WO2024154563A1

WO2024154563A1 - Composition for forming gas separation membrane and method for producing gas separation membrane

Info

Publication number: WO2024154563A1
Application number: PCT/JP2023/046821
Authority: WO
Inventors: 一利小▲高▼
Original assignee: 日産化学株式会社
Priority date: 2023-01-17
Filing date: 2023-12-26
Publication date: 2024-07-25

Abstract

The present invention provides: a composition for forming a gas separation membrane, the composition enabling the production of a gas separation membrane which has improved gas separation membrane characteristics by containing inorganic nanoparticles in a polymer membrane in an appropriately dispersed state; and a method for producing a gas separation membrane. (1) A composition for forming a gas separation membrane, the composition containing a matrix resin, inorganic fine particles having a primary particle diameter of 1 nm to 1,000 nm, and a solvent, wherein: an organic group is bonded to the surfaces of the inorganic particles; and the difference between the HSP of the organic group of the inorganic particles and the HSP of the matrix resin is 5.0 to 15.0 MPa^0.5.

Description

Composition for forming gas separation membrane and method for producing gas separation membrane

The present invention relates to a composition for forming a gas separation membrane, which can form a gas separation membrane with improved gas permeability by adjusting the dispersion state of fine particles in a resin, and a method for producing a gas separation membrane.

In recent years, as part of nanotechnology research, there has been active research on nanometer-order particles (nanoparticles) with an average particle size of about 1 nm to several hundred nm. Unlike conventional bulk materials, nanoparticles made by nanosizing materials are known to be able to express and impart various mechanical properties and characteristics, and are expected to be applied in a wide range of industrial fields. Nanoparticles can be manufactured as primary particles, but due to their fineness, they have strong coagulation properties, and if left alone, they will become aggregates with micro-order particle sizes. For example, when inorganic nanoparticles such as those described above are added to organic components, it is expected that the heat resistance and mechanical strength will be improved, but due to their strong coagulation properties, inorganic nanoparticles will form micro-order aggregates in organic solvents or polymer matrices as they are, and as a result, the expected characteristics and performance of organic-inorganic composite materials may not be obtained. For this reason, in order to maintain the dispersibility of primary particles, it has been proposed to perform uniform chemical modification on the particle surface (see, for example, Patent Document 1), but this alone has not produced results that can be considered sufficient in terms of dispersibility.

Meanwhile, organic-inorganic composite materials, which can synergistically enhance the benefits of both inorganic and organic components by mixing them at the nano- or molecular level, are attracting attention. This concept has also been applied to polymer gas separation membranes, which are attracting attention for their usefulness in solving energy and environmental problems, and it is hoped that by creating organic-inorganic composite materials in which inorganic nanoparticles are added to a polymer matrix, it will be possible to achieve high mechanical strength, thermal stability, and gas permeability properties that could not be achieved with existing methods.

　Methods of separating gases using the gas permeability properties of polymer membranes can separate and recover gases without causing a phase change, and compared to other gas separation methods, they are simpler to operate and allow for the miniaturization of equipment. They also have the advantage of being able to perform gas separation continuously, which places less of a burden on the environment. In recent years, such energy-saving polymer gas separation membrane methods have attracted attention, particularly as a technology for separating and recovering greenhouse gases, producing oxygen-enriched air, and refining natural gas, and there are hopes that they will be put to practical use, but further improvements are needed in terms of gas separation performance and gas permeability.

As mentioned above, attempts have been made to improve gas permeability by incorporating inorganic nanoparticles into polymer membranes, but the problem of nanoparticle aggregation is also a problem in the production of organic-inorganic composite gas separation membranes. With existing organic-inorganic composite gas separation membranes, the aggregation of inorganic nanoparticles in the polymer matrix reduces membrane strength and makes it impossible to achieve a high particle content, resulting in an issue that gas permeability can only be improved by a few times.

Therefore, for example, as a method for improving the properties of a gas separation membrane by incorporating inorganic nanoparticles into a polymer membrane, the surface of silica nanoparticles is treated with an amino group-containing silane coupling agent to silylate the surface, and these silylated particles are further treated with a polymer to produce polymer-grafted silica particles, and the polymer-grafted silica particles thus obtained are dispersed in a polymer to form a resin membrane, and the performance of this membrane as a gas separation membrane has been investigated (see Non-Patent Document 1), but the results obtained have not been sufficient in terms of gas permeation rate, etc.

Also, a gas separation membrane has been proposed that is free from aggregation in organic solvents or polymer matrices, has excellent uniform dispersibility, and greatly improves gas permeability by bonding bulky hyperbranched polymers or dendrimer polymers to the surface of silica nanoparticles (see, for example, Patent Document 2). However, sufficient results have not been obtained in terms of dispersibility in resins or improvement of gas permeability.

As mentioned above, inorganic nanoparticles, which are fine powders with small particle sizes, are usually difficult to disperse in resin. In particular, when the resin and the nanoparticles have different good solvents, it is difficult to highly disperse them in the resin. Furthermore, if the dispersion of the fine particles in the resin is insufficient, the properties of the resulting gas separation membrane are significantly impaired. For example, nanocracks, membrane warping, and membrane pulling can occur in the manufactured gas separation membrane, causing the composite membrane to become weakened.

In addition, one method for improving the dispersibility of fine particles is to optimize the surface modification group, but depending on the combination with the resin used, the effect of adding the modified group may not be sufficient, and the resins that can be used are limited. On the other hand, while the addition of surfactants may improve dispersibility, this is not desirable as it can lead to bleeding out of the dispersant and a decrease in the gas permeability of the gas-permeable membrane.

JP 2007-99607 A JP 2010-222228 A

As mentioned above, when manufacturing gas separation membranes, we tried to prevent aggregation of fine particles as much as possible and improve the dispersibility of the fine particles in the resin as much as possible in order to improve gas permeability, but we found that simply improving dispersibility was not enough to improve the gas permeability of the gas separation membrane.

In view of the above circumstances, the present invention aims to provide a composition for forming a gas separation membrane and a method for producing a gas separation membrane that can produce a gas separation membrane with improved gas separation membrane properties by incorporating inorganic nanoparticles in a moderately dispersed state in a polymer membrane.

The inventors conducted extensive research to solve these problems, and as a result, they considered preventing aggregation of microparticles as much as possible in order to improve gas permeability, and improving the dispersibility of the microparticles in the resin as much as possible. However, they discovered that gas permeability can be improved by appropriately adjusting the aggregation to achieve appropriate dispersibility, rather than improving dispersibility as much as possible. They also discovered that by using a specific HSP as an indicator for understanding the appropriate dispersibility between the microparticles and the resin, it is possible to relatively easily understand the appropriate dispersibility.

That is, the present invention provides:
(1) A composition for forming a gas separation membrane, comprising a matrix resin, inorganic fine particles having a primary particle size of 1 to 1000 nm, and a solvent,
an organic group is bonded to the surface of the inorganic fine particles,
A composition for forming a gas separation membrane, wherein the difference between the HSP of the organic group of the inorganic fine particles and the HSP of the matrix resin is 5.0 to 15.0 MPa ^0.5 .
(2) The composition for forming a gas separation membrane according to (1), wherein the inorganic fine particles are silica.
(3) The composition for forming a gas separation membrane according to (2), characterized in that the organic groups of the inorganic fine particles are bonded via -O-Si- to form the following structure, and the HSP of the organic groups is calculated from the structure of the (organic group) beyond -Si-.

