A covalent triazine-based composite film, and a preparation method and application thereof

Abstract

The application provides a covalent triazine-based composite membrane and a preparation method and application thereof. The covalent triazine-based composite membrane comprises a support layer and a separation layer. The material of the separation layer comprises a covalent triazine polymer. The thickness of the separation layer is 0.01-2 microns. The pore size of the separation layer is 0.4-3 nm. The preparation method of the covalent triazine-based composite membrane comprises the following steps: coating a precursor on the surface of a substrate, and reacting to obtain a separation layer; and laminating the separation layer with a support layer to obtain the covalent triazine-based composite membrane. The precursor comprises a combination of a nitrile monomer and a catalyst. The covalent triazine-based composite membrane can recognize and separate polar solvents through specific thickness and pore size, and has high separation efficiency, a simple separation method and easy control.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of membrane separation technology, and particularly relates to a covalent triazine-based composite membrane and a preparation method and application thereof. BACKGROUND

[0002] Since the late 1960s, membrane separation technology has been gradually applied in industrial production, and more traditional purification methods and separation processes (such as distillation, rectification, evaporation, adsorption, extraction, and chromatographic analysis) use membrane separation technology to achieve better results. At present, the separation method of mutually soluble organic solvents mainly adopts high-energy consumption separation methods such as extractive rectification and pervaporation.

[0003] For example, CN110105171A discloses a separation method for an organic solvent binary azeotrope containing methanol, which comprises repeatedly rectifying by using a rectification tower, then repeatedly purifying by using a pervaporation membrane, and finally performing secondary heating rectification by using a rectification tower. The method is used for separating azeotrope containing methanol. However, the separation method is complex and has high energy consumption.

[0004] CN110681266A discloses a method for separating small molecule solvents in an aprotic polar solvent. The method uses a pervaporation membrane separation device, the pervaporation membrane is a polyimide pervaporation membrane including a support layer and a separation layer, the separation layer is located on the support layer, and the separation layer is a multilayer polyimide membrane. The method can be used in industrial processes such as recovery and purification of aprotic polar organic solvents. However, the separation method needs to use a pervaporation membrane which is easily affected by gas-liquid equilibrium, and has high energy consumption.

[0005] CN113041861A discloses a composite membrane for separating polar solvents in water. The composite membrane uses a polyimide material as a porous support substrate, and a modified polyethylene membrane with similar polarity to the polar solvent is hot-pressed to obtain a modified polyethylene-polyimide composite membrane with a multiple network structure. The obtained modified polyethylene-polyimide composite membrane has high stability and can be used for separating polar solvents and water mixtures at any concentration. However, the composite membrane is not suitable for separating polar organic solvents such as alcohols and weakly polar organic solvents such as alkanes.

[0006] The common defects in the prior art are that the separation process using a pervaporation membrane is easily affected by gas-liquid equilibrium, and the separation method is complex, has high separation condition requirements, high energy consumption, and poor separation efficiency.

[0007] Therefore, it is an urgent problem in the field to develop a separation membrane with high separation efficiency, good stability, simple separation method, low energy consumption, and the ability to identify polar organic solvents. SUMMARY

[0008] In view of the deficiencies of the prior art, the present application aims to provide a covalent triazine-based composite membrane and a preparation method and application thereof. The covalent triazine-based composite membrane has a separation layer made of a triazine polymer, and the thickness and pore size of the separation layer are within a specific range, so that the composite membrane can separate polar organic solvents with high separation efficiency, good stability, long service life, and can separate polar organic solvents under normal temperature and low pressure operation conditions.

[0009] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0010] In a first aspect, the present application provides a covalent triazine-based composite membrane, which comprises a support layer and a separation layer; the material of the separation layer comprises a covalent triazine polymer; the thickness of the separation layer is 0.01-2 μm, and the pore size of the separation layer is 0.4-3 nm.

[0011] In the present application, the separation layer of the covalent triazine-based composite membrane is made of a covalent triazine polymer, and the thickness and pore size of the separation layer are controlled within a specific range, so that the composite membrane can separate mutually soluble organic solvents with high separation efficiency, and the membrane has good stability, long service life, and simple and easy-to-operate separation mode.

