Composite membrane for gas separation and gas separation system using same

Abstract

Provided is a composite membrane for gas separation, having at least a porous support layer, a separation function layer and a coating layer in this order, and having He permeability at 25°C of 1.0 / m 2 s / Pa or more, wherein when He is a non-condensable gas and H2O is a condensable gas, and when nano-permporometry analysis is performed under a condition of a temperature of 40°C, He permeability at a relative humidity of 90% is 90% or more of He permeability at a relative humidity of 20%. According to the present invention, it is possible to provide: a composite membrane for gas separation, which is excellent in selectively separating gasses with small molecular diameters, such as hydrogen, helium, water vapor, and ammonia; a spiral-type composite membrane module for gas separation; and a gas separation system using the composite membrane and the spiral-type composite membrane module.

Description

Composite membrane for gas separation and gas separation system using the same

[0001] The present invention relates to a composite membrane for gas separation capable of selectively separating at least one component in a gas mixture, and a gas separation system using the same.

[0002] In recent years, hydrogen has been attracting attention as a clean energy source. Hydrogen is obtained by reforming and gasifying fossil fuels such as natural gas and coal, and removing unnecessary gases from the mixed gas containing hydrogen and carbon dioxide as its main components. Hydrogen can also be obtained by decomposing water using electricity or photocatalysis, and extracting only the hydrogen from the mixed gas containing hydrogen, oxygen, and water vapor. Hydrogen is also used in the Haber-Bosch process, which synthesizes ammonia. This method synthesizes ammonia by reacting hydrogen and nitrogen at high temperature and pressure, but requires a process to separate and recover the unreacted hydrogen and nitrogen at the production plant.

[0003] As a low-cost method for concentrating specific gases from mixed gases, membrane separation, which utilizes differences in the gas permeability of materials to selectively allow the target gas to pass through, is attracting attention.

[0004] Patent Document 1 proposes a method of improving the selective separation of gases by attaching a surfactant to a single-layer hollow fiber membrane. Non-Patent Document 1 describes a technology for improving the selective separation of helium and carbon dioxide by coating the surface of a polyamide composite membrane with polyphenylene oxide. Non-Patent Document 2 describes a method for improving the selective separation of methane and other gases by coating the surface of an RO membrane with polydimethylsiloxane.

[0005] Japanese Patent Application Publication No. 3-186327

[0006] Seung-Hak Choi and 2 others, 'Journal of Membrane Science', 553, 2018, p. 180-188 Jaesung Park, 2 others, 'Journal of Membrane Science', 604, 2020, 118009

[0007] However, conventional techniques have the problem that it is not possible to efficiently increase the permeation resistance of other gases such as oxygen, nitrogen, and methane, and it is not possible to achieve both high permeability for gases with small molecular diameters such as hydrogen, helium, water vapor, and ammonia, and high selective separation ability for other gases such as oxygen, nitrogen, and methane.

[0008] The present invention has been made in view of the above-mentioned conventional circumstances, and provides a composite membrane for gas separation that has high permeability to gases with small molecular diameters, such as hydrogen, helium, water vapor, and ammonia, and high selective separation ability from other gases, such as oxygen, nitrogen, and methane; a composite module for gas separation using the same; a gas separation system; and a gas separation method for separating helium (He) or hydrogen (H ２ The present invention aims to provide a method for purifying lactic acid bacteria.

[0009] The present inventors have conducted extensive research to solve the above problems and have succeeded in significantly improving the performance, particularly the selectivity, of composite membranes for gas separation.

[0010] (1) A composite membrane for gas separation having at least a porous support layer, a separation function layer, and a coating layer in this order, and having a helium permeability of 1.0 nmol / m at 25°C. ２ / s / Pa or more, and the non-condensable gas is helium and the condensable gas is H ２A composite membrane for gas separation, in which, when nanoperm porometry analysis is performed under conditions of 0 and a temperature of 40°C, the helium permeability at a relative humidity of 90% is 90% or more of the helium permeability at a relative humidity of 20%. (2) The composite membrane for gas separation according to (1), in which the average pore diameter Rc of the coating layer, determined by a positron beam method, is 0.6 nm or more and 1.2 nm or less. (3) The composite membrane for gas separation according to (1) or (2), in which, in a cross section of the composite membrane for gas separation, the penetration depth of the coating layer into the porous support layer is 0 to 150 nm. (4) The composite membrane for gas separation according to any one of (1) to (3), in which, when the helium and hydrogen permeabilities are measured by the pressure sensor method of ISO 15105-1 (2007), the helium permeability at 25°C is 1.10 to 1.65 times the hydrogen permeability. (5) A composite membrane for gas separation according to any one of (1) to (4), wherein the porous support layer is mainly composed of polysulfone or cellulose acetate. (6) A composite membrane for gas separation according to any one of (1) to (5), wherein the separation functional layer is mainly composed of crosslinked aromatic polyamide or polyimide. (7) A composite membrane for gas separation according to any one of (1) to (6), wherein the coating layer is mainly composed of silicone. (8) A composite membrane for gas separation according to any one of (1) to (7), wherein the coating layer has a thickness of 0.2 μm or more and 2.0 μm or less. (9) A composite membrane for gas separation according to any one of (1) to (7), wherein the average pore radius Rf [nm] and the pore diameter d of the composite membrane for gas separation, determined by Equation 2, are expressed as a function of the average pore radius Rf [nm] and the pore diameter d of the composite membrane for gas separation, determined by Equation 2. ＮＫＰ [nm] satisfies formula 1. The composite membrane for gas separation according to any one of (1) to (8). (where "i" is H ２ , N ２ and C.H. ４ "Pi" is the permeability of gas i at 25°C [nmol / m ２ / s / Pa], and P Ｈｅ is the permeability of helium gas at 25°C [nmol / m ２ / s / Pa], Mi is the molecular weight of gas i, M Ｈｅ is the molecular weight of helium gas, and d ｋ,ｉ is the kinetic molecular diameter of gas i [nm], and d ｋ,Ｈｅ(10) The composite membrane for gas separation according to any one of (1) to (9), wherein the separation functional layer has an average pore radius Rf [nm] of 0.2 nm or more and 0.4 nm or less. (11) A composite membrane for gas separation according to any one of (1) to (9), wherein the hydrogen permeability at 25°C is 1 nmol / m ２ / s / Pa or more 100nmol / m ２ (12) A composite membrane for gas separation according to any one of (1) to (10), having a viscosity of 1 / s / Pa or less. (12) A composite membrane for gas separation having at least a porous support layer, a separation function layer, and a coating layer, in this order, wherein the separation function layer is mainly composed of a crosslinked aromatic polyamide, and the coating layer is mainly composed of silicone. (13) The composite membrane for gas separation according to (12), wherein the coating layer has an average pore diameter Rc of 0.6 nm or more and 1.2 nm or less. (14) The composite membrane for gas separation according to (12) or (13), wherein the separation function layer has an average pore radius Rf [nm] of 0.2 nm or more and 0.4 nm or less. (15) A spiral-wound composite membrane module for gas separation, comprising the composite membrane for gas separation according to any one of (1) to (14), a feed-side channel material, and a permeate-side channel material wound around a central tube. (16) A gas separation system comprising the spiral-type composite membrane module for gas separation according to (15). (17) A method for purifying helium or hydrogen using the gas separation system according to (16).

[0011] According to the present invention, it is possible to provide a composite membrane for gas separation, a spiral-type composite membrane module for gas separation, and a gas separation system using the same, which have high selectivity for separating gases with small molecular diameters such as hydrogen, helium, water vapor, and ammonia.

[0012] 1 is a cross-sectional view of a composite membrane for gas separation according to one embodiment of the present invention; FIG. 2 is a perspective view showing a partially exploded spiral-wound composite membrane module for gas separation;

[0013] 1. Gas Separation Composite Membrane The gas separation composite membrane of the present invention is a gas separation composite membrane having at least a porous support layer, a separation functional layer, and a coating layer in this order, and has a helium permeability of 1.0 nmol / m at 25°C. ２ / s / Pa or more, and the non-condensable gas is helium and the condensable gas is H ２When nanoperm porometry analysis is performed under the conditions of 0 and a temperature of 40° C., the helium permeability at a relative humidity of 90% is 90% or more of the helium permeability at a relative humidity of 20%. The composite membrane for gas separation of the present invention will be described in detail below.

[0014] As shown in FIG. 1, the composite membrane for gas separation (51) of this embodiment comprises at least a porous support layer (52), a separation functional layer (53), and a coating layer (54) in this order. It may also have a substrate (55). Furthermore, this composite membrane for gas separation has a helium permeability of 1.0 nmol / m at 25° C. ２ / s / Pa or more, and the non-condensable gas is helium and the condensable gas is H ２ When nanoperm porometry analysis was performed under the conditions of 0 and a temperature of 40°C, the helium permeability at a relative humidity of 90% was 90% or more of the helium permeability at a relative humidity of 20%.

[0015] (Substrate) The composite membrane for gas separation of the present invention may have a substrate. The substrate does not need to have the ability to separate and permeate selectively gases, but it is sufficient that it can provide strength to the entire composite membrane for gas separation by supporting the separation functional layer.

[0016] The resin constituting the substrate is not particularly limited, but examples thereof include polyester polymers, polyamide polymers, polyolefin polymers, polysulfide polymers, and mixtures or copolymers thereof. Among these, polyester polymers and polysulfide polymers, which have high mechanical strength and thermal stability, are particularly preferred as the resin constituting the substrate.

