Method for manufacturing a gas separation membrane and gas separation membrane manufactured thereby

Abstract

The present specification provides a method for preparing a gas separation membrane, and a gas separation membrane prepared using the same, the method including forming a porous layer by coating a hydrophilic polymer solution on a porous substrate; and forming an active layer by coating a composition for forming an active layer including a polymer represented by Chemical Formula 1 on the porous layer, wherein the polymer represented by Chemical Formula 1 is included at 1 to 5 wt% based on the composition for forming an active layer.

Description

Technical Field

[0001] This application claims priority and benefit to Korean Patent Application No. 10-2017-0147530, filed with the Korean Intellectual Property Office on November 7, 2017, the entire contents of which are incorporated herein by reference.

[0002] This specification relates to methods for preparing gas separation membranes and gas separation membranes prepared using the same. Background Technology

[0003] Gas separation membranes consist of a support layer, an active layer, and a protective layer, and selectively separate gases from a gas mixture by utilizing the pore size and structural characteristics of the active layer. Therefore, gas permeability and selectivity are used as important indicators of membrane performance, and such performance is largely influenced by the polymer material forming the active layer.

[0004] Therefore, there is a need to develop methods to increase the permeability and selectivity of gas separation membranes. Summary of the Invention

[0005] Technical issues

[0006] This specification describes a method for preparing a gas separation membrane and a gas separation membrane prepared using the method.

[0007] Technical solution

[0008] One embodiment of this specification provides a method for preparing a gas separation membrane, the method comprising: forming a porous layer by coating a hydrophilic polymer solution onto a porous substrate; and forming an active layer by coating the porous layer with a composition comprising a polymer represented by Chemical Formula 1, wherein the polymer represented by Chemical Formula 1 is included in the composition for forming the active layer at a weight percentage of 1 to 5 wt%.

[0009] [Chemical Formula 1]

[0010]

[0011] In chemical formula 1,

[0012] n is the number of repeating units, and is an integer from 500 to 3,000.

[0013] R1 to R5 may be the same as or different from each other, and each is independently hydrogen; alkyl; or -(C=O)R6, where R6 is alkyl.

[0014] Another embodiment of this specification provides a gas separation membrane comprising: a porous layer; and an active layer formed on the porous layer comprising a polymer represented by chemical formula 1, wherein the gas separation membrane has a methane-based carbon dioxide selectivity of 5 to 30.

[0015] Beneficial effects

[0016] The method for preparing a gas separation membrane according to one embodiment of this specification improves carbon dioxide selectivity and permeability.

[0017] Furthermore, the gas separation membrane according to one embodiment of this specification effectively separates carbon dioxide. Attached Figure Description

[0018] Figure 1 A gas separation membrane according to one embodiment of this specification is shown.

[0019] Figure 2 A gas separation membrane according to another embodiment of this specification is shown.

[0020] [Figure Labels]

[0021] 100, 200: Gas separation membrane

[0022] 10: Porous layer

[0023] 11: Active layer

[0024] 12: Trench layer

[0025] 13: Protective layer Detailed Implementation

[0026] In this specification, the description of a component being placed "on" another component includes not only the case where one component is adjacent to another component, but also the case where there is another component between the two components.

[0027] In this specification, unless otherwise stated to the contrary, a description in which a part “contains” certain ingredients means that it may further contain other ingredients, and does not exclude other ingredients.

[0028] This instruction manual will be described in more detail below.

[0029] One embodiment of this specification provides a method for preparing a gas separation membrane, the method comprising: forming a porous layer by coating a hydrophilic polymer solution onto a porous substrate; and forming an active layer by coating the porous layer with a composition comprising a polymer represented by Chemical Formula 1, wherein the polymer represented by Chemical Formula 1 is included in an amount of 1% to 5% by weight, based on the composition for forming the active layer.

[0030] [Chemical Formula 1]

[0031]

[0032] In chemical formula 1,

[0033] n is the number of repeating units, and is an integer from 500 to 3,000.

[0034] R1 to R5 may be the same as or different from each other, and each is independently hydrogen; alkyl; or -(C=O)R6, and R6 is alkyl. In one embodiment of this specification, R1 and R3 to R5 are alkyl, and R2 is -(C=O)R6.

[0035] The method for preparing a gas separation membrane according to one embodiment of this specification uses a polymer represented by chemical formula 1 in the active layer, and achieves improved results in both carbon dioxide gas permeability and carbon dioxide gas selectivity compared to methane gas, compared to separation membranes using existing active layer materials.