[0012] Preferably, the thickness of the separation layer is 0.01-2 μm, for example, it can be 0.05 μm, 0.1 μm, 0.2 μm, 0.4 μm, 0.6 μm, 0.8 μm, 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, etc.

[0013] In the present application, the thickness of the separation layer is less than 0.01 μm, and defects are easily formed during the synthesis of the film, thereby losing the separation effect; and greater than 2 μm, the thickness of the film is too large, and the filtration experiment cannot be carried out under low pressure operation conditions, which is not suitable for the separation of polar organic solvents driven by pressure.

[0014] Preferably, the pore size of the separation layer is 0.4-3 nm, for example, it can be 0.5 nm, 0.55 nm, 0.6 nm, 0.65 nm, 0.7 nm, 0.75 nm, 0.8 nm, 0.9 nm, 1 nm, 1.2 nm, 1.4 nm, 1.6 nm, 1.8 nm, 2 nm, 2.2 nm, 2.4 nm, 2.6 nm, 2.8 nm, etc.

[0015] In the present application, the pore size of the separation layer is less than 0.4 nm, and the organic solvent cannot penetrate under low pressure; and greater than 3 nm, the separation selectivity is poor.

[0016] As a preferred technical solution of the present application, the thickness of the separation layer is 0.3-1 μm.

[0017] Preferably, the pore size of the separation layer is 0.5-1 nm.

[0018] In the present application, the pore size is characterized by positron annihilation lifetime spectrometer.

[0019] Preferably, the monomer of the covalent triazine polymer comprises a nitrile group monomer.

[0020] Preferably, the nitrile group monomer comprises any one or a combination of at least two of terephthalonitrile, 4,4-biphenyldicarbonitrile, 4,4'-dicyanostilbene, 4,4'-dicyanophenylacetylene, 1,1':4',1''-terphenyl-4,4'-dicarbonitrile or 1,1':4',1'':4'',1'''-quaterphenyl-4,4''-dicarbonitrile.

[0021] Preferably, the support layer comprises any one of a polyacrylonitrile layer, a polyimide layer or a polyvinylidene fluoride layer.

[0022] In a second aspect, the present application provides a preparation method of the covalent triazine-based composite film according to the first aspect, the preparation method comprising the following steps:

[0023] coating a precursor on the surface of a substrate, reacting to obtain a separation layer; laminating the separation layer with a support layer to obtain the covalent triazine-based composite film; the precursor comprises a combination of a nitrile group monomer and a catalyst.

[0024] Preferably, the catalyst comprises trifluoromethanesulfonic acid.

[0025] Preferably, the concentration of the nitrile group monomer in the precursor is 40-400 mg / mL, for example, it can be 45 mg / mL, 50 mg / mL, 60 mg / mL, 65 mg / mL, 70 mg / mL, 80 mg / mL, 90 mg / mL, 100 mg / mL, 120 mg / mL, 140 mg / mL, 160 mg / mL, 180 mg / mL, 200 mg / mL, 220 mg / mL, 240 mg / mL, 280 mg / mL, 320 mg / mL, 360 mg / mL, 380 mg / mL, etc., and further preferably 80-200 mg / mL.

[0026] In the present application, the covalent triazine-based composite film is prepared by using the super strong acid trifluoromethanesulfonic acid as a catalyst, the preparation method is simple and easy to control, the selectivity of the composite film to polar solvents can be improved, and the thickness of the film can be controlled by adjusting the concentration of the nitrile group monomer.

[0027] Preferably, the method for obtaining the precursor comprises mixing the nitrile group monomer with the catalyst to obtain the precursor.

[0028] Preferably, the mixing is carried out in the presence of a protective atmosphere.

[0029] Preferably, the protective atmosphere comprises nitrogen and / or argon.

[0030] Preferably, the temperature of the mixing is -15 to 0℃, for example, it can be -14℃, -12℃, -10℃, -8℃, -6℃, -4℃, -2℃, etc.

[0031] Preferably, the time of the mixing is 1 to 2h, for example, it can be 1h, 1.5h, 2h, etc.

[0032] Preferably, the substrate comprises a glass substrate.

[0033] Preferably, the temperature of the reaction is 50 to 150℃, for example, it can be 60℃, 70℃, 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, etc.

[0034] Preferably, the time of the reaction is 15 to 30min, for example, it can be 16min, 18min, 20min, 22min, 24min, 26min, 28min, etc.

