Composite gas separation membrane as well as preparation method and application thereof

Abstract

The invention relates to the technical field of separation membrane materials, and discloses a composite gas separation membrane and a preparation method and application thereof, the composite gas separation membrane sequentially comprises a base material layer, a porous support layer, a middle layer and a selective layer; wherein the selective layer is a polyoxyethylene copolymer; wherein the crystallinity of the selective layer is 30%-49%. The composite gas separation membrane has high permeability and high selectivity.

Description

Technical Field

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

[0002] Developing carbon capture, utilization, and storage (CCUS) technology is an important solution for mitigating the greenhouse effect and addressing air pollution at present. Membrane carbon capture technology has advantages such as simple process, low investment, small footprint, and environmental friendliness, and is therefore considered a promising carbon dioxide separation technology, attracting widespread attention from researchers both domestically and internationally.

[0003] The development of high-performance carbon dioxide separation membranes includes membrane material development and large-scale membrane fabrication process development. Polyethylene oxide (PEO), as a representative CO2-loving material, has attracted widespread research attention due to its unique "dipole-quadrupole" interaction with CO2, resulting in very high CO2 solubility and ideal CO2 / N2 selectivity. A trade-off effect exists between gas permeability and selectivity, severely hindering the separation performance of traditional polyether-containing polymers and limiting their widespread application in industrial processes. Therefore, to obtain membranes with high permeation flux and selectivity, researchers have employed copolymerization, crosslinking, and other methods to introduce flexible segments into rigid polymers, forming hard-segment-soft-segment copolymers to improve gas separation performance. Currently, commercially available polyether-containing membrane materials have been developed.

[0004] Polyether block polyamides are used in CO2 / N2 gas separation membranes, but different solvents can dissolve them. The gas permeability of the prepared membranes varies greatly. Mojgan Isanejad et al. (Journal of Applied Polymer Science, 2017, 134(9)) used five different solvents to dissolve polyether block polyamide cast membranes to investigate the effect of different solvents on the gas permeability of the membranes. Among them, the membranes obtained by the most commonly used ethanol / water solvent did not have excellent performance. Considering both CO2 permeability coefficient and CO2 / CH4 selectivity, although the membranes cast from dimethylformamide had the best performance, their CO2 permeability coefficient was only 120-150 Barrer. The prepared membranes were only suitable for laboratory research and could not be applied to industrial gas capture. CN112934011A discloses a membrane material and its preparation method for CO2 separation. Pebax is used as the continuous phase, and metal-organic framework material is used as the filler. One or more solvents are selected from water, ethanol, isopropanol, methanol and N,N-dimethylformamide. Mixed matrix membranes under different solvents are obtained. The membrane obtained under the ethanol, water and isopropanol system has the best separation performance, with CO2 / N2 selectivity increasing from 60 to 140. However, the CO2 permeability coefficient decreases from 150 Barrer to 84.4 Barrer compared to the pure Peabx membrane. Moreover, the process is complicated and cannot be used in high-performance CO2 capture gas separation membrane applications.

[0005] Besides selecting suitable membrane materials, the choice of membrane fabrication process is also crucial. Thin-layer composite membranes (TFCMs) are a membrane fabrication technology where the separator and support layers are prepared separately. They are considered an effective membrane structure with practical industrial application value. Most TFCMs are prepared using a top-down coating method, including dip coating, blade coating, and spin coating. To achieve high gas permeation flux, the separator layer should be as thin as possible (<1 μm) during TFCM fabrication. However, this can lead to the casting solution from the separator layer seeping into the micropores of the support layer (separator layer porosity), resulting in reduced membrane permeability and defects in the separator layer. To address these issues, existing technologies often introduce an intermediate layer between the support and separator layers to reduce porosity and improve permeability. In this case, the TFCM structure consists of a porous support layer, a highly permeable and dense intermediate layer, and an ultrathin separator layer.

[0006] Among them, the material of the intermediate layer is generally a rubber-like material with high gas permeation flux, such as polydimethylsiloxane (PDMS), which is a commonly used material with excellent performance. Zhang Xu et al. (Improving the adhesion of silicone rubber to prepare multilayer composite membranes, Membrane Science and Technology, 2020, 40(6):37-43) prepared a three-layer hollow fiber composite membrane using commercial silicone rubber (PDMS) and additives as raw materials as the intermediate layer, which effectively improved the adhesion of the intermediate layer. However, PDMS has low surface energy and exhibits strong hydrophobicity. It has poor interfacial compatibility with separation layer materials such as polyethylene oxide copolymers, low bonding force between layers, and is prone to TFCM defects, delamination and other problems. Therefore, it is necessary to treat the surface of PDMS to improve its hydrophilicity. CN116440715A discloses a method for preparing a polydimethylsiloxane / polyethersulfone ultrathin composite membrane modified with tannic acid, using tannic acid as a polyphenol molecular ligand and iron ions Fe 3+ As an inorganic crosslinking agent, it improves the hydrophilicity of PDMS-coated composite membranes, but its surface modification process requires multiple layer-by-layer assembly and is only suitable for CO2 / O2 separation in gas-liquid two-phase environments. CN115608177A discloses a method for preparing and applying a polyether block polyamide / polydimethylsiloxane composite gas separation membrane. By introducing an amphoteric copolymer PDMS-b-PEO into the intermediate layer to improve the interfacial compatibility with the separation layer, an ultrathin separation layer and a composite membrane with superior separation performance are obtained. However, the viscosity of the intermediate layer casting solution is difficult to control, and there are still many problems in its application to industrial scale-up production.

[0007] Existing polyether block polyamide thin-layer composite membranes prepared using ethanol and water as solvents still exhibit low CO2 permeation flux. Achieving good interfacial compatibility between the separation layer membrane solution and the intermediate layer has become a key technical challenge restricting the preparation of high-permeability, high-selectivity, and continuous defect-free thin-layer composite membranes. Therefore, it is particularly important to provide a membrane preparation method that is simple, controllable, environmentally friendly, and yields better gas separation performance. Summary of the Invention

[0008] The purpose of this invention is to overcome the problem of low CO2 permeation flux in composite gas separation membranes prepared using ethanol and water as solvents in the prior art, and to provide a composite gas separation membrane, its preparation method and application, which has high permeability and high selectivity.

