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 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 technical 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] 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.

[0003] The research groups of Andrew G. Livingston at Imperial College London and Tai-Shung Chung at the National University of Singapore have been at the forefront of scientific research and industry, providing guidance for the commercialization of OSN membranes. Their innovative OSN membranes and preparation methods are based on materials such as polyimide, polyaniline, polyetheretherketone, polybenzimidazole, and polydimethylsiloxane.

[0004] Researchers in related fields around the world have conducted research on organic solvent-resistant nanofiltration membranes.

[0005] CN104689716A and CN104689717A use cross-linked polyarylether polymers and cross-linked polyethersulfone polymers as membrane materials to prepare organic solvent-resistant membranes.

[0006] 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. The organic solvents volatilized by this preparation method are also very harmful to the researchers' health. In addition, the membranes prepared by the general phase change method require further cross-linking to have strong solvent resistance, and the preparation process is complicated.

[0007] Also have a part report to adopt the method for interfacial polymerization, this method film making time is long, and organic phase also uses organic solvent.Along with the progress of mankind, environmentally friendly film making method is more and more paid attention to, and CN1640534A adopts the method for concentrated emulsion polymerization to prepare a kind of preferential dealcoholization film, and this film making method avoids the use of a large amount of organic solvents.But the film thickness prepared by high concentration emulsion is often thicker, and permeation flux can be greatly restricted.

[0008] Most of the organic solvent-resistant membrane materials reported so far are plastic or fiber-based. Only cross-linked polydimethylsiloxane (silicone rubber) has been reported, and other rubber materials have not been reported. This is partly 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.

[0009] 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

[0010] 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.

[0011] 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;

[0012] The casting solution contains rubber latex, water-soluble high molecular polymer and deionized water.

[0013] A second aspect of the present invention provides a method for preparing the aforementioned composite separation membrane, wherein the preparation method comprises:

[0014] (1) first mixing a water-soluble polymer and deionized water to prepare a polymer aqueous solution;

[0015] (2) mixing the polymer aqueous solution and rubber latex for a second time and then subjecting the mixture to a first ultrasonic treatment to obtain a mixed solution; and diluting the mixed solution with deionized water to obtain a casting solution;

[0016] (3) The casting solution is coated on the surface of the support layer and subjected to post-treatment to obtain a composite separation membrane.

[0017] 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.

[0018] Through the above technical solution, the technical solution of the present invention has the following beneficial effects:

[0019] (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;

[0020] (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;

[0021] (3) The composite separation membrane prepared by the present invention has good stability in organic solvents. DETAILED DESCRIPTION

[0022] 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.

[0023] 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;

[0024] The casting solution contains rubber latex, water-soluble high molecular polymer and deionized water.

[0025] 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.

[0026] 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.

[0027] According to the present invention, preferably, the casting solution consists of rubber latex, water-soluble high molecular polymer and deionized water.

[0028] 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.

[0029] 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 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.

[0030] 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.

[0031] According to the present invention, the particle size of the rubber in the rubber latex 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 rubber 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 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.

[0032] 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.

[0033] 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 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] A second aspect of the present invention provides a method for preparing the aforementioned composite separation membrane, wherein the preparation method comprises:

[0040] (1) first mixing a water-soluble polymer and deionized water to prepare a polymer aqueous solution;

[0041] (2) mixing the polymer aqueous solution and rubber latex for a second time and then subjecting the mixture to a first ultrasonic treatment to obtain a mixed solution; and diluting the mixed solution with deionized water to obtain a casting solution;

[0042] (3) The casting solution is coated on the surface of the support layer and subjected to post-treatment to obtain a composite separation membrane.

[0043] According to the present invention, in step (1), the mass concentration of the high molecular weight polymer aqueous solution is 0.1-5%, preferably 0.2-2%, and more preferably 0.3-1%. In the present invention, the above mass concentration is selected so that the water-soluble polymer can be more evenly dissolved in deionized water, and the moderate viscosity can be better mixed with the rubber latex.

[0044] According to the present invention, during the preparation of the casting solution, a water-soluble high molecular polymer 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 can reduce rubber demulsification on the other hand. Specifically, in step (2), under stirring conditions, the high molecular polymer aqueous solution and rubber latex are subjected to a second mixing to prepare a casting solution with a certain rubber concentration. Wherein, the conditions of the second mixing include: a stirring speed of 10-1000rpm, preferably 100-600rpm, more preferably 200-500rpm; a time of the second mixing of 1-100min, preferably 5-60min, more preferably 10-30min; ultrasonic mixing is continued after high-speed stirring, and the time of the first ultrasound is 10-600min, preferably 10-100min, more preferably 20-60min; in addition, in a more preferred case, the ultrasonic intensity of the first ultrasound is 28-100Hz, preferably 30-60Hz, more preferably 35-50Hz.

