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. The polyimide P includes a structural unit A1 derived from a tetracarboxylic dianhydride having a six-membered acid anhydride structure and a structural unit B1 represented by the following formula (B1) derived from a diamine. In formula (B1), R1b-R8b are each independently a hydrogen atom or an optional substituent (excluding cases where all of R1b-R8b are hydrogen atoms and where R2b, R3b, R6b, and R7b are methyl groups and R1b, R4b, R5b, and R8b are hydrogen atoms), Ar1 and Ar2 are each independently an aromatic ring, and X1 is a single bond or an optional linking group.SELECTED DRAWING: None

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, The polyimide includes a structural unit A1 derived from a tetracarboxylic dianhydride having a six-membered ring acid anhydride structure and a structural unit B1 derived from a diamine, The structural unit B1 provides a separation functional layer represented by the following formula (B1). [ka] In the formula (B1), R 1b ~R 8b are each independently a hydrogen atom or an arbitrary substituent (provided that R 1b ~R 8b are all hydrogen atoms, and R 2b , R 3b , R 6b , and R 7b is a methyl group, and R 1b , R 4b , R 5b , and R 8b is a hydrogen atom), Ar 1 and Ar 2 are, independently of each other, aromatic rings, and X 1 is a single bond or any linking group.

[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, The polyimide includes a structural unit A1 derived from a tetracarboxylic dianhydride having a six-membered ring acid anhydride structure and a structural unit B1 derived from a diamine, The structural unit B1 is represented by the following formula (B1). [ka] In the formula (B1), R 1b ~R 8b are each independently a hydrogen atom or an arbitrary substituent (provided that R 1b ~R 8b are all hydrogen atoms, and R 2b , R 3b , R 6b , and R 7b is a methyl group, and R 1b , R 4b , R 5b , and R 8b is a hydrogen atom), Ar 1 and Ar 2 are, independently of each other, aromatic rings, and X 1 is a single bond or any linking group.

[0011] In the second embodiment of the present invention, for example, in the separation functional layer according to the first embodiment, in the formula (B1), R 2b and R 3b and are different from each other, and R 6b and R 7b are different from each other.

[0012] In a third aspect of the present invention, for example, in the separation functional layer according to the first or second aspect, in the formula (B1), the optional substituent is a hydrocarbon group which may have a substituent, or a halogen group.

[0013] In a fourth aspect of the present invention, for example, in the separation functional layer according to the third aspect, the hydrocarbon group in the formula (B1) is an alkyl group.

[0014] In the fifth aspect of the present invention, for example, in the separation functional layer according to any one of the first to fourth aspects, in the formula (B1), Ar 1 and Ar 2 is an optionally substituted benzene ring, and X 1 is a single bond.

[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, in the polyimide, the ratio of the amount of substance of the structural unit B1 to the amount of substance of all structural units B derived from diamines is 50 mol % or more.

[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. 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 and a structural unit B1 derived from a diamine b1. Note that, 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 B1 derived from a diamine b1. The structural unit B1 is a structural unit suitable for improving the separation performance (particularly the permeation rate of acidic gases) of the separation functional layer 1. The diamine b1 is a compound having two primary amino groups and is represented by the following formula (b1): [ka]

[0031] In formula (b1), R 1b ~R 8b are each independently a hydrogen atom or an arbitrary substituent (provided that R 1b ~R 8b are all hydrogen atoms, and R 2b , R 3b , R 6b , and R 7b is a methyl group, and R 1b, R 4b , R 5b , and R 8b is a hydrogen atom), Ar 1 and Ar 2 are, independently of each other, aromatic rings, and X 1 is a single bond or any linking group.

[0032] Typically, Ar 1 In X 1 and the quaternary carbon atom (the two amino group-containing benzene rings in b1, Ar 1 , and Ar 2 The carbon atom bonded to the Ar group and the atom bonded to the Ar group are adjacent in the ring structure. 2 In X 1 and the atom bonded to the quaternary carbon atom are adjacent in the ring structure.