[0009] To achieve the above objectives, the first aspect of the present invention provides a composite gas separation membrane, wherein the composite gas separation membrane comprises, in sequence, a substrate layer, a porous support layer, an intermediate layer, and a selective layer;

[0010] The selective layer is a polyoxyethylene copolymer;

[0011] The crystallinity of the selective layer is 30%-49%.

[0012] A second aspect of the present invention provides a method for preparing a composite gas separation membrane, wherein the method includes: preparing a selective layer on a semi-finished membrane comprising a substrate layer, a porous support layer and an intermediate layer in sequence;

[0013] The method for preparing the selective layer includes: mixing a polyoxyethylene copolymer with a solvent to obtain a coating liquid, coating the coating liquid onto the side of the plasma-treated intermediate layer away from the porous support layer, and drying it to obtain a composite gas separation membrane.

[0014] The solvent includes aqueous solutions of C2-C5 fatty alcohols and fluorinated alcohols;

[0015] The content of the fluorinated alcohol compound is 5-50 wt%, based on the total mass of the solvent.

[0016] A third aspect of the present invention provides a composite gas separation membrane prepared by the above-described preparation method.

[0017] A fourth aspect of the present invention provides an application of the above-mentioned composite gas separation membrane in carbon capture.

[0018] The composite gas separation membrane, its preparation method, and its application provided by the present invention, through the above technical solutions, have the following beneficial effects:

[0019] The selective layer in the composite gas separation membrane of the present invention is a polyoxyethylene copolymer, and the crystallinity of the selective layer is 30%-49%; thus, the composite gas separation membrane of the present invention can have both high CO2 permeability and high CO2 / N2 selectivity.

[0020] This invention involves mixing a polyoxyethylene copolymer with an aqueous solution of a C2-C5 fatty alcohol and a fluorinated alcohol compound, which improves the dissolution of the polyoxyethylene copolymer and allows it to spread on the surface of a plasma-treated intermediate layer. The resulting composite gas separation membrane exhibits high gas permeation flux while maintaining high CO2 / N2 selective separation performance. The preparation method of this invention is simple, quick, environmentally friendly, and low-cost, making it valuable for industrial applications. Attached Figure Description

[0021] Figure 1 These are SEM images of the composite gas separation membrane (a) surface and (b) cross-section obtained in Example 1 of this invention.

[0022] Figure 2 These are SEM images of the composite gas separation membrane (a) surface and (b) cross-section obtained in Example 2 of this invention.

[0023] Figure 3The images show (a) surface and (b) cross-sectional SEM images of the composite gas separation membrane prepared in Comparative Example 3 of this invention.

[0024] Figure 4 The images show the nano-infrared spectra of the composite gas separation membranes prepared in Example 2 and Comparative Example 3 of this invention.

[0025] Figure 5 The X-ray diffraction (XRD) patterns are those of the composite gas separation membranes prepared in Examples 1, 2, 1, and 3 of this invention. Detailed Implementation

[0026] 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.

[0027] The first aspect of the present invention provides a composite gas separation membrane, wherein the composite gas separation membrane comprises, in sequence, a substrate layer, a porous support layer, an intermediate layer and a selective layer;

[0028] The selective layer is a polyoxyethylene copolymer;

[0029] The crystallinity of the selective layer is 30%-49%.

[0030] In this invention, the selective layer in the composite gas separation membrane is a polyoxyethylene copolymer, and the crystallinity of the selective layer is 30%-49%; thus, the composite gas separation membrane of this invention can have both high CO2 permeability and high CO2 / N2 selectivity.

[0031] Furthermore, the crystallinity of the selective layer is 33%-47%.

[0032] According to the present invention, the intermolecular spacing in the selective layer is 3.6-3.77.

[0033] In this invention, when the intermolecular spacing in the selective layer meets the above-mentioned range, the composite gas separation membrane can obtain better gas permeability. This is because the intermolecular spacing parameter is a measure of the distance between molecules in the polymer chains. An increase in the distance between the chains leads to a decrease in the intramolecular van der Waals attraction, thereby giving it a higher free volume fraction and increasing the gas permeability of the membrane.

[0034] Furthermore, the intermolecular spacing in the selective layer is 3.71-3.77.

[0035] According to the present invention, the thickness of the composite gas separation membrane is 110-131 μm.

[0036] According to the present invention, the thickness of the substrate layer is 90-100 μm.

[0037] In this invention, the specific type of the substrate layer is not limited, and it can be a conventional substrate layer in the art. Preferably, the substrate layer is at least one of polyester nonwoven fabric, polyethylene nonwoven fabric, and polypropylene nonwoven fabric.

[0038] According to the present invention, the thickness of the porous support layer is 20-30 μm.

[0039] In this invention, the specific type of porous support layer is not limited, and it can be any conventional porous support layer in the art. Preferably, the porous support layer is selected from at least one of polysulfone, polyethersulfone, polyacrylonitrile, and polyvinylidene fluoride.

[0040] According to the present invention, the thickness of the intermediate layer is 120-400 nm.

[0041] In this invention, when the thickness of the intermediate layer meets the above-mentioned range, it means that the intermediate layer can completely cover the surface of the support layer and partially block the pores of the support layer. This allows the composite gas separation membrane to maintain high gas permeability while also having good separation selectivity.

[0042] Furthermore, the thickness of the intermediate layer is 150-300 nm.

[0043] According to the present invention, the intermediate layer is selected from at least one of polydimethylsiloxane (PDMS), thermoplastic polyurethane (TPU) and polytrimethoxypropyne (PTMSP).

[0044] In this invention, coating the porous support layer with the aforementioned specific type of intermediate layer eliminates surface defects of the porous support layer, providing a smooth, defect-free surface. This allows for complete coating of the selective layer polymer casting solution, achieving anchoring bonding with the support layer. The bond between the porous support layer, intermediate layer, and selective layer is stronger, enabling the composite gas separation membrane to maintain high gas permeability while also exhibiting good separation selectivity.

[0045] In this invention, the intermediate layer is polydimethylsiloxane treated with plasma.

