WO2024195265A1 - Separation functional layer, separation membrane, and method for producing separation functional layer - Google Patents

Abstract

The present invention provides a novel separation functional layer suitable for the separation of an acidic gas from a mixed gas containing the acidic gas. A separation functional layer 1 according to the present invention contains a crosslinked polyimide. The crosslinked polyimide is obtained by crosslinking a polyimide P via a covalent bond. The polyimide P comprises a constituent unit A1 which is derived from a tetracarboxylic acid dianhydride that has an acid anhydride structure having a six-membered ring. A separation membrane 10 according to the present invention comprises: the separation functional layer 1; and a porous support 3 that supports the separation functional layer 1.

Description

Separation functional layer, separation membrane, and method for producing separation functional layer

The present invention relates to a separation functional layer, a separation membrane, and a method for producing a separation functional layer.

Membrane separation has been developed as a method for separating acidic gases from mixed gases that contain acidic gases such as carbon dioxide. Compared to the absorption method, which separates acidic gases contained in a mixed gas by absorbing them into an absorbent, the membrane separation method can efficiently separate acidic gases while keeping operating costs low.

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.

JP 2014-184424 A

There is a need for a new separation functional layer that is suitable for separating acid gases from a gas mixture that contains acid gases.

The present invention relates to
A separation functional layer including a crosslinked polyimide,
The crosslinked polyimide is a polyimide crosslinked via a covalent bond,
The polyimide provides a separation functional layer that contains a structural unit A1 derived from a tetracarboxylic dianhydride having a six-membered ring acid anhydride structure.

Further, the present invention relates to
The above separation functional layer,
A porous support supporting the separation functional layer;
The present invention provides a separation membrane comprising:

Further, the present invention relates to
A method for producing the above separation functional layer,
The manufacturing method includes:
applying a coating liquid containing the polyimide onto a substrate to form a coating film;
drying the coating film to form the crosslinked polyimide from the polyimide;
The present invention provides a method for producing a separation functional layer, comprising the steps of:

The present invention provides a new separation functional layer suitable for separating acid gases from a gas mixture that contains acid gases.

FIG. 2 is a cross-sectional view illustrating a separation functional layer according to one embodiment of the present invention. 1 is a cross-sectional view showing a schematic diagram of a separation membrane according to one embodiment of the present invention. 1 is a schematic cross-sectional view of a membrane separation device equipped with a separation membrane of the present invention. FIG. 11 is a perspective view that illustrates a modified example of a membrane separation device provided with a separation membrane of the present invention.

The separation functional layer according to the first aspect of the present invention is
A separation functional layer including a crosslinked polyimide,
The crosslinked polyimide is a polyimide crosslinked via a covalent bond,
The polyimide contains a structural unit A1 derived from a tetracarboxylic dianhydride having a six-membered ring acid anhydride structure.

In the second aspect of the present invention, for example, in the separation functional layer according to the first aspect, the polyimide further contains a structural unit B1 derived from a diamine, and at least one of the structural units A1 and B1 has at least one functional group f selected from the group consisting of a sulfonic acid group, a carboxyl group, a hydroxyl group, and a thiol group.

In the third aspect of the present invention, for example, in the separation functional layer according to the second aspect, the crosslinked polyimide is formed by reacting the functional group f with a crosslinking agent.

In the fourth aspect of the present invention, for example, in the separation functional layer according to the third aspect, the crosslinking agent includes at least one selected from the group consisting of epoxy-based crosslinking agents and amine-based crosslinking agents.

In the fifth aspect of the present invention, for example, in the separation functional layer according to the third aspect, the crosslinking agent functions as a condensation agent that advances the condensation reaction of the functional group f.

In the sixth aspect of the present invention, for example, in the separation functional layer according to any one of the second to fifth aspects, the structural unit B1 has the functional group f.

In the seventh aspect of the present invention, for example, in the separation functional layer according to the sixth aspect, in the polyimide, the ratio of the amount of substance of the structural unit B1 having the functional group f to the amount of substance of all structural units B derived from diamine is 1 to 60 mol %.

　前記式（Ｂ１）において、Ａｒ¹及びＡｒ²は、互いに独立して、芳香族基であり、Ａｒ³は、前記官能基ｆを含む芳香族基である。 In an eighth aspect of the present invention, for example, in the separation functional layer according to the sixth or seventh aspect, the structural unit B1 is represented by the following formula (B1).

In the formula (B1), Ar ¹ and Ar ² are each independently an aromatic group, and Ar ³ is an aromatic group containing the functional group f.

　前記式（Ｂ２）において、Ｒ^1b～Ｒ^16bは、互いに独立して、水素原子又は任意の置換基である。ただし、Ｒ^9b～Ｒ^16bからなる群より選ばれる少なくとも１つは、前記官能基ｆを含む基である。 In a ninth aspect of the present invention, for example, in the separation functional layer according to any one of the sixth to eighth aspects, the structural unit B1 is represented by the following formula (B2).

In the formula (B2), R ^1b to R ^16b are each independently a hydrogen atom or an arbitrary substituent, provided that at least one selected from the group consisting of R ^9b to R ^16b is a group containing the functional group f.

In a tenth aspect of the present invention, for example, in the separation functional layer according to the ninth aspect, in the formula (B2), at least one selected from the group consisting of R ^9b to R ^12b is a group containing the functional group f, and at least one selected from the group consisting of R ^13b to R ^16b is a group containing the functional group f.

　前記式（Ａ１）において、Ｒ^1a～Ｒ^4aは、互いに独立して、水素原子又は任意の置換基である。 In an eleventh aspect of the present invention, for example, in the separation functional layer according to any one of the first to tenth aspects, the structural unit A1 is represented by the following formula (A1).

In the formula (A1), R ^1a to R ^4a are each independently a hydrogen atom or an arbitrary substituent.

In the twelfth aspect of the present invention, for example, the separation functional layer in any one of the first to eleventh aspects has a gel fraction of 70% or more.

In a thirteenth aspect of the present invention, for example, a separation functional layer according to any one of the first to twelfth aspects is used to separate an acidic gas from a gas mixture containing the acidic gas.

The separation membrane according to the fourteenth aspect of the present invention is
A separation functional layer according to any one of the first to thirteenth aspects;
A porous support supporting the separation functional layer;
Equipped with.

A manufacturing method according to a fifteenth aspect of the present invention includes the steps of:
A method for producing a separation functional layer according to any one of the first to thirteenth aspects, comprising:
The manufacturing method includes:
applying a coating liquid containing the polyimide onto a substrate to form a coating film;
drying the coating film to form the crosslinked polyimide from the polyimide;
Includes.

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.

<Embodiments of Separation Functional Layer>
Fig. 1 is a cross-sectional view of the separation functional layer 1 of this embodiment. The separation functional layer 1 of Fig. 1 can function as a self-supporting film (single layer film). The separation functional layer 1 preferably allows the acidic gas contained in the mixed gas to pass preferentially. The separation functional layer 1 is typically a dense layer (non-porous layer) in which no pores are observed when observed at a magnification of 5000 times using a scanning electron microscope (SEM).

The separation functional layer 1 includes a crosslinked polyimide. In this embodiment, the crosslinked polyimide is polyimide P crosslinked via a covalent bond. In this specification, "polyimide P crosslinked via a covalent bond" means that polyimide P (more specifically, multiple polyimide P molecules) reacts with a crosslinking agent to form a covalent bond, thereby forming a crosslinked structure. It is preferable that the crosslinked polyimide does not have a metal ion or an ionic bond formed by polyimide P coordinating to a metal ion.

Polyimide P preferably contains a structural unit A1 derived from a tetracarboxylic dianhydride a1 having a six-membered acid anhydride structure S, and further contains a structural unit B1 derived from a diamine b1. At least one of structural units A1 and B1 preferably has at least one functional group f selected from the group consisting of a sulfonic acid group, a carboxyl group, a hydroxyl group, and a thiol group, and preferably has a sulfonic acid group as the functional group f. In particular, in polyimide P, structural unit B1 preferably has a functional group f. Structural unit A1 may or may not have a functional group f.

The structural unit A1 derived from the tetracarboxylic dianhydride a1 is a structural unit suitable for improving the permeation rate of an acidic gas that permeates the separation functional layer 1. The tetracarboxylic dianhydride a1 preferably has one or more, preferably two, acid anhydride structures S. The six-membered acid anhydride structure S is typically a glutaric anhydride structure represented by the following formula (1).

