Carbon dioxide separation membrane, method for producing carbon dioxide separation membrane, method for separating carbon dioxide, and carbon dioxide separation membrane module

Abstract

This carbon dioxide separation membrane has a porous membrane and a separation-functional layer formed on the surface of the porous membrane. The separation-functional layer comprises a composition that contains: a copolymer having a component unit represented by formula (1) and a component unit represented by formula (2) or a polymer having a component unit represented by formula (5) (R' represents a hydroxyl group or an organic group having 1 to 30 carbons); and an amine compound having a molecular weight of not more than 500.

Description

Carbon dioxide separation membrane, carbon dioxide separation membrane manufacturing method, carbon dioxide separation method, and carbon dioxide separation membrane module

[0001] The present disclosure relates to a carbon dioxide separation membrane, a method for producing a carbon dioxide separation membrane, a carbon dioxide separation method, and a carbon dioxide separation membrane module.

[0002] It has been known that polymeric materials have inherent gas permeability, and that gas components can be separated using membranes made of polymeric materials (see, for example, Non-Patent Document 1). Gas separation membranes that utilize this property are an energy-saving and space-saving separation technology and are used in a variety of fields.

[0003] Meanwhile, in recent years, attention has been focused on technologies for separating and capturing carbon dioxide, a cause of global warming, before it is emitted into the atmosphere from large-scale sources such as thermal power plants and steelworks blast furnaces. One such technology, a process in which carbon dioxide is absorbed by amines and then desorbed by heating, has reached a practical level. However, the need for heating to desorb carbon dioxide has presented a challenge, as it increases the cost of capture.

[0004] To overcome the above-mentioned problems, carbon dioxide separation and capture processes using membrane separation have been proposed. In particular, processes using polymer membranes have attracted attention because polymer membranes are easy to chemically modify and modularize, and mass production is possible, enabling low-cost production. However, at present, there are no examples of practical application, and studies are limited to pilot-level studies (see, for example, Non-Patent Document 2). One of the reasons for this lack of practical application is that the carbon dioxide permeation flux and carbon dioxide selectivity are low, falling short of the required characteristics.

[0005] Research and development of facilitated transport membranes has been conducted to improve carbon dioxide permeation flux and carbon dioxide selectivity. Facilitated transport membranes are membranes incorporating a substance (carrier) that reversibly and selectively reacts only with specific permeants. The permeants can permeate by forming a reaction product with the carrier in addition to the dissolution-diffusion mechanism through the membrane matrix. This allows for a larger permeation flux and higher selectivity than coexisting components other than the permeants that permeate only via the dissolution-diffusion mechanism. Examples of such facilitated transport membranes include a polymer membrane in which a gel layer composed of a polyvinyl alcohol-polyacrylic acid copolymer gel membrane and 2,3-diaminopropionic acid is supported on a hydrophilic ultrafiltration membrane (see, for example, Patent Document 1), a polymer membrane containing polyvinyl alcohol and a specific amine compound (see, for example, Patent Document 2), and a polymer membrane in which a polyamidoamine dendrimer with a high affinity for carbon dioxide is immobilized inside a polymer obtained by photopolymerizing polyethylene glycol dimethacrylate (see, for example, Patent Document 3).

[0006] JP 2008-36463 A JP 2018-144022 A JP 2009-185118 A

[0007] Toray Research Center, Research and Development Division, "New Developments in Gas Separation Technology," Toray Research Center, Inc., 1990, pp. 345-362. Journal of Membrane Science, 2010, Vol. 359, Issue 1-2, pp. 126-139.

[0008] However, in order to reduce the cost of carbon dioxide capture, a higher carbon dioxide permeation flux and a higher carbon dioxide selectivity are required, and thus higher performance polymer membranes are desired.

[0009] An object of the present disclosure is to provide a carbon dioxide separation membrane having a high carbon dioxide permeation flux and high carbon dioxide selectivity. Another object of the present disclosure is to provide a method for producing the carbon dioxide separation membrane, a carbon dioxide separation method using the carbon dioxide separation membrane, and a carbon dioxide separation membrane module using the carbon dioxide separation membrane.

[0010] As a result of intensive investigations, the inventors of the present disclosure have found that in a carbon dioxide separation membrane having a porous membrane and a separation functional layer formed on the surface thereof, the above-mentioned problems can be solved by using a specific polymer in the separation functional layer.

[0011] [1] A carbon dioxide separation membrane comprising a porous membrane and a separation functional layer formed on the surface of the porous membrane, wherein the separation functional layer is composed of a composition containing a copolymer having a structural unit represented by the following formula (1) and a structural unit represented by the following formula (2), and an amine compound having a molecular weight of 500 or less. The porous membrane is preferably an ultrafiltration membrane (the molecular weight cutoff is preferably 500,000 or less, more preferably 500 to 200,000). The content of the amine compound having a molecular weight of 500 or less in the composition is preferably 2 to 95 wt%, more preferably 30 to 95 wt%, based on the total content of the copolymer and the amine compound having a molecular weight of 500 or less. The content of the structural unit represented by formula (1) in the copolymer is preferably 70 mol% or less. The molar ratio of the structural unit represented by formula (1) to the structural unit represented by formula (2) in the copolymer is preferably 1:99 to 70:30, more preferably 30:70 to 70:30. The weight average molecular weight of the copolymer is preferably 10,000 to 1,000,000. [2] The carbon dioxide separation membrane according to [1], wherein the copolymer further has one or both of a structural unit represented by the following formula (3) and a structural unit represented by the following formula (4): In the copolymer, the molar ratio of the structural unit represented by formula (1): the structural unit represented by formula (3) is preferably 1:99 to 100:0, more preferably 80:20 to 100:0. In the copolymer, the molar ratio of the structural unit represented by formula (2): the structural unit represented by formula (4) is preferably 1:99 to 100:0, more preferably 80:20 to 100:0. (In the formula, R represents an acyl group having 1 to 4 carbon atoms.) [3] A carbon dioxide separation membrane having a porous membrane and a separation functional layer formed on the surface of the porous membrane, wherein the separation functional layer is made of a composition containing a polymer having a structural unit represented by the following formula (5) and an amine compound having a molecular weight of 500 or less. The porous membrane is preferably an ultrafiltration membrane (the molecular weight cutoff is preferably 500,000 or less, more preferably 500 to 200,000). The content of the amine compound having a molecular weight of 500 or less in the composition is preferably 2 to 95 wt %, more preferably 30 to 95 wt %, based on the total content of the copolymer and the amine compound having a molecular weight of 500 or less. The content of the structural unit represented by formula (5) in the polymer is preferably 60 mol % or more and 100 mol % or less. The weight average molecular weight of the polymer is preferably 10,000 to 1,000,000. (In the formula, R' represents a hydroxyl group or an organic group having 1 to 30 carbon atoms, preferably an organic group having 1 to 30 carbon atoms, more preferably a tetrahydrofurfuryl group.) [4] The carbon dioxide separation membrane according to [3], wherein the polymer further has a structural unit represented by the following formula (6): The molar ratio of the structural unit represented by formula (5) to the structural unit represented by formula (6) in the polymer is 60:40 to 100:0. [5] The carbon dioxide separation membrane according to [1] or [2], wherein the porous membrane is a hollow fiber membrane, and the separation function layer is formed on either or both of the outer surface and the inner surface of the hollow fiber membrane. The inner diameter of the hollow fiber of the hollow fiber membrane is preferably 100 to 3,000 μm. [6] The carbon dioxide separation membrane according to [3] or [4], wherein the porous membrane is a hollow fiber membrane, and the separation function layer is formed on either or both of the outer surface and the inner surface of the hollow fiber membrane. The inner diameter of the hollow fiber of the hollow fiber membrane is preferably 100 to 3,000 μm. [7] The carbon dioxide separation membrane according to any of [1] to [6], wherein the amine compound having a molecular weight of 500 or less includes either or both of an amine compound represented by the following formula (7) and an amine compound represented by the following formula (8). The amine compound having a molecular weight of 500 or less is preferably an amine compound represented by the following formula (7), and more preferably N-(2-aminoethyl)ethanolamine. (In formula (7), R １ , R ２ and R ３ each independently represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a hydroxyethyl group, preferably a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and more preferably a hydrogen atom. (In formula (8), R ４ , R ５ and R ６ each independently represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, preferably a hydrogen atom.) [8] A method for producing the carbon dioxide separation membrane according to any one of [1] to [7], comprising: a retaining step of contacting the porous membrane with a solution containing the copolymer or the polymer, the amine compound having a molecular weight of 500 or less, and a solvent, and retaining the solution on the surface of the porous membrane; and a drying step of removing the solvent from the solution retained in the porous membrane. The solvent is preferably water. [9] A method for separating carbon dioxide, comprising: a separation step of contacting a mixed gas containing carbon dioxide with one end of the carbon dioxide separation membrane according to any one of [1] to [7], and permeating the carbon dioxide in the mixed gas to the other end of the carbon dioxide separation membrane.