(4) The composition for forming a gas separation membrane described in (1), wherein the matrix resin is cellulose acetate represented by the following formula (I):

(n is an integer of 50 to 500, R represents -H or _-COCH3 , and at least one of R is _-COCH3 .)

(5) The composition for forming a gas separation membrane according to (1), wherein the matrix resin is a polyimide having a repeating structure represented by the following formula (II) obtained by condensation polymerization of a tetracarboxylic dianhydride represented by the following formula (10) and an aromatic diamine ^R2 ( _NH2 ) ₂ .

( ^R1 represents a tetravalent organic group.)

( ^R1 represents a tetravalent organic group. ^R2 represents a residue obtained by removing an amine from an aromatic diamine, and represents an aromatic group having 6 to 14 carbon atoms. n represents an integer of 50 to 500.)

(6) The composition for forming a gas separation membrane according to (1), wherein the matrix resin is a polymer having intrinsic microporosity.
(7) The composition for forming a gas separation membrane according to (6), wherein the polymer having intrinsic microporosity is PIM-1 represented by the following formula (III):

(n represents an integer of 50 to 1000.)

(8) The composition for forming a gas separation membrane according to (4), wherein the organic group has the following structure:

(9) The composition for forming a gas separation membrane according to (5), wherein the organic group has the following structure:

(10) The composition for forming a gas separation membrane according to (6) or (7), wherein the organic group has the following structure:

(11) A method for producing a gas separation membrane using a composition for forming a gas separation membrane, the composition comprising a matrix resin, inorganic fine particles having a primary particle size of 1 to 1000 nm, and a solvent, comprising:
As the composition for forming a gas separation membrane, a composition for forming a gas separation membrane is used in which an organic group is bonded to the surface of the inorganic fine particles, and the difference between the HSP of the organic group of the inorganic fine particles and the HSP of the matrix resin is 5.0 to 15.0 MPa ^0.5 ;
A method for producing a gas separation membrane, comprising the steps of applying a coating liquid for forming a gas separation membrane, formed from the composition for forming a gas separation membrane, onto a substrate, and evaporating the solvent to form a gas separation membrane.

The present invention makes it possible to incorporate inorganic nanoparticles in a moderately dispersed state into a polymer membrane, thereby realizing a composition for forming a gas separation membrane and a method for producing a gas separation membrane that can produce a gas separation membrane with improved gas separation membrane properties.

FIG. 1 is a diagram for explaining the calculation range of HSP of surface modifying groups of microparticles. FIG. 2 is a diagram showing the structure of the matrix resin HSP calculation target. FIG. 1 is a graph showing the relationship between ΔHSP and the gas permeation properties of each composite membrane in Table 3. 1 is a graph showing the relationship between ΔHSP and the gas permeation properties of each composite membrane in Table 4. FIG. 1 is a graph showing the relationship between ΔHSP and the gas permeation properties of each composite membrane in Table 5.

The present invention will be described in detail below. The inorganic fine particles used in the present invention are nanoparticles with an average particle size of the nano-order, and can be made of any material. Nanoparticles refer to particles with an average primary particle size of 1 nm to 1000 nm, and in particular, particles with an average primary particle size of 2 nm to 500 nm. The average primary particle size is determined by the nitrogen adsorption method (BET method).

Here, examples of inorganic fine particles include silica, zirconia, ceria, metal oxides, etc., but silica fine particles are preferred.

Furthermore, as the silica fine particles, in addition to spherical nanoparticles, irregularly shaped silica nanoparticles, for example, elongated, bead-like or confetti-like silica nanoparticles, can be used to produce a gas separation membrane with significantly improved gas permeation. As the irregularly shaped silica nanoparticles, those described in International Publication WO2018/038027 can be used, including (1) elongated silica nanoparticles having a ratio D1/D2 of the particle diameter D1 measured by dynamic light scattering to the particle diameter D2 measured by nitrogen gas adsorption method of 4 or more, D1 being 40 to 500 nm, and having a uniform thickness within the range of 5 to 40 nm as observed by a transmission electron microscope, (2) spherical colloidal silica particles having a particle diameter D2 measured by nitrogen gas adsorption method of 10 to 80 nm and silica bonding the spherical colloidal silica particles, and having a particle diameter D1 measured by dynamic light scattering method of 10 to 80 nm, and having a particle diameter D2 measured by dynamic light scattering method of 10 to 500 nm, and having a diameter D1 measured by nitrogen gas adsorption method of 10 to 500 nm, and having a diameter D2 measured by nitrogen gas adsorption ... and spherical colloidal silica particles, the ratio D1/D2 being 3 or more, D1 being 40-500 nm, and the spherical colloidal silica particles being linked together in a beaded shape; and (3) colloidal silica particles having a surface roughness S2/S3 in the range of 1.2-10 and an average particle diameter D3 in the range of 10-60 nm, where S2 is the specific surface area measured by the nitrogen gas adsorption method and S3 is the specific surface area converted from the average particle diameter D3 measured by image analysis.

In the present invention, organic group-modified inorganic fine particles in which an organic group is bonded to the surface of an inorganic fine particle are used.
The organic group-modified inorganic fine particles can be obtained, for example, by reacting inorganic fine particles with a surface treatment agent (one-step reaction). When the surface modification group added in the one-step reaction has a reactive functional group, it is possible to obtain inorganic fine particles having various organic groups added thereto by further reacting the surface modification group with an organic compound that reacts with the reactive functional group (two-step reaction).

Hereinafter, the inorganic fine particles will be described in more detail with silica as the inorganic fine particles.
When obtaining organic group-modified silica by a one-step reaction, a silane compound (silane coupling agent or silylating agent) and silica are dispersed in an appropriate solvent and then heat-treated to obtain surface-modified silica.

To obtain organic group-modified silica by a two-step reaction, first, a silane compound (silane coupling agent) having a reactive functional group such as an amino group, a carboxyl group, a mercapto group, a glycidyl group, an acid anhydride group, an acryloyl group, or an isocyanate group is treated with silica under heating conditions to obtain reactive functional group-modified silica, and then an organic compound that reacts with the reactive functional group of this reactive functional group-modified silica is reacted to obtain organic group-modified silica.

The reaction with the silane compound having such a reactive functional group is carried out while the silica is still dispersed in the first solvent, to produce reactive functional group-modified nanosilica particles in which reactive functional groups are added to the surface of the silica. A preferred reactive functional group-containing compound is a silane coupling agent, for example a compound containing an amino group at the end, represented by the general formula (1).

(In the formula, _R1 represents a methyl group or an ethyl group, and _R2 represents an alkylene group having 1 to 5 carbon atoms, an amide group, or an aminoalkylene group.)

In the silane coupling agent represented by general formula (1), the amino group is preferably at the terminal, but does not have to be at the terminal.

Examples of the compound represented by the general formula (1) include 3-aminopropyltriethoxysilane (APTES) and 3-aminopropyltrimethoxysilane. Other representative examples of silane coupling agents having an amino group include 3-ureidopropyltrimethoxysilane, 3-ureidopropyltriethoxysilane, 3-(2-aminoethylamino)propyltriethoxysilane, and 3-(2-aminoethylamino)propyltrimethoxysilane.

In addition, the reactive functional group-containing compound may contain other groups, such as an isocyanate group, a mercapto group, a glycidyl group, a ureido group, or a halogen group, in addition to an amino group.

