WO2024101000A1

WO2024101000A1 - Separation membrane and method for producing same

Info

Publication number: WO2024101000A1
Application number: PCT/JP2023/033990
Authority: WO
Inventors: 伶哉日野; 賢輔谷; 俊亮佐山; 雅士三宅; 信近藤
Original assignee: 日東電工株式会社
Priority date: 2022-11-11
Filing date: 2023-09-19
Publication date: 2024-05-16
Also published as: CN118369151A

Abstract

The present invention provides a novel separation membrane that is suitable for separation of an acidic gas from a gas mixture that contains the acidic gas. A separation membrane 10 according to the present invention is provided with: a separation function layer 1 that contains a polyimide P1; and a porous support 2 that is in direct contact with the separation function layer 1. The polyimide P1 comprises a constituent unit A1 which is derived from a tetracarboxylic acid dianhydride that has an acid anhydride structure having a six-membered ring. With respect to the separation coefficient α of the separation membrane 10, the separation coefficient α being identified by test 1, the ratio R of the value obtained by multiplying the standard deviation σ1 by 3 to the average Av1 is 70% or less.

Description

Separation membrane and method for producing same

The present invention relates to a separation membrane and a method for producing the same.

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 new separation membranes suitable for separating acid gases from gas mixtures that contain acid gases.

The present invention relates to
A separation functional layer including polyimide P1;
A porous support directly contacting the separation functional layer;
Equipped with
The polyimide P1 contains a structural unit A1 derived from a tetracarboxylic dianhydride having a 6-membered ring acid anhydride structure,
The present invention provides a separation membrane having a ratio R of the value obtained by multiplying the standard deviation σ1 by 3 to the average value Av1 for a separation factor α determined by the following Test 1 of 70% or less.
Test 1: The separation membrane is cut to prepare three or more test pieces. For each of the test pieces, a mixed gas consisting of carbon dioxide and nitrogen is supplied to a space adjacent to one side of the test piece, and the space adjacent to the other side of the test piece is depressurized. Based on the results of the operation, a separation coefficient α of carbon dioxide relative to nitrogen is determined for each of the test pieces. Here, in the operation, the carbon dioxide content in the mixed gas is 50 vol% under standard conditions, the mixed gas supplied to the space adjacent to the one side has a temperature of 30° C. and a pressure of 0.1 MPa, and the space adjacent to the other side is depressurized so that the pressure in the space is 0.1 MPa lower than the atmospheric pressure in the measurement environment.

Further, the present invention relates to
A method for producing a separation membrane comprising a separation functional layer containing polyimide P1 and a porous support directly in contact with the separation functional layer,
The manufacturing method includes:
A step I of forming the separation functional layer by applying a first coating liquid containing a material for the separation functional layer onto a substrate and drying the first coating liquid;
A step II of applying a second coating liquid containing a material for the porous support and a porosifying agent onto the separation functional layer to form a coating film;
Step III of removing the porosifying agent from the coating film to form the porous support;
Including,
The polyimide P1 contains a structural unit A1 derived from a tetracarboxylic dianhydride having a six-membered ring acid anhydride structure.

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

1 is a cross-sectional view showing a schematic diagram of a separation membrane according to one embodiment of the present invention. 1A to 1C are diagrams for explaining a method for producing a separation membrane. 1A to 1C are diagrams for explaining a method for producing a separation membrane. 1A to 1C are diagrams for explaining a method for producing a separation membrane. 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 membrane according to the first aspect of the present invention is
A separation functional layer including polyimide P1;
A porous support directly contacting the separation functional layer;
Equipped with
The polyimide P1 contains a structural unit A1 derived from a tetracarboxylic dianhydride having a 6-membered ring acid anhydride structure,
For the separation factor α specified by the following Test 1, the ratio R of the value obtained by multiplying the standard deviation σ1 by 3 to the average value Av1 is 70% or less.
Test 1: The separation membrane is cut to prepare three or more test pieces. For each of the test pieces, a mixed gas consisting of carbon dioxide and nitrogen is supplied to a space adjacent to one side of the test piece, and the space adjacent to the other side of the test piece is depressurized. Based on the results of the operation, a separation coefficient α of carbon dioxide relative to nitrogen is determined for each of the test pieces. Here, in the operation, the carbon dioxide content in the mixed gas is 50 vol% under standard conditions, the mixed gas supplied to the space adjacent to the one side has a temperature of 30° C. and a pressure of 0.1 MPa, and the space adjacent to the other side is depressurized so that the pressure in the space is 0.1 MPa lower than the atmospheric pressure in the measurement environment.

In the second aspect of the present invention, for example, in the separation membrane according to the first aspect, the average value Av1 is 20 or more.

In a third aspect of the present invention, for example, in the separation membrane according to the first or second aspect, the average permeation rate Av2 determined by the following Test 2 is 300 GPU or more.
Test 2: Three or more test pieces are prepared by the same method as in Test 1, and the above operation is carried out for each of the test pieces. Based on the results of the above operation, the permeation rate of carbon dioxide that permeated the test piece is determined for each of the test pieces.

In the fourth aspect of the present invention, for example, in the separation membrane according to any one of the first to third aspects, the thickness of the separation functional layer is 3 μm or less.

In the fifth aspect of the present invention, for example, in the separation membrane according to any one of the first to fourth aspects, the total thickness of the separation functional layer and the porous support is 30 μm or more.

In a sixth aspect of the present invention, for example, in the separation membrane according to any one of the first to fifth aspects, the structural unit A1 is represented by the following formula (A1).

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

In the seventh aspect of the present invention, for example, in the separation membrane according to any one of the first to sixth aspects, the polyimide P1 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 carboxyl group, a hydroxyl group, a thiol group, and metal salts thereof.

In the eighth aspect of the present invention, for example, in the separation membrane according to any one of the first to seventh aspects, the porous support includes polyimide P2.

In the ninth aspect of the present invention, for example, in the separation membrane according to the eighth aspect, the polyimide P2 contains the structural unit A1.

A manufacturing method according to a tenth aspect of the present invention includes the steps of:
A method for producing a separation membrane comprising a separation functional layer containing polyimide P1 and a porous support directly in contact with the separation functional layer,
The manufacturing method includes:
A step I of forming the separation functional layer by applying a first coating liquid containing a material for the separation functional layer onto a substrate and drying the first coating liquid;
A step II of applying a second coating liquid containing a material for the porous support and a porosifying agent onto the separation functional layer to form a coating film;
Step III of removing the porosifying agent from the coating film to form the porous support;
Including,
The polyimide P1 contains a structural unit A1 derived from a tetracarboxylic dianhydride having a six-membered ring acid anhydride structure.

In the eleventh aspect of the present invention, for example, in the manufacturing method according to the tenth aspect, the polyimide P1 further includes 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 carboxyl group, a hydroxyl group, a thiol group, and metal salts thereof.

In the twelfth aspect of the present invention, for example, in the manufacturing method according to the eleventh aspect, at least one of the structural unit A1 and the structural unit B1 has the metal salt.

In the thirteenth aspect of the present invention, for example, in the manufacturing method according to the twelfth aspect, the first coating liquid contains, as the material of the separation functional layer, polyimide P having at least one functional group f selected from the group consisting of a carboxyl group, a hydroxyl group, and a thiol group, and a compound having a metal, and in the step I, the polyimide P1 is formed from the polyimide P.

In a fourteenth aspect of the present invention, for example in the manufacturing method according to the thirteenth aspect, the compound includes a metal complex having the metal and a ligand coordinated to the metal.

In a fifteenth aspect of the present invention, for example, in a manufacturing method according to any one of the tenth to fourteenth aspects, the porosifying agent includes at least one selected from the group consisting of ether compounds and phosphoric acid compounds.