[10] A carbon dioxide separation membrane module comprising the carbon dioxide separation membrane according to any one of [1] to [7].

[0012] According to the present disclosure, it is possible to provide a carbon dioxide separation membrane that has a high carbon dioxide permeation flux and high carbon dioxide selectivity. Furthermore, according to the present disclosure, it is possible to provide a method for producing the carbon dioxide separation membrane, a carbon dioxide separation method using the carbon dioxide separation membrane, and a carbon dioxide separation membrane module using the carbon dioxide separation membrane.

[0013] 1 is a schematic diagram of a gas separation device used in Examples and Comparative Examples. 2 is an IR spectrum before and after the saponification reaction in Synthesis Example 1. 3 is an IR spectrum before and after the aminolysis reaction in Synthesis Example 2.

[0014] The present disclosure will be described in detail below. A carbon dioxide separation membrane according to a first embodiment of the present disclosure has a porous membrane and a separation functional layer formed on the surface of the porous membrane, and the separation functional layer is made of a composition containing a copolymer (hereinafter referred to as a "hydroxymethylene-vinyl alcohol copolymer") having a constitutional unit represented by formula (1) and a constitutional unit represented by formula (2), and an amine compound having a molecular weight of 500 or less.

[0015] Polyvinyl alcohol is known to exhibit excellent properties as a separation functional layer, but since hydroxymethylene-vinyl alcohol copolymer has a higher hydroxyl group density than polyvinyl alcohol, it is thought that the retention amount and stability of the amine compound in the separation functional layer are further improved, and as a result, the carbon dioxide separation properties of the carbon dioxide separation membrane according to the first embodiment of the present disclosure are improved.

[0016] In the first embodiment of the present disclosure, the porous membrane is preferably an ultrafiltration membrane. In the case of an ultrafiltration membrane, the molecular weight cutoff is preferably 500,000 or less, more preferably 500 to 200,000. It may also be a composite membrane composed of multiple layers. When the molecular weight cutoff is within the above range, the interface between the separation functional layer formed on the surface of the porous membrane and the porous membrane becomes clear, suppressing the diffusion of hydroxymethylene-vinyl alcohol copolymer into the interior of the porous membrane, thereby reducing gas permeation resistance and improving the carbon dioxide permeation flux. When the porous membrane is an ultrafiltration membrane, the cutoff characteristics are determined by the molecular weight cutoff, and the average pore size is not particularly specified, but is preferably approximately 1 to 50 nm. In the first embodiment of the present disclosure, several types of marker molecules with different molecular weights are introduced into the porous membrane to measure the rejection rate, and the molecular weight at which the rejection rate is 90% is defined as the molecular weight cutoff of the membrane. Proteins such as insulin, cytochrome C, and pepsin are used as marker molecules.

[0017] Porous membrane shapes include sheet-like flat membranes and hollow fiber membranes, with hollow fiber membranes being preferred. When the porous membrane is a flat membrane, its thickness is preferably 10 to 3,000 μm, and more preferably 50 to 500 μm. Flat membranes are preferred because the above thickness ensures low permeation resistance and mechanical strength. On the other hand, when the porous membrane is a hollow fiber membrane, the inner diameter of the hollow fiber is preferably 100 to 3,000 μm, and the membrane thickness is preferably 25 to 300 μm. The thicknesses of the porous membrane and the separation functional layer are measured by observation with a scanning electron microscope (SEM).

[0018] When the porous membrane is a flat membrane with an asymmetric structure, the separation functional layer is formed on the surface of a dense layer with a small pore size. When the porous membrane is a hollow fiber membrane, the separation functional layer is preferably formed on either or both of the outer and inner surfaces of the hollow fiber membrane. It is more preferable that the separation functional layer be formed on the inner surface, as this allows for uniform formation of the separation functional layer and makes it less susceptible to damage even when membranes come into contact with each other. The thickness of the separation functional layer is not particularly limited, but is preferably in the range of 0.1 to 10.0 μm. When the thickness of the separation functional layer is within this range, the amine compound with a molecular weight of 500 or less contained in the membrane can be stably retained, thereby ensuring durability. Furthermore, a membrane thickness of 10.0 μm or less is preferable because it allows for a high carbon dioxide permeation flux.

[0019] The structure of the porous membrane is not particularly limited, but an asymmetric structure in which the surface layer is a dense layer with small pores and the lower layer is a support layer with large pores is preferred because it reduces permeation resistance and increases permeation flux. The porosity of the porous membrane cross section is preferably 60 to 90%, more preferably 70 to 85%. The porosity of the porous membrane is calculated by mercury intrusion porosimetry or image analysis of the membrane cross section using a scanning electron microscope.

[0020] The material of the porous membrane is not particularly limited, and examples thereof include polyolefins such as polyethylene and polypropylene; fluorine-containing polymers such as polytetrafluoroethylene, polyvinyl fluoride and polyvinylidene fluoride; chlorine-containing polymers such as polyvinyl chloride and polyvinylidene chloride; vinyl polymers such as polystyrene, polyacrylonitrile and polymethyl methacrylate; condensation polymers such as polysulfone, polyethersulfone, polyetherimide, polyamide, polyurethane and polyimide; polysaccharides such as cellulose acetate and chitosan; and the like. Among these, preferred are polysulfone, polyethersulfone, polyetherimide, polyacrylonitrile and polyvinylidene fluoride, and particularly preferred are polysulfone and polyethersulfone.

[0021] In the first embodiment of the present disclosure, the separation functional layer is made of a composition containing a hydroxymethylene-vinyl alcohol copolymer and an amine compound having a molecular weight of 500 or less, and is formed on the surface of the porous membrane. This composition is preferably a homogeneous composition. This is because a carbon dioxide separation membrane having a separation functional layer formed from a homogeneous composition has a larger amount of the amine compound having a molecular weight of 500 or less incorporated into the membrane, thereby improving stability.

