Composite gas separation membrane and preparation method thereof

Abstract

The invention relates to the technical field of separation membrane materials, and discloses a composite gas separation membrane and a preparation method thereof.A groove layer, a selection layer and an optional protection layer are sequentially prepared on a porous substrate layer, and the preparation method comprises the steps that after the porous substrate layer is pre-wetted, first coating of a first solution of pre-crosslinked polydimethylsiloxane is conducted, first drying is conducted, and a second solution of pre-crosslinked polydimethylsiloxane is obtained; carrying out plasma treatment, carrying out second coating by using a second solution, and then carrying out second drying; optionally, performing third coating with a third solution of a fluorine-containing polymer after the second drying, and performing third drying to obtain a composite gas separation membrane; the second solution comprises a polyoxyethylene copolymer, an additive and an initiator; the additive is a polymer of formula I; the average number average molecular weight of the # imgabs0 # additive is 250 to 5000 g / mol; the plasma treatment time is 2-120 s, and the treatment power is 20-120 W; the separation membrane has high CO2 permeability, selectivity and mechanical strength.

Description

Technical Field

[0001] The present invention relates to the technical field of separation membrane materials, and particularly to a composite gas separation membrane and a preparation method thereof. Background Art

[0002] Membrane-based carbon dioxide separation technology has attracted much attention as a clean and low-carbon technology and is considered a promising carbon capture technology to mitigate the impact of rising atmospheric CO 2 levels on global warming. The membrane used for large-scale flue gas CO 2 capture should have a high permeability and a high CO 2 / N 2 selectivity. Existing polymer membrane materials for gas separation, such as polyimide and polyetherimide, have good gas selectivity but low gas permeability; while polydimethylsiloxane and polytrimethylsilylpropyne have high gas permeability but low selectivity. In this regard, polyethylene oxide (PEO), as a representative CO 2 philic material, has attracted extensive research attention due to its special dipole-quadrupole interaction with CO 2 .

[0003] CN105561802A discloses a preparation method of a novel UV-cured polyethylene oxide semi-interpenetrating network gas separation membrane. By adding linear polyethylene oxide dimethyl ether that does not participate in the polymerization reaction to a UV cross-linking system of polyethylene glycol methacrylate and polyethylene glycol dimethacrylate, the CO 2 permeability coefficient of the homogeneous membrane is above 2900 Barrer. Although the membrane has a high permeability to CO 2 , the prepared separation membrane is a PEO homogeneous membrane with a relatively thick membrane (about 50 - 150 μm), which cannot meet the requirements of CO 2 permeability and CO 2 / N 2 selectivity in industrial applications. Summary of the Invention

[0004] The purpose of the present invention is to overcome the problem that the existing composite gas separation membrane cannot balance the CO 2 permeability, CO 2 / N 2 selectivity and mechanical strength. The present invention provides a composite gas separation membrane and a preparation method thereof. The composite gas separation membrane prepared by this method has high CO 2 permeability, CO 2 / N 2 selectivity and mechanical strength.

[0005] To achieve the above object, a first aspect of the present invention provides a method for preparing a composite gas separation membrane, wherein the method comprises successively preparing a groove layer, a selective layer and optionally a protective layer on a porous substrate layer, comprising the following steps:

[0006] (1) Pre-wet the porous substrate layer, and first coat a first solution of pre-crosslinked polydimethylsiloxane on the pre-wetted porous substrate layer, and perform first drying;

[0007] (2) After subjecting the product of the first drying to plasma treatment, second coat with a second solution, and then perform second drying;

[0008] (3) Optionally, third coat a third solution containing a fluoropolymer on the surface of the product after the second drying, and obtain a composite gas separation membrane after third drying;

[0009] The second solution comprises a polyoxyethylene copolymer, an additive and an initiator;

[0010] The additive is a polymer represented by Formula I;

[0011]

[0012] wherein, R 1 is an alkyl group having 1 to 3 carbon atoms, a phenyl group or R 2 is H or a methyl group;

[0013] wherein, the average number-average molecular weight of the additive is 250 - 5,000 g / mol;

[0014] The time of the plasma treatment is 2 - 120 s, and the treatment power is 20 - 120 W.

[0015] A second aspect of the present invention provides a composite gas separation membrane, wherein the composite gas separation membrane is prepared by the above preparation method.

[0016] By the above technical solutions, the composite gas separation membrane and the preparation method provided by the present invention have the following beneficial effects:

[0017] By pre-wetting the porous substrate layer, the present invention can prevent the first solution of pre-crosslinked polydimethylsiloxane from penetrating into the voids of the porous substrate layer, increasing the penetration resistance of the porous substrate layer; the additive in the second solution polymerizes on the groove layer after plasma treatment, and the polymer formed by the polymerization of the additive generates sufficient entanglement with the polyoxyethylene copolymer chains, endowing the composite gas separation membrane with sufficient mechanical strength and high CO 2 permeability and CO 2 / N 2 selectivity. Description of the Drawings

[0018] Figure 1 It is the SEM cross-sectional view of the composite gas separation membrane of Example 1.

