Gas separation membrane manufacturing method

Abstract

To provide a production method of a gas separation membrane being more excellent in gas separation performance than a conventional gas separation membrane.SOLUTION: A production method of a gas separation membrane includes a separation layer formation step to form a separation layer on a base material by an atmospheric pressure plasma chemical vapor deposition method. The separation layer is a silica-based separation layer different in chemical composition or layer structure in a thickness direction. The separation layer formation step is a step A to form the silica-based separation layer by changing discharge gas composition and / or the concentration of a volatile organic silicon compound or a step B to form the silica-based separation layer by forming a vapor deposition layer using a discharge gas containing the volatile organic silicon compound, radiating plasma generated from the discharge gas without containing the volatile organic silicon compound on the surface of the vapor deposition layer and modifying at least the surface of the vapor deposition layer.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] Gas separation membranes that allow specific gases to permeate and separate from a gas mixture are known.

[0003] For example, Patent Document 1 proposes a gas separation membrane having a resin layer containing a compound having a siloxane bond.

[0004] Furthermore, as the gas separation membrane, one having a silica-based separation layer on a porous substrate is known.

[0005] As a method for forming the silica-based separation layer, in addition to a film formation method using a sol-gel process, a film formation method using atmospheric pressure plasma CVD (Chemical Vapor Deposition) is known. The atmospheric pressure plasma CVD method has advantages such as the ability to form films at room temperature and atmospheric pressure, and the ability to form large-area films by continuous processing because it does not require vacuum equipment.

[0006] For example, Patent Document 2 proposes a method for manufacturing a gas separation filter in which a separation layer is formed on a porous substrate by atmospheric pressure plasma chemical vapor deposition, in which a mixed gas of nitrogen and argon is introduced into a discharge section as a discharge gas to generate atmospheric pressure plasma, a volatile organic silicon compound is introduced below the discharge section and mixed with the atmospheric pressure plasma, a separation layer is formed on the porous substrate, and the nitrogen content in the discharge gas is 5.0 volume % or less. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-163871 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-131849 Summary of the Invention [Problem to be solved by the invention]

[0008] However, conventional gas separation membranes have insufficient gas separation performance, and there has been a demand for the development of gas separation membranes with superior gas separation performance to conventional membranes.

[0009] The present invention has been made in view of the above problems, and has an object to provide a method for producing a gas separation membrane that has superior gas separation performance to conventional gas separation membranes. [Means for solving the problem]

[0010] The present invention provides a method for producing a gas separation membrane, which includes a separation layer formation step of forming a separation layer on a substrate by atmospheric pressure plasma chemical vapor deposition, the separation layer is a silica-based separation layer whose chemical composition or layer structure varies in the thickness direction; The method for producing a gas separation membrane is characterized in that the separation layer formation step is either Step A, in which the silica-based separation layer is formed by changing the composition of a discharge gas and / or the concentration of a volatile organosilicon compound, or Step B, in which a vapor deposition layer is formed using a discharge gas containing a volatile organosilicon compound, and then the surface of the vapor deposition layer is irradiated with plasma generated from a discharge gas not containing a volatile organosilicon compound to modify at least the surface of the vapor deposition layer, thereby forming the silica-based separation layer.

[0011] In the step A, it is preferable that the composition of the discharge gas is changed from oxygen-lean to oxygen-rich continuously or stepwise.

[0012] In step A, it is preferable to reduce the concentration of the volatile organosilicon compound continuously or stepwise.

[0013] The silica-based separation layer preferably has an inorganic structure whose proportion increases from the substrate side toward the other side in the thickness direction.

[0014] The silica-based separation layer preferably has an increased content of Si atoms and oxygen atoms and a decreased content of carbon atoms from the substrate side toward the other side in the thickness direction.

[0015] The silica-based separation layer preferably has a multi-layer structure.