[0017] The form of the substrate is not particularly limited, but nonwoven fabrics or woven or knitted fabrics such as long-fiber nonwoven fabrics and short-fiber nonwoven fabrics are preferred, with long-fiber nonwoven fabrics being particularly preferred. Here, long-fiber nonwoven fabric refers to a nonwoven fabric with an average fiber length of 300 mm or more and an average fiber diameter of 3 to 30 μm. The use of long-fiber nonwoven fabric allows for sufficient impregnation with the polymer solution that will form the porous support layer, thereby improving adhesion to the substrate and enhancing the physical stability of the porous support membrane. Furthermore, sufficient impregnation of the substrate with the polymer solution increases the rate of substitution with the nonsolvent during phase separation to form the porous support layer. As a result, the generation of macrovoids can be suppressed, contributing to improved gas permeation selectivity.

[0018] (Porous Support Layer) The composite membrane for gas separation of the present invention has a porous support layer. The porous support layer may be any layer that can permeate hydrogen or helium. The porous support layer may support the separation functional layer and thereby provide strength to the composite membrane for gas separation as a whole. The porous support layer may or may not have selective permeability for separating gases, but having selective permeability is more preferable because it can enhance the selectivity of the composite membrane for gas separation.

[0019] The size and distribution of the pores in the porous support layer are not particularly limited, but for example, the pore size may be uniform throughout the entire porous support layer, or may gradually increase from the surface of the porous support layer that contacts the separation function layer to the other surface.

[0020] The material of the porous support layer is not particularly limited, but examples thereof include homopolymers or copolymers of polysulfone, polyethersulfone, polyamide, polyaramid, polyester, cellulose-based polymer, vinyl polymer, polyphenylene sulfide, polyphenylene sulfide sulfone, polyphenylene sulfone, polyphenylene oxide, etc. These can be used alone or in combination. Examples of cellulose-based polymers include cellulose acetate and cellulose nitrate, and examples of vinyl polymers include polyethylene, polypropylene, polyvinyl chloride, and polyacrylonitrile.

[0021] Among these, the material for the porous support layer is preferably a homopolymer or copolymer such as polysulfone, polyamide, polyester, cellulose acetate, cellulose nitrate, polyvinyl chloride, polyacrylonitrile, polyphenylene sulfide, polyphenylene sulfide sulfone, etc. Cellulose acetate, polysulfone, polyphenylene sulfide sulfone, or polyphenylene sulfone is more preferred because of its high chemical, mechanical, and thermal stability, with polysulfone and cellulose acetate being particularly preferred.

[0022] The thicknesses of the substrate and the porous support layer affect the strength of the composite semipermeable membrane and the packing density when it is made into an element. From the viewpoint of obtaining good mechanical strength and packing density, the total thickness of the substrate and the porous support layer is preferably 30 to 300 μm, more preferably 100 to 220 μm. The thickness of the porous support layer is preferably 20 to 100 μm, more preferably 23 μm to 50 μm, and even more preferably 27 μm to 40 μm. The thickness of the substrate and the porous support layer can be determined by calculating the average thickness of 20 points measured at 20 μm intervals in a direction perpendicular to the thickness direction (in the plane direction of the membrane) during cross-sectional observation. If it is difficult to observe the thickness of the substrate or the thickness of the composite semipermeable membrane under a microscope, it may be measured using a thickness gauge. Since the thickness of the separation functional layer is very thin compared to the thickness of the porous support layer and can be ignored, the thickness of the porous support layer can be considered to be the thickness of the separation functional layer provided on the porous support layer. Therefore, the thickness of the porous support layer can be calculated by measuring the thickness of the composite semipermeable membrane with a digital thickness gauge and subtracting the thickness of the substrate from the thickness of the composite semipermeable membrane. As the digital thickness gauge, PEACOCK manufactured by Ozaki Seisakusho Co., Ltd. can be used.

[0023] (Separation functional layer) The material of the separation functional layer in the composite membrane for gas separation of the present invention is not particularly limited, but it is preferable to use cellulose, polyimide, polyamide, etc., and a composite membrane having a separation functional layer containing polyamide is preferred. When the separation functional layer is mainly composed of polyamide, it can be formed by performing interfacial polycondensation of a polyfunctional amine and a polyfunctional acid halide on a porous support layer.

[0024] "Polyamide is the main component" means that polyamide accounts for 50% by weight or more of the separation functional layer (100% by weight), and the amount of polyamide in 100% by weight of the separation functional layer is preferably 80% by weight or more, more preferably 90% by weight or more and 100% by weight or less.

[0025] The polyamide in the separation functional layer may be a wholly aromatic polyamide, a wholly aliphatic polyamide, or a polyamide containing both aromatic and aliphatic portions, but is preferably a wholly aromatic polyamide in order to achieve higher performance.

[0026] Specifically, the polyfunctional amine is a polyfunctional aromatic amine or a polyfunctional aliphatic amine. The polyfunctional aromatic amine refers to an aromatic amine having two or more amino groups selected from primary amino groups and secondary amino groups in one molecule, at least one of which is a primary amino group. The polyfunctional aliphatic amine refers to an aliphatic amine having two or more amino groups selected from primary amino groups and secondary amino groups in one molecule.

[0027] Examples of polyfunctional aromatic amines include polyfunctional aromatic amines in which two amino groups are bonded to an aromatic ring at the ortho, meta, or para positions, such as o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, o-xylylenediamine, m-xylylenediamine, p-xylylenediamine, o-diaminopyridine, m-diaminopyridine, and p-diaminopyridine.

[0028] Examples of polyfunctional aliphatic amines include ethylenediamine, 1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane, piperazine, 2-methylpiperazine, 2,4-dimethylpiperazine, 2,5-dimethylpiperazine, 2,6-dimethylpiperazine, etc. These polyfunctional amines may be used alone or in combination of two or more.

[0029] The polyfunctional acid halide specifically refers to a polyfunctional aromatic acid halide or a polyfunctional aliphatic acid halide.

[0030] The polyfunctional acid halide refers to an acid halide having at least two halocarbonyl groups in one molecule. For example, a trifunctional acid halide may be trimesoyl chloride, and a bifunctional acid halide may be biphenyldicarboxylic acid dichloride, azobenzenedicarboxylic acid dichloride, terephthalic acid chloride, isophthalic acid chloride, and the like.

[0031] In consideration of the reactivity with polyfunctional amines, the polyfunctional acid halide is preferably a polyfunctional acid chloride. In consideration of the selectivity and heat resistance of the gas separation composite membrane, the polyfunctional acid halide is preferably a polyfunctional acid chloride having 2 to 4 carbonyl chloride groups in one molecule.

[0032] Among these, trimesoyl chloride is more preferred from the viewpoints of availability and ease of handling. These polyfunctional acid halides may be used alone or in combination of two or more.

[0033] The polycondensation reaction is specifically interfacial polycondensation.

[0034] In order to achieve higher performance, the separation functional layer of the present invention preferably contains a crosslinked aromatic polyamide as its main component. The crosslinked aromatic polyamide can be formed by interfacial polycondensation of a polyfunctional aromatic amine and a polyfunctional aromatic acid halide.

[0035] In the separation functional layer, the thin film may have a pleated structure having concave and convex portions. When the thin film has a pleated structure, the surface area having the separation function of the membrane increases relative to the membrane area, thereby increasing the gas permeability.

[0036] (Coating layer) The composite membrane for gas separation of the present invention has a coating layer on the separation functional layer. The separation functional layer contains a small number of regions with significantly high gas permeability, such as coarse pores and defects. In these regions, the contribution of molecular sieving to separation is small, and the selective separation ability for gases with small molecular diameters, such as hydrogen, helium, water vapor, and ammonia, is low. Reducing the contribution of regions with low selective separation ability, such as coarse pores and defects, is important for improving the selective separation ability of the entire membrane.

[0037] By forming a coating layer on the separation functional layer, it is possible to suppress gas permeation through large pores and defects. The coating layer significantly suppresses the permeation of oxygen, nitrogen, methane, etc., but has little effect on the permeation of light gases such as hydrogen and helium, thereby significantly improving selective separation.

[0038] The coating layer does not necessarily need to cover the entire surface of the separation functional layer; there may be cases where the coating layer is partially missing due to uneven coating when forming the coating layer, or where the coating layer is formed only on surfaces with particularly large pores or defects.

[0039] The coating layer can penetrate into the separation functional layer and the support layer. When the coating layer components penetrate into the support layer, they block the gas permeation path, tending to reduce permeability. On the other hand, reducing the adhesive strength between the functional layer and the support layer, or between the support layer and the substrate, or destroying the support layer structure, can cause gas to leak through the voids and reduce selectivity. Therefore, it is preferable that the coating layer penetrates into the support layer as little as possible. The penetration depth of the coating layer into the support layer depends on the structure of the coating layer and the support layer, but this can be determined by mapping the elements contained only in the support layer and only in the coating layer using TEM-EDX (transmission electron microscope-energy dispersive X-ray spectroscopy), or by performing component analysis in the depth direction using TOF-SIMS (time-of-flight secondary ion mass spectrometry). When the support layer is polysulfone and the coating layer is silicone, TEM-EDX is used to map the S contained in the polysulfone and the Si contained in the coating layer, and the penetration depth is determined within the overlapping range. In this case, the overlap of Si and S, that is, the penetration thickness, is preferably 0 to 150 nm, more preferably 0 to 130 nm, and even more preferably 0 to 100 nm.

[0040] In the composite membrane for gas separation of the present invention, the coating layer formed by the positron beam method preferably has an average pore diameter Rc [nm] of 0.6 nm to 1.2 nm, more preferably 0.7 nm to 1.0 nm, and even more preferably 0.75 nm to 0.85 nm. By setting the average pore diameter Rc [nm] of the coating layer to 0.6 nm or more, it is possible to maintain as high a permeability as possible for gases with small molecular diameters, such as hydrogen, helium, water vapor, and ammonia, while by setting it to 1.2 nm or less, it is possible to effectively suppress the permeation of oxygen, nitrogen, methane, and the like, which are caused by large pores and defects in the functional layer.