In the sixteenth aspect of the present invention, for example in the manufacturing method according to any one of the tenth to fifteenth aspects, the porosifying agent is removed from the coating film by drying the coating film.

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 membrane>
As shown in Fig. 1, the separation membrane 10 of this embodiment includes a separation functional layer 1 and a porous support 2, and is, for example, composed of only the separation functional layer 1 and the porous support 2. The porous support 2 is in direct contact with the separation functional layer 1 and supports the separation functional layer 1. The separation functional layer 1 and the porous support 2 are, for example, integrated. In this specification, "integrated" means that the members cannot be separated from each other without destruction.

The separation functional layer 1 contains polyimide P1. Polyimide P1 contains a structural unit A1 derived from tetracarboxylic dianhydride a1 having a six-membered ring acid anhydride structure S.

In the separation membrane 10, with respect to the separation factor α determined by the following test 1, the ratio R of the value obtained by multiplying the standard deviation σ1 by 3 to the average value Av1 is 70% or less.
Test 1: The separation membrane 10 is cut to prepare three or more test pieces. For each test piece, a mixed gas consisting of carbon dioxide and nitrogen is supplied to the space adjacent to one side of the test piece, and the space adjacent to the other side of the test piece is depressurized (separation operation). Based on the results of the separation operation, the separation coefficient α of carbon dioxide relative to nitrogen is specified for each test piece. Here, in the separation operation, the carbon dioxide content in the mixed gas is 50 vol% under standard conditions, the mixed gas supplied to the space adjacent to one side has a temperature of 30° C. and a pressure of 0.1 MPa, and the space adjacent to the other side is depressurized so that the pressure in the space is 0.1 MPa lower than the atmospheric pressure in the measurement environment.

In Test 1, each test piece has the same shape and size, for example, a disk shape with a diameter of 20 mm. The size of the disk-shaped test piece may be 20 mm or more in diameter.

The separation operation of Test 1 can be performed, for example, by the following method. First, the test piece is set in a metal cell and sealed with an O-ring to prevent leakage. Next, the mixed gas is injected into the space (supply space) in the metal cell so that the mixed gas contacts the main surface 11 on the separation function layer side of the test piece. As described above, the carbon dioxide content of the mixed gas injected into the supply space is 50 vol% under standard conditions (0°C, 101 kPa). The mixed gas has a temperature of 30°C and a pressure of 0.1 MPa. In this specification, unless otherwise specified, "pressure" means absolute pressure.

Next, the space (permeation space) in the metal cell adjacent to the main surface 12 on the porous support side of the test piece is depressurized by a vacuum pump. At this time, the permeation space is depressurized so that the pressure in the space is 0.1 MPa lower than the atmospheric pressure in the measurement environment. As a result, a permeation fluid that has permeated the test piece is obtained in the permeation space. The separation factor α (CO ₂ /N ₂ ) of carbon dioxide relative to nitrogen can be calculated based on the weight of the permeation fluid and the volume ratio of carbon dioxide and the volume ratio of nitrogen in the permeation fluid. In detail, 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 permeation fluid that has permeated the test piece, respectively. These volume ratios are values at standard conditions (0° C., 101 kPa).
Separation factor α=( _YA / _YB )/( _XA / _XB )

The average value Av1 and standard deviation σ1 of the separation coefficient α are calculated based on the separation coefficient α of each test piece specified by Test 1. Based on these, the ratio R (%) can be calculated by the following formula.
Ratio R = 100 × 3 × standard deviation σ1 / average value Av1

As described above, the ratio R is 70% or less, preferably 60% or less, and may be 50% or less, 40% or less, 30% or less, 20% or less, 15% or less, or even 10% or less. It can be said that the lower the ratio R, the more the variation in the separation coefficient α in each test piece is suppressed. The lower limit of the ratio R is not particularly limited, and may be, for example, 1% or more, or 5% or more.

In this embodiment, it is preferable that the average value Av1 of the separation coefficient α is large. The average value Av1 is, for example, 20 or more, and may be 25 or more, 30 or more, or even 35 or more. The upper limit of the average value Av1 is not particularly limited, and may be, for example, 100, or 50.

Furthermore, the separation membrane 10 of the present embodiment preferably has an average permeation rate Av2 determined by the following Test 2 of 300 GPU or more.
Test 2: Three or more test pieces are prepared by the same method as in Test 1, and the above-mentioned separation operation is carried out for each of the test pieces. Based on the results of the separation operation, the permeation rate of carbon dioxide that permeated the test piece is determined for each of the test pieces.

In Test 2, each test piece has the same shape and size, for example, a disk shape with a diameter of 20 mm. The size of the disk-shaped test piece may be 20 mm or more in diameter. In Test 2, the permeation rate of carbon dioxide that has permeated the test piece can be specified for each test piece based on the results of the separation operation described above in Test 1. Note that GPU, which is the unit of permeation rate, 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. Based on the permeation rate of each test piece specified by Test 2, the average permeation rate Av2 can be calculated.

In this embodiment, it is preferable that the average value Av2 of the transmission speed is large. The average value Av2 is, for example, 300 GPU or more, and may be 400 GPU or more, 500 GPU or more, 600 GPU or more, 700 GPU or more, 800 GPU or more, 900 GPU or more, 1000 GPU or more, or even 1100 GPU or more. The upper limit of the average value Av2 is not particularly limited, and is, for example, 3000 GPU.

(Separation functional layer)
The separation functional layer 1 is, for example, a layer that allows preferential permeation of acidic gases contained in a mixed gas, and is typically a dense layer (non-porous layer) in which no pores can be identified when observed at a magnification of 5000 times using a scanning electron microscope (SEM).

As described above, in this embodiment, the separation functional layer 1 includes polyimide P1. Polyimide P1 includes a structural unit A1 derived from a tetracarboxylic dianhydride a1 having a six-membered ring acid anhydride structure S, and further includes, for example, a structural unit B1 derived from a diamine b1. At least one of the structural units A1 and B1 has at least one functional group F selected from the group consisting of, for example, a carboxyl group, a hydroxyl group, a thiol group, and metal salts thereof. At least one of the structural units A1 and B1 preferably has a metal salt as the functional group F. In particular, in polyimide P1, it is preferable that the structural unit B1 has a functional group F. The 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 has, for example, 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).

The tetracarboxylic dianhydride a1 may further have at least one functional group f selected from the group consisting of a carboxyl group, a hydroxyl group, and a thiol group, or may not have the functional group f. In this specification, the functional group f is the same as the functional group F, except that metal salts are not included as an option.

The tetracarboxylic dianhydride a1 may have a condensed ring, and the condensed ring may contain an 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 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 represented, for example, 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 P1, the structural unit A1 derived from the tetracarboxylic dianhydride a1 is represented, for example, 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 that has 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 P1, 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 P1 may contain only the structural unit A1 as the structural unit A derived from tetracarboxylic dianhydride. However, the polyimide P1 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 the 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 a compound having two primary amino groups and further having at least one functional group f selected from the group consisting of, for example, a carboxyl group, a hydroxyl group, and a thiol group. The number of functional groups f in diamine b1 is not particularly limited, and is, for example, 5 or less, preferably 2 or less, and particularly preferably 1. The fewer the number of functional groups f in diamine b1, the more improved the solubility of polyimide P1 is, and the easier it tends to be to apply a desired manufacturing method for separation functional layer 1.

The above-mentioned functional group f has a dissociable proton and can form a salt with a counter cation. In particular, from the viewpoint of easily forming a salt, it is preferable that diamine b1 has a carboxyl group as the functional group f. It is preferable that diamine b1 does not have a group having a dissociable proton other than the functional group f, such as a sulfonic acid group. As an example, when diamine b1 does not contain a sulfonic acid group, it is easy to appropriately adjust the solubility of polyimide P1.

