Gas separation membrane and method for manufacturing a gas separation membrane

Abstract

To provide a gas separation membrane and a method for manufacturing the same that have high gas selectivity and high gas permeability for carbon dioxide, and excellent mechanical strength. [Solution] A gas separation membrane for separating carbon dioxide from a mixed gas containing carbon dioxide, comprising: a sheet-like support layer; and a separation layer provided on one side of the support layer, having the function of selectively separating carbon dioxide, and composed of a polymer having polyethylene oxide structural units and polysiloxane structural units, wherein the average thickness of the separation layer is 1 nm or more and 500 nm or less, and when an XPS spectrum is obtained of the separation layer by X-ray photoelectron spectroscopy, and the Si2p peak and C1s peak included in the XPS spectrum are waveform-separated, the intensity ratio of the Si-O peak intensity P(Si-O) to the CO peak intensity P(CO) P(Si-O) / P(CO) is 0.03 or more and 2.0 or less.

Description

[Technical Field]

[0001] This invention relates to a gas separation membrane and a method for producing a gas separation membrane. [Background technology]

[0002] To achieve carbon neutrality and carbon negative emissions, technologies are being considered to capture and recover carbon dioxide emitted from thermal power plants and boiler facilities, as well as carbon dioxide from the atmosphere. One such technology is membrane separation, which uses gas separation membranes to separate carbon dioxide.

[0003] For example, Patent Document 1 discloses a gas separation membrane comprising a porous support, a polymer layer provided on the porous support, and a gel layer provided on the polymer layer. In this gas separation membrane, the polymer layer contains polydimethylsiloxane, and the gel layer contains a liquid such as a crosslinked polymer having a polyethylene glycol backbone and polyethylene glycol. With this configuration, the gel layer has high gas permeability and high gas selectivity, while the polymer layer can suppress the occurrence of defects when the gel layer is thinned, thus allowing the gel layer to be made thinner and its performance to be fully utilized. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2015-160159 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] On the other hand, polydimethylsiloxane has low gas selectivity for carbon dioxide, and crosslinked polymers with a polyethylene glycol backbone have low gas permeability for carbon dioxide and low mechanical strength.

[0006] Therefore, there is a problem of realizing a gas separation membrane that has high gas selectivity and high gas permeability for carbon dioxide and excellent mechanical strength.

Means for Solving the Problems

[0007] The gas separation membrane according to the application example of the present invention is a gas separation membrane that separates carbon dioxide by permeating it from a mixed gas containing carbon dioxide, a sheet-like support layer, a separation layer provided on one surface of the support layer, having a function of selectively separating carbon dioxide, and composed of a polymer having a polyethylene oxide structural unit and a polysiloxane structural unit, and includes the average thickness of the separation layer is 1 nm or more and 500 nm or less, Regarding the separation layer, when an XPS spectrum is obtained by X-ray photoelectron spectroscopy and the Si2p peak and C1s peak included in the XPS spectrum are each waveform-separated, the intensity ratio P(Si-O) / P(C-O) of the Si-O peak intensity P(Si-O) to the C-O peak intensity P(C-O) is 0.03 or more and 2.0 or less.

[0008] The method for manufacturing a gas separation membrane according to the application example of the present invention is a method for manufacturing a gas separation membrane according to the application example of the present invention, a step of mixing a polyethylene glycol compound having a first reactive functional group at the end of the main chain and a polysiloxane compound having a second reactive functional group at the end of the main chain that reacts and binds with the first reactive functional group to obtain a mixture, a step of heating the mixture to react the first reactive functional group and the second reactive functional group to obtain a reaction product, a step of applying the reaction product to one surface of the support layer to form a coating film, a step of applying energy to the coating film to form the separation layer, and includes

Brief Description of the Drawings

[0009] [Figure 1] This is a schematic cross-sectional view showing a gas separation membrane according to an embodiment. [Figure 2] This is a process diagram showing the configuration of a method for manufacturing a gas separation membrane according to an embodiment. [Figure 3] Table 1 shows the configuration of the gas separation membrane and the evaluation results of the gas separation membrane. [Figure 4] Table 2 shows the configuration of the gas separation membrane and the evaluation results of the gas separation membrane. [Figure 5] This is an example of an XPS spectrum (Si2p) near the Si2p peak. [Figure 6] This is an example of an XPS spectrum (C1s) near the C1s peak. [Modes for carrying out the invention]

[0010] The gas separation membrane of the present invention will be described in detail below based on the embodiments shown in the accompanying drawings. 1. Overview of Gas Separation Membranes First, the configuration of the gas separation membrane according to the embodiment will be described.

[0011] Figure 1 is a schematic cross-sectional view showing a gas separation membrane 1 according to an embodiment. In Figure 1 of this application, the X, Y, and Z axes are defined as three mutually orthogonal axes, and are indicated by arrows. The base end of the arrows representing each axis is designated as "minus," and the tip end is designated as "plus."

[0012] In the gas separation membrane 1 shown in Figure 1, the positive Z-axis side is defined as "up" and the negative Z-axis side as "down". A mixed gas is supplied to the top of the gas separation membrane 1. In the gas separation membrane 1 shown in Figure 1, carbon dioxide is separated by permeation from top to bottom.

