Composite separation membrane as well as preparation method and application thereof

Abstract

The invention relates to the field of organic solvent-resistant nanofiltration membrane separation, and discloses a composite separation membrane as well as a preparation method and application thereof. The composite separation membrane comprises a supporting layer and a coating layer coated on the surface of the supporting layer, wherein the coating layer is obtained by coating the surface of the supporting layer with a membrane casting solution and then performing post-treatment; the membrane casting solution contains rubber latex, a water-soluble high-molecular polymer, nano white carbon black and deionized water. According to the composite separation membrane, the problem of organic solvent pollution in the traditional membrane preparation process can be reduced, the composite separation membrane has relatively good stability in an organic solvent, and the membrane with relatively high permeation flux and retention rate can be prepared.

Description

Technical Field

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

[0002] OSN membrane (organic solvent resistant nanofiltration membrane) initially used cellulose acetate membrane to separate liquid hydrocarbon mixtures. Due to the low level of membrane material development and low demand for OSN membranes at that time, it did not attract people's interest until the last two decades.

[0003] The core of OSN technology is the OSN membrane, which must not only have high permeability and high rejection rate, but also chemical stability. In recent years, scientists have conducted a lot of membrane research in the field of OSN membranes, making outstanding contributions to the development of OSN membranes.

[0004] The research of Andrew G. Livingston's group at Imperial College London and Tai-Shung Chung's group at the National University of Singapore has always been at the forefront of scientific research and industry. Since 2008, they have continuously reported innovative OSN membranes and preparation methods. The membrane materials include polyimide, polyaniline, polyetheretherketone, polybenzimidazole, polydimethylsiloxane, etc.

[0005] Researchers in related fields around the world have conducted research on organic solvent-resistant nanofiltration membranes.

[0006] CN110526337 B discloses a method for preparing an oil-water separation membrane, which uses a solution gel method to construct a SiO2 microsphere structure on a cotton fabric to obtain a cotton fabric loaded with silica microspheres. Thiophene is converted into polythiophene by a solid-phase coupling method and coated on the surface of the cotton fabric loaded with silica microspheres to obtain an oil-water separation membrane.

[0007] In the existing technology, the preparation process of OSN membranes mostly involves dissolving the membrane material in a polar organic solvent to form a casting solution. This preparation method is very unfriendly to the environment, the volatilized organic solvent is also very harmful to the researchers' health, and the preparation process is complicated.

[0008] There are also methods using interfacial polymerization, which takes a long time to produce membranes and also uses organic solvents for the organic phase. CN1640534A uses concentrated emulsion polymerization to produce a preferential dealcoholization membrane, which avoids the use of large amounts of organic solvents. However, membranes produced with high-concentration emulsions are often thicker, significantly limiting permeation flux.

[0009] Most of the organic solvent-resistant membrane materials reported so far are plastic or fiber-based. Rubber materials are rarely reported, with only cross-linked polydimethylsiloxane (silicone rubber) being the only one. This is due to the high viscosity of rubber, making it difficult to coat into a thin film. Furthermore, rubber has poor resistance to organic solvents and tends to dissolve in them. These two factors limit the potential of rubber as an OSN membrane material.

[0010] Currently reported polar or hydrophilic organic solvent membranes mainly adopt the method of introducing polar groups by grafting modification on the membrane surface. CN103861466A discloses a method for preparing a hydrophilic separation membrane, in which hydrophilic substances are introduced into the separation layer of the membrane by chemical reaction on the membrane surface.

[0011] Therefore, it is of great significance to research and develop an organic solvent-resistant composite membrane and a green and environmentally friendly preparation method. Summary of the Invention

[0012] The purpose of the present invention is to overcome the defects of the prior art in that the preparation process of organic solvent-resistant nanofiltration membranes is complicated and the use of organic solvents in the preparation process causes environmental pollution, and to provide a composite separation membrane and its preparation method and application. The composite separation membrane can reduce the organic solvent pollution problem in the traditional membrane making process, and the composite separation membrane has good stability in organic solvents, and can prepare membranes with high permeation flux and retention rate.

[0013] In order to achieve the above-mentioned object, the first aspect of the present invention provides a composite separation membrane, wherein the composite separation membrane comprises a support layer and a coating layer coated on the surface of the support layer, wherein the coating layer is obtained by coating a casting liquid on the surface of the support layer and then post-processing;

[0014] The casting solution contains rubber latex, water-soluble high molecular polymer, nano-white carbon black and deionized water.

[0015] A second aspect of the present invention provides a method for preparing the aforementioned composite separation membrane, wherein the preparation method comprises:

[0016] (1) grinding nano-silica and mixing it with deionized water to obtain a mixture of nano-silica and deionized water;

[0017] (2) mixing the mixture and the water-soluble high molecular polymer for a second time and then subjecting the mixture to a first ultrasonic treatment to prepare a mixed solution;

[0018] (3) performing a third mixing of the mixed solution and rubber latex to obtain a mixed solution; and diluting the mixed solution with deionized water to obtain a casting solution;

[0019] (4) The casting solution is coated on the surface of the support layer and subjected to post-processing to obtain a composite separation membrane.

[0020] The third aspect of the present invention provides an application of the aforementioned composite separation membrane in removing impurities from a weakly polar organic solvent.

[0021] Through the above technical solution, the technical solution of the present invention has the following beneficial effects:

[0022] (1) No organic solvent is used in the preparation process of the composite separation membrane of the present invention, thereby avoiding the harm to human health and environmental pollution caused by the use of organic solvents;

[0023] (2) During the preparation of the composite separation membrane of the present invention, no additional cross-linking of the membrane material is required, making the membrane preparation process simpler; it is a green, environmentally friendly and simple membrane preparation method;

[0024] (3) The composite separation membrane prepared by the present invention has good stability in organic solvents. DETAILED DESCRIPTION

[0025] The endpoints of the ranges and any values ​​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 endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0026] As mentioned above, the first aspect of the present invention provides a composite separation membrane, wherein the composite separation membrane comprises a support layer and a coating layer coated on the surface of the support layer, wherein the coating layer is obtained by coating a casting liquid on the surface of the support layer and then post-processing;

[0027] The casting solution contains rubber latex, water-soluble high molecular polymer, nano-white carbon black and deionized water.

