Separation membrane, method for manufacturing a separation membrane, and coating solution for manufacturing a separation membrane

Abstract

To provide a separation membrane with high separation performance for mixed gases containing acidic gases. [Solution] The separation membrane 10 of the present invention comprises a separation functional layer 1 containing graphene oxide, an ionic liquid, and a polymer. The ionic liquid is, for example, hydrophilic and contains imidazolium ions and tetrafluoroborate. The method for producing the separation membrane 10 of the present invention includes applying a coating solution containing graphene oxide, an ionic liquid, and a polymer to a substrate to obtain a coating film, and drying the coating film.

Description

Technical Field

[0001] The present invention relates to a separation membrane, a method for producing the separation membrane, and a coating solution for producing the separation membrane.

Background Art

[0002] As a method for separating an acidic gas from a mixed gas containing an acidic gas such as carbon dioxide, a membrane separation method has been developed. The membrane separation method can efficiently separate an acidic gas while suppressing the operating cost as compared with an absorption method in which the acidic gas contained in the mixed gas is absorbed by an absorbent.

[0003] Examples of the separation membrane used in the membrane separation method include a composite membrane in which a separation functional layer is formed on a porous support. An intermediate layer may be disposed between the separation functional layer and the porous support (for example, Patent Document 1). Patent Document 1 discloses a gel layer containing a polymer and an ionic liquid as the separation functional layer.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] There is a demand for further improving the separation performance of conventional separation membranes with respect to a mixed gas containing an acidic gas.

[0006] Therefore, an object of the present invention is to provide a separation membrane having high separation performance with respect to a mixed gas containing an acidic gas, particularly a mixed gas containing a gas having a larger molecular size than the acidic gas together with the acidic gas.

Means for Solving the Problems

[0007] ​​​The present invention provides a separation membrane equipped with a separation functional layer containing graphene oxide, an ionic liquid, and a polymer.

[0008] Furthermore, the present invention is A coating solution containing graphene oxide, an ionic liquid, and a polymer is applied to a substrate to obtain a coating film. Drying the aforementioned coating film, The present invention provides a method for producing a separation membrane, including [the specified component].

[0009] Furthermore, the present invention is A coating solution applied to a substrate in order to manufacture a separation membrane, The present invention provides a coating solution comprising graphene oxide, an ionic liquid, and a polymer. [Effects of the Invention]

[0010] According to the present invention, a separation membrane with high separation performance for gas mixtures containing acidic gases, particularly gas mixtures containing acidic gases along with gases with larger molecular sizes than the acidic gases, can be provided. [Brief explanation of the drawing]

[0011] [Figure 1] This is a cross-sectional view of a separation membrane according to one embodiment of the present invention. [Figure 2] This is a schematic cross-sectional view of a membrane separation apparatus equipped with the separation membrane of the present invention. [Figure 3] This is a schematic perspective view showing a modified example of a membrane separation apparatus equipped with the separation membrane of the present invention. [Figure 4] This graph shows the results of X-ray diffraction measurements performed on the separation functional layer of the separation membranes in Example 1 and Comparative Example 1. [Modes for carrying out the invention]

[0012] The details of the present invention will be described below, but the following description is not intended to limit the present invention to any particular embodiment.

[0013] <Embodiment of a separation membrane> As shown in Figure 1, the separation membrane 10 of this embodiment comprises a separation functional layer 1, and further comprises, for example, an intermediate layer 2 and a porous support 3. The porous support 3 supports the separation functional layer 1. The intermediate layer 2 is disposed between the separation functional layer 1 and the porous support 3 and is in direct contact with both the separation functional layer 1 and the porous support 3.

[0014] (separation functional layer) The separation functional layer 1 is a layer that can preferentially permeate acidic gases contained in the gas mixture. The separation functional layer 1 comprises graphene oxide (GO), an ionic liquid (IL), and a polymer. The ionic liquid is, for example, a salt (ionic compound) that is liquid below 100°C, and is typically a salt that is liquid at 25°C. For example, in the separation functional layer 1, multiple layers of graphene oxide are arranged in layers. The ionic liquid and polymer may be present between the layers of multiple layers of graphene oxide. The graphene oxide and polymer may be dispersed in the ionic liquid or may be present randomly.

[0015] The graphene oxide contained in the separation functional layer 1 is, for example, an oxide of graphene, and has a structure in which a functional group containing an oxygen atom is introduced into the graphene. Examples of functional groups containing an oxygen atom include hydroxyl groups, carboxyl groups, and epoxy groups. The graphene oxide may also be reduced graphene oxide (rGO), in which some of the functional groups containing oxygen atoms are reduced. The graphene oxide may contain substituents other than functional groups containing oxygen atoms, such as substituents containing functional groups containing nitrogen atoms (such as amino groups), but it is preferable that it is substantially free of them. More specifically, it is preferable that the graphene oxide is substantially free of substituents derived from ionic liquids that may be introduced by reaction with ionic liquids.

[0016] The content of graphene oxide in the separation functional layer 1 is, for example, 0.01 wt% or more, preferably 0.02 wt% or more, from the viewpoint of improving the separation performance of the separation functional layer 1. The upper limit of the graphene oxide content is not particularly limited, but is, for example, 1 wt%, preferably 0.5 wt%, more preferably 0.1 wt%, and even more preferably 0.05 wt%.

[0017] The ionic liquid contained in the separation functional layer 1 includes, for example, at least one selected from the group consisting of imidazolium ions, pyridinium ions, ammonium ions, and phosphonium ions, and preferably includes imidazolium ions. These ions include, for example, substituents having one or more carbon atoms.