[0013] The gas separation membrane 1 shown in Figure 1 has the function of separating carbon dioxide from a mixed gas containing carbon dioxide by permeation. The gas separation membrane 1 shown in Figure 1 comprises a sheet-like support layer 3 that extends along the XY plane, and a separation layer 4 provided on the upper surface 31 (one side) of the support layer 3. The separation layer 4 has the function of preferentially permeating carbon dioxide and is composed of a polymer having polysiloxane structural units and polyethylene oxide structural units. The film thickness of the separation layer 4 is set to be between 1 nm and 500 nm.

[0014] Furthermore, when an XPS spectrum is obtained for the separation layer 4 by X-ray photoelectron spectroscopy, and the Si2p peak and C1s peak included in the XPS spectrum are waveform-separated, the intensity ratio P(Si-O) / P(CO) of the Si-O peak to the intensity P(CO) of the CO peak is between 0.03 and 2.0.

[0015] With this configuration, a gas separation membrane 1 can be realized that has a high gas selectivity and high gas permeability for carbon dioxide, as well as excellent mechanical strength.

[0016] The gas separation membrane according to the present invention may take the form of a sheet (flat plate) as shown in Figure 1, or it may be spiral, tubular, hollow fiber, or the like.

[0017] 1.1.Support layer The support layer 3 is in the form of a sheet and supports the separation layer 4. As a result, even if the separation layer 4 does not have sufficient mechanical properties, the support layer 3 supports the separation layer 4, making it possible to realize a gas separation membrane 1 with excellent mechanical properties.

[0018] Examples of materials that make up the support layer 3 include ceramic materials, metal materials, polymer materials, etc. Furthermore, the materials that make up the support layer 3 may be composite materials of these materials and other materials.

[0019] Examples of ceramic materials include alumina, cordierite, mullite, silicon carbide, and zirconia. Examples of metallic materials include stainless steel.

[0020] Examples of polymer materials include polyolefin resins such as polyethylene and polypropylene, fluorine-containing resins such as polytetrafluoroethylene, polyvinyl fluoride, and polyvinylidene fluoride, as well as polystyrene, cellulose acetate, polyurethane, polyacrylonitrile, polyphenylene oxide, polysulfone, polyethersulfone, polyimide, polyaramid, and polysiloxane.

[0021] Of these, polymer materials are preferably used as the constituent material of the support layer 3, and polysulfone or polysiloxane is preferably used. Alternatively, the constituent material of the support layer 3 may be a composite material in which polysulfone or polysiloxane is the main component (more than 50% by mass) and other resin components are used in combination.

[0022] Polysulfones are polymers composed of monomer units that have an -SO2- bond group in their molecule.

[0023] In this embodiment, aromatic polysulfones having repeating units represented by the following formula (a) or (b) are preferably used. In the following formulas (a) and (b), Ar represents an aromatic ring and a phenyl group.

[0024] -O-Ar-C(CH3)3-Ar-SO3-Ar- (a) -O-Ar-SO3-Ar- (b)

[0025] Furthermore, the polysulfone used in this embodiment may be a modified polysulfone. Examples of modified polysulfones include those in which a functional group or alkyl group is added to the aromatic ring of the aromatic polysulfone represented by formula (a) or (b) above.

[0026] Because such polysulfones have excellent heat resistance, chemical resistance, etc., they are useful as constituent materials for the support layer 3.

[0027] Polysiloxanes, as basic structural units, include monofunctional M units with three organic substituents attached to a silicon atom, difunctional D units with two substituents, trifunctional T units with one substituent, and tetrafunctional Q units with no substituents. A single polysiloxane molecule is composed of combinations of these units. Of these, organopolysiloxanes that contain almost no Q units are preferably used as the polysiloxane in this embodiment. This results in a support layer 3 with good gas permeability to carbon dioxide.

[0028] Specific examples of organopolysiloxanes include polydimethylsiloxane, polymethylphenylsiloxane, polydiphenylsiloxane, polysulfone / polyhydroxystyrene / polydimethylsiloxane copolymer, dimethylsiloxane / methylvinylsiloxane copolymer, dimethylsiloxane / diphenylsiloxane / methylvinylsiloxane copolymer, methyl-3,3,3-trifluoropropylsiloxane / methylvinylsiloxane copolymer, dimethylsiloxane / methylphenylsiloxane / methylvinylsiloxane copolymer, diphenylsiloxane / dimethylsiloxane copolymer with vinyl terminus, polydimethylsiloxane with vinyl terminus, polydimethylsiloxane with H terminus, and dimethylsiloxane-methylhydrosiloxane copolymer. These also include forms in which crosslinked reaction products are formed. Furthermore, the constituent materials of the support layer 3 may be a composite of one or more of these materials, or a composite material in which organopolysiloxane is the main component (more than 50% by mass) and other resin components are used in combination.

[0029] Furthermore, organopolysiloxanes have relatively long interatomic distances between their Si-O and Si-C bonds, resulting in a large free volume. This allows for good diffusion of carbon dioxide molecules and good gas permeability to carbon dioxide. For this reason, they are useful as constituent materials for the support layer 3.

[0030] The average thickness of the support layer 3 is preferably set to be thicker than the average thickness of the separation layer 4. This ensures that the support layer 3 has the necessary and sufficient mechanical properties as the base layer of the gas separation membrane 1. The difference between the average thickness of the support layer 3 and the average thickness of the separation layer 4 is preferably 5 μm or more, and more preferably 30 μm or more.

[0031] The average thickness of the support layer 3 is preferably 10 μm to 300 μm, more preferably 15 μm to 200 μm, and even more preferably 20 μm to 100 μm. This makes it possible to realize a support layer 3 that has the necessary and sufficient mechanical properties as well as sufficient gas permeability.