[0019] Figure 2 It is the SEM cross-sectional view of the groove layer after the CO 2 plasma treatment in Example 1. Detailed implementation manners

[0020] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0021] The first aspect of the present invention provides a method for preparing a composite gas separation membrane. Among them, the method includes successively preparing a groove layer, a selective layer, and optionally a protective layer on a porous substrate layer, including the following steps:

[0022] (1) Pre-wet the porous substrate layer, and first coat a first solution of pre-crosslinked polydimethylsiloxane on the pre-wetted porous substrate layer, and perform first drying;

[0023] (2) After performing plasma treatment on the product of the first drying, perform second coating with a second solution, and then perform second drying;

[0024] (3) Optionally, third coat a third solution containing a fluoropolymer on the surface of the product after the second drying, and obtain a composite gas separation membrane after third drying;

[0025] The second solution contains a polyoxyethylene copolymer, an additive, and an initiator;

[0026] The additive is a polymer represented by Formula I;

[0027]

[0028] Among them, R 1 is an alkyl group with 1-3 carbon atoms, a phenyl group, or R 2 is H or a methyl group;

[0029] Among them, the average number-average molecular weight of the additive is 250-5,000 g / mol;

[0030] The time of the plasma treatment is 2-120 s, and the treatment power is 20-120 W.

[0031] In the present invention, by pre-wetting the porous substrate layer, it is possible to prevent the first solution of pre-crosslinked polydimethylsiloxane from penetrating into the voids of the porous substrate layer, increasing the penetration resistance of the porous substrate layer; additives in the second solution polymerize on the groove layer after plasma treatment, and the polymer formed by the polymerization of the additives generates sufficient entanglement with the polyethylene oxide copolymer chains, enabling the composite gas separation membrane to have sufficient mechanical strength and high CO 2 permeability and CO 2 / N 2 selectivity.

[0032] In the present invention, when the conditions of the plasma treatment satisfy the above range, it is beneficial to improve the compatibility and affinity between the groove layer and the selective layer, and the prepared composite gas separation membrane has high gas permeation flux and CO 2 / N 2 selective separation performance, and at the same time has high tensile strength.

[0033] In the present invention, when the average number-average molecular weight of the polymer shown in Formula I satisfies the above range, a selective layer with a relatively high degree of crosslinking can be obtained, making the selective layer dense and defect-free, with higher gas selectivity, and enabling the separation membrane to have excellent mechanical properties.

[0034] Furthermore, in Formula I, R1 is methyl, phenyl or R 2 is H or methyl.

[0035] Furthermore, the average number-average molecular weight of the additive is 1,000 - 4,000 g / mol.

[0036] Furthermore, the time of the plasma treatment is 20 - 60 s, and the treatment power is 55 - 110 W.

[0037] According to the present invention, in step (1), the porous substrate layer is a non-woven fabric containing a porous support layer.

[0038] In the present invention, there are no special requirements for the non-woven fabric, and it can be a non-woven fabric commonly used in the art. For example, the non-woven fabric can be a polyester non-woven fabric.

[0039] According to the present invention, the porous support layer is selected from at least one of polysulfone, polyethersulfone, polyacrylonitrile, and polyvinylidene fluoride.

[0040] According to the present invention, the thickness of the porous substrate layer is 100 - 140 μm.

[0041] Furthermore, the thickness of the porous substrate layer is 110 - 130 μm.

[0042] In the present invention, there are no special requirements for the dosages of polysulfone, polyethersulfone, polyacrylonitrile or polyvinylidene fluoride, and the dosages can meet the thickness of the porous substrate layer.

[0043] In the present invention, there are no particular limitations on the source of the porous substrate layer, and it can be commercially available. Preferably, in the present invention, the preparation method of the porous substrate layer includes:

[0044] (a) Mixing a polymer with an organic solvent to obtain a casting solution;

[0045] (b) Coating the casting solution on a non-woven fabric to obtain a nascent membrane, and soaking the nascent membrane in a non-solvent and drying to obtain a porous substrate layer.

[0046] In the present invention, in step (a), the polymer is selected from at least one of polysulfone, polyethersulfone, polyacrylonitrile and polyvinylidene fluoride. There are no special limitations on the organic solvent in step (a), and it can be an organic solvent conventionally used in the art, such as N,N-dimethylformamide (DMF).

[0047] There are no special limitations on the dosage of the organic solvent in step (a) of the present invention. Preferably, the content of the polymer in the casting solution is 15-25 wt%.

[0048] In the present invention, in step (b), there are no special limitations on the coating method, and it can be a conventional coating method in the art. For example, the casting solution can be scraped by a knife-coating method. Preferably, the thickness of the knife is 200-250 μm. Preferably, the non-solvent is at least one of ionized water and / or ethanol. Preferably, in step (b), the soaking time is 20-30 h. Preferably, the non-solvent is replaced during the soaking process, and the number of replacements is 3-5 times. Preferably, the drying temperature is 60-100 °C.

[0049] According to the present invention, in step (1), the pre-wetting solvent is selected from at least one of water, alcohol, fluorocarbon solvent and C3-C4 ketones.

[0050] In the present invention, when using the above specific solvents, it is easy to remove them by drying or other means, and thus it can effectively prevent the separation layer membrane solution from invading the porous substrate layer, avoid trench layer defects, and improve the gas permeability of the composite gas separation membrane.

[0051] According to the present invention, the alcohol is C2-C4 alcohol.

[0052] Furthermore, the alcohol is selected from at least one of n-butanol, isobutanol and ethanol.

[0053] According to the present invention, the fluorocarbon solvent is a fluorinated alkane.

[0054] According to the present invention, the boiling point of the fluorocarbon solvent is 40-99 °C.