[0041] The positron beam method is one of the positron annihilation lifetime measurement methods, and measures the time from when a positron is incident on a sample until it annihilates. From the annihilation time, it is a method for non-destructively evaluating information on the size, number density, and size distribution of vacancies of approximately 0.1 to 10 nm. A radioisotope ( ２２ This method differs from the usual positron annihilation method in that it uses a positron beam instead of Na, making it possible to measure thin films with a thickness of several hundred nanometers. The average vacancy diameter Rc [nm] of the coating layer can be determined from the positron annihilation lifetime τ when positrons are implanted at an energy of 1 keV through the surface having the coating layer.

[0042] The average pore diameter Rc [nm] of the coating layer of the composite membrane for gas separation of the present invention is calculated based on the above-mentioned positron annihilation lifetime τ from the following formula 3. Formula 3 shows the relationship when it is assumed that orthopositronium (o-Ps) is present in pores with an average pore diameter Rc in an electron layer with a thickness ΔR, and ΔR has been empirically determined to be 0.166 nm (details are described in Nakanishi et al., Journal of Polymer Science, Part B: Polymer Physics, Vol. 27, p. 1419, John Wiley & Sons, Inc. (1989)).

[0043]

[0044] The material for forming the coating layer may be an organic material such as a silicone resin, a polyolefin resin, polyvinyl alcohol, or polyurethane, or a metal-organic framework such as MOF (Metal Organic Framework), or a metal-based material using palladium or a palladium alloy as a hydrogen permeable material. Polysiloxane is preferred from the viewpoints of availability, ease of handling, and the fact that the average pore diameter Rc [nm] of the material satisfies the above-mentioned range.

[0045] The thickness of the coating layer is preferably 0.2 μm or more and 2.0 μm or less, more preferably 0.5 μm or more and 1.5 μm or less, and even more preferably 0.7 μm or more and 1.2 μm or less. By setting the thickness to 0.2 μm or more, defects in the coating layer due to unevenness in the separation functional layer or uneven coating thickness can be prevented. By setting the thickness to 2.0 μm or less, the reduction in gas permeability due to the coating layer can be minimized, and high gas permeability can be maintained. The coating layer thickness can be determined by observing the cross-section of the gas separation composite membrane using a scanning electron microscope and analyzing the obtained cross-sectional image. The freeze-fracturing method is used to prepare the observation sample. Specifically, a method can be used in which the sample is frozen using a refrigerant such as liquid nitrogen and the cross-section is exposed using a razor or microtome. Image analysis software such as ImageJ or Mac-View can be used for image analysis.

[0046] Si in a region at a depth of 0 to 50 nm from the surface on the coating layer side, as detected by time-of-flight secondary ion mass spectrometry (TOF-SIMS) － The peak is preferably 10,000 counts or more, more preferably 15,000 counts or more, and even more preferably 20,000 counts or more. － When the peak is 10,000 counts or more, a coating having a sufficient thickness for suppressing permeation through the large pores in the separation functional layer can be formed.

[0047] (Gas Permeability of Composite Membrane for Gas Separation) The composite membrane for gas separation of the present invention preferably has a helium permeability at 25°C of 1.10 to 1.65 times, more preferably 1.20 to 1.60 times, and even more preferably 1.30 to 1.50 times, the hydrogen permeability.

[0048] The kinetic molecular diameter (also called the dynamic molecular diameter) of helium is 0.260 nm, and that of hydrogen is 0.289 nm, meaning that helium molecules are slightly smaller than hydrogen. The greater the difference between the helium permeability and hydrogen permeability, the more small pores are distributed in the gas separation composite membrane, which increases the difference in permeability depending on the kinetic molecular diameter of the gas, and also increases the selective separation ability for oxygen, nitrogen, and methane.

[0049] When the helium permeability is 1.10 times or more the hydrogen permeability, selective separation from gases with large molecular diameters can be achieved by screening according to the molecular diameter of the gas, and when it is 1.65 times or less, it is possible to prevent a decrease in hydrogen permeability due to excessively small pores and inhibition of hydrogen permeation due to low hydrogen solubility.

[0050] The hydrogen permeability at 25°C is 1 nmol / m ２ / s / Pa or more 100nmol / m ２ / s / Pa or less is preferable, and 5 nmol / m ２ / s / Pa or more 60nmol / m ２ / s / Pa or less is more preferable, and 10 nmol / m ２ / s / Pa or more 40nmol / m ２ / s / Pa or less is more preferable. ２ / s / Pa or more, the membrane area required for hydrogen separation can be reduced, and ２ By keeping the pressure at 1 / s / Pa or less, it is possible to suppress polarization on the membrane surface when hydrogen permeates under high pressure conditions, and to prevent a decrease in separation performance.

[0051] The composite membrane for gas separation of the present invention separates non-condensable gases into helium and condensable gases into H ２When nanoperm porometry analysis is performed under the conditions of 0 and a temperature of 40°C, the helium permeability at a relative humidity of 90% is 90% to 100% of the helium permeability at a relative humidity of 20%, more preferably 95% or more, even more preferably 96% or more, and particularly preferably 97% or more.

[0052] Nanoperm porometry is an analytical technique that can measure the pore size distribution from 0.5 nm to 50 nm based on the relationship with the capillary condensation diameter by supplying a mixture of condensable and non-condensable gases to a measurement sample, varying the relative pressure of the condensable gas, and measuring the change in the amount of non-condensable gas permeating from the sample. The capillary condensation diameter is 1.2 nm at a temperature of 40°C and a relative humidity of 20%, and 20 nm at a temperature of 40°C and a relative humidity of 90%. When the helium permeability at a relative humidity of 90% is 90% or more of the helium permeability at a relative humidity of 20%, the contribution of capillary condensation diameters of about 1.2 nm to about 20 nm to the helium permeability is 10% or less, meaning that there are few coarse pores of nano-size or larger. The smaller the permeation contribution of coarse pores, the less undesirable permeation of other gases such as oxygen, nitrogen, and methane occurs due to the coarse pores, and high separation performance can be achieved.

[0053] Here, when there are few coarse pores, the difference between the helium permeability at a relative humidity of 90% and that at a relative humidity of 20% may be only at the error level, and the helium permeability at 90% relative humidity may be 100% or more of the helium permeability at 20% relative humidity. In this case, it is defined as 100%. Furthermore, when there are many micropores that are not suitable for gas permeation, there is no difference between the helium permeability at 90% relative humidity and that at 20% relative humidity. Therefore, the helium permeability at 25°C in the present invention is 1.0 nmol / m ２ / s / Pa or more.

[0054] (Rf and d ＮＫＰ The composite membrane for gas separation of the present invention has an average pore radius Rf [nm] of the separating functional layer and a pore diameter d of the composite membrane for gas separation, which is determined by Equation 2. ＮＫＰ It is preferable that [nm] satisfies the formula 1.

[0055]

[0056]

[0057] (where "i" is H ２ , N ２ , C.H. ４ "Pi" is the permeability of gas i at 25°C [nmol / m ２ / s / Pa], and P Ｈｅ is the permeability of helium gas at 25°C [nmol / m ２ / s / Pa], Mi is the molecular weight of gas i, M Ｈｅ is the molecular weight of helium gas, and d ｋ,ｉ is the kinetic molecular diameter of gas i [nm], and d ｋ,Ｈｅ is the kinetic molecular diameter of helium gas [nm].)

[0058] The average pore radius Rf [nm] of the separation functional layer can be calculated from pore size analysis of the separation functional layer observed by a positron beam method or a scanning transmission electron microscope (hereinafter referred to as "STEM").

[0059] The positron beam method is one of the positron annihilation lifetime measurement methods, and measures the time from when a positron is incident on a sample until it annihilates. From the annihilation time, it is a method for non-destructively evaluating information on the size, number density, and size distribution of vacancies of approximately 0.1 to 10 nm. A radioisotope ( ２２ This method differs from the usual positron annihilation method in that it uses a positron beam instead of Na, making it possible to measure thin films with a thickness of about several hundred nanometers. The average pore radius Rf [nm] of the separation functional layer can be determined from the positron annihilation lifetime τ when positrons are implanted at an energy of 1 keV from the surface having the separation functional layer.

[0060] The average pore radius Rf [nm] of the separation functional layer of the gas separation composite membrane of the present invention is calculated based on the positron annihilation lifetime τ described above, using the following formula 4. Formula 4 shows the relationship when it is assumed that orthopositronium (o-Ps) is present in pores of average pore radius Rf in an electron layer of thickness ΔR, and ΔR has been empirically determined to be 0.166 nm (details are described in Nakanishi et al., Journal of Polymer Science, Part B: Polymer Physics, Vol. 27, p. 1419, John Wiley & Sons, Inc. (1989)).

[0061]

[0062] For STEM analysis, the sample, from which the substrate and support layer have been removed, is transferred to a TEM observation grid and measured using scanning electron microscopy (SEM) with the STEM and a secondary electron detector attached to the STEM instrument. The acquired STEM image is deconvolved using DeConvHAADF (HREM Research Inc.) to highlight the pores and polyamide structure. Next, binarization is performed using ImageJ, and particle size analysis is performed to quantitatively analyze the number and size of pores in each region. This analysis allows the pore size and area of ​​each pore to be calculated as the number of pixels in the image.

[0063] The average pore radius Rf [nm] of the separation functional layer is preferably 0.2 nm or more and 0.4 nm or less, more preferably 0.22 nm or more and 0.35 nm or less, and even more preferably 0.24 nm or more and 0.30 nm or less. When the average pore radius Rf [nm] of the separation functional layer is 0.2 nm or more, the permeability of the gas to be transmitted through the membrane can be increased, and when it is 0.4 nm or less, it becomes possible to exhibit selective separation properties according to the molecular diameter of the gas.

