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.The method comprises the steps that a groove layer, a selection layer and an optional protection layer are prepared on a porous substrate layer in sequence, and the method comprises the following steps that the porous substrate layer is pre-wetted; coating the pre-wetted porous substrate layer with a first solution of pre-crosslinked polydimethylsiloxane for the first time, and performing first drying; performing plasma treatment on the first dried product, performing second coating with a second solution of a polyoxyethylene copolymer, and performing second drying; optionally, the surface of the product obtained after the second drying is coated with a third solution of the fluorine-containing polymer for the third time, and the composite gas separation membrane is obtained after third drying; the plasma treatment time is 2 to 120 seconds, and the treatment power is 20 to 120 W. The gas permeation flux of the prepared composite gas separation membrane is increased, and meanwhile high CO2 / N2 selective separation performance is achieved.

Description

Technical Field

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

[0002] Developing efficient carbon capture and storage (CCS) technology is a consensus solution to reduce carbon dioxide emissions and mitigate the negative impacts leading to climate change. Membrane-based carbon dioxide separation technology, as a clean and low-carbon technology, has attracted much attention and shows great potential in large-scale carbon dioxide capture. The research and development of high-performance carbon dioxide separation membranes include the development of suitable membrane materials and large-scale membrane preparation processes. According to the solution-diffusion theory, rubbery polymers have a high CO 2 solubility, which can improve the CO 2 permeation performance. Among them, membranes based on poly(ethylene oxide) (PEO)-containing membrane materials are attractive. PEO-based membrane materials have very high CO 2 solubility and CO 2 solubility and CO 2 / N 2 ideal selectivity due to the "dipole-quadrupole" interaction between the ethylene oxide (EO) units and CO Polaris TM and PolyActive TM have been developed and show high CO 2 separation performance at both laboratory scale and industrial scale. In addition to selecting suitable materials, the membrane must be thin enough to reduce the mass transfer resistance and thus increase the CO 2 permeability.

[0003] Currently, multilayer thin film composite (TFC) membranes are a research hotspot for high-performance gas separation membranes and have practical industrial application value. Most TFC membranes are prepared by a top-down method, including dip coating, spin coating, and blade coating methods, where the polymer casting solution is uniformly coated on the substrate to form an ultrathin selective layer. The transport resistance of the porous substrate layer should be as small as possible, with the pore size and porosity maximized. However, such large pores cause the selective layer to penetrate the pores, resulting in defects in the TFC membrane.

[0004] The literature (ACS, Appl. Mater. Interfaces 2020, 12, 33196 - 33209) uses PDMS as the trench layer, performs a short-time treatment with oxygen plasma, and then coats a PEBAX1657 separation layer on it. However, it is necessary to first synthesize the trench layer and then transfer it to the microporous support layer, which is a complex process and only applicable to the small-scale preparation of a small number of membranes and cannot achieve large-scale production.

[0005] Therefore, it is urgent to develop a kind of 2 multilayer thin film composite membrane with high 2 separation performance and high CO permeability. Summary of the Invention

[0006] The purpose of the present invention is to overcome the problems of poor 2 CO separation performance and low CO permeability of the composite 2 gas separation membrane, and to provide a composite gas separation 2 membrane and a preparation method thereof. The composite gas 2 separation membrane prepared by this method has high CO

[0007] separation performance and CO permeability.

[0008] (1) Pre-wet the porous substrate layer, and first coat a first

[0009] solution of pre-crosslinked polydimethylsiloxane on the pre-wet

[0010] porous substrate layer, and perform first drying;

[0011] (2) After plasma treatment of the product obtained by the first

[0012] drying, second coat a second solution of polyoxyethylene

[0013] copolymer, and then perform second drying; 2 / N 2 (3) Optionally, third coat a third solution of fluoropolymer on the surface of the product obtained by the second drying,

[0014] Figure 1 and obtain the composite gas separation membrane after third drying.

[0011] In step (2), the time of the plasma treatment is 2 - 120 s,

[0012] and the treatment power is 20 - 120 W. The second aspect of

[0013] the present invention provides a composite gas separation 2 / N 2 membrane, which is prepared by the above preparation method. Brief Description of the Drawings

[0014] Figure 1It is the SEM cross-section image of the composite gas separation membrane prepared in Example 1.