Tetracarboxylic dianhydride a1 may have the above-mentioned functional group f together with the acid anhydride structure S, or may not have the functional group f. Tetracarboxylic dianhydride a1 may have a condensed ring, and the condensed ring may contain the acid anhydride structure S. The condensed ring may contain an aromatic ring together with the acid anhydride structure S. The aromatic ring contained in the condensed ring may be composed only of carbon 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 aromatic rings 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 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 are alkyl groups 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 as or different from each other.

The tetracarboxylic dianhydride a1 is preferably represented by the following formula (a1).

In formula (a1), R ^1a to 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.

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 the formula (A1), the nitrogen atom contained in the imide group is derived from the diamine reacted with the tetracarboxylic dianhydride a1.

In formula (A1), R ^1a to R ^4a are the same as those 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).

In the polyimide P, the ratio p1 of the amount of substance of the structural unit A1 to the amount of substance 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. The polyimide P may contain only the structural unit A1 as the structural unit A derived from tetracarboxylic dianhydride. However, the polyimide P may further contain, in addition to the structural unit A1, a structural unit A2 derived from a 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.

The structural unit B1 derived from diamine b1, particularly the structural unit B1 having functional group f, is a structural unit suitable for improving the selectivity of acidic gases that permeate the separation functional layer 1. Diamine b1 is preferably a compound having two primary amino groups and further having the above-mentioned functional group f. The number of functional groups f in diamine b1 is not particularly limited and may be, for example, 1 or more, or 2 or more. The upper limit of the number of functional groups f is, for example, 5 or less.

Diamine b1 may further have an aromatic ring. Examples of the aromatic ring include those described above for tetracarboxylic dianhydride a1. In diamine b1, it is preferable that the substituent of the aromatic ring includes functional group f or a primary amino group. The aromatic ring may have other substituents other than the substituent including functional group f and the substituent including a primary amino group, or may not have other substituents. Examples of the other substituents are not particularly limited, and include halogen groups and hydrocarbon groups. Examples of the halogen groups and hydrocarbon groups include those described above for tetracarboxylic dianhydride a1. In diamine b1, the other substituents may include a photopolymerizable functional group (e.g., a vinyl group).

The diamine b1 is preferably represented by the following formula (b1).

In formula (b1), Ar ¹ and Ar ² are each independently an aromatic group. In this specification, the aromatic group means a group containing an aromatic ring. The aromatic ring contained in Ar ¹ and Ar ² includes those described above for tetracarboxylic dianhydride a1, and is preferably a benzene ring. It is preferable that the nitrogen atom of the amino group in formula (b1) is directly bonded to the aromatic ring contained in Ar ¹ or the aromatic ring contained in Ar ^2. It is preferable that Ar ¹ and Ar ² do not contain the above-mentioned functional group f.

In formula (b1), Ar ³ is an aromatic group containing a functional group f. The aromatic ring contained in Ar ³ may be any of those described above for tetracarboxylic dianhydride a1, and is preferably a fluorene ring. The functional group f is preferably directly bonded to the aromatic ring contained in Ar ^3. In addition, formula (b1) shows that each of Ar ¹ and Ar ² is directly bonded to the aromatic ring contained in Ar ^3. Among the atoms (specifically carbon atoms) constituting the aromatic ring contained in Ar ³ , the atom to which Ar ¹ is bonded is preferably the same as the atom to which Ar ² is bonded, but may be different from each other.

The diamine b1 is preferably represented by the following formula (b2): Formula (b2) is an example of the above formula (b1).

In formula (b2), R ^1b to R ^16b are each independently a hydrogen atom or an arbitrary substituent. However, at least one selected from the group consisting of R ^9b to R ^16b is a group containing a functional group f, and is preferably the functional group f itself. The arbitrary substituent other than the group containing the functional group f 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 for the tetracarboxylic dianhydride a1.

In formula (b2), it is preferred that at least one selected from the group consisting of R ^9b to R ^12b is a group containing a functional group f, and at least one selected from the group consisting of R ^13b to R ^16b is a group containing a functional group f. In a particularly preferred embodiment, one of R ^9b to R ^12b is a group containing a functional group f, and one of R ^13b to R ^16b is a group containing a functional group f. It is preferred that R ^1b to R ^8b do not contain a functional group f.

The structural unit B1 derived from diamine b1 is preferably represented by the following formula (B1): The structural unit B1 represented by formula (B1) is derived from diamine b1 represented by the above formula (b1).

In formula (B1), ^Ar1 and ^Ar2 are the same as those in formula (b1) and are each independently an aromatic group. ^Ar3 is the same as those in formula (b1) and is an aromatic group containing a functional group f.

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).

In formula (B2), R ^1b to R ^16b are each independently a hydrogen atom or an arbitrary substituent. However, at least one selected from the group consisting of R ^9b to R ^16b is a group containing a functional group f, and is preferably the functional group f itself. The arbitrary substituent other than the group containing the functional group f 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 for the tetracarboxylic dianhydride a1.

In formula (B2), it is preferred that at least one selected from the group consisting of R ^9b to R ^12b is a group containing a functional group f, and at least one selected from the group consisting of R ^13b to R ^16b is a group containing a functional group f. In a particularly preferred embodiment, one of R ^9b to R ^12b is a group containing a functional group f, and one of R ^13b to R ^16b is a group containing a functional group f. It is preferred that R ^1b to R ^8b do not contain a functional group f.

In formula (B2), the fluorene rings tend to be arranged in a twisted orientation relative to the two benzene rings due to steric hindrance. As an example, in formula (B2), the fluorene rings extend from the front to the back of the page. Thus, in formula (B2), the direction in which the fluorene rings extend and the direction in which the main chain of polyimide P extends are different from each other, and it is preferable that these directions are perpendicular to each other. In a crosslinked polyimide formed from polyimide P containing such a structural unit B1, appropriate gaps are formed within the molecule, and the permeation of acidic gases tends not to be hindered.

Specific examples of the structural unit B1 represented by formula (B2) include the following formulae (B2-1) and (B2-2).

The diamine b1 and the structural unit B1 are not limited to those described above. As an example, the diamine b1 may be represented by the following formula (c1), formula (c2), or formula (c3).

In formula (c1), R ^1c to R ^4c are each independently a hydrogen atom or an arbitrary substituent. However, at least one selected from the group consisting of R ^1c to R ^4c is a group containing a functional group f, and is preferably the functional group f itself. The arbitrary substituent other than the group containing the functional group f 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 for the tetracarboxylic dianhydride a1.

In formula (c2), R ^5c to R ^12c are each independently a hydrogen atom or an arbitrary substituent, and X ¹ is a single bond or an arbitrary linking group. However, at least one selected from the group consisting of R ^5c to R ^12c is a group containing a functional group f, and is preferably the functional group f itself. The arbitrary substituent other than the group containing the functional group f 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 for the tetracarboxylic dianhydride a1.

In X ¹ of formula (c2), the optional linking group is, 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. The divalent hydrocarbon group may be a halogenated hydrocarbon group in which a hydrogen atom is substituted with a halogen group. X ¹ may contain a functional group such as an ether group or an ester group together with or instead of the divalent hydrocarbon group.

In formula (c3), R ^13c to R ^20c are each independently a hydrogen atom or an arbitrary substituent, and X ² is a single bond or an arbitrary linking group. However, at least one selected from the group consisting of R ^13c to R ^20c is a group containing a functional group f, and is preferably the functional group f itself. The arbitrary substituent other than the group containing the functional group f 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 for the tetracarboxylic dianhydride a1.

In ^X2 of formula (c3), the optional linking group is, for example, a divalent hydrocarbon group. Examples of the divalent hydrocarbon group include those described above for ^X1 . ^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.

In formulas (c1) to (c3), the functional group f does not have to be a sulfonic acid group. In formulas (c1) to (c3), the functional group f may be at least one selected from the group consisting of a carboxyl group, a hydroxyl group, and a thiol group, or may be a carboxyl group.

The structural unit B1 derived from diamine b1 may be represented by the following formula (C1), formula (C2) or formula (C3). The structural unit B1 represented by formula (C1) is derived from diamine b1 represented by the above formula (c1). The structural unit B1 represented by formula (C2) is derived from diamine b1 represented by the above formula (c2). The structural unit B1 represented by formula (C3) is derived from diamine b1 represented by the above formula (c3).

In formula (C1), R ^1c to R ^4c are each independently a hydrogen atom or an arbitrary substituent. However, at least one selected from the group consisting of R ^1c to R ^4c is a group containing a functional group f, and is preferably the functional group f itself. The arbitrary substituent other than the group containing the functional group f 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 for the tetracarboxylic dianhydride a1.

Specific examples of the structural unit B1 represented by formula (C1) include the following formulae (C1-1) to (C1-3).