[0064] The pore diameter d of the composite membrane for gas separation of the present invention ＮＫＰ[nm] is calculated from the following (Equation 2) based on the NKP (Normalized-Knudsen-based Permeance) method. The NKP method measures the membrane permeation flow rates of various non-condensable gases with different molecular diameters, plots the kinetic molecular diameter of the gas on the horizontal axis and the membrane permeation flow rate on the vertical axis, and performs curve fitting using (Equation 2) to determine the pore diameter d ＮＫＰ In this specification, the non-condensable gases are helium, hydrogen, N ２ , C.H. ４ Four types of gases are used (details are described in Lie Meng et al., Journal of Membrane Science, Vol. 496, pp. 211-218, Department of Chemical Engineering, Graduate School of Engineering, Hiroshima University (2015)).

[0065]

[0066] Generally, the separation functional layer of a composite membrane for gas separation has a pore size distribution. Ideally, it would have only appropriate pores with pore sizes appropriate for excellent target gas selectivity. However, in reality, it often has coarse pores with low selectivity. Therefore, in order to improve selectivity, it is important to reduce the contribution of coarse pores.

[0067] In a membrane in which the contribution of coarse pores in the separation functional layer is reduced, the pore diameter d calculated by the NKP method is the pore diameter (2Rf) calculated from the average pore radius Rf [nm] of the separation functional layer. ＮＫＰ The pore diameter d calculated by the NKP method [nm] becomes smaller. ＮＫＰ The pore diameter d [nm] is preferably 0.60 to 0.90 times the pore diameter (2Rf) calculated from the average pore radius Rf [nm] of the separation functional layer, in other words, satisfies formula 1, more preferably 0.65 to 0.85 times, and even more preferably 0.70 to 0.80 times. ＮＫＰ When the "pore diameter d / pore diameter (2Rf)" is 0.60 times or more, the permeation of gases with small molecular diameters such as hydrogen, helium, water vapor, and ammonia can be increased. ＮＫＰBy setting the ratio of the pore diameter (2Rf) to 0.90 or less, the selectivity can be increased.

[0068] Methods for reducing the contribution of coarse pores in the separation functional layer, i.e., methods for satisfying formula 1, include coating the surface of the separation functional layer, adsorption of foreign substances to the functional layer and / or porous support layer, densifying the support membrane by improving the manufacturing method, compacting the porous support layer by applying pressure, etc. Providing gas permeation resistance to locations other than the separation functional layer using these methods is important for reducing the contribution of coarse pores.

[0069] Coarse pores have low gas permeation resistance and therefore significantly high gas permeability. On the other hand, appropriate pores have much higher gas permeation resistance and lower gas permeability than coarse pores. When gas permeation resistance is imparted to a location other than the separation functional layer using the above-mentioned method, gas permeation through the coarse pores is significantly suppressed, but the effect on permeation through appropriate pores is small, making it possible to reduce the contribution of gas permeation through the coarse pores and improving the selective separation properties of the entire membrane.

[0070] In the composite membrane for gas separation of the present invention, the contact angle between the coating layer surface and pure water in air is preferably 50° or more and 130° or less. A contact angle of 50° or more can suppress gas permeation through the coarse pores, significantly suppressing the permeation of oxygen, nitrogen, methane, etc. A contact angle of 130° or less can suppress a decrease in the permeability of light gases such as hydrogen and helium, thereby achieving high selective separation. A contact angle of 80° or more and 130° or less is more preferable, and a contact angle of 100° or more and 130° or less is particularly preferable.

[0071] The contact angle here refers to the static contact angle, and in accordance with ISO 19403-1 (2017), 3.0 μL of distilled water was dropped onto the coating layer side of the composite membrane for gas separation, and the contact angle (the angle between the tangent to the droplet and the solid surface) was measured one second after the water droplet was dropped. When pure water is dropped onto the surface of the coating layer, the following equation 5, known as the "Young's equation," holds true.

[0072]

[0073] (where γ Ｓ is the surface tension of the coating layer, γ Ｌ is the surface tension of pure water, γＳＬ is the interfacial tension between the coating layer and pure water. When this formula is satisfied, the angle θ between the tangent to the pure water and the surface of the coating layer is called the contact angle. The contact angle can be measured using a widely available device, for example, a Contact Angle meter (manufactured by Kyowa Interface Science Co., Ltd.).

[0074] The contact angle gradually decreases over time. In the present invention, when the contact angle 1 second after a drop of pure water is deposited on the surface of the coating layer is defined as X and the contact angle 30 seconds after the drop is Y, the following formula 6 holds true:

[0075]

[0076] Y / X is preferably 0.8 or more and 1 or less, more preferably 0.9 or more and 1 or less, and particularly preferably 0.95 or more and 1 or less. When Y / X is within this range, it is possible to promote permeation of light gases such as hydrogen and helium, and to suppress permeation of gases such as oxygen and nitrogen, thereby achieving high selective separation properties.

[0077] 2. Method for Producing Composite Membrane for Gas Separation Next, an example of a method for producing the composite membrane for gas separation will be described.

[0078] (Formation of Support Membrane) A laminate of a substrate and a porous support layer is referred to as a support membrane, and this case will be described. In the example given below, the method for forming the support membrane includes a step of preparing a polymer solution by dissolving a polymer, which is a component of the porous support layer, in a good solvent for the polymer, a step of applying the polymer solution to the substrate, and a step of wet-coagulating the polymer by immersing the polymer solution in a coagulation bath. The coagulated polymer corresponds to the porous support layer.

[0079] When at least one of polysulfone and polyethersulfone is used as the polymer, a polymer solution is obtained by dissolving it in N,N-dimethylformamide (DMF).Water is preferably used as the coagulation bath.

[0080] Aramid, an example of a polymer, can be obtained by solution polymerization or interfacial polymerization using acid chlorides and diamines as monomers. In solution polymerization, aprotic organic polar solvents such as N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), and dimethylacetamide (DMAc) can be used as solvents. When acid chlorides and diamines are used as monomers to produce polyamides, hydrogen chloride is a by-product. To neutralize the hydrogen chloride, inorganic neutralizing agents such as calcium hydroxide, calcium carbonate, and lithium carbonate, as well as organic neutralizing agents such as ethylene oxide, propylene oxide, ammonia, triethylamine, triethanolamine, and diethanolamine, are used.

[0081] (Formation of Separation Functional Layer) Next, the process of forming the separation functional layer will be described. Below, a separation functional layer made of polyamide, which is an example of a separation functional layer, will be described. The separation functional layer made of polyamide is formed by forming polyamide on the support membrane through interfacial polycondensation of a polyfunctional amine and a polyfunctional acid halide.

[0082] More specifically, the process for forming the separation functional layer includes the following steps: (a) applying an aqueous solution containing a polyfunctional amine onto a porous support layer, and (b) after step (a), applying an organic solvent solution containing a polyfunctional acid halide onto the porous support layer.

[0083] In step (a), the concentration of the polyfunctional amine in the aqueous polyfunctional amine solution is preferably in the range of 0.1 to 20% by weight, more preferably in the range of 0.5 to 15% by weight, which allows for sufficient selective separation and gas permeability.

[0084] The polyfunctional amine aqueous solution may contain a surfactant, an organic solvent, an alkaline compound, an antioxidant, etc., as long as it does not interfere with the reaction between the polyfunctional amine and the polyfunctional acid halide. The surfactant has the effect of improving the wettability of the support membrane surface and reducing the interfacial tension between the polyfunctional amine aqueous solution and the nonpolar solvent.

[0085] The aqueous polyfunctional amine solution is preferably applied uniformly and continuously to the porous support layer. Application refers to contacting the porous support layer with the aqueous polyfunctional amine solution, specifically by coating the surface of the porous support layer with the aqueous polyfunctional amine solution or by immersing a support membrane in the aqueous polyfunctional amine solution. Examples of coating methods include dripping, spraying, and roller application.

[0086] The time from when the aqueous polyfunctional amine solution is applied to the porous support layer until the solution is drained or when the polyfunctional acid halide is applied (i.e., the contact time between the porous support layer and the aqueous polyfunctional amine solution) is preferably from 1 second to 10 minutes, and more preferably from 10 seconds to 3 minutes.

[0087] After the polyfunctional amine aqueous solution is applied to the porous support layer, the solution is drained off so that no droplets remain on the porous support layer. Residual droplets can cause membrane defects, which can lead to reduced separation performance, but draining the solution can prevent this. Methods that can be used include vertically holding the support membrane after application of the polyfunctional amine aqueous solution to allow the excess solution to flow naturally, or spraying a stream of nitrogen or other air from an air nozzle to forcibly drain the solution.

[0088] In step (b), the concentration of the polyfunctional acid halide in the organic solvent solution is preferably in the range of 0.01% by weight to 10% by weight, more preferably in the range of 0.02% by weight to 2.0% by weight, because a concentration of 0.01% by weight or more ensures a sufficient reaction rate, and a concentration of 10% by weight or less can suppress the occurrence of side reactions.

[0089] The organic solvent is preferably immiscible with water, dissolves the polyfunctional acid halide, does not destroy the support film, and is inert to the polyfunctional amine compound and the polyfunctional acid halide. Preferred examples include hydrocarbon compounds such as n-hexane, n-octane, n-nonane, n-decane, n-undecane, n-dodecane, n-tridecane, isooctane, isodecane, and isododecane, as well as mixtures thereof.

[0090] The method for applying the polyfunctional acid halide solution to the porous support layer may be the same as the method for applying the polyfunctional amine aqueous solution to the porous support layer, except that the polyfunctional acid halide solution is preferably applied to only one side of the porous support layer, and therefore is preferably applied by coating rather than dipping.

