Composite gas separation membrane and its preparation method

Abstract

This invention relates to the field of separation membrane materials technology, and discloses a composite gas separation membrane and its preparation method. The method includes sequentially preparing a trench layer, a selective layer, and optionally a protective layer on a porous substrate, comprising the following steps: pre-wetting the porous substrate; first coating the pre-wetted porous substrate with a first solution of pre-crosslinked polydimethylsiloxane, followed by a first drying; plasma treating the first dried product, then second coating it with a second solution of a polyoxyethylene copolymer, followed by a second drying; optionally, third coating the surface of the product after the second drying with a third solution of a fluoropolymer, followed by a third drying to obtain the composite gas separation membrane; the plasma treatment time is 2-120 s, and the treatment power is 20-120 W. The composite gas separation membrane prepared by this invention has increased gas permeation flux and simultaneously achieves high CO2 / N2 selective separation performance.

Description

Technical Field

[0001] This invention relates to the field of separation membrane materials technology, specifically to a composite gas separation membrane and its preparation method. Background Technology

[0002] Developing efficient carbon capture and storage (CCS) technologies is a consensus solution for reducing carbon dioxide emissions and mitigating the negative impacts of climate change. Membrane-based carbon dioxide separation technology, as a clean and low-carbon technology, has attracted much attention and shows great potential for large-scale carbon dioxide capture. The development of high-performance carbon dioxide separation membranes includes the development of suitable membrane materials and large-scale membrane fabrication processes. According to the dissolution-diffusion theory, rubber-like polymers have high CO2 solubility, which can improve CO2 permeation performance. Among them, membranes based on polyoxyethylene (PEO)-containing membrane materials are attractive. PEO-based membrane materials exhibit very high CO2 solubility and ideal CO2 / N2 selectivity due to the "dipole-quadrupole" interaction between ethylene oxide (EO) units and CO2 molecules. They are favored for their excellent mechanical stability and processability. Several PEO-containing copolymers, including… Polaris TM and PolyActive TM It has been developed and has shown high CO2 separation performance on both laboratory and industrial scales. In addition to selecting suitable materials, the membrane must be thin enough to reduce mass transfer resistance, thereby increasing CO2 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 using top-down methods, including dip coating, spin coating, and blade coating, where a polymer casting solution is uniformly coated onto a substrate to form an ultrathin selective layer. The transport resistance of the porous substrate layer should be as low as possible, and the pore size and porosity should be maximized. However, such large pores cause the selective layer to penetrate the pores, thus creating defects in the TFC membrane.

[0004] The literature (ACS, Appl. Mater. Interfaces 2020, 12, 33196-33209) uses PDMS as a trench layer, performs short-time treatment with oxygen plasma, and then coats it with a PEBAX1657 separation layer. However, the trench layer needs to be synthesized first and then transferred to the microporous support layer. The process is complicated and can only be used for small-scale preparation of a small number of membranes, and cannot be scaled up for production.

[0005] Therefore, there is an urgent need to develop a multilayer thin-film composite membrane with high CO2 separation performance and high CO2 permeability. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of poor CO2 separation performance and low CO2 permeability of composite gas separation membranes, and to provide a composite gas separation membrane and its preparation method. The composite gas separation membrane prepared by this method has high CO2 separation performance and CO2 permeability.

[0007] To achieve the above objectives, a first aspect of the present invention provides a method for preparing a composite gas separation membrane, wherein the method includes sequentially preparing a trench layer, a selective layer, and optionally a protective layer on a porous substrate, comprising the following steps:

[0008] (1) The porous substrate is pre-wetted, and a first solution of pre-crosslinked polydimethylsiloxane is first coated on the pre-wetted porous substrate, and then dried.

[0009] (2) After plasma treatment of the first dried product, a second solution of polyoxyethylene copolymer is applied and then dried again.

[0010] (3) Optionally, a third solution of a fluoropolymer is coated on the surface of the product after the second drying, and after the third drying, a composite gas separation membrane is obtained.

[0011] In step (2), the plasma treatment time is 2-120 s, and the treatment power is 20-120 W. A second aspect of the present invention provides a composite gas separation membrane, wherein the composite gas separation membrane is prepared by the above-described preparation method.

[0012] The composite gas separation membrane and its preparation method provided by the present invention have the following beneficial effects through the above technical solutions.