[0033] In formula (b1), the optional substituent is preferably a hydrocarbon group which may have a substituent or a halogen group, and more preferably a hydrocarbon group which may have a substituent. The hydrocarbon group may be a halogenated hydrocarbon in which a hydrogen atom is substituted with a halogen group, or it may be unsubstituted. The hydrocarbon group is preferably an alkyl group. Therefore, in formula (b1), the optional substituent is more preferably an alkyl group. The hydrocarbon group has, for example, 1 to 15 carbon atoms, preferably 1 to 10, more preferably 1 to 5, and even more preferably 1 to 3 carbon atoms. Examples of the alkyl group include those described above as the hydrocarbon group for tetracarboxylic dianhydride a1. Examples of the halogen group include those described above as the hydrocarbon group for tetracarboxylic dianhydride a1.

[0034] In formula (b1), the optional 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.

[0035] The structural unit B1 derived from diamine b1 is represented by the following formula (B1): Therefore, in the separation functional layer 1 of this embodiment, the polyimide P contains the structural unit B1 represented by the following formula (B1): The structural unit B1 represented by formula (B1) is derived from the diamine b1 represented by the above formula (b1). [ka]

[0036] In formula (B1), R 1b ~R 8b are each independently a hydrogen atom or an arbitrary substituent (provided that R 1b ~R 8b are all hydrogen atoms, and R 2b , R 3b , R 6b , and R 7b is a methyl group, and R 1b , R 4b , R 5b , and R 8b is a hydrogen atom), Ar 1 and Ar 2 are, independently of each other, aromatic rings, and X 1 is a single bond or any linking group. That is, R in formula (B1) 1b ~R 6b , Ar 1 , Ar 2 and X 1 is the same as formula (b1). Typically, Ar 1 In X 1 and the quaternary carbon atom (the two amino group-containing benzene rings in b1, Ar 1 , and Ar2 The carbon atom bonded to the Ar group and the atom bonded to the Ar group are adjacent in the ring structure. 2 In X 1 The atom bonded to the quaternary carbon atom is adjacent to the atom bonded to the quaternary carbon atom in the ring structure. The optional substituent is preferably an optionally substituted hydrocarbon group or a halogen group, more preferably an optionally substituted hydrocarbon group. The halogen group and hydrocarbon group are as described above. The optional substituent is preferably an alkyl group.

[0037] In formulas (b1) and (B1), R 2b , R 3b , R 6b , and R 7b It is preferable that at least two selected from the group consisting of are different from each other. For example, R 2b and R 3b and are different from each other, and R 6b and R 7b and may be different from each other. 2b and R 3b one of them may be a hydrogen atom and the other may be an alkyl group, and R 6b and R 7b One of R may be a hydrogen atom and the other may be an alkyl group. 2b and R 7b and are different from each other, and R 3b and R 6b and may be different from each other. 2b and R 7b one of them may be a hydrogen atom and the other may be an alkyl group, and R 3b and R 6b One of R may be a hydrogen atom and the other may be an alkyl group. 2b and R 6b may be the same as each other, and R 3b and R 7b may be the same as each other.

[0038] In formula (b1) and formula (B1), R 1b , R 4b , R5b and R 8b may be the same as each other. 1b , R 4b , R 5b and R 8b is preferably a hydrogen atom.

[0039] In formulas (b1) and (B1), Ar 1 and Ar 2 The aromatic ring represented by the formula (I) may be composed only of carbon atoms and hydrogen atoms, or may be a heteroaromatic ring containing heteroatoms such as oxygen atoms, nitrogen atoms, and sulfur atoms. 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, with a benzene ring being preferred. The aromatic ring may or may not have a substituent.

[0040] In formulas (b1) and (B1), X 1 is preferably a single bond.

[0041] Diamine b1 may or may not contain a functional group other than a primary amino group. Diamine b1 may or may not contain at least one functional group f selected from the group consisting of a carboxyl group, a hydroxyl group, and a thiol group. The optional substituent other than the group containing functional group f is not particularly limited, and examples thereof include a halogen group and a hydrocarbon group. In diamine b1, the other substituent may contain a photopolymerizable functional group (e.g., a vinyl group).