[0046] According to the present invention, the thickness of the selective layer is 60-200 nm.

[0047] In this invention, when the thickness of the selective layer meets the above-mentioned range, it indicates that the selective layer of this invention is relatively thin, which makes the composite gas separation membrane have a high gas permeation flux and a high CO2 / N2 separation selectivity.

[0048] Furthermore, the thickness of the selective layer is 60-150 nm.

[0049] Furthermore, the thickness of the selective layer is 60-115 nm.

[0050] According to the present invention, the weight-average molecular weight of the polyoxyethylene copolymer is 40,000-120,000 g / mol.

[0051] In this invention, when the weight-average molecular weight of the polyoxyethylene copolymer meets the above-mentioned range, the polyoxyethylene copolymer is more soluble in C2-C5 fatty alcohol aqueous solutions and fluorinated alcohol compounds, and the coating solution has good film-forming properties, so that the composite gas separation membrane obtained can maintain high gas permeability while also having good separation selectivity.

[0052] Furthermore, the weight-average molecular weight of the polyoxyethylene copolymer is 70,000-100,000 g / mol.

[0053] According to the present invention, the polyoxyethylene copolymer is at least one of polyoxyethylene-polyamide copolymer, polyoxyethylene-polyimide copolymer, and polyoxyethylene-polyurethane copolymer.

[0054] In this invention, when the selective layer is the aforementioned polymer, the CO2 permeation rate is increased while maintaining good separation selectivity. In this invention, there are no special requirements regarding the source of the polyoxyethylene copolymer; it can be prepared using existing techniques or obtained commercially. For example, the polyoxyethylene-polyamide (PEO-PA) copolymer can be purchased from Arkema's Pebax series elastomers, such as Pebax-1657, Pebax-1074, and Pebax-2533.

[0055] According to a preferred embodiment of the present invention, the polyoxyethylene copolymer is a polyoxyethylene-polyamide (PEO-PA) copolymer.

[0056] According to the present invention, the content of polyoxyethylene in the polyoxyethylene copolymer is 50-80 wt%.

[0057] In this invention, when the content of polyoxyethylene meets the above range, the composite gas separation membrane has good mechanical strength, as well as high CO2 solubility and CO2 / N2 selectivity.

[0058] Furthermore, the polyoxyethylene content in the polyoxyethylene copolymer is 60-80 wt%.

[0059] According to the present invention, the CO2 permeation rate of the composite gas separation membrane is greater than or equal to 1000 GPU.

[0060] Furthermore, the CO2 permeation rate of the composite gas separation membrane is greater than or equal to 2000 GPUs.

[0061] According to the present invention, the ideal separation selectivity of CO2 / N2 is greater than or equal to 20.

[0062] In this invention, the ideal separation selectivity of CO2 / N2 is the ratio of the gas permeation rate of CO2 to the gas permeation rate of N2.

[0063] Furthermore, the ideal separation selectivity of the CO2 / N2 is greater than or equal to 25.

[0064] According to the present invention, the standard deviation of the contact angle between the composite gas separation membrane and water is less than or equal to 5.

[0065] In this invention, 10 points are randomly selected on the composite gas separation membrane to test the water contact angle on the membrane surface, and the standard deviation is calculated according to formula (2).

[0066] Standard deviation

[0067] Where Xi is the water contact angle at the membrane surface (°), and μ is the average value of the water contact angle at the membrane surface (°).

[0068] When the standard deviation of the contact angle between the composite gas separation membrane and water meets the above range, it indicates that there are no defects on the composite gas separation membrane and the selective layer is uniformly coated on the intermediate layer. When defects exist in the composite gas separation membrane, it leads to inconsistent water contact angles on the surface of the membrane, resulting in significant errors.

[0069] Furthermore, the standard deviation of the contact angle between the composite gas separation membrane and water is less than or equal to 3.

[0070] A second aspect of the present invention provides a method for preparing a composite gas separation membrane, wherein the method includes: preparing a selective layer on a semi-finished membrane comprising a substrate layer, a porous support layer and an intermediate layer in sequence;

[0071] The method for preparing the selective layer includes: mixing a polyoxyethylene copolymer with a solvent to obtain a coating liquid, coating the coating liquid onto the side of the plasma-treated intermediate layer away from the porous support layer, and drying it to obtain a composite gas separation membrane.

[0072] The solvent includes aqueous solutions of C2-C5 fatty alcohols and fluorinated alcohols;

[0073] The content of the fluorinated alcohol compound is 5-50 wt%, based on the total mass of the solvent.

[0074] In this invention, a composite gas separation membrane is obtained by mixing a polyoxyethylene copolymer with an aqueous solution of a C2-C5 fatty alcohol and a fluorinated alcohol compound, which improves the dissolution of the polyoxyethylene copolymer and allows it to spread on the surface of the plasma-treated intermediate layer. This results in a membrane with high gas permeation flux while maintaining high CO2 / N2 selective separation performance. The preparation method of this invention is simple, quick, environmentally friendly, and low-cost, making it valuable for industrial applications.

[0075] Furthermore, based on the total mass of the solvent, the content of the fluorinated alcohol compound is 10-45 wt%.

[0076] According to the present invention, in the aqueous solution of the C2-C5 fatty alcohol, the content of the fatty alcohol is 60-90 wt%.

[0077] Furthermore, in the C2-C5 fatty alcohol aqueous solution, the content of the fatty alcohol is 70-90 wt%.

[0078] According to the present invention, the fluoroalcohol compound is selected from at least one of hexafluoroisopropanol, tetrafluoropropanol, difluoroethanol and perfluoroalkylethanol.

[0079] In this invention, the above-mentioned fluoroalcohol compounds have hydrogen bonds, high molecular polarity, low boiling point, and high solubility, which is beneficial to improving the CO2 permeability of the composite gas separation membrane.

[0080] Furthermore, the fluoroalcohol compound is hexafluoroisopropanol and / or tetrafluoropropanol.

[0081] According to a preferred embodiment of the present invention, the content of hexafluoroisopropanol is 10-50 wt%, based on the total mass of the solvent.

