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, a modified supporting layer and a coating layer, wherein the surface of the supporting layer is sequentially coated with the modified supporting layer and the coating layer, and the modified supporting layer is formed by drying a mixed solution of a water-soluble high-molecular polymer and deionized water; the coating layer is obtained by coating a membrane casting solution on the surface of the modified supporting layer and then carrying out post-treatment and drying treatment, and the membrane casting solution contains emulsified rubber, a water-soluble high-molecular polymer and deionized water; holes in the supporting layer are impregnated with a water-soluble high-molecular polymer. 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] Currently, industry uses millions of tons of solvents to manufacture pharmaceuticals, oils, and chemicals. Multiple separation and purification processes must be performed to purify products from the solvents. As a result, OSN membrane separation is gradually becoming an energy-efficient alternative to existing processes. Based on this, the use of membrane technology for organic solvent separation is also one of the biggest challenges currently.

[0003] The core of organic solvent-resistant nanofiltration membrane (OSN membrane) technology is the OSN membrane, which must not only have high permeability and high retention rate, but also chemical stability. In recent years, scientists have conducted extensive membrane research in the field of OSN membranes, making outstanding contributions to the development of OSN membranes.

[0004] Among them, 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, continuously reporting 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] CN103055723A discloses a method for preparing an organic solvent nanofiltration membrane, which uses a solution of a polybenzimidazole homopolymer or a polybenzimidazole copolymer in a polar organic solvent as a casting solution, and cross-links the coating after drying to obtain a membrane that can tolerate organic solvents.

[0007] Most of the preparation processes of OSN membranes disclosed in the prior art involve dissolving the membrane material in a polar organic solvent to form a casting solution and then performing phase change to form the membrane. This preparation method is very environmentally unfriendly, and the membranes prepared by the general phase change method require further cross-linking to have strong solvent resistance, and the preparation process is complicated.

[0008] There are also reports using interfacial polymerization, which takes a long time to prepare membranes and uses an organic solvent in the organic phase. With the advancement of humanity, environmentally friendly membrane preparation methods are gaining increasing attention. CN1640534A uses concentrated emulsion polymerization to prepare a preferential dealcoholization membrane. However, this membrane preparation method uses a high-concentration emulsion, resulting in a thicker membrane and significantly limiting the permeation flux.

[0009] The majority of organic solvent-resistant membrane materials reported so far are plastic or fiber-based. Only cross-linked polydimethylsiloxane (silicone rubber) has been reported. Rubber-based materials are rarely reported. This is due to the high viscosity of rubber, making it difficult to coat into thin films. 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] 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

[0011] The purpose of the present invention is to overcome the defects in the prior art of complex preparation process of organic solvent-resistant nanofiltration membranes and environmental pollution caused by the use of organic solvents in the preparation process, as well as the defect that the organic solvent system membranes in the prior art require additional complex cross-linking modification processes. A composite separation membrane and its preparation method and application are provided. 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.

[0012] In order to achieve the above object, the first aspect of the present invention provides a composite separation membrane, wherein the composite separation membrane comprises a support layer and a modified support layer and a coating layer sequentially coated on the surface of the support layer;

[0013] The modified support layer is formed by drying a mixed solution of a water-soluble high molecular polymer and deionized water;

[0014] The coating layer is obtained by coating a casting liquid on the surface of the modified support layer and then performing post-treatment and drying, wherein the casting liquid contains emulsified rubber, a water-soluble high molecular polymer and deionized water;

[0015] And the holes inside the supporting layer are impregnated with water-soluble high molecular polymer.

[0016] A second aspect of the present invention provides a method for preparing the aforementioned composite separation membrane, wherein the preparation method comprises:

[0017] (1) pre-treating the support layer by immersing the support layer in a mixed solution of a first water-soluble polymer and deionized water, and drying the immersed support layer to obtain a modified support layer;

[0018] (2) performing a second mixing of the second water-soluble polymer and deionized water to prepare a second polymer aqueous solution;

[0019] (3) mixing the second high molecular polymer aqueous solution and the emulsified rubber for a third time and then subjecting the mixture to ultrasonic treatment to obtain a mixed solution; and diluting the mixed solution with deionized water to obtain a casting solution;

[0020] (4) The casting solution is coated on the surface of the modified support layer and subjected to post-treatment to obtain a composite separation membrane.

[0021] A third aspect of the present invention provides a use of the aforementioned composite separation membrane in separating polar impurities in a non-polar organic solvent.

[0022] Through the above technical solution, the technical solution of the present invention has the following beneficial effects:

[0023] (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;

[0024] (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;

[0025] (3) The composite separation membrane prepared by the present invention has good stability in organic solvents. DETAILED DESCRIPTION

[0026] 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.

[0027] 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 modified support layer and a coating layer sequentially coated on the surface of the support layer;

[0028] The modified support layer is formed by drying a mixed solution of a water-soluble high molecular polymer and deionized water;

[0029] The coating layer is obtained by coating a casting liquid on the surface of the modified support layer and then performing post-treatment and drying, wherein the casting liquid contains emulsified rubber, a water-soluble high molecular polymer and deionized water;

[0030] And the holes inside the supporting layer are impregnated with water-soluble high molecular polymer.

[0031] 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.