[0055] Furthermore, the boiling point of the fluorocarbon solvent is 50-90 °C.

[0056] In the present invention, the fluorocarbon solvent can be obtained commercially. For example, FC-72 of 3M's TM electronic fluorinated liquid Fluorinert TM can be selected.

[0057] According to the present invention, in step (1), the pre-wetting time is 10 min - 24 h.

[0058] In the present invention, when the pre-wetting time meets the above range, the micropores of the porous substrate layer can be fully wetted, effectively preventing the film liquid of the trench layer, i.e., the first solution, from invading the porous substrate layer, avoiding trench layer defects, and improving the gas permeability of the composite gas separation membrane.

[0059] Furthermore, the pre-wetting time is 30 min - 12 h.

[0060] According to the present invention, in the first solution in step (1), at 25 °C, the kinematic viscosity of the pre-crosslinked polydimethylsiloxane is 8-30 cP.

[0061] In the present invention, when the kinematic viscosity of the pre-crosslinked polydimethylsiloxane meets the above range, it has the characteristics of good film-forming property, and the prepared trench layer is smoother, thinner, denser and defect-free, which is beneficial to improving the gas permeability of the composite gas separation membrane.

[0062] Furthermore, in the first solution in step (1), at 25 °C, the kinematic viscosity of the pre-crosslinked polydimethylsiloxane is 10-20 cP.

[0063] According to the present invention, the solid content of the first solution is 0.1 wt% - 1 wt%.

[0064] In the present invention, when the solid content of the first solution meets the above range, it has good film-forming property, appropriate viscosity, and appropriate curing time, which is beneficial to the coating operation. The prepared trench layer is smoother, thinner, denser and defect-free, which is beneficial to achieving a higher effect of improving gas permeability.

[0065] Furthermore, the solid content of the first solution is 0.2 wt% - 0.5 wt%.

[0066] According to the present invention, the ratio of the volume of the first solution to the area of the porous substrate layer is 0.01-0.1 mL / cm 2 .

[0067] Further, the ratio of the volume of the first solution to the area of the porous substrate layer is 0.02 - 0.06 mL / cm 2 .

[0068] According to the present invention, the time for the first coating is 2 s - 60 s.

[0069] Further, the time for the first coating is 10 s - 40 s.

[0070] In the present invention, the temperature for the first drying is 30 - 80 °C, and the time for the first drying is 1 - 120 min.

[0071] In the present invention, there is no particular limitation on the source of the pre-crosslinked polydimethylsiloxane, and it can be commercially available. Preferably, in the present invention, the pre-crosslinked polydimethylsiloxane is prepared according to the following steps: in the presence of an organic solvent and a catalyst, polydimethylsiloxane and a crosslinking agent are mixed and then crosslinked to obtain the pre-crosslinked polydimethylsiloxane.

[0072] According to the present invention, based on the total weight of the pre-crosslinked polydimethylsiloxane, the content of the polydimethylsiloxane is 40 - 60 wt%, and the content of the crosslinking agent is 40 - 60 wt%.

[0073] Further, based on the total weight of the pre-crosslinked polydimethylsiloxane, the content of the polydimethylsiloxane is 45 - 55 wt%, and the content of the crosslinking agent is 45 - 55 wt%.

[0074] According to the present invention, based on the total amount of the polydimethylsiloxane and the crosslinking agent, the content of the catalyst is 20 - 50 wt%.

[0075] Further, based on the total amount of the polydimethylsiloxane and the crosslinking agent, the content of the catalyst is 25 - 30 wt%.

[0076] In the present invention, the organic solvent is selected from at least one of n-heptane, n-hexane, and cyclohexane. There is no special limitation on the amount of the organic solvent in the present invention, as long as the polydimethylsiloxane and the crosslinking agent can be dispersed in each other.

[0077] According to the present invention, the number-average molecular weight of the polydimethylsiloxane is 20,000 - 100,000 g / mol.

[0078] According to the present invention, the crosslinking agent is a silicone-based crosslinking agent.

[0079] In the present invention, there is no special limitation on the selection of the silicone crosslinking agent, and it can be a conventional silicone crosslinking agent in the art. Preferably, the crosslinking agent is selected from at least one of tetraethyl orthosilicate, tetramethyl orthosilicate, and 1,2-bis(trimethoxysilyl)ethane.

[0080] According to the present invention, the catalyst is an organotin catalyst.

[0081] In the present invention, there is no special limitation on the type of the organotin catalyst, and it can be a conventional organotin catalyst in the art. Preferably, the catalyst is selected from at least one of dibutyltin dilaurate and dioctyltin dilaurate.

[0082] According to the present invention, the crosslinking temperature is 30-80 °C, and the crosslinking time is 30-120 min.

[0083] In a preferred embodiment of the present invention, the preparation method of the pre-crosslinked polydimethylsiloxane includes: in the presence of an organic solvent and a catalyst, mixing polydimethylsiloxane and a crosslinking agent and then carrying out crosslinking, and degassing under vacuum for 1-5 min to obtain a first solution of the pre-crosslinked polydimethylsiloxane.

[0084] In the present invention, the first solution of the pre-crosslinked polydimethylsiloxane is directly prepared by the above method, so that the continuity of the preparation method of the composite gas separation membrane is better and impurities are not easily introduced. In the present invention, the solvent of the first solution is the same as the organic solvent.