[0013] This invention, by pre-wetting the porous substrate, can prevent the first solution of pre-crosslinked polydimethylsiloxane from penetrating into the pores of the porous substrate, thus avoiding defects in the porous substrate. Combined with specific plasma treatment time and power, it can improve the compatibility and affinity between the trench layer and the selective layer, thereby increasing the gas permeation flux of the resulting composite gas separation membrane and achieving high CO2 / N2 selective separation performance. Attached Figure Description

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

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

[0016] Figure 3XPS characterization of the trench layer surface after CO2 plasma treatment in Example 1. Here, PDMS original film refers to the trench layer film surface in Example 1 without plasma treatment, and PDMS 30s refers to the trench layer film surface in Example 1 after plasma treatment.

[0017] Figure 4 These are SEM images of the trench layer cross-section before and after CO2 plasma treatment in Example 1. Figure (a) shows the surface of the trench layer film in Example 1 without plasma treatment, and Figure (b) shows the surface of the trench layer film in Example 1 after plasma treatment. Detailed Implementation

[0018] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered 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 sequentially preparing a trench layer, a selective layer, and optionally a protective layer on a porous substrate, comprising the following steps:

[0020] (1) The porous substrate is pre-wetted, and a first solution of pre-crosslinked polydimethylsiloxane is first coated on the pre-wetted porous substrate, and then dried.

[0021] (2) After plasma treatment of the first dried product, a second solution of polyoxyethylene copolymer is applied and then dried again.

[0022] (3) Optionally, a third solution of a fluoropolymer is coated on the surface of the product after the second drying, and after the third drying, a composite gas separation membrane is obtained.

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

[0024] In this invention, by pre-wetting the porous substrate, the first solution of pre-crosslinked polydimethylsiloxane can be prevented from penetrating into the pores of the porous substrate, thus avoiding defects in the porous substrate. 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, resulting in increased gas permeation flux of the prepared composite gas separation membrane and achieving high CO2 / N2 selective separation performance.

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

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

[0027] Furthermore, 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 plasma treatment is carbon dioxide.

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

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

[0031] In this invention, there are no special requirements for the nonwoven fabric, which can be any nonwoven fabric commonly used in the art, such as polyester nonwoven 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] Furthermore, the thickness of the porous substrate layer is 110-130 μm.

[0035] In this invention, there are no special requirements for the amount of polysulfone, polyethersulfone, polyacrylonitrile, or polyvinylidene fluoride used, as long as the amount is sufficient to meet the thickness of the porous substrate layer.

[0036] In this invention, the source of the porous substrate layer is not particularly limited and it can be commercially available. Preferably, the method for preparing the porous substrate layer in this invention includes:

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

[0038] (b) The casting solution is coated onto a nonwoven fabric to obtain a nascent film. The nascent film is then immersed in a non-solvent and dried to obtain a porous substrate layer.

[0039] In this invention, in step (a), the polymer is selected from at least one of polysulfone, polyethersulfone, polyacrylonitrile, and polyvinylidene fluoride. This invention does not specifically limit the organic solvent used in step (a), and it can be any organic solvent commonly used in the art, such as N,N-dimethylformamide (DMF).

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

[0041] In this invention, the coating method in step (b) is not particularly limited and can be any conventional coating method in the art, such as a blade-operated coating method for applying the casting solution. Preferably, the blade thickness is 200-250 μm. Preferably, the non-solvent is deionized water and / or C5-18-perfluoroalkane. Preferably, the soaking time in step (b) is 20-30 hours. Preferably, the non-solvent is changed 3-5 times during the soaking process. 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 this invention, the aforementioned specific solvent is easily removed by drying or other methods, thereby effectively preventing the first solution of pre-crosslinked polydimethylsiloxane from penetrating the porous substrate layer, avoiding trench layer defects, and improving the gas permeability of the composite gas separation membrane.

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

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

[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℃.

[0048] In this invention, the fluorocarbon solvent can be commercially available, for example, from 3M. TM Fluorinert electronic fluorinated liquid TM FC-72 (boiling point 50-60℃).

[0049] According to the present invention, the prewetting time is 10 min to 24 h.