Diamine b1 may further have an aromatic ring. Examples of the aromatic ring include those described above for tetracarboxylic dianhydride a1. In diamine b1, the substituent of the aromatic ring includes, for example, functional group f and 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 include, but are not limited to, 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 (for example, a vinyl group).

Diamine b1 is represented, for example, by the following formula (b1), formula (b2) or formula (b3).

In formula (b1), R ^1b to R ^4b are each independently a hydrogen atom or an arbitrary substituent. However, at least one selected from the group consisting of R ^1b to R ^4b 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), R ^5b to R ^12b 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 ^5b to R ^12b 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 (b2), 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 (b3), R ^13b to R ^20b 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 ^13b to R ^20b 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 (b3), 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.

As described above, in the polyimide P1, the structural unit B1 derived from the diamine b1 preferably has a functional group F. In particular, the structural unit B1 preferably contains, as the functional group F, a metal salt of a carboxyl group, a metal salt of a hydroxyl group, or a metal salt of a thiol group, and it is particularly preferable that the structural unit B1 contains a metal salt of a carboxyl group.

The metal contained in the metal salt as functional group F is not particularly limited, and examples thereof include Li, Na, K, Be, Mg, Ca, Ba, Sc, Y, Ti, Zr, V, Cr, Mo, Mn, Fe, Co, Ni, Cu, Ag, Zn, B, Al, Ga, In, Pb, etc., and preferably Mg, Fe, Al, and Ga, and particularly preferably Al. In other words, the metal salt as functional group F is preferably an aluminum salt. The metal contained in the metal salt may be Na, Ca, etc.

In the metal salt as the functional group F, the metal is present, in particular, as a cation. The valence of this metal cation is, for example, 1 or more, preferably 2 or more, and more preferably 3 or more. As an example, the valence of the metal cation is 2 or 3.

When the structural unit B1 contains a metal salt as the functional group F, multiple polyimides P1 can be coordinated to metal cations contained in the metal salt via functional groups such as carboxyl groups. As a result, multiple polyimides P1 are crosslinked with each other via metal cations. By forming such a crosslinked structure, physical aging of the polyimide P1 is suppressed, and thus the separation performance of the separation functional layer 1 tends to be suppressed from decreasing over time. When the polyimide P1 contains a metal salt as the functional group F, the separation performance of the separation functional layer 1 also tends to be improved. As described later, the metal salt as the functional group F can be formed by exchanging a dissociable proton with a metal cation for a functional group f contained in the polyimide P obtained from a monomer group including, for example, tetracarboxylic dianhydride a1 and diamine b1.

The structural unit B1 derived from diamine b1 is represented, for example, by the following formula (B1), formula (B2) or formula (B3). The structural unit B1 represented by formula (B1) is derived from diamine b1 represented by the above formula (b1). The structural unit B1 represented by formula (B2) is derived from diamine b1 represented by the above formula (b2). The structural unit B1 represented by formula (B3) is derived from diamine b1 represented by the above formula (b3).

Specific examples of the structural unit B1 represented by formula (B1) include the following formulae (B1-1) to (B1-6). In formulae (B1-2), (B1-4) and (B1-6), M is any metal cation, preferably an Mg ion, an Fe ion, an Al ion or a Ga ion, and particularly preferably an Al ion. M may also be an Na ion or a Ca ion.

In the formula (B2) ^{, 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 (B2) include the following formulae (B2-1) to (B2-12). In these formulae, M is any metal cation, preferably an Mg ion, an Fe ion, an Al ion, or a Ga ion, and particularly preferably an Al ion. M may also be a Na ion or a Ca ion.

In the formula (B3) ^{, 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 (B3) include the following formulae (B3-1) to (B3-6). In these formulae, M is any metal cation, preferably an Mg ion, an Fe ion, an Al ion, or a Ga ion, and particularly preferably an Al ion. M may also be a Na ion or a Ca ion.

In the polyimide P1, the ratio p2 of the amount of substance of the structural unit B1, particularly the structural unit B1 having a functional group F, to the amount of substance of all structural units B derived from diamine is, for example, 1 mol% or more, and may be 3 mol% or more. The upper limit of the ratio p2 is not particularly limited, and may be, for example, 60 mol%, 50 mol%, 40 mol%, 30 mol%, or even 25 mol%. When the ratio p2 is low, the solubility of the polyimide P1 is improved, and the desired manufacturing method of the separation functional layer 1 tends to be easier to apply. Furthermore, in this case, the strength of the separation functional layer 1 also tends to be improved. The ratio p2 is preferably 1 to 25 mol%. When the ratio p2 is in this range, the separation performance of the separation functional layer 1 tends to be good.

Polyimide P1 may further contain a structural unit B2 derived from diamine b2 having a sulfonyl group (-SO ₂ -). The structural unit B2 is a structural unit suitable for improving the permeation coefficient and permeation rate of acidic gases that permeate through the separation functional layer 1. Diamine b2 is a compound having two primary amino groups together with a sulfonyl group. The number of sulfonyl groups in diamine b2 is not particularly limited and is, for example, 5 or less, and preferably 1. Diamine b2 does not contain a group having a dissociable proton, such as the above-mentioned functional group f.

Diamine b2, for example, 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 contains, for example, a primary amino group. The condensed ring may contain other substituents than the substituent containing the 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.

Diamine b2 is represented, for example, by the following formula (c1).

In formula (c1), R ^1c to R ^6c are each independently a hydrogen atom or an arbitrary substituent. In formula (c1), 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 P1, the structural unit B2 derived from the diamine b2 is represented, for example, by the following formula (C1): The structural unit B2 represented by formula (C1) is derived from the diamine b2 represented by the above formula (c1).

In formula (C1), R ^1c to R ^6c are each independently a hydrogen atom or an arbitrary substituent. In formula (C1), 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 (C1) is suitable for improving the rigidity of the polyimide P1. According to the polyimide P1 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 (C1) include the following formulae (C1-1) and (C1-2).

In polyimide P1, 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, 30 mol% or more, or even 40 mol% or more. The upper limit of 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 P1 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. Diamine b3 does not, for example, 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, the substituent of the aromatic ring includes, for example, a primary amino group. The aromatic ring may have other substituents other than the substituent including the primary amino group, or may not have other substituents. Examples of the other substituents include, but are not limited to, halogen groups and hydrocarbon groups. Examples of the halogen groups and hydrocarbon groups include those described above for tetracarboxylic dianhydride a1.

Diamine b3 is represented, for example, by the following formula (d1), formula (d2) or formula (d3).

In formula (d1), R ^1d to R ^4d 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 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 (d2), R ^5d to R ^8d are each independently a hydrogen atom or an arbitrary substituent. In formula (d2), 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 (d3), R ^9d to R ^16d are each independently a hydrogen atom or an arbitrary substituent, and X ³ is a single bond or an arbitrary linking group. In formula (d3), 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 (d3), 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 represented, for example, by the following formula (D1), formula (D2) or formula (D3). The structural unit B3 represented by formula (D1) is derived from diamine b3 represented by the above formula (d1). The structural unit B3 represented by formula (D2) is derived from diamine b3 represented by the above formula (d2). The structural unit B3 represented by formula (D3) is derived from diamine b3 represented by the above formula (d3).

In formula (D1), R ^1d to R ^4d 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. A specific example of the structural unit B3 represented by formula (D1) is the following formula (D1-1).

In formula (D2), R ^5d to R ^8d are each independently a hydrogen atom or an arbitrary substituent. In formula (D2), 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 (D2) is the following formula (D2-1).