Silane coupling agents having functional groups other than amino groups include 3-isocyanatepropyltriethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-ureidopropyltriethoxysilane, and 3-chloropropyltrimethoxysilane.

In addition, the reactive functional group-containing compound used does not have to be a trialkoxysilane compound such as that represented by the general formula (1) above, and may be, for example, a dialkoxysilane compound or a monoalkoxysilane compound.

The functional group of the reactive functional group-containing compound that reacts with the silanol group of the silica nanoparticles may be a group other than an alkoxy group, such as an isocyanate group, a mercapto group, a glycidyl group, a ureido group, a halogen atom, etc.

In treating silica nanoparticles with a compound containing reactive functional groups, the compound containing reactive functional groups is added to a liquid in which the silica nanoparticles are dispersed in water or an alcohol having 1 to 4 carbon atoms, and the mixture is stirred.

The addition of reactive functional groups to the surface of silica nanoparticles may be carried out by a one-step reaction as described above, or may be carried out by two or more steps as necessary. A specific example of a two-step reaction is the preparation of carboxyl group-modified silica nanoparticles. For example, as described above, first, silica nanoparticles are treated with aminoalkyltrialkoxysilane to prepare amino group-modified silica nanoparticles, and then treated with a dicarboxylic acid compound represented by general formula (2) or its acid anhydride, thereby preparing silica nanoparticles in which the terminal of the reactive functional group added to the silica nanoparticles is a carboxyl group.

(In the formula, _R3 represents an alkylene group or an aromatic group having 1 to 20 carbon atoms.)

Examples of compounds represented by the above general formula (2) include malonic acid, adipic acid, and terephthalic acid. Dicarboxylic acid compounds are not limited to those listed in the above formula.

When reactive functional groups are added to the surface of silica nanoparticles in a reaction that exceeds two stages, a monomer having two amino groups at its terminal, as represented by the following general formula (3), can be added to silica nanoparticles that have been treated with the compound represented by formula (1) and then formula (2) to prepare silica nanoparticles in which the terminals of the surface modifying groups are amino groups, and the above reaction can be repeated.

(In the formula, R ₄ represents an alkylene group having 1 to 20 carbon atoms, an aromatic ring, a heteroaromatic ring, or (C ₂ H ₅ -O-) _p and/or (C ₃ H ₇ -O-) _q , and p and q each independently represent an integer of 1 or more.)

Examples of the monomer represented by the general formula (3) include ethylenediamine, polyoxyethylenebisamine (molecular weight 2,000), o,o'-bis(2-aminopropyl)polypropylene glycol-block-polyethylene glycol (molecular weight 500), etc.

The first solvent dispersion of reactive functional group-modified silica nanoparticles prepared in this manner can be replaced with a second solvent to carry out the next reaction.

The second solvent is a solvent that is more hydrophobic than the first solvent, and is preferably at least one selected from one or more of tetrahydrofuran (THF), N-methylpyrrolidone (NMP), dimethylacetamide (DMAc), dimethylformamide (DMF) and gamma-butyrolactone (GBL), or may be a mixed solvent.

The method of substitution with the second solvent is not particularly limited, and the first solvent dispersion of the reactive functional group-modified silica nanoparticles may be dispersed in the second solvent after drying, or the first solvent dispersion of the reactive functional group-modified silica nanoparticles may be solvent-substituted without drying to form a dispersion in the second solvent.

After the solvent has been replaced in this manner, a second solvent dispersion of the reactive functional group-modified silica nanoparticles is used, and in the presence of the second solvent, an organic compound is reacted with the reactive functional groups of the reactive functional group-modified silica nanoparticles to produce organic group-modified silica.

Here, examples of organic compounds that react with reactive functional groups include organic compounds having a carboxyl group, an amino group, an isocyanate group, a glycidyl group, an acid anhydride group, an acryloyl group, etc.

Examples of organic compounds that react with reactive functional groups include aromatic carboxylic acids such as 3,5-diaminobenzoic acid, 2-aminobenzoic acid, 3-aminobenzoic acid, 4-aminobenzoic acid, 4-(aminomethyl)benzoic acid, 3,5-dimethylbenzoic acid, 3-methylbenzoic acid, 4-methylbenzoic acid, 4-t-butylbenzoic acid, benzoic acid, isonicotinic acid, and 3,5-dimethoxybenzoic acid; organic carboxylic acids such as 1-adamantanecarboxylic acid, pentanoic acid, and octanoic acid; aromatic amines such as aniline, cyclohexylamine, and ethyl 4-aminobenzenecarboxylate; amino acids such as tryptophan, phenylalanine, tyrosine, and histidine; and isocyanate compounds such as cyclohexyl isocyanate and benzyl isocyanate.

The method for obtaining organic group-modified silica is not limited to the above, and conventionally known methods can be used. For example, silica particles having desired organic groups on the surface can be synthesized by using a coupling agent having an organic group in the synthesis stage of silica particles utilizing the sol-gel reaction of a coupling agent such as tetraethoxysilane. In addition, surface-modified silica can be obtained by reacting the silica surface with a modifying agent having a reactive functional group such as a carboxyl group or an amino group in a supercritical state using water or _CO2 as a medium.

An example of the organic group modification of the organic group-modified silica thus produced is shown in formulas (a) to (d).
The organic group modification of formula (a) is an example in which silica that has been reacted with aminopropyltriethoxysilane is reacted with an organic compound having a carboxyl group as a reactive functional group, and preferable R ₁₁ is as exemplified above.
The organic group modification of formula (b) can be obtained by reacting an organic compound having a halogen atom as a reactive functional group with silica that has been reacted with aminopropyltriethoxysilane, or by reacting an organic amine with 3-chloropropyltriethoxysilane, and then subjecting the reaction solution to distillation, crystallization/filtration of amine hydrochloride, or liquid separation to generate a purified aminoalkylsilane, which is then heat-treated with silica in a suitable solvent. In addition, if a commercially available coupling agent already having a desired surface-modifying group is available, it may be used for surface modification. Preferred R ₁₂ is as exemplified above.
The organic group modification of formula (c) is an example in which a silane coupling agent having an aromatic group or an alkyl group is reacted with silica, and preferable R ₁₃ is as exemplified above. The silane coupling agent may be a commercially available one, or a newly synthesized silane compound may be used.
The organic group modification of formula (d) is an example in which a silylating agent having a saturated alkyl group or a methyl group is reacted with silica, and preferable R ₁₄ is as exemplified above. Commercially available silylating agents can be used.

The composition for forming a gas separation membrane of the present invention is a mixture of the inorganic fine particles having organic groups bonded to the surface thereof, a matrix resin, and a solvent. The composition for forming a gas membrane is selected so that the difference between the HSP (Hansen Solubility Parameter) of the organic groups of the inorganic fine particles and the HSP of the matrix resin is 5.0 to 15.0 MPa ^0.5 .

Here, the HSP of the organic group was calculated using the calculation software Winmostar, as described in detail below.

As shown in formulas (a) to (d), when the organic group is bonded via -O-Si- to form the above structure, the organic group is defined as the structure beyond -Si-, and the HSP is calculated from the organic group beyond -Si-. In addition, when the organic group is directly bonded to the silica, the HSP of the organic group is calculated.

For example, in the case of formula (a), the structure within the rectangular frame is treated as the organic group, and the HSP is calculated as shown below.