[0032] Furthermore, the inventors of the present invention found that: first, the support layer (large-pore base membrane) is pre-treated, and the pores of the large-pore support layer are filled with a water-soluble polymer solution, and the surface of the support layer is covered with a water-soluble polymer, and the excess water-soluble polymer on the surface is wiped off after drying. Then, a casting liquid with a certain rubber concentration is prepared by adding deionized water to a highly cross-linked emulsified rubber and a water-soluble polymer. The casting liquid is then scraped onto the large-pore ultrafiltration support membrane at a certain thickness and dehydrated. Finally, the prepared membrane is cleaned to wash off the water-soluble polymer and the emulsifier in the emulsified rubber. The membrane support layer prepared in this way is loose, which reduces the resistance to material penetration and increases the flux of the membrane. The pretreatment of the membrane support layer prevents rubber particles from entering the pores of the support membrane. Post-treatment to wash off the water-soluble polymer and emulsifier will increase the adhesion of the rubber to the support layer. After washing, the membrane is dehydrated and dried at high temperature again. This not only removes the moisture in the membrane pores, but also increases the fluidity of the rubber on the membrane surface, making the functional layer of the membrane more uniform.

[0033] 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.

[0034] According to the present invention, preferably, the casting solution consists of rubber latex, water-soluble high molecular polymer and deionized water.

[0035] According to the present invention, the weight ratio of the water-soluble high molecular weight polymer in the casting solution to the dry rubber in the rubber latex is (0.01-1):100, preferably (0.01-0.6):100, and more preferably (0.1-0.5):100. In the present invention, selecting a 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.

[0036] 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 emulsified rubber is styrene-butadiene latex and / or acrylonitrile-butadiene latex; in the present invention, the emulsified rubber material used has a high degree of crosslinking, and the degree 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, the rubber with a high gel content (high 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 conducive to improving membrane flux. On the other hand, such a high degree of crosslinking can ensure that the membrane material can tolerate common mild organic solvents.

[0037] In addition, it should be noted that in the present invention, the gel content is tested by testing the gel content of the dried membrane material in tetrahydrofuran.

[0038] According to the present invention, the particle size of the rubber in the emulsified rubber is 10-1000 nm, preferably 50-200 nm, more preferably 80-120 nm, and most preferably 90-115 nm. In the present invention, the selection of the latex particle size takes into account the pore size of the supporting layer ultrafiltration membrane, ensuring that the latex particles are not too small to prevent rubber particles from entering the ultrafiltration layer pores during the coating process, blocking the channels and reducing the membrane flux. 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.

[0039] According to the present invention, the mass concentration of rubber in the emulsified rubber is 10-80%, preferably 20-60%, and more preferably 30-50%. In the present invention, the emulsified rubber having the above mass concentration of rubber has better stability and reduces the demulsification rate during the blending process with the water-soluble polymer solution.

[0040] 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 rubber is controlled, on the one hand, because a thinner functional layer is obtained under the thickness of the scraper, which not only improves the adhesion between the functional layer and the support layer, but also increases the flux of the membrane.

[0041] According to the present invention, preferably, the casting liquid is prepared by emulsified rubber and a water-soluble polymer solution, and the water-soluble polymer is any polymer that is soluble in water. 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 10-100 nm, preferably 20-60 nm, and more preferably 30-50 nm; the thickness of the support layer membrane is 1-500 μm, preferably 10-200 μm, and more preferably 50-150 μm; selecting a large-pore loose support layer membrane can reduce the resistance of substances permeating through the membrane and improve the flux of the membrane. Soaking the support layer in a water-soluble polymer solution in advance can allow the large pores of the support layer to be occupied by the water-soluble polymer, thereby preventing rubber particles from entering.

[0044] 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 0.1-0.2 μm.

[0045] A second aspect of the present invention provides a method for preparing the aforementioned composite separation membrane, wherein the preparation method comprises:

[0046] (1) pre-treating the support layer by immersing the support layer in a mixed solution of a first water-soluble polymer and deionized water, and drying the immersed support layer to obtain a modified support layer;

[0047] (2) performing a second mixing of the second water-soluble polymer and deionized water to prepare a second polymer aqueous solution;

[0048] (3) mixing the second high molecular polymer aqueous solution and the emulsified rubber for a third time and then subjecting the mixture to ultrasonic treatment to obtain a mixed solution; and diluting the mixed solution with deionized water to obtain a casting solution;

[0049] (4) The casting solution is coated on the surface of the modified support layer and subjected to post-treatment to obtain a composite separation membrane.

[0050] According to the present invention, in step (1), before immersing the support layer in a mixed solution of the first water-soluble polymer and deionized water, the support layer needs to be dried; wherein, after the macroporous support membrane is dried in a vacuum oven, it is quickly immersed in the water-soluble polymer solution for 1-100 minutes, preferably 5-60 minutes, and most preferably 10-40 minutes. The macroporous support layer is baked in the oven for 1-1000 minutes, preferably 10-500 minutes, and most preferably 20-60 minutes, with the oven temperature set to 30-120°C, preferably 40-100°C, and most preferably 50-80°C, and the oven pressure is 0.001-0.08 MPa, preferably 0.01-0.06 MPa, and most preferably 0.02-0.04 MPa. This can drive away the air in the pores of the support layer, and when it is quickly immersed in the water-soluble polymer solution, the polymer solution can enter the interior of the membrane more quickly.

[0051] According to the present invention, the soaked macroporous support membrane is removed and placed on a smooth glass plate A. Under the influence of gravity, the polymer solution in the support layer flows to the surface of the glass plate. The support membrane and glass plate A are then placed in a vacuum oven for 1-1000 minutes, preferably 10-600 minutes, and most preferably 60-200 minutes. The oven temperature is 20-100°C, preferably 30-80°C, and most preferably 30-60°C. The oven pressure is 0.001-0.08 MPa, preferably 0.01-0.07 MPa, and most preferably 0.02-0.06 MPa. After drying, the water-soluble polymer accumulates at the interface between the support membrane and glass plate A, and subsequent film coating is performed at this interface.