[0016] The silica-based separation layer preferably has at least a first separation layer stacked on the substrate and a second separation layer stacked on the first separation layer, and the content of Si atoms and oxygen atoms in the second separation layer is higher than the content of Si atoms and oxygen atoms in the first separation layer, and the content of carbon atoms in the second separation layer is lower than the content of carbon atoms in the first separation layer.

[0017] It is preferable that the silica-based separation layer has a C / Si ratio, which is the ratio of the number of carbon atoms to the number of Si atoms in the first separation layer, of 1.5 or more and 1.8 or less, and a C / Si ratio, which is the ratio of the number of carbon atoms to the number of Si atoms in the second separation layer, of 1.0 or more and less than 1.5. [Effects of the Invention]

[0018] The gas separation membrane obtained by the production method of the present invention has a silica-based separation layer whose chemical composition or layer structure varies in the thickness direction, and has better gas separation properties (selectivity) (particularly, CO2 / CH4 permeability ratio) than conventional gas separation membranes. The gas separation membrane obtained by the production method of the present invention is also characterized by excellent gas permeability (particularly, permeability of hydrogen and CO2). When the silica-based separation layer has an inorganic structure whose proportion increases continuously or stepwise from the substrate side to the other side in the thickness direction, a gas separation membrane with even better effects can be obtained. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a schematic diagram of a specific example of a separation layer forming apparatus used in atmospheric pressure plasma chemical vapor deposition. [Figure 2] FIG. 10 is a schematic diagram of another specific example of a separation layer forming apparatus used in atmospheric pressure plasma chemical vapor deposition. [Figure 3] 1 is a graph showing the permeability coefficients (He, N2, SF6) and separation coefficients α (He / SF6, N2 / SF6, He / N2) of the gas separation membranes produced in Example 5. [Figure 4] 1 is a graph showing the change in permeability coefficient (He, H 2 , CO 2 , N 2 , CH 4 , SF 6 ) before and after plasma irradiation of the vapor deposition layer surface in Example 6. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, an embodiment of the present invention will be described.

[0021] The method for producing a gas separation membrane of the present invention includes a separation layer formation step of forming a silica-based separation layer having a different chemical composition or layer structure in the thickness direction on a substrate by atmospheric pressure plasma chemical vapor deposition.

[0022] The substrate (support) is not particularly limited as long as it can support the silica-based separation layer, and may be a non-porous substrate or a porous substrate, but is preferably a porous substrate. The substrate may also be an inorganic substrate or an organic substrate such as a polymer membrane substrate, but is preferably a polymer membrane substrate.

[0023] Examples of materials for forming the inorganic substrate include alumina (α-Al2O3 (α-alumina), γ-Al2O3 (γ-alumina)), mullite, zirconia, titania, and ceramics made of composites of these.

[0024] Examples of materials for forming the polymer membrane substrate include polysulfone, polyarylethersulfone such as polyethersulfone, polyester, polyamide, polyimide, silicone, silicone rubber, polyurethane, polyethylene, polypropylene, polystyrene, polycarbonate, polyetheretherketone, polyphenylene oxide, polyacrylonitrile, polyvinyl fluoride, and polyvinylidene fluoride. Polysulfone or polyarylethersulfone is preferred, particularly from the viewpoint of chemical, mechanical, and thermal stability. The thickness of the polymer membrane substrate is typically about 50 to 500 μm, preferably 100 to 200 μm, but is not limited thereto. The polymer membrane substrate may be reinforced with a backing such as a woven fabric or nonwoven fabric.

[0025] When the polymer membrane substrate is a porous substrate, the porous substrate may have a symmetrical or asymmetrical structure, but from the viewpoint of achieving both the support function of the silica-based separation layer and the smoothness of the side surface on which the silica-based separation layer is formed, an asymmetrical structure is preferred. The average pore size of the side surface on which the silica-based separation layer is formed of the porous substrate is preferably 0.01 to 0.5 μm.