[0036] Furthermore, compared to the use of existing active layer materials (especially cellulose acetate), the gas separation membrane according to one embodiment of this specification exhibits excellent methane-based carbon dioxide selectivity, even with low solids content.

[0037] According to one embodiment of this specification, based on the composition for forming the active layer, the polymer represented by chemical formula 1 may be included in 1% to 5% by weight, preferably 1.5% to 5% by weight, more preferably 1.5% to 2.5% by weight, and even more preferably 1.5% to 2% by weight.

[0038] When the content of the polymer represented by Formula 1 is 1% to 5% by weight based on the composition used to form the active layer, the optimal viscosity and gas permeability are obtained according to the solid content in the active layer, and the selectivity for each gas can be maximized.

[0039] According to one embodiment of this specification, the composition for forming the active layer may further comprise nitromethane. In this case, based on the composition for forming the active layer, nitromethane may be included in quantities of 95% to 99% by weight.

[0040] Including nitromethane at 97.5% to 98% wt% effectively yields excellent gas permeability / selectivity properties for the coated active layer. When examining the viscosity of nitromethane contained at 95% to 97.5% wt%, it was determined that the viscosity increases approximately tenfold when the concentration of the coating material (the polymer represented by Formula 1) is doubled. However, the viscosity remains relatively constant even with increasing shear rate, and because no shear thinning effect occurs, the coating amount and active layer thickness can be easily controlled using slot coating. However, careful consideration is needed when making decisions regarding the molecular weight of the material used for coating, its viscosity at dissolution, etc.

[0041] According to one embodiment of this specification, the composition for forming the active layer may comprise a polymer represented by Formula 1 and nitromethane. Nitromethane (CH3NO2) may be included as a solvent for coating acetylated methyl cellulose (AMC). In this case, nitromethane does not dissolve the porous layer (UF support) structure containing polysulfone, thus not reducing the durability of the porous layer and the gas separation membrane, and enabling the formation of an active layer comprising the polymer represented by Formula 1. Furthermore, when forming the active layer, nitromethane (molar mass: 61.04 g / mol, density: 1.1371 g / cm³) is used. 3 (20℃, melting point: 28.38℃, boiling point: 101.19℃, flash point: 35℃) volatilizes at low temperatures and can ensure the constant performance of the gas separation membrane.

[0042] According to another embodiment of this specification, the composition for forming the active layer can be formed from a polymer represented by chemical formula 1 and nitromethane.

[0043] According to one embodiment of this specification, the composition for forming the active layer can be applied using slit coating. When the composition for forming the active layer is applied to a porous layer using slit coating, the thickness of the applied active layer can be easily controlled, and the coating can be performed under conditions that achieve optimal gas separation membrane performance.

[0044] According to one embodiment of this specification, the thickness of the active layer can be from 0.2 μm to 2 μm, depending on the concentration of the composition used to form the active layer and the coating conditions. When the active layer thickness is less than 0.2 μm, the gas selectivity may decrease; while when the active layer thickness is greater than 2 μm, the gas permeability may decrease.

[0045] According to one embodiment of this specification, the alkyl group may be linear or branched, and although not particularly limited thereto, the number of carbon atoms is preferably from 1 to 30. Specifically, the number of carbon atoms is preferably from 1 to 20. More specifically, the number of carbon atoms is preferably from 1 to 10. Specific examples may include methyl, ethyl, propyl, n-propyl, isopropyl, butyl, n-butyl, isobutyl, tert-butyl, sec-butyl, 1-methylbutyl, 1-ethylbutyl, pentyl, n-pentyl, isopentyl, neopentyl, tert-pentyl, hexyl, n-hexyl, 1-methylpentyl, 2-methylpentyl, 4-methyl-2-pentyl, 3,3-dimethylbutyl, 2-ethylbutyl, heptyl, n-heptyl, 1-methylhexyl, cyclopentylmethyl, cyclohexylmethyl, octyl, n-octyl, tert-octyl, 1-methylheptyl, 2-ethylhexyl, 2-propylpentyl, n-nonyl, 2,2-dimethylheptyl, 1-ethylpropyl, 1,1-dimethylpropyl, isohexyl, 2-methylpentyl, 4-methylhexyl, 5-methylhexyl, etc., but are not limited to these.