[0022] The content of the amine compound having a molecular weight of 500 or less in the composition containing a hydroxymethylene-vinyl alcohol copolymer and an amine compound having a molecular weight of 500 or less is not particularly limited, but is preferably 2 to 95% by weight, more preferably 30 to 95% by weight, based on the total content of the hydroxymethylene-vinyl alcohol copolymer and the amine compound having a molecular weight of 500 or less.

[0023] The hydroxymethylene-vinyl alcohol copolymer preferably has 1 to 2,000 constitutional units represented by formula (1) (hereinafter referred to as "hydroxymethylene units") per molecule, and more preferably 50 to 1,000. The vinyl alcohol copolymer preferably has 1 to 2,000 constitutional units represented by formula (2) (hereinafter referred to as "vinyl alcohol units") per molecule, and more preferably 50 to 1,000.

[0024]

[0025]

[0026] From the viewpoint of water solubility, the content of hydroxymethylene units in the hydroxymethylene-vinyl alcohol copolymer is preferably 70 mol % or less. Therefore, the molar ratio of hydroxymethylene units to vinyl alcohol units in the hydroxymethylene-vinyl alcohol copolymer is preferably 1:99 to 70:30 (hydroxymethylene units:vinyl alcohol units), and particularly preferably 30:70 to 70:30 (hydroxymethylene units:vinyl alcohol units).

[0027] The molecular weight of the hydroxymethylene-vinyl alcohol copolymer is preferably in the range of 10,000 to 1,000,000 in weight average molecular weight. A weight average molecular weight in this range is preferable because it ensures the mechanical strength of the separation functional layer, the solution viscosity during coating is within an appropriate range, and the thickness of the separation functional layer is uniform. In the present disclosure, the weight average molecular weight of the polymer is measured by size exclusion chromatography.

[0028] The hydroxymethylene-vinyl alcohol copolymer may have either or both of a structural unit represented by the following formula (3) and a structural unit represented by the following formula (4). When the hydroxymethylene-vinyl alcohol copolymer has a structural unit represented by formula (3) (hereinafter referred to as a "vinylene carbonate unit"), the copolymer preferably has 1 to 2,000 vinylene carbonate units per molecule, and more preferably has 10 to 500 vinyl ester units. When the hydroxymethylene-vinyl alcohol copolymer has a structural unit represented by formula (4) (hereinafter referred to as a "vinyl ester unit"), the copolymer preferably has 1 to 2,000 vinyl ester units per molecule, and more preferably has 10 to 500 vinyl ester units.

[0029]

[0030] (wherein R represents an acyl group having 1 to 4 carbon atoms.)

[0031] R in formula (4) is an acyl group having 1 to 4 carbon atoms. Examples of the acyl group having 1 to 4 carbon atoms include an acetyl group, a propionyl group, an oleyl group, and a benzoyl group.

[0032] When the hydroxymethylene-vinyl alcohol copolymer has either or both of vinylene carbonate units and vinyl ester units, the molar ratio of hydroxymethylene units to vinylene carbonate units in the hydroxymethylene-vinyl alcohol copolymer is preferably hydroxymethylene units:vinylene carbonate units=1:99 to 100:0, particularly preferably hydroxymethylene units:vinylene carbonate units=80:20 to 100:0. Furthermore, the molar ratio of vinyl alcohol units to vinyl ester units in the hydroxymethylene-vinyl alcohol copolymer is preferably vinyl alcohol units:vinyl ester units=1:99 to 100:0, particularly preferably vinyl alcohol units:vinyl ester units=80:20 to 100:0.

[0033] The hydroxymethylene-vinyl alcohol copolymer used in the present disclosure is produced by copolymerizing vinylene carbonate and a vinyl ester followed by saponification. There are no particular limitations on the production method of the vinylene carbonate-vinyl ester copolymer, but a production method using radical polymerization is simple and preferred. Polymerization can be carried out in various forms, including bulk polymerization without a solvent, solution polymerization using a solvent in which the monomer and polymer are soluble, precipitation polymerization using a solvent in which the monomer dissolves but the polymer does not, and dispersion polymerization or suspension polymerization using a solvent in which neither the monomer nor the polymer dissolves. When producing the vinylene carbonate-vinyl ester copolymer by radical polymerization, production conditions can be selected arbitrarily, with the polymerization temperature being 20°C to 120°C and the polymerization time being 10 minutes to 24 hours. Specific examples of vinyl esters include vinyl acetate, vinyl trifluoroacetate, vinyl propionate, vinyl pivalate, vinyl neononanoate, vinyl decanoate, vinyl neodecanoate, vinyl stearate, and vinyl benzoate, with vinyl acetate being preferred.

[0034] The method for saponifying the vinylene carbonate-vinyl ester copolymer is not particularly limited, and the vinylene carbonate-vinyl ester copolymer is dissolved or dispersed in water or a water-containing solvent, and a base is added to carry out the saponification reaction. The reaction conditions can be set arbitrarily within the ranges of a reaction temperature of 0 to 90°C and a reaction time of 30 minutes to 120 hours.

[0035] The amine compound having a molecular weight of 500 or less, which is another component constituting the separation functional layer, is a carrier component that plays a role in adsorbing, transporting, and desorbing carbon dioxide in the carbon dioxide separation membrane according to the first embodiment of the present disclosure. When the molecular weight of the amine compound is 500 or less, the molecular mobility is high and the carbamic acid produced by the reaction of the amine compound with carbon dioxide also diffuses rapidly in the separation functional layer, thereby increasing the carbon dioxide permeation flux and achieving high performance of the separation membrane. In the first embodiment of the present disclosure, suitable amine compounds having a molecular weight of 500 or less include amine compounds represented by the following formula (7) and amine compounds represented by the following formula (8), with the amine compound represented by the following formula (7) being preferred.

[0036] (In formula (7), R １ , R ２ and R ３ each independently represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a hydroxyethyl group.

[0037] (In formula (8), R ４ , R ５ and R ６ each independently represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

[0038] R of the amine compound represented by formula (7) １ ~R ３ is preferably a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and more preferably a hydrogen atom. ４ ~R ６ is preferably a hydrogen atom. １ ~R ３ and R of the amine compound represented by formula (8)４ ~R ６ Examples of the alkyl group having 1 to 4 carbon atoms in the formula include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, and a tert-butyl group.