[0042] Diamine b1 is preferably represented by the following formula (b2): Formula (b2) is an example of the above formula (b1). [ka]

[0043] In formula (b2), R1b ~R 16b are each independently a hydrogen atom or any substituent (provided that R 1b ~R 8b are all hydrogen atoms, and R 2b , R 3b , R 6b , and R 7b is a methyl group, and R 1b , R 4b , R 5b , and R 8b (Except when R is a hydrogen atom.) 9b ~R 16b At least one selected from the group consisting of may be a substituent containing a functional group f. Any substituent other than the group containing the functional group f is preferably a hydrocarbon group or a halogen group. The halogen group and the hydrocarbon group are as described above.

[0044] The structural unit B1 is preferably represented by the following formula (B2): Formula (B2) is an example of the above formula (B1), and is derived from diamine b1 represented by the above formula (b2). [ka]

[0045] In formula (B2), R 1b ~R 16b are each independently a hydrogen atom or any substituent (provided that R 1b ~R 8b are all hydrogen atoms, and R 2b , R 3b , R 6b , and R 7b is a methyl group, and R 1b , R 4b , R 5b , and R 8b is a hydrogen atom). The optional substituents are as defined above.

[0046] In formula (B2), R 2b , R 3b , R 6b , and R 7bIt is preferable that at least two selected from the group consisting of are different from each other. For example, R 2b and R 3b and are different from each other, and R 6b and R 7b and may be different from each other. 2b and R 3b one of them may be a hydrogen atom and the other may be an alkyl group, and R 6b and R 7b One of R may be a hydrogen atom and the other may be an alkyl group. 2b and R 7b and are different from each other, and R 3b and R 6b and may be different from each other. 2b and R 7b one of them may be a hydrogen atom and the other may be an alkyl group, and R 3b and R 6b One of R may be a hydrogen atom and the other may be an alkyl group. 2b and R 6b may be the same as each other, and R 3b and R 7b may be the same as each other. 1b , R 4b , R 5b and R 8b may be the same as each other, and are preferably hydrogen atoms. 9b ~R 16b At least one selected from the group consisting of a carboxyl group, The substituent may be a substituent containing at least one functional group F selected from the group consisting of a hydroxyl group, a thiol group, and metal salts thereof. Any substituent other than the group containing the functional group F is preferably a hydrocarbon group or a halogen group. The halogen group and the hydrocarbon group are as described above.

[0047] 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 specifically exists 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.

[0048] When the structural unit B1 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. For example, when the diamine b1 contains the functional group f, the metal salt as the functional group F can be formed 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 the tetracarboxylic dianhydride a1 and the diamine b1.

[0049] R in formulas (b2) and (B2) 1b ~R 8b In formula (b1) and (B1), R 1b ~R 8b The explanation given for is applicable.

[0050] In formula (B2), the fluorene ring tends to be arranged in a twisted direction relative to the two benzene rings due to steric hindrance. For example, in formula (B2), the fluorene ring extends from the front to the back of the paper. Thus, in formula (B2), the extending direction of the fluorene ring and the extending direction of the main chain of polyimide P are different from each other, and it is preferable that these directions are perpendicular to each other.

[0051] Specific examples of the structural unit B1 represented by formula (B2) include the following formulae (B2-1) to (B2-6). [ka]

[0052] The polyimide P may contain a single type of structural unit B1, or may contain multiple types of structural units B1. That is, the polyimide P may contain a structural unit B1 derived from a single type of diamine b1, or may contain structural units B1 derived from multiple types of diamine b1. Note that the diamine b1 and the structural unit B1 are not limited to those described above.

[0053] In the polyimide P, the ratio p2 of the amount of substance of the structural unit B1 to the amount of substance of all structural units B derived from diamines 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. The polyimide P may contain only the structural unit B1 as the structural unit B derived from diamines. However, the polyimide P may further contain, in addition to the structural unit B1, a structural unit B2 derived from a diamine b2 different from the diamine b1. The diamine b2 typically does not have a cardo structure.