[0035] In the present application, since the catalyst is super strong acid trifluoromethanesulfonic acid, in order to avoid acid corrosion of the support layer, the precursor solution is coated on the surface of the glass substrate to form a film.

[0036] In the present application, the glass substrate comprises a beaker.

[0037] As a preferred technical solution of the present application, the preparation method comprises the following steps:

[0038] In the presence of a protective atmosphere, the nitrile monomer is mixed with the catalyst at -15 to 0℃ for 1 to 2h to obtain a precursor; the precursor is coated on a glass substrate and reacted at 50 to 150℃ for 15 to 30min to obtain a separation layer with a thickness of 0.01 to 2μm and a pore size of 0.4 to 3nm; the separation layer is combined with a support layer to obtain the covalent triazine-based composite film.

[0039] In a third aspect, the present application provides a covalent triazine-based composite film according to the first aspect for use in separating mixed solvents of different polarities.

[0040] In a fourth aspect, the present application provides a separation method for mixed solvents of different polarities, wherein the mixed solvents comprise solvent A and solvent B with different polarities, and the separation method uses the covalent triazine-based composite film according to the first aspect.

[0041] In the present application, the solvent A includes any one of methanol, ethanol, n-propanol, acetonitrile, acetone, chloroform, ethyl acetate or tetrahydrofuran; and the solvent B includes any one of n-heptane, n-hexane, n-octane, cyclohexane, toluene, benzene, methyl tert-butyl ether, ethyl tert-butyl ether, tetrahydrofuran, ethyl acetate, chloroform, acetone, acetonitrile or n-propanol.

[0042] Preferably, the separation method comprises: loading the covalent triazine-based composite membrane into a separation device, adding mixed solvents with different polarities on one side of the covalent triazine-based composite membrane, pressurizing for separation, and collecting the permeate; the separation temperature is room temperature; and the separation pressure is 1-12 bar.

[0043] In the present application, the room temperature refers to 20-30℃, for example, 22℃, 24℃, 25℃, 26℃, 27℃, 28℃, 29℃, etc.

[0044] Preferably, the separation pressure is 1-12 bar, for example, 2 bar, 4 bar, 6 bar, 8 bar, 10 bar, 12 bar, etc.

[0045] The numerical range in the present application not only includes the point values listed above, but also includes any point values between the above numerical ranges that are not listed, and the specific point values included in the range are not listed in the present application due to the limited space and for the purpose of simplicity.

[0046] Compared with the prior art, the present application has the following beneficial effects:

[0047] The covalent triazine-based composite membrane provided by the present application has high selectivity for polar solvents by selecting a separation layer with a specific thickness and pore size, can be used for separating mixed solvents with different polarities, has a separation coefficient greater than 50%, can be separated at room temperature, is easy to operate and control, and is pollution-free; and the membrane has good stability and long service life. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 The scanning electron microscope image of the covalent triazine-based composite membrane provided for Example 1 of the present application;

[0049] Figure 2 The cross-sectional morphology of the covalent triazine-based composite membrane provided for Example 1 of the present application;

[0050] Figure 3 The separation performance diagram of the covalent triazine-based composite membrane provided for Example 1 of the present application for separating different binary polar-weak polar mixed solutions;

[0051] Wherein, the numbers in the figure represent the mole percentage of the solvent in the collected permeate liquid in the ordinate column, and the five groups of mixed liquid combinations in the third column are methanol / methyl tert-butyl ether, ethanol / ethyl tert-butyl ether, acetone / methyl tert-butyl ether, ethyl acetate / methyl tert-butyl ether, and tetrahydrofuran / methyl tert-butyl ether.

[0052] Figure 4 Figure 1 is a stability test diagram of a covalent triazine-based composite membrane provided by the embodiment 1 of the present application for separating an ethanol / n-heptane mixed solution. DETAILED DESCRIPTION

[0053] The technical solutions of the present application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations of the present application.

[0054] The materials used in the examples and comparative examples of the present application are as follows:

[0055] Support layer: polypropylene porous support layer, manufacturer: Ande Membrane Separation Technology Engineering (Beijing) Co., Ltd., model: PAN400;

[0056] The pore size of the covalent triazine-based composite membrane provided by the examples and comparative examples of the present application is characterized by a positron annihilation lifetime spectrometer.