[0046] According to one embodiment of this specification, R1 to R5 may be the same as or different from each other, and each is independently hydrogen; an alkyl group having 1 to 10 carbon atoms; or -(C=O)R6.

[0047] According to one embodiment of this specification, R1 and R3 to R5 may be the same as or different from each other, and each is independently an alkyl group having 1 to 10 carbon atoms.

[0048] According to one embodiment of this specification, R1 and R3 to R5 are methyl groups.

[0049] According to one embodiment of this specification, R2 can be represented by -(C=O)R6.

[0050] According to one embodiment of this specification, R6 is an alkyl group.

[0051] According to one embodiment of this specification, R6 is an alkyl group having 1 to 10 carbon atoms.

[0052] According to one embodiment of this specification, R6 is ethyl.

[0053] According to one embodiment of this specification, the polymer represented by Formula 1 may be acetylated methylcellulose (AMC). Acetylated methylcellulose was purchased from Lotte Fine Chemical Co., Ltd.

[0054] According to one embodiment of this specification, the weight-average molecular weight (Mw) of the polymer represented by chemical formula 1 can be from 100,000 to 700,000, and preferably from 400,000 to 600,000.

[0055] According to one embodiment of this specification, the number average molecular weight (Mn) of the polymer represented by chemical formula 1 can be from 80,000 to 400,000, and preferably from 100,000 to 300,000.

[0056] According to one embodiment of this specification, the molecular weight distribution (multiple distribution) of the polymer represented by chemical formula 1 can be represented by the ratio of weight-average molecular weight to number-average molecular weight (Mw / Mn), and Mw / Mn can be 2 to 4.

[0057] According to one embodiment of this specification, when the average molecular weight and molecular weight distribution of the polymer represented by Formula 1 meet the above-mentioned range, the polymer represented by Formula 1 can increase the carbon dioxide gas permeability and increase the carbon dioxide selectivity compared to methane by being included in the active layer of the gas separation membrane.

[0058] According to one embodiment of this specification, polysulfone, polyethersulfone, polycarbonate, polyethylene oxide, polyimide, polyetherimide, polyetheretherketone, polypropylene, polymethylpentene, polymethyl chloride, polyvinylidene fluoride, etc., can be used as hydrophilic polymers; however, the hydrophilic polymers are not limited to these. Specifically, polysulfone can be used as a hydrophilic polymer material.

[0059] According to one embodiment of this specification, a hydrophilic polymer solution can be formed by dissolving the hydrophilic polymer in a solvent. The solvent is not limited, as long as it can dissolve both the hydrophilic polymer and nitromethane. Examples include, but are not limited to, acetone, acetonitrile, tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), dimethylformamide (DMF), hexamethylphosphoramide (HMPA), etc. Based on the hydrophilic polymer solution, the hydrophilic polymer can be included in an amount of 12% to 20% by weight.

[0060] According to one embodiment of this specification, the porous substrate is not limited, as long as it is a material used as a support for the gas separation membrane, and examples may include, but are not limited to, polyester, polypropylene, nylon, polyethylene, or nonwoven fabrics. Specifically, nonwoven fabrics may be used as the porous substrate.

[0061] According to one embodiment of this specification, a porous layer can be formed by coating a porous substrate with a hydrophilic polymer solution. The porous layer can serve as a support for the separation membrane.

[0062] According to one embodiment of this specification, after forming the porous layer and before forming the active layer, a step of preparing a trench layer on the porous layer may be included. The trench layer is formed on the porous layer, enabling the formation of a uniform active layer. According to one embodiment of this specification, materials commonly used in the art can be used as the composition for forming the trench layer. Specifically, it may include polydimethylsiloxane (PDMS).

[0063] According to one embodiment of this specification, based on the composition used to form the trench layer, the polydimethylsiloxane content can be from 0.1% to 2% by weight, and preferably from 0.1% to 1% by weight.

[0064] According to one embodiment of this specification, the composition for forming the trench layer may further comprise a solvent. In this case, based on the composition for forming the trench layer, the solvent content may be from 98% to 99.9% by weight, and preferably from 99% to 99.9% by weight. The solvent may be an organic solvent, and may specifically be hexane.

[0065] According to one embodiment of this specification, the trench layer thickness can be from 0.01 μm to 1 μm. When the trench layer thickness meets the above range, the composition for forming the active layer coated on the trench layer is uniformly coated, and a uniform active layer can be formed.