[0054] Diamine b2 may be represented by the following formula (c1), formula (c2), formula (c3), formula (c4) or formula (c5). [ka]

[0055] In formulas (c1) to (c5), R 1c ~R 30c 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.

[0056] In formulas (c3) and (c4), X 2 and X 3 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. X 2 and X 3 may contain a functional group such as an ether group or an ester group in addition to or instead of the divalent hydrocarbon group.

[0057] The structural unit B2 derived from diamine b2 may have a functional group F. The functional group F is as described for diamine b1.

[0058] The structural unit B2 derived from diamine b2 is represented, for example, by the following formula (C1), (C2), (C3), (C4) or (C5): The structural units B represented by formulas (C1) to (C5) are derived from the diamines represented by the above formulas (c1) to (c5), respectively. [ka]

[0059] In formula (C1), R 1c ~R 4c are each independently a hydrogen atom or an arbitrary substituent. In formula (C1), 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.

[0060] Specific examples of the structural unit B2 represented by formula (C1) include the following formulae (C1-1) to (C1-7): In these formulae, M represents any metal cation. [ka]

[0061] In formula (C2), R 5c ~R 8c are each independently a hydrogen atom or an arbitrary substituent. In formula (C2), 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. Specific examples of the structural unit B represented by formula (C2) include the following formula (C2-1). [ka]

[0062] In formula (C3), R 9c ~R 16c are each independently a hydrogen atom or an arbitrary substituent, and X 2 is a single bond or an arbitrary linking group. In formula (C3), 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.

[0063] X in formula (C3) 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.

[0064] Specific examples of the structural unit B2 represented by formula (C3) include the following formulae (C3-1) to (C3-13): In these formulae, M represents any metal cation. [ka]

[0065] In formula (C4), R 17c ~R 24c are each independently a hydrogen atom or an arbitrary substituent, and X 3 is a single bond or an arbitrary linking group. In formula (C4), 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.

[0066] X in formula (C4) 3 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 3 may contain a functional group such as an ether group or an ester group in addition to or instead of the divalent hydrocarbon group.

[0067] Specific examples of the structural unit B represented by formula (C4) include the following formulae (C4-1) to (C4-6): In these formulae, M represents any metal cation. [ka]

[0068] In formula (C5), R 25c ~R 30c are each independently a hydrogen atom or an arbitrary substituent. In formula (C5), 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 B2 represented by formula (C5) 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.

[0069] Specific examples of the structural unit B2 represented by formula (C5) include the following formulae (C5-1) and (C5-2). [ka]

[0070] In polyimide P, structural units A derived from tetracarboxylic dianhydride and structural units B derived from diamine are arranged alternately. In polyimide P, examples of the combination of adjacent structural units A and B include the following formula (A1-B2). In this formula, R 1a ~R 4a , R 1b ~R 4b is the same as described above for formula (A1) and formula (B2). [ka]

[0071] 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, 300,000. 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).

[0072] 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 100 wt% or less. The separation functional layer 1 may be composed essentially of polyimide P only.

[0073] The separation functional layer 1 may further contain other components in addition to polyimide P. Examples of 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.

[0074] 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, or even 20 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.

[0075] (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 onto a substrate to form a coating film, and drying the coating film to form the separation functional layer 1.

[0076] Polyimide P can be prepared by the following method. First, a diamine group including the diamine b1 is dissolved in a solvent to obtain a solution. Examples of the solvent include N-methyl-2-pyrrolidone, nitrobenzene, benzonitrile, α-chloronaphthalene, phenol, m-cresol, and p-chlorophenol.

[0077] Next, tetracarboxylic dianhydrides including the tetracarboxylic dianhydride a1 are gradually added to the resulting solution. This causes a reaction between the tetracarboxylic dianhydride a1 and 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. Polyimide P can be obtained by imidizing the polyamic acid. 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. The polyamic acid formation reaction and the imidization of polyamic acid may proceed in parallel. The polyimide P formation reaction (imidization) may be carried out in the presence of a catalyst that promotes polyimide formation. Such catalysts include, for example, aromatic carboxylic acids such as benzoic acid and p-hydroxybenzoic acid, and aromatic amines such as isoquinoline.