[0018] Examples of substituents having one or more carbon atoms include alkyl groups having one to 20 carbon atoms, cycloalkyl groups having three to 14 carbon atoms, and aryl groups having six to 20 carbon atoms. These may be further substituted with hydroxyl groups, cyano groups, amino groups, monovalent ether groups, etc. (for example, hydroxyalkyl groups having one to 20 carbon atoms).

[0019] Examples of alkyl groups having 1 to 20 carbon atoms include methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecyl, n-hexadecyl, n-heptadecyl, n-octadecyl, n-nonadecyl, and n-eicosadecyl. Examples include hydroxyl groups, i-propyl groups, sec-butyl groups, i-butyl groups, 1-methylbutyl groups, 1-ethylpropyl groups, 2-methylbutyl groups, i-pentyl groups, neopentyl groups, 1,2-dimethylpropyl groups, 1,1-dimethylpropyl groups, t-pentyl groups, 2-ethylhexyl groups, and 1,5-dimethylhexyl groups, which may be further substituted with hydroxyl groups, cyano groups, amino groups, monovalent ether groups, etc.

[0020] The alkyl groups described above may be substituted with cycloalkyl groups. The number of carbon atoms in the alkyl groups substituted with cycloalkyl groups is, for example, 1 to 20. Examples of alkyl groups substituted with cycloalkyl groups include cyclopropylmethyl group, cyclobutylmethyl group, cyclohexylmethyl group, and cyclohexylpropyl group, which may be further substituted with hydroxyl groups, cyano groups, amino groups, monovalent ether groups, etc.

[0021] Examples of cycloalkyl groups having 3 to 14 carbon atoms include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclododecyl, norbornyl, bornyl, and adamantyl groups, which may be further substituted with hydroxyl, cyano, amino, or monovalent ether groups.

[0022] Examples of aryl groups having 6 to 20 carbon atoms include phenyl, toluyl, xylyl, mesityl, anisyl, naphthyl, and benzyl groups, which may be further substituted with hydroxyl, cyano, amino, or monovalent ether groups.

[0023] In this embodiment, the ionic liquid preferably contains imidazolium ions represented by the following formula (1). [ka]

[0024] In equation (1), R 1 ~R 5 Each of these is independently a hydrogen atom or one or more carbon atoms as described above. 1 The substituent is preferably having 1 or more carbon atoms, more preferably an alkyl group having 1 to 20 carbon atoms, even more preferably an alkyl group having 3 to 10 carbon atoms, and particularly preferably an n-butyl group. 3The substituent is preferably having 1 or more carbon atoms, more preferably an alkyl group having 1 to 20 carbon atoms, even more preferably an alkyl group having 1 to 10 carbon atoms, and particularly preferably a methyl group. 2 , R 4 and R 5 Each of these is preferably a hydrogen atom.

[0025] In ionic liquids, the ions mentioned above may form salts with counter anions. Examples of counter anions include alkyl sulfates, tosylates, methanesulfonates, trifluoromethanesulfonates, toluenesulfonates, acetates, bis(fluorosulfonyl)imides, bis(trifluoromethanesulfonyl)imides, thiocyanates, dicyanamides, tricyanomethanides, tetracyanoborates, hexafluorophosphates, tetrafluoroborates, halides, etc., with tetrafluoroborate being preferred. In other words, it is preferable that the ionic liquid contains tetrafluoroborate.

[0026] Specific examples of ionic liquids include 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide, 1-ethyl-3-methylimidazolium dicyanamide, 1-butyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium trifluoromethanesulfonate, 1-butyl-3-methylimidazolium tetrachloroferate, 1-butyl-3-methylimidazolium iodide, 1-butyl-2,3-dimethylimidazolium chloride, 1-butyl-2,3-dimethylimidazolium hexafluorophosphate, and 1-butyl-2,3-dimethylimidazolium chloride. Ruimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-butyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide, 1-butyl-3-methylimidazolium trifluoro(trifluoromethyl)borate, 1-butyl-3-methylimidazolium tribromide, 1,3-dimesitylyimidazolium chloride, 1,3-bis(2,6-diisopropylphenyl)imidazolium chloride, 1,3-diisopropylimidazolium tetrafluoroborate, 1,3-di-tert-butylimidazolium tetrafluoroborate, 1,3-dicyclohexylimidazolium tetrafluoroborate, 1,3-dicyclohexylimidazolium chloride, 1,2-dimethyl-3-propylimidazolium iodide, 1-hexyl-3-methylimidazolium chloride, 1-hexyl-3-methylimidazolium hexafluorophosphate, 1-hexyl-3-methylimidazolium tetrafluoroborate, 1-hexyl-3-methylimidazolium bromide, 1-methyl-3-propylimidazolium iodide, 1-methyl-3-n-octylimidazolium bromide, 1-methyl-3-n-octylimidazolium Examples include dazolium chloride, 1-methyl-3-n-octylimidazolium hexafluorophosphate, 1-methyl-3-[6-(methylsulfinyl)hexyl]imidazolium p-toluenesulfonate, 1-ethyl-3-methylimidazolium tricyanomethanide, 1-ethyl-3-methylimidazolium tetracyanoborate, and 1-(2-hydroxyethyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)imide.

[0027] The ionic liquid is particularly preferably 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]). [BMIM][BF4] is particularly suitable for the fabrication of the separation functional layer 1.