[0082] According to another preferred embodiment of the present invention, the content of tetrafluoropropanol is 10-40 wt%, based on the total mass of the solvent.

[0083] According to the present invention, the weight-average molecular weight of the polyoxyethylene copolymer is 40,000-120,000 g / mol.

[0084] In this invention, when the above-mentioned polyoxyethylene copolymer with a weight-average molecular weight is used as a raw material, the polyoxyethylene copolymer is more soluble in C2-C5 fatty alcohol aqueous solutions and fluorinated alcohol compounds, and the film-forming liquid has good film-forming properties, so that the composite gas separation membrane obtained can maintain high gas permeability while also having good separation selectivity.

[0085] Furthermore, the weight-average molecular weight of the polyoxyethylene copolymer is 70,000-100,000 g / mol.

[0086] According to the present invention, the polyoxyethylene copolymer is at least one of polyoxyethylene-polyamide copolymer, polyoxyethylene-polyimide copolymer, and polyoxyethylene-polyurethane copolymer.

[0087] In this invention, there are no special requirements regarding the source of the polyoxyethylene copolymer; it can be prepared according to existing technology or obtained commercially. For example, the polyoxyethylene-polyamide (PEO-PA) copolymer can be purchased from Arkema's Pebax series elastomers, such as Pebax-1657, Pebax-1074, and Pebax-2533.

[0088] Furthermore, the polyoxyethylene copolymer is a polyoxyethylene-polyamide copolymer.

[0089] In this invention, when polyoxyethylene-polyamide copolymer is dissolved in the solvent of this invention, the hydrogen bonding between the PA segments of the polyoxyethylene-polyamide copolymer (PEO-PA) is weakened, the amorphous region is increased, and the obtained selective layer has appropriate crystallinity, which further improves the gas permeation flux of the composite gas separation membrane while maintaining high CO2 / N2 separation selectivity.

[0090] According to the present invention, the content of polyoxyethylene in the polyoxyethylene copolymer is 50-80 wt%.

[0091] Furthermore, the polyoxyethylene content in the polyoxyethylene copolymer is 60-80 wt%.

[0092] According to the present invention, the solid content of the coating liquid is 0.2wt%-3wt%.

[0093] Furthermore, the solid content of the coating liquid is 0.2wt%-2wt%.

[0094] According to the present invention, the mixture of polyoxyethylene copolymer and solvent is subjected to reflux condensation treatment, or the mixture is subjected to shaking treatment.

[0095] In this invention, reflux condensation or shaking treatment of the mixture of polyoxyethylene copolymer and solvent is beneficial to the dissolution of polyoxyethylene copolymer in C2-C5 fatty alcohol aqueous solution and fluorinated alcohol compounds.

[0096] According to the present invention, the temperature of the reflux condensation treatment is 60-120°C, and the time of the reflux condensation treatment is 120-200 min.

[0097] According to the present invention, the temperature of the vibration treatment is 30-50°C, and the vibration treatment time is 8-16 hours.

[0098] In this invention, when the conditions of reflux condensation treatment or vibration treatment meet the above range, it is beneficial for the polyoxyethylene copolymer to be fully dissolved in C2-C5 fatty alcohol aqueous solution and fluorinated alcohol compound to obtain a uniform and stable coating liquid. After coating, a smooth and flat composite gas separation membrane with good performance can be obtained.

[0099] Furthermore, the temperature of the reflux condensation treatment is 60-80℃, and the time of the reflux condensation treatment is 120-180 min.

[0100] Furthermore, the temperature of the oscillation treatment is 30-40℃, and the oscillation treatment time is 10-12h.

[0101] According to the present invention, the product after reflux condensation treatment or shaking treatment is allowed to stand.

[0102] In this invention, the settling temperature is 30-50℃, and the settling time is 10-16h.

[0103] According to the present invention, the coating is performed by dip coating.

[0104] According to the present invention, the dwell time of the dip coating is 10-90 s.

[0105] In this invention, when the residence time of the dip coating meets the above-mentioned range, a thinner and defect-free selective layer can be obtained, which further improves the CO2 / N2 separation selectivity while ensuring that the composite gas separation membrane has a good gas permeation flux.

[0106] Furthermore, the dwell time for the dip coating is 30-60 seconds.

[0107] According to the present invention, the drying temperature is 30-80°C and the drying time is 4-24 hours.

[0108] According to a preferred embodiment of the present invention, the drying conditions include: drying at 20-25°C for 25-35 minutes, followed by drying at 30-80°C for 4-24 hours.

[0109] According to the present invention, the gas source of the plasma is selected from at least one of argon, oxygen and carbon dioxide.

[0110] Furthermore, the gas source for the plasma is carbon dioxide.

[0111] According to the present invention, the plasma treatment time is 15-60s, the power is 25-125W, and the flow rate of the gas source is 100-700mL / min.

[0112] Furthermore, the plasma treatment time is 15-30s, the power is 25-110W, and the gas source flow rate is 200-500mL / min.

[0113] A third aspect of the present invention provides a composite gas separation membrane prepared by the above-described preparation method.

[0114] A fourth aspect of the present invention provides an application of the above-mentioned composite gas separation membrane in carbon capture.

[0115] In this invention, the composite gas separation membrane is used in the capture of carbon dioxide in flue gas.

[0116] The present invention will be described in detail below through embodiments.

[0117] Crystallinity of selective layer: The coating liquids in the examples and comparative examples were poured into polytetrafluoroethylene culture dishes in sequence, dried at room temperature for 0.5 h, and then dried at 60 °C for 4 h to form a dense film. The dense film was tested by XRD and the crystallinity was calculated by spectral analysis according to formula (1).

[0118]

[0119] Among them, X c and X a These represent the areas of the crystalline and amorphous regions in the XRD patterns obtained through curve fitting, respectively.

[0120] The intermolecular distance in the selective layer is calculated using the Bragg equation (nλ = 2d sinθ) (where n is a positive integer, λ is the wavelength, θ is the incident angle, and d is the molecular distance between polymer chains).

[0121] The thicknesses of the intermediate and selective layers of the composite gas separation membrane were measured using a scanning electron microscope.