[0078] 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 %.

[0079] The coating liquid preferably further contains a solvent. The solvent is typically a good solvent capable of dissolving polyimide P. Examples of the solvent include amide compounds, lactone compounds, 1,3-dioxolane, nitrobenzene, benzonitrile, α-chloronaphthalene, phenol, m-cresol, and p-chlorophenol. 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 the amide compound include N,N-dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), and N,N-dimethylacetamide (DMAc). Examples of the lactone compound include γ-butyrolactone.

[0080] The content of the solvent in the coating liquid is not particularly limited, and is, for example, 30 wt % to 99 wt %.

[0081] The substrate to which the coating liquid containing polyimide P is applied is typically a release liner or glass. Examples of the substrate include soda glass; a film containing a resin; paper; and a sheet containing a metal material such as aluminum or stainless steel. Sheets containing metal materials tend to have high heat resistance. In terms of excellent surface smoothness, the substrate is preferably a film containing a resin or a laminate of such a film and soda glass. 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.

[0082] 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.

[0083] The thickness of the substrate is not particularly limited and is, for example, 5 to 100 μm, and preferably 10 to 50 μm.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] The temperature of the heat treatment may be, for example, higher than 200°C, 230°C or higher, or even 250°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.

[0091] 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.

[0092] 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.

[0093] (Characteristics of the separation functional layer) As described above, it is preferable that the separation functional layer 1 preferentially permeates the acidic gas contained in the mixed gas. As an example, when a mixed gas consisting of carbon dioxide and methane is supplied to a space adjacent to one surface of the separation functional layer 1, the permeation rate T of carbon dioxide permeating the separation functional layer 1 is CO2 is, for example, 30 GPU or more, and may be 40 GPU or more, 50 GPU or more, 100 GPU or more, or even 200 GPU or more. CO2 The upper limit is not particularly limited, and is, for example, 1000 GPUs. -6 ·cm 3 (STP) / (sec cm 2 ·cmHg).

[0094] As an example, the permeability coefficient C of carbon dioxide passing through the separation functional layer 1 when a mixed gas consisting of carbon dioxide and methane is supplied to a space adjacent to one surface of the separation functional layer 1 is taken into consideration. CO2 is, for example, 300 Barrer or more, and may be 500 Barrer or more, 550 Barrer or more, or even 700 Barrer or more. CO2 The upper limit of the value is not particularly limited, and is, for example, 5000 Barrer. -10 ·cm 3 (STP)·cm / (sec·cm 2 cm 3 (STP) means the volume of carbon dioxide at 1 atmosphere and 0°C. CO2 [Barrer] is the permeation rate T CO2 This is the value obtained by multiplying [GPU] by the thickness (μm) of the separation functional layer 1.

[0095] As described above, the separation functional layer 1 of this embodiment contains polyimide P containing structural units B1 derived from diamine b1. This separation functional layer 1 has an excellent permeation rate and permeation coefficient for acidic gases.

[0096] Permeability coefficient C CO2 and permeation rate T CO2 can be determined by the following method. First, a mixed gas consisting of carbon dioxide and methane is supplied to the space adjacent to one surface of the separation functional layer 1, and the pressure in the space adjacent to the other surface of the separation functional layer 1 is reduced. This results in a permeated fluid that has permeated 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 methane in the permeated fluid, are measured. From the measurement results, the permeation coefficient C CO2 and permeation rate T CO2 can be calculated. In the above operation, the concentration of carbon dioxide 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 decompressed so that the pressure within the space is 0.1 MPa lower than the atmospheric pressure in the measurement environment.

