A high-strength organic solvent-resistant nanofiber composite membrane and its preparation method

Abstract

The present invention discloses a high-strength organic solvent-resistant nanofiber composite membrane and a preparation method thereof. The preparation method comprises the following steps: 1) using a solvent-resistant gel membrane as a base membrane, and performing a polymerization reaction on the surface of the base membrane by an interfacial polymerization method to obtain a gel composite membrane; 2) the gel composite membrane obtained in step 1) is then dehydrated with a solvent, and dried to obtain a high-strength organic solvent-resistant nanofiber composite membrane. The present invention changes the traditional chemical cross-linking method, and uses a low-boiling point solvent to dehydrate and dry the gel composite membrane to remove the gel properties. The base membrane is transformed from a porous structure to a tightly arranged layer, solving the problems of poor solvent resistance and poor molecular retention performance of the gel composite membrane prepared by the prior art, and obtaining a nanofiber composite membrane that is resistant to high pressure, strong polar solvents, and has excellent molecular separation performance. The obtained composite membrane can be widely used in the recovery of organic solvents and the concentration and separation of small molecules in the chemical, pharmaceutical, food, petroleum and other industries.

Description

Technical Field

[0001] The present invention relates to the technical field of membrane preparation, and in particular to a high-strength organic solvent-resistant nanofiber composite membrane and a preparation method thereof. Background Art

[0002] Organic solvent-resistant nanofiltration membranes are pressure-driven membranes capable of separating molecules with a molecular weight range of 200 to 1000 Da from organic solvents. Due to the absence of phase transitions, low energy consumption, and simple operation, organic solvent-resistant nanofiltration offers significant economic and environmental benefits compared to traditional methods such as thermal distillation or fractionation. Organic solvent-resistant nanofiltration membranes can separate, purify, recover, and concentrate organic solvents, and are widely used in the chemical, pharmaceutical, and catalytic industries.

[0003] Currently, commercial organic solvent-resistant nanofiltration membranes are typically produced using a chemical crosslinking method. This involves dissolving a diamine or dihalogenated compound in an organic solvent (such as isopropyl alcohol), then immersing the polymer-based membrane prepared by a phase inversion method in the solvent. Chemical crosslinking imparts solvent resistance, and the separation membrane is then removed through multiple solvent replacements or heating to remove residual solvent and crosslinker. This process consumes large amounts of toxic reagents and replacement solvents, generating significant amounts of wastewater. Furthermore, the highly crosslinked, dense cortex results in very low solvent flux.

[0004] Para-aramid fiber (Kevlar) boasts numerous advantages, including high strength, high modulus, high chemical stability, and high heat resistance, making it an ideal material for preparing separation membranes. Existing technologies, such as patent CN110064312A, first strip Kevlar fibers into nanofibers, which are then used to form a gel membrane on a porous support material. A gel composite membrane is then prepared on the gel membrane through interfacial polymerization. The gel composite membrane is then impregnated with 5-40 wt% glycerol for 5-30 minutes and finally dried with hot air for 30 minutes to 6 hours. However, because glycerol has a boiling point of 290°C, the separation layer of the composite membrane can only withstand temperatures below 150°C. Soaking in glycerol followed by drying cannot completely remove the glycerol, and the base membrane of the composite membrane remains in a gel state. Patent CN110292867A, for example, uses an activating solvent, such as N-dimethylformamide, N,N-dimethylacetamide, or dimethyl sulfoxide, to post-activate the interfacially polymerized gel composite membrane. Although the solvent flux of the composite membrane was significantly improved, the composite membrane remained in a gel state. Para-aramid gel-based membranes have a loose, porous network structure that cannot withstand high pressure (30 bar) and is prone to structural collapse, resulting in reduced molecular retention. Furthermore, due to swelling, the gel membrane has poor tolerance to highly polar solvents, resulting in a high molecular weight cut-off. Summary of the Invention

[0005] In order to overcome the shortcomings of the existing technology, one of the purposes of the present invention is to provide a method for preparing a high-strength organic solvent-resistant nanofiber composite membrane, which uses a non-woven fabric or porous material as a support, and a certain thickness of para-aramid nanofiber casting liquid is coated thereon, and a gel-based membrane is obtained by phase inversion. The process is simple, easy to prepare, and has good industrial applicability; the second purpose of the present invention is to provide a high-strength organic solvent-resistant nanofiber composite membrane, which has significantly reduced swelling performance and significantly improved molecular separation performance, overcomes the current technical difficulties of nanofiltration membranes with poor resistance to strong polar solvents and poor small molecule separation performance, can withstand stronger organic solvents, and the nanofiltration separation performance is greatly improved.