[0052] According to the present invention, the first high molecular polymer and the second high molecular polymer are the same or different, and are each selected from one or more of sodium carboxymethyl cellulose, sodium polyacrylate, sodium alginate, sodium polymethacrylate and sodium polyphosphate.

[0053] According to the present invention, the mass concentration of the first high molecular weight polymer aqueous solution is 0.1-10%, preferably 0.5-5%, and more preferably 0.8-2%. In the present invention, the above mass concentration is selected to, on the one hand, enable the first water-soluble polymer to be more evenly dissolved in the deionized water, and on the other hand, provide a moderate viscosity to better penetrate into the pores of the support layer or coat the surface of the support layer.

[0054] According to the present invention, the mass concentration of the second high molecular weight polymer aqueous solution is 0.1-5%, preferably 0.2-2%, and most preferably 0.3-1%. In the present invention, the above mass concentration is selected so that the second water-soluble polymer can be more evenly dissolved in deionized water, and the moderate viscosity can be better mixed with the rubber latex.

[0055] According to the present invention, during the preparation of the casting solution, the second polymer aqueous solution is slowly added to the emulsified rubber while stirring. After the addition is completed, a certain amount of deionized water is slowly added to the mixture while stirring. Slow addition can make the mixing more uniform on the one hand, and reduce rubber demulsification on the other hand. Specifically, in step (3), under stirring conditions, the second polymer aqueous solution and rubber latex are subjected to a third mixing to prepare a casting solution with a certain rubber concentration. Wherein, the conditions of the third mixing include: a stirring speed of 10-1000rpm, preferably 100-600rpm, more preferably 200-500rpm; a time of the third mixing of 1-100min, preferably 5-60min, more preferably 10-30min; ultrasonic mixing is continued after high-speed stirring, and the ultrasonic time is 10-600min, preferably 10-100min, more preferably 20-60min; in addition, in a more preferred case, the ultrasonic intensity of the ultrasound is 28-100Hz, preferably 30-60Hz, more preferably 35-50Hz.

[0056] According to the present invention, the preparation method further comprises filtering the uniformly mixed casting solution to remove demulsified rubber and prevent membrane defects caused by demulsified rubber particles. In the present invention, the filtration is preferably performed using a sieve having a mesh size of 40-2800 mesh, preferably 50-500 mesh, and more preferably 80-200 mesh, to better remove demulsified rubber particles from the casting solution.

[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.

[0058] 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 with 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 with 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. Before coating, the treated macroporous support layer is peeled off from the glass plate, and the other side of the membrane is in contact with a clean and smooth glass plate. Specifically, before coating, the treated macroporous support layer is peeled off from the glass plate A and placed on another smooth and clean glass plate B. The contact surface between the membrane and the glass plate B is the opposite surface to the contact surface of the glass plate A. Then, the excess water-soluble polymer on the contact surface between the support membrane and the glass plate A is gently wiped off with a soft wet cloth. The film is then scraped and 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 film surface evaporates, the film is initially shaped, and the casting solution is prevented from flowing. The film is then placed in a vacuum oven for further drying to further remove water from the interior of the film.

[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-treatment to remove water-soluble polymers from the membrane and emulsifiers from the rubber. This is accomplished by placing the membrane in deionized water and ultrasonically cleaning it. Specifically, the membrane, after the first drying step, is placed in deionized water and ultrasonically cleaned to remove the water-soluble polymers and emulsifiers. The ultrasonic cleaning time is 30-1000 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.

[0061] According to the present invention, the cleaned membrane is then placed in a vacuum oven for further drying. This not only removes water molecules that have entered the membrane during the cleaning process, but also allows the rubber molecules to stretch further, making the membrane surface more uniform. Specifically, the membrane, which has been ultrasonically cleaned by immersing it in deionized water, is placed in a vacuum oven for further drying to perform a second drying process. The conditions for this second drying process include: an absolute pressure of 0.01-0.08 MPa, preferably 0.02-0.07 MPa, and more preferably 0.03-0.06 MPa; a temperature of 40-120°C, preferably 50-100°C, and more preferably 60-90°C; and a drying time of 10-1000 min, preferably 20-200 min, and most preferably 30-100 min.

[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 zero-organic solvent casting solution is prepared: highly cross-linked rubber latex is mixed with a water-soluble high molecular polymer aqueous solution, and the resulting mixture is diluted to a certain concentration as the 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 not only makes the membrane surface more porous, but also removes impurities, thereby increasing the adhesion of the rubber to the support layer. Furthermore, after washing, high-temperature dehydration and drying are performed again, which not only removes moisture from the membrane pores but also increases the fluidity of the rubber on the membrane surface, making the functional layer of the membrane more uniform.

[0067] A third aspect of the present invention provides a use of the aforementioned composite separation membrane in separating polar impurities in a non-polar organic solvent.

[0068] According to the present invention, the non-polar organic solvent can be selected from one or more of C4-C8 alkanes, cycloalkanes and aromatic hydrocarbons, preferably benzene, more preferably toluene.

[0069] Specifically, the present invention provides an application of the aforementioned composite separation membrane in separating trace polar impurities in a non-polar organic solvent.

[0070] According to the present invention, preferably, the separation of hexane and trace amounts of water 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 40 nm and a thickness of 120 μm.

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

[0077] Hexane and trace water were separated in a cross-flow evaluation system, which consisted 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 was 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.

[0078] The oven was purchased from Tester, model DZ-IBCIV.

[0079] Example 1

[0080] This embodiment is intended to illustrate the composite separation membrane prepared by the method of the present invention.

[0081] (1) Weigh 10 g of sodium carboxymethyl cellulose using an electronic balance and add it to a beaker. Add 990 g of deionized water to the beaker to prepare a 1% solution and stir thoroughly to mix.