[0097] The above transmission coefficient C CO2 and permeation rate T CO2 Under the measurement conditions, the separation coefficient α of the separation functional layer 1 for carbon dioxide relative to methane is not particularly limited, and may be, for example, 15 or more, or 20 or more. The upper limit of the separation coefficient α is not particularly limited, and may be, for example, 100 or 60. The separation coefficient α can be calculated from the following formula. In the following formula, the permeation rate T CH4 is the transmission coefficient C CO2 and permeation rate T CO2 This is the permeation rate of methane that permeates through the separating functional layer 1 under the measurement conditions. Separation coefficient α = permeation rate T CO2 / transmission rate T CH4

[0098] (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 also contains other gases besides 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 methane. However, the use of the separation functional layer 1 is not limited to separating acidic gases from the above-mentioned gas mixture.

[0099] <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.

[0100] (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.

[0101] 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.

[0102] 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.

[0103] 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]

[0104] 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.

[0105] 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]

[0106] 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.

[0107] 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.

[0108] In the nanoparticles, the surface modified with the modifying group is preferably represented by the following formula (V). [ka]

[0109] 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.

[0110] 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 hydroxy 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.

[0111] 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.

[0112] 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%.

[0113] 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.

[0114] (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.

[0115] 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.

[0116] (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.

[0117] 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.

[0118] 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.

[0119] (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.

[0120] <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.

[0121] 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.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] <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.

[0129] 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.

[0130] 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).

[0131] 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).

[0132] 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]

[0133] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0134] [Fabrication of separation functional layer] Example 1 First, polyimide synthesis was performed using an automated polymerization apparatus (Mettler-Toledo, EasyMax 402). The attached separable flask (400 mL capacity) was equipped with a Dimroth tube, a stirrer, an internal thermometer, a nitrogen inlet tube, and a flat stopper. A Dimroth chiller was used to circulate a coolant set at 10 °C. N2 gas was passed through the flask at a flow rate of 100 mL / min. The stirring speed was set at 300 rpm. Next, 38.7 g of 1-methyl-2-pyrrolidone (superhydrous) (NMP) as the solvent and 7.53 g (20 mmol) of 9,9-bis(3-methyl-4-aminophenyl)fluorene (hereinafter referred to as "diamine 1") as the diamine were added to the flask. The mixture was stirred at room temperature to dissolve the diamine in the solvent. To the resulting solution, 5.36 g (20 mmol) of naphthalene-1,4,5,8-tetracarboxylic dianhydride (NTDA) and 4.88 g (40 mmol) of benzoic acid were further added as tetracarboxylic dianhydride. The jacket temperature of the apparatus was raised to 180°C, and the mixture was stirred for 8 hours. Due to an increase in the viscosity of the reaction mixture, 12.9 g of NMP was added 30 minutes after the start of the temperature increase, and 21.5 g of NMP was added 1 hour after the temperature increase. 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.

[0135] 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 to stand overnight, 172 g of NMP was added to dilute the reaction solution. Next, using a dropping funnel, 450 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 150 mL of methanol. After washing, the filtered polyimide was dried in a hot air circulation dryer at 60°C for 24 hours. This yielded 11.4 g of polyimide.

[0136] Next, the prepared polyimide was dissolved in NMP to prepare a coating solution. The ratio of polyimide in the coating solution was 10 wt%. A coating film was obtained by applying the coating solution to soda glass. The coating film had a thickness of 250 μm. This coating film was heated and dried at 130°C for 60 minutes. After peeling the coating film from the soda glass, it was further heated at 300°C for 30 minutes in a nitrogen atmosphere to obtain the separation functional layer (freestanding film) of Example 1. The separation functional layer of Example 1 had a thickness of 15.7 μm.

[0137] Example 2 A polyimide was prepared in the same manner as in Example 1, and a coating solution was prepared. Next, a substrate was prepared by attaching a release liner (manufactured by Fujiko, PI-50-SCA0) that had been corona-treated (0.5 kW, 3 m / min) to soda glass. The coating solution was placed on the release liner, and a coating film was formed using a spin coater (1000 rpm, 30-second rotation). The coating film was dried at 130°C for 1 hour and then further heat-treated at 300°C for 30 minutes in a nitrogen atmosphere, yielding a separation functional layer (freestanding film) for Example 2. The thickness of the separation functional layer for Example 2 was 1.8 μm. This freestanding film was peeled off from the release liner and used.