[0028] It is preferable that the ionic liquid has substantially no reactivity with graphene oxide. Furthermore, it is preferable that the ionic liquid is hydrophilic from the viewpoint of easily fabricating the separation functional layer 1. In this specification, "the ionic liquid is hydrophilic" means that when the following tests 1 and 2 are performed, in test 1 the ionic liquid dissolves in water, and in test 2 the ionic liquid does not dissolve in isopropyl alcohol (IPA), and phase separation is confirmed. Test 1: Under room temperature (25°C), add 0.5g of ionic liquid to a container such as a microtube, and then add 0.5g of water (deionized water) to the container. Next, seal the container and shake it by hand about 10 times. Let the container stand for 1 minute, and visually check whether the ionic liquid has dissolved in the water inside the container. Test 2: Under room temperature conditions, add 0.5 g of ionic liquid to a container such as a microtube, and then add 0.5 g of isopropyl alcohol to the container. Next, seal the container and shake it by hand about 10 times. Let the container stand for 1 minute, and visually check whether the ionic liquid has dissolved in the isopropyl alcohol inside the container.

[0029] In this specification, if, in Test 1, the ionic liquid does not dissolve in water and phase separation is confirmed, the ionic liquid is determined to be hydrophobic. Furthermore, if, in Test 1, the ionic liquid dissolves in water, and in Test 2, the ionic liquid dissolves in isopropyl alcohol, the ionic liquid is determined to be amphiphilic.

[0030] From the viewpoint of easily fabricating the separation functional layer 1, it is preferable that the ionic liquid has high viscosity. The viscosity of the ionic liquid at 25°C is, for example, 0.20 Pa·s or higher, and preferably 0.30 Pa·s or higher. The upper limit of the viscosity of the ionic liquid at 25°C is not particularly limited, but is, for example, 0.50 Pa·s. The viscosity of the ionic liquid can be measured using a commercially available viscosity / viscoelasticity measuring device (for example, a Rheostress RS600 manufactured by Thermo HAAKE) under the following conditions. Cone: C60 / Ti Measurement temperature: 25℃ (room temperature) Shear rate γ(dγ / dt): 1[1 / s] Rotation speed: 30 [s]

[0031] The content of the ionic liquid in the separation functional layer 1 may be higher than the content of graphene oxide and the polymer, for example, 50 wt% or more, preferably 60 wt% or more, more preferably 70 wt% or more, even more preferably 80 wt% or more, and particularly preferably 90 wt% or more. The higher the content of the ionic liquid, the more likely the separation functional layer 1 is to be able to preferentially permeate the acidic gas contained in the mixed gas. The upper limit of the ionic liquid content is not particularly limited, for example, 95 wt%.

[0032] From the viewpoint of enabling easy production of the separation functional layer 1, the polymer contained in the separation functional layer 1 preferably has hydrophilicity. In this specification, "the polymer has hydrophilicity" means that the distance Ra between the Hansen solubility parameter of the polymer and the Hansen solubility parameter of H2O is less than 19 MPa 1 / 2 . However, depending on the composition of the separation functional layer 1, the composition of the intermediate layer 2, the use of the separation membrane 10, etc., the distance Ra may be 19 MPa 1 / 2 or more.

[0033] The Hansen solubility parameter is the solubility parameter introduced by Hildebrand divided into three components: the dispersion term δD, the polar term δP, and the hydrogen bonding term δH. Details of the Hansen solubility parameter are disclosed in "Hansen Solubility Parameters; A Users Handbook (CRC Press, 2007)". The Hansen solubility parameter can be calculated using known software such as HSPiP, for example.

[0034] The distance Ra between the Hansen solubility parameter of the polymer and the Hansen solubility parameter of H2O can be calculated from the following formula (i). However, in formula (i), δD1, δP1, and δH1 are the dispersion term (MPa 1 / 2 ), the polar term (MPa 1 / 2 ), and the hydrogen bonding term (MPa 1 / 2 ) of the polymer, respectively. δD2, δP2, and δH2 are the dispersion term (18.1 MPa 1 / 2 ), the polar term (17.1 MPa 1 / 2 ), and the hydrogen bonding term (16.9 MPa 1 / 2 ) of H2O, respectively. Ra = {4×(δD1 - δD2) 2 +(δP1 - δP2) 2 +(δH1 - δH2) 2}^(1 / 2) 1 / 2 (i)

[0035] The distance Ra between the Hansen solubility parameter of the polymer and the Hansen solubility parameter of H2O is preferably 18 MPa. 1 / 2 The following is more preferable: 17 MPa 1 / 2 The following, and more preferably 16 MPa 1 / 2 The following, and particularly preferably 15 MPa 1 / 2 The following applies: The lower limit of distance Ra is preferably 5 MPa. 1 / 2 More preferably 8MPa 1 / 2 And in some cases, it can reach 10 MPa. 1 / 2 It may also be 13 MPa 1 / 2 That's fine.

[0036] The polymer has, for example, a polar group. The polar group includes, for example, at least one selected from the group consisting of a hydroxyl group, an ether group, and an amide group, and preferably includes an amide group. Polymers having such polar groups tend to be hydrophilic. Specific examples of polymers include polyether block amides, polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyacrylamide (PAA), polyhydroxyethyl methacrylate (PHEMA), and derivatives thereof. The separation functional layer 1 preferably contains a polyether block amide as the polymer.

[0037] Polyether block amides are block copolymers containing polyether block PE and polyamide block PA. Polyether block amides can be represented, for example, by the following formula (2). [ka]

[0038] In equation (2), R 6 R is a divalent hydrocarbon group having 1 to 15 carbon atoms. 6 In this, the number of carbon atoms in the divalent hydrocarbon group may be 1 to 10 or 1 to 5. 6 In this, the divalent hydrocarbon group is preferably a linear or branched alkylene group. 6Specific examples include the ethylene group and the butane-1,4-diyl group. 7 R is a divalent hydrocarbon group having 1 to 20 carbon atoms. 7 In this, the number of carbon atoms in the divalent hydrocarbon group may be 3 to 18 or 3 to 15. 7 In this, the divalent hydrocarbon group is preferably a linear or branched alkylene group. 7 Specific examples include the pentane-1,5-diyl group and the undecane-1,11-diyl group.