[0085] According to the present invention, the gas source for the plasma treatment is selected from at least one of argon, oxygen, and carbon dioxide.

[0086] Furthermore, the gas source for the plasma treatment is oxygen and / or carbon dioxide.

[0087] In the present invention, the inlet gas flow rate of the gas source is 25-500 mL / min.

[0088] According to the present invention, in step (2), in the second solution, the content of the polyethylene oxide copolymer is 0.5 wt%-3 wt%, the content of the additive is 0.1 wt%-5 wt%, and the content of the initiator is 0.1 wt%-1 wt%.

[0089] In the present invention, when the contents of the components in the second solution meet the above ranges, a selection layer with a higher degree of crosslinking can be obtained, making the selection layer dense and defect-free, with higher gas selectivity and superior mechanical properties.

[0090] Further, in the second solution, the content of the polyoxyethylene copolymer is 0.5 wt% - 1 wt%, the content of the additive is 0.5 wt% - 3 wt%, and the content of the initiator is 0.5 wt% - 1 wt%.

[0091] According to the present invention, the polyoxyethylene copolymer is selected from at least one of polyoxyethylene - polyamide copolymer (PEO - PA), polyoxyethylene - polyimide copolymer (PEO - PI), and polyoxyethylene - polybutylene terephthalate (PEO - PBT).

[0092] In the present invention, the polyoxyethylene - polyamide copolymer can be obtained by commercial purchase, such as pebax1657 and / or pebax2533 of Arkema.

[0093] According to the present invention, the initiator is an azo compound and / or an organic peroxide.

[0094] Further, the initiator is selected from at least one of azobisisobutyronitrile (AIBN), azobisisoheptonitrile (ABVN), and dimethyl azobisisobutyrate (AIBME).

[0095] According to the present invention, the solvent of the second solution is alcohol and / or water, preferably selected from at least one of ethanol, water, n - butanol, and isobutanol.

[0096] In a preferred embodiment of the present invention, the preparation method of the second solution includes: stirring the polyoxyethylene copolymer, the additive, the initiator, and the solvent at 20 - 50 °C for 30 min - 120 min, and performing vacuum degassing for 1 - 5 min to obtain the second solution.

[0097] According to the present invention, in step (2), the temperature of the second drying is 80 - 100 °C, and the time of the second drying is 1 - 4 h.

[0098] According to the present invention, the ratio of the volume of the second solution to the area of the porous substrate layer is 0.02 - 0.2 mL / cm 2 .

[0099] According to the present invention, the time of the second coating is 10 s - 120 s.

[0100] Further, the ratio of the volume of the second solution to the area of the porous substrate layer is 0.05 - 0.15 mL / cm 2 .

[0101] Further, the time of the second coating is 30 s - 60 s.

[0102] According to the present invention, the cross - linking degree of the selective layer is 50% - 90%.

[0103] In the present invention, when the crosslinking degree of the selective layer meets the above range, it indicates that covalent bonding connections are formed between polymer molecules to form a network structure. The obtained composite gas separation membrane not only has high CO 2 permeability and CO 2 / N 2 selectivity, but also has high mechanical strength.

[0104] Furthermore, the crosslinking degree of the selective layer is 60%-75%.

[0105] In a preferred embodiment of the present invention, the method includes successively preparing a groove layer, a selective layer, and a protective layer on a porous substrate layer.

[0106] In the present invention, the protective layer is a fluoropolymer layer, which can make the composite gas separation membrane have good heat resistance and waterproof performance while maintaining the separation performance of the composite gas separation membrane.

[0107] According to the present invention, in step (3), in the third solution, the content of the fluoropolymer is 0.1 wt%-1 wt%.

[0108] According to the present invention, the fluoropolymer is selected from at least one of a copolymer of perfluoro-2,2-dimethyl-1,3-dioxolene and tetrafluoroethylene (PDD-TFE), a copolymer of 2,2,4-trifluoro-5-trifluoromethoxy-1,3-dioxolene and tetrafluoroethylene (TTD-TFE), and a homopolymer of perfluoro 4-vinyl oxy-1-butene (BVE).

[0109] In the present invention, the fluoropolymer can be obtained by commercial purchase. For example, the copolymer of perfluoro-2,2-dimethyl-1,3-dioxolene and tetrafluoroethylene (PDD-TFE) is Teflon AF2400, the copolymer of 2,2,4-trifluoro-5-trifluoromethoxy-1,3-dioxolene and tetrafluoroethylene (TTD-TFE) is Hyflon AD60, and the homopolymer of perfluoro 4-vinyl oxy-1-butene (BVE) is Cytop.

[0110] According to the present invention, the solvent of the third solution is a perfluoropolyether solution.

[0111] In the present invention, the perfluoropolyether solution can be obtained by commercial purchase. For example, GALDEN HT110 from Solvay.

[0112] According to the present invention, the temperature of the third drying is 50-80 °C, and the time of the third drying is 1-24 h.

[0113] According to the present invention, the ratio of the volume of the third solution to the area of the porous substrate layer is 0.01 - 0.1 mL / cm 2 .

[0114] According to the present invention, the time for the third coating is 2 s - 60 s.

[0115] In the present invention, when the ratio of the volume of the third solution to the area of the porous substrate layer and / or the time for the third coating satisfy the above ranges, the composite gas separation membrane has good heat resistance and high gas permeation flux and CO 2 / N 2 selective separation performance at high temperatures.