[0028] The inventors of the present invention have discovered through research that the present invention uses highly cross-linked rubber latex as the membrane material, which, on the one hand, can overcome the problem of high viscosity of rubber solution making it difficult to apply the film, and on the other hand, the rubber is highly cross-linked and can remain stable in organic solvents; in addition, the present invention uses rubber material to prepare OSN membranes, which greatly reduces the cost of membrane production.

[0029] Furthermore, the inventors of the present invention used a nano-doping method to introduce polar nano-silica into the coating layer (functional layer) of the membrane. Since nano-silica and the membrane material have a strong interaction, a membrane with high permeation flux and retention rate and good solvent resistance can be prepared.

[0030] In the present invention, it should be noted that “dry rubber” and “dry rubber” refer to the remaining rubber after water and a part of the emulsifier are removed from the rubber latex composed of rubber, water and an emulsifier.

[0031] According to the present invention, preferably, the casting solution consists of rubber latex, water-soluble high molecular polymer, nano-silica and deionized water.

[0032] According to the present invention, in the casting solution, the weight ratio of the nano-silica to the dry rubber in the rubber latex is (1-100):100, preferably (3-50):100, and more preferably (5-10):100.

[0033] According to the present invention, in the casting solution, the weight ratio of the water-soluble high molecular weight polymer to the dry rubber in the rubber latex is (0.01-2):100, preferably (0.2-1):100, and more preferably (0.3-0.8):100. In the present invention, selecting the weight ratio within the above range allows the water-soluble polymer to stabilize and uniformly disperse the latex particles while preventing the adhesion between the rubber and the support film from being affected by excessively high concentrations.

[0034] According to the present invention, in the process of preparing polar organic solvent-resistant nanofiltration membrane, the main material used is emulsified rubber material, preferably, the rubber latex is styrene-butadiene latex and / or acrylonitrile-butadiene latex; in the present invention, the rubber latex material used has a high degree of crosslinking, and the level of crosslinking is characterized by the gel content of the dry rubber after latex coagulation in a polar organic solvent (such as tetrahydrofuran). Preferably, the gel content in the rubber latex is 50-99%, preferably 70-95%, and more preferably 80-90%. In the present invention, a rubber with a high gel content (crosslinking degree) is selected. On the one hand, the rubber is not 100% crosslinked, has a certain flexibility, can maintain the mobility of the rubber molecular chain, and is beneficial to the flux of the membrane. On the other hand, such a high degree of crosslinking can ensure that the membrane material can tolerate common mild organic solvents.

[0035] In addition, it should be noted that in the present invention, the gel content test is to test the gel content of the dried membrane material in tetrahydrofuran.

[0036] According to the present invention, the particle size of the rubber in the rubber latex is 10-1000nm, preferably 50-200nm, preferably 80-120nm, and most preferably 90-115nm. In the present invention, the selection of the particle size of the rubber latex takes into account the pore size of the supporting layer ultrafiltration membrane, ensuring that the latex particles are not too small to prevent the rubber particles from entering the ultrafiltration layer pores during the coating process, blocking the channels and reducing the flux of the membrane. On the other hand, it is considered that too large a particle size will make it difficult to control the membrane thickness, resulting in poor membrane surface uniformity.

[0037] According to the present invention, the mass concentration of rubber in the rubber latex is 10-80%, preferably 20-60%, and more preferably 30-50%. In the present invention, the rubber in the rubber latex satisfies the above mass concentration, and such rubber latex has good stability and reduces the demulsification ratio during the process of blending with the water-soluble polymer solution.

[0038] According to the present invention, deionized water needs to be added to adjust the concentration of dry rubber in the mixture. The mass concentration of dry rubber in the casting solution is 0.1-10%, preferably 0.3-5%, and more preferably 0.5-1%. The mass concentration of dry rubber is controlled because a thinner functional layer is obtained at the thickness of the scraper, which not only improves the adhesion between the functional layer and the support layer, but also improves the membrane flux.

[0039] According to the present invention, during the preparation of the casting solution, the selected nano-silica particle size is 5-100 nm, preferably 10-50 nm, and most preferably 15-30 nm.

[0040] According to the present invention, the mass ratio of the nano-silica to the dry rubber in the rubber latex is (1-100):100, preferably (3-50):100, and more preferably (5-10):100.

[0041] According to the present invention, a water-soluble polymer is added before mixing the highly cross-linked rubber latex and nano-silica to improve their mechanical stability. The water-soluble polymer is any water-soluble polymer. In the present invention, preferably, the water-soluble polymer is selected from one or more of sodium carboxymethyl cellulose, sodium polyacrylate, sodium alginate, sodium polymethacrylate, and sodium polyphosphate.

[0042] According to the present invention, the support layer is an ultrafiltration support layer, and the ultrafiltration support membrane is any polymer or polymer-modified membrane with suitable pore size and resistance to organic solvents. In the present invention, preferably, the support layer is selected from one or more of polyacrylonitrile, polyetherimide and polyimide ultrafiltration membranes.

[0043] According to the present invention, the average pore size of the support layer is 5-50 nm, preferably 10-40 nm, and more preferably 15-25 nm. This pore size can prevent latex particles from entering the pores and clogging the channels during the membrane preparation process.

[0044] According to the present invention, the thickness of the support layer membrane is 1-500 μm, preferably 10-200 μm, more preferably 50-150 μm. The support layer of this thickness can provide the membrane with a suitable flux.

[0045] In the present invention, it should be noted that the thickness of the coating layer refers to the thickness after the final drying process. Preferably, the thickness of the coating layer (ie, the final thickness of the coating layer) is 0.1-0.3 μm, preferably 0.11-0.21 μm.

[0046] A second aspect of the present invention provides a method for preparing the aforementioned composite separation membrane, wherein the preparation method comprises:

[0047] (1) grinding nano-silica and mixing it with deionized water to obtain a mixture of nano-silica and deionized water;

[0048] (2) mixing the mixture and the water-soluble high molecular polymer for a second time and then subjecting the mixture to a first ultrasonic treatment to prepare a mixed solution;

[0049] (3) performing a third mixing of the mixed solution and rubber latex to obtain a mixed solution; and diluting the mixed solution with deionized water to obtain a casting solution;

[0050] (4) The casting solution is coated on the surface of the support layer and subjected to post-processing to obtain a composite separation membrane.

[0051] According to the present invention, in step (1), in order to make the nano-silica particles more uniform and fine, the nano-silica is first ground in a mortar, and then added to deionized water and stirred to disperse it. During the stirring process, a water-soluble high molecular polymer is gradually added, and after mixing evenly, the mixture is ultrasonically mixed.