[0039] In equation (2), the ratio of x to y (x:y) is, for example, 1:9 to 9:1, preferably 5:5 to 9:1, and more preferably 6:4 to 8:2. n is an integer greater than or equal to 1.

[0040] Specific examples of polyether block amides include Pebax® 2533 and 1657 manufactured by Arkema. The distance Ra between the Hansen solubility parameter of Pebax 2533 and the Hansen solubility parameter of H2O is 16.5 MPa. 1 / 2 The distance Ra between the Hansen solubility parameter of Pebax1657 and the Hansen solubility parameter of H2O is 12.4 MPa. 1 / 2 That is the case.

[0041] It is preferable that the polymer is compatible with both graphene oxide and the ionic liquid. That is, in the separation functional layer 1 and the coating solution for producing the separation functional layer 1, it is preferable that the polymer mixes sufficiently with the graphene oxide and the ionic liquid without substantially separating.

[0042] The polymer content in the separation functional layer 1 is, for example, 1 wt% or more, preferably 3 wt% or more, and more preferably 5 wt% or more. The upper limit of the polymer content is not particularly limited, but is, for example, 10 wt%.

[0043] The thickness of the separation functional layer 1 is, for example, 50 μm or less, preferably 25 μm or less, and more preferably 15 μm or less. The thickness of the separation functional layer 1 may, in some cases, be 10 μm or less, 5.0 μm or less, or 2.0 μm or less. The thickness of the separation functional layer 1 may be 0.05 μm or more, or 0.1 μm or more.

[0044] (Middle class) The intermediate layer 2 may, for example, contain a resin and further contain nanoparticles dispersed in the resin (matrix). The nanoparticles may be spaced apart from each other in the matrix or partially aggregated. The material of the matrix is ​​not particularly limited and includes, for example, silicone resins such as polydimethylsiloxane; fluororesins such as polytetrafluoroethylene; epoxy resins such as polyethylene oxide; polyimide resins; polysulfone resins; polyacetylene resins such as polytrimethylsilylpropyne and polydiphenylacetylene; and polyolefin resins such as polymethylpentene. The matrix preferably contains a silicone resin.

[0045] Nanoparticles may contain inorganic materials or organic materials. Examples of inorganic materials that can be included in nanoparticles include silica, titania, and alumina. It is preferable that the nanoparticles contain silica.

[0046] Nanoparticles may have a surface modified with a modifying group containing carbon atoms. Nanoparticles having such a modified surface exhibit excellent dispersibility in a matrix. For example, the nanoparticles are silica nanoparticles that may have a surface modified with a modifying group. The modifying group further contains, for example, silicon atoms. In nanoparticles, the surface modified with a modifying group can be represented, for example, by the following formulas (I) to (III). [ka]

[0047] R in equations (I) to (III) 8~R 13 These are hydrocarbon groups that may have substituents independently of each other. The number of carbon atoms in the hydrocarbon group is not particularly limited as long as it is 1 or more. The number of carbon atoms in the hydrocarbon group may be, for example, 25 or less, 20 or less, 10 or less, or 5 or less. In some cases, the number of carbon atoms in the hydrocarbon group may be greater than 25. The hydrocarbon group may be a linear or branched chain hydrocarbon group, or an alicyclic or aromatic cyclic hydrocarbon group. In a preferred embodiment, the hydrocarbon group is a linear or branched alkyl group having 1 to 8 carbon atoms. The hydrocarbon group is, for example, a methyl group or an octyl group, and is preferably a methyl group. Examples of substituents on the hydrocarbon group include an amino group and an acyloxy group. An example of an acyloxy group is a (meth)acryloyloxy group.

[0048] In another preferred form, R in equations (I) to (III) 8 ~R 13 The hydrocarbon group which may have the substituents mentioned above is represented by the following formula (IV). Nanoparticles having a surface modified with a modifying group containing the hydrocarbon group represented by formula (IV) are suitable for improving the permeation rate of acidic gas in the separation membrane 10. [ka]

[0049] In equation (IV), R 14 This is an alkylene group having 1 to 5 carbon atoms, which may have substituents. The alkylene group may be linear or branched. Examples of alkylene groups include methylene, ethylene, propane-1,3-diyl, butane-1,4-diyl, and pentane-1,5-diyl, with propane-1,3-diyl being preferred. Examples of substituents on the alkylene group include amide groups and aminoalkylene groups.

[0050] In equation (IV), R 15R is an alkyl or aryl group having 1 to 20 carbon atoms, which may have substituents. The alkyl group may be linear or branched. Examples of alkyl and aryl groups include those mentioned above for ionic liquids. Examples of substituents on alkyl and aryl groups include amino groups and carboxyl groups. 15 For example, this is a 3,5-diaminophenyl group.

[0051] In nanoparticles, the surface modified by the modifying group is preferably represented by the following formula (V). [ka]

[0052] The modifying group is not limited to the structures shown in formulas (I) to (III). The modifying group is R in formulas (I) to (III). 8 ~R 13 Alternatively, the polymer chain may contain a polyamide structure or a polydimethylsiloxane structure. In the modifying group, for example, this polymer chain is directly bonded to a silicon atom. Examples of the polymer chain's shape include linear, dendrimeric, and hyperbranched structures.