In formula (D3), R ^9d to R ^16d are each independently a hydrogen atom or an arbitrary substituent, and X ³ is a single bond or an arbitrary linking group. In formula (D3), 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 (D3), 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 (D3) include the following formulae (D3-1) to (D3-3).

In polyimide P1, 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, 30 mol% or more, or even 40 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 P1, structural units A derived from tetracarboxylic dianhydride and structural units B derived from diamine are arranged alternately. In polyimide P1, examples of combinations of adjacent structural units A and B include the following formulae (A1-B1), (A1-B2), (A1-C1), and (A1-D1). In these formulae, R ^1a to R ^4a , R ^1b to R ^12b , R ^1c to R ^6c , and R ^1d to R ^4d are the same as those described above for formulae (A1), (B1), (B2), (C1), and (D1).

The weight average molecular weight (Mw) of polyimide P1 is, for example, 30,000 or more, preferably 50,000 or more, and more preferably 75,000 or more, from the viewpoint of the mechanical strength of the separation functional layer 1. The upper limit of the weight average molecular weight of polyimide P1 is not particularly limited, and is, for example, 1 million. The weight average molecular weight of polyimide P1 can be calculated, for example, by measuring the molecular weight distribution of polyimide P1 using a gel permeation chromatograph (GPC) equipped with a refractive index detector (RID) and using a calibration curve based on standard polystyrene from the obtained chromatogram (chart).

The content of polyimide P1 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 only polyimide P1.

The separation functional layer 1 may further contain other components in addition to polyimide P1. Examples of other components include fillers such as nanoparticles. The nanoparticles may contain an inorganic material or may contain an organic material. Examples of inorganic materials contained in the nanoparticles include silica, titania, and alumina. In the separation functional layer 1, the fillers are dispersed in a matrix containing, for example, polyimide P1. The fillers may be spaced apart from each other within the matrix, or may be partially aggregated.

In this embodiment, the thickness of the separation functional layer 1 is, for example, 50 μm or less, and may be 25 μm or less, 15 μm or less, 10 μm or less, 8 μm or less, 5 μm or less, 3 μm or less, 2.5 μm or less, 2 μm or less, or even 1.5 μm or less. The lower limit of the thickness of the separation functional layer 1 may be 0.05 μm or 0.1 μm.

The thickness of the separation functional layer 1 can be determined by the following method. First, the cross section of the separation membrane 10 is observed with a scanning electron microscope. Using the obtained electron microscope image, the distance between a pair of opposing main surfaces of the separation functional layer 1 is measured. The above distance is measured at three or more positions, and the average of the obtained values can be regarded as the thickness of the separation functional layer 1. In this embodiment, the variation in the distance between the pair of opposing main surfaces in the separation functional layer 1 tends to be suppressed. In other words, the variation in thickness within the separation functional layer 1 tends to be suppressed. When the variation in thickness within the separation functional layer 1 is suppressed, it can be said that the separation functional layer 1 has a smooth surface. Whether the surface of the separation functional layer 1 is smooth can also be determined by visually observing the reflection of light (visible light) on the surface of the separation functional layer 1.

(Porous Support)
As described above, the porous support 2 is in direct contact with the separation functional layer 1 and supports the separation functional layer 1. The porous support 2 has a porous structure. From the viewpoint of improving the permeation coefficient and permeation rate of the acidic gas permeating the separation membrane 10, the porous support 2 preferably has continuous pores formed continuously in a three-dimensional shape. However, the porous support 2 may have independent pores, or may have both continuous pores and independent pores. The porous support 2 may have through holes penetrating the porous support 2.

The porous support 2 includes, for example, a polymer. Specific examples of the polymer included in the porous support 2 include polyimide P2, polyamide, polyamideimide, polyether ether ketone, polyphenylene sulfide, and the like. It is preferable that the porous support 2 includes polyimide P2. The polyimide P2 included in the porous support 2 may be the polyimide P1 included in the separation functional layer 1 described above, or may be the same as the polyimide P1. In other words, the polyimide P2 may include the structural unit A1 described above. However, the polyimide P2 may be a polyimide other than the polyimide P1 described above.

The polymer (particularly polyimide P2) content in the porous support 2 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 porous support 2 may be composed essentially of polymer only.

In this embodiment, the thickness of the porous support 2 is, for example, 10 μm or more, and may be 30 μm or more, 50 μm or more, 70 μm or more, 90 μm or more, 100 μm or more, or even 110 μm or more. The greater the thickness of the porous support 2, the greater the rigidity of the separation membrane 10 and the easier it tends to be to handle. The upper limit of the thickness of the porous support 2 is, for example, 300 μm.

The thickness of the porous support 2 can be determined by the following method. First, the cross section of the separation membrane 10 is observed with a scanning electron microscope. Using the obtained electron microscope image, the distance between a pair of opposing main surfaces of the porous support 2 is measured. The above distance is measured at three or more positions, and the average of the obtained values can be regarded as the thickness of the porous support 2.

The total value V of the thickness of the separation functional layer 1 and the thickness of the porous support 2 (typically, the thickness of the separation membrane 10) is, for example, 10 μm or more, and may be 30 μm or more, 50 μm or more, 70 μm or more, 90 μm or more, 100 μm or more, or even 110 μm or more. The upper limit of the total value V is, for example, 300 μm.

(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, for example, a hollow fiber membrane.

(Method for producing separation membrane)
2A to 2C, the method for producing the separation membrane 10 of this embodiment is described below. The method for producing the separation membrane 10 includes, for example, step I (FIG. 2A) of forming the separation functional layer 1 by applying a first coating liquid containing the material of the separation functional layer 1 onto a substrate 5 and drying it, step II (FIG. 2B) of forming the coating film 6 by applying a second coating liquid containing the material of the porous support 2 and a porogen onto the separation functional layer 1, and step III (FIG. 2C) of forming the porous support 2 by removing the porogen from the coating film 6.

[Step I]
In step I, in a preferred embodiment, the first coating liquid contains, as materials for the separation functional layer 1, a polyimide P having at least one functional group f selected from the group consisting of a carboxyl group, a hydroxyl group, and a thiol group, and a compound M having a metal. In this embodiment, the polyimide P is a precursor of the polyimide P1, and the polyimide P1 can be formed from the polyimide P by exchanging the dissociative proton of the functional group f with a metal cation. As described later, this first coating liquid can form a polyimide P1 having a metal salt as the functional group F.

Polyimide P can be prepared, for example, by the following method. First, a diamine group including the above-mentioned 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 and 1,3-dioxolane.

Next, the tetracarboxylic dianhydride group including the above-mentioned 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 polyamic acid. The addition of the tetracarboxylic dianhydride group is carried out under stirring conditions, for example, 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, for example, 180°C or higher.

The content of polyimide P in the first coating liquid can be adjusted appropriately depending on the solubility of polyimide P, and is, for example, 1 wt% to 30 wt%. In the first coating liquid, the ratio of the weight of polyimide P to the total weight of polyimide P and the solvent is, for example, 1 wt% to 30 wt%.

The metal contained in compound M includes those mentioned above as the metal contained in the metal salt as functional group F. In compound M, the metal exists, for example, as a cation. Examples of compound M include a metal complex having a metal and a ligand coordinated to the metal, and an inorganic salt containing a metal. Compound M preferably contains a metal complex.

In the metal complex, it is preferable that the ligand is volatile. As an example, the boiling point of the ligand may be 20°C to 260°C under atmospheric pressure (101.325 kPa). A volatile ligand is likely to volatilize when the first coating film described below is dried, and is unlikely to remain in the separation functional layer 1. The ligand does not have to be volatile. In this case, the ligand can be easily removed from the separation functional layer 1 by performing a cleaning operation after the formation of the separation functional layer 1 (or separation membrane 10).