In the present invention, the matrix resin may be, for example, a known resin that has been conventionally used to form gas separation membranes. Specific examples include, but are not limited to, polyimide, cellulose diacetate, polysulfone, polyethersulfone, polyethylene glycol crosslinked body, dimethyl silicone, polyvinyl alcohol, modified polyvinyl alcohol, polysubstituted acetylene, poly-4-methylpentene, natural rubber, and microporous polymer. In the present invention, microporous polymer, dimethyl silicone, polyvinyl alcohol, polyimide, and cellulose acetate are preferred, and polyimide, cellulose acetate, and microporous polymer are particularly preferred.

Cellulose acetate has the structure represented by the following formula (I):

As the matrix resin, a polyimide having a repeating structure represented by the following formula (II) obtained by condensation polymerization of a tetracarboxylic dianhydride represented by the following formula (10) and an aromatic diamine ^R2 ( _NH2 ) ₂ is preferred.

( ^R1 represents a tetravalent organic group.)

Here, R ¹ is a tetravalent residue obtained by removing a carboxy group from the tetracarboxylic acid of formula (1), and is represented by the following general formulae (3) to (5) (in general formula (4), X is -C(CF ₃ ) ₂ -, -C(CF ₃ )(C ₆ H ₅ )-, -C(CH ₃ )(C ₆ H ₅ )-, -CH ₂ -, -C(CH ₃ ) ₂ -, -CO-, -SO ₂ -, -O-, -S-, -NH-, -COO-, -CONH-, -Si(CH ₃ ) ₂ -, -O-C ₆ H ₄ -C(CH ₃ ) ₂ -C ₆ H ₄ -O-, -O-C ₆ H ₄ -O-, -O-CH ₂ -CH 2 -O-, -CF ₂ _CF ₂ It is preferable that the alkyl group is at least one organic group selected from the group consisting of --CF ₂ --, --CO--C ₆ H ₄ --CO--, and --O--C ₆ H ₄ --S--C ₆ H ₄ --O--.

Furthermore, the matrix resin is preferably a microporous polymer.
Here, the microporous polymer is an inherently microporous polymer, which is one of the microporous organic materials, and is one class of microporous organic materials. Reference can be made to the following literature.
(Reference 1) Budd, P. M. et al., Solution-Processed, Organophilic Membrane Derived from a Polymer of Intrinsic Microporosity. Adv. Mater. 16, 456-459 (2004).
(Reference 2) McKeown, N. B. et al., Polymers of intrinsic microporosity (PIMs): Bridging the void between microporous and polymeric materials. Chemistry - A European Journal 11, 2610-2620 (2005).
(Reference 3) Budd, P. M. et al., Gas separation membranes from polymers of intrinsic microporosity. J. Membr. Sci. 251, 263-269 (2005).
(Reference 4) McKeown, N. B. & Budd, P. M., Polymers of intrinsic microporosity (PIMs): Organic materials for membrane separations, heterogeneous catalysis and hydrogen storage. Chem. Soc. Rev.35, 675-683 (2006).
(Reference 5) Du, N. et al., Polymer nanosieve membranes for CO2-capture applications. Nat. Mater. 10, 372-375 (2011).
(Reference 6) Carta, M. et al., An Efficient Polymer Molecular Sieve for Membrane Gas Separations. Science 339, 303-307 (2013).
(Reference 7) Special table publication No. 2017-509744

The concept of polymers with intrinsic microporosity was first proposed by Budd and McKeown in 2002.
International Publication WO 2003/000774 A1 describes organic microporous network materials that contain rigid 3-dimensional networks of planar porphyrin macrocycles, in which the pyrrole residues of adjacent macrocycles are connected by rigid linkers that immobilize these adjacent macrocycles, resulting in a non-coplanar orientation of the porphyrin planes. A preferred material of the invention is a phthalocyanine network. These organic microporous materials are known as network PIMs.

Another invention by Budd and McKeown, International Publication No. WO 2005/012397 A2 and US Patent No. 7,690,514 B2, describes microporous organic macromolecules that include a first generally planar species connected by a rigid linker at points of distortion, where two adjacent first planar species connected by the linker are in a non-coplanar orientation, with the proviso that the first planar species is other than a porphyrin macrocycle.
Among these microporous polymers, PIM-1 represented by the structure shown in the following formula (III) is particularly preferred.

(n represents an integer of 50 to 1000.)

The solvent used in producing the gas separation membrane composition can be of any type as long as it dissolves the polymer and is compatible with the solvent used to disperse the inorganic fine particles. Examples of such solvents include tetrahydrofuran (THF), chloroform, dimethylacetamide (DMAc), toluene, linear alcohols with 1 to 6 carbon atoms, branched alcohols with 1 to 6 carbon atoms, hexane, heptane, octane, decane, N-methyl-2-pyrrolidone (NMP), and N,N-dimethylformamide (DMF), either alone or in combination of two or more of these.

The mass ratio of resin to surface-modified silica in the film-forming composition is 100/0.1 to 100/50, preferably 100/1 to 100/30, and more preferably 100/1 to 100/15.

The mass ratio of resin to solvent in the film-forming composition is 100/10,000 to 100/500, preferably 100/3,000 to 100/1,000, and more preferably 100/2,000 to 100/1,333.

The HSP of such a matrix resin is, for example, the HSP calculated from the repeating units represented by formulas (I), (II), and (III).
Here, the cellulose acetate of formula (I) has an HSP of 23.3.
Moreover, the polyimide of formula (II) has an HSP of 23.0.
Furthermore, PIM-1 of formula (III) has an HSP of 21.9.

Therefore, the organic group-modified inorganic fine particles to be mixed with these matrix resins must be selected such that the difference between the HSP value of the organic group and the HSP value of the matrix resin is 5.0 to 15.0 MPa ^0.5 .

Thus, the difference between the HSP value of the organic group of the organic group-modified inorganic fine particles and the HSP of the matrix resin in the present invention is set to 5.0 to 15.0 MPa ^0.5 in order to obtain a composition for forming a gas separation membrane capable of producing a gas separation membrane with improved gas separation membrane properties by appropriately adjusting the dispersion of the organic group-modified inorganic fine particles in the matrix resin when producing a gas separation membrane. If the HSP difference is larger than the upper limit, there is a risk that the dispersion of the organic group-modified inorganic fine particles in the matrix resin is insufficient and a gas separation membrane having sufficient strength cannot be produced, and if it is smaller than the lower limit, the organic group-modified inorganic fine particles are too dispersed in the matrix resin and do not aggregate appropriately, and the effect of improving the permeability of the gas separation membrane cannot be sufficiently obtained.

These HSP specifications are based on the knowledge that if the organic-group-modified inorganic fine particles are completely and well dispersed in the matrix resin, the effect of improving the permeability of the gas separation membrane by adding the organic-group-modified inorganic fine particles is not fully achieved, and that the effect of improving the permeability by adding the organic-group-modified inorganic fine particles is more fully achieved if the particles are aggregated to a certain extent.

