matrix is ​​not particularly limited, and examples thereof include silicone resins such as polydimethylsiloxane, fluororesins such as polytetrafluoroethylene, epoxy resins such as polyethylene oxide, polyimide resins, polysulfone resins, polyacetylene resins such as polytrimethylsilylpropyne and polydiphenylacetylene, polyolefin resins such as polymethylpentene, polyurethane resins, etc. The matrix preferably contains a silicone resin and a polyurethane resin.

[0116] The nanoparticles may contain an inorganic material or an organic material. Examples of inorganic materials contained in the nanoparticles include silica, titania, and alumina. The nanoparticles preferably contain silica.

[0117] The nanoparticles may have a surface modified with a modifying group containing a carbon atom. Nanoparticles having a surface modified with this modifying group have excellent dispersibility in a matrix. The nanoparticles are preferably silica nanoparticles which may have a surface modified with a modifying group. The modifying group preferably further contains a silicon atom. In the nanoparticles, the surface modified with the modifying group is preferably represented by the following formulas (I) to (III). [ka]

[0118] R in formulas (I) to (III) 1 ~R 6are each independently a hydrocarbon group which may have a substituent. The number of carbon atoms in the hydrocarbon group is not particularly limited as long as it is 1 or more. The number of carbon atoms in the hydrocarbon group may be, for example, 25 or less, 20 or less, 10 or less, or 5 or less. In some cases, the number of carbon atoms in the hydrocarbon group may be more than 25. The hydrocarbon group may be a linear or branched chain hydrocarbon group, or an alicyclic or aromatic cyclic hydrocarbon group. In a preferred embodiment, the hydrocarbon group is a linear or branched alkyl group having 1 to 8 carbon atoms. The hydrocarbon group is, for example, a methyl group or an octyl group, preferably a methyl group. Examples of the substituent on the hydrocarbon group include an amino group and an acyloxy group. Examples of the acyloxy group include a (meth)acryloyloxy group.

[0119] In another preferred embodiment, R 1 ~R 6 The hydrocarbon group, which may have the substituent described above, is represented by the following formula (IV): Nanoparticles having a surface modified with a modifying group containing a hydrocarbon group represented by formula (IV) are suitable for improving the permeability coefficient of acidic gases in separation membrane 10. [ka]

[0120] In formula (IV), R 7 is an alkylene group having 1 to 5 carbon atoms which may have a substituent. The alkylene group may be linear or branched. Examples of the alkylene group include a methylene group, an ethylene group, a propane-1,3-diyl group, a butane-1,4-diyl group, and a pentane-1,5-diyl group, and preferably a propane-1,3-diyl group. Examples of the substituent of the alkylene group include an amide group and an amino alkylene group.

[0121] In formula (IV), R 8R is an alkyl group or aryl group having 1 to 20 carbon atoms, which may have a substituent. The alkyl group may be linear or branched. Examples of the substituents on the alkyl group and aryl group include an amino group and a carboxyl group. 8 is, for example, a 3,5-diaminophenyl group.

[0122] In the nanoparticles, the surface modified with the modifying group is preferably represented by the following formula (V). [ka]

[0123] The modifying group is not limited to the structures shown in formulas (I) to (III). The modifying group may be any of R 1 ~R 6 Instead of the above, the modifying group may contain a polymer chain having a polyamide structure or a polydimethylsiloxane structure. In the modifying group, the polymer chain is preferably directly bonded to the silicon atom. The shape of the polymer chain may be, for example, linear, dendrimer, or hyperbranched.

[0124] The method for modifying the surface of nanoparticles with a modifying group is not particularly limited. As an example, the surface of nanoparticles can be modified by reacting hydroxyl groups present on the surface of nanoparticles with a known silane coupling agent. When the modifying group contains a polyamide structure, the surface of nanoparticles can be modified by the method disclosed in JP 2010-222228 A.