[0122] The thickness of the composite gas separation membrane is the sum of the thicknesses of the substrate layer, the porous support layer, the intermediate layer, and the selective layer.

[0123] CO2 and N2 permeation rates of the composite gas separation membrane: CO2 and N2 pure gases were used as feed gases in sequence, and the flow rate of the gas on the permeation side was measured by a soap film flow meter. The permeation performance is shown in Table 1.

[0124] The ideal separation selectivity of CO2 / N2 for composite gas separation membranes is the ratio of the gas permeation rate of CO2 to that of N2.

[0125] Standard deviation of the contact angle between the composite gas separation membrane and water: Ten points were randomly selected on the composite gas separation membrane to test the water contact angle on the membrane surface, and the standard deviation was calculated according to formula (2).

[0126] Standard deviation

[0127] Where Xi is the water contact angle at the membrane surface (°), and μ is the average value of the water contact angle at the membrane surface (°).

[0128] Polyoxyethylene-polyamide (PEO-PA) copolymer (Pebax-1657): purchased from Arkema, with a weight-average molecular weight of 100,000 g / mol and a polyoxyethylene content of 60 wt%.

[0129] Semi-finished membrane: PDMS / PSF base film (polysulfone and polydimethylsiloxane coated on polyester nonwoven fabric) was purchased from Tianjin University of Technology; the thickness of the substrate layer is 96μm and the thickness of the porous support layer is 28μm.

[0130] Plasma cleaner: Brand: PVA TePla, Model: Plasma System ION40.

[0131] Preparation Example

[0132] The PDMS / PSF base film was subjected to surface plasma treatment. The purge gas was N2, the purge pressure was 0.5 MPa, the reaction gas was CO2, the inlet pressure was 0.1 MPa, the gas flow rate was 500 mL / min, the treatment time was 30 s, and the treatment power was 110 W, thus obtaining the plasma-treated PDMS / PSF base film.

[0133] Example 1

[0134] Polyoxyethylene-polyamide (PEO-PA) copolymer (Pebax-1657) was dissolved in a mixed solvent consisting of aqueous ethanol and hexafluoroisopropanol (the ethanol content in the aqueous ethanol solution was 70 wt%). Based on the total mass of the mixed solvent, the content of the fluorinated alcohol compound was 10 wt%. The mixture was refluxed and stirred at 80°C in an oil bath for 120 min, and then allowed to stand in an oven at 40°C for 12 h to prepare a coating solution of 0.4 wt% polyoxyethylene-polyamide (PEO-PA) copolymer (Pebax-1657). The coating solution was then dipped onto a plasma-treated PDMS / PSF base film to obtain a PEBAX1657 / PDMS / PSF film.

[0135] The dip-coating residence time is 60s, and the membrane is first dried at room temperature for 0.5h, and then dried at 60℃ for 4h to obtain the composite gas separation membrane.

[0136] The prepared composite gas separation membrane was characterized. A scanning electron microscopy (SEM) image of the composite gas separation membrane in Example 1 is shown below. Figure 1 As shown, Figure 1(a) shows the surface morphology of the membrane at 400 nm. It can be seen that the surface of the composite gas separation membrane is smooth and flat with no obvious defects. Figure 1 (b) shows the cross-sectional morphology of the membrane at 4 μm, revealing the different layers of the membrane, and no splitting was observed between the layers.

[0137] Other parameters of the composite gas separation membrane are shown in Table 1.

[0138] Example 2

[0139] Polyoxyethylene-polyamide (PEO-PA) copolymer (Pebax-1657) was dissolved in a mixed solvent consisting of aqueous ethanol and hexafluoroisopropanol (the ethanol content in the aqueous ethanol solution was 70 wt%). Based on the total mass of the solvent, the content of the fluorinated alcohol compound was 20 wt%. The mixture was refluxed and stirred at 80°C in an oil bath for 120 min, and then allowed to stand in an oven at 40°C for 12 h to prepare a coating solution of 0.4 wt% polyoxyethylene-polyamide (PEO-PA) copolymer (Pebax-1657). The coating solution was then dipped onto a plasma-treated PDMS / PSF base film to obtain a PEBAX1657 / PDMS / PSF film.

[0140] The dip-coating residence time is 60s, and the membrane is first dried at room temperature for 0.5h, and then dried at 60℃ for 4h to obtain the composite gas separation membrane.

[0141] Scanning electron microscopy (SEM) images of the composite gas separation membrane are shown below. Figure 2 As shown, Figure 2 (a) shows the surface morphology of the film at 400 nm. It can be seen that the film surface is smooth and flat with no obvious defects. Figure 2 (b) shows the cross-sectional morphology of the film at 4 μm, which shows a distinct layered structure and no splitting was observed between the layers.

[0142] The nano-infrared spectrum of the composite gas separation membrane in Example 2 is shown below. Figure 4 As shown, the composite gas separation membrane can be seen at 1732 cm⁻¹. -1 (OC = O stretching vibration), 1640cm -1 (NH-C=O stretching vibration) and 1014 cm -1 The presence of characteristic peaks at the (COC tensile vibration) location indicates that Pebax has been successfully present on the surface of the composite gas separation membrane.

[0143] Other parameters of the composite gas separation membrane are shown in Table 1.

[0144] Example 3

[0145] Polyoxyethylene-polyamide (PEO-PA) copolymer (Pebax-1657) was dissolved in a mixed solvent consisting of aqueous ethanol and hexafluoroisopropanol (the ethanol content in the aqueous ethanol solution was 70 wt%). Based on the total mass of the solvent, the content of the fluorinated alcohol compound was 30 wt%. The mixture was refluxed and stirred at 80°C in an oil bath for 120 min, and then allowed to stand in an oven at 40°C for 12 h to prepare a coating solution of 0.4 wt% polyoxyethylene-polyamide (PEO-PA) copolymer (Pebax-1657). The coating solution was then dipped onto a plasma-treated PDMS / PSF base film to obtain a PEBAX1657 / PDMS / PSF film.

[0146] The dip-coating residence time is 60s, and the membrane is first dried at room temperature for 0.5h, and then dried at 60℃ for 4h to obtain the composite gas separation membrane.

[0147] Other parameters of the composite gas separation membrane are shown in Table 1.