[0032] The average thickness of the support layer 3 can be determined, for example, by observing a magnified cross-section of the gas separation membrane 1 and taking the average of the thicknesses measured at 10 locations on the support layer 3.

[0033] Furthermore, it is preferable that the gas permeability of carbon dioxide through the support layer 3 is set higher than that of the gas permeability of carbon dioxide through the separation layer 4. This allows the support layer 3 to mechanically support the separation layer 4 while providing good gas permeability to the gas separation membrane 1.

[0034] The support layer 3 can be manufactured by methods for manufacturing sheets or films. It can also be manufactured by a method in which the support layer is formed on a sacrificial layer and then the sacrificial layer is removed.

[0035] Furthermore, the support layer 3 may be a porous layer. This provides a support layer 3 with good gas permeability to carbon dioxide.

[0036] The porous layer has pores, and its average inner diameter is called the "average pore diameter." The average pore diameter of the support layer 3 is preferably 0.2 μm or less, more preferably 0.01 μm to 0.15 μm, even more preferably 0.01 μm to 0.09 μm, and particularly preferably 0.01 μm to 0.07 μm. This ensures sufficient gas permeability of carbon dioxide through the support layer 3 while suppressing the separation layer 4 from escaping to the downstream side of the support layer 3. If the average pore diameter of the porous layer falls below the lower limit, the gas permeability of carbon dioxide through the support layer 3 may decrease. On the other hand, if the average pore diameter of the porous layer exceeds the upper limit, the separation layer 4 may escaping to the downstream side of the support layer 3.

[0037] The average pore size of the porous layer is measured using a through-pore diameter evaluation device after removing the separation layer 4 from the gas separation membrane 1 and obtaining the support layer 3 on its own. An example of a through-pore diameter evaluation device is a palm porometer manufactured by PMI.

[0038] The porosity of the porous layer is preferably between 20% and 90%, and more preferably between 30% and 80%. This allows the porous layer to achieve both good gas permeability and sufficient rigidity.

[0039] The porosity of the porous layer is measured using the aforementioned through-pore diameter evaluation device after removing the separation layer 4 from the gas separation membrane 1.

[0040] Furthermore, the support layer 3 may be a composite material of the above-mentioned polymer material and fibers. The fibers may be used in the form of fibrous pieces such as chopped strands, but preferably they are used in the form of fabrics such as woven fabrics, nonwoven fabrics, or mesh fabrics. This further enhances the mechanical properties of the support layer 3.

[0041] 1.2. Separation layer The separation layer 4 is provided on the upper surface 31 (one side) of the support layer 3. The separation layer 4 has gas selectivity for carbon dioxide relative to nitrogen.

[0042] 1.2.1. Constituent Materials The constituent material of the separation layer 4 is a polymer having polyethylene oxide structural units and polysiloxane structural units.

[0043] Of these, the polyethylene oxide structural unit is a repeating unit having a -CCO- structure as its main chain, as will be described later. Such structural units have a high affinity for carbon dioxide. Therefore, having such structural units enhances the gas selectivity of carbon dioxide in the separation layer 4. In addition, having polyethylene oxide structural units tends to increase the flexibility of the separation layer 4. Therefore, having such structural units enhances the adhesion of the separation layer 4 to the support layer 3, thereby improving the durability of the gas separation membrane 1.

[0044] As will be described later, polysiloxane structural units are repeating units with a -Si-O- structure as the main chain. Such structural units have high gas permeability due to their relatively flexible siloxane bonds and large free volume. Therefore, the gas permeability of carbon dioxide in the separation layer 4 can be increased.

[0045] Therefore, by using the above polymer as the constituent material of the separation layer 4, a gas separation membrane 1 can be realized that has high gas selectivity and high gas permeability for carbon dioxide, as well as excellent mechanical strength. These structural units will be further explained below.

[0046] The polyethylene oxide structural unit is a structural unit represented by the following formula (1).

[0047] [ka] [In formula (1), R 1 , R 2 , R 3 and R 4 Each of these independently represents either a hydrogen atom or an alkyl group having between 1 and 6 carbon atoms. m is a positive integer.

[0048] R in the above formula (1) 1 ~R 4 Examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a t-butyl group, an n-pentyl group, an isopentyl group, an n-hexyl group, an isohexyl group, and the like.

[0049] Among these, R 1 ~R 4 is preferably, independently of each other, a hydrogen atom or an alkyl group having 1 to 3 carbon atoms.

[0050] m in the above formula (1) is a positive integer, and is appropriately set so that the molecular weight of the polyethylene oxide structural unit is preferably 100 or more and 50,000 or less, more preferably 1,000 or more and 100,000 or less.

[0051] This molecular weight is a weight average molecular weight and is a polystyrene equivalent molecular weight measured by gel permeation chromatography (GPC method).

[0052] The polysiloxane structural unit is a structural unit represented by the following formula (2).

[0053] [Chemical formula] [In formula (2), R 5 and R 6 each independently represent an alkyl group having 1 to 6 carbon atoms. n is a positive integer.]

[0054] Examples of the alkyl group of R 5 and R 6 in the above formula (2) include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a t-butyl group, an n-pentyl group, an isopentyl group, an n-hexyl group, an isohexyl group, and the like.

[0055] Among these, R 5and R 6 Each of these is preferably an alkyl group having 1 to 3 carbon atoms, and more preferably both are methyl groups.