[0066] According to one embodiment of this specification, after forming the active layer, a step of preparing a protective layer on the active layer may be further included. By coating the active layer, the protective layer protects the surface of the gas separation membrane, thereby improving durability and contamination resistance.

[0067] According to one embodiment of this specification, materials commonly used in the art can be used as the composition for forming the protective layer. Specifically, it may include polydimethylsiloxane (PDMS).

[0068] According to one embodiment of this specification, based on the composition used to form the protective layer, the polydimethylsiloxane content can be from 0.1% to 2% by weight, and preferably from 0.1% to 1% by weight.

[0069] According to one embodiment of this specification, the composition for forming the protective layer may further comprise a solvent. In this case, based on the composition for forming the protective layer, the solvent content may be from 98% to 99.9% by weight, and preferably from 99% to 99.9% by weight. The solvent may be an organic solvent, and may specifically be hexane.

[0070] According to one embodiment of this specification, the thickness of the protective layer can be from 0.01 μm to 2 μm.

[0071] Furthermore, one embodiment of this specification provides a gas separation membrane comprising: a porous layer; and an active layer formed on the porous layer comprising a polymer represented by chemical formula 1, wherein the gas separation membrane has a methane-based carbon dioxide selectivity of 5 to 30.

[0072] According to one embodiment of this specification, the carbon dioxide permeability of the gas separation membrane can be from 10 GPU to 150 GPU (gas permeation units, 10 -6 cm 3 (STP) / cm 2 The per second (cmHg) is preferably 80 to 125 GPUs, more preferably 100 to 125 GPUs, and even more preferably 120 to 125 GPUs.

[0073] According to one embodiment of this specification, the methane permeability of the gas separation membrane can be from 0.5 GPU to 15 GPU, preferably from 4 GPU to 5 GPU, and more preferably from 4.5 GPU to 5.0 GPU.

[0074] According to one embodiment of this specification, the methane-based carbon dioxide selectivity of the gas separation membrane can be from 10 to 30, preferably from 10 to 26.7, and more preferably from 25 to 26.7.

[0075] According to one embodiment of this specification, the active layer thickness can be from 0.2 μm to 2 μm. When the active layer thickness is less than 0.2 μm, the gas selectivity may decrease; while when the active layer thickness is greater than 2 μm, the gas permeability may decrease.

[0076] According to one embodiment of this specification, the gas separation membrane may further include a trench layer. The description of the trench layer is the same as that provided above.

[0077] According to one embodiment of this specification, the gas separation membrane may further include a protective layer. The description of the protective layer is the same as that provided above.

[0078] According to one embodiment of this specification, the thickness of the gas separation membrane can be from 100 μm to 200 μm. A gas separation membrane thickness of 100 μm or greater effectively prevents a decrease in the gas selectivity of the separation membrane, while a thickness of 200 μm or less effectively prevents a decrease in the gas permeability of the gas separation membrane.

[0079] According to one embodiment of this specification, the thickness of the porous layer can be from 100 μm to 200 μm, but is not limited thereto, and can be adjusted as needed. Furthermore, the pore size of the porous layer is preferably from 1 nm to 500 nm, but is not limited thereto.

[0080] Figure 1 The structure of a gas separation membrane according to one embodiment of this specification is shown.

[0081] Figure 1 A gas separation membrane 100 is shown, comprising: a porous layer 10 formed by coating a hydrophilic polymer solution onto a porous substrate; and an active layer 11 formed by coating a composition for forming an active layer disposed on the porous layer 10. The composition for forming the active layer may comprise a polymer represented by chemical formula 1.

[0082] Figure 2 The structure of a gas separation membrane according to another embodiment of this specification is shown.

[0083] Figure 2 A gas separation membrane 200 is shown, comprising: a porous layer 10 formed by coating a hydrophilic polymer solution onto a porous substrate; a trench layer 12 on the porous layer 10 for forming a uniform active layer; an active layer 11 formed by coating the trench layer 12 with a composition for forming the active layer; and a protective layer 13 on the active layer 11 for protecting the surface of the active layer and preventing defects. The composition for forming the active layer may comprise a polymer represented by chemical formula 1.

[0084] Another embodiment of this specification provides a gas separation membrane module including the gas separation membrane described above.

[0085] Another embodiment of this specification provides a gas separation membrane device comprising one or more of the above-described gas separation membrane modules.