In formula (C2), R ^5c to R ^12c are each independently a hydrogen atom or an arbitrary substituent, and X ¹ is a single bond or an arbitrary linking group. However, at least one selected from the group consisting of R ^5c to R ^12c is a group containing a functional group f, and is preferably the functional group f itself. The arbitrary substituent other than the group containing the functional group f 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 for the tetracarboxylic dianhydride a1.

In the formula (C2), the optional linking group is, for example, ^a divalent hydrocarbon group. Examples of the divalent hydrocarbon group include those described above. ^X1 may contain a functional group such as an ether group or an ester group together with or instead of the divalent hydrocarbon group.

Specific examples of the structural unit B1 represented by formula (C2) include the following formulae (C2-1) to (C2-6).

In formula (C3), R ^13c to R ^20c are each independently a hydrogen atom or an arbitrary substituent, and X ² is a single bond or an arbitrary linking group. However, at least one selected from the group consisting of R ^13c to R ^20c is a group containing a functional group f, and is preferably the functional group f itself. The arbitrary substituent other than the group containing the functional group f 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 for the tetracarboxylic dianhydride a1.

In the formula ( ^C3 ), the optional linking group is, for example, a divalent hydrocarbon group. Examples of the divalent hydrocarbon group include those described above. ^X2 may contain a functional group such as an ether group or an ester group together with or instead of the divalent hydrocarbon group.

Specific examples of the structural unit B1 represented by formula (C3) include the following formulae (C3-1) to (C3-3).

In polyimide P, the ratio p2 of the amount of substance of structural unit B1 having functional group f, particularly structural unit B1 represented by formula (B2), to the amount of substance of all structural units B derived from diamine is, for example, 1 mol% or more, and preferably 3 mol% or more. The upper limit of ratio p2 is not particularly limited, and may be, for example, 60 mol%, 50 mol%, 40 mol%, 30 mol%, or even 25 mol%. When ratio p2 is low, the solubility of polyimide P is improved, and the desired manufacturing method of separation functional layer 1 tends to be easier to apply. Furthermore, in this case, the strength of separation functional layer 1 also tends to be improved. Ratio p2 is preferably 1 to 60 mol%. When ratio p2 is in this range, separation functional layer 1 tends to have good separation performance.

The polyimide P may further contain a structural unit B2 derived from a diamine b2 having a sulfonyl group (-SO ₂ -). The structural unit B2 is a structural unit suitable for improving the permeation rate of an acidic gas that permeates the separation functional layer 1. The diamine b2 is a compound having two primary amino groups together with a sulfonyl group. The number of sulfonyl groups in the diamine b2 is not particularly limited and is, for example, 5 or less, and preferably 1. It is preferable that the diamine b2 does not contain a group having a dissociable proton such as the above-mentioned functional group f.

The diamine b2 preferably contains a ring structure having a sulfonyl group. The ring structure having a sulfonyl group is typically a thiophene 1,1-dioxide ring or a tetrahydrothiophene 1,1-dioxide ring.

The diamine b2 may have a condensed ring, and the condensed ring may contain a ring structure having a sulfonyl group. The condensed ring may contain an aromatic ring together with the ring structure having a sulfonyl group. Examples of the aromatic ring include those described above for the tetracarboxylic dianhydride a1.

In diamine b2, the substituent of the condensed ring preferably contains a primary amino group. The condensed ring may contain other substituents than the substituent containing a primary amino group, or may not contain other substituents. The other substituents are not particularly limited, and examples thereof include halogen groups and hydrocarbon groups. Examples of halogen groups and hydrocarbon groups include those described above for tetracarboxylic dianhydride a1.

The diamine b2 is preferably represented by the following formula (d1).

In formula (d1), R ^1d to R ^6d are each independently a hydrogen atom or an arbitrary substituent. In formula (d1), the arbitrary substituent is, for example, a substituent other than the group containing the functional group f, and more specifically, 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.

In the polyimide P, the structural unit B2 derived from the diamine b2 is preferably represented by the following formula (D1): The structural unit B2 represented by formula (D1) is derived from the diamine b2 represented by the above formula (d1).

In formula (D1), R ^1d to R ^6d are each independently a hydrogen atom or an arbitrary substituent. In formula (D1), the arbitrary substituent is, for example, a substituent other than the group containing the functional group f, and specifically, 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 (D1) is suitable for improving the rigidity of the polyimide P. According to the polyimide P having excellent rigidity, even when the pressure of the mixed gas to be separated is high, the separation functional layer 1 tends to be suppressed from being plasticized.

Specific examples of the structural unit B2 represented by formula (D1) include the following formulae (D1-1) and (D1-2).

In polyimide P, the ratio p3 of the amount of substance of the structural unit B2 to the amount of substances of all structural units B derived from diamine is not particularly limited, and may be, for example, 5 mol% or more, 10 mol% or more, 20 mol% or more, or even 30 mol% or more. The upper limit of the ratio p3 is not particularly limited, and may be, for example, 95 mol%, 90 mol%, 80 mol%, 70 mol%, 60 mol%, or even 50 mol%.

Polyimide P may further contain a structural unit B3 derived from a diamine b3 other than diamines b1 and b2. Diamine b3 is a compound that does not have the above-mentioned functional group f or a sulfonyl group, and has two primary amino groups. It is preferable that diamine b3 does not contain a group having a dissociable proton.

Diamine b3 may further have an aromatic ring. Examples of the aromatic ring include those described above for tetracarboxylic dianhydride a1. In diamine b3, it is preferable that the substituent of the aromatic ring includes 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. Examples of the other substituent include, but are not limited to, a halogen group and a hydrocarbon group. Examples of the halogen group and the hydrocarbon group include those described above for tetracarboxylic dianhydride a1.

The diamine b3 is preferably represented by the following formula (e1), formula (e2) or formula (e3).

In formula (e1), R ^1e to R ^4e are each independently a hydrogen atom or an arbitrary substituent. In formula (e1), the arbitrary substituent is, for example, a substituent other than the group containing the functional group f and the group containing a sulfonyl group, and more specifically, 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.

In formula (e2), R ^5e to R ^8e are each independently a hydrogen atom or an arbitrary substituent. In formula (e2), the arbitrary substituent is, for example, a substituent other than the group containing the functional group f and the group containing a sulfonyl group, and more specifically, 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.

In formula (e3), R ^9e to R ^16e are each independently a hydrogen atom or an arbitrary substituent, and X ³ is a single bond or an arbitrary linking group. In formula (e3), the arbitrary substituent is, for example, a substituent other than the group containing the functional group f and the group containing a sulfonyl group, and more specifically, 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.

In ^X3 of formula (e3), the optional linking group is, for example, a divalent hydrocarbon group. Examples of the divalent hydrocarbon group include those mentioned above. In ^X3 , the divalent hydrocarbon group may further have an aromatic ring. Examples of the aromatic ring include those mentioned above for the tetracarboxylic dianhydride a1. The divalent hydrocarbon group in ^X3 may be a fluorenediyl group. ^X3 may contain a functional group such as an ether group or an ester group together with or instead of the divalent hydrocarbon group.

The structural unit B3 derived from diamine b3 is preferably represented by the following formula (E1), formula (E2) or formula (E3). The structural unit B3 represented by formula (E1) is derived from diamine b3 represented by the above formula (e1). The structural unit B3 represented by formula (E2) is derived from diamine b3 represented by the above formula (e2). The structural unit B3 represented by formula (E3) is derived from diamine b3 represented by the above formula (e3).

In formula (E1), R ^1e to R ^4e are each independently a hydrogen atom or an arbitrary substituent. In formula (E1), the arbitrary substituent is, for example, a substituent other than the group containing the functional group f, and more specifically, 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. A specific example of the structural unit B3 represented by formula (E1) is the following formula (E1-1).

In formula (E2), R ^5e to R ^8e are each independently a hydrogen atom or an arbitrary substituent. In formula (E2), the arbitrary substituent is, for example, a substituent other than the group containing the functional group f, and more specifically, 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. A specific example of the structural unit B3 represented by formula (E2) is the following formula (E2-1).

In formula (E3), R ^9e to R ^16e are each independently a hydrogen atom or an arbitrary substituent, and X ³ is a single bond or an arbitrary linking group. In formula (E3), the arbitrary substituent is, for example, a substituent other than the group containing the functional group f, and in detail, is 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. In formula (E3), the arbitrary linking group is, for example, a divalent hydrocarbon group. Examples of the divalent hydrocarbon group include those described above. X ³ may contain a functional group such as an ether group or an ester group together with or instead of the divalent hydrocarbon group. Specific examples of the structural unit ^B3 represented by formula (E3) include the following formulae (E3-1) to (E3-3).