[0056] In formula (2) above, n is a positive integer, but is set appropriately so that the molecular weight of the polysiloxane structural unit is preferably between 100 and 500,000, and more preferably between 1,000 and 100,000.

[0057] Note that this molecular weight is the weight-average molecular weight, and is the polystyrene-equivalent molecular weight measured by gel permeation chromatography (GPC method).

[0058] At least one of the two bonds in formula (2) above is bonded to a polyethylene oxide structural unit. This results in a polymer chain containing both polyethylene oxide structural units and polysiloxane structural units. In other words, the polymer chain is composed of a copolymer of polyethylene oxide structural units and polysiloxane structural units. This copolymer may be a block copolymer or a random copolymer.

[0059] Polyethylene oxide structural units and polysiloxane structural units may be directly bonded (bonded by single bonds) or bonded via linking groups. Examples of linking groups include ester bonds, ether bonds, amide bonds, imide bonds, urethane bonds, urea bonds, silyl ether bonds, and carbonyl bonds.

[0060] The constituent material of the support layer 3 is preferably mainly composed of the polymer chains described above. In other words, the total content of polyethylene oxide structural units and polysiloxane structural units in the constituent material of the support layer 3 is preferably 50% by mass or more, and more preferably 60% by mass or more.

[0061] Furthermore, the ratio of polyethylene oxide structural units to polysiloxane structural units is appropriately set so that the intensity ratio P(Si-O) / P(CO) in the XPS spectrum described above falls within a predetermined range. For example, the intensity ratio P(Si-O) / P(CO) can be increased by increasing the ratio of polysiloxane structural units to polyethylene oxide structural units. As another example, the ratio of polysiloxane structural units to polyethylene oxide structural units is preferably 6 / 4 or more and 9 / 1 or less in molar ratio. By setting the ratio of the contents within such a range, a separation layer 4 with an intensity ratio P(Si-O) / P(CO) within a predetermined range can be easily formed.

[0062] 1.2.2. Thickness The average thickness of the separation layer 4 is 1 nm to 500 nm, preferably 5 nm to 300 nm, and more preferably 10 nm to 200 nm. This ensures gas selectivity for carbon dioxide in the separation layer 4 while increasing gas permeability of carbon dioxide. If the average thickness of the separation layer 4 falls below the lower limit, the gas selectivity for carbon dioxide in the separation layer 4 decreases. On the other hand, if the average thickness of the separation layer 4 exceeds the upper limit, the gas permeability of carbon dioxide in the separation layer 4 decreases.

[0063] The average thickness of the separation layer 4 can be determined, for example, by observing a magnified cross-section of the gas separation membrane 1 and taking the average of the thicknesses measured at 10 locations on the separation layer 4.

[0064] 1.2.3. Analysis using XPS The gas separation membrane 1 is subjected to X-ray photoelectron spectroscopy (XPS) by irradiating it with X-rays from the surface side of the separation layer 4. For X-ray photoelectron spectroscopy, for example, the PHI X-tool X-ray photoelectron spectrometer manufactured by ULVAC-PHI is used. The X-ray irradiation conditions are a beam diameter of 100 μm and an output of 25 W. The analysis conditions are a pass energy of 55 eV and an integration count of 20 or more. The analysis software used is MultiPak manufactured by ULVAC-PHI. Waveform separation processing of the XPS spectrum by the analysis software is performed as follows.

[0065] First, the acquired XPS spectrum is imported into the analysis software, and the peak positions are corrected. The CC peak included in the C1s peak is used as the reference peak for correction, and the peak top is corrected to 284.8 eV.

[0066] Next, waveform separation is performed on the Si2p peak located at 102.5 ± 3.0 eV using a Gaussian function as the fitting function. Through waveform separation, the Si-O peak is separated as the main peak. The intensity of the separated Si-O peak is recorded as "Intensity P(Si-O)". The Si-O peak is usually located around 102.5 eV.

[0067] Next, waveform separation is performed on the C1s peak located at 282-290 eV using a Gaussian function as the fitting function. Through waveform separation, the CO peak and CC peak are separated as the main peaks. The intensity of the separated CO peak is recorded as "Intensity P(CO)". The CO peak is usually located around 286.3 eV, and the CC peak is usually located around 284.8 eV.

[0068] Next, the ratio of intensity P(Si-O) to intensity P(CO) is calculated as "intensity ratio P(Si-O) / P(CO)".

[0069] In the separation layer 4, the intensity ratio P(Si-O) / P(CO) is between 0.03 and 2.0. The CO bond, which is the origin of intensity P(CO), affects the gas selectivity of carbon dioxide in the separation layer 4 and the adhesion of the separation layer 4 to the support layer 3. The Si-O bond, which is the origin of intensity P(Si-O), affects the gas permeability of carbon dioxide. By keeping the intensity ratio P(Si-O) / P(CO) within the above range, it is possible to optimize the balance between the gas selectivity and adhesion to the support layer 3 derived from the CO bond and the gas permeability derived from the Si-O bond, thereby realizing a gas separation membrane 1 that achieves both of these characteristics.

[0070] Furthermore, if the intensity ratio P(Si-O) / P(CO) falls below the lower limit, the relative amount of Si-O bonds decreases, resulting in a decrease in the gas permeability of the gas separation membrane 1 to carbon dioxide. On the other hand, if the intensity ratio P(Si-O) / P(CO) exceeds the upper limit, the relative amount of CO bonds decreases, resulting in a decrease in the gas selectivity of the gas separation membrane 1 to carbon dioxide or a decrease in the adhesion of the separation layer 4 to the support layer 3.