[0053] The method for modifying the surface of nanoparticles with a modifying group is not particularly limited. For example, the surface of nanoparticles can be modified by reacting hydroxyl groups present on the surface of nanoparticles with a known silane coupling agent. If the modifying group includes a polyamide structure, the surface of nanoparticles can be modified, for example, by the method disclosed in Japanese Patent Application Publication No. 2010-222228.

[0054] The average particle size of the nanoparticles is not particularly limited as long as it is on the order of nanometers (<1000 nm), for example, 100 nm or less, preferably 50 nm or less, and more preferably 20 nm or less. The lower limit of the average particle size of the nanoparticles is, for example, 1 nm. The average particle size of the nanoparticles can be determined, for example, by the following method: First, a cross-section of the intermediate layer 2 is observed with a transmission electron microscope. In the obtained electron microscope image, the area of ​​a specific nanoparticle is calculated by image processing. The diameter of a circle having the same area as the calculated area is considered to be the particle size (diameter of the particle) of that specific nanoparticle. The particle size of any number of nanoparticles (at least 50) is calculated, and the average of the calculated values ​​is considered to be the average particle size of the nanoparticles. The shape of the nanoparticles is not particularly limited and may be spherical, ellipsoidal, flaky, or fibrous.

[0055] The nanoparticle content in the intermediate layer 2 is, for example, 5 wt% or more, preferably 10 wt% or more, and more preferably 15 wt% or more. The upper limit of the nanoparticle content in the intermediate layer 2 is not particularly limited, but is, for example, 30 wt%.

[0056] The thickness of the intermediate layer 2 is not particularly limited, and is, for example, less than 50 μm, preferably 40 μm or less, and more preferably 30 μm or less. The lower limit of the thickness of the intermediate layer 2 is not particularly limited, and is, for example, 1 μm. The intermediate layer 2 is, for example, a layer having a thickness of less than 50 μm.

[0057] (porous support) The porous support 3 supports the separation functional layer 1 via the intermediate layer 2. Examples of the porous support 3 include nonwoven fabric; porous polytetrafluoroethylene; aromatic polyamide fiber; porous metal; sintered metal; porous ceramic; porous polyester; porous nylon; activated carbon fiber; latex; silicone; silicone rubber; permeable (porous) polymer containing at least one selected from the group consisting of polyvinyl fluoride, polyvinylidene fluoride, polyurethane, polypropylene, polyethylene, polystyrene, polycarbonate, polysulfone, polyetheretherketone, polyacrylonitrile, polyimide, and polyphenylene oxide; metal foam having open or closed cells; polymer foam having open or closed cells; silica; porous glass; mesh screen, etc. The porous support 3 may be a combination of two or more of these.

[0058] The porous support 3 has an average pore diameter of, for example, 0.01 to 0.4 μm. The thickness of the porous support 3 is not particularly limited, but is, for example, 10 μm or more, preferably 20 μm or more, and more preferably 50 μm or more. The thickness of the porous support 3 is, for example, 300 μm or less, preferably 200 μm or less, and more preferably 150 μm or less.

[0059] (Method for manufacturing separation membranes) The separation membrane 10 can be prepared, for example, by the following method. First, a coating solution containing graphene oxide, an ionic liquid, and a polymer is prepared. The coating solution may further contain a solvent such as water or an organic solvent. The coating solution may be subjected to ultrasonic treatment or stirring beforehand.

[0060] From the viewpoint of easily fabricating the separation functional layer 1, the coating solution preferably has high viscosity. Coating solutions with high viscosity tend to have excellent film-forming properties. The viscosity of the coating solution at 25°C is, for example, 0.15 Pa·s or higher, and preferably 0.20 Pa·s or higher. The upper limit of the viscosity of the coating solution at 25°C is not particularly limited, but is, for example, 0.50 Pa·s. The viscosity of the coating solution can be measured for ionic liquids by the method and conditions described above.

[0061] Next, this coating solution is applied to the substrate to obtain a coating film. The method of applying the coating solution is not particularly limited, and for example, a spin coating method can be used. By adjusting the rotation speed of the spin coater, the solid content concentration in the coating solution, etc., the thickness of the separation functional layer 1 formed from the coating film can be adjusted.

[0062] The substrate to which the coating solution is applied is typically a laminate of a porous support 3 and an intermediate layer 2. This laminate can be manufactured, for example, by the following method. First, a coating solution containing the material for the intermediate layer 2 is prepared. Next, the coating solution containing the material for the intermediate layer 2 is applied onto the porous support 3 to form a coating film. The method of applying the coating solution is not particularly limited, and for example, a dip-coating method can be used. The coating solution may also be applied using a wire bar or the like. Next, the coating film is dried to form the intermediate layer 2. Drying of the coating film can be carried out, for example, under heating conditions. The heating temperature of the coating film is, for example, 50°C or higher. The heating time of the coating film is, for example, 1 minute or more, and may be 5 minutes or more. Furthermore, the surface of the intermediate layer 2 may be treated with an easy-adhesion treatment as needed. Examples of easy-adhesion treatments include surface treatments such as application of a primer, corona discharge treatment, and plasma treatment.

[0063] When the substrate is a laminate of a porous support 3 and an intermediate layer 2, a separation functional layer 1 is formed by drying the coating film formed on the substrate, and a separation film 10 is obtained. The drying conditions for the coating film can be the same as those described above for the intermediate layer 2.