[0050] In this invention, when the pre-wetting time meets the above-mentioned range, the micropores of the porous substrate layer can be fully wetted, effectively preventing the trench layer membrane liquid, 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] Furthermore, the pre-wetting time is 30 min to 12 h.

[0052] Furthermore, the prewetting time is 30-70 minutes.

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

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

[0055] In this invention, when the dynamic viscosity of the pre-crosslinked polydimethylsiloxane meets the above-mentioned range, it has good film-forming properties, and the resulting 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), the viscosity of the pre-crosslinked polydimethylsiloxane in the first solution is 10 cP-30 cP at 25°C.

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

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

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

[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 / cm². 2 .

[0061] Furthermore, the ratio of the volume of the first solution to the area of ​​the porous substrate is 0.02-0.06 mL / cm². 2 .

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

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

[0064] In this invention, there is no particular limitation on the source of the pre-crosslinked polydimethylsiloxane, which can be commercially available. Preferably, in this 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 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 this invention, when the contents of polydimethylsiloxane and crosslinking agent meet the above-mentioned range, the pre-crosslinked polydimethylsiloxane obtained has the characteristics of good film-forming properties, and the resulting trench layer is smoother, thinner, denser and defect-free, which is beneficial to improving the gas permeability and gas selectivity of the composite gas separation membrane.

[0067] Furthermore, 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, the content of the catalyst is 20-50 wt%, based on the total amount of the polydimethylsiloxane and the crosslinking agent.

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

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

[0071] In this invention, there is no special limitation on the amount of organic solvent used, as long as it is sufficient to disperse the polydimethylsiloxane and the crosslinking agent.

[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 a de-alcoholized silane crosslinking agent.

[0074] In this invention, there is no particular limitation on the type of dealcohol-type silane crosslinking agent. Preferably, the crosslinking agent is selected from at least one of tetraethyl orthosilicate, methyl orthosilicate, and 1,2-bis(trimethoxysilyl)ethane.

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

[0076] In this invention, there is no particular limitation on the type of organotin catalyst. Preferably, the catalyst is dibutyltin dicalsilicate and / or dioctyltin dicalsilicate.

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

[0078] Furthermore, the crosslinking temperature is 50-80℃, and the crosslinking time is 20-60 min.

[0079] In a preferred embodiment of the present invention, the method for preparing pre-crosslinked polydimethylsiloxane includes: mixing polydimethylsiloxane and a crosslinking agent in the presence of an organic solvent and a catalyst, then crosslinking the mixture, and degassing it under vacuum for 1-5 minutes to obtain a first solution of pre-crosslinked polydimethylsiloxane.

[0080] In this invention, the first solution of pre-crosslinked polydimethylsiloxane is directly prepared using the above method, which improves the continuity of the preparation method of the composite gas separation membrane and makes it less prone to introducing impurities. In this 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 0.2wt%-3wt%, and the content of the additive is 0-5wt%.

[0083] In this invention, when the content of each component in the second solution meets the above-mentioned range, 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 0.2wt%-1wt%, and the content of the additive is 0.5wt%-3wt%.

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

[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-polybutadiene terephthalate (PEO-PBT).

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

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

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

[0090] In this invention, when the above-mentioned additives are used, the polyoxyethylene copolymer and the additives 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 additive has an average number-average molecular weight of 2,000-5,000 g / mol.

[0093] In this 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.

[0094] In a preferred embodiment of the present invention, the preparation method of the second solution includes: stirring the polyoxyethylene copolymer, optionally the additives and the solvent at 50-90°C for 60-180 min, and then degassing under vacuum 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 4-24h.

[0096] According to the present invention, the volume ratio of the second solution to the area of ​​the porous substrate is 0.01-0.2 mL / cm². 2 .

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

[0098] In this invention, when the ratio of the volume of the second solution to the area of ​​the porous substrate and / or the second coating time meets the above-mentioned range, it is beneficial to improve the gas permeability of the composite gas separation membrane.

[0099] Furthermore, the volume ratio of the second solution to the area of ​​the porous substrate is 0.05-0.1 mL / cm². 2 .

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

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

[0102] In this invention, the protective layer is a fluoropolymer layer, which can maintain the separation performance of the composite gas separation membrane while giving the composite gas separation membrane good heat resistance and waterproof performance.