[0039] Examples of the amine compound having a molecular weight of 500 or less include ethylenediamine compounds, diethylenetriamine (DETA) compounds, triethylenetetramine (TETA) compounds, tetraethylenepentamine (TEPA) compounds, tetraethylenepentamine (TEPA) compounds, pentaethylenehexamine (PEHA) compounds, and the like. More specifically, N-(2-aminoethyl)ethanolamine, N-[2-(dimethylamino)ethyl]-N-methylethanolamine, N-[2-(diethylamino)ethyl]ethanolamine, N-(1,2-dihydro N-[(1-hydroxymethyl-2-hydroxy)-n-propyl]piperazine, N-[(1-hydroxy-2-hydroxymethyl)-n-propyl]piperazine, N-(1,2-dihydroxy-n-propyl)-N'-methyl-piperazine, N-[1,2-bis(hydroxymethyl)-n-propyl]piperazine, N-[1,2-bis(hydroxymethyl)-n-propyl]-N'-methyl-piperazine, diethylenetriamine (DETA), 1,4,7,10-tetraazadecane, N,N-bis(2-amino) N,N,N'-tris(2-aminoethyl)-1,2-ethanediamine, 1-[2-[2-[(2-aminoethyl)amino]ethyl]amino]ethyl]-piperazine, 1,4-bis(2-aminoethyl)-piperazine, triethylenetetramine (TETA), 1,4,7,10,13-pentaazatridecane, N,N,N'-tris(2-aminoethyl)-1,2-ethanediamine, 1-[2-[2-[2-[(2-aminoethyl)amino]ethyl]amino]ethyl]-piperazine, 1-[2-[bis(2-aminoethyl)amino]ethyl]-piperazine, bis[2-(1-piperazinyl)ethyl]amine, Tetraethylenepentamine (TEPA), 1,4,7,10,13,16-hexaazahexadecane, N,N,N',N'-tetrakis(2-aminoethyl)-1,2-ethanediamine, N,N-bis(2-aminoethyl)-N'-[2-[(2-aminoethyl)amino]ethyl]-1,2-ethanediamine, 1-[2-[2-[2-[2-[2-[(2-aminoethyl)amino]ethyl]amino]ethyl]amino]ethyl]-piperazine, 1-[2-[2-[2-[bis(2-aminoethyl)amino]ethyl]amino]ethyl]piperazine, N,Examples include N'-bis[2-(1-piperazinyl)ethyl]-1,2-ethanediamine, pentaethylenehexamine (PEHA), and the like. Among these, N-(2-aminoethyl)ethanolamine, N-[2-(dimethylamino)ethyl]-N-methylethanolamine, N-[2-(diethylamino)ethyl]ethanolamine, N-(1,2-dihydroxy-n-propyl)piperazine, N-[(1-hydroxymethyl-2-hydroxy)-n-propyl]piperazine, N-[(1-hydroxy-2-hydroxymethyl)-n-propyl]piperazine, N-(1,2-dihydroxy-n-propyl)-N'-methyl-piperazine, N-[1,2-bis(hydroxymethyl)-n-propyl]piperazine, and N-[1,2-bis(hydroxymethyl)-n-propyl]-N'-methyl-piperazine are preferred as amine compounds having a molecular weight of 500 or less, with N-(2-aminoethyl)ethanolamine and N-(1,2-dihydroxy-n-propyl)piperazine being particularly preferred.

[0040] Furthermore, the composition constituting the separation functional layer may contain other components in addition to the hydroxymethylene-vinyl alcohol copolymer and the amine compound having a molecular weight of 500 or less, as long as the above-mentioned effects are not impaired. When the composition contains other components, the content of the other components in the composition is preferably 30% by weight or less. Examples of such other components include polyvinyl alcohol, poly(meth)acrylic acid, polyethylene glycol, polyvinylpyrrolidone, polyethyleneimine, polyallylamine, polysaccharides, salts thereof, copolymers thereof, and blends thereof. In the present disclosure, "(meth)acrylic acid" refers to either or both of acrylic acid and methacrylic acid.

[0041] Next, a carbon dioxide separation membrane according to a second embodiment of the present disclosure has a porous membrane and a separation functional layer formed on the surface of the porous membrane, and the separation functional layer is made of a composition containing a polymer having a structural unit represented by formula (5) (hereinafter referred to as a "polymer having hydroxyurethane as a structural unit") and an amine compound having a molecular weight of 500 or less.

[0042] Polyvinyl alcohol is known to exhibit excellent properties as a separation functional layer, but a polymer having a structural unit represented by formula (5) has a hydroxyl group density equivalent to that of polyvinyl alcohol and also contains urethane bonds that have excellent affinity for amine compounds, thereby further improving the retention and stability of the amine compound in the separation functional layer, and as a result, it is believed that the carbon dioxide separation characteristics of the carbon dioxide separation membrane according to the second embodiment of the present disclosure are improved. Furthermore, fully saponified polyvinyl alcohols have traditionally been used in facilitated transport membranes. However, fully saponified polyvinyl alcohols require high temperatures and long periods of time to dissolve in water, making the preparation of an aqueous solution complicated and resulting in poor aqueous solution stability. In contrast, polymers having polyhydroxyurethane as a structural unit are characterized by their high water solubility, ease of preparation of aqueous solutions, and excellent aqueous solution stability.

[0043] The porous membrane in the second embodiment of the present disclosure is preferably an ultrafiltration membrane, and the molecular weight cutoff, shape, material, and structure of the porous membrane are the same as those described in the first embodiment of the present disclosure.

[0044] When the porous membrane is a flat membrane with an asymmetric structure, the separation functional layer is formed on the surface of a dense layer with a small pore size. When the porous membrane is a hollow fiber membrane, the separation functional layer is preferably formed on either or both of the outer and inner surfaces of the hollow fiber membrane. It is more preferable that the separation functional layer be formed on the inner surface, as this allows for uniform formation of the separation functional layer and makes it less susceptible to damage even when membranes come into contact with each other. The thickness of the separation functional layer is not particularly limited, but is preferably in the range of 0.1 to 10.0 μm. When the thickness of the separation functional layer is within this range, the amine compound with a molecular weight of 500 or less contained in the membrane can be stably retained, thereby ensuring durability. Furthermore, a membrane thickness of 10.0 μm or less is preferable because it allows for a high carbon dioxide permeation flux.

[0045] In a second embodiment of the present disclosure, the separation functional layer is made of a composition containing a polymer having hydroxyurethane as a structural unit and an amine compound having a molecular weight of 500 or less, and is formed on the surface of the porous membrane. This composition is preferably a homogeneous composition. This is because a carbon dioxide separation membrane having a separation functional layer formed from a homogeneous composition has a larger amount of amine compound having a molecular weight of 500 or less incorporated into the membrane, thereby improving stability.

[0046] The content of the amine compound having a molecular weight of 500 or less in a composition containing a polymer having hydroxyurethane as a structural unit and an amine compound having a molecular weight of 500 or less is not particularly limited, but is preferably 2 to 95 wt %, and more preferably 30 to 95 wt %, of the total content of the polymer having hydroxyurethane as a structural unit and the amine compound having a molecular weight of 500 or less.

[0047] The polymer having hydroxyurethane as a structural unit preferably has 1 to 2,000 structural units represented by formula (5) per molecule, and more preferably 50 to 1,000. From the viewpoint of water solubility, the content of the structural unit represented by formula (5) in the polymer having hydroxyurethane as a structural unit is preferably 60 mol % or more and 100 mol % or less.

[0048] (In the formula, R' represents a hydroxyl group or an organic group having 1 to 30 carbon atoms.)

[0049] R' in formula (5) represents a hydroxyl group or an organic group having 1 to 30 carbon atoms, preferably an organic group having 1 to 30 carbon atoms. The organic group referred to here is a group that may contain oxygen, nitrogen, sulfur, halogen, etc. in addition to carbon and hydrogen. Examples of the organic group having 1 to 30 carbon atoms include a methyl group, an ethyl group, a propyl group, a butyl group, a hexyl group, an octyl group, a phenyl group, a benzyl group, a methylphenyl group, a trichlorophenyl group, a cyclohexyl group, a hydroxymethyl group, a hydroxyethyl group, a hydroxypropyl group, a methoxymethyl group, a methoxyethyl group, a methoxypropyl group, an ethoxyethyl group, an ethoxypropyl group, an isopropoxypropyl group, a phenoxymethyl group, a tetrahydrofurfuryl group, an N,N-dimethylaminoethyl group, an N,N-dimethylaminopropyl group, a methylthiophenyl group, and a methylthiobenzimidazole group, and preferably a tetrahydrofurfuryl group.