[0125] The average particle size of the nanoparticles is not particularly limited as long as it is on the nanometer order (<1000 nm), and is, for example, 100 nm or less, preferably 50 nm or less, and more preferably 20 nm or less. The lower limit of the average particle size of the nanoparticles is, for example, 1 nm. The average particle size of the nanoparticles can be determined by the following method. First, the cross section of the intermediate layer 2 is observed with a transmission electron microscope. In the obtained electron microscope image, the area of ​​a specific nanoparticle is calculated by image processing. The diameter of a circle having the same area as the calculated area is regarded as the particle size of that specific nanoparticle (particle diameter). The particle sizes of an arbitrary number (at least 50) of nanoparticles are calculated, and the average of the calculated values ​​is regarded as the average particle size of the nanoparticles. The shape of the nanoparticles is not particularly limited, and may be spherical, ellipsoidal, scaly, or fibrous.

[0126] The nanoparticle content in the intermediate layer 2 is, for example, 5 wt% or more, preferably 10 wt% or more, and more preferably 15 wt% or more. There is no particular upper limit to the nanoparticle content in the intermediate layer 2, and it is, for example, 30 wt%.

[0127] The thickness of the intermediate layer 2 is not particularly limited and is, for example, less than 50 μm, preferably 40 μm or less, and more preferably 30 μm or less. The lower limit of the thickness of the intermediate layer 2 is not particularly limited and is, for example, 1 μm. The intermediate layer 2 is preferably a layer having a thickness of less than 50 μm.

[0128] (porous support) Examples of the porous support 3 include nonwoven fabrics, porous polytetrafluoroethylene, aromatic polyamide fibers, porous metals, sintered metals, porous ceramics, porous polyesters, porous nylons, activated carbon fibers, latex, silicone, silicone rubber, permeable (porous) polymers containing at least one selected from the group consisting of polyvinyl fluoride, polyvinylidene fluoride, polyurethane, polypropylene, polyethylene, polystyrene, polycarbonate, polysulfone, polyether ether ketone, polyacrylonitrile, polyimide, and polyphenylene oxide, open-cell or closed-cell metal foams, open-cell or closed-cell polymer foams, silica, porous glass, and mesh screens. The porous support 3 may also be a combination of two or more of these materials. For example, the porous support 3 may be a laminate of a nonwoven fabric and a porous polysulfone layer.

[0129] The porous support 3 has an average pore size of, for example, 0.01 μm to 0.4 μm. The thickness of the porous support 3 is not particularly limited and is, for example, 10 μm or more, preferably 20 μm or more, and more preferably 50 μm or more. The thickness of the porous support 3 is, for example, 300 μm or less, preferably 200 μm or less, and more preferably 150 μm or less.

[0130] (Method of manufacturing separation membrane) The separation membrane 10 can be produced by the following method. First, a laminate of a porous support 3 and an intermediate layer 2 is prepared. This laminate can be produced by the following method. First, a coating liquid containing the material for the intermediate layer 2 is prepared. Next, the coating liquid containing the material for the intermediate layer 2 is applied onto the porous support 3 to form a coating film. The method for applying the coating liquid is not particularly limited, and for example, spin coating or dip coating can be used. The coating liquid may also be applied using a wire bar or the like. Next, the coating film is dried to form the intermediate layer 2. The coating film can be dried under heating conditions. The heating temperature of the coating film is, for example, 50°C or higher. The heating time of the coating film is, for example, 1 minute or more, and may be 5 minutes or more. Furthermore, the surface of the intermediate layer 2 may be subjected to an adhesion-promoting treatment if necessary. Examples of adhesion-promoting treatments include surface treatments such as application of a primer, corona discharge treatment, and plasma treatment.

[0131] Next, the separation functional layer 1 is formed on the intermediate layer 2 in the laminate of the porous support 3 and the intermediate layer 2. This allows for the production of the separation membrane 10. As an example, the separation membrane 10 can be produced by using the laminate of the porous support 3 and the intermediate layer 2 as a substrate and carrying out the production method described above for the separation functional layer 1.