[0015] Figure 2 It is the SEM cross-section image of the composite gas separation membrane prepared in Example 2.

[0016] Figure 3 It is the XPS characterization of the surface of the groove layer after the CO 2 plasma treatment in Example 1. Among them, the PDMS original membrane refers to the surface of the groove layer membrane without plasma treatment in Example 1, and PDMS 30s refers to the surface of the groove layer membrane after plasma treatment in Example 1.

[0017] Figure 4 It is the SEM cross-section images of the groove layer before and after the CO 2 plasma treatment in Example 1. Among them, Figure (a) is the surface of the groove layer membrane without plasma treatment in Example 1, and Figure (b) is the surface of the groove layer membrane after plasma treatment in Example 1. Detailed implementation manners

[0018] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and 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 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.

[0019] The first aspect of the present invention provides a method for preparing a composite gas separation membrane, wherein 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:

[0020] (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;

[0021] (2) After performing plasma treatment on the product of the first drying, second coat a second solution of a polyoxyethylene copolymer, and then perform second drying;

[0022] (3) Optionally, third coat a third solution of a fluoropolymer on the surface of the product after the second drying, and after third drying, obtain a composite gas separation membrane;

[0023] In step (2), the time of the plasma treatment is 2 - 120 s, and the treatment power is 20 - 120 W.

[0024] 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, avoiding defects in the porous substrate layer. At the same time, by combining specific plasma treatment time and power, the compatibility and affinity between the trench layer and the selective layer can be improved, and the gas permeation flux of the prepared composite gas separation membrane increases, while achieving high CO 2 / N 2 selective separation performance.

[0025] Further, in step (2), the time of the plasma treatment is 20 - 60 s, and the treatment power is 50 - 110 W.

[0026] According to the present invention, in step (2), the gas source for the plasma treatment is selected from at least one of argon, oxygen, and carbon dioxide.

[0027] Further, the gas source for the plasma treatment is oxygen and / or carbon dioxide.

[0028] In a preferred embodiment of the present invention, the gas source for the plasma treatment is carbon dioxide.

[0029] In the present invention, the inlet gas flow rate of the plasma treatment is 25 - 500 mL / min.

[0030] According to the present invention, in step (1), the porous substrate layer is a non-woven fabric containing a porous support layer.

[0031] 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.

[0032] According to the present invention, the porous support layer is selected from at least one of polysulfone, polyethersulfone, polyacrylonitrile, and polyvinylidene fluoride.

[0033] According to the present invention, the thickness of the porous substrate layer is 100 - 140 μm.

[0034] Further, the thickness of the porous substrate layer is 110 - 130 μm.

[0035] In the present invention, there are no special requirements for the dosage of polysulfone, polyethersulfone, polyacrylonitrile, or polyvinylidene fluoride, and the dosage can meet the thickness of the porous substrate layer.

[0036] In the present invention, there is no particular limitation on the source of the porous substrate layer, and it can be purchased commercially. Preferably, in the present invention, the preparation method of the porous substrate layer includes:

[0037] (a) Mixing a polymer with an organic solvent to obtain a casting solution;

[0038] (b) Coating the casting solution on the non-woven fabric to obtain a nascent membrane, immersing the nascent membrane in a non-solvent, and drying to obtain a porous substrate layer.

[0039] In the present invention, in step (a), the polymer is selected from at least one of polysulfone, polyethersulfone, polyacrylonitrile, and polyvinylidene fluoride. There is no special limitation on the organic solvent in step (a) of the present invention, and it can be an organic solvent commonly used in the art, such as N,N-dimethylformamide (DMF).

[0040] In the present invention, there is no special limitation on the amount of the organic solvent in step (a). Preferably, the content of the polymer in the casting solution is 15-25 wt%.

[0041] In the present invention, in step (b), there is no special limitation 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 doctor blade is 200-250 μm. Preferably, the non-solvent is deionized water and / or C5-18-perfluoroalkane. Preferably, in step (b), the immersion time is 20-30 h. Preferably, the non-solvent is replaced during the immersion process, and the number of replacements is 3-5 times. Preferably, the drying temperature is 60-100 °C.