[0138] Example 3 A polyimide was prepared and a coating solution was obtained in the same manner as in Example 1, except that the diamine was changed to 12.13 g (30 mmol) of 9,9-bis(3-ethyl-4-aminophenyl)fluorene (hereinafter sometimes referred to as "diamine 2") and the amount of naphthalene-1,4,5,8-tetracarboxylic dianhydride (NTDA) added was changed to 8.05 g (30 mmol). A separation functional layer (freestanding membrane) of Example 3 was obtained in the same manner as in Example 1, except that the above coating solution was used. The thickness of the separation functional layer of Example 3 was 18.7 μm.

[0139] Example 4 A polyimide was produced and a coating solution was prepared in the same manner as in Example 3. Except for using the above coating solution, a separation functional layer (freestanding film) of Example 4 was produced in the same manner as in Example 2. The thickness of the separation functional layer of this example was 1.4 μm.

[0140] Example 5 A polyimide was prepared and a coating solution was obtained in the same manner as in Example 1, except that the diamine was changed to 7.53 g (20 mmol) of diamine 1 and 8.09 g (20 mmol) of diamine 2, and the amount of naphthalene-1,4,5,8-tetracarboxylic dianhydride (NTDA) added was changed to 10.72 g (40 mmol). A separation functional layer (freestanding membrane) of Example 5 was obtained in the same manner as in Example 1, except that the above coating solution was used. The thickness of the separation functional layer of Example 3 was 12.0 μm.

[0141] Example 6 A polyimide was produced and a coating solution was prepared in the same manner as in Example 5. A separation functional layer (freestanding film) of Example 6 was produced in the same manner as in Example 2, except that the above coating solution was used. The thickness of the separation functional layer of this example was 2.2 μm.

[0142] (Comparative Example 1) A polyimide was prepared in the same manner as in Example 1, except that the diamine was changed to 10.45 g (30 mmol) of 9,9-bis(4-aminophenyl)fluorene (hereinafter sometimes referred to as "diamine 3") and the amount of naphthalene-1,4,5,8-tetracarboxylic dianhydride (NTDA) added was changed to 8.05 g (30 mmol). When an attempt was made to prepare a coating solution containing the prepared polyimide, the polyimide did not dissolve in the solvent, and the coating solution could not be prepared. Therefore, a separation functional layer could not be prepared.

[0143] (Comparative Example 2) A polyimide was prepared in the same manner as in Example 1, except that the diamine was changed to 12.20 g (30 mmol) of 9,9-bis(3,5-dimethyl-4-aminophenyl)fluorene (hereinafter sometimes referred to as "diamine 4") and the amount of naphthalene-1,4,5,8-tetracarboxylic dianhydride (NTDA) added was changed to 8.05 g (30 mmol). When an attempt was made to prepare a coating solution containing the prepared polyimide, the polyimide did not dissolve in the solvent, and the coating solution could not be prepared. Therefore, a separation functional layer could not be prepared.

[0144] (Comparative Example 3) The same automatic polymerization apparatus as in Example 1 was used. 58.4 g of NMP as a solvent and 10.45 g (30 mmol) of 9,9-bis(4-aminophenyl)fluorene (diamine 3) as a diamine were added to a flask. The mixture was stirred at room temperature to dissolve the diamine in the solvent. 9.00 g (30 mmol) of 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic anhydride (hereinafter sometimes referred to as "13912-65-7") as a tetracarboxylic dianhydride and 7.32 g (60 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. 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.

[0145] Next, 7.75 g (60 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 to stand overnight, 51.9 g of NMP was added to dilute the reaction solution. Next, using a dropping funnel, 600 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 200 mL of methanol. After washing, the filtered polyimide was dried in a hot air circulation dryer at 60°C for 15 hours. This yielded 17.7 g of polyimide.