In polyimide P, the ratio p4 of the amount of substance of the structural unit B3 to the amount of substances of all structural units B derived from diamine is not particularly limited, and may be, for example, 5 mol% or more, 10 mol% or more, 20 mol% or more, or even 30 mol% or more. The upper limit of ratio p4 is not particularly limited, and may be, for example, 95 mol%, 90 mol%, 80 mol%, 70 mol%, 60 mol%, or even 50 mol%.

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 combinations of adjacent structural units A and B include the following formulae (A1-B2), (A1-C2), (A1-D1), and (A1-E1). In these formulae, R ^1a to R ^4a , R ^1b to R ^16b , R ^5c to R ^12c , R ^1d to R ^6d , and R ^1e to R ^4e are the same as those described above for formulae (A1), (B2), (C2), (D1), and (E1).

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

In this embodiment, the crosslinked polyimide is preferably formed by reacting the functional group f in the polyimide P with a crosslinking agent. In this case, the structure and performance of the crosslinked polyimide can be easily adjusted depending on the type of crosslinking agent.

As an example, the functional group f reacts with the functional group H contained in the crosslinking agent to form a covalent bond between the functional group f and the crosslinking agent. In the molecules of multiple polyimide P, the functional group f reacts with the functional group H of the crosslinking agent to form a crosslinked structure. In this case, the crosslinked polyimide usually has a crosslinked structure in which the molecules of multiple polyimide P are indirectly bonded to each other via the crosslinking agent. However, the crosslinking agent may be a condensing agent that forms a crosslinked structure by promoting a condensation reaction between the functional groups f in the molecules of multiple polyimide P. In this specification, such a condensing agent is also classified as a crosslinking agent that reacts with the functional group f. When a condensing agent is used, the crosslinked polyimide usually has a crosslinked structure in which the molecules of multiple polyimide P are directly bonded to each other.

Crosslinking agents containing a functional group H include epoxy-based crosslinking agents, amine-based crosslinking agents, and isocyanate-based crosslinking agents. It is preferable that the crosslinking agent contains at least one selected from the group consisting of epoxy-based crosslinking agents and amine-based crosslinking agents.

The epoxy crosslinking agent is a compound (epoxy compound) that contains an epoxy group as a functional group H. The number of epoxy groups contained in the epoxy compound is typically 2 or more, and may be 3 to 5. The epoxy compound may be used alone or in combination of two or more types.

Specific examples of epoxy compounds include N,N,N',N'-tetraglycidyl-m-xylylenediamine, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, polyethylene glycol diglycidyl ether, polyglycerol polyglycidyl ether, etc.

Commercially available epoxy crosslinking agents include Mitsubishi Gas Chemical Company's "TETRAD-C" and "TETRAD-X," DIC Corporation's "Epicron CR-5L," Nagase ChemteX Corporation's "Denacol EX-512," and Nissan Chemical Industries' "TEPIC-G."

The amine-based crosslinking agent is a compound (amine compound) that contains an amino group as a functional group H. The number of amino groups contained in the amine compound is typically 2 or more, and may be 3 or more. The amine compound may be used alone or in combination of two or more.

Specific examples of amine compounds include aziridine and polyethyleneimine.

An isocyanate-based crosslinking agent is a compound (isocyanate compound) that contains an isocyanate group as a functional group H. The number of isocyanate groups contained in the isocyanate compound is typically 2 or more, and may be 3 to 5. The isocyanate compound may be used alone or in combination of two or more types.

Isocyanate compounds include aliphatic isocyanate compounds, alicyclic isocyanate compounds, aromatic isocyanate compounds, etc.

Aliphatic isocyanate compounds include 1,2-ethylene diisocyanate; tetramethylene diisocyanates such as 1,2-tetramethylene diisocyanate, 1,3-tetramethylene diisocyanate, and 1,4-tetramethylene diisocyanate; hexamethylene diisocyanates such as 1,2-hexamethylene diisocyanate, 1,3-hexamethylene diisocyanate, 1,4-hexamethylene diisocyanate, 1,5-hexamethylene diisocyanate, 1,6-hexamethylene diisocyanate, and 2,5-hexamethylene diisocyanate; 2-methyl-1,5-pentane diisocyanate, 3-methyl-1,5-pentane diisocyanate, and lysine diisocyanate.

Alicyclic isocyanate compounds include isophorone diisocyanate; cyclohexyl diisocyanates such as 1,2-cyclohexyl diisocyanate, 1,3-cyclohexyl diisocyanate, and 1,4-cyclohexyl diisocyanate; cyclopentyl diisocyanates such as 1,2-cyclopentyl diisocyanate and 1,3-cyclopentyl diisocyanate; hydrogenated xylylene diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated tetramethylxylene diisocyanate, and 4,4'-dicyclohexylmethane diisocyanate.

Aromatic isocyanate compounds include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, 4,4'-diphenylether diisocyanate, 2-nitrodiphenyl-4,4'-diisocyanate, 2,2'-diphenylpropane-4,4'-diisocyanate, 3, Examples include 3'-dimethyldiphenylmethane-4,4'-diisocyanate, 4,4'-diphenylpropane diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, naphthylene-1,4-diisocyanate, naphthylene-1,5-diisocyanate, 3,3'-dimethoxydiphenyl-4,4'-diisocyanate, xylylene-1,4-diisocyanate, and xylylene-1,3-diisocyanate.

Examples of isocyanate-based crosslinking agents include polymers (dimers, trimers, pentamers, etc.) of the above isocyanate compounds, adducts obtained by adding them to polyhydric alcohols such as trimethylolpropane, urea-modified products, biuret-modified products, allophanate-modified products, isocyanurate-modified products, carbodiimide-modified products, and urethane prepolymers obtained by adding them to polyether polyols, polyester polyols, acrylic polyols, polybutadiene polyols, polyisoprene polyols, etc.

Commercially available isocyanate crosslinking agents include, for example, "Duranate TPA-100" manufactured by Asahi Kasei Chemicals Corporation, and "Coronate L," "Coronate HL," "Coronate HK," "Coronate HX," and "Coronate 2096" manufactured by Tosoh Corporation.

Examples of crosslinking agents that function as condensing agents include acidic compounds such as Eaton's reagent (a mixture of _P2O5 and _{methanesulfonic} acid) and polyphosphoric acid. In particular, Eaton's reagent is suitable for sufficiently promoting the crosslinking reaction of polyimide P to increase the gel fraction of the separation functional layer 1.

The content of crosslinked polyimide 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. The separation functional layer 1 may be substantially composed of crosslinked polyimide only. However, the separation functional layer 1 may contain uncrosslinked polyimide P in addition to the crosslinked polyimide.

The separation functional layer 1 may further contain other components in addition to the crosslinked polyimide. 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 preferably dispersed in a matrix containing the crosslinked polyimide. The nanoparticles may be spaced apart from one another within the matrix, or may be partially aggregated.

The thickness of the separation functional layer 1 may be, for example, 500 μm or less, 300 μm or less, 100 μm or less, 50 μm or less, 25 μm or less, 15 μm or less, 10 μm or less, 5.0 μm or less, or even 2.0 μm or less. The thickness of the separation functional layer 1 may be 0.05 μm or more, or 0.1 μm or more. According to the study by the inventors, when a conventional separation functional layer having a thickness of about 5.0 μm or less is used, the separation functional layer is easily deteriorated and the separation performance (especially the permeation rate of acidic gas) is easily reduced when the separation functional layer is used for a long period of time. However, in the separation functional layer 1 of this embodiment, even if the thickness is small, the deterioration of the separation performance when used for a long period of time tends to be suppressed due to the inclusion of crosslinked polyimide.

The gel fraction of the separation functional layer 1 is not particularly limited, and may be, for example, 60% or more, 70% or more, 80% or more, 85% or more, or even 90% or more. The higher the gel fraction of the separation functional layer 1, the more likely it is that the separation functional layer 1 will be able to suppress a decrease in separation performance when used for a long period of time. The upper limit of the gel fraction of the separation functional layer 1 is, for example, 99% or less.

The gel fraction of the separation functional layer 1 can be evaluated by the following method. First, a separation functional layer 1 in a dry state is prepared. In this specification, "dry state" means that the content of liquids such as water in the separation functional layer 1 is 0.5 wt % or less.