[0132] The method for producing the separation membrane 10 is not limited to the above method, and the separation membrane 10 may also be produced by the following method. First, a separation functional layer 1 formed on a substrate is prepared by the above method. Next, a coating liquid containing the material for the intermediate layer 2 is applied onto the separation functional layer 1 and dried to form the intermediate layer 2. The laminate of the intermediate layer 2 and the separation functional layer 1 is transferred to the porous support 3. In this way, the separation membrane 10 is obtained.

[0133] (Separation membrane shape) In this embodiment, the separation membrane 10 is typically a flat membrane. However, the separation membrane 10 may have a shape other than a flat membrane, for example, a hollow fiber membrane. As an example, the separation membrane 10 as a hollow fiber membrane may include a separation function layer 1 and a porous support 3, but may not include an intermediate layer 2.

[0134] <Embodiment of Membrane Separation Device> As shown in FIG. 3, the membrane separation device 100 of this embodiment includes a separation membrane 10 and a tank 20. In the membrane separation device 100, it is also possible to use a separation functional layer 1 alone instead of the separation membrane 10. The tank 20 includes a first chamber 21 and a second chamber 22. The separation membrane 10 is disposed inside the tank 20. Inside the tank 20, the separation membrane 10 separates the first chamber 21 and the second chamber 22. The separation membrane 10 extends from one to the other of a pair of wall surfaces of the tank 20.

[0135] The first chamber 21 has an inlet 21a and an outlet 21b. The second chamber 22 has an outlet 22a. The inlet 21a, the outlet 21b, and the outlet 22a are preferably openings formed in the wall surface of the tank 20.

[0136] Membrane separation using the membrane separation device 100 is performed by the following method. First, a gas mixture 30 containing an acidic gas is supplied to the first chamber 21 through the inlet 21a. The concentration of the acidic gas in the gas mixture 30 is not particularly limited, and is, for example, 0.01 vol% (100 ppm) or more under standard conditions, preferably 1 vol% or more, more preferably 10 vol% or more, even more preferably 30 vol% or more, and particularly preferably 50 vol% or more. The upper limit of the concentration of the acidic gas in the gas mixture 30 is not particularly limited, and is, for example, 90 vol% under standard conditions.

[0137] The pressure inside the first chamber 21 may be increased by the supply of the mixed gas 30. The membrane separation apparatus 100 may further include a pump (not shown) for increasing the pressure of the mixed gas 30. The pressure of the mixed gas 30 supplied to the first chamber 21 is, for example, 0.1 MPa or more, and preferably 0.3 MPa or more.

[0138] The pressure inside the second chamber 22 may be reduced while the gas mixture 30 is being supplied to the first chamber 21. The membrane separation device 100 may further include a pump (not shown) for reducing the pressure inside the second chamber 22. The pressure inside the second chamber 22 may be reduced, for example, by 10 kPa or more, preferably 50 kPa or more, and more preferably 100 kPa or more, relative to the atmospheric pressure in the measurement environment.

[0139] By supplying the gas mixture 30 into the first chamber 21, a permeated fluid 35 having a higher acid gas content than the gas mixture 30 can be obtained on the other side of the separation membrane 10. That is, the permeated fluid 35 is supplied to the second chamber 22. The permeated fluid 35 preferably contains an acid gas as a main component. However, the permeated fluid 35 may contain small amounts of gases other than the acid gas. The permeated fluid 35 is discharged to the outside of the tank 20 through the outlet 22a.

[0140] The concentration of acid gas in the mixed gas 30 gradually decreases from the inlet 21a toward the outlet 21b of the first chamber 21. The mixed gas 30 (non-permeated fluid 36) treated in the first chamber 21 is discharged to the outside of the tank 20 through the outlet 21b.

[0141] The membrane separation apparatus 100 of this embodiment is suitable for a flow-through (continuous) membrane separation method, but may also be used for a batch-type membrane separation method.