[0116] Furthermore, the ratio of the volume of the third solution to the area of the porous substrate layer is 0.02 - 0.05 mL / cm 2 .

[0117] Furthermore, the time for the third coating is 10 s - 30 s.

[0118] In a preferred embodiment of the present invention, the method for preparing the third solution includes: mixing a fluoropolymer with a perfluoropolyether solution and degassing under vacuum for 1 - 5 min to obtain the third solution.

[0119] The second aspect of the present invention provides a composite gas separation membrane, wherein the composite gas separation membrane is prepared by the above preparation method.

[0120] According to the present invention, the CO 2 permeation rate of the composite gas separation membrane is greater than or equal to 500 GPU.

[0121] Furthermore, the CO 2 permeation rate of the composite gas separation membrane is greater than or equal to 1000 GPU.

[0122] According to the present invention, the separation selectivity of the composite gas separation membrane for CO 2 and N 2 is greater than or equal to 30.

[0123] Furthermore, the separation selectivity of the composite gas separation membrane for CO 2 and N 2 is greater than or equal to 50.

[0124] According to the present invention, the strength of the composite gas separation membrane is greater than or equal to 10 MPa.

[0125] Furthermore, the strength of the composite gas separation membrane is greater than or equal to 50 MPa.

[0126] According to the present invention, the thickness of the composite gas separation membrane is 110 μm - 150 μm.

[0127] According to the present invention, the composite gas separation membrane sequentially includes a porous substrate layer, a groove layer, a selective layer, and optionally a protective layer.

[0128] According to the present invention, the groove layer is crosslinked polydimethylsiloxane.

[0129] According to the present invention, the selective layer contains a combination of a polyethylene oxide copolymer and at least one selected from methoxypolyethylene glycol acrylate, polyethyleneglycol methyl ether acrylate, phenylpolyethylene glycol acrylate, and polyethylene glycol diacrylate.

[0130] According to the present invention, in the selective layer, the content of the polyethylene oxide copolymer is 30 - 90 wt%.

[0131] In the present invention, the content of the polyethylene oxide copolymer in the selective layer is calculated according to the feeding amounts of the polyethylene oxide copolymer and the additive.

[0132] Furthermore, in the selective layer, the content of the polyethylene oxide copolymer is 50 - 70 wt%.

[0133] According to the present invention, the protective layer is a fluoropolymer.

[0134] The present invention will be described in detail below through examples.

[0135] The thickness of the porous substrate layer and the composite gas separation membrane is measured by scanning electron microscopy.

[0136] The crosslinking degree of the selective layer is measured by the equilibrium swelling method.

[0137] The dynamic viscosity of the pre-crosslinked polydimethylsiloxane is measured by a digital display rotational viscometer (Brookfield, USA), and the test temperature is 25 °C.

[0138] The degree of polymerization of the additive is measured by nuclear magnetic resonance method, and the average number-average molecular weight of the additive is calculated.

[0139] CO 2 Permeation rate: CO 2 and N 2 mixed gas is used to simulate flue gas (composed of 15% CO 2 by mole fraction and 85% N 2The gas mixture (composition) was used as the feed gas, and Ar was used as the purge gas. The inlet pressure was 0.2 MPa, the temperature was 25 °C, the flow rate of the purge gas was kept constant at 35 mL / min, and the gas on the permeate side was sent to an Agilent gas chromatograph for detection and analysis by the Ar purge gas through a mass flow meter. The total permeate side flow rate was measured by a soap film flow meter, and the flow rate of the gas components on the permeate side was calculated based on the mass fraction of the gas components on the permeate side measured by the gas chromatograph.

[0140] Component CO 2 Permeation rate R i was calculated by Equation 1:

[0141]

[0142] Q is the total flow rate of the permeate gas and the purge gas, cm 3 / s; A is the membrane area, in cm 2 ; Δp i is the pressure difference of component i across the membrane, cmHg; R i is the permeation rate of gas component i. To simplify the units, GPU was introduced as the permeability unit, as shown in Equation 2.

[0143] GPU = 10 -6 ·cm 3 (STP)·cm -2 ·s -1 ·cmHg -1 (2)

[0144] In the formula, 1 cmHg = 1.33 kPa; STP represents the standard condition, that is, the temperature is 273.15 K (i.e., 0 °C) and the pressure is 101.325 kPa.

[0145] CO 2 and N 2 The ratio of the permeability (permeability coefficient) when passing through the membrane is the separation selectivity, denoted by α i / j. It was calculated by Equation 3

[0146]

[0147] In the formula, R i is the permeation rate of gas component CO 2 and R j is the permeation rate of gas component N 2 .

[0148] The tensile strength was measured according to the standard measured by GB / T 1040.3-2006. Test conditions: sample strip with a width of 1 cm and a length of 4 cm, tensile speed of 40 mm / min.

[0149] The plasma treatment was carried out using a plasma cleaner (PVA TePla Plasma System ION40).

[0150] Poly(ethylene oxide)-polyamide (PEO-PA) copolymer A: purchased from Arkema France, grade Pebax 2533, and the content of poly(ethylene oxide) structural units in copolymer A was 80 wt%.

[0151] Poly(ethylene oxide)-polyamide (PEO-PA) copolymer B: purchased from Arkema France, grade Pebax 1657, and the content of poly(ethylene oxide) structural units in copolymer B was 60 wt%.