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

[0104] In this invention, when the content of fluoropolymer meets the above range, the obtained protective layer has good heat resistance, hydrophobicity and anti-plasticization properties, and the obtained composite gas separation membrane still has high gas permeation flux and high CO2 / N2 selective separation performance under high temperature conditions.

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

[0106] According to the present invention, the fluoropolymer is selected from at least one of the following: a copolymer of perfluoro-2,2-dimethyl-1,3-dioxacyclopentene and tetrafluoroethylene (PDD-TFE), a copolymer of 2,2,4-trifluoro-5-trifluoromethoxy-1,3-dioxacyclopentene and tetrafluoroethylene (TTD-TFE), and a perfluoro-4-ethoxy-1-butene homopolymer (BVE).

[0107] In this invention, the fluoropolymer can be commercially available, for example, the copolymer of perfluoro-2,2-dimethyl-1,3-dioxane-tetrafluoroethylene (PDD-TFE) is Teflon AF2400, the copolymer of 2,2,4-trifluoro-5-trifluoromethoxy-1,3-dioxane-tetrafluoroethylene (TTD-TFE) is Hyflon AD60, and the perfluoro-4-ethoxy-1-butene homopolymer (BVE) is Cytop.

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

[0109] In this invention, the perfluoropolyether solution can be commercially available, such as GaldenHT110 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 hours.

[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 / cm². 2 .

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

[0113] In this invention, when the ratio of the volume of the third solution to the area of ​​the porous substrate and / or the third coating time meets the above-mentioned range, the composite gas separation membrane has good heat resistance and high gas permeation flux and CO2 / N2 selective separation performance at high temperatures.

[0114] Furthermore, the volume ratio of the third solution to the area of ​​the porous substrate is 0.02-0.05 mL / cm². 2 .

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

[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 minutes to obtain the third solution.

[0117] A second aspect of the present invention provides a composite gas separation membrane, wherein the composite gas separation membrane is prepared by the above-described preparation method.

[0118] According to the present invention, the CO2 permeation rate of the composite gas separation membrane is greater than or equal to 500 GPUs.

[0119] Furthermore, the CO2 permeation rate of the composite gas separation membrane is greater than or equal to 1000 GPUs.

[0120] According to the present invention, the composite gas separation membrane has a separation selectivity of greater than or equal to 30 for CO2 and N2.

[0121] Furthermore, the composite gas separation membrane exhibits a separation selectivity of greater than or equal to 50 for CO2 and N2.

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

[0123] According to the present invention, the composite gas separation membrane comprises, in sequence, a porous substrate layer, a trench layer, a selective layer, and an optional protective layer.

[0124] According to the present invention, the trench layer is a cross-linked 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-polybutadiene terephthalate.

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

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

[0128] The thickness of the porous substrate and the composite gas separation membrane were measured by scanning electron microscopy.

[0129] The dynamic viscosity of the pre-crosslinked polydimethylsiloxane was measured using a digital rotational viscometer (Brookfield, USA) at a temperature of 25°C.

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

[0131] CO2 permeation rate and CO2 / N2 separation selectivity at 25℃ and 0.2MPa: A CO2 and N2 mixture simulating flue gas (composed of 15% CO2 and 85% N2 molar fractions) was used as the feed gas at a pressure of 0.2MPa and a temperature of 25℃. Ar was used as the purge gas. The purge gas flow rate was kept constant at 35mL / min. The permeate gas was sent to an Agilent gas chromatograph via a mass flow meter using the Ar purge gas for detection and analysis. The total permeate flow rate was measured by a soap film flow meter, and the flow rates of the permeate gas components were calculated based on the mass fractions of the permeate gas components measured by gas chromatography.

[0132] The permeation rate R of component CO2 i Calculated from Equation 1:

[0133]

[0134] Q is the total flow rate of permeate and purge gas, in cm⁻¹ 3 / s; A is the membrane area, cm² -2 ;Δp i R represents the pressure difference between the upstream and downstream sides of the membrane for component i, in cmHg; i Let be the permeation rate of gas component i. To simplify the units, GPU is introduced as the unit of permeability, 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 standard conditions, i.e., temperature of 273.15 K (i.e., 0 °C) and pressure of 101.325 kPa.

[0137] CO 2 With N 2 The ratio of permeability (permeability coefficient) passing through the membrane is the separation selectivity, denoted by α. i / j represents. Calculated from Equation 3.