[0064] The substrate is not limited to a laminate of a porous support 3 and an intermediate layer 2, but may also be a transfer film. When the substrate is a transfer film, the separation membrane 10 can be produced by the following method. First, a separation functional layer 1 is formed by drying a coating film formed on the substrate. Next, an intermediate layer 2 is formed by coating a coating solution containing the material for the intermediate layer 2 onto the separation functional layer 1 and drying it. The laminate of the intermediate layer 2 and the separation functional layer 1 is transferred to the porous support 3. This gives the separation membrane 10.

[0065] (Characteristics of the separation membrane) In the separation membrane 10 of this embodiment, the separation functional layer 1 contains graphene oxide, an ionic liquid, and a polymer. The ionic liquid tends to improve the permeation rate of acidic gases in the separation membrane 10. Furthermore, graphene oxide, when combined with the ionic liquid and polymer, tends to suppress the permeation of gases with relatively large molecular sizes through the separation functional layer 1. Thus, because the separation functional layer 1 contains graphene oxide, an ionic liquid, and a polymer, the separation membrane 10 tends to have high separation performance for mixed gases containing acidic gases, particularly mixed gases containing acidic gases along with gases with larger molecular sizes than the acidic gases.

[0066] Examples of gas mixtures containing an acidic gas along with a gas with a larger molecular size than the acidic gas include a mixture containing carbon dioxide (molecular size: 0.33 nm) and nitrogen (molecular size: 0.364 nm). In other words, the separation membrane 10 is suitable for use in separating carbon dioxide from a gas mixture containing carbon dioxide and nitrogen. Examples of gas mixtures containing carbon dioxide and nitrogen include off-gas used in chemical plants or thermal power plants.

[0067] As an example, the separation coefficient α of carbon dioxide relative to nitrogen in the separation membrane 10 is, for example, 70 or more, preferably 80 or more, and more preferably 90 or more. The upper limit of the separation coefficient α is not particularly limited, but is, for example, 200.

[0068] The separation coefficient α can be measured by the following method. First, a mixed gas consisting of carbon dioxide and nitrogen is supplied to the space adjacent to one side of the separation membrane 10 (for example, the main surface 11 on the separation functional layer side of the separation membrane 10). This yields a permeate fluid that has permeated through the separation membrane 10 in the space adjacent to the other side of the separation membrane 10 (for example, the main surface 12 on the porous support side of the separation membrane 10). The weight of the permeate fluid, as well as the volume ratio of carbon dioxide and nitrogen in the permeate fluid, are measured. In the above operation, the concentration of carbon dioxide in the mixed gas is 50 vol% under standard conditions (0°C, 101 kPa). The mixed gas supplied to the space adjacent to one side of the separation membrane 10 is at a temperature of 30°C and a pressure of 0.1 MPa. The separation coefficient α can be calculated from the following formula. However, in the following formula, X A and X B These are the volume ratios of carbon dioxide and nitrogen in the gas mixture, respectively. A and Y B These are the volume ratios of carbon dioxide and nitrogen in the permeate fluid that has passed through the separation membrane 10, respectively. Separation coefficient α = (Y A / Y B ) / (X A / X B )

[0069] Under the above measurement conditions for the separation coefficient α, the permeation rate T of carbon dioxide passing through the separation membrane 10 is, for example, 50 GPU or more, preferably 100 GPU or more. The upper limit of the permeation rate T is not particularly limited, and may be, for example, 500 GPU or 350 GPU. However, the GPU is 10 -6 ·cm 3 (STP) / (sec·cm 2 This means cmHg. 3 (STP) refers to the volume of carbon dioxide at 1 atmosphere and 0°C.

[0070] (Embodiment of a membrane separation apparatus) As shown in Figure 2, the membrane separation apparatus 100 of this embodiment comprises a separation membrane 10 and a tank 20. The tank 20 comprises a first chamber 21 and a second chamber 22. The separation membrane 10 is located inside the tank 20. Inside the tank 20, the separation membrane 10 separates the first chamber 21 and the second chamber 22. The separation membrane 10 extends from one of a pair of walls of the tank 20 to the other.

[0071] The first chamber 21 has an inlet 21a and an outlet 21b. The second chamber 22 has an outlet 22a. Each of the inlet 21a, outlet 21b, and outlet 22a is, for example, an opening formed in the wall of the tank 20.

[0072] Membrane separation using the membrane separation apparatus 100 is performed, for example, by the following method. First, a mixed gas 30 containing an acidic gas is supplied to the first chamber 21 through the inlet 21a. Examples of the acidic gas in the mixed gas 30 include carbon dioxide, hydrogen sulfide, carbonyl sulfide, sulfur oxides (SOx), hydrogen cyanide, nitrogen oxides (NOx), and preferably carbon dioxide. The mixed gas 30 contains other gases besides the acidic gas. Examples of other gases include nonpolar gases such as hydrogen and nitrogen, and inert gases such as helium, and preferably nitrogen. The concentration of the acidic gas in the mixed gas 30 is not particularly limited, and under standard conditions, it is, for example, 0.01 vol% (100 ppm) or more, preferably 1 vol% or more, more preferably 10 vol% or more, even more preferably 30 vol% or more, and particularly preferably 50 vol% or more. The upper limit of the concentration of the acidic gas in the mixed gas 30 is not particularly limited, and under standard conditions, it is, for example, 90 vol%.

[0073] The pressure inside the first chamber 21 may be increased by supplying the mixed gas 30. The membrane separator 100 may further include a pump (not shown) for increasing the pressure of the mixed gas 30. The pressure of the mixed gas 30 supplied to the first chamber 21 is, for example, 0.1 MPa or more, preferably 0.3 MPa or more.