[0042] 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 ketone.

[0043] In the present invention, the use of the above specific solvent is easy to remove through drying or the like, and thus can effectively prevent the first solution of pre-crosslinked polydimethylsiloxane from invading the porous substrate layer, avoid trench layer defects, and improve the gas permeability of the composite gas separation membrane.

[0044] Furthermore, the alcohol is selected from C2-C4 alcohols, preferably selected from at least one of n-butanol, isobutanol, and ethanol.

[0045] According to the present invention, the fluorocarbon solvent is a fluorinated alkane.

[0046] According to the present invention, the boiling point of the fluorocarbon solvent is 40-99 °C.

[0047] Furthermore, the boiling point of the fluorocarbon solvent is 50-90 °C.

[0048] In the present invention, the fluorocarbon solvent can be obtained through commercial purchase, such as 3M TM Electronic fluorinated liquid Fluorinert TM FC-72 (boiling point is 50-60 °C).

[0049] According to the present invention, the time of the pre-wetting is 10 min - 24 h.

[0050] In the present invention, when the time of the pre-wetting 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.

[0051] Further, the time of the pre-wetting is 30 min - 12 h.

[0052] Still further, the time of the pre-wetting is 30 min - 70 min.

[0053] In the present invention, the temperature of the first drying is 30 - 80 °C, and the time of the first drying is 1 - 120 min.

[0054] According to the present invention, in step (1), in the first solution, the dynamic viscosity of the pre-crosslinked polydimethylsiloxane at 25 °C is 8 cP - 50 cP.

[0055] In the present invention, when the dynamic viscosity of the pre-crosslinked polydimethylsiloxane meets the above range, it has good film-forming property, and the formed trench layer is smoother, thinner, denser and defect-free, which is beneficial to improving the gas permeability of the composite gas separation membrane.

[0056] Further, in step (1), in the first solution, the viscosity of the pre-crosslinked polydimethylsiloxane at 25 °C is 10 cP - 30 cP.

[0057] According to the present invention, the solid content of the first solution is 0.1 wt% - 1 wt%.

[0058] In the present invention, when the solid content of the first solution meets the above range, it has good film-forming property, and the formed trench layer is smoother, thinner, denser and defect-free, which is beneficial to improving the gas permeability of the composite gas separation membrane.

[0059] Further, the solid content of the first solution is 0.2 wt% - 0.5 wt%.

[0060] 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 .

[0061] 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 .

[0062] According to the present invention, the time of the first coating is 2 s - 60 s.

[0063] Further, the time for the first coating is 10 s - 40 s.

[0064] 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.

[0065] 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%.

[0066] In the present invention, when the contents of the polydimethylsiloxane and the crosslinking agent satisfy the above ranges, the prepared pre-crosslinked polydimethylsiloxane has the characteristics of good film-forming property, and the formed trench layer is smoother, thinner, dense and defect-free, which is beneficial to improving the gas permeability and gas selectivity of the composite gas separation membrane.

[0067] 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%.

[0068] 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%.

[0069] Further, based on the total amount of the polydimethylsiloxane and the crosslinking agent, the content of the catalyst is 25 - 30 wt%.

[0070] In the present invention, the organic solvent is selected from at least one of n-heptane, n-hexane and cyclohexane.

[0071] In the present invention, there is no special limitation on the amount of the organic solvent, as long as it can disperse the polydimethylsiloxane and the crosslinking agent with each other.

[0072] According to the present invention, the number-average molecular weight of the polydimethylsiloxane is 20,000 - 100,000 g / mol.

[0073] According to the present invention, the crosslinking agent is an alcohol-eliminating type silane crosslinking agent.

[0074] In the present invention, there is no special limitation on the type of the alcohol-eliminating type silane crosslinking agent. Preferably, the crosslinking agent is selected from at least one of tetraethyl orthosilicate, tetramethyl orthosilicate and 1,2-bis(trimethoxysilyl)ethane.