[0142] <Modification of Membrane Separation Device> The membrane separation device 100 may be a spiral membrane element, a hollow fiber membrane element, or the like. Fig. 4 shows a spiral membrane element. The membrane separation device 110 of Fig. 4 includes a central tube 41 and a laminate 42. The laminate 42 includes a separation membrane 10. The laminate 42 may include a separation functional layer 1 alone, instead of the separation membrane 10.

[0143] The central tube 41 has a cylindrical shape. A plurality of holes are formed on the surface of the central tube 41 to allow the permeating fluid 35 to flow into the interior of the central tube 41. Examples of materials for the central tube 41 include resins such as acrylonitrile-butadiene-styrene copolymer resin (ABS resin), polyphenylene ether resin (PPE resin), and polysulfone resin (PSF resin); and metals such as stainless steel and titanium. The inner diameter of the central tube 41 is, for example, in the range of 20 to 100 mm.

[0144] In addition to the separation membrane 10, the laminate 42 further includes a feed-side channel material 43 and a permeate-side channel material 44. The laminate 42 is wound around a central tube 41. The membrane separation device 110 may further include an exterior material (not shown).

[0145] The feed-side channel material 43 and the permeate-side channel material 44 may be, for example, a resin net made of polyphenylene sulfide (PPS) or ethylene-chlorotrifluoroethylene copolymer (ECTFE).

[0146] Membrane separation using the membrane separation device 110 is performed in the following manner. First, the mixed gas 30 is supplied to one end of the wound stack 42. The permeated fluid 35 that has permeated the separation membrane 10 of the stack 42 moves into the interior of the central tube 41. The permeated fluid 35 is discharged to the outside through the central tube 41. The mixed gas 30 (non-permeated fluid 36) that has been treated in the membrane separation device 110 is discharged to the outside from the other end of the wound stack 42. This allows acid gases to be separated from the mixed gas 30. [Example]

[0147] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0148] [Fabrication of separation functional layer] Example 1 First, polyimide P1 was synthesized using an automatic polymerization apparatus (Mettler-Toledo, EasyMax402). The separable flask (400 mL capacity) attached to the apparatus was equipped with a Dimroth tube, a stirring rod, an internal thermometer, a nitrogen inlet tube, and a flat stopper. A cooling liquid set to 10°C was circulated through the Dimroth chiller. N2 gas was circulated through the flask at a flow rate of 100 mL / min. The stirring speed was set to 300 rpm. Next, 185 g of 1-methyl-2-pyrrolidone (super-dehydrated) as a solvent and 4.78 g (31.8 mmol) of 2,4,6-trimethyl-1,3-phenylenediamine (TrMPD) as diamines, 8.27 g (31.8 mmol) of 3,7-diamino-2,8-dimethyldibenzothiophene sulfone (DDBT), and 0.96 g (3.4 mmol) of 5,5'-methylenebis(2-aminobenzoic acid) (MBAA) were added to the flask. The mixture was stirred at room temperature to dissolve the diamine in the solvent. To the resulting solution, 18.22 g (67.9 mmol) of naphthalene-1,4,5,8-tetracarboxylic dianhydride (NTDA) as a tetracarboxylic dianhydride and 16.35 g (134 mmol) of benzoic acid were further added. The jacket temperature of the apparatus was raised to 180 °C, and the mixture was stirred for 8 hours. At this time, the internal temperature of the flask was 172 to 175° C. After stirring, the internal temperature of the flask was cooled to 25° C. and allowed to stand overnight.

[0149] Next, 17.29 g (134 mmol) of isoquinoline was added, and the jacket temperature was raised again to 180 °C and stirred for 8 hours. After leaving the reaction solution overnight, 435 g of 1-methyl-2-pyrrolidone (NMP) was added to dilute the reaction solution. Next, using a dropping funnel, 1174 mL of methanol was added dropwise to the reaction solution over approximately 30 minutes to perform reprecipitation purification. The precipitated polyimide was filtered and washed three times with 391 mL of methanol. After washing, the filtered polyimide was dried in a hot air circulation dryer at 60 °C for 15 hours and then further dried in a vacuum dryer at 100 °C for 8 hours. This yielded 30.6 g of polyimide P1.