[0057] Example 1

[0058] The present embodiment provides a covalent triazine-based composite membrane, which comprises a polyacrylonitrile porous support layer and a covalent triazine polymer separation layer (thickness: 300 nm, pore size: 0.66 nm) arranged in sequence; the monomer of the covalent triazine polymer is 4,4'-diphenyl dicarbonitrile.

[0059] The present embodiment provides a preparation method of the covalent triazine-based composite membrane, and the specific steps include:

[0060] 120 mg of 4,4'-diphenyl dicarbonitrile powder is weighed, 1.5 mL of trifluoromethanesulfonic acid is added, nitrogen protection is carried out in a reaction tube, and stirring is carried out at-10℃ for 1.5 h. After standing, the separation layer is uniformly coated on the inner wall of a 500 ml beaker, sealed with tin foil paper, and placed upside down in a 100℃ oven. After 20 min, it is taken out to obtain the separation layer. After the trifluoromethanesulfonic acid volatilizes, the separation layer is transferred to the surface of distilled water and combined with the polyacrylonitrile porous support layer. After drying at room temperature, the covalent triazine-based composite membrane is obtained.

[0061] The morphology of the covalent triazine-based composite membrane is characterized by a scanning electron microscope (Hitachi SU8220), and the scanning electron microscope graph of the composite membrane is as shown in Figure 1 The cross-sectional morphology graph of the composite membrane is as shown in Figure 2as shown.

[0062] Embodiment 2

[0063] The embodiment provides a covalent triazine-based composite membrane, which comprises a polyacrylonitrile porous support layer and a covalent triazine polymer separation layer (700 nm in thickness and 0.66 nm in pore size) arranged in sequence; and a monomer of the covalent triazine polymer is 4,4'-diphenyl dicarbonitrile.

[0064] The embodiment provides a preparation method of the covalent triazine-based composite membrane, and specific steps comprise the following:

[0065] 200 mg of 4,4'-diphenyl dicarbonitrile powder is weighed, 1.5 mL of trifluoromethanesulfonic acid is added, nitrogen is introduced into a reaction tube for protection, and the mixture is fully stirred at-10 ℃ for 1.5 h; after standing, the mixture is uniformly coated on the inner wall of a 500-ml beaker, sealed with tin foil paper, and placed upside down in a 100-℃ oven; after 20 min, the separation layer is obtained; after the trifluoromethanesulfonic acid volatilizes, the separation layer is transferred to the surface of distilled water, combined with a polyacrylonitrile porous support layer, and dried at room temperature to obtain the covalent triazine-based composite membrane.

[0066] Embodiment 3

[0067] The embodiment provides a covalent triazine-based composite membrane, which comprises a polyacrylonitrile porous support layer and a covalent triazine polymer separation layer (300 nm in thickness and 0.57 nm in pore size) arranged in sequence; and a monomer of the covalent triazine polymer is terephthalonitrile.

[0068] The embodiment provides a preparation method of the covalent triazine-based composite membrane, and specific steps comprise the following:

[0069] 250 mg of terephthalonitrile powder is weighed, 1.5 mL of trifluoromethanesulfonic acid is added, nitrogen is introduced into a reaction tube for protection, and the mixture is fully stirred at-10 ℃ for 1.5 h; after standing, the mixture is uniformly coated on the inner wall of a 250-ml beaker, sealed with tin foil paper, and placed upside down in a 100-℃ oven; after 20 min, the separation layer is obtained; after the trifluoromethanesulfonic acid volatilizes, the separation layer is transferred to the surface of distilled water, combined with a polyacrylonitrile porous support layer, and dried at room temperature to obtain the covalent triazine-based composite membrane.

[0070] Embodiment 4

[0071] The embodiment provides a covalent triazine-based composite membrane, which comprises a polyacrylonitrile porous support layer and a covalent triazine polymer separation layer (300 nm in thickness and 0.77 nm in pore size) arranged in sequence; and a monomer of the covalent triazine polymer is [1,1':4',1''-terphenyl]-4,4'-dicarbonitrile.