[0026] The method for producing a gas separation membrane of the present invention may include an intermediate layer forming step of forming an intermediate layer on the substrate before the separation layer forming step.

[0027] By forming an intermediate layer on a substrate and then forming a silica-based separation layer on the intermediate layer by atmospheric pressure plasma chemical vapor deposition, the thickness of the silica-based separation layer can be made uniform, thereby improving gas separation performance.

[0028] The intermediate layer may have either a non-porous structure or a porous structure, but preferably has a non-porous structure from the viewpoint of improving the smoothness of the silica-based separation layer and thereby improving the gas separation performance.

[0029] The material for forming the intermediate layer may be an inorganic material or an organic material. Examples of inorganic materials include silica, titania, alumina, and silica-zirconia. These may be used alone or in combination of two or more. Examples of organic materials include polysiloxanes such as polydimethylsiloxane, polydiethylsiloxane, polymethylphenylsiloxane, and polydimethyldiphenylsiloxane; 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. These may be used alone or in combination of two or more. Among these, polysiloxanes are preferred from the viewpoint of improving gas separation performance and gas permeability, and polydimethylsiloxane is more preferred.

[0030] The intermediate layer may include nanoparticles such as silica particles, titania particles, and alumina particles.

[0031] The thickness of the intermediate layer is usually 0.05 to 10 μm, and from the viewpoint of improving gas separation performance and gas permeability, it is preferably 0.05 to 5 μm, more preferably 0.05 to 3 μm.

[0032] When the intermediate layer has a porous structure, the pore size is not particularly limited, but is preferably 0.5 to 10 nm, more preferably 0.5 to 2 nm, from the viewpoint of improving gas separation performance and gas permeability.

[0033] The intermediate layer can be formed by a known method, for example, by applying a composition containing a material for forming the intermediate layer onto the substrate, followed by drying and baking.

[0034] The silica-based separation layer is a layer that has the function of separating gases with different molecular diameters by allowing gases with small molecular diameters to permeate from a mixed gas containing two or more gases with different molecular diameters and inhibiting the permeation of gases with large molecular diameters.

[0035] The silica-based separation layer is formed on the substrate or the intermediate layer by atmospheric pressure plasma chemical vapor deposition.

[0036] The separation layer deposition apparatus used in atmospheric pressure plasma chemical vapor deposition can be a known separation layer deposition apparatus, for example, the separation layer deposition apparatus 1 shown in FIG.

[0037] The raw material for the silica-based separation layer is not particularly limited as long as it can be chemically vapor deposited using atmospheric pressure plasma. Examples of the raw material include volatile organosilicon compounds such as hexamethyldisiloxane, trimethylethoxysilane, and methyltriethoxysilane. From the viewpoint of improving gas separation properties and gas permeability, hexamethyldisiloxane is preferred.

[0038] Discharge gas cylinder 2 is filled with a discharge gas (such as N2, Air, or O2), and carrier gas cylinder 3 is filled with a carrier gas (such as Ar). A carrier gas containing a volatile organosilicon compound is obtained by passing the carrier gas through bubbler 4 containing a liquid volatile organosilicon compound. The mixed gas, which is a mixture of the carrier gas containing the volatile organosilicon compound and the discharge gas, is then supplied to plasma generator 5. The volatile organosilicon compound is decomposed by atmospheric pressure plasma generated in discharge unit 6, and a silica-based separation layer is formed on substrate 7 by chemical vapor deposition. A silica-based separation layer with a uniform thickness can be obtained by depositing the silica-based separation layer while moving substrate 7. Furthermore, deposition may be performed multiple times (multiple cycles) to form a thick silica-based separation layer. An intermediate layer may be provided on substrate 7.