[0086] This specification will be described in detail below with reference to embodiments. However, embodiments according to this specification can be modified in various other forms, and the scope of this specification should not be construed as limited to the embodiments described below. Embodiments of this specification are provided to more fully describe this specification to those skilled in the art.

[0087] Invention Embodiments

[0088] <Preparation Example> Preparation of Porous Layers

[0089] 18% by weight of polysulfone solids were introduced into N,N-dimethylformamide (DMF) solvent and dissolved at 80°C for 12 hours or longer to obtain a homogeneous liquid phase. The solution was then cast to a thickness of 50 μm on a 100 μm thick nonwoven fabric made of polyester to form a polysulfone porous layer.

[0090] <Example 1>

[0091] To form the trench layer, a solution of polydimethylsiloxane (PDMS, 1 wt%) and hexane (99 wt%) was coated onto the polysulfone porous layer prepared in the preparation example, and the result was dried in an oven at 60°C for 0.5 minutes. Subsequently, to form the active layer, a composition solution containing acetylated methylcellulose (AMC, 5 wt%) and nitromethane (95 wt%) for forming the active layer was coated onto the porous polysulfone support / trench layer using slit coating, and the result was dried in an oven at 60°C for 2 minutes. To form the protective layer, a solution of polydimethylsiloxane (PDMS, 1 wt%) and hexane (99 wt%) was coated onto the surface of the active layer, and the result was dried in an oven at 60°C for 1 minute, thus preparing a gas separation membrane.

[0092] <Example 2>

[0093] The gas separation membrane was prepared in the same manner as in Example 1, except that acetylated methylcellulose (AMC) was used instead of 5% by weight at 2.5% by weight.

[0094] <Example 3>

[0095] The gas separation membrane was prepared in the same manner as in Example 1, except that acetylated methylcellulose (AMC) was used instead of 5% by weight at 2.0% by weight.

[0096] <Example 4>

[0097] The gas separation membrane was prepared in the same manner as in Example 1, except that acetylated methylcellulose (AMC) was used instead of 5% by weight at 1.75% by weight.

[0098] <Example 5>

[0099] The gas separation membrane was prepared in the same manner as in Example 1, except that acetylated methylcellulose (AMC) was used instead of 5% by weight at 1.5% by weight.

[0100] <Example 6>

[0101] The gas separation membrane was prepared in the same manner as in Example 1, except that acetylated methylcellulose (AMC) was used instead of 5% by weight at 1.0% by weight.

[0102] <Comparative Example 1>

[0103] The gas separation membrane was prepared in the same manner as in Example 1, except that 5% by weight of cellulose acetate was used instead of 5% by weight of acetylated methyl cellulose (AMC).

[0104] <Comparative Example 2>

[0105] The gas separation membrane was prepared in the same manner as in Example 1, except that cellulose acetate was used at 2.5% by weight instead of acetylated methyl cellulose (AMC) at 5% by weight.

[0106] <Comparative Example 3>

[0107] The gas separation membrane was prepared in the same manner as in Example 1, except that cellulose acetate was used at 1.0 wt% instead of acetylated methyl cellulose (AMC) at 5 wt%.

[0108] <Comparative Example 4>

[0109] The gas separation membrane was prepared in the same manner as in Example 1, except that acetylated methylcellulose (AMC) was used instead of 5% by weight at 0.5% by weight.

[0110] <Comparative Example 5>

[0111] The gas separation membrane was prepared in the same manner as in Example 1, except that acetylated methylcellulose (AMC) was used instead of 5% by weight at 10% by weight.

[0112] <Experimental Example>

[0113] The gas separation membranes prepared in Examples 1 to 6 and Comparative Examples 1 to 5 were evaluated. Gas permeation was induced by the pressure difference between the upper and lower parts of the membrane by injecting gas into the upper part of the gas permeation unit at a constant pressure (50 psi, 80 psi, 100 psi, 200 psi, etc.) (1 psi = 6,895 Pa) using a pressure regulator at room temperature. Here, the flow rate of gas permeating through the separation membrane was measured using a bubble flow meter, and the permeability of the separation membrane was measured considering the settling time (>1 hour). The results of the gas permeability measurements are described in Table 1 below.

[0114] [Table 1]

[0115]

[0116] P CO2 and P CH4 These refer to the permeability of CO2 and CH4, respectively. CO2 / CH4 selectivity refers to the gas selectivity of carbon dioxide gas based on methane gas.