[0071] 1.3. Other Configurations The gas separation membrane 1 according to the embodiment has been described above, but any layer may be provided downstream of the support layer 3. For example, a porous plate with higher rigidity than the support layer 3 may be provided downstream of the support layer 3. The porous plate has a large number of through holes formed in it so that the pressure loss of the gas passing through it is smaller than that of the support layer 3. This allows the gas separation membrane 1 to be supported without hindering the gas selectivity ratio of carbon dioxide in the gas separation membrane 1. Examples of materials that make up the porous plate include ceramic materials, metal materials, polymer materials, etc.

[0072] 1.4. Characteristics of gas separation membranes Gas permeability R of carbon dioxide through gas separation membrane 1 CO2 500×10 -6 cm 3 (STP) / cm 2 It is preferable that the pressure is 500 GPU or more (5,000 GPU or more and 1,000,000 GPU or less), more preferably 10,000 GPU or more and 800,000 GPU or less. This makes it possible to obtain a gas separation membrane 1 with high carbon dioxide separation efficiency. Furthermore, it is possible to realize a gas separation membrane 1 that can reduce the amount of energy input required for separation, specifically by reducing the pressure difference between the upstream and downstream sides of the gas separation membrane 1. Note that the gas permeability R of carbon dioxide CO2 This is measured by the method described later.

[0073] The nitrogen gas permeability through gas separation membrane 1 is R N2 Let R be the gas permeability of carbon dioxide. CO2 Let's assume that the gas selectivity ratio R of the gas separation membrane 1 is as follows.CO2 / R N2 The gas selectivity ratio R is preferably 15 or more, and more preferably 20 or more. CO2 / R N2 When the gas selectivity ratio R is within the range described above, the gas separation membrane 1 can efficiently separate and recover carbon dioxide from the mixed gas. CO2 / R N2 While an upper limit does not necessarily have to be set, it is preferable that it be 100 or less from the viewpoint of improving the ease of manufacturing the gas separation membrane 1.

[0074] 2. Method for manufacturing gas separation membranes Next, a method for manufacturing the gas separation membrane according to the embodiment will be described. In the following description, the method for manufacturing the gas separation membrane 1 shown in Figure 1 will be used as an example.

[0075] Figure 2 is a process diagram showing the configuration of a method for manufacturing a gas separation membrane according to an embodiment.

[0076] The method for manufacturing the gas separation membrane shown in Figure 2 comprises a mixing step S102, a reaction step S104, a coating step S106, and an energy imparting step S108. With this configuration, a gas separation membrane 1 having high gas selectivity and high gas permeability for carbon dioxide, as well as excellent mechanical strength, can be efficiently manufactured. Each step will be described below.

[0077] 2.1.Mixing process In mixing step S102, the polyethylene glycol compound and the polysiloxane compound are mixed to prepare the mixture.

[0078] Polyethylene glycol compounds are represented by the following formula (3).

[0079] [ka] [In formula (3), R 1 , R 2 , R 3 and R 4Each of these independently represents either a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. 1 and X 2 m is a first reactive functional group that may be the same or different from the others.

[0080] R in equation (3) above 1 ~R 4 The alkyl group is R in formula (1) above. 1 ~R 4 It is similar to the alkyl group.

[0081] X 1 and X 2 X is a first reactive functional group located at the end of the main chain of formula (3) above, which has reactivity with the second reactive functional group described later and can bond with the second reactive functional group. 1 and X 2 These may be the same first reactive functional group or different first reactive functional groups.

[0082] Examples of the first reactive functional group include hydroxyl group, carboxyl group, vinyl group, acrylic group, isocyanate group, mercapto group, isothiocyanate group, epoxy group, aziridine group, azulactone group, maleimide group, amino group, thiol group, azide group, chloro-s-triazine group, and β-chloroethylaminosulfonyl group, and one or more of these can be used in combination. Of these, one or more selected from the group consisting of hydroxyl group, carboxyl group, vinyl group, acrylic group, isocyanate group, and mercapto group are preferably used as the first reactive functional group. By using these functional groups in the polyethylene glycol compound, the reactivity of the first reactive functional group can be further enhanced, so that a separation layer 4 with excellent coating properties can be efficiently formed.

[0083] Polysiloxane compounds are represented by the following formula (4).

[0084] [ka]

[0085] R in equation (4) above 5 and R 6 The alkyl group is R in formula (2) above. 5 and R 6 It is similar to the alkyl group.

[0086] X 3 and X 4 X is a second reactive functional group located at the end of the main chain of formula (4) above, which has reactivity with the first reactive functional group described above and can bond with the first reactive functional group. 3 and X 4 These may be the same secondary reactive functional group or different secondary reactive functional groups.

[0087] The second reactive functional group is not particularly limited as long as it is a functional group that can react and bond with the first reactive functional group, but for example, it can be appropriately selected from the first reactive functional groups listed above. Of these, one or more selected from the group consisting of hydroxyl groups, carboxyl groups, vinyl groups, acrylic groups, isocyanate groups, and mercapto groups are preferably used as the second reactive functional group. By using these functional groups in the polyethylene glycol compound, the reactivity of the second reactive functional group can be further enhanced, so that a separation layer 4 with excellent coating properties can be efficiently formed.

[0088] As the polysiloxane compound represented by formula (4) above, polydimethylsiloxane having a second reactive functional group at both ends of the main chain is particularly preferred. Due to factors such as the increased intermolecular spacing caused by the presence of Si-CH3 bonds, polydimethylsiloxane has particularly good gas permeability to carbon dioxide and also excellent weather resistance. For this reason, it is useful as a polysiloxane compound used in the formation of the separation layer 4.