[0039] Alternatively, the separation layer deposition apparatus 1 shown in FIG. 2 may be used. The discharge gas cylinder 2 is filled with a discharge gas (such as N2, Air, or O2), and the carrier gas cylinder 3 is filled with a carrier gas (such as Ar). A carrier gas containing a volatile organosilicon compound is obtained by passing the carrier gas through a bubbler 4 containing a liquid volatile organosilicon compound. The mixed gas of the carrier gas containing the volatile organosilicon compound and the discharge gas is then supplied to a plasma generator 5. The volatile organosilicon compound is decomposed by atmospheric pressure plasma generated in the discharge unit 6, and a silica-based separation layer is formed on the substrate by chemical vapor deposition. The substrate is placed in the discharge unit 6, and deposition during discharge results in a silica-based separation layer with a uniform thickness. Deposition may be performed for a long period of time to form a thick silica-based separation layer. An intermediate layer may be provided on the substrate.

[0040] The separation layer forming step is either Step A, in which the silica-based separation layer is formed by changing the composition of the discharge gas and / or the concentration of the volatile organosilicon compound, or Step B, in which a vapor deposition layer is formed using a discharge gas containing a volatile organosilicon compound, and then the surface of the vapor deposition layer is irradiated with plasma generated from a discharge gas not containing a volatile organosilicon compound to modify at least the surface of the vapor deposition layer, thereby forming the silica-based separation layer.

[0041] <Process A> (1) A method of changing the composition of the discharge gas continuously or stepwise By varying the composition of the discharge gas continuously or stepwise, it is possible to form a silica-based separation layer whose chemical composition or layer structure varies continuously or stepwise in the thickness direction.

[0042] For example, when forming a silica-based separation layer having a three-layer structure consisting of a first separation layer, a second separation layer, and a third separation layer, N2 is used as the discharge gas when forming the first separation layer, Air is used as the discharge gas when forming the second separation layer, and O2 is used as the discharge gas when forming the third separation layer. Alternatively, a discharge gas containing N2 and O2 may be used as the discharge gas, and the mixture ratio of N2 and O2 may be changed when forming each of the first separation layer, the second separation layer, and the third separation layer.

[0043] By changing the composition of the discharge gas from oxygen-lean to oxygen-rich continuously or stepwise, it is possible to form a silica-based separation layer in which the proportion of inorganic structures increases continuously or stepwise from the substrate side to the other side in the thickness direction, specifically, a silica-based separation layer in which the contents of Si atoms and oxygen atoms increase continuously or stepwise from the substrate side to the other side in the thickness direction, and the content of carbon atoms decreases continuously or stepwise. This silica-based separation layer has superior gas separation properties and gas permeability.

[0044] (2) A method of continuously or stepwise changing the concentration of volatile organosilicon compounds in a mixed gas By varying the concentration of the volatile organosilicon compound in the mixed gas continuously or stepwise, it is possible to form a silica-based separation layer whose chemical composition or layer structure varies continuously or stepwise in the thickness direction.

[0045] For example, when forming a silica-based separation layer having a two-layer structure consisting of a first separation layer and a second separation layer, the concentration of the volatile organosilicon compound is increased (e.g., 125 to 800 ppm) when forming the first separation layer, and decreased (e.g., 50 to 100 ppm) when forming the second separation layer.

[0046] By continuously or stepwise decreasing the concentration of the volatile organosilicon compound in the mixed gas, it is possible to form a silica-based separation layer in which the proportion of inorganic structures increases continuously or stepwise from the substrate side to the other side in the thickness direction, specifically, a silica-based separation layer in which the contents of Si atoms and oxygen atoms increase continuously or stepwise from the substrate side to the other side in the thickness direction, and the content of carbon atoms decreases continuously or stepwise. This silica-based separation layer has superior gas separation properties and gas permeability.

[0047] <Process B> A deposition layer is formed using a discharge gas containing a volatile organosilicon compound, and then the surface of the deposition layer is irradiated with plasma generated from a discharge gas that does not contain a volatile organosilicon compound, thereby modifying at least the surface of the deposition layer, thereby forming a silica-based separation layer whose chemical composition or layer structure varies continuously or stepwise in the thickness direction.