In the metal complex, the ligand is typically an organic ligand having a functional group for coordinating to the metal. The number of carbon atoms in the organic ligand is not particularly limited, and may be, for example, 1 to 10. Examples of the functional group contained in the organic ligand include a carbonyl group such as a ketone group. The number of functional groups contained in the organic ligand may be, for example, 1 or more, and may be 2 or more. A specific example of the organic ligand is acetylacetonate (acac). A specific example of the metal complex is Al(acac) ₃ .

Examples of inorganic salts include chlorides, nitrates, sulfates, etc., and more specifically, LiCl, NaCl, KCl, _AgNO3 , _MgCl2 , _CaCl2 , _BaCl2 , _NiCl2 , _ZnCl2 , _CuCl2 , Pb( _NO3 ) ₂ , Al( _NO3 ) ₃ , _Fe2 ( _SO4 ) ₃ , etc.

In the first coating liquid, the ratio of the weight of compound M to the weight of polyimide P can be adjusted appropriately depending on the composition of polyimide P, and is, for example, 1 to 10 wt %.

When the first coating liquid contains a metal complex as compound M, the first coating liquid may further contain a ligand. In the first coating liquid, the ratio of the weight of the ligand to the weight of the polyimide P can be appropriately adjusted depending on the content of the polyimide P and the metal complex, and is, for example, 1 to 10 wt %.

The first coating liquid further contains, for example, 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 content of the solvent in the first coating liquid is, for example, 30 wt% to 95 wt%. In the first coating liquid, the ratio of the weight of the solvent to the total weight of the polyimide P and the solvent is, for example, 30 wt% to 95 wt%.

The first coating liquid is not limited to the above-mentioned composition. In another preferred embodiment, the first coating liquid contains polyimide P1 instead of the above-mentioned polyimide P and compound M. In this embodiment, polyimide P1 has at least one functional group F selected from the group consisting of, for example, a carboxyl group, a hydroxyl group, a thiol group, and metal salts thereof.

In step I, examples of the substrate 5 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 5 is preferably a film containing resin, since it has excellent surface smoothness. In the substrate 5, examples of the polymer contained in the resin include polyolefins such as polyethylene, polypropylene, polybutene, polybutadiene, and polymethylpentene; polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; polyvinyl chloride, vinyl chloride copolymers; polyurethane; ethylene-vinyl acetate copolymers; and polyimides, with polyesters, particularly polyethylene terephthalate, being preferred.

The surface of the substrate 5 may be subjected to a release treatment. The release treatment may be performed, for example, by applying a release treatment agent to the surface of the substrate 5. 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 5 is preferably a polyethylene terephthalate (PET) film that has been subjected to a release treatment.

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

In step I, a surface modification treatment may be performed on the substrate 5 before the first coating liquid is applied. If the substrate 5 has been subjected to a release treatment, the surface modification treatment may be performed on the surface of the substrate 5 that has been subjected to the release treatment. Examples of the surface modification treatment include corona treatment, plasma treatment, excimer treatment, and frame treatment, and corona treatment is preferred.

The surface modification treatment can be carried out, for example, by irradiating the surface of the substrate 5 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 of applying the first coating liquid to the substrate 5 is not particularly limited, and may be, for example, a spin coating method, a dip coating method, a slot die coating method, or the like. The first coating liquid may be applied to the substrate 5 using an applicator or a wire bar. The first coating liquid may be applied, for example, to the surface of the substrate 5 that has been subjected to a peeling treatment or a surface modification treatment.

A coating film (first coating film) is formed by applying the first coating liquid to the substrate 5. The thickness of the first coating film can be adjusted appropriately according to the desired thickness of the separation functional layer 1, and is, for example, 1 μm to 100 μm.

In step I, the first coating film is dried to obtain the separation functional layer 1 (Figure 2A). The drying conditions for the first 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 first coating film can be dried, for example, using a heater. As an example, the first coating film may be dried by passing it through a heating unit equipped with a heater. The first coating film may be dried by passing it through multiple heating units. The set temperatures of the multiple heating units may be the same or different.

When the first coating liquid contains polyimide P having a functional group f and compound M having a metal, for example, when the first coating film is dried, the dissociable protons contained in the functional group f of polyimide P are exchanged with the metal (metal cation) of compound M. In particular, when compound M is a metal complex and the ligand contained in the metal complex is volatile, the ligand volatilizes during drying, which tends to promote the exchange between the dissociable protons of functional group f and the metal of compound M. The exchange between the dissociable protons of functional group f and the metal of compound M forms a metal salt of functional group f, and polyimide P1 is formed from polyimide P. In the separation functional layer 1 obtained by this method, multiple polyimides P1 are usually crosslinked with each other via metal cations. Due to this crosslinked structure, the separation functional layer 1 tends to have high solvent resistance. Therefore, in this embodiment, when the second coating liquid is applied onto the separation functional layer 1 in step II described later, the separation functional layer 1 tends to be less soluble in the solvent contained in the second coating liquid.

The exchange of the dissociable protons contained in the functional group f of the polyimide P with the metal of the compound M may be performed after the formation of the separation functional layer 1. For example, a first coating liquid containing the above-mentioned polyimide P and a solvent is applied onto the substrate 5 and dried to form the separation functional layer 1. The separation functional layer 1 may be immersed in a solution containing the above-mentioned compound M to exchange the dissociable protons of the functional group f with the metal of the compound M.

Step I is not limited to the above-mentioned method, and for example, the separation functional layer 1 may be formed by applying a first coating liquid containing the above-mentioned polyimide P1 and a solvent onto the substrate 5 and drying it. Alternatively, the separation functional layer 1 may be produced by applying a first coating liquid containing polyamic acid, which is a precursor of polyimide P1, onto the substrate 5 and imidizing the polyamic acid to form polyimide P1.

[Step II]
In step II, the second coating liquid preferably contains the material of the porous support 2 and a porogen, and further contains a solvent. Examples of the material of the porous support 2 include the above-mentioned polymers. When the porous support 2 contains polyimide P2, the composition of the second coating liquid may be the same as the composition described above for the first coating liquid, except for the porogen. That is, the second coating liquid may contain, as the material of the porous support 2, a polyimide P having a functional group f and a compound M having a metal. In this embodiment, the polyimide P is a precursor of the polyimide P2, and the polyimide P2 can be formed from the polyimide P by exchanging the dissociative proton of the functional group f with a metal cation.

The content of the polymer (e.g., polyimide P) in the second coating liquid can be adjusted as appropriate depending on the solubility of the polymer, and is, for example, 1 wt% to 30 wt%. In the second coating liquid, the ratio of the weight of the polymer to the total weight of the polymer, solvent, and porosifying agent is, for example, 1 wt% to 30 wt%.

The porosity-inducing agent is, for example, a poor solvent that hardly dissolves the material of the porous support 2 (for example, polyimide P). The porosity-inducing agent preferably contains at least one selected from the group consisting of ether compounds and phosphoric acid compounds, and more preferably contains a phosphoric acid compound. Examples of ether compounds include glycol compounds such as diethylene glycol, diethylene glycol monomethyl ether, triethylene glycol, triethylene glycol monomethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol, tetraethylene glycol monomethyl ether, tetraethylene glycol dimethyl ether, diethylene glycol butyl methyl ether, tripropylene glycol dimethyl ether, diethylene glycol monobutyl ether, ethylene glycol monophenyl ether, diethylene glycol dibutyl ether, triethylene glycol butyl methyl ether, polyethylene glycol dimethyl ether, polyethylene glycol monomethyl ether, and polyethylene glycol.

Examples of phosphoric acid compounds include phosphate ester compounds such as trimethyl phosphate, ethyl dimethyl phosphate, diethyl methyl phosphate, and triethyl phosphate, with triethyl phosphate being preferred.