[0006] One of the purposes of the present invention is achieved by the following technical solution:

[0007] A method for preparing a high-strength organic solvent-resistant nanofiber composite membrane comprises the following steps:

[0008] 1) Using a solvent-resistant gel film as a base film, polymerizing the base film surface by interfacial polymerization to obtain a gel composite film; wherein, on the surface of the base film, a separation layer is formed by interfacial polymerization between an aqueous solution and an oily solution, and the separation layer is deposited on the base film surface;

[0009] 2) The gel composite membrane obtained in step 1) is then dehydrated by a solvent and dried to obtain a high-strength organic solvent-resistant nanofiber composite membrane.

[0010] Furthermore, the solvent-resistant gel membrane is para-aramid nanofiber.

[0011] Furthermore, the preparation method of the solvent-resistant gel membrane is: coating a para-aramid nanofiber casting liquid with a concentration of 0.5 to 5 wt% on a non-woven fabric or other porous material support layer, and then immersing the support layer coated with the para-aramid nanofiber casting liquid in water to obtain a para-aramid nanofiber gel membrane.

[0012] Furthermore, the aqueous phase solution contains an aqueous phase monomer; the aqueous phase monomer is one or a combination of two or more of m-phenylenediamine, m-phenylenediamine, piperazine, polyethyleneimine, p-phenylenediamine, s-phenylenediamine, 4,4'-diaminodiphenylmethane, 1,4-diaminopiperazine, 4-aminomethylpiperidine, 5,10,15,20-tetrakis(4-aminophenyl)porphyrin, 2-methylpiperazine, 2,5-dimethylpiperazine, 2,5-diethylpiperazine, diaminotoluene, ethylenediamine, propylenediamine, xylylenediamine, 1,3-diaminocyclohexane, or 1,4-diaminocyclohexane; the aqueous phase monomer concentration in the aqueous phase solution is 0.01 to 5.0 wt %. Preferably, the aqueous phase monomer is m-phenylenediamine or piperazine.

[0013] Furthermore, the oil phase solution contains an oil phase monomer; the oil phase monomer is one or a combination of two or more of trimesoyl chloride, terephthaloyl chloride, isophthaloyl chloride, pyromellitoyl chloride, triptycene-1,3,6,8-tetraacetyl chloride, biphenyl dicarboxylic acid chloride, benzene trisulfonyl chloride, propanoyl chloride, succinoyl chloride, glutaryl chloride, glutaryl chloride, adipoyl chloride, maleic chloride, cyclopropanetrichloride, cyclobutanetrichloride, cyclobutanetetrachloride, cyclopentanedichloride, cyclopentanetrichloride, cyclopentanetetrachloride, cyclohexanedichloride, cyclohexanetrichloride or cyclohexanetetrachloride; the concentration of the oil phase monomer in the oil phase solution is 0.01 to 5.0 wt%.

[0014] Furthermore, the organic solvent used in the aqueous phase solution and the oil phase solution is one or a combination of two or more of n-hexane, cyclohexane, heptane, octane, toluene, naphtha, Isopar-G, Isopar-E, Isopar-L or mineral oil.

[0015] Furthermore, in step 1), the surface of the solvent-resistant gel membrane is immersed in an aqueous solution for 30 seconds to 10 minutes. After the water droplets on the surface are dried, it is immersed in an oil solution for 10 seconds to 10 minutes. The temperature of the oil solution is 20 to 100°C. After the reaction is completed, the membrane surface is rinsed with a pure solvent.

[0016] Furthermore, in step 2), the gel composite membrane obtained in step 1) is immersed in a dehydrating solvent for 1 to 30 minutes to displace the water in the gel, and then the membrane is dried for 1 minute to 10 hours to remove the gel properties. Finally, the membrane is immersed in a dehydrating solvent and then air-dried to obtain a high-strength organic solvent-resistant nanofiber composite membrane. Preferably, the dehydrating solvent is isopropyl alcohol and glycerol in a volume ratio of 7:3 to maintain pores.

[0017] Furthermore, the dehydration solvent used in the solvent dehydration step is one or a combination of two or more of acetone, methanol, ethanol, isopropanol, ethanol / n-hexane, and ethanol / toluene.