[0089] The mixing ratio of polyethylene glycol compound and polysiloxane compound in the mixture is set appropriately according to the desired strength ratio P(Si-O) / P(CO).

[0090] A solvent that dissolves these compounds may be used in the mixture. The solvent is not limited as long as it does not inhibit the reaction, and examples include hydrocarbon solvents such as hexane and heptane; aromatic hydrocarbon solvents such as benzene, toluene, and xylene; ether solvents such as diethyl ether, tetrahydrofuran, and dioxane; halogenated hydrocarbon solvents such as methylene chloride and carbon tetrachloride; and ester solvents such as ethyl acetate. These solvents may be used individually or in combination.

[0091] 2.2. Reaction Process In reaction step S104, the mixture is heated to react the first reactive functional group with the second reactive functional group. This yields the reactant.

[0092] The heating temperature of the mixture is not particularly limited, but is preferably between 40°C and 250°C, and more preferably between 50°C and 100°C. This allows the first reactive functional group and the second reactive functional group to react efficiently while suppressing unintended side reactions and evaporation of the raw materials.

[0093] Furthermore, during heating, the mixture may be subjected to stirring, ultrasonic irradiation, or other treatments as needed.

[0094] 2.3.Coating process In the coating step S106, the prepared reaction mixture is applied to the upper surface 31 (one side) of the support layer 3. This forms a coating film.

[0095] The coating method is not particularly limited, but examples include immersion, dropping, inkjet, dispenser, spray, screen printing, coater coating, and spin coating.

[0096] Prior to applying the reactant, the upper surface 31 of the support layer 3 may be subjected to an activation treatment. The activation treatment is not particularly limited as long as it is a treatment that activates the upper surface 31. Examples of activation treatments include irradiating the upper surface 31 with energy rays, heating the upper surface 31, exposing the upper surface 31 to plasma or corona, and exposing the upper surface 31 to ozone gas. Examples of energy rays include infrared rays, ultraviolet rays, and visible light.

[0097] After the coating film is formed, it is dried as needed. The drying method is not particularly limited and may be natural drying or forced drying.

[0098] 2.4. Energy Transfer Process In the energy impartment step S108, energy is imparted to the coating film. This causes a polymerization reaction to occur.

[0099] The method of supplying energy is not particularly limited, but examples include irradiation with light and irradiation with plasma. Of these, the method of irradiation with plasma is preferred. By using plasma, the polymerization reaction can be carried out efficiently while suppressing the rise in temperature. This allows the separation layer 4 to be formed in a shorter time while suppressing thermal degradation of the support layer 3.

[0100] Furthermore, it is preferable to apply energy from the surface side of the coating film. This allows the polymerization reaction to proceed preferentially on the surface side of the coating film, leading to film formation. On the other hand, the polymerization reaction will not proceed on the back side of the coating film, or will proceed more slowly than on the surface side. For this reason, the application of energy may be stopped once film formation has progressed to a certain extent. In this case, unreacted material will remain, but this unreacted material can be removed by washing from the back side. A solvent capable of dissolving the unreacted material is used for washing. By this method, the film thickness of the separation layer 4 can be controlled with greater precision.

[0101] The method for generating plasma is not particularly limited, but an atmospheric pressure plasma device is preferably used. Furthermore, the method for irradiating with plasma is not particularly limited, but by using a method that involves transporting the plasma generated at the plasma generation site and irradiating it (plasma jet method), deterioration of the workpiece due to discharge, etc., can be suppressed.

[0102] 3. Applications of gas separation membranes The gas separation membrane 1 according to this embodiment can be used for the separation and recovery of carbon dioxide from a mixed gas containing carbon dioxide, the separation and purification of carbon dioxide, and the like. In particular, the use of the gas separation membrane 1 is effective in techniques for separating and recovering carbon dioxide contained in the atmosphere (direct air recovery (DAC)).

[0103] 4. Effects achieved by the above embodiment As described above, the gas separation membrane 1 according to the embodiment is a gas separation membrane that separates carbon dioxide from a mixed gas containing carbon dioxide by permeation. Such a gas separation membrane 1 comprises a sheet-like support layer 3 and a separation layer 4 provided on the upper surface 31 (one side) of the support layer 3. The separation layer 4 has the function of selectively separating carbon dioxide and is composed of a polymer having polyethylene oxide structural units and polysiloxane structural units. The average thickness of the separation layer 4 is 1 nm to 500 nm. Furthermore, when an XPS spectrum is obtained for the separation layer 4 by X-ray photoelectron spectroscopy and the Si2p peak and C1s peak included in the XPS spectrum are waveform-separated, the intensity ratio P(Si-O) / P(CO) of the Si-O peak to the intensity P(CO) of the CO peak is 0.03 to 2.0.

[0104] With this configuration, a gas separation membrane 1 can be realized that has high gas selectivity and high gas permeability for carbon dioxide, as well as excellent mechanical strength.

[0105] In the gas separation membrane 1 according to the above embodiment, it is preferable that the ratio of the polysiloxane structural unit content to the polyethylene oxide structural unit content is 6 / 4 or more and 9 / 1 or less in molar ratio.

[0106] With this configuration, a separation layer 4 having an intensity ratio P(Si-O) / P(CO) within a predetermined range can be easily formed.