[0052] According to the present invention, in step (2), the mass concentration of the high molecular weight polymer aqueous solution is 0.1-5%, preferably 0.3-2%, and more preferably 0.5-1%. In the present invention, the above mass concentration is selected to, on the one hand, enable the water-soluble polymer to be more evenly dissolved in deionized water and dispersed evenly with the nano-silica, ensuring that the nano-silica does not aggregate or sink to the bottom, and on the other hand, the moderate viscosity enables better mixing with the rubber latex.

[0053] According to the present invention, in step (2), a water-soluble polymer is slowly added to a mixture of nano-silica and deionized water, stirred until completely mixed and then further dispersed with ultrasound, and no undissolved particles and small lumps, as well as particles that have settled to the bottom, are observed with the naked eye. The resulting mixture is transparent and uniform, and almost no bubbles are observed in the solution after being placed for a few minutes. Wherein, the conditions for the second mixing include: a stirring speed of 100-1000 rpm, preferably 100-600 rpm, more preferably 200-500 rpm; a time for the second mixing of 1-100 min, preferably 5-60 min, more preferably 10-30 min; ultrasonic mixing is continued after high-speed stirring, so that the particles and small lumps can be dissolved, the time for the first ultrasound is 10-600 min, preferably 20-200 min, more preferably 30-100 min; in addition, in a more preferred case, the ultrasonic intensity of the first ultrasound is 28-100 Hz, preferably 30-60 Hz, more preferably 35-50 Hz.

[0054] According to the present invention, in step (3), during the preparation of the casting solution, a mixture of a water-soluble high molecular polymer and white carbon black deionized water is slowly added to the rubber latex emulsion while stirring. After the addition is completed, a certain amount of deionized water is slowly added to the mixture while stirring for a third mixing, wherein the conditions for the third mixing include: the time of the third mixing is 1-100 min, preferably 5-60 min, and more preferably 10-30 min; preferably, the third mixing is carried out under stirring conditions and second ultrasonic conditions, wherein the stirring rate is 10-1000 rpm, preferably 100-600 rpm, and more preferably 200-500 rpm; the time of the second ultrasonication is 10-600 min, preferably 20-200 min, and more preferably 30-100 min; in addition, more preferably, the ultrasonic intensity of the ultrasonication is 28-100 Hz, preferably 30-60 Hz, and more preferably 35-50 Hz.

[0055] According to the present invention, the preparation method further comprises filtering the uniformly mixed casting solution to remove demulsified rubber in order to ensure that the latex particles are very evenly dispersed in the casting solution. In the present invention, the filtration is preferably performed using a sieve having a mesh size of 20-1000 mesh, preferably 40-500 mesh, and more preferably 50-150 mesh, so as to better remove demulsified rubber particles and agglomerated silica particles in the casting solution.

[0056] According to the present invention, in step (4), the casting solution is coated on the surface of the support layer. The casting solution can be scraped onto the ultrafiltration support membrane using a scraper having a thickness of 10-50 μm. In the present invention, the scraper scrapes the casting solution onto the ultrafiltration support membrane, thereby forming a coating layer having an initial thickness on the ultrafiltration support membrane. In the present invention, the initial thickness of the coating layer is 10-50 μm, preferably 15-45 μm, and more preferably 20-40 μm.

[0057] According to the present invention, in step (4), the post-treatment conditions include: allowing the support layer coated with the casting solution to stand, first drying the support layer, and then immersing the support layer in deionized water for ultrasonic cleaning to remove the water-soluble polymer and emulsifier in the membrane.

[0058] According to the present invention, the support layer coated with the casting solution is allowed to stand at room temperature for 1-30 minutes, preferably 5-25 minutes, and more preferably 10-20 minutes, to ensure that moisture on the membrane surface evaporates, the membrane is initially shaped, and the casting solution is prevented from flowing. The support layer is then placed in a vacuum oven for further drying to further remove water from the membrane interior.

[0059] According to the present invention, the conditions for the first drying treatment include: an oven absolute pressure of 0.01-0.08 MPa, preferably 0.02-0.07 MPa, more preferably 0.03-0.06 MPa; a temperature of 20-80°C, preferably 30-70°C, more preferably 40-60°C; a drying time of 10-1000 min, preferably 30-500 min, most preferably 60-200 min; the removal of water inside the membrane can bring some rubber emulsifier molecules to the surface of the membrane, forming microchannels inside the membrane.

[0060] According to the present invention, the dried membrane requires further post-processing to remove the water-soluble polymer in the membrane and the emulsifier in the rubber. This process involves ultrasonic cleaning in deionized water. Specifically, the dried membrane after the first drying step is placed in deionized water and ultrasonically cleaned to remove the water-soluble polymer and emulsifier in the membrane. The ultrasonic cleaning time is 10-1000 minutes, preferably 20-500 minutes, and more preferably 30-200 minutes; the ultrasonic intensity is 28-100 Hz, preferably 30-60 Hz, and most preferably 35-50 Hz. This can make the membrane surface more porous, and removing impurities can increase the rubber's adhesion to the support layer.

[0061] According to the present invention, after washing, the membrane is dehydrated and dried again at high temperature. This not only removes moisture from the membrane pores, but also makes the functional layer polymer molecular chains more stretched, increases the binding force with nano-silica, and makes the functional layer of the membrane more uniform. The specific operation is: the membrane that has been immersed in deionized water and ultrasonically cleaned is added to a vacuum oven for heating and drying again for a second drying treatment; wherein the conditions of the second drying treatment include: an absolute pressure of 0.01-0.08MPa, preferably 0.02-0.07MPa, more preferably 0.03-0.06MPa; a temperature of 40-120℃, preferably 50-100℃, more preferably 60-90℃; and a drying time of 10-1000min, preferably 20-200min, and most preferably 30-100min.

[0062] According to a particularly preferred embodiment of the present invention, in order to make the membrane preparation process of the organic solvent-resistant nanofiltration composite membrane green, environmentally friendly, efficient and simple, the preparation method of the organic solvent-resistant nanofiltration composite membrane provided by the present invention includes three steps:

[0063] First, a casting solution is prepared: a mixture of nano-silica and deionized water, a highly cross-linked rubber latex and a water-soluble polymer aqueous solution are mixed, and the resulting mixture is diluted to a certain concentration as a casting solution;

[0064] Then, the casting solution is applied to an ultrafiltration support membrane with a certain pore size by scraping at a certain thickness, and then dehydrated and dried;

[0065] Finally, the prepared membrane is washed to remove the water-soluble high molecular polymer and the emulsifier in the rubber latex.