[0018] The second object of the present invention is achieved by adopting the following technical solution:

[0019] A high-strength organic solvent-resistant nanofiber composite membrane is prepared by the above-mentioned method for preparing the high-strength organic solvent-resistant nanofiber composite membrane.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) The present invention uses a solvent-resistant gel membrane as a base membrane, and obtains a gel composite membrane by polymerizing the base membrane surface through an interfacial polymerization method; the obtained gel composite membrane is then subjected to solvent dehydration and rapid drying to obtain a high-strength organic solvent-resistant nanofiber composite membrane. The present invention changes the traditional chemical cross-linking method and uses a low-boiling point solvent to dehydrate and dry the gel composite membrane to remove the gel properties. The base membrane is transformed from a porous structure to a tightly packed sheet, solving the problems of poor solvent resistance and poor molecular retention performance of the gel composite membrane prepared by the prior art, and obtains a nanofiber composite membrane that is resistant to high pressure and strong polar solvents and has excellent molecular separation performance. The obtained composite membrane can be widely used in the recovery of organic solvents and the concentration and separation of small molecules in the chemical, pharmaceutical, food, petroleum and other industries.

[0022] (2) The method for preparing a high-strength organic solvent-resistant nanofiber composite membrane of the present invention is to use a non-woven fabric or a porous material as a support, apply a certain thickness of para-aramid nanofiber casting liquid thereon, and obtain a gel-based membrane by phase inversion. Interfacial polymerization is carried out on the gel-based membrane to prepare an ultra-thin separation layer, and finally the composite membrane is degelated by solvent dehydration and rapid drying. The present invention changes the method of glycerol soaking followed by heat drying in the prior art, and directly uses a low-boiling point organic solvent to perform solvent replacement and rapid drying on the composite membrane to remove the gel properties of the composite membrane. Due to the regeneration of hydrogen bonds between nanofibers and the stacking effect of benzene rings, the base membrane structure is transformed from loose and porous to tightly arranged layers. The swelling properties of the resulting composite membrane are significantly reduced, and the molecular separation performance is significantly improved, overcoming the technical difficulties of the current nanofiltration membrane's poor resistance to strong polar solvents and poor small molecule separation performance. The method is simple in process, easy to prepare, and has good industrial applicability.

[0023] (2) The present application performs solvent replacement and rapid drying treatment on the gel composite membrane to remove the gel properties of the gel composite membrane, and finally treats the membrane with a pore preserving agent (isopropyl alcohol / glycerol). After the solvent replacement, the moisture between the nanofibers is removed, and the hydrogen bond interaction and benzene ring stacking effect between the para-aramid nanofibers during the rapid volatilization of the solvent cause the nanofibers to rearrange, and the base membrane structure of the composite membrane is transformed from a loose porous network structure to a densely arranged lamellar structure. The densely arranged lamellar structure can greatly increase the pressure resistance and solvent resistance of the base membrane, and improve the nanofiltration separation performance of the composite membrane. There is no need to use any chemical cross-linking agent to cross-link the base membrane, and the strong organic solvent resistance of the base membrane material is achieved through simple solvent treatment. The process is simple, easy to prepare, and the raw material price is low, which has good industrial applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is an electron microscope cross-sectional view of the porous network structure of the gel composite membrane of Example 1 after being dried with supercritical carbon dioxide;

[0025] Figure 2 This is an electron microscope cross-sectional morphology of the gel composite membrane in Example 1 after dehydration and drying with acetone. DETAILED DESCRIPTION

[0026] The present invention will be further described below in conjunction with the accompanying drawings and specific implementation methods. It should be noted that, under the premise of no conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0027] Example 1

[0028] A method for preparing a high-strength organic solvent-resistant nanofiber composite membrane comprises the following steps:

[0029] 1) Weighing 4 g of para-aramid fiber and dissolving it in a mixed solution of 6 g of potassium hydroxide and 200 ml of dimethyl sulfoxide, and stirring at room temperature to obtain an aramid nanofiber casting solution with a concentration of 2 w / v%;

[0030] 2) After the casting solution in step 1) is allowed to stand and degas, the casting solution is applied to a polypropylene non-woven fabric to a thickness of 250 μm by knife coating, and the fabric is immediately placed in water for phase inversion to obtain a gel-based membrane; the gel-based membrane is then transferred to pure water and soaked overnight;

[0031] 3) Soak the gel-based membrane in step 2) in an aqueous solution containing 2 wt% m-phenylenediamine for 5 minutes; discard the aqueous phase and dry for 3 minutes; then pour 25°C n-hexane containing 0.1 w / v% trimesoyl chloride onto the membrane surface and allow to react for 1 minute; discard the oil phase and immediately rinse the membrane surface with n-hexane; take a portion of the gel composite membrane and dry it with supercritical carbon dioxide. Figure 1 ;