[0150] Next, the porous particles of Example 1 were synthesized as follows. In an Ar glove box, 0.57 g (3.62 mmol) of 2,2'-bipyridyl as a ligand was dissolved in a mixture of 75 mL of ultra-dehydrated N,N-dimethylformamide and 75 mL of ultra-dehydrated tetrahydrofuran. 1.00 g (3.64 mmol) of bis(1,5-cyclooctadiene)nickel(0) as a catalyst was added and stirred for 3 minutes. After that, 0.51 g (0.81 mmol) of tetrakis(4-bromophenyl)methane was added and stirred at 25°C for 24 hours to allow the coupling reaction (Yamamoto Coupling) to proceed. 50 mL of 6 M hydrochloric acid was added to the reaction solution and stirred at 25°C for 6 hours. The resulting precipitate was washed with methanol and water and then vacuum-dried at 80°C for 6 hours to synthesize white powder PAF-1. In this way, the porous particles (PAF-1) of Example 1 were obtained. The specific surface area of ​​the porous particles is 4023m 2 / g.

[0151] The porous particles and NMP were mixed and dispersed using an ultrasonic homogenizer for 10 minutes. The dispersion and the polyimide P1 were added to a 50 mL screw tube to obtain a mixed solution. This mixed solution was stirred for 5 minutes and degassed twice. Next, Al(acac)3 and the mixed solution were further mixed, and the stirring and degassing procedures were repeated twice. The Al(acac)3 content was 6 wt% relative to the polyimide P1, and the porous particles were 10 wt% relative to the polyimide P1. In this way, a coating solution was prepared. The polyimide content in the coating solution was 10 wt%. The stirring and degassing procedures were performed using a Thinky Mixer. In the coating solution, the dissociative protons of the carboxyl groups contained in the polyimide were exchanged with aluminum cations. That is, the polyimide P1 contained aluminum salts of the carboxyl groups.

[0152] A coating film was obtained by applying the coating solution to a release liner (SCA0, manufactured by Fujiko Co., Ltd.). The release liner used here had been subjected to corona treatment under conditions of a discharge amount of 0.5 kW and a speed of 3 m / min. The coating gap was set to 50 to 100 μm so that the separation functional layer would have the desired thickness. This coating film was dried by heating at 130°C for 60 minutes to obtain the separation functional layer (freestanding film) of Example 1. In the comparative examples, the freestanding film was peeled off from the release liner and further heat-treated at 150°C for 30 minutes in a nitrogen atmosphere before use.

[0153] Example 2 The porous particles of Example 2 were synthesized as follows. 0.93 g (5.75 mmol) of FeCl3 (anhydrous) was added to 12.9 mL of 1,2-dichloroethane to obtain an FeCl3 solution. The FeCl3 solution was added to a solution of 1.00 g (5.71 mmol) of α,α'-dichloro-p-xylene dissolved in 12.9 mL of 1,2-dichloroethane. pDCX was synthesized by polymerization (Friedel-Crafts alkylation) at 25°C for 10 minutes. After washing with water, methanol, and diethyl ether in that order, brown powder was obtained by vacuum drying at 60°C for 8 hours. In this way, the porous particles (pDCX) of Example 2 were obtained. The specific surface area of ​​the porous particles was 1137 m 2 / g.

[0154] A separation functional layer (freestanding membrane) of Example 2 was produced in the same manner as in Example 1, except that the above porous particles were used.

[0155] (Comparative Example 1) A separation functional layer (self-supporting membrane) of Comparative Example 1 was produced in the same manner as in Example 1, except that porous particles were not added to the coating liquid.