[0066] In the present invention, this method can not only make the membrane surface more porous, but also remove impurities, thereby increasing the adhesion of the rubber to the support layer. Furthermore, after washing, high-temperature dehydration and drying are performed again. This method can firstly remove moisture from the membrane pores; secondly, it can further stretch the functional layer polymer molecular chains, thereby increasing the binding force with nano-silica; and thirdly, it can increase the migration of nano-silica to the membrane surface, compensating for the nano-silica lost due to cleaning, and making the arrangement of nano-silica on the membrane surface more uniform.

[0067] The third aspect of the present invention provides an application of the aforementioned composite separation membrane in removing impurities from a weakly polar organic solvent.

[0068] In the present invention, the weakly polar organic solvent may be an organic solvent with relatively low polarity, preferably an alcohol, more preferably one or more of methanol, ethanol and propanol.

[0069] Specifically, the present invention provides an application of the aforementioned composite separation membrane in removing trace impurities from weakly polar organic solvents.

[0070] According to the present invention, preferably, the separation of ethanol and the dye molecule Rose Bengal is targeted.

[0071] The present invention will be described in detail below through examples.

[0072] In the following examples and comparative examples:

[0073] The highly cross-linked emulsified rubber used was all styrene-butadiene latex purchased from Ruiong with a product brand of 430B. The latex particle size was 111 nm, the rubber content in the latex was 40% wt, and the gel content in tetrahydrofuran was 85%.

[0074] Sodium carboxymethyl cellulose, purchased from Innochem, brand name Innochem A05925, MW 250000 (DS = 0.9), 1500-3100 mPa.s.

[0075] The ultrafiltration support membrane used was cross-linked polyacrylonitrile, with an average pore size of 20 nm and a thickness of 120 μm.

[0076] All filter screens are 100-mesh stainless steel screens.

[0077] The nano-silica used is HN series nano-silica with an average particle size of 10-30nm and a purity of 99.5%-99.9%.

[0078] The cross-flow evaluation system is used to separate ethanol and dye molecules. The cross-flow evaluation system consists of two membrane cassettes connected in series, a flow pump, a solution tank, a temperature control system, and a pressure control system. The effective area of ​​the membrane in each cassette is 14.2 cm. 2 The flow pump only provides flow, not pressure, and its flow rate is fixed at 60L / h. The feed tank holds 700ml. System pressure is provided by a high-pressure nitrogen cylinder, which is adjusted by controlling a pressure reducing valve. System temperature control is achieved by immersing the feed tank in an ethylene glycol bath and adjusting the bath's temperature. The entire device is constructed from 316 stainless steel and has a pressure resistance of 69 bar.

[0079] The oven was purchased from Tester, model DZ-IBCIV.

[0080] Example 1

[0081] This embodiment is intended to illustrate the composite separation membrane prepared by the method of the present invention.

[0082] (1) Weigh 5 g of nano-silica using an electronic balance, add it to a mortar and grind it for 10 minutes, then slowly add 2.4 g of it to 22.7 g of deionized water to obtain an aqueous solution with a mass concentration of 8% nano-silica. Stir while adding. Continue stirring for 10 minutes after all the solution is added.

[0083] (2) 0.16 g of sodium carboxymethyl cellulose was weighed using an electronic balance and slowly added to the mixture of nano-silica and water. The mixture was stirred until completely mixed and then further ultrasonically dispersed at an ultrasonic intensity of 30 Hz for 30 min. No undissolved particles, small lumps, or particles that settled to the bottom were observed with the naked eye. The resulting mixture was transparent and uniform, and almost no bubbles were observed in the solution after a few minutes.

[0084] (3) Take another clean beaker and add 10g of styrene-butadiene rubber latex. Use a dropper to take 2.4g of the prepared sodium carboxymethyl cellulose solution and add it to the styrene-butadiene rubber latex. At this time, the mass ratio of sodium carboxymethyl cellulose to dry styrene-butadiene rubber is 0.4%.

[0085] After stirring evenly, slowly add 654g of deionized water while stirring. After adding the deionized water, continue stirring for 20 minutes at a stirring speed of 300rpm. At this time, the mass content of styrene-butadiene rubber in the mixture is 0.6%. After stirring evenly, continue ultrasonic mixing for 50 minutes.

[0086] (4) The demulsified rubber was then filtered out using a 100-mesh stainless steel sieve. A 20-μm-thick scraper was used to scrape the surface of the ultrafiltration membrane to form a membrane with an initial coating layer thickness of 20 μm. The membrane was allowed to stand in air for 20 minutes before forming and then placed in an oven for further drying. The oven pressure was set to 0.05 MPa, the temperature was 50°C, and the drying time was 100 minutes. Finally, the membrane was post-treated by washing it in an ultrasonic deionized water bath at an ultrasonic frequency of 40 Hz for 100 minutes. After washing, it was placed in an oven for drying for 60 minutes at a pressure of 0.04 MPa and a temperature of 70°C.

[0087] Results The thickness of the coating layer of the prepared composite separation membrane was 0.13 μm.

[0088] The composite separation membrane prepared by cutting into appropriate size was used to separate ethanol and dye molecule rose bengal in a cross-flow evaluation system. The mass concentration of rose bengal in the raw liquid was 5%, and the ethanol flux at the permeate end was 3.5 L / m 2 / bar / h, the Rose Bengal content in the ethanol at the permeate end was 1000ppm. After the experiment, the membrane was immersed in the ethanol system for one month and then tested again. The mass concentration of Rose Bengal in the raw liquid was 5%, and the ethanol flux at the permeate end was 3.6L / m 2 / bar / h, the content of rose bengal in ethanol at the permeate end was 1030ppm.

[0089] This indicates that the composite separation membrane prepared by the method of the present invention has good stability in organic solvents.

[0090] Example 2

[0091] This embodiment is intended to illustrate the composite separation membrane prepared by the method of the present invention.

[0092] (1) Weigh 5 g of nano-silica using an electronic balance, add it to a mortar and grind it for 10 minutes. Then, take 2.8 g and slowly add it to 31 g of deionized water while stirring. Continue stirring for 10 minutes after all the water is added.