[0082] The support film was placed in an oven and baked for 40 minutes at an oven temperature of 60°C and a pressure of 0.04 MPa.

[0083] Pour the mixed sodium carboxymethyl cellulose solution into an enamel dish, quickly take out the baked support film from the oven and immerse it in the carboxymethyl cellulose aqueous solution for 20 minutes;

[0084] Take out the impregnated support film and place it on a smooth and flat glass plate. After scraping it flat, put it into an oven together with the glass plate and bake it for 100 minutes at an oven temperature of 40°C and a pressure of 0.03 MPa.

[0085] Remove the support film from the oven. Grasp one end of the film with tweezers to peel it off the glass plate. Place it on another clean, smooth glass plate, bottom side up and top side down. Gently wipe off any excess sodium carboxymethyl cellulose on the surface with a damp, soft gauze.

[0086] (2) Weigh 0.5 g of sodium carboxymethyl cellulose using an electronic balance and add it to a beaker. Add 99.5 g of deionized water to the beaker and stir until the mixture is completely mixed. No undissolved particles or small lumps are observed with the naked eye. The resulting solution is homogeneous and transparent. After standing for a few minutes, almost no bubbles are observed in the solution.

[0087] (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 0.3%;

[0088] After stirring evenly, slowly add 653g of deionized water while stirring. After adding the deionized water, continue stirring for 15 minutes at a stirring speed of 400rmin. At this time, the mass content of styrene-butadiene rubber in the casting liquid is 0.6%. After stirring evenly, continue ultrasonic mixing for 50 minutes.

[0089] Then use a sieve to filter out the demulsified rubber;

[0090] (4) The casting solution was scraped onto the surface of the support film using a 20 μm thick scraper to form a film with an initial coating layer thickness of 20 μm; the film 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 0.04 MPa, the temperature was 50°C, and the drying time was 150 minutes;

[0091] Finally, the membrane was post-treated by washing it in an ultrasonic deionized water bath at an ultrasonic frequency of 40 Hz for 100 min, and then drying it in an oven at a pressure of 0.04 MPa and a temperature of 80°C for 50 min.

[0092] Results In the prepared composite separation membrane, the thickness of the coating layer was 0.12 μm.

[0093] The composite separation membrane prepared by cutting into appropriate size was used to separate hexane and trace water in the cross-flow evaluation system. The water content of hexane in the raw liquid was 220ppm, and the hexane flux at the permeate end was 6.3L / m 2 / bar / h, the water content of hexane at the permeate end was 42ppm. After the experiment, the membrane was immersed in the hexane system for one month and then tested again. The hexane water content in the raw liquid was 220ppm, and the hexane flux at the permeate end was 6.4L / m 2 / bar / h, the water content in hexane at the permeate end is 43ppm.

[0094] This indicates that the composite separation membrane prepared by the method of the present invention has good stability in organic solvents.

[0095] Example 2

[0096] (1) Weigh 15 g of sodium carboxymethyl cellulose using an electronic balance and add it to a beaker. Add 985 g of deionized water to the beaker to prepare a 1.5% solution and stir thoroughly to mix.

[0097] The support film was placed in an oven and baked for 50 minutes at an oven temperature of 70°C and a pressure of 0.03 MPa.

[0098] Pour the mixed sodium carboxymethyl cellulose solution into an enamel dish, quickly take out the baked support film from the oven and immerse it in the carboxymethyl cellulose aqueous solution for 30 minutes;

[0099] Take out the impregnated support film and place it on a smooth and flat glass plate. After scraping it flat, put it into an oven together with the glass plate and bake it for 150 minutes at an oven temperature of 50°C and a pressure of 0.04 MPa.

[0100] Remove the support film from the oven. Grasp one end of the film with tweezers to peel it off the glass plate. Place it on another clean, smooth glass plate, bottom side up and top side down. Gently wipe off any excess sodium carboxymethyl cellulose on the surface with a damp, soft gauze.

[0101] (2) Weigh 0.7 g of sodium carboxymethyl cellulose using an electronic balance and add it to a beaker. Add 99.3 g of deionized water to the beaker and stir until the mixture is completely mixed. No undissolved particles or small lumps are observed with the naked eye. The resulting solution is homogeneous and transparent. After standing for a few minutes, almost no bubbles are observed in the solution.

[0102] (3) Take another clean beaker and add 10g of styrene-butadiene rubber latex. Use a dropper to take 2.3g 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%;

[0103] After stirring evenly, slowly add 559g of deionized water while stirring. After the deionized water is added, continue stirring for 25 minutes at a stirring speed of 300 rpm. At this time, the mass content of styrene-butadiene rubber in the casting solution is 0.7%. After stirring evenly, continue ultrasonic mixing for 40 minutes.

[0104] Then use a sieve to filter out the demulsified rubber;

[0105] (4) The casting liquid is scraped onto the surface of the support film using a 20 μm thick scraper to form a film, obtaining a coating layer with an initial thickness of 20 μm; the film is formed after standing in the air for 10 minutes, and then placed in an oven for further drying. The oven pressure is set to 0.05 MPa, the temperature is 40°C, and the drying time is 200 minutes.

[0106] Finally, the membrane was post-treated by washing it in an ultrasonic deionized water bath at an ultrasonic frequency of 50 Hz for 60 min, and then drying it in an oven at a pressure of 0.03 MPa and a temperature of 70°C for 60 min.

[0107] Results In the prepared composite separation membrane, the thickness of the coating layer was 0.14 μm.