[0148] Example 4

[0149] Polyoxyethylene-polyamide (PEO-PA) copolymer (Pebax-1657) was dissolved in a mixed solvent consisting of aqueous ethanol and hexafluoroisopropanol (the ethanol content in the aqueous ethanol solution was 70 wt%). Based on the total mass of the solvent, the content of the fluorinated alcohol compound was 40 wt%. The mixture was refluxed and stirred at 80°C in an oil bath for 120 min, and then allowed to stand in an oven at 40°C for 12 h to prepare a coating solution with a mass fraction of 0.4 wt% of polyoxyethylene-polyamide (PEO-PA) copolymer (Pebax-1657). The coating solution was then dipped onto a plasma-treated PDMS / PSF base film to obtain a PEBAX1657 / PDMS / PSF film.

[0150] The dip-coating residence time is 60s, and the membrane is first dried at room temperature for 0.5h, and then dried at 60℃ for 4h to obtain the composite gas separation membrane.

[0151] Other parameters of the composite gas separation membrane are shown in Table 1.

[0152] Example 5

[0153] Polyoxyethylene-polyamide (PEO-PA) copolymer (Pebax-1657) was dissolved in a mixed solvent consisting of aqueous ethanol and hexafluoroisopropanol (the ethanol content in the aqueous ethanol solution was 70 wt%). Based on the total mass of the solvent, the content of the fluorinated alcohol compound was 50 wt%. The mixture was refluxed and stirred at 80°C in an oil bath for 120 min, and then allowed to stand in an oven at 40°C for 12 h to prepare a coating solution with a mass fraction of 0.4 wt% of polyoxyethylene-polyamide (PEO-PA) copolymer (Pebax-1657). The coating solution was then dipped onto a plasma-treated PDMS / PSF base film to obtain a PEBAX1657 / PDMS / PSF film.

[0154] The dip-coating residence time is 60s, and the membrane is first dried at room temperature for 0.5h, and then dried at 60℃ for 4h to obtain the composite gas separation membrane.

[0155] Other parameters of the composite gas separation membrane are shown in Table 1.

[0156] Example 6

[0157] Polyoxyethylene-polyamide (PEO-PA) copolymer (Pebax-1657) was dissolved in a mixed solvent consisting of aqueous ethanol and tetrafluoropropanol (the ethanol content in the aqueous ethanol solution was 70 wt%). Based on the total mass of the solvent, the content of the fluorinated alcohol compound was 10 wt%. The mixture was refluxed and stirred at 80°C in an oil bath for 120 min, and then allowed to stand in an oven at 40°C for 12 h to prepare a coating solution with a mass fraction of 0.4 wt% of polyoxyethylene-polyamide (PEO-PA) copolymer (Pebax-1657). The coating solution was then dipped onto a plasma-treated PDMS / PSF base film to obtain a PEBAX1657 / PDMS / PSF film.

[0158] The dip-coating residence time is 60s, and the membrane is first dried at room temperature for 0.5h, and then dried at 60℃ for 4h to obtain the composite gas separation membrane.

[0159] Other parameters of the composite gas separation membrane are shown in Table 1.

[0160] Example 7

[0161] Polyoxyethylene-polyamide (PEO-PA) copolymer (Pebax-1657) was dissolved in a mixed solvent consisting of aqueous ethanol and tetrafluoropropanol (the ethanol content in the aqueous ethanol solution was 70 wt%). Based on the total mass of the solvent, the content of the fluorinated alcohol compound was 20 wt%. The mixture was refluxed and stirred at 80°C in an oil bath for 120 min, and then allowed to stand in an oven at 40°C for 12 h to prepare a coating solution with a mass fraction of 0.4 wt% of polyoxyethylene-polyamide (PEO-PA) copolymer (Pebax-1657). The coating solution was then dipped onto a plasma-treated PDMS / PSF base film to obtain a PEBAX1657 / PDMS / PSF film.

[0162] The dip-coating residence time is 60s, and the membrane is first dried at room temperature for 0.5h, and then dried at 60℃ for 4h to obtain the composite gas separation membrane.

[0163] Other parameters of the composite gas separation membrane are shown in Table 1.

[0164] Example 8

[0165] Polyoxyethylene-polyamide (PEO-PA) copolymer (Pebax-1657) was dissolved in a mixed solvent consisting of aqueous ethanol, tetrafluoropropanol, and hexafluoroisopropanol (the ethanol content in the aqueous ethanol solution was 70 wt%). Based on the total mass of the solvent, the content of hexafluoroisopropanol was 10 wt% and the content of tetrafluoropropanol was 10 wt%. The mixture was refluxed and stirred at 80°C in an oil bath for 120 min, and then allowed to stand in an oven at 40°C for 12 h to prepare a coating solution with a mass fraction of 0.4 wt% of polyoxyethylene-polyamide (PEO-PA) copolymer (Pebax-1657). The coating solution was then dipped onto a plasma-treated PDMS / PSF base film to obtain a PEBAX1657 / PDMS / PSF film.

[0166] The dip-coating residence time is 60s, and the membrane is first dried at room temperature for 0.5h, and then dried at 60℃ for 4h to obtain the composite gas separation membrane.

[0167] Other parameters of the composite gas separation membrane are shown in Table 1.

[0168] Example 9

[0169] Polyoxyethylene-polyamide (PEO-PA) copolymer (Pebax-1657) was dissolved in a mixed solvent consisting of aqueous ethanol and hexafluoroisopropanol (the ethanol content in the aqueous ethanol solution was 70 wt%). Based on the total mass of the solvent, the content of the fluorinated alcohol compound was 20 wt%. The mixture was refluxed and stirred at 80°C in an oil bath for 120 min, and then allowed to stand in an oven at 40°C for 12 h to prepare a coating solution of 0.4 wt% polyoxyethylene-polyamide (PEO-PA) copolymer (Pebax-1657). The coating solution was then dipped onto a plasma-treated PDMS / PSF base film to obtain a PEBAX1657 / PDMS / PSF film.

[0170] The dip-coating residence time was 120s, and the membrane was first dried at room temperature for 0.5h, followed by drying at 60℃ for 4h to obtain the composite gas separation membrane.