[0032] 4) The obtained gel composite film was heat-treated at 90° C. for 5 minutes, then immersed in 40 wt % glycerol for 30 minutes, and finally dried with hot air;

[0033] 5) Soak the remaining gel composite membrane in acetone for 10 minutes, then place the membrane in air to dry for 5 minutes to remove the gel property, and obtain a nanofiber composite membrane. Finally, soak the membrane in a 7 / 3 (v / v) isopropanol / glycerol solution and dry it to obtain the following: Figure 2 The high-strength organic solvent-resistant nanofiber composite membrane shown.

[0034] Separation membrane performance test:

[0035] Solvent flux test of separation membrane. Solvent flux is the amount of solvent that passes through unit membrane area (A, m2) per unit time (t, h) under unit pressure (P, bar) under certain operating conditions. 2) of the solvent (V, L); place the separation membrane in a cross-flow device, operate it under a certain pressure, and record the flow rate of the solvent per unit time; finally, calculate the solvent flux according to the following formula:

[0036] F = V / (A·t·P).

[0037] The retention performance test of the separation membrane is that the retention rate is the ability of the membrane to prevent a component in the feed liquid from passing through or to retain a component in it. The retention rate test is obtained by measuring the solute concentration (C2) of the filtrate during the membrane filtration process and the solute concentration (C1) in the filtration liquid, and is calculated by the following formula:

[0038] R = (1-C2 / C1) × 100%;

[0039] The present invention tested the nanofiltration separation performance of the gel composite membrane and nanofiber composite membrane in this example. The feed solutions were N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), and N-methylpyrrolidone (NMP), respectively, containing 100 mg / L of the neutral small molecule Sudan Black B dye (molecular weight: 456.5 g / mol). The test was conducted in a cross-flow test apparatus at room temperature, a cross-flow rate of 60 L / h, and a pressure of 30 bar for 100 hours. The long-term flux and retention of the nanofiltration composite membrane of this example are shown in Table 1.

[0040] Table 1 Flux and Sudan Black B retention rate of the nanofiber composite membrane and gel composite membrane obtained in Example 1 in organic solvent test

[0041]

[0042] From the test results in Table 1, it can be found that under high pressure test conditions, the retention rate of the nanofiber composite membrane for small molecule Sudan Black B is significantly higher than the molecular retention performance of the gel composite membrane, which indicates that the nanofiber composite membrane has stronger pressure resistance and resistance to strong polar solvents.

[0043] pass Figure 1 and Figure 2 The cross-sectional structure of the gel membrane undergoes significant changes after dehydration and drying. After water removal, the porous network structure rearranges due to hydrogen bonding between the amide bonds in the para-aramid molecular chains and π-π conjugation between the benzene rings, forming a very dense lamellar structure. This gives the composite membrane higher compressive strength and resistance to highly polar solvents.

[0044] Comparative Example 1

[0045] A method for preparing an organic solvent-resistant nanofiltration membrane comprises the following steps:

[0046] 1) dissolving polyimide (P84) in a mixed solvent of 1,4-dioxane and DMF in a mass ratio of 1:4 to obtain a 24 wt % polymer solution, and allowing the solution to stand for 10 h to obtain a degassed polymer casting solution;

[0047] 2) After the casting solution from step 1) was allowed to stand for degassing, the casting solution was applied to a polypropylene non-woven fabric to a thickness of 250 μm by knife coating, and the fabric was immersed in water to obtain a polyimide base film. The base film was then transferred to pure water and immersed overnight, and then immersed in a 120 g / L hexamethylenediamine / isopropyl alcohol solvent for crosslinking for 16 hours. Finally, the crosslinked base film was rinsed with isopropyl alcohol for 3 hours to obtain an organic solvent-resistant base film.

[0048] 3) Interfacial polymerization was performed on a polyimide-based membrane by immersing it in an aqueous solution containing 3 wt% m-phenylenediamine for 5 minutes. The aqueous phase was discarded and dried for 3 minutes. A 25°C n-hexane solvent containing 0.15 w / v% trimesoyl chloride was then poured onto the membrane surface for 1 minute. After the oil phase was discarded, the membrane surface was immediately rinsed with n-hexane to obtain an organic solvent-resistant nanofiltration membrane.