[0072] The embodiment provides a preparation method of the covalent triazine-based composite film, and specific steps include the following:

[0073] 120 mg of [1,1':4',1''-triphenyl]-4,4'-dicarbonitrile powder is weighed, 1.5 mL of trifluoromethanesulfonic acid is added, nitrogen is introduced into a reaction tube for protection, and the mixture is fully stirred at-10 DEG C for 1.5 hours; after standing, the mixture is uniformly coated on the inner wall of a 500-milliliter beaker, the beaker is sealed with tin foil paper, and the beaker is placed upside down in an oven at 100 DEG C; after 20 minutes, the beaker is taken out, and a separation layer is obtained; after the trifluoromethanesulfonic acid volatilizes, the separation layer is transferred to the surface of distilled water, and is combined with a polyacrylonitrile porous support layer; and the combination is dried at room temperature, so that the covalent triazine-based composite film is obtained.

[0074] Embodiment 5

[0075] The embodiment provides a covalent triazine-based composite film, which is different from the covalent triazine-based composite film in Embodiment 1 only in that the thickness of the separation layer in the covalent triazine-based composite film is 2 micrometers.

[0076] The embodiment provides a preparation method of the covalent triazine-based composite film, and specific steps include the following:

[0077] 300 mg of 4,4'-diphenyl dicarbonitrile powder is weighed, 1.5 mL of trifluoromethanesulfonic acid is added, nitrogen is introduced into a reaction tube for protection, and the mixture is fully stirred at-10 DEG C for 1.5 hours; after standing, the mixture is uniformly coated on the inner wall of a 250-milliliter beaker, the beaker is sealed with tin foil paper, and the beaker is placed upside down in an oven at 100 DEG C; after 20 minutes, the beaker is taken out, and a separation layer is obtained; after the trifluoromethanesulfonic acid volatilizes, the separation layer is transferred to the surface of distilled water, and is combined with a polyacrylonitrile porous support layer; and the combination is dried at room temperature, so that the covalent triazine-based composite film is obtained.

[0078] Embodiment 6

[0079] The embodiment provides a covalent triazine-based composite film, which comprises a polyacrylonitrile porous support layer and a covalent triazine polymer separation layer (thickness: 300 nm, pore size: greater than 1 nm) arranged in sequence; and a monomer of the covalent triazine polymer is 1,1':4',1'':4'',1'''-tetraphenyl-4,4'''-dicarbonitrile.

[0080] 120 mg of 1':4',1 ":4 ",1 "-tetra-terpenyl-4,4 "-dicarbonitrile powder was weighed, 1.5 mL of trifluoromethanesulfonic acid was added, and nitrogen was introduced into the reaction tube for protection. After stirring at -10°C for 1.5 h, the mixture was left to stand, uniformly coated on the inner wall of a 500 mL beaker, sealed with tin foil paper, and placed upside down in a 100°C oven. After 20 min, the separation layer was obtained. After the trifluoromethanesulfonic acid evaporated, the separation layer was transferred to the surface of distilled water and combined with a polyacrylonitrile porous support layer. After drying at room temperature, the covalent triazine-based composite membrane was obtained.

[0081] Performance test

[0082] (1) Separation performance test: The covalent triazine-based composite membrane provided by Examples 1-6 was loaded into a separation device, 10 mL of mixed solvent with different polarity (molar ratio of mixed solvent stock solution was 1:1) was added upstream of the membrane, and the pressure was maintained at 4 bar. The downstream of the membrane was at atmospheric pressure, and the permeate was collected. The permeation flux and separation factor of the more polar solvent were calculated.

[0083]

[0084] Wherein, P represents the permeation flux, unit is kg / (m 2 ·h·bar), M represents the mass of the collected permeate organic solution, unit is kg, A represents the effective area of the membrane, unit is m 2 , t represents the time, unit is h, and ΔP represents the pressure, unit is bar.

[0085]

[0086] Wherein, α represents the separation factor, y PA represents the mole fraction of the polar component A in the permeate, y PB represents the mole fraction of the non-polar component B in the permeate, y FA represents the mole fraction of the polar component A in the stock solution, y FB represents the mole fraction of the non-polar component B in the stock solution.