[0048] By irradiating the surface of the vapor deposition layer with plasma, polymerization progresses closer to the surface, increasing the proportion of inorganic structures, making it possible to form a silica-based separation layer with a different chemical composition or layer structure in the thickness direction.

[0049] For example, after forming a deposition layer (a layer having a single layer structure) by a conventional method, the surface of the deposition layer is irradiated with plasma generated by ionizing molecules of a discharge gas (e.g., N2 / Ar, etc.).

[0050] By irradiating the surface of the vapor deposition layer with plasma, it is possible to form a silica-based separation layer in which the proportion of inorganic structures increases continuously or stepwise from the substrate side to the other side in the thickness direction, specifically, a silica-based separation layer in which the contents of Si atoms and oxygen atoms increase continuously or stepwise from the substrate side to the other side in the thickness direction, and the content of carbon atoms decreases continuously or stepwise. This silica-based separation layer has superior gas separation properties and gas permeability.

[0051] After the silica-based separation layer is formed on the substrate or the intermediate layer, it may be subjected to heat treatment (annealing).

[0052] The silica-based separation layer obtained by the production method of the present invention has a chemical composition or layer structure that varies in the thickness direction. The silica-based separation layer preferably has a proportion of inorganic structure that increases continuously or stepwise from the substrate side (the intermediate layer side if an intermediate layer is present) to the other side in the thickness direction, and more preferably has a proportion of Si atoms and oxygen atoms that increases continuously or stepwise and a proportion of carbon atoms that decreases continuously or stepwise from the substrate side (the intermediate layer side if an intermediate layer is present) to the other side in the thickness direction.

[0053] From the viewpoint of improving gas separation performance and gas permeability, the ratio of the number of oxygen atoms to the number of Si atoms, O / Si, on the surface of the silica-based separation layer is preferably less than 1.7, more preferably 1.65 or less, and even more preferably 1.60 or less. The lower limit of O / Si is usually 1.25 or more, preferably 1.30 or more, and more preferably 1.40 or more.

[0054] The silica-based separation layer may be a single layer or a multilayer structure of two or more layers. However, from the viewpoint of improving gas separation performance and gas permeability and from the viewpoint of ease of manufacture, a multilayer structure of two or more layers is preferable, and a two-layer structure or a three-layer structure is more preferable. Specifically, the silica-based separation layer has at least a first separation layer laminated on the substrate or the intermediate layer and a second separation layer laminated on the first separation layer, and the content of Si atoms and oxygen atoms in the second separation layer is preferably higher than the content of Si atoms and oxygen atoms in the first separation layer, and the content of carbon atoms in the second separation layer is preferably lower than the content of carbon atoms in the first separation layer. Furthermore, when the silica-based separation layer further has a third or more separation layers on the second separation layer, it is preferable that the content of Si atoms and oxygen atoms in each of the third or more separation layers increases stepwise, and the content of carbon atoms decreases stepwise.

[0055] From the viewpoint of improving gas separation performance and gas permeability, the ratio of the number of carbon atoms to the number of Si atoms in the first separation layer, C / Si, is preferably 1.5 or more and 1.8 or less, more preferably 1.5 or more and 1.7 or less, and the ratio of the number of carbon atoms to the number of Si atoms in the second separation layer, C / Si, is preferably 1.0 or more and less than 1.5, more preferably 1.2 or more and 1.4 or less.

[0056] The thickness of the silica-based separation layer (total thickness in the case of a multi-layer structure) is not particularly limited, but from the viewpoint of improving gas separation performance and gas permeability, it is preferably 0.01 to 2 μm, more preferably 0.1 to 1.5 μm, and even more preferably 0.5 to 1.2 μm.