[0049] The present invention tested the separation performance of the solvent-resistant nanofiltration composite membrane in this comparative example: the feed solutions were N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), and N-methylpyrrolidone (NMP), respectively, containing 100 mg / L of the neutral small molecule Sudan Black B dye (molecular weight: 456.5 g / mol). The test was conducted in a cross-flow test apparatus at room temperature, a cross-flow rate of 60 L / h, and a pressure of 30 bar for 100 hours. The long-term flux and retention of the nanofiltration composite membrane of this example are shown in Table 2.

[0050] Table 2 Flux and Sudan Black B retention rate of the organic solvent resistant nanofiltration membrane obtained in Comparative Example 1 in the organic solvent test

[0051]

[0052]

[0053] By comparing the test results in Table 1 and Table 2, it can be found that the Sudan Black B molecule rejection rate and solvent flux of the composite membrane prepared by chemical cross-linking of the polymer are much lower than those of the nanofiber composite membrane, indicating that the nanofiber composite membrane prepared by solvent dehydration and drying of the gel composite membrane has excellent solvent resistance and molecular separation performance.

[0054] Example 2

[0055] A method for preparing a high-strength organic solvent-resistant nanofiber composite membrane comprises the following steps:

[0056] 1) Weighing 6 g of para-aramid fiber and dissolving it in a mixed solution of 6 g of potassium hydroxide and 200 ml of dimethyl sulfoxide, and stirring at room temperature to obtain an aramid nanofiber casting solution with a concentration of 3 w / v%;

[0057] 2) After the casting solution in step 1) is allowed to stand and degas, the casting solution is applied to a polypropylene non-woven fabric to a thickness of 150 μm by knife coating, and the fabric is placed in water for phase inversion to obtain a gel-based membrane; the gel-based membrane is then transferred to pure water and soaked overnight;

[0058] 3) Soaking the gel-based membrane from step 2) in an aqueous solution containing 3 wt% m-phenylenediamine for 5 minutes; discarding the aqueous phase and drying for 3 minutes; then pouring a 100° C. Isopar solvent containing 0.15 w / v% trimesoyl chloride onto the membrane surface to react for 5 minutes; discarding the oil phase and rinsing the membrane surface with isopropyl alcohol to obtain a gel composite membrane;

[0059] 4) The obtained gel composite film was heat-treated at 25° C. for 10 min, then immersed in 40 wt % glycerol for 30 min, and finally dried with hot air.

[0060] 5) Soaking the gel composite membrane obtained in step 3) in methanol for 10 minutes, then placing the membrane in air and drying at room temperature for 30 minutes to remove the gel properties, and finally soaking the membrane in a 7 / 3 (v / v) isopropanol / glycerol solution and drying it to obtain a high-strength organic solvent-resistant nanofiber composite membrane.

[0061] The present invention tested the nanofiltration separation performance of the gel composite membrane and nanofiber composite membrane in this example. The feed solutions were N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), and N-methylpyrrolidone (NMP), respectively, containing 100 mg / L of the neutral small molecule Sudan Black B dye (molecular weight: 456.5 g / mol). The test was conducted in a cross-flow test apparatus at room temperature, a cross-flow rate of 60 L / h, and a pressure of 30 bar for 100 hours. The long-term flux and retention of the nanofiltration composite membrane of this example are shown in Table 3.

[0062] Table 3 Flux and Sudan Black B retention rate of the nanofiber composite membrane and gel composite membrane obtained in Example 2 in organic solvent test

[0063]

[0064] Example 3

[0065] A method for preparing a high-strength organic solvent-resistant nanofiber composite membrane comprises the following steps:

[0066] 1) Weighing 4 g of para-aramid fiber and dissolving it in a mixed solution of 6 g of potassium hydroxide and 200 ml of dimethyl sulfoxide, and stirring at room temperature to obtain an aramid nanofiber casting solution with a concentration of 2 w / v%;

[0067] 2) After the casting solution in step 1) is allowed to stand and degas, the casting solution is applied to a polypropylene non-woven fabric to a thickness of 250 μm by knife coating, and the fabric is immediately placed in water for phase inversion to obtain a gel-based membrane; the gel-based membrane is then transferred to pure water and soaked overnight;

[0068] 3) Soaking the gel-based membrane from step 2) in an aqueous solution containing 3 wt% m-phenylenediamine for 5 minutes; discarding the aqueous phase and drying for 3 minutes; then pouring a 25°C n-hexane solvent containing 0.15 w / v% trimesoyl chloride onto the membrane surface to react for 10 minutes; discarding the oil phase and immediately rinsing the membrane surface with n-hexane;

[0069] 4) The obtained gel composite film was heat-treated at 70° C. for 5 min, then immersed in 40 wt % glycerol for 30 min, and finally dried with hot air.