[0108] The composite separation membrane prepared by cutting into appropriate size was used to separate hexane and trace water in the cross-flow evaluation system. The water content of hexane in the raw liquid was 220ppm, and the hexane flux at the permeate end was 6.0L / m 2 / bar / h, the water content of hexane at the permeate end was 41ppm. After the experiment, the membrane was immersed in the hexane system for one month and then tested again. The hexane water content in the raw liquid was 220ppm, and the hexane flux at the permeate end was 6.1L / m 2 / bar / h, the water content in hexane at the permeate end is 41ppm.

[0109] This indicates that the composite separation membrane prepared by the method of the present invention has good stability in organic solvents.

[0110] Example 3

[0111] (1) Weigh 16 g of sodium carboxymethyl cellulose using an electronic balance and add it to a beaker. Add 1984 g of deionized water to the beaker to prepare a 0.8% solution, and stir thoroughly to mix.

[0112] Place the support film in an oven and bake for 30 minutes at a temperature of 80°C and a pressure of 0.02 MPa.

[0113] Pour the mixed sodium carboxymethyl cellulose solution into an enamel dish, quickly take out the baked support film from the oven and immerse it in the carboxymethyl cellulose aqueous solution for 10 minutes;

[0114] Take out the impregnated support film and place it on a smooth and flat glass plate. After scraping it flat, put it into an oven together with the glass plate and bake it for 60 minutes at an oven temperature of 30°C and a pressure of 0.05 MPa.

[0115] Remove the support film from the oven. Grasp one end of the film with tweezers to peel it off the glass plate. Place it on another clean, smooth glass plate, bottom side up and top side down. Gently wipe off any excess sodium carboxymethyl cellulose on the surface with a damp, soft gauze.

[0116] (2) Weigh 0.5 g of sodium carboxymethyl cellulose using an electronic balance and add it to a beaker. Add 49.5 g of deionized water to the beaker and stir until the mixture is completely mixed. No undissolved particles or small lumps are observed with the naked eye. The resulting solution is homogeneous and transparent. After standing for a few minutes, almost no bubbles are observed in the solution.

[0117] (3) Take another clean beaker and add 10g of styrene-butadiene rubber latex. Use a dropper to take 2g 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%;

[0118] After stirring evenly, slowly add 498g of deionized water while stirring. After the deionized water is added, continue stirring for 30min at a stirring speed of 200rmin. At this time, the mass content of styrene-butadiene rubber in the casting solution is 0.8%. After stirring evenly, continue ultrasonic mixing for 60min.

[0119] Then use a sieve to filter out the demulsified rubber;

[0120] (4) The casting solution was scraped onto the surface of the support film using a 20 μm thick scraper to form a film with an initial coating layer thickness of 20 μm; the film was allowed to stand in air for 20 minutes before being formed, and then placed in an oven for further drying. The oven pressure was set to 0.06 MPa, the temperature was 60°C, and the drying time was 100 minutes;

[0121] Finally, the membrane was post-treated by washing it in an ultrasonic deionized water bath at an ultrasonic frequency of 35 Hz for 150 min. After washing, it was dried in an oven at a pressure of 0.05 MPa and a temperature of 90°C for 70 min.

[0122] Results In the prepared composite separation membrane, the thickness of the coating layer was 0.16 μm.

[0123] The composite separation membrane prepared by cutting into appropriate size was used to separate hexane and trace water in the cross-flow evaluation system. The water content of hexane in the raw liquid was 220ppm, and the hexane flux at the permeate end was 5.9L / m 2 / bar / h, the water content of hexane at the permeate end was 40ppm. After the experiment, the membrane was immersed in the hexane system for one month and then tested again. The hexane water content in the raw liquid was 220ppm, and the hexane flux at the permeate end was 6.0L / m 2 / bar / h, the water content in hexane at the permeate end is 40ppm.

[0124] This indicates that the composite separation membrane prepared by the method of the present invention has good stability in organic solvents.

[0125] Example 4

[0126] (1) Weigh 20 g of sodium carboxymethyl cellulose using an electronic balance and add it to a beaker. Add 980 g of deionized water to the beaker to prepare a 2% solution and stir thoroughly to mix.

[0127] The support film was placed in an oven and baked for 60 min at an oven temperature of 55°C and a pressure of 0.05 MPa.

[0128] Pour the mixed sodium carboxymethyl cellulose solution into an enamel dish, quickly take out the baked support film from the oven and immerse it in the carboxymethyl cellulose aqueous solution for 40 minutes;

[0129] Take out the impregnated support film and place it on a smooth and flat glass plate. After scraping it flat, put it into an oven together with the glass plate and bake it for 200 minutes at an oven temperature of 60°C and a pressure of 0.06 MPa.

[0130] Remove the support film from the oven. Grasp one end of the film with tweezers to peel it off the glass plate. Place it on another clean, smooth glass plate, bottom side up and top side down. Gently wipe off any excess sodium carboxymethyl cellulose on the surface with a damp, soft gauze.

[0131] (2) Weigh 0.3 g of sodium carboxymethyl cellulose using an electronic balance and add it to a beaker. Add 99.7 g of deionized water to the beaker and stir until the mixture is completely mixed. No undissolved particles or small lumps are observed with the naked eye. The resulting solution is homogeneous and transparent. After standing for a few minutes, almost no bubbles are observed in the solution.

[0132] (3) Take another clean beaker and add 10g of styrene-butadiene rubber latex. Use a dropper to take 1.4g 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 0.1%;

[0133] After stirring evenly, slowly add 388g of deionized water while stirring. After the deionized water is added, continue stirring for 10 minutes at a stirring speed of 500 rpm. At this time, the mass content of styrene-butadiene rubber in the casting solution is 1%. After stirring evenly, continue ultrasonic mixing for 30 minutes;

[0134] Then use a sieve to filter out the demulsified rubber;

[0135] (4) The casting solution was scraped onto the surface of the support film using a 20 μm thick scraper to form a film with an initial coating layer thickness of 20 μm. The film was allowed to stand in air for 17 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 55°C, and the drying time was 60 minutes. Finally, the film was post-treated by washing it in an ultrasonic deionized water bath at an ultrasonic frequency of 45 Hz for 200 minutes. After washing, it was placed in an oven for drying for 100 minutes at an oven pressure of 0.06 MPa and a temperature of 65°C.