[0093] (2) 0.2 g of sodium carboxymethyl cellulose was weighed using an electronic balance and slowly added to the mixture of nano-silica and water. The mixture was stirred until completely mixed and then further ultrasonically dispersed at an ultrasonic intensity of 30 Hz for 30 min. No undissolved particles, small lumps, or particles that settled to the bottom were observed with the naked eye. The resulting mixture was transparent and uniform, and almost no bubbles were observed in the solution after a few minutes.

[0094] (3) Take another clean beaker and add 10g of styrene-butadiene rubber latex. Use a dropper to take 3.4g of the prepared sodium carboxymethyl cellulose solution and add it to the styrene-butadiene rubber latex. At this time, the mass ratio of sodium carboxymethyl cellulose to dry styrene-butadiene rubber is 0.5%.

[0095] After stirring evenly, slowly add 558g of deionized water while stirring. After adding the deionized water, continue stirring for 15 minutes at a stirring speed of 250rpm. At this time, the mass content of styrene-butadiene rubber in the mixture is 0.7%. After stirring evenly, continue ultrasonic mixing for 100 minutes.

[0096] (4) The demulsified rubber was then filtered out using a 100-mesh stainless steel sieve. A 20-μm-thick scraper was used to scrape the ultrafiltration membrane surface to form a membrane with an initial coating thickness of 20 μm. The membrane was allowed to stand in air for 15 minutes before forming and then placed in an oven for further drying. The oven pressure was set to 0.06 MPa, the temperature was 40°C, and the drying time was 150 minutes. Finally, the membrane was post-treated by washing it in an ultrasonic deionized water bath at an ultrasonic frequency of 35 Hz for 30 minutes. After washing, it was placed in an oven for drying for 70 minutes at a pressure of 0.03 MPa and a temperature of 60°C.

[0097] Results The thickness of the coating layer of the prepared composite separation membrane was 0.15 μm.

[0098] The composite separation membrane prepared by cutting into appropriate size was used to separate ethanol and dye molecule rose bengal in a cross-flow evaluation system. The mass concentration of rose bengal in the raw liquid was 5%, and the ethanol flux at the permeate end was 3.4 L / m 2 / bar / h, the Rose Bengal content in the ethanol at the permeate end was 980ppm. After the experiment, the membrane was immersed in the ethanol system for one month and then the experiment was repeated. The mass concentration of Rose Bengal in the raw liquid was 5%, and the ethanol flux at the permeate end was 3.5L / m 2 / bar / h, and the content of Rose Bengal in ethanol at the permeate end was 1000 ppm. This indicates that the membrane prepared by our method has good stability in organic solvents.

[0099] Example 3

[0100] This embodiment is intended to illustrate the composite separation membrane prepared by the method of the present invention.

[0101] (1) Weigh 5 g of nano-silica using an electronic balance, add it to a mortar and grind it for 10 minutes, then slowly add 4 g of it to 12 g of deionized water while stirring. Continue stirring for 10 minutes after all the water is added.

[0102] (2) 1.2 g of sodium carboxymethyl cellulose was weighed using an electronic balance and slowly added to the mixture of nano-silica and water. The mixture was stirred until completely mixed and then further ultrasonically dispersed at an ultrasonic intensity of 25 Hz for 30 min. No undissolved particles, small lumps, or particles that settled to the bottom were observed with the naked eye. The resulting mixture was transparent and uniform, and almost no bubbles were observed in the solution after a few minutes.

[0103] (3) Take another clean beaker and add 10g of styrene-butadiene rubber latex. Use a dropper to take 1.7g of the prepared sodium carboxymethyl cellulose solution and add it to the styrene-butadiene rubber latex. At this time, the mass ratio of sodium carboxymethyl cellulose to dry styrene-butadiene rubber is 0.3%.

[0104] After stirring evenly, slowly add 488g of deionized water while stirring. After adding the deionized water, continue stirring for 10 minutes at a stirring speed of 400rpm. At this time, the mass content of styrene-butadiene rubber in the mixture is 0.8%. After stirring evenly, continue ultrasonic mixing for 60 minutes.

[0105] (4) The demulsified rubber was then filtered out using a 100-mesh stainless steel sieve. A 20-μm-thick scraper was used to scrape the ultrafiltration membrane surface to form a membrane with an initial coating layer thickness of 20 μm. The membrane was allowed to stand in air for 10 minutes before being formed and then placed in an oven for further drying. The oven pressure was set to 0.03 MPa, the temperature was 60°C, and the drying time was 200 minutes. Finally, the membrane was post-treated by washing it in an ultrasonic deionized water bath at an ultrasonic frequency of 50 Hz for 200 minutes. After washing, it was placed in an oven for drying for 30 minutes at a pressure of 0.05 MPa and a temperature of 90°C.

[0106] Results The thickness of the coating layer of the prepared composite separation membrane was 0.17 μm.

[0107] The composite separation membrane prepared by cutting into appropriate size was used to separate ethanol and dye molecule rose bengal in a cross-flow evaluation system. The mass concentration of rose bengal in the raw liquid was 5%, and the ethanol flux at the permeate end was 3.2 L / m 2 / bar / h, the Rose Bengal content in the ethanol at the permeate end was 950ppm. After the experiment, the membrane was immersed in the ethanol system for one month and then tested again. The mass concentration of Rose Bengal in the raw liquid was 5%, and the ethanol flux at the permeate end was 3.3L / m 2 / bar / h, and the Rose Bengal content in ethanol at the permeate end was 980 ppm, indicating that the membrane prepared by our method has good stability in organic solvents.

[0108] Example 4

[0109] This embodiment is intended to illustrate the composite separation membrane prepared by the method of the present invention.

[0110] (1) Weigh 5 g of nano-silica using an electronic balance, add it to a mortar and grind it for 10 min. Then, slowly add 2 g of it to 64 g of deionized water while stirring. Continue stirring for 10 min after all the water is added.

[0111] (2) 0.32 g of sodium carboxymethyl cellulose was weighed using an electronic balance and slowly added to the mixture of nano-silica and water. The mixture was stirred until completely mixed and then further ultrasonically dispersed at an ultrasonic intensity of 25 Hz for 30 min. No undissolved particles, small lumps, or particles that settled to the bottom were observed with the naked eye. The resulting mixture was transparent and uniform, and almost no bubbles were observed in the solution after a few minutes.