[0087] (2) Stability test: The covalent triazine-based composite membrane provided by Examples 1-6 was loaded into a separation device, and an ethanol / n-heptane mixed solution (molar ratio of mixed solvent stock solution was 9:1) was added upstream of the membrane. The pressure was maintained at 4 bar, and the downstream of the membrane was at atmospheric pressure. The permeability and selectivity were tested continuously for 10 days, and the permeate was collected every 12 hours. The mole fraction of ethanol in the permeate was maintained at more than 99%, and the permeation flux remained basically unchanged.

[0088] The separation performance results of the covalent triazine-based composite membrane provided in Example 1 of the present application for other solvents with different polarities (molar ratio of 1:1) are shown in Table 1. Figure 3 In the table, the values are the molar percentages of the solvents in the collected permeate.

[0089] In the present application, the polarity difference between ethanol / n-heptane is the largest in the mixed solvents.

[0090] The stability test results of the covalent triazine-based composite membrane provided in Example 1 of the present application for ethanol / n-heptane mixed solution (molar ratio of the mixed solvent stock solution is 9:1) are shown in Table 2. Figure 4

[0091] As shown in Table 2, Figures 1-4 It can be seen that the covalent triazine-based composite membrane provided in the present application can separate polar organic solvents by selecting a triazine-based separation layer with a specific thickness and pore size, and has high separation efficiency, simple separation method, and good stability. The molar fraction of ethanol in the permeate can remain above 99% and the permeation flux remains basically unchanged after 10 days of testing.

[0092] The separation effect of the covalent triazine-based composite membrane provided in Example 1 of the present application for mixed solution is as follows: for ethanol / n-heptane (molar ratio 1:1) mixed solution, the permeation flux is 0.05 kg / (m 2 ·h·bar), and the separation factor is 999; for ethanol / toluene (molar ratio 1:1) mixed solution, the permeation flux is 0.07 kg / (m 2 ·h·bar), and the separation factor is 70.4; for ethanol / ethyl tert-butyl ether (molar ratio 1:1) mixed solution, the permeation flux is 0.08 kg / (m 2 ·h·bar), and the separation factor is 57.8.

[0093] The separation effect of the covalent triazine-based composite membrane provided in Example 2 of the present application for mixed solution is as follows: for ethanol / n-heptane (molar ratio 1:1) mixed solution, the permeation flux is 0.02 kg / (m 2 ·h·bar), and the separation factor is 999.

[0094] The separation effect of the covalent triazine-based composite membrane provided in Example 3 of the present application for mixed solution is as follows: for ethanol / ethyl tert-butyl ether (molar ratio 1:1) mixed solution, the permeation flux is 0.04 kg / (m 2 ·h·bar), and the separation factor is 70.4.

[0095] ​The covalent triazine-based composite membrane provided in Example 4 of the present application has the following separation effect for a mixed solution: for an ethanol / n-heptane (molar ratio 1:1) mixed solution, the permeation flux is 0.35 kg / (m 2 ·h·bar), and the separation factor is 65.7.

[0096] The covalent triazine-based composite membrane provided in Example 5 of the present application has a thickness greater than 1 μm, and in the pressure range, the solvent cannot permeate.

[0097] The covalent triazine-based composite membrane provided in Example 6 of the present application has a pore size greater than 1 nm, and for mutually soluble organic mixed solvents with a polarity difference, almost no separation effect is obtained.

[0098] From the comparison of the separation effect of ethanol / n-heptane in Example 1 and Example 2, it can be seen that when the thickness of the separation layer in the covalent triazine-based composite membrane is increased, the permeability of the solvent is reduced.

[0099] From the comparison of ethanol / ethyl tert-butyl ether in Example 1 and Example 3, it can be seen that when the pore size of the separation layer in the covalent triazine-based composite membrane is reduced, the solvent selectivity is increased, but the flux is reduced. However, when the pore size is too small, less than 0.4 nm (less than the kinetic diameter of the solvent molecules used), the solution cannot permeate through the pores.

[0100] From the comparison of ethanol / n-heptane in Example 1 and Example 4, it can be seen that when the pore size of the separation layer in the covalent triazine-based composite membrane is increased, the solvent permeability is increased, but the selectivity is reduced.

[0101] From Example 5, it can be seen that when the thickness of the separation layer is too large, the solution cannot permeate through the membrane at low pressure.

[0102] From Example 6, it can be seen that when the pore size of the separation layer is too large, the separation selectivity will be lost.