[0070] 5) Soaking the gel composite membrane obtained in step 3) in acetone for 2 minutes, then air-drying the membrane for 5 minutes to remove the gel properties, thereby obtaining a nanofiber composite membrane. Finally, soaking the membrane in a 7 / 3 (v / v) isopropyl alcohol / glycerol solution and air-drying the solution yields a high-strength, organic solvent-resistant nanofiber composite membrane.

[0071] Swelling performance test:

[0072] Swelling properties were tested gravimetrically. The composite membrane was cut into 4cm x 3cm pieces, vacuum-dried overnight at 60°C, and weighed to obtain a mass w1. The membrane pieces were then placed in 50ml of different organic solvents, allowed to stand for a week, and then removed. The solvent on the membrane surface was quickly wiped clean and the membrane was immediately weighed to obtain a mass w2. To prevent structural changes in the gel membrane, the gel composite membrane was placed in different organic solvents for a week, then removed and weighed to obtain a mass w2. The membrane was then vacuum-dried overnight at 60°C to obtain a mass w1. Finally, the degree of swelling was calculated using the following formula:

[0073] Swelling degree (gg -1 )=(w2-w1) / w1.

[0074] This Example 3 compares the swelling degrees of the gel composite membrane and the nanofiber composite membrane in methanol, ethanol, isopropanol, acetone, DMF, DMAc, NMP, and water. The swelling degree results are shown in Table 4.

[0075] Table 4 Swelling degree of gel composite membrane and nanofiber composite membrane in different solvents (unit: g -1 ).

[0076]

[0077]

[0078] By comparing Table 4, it is found that the gel composite membrane has significantly better anti-swelling performance after solvent dehydration and structural drying deformation, and the swelling degree in different solvents is much lower than that of the gel composite membrane, indicating that solvent dehydration and drying makes the base membrane structure of the composite membrane more compact and can tolerate stronger organic solvents.

[0079] Comparative Example 2

[0080] A method for preparing an organic solvent-resistant nanofiltration membrane comprises the following steps:

[0081] 1) dissolving polyimide (P84) in a mixed solvent of 1,4-dioxane and DMF in a mass ratio of 1:4 to obtain a 24 wt % polymer solution, and allowing the solution to stand for 10 h to obtain a degassed polymer casting solution;

[0082] 2) After the casting solution from step 1) was allowed to stand for degassing, the casting solution was applied to a polypropylene non-woven fabric to a thickness of 250 μm by knife coating, and the fabric was immersed in water to obtain a polyimide base film. The base film was then transferred to pure water and immersed overnight, and then immersed in a 120 g / L hexamethylenediamine / isopropyl alcohol solvent for crosslinking for 16 hours. Finally, the crosslinked base film was rinsed with isopropyl alcohol for 3 hours to obtain an organic solvent-resistant base film.

[0083] 3) Interfacial polymerization was performed on a polyimide-based membrane by immersing it in an aqueous solution containing 3 wt% m-phenylenediamine for 5 minutes. The aqueous phase was discarded and dried for 3 minutes. A 25°C n-hexane solvent containing 0.15 w / v% trimesoyl chloride was then poured onto the membrane surface and allowed to react for 10 minutes. After the oil phase was discarded, the membrane surface was immediately rinsed with n-hexane to obtain an organic solvent-resistant nanofiltration membrane.

[0084] Comparative Example 2 investigated the swelling of the polyimide composite membrane in methanol, ethanol, isopropanol, acetone, DMF, DMAc, NMP, and water. The swelling results are shown in Table 5.

[0085] Table 5 Swelling degree of gel composite membrane and nanofiber composite membrane in different solvents (unit: g -1 )

[0086]

[0087]

[0088] By comparing Example 3 and Comparative Example 2, it can be found that the nanofiber composite membrane has a lower swelling degree than the traditional polymer cross-linked polyimide composite membrane, indicating that a high-strength nanofiber base membrane can be obtained by the solvent dehydration and drying method, which is more resistant to strong polar solvents than the traditional polymer chain cross-linked base membrane.