[0091] At this time, the porous support layer contacted with the organic solvent solution of the polyfunctional acid halide may be heated. The temperature for the heat treatment is 50°C or higher and 180°C or lower, preferably 60°C or higher and 160°C or lower. Heating at 60°C or higher can compensate for the decrease in reactivity associated with the consumption of monomers in the interfacial polymerization reaction by the thermal reaction acceleration effect. Heating at 160°C or lower can prevent the solvent from completely volatilizing, which would significantly reduce the reaction efficiency. Furthermore, the heat treatment time for each time is preferably 5 seconds or higher and 600 seconds or lower. A time of 5 seconds or longer can achieve the reaction acceleration effect, while a time of 600 seconds or shorter can prevent the solvent from completely volatilizing.

[0092] Furthermore, a polyfunctional halide may be added during the interfacial polycondensation reaction to promote consumption of the polyfunctional amine.

[0093] (Formation of Coating Layer) Next, the process of forming the coating layer will be described. The coating layer is preferably formed by contacting the separation functional layer with a solution or emulsion containing a substance that forms the coating layer. The contact method is not particularly limited, but it is preferable to coat the separation functional layer with a solution or emulsion containing a substance that forms the coating layer, as this makes it easy to control the thickness of the coating layer. Other contact methods include application from the porous support layer side and immersion of the membrane in a solution.

[0094] The coating method is not particularly limited, but microgravure, bar coating, spin coating, and the like, which are suitable for thin film coating, are preferred.

[0095] Examples of solvents for the solution or emulsion containing the substance that forms the coating layer include water, alcohols such as ethanol, 2-butanol, and isopropanol, alkanes such as pentane, hexane, heptane, octane, nonane, decane, and dodecane, benzene, toluene, and chloroform, with water, ethanol, and hexane being preferred in that they cause less deterioration of the separation functional layer and the porous support layer. When water is used as the solvent, the pH of the aqueous solution is preferably in the range of 3 to 11 in order to minimize deterioration of the composite membrane for gas separation.

[0096] As described above, the coating layer can be formed from organic materials such as silicone resin, polyolefin resin, polyvinyl alcohol, and polyurethane, as well as metal-organic frameworks (MOFs), and metal-based materials using palladium or palladium alloys as hydrogen permeable materials. From the viewpoints of availability, ease of handling, and the fact that the average pore diameter Rc [nm] satisfies the above-mentioned range, it is preferable to use polysiloxane as the main component. The polysiloxane may be contacted with the separation functional layer as a polysiloxane, or the polysiloxane may be formed after contact. Examples of such reagents include methyltris(methylethylketoxime)silane, vinyltris(methylethylketoxime)silane, aminoethylaminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, octamethylcyclotetrasiloxane, cyclic siloxane ester, and polydimethylsiloxane. Furthermore, among these, a polymer obtained by polymerizing one type of monomer, a polymer obtained by polymerizing two or more types of monomer, or a solution containing a commercially available mixture may be brought into contact, and for example, the TSE series manufactured by Momentive Performance Materials, Inc., or a silicone resin, silicone oligomer, or silicone emulsion manufactured by Shin-Etsu Silicones Co., Ltd. may be used.

[0097] 3. Spiral-Wound Composite Membrane Module for Gas Separation (Overview) When the composite membrane for gas separation of the present invention has a flat membrane shape, it can be applied to a spiral-wound module or a stack-type module, and when it has a hollow fiber shape, it can be applied to a hollow fiber module. However, the following description will focus on a spiral-wound module.

[0098] The spiral-type composite membrane module for gas separation of the present invention is a composite membrane module for gas separation in which the above-mentioned composite membrane for gas separation of the present invention, a feed-side channel material, and a permeation-side channel material are wound around a central tube that collects permeate gas, and will be described in detail below.

[0099] 2 is a partially exploded perspective view of the spiral-wound composite membrane module for gas separation (50). As shown in FIG. 2, the spiral-wound composite membrane module for gas separation (50) includes a central tube (56), a composite membrane for gas separation (51), a feed-side channel material (57), and a permeate-side channel material (58).

[0100] (Central Tube) The central tube (56) is a hollow cylindrical member with a through hole formed in the side. The material of the central tube (56) may be any material that does not deteriorate depending on the pressure, temperature, or type of gas on the supply side during use of the module. In Figure 2, G1 represents the mixed gas, G2 represents the permeated gas, and G3 represents the concentrated gas.

[0101] (Gas Separation Composite Membrane) The gas separation composite membrane (51) is as described above. The gas separation composite membrane (51) is stacked with a feed-side channel material (57) and a permeate-side channel material (58), and is spirally wound around a central tube (56).

[0102] One spiral-wound module can include a plurality of gas separation composite membranes 51. By including these wound components, the spiral-wound composite membrane module 50 for gas separation has a generally cylindrical appearance with its major axis aligned with the longitudinal direction of the central tube 56.

[0103] The composite membranes for gas separation (51) are stacked so that the surfaces on the coating layer side (feed side) face each other and the surfaces on the porous support layer or substrate side (permeation side) face each other.

[0104] A feed-side channel material (57) is inserted between the surfaces of the gas separation composite membrane (51) on the separation function layer side, and a permeation-side channel material (58) is inserted between the surfaces of the permeation side.

[0105] The feed-side flow passages are open at both longitudinal ends of the central tube (56). That is, a feed-side inlet is provided at one end of the spiral-wound composite membrane module (50) for gas separation, and a feed-side outlet is provided at the other end. On the other hand, the feed-side flow passages are sealed at the end on the inner side in the winding direction, i.e., the end on the central tube side. The sealing is formed by folding the composite membrane for gas separation, bonding the composite membrane for gas separation with a hot melt or chemical adhesive, or fusing the composite membranes together using a laser or the like.

[0106] (Channel Material) The feed-side channel material (57) and the permeate-side channel material (58) are spacers that secure channels between the composite membranes for gas separation. The permeate-side channel material and the feed-side channel material may be the same material or different materials. Hereinafter, the permeate-side channel material and the feed-side channel material will be collectively referred to as "channel material."

[0107] Examples of the flow path material include porous sheets such as nets, nonwoven fabrics, woven fabrics, knitted fabrics, and films. Protrusions made of resin or the like may be provided on one or both sides of the sheet. Alternatively, protrusions may be directly fixed to the composite membrane for gas separation, and these protrusions may be used as the flow path material.

[0108] When the flow path material has a sheet and protrusions, the shape of the protrusions may be dots, curved, or linear. If the protrusions are curved or linear, the gas flow can be controlled along the shape. The composition of the protrusions may be any composition that does not deteriorate depending on the pressure, temperature, or type of supply gas during use.

[0109] The flow path material is preferably formed of a thermoplastic resin. From the viewpoint of suppressing damage to the gas separation composite membrane, the thermoplastic resin is preferably polyester, nylon, polyphenylene sulfide, polyethylene, polypropylene, polysulfone, polyethersulfone, ABS (acrylonitrile-butadiene-styrene) resin, or UV-curable resin.

[0110] The thickness of at least one of the feed-side channel material and the permeation-side channel material, and preferably both, is preferably 1000 μm or less, more preferably 700 μm or less, and particularly preferably 400 μm or less. By thinning the channel material in this way, the rigidity against bending is reduced and it becomes less likely to crack. Furthermore, by thinning the channel material, it is possible to increase the area of ​​the composite membrane for gas separation that can be packed while maintaining the volume of the composite membrane module for gas separation.

[0111] 4. Gas Separation System The above-described composite membrane for gas separation is capable of selectively permeating gases with small molecular diameters, such as hydrogen, helium, water vapor, and ammonia, and is applied to gas separation systems.

[0112] The gas separation system according to this embodiment includes the following steps: (1) supplying a mixed gas containing Gas A, a permeable component, and Gas B, a non-permeable component, to one side of a gas separation composite membrane, and (2) obtaining a gas having a higher molar ratio of Gas A / Gas B than that of the mixed gas from the other side of the gas separation composite membrane.

[0113] In other words, this separation system utilizes the difference in the permeability of the gas separation composite membrane to gas A and to gas B, an unwanted component, to obtain a permeable gas with a reduced concentration of gas B from a mixed gas of gas A and gas B.

[0114] Although the gas B is not limited to a specific type, the mixed gas preferably contains at least one gas selected from the group consisting of oxygen, nitrogen, and methane as the gas B. This is because the composite gas separation membrane has a large difference in permeability between gases with small molecular diameters, such as hydrogen, helium, water vapor, and ammonia, and the permeability of oxygen, nitrogen, and methane, and therefore can efficiently separate gases with small molecular diameters, such as hydrogen, helium, water vapor, and ammonia.

[0115] The mixed gas may also contain water vapor. Water vapor adheres to the membrane and causes a decrease in the selective separation of light gases, but the composite membrane for gas separation exhibits excellent selective gas separation even when the feed gas contains water vapor.

[0116] The gas separation system of the present invention can use the spiral-wound composite membrane module for gas separation described above. Furthermore, in the gas separation system of the present invention, pressure vessels can be connected in series and / or parallel and housed in the pressure vessel.

[0117] In step (1), the feed gas may be pressurized by a compressor and then fed to the composite membrane for gas separation (its elements), or the permeate side of the composite membrane for gas separation may be depressurized by a pump.

[0118] Alternatively, multiple elements may be connected in series. When multiple elements are used, either the permeate gas or non-permeate gas from the upstream element may be supplied to the downstream element. Alternatively, the permeate gas or non-permeate gas from the downstream element may be mixed with the gas supplied to the upstream element. The permeate gas or non-permeate gas may be supplied to the subsequent element, which may be pressurized by a compressor.