[0171] Comparative Example 1

[0172] Polyoxyethylene-polyamide (PEO-PA) copolymer (Pebax-1657) was dissolved in an aqueous ethanol solution (ethanol content was 70 wt%), and stirred under reflux at 80 °C in an oil bath for 120 min. Then it was allowed to stand in an oven at 40 °C for 12 h to prepare a coating solution of 0.5 wt% polyoxyethylene-polyamide (PEO-PA) copolymer (Pebax-1657). The coating solution was then dipped onto a plasma-treated PDMS / PSF base film to obtain a PEBAX1657 / PDMS / PSF film.

[0173] The dip-coating residence time is 60s, and the membrane is first dried at room temperature for 0.5h, and then dried at 60℃ for 4h to obtain the composite gas separation membrane.

[0174] Other parameters of the composite gas separation membrane are shown in Table 1.

[0175] Comparative Example 2

[0176] Polyoxyethylene-polyamide (PEO-PA) copolymer (Pebax-1657) was dissolved in a mixed solvent consisting of aqueous ethanol and hexafluoroisopropanol (the ethanol content in the aqueous ethanol solution was 70 wt%). Based on the total mass of the solvent, the content of the fluorinated alcohol compound was 60 wt%. The mixture was refluxed and stirred at 80°C in an oil bath for 120 min, and then allowed to stand in an oven at 40°C for 12 h to prepare a coating solution of 0.4 wt% polyoxyethylene-polyamide (PEO-PA) copolymer (Pebax-1657). The coating solution was then dipped onto a plasma-treated PDMS / PSF base film to obtain a PEBAX1657 / PDMS / PSF film.

[0177] The dip-coating residence time is 60s, and the membrane is first dried at room temperature for 0.5h, and then dried at 60℃ for 4h to obtain the composite gas separation membrane.

[0178] Other parameters of the composite gas separation membrane are shown in Table 1.

[0179] Comparative Example 3

[0180] Polyoxyethylene-polyamide (PEO-PA) copolymer (Pebax-1657) was dissolved in hexafluoroisopropanol and refluxed and stirred in an oil bath at 80°C for 120 min. Then it was allowed to stand in an oven at 40°C for 12 h to prepare a coating solution of polyoxyethylene-polyamide (PEO-PA) copolymer (Pebax-1657) with a mass fraction of 0.4 wt%. The coating solution was then dipped onto a plasma-treated PDMS / PSF base film to obtain a PEBAX1657 / PDMS / PSF film.

[0181] The dip-coating residence time is 60s, and the membrane is first dried at room temperature for 0.5h, and then dried at 60℃ for 4h to obtain the composite gas separation membrane.

[0182] Scanning electron microscopy (SEM) image of the composite gas separation membrane in Comparative Example 3 is shown below. Figure 3 As shown, Figure 3 (a) shows the surface morphology of the film at 400 nm, which shows that condensation occurs on the film surface and the wrinkles are relatively large. Figure 3 (b) shows the cross-sectional morphology of the 4μm lower film. It can be seen that the thin intermediate layer on the support layer is no longer complete, and... Figure 1 , 2 The cross-sectional comparison shows that the interface of the intermediate layer in Comparative Example 3 is blurred, indicating that the intermediate layer material of the composite gas separation membrane is partially dissolved.

[0183] The nano-infrared spectrum of the composite gas separation membrane in Comparative Example 3 is shown below. Figure 4 As shown, 1260cm -1 (Si-CH3 stretching vibration) and 1152 cm⁻¹ -1 (Si-O-Si stretching vibration) is the infrared characteristic peak of polydimethylsiloxane. It can be seen that the composite gas separation membrane of Comparative Example 3 does not have obvious characteristic peaks at these two locations, indicating that the middle layer of the composite gas separation membrane has been partially dissolved, which is consistent with the SEM analysis.

[0184] Other parameters of the composite gas separation membrane are shown in Table 1.

[0185] Comparative Example 4

[0186] Polyoxyethylene-polyamide (PEO-PA) copolymer (Pebax-1657) was dissolved in a mixed solvent consisting of aqueous ethanol, tetrafluoropropanol, and hexafluoroisopropanol (the ethanol content in the aqueous ethanol solution was 70 wt%). Based on the total mass of the solvent, the content of hexafluoroisopropanol was 80 wt% and the content of tetrafluoropropanol was 10 wt%. The mixture was refluxed and stirred at 80°C in an oil bath for 120 min, and then allowed to stand in an oven at 40°C for 12 h to prepare a coating solution with a mass fraction of 0.4 wt% of polyoxyethylene-polyamide (PEO-PA) copolymer (Pebax-1657). The coating solution was then dipped onto a plasma-treated PDMS / PSF base film to obtain a PEBAX1657 / PDMS / PSF film.

[0187] The dip-coating residence time is 60s, and the membrane is first dried at room temperature for 0.5h, and then dried at 60℃ for 4h to obtain the composite gas separation membrane.

[0188] Other parameters of the composite gas separation membrane are shown in Table 1.

[0189] Comparative Example 5

[0190] Polyoxyethylene-polyamide (PEO-PA) copolymer (Pebax-1657) was dissolved in a mixed solvent consisting of aqueous ethanol and hexafluoroisopropanol (the ethanol content in the aqueous ethanol solution was 70 wt%). Based on the total mass of the solvent, the content of the fluorinated alcohol compound was 20 wt%. The mixture was refluxed and stirred at 80°C in an oil bath for 120 min, and then allowed to stand in an oven at 40°C for 12 h to prepare a coating solution with a mass fraction of 0.4 wt% of polyoxyethylene-polyamide (PEO-PA) copolymer (Pebax-1657). The difference was that the coating solution was directly dipped onto the PDMS / PSF base film without plasma treatment to obtain the PEBAX1657 / PDMS / PSF film.

[0191] The dip-coating residence time is 60s, and the membrane is first dried at room temperature for 0.5h, and then dried at 60℃ for 4h to obtain the composite gas separation membrane.

[0192] Other parameters of the composite gas separation membrane are shown in Table 1.