From the viewpoint of easily producing the porous support 2, it is preferable that the boiling point of the porosity agent is higher than the boiling point of the solvent contained in the second coating liquid. The boiling point of the porosity agent may be, for example, 50°C or more higher than the boiling point of the solvent, 80°C or more, or even 100°C or more higher. The boiling point of the porosity agent is, for example, 200°C to 350°C.

The content of the porosity agent in the second coating liquid is, for example, 10 wt% to 60 wt%. The content of the porosity agent is preferably higher than the content of the material of the porous support 2. Furthermore, the content of the porosity agent is preferably 25 wt% or more from the viewpoint of suppressing the formation of a dense layer (skin layer) near the surface of the coating film 6 when the coating film 6 is dried, etc. In the second coating liquid, the ratio of the weight of the porosity agent to the total weight of the polymer, solvent, and porosity agent is, for example, 10 wt% to 60 wt%, and preferably 25 wt% or more.

Examples of the solvent contained in the second coating liquid include those mentioned above for the first coating liquid. In the second coating liquid, it is desirable to adjust the type and content of the solvent so that the separation functional layer 1 is hardly dissolved. The content of the solvent in the second coating liquid is, for example, 30 wt% to 80 wt%. In the second coating liquid, the ratio of the weight of the solvent to the total weight of the polymer, solvent, and porosifying agent is, for example, 30 wt% to 80 wt%.

In step II, the method of applying the second coating liquid to the separation functional layer 1 is not particularly limited, and can be performed by the method described above for step I. A coating film (second coating film) 6 is formed by applying the second coating liquid to the separation functional layer 1 (Figure 2B). The thickness of the second coating film 6 can be adjusted appropriately depending on the desired thickness of the porous support 2, and is, for example, 50 μm to 1000 μm.

[Step III]
In step III, when the porogen is removed from the second coating film 6, holes are formed due to the porogen, and the porous support 2 is formed (FIG. 2C). In the manufacturing method of this embodiment, for example, the porogen can be removed from the second coating film 6 by drying the second coating film 6. The drying conditions and drying method of the second coating film 6 are as described above for step I. When the porogen is removed from the second coating film 6, the solvent also tends to be removed from the second coating film 6.

If the second coating liquid contains polyimide P having a functional group f and compound M having a metal, for example, when the second coating film 6 is dried, the dissociable protons contained in the functional group f of the polyimide P are exchanged with the metal (metal cation) of the compound M. The exchange of the dissociable protons of the functional group f with the metal of the compound M forms a metal salt of the functional group f, and polyimide P2 is formed from the polyimide P.

The exchange of the dissociable protons contained in the functional group f of the polyimide P with the metal of the compound M may be carried out after the formation of the porous support 2. For example, a second coating liquid containing the polyimide P, a porosifying agent, and a solvent is applied to the separation functional layer 1, and dried to form the porous support 2. The dissociable protons of the functional group f may be exchanged with the metal of the compound M by immersing the porous support 2 in a solution containing the compound M.

[Step IV]
The manufacturing method of this embodiment may further include step IV, in which the separation functional layer 1 and the porous support 2 are subjected to a heat treatment (annealing treatment) after step III. Step IV tends to improve the separation performance of the separation membrane 10 and also suppress the separation performance of the separation membrane 10 from decreasing over time. Step IV also makes it possible to obtain a separation membrane 10 that contains almost no residual solvent by sufficiently volatilizing the solvent. Step IV may be performed after the step of removing the substrate 5 from the laminate including the separation functional layer 1 and the porous support 2 (step V described below).

In step IV, 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 temperature of the heat treatment is not particularly limited, and may be, for example, 350°C or lower, or may be 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 may be 30 minutes or more. The upper limit of the time of the heat treatment is not particularly limited, and may be, for example, 24 hours or less.

[Process V]
The manufacturing method of this embodiment further includes, for example, after step III or step IV, step V of removing the substrate 5 from the laminate including the separation functional layer 1 and the porous support 2. By removing the substrate 5, a separation membrane 10 can be obtained ( FIG. 1 ).

In step I of the manufacturing method of this embodiment, the first coating film is dried in contact with the substrate 5 to form the separation functional layer 1. When the separation functional layer 1 is formed, its surface is in contact with the substrate 5, so that defects such as pinholes tend not to form on the surface. The separation functional layer 1 produced by this method also tends to have reduced thickness variation within the membrane. Due to these factors, the separation membrane 10 produced by the manufacturing method of this embodiment has reduced separation performance variation within the membrane. In this way, the manufacturing method of this embodiment is suitable for reducing the above-mentioned ratio R related to the separation coefficient α of the separation membrane 10. Furthermore, the manufacturing method of this embodiment has the advantage that the thicknesses of the separation functional layer 1 and the porous support 2 can be easily adjusted independently.

According to the study of the present inventors, for example, when a coating solution containing polyimide and a porosifying agent is applied onto a substrate and the porosifying agent is removed from the resulting coating film, a dense layer (skin layer) may be formed near the surface of the coating film depending on the composition of the coating solution and the conditions for removing the porosifying agent, resulting in the formation of a porous support having pores caused by the porosifying agent and a separation functional layer equivalent to the skin layer. However, in this case, the skin layer is formed on the surface of the coating film opposite the substrate (the surface exposed to the outside). According to the study of the present inventors, when the skin layer is formed, if the surface is exposed to the outside, defects such as pinholes are likely to occur on the surface. Furthermore, in this method, there is a tendency for the thickness of the skin layer to vary widely. Therefore, in this method, it is difficult to sufficiently suppress the variation in the separation performance within the separation membrane. In this method, it is also difficult to independently adjust the thickness of the separation functional layer and the porous support.

It is also possible to prepare a separation membrane by transferring the separation functional layer prepared in step I above to a porous support. However, separation functional layers containing polyimide usually have poor adhesion to porous supports. Therefore, in order to transfer the separation functional layer to the porous support, it is necessary to place a layer (intermediate layer) that can adhere sufficiently to these members between the separation functional layer and the porous support, which increases manufacturing costs. If an intermediate layer is present, the permeation speed of the fluid passing through the separation membrane also tends to decrease.

(Use of separation membrane)
The use of the separation membrane 10 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. In particular, the separation membrane 10 of this embodiment is suitable for separating carbon dioxide from a mixed gas containing carbon dioxide and nitrogen. However, the use of the separation membrane 10 is not limited to the use of separating an acidic gas from the above-mentioned mixed gas.

<Embodiment of Membrane Separation Apparatus>
3, the membrane separation device 100 of the present embodiment includes a separation membrane 10 and a tank 20. 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 from the second chamber 22. The separation membrane 10 extends from one of a pair of wall surfaces of the tank 20 to the other.

The first chamber 21 has an inlet 21a and an outlet 21b. The second chamber 22 has an outlet 22a. Each of the inlet 21a, the outlet 21b, and the outlet 22a is, for example, an opening formed in the wall surface of the tank 20.

Membrane separation using the membrane separation device 100 is performed, for example, 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 content 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 content 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 contains, for example, an 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 acid gas content 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 stack 42. The stack 42 includes 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, for example, by the following method. 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 inside 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 by 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.