[0075] According to the present invention, the catalyst is an organotin catalyst.

[0076] In the present invention, there is no special limitation on the type of the organotin catalyst. Preferably, the catalyst is dibutyltin dilaurate and / or dioctyltin dilaurate.

[0077] According to the present invention, the crosslinking temperature is 30 - 80 °C, and the crosslinking time is 30 - 120 min.

[0078] Further, the crosslinking temperature is 50 - 80 °C, and the crosslinking time is 20 - 60 min.

[0079] 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.

[0080] In the present invention, directly preparing the first solution of the pre-crosslinked polydimethylsiloxane by the above method makes the preparation method of the composite gas separation membrane have better continuity and is not easy to introduce impurities. In the present invention, the solvent of the first solution is the same as the organic solvent.

[0081] According to the present invention, in step (2), the second solution includes a polyoxyethylene copolymer and optionally an additive.

[0082] According to the present invention, in the second solution, the content of the polyoxyethylene copolymer is 0.2 wt% - 3 wt%, and the content of the additive is 0 - 5 wt%.

[0083] In the present invention, when the contents of the components in the second solution meet the above ranges, the compatibility between the polyoxyethylene copolymer and the additive is good, which is beneficial to obtaining a dense and defect-free selective layer and improving the gas permeability of the composite gas separation membrane.

[0084] Further, in the second solution, the content of the polyoxyethylene copolymer is 0.2 wt% - 1 wt%, and the content of the additive is 0.5 wt% - 3 wt%.

[0085] Further, in the second solution, the content of the polyoxyethylene copolymer is 0.2 wt% - 0.7 wt%, and the content of the additive is 0.5 wt% - 1.5 wt%.

[0086] 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), polyoxyethylene - polyimide copolymer (PEO - PI), and polyoxyethylene - polybutylene terephthalate (PEO - PBT).

[0087] In the present invention, in the polyoxyethylene copolymer, the content of the polyoxyethylene structural unit is 55 - 85 wt%.

[0088] In the present invention, the polyoxyethylene - polyamide copolymer can be obtained commercially, such as pebax1657 and / or pebax2533 from Arkema.

[0089] According to the present invention, the additive is a polyether polyol, preferably at least one of polyethylene glycol monomethyl ether (PEGME), polyethylene glycol dimethyl ether (PEGDME), and polyethylene glycol ethyl ether (PEGEE).

[0090] In the present invention, when the above - mentioned additive is used, it makes the polyoxyethylene copolymer and the additive have excellent compatibility, which is beneficial to obtaining a dense and defect - free selective layer and improving the gas permeability of the composite gas separation membrane.

[0091] According to the present invention, the average number - average molecular weight of the additive is 500 - 6,000 g / mol.

[0092] Furthermore, the average number - average molecular weight of the additive is 2,000 - 5,000 g / mol.

[0093] In the present invention, the solvent of the second solution is alcohol and / or water, preferably at least one selected from ethanol, water, n - butanol, and isobutanol.

[0094] In a preferred embodiment of the present invention, the preparation method of the second solution includes: stirring the polyoxyethylene copolymer, optionally the additive, and the solvent at 50 - 90 °C for 60 - 180 min, and performing vacuum degassing for 1 - 5 min to obtain the second solution.

[0095] According to the present invention, in step (2), the temperature of the second drying is 30 - 80 °C, and the time of the second drying is 4 - 24 h.

[0096] According to the present invention, the ratio of the volume of the second solution to the area of the porous substrate layer is 0.01 - 0.2 mL / cm 2 .

[0097] According to the present invention, the time of the second coating is 2 s - 60 s.

[0098] In the present invention, when the ratio of the volume of the second solution to the area of the porous substrate layer and / or the time of the second coating satisfy the above ranges, it is beneficial to improve the gas permeability of the composite gas separation membrane.

[0099] Furthermore, the ratio of the volume of the second solution to the area of the porous substrate layer is 0.05 - 0.1 mL / cm 2 .

[0100] Further, the time of the second coating is 10 s - 30 s.

[0101] In a preferred embodiment of the present invention, the method includes successively preparing a trench layer, a selective layer, and a protective layer on a porous substrate layer.