[0117] According to Table 1, the gas separation membranes of Examples 1 to 6 have a methane-based carbon dioxide selectivity of 10 or greater, and the gas separation membranes including an active layer using acetylated methyl cellulose (AMC) exhibit excellent carbon dioxide permeability and selectivity.

[0118] Compared with the gas separation membrane according to Comparative Example 1, which includes an active layer using cellulose acetate, the gas separation membrane according to Example 1, which includes an active layer using AMC, has higher carbon dioxide permeability and lower methane permeability, and CO2 / CH4 selectivity is increased by 10 times or more.

[0119] Similarly, compared with the gas separation membranes according to Comparative Examples 2 and 3, which include an active layer using cellulose acetate, the gas separation membranes according to Examples 2 and 6, which include an active layer using AMC, have a higher carbon dioxide permeability than methane permeability and a CO2 / CH4 selectivity that is 2 times or more improved.

[0120] Furthermore, the gas separation membranes according to Examples 3 and 6, which include an active layer using AMC, have a carbon dioxide permeability of 100 GPU or greater, and exhibit significantly superior carbon dioxide permeability compared to gas separation membranes containing cellulose acetate.

[0121] In particular, the gas separation membranes prepared according to Examples 3 to 5 with AMC of greater than or equal to 1.5% by weight and less than or equal to 2.0% by weight have a CO2 / CH4 selectivity of 25 or higher, and exhibit significantly superior CO2 / CH4 selectivity compared to gas separation membranes containing cellulose acetate.

[0122] Meanwhile, it was determined that Comparative Example 4, with an AMC content of less than 1% by weight, had a CO2 / CH4 selectivity that was reduced to about one-quarter of that of Example 1. Furthermore, Comparative Example 5, with an AMC content of greater than 5% by weight, was determined to have a CO2 / CH4 selectivity similar to that of Example 1, but with significantly lower carbon dioxide and methane permeability compared to Example 1.

[0123] Preferred embodiments of the present disclosure have been described above; however, the present disclosure is not limited thereto, and various modifications can be made within the scope of the claims and detailed description of the present invention, and such modifications also fall within the scope of the present disclosure.

Claims

1. A method for preparing a gas separation membrane, comprising: A porous layer is formed by coating a porous substrate with a hydrophilic polymer solution; as well as An active layer is formed by coating the porous layer with a composition comprising a polymer represented by the following chemical formula 1 and nitromethane for forming an active layer. The method further includes, after the formation of the porous layer and before the formation of the active layer, preparing a trench layer on the porous layer using a composition comprising polydimethylsiloxane for forming trench layers. The method further includes, after the formation of the active layer, preparing a protective layer on the active layer using a composition comprising polydimethylsiloxane for forming a protective layer. The polymer represented by Formula 1 is included in the composition for forming the active layer at a concentration of 1.5% to 2% by weight: [Chemical Formula 1] In chemical formula 1, n is the number of repeating units, and is an integer from 500 to 3,000; and R1 and R3 through R5 are methyl, R2 is -(C=O)R6, and R6 is ethyl.

2. The method for preparing a gas separation membrane according to claim 1, wherein the composition for forming the active layer is applied using slit coating.

3. The method for preparing a gas separation membrane according to claim 1, wherein the hydrophilic polymer is polysulfone, polyethersulfone, polycarbonate, polyethylene oxide, polyimide, polyetherimide, polyetheretherketone, polypropylene, polymethylpentene, or polyvinylidene fluoride.

4. The method for preparing a gas separation membrane according to claim 1, wherein the polymer represented by chemical formula 1 has a weight-average molecular weight Mw of 100,000 to 700,000.

5. The method for preparing a gas separation membrane according to claim 1, wherein the number-average molecular weight Mn of the polymer represented by chemical formula 1 is from 80,000 to 400,000.

6. A gas separation membrane prepared by the method for preparing a gas separation membrane according to any one of claims 1 to 5, comprising: Porous layer; Trench layer containing polydimethylsiloxane; An active layer comprising a polymer represented by the following chemical formula 1 is formed on the porous layer; and A protective layer containing polydimethylsiloxane. The methane-based carbon dioxide selectivity of the gas separation membrane is said to be 25 to 26.

7. [Chemical Formula 1] In chemical formula 1, n is the number of repeating units, and is an integer from 500 to 3,000; and R1 and R3 through R5 are methyl, R2 is -(C=O)R6, and R6 is ethyl.

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