[0057] The gas separation membrane obtained by the production method of the present invention preferably has a CO2 permeability at 25°C of 90 GPU or more, more preferably 95 GPU or more, even more preferably 100 GPU or more, even more preferably 130 GPU or more, even more preferably 150 GPU or more, even more preferably 200 GPU or more, and even more preferably 250 GPU or more.

[0058] Furthermore, the gas separation membrane obtained by the production method of the present invention preferably has a CO2 permeability at 150°C of 90 GPU or more, more preferably 100 GPU or more, even more preferably 150 GPU or more, even more preferably 200 GPU or more, even more preferably 250 GPU or more, and even more preferably 300 GPU or more.

[0059] Furthermore, the gas separation membrane obtained by the production method of the present invention preferably has a CO2 / CH4 permeability ratio at 25°C of 15 or more, more preferably 30 or more, even more preferably 35 or more, and even more preferably 40 or more.

[0060] Furthermore, the gas separation membrane obtained by the production method of the present invention preferably has a CO2 / CH4 permeability ratio at 150°C of 9 or more, more preferably 9.5 or more, even more preferably 10 or more, and even more preferably 12 or more.

[0061] Furthermore, the gas separation membrane obtained by the production method of the present invention preferably has an H2 permeability at 200°C of 1000 GPU or more, more preferably 3000 GPU or more, and even more preferably 5000 GPU or more.

[0062] Furthermore, the gas separation membrane obtained by the production method of the present invention preferably has an H2 / SF6 permeability ratio at 200°C of 100 or more, more preferably 500 or more, even more preferably 1000 or more, and even more preferably 5000 or more.

[0063] The gas separation membrane obtained by the production method of the present invention is not limited in shape, and may have any conceivable membrane shape, such as a flat membrane, a cylindrical membrane, or a spiral element membrane. [Example]

[0064] The present invention will be described below with reference to examples, but the present invention is not limited to these examples in any way.

[0065] Example 1 A coating solution containing polydimethylsiloxane (PDMS) was applied onto a porous polysulfone support (manufactured by Nitto Denko Corporation, CF-30K) by spin coating and dried to form an intermediate layer (thickness: 3 μm). Using a separation layer deposition device, a two-layer silica-based separation layer (total thickness: 1.2 μm) consisting of a first separation layer (thickness: 400 nm) and a second separation layer (thickness: 800 nm) was deposited on the intermediate layer by atmospheric pressure plasma CVD under the production conditions listed in Table 2, thereby producing a gas separation membrane.

[0066] The silica-based separation layer was subjected to elemental analysis and the gas permeability of the gas separation membrane was evaluated by the following methods. The results are shown in Table 1.

[0067] In the silica-based separation layer of Example 1, the content of Si atoms and oxygen atoms was higher in the second separation layer than in the first separation layer. Conversely, the content of carbon atoms was lower in the second separation layer than in the first separation layer. In other words, in the silica-based separation layer of Example 1, the proportion of inorganic structures was higher in the second separation layer than in the first separation layer.

[0068] Examples 2 to 4 A gas separation membrane was produced in the same manner as in Example 1, except that the production conditions shown in Table 2 were used in the production of the silica-based separation layer.

[0069] The silica-based separation layer was subjected to elemental analysis and the gas permeability of the gas separation membrane was evaluated by the following methods. The results are shown in Table 1.

[0070] In the silica-based separation layers of Examples 2 to 4, the second separation layer had a higher content of Si atoms and oxygen atoms than the first separation layer. Conversely, the second separation layer had a lower content of carbon atoms than the first separation layer. In other words, in the silica-based separation layers of Examples 2 to 4, the second separation layer had a higher proportion of inorganic structures than the first separation layer.

[0071] Comparative Example 1 A coating solution containing polydimethylsiloxane (PDMS) was spin-coated onto a porous polysulfone support (Nitto Denko Corporation, CF-30K) and dried to form an intermediate layer (thickness: 3 μm). The surface of the intermediate layer was then irradiated with plasma under the conditions listed in Table 2 to modify the surface of the intermediate layer and form a separation layer, thereby producing a gas separation membrane.