[0102] In the present invention, the protective layer is a fluoropolymer layer, which can enable the composite gas separation membrane to have good heat resistance and waterproof performance while maintaining the separation performance of the composite gas separation membrane.

[0103] According to the present invention, in step (3), in the third solution, the content of the fluoropolymer is 0.1 wt% - 1 wt%.

[0104] In the present invention, when the content of the fluoropolymer meets the above range, the obtained protective layer has good heat resistance, hydrophobic performance, and anti-plasticization performance, and the obtained composite gas separation membrane still has a high gas permeation flux and high CO 2 / N 2 selective separation performance.

[0105] Further, in step (3), in the third solution, the content of the fluoropolymer is 0.2 wt% - 0.5 wt%.

[0106] 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).

[0107] 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.

[0108] According to the present invention, the solvent of the third solution is a perfluoropolyether solution.

[0109] In the present invention, the perfluoropolyether solution can be obtained by commercial purchase. For example, GALDEN HT110 from Solvay.

[0110] 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.

[0111] 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 .

[0112] According to the present invention, the time of the third coating is 2 s - 60 s.

[0113] 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 of 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.

[0114] 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 .

[0115] Furthermore, the time of the third coating is 10 s - 30 s.

[0116] In a preferred embodiment of the present invention, the preparation method of the third solution includes: mixing a fluoropolymer with a perfluoropolyether solution and degassing under vacuum for 1 - 5 min to obtain the third solution.

[0117] 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.

[0118] According to the present invention, the CO 2 permeation rate of the composite gas separation membrane is greater than or equal to 500 GPU.

[0119] Furthermore, the CO 2 permeation rate of the composite gas separation membrane is greater than or equal to 1000 GPU.

[0120] 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.

[0121] Furthermore, the separation selectivity of the composite gas separation membrane for CO 2 and N 2 is greater than or equal to 50.

[0122] According to the present invention, the thickness of the composite gas separation membrane is 110 μm - 150 μm.

[0123] According to the present invention, the composite gas separation membrane successively comprises a porous substrate layer, a groove layer, a selective layer, and optionally a protective layer.

[0124] According to the present invention, the groove layer is crosslinked polydimethylsiloxane.

[0125] According to the present invention, the selective layer is selected from at least one of polyoxyethylene-polyamide copolymer, polyoxyethylene-polyimide copolymer, polyoxyethylene-polyimide copolymer, and polyoxyethylene-polybutylene terephthalate.

[0126] According to the present invention, the protective layer is a fluoropolymer.

[0127] The present invention will be described in detail below through examples.

[0128] The thickness of the porous substrate layer and the thickness of the composite gas separation membrane are measured by a scanning electron microscope method.

[0129] The kinematic viscosity of the pre-crosslinked polydimethylsiloxane is measured by a digital display rotational viscometer (Brookfield, USA), and the test temperature is 25 °C.

[0130] The degree of polymerization of the additive is measured by nuclear magnetic method, and the average number-average molecular weight of the additive is calculated.

[0131] CO at 25 °C and 0.2 MPa 2 permeation rate and CO 2 / N 2 separation selectivity: Using CO 2 and N 2 mixed gas to simulate flue gas (composed of 15% CO by mole fraction 2 and 85% N 2 composition) as the feed gas, the feed gas pressure is 0.2 MPa, the temperature is 25 °C, and Ar is used as the purge gas. The flow rate of the purge gas is kept constant at 35 mL / min, and the gas on the permeate side is 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 is measured by a soap film flow meter, and the flow rate of the gas components on the permeate side is calculated according to the mass fraction of the gas components on the permeate side tested by the gas chromatograph.

[0132] Component CO 2 permeation rate R i is calculated by Equation 1:

[0133]

[0134] Q is the total flow rate of the permeate gas and the purge gas, cm 3 / s; A is the membrane area, cm -2 ; Δp iis the pressure difference of component i across the membrane, cmHg; R i is the permeation rate of gas component i. To simplify the unit, GPU is introduced as the permeability unit, as shown in Equation 2.