[0074] The second chamber 22 may be depressurized while the mixed gas 30 is supplied to the first chamber 21. The membrane separation device 100 may further include a pump (not shown) for depressurizing the second chamber 22. The second chamber 22 may be depressurized such that the space inside the second chamber 22 is, for example, 10 kPa or more, preferably 50 kPa or more, and more preferably 100 kPa or more, than the atmospheric pressure in the measurement environment.

[0075] By supplying the mixed gas 30 into the first chamber 21, a permeate fluid 35 with a higher acidic gas content than the mixed gas 30 can be obtained on the other side of the separation membrane 10. That is, the permeate fluid 35 is supplied to the second chamber 22. The permeate fluid 35 mainly contains, for example, an acidic gas. However, the permeate fluid 35 may also contain small amounts of other gases besides acidic gases. The permeate fluid 35 is discharged to the outside of the tank 20 through the outlet 22a.

[0076] The concentration of acidic gas in the gas mixture 30 gradually increases from the inlet 21a to the outlet 21b of the first chamber 21. The gas mixture 30 (concentrated fluid 36) treated in the first chamber 21 is discharged to the outside of the tank 20 through the outlet 21b.

[0077] The membrane separation apparatus 100 of this embodiment is suitable for a continuous flow membrane separation method. However, the membrane separation apparatus 100 of this embodiment may also be used for a batch membrane separation method.

[0078] (A modified example of a membrane separation apparatus) As shown in Figure 3, the membrane separation device 110 of this embodiment comprises a central tube 41 and a laminate 42. The laminate 42 contains the separation membrane 10. The membrane separation device 110 is a spiral-shaped membrane element.

[0079] The central tube 41 has a cylindrical shape. Multiple holes are formed on the surface of the central tube 41 to allow the permeable fluid 35 to flow into the interior of the central tube 41. Examples of materials for the central tube 41 include resins such as acrylonitrile-butadiene-styrene copolymer resin (ABS resin), polyphenylene ether resin (PPE resin), and polysulfone resin (PSF resin); and metals such as stainless steel and titanium. The inner diameter of the central tube 41 is, for example, in the range of 20 to 100 mm.

[0080] The laminate 42 further includes a supply-side channel material 43 and a permeate-side channel material 44 in addition to the separation membrane 10. The laminate 42 is wound around the central tube 41. The membrane separation device 110 may further include an outer casing material (not shown).

[0081] For the supply-side channel material 43 and the permeate-side channel material 44, for example, a resin net made of polyphenylene sulfide (PPS) or ethylene-chlorotrifluoroethylene copolymer (ECTFE) can be used.

[0082] Membrane separation using the membrane separation device 110 is performed, for example, by the following method. First, a mixed gas 30 is supplied to one end of the wound laminate 42. The permeate fluid 35 that has permeated through the separation membrane 10 of the laminate 42 moves into the center tube 41. The permeate fluid 35 is discharged to the outside through the center tube 41. The mixed gas 30 (concentrated fluid 36) processed by the membrane separation device 110 is discharged to the outside from the other end of the wound laminate 42. This makes it possible to separate acidic gases from the mixed gas 30. [Examples]

[0083] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited thereto.

[0084] [Properties of ionic liquids] First, the solubility of 33 commercially available ionic liquids in water and isopropyl alcohol was evaluated by performing the tests 1 and 2 described above. The results are shown in Table 1. Table 1 shows the combinations of cations and anions that make up the ionic liquids, and the properties of the ionic liquids for each combination. For example, from Table 1, it can be seen that 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) is hydrophilic. In Table 1, the evaluation criteria for the properties of the ionic liquids are as follows. Hydrophilicity: In Test 1, the ionic liquid dissolved in water, and in Test 2, the ionic liquid did not dissolve in isopropyl alcohol. Hydrophobicity: In Test 1, the ionic liquid did not dissolve in water. Amphiphilicity: In Test 1, the ionic liquid dissolves in water, and in Test 2, the ionic liquid dissolves in isopropyl alcohol.

[0085] [Table 1]

[0086] The abbreviations used in Table 1 are as follows: [EMIM]: 1-ethyl-3-methylimidazolium [BMIM]: 1-Butyl-3-methylimidazolium [HMIM]: 1-Hexyl-3-methylimidazolium [OMIM]: 1-Octyl-3-methylimidazolium N 1,4,4,4 :N-methyl-N,N,N-tributylammonium N 1,8,8,8 :N-methyl-N,N,N-trioctylammonium P 4,4,4,12 : Tributyldodecylphosphonium P 6,6,6,14 : Trihexyltetradecylphosphonium [FSI]: Bis(fluorosulfonyl)imide [TFSI]: Bis(trifluoromethanesulfonyl)imide [FEP]: Tris(pentafluoroethyl)trifluorophosphate

[0087] As can be seen from Table 1, ionic liquids containing cations with alkyl groups having a relatively large number of carbon atoms, and ionic liquids containing anions with fluorine atoms and relatively large molecular sizes (e.g., [FSI], [TFSI], [FEP]) tend to exhibit hydrophobicity.

[0088] (Example 1) First, a dispersion containing polydimethylsiloxane was prepared, and the resulting dispersion was coated onto a porous support. Polysulfone (PSF) was used as the porous support. The dispersion was coated by a dip coating method. Next, the resulting coated film was heated at 120°C for 2 minutes and dried to produce a laminate of the porous support and the intermediate layer. The surface of the intermediate layer was subjected to corona discharge treatment.

[0089] Next, dispersion A, containing 5 wt% polyether block amide (Pebax, manufactured by Arkema), dispersion B, containing 0.4 wt% graphene oxide, and an ionic liquid were mixed to obtain a mixture. Dispersion A contained isopropyl alcohol and water (weight ratio 70:30) in addition to polyether block amide. Dispersion B contained water in addition to graphene oxide. 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) was used as the ionic liquid. The resulting mixture was subjected to sonication for 1 hour, followed by stirring for 30 minutes to prepare a coating solution. The viscosity of the coating solution at 25°C was 0.20 Pa·s.