[0138]

[0139] In the formula, R i R is the permeation rate of the gaseous component CO2. j The permeation rate of the gaseous component N2.

[0140] CO2 permeation rate and CO2 / N2 separation selectivity at 80℃ and 0.2MPa: The test method for CO2 permeation rate and CO2 / N2 separation selectivity at 25℃ and 0.2MPa was the same as above, except that the feed gas pressure was 0.2MPa and the temperature was 80℃.

[0141] The plasma treatment uses a plasma cleaning machine (PVA TePla Plasma System ION40).

[0142] Fluorocarbon solvent A is 3M TM Fluorinert electronic fluorinated liquid TM FC-72 has a boiling point of 60℃.

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

[0144] Polyoxyethylene-polyamide (PEO-PA) copolymer B: purchased from Arkema, France, brand name Pebax 1657, the content of polyoxyethylene structural units in copolymer B is 60wt%.

[0145] Unless otherwise specified, the ethanol-water solution mentioned in the examples refers to a solution with a volume ratio of ethanol to water of 70:30.

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

[0147] Porous substrate preparation

[0148] A casting solution was prepared, consisting of 20% polysulfone and 80% N,N-dimethylformamide solvent DMF. The casting solution was applied to a polyester nonwoven fabric using a blade-based coating method at a blade speed of 6 m / min, with a blade thickness of 220 μm (i.e., the initial film thickness). Deionized water was used as the non-solvent. The resulting initial film was immersed in deionized water for 24 h, followed by three deionized water replacements, and then dried at 70 °C to obtain a porous substrate layer with a thickness of 110 μm.

[0149] Preparation Example 1

[0150] Polydimethylsiloxane (PDMS with a number average molecular weight of 20,000 g / mol), tetraethyl orthosilicate (TEOS) as a crosslinking agent, and dibutyltin dibutylsilicate (DBD) as a catalyst were added to n-heptane. Based on the total weight of the pre-crosslinked PDMS, the content of PDMS was 50 wt%, and the content of the crosslinking agent was 50 wt%. Based on the total amount of PDMS and the crosslinking agent, the content of the catalyst was 25 wt%. The mixture was stirred at 30 °C for 60 minutes and degassed under vacuum for 5 minutes to obtain the first solution A. The measured parameters are shown in Table 1.

[0151] Preparation Example 2

[0152] The first solution B was prepared according to Preparation Example 1, except that the amounts of polydimethylsiloxane, dibutyltin dimethylsiloxane, and dibutyltin dimethylsiloxane were different from those in Preparation Example 1. The specific contents are shown in Table 1.

[0153] Table 1

[0154]

[0155] *Based on the total weight of pre-crosslinked polydimethylsiloxane, the content of polydimethylsiloxane and crosslinking agent.

[0156] *DBD content: Based on the total amount of polydimethylsiloxane and crosslinking agent used, the DBD content is calculated.

[0157] Example 1

[0158] (1) Trench layer: The first solution A was coated onto a porous substrate pre-wetted with water for 30 min by dip coating, and then dried at 50°C for 120 min. Specifically, the volume ratio of the first solution A to the area of ​​the porous substrate was 0.05 mL / cm². 2 The first coating time is 10 seconds.

[0159] (2) Selective Layer: The trench layer from step (1) was subjected to plasma treatment, with a carbon dioxide flow rate of 500 mL / min, a treatment time of 30 s, and a treatment power of 110 W. Polyoxyethylene-polyamide (PEO-PA) copolymer (Pebax 2533), the additive polyethylene glycol monomethyl ether (PEGME), and n-butanol were stirred at 80 °C for 60 min, followed by vacuum degassing for 5 min to obtain a second solution (Pebax 2533 content: 0.5 wt%, PEGME content: 0.5 wt%). The second solution of the polyoxyethylene copolymer was coated onto 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 / cm². 2 The second coating takes 10 seconds.

[0160] (3) Protective Layer: A third solution containing a fluoropolymer is coated onto the selective layer from step (2). Specifically, the fluoropolymer (Teflon AF2400) is mixed with a perfluoropolyether solution GALDEN HT110, and degassed under vacuum for 5 minutes to obtain the third solution (the fluoropolymer content in the third solution is 0.1 wt%). The fluoropolymer layer is dried at 80°C for 1 hour to obtain the composite gas separation membrane. Specifically, the volume ratio of the third solution to the area of ​​the porous substrate layer is 0.03 mL / cm². 2 The third coating process takes 10 seconds.