[0136] Results In the prepared composite separation membrane, the thickness of the coating layer was 0.2 μm.

[0137] The composite separation membrane prepared by cutting into appropriate size was used to separate hexane and trace water in the cross-flow evaluation system. The water content of hexane in the raw liquid was 220ppm, and the hexane flux at the permeate end was 5.7L / m 2 / bar / h, the water content of hexane at the permeate end was 43ppm. After the experiment, the membrane was immersed in the hexane system for one month and then tested again. The hexane water content in the raw liquid was 220ppm, and the hexane flux at the permeate end was 5.8L / m 2 / bar / h, the water content in hexane at the permeate end is 43ppm.

[0138] This indicates that the composite separation membrane prepared by the method of the present invention has good stability in organic solvents.

[0139] Example 5

[0140] (1) Weigh 13 g of sodium carboxymethyl cellulose using an electronic balance and add it to a beaker. Add 987 g of deionized water to the beaker to prepare a 1.3% solution, and stir thoroughly to mix.

[0141] The support film was placed in an oven and baked for 20 minutes at an oven temperature of 50°C and a pressure of 0.035 MPa.

[0142] Pour the mixed sodium carboxymethyl cellulose solution into an enamel dish, quickly take out the baked support film from the oven and immerse it in the carboxymethyl cellulose aqueous solution for 25 minutes;

[0143] Take out the impregnated support film and place it on a smooth and flat glass plate. After scraping it flat, put it into an oven together with the glass plate and bake it for 120 minutes at an oven temperature of 45°C and a pressure of 0.035 MPa.

[0144] Remove the support film from the oven. Grasp one end of the film with tweezers to peel it off the glass plate. Place it on another clean, smooth glass plate, bottom side up and top side down. Gently wipe off any excess sodium carboxymethyl cellulose on the surface with a damp, soft gauze.

[0145] (2) Weigh 0.8 g of sodium carboxymethyl cellulose using an electronic balance and add it to a beaker. Add 99.2 g of deionized water to the beaker and stir until the mixture is completely mixed. No undissolved particles or small lumps are observed with the naked eye. The resulting solution is homogeneous and transparent. After standing for a few minutes, almost no bubbles are observed in the solution.

[0146] (3) Take another clean beaker and add 10g of styrene-butadiene rubber latex. Use a dropper to take 1g 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 0.2%;

[0147] After stirring evenly, slowly add 789g of deionized water while stirring. After the deionized water is added, continue stirring for 20 minutes at a stirring speed of 350rmin. At this time, the mass content of styrene-butadiene rubber in the casting solution is 0.5%. After stirring evenly, continue ultrasonic mixing for 25 minutes;

[0148] Then use a sieve to filter out the demulsified rubber;

[0149] (4) The casting solution was scraped onto the surface of the support film using a 20 μm thick scraper to form a film with an initial coating layer thickness of 20 μm; the film 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 0.035 MPa, the temperature was 40°C, and the drying time was 90 minutes;

[0150] Finally, the membrane was post-treated by washing it in an ultrasonic deionized water bath at an ultrasonic frequency of 40 Hz for 130 min. After washing, it was placed in an oven to dry for 30 min at a pressure of 0.045 MPa and a temperature of 60°C.

[0151] Results In the prepared composite separation membrane, the thickness of the coating layer was 0.1 μm.

[0152] The composite separation membrane prepared by cutting into appropriate size was used to separate hexane and trace water in the cross-flow evaluation system. The water content of hexane in the raw liquid was 220ppm, and the hexane flux at the permeate end was 6.5L / m 2 / bar / h, the water content of hexane at the permeate end was 44ppm. After the experiment, the membrane was immersed in the hexane system for one month and then tested again. The hexane water content in the raw liquid was 220ppm, and the hexane flux at the permeate end was 6.6L / m 2 / bar / h, the water content in hexane at the permeate end is 45ppm.

[0153] This indicates that the composite separation membrane prepared by the method of the present invention has good stability in organic solvents.

[0154] Comparative Example 1

[0155] (1) Weigh 0.5 g of sodium carboxymethyl cellulose using an electronic balance and add it to a beaker. Add 99.5 g of deionized water to the beaker and stir until the mixture is completely mixed. No undissolved particles or small lumps are observed with the naked eye. The resulting solution is homogeneous and transparent. After standing for a few minutes, almost no bubbles are observed in the solution.

[0156] (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 0.3%;

[0157] After stirring evenly, slowly add 653g of deionized water while stirring. After the deionized water is added, continue stirring for 15 minutes at a stirring speed of 400 rpm. At this time, the mass content of styrene-butadiene rubber in the casting solution is 0.6%. After stirring evenly, continue ultrasonic mixing for 50 minutes;

[0158] Then use a sieve to filter out the demulsified rubber;

[0159] (3) The casting solution was scraped onto the surface of the untreated support film using a 20 μm thick scraper to form a film with an initial coating layer thickness of 20 μm. The film was allowed to stand in air for 15 minutes before being formed and then placed in an oven for further drying. The oven pressure was set to 0.04 MPa, the temperature was 50°C, and the drying time was 150 minutes. Finally, the film 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 again for 50 minutes at an oven pressure of 0.04 MPa and a temperature of 80°C.