[0112] (3) Take another clean beaker and add 10g of styrene-butadiene rubber latex. Use a dropper to take 6.6g of the prepared sodium carboxymethyl cellulose solution and add it to the styrene-butadiene rubber latex. At this time, the mass ratio of sodium carboxymethyl cellulose to dry styrene-butadiene rubber is 0.8%.

[0113] After stirring evenly, slowly add 783g of deionized water while stirring. After adding the deionized water, continue stirring for 25 minutes at a stirring speed of 200rpm. At this time, the mass content of styrene-butadiene rubber in the mixture is 0.5%. After stirring evenly, continue ultrasonic mixing for 30 minutes.

[0114] (4) The demulsified rubber was then filtered out using a 100-mesh stainless steel mesh screen. A 20-μm-thick scraper was used to scrape the ultrafiltration membrane surface to form a membrane with an initial coating thickness of 20 μm. The membrane was allowed to stand in air for 12 minutes before forming and then placed in an oven for further drying. The oven pressure was set to 0.04 MPa, the temperature was 45°C, and the drying time was 60 minutes. Finally, the membrane was post-treated by washing it in an ultrasonic deionized water bath at an ultrasonic frequency of 45 Hz for 60 minutes. After washing, it was placed in an oven for drying again for 100 minutes at an oven pressure of 0.06 MPa and a temperature of 65°C.

[0115] Results The thickness of the coating layer of the prepared composite separation membrane was 0.11 μm.

[0116] The composite separation membrane prepared by cutting into appropriate size was used to separate ethanol and dye molecule rose bengal in a cross-flow evaluation system. The mass concentration of rose bengal in the raw liquid was 5%, and the ethanol flux at the permeate end was 3.7 L / m 2 / bar / h, the Rose Bengal content in the ethanol at the permeate end was 1050ppm. After the experiment, the membrane was immersed in the ethanol system for one month and then tested again. The mass concentration of Rose Bengal in the raw liquid was 5%, and the ethanol flux at the permeate end was 3.8L / m 2 / bar / h, and the content of Rose Bengal in ethanol at the permeate end was 1100 ppm. This indicates that the membrane prepared by our method has good stability in organic solvents.

[0117] Example 5

[0118] This embodiment is intended to illustrate the composite separation membrane prepared by the method of the present invention.

[0119] (1) Weigh 5 g of nano-silica using an electronic balance, add it to a mortar and grind it for 10 min. Then, take 3.2 g and slowly add it to 35 g of deionized water while stirring. Continue stirring for 10 min after all the water is added.

[0120] (2) 0.28 g of sodium carboxymethyl cellulose was weighed using an electronic balance and slowly added to the mixture of nano-silica and water. The mixture was stirred until completely mixed and then further ultrasonically dispersed at an ultrasonic intensity of 30 Hz for 30 min. No undissolved particles, small lumps, or particles that settled to the bottom were observed with the naked eye. The resulting mixture was transparent and uniform, and almost no bubbles were observed in the solution after a few minutes.

[0121] (3) Take another clean beaker and add 10g of styrene-butadiene rubber latex. Use a dropper to take 3.8g of the prepared sodium carboxymethyl cellulose solution and add it to the styrene-butadiene rubber latex. At this time, the mass ratio of sodium carboxymethyl cellulose to dry styrene-butadiene rubber is 0.7%.

[0122] After stirring evenly, 386 g of deionized water was slowly added while stirring. After the deionized water was added, stirring was continued for 30 minutes at a stirring speed of 500 rpm. At this time, the mass content of styrene-butadiene rubber in the mixture was 1%. After stirring evenly, ultrasonic mixing was continued for 80 minutes.

[0123] (4) The demulsified rubber was then filtered out using a 100-mesh stainless steel mesh screen. A 20-μm-thick scraper was used to scrape the ultrafiltration membrane surface to form a membrane with an initial coating layer thickness of 20 μm. The membrane was allowed to stand in air for 18 minutes before forming and then further dried in an oven at a pressure of 0.05 MPa, a temperature of 55°C, and a drying time of 80 minutes. Finally, the membrane was post-treated by washing it in an ultrasonic deionized water bath at an ultrasonic frequency of 40 Hz for 150 minutes. After washing, it was again dried in an oven at a pressure of 0.04 MPa and a temperature of 80°C for 50 minutes.

[0124] Results The thickness of the coating layer of the prepared composite separation membrane was 0.21 μm.

[0125] The composite separation membrane prepared by cutting into appropriate size was used to separate ethanol and dye molecule rose bengal in a cross-flow evaluation system. The mass concentration of rose bengal in the raw liquid was 5%, and the ethanol flux at the permeate end was 3.0 L / m 2 / bar / h, the Rose Bengal content in the ethanol at the permeate end was 700ppm. After the experiment, the membrane was immersed in the ethanol system for one month and then tested again. The mass concentration of Rose Bengal in the raw liquid was 5%, and the ethanol flux at the permeate end was 3.1L / m 2 / bar / h, and the Rose Bengal content in ethanol at the permeate end was 750 ppm. This indicates that the membrane prepared by our method has good stability in organic solvents.

[0126] Comparative Example 1

[0127] (1) 0.16 g of sodium carboxymethyl cellulose was weighed using an electronic balance and slowly added to 22.7 g of deionized water to prepare a 0.7% aqueous solution. The mixture was stirred until completely mixed and then further ultrasonically dispersed at an ultrasonic intensity of 25 Hz for 30 min. No undissolved particles or small lumps were observed with the naked eye. The resulting mixture was transparent and uniform. After standing for a few minutes, almost no bubbles were observed in the solution.

[0128] (2) Take another clean beaker and add 10g of styrene-butadiene rubber latex. Use a dropper to take 2.4g of the prepared sodium carboxymethyl cellulose solution and add it to the styrene-butadiene rubber latex. At this time, the mass ratio of sodium carboxymethyl cellulose to dry styrene-butadiene rubber is 0.4%.

[0129] After stirring evenly, slowly add 654g of deionized water while stirring. After adding the deionized water, continue stirring for 20 minutes at a stirring speed of 300rpm. At this time, the mass content of styrene-butadiene rubber in the mixture is 0.6%. After stirring evenly, continue ultrasonic mixing for 50 minutes.