[0072] The gas permeability of the gas separation membrane was evaluated by the following method, and the results are shown in Table 1.

[0073] In the intermediate layer including the separation layer of Comparative Example 1, the content of Si atoms and oxygen atoms was higher at the surface of the separation layer than at the center of the intermediate layer. Conversely, the content of carbon atoms was lower at the surface of the separation layer than at the center of the intermediate layer. In other words, in the intermediate layer including the separation layer of Comparative Example 1, the proportion of inorganic structures was higher at the surface of the separation layer than at the center of the intermediate layer.

[0074] Comparative Examples 2 and 3 A coating solution containing polydimethylsiloxane (PDMS) was applied onto a porous polysulfone support (manufactured by Nitto Denko Corporation, CF-30K) by spin coating and dried to form an intermediate layer (thickness: 5 μm). Using a separation layer forming apparatus, a single silica-based separation layer (thickness: 1.2 μm) was formed on the intermediate layer by atmospheric pressure plasma CVD under the production conditions listed in Table 2, thereby producing a gas separation membrane.

[0075] The silica-based separation layer was subjected to elemental analysis and the gas permeability of the gas separation membrane was evaluated by the following methods. The results are shown in Table 1.

[0076] The silica-based separation layers of Comparative Examples 2 and 3 had the same contents of Si atoms, oxygen atoms, and carbon atoms in the thickness direction.

[0077] [Measurement and evaluation methods] (Elemental analysis of silica-based separation layer) The silica-based separation layer was subjected to elemental analysis using X-ray electron spectroscopy. A silicon wafer was used as the substrate, and a silica-based separation layer was formed by film formation under the same conditions as those for film formation on the porous support, but with varying concentrations of hexamethyldisiloxane. The elemental composition of the surface of the formed silica-based separation layer was then quantified.

[0078] (gas permeability) The gas permeability of the resulting gas separation membrane was evaluated using pure gases (CO2, CH4). The upstream side of the gas separation membrane was pressurized to atmospheric pressure or slightly elevated pressure (100-110 kPaG), and the permeation side, which had a known volume, was evacuated. After evacuating, the membrane was separated from the evacuation system, and the gas permeability was calculated from the rate of pressure rise (using the quasi-steady-state method).

[0079] [Table 1]

[0080] [Table 2]

[0081] Example 5 Using a separation layer deposition device, a three-layer silica-based separation layer consisting of a first separation layer, a second separation layer, and a third separation layer was deposited on an inorganic substrate (SiO2-ZrO2 / α-Al2O3) by atmospheric pressure plasma CVD under the following deposition conditions to produce a gas separation membrane. The permeability coefficients (He, N2, SF6) and separation factors α (He / SF6, N2 / SF6, He / N2) of the produced gas separation membrane are shown in Figure 3. Figure 3 shows that the produced gas separation membrane has excellent gas selectivity while maintaining gas permeability. <Membrane formation conditions for silica-based separation layer> Raw material monomer for silica-based separation layer: hexamethyldisiloxane (concentration: 26 ppm) Carrier gas: Ar Discharge gas: N2 (0.25 vol%) when forming the first separation layer, Air (0.25 vol%) when forming the second separation layer, O2 (0.25 vol%) when forming the third separation layer Applied voltage: 4.5 kV Input power: 3.2~3.7W Deposition temperature: 200℃ Number of deposition cycles: 2