[0135] GPU = 10 -6 ·cm 3 (STP)·cm -2 ·s -1 ·cmHg -1 (2)

[0136] 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.

[0137] 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 is calculated by Equation 3

[0138]

[0139] 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 .

[0140] The permeation rate of CO 2 and the separation selectivity of CO 2 / N 2 at 80 °C and 0.2 MPa: According to the test method of the permeation rate of CO 2 and the separation selectivity of CO 2 / N 2 at 25 °C and 0.2 MPa mentioned above, the difference is that: the raw gas pressure is 0.2 MPa and the temperature is 80 °C.

[0141] The plasma treatment is carried out using a plasma cleaner (PVA TePla Plasma System ION40).

[0142] Fluorocarbon solvent A is 3M TM electronic fluorinated liquid Fluorinert TM FC-72, with a boiling point of 60 °C.

[0143] Polyoxyethylene-polyamide (PEO-PA) copolymer A: purchased from Arkema France, with the trade name Pebax 2533. The content of polyoxyethylene structural units in copolymer A is 80 wt%.

[0144] Poly(ethylene oxide)-polyamide (PEO-PA) copolymer B: Purchased from Arkema France, with the grade of Pebax 1657. The content of poly(ethylene oxide) structural units in copolymer B is 60 wt%.

[0145] 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.

[0146] Other raw materials used in the examples and comparative examples are all commercially available products.

[0147] Preparation of the porous substrate layer

[0148] Prepare a casting solution composed of 20 wt% polysulfone and 80 wt% N,N-dimethylformamide solvent DMF. At a scraping speed of 6 m / min, scrape the casting solution on the polyester non-woven fabric by the method of blade moving coating. The thickness of the blade is 220 μm (i.e., the thickness of the as-cast film). Use deionized water as the non-solvent. The obtained as-cast film is immersed in deionized water for 24 h and undergoes three replacements with deionized water, and then dried at 70 °C to obtain the porous substrate layer with a thickness of 110 μm.

[0149] Preparation Example 1

[0150] Add polydimethylsiloxane (the number-average molecular weight of PDMS is 20,000 g / mol), cross-linking agent tetraethyl orthosilicate (TEOS), and catalyst dibutyltin dilaurate (DBD) to n-heptane. Based on the total weight of the pre-crosslinked polydimethylsiloxane, the content of polydimethylsiloxane is 50 wt%, and the content of the cross-linking agent is 50 wt%; based on the total amount of polydimethylsiloxane and the cross-linking agent, the content of the catalyst is 25 wt%. Stir at 30 °C for 60 minutes and degas under vacuum for 5 minutes to prepare the first solution A, and the measured parameters are shown in Table 1.

[0151] Preparation Example 2

[0152] Prepare the first solution B according to Preparation Example 1, except that the dosages of polydimethylsiloxane, tetraethyl orthosilicate, and dibutyltin dilaurate are different from those in Preparation Example 1, and the specific contents are shown in Table 1.

[0153] Table 1

[0154]

[0155] * Based on the total weight of the pre-crosslinked polydimethylsiloxane, the contents of polydimethylsiloxane and the cross-linking agent.

[0156] * Content of DBD: Based on the total amount of polydimethylsiloxane and the cross-linking agent, the content of DBD.

[0157] Example 1

[0158] (1) Groove layer: The first solution A was coated on the porous substrate layer pre-wetted with water for 30 min by dip coating and dried at 50 °C for 120 min. Specifically, the volume ratio of the first solution A to the area of the porous substrate layer was 0.05 mL / cm 2 , and the time for the first coating was 10 s.

[0159] (2) Selective layer: The groove layer in step (1) was subjected to plasma treatment. Among them, the carbon dioxide flow rate was 500 mL / min, the treatment time was 30 s, and the treatment power was 110 W. Poly(ethylene oxide)-polyamide (PEO-PA) copolymer (Pebax 2533), additive polyethylene glycol monomethyl ether (PEGME) and n-butanol were stirred at 80 °C for 60 min and degassed under vacuum for 5 min to obtain a second solution (the content of Pebax 2533 was 0.5 wt%, and the content of PEGME was 0.5 wt%). The second solution of the poly(ethylene oxide) copolymer was coated on the plasma-treated PDMS membrane, and the selective layer was dried at 50 °C for 4 h. Specifically, the volume ratio of the second solution to the area of the porous substrate layer was 0.05 mL / cm 2 , and the time for the second coating was 10 s.