When cellulose acetate of formula (I) is used as the matrix resin, examples of the organic groups of the organic group-modified inorganic fine particles include the following organic groups, and the HSP is calculated from the following structure:

When the polyimide of formula (II) is used as the matrix resin, examples of the organic groups of the organic group-modified inorganic fine particles include the following organic groups, and the HSP is calculated from the following structure:

When PIM-1 of formula (III) is used as the matrix resin, examples of the organic groups of the organic group-modified inorganic fine particles include the following organic groups, and the HSP is calculated from the following structure:

The solvent used to manufacture the gas separation membrane composition is a solvent suitable for dissolving the matrix resin and dispersing the organic group-modified inorganic fine particles, such as 4-methyltetrahydropyran, THF, chloroform, toluene, xylene, linear alcohols having 1 to 10 carbon atoms, branched alcohols having 1 to 6 carbon atoms, hydrocarbon solvents such as hexane, heptane, octane, nonane, and decane, aprotic polar solvents such as DMAc, NMP, 1,3-dimethyl-2-imidazolidinone (DMI), and DMF, either alone or in a mixture of two or more of them.

In the method for producing a gas separation membrane of the present invention, when preparing a composition for forming a gas separation membrane containing a matrix resin, inorganic fine particles having a primary particle diameter of 1 to 1000 nm, and a solvent, the inorganic fine particles are organic group-modified inorganic fine particles having an organic group bonded to the surface, and the difference between the HSP of the organic group of the organic group-modified inorganic fine particles and the HSP of the matrix resin is 5.0 MPa ^0.5 or more and 15.0 MPa ^0.5 or less, and the composition for forming a gas molecule membrane is prepared using the inorganic fine particles, uniformly dispersed, and applied onto a substrate, and the solvent is then evaporated. As the substrate to be applied, there is no restriction on the material or surface condition as long as it is not deteriorated by the solvent, and examples thereof include Si wafers and porous substrates with no unevenness on the surface.

The method includes a step of applying a coating liquid for forming a gas separation membrane, which is formed from the composition for forming a gas separation membrane, to a substrate and evaporating the solvent to form a gas separation membrane.

The coating method is preferably one that can apply the coating evenly and without unevenness onto the substrate, and examples of the method include dip coating (immersion method), spin coating, blade coating, spray coating, gravure coating, die coating, and slit coating. However, the blade coating method is preferred, and it is particularly preferred to use a doctor blade.

The present invention will be explained in detail below with reference to examples, but the present invention is not limited to these in any way.

[Synthesis of PIM-1]
85.0 g of 3,3,3',3'-tetramethyl-1,1'-spirobiindan-5,5',6,6'-tetraol (Fujifilm Wako Pure Chemical Industries, 250 mmol) and 2537 g of N,N-dimethylacetamide (DMAc, Tokyo Chemical Industry Co., Ltd.) were weighed into a 5 L four-neck round-bottom separable flask equipped with a thermometer, stirring blades, and a cooling tube, and then stirred at room temperature to dissolve the substrate. Next, 48.5 g of tetrafluoroterephthalonitrile (Tokyo Chemical Industry Co., Ltd., 242 mmol) and 69.0 g of potassium carbonate (fine powder, Kanto Chemical Industry Co., Ltd.) were added in this order, and then stirred at 80°C for 2 hours. After filtering the reaction solution, it was filtered and washed with 800 mL of DMAc twice and 800 mL of methanol twice in that order. The filtered residue was poured into 2700 mL of pure water and boiled while stirring. After cooling, it was filtered and washed with pure water. This boiling, filtering, and washing process was repeated again. The collected residue was dried under reduced pressure (110°C, 3 hours), and then the residue (75.3 g) was dissolved in THF (1430 g). This solution was cut through a filter paper (mesh size 4 μm), and then slowly poured into 2000 g of methanol to perform reprecipitation. After filtering this slurry, it was washed with methanol, and then dried under reduced pressure (110°C, 3 hours) to collect 70.6 g of a yellow granular polymer. The physical properties of the obtained polymer were as follows.
・Weight average molecular weight (Mw): 105,000 (GPC measurement)
・Polydispersity (Mw/Mn): 2.70 (GPC measurement)

[Synthesis of fluorine-containing polyimide (6FDA-3MPA)]
3.01 g of 2,4,6-trimethyl-1,3-phenylenediamine (3 MPA, Tokyo Chemical Industry Co., Ltd., 20.0 mmol) and 108 g of N-methylpyrrolidone (Tokyo Chemical Industry Co., Ltd.) were weighed into a 200 mL four-neck flask equipped with a thermometer, stirring blade, and stopcock, and the mixture was stirred at room temperature to dissolve the substrate. Next, 8.97 g of 4,4-(hexafluoroisopropylidene)diphthalic anhydride (6FDA, Tokyo Chemical Industry Co., Ltd., 20.2 mmol) was added, and the mixture was stirred at room temperature for 27 hours under a nitrogen atmosphere. The viscosity of the reaction solution prepared was 109.3 mPa s. An additional 15.2 mg of 3 MPA (manufactured by Tokyo Chemical Industry Co., Ltd., 0.101 mmol) was added and stirred at room temperature for 3 hours, after which 45.2 mg of 6FDA (manufactured by Tokyo Chemical Industry Co., Ltd., 0.102 mmol) was added and stirred for 25 hours to prepare a polyamic acid-NMP solution with a solution viscosity of 119 mPa·s.

To the entire amount of the obtained polyamic acid-NMP solution, 6.17 g of acetic anhydride (manufactured by Tokyo Chemical Industry Co., Ltd., 60 mmol) and 4.17 g of pyridine (manufactured by Tokyo Chemical Industry Co., Ltd., 60 mmol) were added, and the mixture was stirred at 70° C. for 5 hours under a nitrogen atmosphere to perform imidization. After cooling, the reaction solution was slowly poured into methanol in an amount three times the amount of the reaction solution to precipitate a polymer component. The precipitate was filtered with a PTFE membrane filter (Omnipore (registered trademark) membrane filter, JAWP09025, pore size 1 μm) manufactured by Millipore, and the filtered matter was transferred to an appropriate beaker, and then methanol in an amount four times the weight of the wet filtered matter was poured in and stirred. The mixture was filtered with a membrane filter in the same manner as above, and washed with methanol in an amount three times the weight of the filtered matter in the same manner as above. The filtered matter was collected and then dried under reduced pressure (130° C., 5 hours), and 9.15 g of fluorine-containing polyimide was collected. The physical properties of the obtained fluorine-containing polyimide were as follows.
・Weight average molecular weight (Mw): 110,000 (GPC measurement)
・Polydispersity (Mw/Mn): 3.98 (GPC measurement)
Imidization rate: 100% (measured by ¹ H-NMR, protons at amide bond sites below detection limit)

[Synthesis of surface-modified silica 1]
In a 3000 mL four-neck round-bottom flask equipped with a cooling tube, a thermometer and a stirrer, 492 g of isopropanol (IPA) dispersion of silica nanoparticles (IPA-ST, manufactured by Nissan Chemical Industries, Ltd., silica concentration: 30.5 mass%, average primary particle diameter 12 nm), 2495 g of IPA, 2.69 g of pure water, and 11.0 g of APTES (manufactured by Tokyo Chemical Industry Co., Ltd.) were weighed and stirred under reflux for 1 hour. The obtained dispersion was charged with 1-methyl-2-pyrrolidone (NMP) while distilling off IPA and water with an evaporator, and the water content in the solution was confirmed to reach 0.1 mass% or less using a Karl Fischer moisture meter, and then the process was terminated. Next, the APTES-modified silica concentration was adjusted to about 5.4 mass% with NMP. This solution was designated as ST-G0-NMP dispersion.