[0152] The additives PEGMEA-300, PEGMEA-500, PEGMEA-1000, and PEGMEA-4000 were purchased from Merck, and the average number-average molecular weights were 300 g / mol, 500 g / mol, 1000 g / mol, and 4000 g / mol respectively. R 1 is methyl, and R 2 is methyl.

[0153] Unless otherwise specified, the ethanol aqueous solution described in the examples refers to a solution with a volume ratio of ethanol to water of 70:30.

[0154] All other raw materials used in the examples and comparative examples were commercially available products.

[0155] Preparation of the porous substrate layer

[0156] A casting solution composed of 20% by mass of polysulfone and 80% of N,N-dimethylformamide solvent (DMF) was prepared. At a scraping speed of 6 m / min, the casting solution was scraped on a polyester non-woven fabric by the method of blade moving coating. The thickness of the blade was 220 μm (i.e., the thickness of the nascent film). Deionized water was used as the non-solvent. The obtained nascent film was immersed in deionized water for 24 h and subjected to three deionized water replacements, and then dried at 70 °C to obtain a porous substrate layer with a thickness of 110 μm.

[0157] Preparation Example 1

[0158] Polydimethylsiloxane (PDMS with a number-average molecular weight of 20,000 g / mol), cross-linking agent tetraethyl orthosilicate (TEOS), and catalyst dibutyltin dilaurate (DBD) were added to n-heptane. Based on the total weight of the pre-crosslinked polydimethylsiloxane, the content of polydimethylsiloxane was 50 wt%, the content of the cross-linking agent was 50 wt%, and based on the total amount of polydimethylsiloxane and the cross-linking agent, the content of the catalyst was 25 wt%. Stir at 30 °C for 60 minutes and defoam under vacuum for 5 minutes to obtain the first solution A, and the measured parameters are shown in Table 1.

[0159] Preparation Example 2

[0160] The first solution B was prepared according to Preparation Example 1, except that polydimethylsiloxane (number-average molecular weight of PDMS was 20,000 g / mol), crosslinking agent tetraethyl orthosilicate (TEOS), and catalyst dibutyltin dilaurate (DBD) were added to n-heptane. Based on the total weight of the pre-crosslinked polydimethylsiloxane, the content of the polydimethylsiloxane was 50 wt%, the content of the crosslinking agent was 50 wt%, and based on the total amount of the polydimethylsiloxane and the crosslinking agent, the content of the catalyst was 25 wt%. Stir at 30 °C for 30 minutes and defoam under vacuum for 5 minutes to obtain the first solution B. The measured parameters are shown in Table 1.

[0161] Table 1

[0162]

[0163] Example 1

[0164] (1) Groove layer: The first solution A was coated on a porous substrate layer pre-wetted with water for 30 min by dip coating. Dry at 50 °C for 120 min to obtain the groove layer. The ratio of the volume of the first solution A to the area of the porous substrate layer was 0.03 mL / cm 2 , and the time of the first coating was 20 s.

[0165] (2) Selective layer: The groove layer obtained in step (1) was subjected to plasma treatment, wherein the flow rate of carbon dioxide was 500 mL / min, the treatment time was 30 s, and the treatment power was 110 W. Polyethylene oxide-polyamide (PEO-PA) copolymer (Pebax 2533), poly(ethylene glycol) methyl ether acrylate (PEGMEA, Mn 4000), azobisisobutyronitrile (AIBN), and n-butanol were stirred at 30 °C for 60 min and defoamed under vacuum for 5 min to obtain a second solution (the content of Pebax 2533 was 0.5 wt%, the content of PEGMEA-4000 was 0.5 wt%, and the content of AIBN was 0.5 wt%). The second solution was coated on the groove layer after plasma treatment. The ratio of the volume of the second solution to the area of the porous substrate layer was 0.1 mL / cm 2 , and the time of the second coating was 35 s. Dry at 80 °C for 4 h. The crosslinking degree of the selective layer was tested, and the test results are shown in Table 3.

[0166] (3) Protective layer: A third solution containing a fluoropolymer is coated on the selected layer in step (2). Specifically, a fluoropolymer (Teflon AF2400) and a perfluoropolyether solution (GALDEN HT110) are stirred for 30 min and degassed under vacuum for 5 minutes to obtain a third solution (the content of the fluoropolymer is 0.1 wt%). The fluoropolymer layer is dried at 80 °C for 1 h to obtain a composite gas separation membrane. Specifically, the ratio of the volume of the third solution to the area of the porous substrate layer is 0.03 mL / cm 2 , and the time for the third coating is 20 s.

[0167] The performance test results of this composite gas separation membrane are shown in Table 3.

[0168] Examples 2 - 13

[0169] A composite gas separation membrane is prepared according to the method of Example 1, and the specific parameters are shown in Table 2. The test results of the prepared composite gas separation membrane are shown in Table 3.

[0170] Example 14

[0171] A composite gas separation membrane is prepared according to the method of Example 1, except that step (3) is not included and the crosslinking degree of the selected layer is 63%. The test results of the composite gas separation membrane are shown in Table 3.