Next, the separation functional layer 1 is cut into a test piece of 2 cm length x 2 cm width, and the weight A (g) of the test piece is measured. The test piece is immersed in N-methyl-2-pyrrolidone (NMP) in a sample bottle and left at room temperature (25 ° C) for one week. Next, the weight C (g) of the filter paper is measured, and the contents of the sample bottle are filtered with the filter paper. During filtration, the filter paper is washed with NMP. The filter paper and the insoluble matter attached to the filter paper are collected, and these are washed with methanol to remove the NMP. Next, it is dried at 130 ° C for one hour, and the weight D (g) after drying is measured. The value obtained by subtracting the weight C from the weight D is the weight B (g) of the insoluble matter (B = D - C). Based on the weights A and B, the gel fraction (%) of the separation functional layer 1 can be calculated by the following formula.
Gel fraction (%) = 100 x B/A

(Method for producing separation functional layer)
In this embodiment, the manufacturing method of the separation functional layer 1 preferably includes applying a coating liquid containing polyimide P onto a substrate to form a coating film, and drying the coating film to form a cross-linked polyimide from the polyimide P.

Polyimide P can be produced by the following method. First, a diamine group including the above diamine b1 is dissolved in a solvent to obtain a solution. Examples of the solvent include polar organic solvents such as N-methyl-2-pyrrolidone.

Next, the tetracarboxylic dianhydride group including the above tetracarboxylic dianhydride a1 is gradually added to the obtained solution. This causes the tetracarboxylic dianhydride a1 to react with the monomer group including the diamine b1 to form a polyamic acid. The addition of the tetracarboxylic dianhydride group is preferably carried out under stirring conditions for 3 to 20 hours in a heated environment of 140°C or higher.

Then, polyimide P can be obtained by imidizing polyamic acid. Examples of the imidization method include chemical imidization and thermal imidization. The chemical imidization method is a method in which polyamic acid is imidized, for example, at room temperature using a dehydrating condensation agent. Examples of the dehydrating condensation agent include acetic anhydride, pyridine, and triethylamine. The thermal imidization method is a method in which polyamic acid is imidized by heat treatment. The temperature of the heat treatment is not particularly limited, and is, for example, 180°C or higher.

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 %.

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.

The solvent content in the coating liquid is not particularly limited, but is, for example, 30 wt% to 99 wt%.

The coating liquid preferably further contains a crosslinking agent. Examples of crosslinking agents include those mentioned above. In the coating liquid, the ratio of the weight of the crosslinking agent to the weight of the polyimide P can be appropriately adjusted depending on the composition of the polyimide P, and may be, for example, 0.01 wt% or more, 0.1 wt% or more, or even 0.5 wt% or more. The upper limit of this ratio is not particularly limited, and may be, for example, 20 wt% or less, 10 wt% or less, or even 5 wt% or less. In the coating liquid, the ratio of the substance amount of the crosslinking agent to the substance amount of the functional group f contained in the polyimide P is not particularly limited, and is, for example, 2.0 or more.

The substrate to which the coating solution containing polyimide P is applied is typically a release liner. Examples of substrates 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, since it has excellent surface smoothness. In the substrate, examples of polymers 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; polyurethane; ethylene-vinyl acetate copolymers; and polyimides, with polyimides being preferred.

The surface of the substrate may be subjected to a release treatment. The release treatment can be performed 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 is preferably a polyimide film that has been subjected to a release treatment.

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

Before applying the coating liquid, the substrate may be subjected to a surface modification treatment. If 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 surface modification treatments include corona treatment, plasma treatment, excimer treatment, and frame treatment, with corona treatment being preferred.

The 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 carried out as the surface modification treatment, the discharge amount is, for example, 0.1 kW·min/ ^m2 or more. The upper limit of the discharge amount is not particularly limited, and is, for example, 10 kW·min/ ^m2 .

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 or wire bar. The coating liquid may be applied onto the surface of a substrate that has been subjected to a peeling treatment or surface modification treatment.

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.

In this embodiment, as described above, the separation functional layer 1 is obtained by drying the coating film and forming a crosslinked polyimide from the polyimide P. 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 can be dried by passing it through a heating section equipped with a heater. The coating film can be dried by passing it through multiple heating sections. The set temperatures of the multiple heating sections may be the same or different.

If the coating solution contains a cross-linking agent, the functional group f of the polyimide P tends to react with the cross-linking agent when the coating film is dried. This forms a cross-linked structure, resulting in a cross-linked polyimide.

The crosslinked polyimide may be formed after drying the coating film to form a dry film. For example, a coating liquid containing the above polyimide P and a solvent is applied onto a substrate, and dried to form a dry film. This dry film may be immersed in a solution containing a crosslinking agent, and a heat treatment may be further performed as necessary to form a crosslinked polyimide. The conditions for the heat treatment are not particularly limited, and for example, the heating temperature is 50°C to 100°C, and the heating time is 1 minute to 10 hours. This method is suitable for an embodiment in which a condensation agent such as Eaton's reagent is used as the crosslinking agent.

After immersion in the above solution, the membrane may be further washed with water and dried.

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 the 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 evaporating the solvent. The annealing treatment may be performed before removing the substrate from the laminate of the separation functional layer 1 and substrate, or may be performed after removing the substrate.

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 time of the heat treatment is, for example, 1 minute or more, and may be 10 minutes or more, or 30 minutes or more. The upper limit of the heat treatment time is not particularly limited, and may be, for example, 24 hours or less.

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.

The manufacturing method of this embodiment is not limited to the above. Instead of the coating liquid containing polyimide P, a coating liquid containing polyamic acid, which is a precursor of polyimide P, may be used. This coating liquid may be applied onto a substrate, the polyamic acid may be imidized to form polyimide P, and a crosslinked polyimide may be formed from the polyimide P to produce the separation functional layer 1.

(Characteristics of the separation functional layer)
As described above, the separation functional layer 1 is preferably configured to preferentially transmit the acid gas contained in the mixed gas. As an example, the permeation rate T1 of carbon dioxide permeating the separation functional layer 1 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 the initial state is, for example, 30 GPU or more, and may be 50 GPU or more, 60 GPU or more, 70 GPU or more, 80 GPU or more, or even 90 GPU or more. The upper limit of the permeation rate T1 is not particularly limited, and is, for example, 300 GPU. Note that GPU means 10 ^-6 cm ³ (STP)/(sec cm ² cmHg). cm ³ (STP) means the volume of carbon dioxide at 1 atmosphere and 0°C.

The permeation rate T1 can be determined by the following method. First, a mixed gas consisting of carbon dioxide and nitrogen is supplied to the space adjacent to one side of the separation functional layer 1, and the space adjacent to the other side of the separation functional layer 1 is depressurized. This results in a permeating fluid that has permeated the separation functional layer 1. The weight of the permeating fluid, as well as the volume ratio of carbon dioxide and the volume ratio of nitrogen in the permeating fluid are measured. The permeation rate T1 can be calculated from the measurement results. 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 side 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 side 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.

Under the measurement conditions for the above-mentioned permeation rate T1, the separation factor α of carbon dioxide relative to nitrogen of the separation functional layer 1 is, for example, 20 or more, and may be 30 or more, 35 or more, 38 or more, or even 40 or more. The upper limit of the separation factor α is not particularly limited, and may be, for example, 100 or 60. The separation factor α can be calculated from the following formula. In the following formula, X _A and X _B are the volume ratio of carbon dioxide and the volume ratio of nitrogen in the mixed gas, respectively. Y _A and Y _B are the volume ratio of carbon dioxide and the volume ratio of nitrogen in the permeating fluid that has permeated the separation functional layer 1, respectively.
Separation factor α=(Y _A /Y _B )/(X _A /X _B )

As described above, the separation functional layer 1 of this embodiment contains cross-linked polyimide. In this separation functional layer 1, physical aging of the cross-linked polyimide is suppressed, which tends to suppress the deterioration of the separation performance of the separation functional layer 1 over time. In particular, the separation functional layer 1 of this embodiment tends to suppress the deterioration of the separation performance (particularly the permeation rate of acidic gases) when used for a long period of time.

The deterioration of the separation performance of the separation functional layer 1 due to long-term use can be evaluated by the following method. First, the separation functional layer 1 is heat-treated at 85°C for 500 hours (durability test). After the durability test, the carbon dioxide permeation rate T2 of the separation functional layer 1 is measured by the same method as for the permeation rate T1. The deterioration of the separation performance can be evaluated based on the ratio T2/T1 of the permeation rate T2 to the permeation rate T1 (permeation rate maintenance rate).

In the separation functional layer 1, the ratio T2/T1 is, for example, 70% or more, and may be 75% or more, 80% or more, 85% or more, or even 90% or more. The upper limit of the ratio T2/T1 is, for example, 110%.