[0107] In the gas separation membrane 1 according to the above embodiment, the gas permeability of nitrogen is R N2 Let R be the gas permeability of carbon dioxide. CO2 In this case, the gas selectivity ratio R CO2 / R N2 However, it is 15 or higher, and the gas permeability of carbon dioxide R CO2 However, a GPU of 500 or more is preferable.

[0108] This configuration makes it possible to realize a gas separation membrane 1 that can efficiently separate and recover carbon dioxide from a mixed gas.

[0109] The method for manufacturing a gas separation membrane according to the above embodiment is a method for manufacturing a gas separation membrane 1 according to the above embodiment, and comprises a mixing step S102, a reaction step S104, a coating step S106, and an energy imparting step S108. In the mixing step S102, a polyethylene glycol compound having a first reactive functional group at the end of its main chain and a polysiloxane compound having a second reactive functional group at the end of its main chain that reacts with and binds to the first reactive functional group are mixed to obtain a mixture. In the reaction step S104, the mixture is heated to react the first reactive functional group and the second reactive functional group to obtain a reaction product. In the coating step S106, the reaction product is applied to the upper surface 31 (one side) of the support layer 3 to form a coating film. In the energy imparting step S108, energy is imparted to the coating film to form a separation layer 4.

[0110] With this configuration, a gas separation membrane 1 that has high gas selectivity and high gas permeability for carbon dioxide, as well as excellent mechanical strength, can be efficiently manufactured.

[0111] In the method for producing a gas separation membrane according to the above embodiment, at least one of the first reactive functional group and the second reactive functional group may be selected from the group consisting of hydroxyl groups, carboxyl groups, vinyl groups, acrylic groups, isocyanate groups, and mercapto groups.

[0112] With this configuration, the reactivity of the first and second reactive functional groups can be further enhanced, allowing for the efficient formation of a separation layer 4 with excellent coating properties.

[0113] In the method for producing a gas separation membrane according to the above embodiment, the polysiloxane compound may be a polydimethylsiloxane having a second reactive functional group at the end of its main chain.

[0114] With this configuration, the separation layer 4 exhibits particularly good gas permeability for carbon dioxide and also has excellent weather resistance, due to factors such as increased intermolecular spacing in the polydimethylsiloxane.

[0115] Although the gas separation membrane and method for producing the gas separation membrane according to the present invention have been described above based on preferred embodiments, the present invention is not limited thereto.

[0116] For example, the gas separation membrane according to the present invention may be one in which each part of the above embodiment is replaced with a component having a similar function, or any component may be added to the above embodiment.

[0117] Furthermore, the method for manufacturing a gas separation membrane according to the present invention may be modified by adding any desired steps to the above embodiment. [Examples]

[0118] Next, specific embodiments of the present invention will be described. 5. Fabrication of gas separation membrane 5.1. Example 1 First, a PS sheet was prepared to serve as the support layer. The PS sheet is a porous sheet made of polysulfone (PS) with an average thickness as shown in Table 1 (Figure 3). Next, one side of the PS sheet was subjected to corona treatment as an activation treatment.

[0119] Next, polyethylene glycol and polydimethylsiloxane were mixed to prepare a mixture. Then, the prepared mixture was heated at 80°C for 30 minutes while stirring with a stirrer to obtain a reaction product. The mixing ratio of polyethylene glycol to polydimethylsiloxane was such that the ratio of polysiloxane structural units to polyethylene oxide structural units was in the range of 6 / 4 to 9 / 1 in molar ratio.

[0120] Next, the reaction mixture was applied to one side of the PS sheet to obtain a coating. Spin coating was used for the application method. After that, the coating was dried.

[0121] Next, the coating film was subjected to plasma irradiation. An atmospheric pressure plasma device was used for the plasma irradiation. This caused the raw materials to form a film. Then, a separation layer was formed consisting of a polymer having polyethylene oxide structural units (PEO) and polysiloxane structural units (PDMS), and a gas separation membrane was obtained. Next, the resulting gas separation membrane was immersed in an organic solvent to remove unreacted substances.

[0122] 5.2. Examples 2-13 and Comparative Examples 1-3 A gas separation membrane was obtained in the same manner as in Example 1, except that the configuration of the gas separation membrane was changed as shown in Table 1 (Figure 3) or Table 2 (Figure 4). Note that "PDMS" in the supporting layer material refers to a polydimethylsiloxane sheet.

[0123] 5.3. Comparative Example 4 A gas separation membrane was obtained in the same manner as in Example 1, except that the separation layer was composed solely of polyethylene oxide structural units (PEO), and the other components were as shown in Table 1.

[0124] 5.4. Comparative Example 5 A gas separation membrane was obtained in the same manner as in Example 1, except that the separation layer was composed solely of polysiloxane structural units (PDMS) and the other components were as shown in Table 1.

[0125] Figure 3 is Table 1, showing the configuration of the gas separation membrane and the evaluation results of the gas separation membrane. Figure 4 is Table 2, showing the configuration of the gas separation membrane and the evaluation results of the gas separation membrane.

[0126] 6. X-ray photoelectron spectroscopy analysis of gas separation membranes X-ray photoelectron spectroscopy analysis was performed on the gas separation membranes of each example and comparative example. Waveform separation processing was then performed on the XPS spectra using analysis software to obtain the intensities P(CO) and P(Si-O). The intensity ratio P(Si-O) / P(CO) was also calculated. The calculated intensity ratios P(Si-O) / P(CO) are shown in Tables 1 and 2.