[0082] Example 6 Using a separation layer deposition device, a single vapor deposition layer was deposited on a UF membrane by atmospheric pressure plasma CVD under the following deposition conditions. The surface of the vapor deposition layer was then irradiated with plasma under the following conditions to modify at least the surface of the vapor deposition layer, forming a silica-based separation layer and producing a gas separation membrane. Figure 4 shows the change in permeability coefficient (He, H, CO, N, CH, SF) before and after plasma irradiation. Figure 4 shows that gas selectivity was improved by irradiating the surface of the vapor deposition layer with plasma and modifying at least the surface of the vapor deposition layer. <Deposition layer deposition conditions> Raw material monomer for the deposition layer: hexamethyldisiloxane (flow rate: 1.3 × 10 -6 mol / s) Carrier gas: Ar Discharge gas: N2 (0.25 vol%) Input power: 10W Deposition temperature: 25℃ Number of deposition cycles: 4 <Plasma irradiation conditions> Carrier gas: Ar Discharge gas: N2 (0.25 vol%) Input power: 6W Temperature: 25℃ Number of plasma irradiation cycles: 3 [Industrial Applicability]

[0083] The gas separation membrane of the present invention can be used as a separation membrane that allows a specific gas to permeate and separate from a mixed gas. [Explanation of symbols]

[0084] 1: Separation layer film forming equipment 2: Discharge gas cylinder 3: Carrier gas cylinder 4: Bubbler 5: Plasma generator 6:Discharge part 7: Base material 8: Ground electrode 9: Internal electrode 10: High voltage power supply 11: Heater

Claims

1. A method for producing a gas separation membrane for gas separation, comprising: a separation layer forming step of forming a separation layer on a substrate by atmospheric pressure plasma chemical vapor deposition; the separation layer is a silica-based separation layer whose chemical composition or layer structure varies in the thickness direction; The separation layer forming step is either a step A in which the silica-based separation layer is formed by changing the composition of a discharge gas and / or the concentration of a volatile organosilicon compound, or a step B in which a vapor deposition layer is formed using a discharge gas containing a volatile organosilicon compound, and then the surface of the vapor deposition layer is irradiated with plasma generated from a discharge gas not containing a volatile organosilicon compound to modify at least the surface of the vapor deposition layer, thereby forming the silica-based separation layer.

2. A method for manufacturing a gas separation membrane as described in claim 1, wherein the gas separation membrane is used to separate a mixture of two or more gases selected from the group consisting of He, H 2 , CO 2 , N 2 , CH 4 and SF 6 .

3. The method for manufacturing a gas separation membrane according to claim 1, wherein the gas separation membrane is used to separate a mixed gas of CO 2 and CH 4 .

4. 4. The method for producing a gas separation membrane according to claim 1, wherein in step A, the composition of the discharge gas is changed continuously or stepwise from oxygen-lean to oxygen-rich.

5. 5. The method for producing a gas separation membrane according to claim 1, wherein in step A, the concentration of the volatile organosilicon compound is reduced continuously or stepwise.

6. The method for producing a gas separation membrane according to any one of claims 1 to 5, wherein the silica-based separation layer has an increasing proportion of inorganic structures in a thickness direction from the substrate side to the other side.

7. The method for producing a gas separation membrane according to any one of claims 1 to 6, wherein the silica-based separation layer has an increasing content of Si atoms and oxygen atoms and a decreasing content of carbon atoms in a thickness direction from the substrate side to the other side.

8. The method for producing a gas separation membrane according to any one of claims 1 to 7, wherein the silica-based separation layer has a multilayer structure.

9. The method for producing a gas separation membrane according to any one of claims 1 to 8, wherein the silica-based separation layer has at least a first separation layer laminated on the substrate and a second separation layer laminated on the first separation layer, the content of Si atoms and oxygen atoms in the second separation layer being higher than the content of Si atoms and oxygen atoms in the first separation layer, and the content of carbon atoms in the second separation layer being lower than the content of carbon atoms in the first separation layer.

10. 10. The method for producing a gas separation membrane according to claim 9, wherein the ratio of the number of carbon atoms to the number of Si atoms in the first separation layer, C / Si, is 1.5 or more and 1.8 or less, and the ratio of the number of carbon atoms to the number of Si atoms in the second separation layer, C / Si, is 1.0 or more and less than 1.5.

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