[0050] The molecular weight of the polymer having hydroxyurethane as a constituent unit is preferably in the range of 10,000 to 1,000,000 in weight average molecular weight. A weight average molecular weight in this range is preferable because it ensures the mechanical strength of the separation functional layer, the solution viscosity during coating is within an appropriate range, and the thickness of the separation functional layer is uniform. In the present disclosure, the weight average molecular weight of the polymer is measured by size exclusion chromatography.

[0051] The polymer having hydroxyurethane as a structural unit may have a structural unit represented by the following formula (6): When the polymer having hydroxyurethane as a structural unit has a structural unit represented by formula (6), the polymer preferably has 1 to 2,000, and more preferably 10 to 500, structural units represented by formula (6) per molecule.

[0052]

[0053] When a polymer having hydroxyurethane as a structural unit has a structural unit represented by formula (6), the molar ratio of the structural unit represented by formula (5) and the structural unit represented by formula (6) in the polymer having hydroxyurethane as a structural unit is arbitrary, but from the viewpoint of the water solubility of the polymer having hydroxyurethane as a structural unit, the structural unit represented by formula (5):structural unit represented by formula (6) (molar ratio) is preferably 60:40 to 100:0.

[0054] A polymer having hydroxyurethane as a structural unit is produced by polymerizing vinylene carbonate and then aminolyzing the polymer with an amino group-containing compound. There are no particular limitations on the method for polymerizing vinylene carbonate, and the polymer can be produced by the same method as described in the first embodiment of the present disclosure.

[0055] There are no particular limitations on the aminolysis reaction between polyvinylene carbonate obtained by polymerizing vinylene carbonate and an amino group-containing compound, and the amino group-containing compound is added to the polyvinylene carbonate dissolved or dispersed in a solvent to carry out the aminolysis reaction. The reaction conditions can be set arbitrarily within the ranges of a reaction temperature of 30 to 120°C and a reaction time of 1 to 72 hours.

[0056] The amino group-containing compound used in the aminolysis reaction is a compound having a primary amine or a secondary amine, and examples thereof include methylamine, ethylamine, propylamine, butylamine, hexylamine, dimethylamine, diethylamine, ethanolamine, propanolamine, butanolamine, aniline, benzylamine, toluidine, trichloroaniline, cyclohexylamine, methoxyethanolamine, methoxypropanolamine, tetrahydrofurfurylamine, and mixtures thereof.

[0057] Although the aminolysis reaction can be carried out without using a solvent, it is preferable to use a solvent to ensure uniform and quantitative reaction. Examples of the solvent include alcohols such as water, methanol, and ethanol; ethers such as diethyl ether, tetrahydrofuran, and dioxane; esters such as ethyl acetate, isopropyl acetate, and butyl acetate; ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; amides such as formamide, dimethylformamide, dimethylacetamide, and N-methyl-2-pyrrolidone; and dimethyl sulfoxide.

[0058] The amine compound having a molecular weight of 500 or less, which is another component constituting the separation functional layer, is a carrier component that plays a role in adsorbing, transporting, and desorbing carbon dioxide in the carbon dioxide separation membrane according to the second embodiment. When the molecular weight of the amine compound is 500 or less, molecular mobility is high and the carbamic acid produced by the reaction of the amine compound with carbon dioxide also diffuses rapidly in the separation functional layer, thereby increasing the carbon dioxide permeation flux and achieving high performance of the separation membrane. In the second embodiment of the present disclosure, examples of amine compounds having a molecular weight of 500 or less that are preferably used include the same amine compounds as in the first embodiment of the present disclosure.

[0059] Furthermore, the composition constituting the separation functional layer may contain other components in addition to the polymer having hydroxyurethane as a structural unit and the amine compound having a molecular weight of 500 or less, as long as the above-mentioned effect is not impaired. When the composition contains other components, the content of the other components in the composition is preferably 30% by weight or less. Examples of such other components include polyvinyl alcohol, poly(meth)acrylic acid, polyethylene glycol, polyvinylpyrrolidone, polyethyleneimine, polyallylamine, polysaccharides, salts thereof, copolymers thereof, and blends thereof. In the present disclosure, "(meth)acrylic acid" refers to either or both of acrylic acid and methacrylic acid.

[0060] Next, a method for producing a carbon dioxide separation membrane according to a third embodiment of the present disclosure will be described. The method for producing a carbon dioxide separation membrane according to the third embodiment of the present disclosure is the same as the method for producing a carbon dioxide separation membrane according to the first or second embodiment of the present disclosure, and includes a retention step of bringing a porous membrane into contact with a solution obtained by dissolving a hydroxymethylene-vinyl alcohol copolymer or a polymer having hydroxyurethane as a structural unit and an amine compound having a molecular weight of 500 or less in a solvent, and retaining the solution on the surface of the porous membrane, and a drying step of removing the solvent from the solution retained in the porous membrane.

[0061] The solvent used in the third embodiment of the present disclosure is not particularly limited as long as it dissolves and does not react with an amine compound having a molecular weight of 500 or less and a hydroxymethylene-vinyl alcohol copolymer or a polymer having hydroxyurethane as a structural unit, but from the viewpoint of solubility, at least one solvent selected from the group consisting of water, methanol, ethanol, propanol, ethylene glycol, acetone, dimethylacetamide, dimethyl sulfoxide, tetrahydrofuran, and dioxane is used. Among these, water, methanol, ethanol, propanol, and ethylene glycol are preferred solvents, and water is particularly preferred.

[0062] The mixing method used in preparing the solution is not particularly limited, and known methods can be used. Examples include stirring with a stirring blade, stirring with a stirrer and stirring bar, stirring with a shaker, stirring with a roller mixer, and stirring with ultrasonic waves (homogenizer). As for stirring conditions, for example, when stirring with a stirring blade, the rotation speed of the stirring blade is usually in the range of 1 to 1,000 rpm, preferably in the range of 10 to 400 rpm.

[0063] The order of mixing is not particularly limited. For example, it is preferable to thoroughly dissolve a hydroxymethylene-vinyl alcohol copolymer or a polymer having hydroxyurethane as a structural unit in a solvent, and then add and mix an amine compound having a molecular weight of 500 or less. By mixing a sufficiently dissolved polymer having hydroxymethylene-vinyl alcohol copolymer or hydroxyurethane as a structural unit with an amine compound having a molecular weight of 500 or less, the formation of coarse particles, which would result in a long dissolution time, or a loss of uniformity during film formation, can be suppressed. Furthermore, when preparing the solution, the polymer having hydroxymethylene-vinyl alcohol copolymer or hydroxyurethane as a structural unit and the amine compound having a molecular weight of 500 or less may be mixed while heating. The heating temperature is not particularly limited as long as it is equal to or higher than the temperature at which each of the above-mentioned components solidifies and equal to or lower than the temperature at which each component decomposes, boils, or reacts. It is usually in the range of 30 to 100°C, preferably in the range of 30 to 80°C.