[0089] Example 4

[0090] A method for preparing a high-strength organic solvent-resistant nanofiber composite membrane comprises the following steps:

[0091] 1) Weighing 4 g of para-aramid fiber and dissolving it in a mixed solution of 6 g of potassium hydroxide and 200 ml of dimethyl sulfoxide, and stirring at room temperature to obtain an aramid nanofiber casting solution with a concentration of 2 w / v%;

[0092] 2) After the casting solution in step 1) is allowed to stand and degas, the casting solution is applied to a polyester non-woven fabric with a thickness of 250 μm by knife coating, and the fabric is immediately placed in water for phase inversion to obtain a gel-based membrane; the gel-based membrane is then transferred to pure water and soaked overnight;

[0093] 3) Soaking the gel-based membrane from step 2) in an aqueous solution containing 3 wt% m-xylenediamine for 5 minutes; discarding the aqueous phase and drying for 1 minute; then pouring a 25°C n-hexane solvent containing 0.15 w / v% trimesoyl chloride onto the membrane surface to react for 5 minutes; discarding the oil phase and rinsing the membrane surface with n-hexane to obtain a gel composite membrane;

[0094] 4) Soaking the gel composite membrane obtained in step 3) in acetone for 5 minutes, then placing the membrane in air to dry at room temperature for 1 minute to obtain a nanofiber composite membrane, and finally soaking the membrane in a 7 / 3 (v / v) isopropanol / glycerol solution and drying it to obtain a high-strength organic solvent-resistant nanofiber composite membrane.

[0095] The present invention tested the nanofiltration separation performance of the gel composite membrane and nanofiber composite membrane of this example. The feed solutions were N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMAc), respectively, containing 100 mg / L of Sudan Black dye (molecular weight: 456.5 g / mol). The test was conducted in a cross-flow test apparatus at room temperature, a cross-flow rate of 60 L / h, and a pressure of 30 bar for 100 hours. The long-term flux and retention of the nanofiltration composite membrane of this example are shown in Table 6.

[0096] Table 6 Flux and Sudan Black B retention rate of the nanofiber composite membrane and gel composite membrane obtained in Example 4 in organic solvent test

[0097]

[0098] Example 5

[0099] A method for preparing a high-strength organic solvent-resistant nanofiber composite membrane comprises the following steps:

[0100] 1) Weighing 3 g of para-aramid fiber and dissolving it in a mixed solution of 6 g of potassium hydroxide and 200 ml of dimethyl sulfoxide, and stirring at room temperature to obtain an aramid nanofiber casting solution with a concentration of 1.5 w / v%;

[0101] 2) After the casting solution in step 1) is allowed to stand and degas, the casting solution is applied to a polypropylene non-woven fabric to a thickness of 200 μm by knife coating, and the fabric is immediately placed in water for phase inversion to obtain a gel-based membrane; the gel-based membrane is then transferred to pure water and soaked overnight;

[0102] 3) Soaking the gel-based membrane from step 2) in an aqueous solution containing 0.25 wt% piperazine for 5 minutes; discarding the aqueous phase and drying for 3 minutes; then pouring a 25°C n-hexane solvent containing 0.2 w / v% trimesoyl chloride onto the membrane surface and reacting for 5 minutes; discarding the oil phase and rinsing the membrane surface with n-hexane to obtain a gel composite membrane;

[0103] 4) Soaking the gel composite membrane obtained in step 3) in acetone for 5 minutes, then placing the membrane in air to dry at room temperature for 3 minutes, and finally soaking the membrane in a 7 / 3 (v / v) isopropanol / glycerol solution and drying it to obtain a high-strength organic solvent-resistant nanofiber composite membrane.

[0104] The present invention tested the nanofiltration separation performance of the gel composite membrane and nanofiber composite membrane of this example. The feed solutions were N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMAC), respectively, containing 100 mg / L of Sudan Black dye (molecular weight: 456.5 g / mol). The test was conducted in a cross-flow test apparatus at room temperature, a cross-flow rate of 60 L / h, and a pressure of 30 bar for 100 hours. The long-term flux and retention of the nanofiltration composite membrane of this example are shown in Table 7.