[0119] The gas supply pressure is not particularly limited, but is preferably 0.1 MPa to 10 MPa. A pressure of 0.1 MPa or higher increases the gas permeation rate, while a pressure of 10 MPa or lower prevents pressure deformation of the gas separation composite membrane and its element components. The value of "supply side pressure / permeation side pressure" is also not particularly limited, but is preferably 1.01 to 100,000, more preferably 1.10 to 1,000, and particularly preferably 1.50 to 100. A "supply side pressure / permeation side pressure" value of 1.01 or higher increases the gas permeation rate, while a pressure of 100,000 or lower reduces the power costs for increasing the pressure on the supply side and reducing the pressure on the permeation side.

[0120] The gas supply temperature is not particularly limited, but is preferably 0°C to 200°C, and more preferably 15°C to 180°C. A temperature of 15°C or higher provides good gas permeability, while a temperature of 180°C or lower prevents thermal deformation of the components that make up the gas separation composite membrane element. Use of the above-mentioned gas separation composite membrane makes it possible to supply gas at temperatures of 80°C or higher, 90°C or higher, or 100°C or higher.

[0121] 5. Applications The composite membrane for gas separation of the present invention has excellent separation performance and is suitable for use in, for example, separating hydrogen gas from a mixed gas containing hydrogen and nitrogen, etc.; separating hydrogen gas from a mixed gas containing hydrogen and oxygen, nitrogen, ammonia, etc.; separating helium from a mixed gas containing helium and oxygen, nitrogen, etc.; and purifying helium and hydrogen.

[0122] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0123] A. Preparation of porous support membrane Unless otherwise specified, the temperature conditions are room temperature (25°C). ２ A 16 wt % solution of polysulfone (PSf) in dimethylformamide (DMF) was cast onto the substrate (1000 nm / sec) at 25°C to a thickness of 200 µm, and the resultant was immediately immersed in pure water and left for 5 minutes to form a porous support layer. In this way, a porous support membrane having a substrate and a porous support layer was produced.

[0124] B. Preparation of separation functional layer (composite separation membrane P) The porous support membrane obtained in A. was immersed in a 0.2 wt% aqueous piperazine solution for 2 minutes. The porous support membrane was slowly pulled up vertically, and nitrogen was blown from an air nozzle to remove excess aqueous solution from the surface of the porous support layer.

[0125] Next, an n-decane solution containing 0.2 wt % trimesoyl chloride (TMC) was applied to the surface of the porous support layer so that it was completely wet, and the layer was left to stand for 100 seconds at 25° C. Thereafter, in order to remove excess solution from the separation membrane, the separation membrane was held vertically to allow the solution to flow, and then a blower was used to blow air at 25° C. onto the membrane to dry it, thereby draining the solution.

[0126] (Composite Separation Membrane Q) The porous support membrane obtained in A. was immersed for 2 minutes in an aqueous solution containing 2.0 wt% m-phenylenediamine (m-PDA) and 1.0 wt% ε-caprolactam. The porous support membrane was slowly pulled up vertically, and excess aqueous solution was removed from the surface of the porous support layer by blowing nitrogen from an air nozzle.

[0127] Next, an n-decane solution containing 0.10 wt % trimesoyl chloride (TMC) was applied to the surface of the porous support layer so that it was completely wet, and then dried for 180 seconds at 25° C. Thereafter, in order to remove excess solution from the separation membrane, the separation membrane was held vertically to allow the solution to flow, and then air at 25° C. was blown onto the membrane using a blower to dry it, thereby draining the solution.

[0128] (Composite Separation Membrane R) The porous support membrane obtained in A. was immersed in a 2.0 wt % aqueous solution of m-phenylenediamine (m-PDA) for 2 minutes. The porous support membrane was slowly pulled up vertically, and nitrogen was blown from an air nozzle to remove excess aqueous solution from the surface of the porous support layer.

[0129] Next, an n-decane solution containing 0.10 wt % trimesoyl chloride (TMC) was applied to the surface of the porous support layer so that it was completely wet, and then dried for 60 seconds at 50° C. Thereafter, in order to remove excess solution from the separation membrane, the separation membrane was held vertically to allow the solution to flow, and then air at 25° C. was blown onto the membrane using a blower to dry it, thereby draining the solution.

[0130] (Composite Separation Membrane S) The porous support membrane obtained in A. was immersed in a 4.0 wt % m-phenylenediamine (m-PDA) aqueous solution for 2 minutes. The porous support membrane was slowly pulled up vertically, and nitrogen was blown from an air nozzle to remove excess aqueous solution from the surface of the porous support layer.

[0131] Next, an n-decane solution containing 0.20 wt % trimesoyl chloride (TMC) was applied to the surface of the porous support layer so that it was completely wet, and then dried for 60 seconds at 80° C. Thereafter, in order to remove excess solution from the separation membrane, the separation membrane was held vertically to allow the solution to flow, and then air at 25° C. was blown onto the membrane using a blower to dry it, thereby draining the solution.

[0132] (Composite Separation Membrane T) The porous support membrane obtained in A. was immersed in a 4.0 wt % m-phenylenediamine (m-PDA) aqueous solution for 2 minutes. The porous support membrane was slowly pulled up vertically, and excess aqueous solution was removed from the surface of the porous support layer by blowing nitrogen from an air nozzle.

[0133] Next, an n-decane solution containing 0.20 wt % trimesoyl chloride (TMC) was applied to the surface of the porous support layer so that it was completely wet, and the layer was left to stand for 120 seconds at 80° C. Thereafter, in order to remove excess solution from the separation membrane, the separation membrane was held vertically to allow the solution to flow, and then air at 25° C. was blown onto the membrane using a blower to dry it, thereby draining the solution.

[0134] C. Gas Permeability Measurement (Helium, Hydrogen, Nitrogen, Methane Permeability and Selectivity) A separation membrane was held between the feed-side cell and the permeate-side cell of a test cell having a feed-side cell and a permeate-side cell. Helium and nitrogen were used as measurement gases, and the permeate-side pressure change per unit time of helium, hydrogen, nitrogen, and methane was measured at a measurement temperature of 25°C in accordance with the pressure sensor method of ISO 15105-1 (2007). Here, the feed side was set to 100 kPa, the permeate side to 0 kPa, and the pressure difference between the feed side and the permeate side was set to 100 kPa. Next, the permeation rate Q of the permeated gas was calculated using the following formula, and the gas permeability was determined by the arithmetic mean of measurements taken at five arbitrary points on the same membrane. Then, the selectivity was calculated as the ratio of the permeation rates of the gases of each component. Note that STP means standard conditions. Q = [gas permeation flow rate (m ３ ・STP)] / [Membrane area (m ２ ) × time (s) × pressure difference (Pa)]

[0135] D. Nanoperm Porometry Analysis A test cell had a feed cell and a permeate cell, and a separation membrane was held between the feed cell and the permeate cell. H was used as the condensable gas. ２Using helium as the non-condensable gas, the helium permeation rate was measured at a total of 21 points at a measurement temperature of 40°C and relative humidity settings of 0% to 95% at approximately 5% intervals. Of the two points on either side of 20% relative humidity, the value closer to 20% was taken as the helium permeation rate at 20%, and of the two points on either side of 90% humidity, the value closer to 90% was taken as the helium permeation rate at 90%. Here, the supply side was set to 190 kPa and the permeation side to 100 kPa, and the flow rate was measured using a flow meter to calculate the helium permeability. (Details of the measuring apparatus are described in Toshinori Tsuru et al., Journal of Membrane Science, Vol. 186, pp. 257-265, Department of Chemical Engineering, Hiroshima University (2001).) Measurements were taken at three random locations on the same membrane, and the helium permeability at each humidity was determined as the arithmetic mean.

[0136] E. Measurement of the average pore radius Rf [nm] of the separation functional layer and the average pore diameter Rc [nm] of the coating layer by positron beam method The positron annihilation lifetime measurement of the separation functional layer in each example was carried out using a positron beam method as follows. That is, the separation functional layer was dried at room temperature under reduced pressure and cut into a 1.5 cm x 1.5 cm square to prepare a test sample. The test sample was measured using a thin film positron annihilation lifetime measurement device equipped with a positron beam generator (this device is described in detail, for example, in Radiation Physics and C Helium Mistry, 58,603, Pergamon (2000)) at a beam intensity of 1 keV, room temperature, and under vacuum using a barium difluoride scintillation counter with a photomultiplier tube at a total count of 5 million, and analyzed using POSI TRONFIT. From the average positron annihilation lifetime τ of the fourth component obtained by analysis, the average pore diameter Rc was calculated using Equation 3, and Rf [nm] was calculated using Equation 4. Rc and Rf were determined as the arithmetic mean of measurements taken at five random locations on the same film.

[0137] F. TOF-SIMS Peak Intensity The separation membrane was dried at room temperature under vacuum and subjected to time-of-flight secondary ion mass spectrometry using a TOF SIMS 5 (manufactured by ION TOF) instrument (secondary ion polarity: negative, mass range (m / z) = 0-2500, raster size: 300 μm, number of scans: 1 scan / cycle, number of pixels (one side): 128 pixels, measurement vacuum (before sample introduction): 4 × 10 －７ Pa or less, charge neutralization: yes, post-stage acceleration: 9.5 kV, primary ion species: Bi ３ ＋＋ , primary ion acceleration voltage: 30 kV, pulse width: 14.1 ns, bunching: yes, edging ion: Ar-GCIV, edging ion acceleration voltage: 5 kV). － The peak intensity of Si in the region from the surface of the coating layer side to a depth of 0 to 50 nm was measured at intervals of 2.5 nm or less. － The average of the peak intensities was calculated. The Si content was calculated by taking the arithmetic mean of measurements taken at five arbitrary points on the same film. － The peak intensities were determined.