[0172] Table 2

[0173]

[0174] Continued Table 2

[0175]

[0176]

[0177] Comparative Example 1

[0178] The casting solution contains poly(ethylene glycol) methyl ether acrylate (PEGMEA), poly(ethylene glycol) dimethacrylate (PEGDA), and linear poly(ethylene glycol) dimethyl ether (PEGDME). The mass ratio of PEGMEA, PEGDA, and PEGDME is 7:3:3. The number-average molecular weight of PEGMEA is 500 g / mol, the number-average molecular weight of PEGDA is 700 g / mol, and the number-average molecular weight of PEGDME is 500 g / mol. 0.5 wt% photoinitiator (4-phenylbenzophenone) is added to the casting solution, mechanically stirred and dispersed for 0.5 h, and degassed by ultrasound for 10 min. The ultrasound is 40 W and 40 KHz. 0.5 mL of the prepared casting solution is dropped between two quartz glasses with a distance of 50 μm between the quartz glasses. The quartz glass slides with the casting solution are placed in an ultraviolet lamp box and cured for 60 s to obtain a homogeneous membrane with a thickness of 45 μm. The performance test results are shown in Table 3.

[0179] Comparative Example 2

[0180] The composite gas separation membrane was prepared according to the method of Example 1, except that plasma treatment was not used in step (2). The performance test results of the composite gas separation membrane are shown in Table 3.

[0181] Comparative Example 3

[0182] The composite gas separation membrane was prepared according to the method of Example 1, except that the plasma treatment time in step (2) was 30 s and the treatment power was 180 W. The test results of the composite gas separation membrane are shown in Table 3.

[0183] Comparative Example 4

[0184] The composite gas separation membrane was prepared according to the method of Example 1, except that in step (2), the second solution did not contain azobisisobutyronitrile (AIBN). The test results of the composite gas separation membrane are shown in Table 3.

[0185] Comparative Example 5

[0186] The composite gas separation membrane was prepared according to the method of Example 1, except that in step (1), the porous substrate layer was not pre-wetted, and the first solution A was directly coated on the porous substrate layer. The test results of the composite gas separation membrane are shown in Table 3.

[0187] Table 3

[0188]

[0189]

[0190] It can be seen from the results that the composite gas separation membrane of the present invention has better CO 2 permeation rate and CO 2 / N2 Separation selectivity, and at the same time, it also has excellent tensile strength.

[0191] Figure 1 It is the SEM cross-sectional view of the composite gas separation membrane in Example 1. It can be seen that the separation layer is thin and dense, and is tightly combined with the porous substrate layer, indicating that pre-wetting the porous substrate layer adopted in the present invention can effectively prevent the first solution of pre-crosslinked polydimethylsiloxane from invading the porous substrate layer. Adopting a plasma-modified groove layer can make the selective layer film liquid evenly coated, and a thin and dense selective layer can be obtained after crosslinking.

[0192] Figure 2 It is the cross-sectional SEM view of the groove layer after the CO 2 plasma treatment in Example 1. It can be seen that the groove layer is thin and dense, indicating that the plasma treatment enables the groove layer to still maintain a dense structure.

[0193] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A method for preparing a composite gas separation membrane, characterized in that, the method comprises successively preparing a groove layer, a selective layer and optionally a protective layer on a porous substrate layer, and includes the following steps: (1) Pre-wetting the porous substrate layer, and first coating a first solution of pre-crosslinked polydimethylsiloxane on the pre-wetted porous substrate layer, and performing first drying; (2) After performing plasma treatment on the product of the first drying, second coating with a second solution, and then performing second drying; (3) Optionally, third coating a third solution containing a fluoropolymer on the surface of the product after the second drying, and obtaining a composite gas separation membrane after third drying; the second solution contains a polyoxyethylene copolymer, an additive and an initiator; the additive is a polymer represented by formula I; wherein, R 1 is an alkyl group having 1 to 3 carbon atoms, a phenyl group or R 2 is H or methyl; wherein, the average number-average molecular weight of the additive is 250 - 5,000 g / mol; the time of the plasma treatment is 2 - 120 s, and the treatment power is 20 - 120 W.

2. The preparation method according to claim 1, wherein, In Formula I, R1 is methyl, phenyl or R 2 is H or methyl; preferably, the average number-average molecular weight of the additive is 1,000 - 4,000 g / mol; preferably, in step (1), the porous substrate layer is a non-woven fabric containing a porous support layer; preferably, the porous support layer is selected from at least one of polysulfone, polyethersulfone, polyacrylonitrile and polyvinylidene fluoride; preferably, the thickness of the porous substrate layer is 100 - 140 μm, preferably 110 - 130 μm.

3. The preparation method according to claim 1 or 2, wherein, in step (1), the solvent for pre-wetting is selected from at least one of water, alcohol, fluorocarbon solvent and C3 - C4 ketones; preferably, the alcohol is C2 - C4 alcohol, preferably selected from at least one of n-butanol, isobutanol and ethanol; preferably, the fluorocarbon solvent is a fluorinated alkane; preferably, the boiling point of the fluorocarbon solvent is 40 - 99 °C, preferably 50 - 90 °C; preferably, the time of pre-wetting is 10 min - 24 h, preferably 30 min - 12 h.

4. The preparation method according to any one of claims 1 - 3, wherein, in step (1), in the first solution, at 25 °C, the kinematic viscosity of the pre-crosslinked polydimethylsiloxane is 8 - 30 cP, preferably 10 - 20 cP; preferably, the solid content of the first solution is 0.1 wt% - 1 wt%, preferably 0.2 wt% - 0.5 wt%; Preferably, the ratio of the volume of the first solution to the area of the porous substrate layer is 0.01 - 0.1 mL / cm 2 , preferably 0.02 - 0.06 mL / cm 2 ; preferably, the time of the first coating is 2 s - 60 s, preferably 10 s - 40 s.