The total amount of the ST-G0-NMP dispersion obtained was weighed into a 3000 mL four-neck round-bottom flask equipped with a cooling tube, a thermometer, and a stirrer, and 22.8 g of 1,3-diaminobenzoic acid (DABA) (manufactured by Aldrich), 15.1 g of triethylamine (TEA) (manufactured by Kanto Chemical Co., Ltd.), and 66.1 g of Benzotriazol-1-yloxytris(dimethylamino)phosphonium hexafluorophosphate (BOP) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were reacted for 1 hour at 80 ° C. This reaction solution was subjected to ultrafiltration washing (discharge pressure 0.2 MPa) with 1700 g of methanol using a Mitsubishi Kakoki Dynafilter (ceramic filter pore size 7 nm). The physical properties of the recovered methanol dispersion of surface-modified silica 1 were as follows. The surface modification amount here means the total amount of organic groups resulting from the reaction of aminopropyl groups derived from the coupling agent with organic carboxylic acid, and the same applies to the subsequent surface modification groups.
pH: 5.4
Electrical conductivity: 14.0 μm/s
Solid content in dispersion: 5.40% by mass
・Surface modification amount: 9.10% by mass

[Synthesis of surface-modified silica 2 (STO-MAB)]
In a 3000 mL four-neck round-bottom flask equipped with a cooling tube, a thermometer, and a stirrer, 164 g of an isopropanol (IPA) dispersion of silica nanoparticles (IPA-ST, manufactured by Nissan Chemical Industries, Ltd., silica concentration: 30.5 mass%, average primary particle diameter 12 nm), 832 g of IPA, 0.897 g of pure water, and 3.68 g of APTES (manufactured by Tokyo Chemical Industry Co., Ltd.) were weighed and stirred under reflux for 1 hour. The obtained dispersion was charged with 1-methyl-2-pyrrolidone (NMP) while distilling off IPA and water with an evaporator, and the water content in the solution was confirmed to reach 0.1 mass% or less using a Karl Fischer moisture meter, and then the process was terminated. This solution was designated as ST-G0-NMP dispersion.

100 g of the obtained ST-G0-NMP dispersion, 0.683 g of m-aminobenzoic acid (MBA, manufactured by Tokyo Chemical Industry Co., Ltd.), 0.504 g of triethylamine (TEA, manufactured by Tokyo Chemical Industry Co., Ltd.), and 2.20 g of Benzotriazol-1-yloxytris(dimethylamino)phosphonium hexafluorophosphate (BOP, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were weighed into a 300 mL four-neck round-bottom flask equipped with a cooling tube, a thermometer, and a stirrer, and then reacted at 80 ° C. for 1 hour. This reaction liquid was poured into 0.9 kg of methanol and diluted. The diluted liquid was concentrated using a Mitsubishi Kakoki Dynafilter (ceramic filter pore size 7 nm) (filtrate discharge: 720 g). Next, ultrafiltration washing (discharge pressure 0.2 MPa) was performed with 1700 g of methanol. The physical properties of the recovered methanol dispersion of surface-modified silica 2 were as follows.
pH: 4.51
Electrical conductivity: 15.5 μm/s
Solid content in dispersion: 2.34% by mass
・Surface modification amount: 9.14% by mass

[Synthesis of surface-modified silica 3]
To a 500 mL four-neck round-bottom flask equipped with a thermometer, a stirrer, and a stopcock, 49.2 g of a silica nanoparticle-isopropanol (IPA) dispersion (IPA-ST, manufactured by Nissan Chemical Industries, Ltd., silica concentration: 30.5 mass%, average primary particle size: 12 nm), 241 g of methanol (manufactured by Tokyo Chemical Industry Co., Ltd.), 1.10 g of 3-aminopropyltriethoxysilane (manufactured by Nacalai Tech), and 0.269 g of pure water were added in this order, and the mixture was heated to 60° C. under a nitrogen atmosphere while stirring at a rotation speed of 150 rpm, and then reacted for 4 hours.

After cooling to 35°C or less, a solution of isonicotinic acid (0.736 g, manufactured by Tokyo Chemical Industry Co., Ltd.)-methanol (6.63 g, manufactured by Tokyo Chemical Industry Co., Ltd.) and a solution of 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMT-MM, 1.66 g, manufactured by Chem-Impex International)-methanol (14.9 g, manufactured by Tokyo Chemical Industry Co., Ltd.) were added in this order, and the reaction was carried out at room temperature and at a rotation speed of 150 rpm for 2 hours. The surface-modified silica was washed using an ultrafiltration device under the same conditions as above, and a methanol dispersion was obtained. Various physical properties were as follows.
pH: 6.11
Electrical conductivity: 3.80 μm/s
Solid content in dispersion: 6.58% by mass
・Surface modification amount: 7.78% by mass

[Synthesis of surface-modified silica 4]
The same experimental procedure was carried out, except that the isonicotinic acid-methanol solution used in Surface-modified Silica 3 was changed to a 3,5-dimethoxybenzoic acid (1.09 g, manufactured by Tokyo Chemical Industry Co., Ltd.)-methanol (9.80 g) solution. The various physical properties were as follows.
pH: 7.23
Electrical conductivity: 2.22 μm/s
Solid content in dispersion: 6.62% by mass
・Surface modification amount: 9.23% by mass

[Synthesis of surface-modified silica 5]
The same experimental procedure was carried out, except that the isonicotinic acid-methanol solution used in Surface-modified Silica 3 was changed to a 3,5-dimethylbenzoic acid (0.898 g, manufactured by Tokyo Chemical Industry Co., Ltd.)-methanol (8.11 g) solution. The various physical properties were as follows.
pH: 6.71
Electrical conductivity: 5.01 μm/s
Solid content in dispersion: 6.33% by mass
・Surface modification amount: 7.95% by mass

[Synthesis of surface-modified silica 6]
The same experimental procedure was carried out, except that the isonicotinic acid-methanol solution used in Surface-modified Silica 3 was changed to a 4-t-butylbenzoic acid (1.07 g, manufactured by Tokyo Chemical Industry Co., Ltd.)-methanol (9.60 g) solution. The various physical properties were as follows.
pH: 6.89
Electrical conductivity: 5.62 μm/s
Solid content in dispersion: 4.81% by mass
・Surface modification amount: 9.26% by mass

[Synthesis of surface-modified silica 7]
To a 500 mL four-neck round-bottom flask equipped with a thermometer, a stirrer, and a stopcock, 32.8 g of a silica nanoparticle-isopropanol (IPA) dispersion (IPA-ST, manufactured by Nissan Chemical Industries, Ltd., silica concentration: 30.5 mass%, average primary particle size: 12 nm), 162 g of IPA (manufactured by Tokyo Chemical Industry Co., Ltd.), 0.849 g of N-phenyl-3-aminopropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., (KBM-573), and 0.179 g of pure water were added in this order, and the mixture was refluxed for 1 hour under a nitrogen atmosphere while stirring at a rotation speed of 150 rpm. After cooling, the solid content concentration (non-volatile components) in the reaction liquid was 5.32 mass%.