[0146] Using the prepared polyimide, a coating solution was prepared in the same manner as in Example 1. Except for using the above coating solution, a separation functional layer (freestanding film) of Comparative Example 3 was obtained in the same manner as in Example 1. The thickness of the separation functional layer of Comparative Example 3 was 17.1 μm.

[0147] [Characteristics evaluation of the separation functional layer] (Gas permeation test) The carbon dioxide permeation rate T for the separating functional layers of Examples 1 to 6 and Comparative Example 3 was measured by the following method. CO2 , the transmission coefficient C CO2 The separation coefficient α of carbon dioxide relative to methane was measured. First, the separation functional layer was set 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 in 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 in 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. Based on the composition, weight, etc. of the obtained permeated fluid, the permeation rate T CO2 , the transmission coefficient C CO2 and the separation factor α was calculated.

[0148] [Table 1]

[0149] The abbreviations in Table 1 are as follows: NTDA: naphthalene-1,4,5,8-tetracarboxylic dianhydride (in formula (a1), R 1a ~R 4a is a hydrogen atom) 13912-65-7: 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic acid anhydride (a tetracarboxylic acid dianhydride with a five-membered ring structure) Diamine 1: 9,9-bis(3-methyl-4-aminophenyl)fluorene (in formula (b2), R 3b and R 7b is a methyl group, and R 1b , R 2b , R 4b ~R 6b , and R 8b ~R 16b is a hydrogen atom) Diamine 2: 9,9-bis(3-ethyl-4-aminophenyl)fluorene (in formula (b2), R 3b and R 7b is an ethyl group, and R 1b , R 2b , R 4b ~R 6b , and R 8b ~R 16b is a hydrogen atom) Diamine 3: 9,9-bis(4-aminophenyl)fluorene (in formula (b2), R 1b ~R 16b is a hydrogen atom) Diamine 4: 9,9-bis(3,5-dimethyl-4-aminophenyl)fluorene (in formula (b2), R 2b , R 3b , R 6b , and R 7b is a methyl group, and R 1b , R 4b , R 5b , and R 8b ~R 16b is a hydrogen atom)

[0150] As can be seen from Table 1, the separation functional layers of Examples 1 to 6 had a higher permeation rate T CO2 , the transmission coefficient C CO2and the separation factor α showed high values, which were favorable. From these 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.

[0151] As described above, with the polyimide compositions of Comparative Examples 1 and 2, it was not possible to prepare a separation functional layer. [Industrial Applicability]

[0152] 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 biogas. [Explanation of symbols]

[0153] 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, The polyimide includes a structural unit A1 derived from a tetracarboxylic dianhydride having a six-membered ring acid anhydride structure and a structural unit B1 derived from a diamine, The structural unit B1 is a separation functional layer represented by the following formula (B1). 【Chemical 1】 In the formula (B1), R 1b ~R 8b are each independently a hydrogen atom or an arbitrary substituent (provided that R 1b ~R 8b are all hydrogen atoms, and R 2b , R 3b , R 6b , and R 7b is a methyl group, and R 1b , R 4b , R 5b , and R 8b is a hydrogen atom), Ar 1 and Ar 2 are each independently an aromatic ring, and X 1 is a single bond or any linking group.

2. In the formula (B1), R 2b and R 3b and are different from each other, and R 6b and R 7b The separation functional layer according to claim 1 , wherein

3. The separation functional layer according to claim 1 , wherein in formula (B1), the arbitrary substituent is a hydrocarbon group which may have a substituent, or a halogen group.

4. The separation functional layer according to claim 3 , wherein in the formula (B1), the hydrocarbon group is an alkyl group.

5. In the formula (B1), Ar 1 and Ar 2 is a benzene ring which may have a substituent, and X 1 The separation functional layer according to claim 1 , wherein is a single bond.

6. 2. The separation functional layer according to claim 1, wherein in the polyimide, the ratio of the amount of substance of the structural unit B1 to the amount of substance of all structural units B derived from diamines is 50 mol % or more.

7. The separation functional layer according to claim 1 , wherein the structural unit A1 is represented by the following formula (A1): 【Chemistry 2】 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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