5. The preparation method according to any one of claims 1 - 4, wherein, the preparation method of the pre-crosslinked polydimethylsiloxane includes: mixing polydimethylsiloxane and a crosslinking agent in the presence of an organic solvent and a catalyst, and performing crosslinking to obtain pre-crosslinked polydimethylsiloxane; preferably, based on the total weight of the pre-crosslinked polydimethylsiloxane, the content of polydimethylsiloxane is 40 - 60 wt%, preferably 45 - 55 wt%; the content of the crosslinking agent is 40 - 60 wt%, preferably 45 - 55 wt%; Preferably, based on the total amount of the polydimethylsiloxane and the crosslinking agent, the content of the catalyst is 20 - 50 wt%, preferably 25 - 30 wt%; Preferably, the number-average molecular weight of the polydimethylsiloxane is 20,000 - 100,000 g / mol; Preferably, the crosslinking agent is a silicone-based crosslinking agent; Preferably, the catalyst is an organotin catalyst; Preferably, the crosslinking temperature is 30 - 83 °C and the crosslinking time is 30 - 120 min.

6. According to the preparation method described in claims 1 - 5, wherein, In step (2), the time of the plasma treatment is 20 - 60 s; the treatment power is 55 - 110 W; Preferably, the gas source for the plasma treatment is selected from at least one of argon, oxygen, and carbon dioxide, preferably oxygen and / or carbon dioxide.

7. According to the preparation method described in any one of claims 1 - 6, wherein, In step (2), in the second solution, the content of the polyethylene oxide copolymer is 0.5 wt% - 3 wt%, preferably 0.5 wt% - 1 wt%; the content of the additive is 0.1 wt% - 5 wt%, preferably 0.5 wt% - 3 wt%; the content of the initiator is 0.1 wt% - 1 wt%, preferably 0.5 wt% - 1 wt%; Preferably, the polyethylene oxide copolymer is selected from at least one of polyethylene oxide - polyamide copolymer, polyethylene oxide - polyimide copolymer, and polyethylene oxide - polybutylene terephthalate; Preferably, the initiator is an azo compound and / or an organic peroxide, preferably selected from at least one of azobisisobutyronitrile, azobisisoheptonitrile, and dimethyl azobisisobutyrate.

8. According to the preparation method described in any one of claims 1 - 7, wherein, In step (2), the temperature of the second drying is 80 - 100 °C and the time of the second drying is 1 - 4 h; Preferably, the ratio of the volume of the second solution to the area of the porous substrate layer is 0.02 - 0.2 mL / cm 2 , preferably 0.05 - 0.15 mL / cm 2 ; Preferably, the time of the second coating is 10 s - 120 s, preferably 30 s - 60 s; Preferably, the crosslinking degree of the selective layer is 50% - 90%, preferably 60% - 75%.

9. According to the preparation method described in any one of claims 1 - 8, wherein, In step (3), in the third solution, the content of the fluoropolymer is 0.1 wt% - 1 wt%; Preferably, the fluoropolymer is selected from at least one of the copolymer of perfluoro - 2,2 - dimethyl - 1,3 - dioxolene and tetrafluoroethylene, the copolymer of 2,2,4 - trifluoro - 5 - trifluoromethoxy - 1,3 - dioxolene and tetrafluoroethylene, and the homopolymer of perfluoro 4 - vinyloxy - 1 - butene; Preferably, the solvent of the third solution is a perfluoropolyether solution; Preferably, the temperature of the third drying is 50 - 80 °C and the time of the third drying is 1 - 24 h; Preferably, the ratio of the volume of the third solution to the area of the porous substrate layer is 0.01-0.1 mL / cm 2 , preferably 0.02-0.05 mL / cm 2 ; Preferably, the time of the third coating is 2 s - 60 s, preferably 10 s - 30 s.

10. A composite gas separation membrane, characterized in that, the composite gas separation membrane is prepared by the preparation method described in any one of claims 1 - 9.

11. The composite gas separation membrane according to claim 10, wherein, The CO of the composite gas separation membrane 2 has an osmotic rate greater than or equal to 500 GPU, preferably greater than or equal to 1000 GPU; Preferably, the composite gas separation membrane has a separation selectivity for CO 2 and N 2 of greater than or equal to 30, preferably greater than or equal to 50; preferably, the strength of the composite gas separation membrane is greater than or equal to 10 MPa, preferably greater than or equal to 50 MPa; preferably, the thickness of the composite gas separation membrane is 110 μm - 150 μm.

12. The composite gas separation membrane according to claim 10 or 11, wherein, the composite gas separation membrane sequentially includes a porous substrate layer, a groove layer, a selective layer and optionally a protective layer; preferably, the groove layer is crosslinked polydimethylsiloxane; preferably, the selective layer comprises a combination of a polyethylene oxide copolymer and at least one selected from polyethylene glycol methyl ether acrylate, polyethylene glycol monomethyl ether acrylate, polyethylene glycol phenyl ether acrylate and polyethylene glycol diacrylate; preferably, in the selective layer, the content of the polyethylene oxide copolymer is 30 - 90 wt%, preferably 50 - 70 wt%; preferably, the protective layer is a fluoropolymer.

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