[Synthesis of Polyimide P]
First, polyimide P was synthesized using an automatic polymerization apparatus (Mettler Toledo, EasyMax402). A separable flask (capacity 400 mL) attached to the apparatus was equipped with a Dimroth, stirring rod, internal thermometer, nitrogen inlet tube and 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, 96.1 g of 1-methyl-2-pyrrolidone (super dehydrated) as a solvent, 2.62 g (17.5 mmol) of 2,4,6-trimethyl-1,3-phenylenediamine (TrMPD) as a diamine, 4.80 g (17.5 mmol) of 3,7-diamino-2,8-dimethyldibenzothiophenesulfone (DDBT), and 2.11 g (0.5 mmol) of 5,5'-methylenebis(2-aminobenzoic acid) (MBAA) were added to the flask. The diamine was dissolved in the solvent by stirring at room temperature. 9.53 g (35.5 mmol) of naphthalene-1,4,5,8-tetracarboxylic dianhydride (NTDA) as a tetracarboxylic dianhydride, and 8.54 g (70 mmol) of benzoic acid were further added to the obtained solution. The jacket temperature of the apparatus was raised to 180°C, and the mixture was stirred for 8 hours. At this time, the internal temperature of the flask was 172 to 175° C. After stirring, the internal temperature of the flask was cooled to 25° C. and allowed to stand overnight.

Next, 9.04 g (70 mmol) of isoquinoline was added, the jacket temperature was raised to 180°C again, and the mixture was stirred for 8 hours. After leaving the reaction solution to stand overnight, 226 g of 1-methyl-2-pyrrolidone was added to dilute the reaction solution. Next, using a dropping funnel, 650 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 300 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. As a result, polyimide P was obtained with a yield of 17.1 g.

(Example 1)
[Step I]
The polyimide P 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. The 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 compound M (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 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 first coating solution.

In the first coating liquid, the ratio of the weight of polyimide P to the total weight of polyimide P and NMP was 8 wt %, and the ratio of the weight of NMP to the total weight was 92 wt %. In the first coating liquid, the ratio of the weight of Al(acac) ₃ to the weight of polyimide P and the weight of acetylacetone to the weight of polyimide P 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-mentioned first coating liquid was applied onto the substrate to form a first coating film (thickness 20 μm). The first coating liquid was applied using a slot die.

Then, the first coating film was transported at a speed of 1 m/min and passed through three heating sections to dry the first coating film. In detail, the first 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 first coating film to pass through the first to third heating sections was 6 minutes. The first coating film was dried to obtain a separation functional layer. Note that, as the first coating film dried, the dissociative protons of the carboxyl group contained in the polyimide P were exchanged with Al of the compound M. As a result, an Al salt of the carboxyl group was formed, and polyimide P1 was obtained.

[Step II]
The polyimide P was added to a 10L pail, and N,N-dimethylformamide (DMF) was added as a solvent, triethyl phosphate as a porosifying agent, and acetylacetone as a ligand to obtain a mixed solution. The mixed solution was stirred for 1 hour at 700 to 1400 rpm using a propeller-type stirring blade. Next, DMF and Al(acac) ₃ as compound M (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 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 second coating solution.

In the second coating liquid, the ratio of the weight of polyimide P to the total weight of polyimide P, DMF, and the porosifier (triethyl phosphate) was 10 wt%, the ratio of the weight of DMF to the total weight was 45 wt%, and the ratio of the weight of the porosifier to the total weight was 45 wt%. In the second coating liquid, the ratio of the weight of Al(acac) ₃ to the weight of polyimide P and the ratio of the weight of acetylacetone to the weight of polyimide P were both 6 wt%.

Next, the second coating liquid was applied onto the separation functional layer obtained in step I to form a second coating film (thickness 250 μm). The second coating liquid was applied using a slot die.

[Step III]
Next, the second coating film was dried to remove the porosity agent from the second coating film. The drying of the second coating film was performed by the following method. First, the second coating film was conveyed at a speed of 1 m/min and passed through three heating sections. In detail, the second 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 60° C., the set temperature of the second heating section was 60° C., and the set temperature of the third heating section was 90° C. The time (drying time) for the second coating film to pass through the first to third heating sections was 6 minutes. After passing through the first to third heating sections, the second coating film was further heated at 150° C. for 30 minutes. The porosity agent was removed from the second coating film to obtain a porous support. In addition, by drying the second coating film, the dissociative protons of the carboxyl group contained in the polyimide P were exchanged with Al of the compound M. As a result, an Al salt of the carboxyl group was formed, and polyimide P2 was obtained. Polyimide P2 had the same composition as Polyimide P1 above.

[Steps IV and V]
After the above step III, the substrate was removed from the laminate including the separation functional layer and the porous support (step V). Furthermore, the separation functional layer and the porous support were further subjected to a heat treatment (step IV). The heat treatment was performed at 300° C. for 30 minutes. Thus, the separation membrane of Example 1 was obtained.

(Example 2)
The separation membrane of Example 2 was obtained in the same manner as in Example 1, except that in step I, the thickness of the first coating film was changed to 10 μm, a polyimide (PI) film (manufactured by Fujiko Co., Ltd., SCA0) that had been release-treated with a silicone-based release treatment agent was used as the substrate, and in step III, the set temperature of the third heating section was changed to 60° C.

(Example 3)
The separation membrane of Example 3 was obtained by the same method as in Example 1, except that in step I, the discharge amount of the corona treatment on the substrate was changed to 0.45 kW min/ ^m2 , in step II, the second coating liquid was prepared using a Thinky Corporation foam remover mixer instead of a propeller-type stirring blade, and the second coating liquid was applied using an applicator instead of a slot die, and in step III, the second coating film was heated at 130°C for 30 minutes to remove the porosifying agent from the second coating film. Note that in Example 3, the operation of passing the second coating film through the first to third heating sections was not performed in step III.

(Examples 4 to 7)
Separation membranes of Examples 4 to 7 were obtained in the same manner as in Example 3, except that the composition of the second coating solution and the thickness of the second coating film were changed as shown in Table 1.

[Smoothness]
The surface of the separation functional layer side of the separation membranes of Examples 1 to 7 was visually observed for light (visible light) reflection, and the smoothness was evaluated according to the following criteria.
(Evaluation criteria)
⊚: The surface is almost free of irregularities and has excellent smoothness.
◯: There is slight unevenness on the surface.
Δ: The surface is uneven and has poor smoothness.

[Transmission rate]
The above-mentioned Test 2 was carried out on the separation membranes of Examples 1 to 7. Based on the results of Test 2, the average value Av2 of the carbon dioxide permeation rate was specified.

[Separation factor α]
The above-mentioned Test 1 was carried out for the separation membranes of Examples 1 to 7. Based on the results of Test 1, the ratio R of the value obtained by multiplying the standard deviation σ1 by 3 to the average value Av1 was determined for the separation coefficient α of carbon dioxide relative to nitrogen.

[thickness]
For the separation membranes of Examples 1 to 7, the thicknesses of the separation functional layer and the porous support were measured by the method described above.

[Hardness]
The hardness of the separation membranes of Examples 1 to 7 was evaluated according to the feel when held in the hand, using the following criteria.
◎: High rigidity and tear resistance.
◯: Relatively high rigidity.
x: Low rigidity and prone to tearing.

(Example 8)
First, the above-mentioned polyimide P was added to a 50 mL screw tube, and further, N,N-dimethylformamide (DMF) as a solvent, polyethylene glycol 200 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., PEG200) as a porosifying agent, and acetylacetone as a ligand were added to obtain a mixed solution. The mixed solution was stirred for 5 minutes and degassed for 5 minutes twice. Next, DMF and Al(acac) ₃ as compound M (metal complex) were added to another screw tube, and further, an ultrasonic treatment was performed using an ultrasonic cleaner to obtain an Al(acac) ₃ solution. The Al(acac) ₃ solution and the above-mentioned mixed solution were further mixed, and a stirring operation for 5 minutes and a degassing operation for 5 minutes were repeated twice to prepare a coating solution. The stirring operation and degassing operation were performed using a Thinky Corporation's Foaming Mixer.