[0138] G. Coating Layer Thickness After freezing the gas separation composite membrane with liquid nitrogen, the cross section was exposed with a razor. The exposed cross section of the gas separation composite membrane was observed at 10,000x magnification using a scanning electron microscope (S-5500 model, manufactured by Hitachi High-Technologies Corporation). The area observed ranged from the surface layer of the gas separation composite membrane to the porous support layer. Prior to observation with the SEM, the membrane was coated with platinum-palladium. The obtained cross-sectional image was binarized using ImageJ and subjected to image analysis to determine the coating layer thickness. Specifically, a threshold was applied to the cross-sectional image using ImageJ, and the black layer extending continuously from the surface of the gas separation composite membrane was determined as the coating layer. The coating layer thickness was measured at three locations: the center, right edge, and left edge of the image, and the coating layer thickness in the obtained cross-sectional image was calculated as the arithmetic mean of the three locations. The same procedure was carried out for five slice samples, and three fields of view were observed for each sample, and the coating layer thickness was determined by arithmetic averaging of a total of 15 data points.

[0139] H. Measurement of penetration thickness of coating layer into support film When the main component of the support layer was polysulfone and the main component of the coating layer was silicone, the penetration thickness was measured using TEM-EDX as follows.

[0140] The sample was sliced ​​in the cross-sectional direction using a focused ion beam (FIB) method and observed using an analytical electron microscope (JEOL JEM-F200). Elemental mapping was performed at an acceleration voltage of 200 kV using an energy dispersive X-ray spectroscopy (EDX) detector (JEOL JED2300T 100 mm2 silicon drift (SDD) type). For the resulting 1 μm square image, a mapping image of Si contained in the coating layer and a mapping image of S contained in the support layer were superimposed. Next, the overlap of Si and S was measured at 10 points in the width direction, and the penetration thickness of the coating layer in the obtained cross-sectional image was calculated by arithmetic averaging of the 10 points. The same operation was performed in two fields of view, and the arithmetic mean of the two fields of view was used as the penetration thickness of the coating layer.

[0141] When the main component of the support layer was other than polysulfone, or when the main component of the coating layer was other than silicone, an SEM cross-sectional image was obtained as described in G above, and the thickness of the coating layer penetrating into the support layer was determined in the same manner as in calculating the thickness of the coating layer.

[0142] I. Contact Angle Measurement The contact angle was measured in accordance with ISO 19403-1 (2017) by dropping 3.0 μL of distilled water onto the separation functional layer side of the gas separation composite membrane, and measuring the contact angle (the angle between the tangent to the droplet and the solid surface) one second after the water droplet had been dropped. The contact angle one second after the pure water had landed on the surface of the coating layer was defined as X, and the contact angle 30 seconds later as Y, giving the Y / X value.

[0143] J. Measurement of Support Layer Thickness Since the functional layer thickness of the gas separation composite membrane is very thin, the support layer thickness was determined by subtracting the coating layer thickness obtained in G above and the thickness of the substrate alone from the thickness of the gas separation composite membrane after the coating layer was formed. First, the thickness of the gas separation composite membrane was measured using a PEACOCK digital thickness gauge manufactured by Ozaki Seisakusho Co., Ltd. Measurements were taken at 20 points in each width direction, and the average value was calculated. Next, the coating layer, functional layer, and support layer portions of the gas separation composite membrane were peeled off from the substrate, and the thickness of the substrate was measured in the same manner. Support layer thickness (μm) = gas separation composite membrane thickness (μm) - substrate thickness (μm) - coating layer thickness (μm)

[0144] K. Measurement of the average pore radius Rf [nm] of the separation functional layer using STEM. When it was difficult to peel the coating layer from the separation functional layer and Rf could not be calculated using the method E above, the support layer was dissolved to separate the separation functional layer from the support layer, forming a sample consisting only of the separation functional layer and coating layer, and Rf was determined by STEM observation of the separation functional layer side. When the main component of the support layer was polysulfone and the main component of the coating layer was silicone, the substrate was physically peeled off and the polysulfone was dissolved with dichloromethane to obtain a sample consisting only of the separation functional layer and coating layer. The sample was transferred to a TEM observation grid and prepared so that the separation functional layer could be observed from the side that was in contact with the support layer. The prepared sample was photographed using a field emission transmission electron microscope (Hitachi High-Tech HF5000) at an accelerating voltage of 200 kV, and a STEM image at a magnification of 100,000 was obtained. The obtained image was then analyzed using image processing software to calculate the pore size.

[0145] (Example 1) The composite separation membrane P obtained in B. was separated into 25 cm ２ The membrane was cut into a circular shape. TSE389 (manufactured by Momentive Performance Materials) was dissolved in hexane (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) to prepare a 16 wt% TSE389 hexane solution. 1 mL of this solution was dropped onto the surface of the separation functional layer, and spin-coated at a speed of 1000 rpm for 30 seconds to form a coating layer. Finally, the membrane was air-dried at 25°C for 12 hours or more to obtain a composite membrane for gas separation. The obtained composite membrane for gas separation was evaluated, and the results are shown in Table 1.

[0146] Example 2 A composite membrane for gas separation was produced by forming a polydimethylsiloxane coating layer by carrying out the same process as in Example 1, except that a 5.0 wt % solution of TSE389 (manufactured by Momentive Performance Materials, Inc.) was used. The composite membrane for gas separation thus obtained was evaluated, and the results are shown in Table 1.

[0147] Example 3 A composite membrane for gas separation was produced by forming a coating layer mainly composed of silicone by the same process as in Example 1, except that the composite separation membrane was designated Q and the coating solution was a 0.8 wt% hexane solution of KBM602 (manufactured by Shin-Etsu Silicones Co., Ltd.). The obtained composite membrane for gas separation was evaluated, and the results are shown in Table 1.

[0148] Example 4 A composite membrane for gas separation was produced by forming a coating layer mainly composed of silicone by carrying out the same process as in Example 3, except that the coating solution was a 1.5 wt % hexane solution of TSE382 (manufactured by Momentive Performance Materials, Inc.). The obtained composite membrane for gas separation was evaluated, and the results are shown in Table 1.

[0149] Example 5 A composite membrane for gas separation was produced by forming a coating layer mainly composed of silicone by the same process as in Example 3, except that the coating solution was a 6.0 wt % hexane solution of TSE387 (manufactured by Momentive Performance Materials, Inc.). The composite membrane for gas separation thus obtained was evaluated, and the results are shown in Table 1.

[0150] Example 6 A composite membrane for gas separation was produced by forming a coating layer mainly composed of silicone by carrying out the same process as in Example 3, except that the coating solution was a 4.0 wt% hexane solution of TSE387. The obtained composite membrane for gas separation was evaluated, and the results are shown in Table 1.

[0151] Example 7 A composite membrane for gas separation was produced by forming a coating layer mainly composed of silicone by the same process as in Example 3, except that the coating solution was an 8.0 wt % hexane solution of TSE322 (manufactured by Momentive Performance Materials, Inc.). The obtained composite membrane for gas separation was evaluated, and the results are shown in Table 1.

[0152] (Example 8) A composite membrane for gas separation was produced by forming a coating layer mainly composed of silicone by carrying out the same process as in Example 6, except that the composite separation membrane was R. The obtained composite membrane for gas separation was evaluated, and the results are shown in Table 1.

[0153] (Example 9) A composite membrane for gas separation was produced by forming a coating layer mainly composed of silicone by carrying out the same process as in Example 6, except that the composite separation membrane was changed to S. The obtained composite membrane for gas separation was evaluated, and the results are shown in Table 2.

[0154] (Example 10) When forming the support membrane, a polyester short fiber nonwoven fabric (air permeability 1.0 cc / cm) was used instead of the long fiber nonwoven fabric. ２ A composite membrane for gas separation was produced by forming a coating layer mainly composed of silicone by the same process as in Example 9, except that a silicone-based coating layer was used. The composite membrane for gas separation thus obtained was evaluated, and the results are shown in Table 2.

[0155] (Example 11) A composite membrane for gas separation was produced by forming a coating layer mainly composed of polymethylpentene by the same process as in Example 6, except that the composite separation membrane was T and polymethylpentene was used instead of TSE387. The obtained composite membrane for gas separation was evaluated, and the results are shown in Table 2.

[0156] (Example 12) A composite membrane for gas separation was produced by forming a coating layer mainly composed of polymethylpentene by carrying out the same process as in Example 11, except that the composite separation membrane was changed to P. The obtained composite membrane for gas separation was evaluated, and the results are shown in Table 2.

[0157] Example 13 A composite membrane for gas separation was produced by forming a coating layer mainly composed of silicone by carrying out the same process as in Example 6, except that silicone oligomer KR-510 (manufactured by Shin-Etsu Silicones Co., Ltd.) was used as the coating solution. The obtained composite membrane for gas separation was evaluated, and the results are shown in Table 2.

[0158] Example 14 A composite membrane for gas separation was produced by applying 2 mL of the coating solution dropwise, covering it with a film, holding it for 10 minutes, and then spin-coating it in the same manner as in Example 6. The composite membrane for gas separation thus obtained was evaluated, and the results are shown in Table 2.

[0159] Example 15 A composite membrane for gas separation was produced by applying 2 mL of the coating solution dropwise, covering it with a film, holding it for 2 minutes, and then spin-coating it in the same manner as in Example 6. The composite membrane for gas separation thus obtained was evaluated, and the results are shown in Table 2.

[0160] A comparison of Examples 6, 14, and 15 reveals that when the coating layer penetrates into the support layer, the permeability of hydrogen and helium decreases, and the selectivity also decreases.

[0161] (Example 16) A composite membrane for gas separation was produced by forming a coating layer mainly composed of silicone by carrying out the same process as in Example 6, except that the composite separation membrane was changed to T. The obtained composite membrane for gas separation was evaluated, and the results are shown in Table 3.