[0103] In summary, the covalent triazine-based composite membrane provided in the present application has high selectivity for polar solvents and high separation efficiency by controlling the thickness and pore size of the separation layer. The separation process is not affected by gas-liquid equilibrium and does not have a phase change. Compared with traditional distillation and extraction, the energy consumption of pervaporation is greatly reduced. In addition, the composite membrane can realize the separation of organic solvents at room temperature by pressure driving, which is simple to operate, reduces costs, and has a simple preparation method without pollution.

[0104] The applicant declares that the above description is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto. It should be understood by those skilled in the art that any changes or replacements within the technical scope disclosed in the present application can be easily thought of by those skilled in the art, and all fall within the protection scope and disclosure scope of the present application.

Claims

1. A method for separating mixed organic solvents of different polarity, characterized by, The mixed organic solvent is solvent A and solvent B with different polarities, the temperature of the separation method is room temperature; the room temperature is 20-30℃; the pressure of the separation method is 4-12 bar; The solvent A is any one of methanol, ethanol, n-propanol, acetonitrile, acetone, chloroform, ethyl acetate or tetrahydrofuran; The solvent B is any one of n-heptane, n-hexane, n-octane, cyclohexane, toluene, benzene, methyl tert-butyl ether, ethyl tert-butyl ether, tetrahydrofuran, ethyl acetate, chloroform, acetone, acetonitrile or n-propanol; The separation method uses a covalent triazine-based composite membrane; The covalent triazine-based composite membrane comprises a support layer and a separation layer; The thickness of the separation layer is 0.3-1 μm; The pore size of the separation layer is 0.5-1 nm; The material of the separation layer comprises a covalent triazine polymer; The monomer of the covalent triazine polymer comprises a nitrile group monomer; The nitrile group monomer comprises any one or a combination of at least two of terephthalonitrile, 4,4'-diphenyl dicarbonitrile, 4,4'-dicyano-stilbene, 4,4'-dicyano-diphenyl acetylene or 1,1':4',1''-terphenyl-4,4''-dicarbonitrile; The preparation method of the covalent triazine-based composite membrane comprises the following steps: coating a precursor on the surface of a substrate, reacting to obtain a separation layer; laminating the separation layer with a support layer to obtain the covalent triazine-based composite membrane; the precursor comprises a combination of a nitrile group monomer and a catalyst.

2. The separation method of claim 1, wherein, The support layer comprises any one of a polyacrylonitrile layer, a polyimide layer or a polyvinylidene fluoride layer.

3. The separation method of claim 1, wherein, The catalyst comprises trifluoromethanesulfonic acid.

4. The separation method of claim 1, wherein, The concentration of the nitrile group monomer in the precursor is 80-200 mg / mL.

5. The separation method of claim 1, wherein, The method for obtaining the precursor comprises: mixing the nitrile group monomer with the catalyst to obtain the precursor.

6. The separation method of claim 5, wherein, The mixing is carried out in the presence of a protective atmosphere.

7. The separation method of claim 5, wherein, The temperature of the mixing is -15-0℃.

8. The separation method of claim 5, wherein, The mixing time is 1-2 h.

9. The separation method of claim 1, wherein, The substrate comprises a glass substrate.

10. The separation method of claim 1, wherein, The temperature of the reaction is 50-150℃.

11. The separation method of claim 1, wherein, The reaction time is 15-30 min.

12. The separation method of claim 1, wherein, The preparation method comprises the following steps: mixing the nitrile group monomer with the catalyst in the presence of a protective atmosphere at -15-0℃ for 1-2 h to obtain a precursor; coating the precursor on a glass substrate and reacting at 50-150℃ for 15-30 min to obtain a separation layer with a thickness of 0.3-1 μm and a pore size of 0.5-1 nm; laminating the separation layer with a support layer to obtain the covalent triazine-based composite membrane.

13. The separation method of claim 1, wherein, The separation method comprises: loading the covalent triazine-based composite membrane into a separation device, adding mixed organic solvents with different polarities to one side of the covalent triazine-based composite membrane, pressurizing for separation, and collecting the permeate.

14. Use of a covalent triazine-based composite membrane in the separation method according to claim 1 in the separation of mixed organic solvents with different polarities at room temperature.

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