[0064] The concentration of the solution is not particularly limited as long as the solution has appropriate fluidity, and the total concentration of the polymer having a hydroxymethylene-vinyl alcohol copolymer or hydroxyurethane as a constituent unit and the concentration of the amine compound having a molecular weight of 500 or less can be selected from the range of 0.05 to 10% by weight. The content ratio of the polymer having a hydroxymethylene-vinyl alcohol copolymer or hydroxyurethane as a constituent unit to the amine compound having a molecular weight of 500 or less is also not particularly limited, but the content of the amine compound having a molecular weight of 500 or less is preferably 2 to 95% by weight, more preferably 30 to 90% by weight, of the total content of the polymer having a hydroxymethylene-vinyl alcohol copolymer or hydroxyurethane as a constituent unit and the amine compound having a molecular weight of 500 or less.

[0065] In the method for producing a carbon dioxide separation membrane according to the third embodiment of the present disclosure, the porous membrane can be contacted with a solution containing a polymer having a hydroxymethylene-vinyl alcohol copolymer or a hydroxyurethane as a structural unit, an amine compound having a molecular weight of 500 or less, and a solvent. If the porous membrane is a flat membrane, methods such as spin coating, bar coating, die coating, blade coating, knife coating, gravure coating, roll coating, spray coating, dip coating, casting, comma roll coating, kiss coating, screen printing, inkjet printing, and spin coating can be used. Furthermore, if the porous membrane is a hollow fiber membrane, methods such as dip coating and circulating coating can be used. The circulating coating method referred to here refers to a method in which a solution containing a polymer having a hydroxymethylene-vinyl alcohol copolymer or a hydroxyurethane as a structural unit, an amine compound having a molecular weight of 500 or less, and a solvent is passed through the hollow fiber membrane and circulated to form a separation functional layer as a dynamic layer on the inside (inner surface) or outside (outer surface) of the hollow fiber membrane.

[0066] In the retention step, the amount of solution retained on the surface of the porous membrane may be adjusted appropriately depending on the desired thickness of the carbon dioxide separation membrane separation function layer, but it is usually sufficient to retain the solution so that the thickness of the separation function layer after drying is in the range of 0.01 to 50 μm, preferably 0.05 to 10 μm.

[0067] In the drying step, the drying conditions for removing the solution retained in the porous membrane to form a separation functional layer are not particularly limited, but include methods of drying under reduced pressure, in the atmosphere, or in a non-oxidizing atmosphere such as helium, argon, or nitrogen. There are also no particular limitations on the drying temperature or drying time, and these can be selected appropriately as long as the solvent volatilizes at an appropriate rate and the amine compound with a molecular weight of 500 or less is not dissipated. Specifically, the drying temperature is 20 to 150°C, and the drying time is approximately 5 minutes to 48 hours.

[0068] Next, a carbon dioxide separation method according to a fourth embodiment of the present disclosure will be described. The carbon dioxide separation method according to the fourth embodiment of the present disclosure includes a separation step of bringing a mixed gas containing carbon dioxide into contact with one end of a separation functional layer of a carbon dioxide separation membrane according to the first or second embodiment of the present disclosure, and allowing the carbon dioxide in the mixed gas to permeate to the other end of the carbon dioxide separation membrane. When a hollow fiber membrane module having a separation functional layer formed on the inside of a hollow fiber membrane is used for carbon dioxide separation, the mixed gas containing carbon dioxide is introduced into the primary side that communicates with the inside of the hollow fiber membrane of the hollow fiber membrane module, and the carbon dioxide in the mixed gas is allowed to permeate to the secondary side that communicates with the outer peripheral space of the hollow fiber membrane.

[0069] In the separation method according to the fourth embodiment of the present disclosure, it is preferable to provide a pressure difference between the gas supply side and the gas permeation side of the separation membrane. This pressure difference is provided by pressurizing the gas supply side of the separation membrane or by reducing the pressure on the gas permeation side. Furthermore, the separation method according to the fourth embodiment of the present disclosure is desirably carried out under temperature conditions of typically 5 to 140°C, preferably 20 to 100°C.

[0070] The mixed gas that can be applied to the separation method according to the fourth embodiment of the present disclosure is not particularly limited as long as it is a mixed gas that contains carbon dioxide. However, in order to improve the separation performance between carbon dioxide and other gases, it is desirable to adjust the relative humidity of the mixed gas to 30% or more, preferably 60 to 100%.

[0071] Examples of gases other than carbon dioxide in the mixed gas include nitrogen, helium, argon, hydrogen, methane, ethane, and propane, with nitrogen being preferred. The proportion of carbon dioxide in the mixed gas is preferably 5 to 30%.

[0072] In the fourth embodiment of the present disclosure, the value of the separation selectivity for carbon dioxide and nitrogen at 40°C calculated by the following formula (9) is preferably 100 or more. The upper limit of the separation selectivity for carbon dioxide and nitrogen at 40°C is not particularly limited because the higher the value, the better the separation performance of the membrane, but it is preferable to exhibit appropriate separation selectivity in balance with the permeation flux. Specific examples of the upper limit include values ​​of 1,000 or less, but the upper limit is not limited to these. ２ / N ２ Separation selectivity = (CO ２ Gas permeability) / (N ２ Gas permeability) (9) The separation selectivity of carbon dioxide and nitrogen expressed by formula (9) may be expressed as a carbon dioxide selectivity coefficient α. The carbon dioxide selectivity coefficient α is calculated by the formula described in the examples below, and is the same value as the separation selectivity of carbon dioxide and nitrogen expressed by formula (9).

[0073] In the separation method according to the fourth embodiment of the present disclosure, any additional steps other than the separation step may be performed, such as a cooling step, a heating step, a washing step, an extraction step, an ultrasonic treatment step, a distillation step, and other steps of treating with chemicals.

[0074] Furthermore, the separation method according to the fourth embodiment of the present disclosure can be applied to separating carbon dioxide from combustion exhaust gas generated in, for example, thermal power plants, steel plants, cement factories, etc. Furthermore, the separation method according to the fourth embodiment of the present disclosure can also be applied to refining light hydrocarbons in natural gas fields and refining methane in biogas.

[0075] Next, a carbon dioxide separation membrane module according to a fifth embodiment of the present disclosure will be described. The carbon dioxide separation membrane module according to the fifth embodiment of the present disclosure comprises a carbon dioxide separation membrane according to the first or second embodiment of the present disclosure housed within a housing. When the carbon dioxide separation membrane is a flat membrane, specific examples of the carbon dioxide separation membrane module include a stacked module in which membranes are stacked as they are, or membrane elements are prepared from the membranes and stacked; a pleated module in which flat membranes are folded and housed in a cylindrical container; and a spiral module in which flat membranes are bonded in an envelope shape with a permeate side spacer (mesh) sandwiched between them, and then wound around an axis serving as a permeation flow path via a feed side spacer. On the other hand, when the carbon dioxide separation membrane is a tubular, pipe, or hollow fiber membrane, examples of the carbon dioxide separation membrane module include a tubular module and a hollow fiber module in which these elements are bundled together. Furthermore, when the carbon dioxide separation membrane is a monolithic type, examples of the carbon dioxide separation membrane module include a tubular module in which monolithic elements are bundled together.

[0076] The present disclosure will be described in more detail below based on examples, but the present disclosure is not limited to these examples.