[0193] Table 1

[0194]

[0195]

[0196] Continued from Table 1

[0197]

[0198] Continued from Table 1

[0199]

[0200]

[0201] As can be seen from the results in Table 1, the composite gas separation membrane prepared by the present invention has a high CO2 permeation rate and high CO2 / N2 separation selectivity.

[0202] Figure 5 The XRD diffraction patterns of the composite gas separation membranes prepared in Examples 1, 2, 1, and 3 are shown. It can be seen that with the increase of fluorinated alcohol compounds, the peak position at 2θ = 24° shifts to a smaller angle, indicating an increase in the inter-chain distance of the polymer. This leads to a higher free volume fraction and more amorphous regions, resulting in appropriate crystallinity of the selective layer and thus increased gas permeability of the membrane. However, when the fluorinated alcohol compound continues to increase (as in Comparative Example 3), the peak position at 2θ = 24° shifts to the right, indicating that the intramolecular interactions of the polymer are enhanced, the polymer chains become more compact, and the gas permeability of the composite membrane decreases accordingly.

[0203] 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 composite gas separation membrane, characterized in that, The composite gas separation membrane comprises, in sequence, a substrate layer, a porous support layer, an intermediate layer, and a selective layer; The selective layer is a polyoxyethylene copolymer; The crystallinity of the selective layer is 30%-49%.

2. The composite gas separation membrane according to claim 1, wherein, The crystallinity of the selective layer is 33%-47%; Preferably, the intermolecular spacing in the selective layer is 3.6-3.77, more preferably 3.71-3.

77.

3. The composite gas separation membrane according to claim 1 or 2, wherein, The thickness of the composite gas separation membrane is 110-131 μm; Preferably, the thickness of the substrate layer is 90-100 μm; Preferably, the thickness of the porous support layer is 20-30 μm; Preferably, the thickness of the intermediate layer is 120-400 nm, and more preferably 150-300 nm; Preferably, the thickness of the selective layer is 60-200 nm, and more preferably 60-150 nm.

4. The composite gas separation membrane according to any one of claims 1-3, wherein, The intermediate layer is selected from at least one of polydimethylsiloxane, thermoplastic polyurethane, and polytrimethylsilylpropyne; Preferably, the polyoxyethylene copolymer is at least one selected from polyoxyethylene-polyamide copolymer, polyoxyethylene-polyimide copolymer, and polyoxyethylene-polyurethane copolymer; Preferably, the weight-average molecular weight of the polyoxyethylene copolymer is 40,000-120,000 g / mol, and more preferably 70,000-100,000 g / mol. Preferably, the polyoxyethylene content in the polyoxyethylene copolymer is 50-80 wt%, and more preferably 60-80 wt%.

5. The composite gas separation membrane according to any one of claims 1-4, wherein, The CO2 permeation rate of the composite gas separation membrane is greater than or equal to 1000 GPU, preferably greater than or equal to 2000 GPU. Preferably, the ideal separation selectivity of CO2 / N2 is greater than or equal to 20, and more preferably greater than or equal to 25; Preferably, the standard deviation of the contact angle between the composite gas separation membrane and water is less than or equal to 5.

6. A method for preparing a composite gas separation membrane, characterized in that, The preparation method includes: preparing a selective layer on a semi-finished membrane that sequentially comprises a substrate layer, a porous support layer and an intermediate layer; The method for preparing the selective layer includes: mixing a polyoxyethylene copolymer with a solvent to obtain a coating liquid, coating the coating liquid onto the side of the plasma-treated intermediate layer away from the porous support layer, and drying it to obtain a composite gas separation membrane. The solvent includes aqueous solutions of C2-C5 fatty alcohols and fluorinated alcohols; The content of the fluorinated alcohol compound is 5-50 wt%, based on the total mass of the solvent.

7. The preparation method according to claim 6, wherein, Based on the total mass of the solvent, the content of the fluorinated alcohol compound is 10-45 wt%. Preferably, in the C2-C5 fatty alcohol aqueous solution, the content of the fatty alcohol is 60-90 wt%, more preferably 70-90 wt%. Preferably, the fluoroalcohol compound is selected from at least one of hexafluoroisopropanol, tetrafluoropropanol, difluoroethanol, and perfluoroalkyl ethanol; more preferably, hexafluoroisopropanol and / or tetrafluoropropanol. Preferably, the polyoxyethylene copolymer is at least one selected from polyoxyethylene-polyamide copolymer, polyoxyethylene-polyimide copolymer, and polyoxyethylene-polyurethane copolymer; Preferably, the weight-average molecular weight of the polyoxyethylene copolymer is 40,000-120,000 g / mol, and more preferably 70,000-100,000 g / mol. Preferably, the polyoxyethylene content in the polyoxyethylene copolymer is 50-80 wt%, and more preferably 60-80 wt%. Preferably, the solid content of the coating liquid is 0.2wt%-3wt%, more preferably 0.2wt%-2wt%.

8. The preparation method according to claim 6 or 7, wherein, The mixture of polyoxyethylene copolymer and solvent is subjected to reflux condensation treatment, or the mixture of polyoxyethylene copolymer and solvent is subjected to shaking treatment. Preferably, the temperature of the reflux condensation treatment is 60-120℃, more preferably 60-80℃, and the time of the reflux condensation treatment is 120-200min, more preferably 120-180min; Preferably, the temperature of the vibration treatment is 30-50℃, more preferably 30-40℃, and the vibration treatment time is 8-16h, more preferably 10-12h; Preferably, the product after reflux condensation treatment or shaking treatment is allowed to stand; Preferably, the coating is applied by dip coating. Preferably, the dwell time for the dip coating is 10-90 seconds, more preferably 30-60 seconds; Preferably, the drying temperature is 30-80℃ and the drying time is 4-24h.

9. The method according to any one of claims 6-8, wherein, The gas source for the plasma is selected from at least one of argon, oxygen, and carbon dioxide; Preferably, the plasma treatment time is 15-60s, the power is 25-125W, and the gas source flow rate is 100-700ml / min.

10. A composite gas separation membrane prepared by any one of claims 6-9.

11. The application of the composite gas separation membrane according to any one of claims 1-5 and 10 in carbon capture.

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