[0130] (3) The demulsified rubber was then filtered out using a 100-mesh stainless steel sieve. A 20-μm-thick scraper was used to scrape the ultrafiltration membrane surface to form a membrane with an initial coating thickness of 20 μm. The membrane was allowed to stand in air for 20 minutes before forming and then further dried in an oven at a pressure of 0.05 MPa, a temperature of 50°C, and a drying time of 100 minutes. Finally, the membrane was post-treated by washing it in an ultrasonic deionized water bath at an ultrasonic frequency of 40 Hz for 100 minutes. After washing, it was again dried in an oven at a pressure of 0.04 MPa and a temperature of 70°C for 60 minutes.

[0131] Results The thickness of the coating layer of the prepared composite separation membrane was 0.12 μm.

[0132] The composite separation membrane prepared by cutting into appropriate size was used to separate ethanol and dye molecule rose bengal in a cross-flow evaluation system. The mass concentration of rose bengal in the raw liquid was 5%, and the ethanol flux at the permeate end was 0.5 L / m 2 / bar / h, the Rose Bengal content in the ethanol at the permeate end was 1000ppm. After the experiment, the membrane was immersed in the ethanol system for one month and then the experiment was repeated. The mass concentration of Rose Bengal in the raw liquid was 5%, and the ethanol flux at the permeate end was 0.6L / m 2 / bar / h, the content of rose bengal in ethanol at the permeate end was 1030ppm.

[0133] This shows that the addition of nano-silica in Example 1 can modify the membrane surface, increase the polarity of the membrane surface, and significantly improve the flux of polar solvents. In Comparative Example 1, since nano-silica was not added to the casting solution, the solvent flux was reduced.

[0134] Comparative Example 2

[0135] (1) 20 g of nano-silica was weighed using an electronic balance, added to a mortar and ground for 10 min, and 10 g was slowly added to 22.7 g of deionized water while stirring. After all the water was added, stirring was continued for 10 min. In this comparative example 2, the amount of silica was greatly increased compared with that in Example 1.

[0136] (1) 0.16 g of sodium carboxymethyl cellulose was weighed using an electronic balance and slowly added to the mixture of nano-silica and water. The mixture was stirred until completely mixed and then further ultrasonically dispersed at an ultrasonic intensity of 30 Hz for 30 min. After standing for a few minutes, almost no bubbles were observed in the solution.

[0137] (3) Take another clean beaker and add 10g of styrene-butadiene rubber latex. Use a dropper to take 2.4g of the prepared sodium carboxymethyl cellulose solution and add it to the styrene-butadiene rubber latex. At this time, the mass ratio of sodium carboxymethyl cellulose to dry styrene-butadiene rubber is 0.4%.

[0138] After stirring evenly, slowly add 654g of deionized water while stirring. After adding the deionized water, continue stirring for 20 minutes at a stirring speed of 300rpm. At this time, the mass content of styrene-butadiene rubber in the mixture is 0.6%. After stirring evenly, continue ultrasonic mixing for 50 minutes.

[0139] (4) The demulsified rubber was then filtered out using a sieve. A significant increase in precipitated particles was observed, indicating that the latex particles were severely demulsified. A 20 μm thick scraper was used to scrape the surface of the ultrafiltration membrane to form a membrane with an initial coating thickness of 20 μm. The membrane was then placed in air for 20 minutes to form a membrane, and then placed in an oven for further drying. The oven pressure was set to 0.05 MPa, the temperature was 50°C, and the drying time was 100 minutes. Finally, the membrane was post-treated. The membrane was washed in an ultrasonic deionized water bath at an ultrasonic frequency of 40 Hz for 100 minutes. After washing, it was placed in an oven again for drying for 60 minutes at an oven pressure of 0.04 MPa and a temperature of 70°C.

[0140] Results The thickness of the coating layer of the prepared composite separation membrane was 0.13 μm.

[0141] The composite separation membrane prepared by cutting into appropriate size was used to separate ethanol and dye molecule rose bengal in a cross-flow evaluation system. The mass concentration of rose bengal in the raw liquid was 5%, and the ethanol flux at the permeate end was 5.5 L / m 2 / bar / h, the Rose Bengal content in the ethanol at the permeate end was 2%. After the experiment, the membrane was immersed in the ethanol system for one month and then the experiment was repeated. The mass concentration of Rose Bengal in the raw liquid was 5%, and the ethanol flux at the permeate end was 8.6L / m 2 / bar / h, and the rose bengal content in ethanol at the permeate end was 4%. This indicates that excessive white carbon black content can easily cause latex particles to break up, and rubber breakage before membrane formation can easily cause local membrane defects.

[0142] Comparative Example 3

[0143] (1) Weigh 5 g of nano-silica using an electronic balance, add it to a mortar and grind it for 10 min. Then, take 2.4 g and slowly add it to 22.7 g of deionized water while stirring. Continue stirring for 10 min after all the water is added.

[0144] (2) Take another clean beaker and add 10g of styrene butadiene rubber latex, take 2.4g of the prepared mixture of nano-silica and water with a dropper and add it to the styrene butadiene rubber latex, stir evenly and then slowly add 654g of deionized water while stirring. After the deionized water is added, continue stirring for 20min at a stirring speed of 300rpm. At this time, the mass content of styrene butadiene rubber in the mixture is 0.6%. After stirring evenly, continue ultrasonic mixing for 50min.

[0145] (3) The demulsified rubber was then filtered out using a sieve, and a 20 μm-thick scraper was used to scrape the ultrafiltration membrane surface to form a membrane with an initial coating layer thickness of 20 μm. The membrane was allowed to stand in air for 20 minutes before forming and then further dried in an oven at a pressure of 0.05 MPa, a temperature of 50°C, and a drying time of 100 minutes. Finally, the membrane was post-treated by washing it in an ultrasonic deionized water bath for 100 minutes at an ultrasonic frequency of 40 Hz. After washing, it was again dried in an oven at a pressure of 0.04 MPa and a temperature of 70°C for 60 minutes. Compared to Example 1, no sodium carboxymethyl cellulose was added to the mixture with the nano-silica.

[0146] Results The thickness of the coating layer of the prepared composite separation membrane was 0.13 μm.

[0147] The prepared membrane was cut to appropriate size and used to separate ethanol and the dye molecule Rose Bengal in a cross-flow evaluation system. The mass concentration of Rose Bengal in the raw liquid was 5%, and the ethanol flux at the permeate end was 5.5 L / m 2 / bar / h, the Rose Bengal content in the ethanol at the permeate end was 5000ppm. After the experiment, the membrane was immersed in the ethanol system for one month and then tested again. The mass concentration of Rose Bengal in the raw liquid was 5%, and the ethanol flux at the permeate end was 6.6L / m 2 / bar / h, and the Rose Bengal content in ethanol at the permeate end was 6000ppm. This indicates that without the addition of the water-soluble polymer sodium carboxymethyl cellulose, the latex and silica cannot be properly mixed, resulting in poor membrane uniformity, many local defects, and poor membrane retention.