[0160] Results In the prepared composite separation membrane, the thickness of the coating layer was 0.12 μm;

[0161] The composite separation membrane prepared by cutting into appropriate size was used to separate hexane and trace water in the cross-flow evaluation system. The water content of hexane in the raw liquid was 220ppm, and the hexane flux at the permeate end was 4.6L / m 2 / bar / h, the water content of hexane at the permeate end was 42ppm. After the experiment, the membrane was immersed in the hexane system for one month and then tested again. The hexane water content in the raw liquid was 220ppm, and the hexane flux at the permeate end was 4.8L / m 2 / bar / h, the water content in hexane at the permeate end is 42ppm.

[0162] This indicates that direct coating of an untreated support membrane will cause some rubber latex particles to enter the voids, blocking the pores and reducing the flux of the membrane.

[0163] Comparative Example 2

[0164] (1) Weigh 10 g of sodium carboxymethyl cellulose using an electronic balance and add it to a beaker. Add 990 g of deionized water to the beaker to prepare a 1% solution and stir thoroughly to mix.

[0165] The support film was placed in an oven and baked for 40 minutes at an oven temperature of 60°C and a pressure of 0.04 MPa.

[0166] Pour the mixed sodium carboxymethyl cellulose solution into an enamel dish, quickly take out the baked support film from the oven and immerse it in the carboxymethyl cellulose aqueous solution for 20 minutes;

[0167] Take out the impregnated support film and place it on a smooth and flat glass plate. After scraping it flat, put it into an oven together with the glass plate and bake it for 100 minutes at an oven temperature of 40°C and a pressure of 0.03 MPa.

[0168] (2) Weigh 0.5 g of sodium carboxymethyl cellulose using an electronic balance and add it to a beaker. Add 99.5 g of deionized water to the beaker and stir until the mixture is completely mixed. No undissolved particles or small lumps are observed with the naked eye. The resulting solution is homogeneous and transparent. After standing for a few minutes, almost no bubbles are observed in the solution.

[0169] (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 the sodium carboxymethyl cellulose to the mass of the dry styrene-butadiene rubber is 0.3%. After stirring evenly, slowly add 653g of deionized water while stirring. After the deionized water is added, continue stirring for 15 minutes at a stirring speed of 400 rpm. At this time, the mass content of the dry styrene-butadiene rubber in the mixture is 0.6%. After stirring evenly, continue ultrasonic mixing for 50 minutes. Then filter out the demulsified rubber with a sieve;

[0170] (4) Remove the support film from the oven, grasp one end of the film with tweezers, peel it off from the glass plate, and place it on another clean, smooth glass plate with the bottom surface facing up and the top surface facing down;

[0171] Compared with Example 1, the excess sodium carboxymethyl cellulose on the surface was not wiped off with a soft wet gauze. Instead, the casting solution was directly coated on the surface of the support membrane with a 20 μm thick scraper to form a film, thereby obtaining a coating layer with an initial thickness of 20 μm.

[0172] (5) The film was formed after standing in air for 15 minutes and then placed in an oven for further drying. The oven pressure was set to 0.04 MPa, the temperature was 50°C, and the drying time was 150 minutes.

[0173] Finally, the membrane was post-treated by washing it in an ultrasonic deionized water bath at an ultrasonic frequency of 40 Hz for 100 min, and then drying it in an oven at a pressure of 0.04 MPa and a temperature of 80°C for 50 min.

[0174] Results In the prepared composite separation membrane, the thickness of the coating layer was 0.12 μm.

[0175] The composite separation membrane prepared by cutting into appropriate size was used to separate hexane and trace water in the cross-flow evaluation system. The water content of hexane in the raw liquid was 220ppm, and the hexane flux at the permeate end was 6.0L / m 2 / bar / h, the water content in hexane at the permeate end was 42ppm. After the experiment, the membrane was immersed in the hexane system for one month. It was found that part of the functional layer of the membrane was peeling off from the support layer. The experiment was repeated. The hexane water content in the raw liquid was 220ppm, and the hexane flux at the permeate end was 9.4L / m 2 / bar / h, and the water content in hexane at the permeate end was 160ppm, indicating that the functional layer of the membrane was partially damaged and the membrane lost its retention function.

[0176] Comparative Example 3

[0177] (1) Weigh 10 g of sodium carboxymethyl cellulose using an electronic balance and add it to a beaker. Add 990 g of deionized water to the beaker to prepare a 1% solution and stir thoroughly to mix.

[0178] Place the support film in an oven and bake for 40 minutes at a temperature of 60°C and a pressure of 0.04 MPa.

[0179] Pour the mixed sodium carboxymethyl cellulose solution into an enamel dish, quickly take out the baked support film from the oven and immerse it in the carboxymethyl cellulose aqueous solution for 20 minutes;

[0180] Take out the impregnated support film and place it on a smooth and flat glass plate. After scraping it flat, put it into an oven together with the glass plate and bake it for 100 minutes at an oven temperature of 40°C and a pressure of 0.03 MPa.

[0181] Remove the support film from the oven. Grasp one end of the film with tweezers to peel it off the glass plate. Place it on another clean, smooth glass plate, bottom side up and top side down. Gently wipe off any excess sodium carboxymethyl cellulose on the surface with a damp, soft gauze.

[0182] (2) Weigh 0.5 g of sodium carboxymethyl cellulose using an electronic balance and add it to a beaker. Add 99.5 g of deionized water to the beaker and stir until the mixture is completely mixed. No undissolved particles or small lumps are observed with the naked eye. The resulting solution is homogeneous and transparent. After standing for a few minutes, almost no bubbles are observed in the solution.