The permeation rate T2 after the durability test is, for example, 30 GPU or more, and may be 50 GPU or more, 60 GPU or more, 70 GPU or more, or even 75 GPU or more. The upper limit of the permeation rate T2 is not particularly limited, and is, for example, 300 GPU.

The separation factor α of carbon dioxide relative to nitrogen of the separation functional layer 1 after the durability test is, for example, 20 or more, and may be 25 or more, or even 30 or more. The upper limit of the separation factor α after the durability test is not particularly limited, and may be, for example, 100 or 60. The separation factor α after the durability test can be determined by the same method as described above, except that the separation functional layer 1 after the durability test is used.

(Use of separation functional layer)
The use of the separation functional layer 1 of this embodiment includes the use of separating an acidic gas from a mixed gas containing an acidic gas. Examples of the acidic gas in the mixed gas include carbon dioxide, hydrogen sulfide, carbonyl sulfide, sulfur oxides (SOx), hydrogen cyanide, and nitrogen oxides (NOx), and preferably carbon dioxide. The mixed gas contains other gases other than the acidic gas. Examples of the other gases include non-polar gases such as hydrogen, nitrogen, and methane, and inert gases such as helium, and preferably nitrogen and methane. In particular, the separation functional layer 1 of this embodiment is suitable for separating carbon dioxide from a mixed gas containing carbon dioxide and nitrogen. However, the use of the separation functional layer 1 is not limited to the use of separating an acidic gas from the above-mentioned mixed gas.

<Embodiments of separation membrane>
2, the separation membrane 10 of the present embodiment preferably includes the above-mentioned separation functional layer 1, and further includes an intermediate layer 2 and a porous support 3. The porous support 3 supports the separation functional layer 1. The intermediate layer 2 is disposed between the separation functional layer 1 and the porous support 3, and is in direct contact with both the separation functional layer 1 and the porous support 3.

(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 each other in the matrix, or may be partially aggregated. However, the intermediate layer 2 may not contain nanoparticles, and may be substantially composed of a resin.

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; and polyurethane resins. The matrix preferably contains a silicone resin and a polyurethane resin.

The nanoparticles may contain an inorganic material or an organic material. Examples of inorganic materials contained in the nanoparticles include silica, titania, and alumina. It is preferable that the nanoparticles contain silica.

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

R ¹ to R ⁶ in formulae (I) to (III) are 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, and is preferably a methyl group. Examples of the substituent of the hydrocarbon group include an amino group and an acyloxy group. Examples of the acyloxy group include a (meth)acryloyloxy group.

In another preferred embodiment, the hydrocarbon group which may have the substituents described above for R ¹ to R ⁶ in formulas (I) to (III) 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 permeation rate of acidic gases through the separation membrane 10.

In formula (IV), ^R7 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.

In formula (IV), ^R8 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 of the alkyl group and the aryl group include an amino group and a carboxyl group. For example, ^R8 is a 3,5-diaminophenyl group.

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

The modifying group is not limited to the structures shown in formulas (I) to (III). The modifying group may contain a polymer chain having a polyamide structure or a polydimethylsiloxane structure in place of R ¹ to R ⁶ in formulas (I) to (III). In the modifying group, it is preferable that the polymer chain is directly bonded to a silicon atom. Examples of the shape of the polymer chain include a linear shape, a dendrimer shape, and a hyperbranched shape.

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 the nanoparticles with a known silane coupling agent. When the modifying group contains a polyamide structure, the surface of the nanoparticles can be modified by the method disclosed in JP 2010-222228 A.

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 specified 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 of nanoparticles (at least 50) 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.

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. The upper limit of the nanoparticle content in the intermediate layer 2 is not particularly limited, and is, for example, 30 wt%.

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. It is preferable that the intermediate layer 2 is a layer having a thickness of less than 50 μm.

(Porous Support)
The porous support 3 supports the separation function layer 1 via the intermediate layer 2. Examples of the porous support 3 include nonwoven fabric, porous polytetrafluoroethylene, aromatic polyamide fiber, porous metal, sintered metal, porous ceramic, porous polyester, porous nylon, activated carbon fiber, latex, silicone, silicone rubber, permeable (porous) polymers including 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, metal foam having open or closed cells, polymer foam having open or closed cells, silica, porous glass, mesh screen, etc. The porous support 3 may be a combination of two or more of these. As an example, the porous support 3 may be a laminate of a nonwoven fabric and a polysulfone porous layer.

The porous support 3 has an average pore size of, for example, 0.01 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.

(Method for producing separation membrane)
The separation membrane 10 can be produced by the following method. First, a laminate of the porous support 3 and the intermediate layer 2 is prepared. This laminate can be produced by the following method. First, a coating liquid containing the material of the intermediate layer 2 is prepared. Next, a coating liquid containing the material of the intermediate layer 2 is applied onto the porous support 3 to form a coating film. The method of applying the coating liquid is not particularly limited, and for example, a spin coating method, a dip coating method, or the like can be used. The coating liquid may 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 easy-adhesion treatment as necessary. Examples of the easy-adhesion treatment include surface treatments such as application of an undercoat agent, corona discharge treatment, and plasma treatment.

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 the separation membrane 10 to be obtained. 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 manufacturing method described above for the separation functional layer 1.

The method for producing the separation membrane 10 is not limited to the above method, and the separation membrane 10 may be produced by the following method. First, a separation functional layer 1 formed on a substrate such as a release liner 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. This results in the separation membrane 10.

(Shape of separation membrane)
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, and may be 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.

<Embodiment of Membrane Separation Apparatus>
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 walls of the tank 20.

The first chamber 21 has an inlet 21a and an outlet 21b. The second chamber 22 has an outlet 22a. It is preferable that each of the inlet 21a, the outlet 21b, and the outlet 22a is an opening formed in the wall surface of the tank 20.

Membrane separation using the membrane separation device 100 is performed by the following method. First, the mixed gas 30 containing the acidic gas is supplied to the first chamber 21 through the inlet 21a. The concentration of the acidic gas in the mixed gas 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 mixed gas 30 is not particularly limited, and is, for example, 90 vol% under standard conditions.

The pressure inside the first chamber 21 may be increased by supplying the mixed gas 30. The membrane separation device 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, preferably 0.3 MPa or more.

The second chamber 22 may be depressurized while the mixed gas 30 is being supplied to the first chamber 21. The membrane separation device 100 may further include a pump (not shown) for depressurizing the second chamber 22. The second chamber 22 may be depressurized so that the space within the second chamber 22 is reduced by, for example, 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.

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

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

The membrane separation device 100 of this embodiment is suitable for a flow-through (continuous) membrane separation method. However, the membrane separation device 100 of this embodiment may also be used for a batch-type membrane separation method.

<Modification of Membrane Separation Device>
The membrane separation device 100 may be a spiral-type membrane element, a hollow fiber membrane element, or the like. Fig. 4 shows a spiral-type membrane element. The membrane separation device 110 in 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.

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 permeation 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.

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

The supply-side flow passage material 43 and the permeate-side flow passage material 44 can be, for example, a resin net made of polyphenylene sulfide (PPS) or ethylene-chlorotrifluoroethylene copolymer (ECTFE).

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 rolled stack 42. The permeating fluid 35 that has permeated the separation membrane 10 of the stack 42 moves into the interior of the central tube 41. The permeating fluid 35 is discharged to the outside through the central tube 41. The mixed gas 30 (non-permeating fluid 36) that has been treated in the membrane separation device 110 is discharged to the outside from the other end of the rolled stack 42. This allows the acid gas to be separated from the mixed gas 30.

The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited thereto.

(Example 1)
[Synthesis of sulfonated diamine]
9,9-bis(4-aminophenyl)fluorene-2,7-disulfonic acid (BAPFDS) was synthesized by the following method. First, 25.0 g (71.75 mmol) of 9,9-bis(4-aminophenyl)fluorene (BAPF) was added to a 500 mL three-neck flask equipped with a stirrer under a _N2 atmosphere, and cooled to 0°C in an ice-water bath. Next, 100 mL of concentrated sulfuric acid was added while cooling in an ice-water bath under a _N2 atmosphere, and the mixture was stirred at a stirring speed of 100 rpm for 30 minutes.

The flask was then removed from the ice water bath and slowly heated to 55°C until the BAPF was completely dissolved in the concentrated sulfuric acid. It was then heated to 100°C and reacted for 5 hours. The reaction solution was cooled to room temperature and then transferred to 1,000 g of ice water, causing a large amount of white cotton-like solid to precipitate. The precipitate was washed by stirring in ice water several times.