[0160] (3) Protective layer: A third solution containing a fluoropolymer was coated on the selective layer in step (2). Specifically, a fluoropolymer (Teflon AF2400) was mixed with a perfluoropolyether solution GALDEN HT110 and degassed under vacuum for 5 min to obtain a third solution (in the third solution, the content of the fluoropolymer was 0.1 wt%). The fluoropolymer layer was dried at 80 °C for 1 h to obtain a composite gas separation membrane. Specifically, the volume ratio of the third solution to the area of the porous substrate layer was 0.03 mL / cm 2 , and the time for the third coating was 10 s.

[0161] The test results of the composite gas separation membrane are shown in Table 3.

[0162] Example 2-13

[0163] The composite gas separation membrane was 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.

[0164] Table 2

[0165]

[0166]

[0167] Continued Table 2

[0168]

[0169] Continued Table 2

[0170]

[0171] Example 14

[0172] Prepare the composite gas separation membrane according to the method of Example 1, except that step (3) is not included. The thickness of the composite gas separation membrane is measured to be about 110.5 μm. The test results of the composite gas separation membrane are shown in Table 3.

[0173] Example 15

[0174] Prepare the composite gas separation membrane according to the method of Example 1, except that in step (3), the ratio of the volume of the third solution to the area of the porous substrate layer is 0.1 mL / cm 2 , and the coating time of the third coating is 60 s. The test results of the composite gas separation membrane are shown in Table 3.

[0175] Example 16

[0176] Prepare the composite gas separation membrane according to the method of Example 1, except that in step (3), the content of the fluoropolymer in the third solution is 1 wt%. The test results of the composite gas separation membrane are shown in Table 3.

[0177] Comparative Example 1

[0178] Prepare the composite gas separation membrane according to the method of Example 1, except that in step (2), the plasma treatment time is 3 min and the treatment power is 110 W. The test results of the prepared composite gas separation membrane are shown in Table 3.

[0179] Comparative Example 2

[0180] Prepare the composite gas separation membrane according to the method of Example 1, except that in step (2), plasma treatment is not used. The selective layer coating is uneven and the membrane has defects. The test results of the prepared composite gas separation membrane are shown in Table 3.

[0181] Comparative Example 3

[0182] Prepare the composite gas separation membrane according to the method of Example 1, except that in step (2), the plasma treatment time is 30 s and the treatment power is 180 W. The test results of the prepared 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 the porous substrate layer in step (1) was not pre-wetted, and the first solution A was directly coated on the porous substrate layer. The test results of the prepared composite gas separation membrane are shown in Table 3.

[0185] Table 3

[0186]

[0187] It can be seen from the test results that the composite gas separation membrane prepared by the present invention has better CO 2 permeation rate and CO 2 / N 2 separation selectivity. When the preferred pre-wetting and plasma treatment methods are adopted, there is a synergistic effect, which can further improve the CO 2 permeation rate and CO 2 / N 2 separation selectivity of the separation membrane. The composite gas separation membrane containing the protective layer still maintains a high CO 2 permeation rate and CO 2 / N 2 separation selectivity at 80 °C and 0.2 MPa, indicating that coating the protective layer can improve the high-temperature resistance of the separation membrane.

[0188] Figure 1 and Figure 2 are the cross-sectional SEM images of the composite gas separation membranes prepared in Example 1 and Example 2 respectively. It can be seen that the separation layer is thin and dense, and is tightly combined with the porous substrate layer, indicating that in the present invention, by pre-wetting the porous substrate layer, the intrusion of the first solution of pre-crosslinked polydimethylsiloxane into the porous substrate layer can be effectively prevented, and a thin and dense selective layer can be obtained by plasma modification.