[0077] <Production of Hydroxymethylene-Vinyl Alcohol Copolymer> (Synthesis Example 1) 7.75 g of vinylene carbonate (Tokyo Chemical Industry Co., Ltd.), 7.74 g of vinyl acetate (Sigma-Aldrich), 0.24 g of 2,2'-azobis(isobutyronitrile) (Fujifilm Wako Pure Chemical Industries, Ltd.), and 28.8 g of ethylene carbonate (Fujifilm Wako Pure Chemical Industries, Ltd.) were mixed to form a homogeneous solution, which was then stirred overnight at 10°C under a nitrogen stream. The solution was then sealed and heated to 60°C, where it was polymerized for 6 hours. After polymerization was complete, the reaction solution was cooled and diluted with dimethylformamide (Fujifilm Wako Pure Chemical Industries, Ltd.; hereinafter abbreviated as DMF). The solution was then added dropwise to methanol (Fujifilm Wako Pure Chemical Industries, Ltd.) to produce a white precipitate. The resulting white precipitate was isolated by filtration, air-dried, and then dried under reduced pressure at 70°C to obtain a vinylene carbonate-vinyl acetate copolymer. The yield of the vinylene carbonate-vinyl acetate copolymer was 12.2 g, representing a 79% yield. The composition of the vinylene carbonate-vinyl acetate copolymer calculated from elemental analysis was vinylene carbonate:vinyl acetate = 42:58 (molar ratio). The number average molecular weight of the vinylene carbonate-vinyl acetate copolymer measured using GPC was 50,000, and the weight average molecular weight was 141,000.

[0078] 8.0 g of sodium hydroxide (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) was dissolved in 100 mL of ultrapure water, and 8.0 g of the vinylene carbonate-vinyl acetate copolymer was added. The saponification reaction was carried out at room temperature with stirring for 91 hours. The copolymer gradually dissolved, eventually resulting in a viscous aqueous solution. After the reaction, acetic acid (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) was added to adjust the pH to 5, and then the solution was added dropwise to ethanol (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) to produce a white precipitate. The precipitate was isolated by filtration, air-dried, and then dried under reduced pressure at 70°C to obtain a hydroxymethylene-vinyl alcohol copolymer. The yield of the hydroxymethylene-vinyl alcohol copolymer was 4.7 g, a 100% yield. The number-average molecular weight of the hydroxymethylene-vinyl alcohol copolymer measured using GPC was 16,000, and the weight-average molecular weight was 96,000. IR spectra before and after the saponification reaction are shown in Figure 2. The absorption (1817 cm) due to the carbonyl of carbonate and ester present in the vinylene carbonate-vinyl acetate copolymer before the saponification reaction －１ , 1742 cm －１ ) disappeared after the saponification reaction, and a new absorption due to hydroxyl groups (3300 cm －１ ) was observed, it was confirmed that the saponification reaction proceeded quantitatively and a hydroxymethylene-vinyl alcohol copolymer was obtained.

[0079] <Production of Hydroxyurethane Polymer> (Synthesis Example 2): Poly(β-hydroxyvinyl N-2-hydroxyethylcarbamate) 12.9 g of vinylene carbonate, 0.24 g of 2,2'-azobis(isobutyronitrile), and 15.8 g of ethylene carbonate were mixed to form a homogeneous solution, which was then stirred overnight at 10°C under a nitrogen stream. The solution was then sealed and heated to 60°C, where it was polymerized for 6 hours. After polymerization, the solution was cooled and diluted with DMF, and then added dropwise to isopropanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) to produce a white precipitate. The resulting white precipitate was isolated by filtration, air-dried, and then dried under reduced pressure at 70°C to obtain polyvinylene carbonate. The yield of polyvinylene carbonate was 10.4 g, representing a yield of 81%. The number-average molecular weight of the polyvinylene carbonate measured using GPC was 79,000, and the weight-average molecular weight was 141,000.

[0080] 4.0 g of the polyvinylene carbonate was taken and dissolved in 16 mL of DMF, followed by the addition of 5.68 g of monoethanolamine (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and the aminolysis reaction was carried out at 60°C for 27 hours. After the reaction was completed, the mixture was cooled and added dropwise to methyl ethyl ketone (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) to produce a precipitate. The resulting precipitate was collected by filtration and dried under reduced pressure at 70°C to obtain a hydroxyurethane polymer. The yield of the hydroxyurethane polymer was 7.1 g, a 73% yield. The number-average molecular weight of the hydroxyurethane polymer measured using GPC was 28,000, and the weight-average molecular weight was 80,000. IR spectra before and after the aminolysis reaction are shown in Figure 3. The absorption (1817 cm) derived from the carbonate carbonyl present in the polyvinylene carbonate before the reaction was observed. －１ ) disappeared after the reaction, and a new absorption due to the hydroxyl group (3300 cm －１ ) and absorption due to the carbonyl of the urethane bond (1700 cm －１ ) was observed, it was confirmed that the aminolysis reaction proceeded quantitatively and a hydroxyurethane polymer was obtained.

[0081] Synthesis Example 3: Poly(β-hydroxyvinyl N-2-tetrahydrofurfurylcarbamate) Polyvinylene carbonate was produced in the same manner as in Synthesis Example 2. The yield of polyvinylene carbonate was 12.1 g, a yield of 94%, and the number average molecular weight of the polyvinylene carbonate measured using GPC was 83,000 and the weight average molecular weight was 146,000.

[0082] 4.0 g of the polyvinylene carbonate was taken and dissolved in 16 mL of DMF. 9.4 g of tetrahydrofurfurylamine (Tokyo Chemical Industry Co., Ltd.) was added, and the aminolysis reaction was carried out at 60°C for 24 hours. After the reaction was completed, the mixture was cooled and added dropwise to methyl ethyl ketone to produce a precipitate. The resulting precipitate was collected by filtration and dried under reduced pressure at 70°C to obtain poly(β-hydroxyvinyl N-2-tetrahydrofurfurylcarbamate). The yield of poly(β-hydroxyvinyl N-2-tetrahydrofurfurylcarbamate) was 4.6 g, a 34% yield. The number average molecular weight of poly(β-hydroxyvinyl N-2-tetrahydrofurfurylcarbamate) measured using GPC was 35,000, and the weight average molecular weight was 89,000. Comparing the IR spectra before and after the aminolysis reaction, the absorption due to the carbonate carbonyl present in the polyvinylene carbonate before the reaction (1817 cm －１ ) disappeared after the reaction, and a new absorption due to the hydroxyl group (3300 cm －１ ) and absorption due to the carbonyl of the urethane bond (1700 cm －１ ) was observed, it was confirmed that the aminolysis reaction had proceeded quantitatively and poly(β-hydroxyvinyl N-2-tetrahydrofurfurylcarbamate) was obtained.

[0083] <Manufacture of Carbon Dioxide Separation Membrane Module> (Example 1) 1.2 g of the hydroxymethylene-vinyl alcohol copolymer produced in Synthesis Example 1 was dissolved in 584 g of pure water, and then 15 g of N-(2-aminoethyl)ethanolamine (manufactured by Tokyo Chemical Industry Co., Ltd.) as an amine compound with a molecular weight of 500 or less was added to prepare a mixed solution. The resulting mixed solution was then introduced into the primary side of a hollow fiber membrane module (manufactured by Kitz Microfilter, hollow fiber inner diameter 0.36 mm, molecular weight cutoff 10,000) leading to the hollow fiber membrane, and the solution was allowed to pass for 10 minutes. The hollow fiber membrane module that had been subjected to the liquid passing treatment was then dried at 20°C under atmospheric pressure for 24 hours, yielding a hollow fiber membrane module in which a separation function layer was formed on the hollow fiber inner membrane side. The resulting carbon dioxide separation membrane module is hereinafter referred to as "separation membrane module 1."