In the coating solution, the ratio of the weight of polyimide P to the total weight of polyimide P, DMF, and porosifier (PEG200) was 19.5 wt%, the ratio of the weight of DMF to the total weight was 66.9 wt%, and the ratio of the weight of the porosifier to the total weight was 13.7 wt%. In the coating solution, the ratio of the weight of Al(acac) ₃ to the weight of polyimide P and the ratio of the weight of acetylacetone to the weight of polyimide P were both 6 wt%.

Next, a release-treated PET film (PET125 SG1, manufactured by PANAC) was prepared as a substrate. The above coating solution was applied onto this substrate to form a coating film (thickness 350 μm). The coating solution was applied using a comma coater.

Next, the coating film was transported at a speed of 0.5 m/min and dried by passing through the heating section. The temperature of the heating section was set to 60°C. The time (drying time) for the coating film to pass through the heating section was 9 minutes. Next, the coating film was immersed in methanol at room temperature for 480 minutes, and then dried at 40°C for 30 minutes. As a result, the porosity-inducing agent was removed from the coating film, and a porous support having pores caused by the porosity-inducing agent and a separation function layer corresponding to the skin layer were formed. Next, the substrate was removed from the laminate including the separation function layer and the porous support. The separation function layer and the porous support were subjected to a heat treatment at 300°C for 30 minutes to obtain the separation membrane of Example 8. In Example 8, the dissociable protons of the carboxyl group contained in the polyimide P were exchanged with Al of the compound M.

(Example 9)
First, a coating solution was prepared in the same manner as in Example 8, except that the composition of the coating solution was changed as shown in Table 3. In Example 9, polyethylene glycol monomethyl ether 400 (M400, manufactured by NOF Corp.) was used as the porosifying agent. Next, a release-treated PET film (PET100 SG2, manufactured by PANAC Corp.) was prepared as the substrate. The above coating solution was applied onto this substrate to form a coating film (thickness 300 μm). The coating solution was applied using a comma coater.

Then, the coating film was transported at a speed of 0.2 m/min and dried by passing through the heating section. The temperature of the heating section was set to 60°C. The time (drying time) for the coating film to pass through the heating section was 30 minutes. Next, the coating film was immersed in methanol at room temperature for 30 minutes, and further dried at 60°C for 60 minutes. As a result, the porosity agent was removed from the coating film, and a porous support having pores caused by the porosity agent and a separation function layer corresponding to the skin layer were formed. Next, the substrate was removed from the laminate including the separation function layer and the porous support. The separation function layer and the porous support were subjected to a heat treatment at 300°C for 30 minutes to obtain the separation membrane of Example 9. In Example 9, the dissociable protons of the carboxyl group contained in the polyimide P were exchanged with Al of the compound M.

(Example 10)
A separation membrane of Example 10 was obtained by the same method as in Example 9, except that the composition of the coating solution was changed as shown in Table 3. In Example 10, the dissociable proton of the carboxyl group contained in polyimide P was exchanged with Al of compound M.

[evaluation]
The separation membranes of Examples 8 to 10 were evaluated for smoothness, permeation rate, separation factor α, thickness and hardness by the same methods as those of Examples 1 to 7.

As can be seen from Tables 1 to 4, the separation membranes of Examples 1 to 7 produced by the manufacturing method of this embodiment all had a smooth surface for the separation functional layer, and the ratio R for the separation factor α was 70% or less. The separation membranes of Examples 1 to 7, which have a ratio R of 70% or less, have reduced variation in the separation factor α compared to the separation membranes of Examples 8 to 10, and can be said to be suitable for separating acidic gases from mixed gases that contain acidic gases. According to the manufacturing method of this embodiment, it is possible to produce separation membranes with reduced variation in the separation factor α, which is presumably expected to improve yields.

All of the separation membranes of Examples 1 to 7 had good hardness evaluation results and were easy to handle. In particular, the separation membranes of Examples 5 to 7 were highly rigid and are expected to be easily incorporated into membrane separation equipment.

The separation membrane of this embodiment is suitable for separating acid gas from a gas mixture containing acid gas. In particular, the separation membrane of this embodiment is suitable for separating carbon dioxide from off-gas of chemical plants or thermal power plants.

Claims

A separation functional layer including polyimide P1;
A porous support directly contacting the separation functional layer;
Equipped with
The polyimide P1 contains a structural unit A1 derived from a tetracarboxylic dianhydride having a 6-membered ring acid anhydride structure,
A separation membrane, in which the ratio R of the value obtained by multiplying the standard deviation σ1 by 3 to the average value Av1 for the separation factor α specified by the following Test 1 is 70% or less.
Test 1: The separation membrane is cut to prepare three or more test pieces. For each of the test pieces, a mixed gas consisting of carbon dioxide and nitrogen is supplied to a space adjacent to one side of the test piece, and the space adjacent to the other side of the test piece is depressurized. Based on the results of the operation, a separation coefficient α of carbon dioxide relative to nitrogen is determined for each of the test pieces. Here, in the operation, the carbon dioxide content in the mixed gas is 50 vol% under standard conditions, the mixed gas supplied to the space adjacent to the one side has a temperature of 30° C. and a pressure of 0.1 MPa, and the space adjacent to the other side is depressurized so that the pressure in the space is 0.1 MPa lower than the atmospheric pressure in the measurement environment.
The separation membrane according to claim 1, wherein the average value Av1 is 20 or more.
The separation membrane according to claim 1, wherein the average permeation rate Av2 determined by the following Test 2 is 300 GPU or more.
Test 2: Three or more test pieces are prepared by the same method as in Test 1, and the above operation is carried out for each of the test pieces. Based on the results of the above operation, the permeation rate of carbon dioxide that permeated the test piece is determined for each of the test pieces.
The separation membrane according to claim 1, wherein the thickness of the separation functional layer is 3 μm or less.
The separation membrane according to claim 1, wherein the sum of the thickness of the separation functional layer and the thickness of the porous support is 30 μm or more.
The separation membrane 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 polyimide P1 further includes a structural unit B1 derived from a diamine,
2. The separation membrane 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 carboxyl group, a hydroxyl group, a thiol group, and metal salts thereof.
The separation membrane of claim 1, wherein the porous support comprises polyimide P2.
The separation membrane according to claim 8, wherein the polyimide P2 contains the structural unit A1.
A method for producing a separation membrane comprising a separation functional layer containing polyimide P1 and a porous support directly in contact with the separation functional layer,
The manufacturing method includes:
A step I of forming the separation functional layer by applying a first coating liquid containing a material for the separation functional layer onto a substrate and drying the first coating liquid;
A step II of applying a second coating liquid containing a material for the porous support and a porosifying agent onto the separation functional layer to form a coating film;
Step III of removing the porosifying agent from the coating film to form the porous support;
Including,
The polyimide P1 contains a structural unit A1 derived from a tetracarboxylic dianhydride having a six-membered ring acid anhydride structure.
The polyimide P1 further includes a structural unit B1 derived from a diamine,
The method according to claim 10, 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 carboxyl group, a hydroxyl group, a thiol group, and metal salts thereof.
The method of claim 11, wherein at least one of the structural unit A1 and the structural unit B1 has the metal salt.
the first coating liquid contains, as the material of the separation functional layer, a polyimide P having at least one functional group f selected from the group consisting of a carboxyl group, a hydroxyl group, and a thiol group, and a compound having a metal;
The method according to claim 12 , wherein in the step I, the polyimide P1 is formed from the polyimide P.
The method of claim 13, wherein the compound includes a metal complex having the metal and a ligand coordinated to the metal.
The manufacturing method according to claim 10, wherein the porosifying agent includes at least one selected from the group consisting of ether compounds and phosphoric acid compounds.
The manufacturing method according to claim 10, wherein the porosifying agent is removed from the coating film by drying the coating film.