[Synthesis of surface-modified silica 8]
A 200 mL four-neck round-bottom flask equipped with a thermometer, stirrer, and stopcock was charged with 16.4 g of silica nanoparticle-isopropanol (IPA) dispersion (IPA-ST, Nissan Chemical Industries, Ltd., silica concentration: 30.5 mass%, average primary particle size 12 nm), 83.6 g of IPA (Tokyo Chemical Industry Co., Ltd.), 0.413 g of n-hexyltrimethoxysilane (Shin-Etsu Chemical Co., Ltd., KBM3063), and 0.0897 g of pure water in that order, and refluxed for 1 hour under a nitrogen atmosphere while stirring at a rotation speed of 150 rpm. The solid content concentration (non-volatile components) in the reaction solution after cooling was 5.59 mass%.

[Synthesis of surface-modified silica 9]
A 200 mL four-neck round-bottom flask equipped with a thermometer, stirrer, and stopcock was charged with 16.4 g of silica nanoparticle-isopropanol (IPA) dispersion (IPA-ST, Nissan Chemical Industries, Ltd., silica concentration: 30.5 mass%, average primary particle size: 12 nm), 83.6 g of IPA (Tokyo Chemical Industry Co., Ltd.), 0.196 g of trimethylmethoxysilane (Tokyo Chemical Industry Co., Ltd.), and 0.0299 g of pure water in that order, and refluxed for 1 hour under a nitrogen atmosphere while stirring at 150 rpm. The solids concentration (non-volatile components) in the reaction solution after cooling was 5.55 mass%.

[Synthesis of surface-modified silica 10]
32.8 g of silica nanoparticle-isopropanol (IPA) dispersion (IPA-ST, Nissan Chemical Industries, Ltd., silica concentration: 30.5% by mass, average primary particle size: 12 nm), 0.871 g of X-12-967C (Shin-Etsu Chemical Co., Ltd.), and 0.299 g of pure water were added in this order to a 100 mL four-neck round-bottom flask equipped with a thermometer, a stirrer, and a stopcock, and the mixture was refluxed for 5 hours with stirring under a nitrogen atmosphere. After cooling, the solids concentration (non-volatile components) in the reaction liquid was 31.5% by mass.

[Preparation of fluorinated polyimide/surface-modified silica composite membrane and evaluation of gas permeability]
A dispersion of various surface-modified silicas (1, 2, 4, 6, 7) equivalent to 250 mg of solid content and 4.75 g of NMP were weighed into a recovery flask, and the alcohol in the mixed solution was distilled off with an evaporator until the alcohol coagulated in the cooling tube could not be visually confirmed. After cooling, NMP was added so that the concentration of surface-modified silica in the solution was 5% by mass. A 5% by mass surface-modified silica-NMP mixed solution was gradually added to a 5% by mass fluorine-containing polyimide (6FDA-3MPA)-THF solution while stirring so that the surface-modified silica and the resin were the same mass, and a mixed solution was adjusted. This mixed solution was dropped into three times the amount of methanol to precipitate a composite of surface-modified silica/resin. The obtained suspension was filtered, washed with the same amount of methanol as in the precipitation operation, and the filtered residue was dried under reduced pressure (130°C, 5 hours) to obtain a composite of surface-modified silica and resin (composition ratio = 100 parts by mass/100 parts by mass).

42.0 mg of the composite was mixed with 168 mg of fluorine-containing polyimide (6FDA-3MPA) as a matrix resin and 2.79 g of THF as a solvent. After stirring with a magnetic stirrer, ultrasonic irradiation was performed for 3 minutes to prepare a film-forming composition (surface-modified silica: 10% by mass, resin: 90% by mass, total solids concentration: 7% by mass). The total solids concentration here refers to the total weight concentration of the surface-modified silica and resin. The film-forming composition was placed in a petri dish and left to dry (overnight at room temperature), then dried under reduced pressure (35°C, 3 hours) to obtain a free-standing film. The free-standing film was cut to an appropriate size and masked with aluminum sealing tape to an appropriate area, and then a gas permeability test (35°C, 1 atm, differential pressure method) was performed.

[Preparation of PIM-1/surface-modified silica composite membrane and evaluation of gas permeability]
Surface-modified silicas 1 to 5 and 7 were used, and self-supporting membranes were prepared and their gas permeability characteristics were evaluated in the same manner as above, except that the fluorine-containing polyimide described above was changed to PIM-1.

[Preparation of CDA/surface-modified silica composite membrane and evaluation of gas permeability]
For the composite of surface-modified silica 1 to 4 and CDA, the same procedure as above was carried out, except that the matrix resin was changed to commercially available cellulose acetate (CDA, Fujifilm Wako Pure Chemical Industries, Ltd., model number: 039-01695).

To composite surface-modified silica 5-8 with CDA, various synthesized surface-modified silica-alcohol dispersions and 2.5% by mass of CDA-THF mixed solution were weighed into an eggplant flask so that the various surface-modified silicas and CDA were equal in mass, and the solvent was removed using an evaporator until the contents were solid and dry. The solvent was then completely removed using a reduced-pressure dryer (130°C, 3 hours) to obtain a composite of surface-modified silica and resin. The composition ratio of the composite at this point was equal parts by mass. The preparation of free-standing membranes and gas permeability tests following composite formation were carried out using the same procedures as described above.

The various analyses and physical property evaluations carried out in this invention are as follows:

[Viscosity Measurement of Polyamic Acid-NMP Solution]
Measurements were made using a TV-22 or 25 model viscometer manufactured by Toki Sangyo Co., Ltd. Approximately 1 mL of the film-forming composition was dispensed into a sample cup, and the value was measured after holding the sample cup for 2 minutes at a measurement temperature of 25° C. and a predetermined shear rate of 76.6 s ⁻¹ using a cone-plate type rotor.

[GPC Measurement of Polymer]
The polymer was diluted and dissolved in a solvent such as THF to a polymer concentration of 1% by mass, and then passed through a 0.1 μm PTFE syringe filter and measured using a Tosoh HLC-8320GPC.
Measurement condition:
Developing solvent: THF
Flow rate: 0.3mL/min
Column temperature: 40°C
Column type: Tosoh TSKgel SperHZM-N, 2 columns connected

[Calculation of imidization rate]
The concentration of fluorine-containing PI (6FDA-3MPA) in DMSO-d6 was adjusted to 1% by mass, and the total number of protons in the benzene ring and the number of protons in the amide bond were determined by ¹ H-NMR, and the imidization rate was calculated from the ratio of these.
Imidization rate (%)=((total number of protons on benzene ring/6)−(number of protons on amide bond/2))/(total number of protons on benzene ring/6)×100

[Evaluation of liquid properties of surface-modified silica-methanol dispersion]
Each dispersion was diluted two-fold with pure water, and the pH and electrical conductivity of the diluted solution were measured.

[Measurement of solid content of surface-modified silica in methanol dispersion]
The methanol dispersion was weighed (S1) into a tared screw tube (W1), dried at 110° C. for 2 hours and then at 130° C. for 3 hours, and then weighed (W2). The solid content was calculated using the following formula.
Solid concentration (mass%) = (W2-W1)/S1 x 100

[Calculation of the amount of surface modification]
5 to 10 mg of each surface-modified silica dried as described above was weighed onto a platinum pan, and then heated (5°C/min) from room temperature to 1000°C in an air atmosphere using a BRUKER TG-DTA2000SA. The same measurements were also carried out for unmodified silica. The difference between the weight loss of the surface-modified silica from 210 to 1000°C and the weight loss of the unmodified silica in the same temperature range was calculated as the amount of surface-modifying groups.