[0189] Figure 3 is the XPS characterization of the surface of the groove layer after CO 2 plasma treatment in Example 1. Among them, the PDMS original film refers to the surface of the groove layer film in Example 1 without plasma treatment, and PDMS 30s refers to the surface of the groove layer film in Example 1 after plasma treatment. It can be seen that hydrophilic C-O\C=O groups and barrier Si-O 3 \Si-O 4 are generated on the membrane surface, indicating that the hydrophilicity of the membrane surface of the groove layer after treatment is improved, which is beneficial to improving the affinity of the separation layer membrane liquid.

[0190] Figure 4 is the CO 2SEM cross-sectional views of the trench layer before and after plasma treatment. Among them, Figure (a) is the surface of the trench layer film without plasma treatment in Example 1, and Figure (b) is the surface of the trench layer film after plasma treatment in Example 1. It can be seen that the trench layer in Figure (b) becomes thinner but remains dense, indicating that the plasma treatment enables the trench layer to still maintain a dense structure.

[0191] 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 includes 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 plasma treatment of the product after the first drying, second coating a second solution of a polyoxyethylene copolymer, and then performing second drying; (3) Optionally, third coating a third solution of a fluoropolymer on the surface of the product after the second drying, and obtaining a composite gas separation membrane after third drying; In step (2), 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 step (2), the time of the plasma treatment is 20 s - 60 s, and the treatment power is 50 - 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.

3. The preparation method according to claim 1 or 2, wherein, 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.

4. The preparation method according to claims 1 - 3, 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 selected from C2 - C4 alcohols, preferably 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 for pre-wetting is 10 min - 24 h, preferably 30 min - 12 h.

5. The preparation method according to any one of claims 1 - 4, wherein, in step (1), in the first solution, the dynamic viscosity of the pre-crosslinked polydimethylsiloxane at 25 °C is 8 cP - 50 cP, preferably 10 cP - 30 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 for the first coating is 2 s - 60 s, preferably 10 s - 40 s.

6. The preparation method according to claims 1 - 5, wherein, 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 performing crosslinking to obtain pre-crosslinked polydimethylsiloxane; Preferably, based on the total weight of the pre-crosslinked polydimethylsiloxane, the content of the 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 an alcohol-eliminating silane crosslinking agent; Preferably, the catalyst is an organotin catalyst; Preferably, the crosslinking temperature is 30-80 °C, and the crosslinking time is 30-120 min.

7. The preparation method according to any one of claims 1-6, wherein, in step (2), the second solution includes a polyethylene oxide copolymer and optionally an additive; Preferably, in the second solution, the content of the polyethylene oxide copolymer is 0.2 wt%-3 wt%, preferably 0.2 wt%-1 wt%; the content of the additive is 0-5 wt%, preferably 0.5 wt%-3 wt%; Preferably, the polyethylene oxide copolymer is selected from at least one of polyethylene oxide-polyamide copolymer, polyethylene oxide-polyimide copolymer, polyethylene oxide-polyimide copolymer, and polyethylene oxide-polybutylene terephthalate; Preferably, the additive is a polyether polyol, preferably at least one of polyethylene glycol monomethyl ether, polyethylene glycol dimethyl ether, and polyethylene glycol ethyl ether; Preferably, the average number-average molecular weight of the additive is 500-6,000 g / mol, preferably 2,000-5,000 g / mol.

8. The preparation method according to any one of claims 1-7, wherein, in step (2), the temperature of the second drying is 30-80 °C, and the time of the second drying is 4-24 h; Preferably, the ratio of the volume of the second solution to the area of the porous substrate layer is 0.01-0.2 mL / cm 2 , preferably 0.05-0.1 mL / cm 2 ; Preferably, the time of the second coating is 2 s-60 s, preferably 10 s-30 s.

9. The preparation method according to claims 1-8, wherein, in the third solution in step (3), the content of the fluoropolymer is 0.1 wt%-1 wt%, preferably 0.2 wt%-0.5 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-vinyl-oxy-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 according to 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 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 is selected from at least one of polyoxyethylene-polyamide copolymer, polyoxyethylene-polyimide copolymer, polyoxyethylene-polyimide copolymer, and polyoxyethylene-polybutylene terephthalate; preferably, the protective layer is a fluoropolymer.

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