[0156] (Comparative Example 2) A separation functional layer (freestanding membrane) of Comparative Example 2 was produced in the same manner as in Example 1, except that α-cyclodextrin (CD) (manufactured by Tokyo Chemical Industry Co., Ltd.) was used instead of the porous particles.

[0157] [Characteristics evaluation of the separation functional layer] (Gas permeation test) The carbon dioxide permeability coefficient C1 was measured for the separation functional layers of Examples 1 and 2 and Comparative Examples 1 and 2 using the following method. First, the separation functional layer was placed in a metal cell and sealed with an O-ring to prevent leakage. Next, a mixed gas was injected into the metal cell so that the mixed gas contacted one main surface of the separation functional layer. The mixed gas consisted essentially of carbon dioxide and nitrogen. The carbon dioxide concentration in the mixed gas was 50 vol% under standard conditions. The mixed gas injected into the metal cell had a temperature of 30°C and a pressure of 0.1 MPa. Next, the space within the metal cell adjacent to the other main surface of the separation functional layer was depressurized using a vacuum pump. At this time, the pressure in this space was depressurized so that the pressure within the space was 0.1 MPa lower than the atmospheric pressure in the measurement environment. As a result, a permeated fluid was obtained from the other main surface of the separation functional layer. The permeability coefficient C1 was calculated based on the composition and weight of the obtained permeated fluid.

[0158] (Durability test) The prepared separation functional layer was subjected to a durability test by storing it at 85°C for 500 hours. After the durability test, the carbon dioxide permeability coefficient C2 of the separation functional layer was measured using the same method as for the permeability coefficient C1, and the separation coefficient α2 was calculated.

[0159] [Table 1]

[0160] As can be seen from Table 1, the separation functional layers of Examples 1 and 2 exhibited higher values ​​of permeability coefficient C2 and were better than the separation functional layers of Comparative Example 1, which did not contain porous particles, and Comparative Example 2, which did not contain porous particles as an additive. Furthermore, the separation functional layers of Examples 1 and 2 also exhibited higher values ​​of permeability coefficient C1 and were better than the separation functional layers of Comparative Examples 1 and 2.

[0161] Example 3 First, polyimide P2 was synthesized using an automatic polymerization apparatus prepared in the same manner as in Example 1. 38.7 g of 1-methyl-2-pyrrolidone (super-dehydrated) as a solvent and 7.53 g (20 mmol) of 9,9-bis(3-methyl-4-aminophenyl)fluorene as a diamine were added to a flask. The mixture was stirred at room temperature to dissolve the diamine in the solvent. 5.36 g (20 mmol) of naphthalene-1,4,5,8-tetracarboxylic dianhydride (NTDA) as a tetracarboxylic dianhydride and 4.88 g (40 mmol) of benzoic acid were further added to the resulting solution. The jacket temperature of the apparatus was raised to 180°C, and the mixture was stirred for 8 hours. During this time, the internal temperature of the flask was 172 to 175°C. After stirring, the internal temperature of the flask was cooled to 25°C and allowed to stand overnight.

[0162] Next, 5.17 g (40 mmol) of isoquinoline was added, and the jacket temperature was raised again to 180 °C and stirred for 8 hours. After leaving the reaction solution overnight, 172 g of 1-methyl-2-pyrrolidone was added to dilute the reaction solution. Next, using a dropping funnel, 1000 mL of methanol was added dropwise to the reaction solution over approximately 30 minutes to perform reprecipitation purification. The precipitated polyimide was filtered and washed twice with 500 mL of methanol. After washing, the filtered polyimide was dried in a hot air circulation dryer at 60 °C for 15 hours and then further dried in a vacuum dryer at 100 °C for 8 hours. This yielded 11.4 g of polyimide P2.

[0163] In the same manner as in Example 2, porous particles (pDCX) of Example 3 were obtained.

[0164] A separation functional layer (freestanding membrane) of Example 3 was produced in the same manner as in Example 1, except that the above polyimide P2 and porous particles were used.