[0090] Next, the coating solution was applied onto the intermediate layer of the laminate described above. The coating solution was applied by spin coating. At this time, the spin coater was rotated at a rotation speed of 2000 rpm for 1 minute. Next, the obtained coating film was heated at 100°C for 15 minutes and dried to produce a separation functional layer. The thickness of the separation functional layer was approximately 3 μm. The content of polyether block amide in the separation functional layer was 7.83 wt%, the content of graphene oxide was 0.050 wt%, and the content of ionic liquid was 92.12 wt%. This obtained the separation film of Example 1.

[0091] (Comparative Examples 1-3) The separation membranes of Comparative Examples 1 to 3 were obtained by the same method as in Example 1, except that the type of ionic liquid, the presence or absence of graphene oxide, and the presence or absence of polyether block amide were changed as shown in Table 2.

[0092] [Characterization of separation membranes] Next, the separation coefficient α (CO2 / N2) for carbon dioxide relative to nitrogen and the carbon dioxide permeation rate T were measured for the separation membranes of the examples and comparative examples using the following method. First, the separation membrane was set in a metal cell and sealed with an O-ring to prevent leakage. Next, a mixed gas was injected into the metal cell so that it came into contact with the main surface of the separation functional layer side of the separation membrane. The mixed gas consisted substantially of carbon dioxide and nitrogen. The concentration of carbon dioxide in the mixed gas was 50 vol% under standard conditions. The temperature of the mixed gas injected into the metal cell was 30°C. The pressure of the mixed gas was 0.1 MPa. As a result, a permeate fluid was obtained from the main surface of the porous support side of the separation membrane. Based on the composition and weight of the obtained permeate fluid, the separation coefficient α and the carbon dioxide permeation rate T were calculated. The results are shown in Table 2.

[0093] [Table 2]

[0094] Table 2 shows that the separation membrane of Example 1, which has a separation functional layer containing graphene oxide, ionic liquid, and polymer, has a higher separation coefficient α for carbon dioxide relative to nitrogen and higher separation performance for mixed gases containing acidic gases compared to the separation membrane of the comparative example.

[0095] [X-ray diffraction measurement] Next, X-ray diffraction (XRD) measurements were performed on the separation functional layers of Example 1 and Comparative Example 1. The results are shown in Figure 4. Comparing Example 1 and Comparative Example 1, it can be seen that in Example 1, the peak originating from graphene oxide is located at a diffraction angle of 2θ = 11.77°. From this result, it can be seen that in Example 1, multiple graphene oxides are arranged in layers in the separation functional layer, and the interlayer distance is 0.751 nm. In graphene oxide, functional groups containing oxygen atoms tend to extend in a direction perpendicular to the plane direction of the graphene oxide (stacking direction). Considering that the length of the CO bond is about 0.191 nm, in Example 1, the shortest distance between two adjacent graphene oxides in the stacking direction is about 0.369 nm, which is about the same as the molecular size of nitrogen (0.364 nm). From this, it can be inferred that in Example 1, it was difficult for nitrogen molecules to pass between two adjacent graphene oxides in the stacking direction, and this suppressed the permeation of nitrogen molecules through the separation functional layer. [Industrial applicability]

[0096] The separation membrane of this embodiment is suitable for separating acidic gases from a gas mixture containing acidic gases. In particular, the separation membrane of this embodiment is suitable for separating carbon dioxide from off-gas in chemical plants or thermal power plants.

Claims

1. A separation membrane comprising a separation functional layer containing graphene oxide, an ionic liquid, and a polymer.

2. The separation membrane according to claim 1, wherein the ionic liquid is hydrophilic.

3. The separation membrane according to claim 1 or 2, wherein the ionic liquid contains imidazolium ions.

4. The separation membrane according to any one of claims 1 to 3, wherein the ionic liquid contains tetrafluoroborate.

5. The separation membrane according to any one of claims 1 to 4, wherein the content of the ionic liquid in the separation functional layer is 50 wt% or more.

6. The separation membrane according to any one of claims 1 to 5, wherein the polymer is compatible with both the graphene oxide and the ionic liquid.

7. The separation membrane according to any one of claims 1 to 6, wherein the polymer has polar groups.

8. The separation membrane according to claim 7, wherein the polar group comprises at least one selected from the group consisting of a hydroxyl group, an ether group, and an amide group.

9. The separation membrane according to any one of claims 1 to 8, wherein the polymer comprises a polyether block amide.

10. The separation membrane according to any one of claims 1 to 9, further comprising a porous support that supports the separation functional layer.

11. The separation membrane according to claim 10, further comprising an intermediate layer disposed between the separation functional layer and the porous support.

12. A separation membrane according to any one of claims 1 to 11, used for separating carbon dioxide from a mixed gas containing carbon dioxide and nitrogen.

13. A coating solution containing graphene oxide, an ionic liquid, and a polymer is applied to a substrate to obtain a coating film. Drying the aforementioned coating film, A method for producing a separation membrane, including the following:

14. The manufacturing method according to claim 13, wherein the viscosity of the coating solution at 25°C is 0.15 Pa·s or more.

15. A coating solution applied to a substrate in order to manufacture a separation membrane, A coating solution comprising graphene oxide, an ionic liquid, and a polymer.

16. The coating solution according to claim 15, wherein the viscosity of the coating solution at 25°C is 0.15 Pa·s or more.

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