[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 in 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 from Table 2

[0168]

[0169] Continued from Table 2

[0170]

[0171] Example 14

[0172] The composite gas separation membrane was prepared according to the method of Example 1, except that step (3) was omitted. The thickness of the composite gas separation membrane was measured to be approximately 110.5 μm. The test results of the composite gas separation membrane are shown in Table 3.

[0173] Example 15

[0174] The composite gas separation membrane was prepared 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 was 0.1 mL / cm². 2 The third coating time was 60 seconds. The test results of the composite gas separation membrane are shown in Table 3.

[0175] Example 16

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

[0177] Comparative Example 1

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

[0179] Comparative Example 2

[0180] The composite gas separation membrane was prepared according to the method in Example 1, except that plasma treatment was not used in step (2). The selective layer coating was uneven, and the membrane had defects. The test results of the prepared 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 in 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 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 in step (1) was not pre-wetted, and the first solution A was directly coated onto the porous substrate. The test results of the prepared composite gas separation membrane are shown in Table 3.

[0185] Table 3

[0186]

[0187] The test results show that the composite gas separation membrane prepared by this invention has better CO2 permeation rate and CO2 / N2 separation selectivity. When the preferred pre-wetting and plasma treatment methods are used, a synergistic effect is achieved, further improving the CO2 permeation rate and CO2 / N2 separation selectivity of the separation membrane. The composite gas separation membrane with a protective layer maintains a high CO2 permeation rate and CO2 / N2 separation selectivity at 80℃ and 0.2MPa, indicating that coating with a protective layer can improve the high-temperature resistance of the separation membrane.

[0188] Figure 1 , Figure 2The images shown are cross-sectional SEM images of the composite gas separation membranes prepared in Examples 1 and 2, respectively. It can be seen that the separation layer is thin and dense and tightly bonded to the porous substrate layer. This indicates that by pre-wetting the porous substrate layer in this invention, the first solution of pre-crosslinked polydimethylsiloxane can be effectively prevented from penetrating the porous substrate layer. Plasma modification can produce a thin and dense selective layer.

[0189] Figure 3 XPS characterization of the trench layer surface after CO2 plasma treatment in Example 1. Here, the original PDMS membrane refers to the trench layer membrane surface in Example 1 without plasma treatment, and PDMS 30s refers to the trench layer membrane surface in Example 1 after plasma treatment. It can be seen that hydrophilic CO / C=O groups and barrier Si-O3 / Si-O4 groups are generated on the membrane surface, indicating that the hydrophilicity of the trench layer membrane surface is improved after treatment, which is beneficial to improving the affinity of the separation layer membrane solution.

[0190] Figure 4 These are SEM images of the trench layer before and after CO2 plasma treatment in Example 1. Figure (a) shows the surface of the trench layer film without plasma treatment in Example 1, and Figure (b) shows the surface of the trench layer film after plasma treatment in Example 1. It can be seen that the trench layer in Figure (b) is thinner but still dense, indicating that plasma treatment allows the trench layer to 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 inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all 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 sequentially preparing a trench layer, a selection layer, and a protective layer on a porous substrate, comprising the following steps: (1) The porous substrate is pre-wetted, and a first solution of pre-crosslinked polydimethylsiloxane is first coated on the pre-wetted porous substrate, and then dried. (2) After plasma treatment of the first dried product, a second solution of polyoxyethylene copolymer is applied to the second dried product, followed by a second drying process. (3) A third solution of fluoropolymer is coated on the surface of the product after the second drying, and after the third drying, a composite gas separation membrane is obtained; In step (2), the plasma treatment time is 2-120s and the treatment power is 20-120W.

2. The preparation method according to claim 1, wherein, In step (2), the plasma treatment time is 20s-60s and the treatment power is 50-110W.

3. The preparation method according to claim 1, wherein, The gas source for plasma treatment is selected from at least one of argon, oxygen, and carbon dioxide.

4. The preparation method according to claim 3, wherein, The gas source for the plasma treatment is oxygen and / or carbon dioxide.