[0148] Comparative Example 4

[0149] A composite separation membrane was prepared in the same manner as in Example 1, except that: instead of using the "styrene-butadiene latex" in Example 1, "10 g of styrene-butadiene latex with a low degree of cross-linking (the latex was homemade, with a latex particle size of 100 nm, a rubber content of 40 wt %, and a gel content of approximately 30% as measured by tetrahydrofuran)" was used.

[0150] Results The thickness of the coating layer of the prepared composite separation membrane was 0.13 μm.

[0151] The composite separation membrane prepared by cutting into appropriate size was used to separate ethanol and dye molecule rose bengal in a cross-flow evaluation system. The mass concentration of rose bengal in the raw liquid was 5%, and the ethanol flux at the permeate end was 20L / m 2 / bar / h, the Rose Bengal content in the ethanol at the permeate end was 40000ppm. After the experiment, the membrane was immersed in the ethanol system for one month and then the experiment was repeated. The mass concentration of Rose Bengal in the raw liquid was 5%, and the ethanol flux at the permeate end was 30L / m 2 / bar / h, the content of rose bengal in ethanol at the permeate end is 45000ppm.

[0152] The membrane had no rejection performance compared to Example 1.

[0153] In summary, the organic solvent-resistant nanofiltration composite membrane of the present invention does not use organic solvents in the preparation process, which can effectively avoid the harm of organic solvents to the human body and the environment. The membrane preparation process is simple, which greatly saves membrane preparation time; the preparation method is green, environmentally friendly, and efficient; and can prepare membranes with high permeation flux and retention rate.

[0154] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A composite separation membrane, characterized in that The composite separation membrane comprises a support layer and a coating layer coated on the surface of the support layer, wherein the coating layer is obtained by coating a casting liquid on the surface of the support layer and then performing post-processing; The casting solution contains rubber latex, water-soluble high molecular polymer, nano-white carbon black and deionized water.

2. The composite separation membrane according to claim 1, wherein The casting solution is composed of rubber latex, water-soluble high molecular polymer, nano-white carbon black and deionized water; Preferably, in the casting solution, the weight ratio of the nano-silica to the dry rubber in the rubber latex is (1-100):100, preferably (3-50):100; Preferably, in the casting solution, the weight ratio of the water-soluble high molecular polymer to the dry rubber in the rubber latex is (0.01-2):100, preferably (0.2-1):

100.

3. The composite separation membrane according to claim 1 or 2, wherein The rubber latex is styrene-butadiene latex and / or nitrile-butadiene latex; Preferably, the gel content of the rubber latex is 50-99%, preferably 70-95%; Preferably, the particle size of the rubber in the rubber latex is 10-1000 nm, preferably 50-200 nm; Preferably, the mass concentration of rubber in the rubber latex is 10-80%.

4. The composite separation membrane according to any one of claims 1 to 3, wherein The mass concentration of dry rubber in the casting solution is 0.1-10%, preferably 0.3-5%, more preferably 0.5-1%.

5. The composite separation membrane according to any one of claims 1 to 3, wherein The water-soluble high molecular polymer is selected from one or more of sodium carboxymethyl cellulose, sodium polyacrylate, sodium alginate, sodium polymethacrylate and sodium polyphosphate; And / or, the particle size of the nano-silica is 5-100 nm, preferably 10-50 nm. The composite separation membrane according to claim 1 , wherein The support layer is an ultrafiltration support layer; Preferably, the support layer is selected from one or more of polyacrylonitrile, polyetherimide and polyimide ultrafiltration membranes; Preferably, the average pore size of the support layer is 5-50 nm, preferably 10-40 nm, more preferably 15-25 nm.

7. The composite separation membrane according to any one of claims 1 to 6, wherein: The thickness of the coating layer is 0.1-0.3 μm, preferably 0.11-0.21 μm; And / or, the thickness of the support layer membrane is 1-500 μm, preferably 10-200 μm, more preferably 50-150 μm.

8. A method for preparing the composite separation membrane according to any one of claims 1 to 7, characterized in that: The preparation method comprises: (1) grinding nano-silica and mixing it with deionized water to obtain a mixture of nano-silica and deionized water; (2) mixing the mixture and the water-soluble high molecular polymer for a second time and then subjecting the mixture to a first ultrasonic treatment to prepare a mixed solution; (3) performing a third mixing of the mixed solution and rubber latex to obtain a mixed solution; and diluting the mixed solution with deionized water to obtain a casting solution; (4) The casting solution is coated on the surface of the support layer and subjected to post-processing to obtain a composite separation membrane.

9. The preparation method according to claim 8, wherein In step (1), the first mixing time is 1-100 min; And / or, in step (2), the mass concentration of the high molecular polymer aqueous solution is 0.1-5%; And / or, in step (2), the second mixing conditions include: a stirring speed of 100-1000 rpm, a second mixing time of 1-100 min, and a first ultrasonic time of 10-600 min; And / or, in step (3), the third mixing time is 1-100 min; And / or, in step (4), the post-treatment conditions include: allowing the support layer coated with the casting solution to stand, first drying the support layer, and then immersing the support layer in deionized water for ultrasonic cleaning; Preferably, the standing time is 1-30 min; Preferably, the conditions of the first drying treatment include: absolute pressure of 0.01-0.08 MPa, temperature of 20-80° C., and the first drying time of 10-1000 min; Preferably, the ultrasonic cleaning time is 10-1000 min.

10. The preparation method according to claim 9, wherein The preparation method further comprises: in step (4), subjecting the membrane after ultrasonic cleaning by immersion in deionized water to a second drying treatment; Preferably, the conditions of the second drying treatment include: absolute pressure of 0.01-0.08 MPa, temperature of 40-120° C., and drying time of 10-1000 min.

11. The preparation method according to any one of claims 8 to 10, wherein The preparation method further comprises: filtering the casting solution; Preferably, the filtration is performed using a mesh screen, the mesh size of which is 20-1000 mesh, preferably 40-500 mesh.

12. Use of the composite separation membrane according to any one of claims 1 to 7 in removing impurities from weakly polar organic solvents.