[0162] Example 17 A composite membrane for gas separation was produced by forming a coating layer mainly composed of poly(1-trimethylsilyl-1-propyne) by carrying out the same process as in Example 16, except that poly(1-trimethylsilyl-1-propyne) was used instead of polydimethylsiloxane. The obtained composite membrane for gas separation was evaluated, and the results are shown in Table 3.

[0163] (Example 18) A composite membrane for gas separation was produced by forming a coating layer mainly composed of silicone through the same process as in Example 9, except that the clearance was adjusted during the formation of the support membrane to make the support layer thickness 18 μm. The obtained composite membrane for gas separation was evaluated, and the results are shown in Table 4.

[0164] Example 19 A composite membrane for gas separation was produced by forming a coating layer mainly composed of silicone through the same process as in Example 9, except that the clearance was adjusted during the formation of the support membrane and the support layer thickness was set to 25 μm. The obtained composite membrane for gas separation was evaluated, and the results are shown in Table 4.

[0165] Example 20 A composite membrane for gas separation was produced by forming a coating layer mainly composed of silicone through the same process as in Example 9, except that the clearance was adjusted during the formation of the support membrane to make the support layer 55 μm thick. The obtained composite membrane for gas separation was evaluated, and the results are shown in Table 4.

[0166]

[0167]

[0168]

[0169]

[0170] (Comparative Example 1) Composite separation membrane P was evaluated as a composite membrane for gas separation without forming a coating layer, and the results are shown in Table 5. Because it did not have a coating layer, permeation through the coarse pores was not suppressed, and when nanoperm porometry analysis was performed, the helium permeability at a relative humidity of 90% was 65% of the helium permeability at a relative humidity of 20%, meaning that selectivity could not be sufficiently improved.

[0171] (Comparative Example 2) Composite separation membrane Q was evaluated as a composite membrane for gas separation without forming a coating layer, and the results are shown in Table 5. Because it did not have a coating layer, permeation through the coarse pores was not suppressed, and when nanoperm porometry analysis was performed, the helium permeability at a relative humidity of 90% was 71% of the helium permeability at a relative humidity of 20%, meaning that selectivity could not be sufficiently improved.

[0172] (Comparative Example 3) Composite separation membrane R was evaluated as a composite membrane for gas separation without forming a coating layer, and the results are shown in Table 5. Because it did not have a coating layer, permeation through the coarse pores was not suppressed, and when nanoperm porometry analysis was performed, the helium permeability at a relative humidity of 90% was 79% of the helium permeability at a relative humidity of 20%, meaning that selectivity could not be sufficiently improved.

[0173] (Comparative Example 4) Composite separation membrane S was evaluated as a composite membrane for gas separation without forming a coating layer, and the results are shown in Table 5. Because it did not have a coating layer, permeation through the coarse pores was not suppressed, and when nanoperm porometry analysis was performed, the helium permeability at a relative humidity of 90% was 82% of the helium permeability at a relative humidity of 20%, meaning that selectivity could not be sufficiently improved.

[0174] (Comparative Example 5) Composite separation membrane T was evaluated as a composite membrane for gas separation without forming a coating layer, and the results are shown in Table 5. Because it did not have a coating layer, permeation through the coarse pores was not suppressed, and when nanoperm porometry analysis was performed, the helium permeability at a relative humidity of 90% was 88% of the helium permeability at a relative humidity of 20%, and selectivity could not be sufficiently improved. The results of Comparative Examples 1 to 5 are shown in Table 5.

[0175]

[0176] Comparative Example 6 A composite membrane for gas separation was prepared in the same manner as in Example 11, except that polyethersulfone was used instead of polymethylpentene and N-methyl-2-pyrrolidone was used instead of hexane. The composite membrane for gas separation thus obtained was evaluated, and the results are shown in Table 6. The average pore diameter Rc of the coating layer was small, and the gas permeability of the coating layer was low, so the helium permeability at 25°C was 1.0 nmol / m ２ / s / Pa, and the hydrogen permeability also decreased.

[0177] Comparative Example 7 A composite membrane for gas separation was prepared in the same manner as in Comparative Example 6, except that the polyethersulfone content was 0.4 wt %. The obtained composite membrane for gas separation was evaluated, and the results are shown in Table 6. Although gas permeability could be increased by reducing the thickness of the coating layer, the coating layer was not thick enough, which resulted in defects in the coating layer, making it impossible to suppress permeation through the coarse pores at the same time, and selectivity was not sufficiently improved.

[0178] (Comparative Example 8) A composite membrane for gas separation was prepared in the same manner as in Example 1, except that 3 mL of a 25.0 wt % TSE389 hexane solution was dropped onto the porous support membrane obtained in A. The composite membrane for gas separation obtained was evaluated, and the results are shown in Table 6. Since there was no separation functional layer and no pores that would cause sieving according to the molecular diameter of the gas, the selectivity was reduced.

[0179] (Reference Example 1) The composite separation membrane described in Non-Patent Document 2, in which a polydimethylsiloxane coating layer is applied to the surface of a polyamide composite membrane, has a high ratio of helium permeability to hydrogen permeability of 1.83, and although the selectivity is good, the hydrogen permeability is low (Table 4). Furthermore, from the image in Non-Patent Document 2, it can be seen that the coating layer penetrates 192 nm into the support layer.

[0180] (Reference Example 2) The composite separation membrane described in Non-Patent Document 1, in which a polyphenylene oxide coating layer is applied to the surface of a polyamide composite membrane, has very low nitrogen and methane permeabilities, and is therefore presumed to have very good selectivity, but its helium permeability and hydrogen permeability are also very low (Table 4). It can also be seen that the coating layer penetrates 444 nm into the support layer.

[0181] The results of Comparative Examples 6 to 8 and Reference Examples 1 and 2 are shown in Table 6.

[0182]

[0183] The composite membrane for gas separation of the present invention is suitably used for separating and purifying a specific gas from a mixed gas.

[0184] 50: Spiral-type composite membrane module for gas separation 51: Composite membrane for gas separation 52: Porous support layer 53: Separation function layer 54: Coating layer 55: Substrate 56: Center tube 57: Feed-side passage material 58: Permeation-side passage material G1: Mixed gas G2: Permeate gas G3: Concentrated gas

Claims

1. A composite membrane for gas separation having at least a porous support layer, a separation functional layer, and a coating layer in this order, and having a He permeability of 1.0 nmol / m at 25°C. ２ / s / Pa or more, with non-condensable gas being He and condensable gas being H ２ A composite membrane for gas separation, in which, when nanoperm porometry analysis is performed under conditions of 0 and a temperature of 40° C., the He permeability at a relative humidity of 90% is 90% or more of the He permeability at a relative humidity of 20%, and the penetration depth of the coating layer into the porous support layer in a cross section of the composite membrane for gas separation is 0 to 150 nm.

2. 2. The composite membrane for gas separation according to claim 1, wherein the average pore diameter Rc of the coating layer determined by a positron beam method is 0.6 nm or more and 1.2 nm or less.

3. He and H according to the pressure sensor method of ISO 15105-1 (2007) ２ When the permeability was measured, the He permeability at 25° C. was H ２ 2. The composite membrane for gas separation according to claim 1, having a permeability of 1.10 to 1.65 times the permeability of the mixture.

4. 2. The composite membrane for gas separation according to claim 1, wherein the main component of said porous support layer is polysulfone or cellulose acetate.

5. 2. The composite membrane for gas separation according to claim 1, wherein the main component of the separating functional layer is a crosslinked aromatic polyamide or polyimide.

6. 2. The composite membrane for gas separation according to claim 1, wherein the main component of said coating layer is silicone.

7. 2. The composite membrane for gas separation according to claim 1, wherein the coating layer has a thickness of 0.2 μm or more and 2.0 μm or less.

8. The average pore radius Rf [nm] and the pore diameter d of the composite membrane for gas separation determined by Equation 2 ＮＫＰ The composite membrane for gas separation according to claim 1 , wherein [nm] satisfies formula 1. [0010] [0025] (where "i" is H ２ , N ２ and C.H. ４ and "Pi" is the permeability of gas i at 25°C [nmol / m ２ / s / Pa], and P Ｈｅ is the He gas permeability at 25°C [nmol / m ２ / s / Pa], M is the molecular weight of gas i, M Ｈｅ is the molecular weight of He gas, and d ｋ,ｉ is the kinetic molecular diameter of gas i [nm], d ｋ,Ｈｅ is the kinetic molecular diameter of He gas [nm].)

9. 2. The composite membrane for gas separation according to claim 1, wherein the average pore radius Rf [nm] of the separating functional layer is 0.2 nm or more and 0.4 nm or less.

10. H at 25°C ２ Permeability is 1 nmol / m ２ / s / Pa or more 100nmol / m ２ 2. The composite membrane for gas separation according to claim 1, wherein the viscosity is 1 / s / Pa or less.

11. A composite membrane for gas separation having at least a porous support layer, a separation functional layer, and a coating layer in this order, wherein the separation functional layer is mainly composed of a crosslinked aromatic polyamide, the coating layer is mainly composed of silicone, and the penetration depth of the coating layer into the porous support layer is 0 to 150 nm in a cross section of the composite membrane for gas separation.

12. 12. The composite membrane for gas separation according to claim 11, wherein the average pore diameter Rc of the coating layer determined by a positron beam method is 0.6 nm or more and 1.2 nm or less.

13. 12. The composite membrane for gas separation according to claim 11, wherein the average pore radius Rf [nm] of the separating functional layer is 0.2 nm or more and 0.4 nm or less.

14. 14. A spiral-type composite membrane module for gas separation, comprising the composite membrane for gas separation according to any one of claims 1 to 13, a feed-side flow path material, and a permeate-side flow path material wound around a central tube.

15. A gas separation system comprising the spiral-type composite membrane module for gas separation according to claim 14.

16. He or H using the gas separation system of claim 14 ２ A method for refining.