[Gas permeability measurement]
The gas permeability of each composite membrane to _CO2 and _N2 was measured by a differential pressure method (1 atm, 35°C) using GTR-6ADF manufactured by GTR Tech. The measurement sample was prepared by masking the composite membrane with an aluminum seal and adjusting the measurement area appropriately. The measurement conditions were 7 minutes for evacuation inside the measurement cell, and the measurement time was adjusted appropriately within the range of about 1 to 10 minutes so that the gas permeation flow rate was in a steady state. Measurements were repeated five times under these conditions, and the value of the fifth gas permeation amount was taken as the gas permeation amount of the coating membrane. The measurement was performed twice, and the average value was adopted. The measurement unit used is Barrer, which is 1 x ^10-10 ^cm3 (STP) cm/(s ^cm2 cmHg), and ^cm3 (STP) means the gas volume at 1 atmosphere and 0°C.

[Gas selectivity calculation]
The gas selectivity of each composite membrane was calculated as the ratio of _CO2 permeability to _N2 permeability of each composite membrane.

[Hansen Solubility Parameter (HSP) Calculation of Surface Modification Groups and Resins]
Using the calculation software Winmostar, the HSP of the surface modification group of the inorganic fine particles and the HSP of the matrix resin were calculated.

The calculation range of the HSP of the surface modification group of the microparticles is shown in Figure 1. As shown in Figure 1, the calculation range of the surface modification group of the microparticles targets the organic groups outside the Si atom derived from the coupling agent, and the calculation target is the structure in which H is added to the organic group R detached from Si, which is adopted as the HSP of the surface modification group. In other words, when the organic group R is bonded via Si, the HSP of the structural formula R-H is adopted. Note that when Si is not involved, the calculation target is the structure in which all organic groups are detached and H is added.

The calculation target for the HSP of the matrix resin was a structure in which the bonds between the repeating monomer units were cut and H was added to the cut sites.

FIG. 2 shows the structure of the matrix resin used in the examples that is the subject of calculation.
Formula (A) is the structure of the fluorine-containing polyimide (6FDA-3MPA) to be calculated, formula (B) is the structure of the cellulose acetate (CDA), and formula (C) is the structure of the PIM-1 to be calculated. However, due to restrictions of the calculation software, only two bond points can be selected, so for PIM-1, the repeating unit was changed to that represented by formula (C) in Figure 2 and calculations were performed. For ease of understanding, the added H is shown in bold.

[HSP of surface modifying group of silica]
The HSP of the organic group outside the Si of the synthesized surface-modified silica is shown in Table 1.

[HSP of matrix resin]
The HSP of the matrix resin used in the examples of the present invention is shown in Table 2.

[ΔHSP of surface modifying group and matrix resin]
HSP is calculated from three parameters (dispersion term: δD, polarity term: δP, hydrogen bond term: δH). When these values are considered as coordinates in three-dimensional space, ΔHSP means the difference in three-dimensional space between the HSP of the surface modifying group and the HSP of the matrix resin, and is calculated by the following formula:

[Correlation between gas permeability and ΔHSP of composite membrane]
The gas permeability characteristics and ΔHSP results of each composite membrane obtained by the above-mentioned evaluation method are summarized in Tables 3 to 5. In addition, the relationship between ΔHSP and the gas permeability characteristics of each composite membrane in each table is shown in Figs. 3 to 5.

In each table, it was confirmed that when ΔHSP is 5 MPa ^0.5 or more as in the examples, the gas permeability of the composite membrane is higher than that of the comparative example (blank) that does not contain surface-modified silica. On the other hand, the composite membrane using the membrane-forming composition that has ΔHSP of less than 5 MPa ^0.5 as in the comparative example tends to have the same or lower gas permeability than the blank, and a correlation between ΔHSP and gas permeability was confirmed.

In addition, since the dispersibility of the surface-modified silica in the resin tends to decrease as the ΔHSP increases, when the ΔHSP exceeds ^15.0 MPa, the dispersibility of the surface-modified silica in the resin decreases significantly, making it difficult to prepare a film-forming composition, and therefore no test was performed.
In the present study, when ΔHSP was 5.0 MPa ^0.5 or more and 15.0 MPa ^0.5 or less, a membrane that functioned as a gas separation membrane without membrane defects could be obtained.

The above results demonstrate that determining ΔHSP, which is the difference between the HSP of the surface modification group and the HSP of the matrix resin, is a useful method for determining whether a gas separation membrane made of a composition for forming a gas separation membrane has excellent gas permeability. In addition, the setting of the structural range in the HSP calculation performed in this invention is also unique. Furthermore, since similar trends were confirmed in polymers and surface modification groups with different structures and polarities, it is inferred that this index can be applied to a wide range of resins and surface modification groups, without being limited to specific resins or surface modification groups.

Claims

A composition for forming a gas separation membrane comprising a matrix resin, inorganic fine particles having a primary particle size of 1 to 1000 nm, and a solvent,
an organic group is bonded to the surface of the inorganic fine particles,
A composition for forming a gas separation membrane, wherein the difference between the HSP of the organic group of the inorganic fine particles and the HSP of the matrix resin is 5.0 to 15.0 MPa 0.5 .
The composition for forming a gas separation membrane according to claim 1, wherein the inorganic fine particles are silica.
The composition for forming a gas separation membrane according to claim 2, characterized in that the organic groups of the inorganic fine particles are bonded via -O-Si- to form the following structure, and the HSP of the organic groups is calculated from the structure of the (organic group) beyond -Si-.
2. The composition for forming a gas separation membrane according to claim 1, wherein the matrix resin is a cellulose acetate represented by the following formula (I):
(n is an integer of 50 to 500, R represents -H or -COCH3 , and at least one of R is -COCH3 .)
The composition for forming a gas separation membrane according to claim 1 , wherein the matrix resin is a polyimide having a repeating structure represented by the following formula (II) obtained by condensation polymerization of a tetracarboxylic dianhydride represented by the following formula (10) and an aromatic diamine R2 ( NH2 )2.
( R1 represents a tetravalent organic group.)
( R1 represents a tetravalent organic group. R2 represents a residue obtained by removing an amine from an aromatic diamine, and represents an aromatic group having 6 to 14 carbon atoms. n represents an integer of 50 to 500.)
The composition for forming a gas separation membrane according to claim 1, wherein the matrix resin is an inherently microporous polymer.
The composition for forming a gas separation membrane according to claim 6, wherein the polymer having intrinsic microporosity is PIM-1 represented by the following formula (III):
(n represents an integer of 50 to 1000.)
The composition for forming a gas separation membrane according to claim 4 , wherein the organic group has the following structure:
The composition for forming a gas separation membrane according to claim 5 , wherein the organic group has the following structure:
The composition for forming a gas separation membrane according to claim 6 or 7, wherein the organic group has the following structure:
A method for producing a gas separation membrane using a composition for forming a gas separation membrane, the composition comprising a matrix resin, inorganic fine particles having a primary particle size of 1 to 1000 nm, and a solvent, the method comprising the steps of:
As the composition for forming a gas separation membrane, a composition for forming a gas separation membrane is used in which an organic group is bonded to the surface of the inorganic fine particles, and the difference between the HSP of the organic group of the inorganic fine particles and the HSP of the matrix resin is 5.0 to 15.0 MPa 0.5 ;
A method for producing a gas separation membrane, comprising the steps of applying a coating liquid for forming a gas separation membrane, formed from the composition for forming a gas separation membrane, onto a substrate, and evaporating the solvent to form a gas separation membrane.