[0165] Example 4 The porous particles of Example 4 were synthesized as follows. First, pDCX was synthesized in the same manner as in Example 2. Next, 0.6 g of pDCX was mixed with 0.077 g (0.82 mmol) of phenol and 0.65 g (8.52 mmol) of dimethoxymethane in 19.5 mL of 1,2-dichloroethane and stirred for 10 minutes to prepare a pDCX mixed solution. Separately, 1.38 g (8.51 mmol) of (anhydrous) FeCl3 was added to 6 mL of 1,2-dichloroethane. The resulting FeCl3 solution was mixed with the pDCX mixed solution and reacted at 80°C for 8 hours. After cooling to room temperature, the resulting pDCX-OH was washed with water and methanol, then with diethyl ether, and then dried at 60°C for 8 hours. In this way, the porous particles (pDCX-OH) of Example 4 were obtained. The specific surface area of ​​the porous particles was 1101 m 2 / g.

[0166] A separation functional layer (freestanding membrane) of Example 4 was produced in the same manner as in Example 3, except that the above porous particles were used.

[0167] Example 5 The porous particles of Example 5 were synthesized as follows. First, pDCX was synthesized in the same manner as in Example 2. Next, 0.6 g of pDCX, 0.16 g (1.74 mmol) of aniline, and 0.64 g (8.40 mmol) of dimethoxymethane were added to 19.5 mL of 1,2-dichloroethane and stirred for 10 minutes to prepare a pDCX mixed solution. Separately, 1.36 g (8.50 mmol) of (anhydrous) FeCl3 was added to 6 mL of 1,2-dichloroethane to prepare an FeCl3 solution. The FeCl3 solution and the pDCX mixed solution were mixed and reacted at 80°C for 8 hours. After cooling to room temperature, the obtained pDCX-NH2 was washed with water and methanol, and then further washed with diethyl ether, and then dried at 60°C for 8 hours. In this way, the porous particles (pDCX-NH2) of Example 5 were obtained. The specific surface area of ​​the porous particles was 750 m 2 / g.

[0168] A separation functional layer (freestanding membrane) of Example 5 was produced in the same manner as in Example 3, except that the above porous particles were used.

[0169] Example 6 The porous particles of Example 6 were synthesized as follows. 0.93 g (5.75 mmol) of FeCl3 (anhydrous) was added to 12.9 mL of 1,2-dichloroethane to obtain a solution. The above FeCl3 solution was added to a solution prepared by dissolving 0.50 g (2.86 mmol) of α,α'-dichloro-p-xylene and 0.62 g (2.86 mmol) of 2,4-bis(chloromethyl)-1,3,5-trimethylbenzene in 12.9 mL of 1,2-dichloroethane. p(DCX-co-TMDCX) was synthesized by polymerization (Friedel-Crafts alkylation) at 25 °C for 10 minutes. After washing with water, methanol, and diethyl ether, the particles were dried in vacuum at 60 °C for 8 hours to obtain a brown powder. In this manner, the porous particles of Example 6 (p(DCX-co-TMDCX)) were obtained.

[0170] A separation functional layer (freestanding membrane) of Example 6 was produced in the same manner as in Example 3, except that the above porous particles were used.

[0171] Example 7 The porous particles of Example 7 were synthesized as follows. 0.93 g (5.75 mmol) of FeCl3 (anhydrous) was added to 12.9 mL of 1,2-dichloroethane to obtain an FeCl3 solution. The FeCl3 solution was added to a solution of 0.50 g (2.86 mmol) of α,α'-dichloro-p-xylene and 0.52 g (2.86 mmol) of 4-tert-butylbenzyl chloride dissolved in 12.9 mL of 1,2-dichloroethane. p(DCX-co-tBuBnC) was synthesized by polymerization (Friedel-Crafts alkylation) at 25 °C for 10 minutes. After washing with water, methanol, and diethyl ether, the resulting product was vacuum-dried at 60 °C for 8 hours to obtain a brown powder. Thus, the porous particles of Example 7 (p(DCX-co-tBuBnC)) were obtained.