Next, 100 g of 5 wt % NaOH solution was dropped into the solution to completely dissolve the precipitate. This solution was suction filtered to recover the filtrate. Dilute hydrochloric acid solution (38% concentrated hydrochloric acid/ion-exchanged water = 20/80 vol%) was dropped into the recovered filtrate until the pH reached approximately 3. This caused a white cotton-like solid to precipitate again. The precipitate was washed with ion-exchanged water until it became neutral, and then dried at 150°C for 10 hours to obtain BAPFDS.

[Synthesis of polyimide P1]
Next, polyimide P1 was synthesized using a separable flask (volume 2000 mL) and an oil bath. The separable flask was equipped with a Dimroth, a stirring rod, an internal thermometer, a nitrogen inlet tube, and a flat stopper. A cooling liquid set to 10°C was circulated in the Dimroth chiller. _N2 gas was circulated in the flask at a flow rate of 100 mL/min. The stirring speed was set to 300 rpm. Next, 610 g of 1-methyl-2-pyrrolidone (super dehydrated) as a solvent, 9.859 g (0.066 mol) of 2,4,6-trimethyl-1,3-phenylenediamine (TrMPD) as a diamine, 18.003 g (0.066 mol) of 3,7-diamino-2,8-dimethyldibenzothiophenesulfone (DDBT), 28.606 g (0.056 mol) of 9,9-bis(4-aminophenyl)fluorene-2,7-disulfonic acid (BAPFDS), and 11.384 g (0.112 mol) of triethylamine were added to the flask. The diamine was dissolved in the solvent by stirring at room temperature. To the obtained solution, 51.036 g (0.190 mol) of naphthalene-1,4,5,8-tetracarboxylic dianhydride (NTDA) as a tetracarboxylic dianhydride and 45.794 g (0.375 mol) of benzoic acid were further added. The temperature of the oil bath 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 the mixture was allowed to stand overnight.

Next, 48.433 g (0.375 mol) of isoquinoline was added, the temperature of the oil bath was raised again to 180°C, and the mixture was stirred for 8 hours. After leaving the reaction solution to stand overnight, 1500 g of 1-methyl-2-pyrrolidone was added to dilute the reaction solution. Next, using a dropping funnel, 5000 mL of methanol was dropped into the reaction solution over about 30 minutes to perform reprecipitation purification. The precipitated polyimide was filtered off, and the polyimide was washed twice using 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 resulted in a polyimide whose sulfonic acid groups were modified with triethylamine.

Then, the obtained polyimide was added to 1000 g of a dilute hydrochloric acid solution (38% concentrated hydrochloric acid/ion-exchanged water = 20/80 vol%) and stirred at 100 rpm for 48 hours to remove the triethylamine modification. The polyimide was then filtered and washed with ion-exchanged water, and this operation was repeated several times. Next, it was dried in a hot air circulation dryer at 60°C for 15 hours, and further dried in a vacuum dryer at 100°C for 8 hours. This resulted in polyimide P1 being obtained in a yield of 71.6 g. Polyimide P1 had a sulfonic acid group as the functional group f.

[Preparation of separation functional layer]
The polyimide P1 was dissolved in N-methyl-2-pyrrolidone (NMP) to obtain a coating solution with a solid concentration of 4 wt%. This coating solution was applied onto a polyimide film that had been subjected to a peeling treatment to obtain a coating film. The thickness of the coating film was adjusted to 3 μm after drying. This coating film was heated and dried at 130° C. for 30 minutes, and further heated at 300° C. for 10 minutes in a nitrogen atmosphere to obtain a separation functional layer (self-supporting film) of Example 1. This self-supporting film was peeled off from the polyimide film and used. In Example 1, crosslinked polyimide was not formed from the polyimide P1.

(Examples 2 to 3)
The separation functional layers (freestanding membranes) of Examples 2 to 3 were obtained by the same method as Example 1, except that when preparing the separation functional layer, an epoxy-based crosslinking agent (TETRAD-C (1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane) manufactured by Mitsubishi Gas Chemical Company, Inc.) was added to the coating solution, and the weight ratio of the epoxy-based crosslinking agent to the weight of polyimide P1 was adjusted as shown in Table 1. In Examples 2 to 3, when the coating film was dried, the functional group f (sulfonic acid group) contained in polyimide P1 reacted with the epoxy-based crosslinking agent to form a crosslinked polyimide from polyimide P1. This crosslinked polyimide had a structure in which polyimide P1 was crosslinked via a covalent bond.

(Examples 4-5)
The separation functional layers (self-supporting membranes) of Examples 4 to 5 were obtained by the same method as in Example 1, except that when preparing the separation functional layer, an amine-based crosslinking agent (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., Epomin (polyethyleneimine), weight average molecular weight 600) was added to the coating solution, and the weight ratio of the amine-based crosslinking agent to the weight of polyimide P1 was adjusted as shown in Table 1. In Examples 4 to 5, when the coating film was dried, the functional group f (sulfonic acid group) contained in polyimide P1 reacted with the amine-based crosslinking agent to form a crosslinked polyimide from polyimide P1. This crosslinked polyimide had a structure in which polyimide P1 was crosslinked via a covalent bond.

(Example 6)
First, a separation functional layer (dried membrane) was prepared by the same method as in Example 1. The membrane was peeled off from the polyimide film and immersed in Eaton's reagent in a glass container. In this state, by heating at 80°C for 2 hours, a condensation reaction of the functional group f (sulfonic acid group) contained in polyimide P1 proceeded, and a crosslinked polyimide was formed. This crosslinked polyimide had a structure in which polyimide P1 was crosslinked via a covalent bond. The membrane was taken out of the container, and the operation of immersing in ion-exchanged water for 4 hours and washing was repeated three times, and a drying process was performed to obtain a separation functional layer (self-supporting membrane) of Example 6.

(Example 7)
First, polyimide P2 was prepared in the same manner as in Example 1, except that the types and ratios of diamines were changed as shown in Table 1 and the treatment with dilute hydrochloric acid solution was omitted. Polyimide P2 had a carboxyl group as the functional group f.

Next, polyimide P2 was added to a 10L pail, and N-methyl-2-pyrrolidone (NMP) as a solvent and acetylacetone as a ligand were added to obtain a mixed solution. This mixed solution was stirred for 1 hour at 700 to 1400 rpm using a propeller-type stirring blade. Next, NMP and Al(acac) ₃ as a metal complex were added to another screw tube, and an ultrasonic treatment was performed using an ultrasonic cleaner to obtain an Al(acac) ₃ solution. The Al(acac) ₃ solution and the above mixed solution were further mixed, and the mixture was stirred for 1 hour at 700 to 1400 rpm using a propeller-type stirring blade to prepare a coating solution.

In the coating solution, the ratio of the weight of polyimide P2 to the total weight of polyimide P2 and NMP was 8 wt %, and the ratio of the weight of NMP to the total weight was 92 wt %. In the coating solution, the ratio of the weight of Al(acac) ₃ to the weight of polyimide P2 and the weight of acetylacetone to the weight of polyimide P2 were both 6 wt %.

Next, a release-treated polyethylene terephthalate (PET) film (Mitsubishi Chemical Corporation, MRF75T302) was prepared as a substrate. Corona treatment was performed on the release-treated surface of this substrate under the condition of a discharge amount of 0.25 kW min/ ^m2 . Next, the above coating liquid was applied onto the substrate to form a coating film. The coating liquid was applied using a slot die.

Then, the coating film was transported at a speed of 1 m/min and passed through three heating sections to dry the coating film. In detail, the coating film passed through the first heating section, the second heating section, and the third heating section in this order. The set temperature of the first heating section was 100°C, the set temperature of the second heating section was 130°C, and the set temperature of the third heating section was 130°C. The time (drying time) for the coating film to pass through the first to third heating sections was 6 minutes. The coating film was dried to obtain a separation functional layer. Note that, as the coating film dried, the dissociative protons of the functional group f (carboxyl group) contained in the polyimide P2 were exchanged with Al of the metal complex. As a result, a crosslinked polyimide in which the polyimide P2 was crosslinked via ionic bonds was formed.

Then, the substrate was removed from the laminate of the separation functional layer and the substrate. Furthermore, the separation functional layer was subjected to a further heat treatment. The heat treatment was performed at 300°C for 30 minutes. This resulted in the separation functional layer (freestanding film) of Example 7.

(Example 8)
First, polyimide P3 was prepared by the same method as in Example 1, except that the types and ratios of diamines were changed as shown in Table 1. Polyimide P3 had a sulfonic acid group as the functional group f.