[0084] Example 2 A carbon dioxide separation membrane module was produced in the same manner as in Example 1, except that poly(β-hydroxyvinyl N-2-hydroxyethylcarbamate) produced in Synthesis Example 2 was used instead of the hydroxymethylene-vinyl alcohol copolymer. The obtained carbon dioxide separation membrane module is hereinafter referred to as "separation membrane module 2."

[0085] Example 3 A carbon dioxide separation membrane module was produced in the same manner as in Example 1, except that poly(β-hydroxyvinyl N-2-tetrahydrofurfurylcarbamate) produced in Synthesis Example 3 was used instead of the hydroxymethylene-vinyl alcohol copolymer. The obtained carbon dioxide separation membrane module is hereinafter referred to as "separation membrane module 3."

[0086] (Comparative Example 1) A carbon dioxide separation membrane module was produced in the same manner as in Example 1, except that polyvinyl alcohol (molecular weight approximately 60,000, fully saponified, manufactured by Sigma-Aldrich) was used instead of the hydroxymethylene-vinyl alcohol copolymer. The obtained carbon dioxide separation membrane module is hereinafter referred to as "separation membrane module 4."

[0087] <Separation test of carbon dioxide and coexisting gases> (Examples 4, 5, 6 and Comparative Example 2) Carbon dioxide separation ability was measured using the carbon dioxide separation membrane modules (separation membrane modules 1 to 4) produced in Examples 1, 2, 3 and Comparative Example 1. In the following explanation and formulas, carbon dioxide is referred to as CO ２ , nitrogen as N ２ Abbreviated as .

[0088] The outline of the gas separation apparatus used to measure the carbon dioxide separation ability is shown in Figure 3. ２ Gas cylinder 1 and N ２ From gas cylinder 2, CO ２ and N ２ and a mixed gas (CO ２ 10%, N ２90%) is prepared. This mixed gas is controlled to a predetermined gas flow rate by a flow rate controller 4, and the relative humidity is adjusted to 90% by a humidifier 5, and then supplied to a carbon dioxide separation membrane module 8 at a predetermined pressure. Furthermore, helium supplied from a helium gas cylinder 3 is humidified by the humidifier 5, and the resulting sweep gas is supplied to the permeation side of the carbon dioxide separation membrane module 8 at a predetermined pressure. The relative humidities of the mixed gas and the sweep gas are measured by a dew point meter 7, and the pressures of the mixed gas and the sweep gas supplied to the carbon dioxide separation membrane module 8 are measured by a pressure meter 6. The gas discharged from the carbon dioxide separation membrane module 8 is dried by a dehumidifying trap 9 and then introduced into a gas chromatograph 10. The permeation flux Q(CO ２ ) and Q(N ２ ) (unit: 1 GPU = 7.5 x 10 －１２ m ３ (STP) / (s・m ２ The measurement conditions are as follows, and the permeation flux is calculated according to the following formula (10):

[0089] The permeability coefficient of the carbon dioxide separation membrane module measured using the gas separation apparatus shown in FIG. 1 and the carbon dioxide selectivity coefficient α (CO ２ / N ２ ) = (Q(CO ２ ) / Q (N ２ )) are shown in Table 1.

[0090]

[0091] (In the formula, Q is the permeation flux, n is the gas volume, A is the membrane area, t is time, and Δp is the difference between the feed side partial pressure and the permeation side partial pressure. The subscript i represents each gas.)

[0092] [Gas permeation measurement conditions] Supply gas amount: 450 mL / min Measurement temperature: 40°C Supply gas composition: CO ２ / N ２ = 10 / 90 (vol / vol) Permeation side sweep gas: Helium Sweep gas amount: 300 mL / min Relative humidity: 90% Pressure (abs): Feed side = 105 kPa, Permeation side = 105 kPa

[0093] From Table 1, the CO ２ The separation membrane module is CO ２ Not only is the permeation flux of CO ２ High selectivity for CO ２ It is clear that this is an excellent separation membrane module.

[0094]

[0095] As described above, the present disclosure can provide a carbon dioxide separation membrane with a high carbon dioxide permeation flux and high carbon dioxide selectivity, a method for producing the carbon dioxide separation membrane, a carbon dioxide separation method using the carbon dioxide separation membrane, and a carbon dioxide separation membrane module using the carbon dioxide separation membrane. Because the carbon dioxide separation membrane and carbon dioxide separation membrane module of the present disclosure have excellent carbon dioxide separation properties, they are expected to enable low-cost separation and capture of carbon dioxide from exhaust gases from large-scale sources such as thermal power plants, steelworks blast furnaces, and cement factories. Furthermore, because the separation membrane system is compact, they are expected to enable efficient separation and capture of carbon dioxide from relatively small-scale carbon dioxide sources. Thus, the carbon dioxide separation membrane of the present disclosure is expected to make a significant contribution to reducing carbon dioxide emissions.

[0096] 1 CO ２ Gas cylinder 2N ２ Gas cylinder 3 Helium gas cylinder 4 Flow control meter 5 Humidifier 6 Pressure gauge 7 Dew point meter 8 Carbon dioxide separation membrane module 9 Dehumidification trap 10 Gas chromatograph

Claims

1. A carbon dioxide separation membrane having a porous membrane and a separation functional layer formed on the surface of the porous membrane, wherein the separation functional layer is made of a composition containing a copolymer having a structural unit represented by the following formula (1) and a structural unit represented by the following formula (2), and an amine compound having a molecular weight of 500 or less.

2. The carbon dioxide separation membrane according to claim 1, wherein the copolymer further comprises one or both of a structural unit represented by the following formula (3) and a structural unit represented by the following formula (4): (wherein R represents an acyl group having 1 to 4 carbon atoms.) 3. A carbon dioxide separation membrane having a porous membrane and a separation functional layer formed on the surface of the porous membrane, wherein the separation functional layer is made of a composition containing a polymer having a structural unit represented by the following formula (5) and an amine compound having a molecular weight of 500 or less. (In the formula, R' represents a hydroxyl group or an organic group having 1 to 30 carbon atoms.) 4. The carbon dioxide separation membrane according to claim 3, wherein the polymer further comprises a structural unit represented by the following formula (6):

5. The carbon dioxide separation membrane according to claim 1, wherein the porous membrane is a hollow fiber membrane, and the separation function layer is formed on either or both of the outer surface and the inner surface of the hollow fiber membrane.

6. The carbon dioxide separation membrane according to claim 3, wherein the porous membrane is a hollow fiber membrane, and the separation function layer is formed on either or both of the outer surface and the inner surface of the hollow fiber membrane.

7. A method for producing a carbon dioxide separation membrane according to any one of claims 1 to 6, comprising: a retaining step of bringing the porous membrane into contact with a solution containing the copolymer or the polymer, the amine compound having a molecular weight of 500 or less, and a solvent, and retaining the solution on the surface of the porous membrane; and a drying step of removing the solvent from the solution retained in the porous membrane.

8. A method for separating carbon dioxide, comprising a separation step of contacting a mixed gas containing carbon dioxide with one end of the carbon dioxide separation membrane described in any one of claims 1 to 6 and allowing the carbon dioxide in the mixed gas to permeate to the other end of the carbon dioxide separation membrane.

9. A carbon dioxide separation membrane module comprising the carbon dioxide separation membrane according to any one of claims 1 to 6.

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