5. The preparation method according to claim 1, wherein, In step (1), the porous substrate layer is a nonwoven fabric containing a porous support layer.

6. The preparation method according to claim 5, wherein, The porous support layer is selected from at least one of polysulfone, polyethersulfone, polyacrylonitrile, and polyvinylidene fluoride.

7. The preparation method according to claim 1, wherein, The thickness of the porous substrate layer is 100-140 μm.

8. The preparation method according to claim 7, wherein, The thickness of the porous substrate layer is 110-130 μm.

9. The preparation method according to claim 1, wherein, In step (1), the pre-wetting solvent is selected from at least one of water, alcohol, fluorocarbon solvent and C3-C4 ketone.

10. The preparation method according to claim 9, wherein, The alcohol is selected from C2-C4 alcohols.

11. The preparation method according to claim 10, wherein, The alcohol is selected from at least one of n-butanol, isobutanol, and ethanol.

12. The preparation method according to claim 9, wherein, The fluorocarbon solvent is a fluorinated alkane.

13. The preparation method according to claim 9, wherein, The boiling point of the fluorocarbon solvent is 40-99℃.

14. The preparation method according to claim 13, wherein, The boiling point of the fluorocarbon solvent is 50-90℃.

15. The preparation method according to claim 1, wherein, The prewetting time is 10 min to 24 h.

16. The preparation method according to claim 15, wherein, The prewetting time is 30 min to 12 h.

17. The preparation method according to claim 1, wherein, In step (1), the pre-crosslinked polydimethylsiloxane in the first solution has a dynamic viscosity of 8 cP-50 cP at 25°C.

18. The preparation method according to claim 17, wherein, The pre-crosslinked polydimethylsiloxane has a dynamic viscosity of 10 cP-30 cP at 25°C.

19. The preparation method according to claim 1, wherein, The solid content of the first solution is 0.1wt%-1wt%.

20. The preparation method according to claim 19, wherein, The solid content of the first solution is 0.2wt%-0.5wt%.

21. The preparation method according to claim 1, wherein, The volume ratio of the first solution to the area of ​​the porous substrate is 0.01-0.1 mL / cm². 2 .

22. The preparation method according to claim 21, wherein, The volume ratio of the first solution to the area of ​​the porous substrate is 0.02-0.06 mL / cm². 2 .

23. The preparation method according to claim 1, wherein, The first coating time is 2s-60s.

24. The preparation method according to claim 23, wherein, The first coating time is 10s-40s.

25. The preparation method according to claim 1, wherein, The method for preparing the pre-crosslinked polydimethylsiloxane includes: mixing polydimethylsiloxane and a crosslinking agent in the presence of an organic solvent and a catalyst, and then crosslinking the mixture to obtain the pre-crosslinked polydimethylsiloxane.

26. The preparation method according to claim 25, wherein, 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%.

27. The preparation method according to claim 26, wherein, 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%.

28. The preparation method according to claim 25, wherein, Based on the total amount of the polydimethylsiloxane and the crosslinking agent, the content of the catalyst is 20-50 wt%.

29. The preparation method according to claim 28, wherein, Based on the total amount of the polydimethylsiloxane and the crosslinking agent, the content of the catalyst is 25-30 wt%.

30. The preparation method according to claim 25, wherein, The polydimethylsiloxane has a number-average molecular weight of 20,000-100,000 g / mol.

31. The preparation method according to claim 25, wherein, The crosslinking agent is a de-alcoholized silane crosslinking agent.

32. The preparation method according to claim 25, wherein, The catalyst is an organotin catalyst.

33. The preparation method according to claim 25, wherein, The crosslinking temperature is 30-80℃, and the crosslinking time is 30-120 min.

34. The preparation method according to claim 1, wherein, In step (2), the second solution includes a polyoxyethylene copolymer and optionally an additive.

35. The preparation method according to claim 34, wherein, In the second solution, the content of the polyoxyethylene copolymer is 0.2wt%-3wt%, and the content of the additive is 0-5wt%.

36. The preparation method according to claim 35, wherein, In the second solution, the content of the polyoxyethylene copolymer is 0.2wt%-1wt%, and the content of the additive is 0.5wt%-3wt%.