Next, a separation functional layer (dried membrane) was prepared by the same method as in Example 1, except that polyimide P3 was used. This membrane was peeled off from the polyimide film, immersed in methanol for 24 hours, and then removed and immersed in acetone for 15 hours. The immersed membrane was dried for 8 hours in a vacuum dryer at 120°C. The dried membrane was immersed in an aqueous solution of Al( _NO3 ) ₃ with a concentration of 0.1 mol/L for 24 hours. At this time, the aqueous solution was replaced with a new one three times during the 24 hours. This operation caused the dissociative protons of the functional group f (sulfonic acid group) contained in polyimide P3 to be exchanged with Al. As a result, a crosslinked polyimide in which polyimide P3 was crosslinked via ionic bonds was formed.

Then, the membrane was immersed in ion-exchanged water for 24 hours to wash it. During this operation, the ion-exchanged water was replaced with fresh water three times. Next, the membrane was dried at 120°C for 8 hours. This resulted in the separation functional layer (freestanding membrane) of Example 8.

(Example 9)
The separation functional layer (free-standing membrane) of Example 9 was obtained by the same method as in Example 8, except that polyimide P4 was prepared by changing the diamine ratio as shown in Table 1 and polyimide P4 was used instead of polyimide P3.

(Example 10)
A separation functional layer (self-supporting film) of Example 10 was obtained by the same method as in Example 7, except that the polyimide P2 was replaced by the polyimide P1 prepared in Example 1, and the weight ratio of Al(acac) ₃ to the weight of polyimide P1 in the coating solution and the weight of acetylacetone to the weight of polyimide P1 were changed to 15 wt %.

(Example 11)
The separation functional layer (self-supporting membrane) of Example 11 was obtained by the same method as in Example 7, except that the ratio of diamines was changed as shown in Table 1 to prepare polyimide P5, polyimide P2 was replaced with polyimide P5, and the weight ratio of Al(acac) ₃ to polyimide P5 and the weight of acetylacetone to polyimide P5 in the coating solution were changed to 25 wt %.

[Evaluation of characteristics of separation functional layer]
(Gas Permeability Test)
The carbon dioxide permeation rate T1 and the separation factor α (CO ₂ /N ₂ ) of carbon dioxide relative to nitrogen were measured for the prepared separation functional layer by the following method. 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 was substantially composed of carbon dioxide and nitrogen. The concentration of carbon dioxide 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 by 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 permeation fluid was obtained from the other main surface of the separation functional layer. The permeation rate T1 and the separation factor α were calculated based on the composition of the obtained permeation fluid, the weight of the permeation fluid, and the like.

(Durability test)
The prepared separation functional layer was subjected to a durability test by heat treatment at 85° C. for 500 hours. After the durability test, the separation functional layer was measured for the carbon dioxide permeation rate T2 by the same method as for the permeation rate T1. From the obtained results, the ratio T2/T1 of the permeation rate T2 to the permeation rate T1 (permeation rate maintenance rate) was calculated.

[Mechanical strength]
The prepared separation functional layer was subjected to a bending test by the following method. First, the separation functional layer was cut into a size of 50 mm length x 50 mm width to prepare a test piece. Next, this test piece was wound up into a cylindrical roll with an outer diameter of 5 mm and left in a room temperature environment for 24 hours. After the bending test, the separation functional layer was visually checked for the presence or absence of breakage.

[Gel fraction]
The gel fraction of the prepared separation functional layer was measured by the method described above.

The abbreviations in Table 1 are as follows.
NTDA: naphthalene-1,4,5,8-tetracarboxylic dianhydride (a compound represented by formula (a1) in which R ^1a to R ^4a are hydrogen atoms)
TrMPD: 2,4,6-trimethyl-1,3-phenylenediamine (a compound represented by formula (e1) in which R ^1e , R ^2e and R ^4e are methyl groups and R ^3e is a hydrogen atom)
DDBT: 3,7-diamino-2,8-dimethyldibenzothiophene sulfone (a compound represented by formula (d1) in which R ^2d and R ^5d are methyl groups, and R ^1d , R ^3d , R ^4d and R ^6d are hydrogen atoms)
MBAA: 5,5'-methylenebis(2-aminobenzoic acid) (a compound in which, in formula (c2), R ^5c and R ^10c are carboxyl groups, R ^6c to R ^9c , R ^11c and R ^12c are hydrogen atoms, and X ¹ is a methylene group)
BAPFDS: 9,9-bis(4-aminophenyl)fluorene-2,7-disulfonic acid (a compound in which, in formula (b2), R ^10b and R ^15b are sulfonic acid groups, and R ^1b to R ^9b , R ^11b to R ^14b and R ^16b are hydrogen atoms)
TETRAD-C: Epoxy crosslinking agent (manufactured by Mitsubishi Gas Chemical Company, Inc., TETRAD-C (1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane))
PEI: Amine-based crosslinking agent (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., Epomin (polyethyleneimine), weight average molecular weight 600)

As can be seen from Table 1, the separation functional layers of Examples 2 to 6, which contain crosslinked polyimides in which polyimides are crosslinked via covalent bonds, had a higher retention rate of permeation rate than the separation functional layer of Example 1, which does not contain crosslinked polyimide, and the separation functional layers of Examples 7 to 11, which contain crosslinked polyimides in which polyimides are crosslinked via ionic bonds. 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.

The separation functional layers of Examples 2 to 6 also tended to have a higher gel fraction than the separation functional layers of Examples 7 to 11. The separation functional layers of Examples 2 to 6 had an initial permeation rate T1 of 50 GPU or more and a separation coefficient α of 30 or more, both of which were sufficient for practical use.

The separation functional layer and separation membrane of the present embodiment are suitable for separating an acidic gas from a mixed gas containing the acidic gas. In particular, the separation functional layer and separation membrane of the present embodiment are suitable for separating carbon dioxide from off-gas of a chemical plant or thermal power plant.

Claims (15)

A separation functional layer including a crosslinked polyimide,
The crosslinked polyimide is a polyimide crosslinked via a covalent bond,
The polyimide comprises a structural unit A1 derived from a tetracarboxylic dianhydride having a six-membered ring acid anhydride structure. The polyimide further includes a structural unit B1 derived from a diamine,
2. The separation functional layer according to claim 1, wherein at least one of the structural unit A1 and the structural unit B1 has at least one functional group f selected from the group consisting of a sulfonic acid group, a carboxyl group, a hydroxyl group, and a thiol group. The separation functional layer according to claim 2, wherein the cross-linked polyimide is formed by reacting the functional group f with a cross-linking agent. The separation functional layer according to claim 3, wherein the crosslinking agent includes at least one selected from the group consisting of epoxy-based crosslinking agents and amine-based crosslinking agents. The separation functional layer according to claim 3, wherein the crosslinking agent functions as a condensation agent that promotes the condensation reaction of the functional group f. The separation functional layer according to claim 2, wherein the structural unit B1 has the functional group f. The separation functional layer according to claim 6, wherein in the polyimide, the ratio of the amount of substance of the structural unit B1 having the functional group f to the amount of substance of all structural units B derived from diamine is 1 to 60 mol %. The separation functional layer according to claim 6 , wherein the structural unit B1 is represented by the following formula (B1):

In the formula (B1), Ar ¹ and Ar ² are each independently an aromatic group, and Ar ³ is an aromatic group containing the functional group f. The separation functional layer according to claim 6 , wherein the structural unit B1 is represented by the following formula (B2):

In the formula (B2), R ^1b to R ^16b are each independently a hydrogen atom or an arbitrary substituent, provided that at least one selected from the group consisting of R ^9b to R ^16b is a group containing the functional group f. The separation functional layer according to claim 9, wherein, in formula (B2), at least one selected from the group consisting of R ^9b to R ^12b is a group containing the functional group f, and at least one selected from the group consisting of R ^13b to R ^16b is a group containing the functional group f. The separation functional layer according to claim 1 , wherein the structural unit A1 is represented by the following formula (A1):

In the formula (A1), R ^1a to R ^4a are each independently a hydrogen atom or an arbitrary substituent. The separation functional layer according to claim 1, having a gel fraction of 70% or more. The separation functional layer according to claim 1, which is used to separate an acidic gas from a gas mixture containing the acidic gas. A separation functional layer according to any one of claims 1 to 13,
A porous support supporting the separation functional layer;
A separation membrane comprising: A method for producing the separation functional layer according to any one of claims 1 to 13,
The manufacturing method includes:
applying a coating liquid containing the polyimide onto a substrate to form a coating film;
drying the coating film to form the crosslinked polyimide from the polyimide;
A method for producing a separation functional layer, comprising:

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