[0183] (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 0.3%;

[0184] After stirring evenly, slowly add 653g of deionized water while stirring. After the deionized water is added, continue stirring for 15 minutes at a stirring speed of 400 rpm. At this time, the mass content of styrene-butadiene rubber in the casting solution is 0.6%. After stirring evenly, continue ultrasonic mixing for 50 minutes;

[0185] Then use a sieve to filter out the demulsified rubber;

[0186] (4) The casting solution was scraped onto the surface of the support film using a 20 μm thick scraper to form a film with an initial coating layer thickness of 20 μm. The film was allowed to stand in air for 15 minutes before being formed and then placed in an oven for further drying. The oven pressure was set to 0.04 MPa, the temperature was 50°C, and the drying time was 150 minutes. Finally, the film was post-treated by washing it in an ultrasonic deionized water bath at an ultrasonic frequency of 40 Hz for 10 minutes. After washing, it was placed in an oven for drying again for 50 minutes at an oven pressure of 0.04 MPa and a temperature of 80°C.

[0187] Compared with Example 1, the membrane ultrasonic cleaning time is greatly shortened;

[0188] Results In the prepared composite separation membrane, the thickness of the coating layer was 0.12 μm.

[0189] The composite separation membrane prepared by cutting into appropriate size was used to separate hexane and trace water in the cross-flow evaluation system. The water content of hexane in the raw liquid was 220ppm, and the hexane flux at the permeate end was 3.3L / m 2 / bar / h, the water content of hexane at the permeate end was 42ppm. After the experiment, the membrane was immersed in the hexane system for one month and then tested again. The hexane water content in the raw liquid was 220ppm, and the hexane flux at the permeate end was 4.4L / m 2 / bar / h, the water content in hexane at the permeate end is 43ppm.

[0190] This indicates that the cleaning time is not long enough, and the sodium carboxymethyl cellulose in the supporting membrane pores will block the membrane pores, greatly reducing the membrane flux.

[0191] Comparative Example 4

[0192] 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 (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.

[0193] Results In the prepared composite separation membrane, the thickness of the coating layer was 0.12 μm.

[0194] The composite separation membrane prepared by cutting into appropriate size was used to separate hexane and trace water in the cross-flow evaluation system. The water content of hexane in the raw liquid was 220ppm, and the hexane flux at the permeate end was 10L / m 2 / bar / h, the water content of hexane at the permeate end was 180ppm. After the experiment, the membrane was immersed in the hexane system for one month and then the experiment was repeated. The water content of hexane in the raw liquid was 220ppm, and the hexane flux at the permeate end was 20L / m 2 / bar / h, the water content in hexane at the permeate end is 220ppm.

[0195] The membrane had no rejection performance compared to Example 1.

[0196] 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.

[0197] 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 modified support layer and a coating layer sequentially coated on the surface of the support layer; The modified support layer is formed by drying a mixed solution of a water-soluble high molecular polymer and deionized water; The coating layer is obtained by coating a casting liquid on the surface of the modified support layer and then performing post-treatment and drying, wherein the casting liquid contains emulsified rubber, a water-soluble high molecular polymer and deionized water; And the holes inside the supporting layer are impregnated with water-soluble high molecular polymer.

2. The composite separation membrane according to claim 1, wherein The casting solution consists of emulsified rubber, water-soluble high molecular polymer and deionized water; Preferably, in the casting solution, the weight ratio of the water-soluble high molecular polymer to the dry rubber in the emulsified rubber is (0.01-1):100, preferably (0.01-0.6):100, and more preferably (0.1-0.5):

100.

3. The composite separation membrane according to claim 1 or 2, wherein The emulsified rubber is styrene-butadiene latex and / or nitrile-butadiene latex; Preferably, the gel content in the emulsified rubber is 50-99%, preferably 70-95%; Preferably, the particle size of the rubber in the emulsified rubber is 10-1000 nm, preferably 50-200 nm; Preferably, the mass concentration of rubber in the emulsified rubber 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. The composite separation membrane according to claim 1 , wherein 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 10-100 nm, preferably 20-60 nm, more preferably 30-50 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 0.1-0.2 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) pre-treating the support layer by immersing the support layer in a mixed solution of a first water-soluble polymer and deionized water, and drying the immersed support layer to obtain a modified support layer; (2) performing a second mixing of the second water-soluble polymer and deionized water to prepare a second polymer aqueous solution; (3) mixing the second high molecular polymer aqueous solution and the emulsified rubber for a third time and then subjecting the mixture to ultrasonic treatment 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 modified support layer and subjected to post-treatment to obtain a composite separation membrane.

9. The preparation method according to claim 8, wherein In step (1), the conditions for the immersion include: the immersion time is 1-100 min; And / or, in step (1), before immersing the support layer in the mixed solution of the first water-soluble polymer and deionized water, the support layer needs to be dried; and / or, the first high molecular weight polymer and the second high molecular weight polymer are the same or different, and are each selected from one or more of sodium carboxymethyl cellulose, sodium polyacrylate, sodium alginate, sodium polymethacrylate and sodium polyphosphate; And / or, the weight concentration of the first high molecular polymer aqueous solution is 0.1-10%; the mass concentration of the second high molecular polymer aqueous solution is 0.1-5%; And / or, in step (3), the conditions of the third mixing include: a stirring rate of 10-1000 rpm, a time of the third mixing of 1-100 min, and a time of the ultrasonication of 10-600 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 drying time of 10-1000 min; Preferably, the ultrasonic cleaning time is 30-1000 min.

10. The preparation method according to claim 9, wherein The preparation method further comprises: in step (4), subjecting the membrane after the ultrasonic treatment 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 sieve having a mesh size of 40-2800 meshes, preferably 50-500 meshes.

12. Use of the composite separation membrane according to any one of claims 1 to 7 in separating polar impurities in a non-polar organic solvent.