37. The preparation method according to claim 1, wherein, The polyoxyethylene copolymer is selected from at least one of polyoxyethylene-polyamide copolymer, polyoxyethylene-polyimide copolymer, polyoxyethylene-polyimide copolymer, and polyoxyethylene-polybutadiene terephthalate.

38. The preparation method according to claim 34, wherein, The additive is a polyether polyol.

39. The preparation method according to claim 38, wherein, The additive is at least one of polyethylene glycol monomethyl ether, polyethylene glycol dimethyl ether, and polyethylene glycol ethyl ether.

40. The preparation method according to claim 34, wherein, The additive has an average number-average molecular weight of 500-6,000 g / mol.

41. The preparation method according to claim 40, wherein, The additive has an average number-average molecular weight of 2,000-5,000 g / mol.

42. The preparation method according to claim 1, wherein, In step (2), the temperature of the second drying is 30-80℃, and the drying time is 4-24h.

43. The preparation method according to claim 1, wherein, The volume ratio of the second solution to the area of ​​the porous substrate is 0.01-0.2 mL / cm². 2 .

44. The preparation method according to claim 43, wherein, The volume ratio of the second solution to the area of ​​the porous substrate is 0.05-0.1 mL / cm². 2 .

45. The preparation method according to claim 1, wherein, The second coating time is 2s-60s.

46. ​​The preparation method according to claim 45, wherein, The second coating time is 10s-30s.

47. The preparation method according to claim 1, wherein, In step (3), the content of the fluoropolymer in the third solution is 0.1wt%-1wt%.

48. The preparation method according to claim 47, wherein, In step (3), the content of the fluoropolymer in the third solution is 0.2wt%-0.5wt%.

49. The preparation method according to claim 1, wherein, The fluoropolymer is selected from at least one of the following: a copolymer of perfluoro-2,2-dimethyl-1,3-dioxacyclopentene and tetrafluoroethylene, a copolymer of 2,2,4-trifluoro-5-trifluoromethoxy-1,3-dioxacyclopentene and tetrafluoroethylene, and a perfluoro-4-ethoxy-1-butene homopolymer.

50. The preparation method according to claim 1, wherein, The solvent for the third solution is a perfluoropolyether solution.

51. The preparation method according to claim 1, wherein, The temperature of the third drying process is 50-80℃, and the drying time is 1-24 hours.

52. The preparation method according to claim 1, wherein, The volume ratio of the third solution to the area of ​​the porous substrate is 0.01-0.1 mL / cm². 2 .

53. The preparation method according to claim 1, wherein, The volume ratio of the third solution to the area of ​​the porous substrate is 0.02-0.05 mL / cm². 2 .

54. The preparation method according to claim 1, wherein, The third coating process takes 2-60 seconds.

55. The preparation method according to claim 54, wherein, The third coating is applied over a period of 10-30 seconds.

56. 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 1-55.

57. The composite gas separation membrane according to claim 56, wherein, The CO2 permeation rate of the composite gas separation membrane is greater than or equal to 500 GPU.

58. The composite gas separation membrane according to claim 57, wherein, The CO2 permeation rate of the composite gas separation membrane is greater than or equal to 1000 GPU.

59. The composite gas separation membrane according to claim 56, wherein, The composite gas separation membrane exhibits a selectivity of 30 or greater for separating CO2 and N2.

60. The composite gas separation membrane according to claim 59, wherein, The composite gas separation membrane exhibits a selectivity of greater than or equal to 50 for separating CO2 and N2.

61. The composite gas separation membrane according to claim 56, wherein, The thickness of the composite gas separation membrane is 110μm-150μm.

62. The composite gas separation membrane according to claim 56, wherein, The composite gas separation membrane comprises, in sequence, a porous substrate layer, a trench layer, a selective layer, and a protective layer.

63. The composite gas separation membrane according to claim 62, wherein, The trench layer is a cross-linked polydimethylsiloxane.

64. The composite gas separation membrane according to claim 62, wherein, The selective layer is selected from at least one of polyoxyethylene-polyamide copolymer, polyoxyethylene-polyimide copolymer, polyoxyethylene-polyimide copolymer, and polyoxyethylene-polybutadiene terephthalate.

65. The composite gas separation membrane according to claim 62, wherein, The protective layer is a fluoropolymer.

Images