[0172] A separation functional layer (freestanding membrane) of Example 7 was produced in the same manner as in Example 3, except that the above porous particles were used.

[0173] (Comparative Example 3) A separation functional layer (freestanding film) of Comparative Example 3 was produced in the same manner as in Example 3, except that porous particles were not added to the coating liquid.

[0174] [Characteristics evaluation of the separation functional layer] (Gas permeation test) The carbon dioxide permeability coefficient C3 was measured for the separation functional layers of Examples 3 to 7 and Comparative Example 3 using the following method. First, the separation functional layer was placed in a metal cell and sealed with an O-ring to prevent leakage. Next, a mixed gas was injected into the metal cell so that the mixed gas contacted one main surface of the separation functional layer. The mixed gas consisted essentially of carbon dioxide and methane. The carbon dioxide concentration in the mixed gas was 50 vol% under standard conditions. The mixed gas injected into the metal cell had a temperature of 30°C and a pressure of 0.1 MPa. Next, the space within the metal cell adjacent to the other main surface of the separation functional layer was depressurized using a vacuum pump. At this time, the pressure in this space was depressurized so that the pressure within the space was 0.1 MPa lower than the atmospheric pressure in the measurement environment. As a result, a permeated fluid was obtained from the other main surface of the separation functional layer. The permeability coefficient C3 was calculated based on the composition and weight of the obtained permeated fluid.

[0175] (Durability test) For the separation functional layers of Examples 3 to 7 and Comparative Example 3, durability tests were conducted using the same method as in Example 1, and then the carbon dioxide permeability coefficient C4 was measured using the same method as for the permeability coefficient C3, and the separation coefficient α4 was calculated.

[0176] [Table 2]

[0177] As can be seen from Table 2, the separation functional layers of Examples 3 to 7 exhibited higher values ​​of permeability coefficient C4 and were better than the separation functional layer of Comparative Example 3, which did not contain porous particles. Furthermore, the separation functional layers of Examples 3 to 7 also exhibited higher values ​​of permeability coefficient C3 and were better than the separation functional layer of Comparative Example 3.

[0178] From the above results, it can be said that the separation functional layer of this embodiment is suitable for separating acidic gases from a mixed gas containing acidic gases. [Industrial Applicability]

[0179] The separation functional layer and separation membrane of this embodiment are suitable for separating acidic gases from a gas mixture containing acidic gases, and in particular, for separating carbon dioxide from off-gas from a chemical plant or thermal power plant. [Explanation of symbols]

[0180] 1 Separation functional layer 2. Middle class 3 Porous support 10 Separation membrane 100,110 Membrane separation equipment

Claims

1. A separation functional layer containing polyimide and porous particles, The polyimide contains a structural unit A1 derived from a tetracarboxylic dianhydride having a six-membered ring acid anhydride structure.

2. The separation functional layer according to claim 1 , wherein the porous particles include an organic polymer.

3. The separation functional layer according to claim 2 , wherein the organic polymer contains an aromatic ring.

4. The separation functional layer according to claim 3 , wherein the organic polymer is a porous polymer.

5. The separation functional layer according to claim 1 , wherein the porous particles are surface-modified.

6. The separation functional layer according to claim 1 , wherein the content of the porous particles is 5% by weight or more and 50% by weight or less with respect to the polyimide.

7. The separation functional layer according to claim 1 , wherein the structural unit A1 is represented by the following formula (A1): 【Chemical 1】 In the formula (A1), R 1a ~R 4a are each independently a hydrogen atom or an optional substituent.

8. The separation functional layer according to claim 1 , which is used to separate an acidic gas from a gas mixture containing the acidic gas.

9. The separation functional layer according to any one of claims 1 to 8, a porous support supporting the separation functional layer; A separation membrane comprising:

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