[0127] Figure 5 shows an example of the XPS spectrum (Si2p) near the Si2p peak. Figure 6 shows an example of the XPS spectrum (C1s) near the C1s peak. Figure 6 also shows the CC and CO peaks separated by waveform separation processing.

[0128] 7. Evaluation of gas separation membranes The following evaluations were performed on the gas separation membranes of each example and each comparative example.

[0129] 7.1. Gas permeability (CO2 permeability) Test samples were prepared by cutting the gas separation membranes of each example and comparative example into circles with a diameter of 5 cm. Next, a gas permeability measuring device was used to supply a mixed gas, consisting of carbon dioxide and nitrogen in a volume ratio of 13:87, to the upstream side of the test sample. At this time, the upstream total pressure was adjusted to 5 MPa, the partial pressure of carbon dioxide to 0.65 MPa, the flow rate of the mixed gas to 500 mL / min, and the temperature to 40°C. Gas permeability was measured in accordance with the gas permeability test method (Part 1: Differential Pressure Method) specified in JIS K 7126-1:2006. A GTR-11A / 31A gas permeability measuring device manufactured by GTR Tech Co., Ltd. was used. In this device, the gas that has permeated through the test sample is introduced into a gas chromatograph, and the gas permeability of each component is measured.

[0130] Next, the CO2 permeability through the gas separation membrane was calculated from the analysis results. The calculation results are shown in Tables 1 and 2.

[0131] 7.2. Gas selectivity (CO2 / N2 selectivity ratio) Based on the analysis results described above, the N2 permeability in the gas separation membrane was calculated. Next, the ratio of CO2 permeability to N2 permeability was calculated as the "CO2 / N2 selectivity ratio". The calculation results are shown in Tables 1 and 2.

[0132] 7.3.Durability The gas separation membranes of each example and comparative example were set in a gas permeability measuring device, and the downstream side was depressurized so that the pressure difference (differential pressure) between the upstream and downstream sides was 0.1 MPa. This state was then maintained for one week.

[0133] After one week, the gas separation membrane was removed and examined under magnification to check for damage. The observation results were then evaluated against the following criteria. The evaluation results are shown in Tables 1 and 2.

[0134] A: No damage was observed in the gas separation membrane. C: Damage was observed in the gas separation membrane.

[0135] Next, the gas separation membrane that had been observed under magnification was placed back into the gas permeability measuring device, and a pressure difference was applied as described above and maintained for one week.

[0136] After one week, the gas separation membrane was removed and examined under magnification to check for damage. The observation results were then evaluated against the following criteria. The evaluation results are shown in Tables 1 and 2.

[0137] A: No damage was observed in the gas separation membrane. B: Damage was found in the gas separation membrane.

[0138] As is clear from Tables 1 and 2, the gas separation membranes of each example were found to have high gas selectivity and high gas permeability for carbon dioxide, as well as excellent mechanical strength. [Explanation of Symbols]

[0139] 1...Gas separation membrane, 3...Support layer, 4...Separation layer, 31...Top surface, S102...Mixing process, S104...Reaction process, S106...Coating process, S108...Energy imparting process, (Si2p)...XPS spectrum, (C1s)...XPS spectrum

Claims

1. A gas separation membrane that separates carbon dioxide from a mixed gas containing carbon dioxide by permeating it, A sheet-like support layer, A separation layer is provided on one side of the support layer, has the function of selectively separating carbon dioxide, and is composed of a polymer having polyethylene oxide structural units and polysiloxane structural units, Equipped with, The average thickness of the separation layer is 1 nm or more and 500 nm or less. A gas separation membrane characterized in that, when an XPS spectrum is obtained from the separation layer by X-ray photoelectron spectroscopy, and the Si2p peak and C1s peak included in the XPS spectrum are waveform-separated, the intensity ratio P(Si-O) / P(C-O) of the Si-O peak to the intensity P(C-O) of the C-O peak is 0.03 or more and 2.0 or less.

2. The gas separation membrane according to claim 1, wherein the ratio of the content of polysiloxane structural units to the content of polyethylene oxide structural units is 6 / 4 or more and 9 / 1 or less in molar ratio.

3. The nitrogen gas permeability is R Ｎ２ Let R be the gas permeability of carbon dioxide. ＣＯ２ In this case, the gas selectivity ratio R ＣＯ２ / R Ｎ２ However, it is 15 or more, Carbon dioxide gas permeability R ＣＯ２ The gas separation membrane according to claim 1 or 2, wherein the capacity is 500 GPU or more.

4. A method for producing a gas separation membrane according to claim 1 or 2, A step of mixing a polyethylene glycol compound having a first reactive functional group at the end of its main chain with a polysiloxane compound having a second reactive functional group at the end of its main chain that reacts with and binds to the first reactive functional group, to obtain a mixture. The steps include heating the mixture to react the first reactive functional group with the second reactive functional group to obtain a reactant, The steps include applying the reactant to one surface of the support layer to form a coating film, A step of applying energy to the coating film to form the separation layer, A method for producing a gas separation membrane, characterized by having [a certain characteristic].

5. The method for producing a gas separation membrane according to claim 4, wherein at least one of the first reactive functional group and the second reactive functional group is selected from the group consisting of a hydroxyl group, a carboxyl group, a vinyl group, an acrylic group, an isocyanate group, and a mercapto group.

6. The method for producing a gas separation membrane according to claim 4, wherein the polysiloxane compound is a polydimethylsiloxane having the second reactive functional group at the end of the main chain.

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