[0105] Table 7 Flux and Sudan Black B retention rate of the nanofiber composite membrane and gel composite membrane obtained in Example 5 in organic solvent test

[0106]

[0107] Example 6

[0108] A method for preparing a high-strength organic solvent-resistant nanofiber composite membrane comprises the following steps:

[0109] 1) Weighing 4 g of para-aramid fiber and dissolving it in a mixed solution of 6 g of potassium hydroxide and 200 ml of dimethyl sulfoxide, and stirring at room temperature to obtain an aramid nanofiber casting solution with a concentration of 2 w / v%;

[0110] 2) After the casting solution in step 1) is allowed to stand and degas, the casting solution is applied to a polypropylene non-woven fabric to a thickness of 250 μm by knife coating, and the fabric is immediately placed in water for phase inversion to obtain a gel-based membrane; the gel-based membrane is then transferred to pure water and soaked overnight;

[0111] 3) Soaking the gel-based membrane from step 2) in an aqueous solution containing 0.5 wt% polyethyleneimine for 10 minutes; discarding the aqueous phase and drying for 1 minute; then pouring n-hexane containing 0.1 w / v% trimesoyl chloride at 25° C. onto the membrane surface and reacting for 2 minutes; discarding the oil phase and rinsing the membrane surface with n-hexane;

[0112] 4) The gel composite membrane obtained in step 3) was soaked in ethanol for 5 minutes and then transferred to n-hexane solvent. The membrane was then placed in air to dry at room temperature for 10 minutes. Finally, the membrane was soaked in 7 / 3 (v / v) isopropanol / glycerol solution and dried.

[0113] The present invention tested the nanofiltration separation performance of the gel composite membrane and nanofiber composite membrane in this example. The feed solutions were N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMAc), respectively, containing 100 mg / L of Sudan Black dye (molecular weight 456.5 g / mol). The test was conducted in a cross-flow test apparatus at room temperature, a cross-flow rate of 60 L / h, and a pressure of 30 bar for 100 hours. The long-term flux and retention of the nanofiltration composite membranes of this example are shown in Table 8.

[0114] Table 8 Flux and Sudan Black B retention rate of the nanofiber composite membrane obtained in Example 6 in the organic solvent test.

[0115]

[0116] The above embodiments are only preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and replacements made by technicians in this field on the basis of the present invention fall within the scope of protection required by the present invention.

Claims

1. A method for preparing a high-strength organic solvent-resistant nanofiber composite membrane, characterized in that: The following steps are involved: 1) Using a solvent-resistant gel film as a base film, a gel composite film is obtained by polymerizing on the surface of the base film through interfacial polymerization; The specific steps are as follows: immersing the surface of the solvent-resistant gel membrane in an aqueous solution for 30s-10 min, drying the surface water droplets, and then immersing it in an oil solution for a reaction time of 10s-10min, the oil solution temperature is 20-100°C, and after the reaction is completed, rinsing the membrane surface with a pure solvent; wherein the solvent-resistant gel membrane is a para-aramid nanofiber membrane; the aqueous solution contains an aqueous monomer; the aqueous monomer is one of m-phenylenediamine, piperazine and polyethyleneimine; the preparation method of the solvent-resistant gel membrane is as follows: coating a para-aramid nanofiber casting solution with a concentration of 0.5-5 wt% on a non-woven fabric or other porous material support layer, and then immersing the support layer coated with the para-aramid nanofiber casting solution in water to obtain a para-aramid nanofiber gel membrane; 2) soaking the gel composite membrane obtained in step 1) in a dehydrating solvent for 1-30 minutes to displace water in the gel, then drying the membrane for 1 minute to 10 hours to remove the gel properties, and finally soaking the membrane in a dehydrating solvent of isopropanol and glycerol in a volume ratio of 7:3 and then drying it to obtain a high-strength organic solvent-resistant nanofiber composite membrane; the dehydrating solvent used to displace water in the gel is one or a combination of two or more of acetone, methanol, ethanol, isopropanol, ethanol / n-hexane, and ethanol / toluene.

2. The method for preparing a high-strength organic solvent-resistant nanofiber composite membrane according to claim 1, wherein: The concentration of the aqueous monomer in the aqueous solution is 0.01-5.0 wt %.

3. The method for preparing a high-strength organic solvent-resistant nanofiber composite membrane according to claim 1, wherein: The oil phase solution contains an oil phase monomer; the oil phase monomer is trimesoyl chloride, and the concentration of the oil phase monomer in the oil phase solution is 0.01-5.0 wt %.

4. The method for preparing a high-strength organic solvent-resistant nanofiber composite membrane according to claim 1, wherein: The organic solvent used in the oil phase solution is at least one of n-hexane, Isopar-G, Isopar-E, and Isopar-L.

5. A high-strength organic solvent-resistant nanofiber composite membrane, characterized in that: The composite membrane is prepared by the preparation method of the high-strength organic solvent-resistant nanofiber composite membrane according to any one of claims 1 to 4.

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