[0045] 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 mesh screen having a mesh size of 40-2800 mesh, preferably 50-500 mesh, and more preferably 80-200 mesh, so as to better remove demulsified rubber particles from the casting solution.

[0046] According to the present invention, in step (3), the casting solution is coated on the surface of the support layer, and 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.

[0047] According to the present invention, in step (3), 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.

[0048] 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. This ensures 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.

[0049] 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.

[0050] According to the present invention, the dried membrane requires further post-treatment to remove water-soluble polymers and emulsifiers from the rubber. This is accomplished by placing the membrane in deionized water and performing a second ultrasonic cleaning. 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 second ultrasonic cleaning duration 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.

[0051] 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.

[0052] 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:

[0053] 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;

[0054] 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;

[0055] Finally, the prepared membrane is washed to remove the water-soluble high molecular polymer and the emulsifier in the rubber latex.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] Specifically, the present invention provides an application of the aforementioned composite separation membrane in separating trace polar impurities in a non-polar organic solvent.

[0060] According to the present invention, preferably, the separation of hexane and trace amounts of water is targeted.

[0061] The present invention will be described in detail below through examples.

[0062] In the following examples and comparative examples:

[0063] 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%.

[0064] Sodium carboxymethyl cellulose, purchased from Innochem, brand name Innochem A05925, MW 250000 (DS = 0.9), 1500-3100 mPa.s.

[0065] The ultrafiltration support membrane used was cross-linked polyacrylonitrile, with an average pore size of 20 nm and a thickness of 120 μm.

[0066] All filter screens are 100-mesh stainless steel screens.

[0067] 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. 2The 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.

[0068] The oven was purchased from Tester, model DZ-IBCIV.

[0069] Example 1

[0070] This embodiment is intended to illustrate the composite separation membrane prepared by the method of the present invention.

[0071] (1) 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.

[0072] (2) Take another clean beaker and add 10g of styrene-butadiene rubber latex (the rubber content in the latex is 40wt%, and the calculated dry styrene-butadiene rubber is 4g), and use a dropper to take 4g of the prepared sodium carboxymethyl cellulose solution (4g×0.3%=0.012g) and add it to the styrene-butadiene latex. At this time, the mass ratio of sodium carboxymethyl cellulose to the dry styrene-butadiene rubber is 0.3% (0.012g÷4g=0.3%);

[0073] After stirring evenly, slowly add 557g of deionized water while stirring. After the deionized water is added, continue stirring for 20 minutes at a stirring speed of 300 rpm. At this time, the mass content of dry styrene-butadiene rubber in the casting solution is 0.7%. After stirring evenly, continue ultrasonic mixing for 40 minutes;

[0074] (3) The demulsified rubber was then filtered out using a 100-mesh stainless steel mesh screen, and a 20-μm-thick scraper was used to scrape the surface of the ultrafiltration membrane to form a film, obtaining a coating layer with an initial 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 0.04 MPa, the temperature was 50°C, and the drying time was 100 minutes.

[0075] Finally, the membrane was post-treated. Under the condition of ultrasonic frequency of 40 Hz, the membrane was placed in an ultrasonic deionized water bath for cleaning for 60 minutes. After cleaning, it was placed in an oven for drying for 60 minutes. The oven pressure was 0.05 MPa and the temperature was 80°C.

[0076] Results The thickness of the coating layer of the prepared composite separation membrane was 0.14 μm.

[0077] 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 value of hexane in the raw liquid (the water content in hexane) was 200ppm, and the hexane flux at the permeate end was 5.1L / 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 200ppm, and the hexane flux at the permeate end was 5.2L / m 2 / bar / h, the water content in hexane at the permeate end is 40ppm.

[0078] This indicates that the composite separation membrane prepared by the method of the present invention has good stability in organic solvents.

[0079] Example 2

[0080] (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.

[0081] (2) Take another clean beaker and add 10g of styrene-butadiene rubber latex (the rubber content in the latex is 40wt%, and the calculated dry styrene-butadiene rubber is 4g). Use a dropper to take 4g of the prepared sodium carboxymethyl cellulose solution and add it to the styrene-butadiene latex. At this time, the mass ratio of sodium carboxymethyl cellulose to dry styrene-butadiene rubber is 0.5%.

[0082] After stirring evenly, slowly add 786g of deionized water while stirring. After the deionized water is added, continue stirring for 30 minutes at a stirring speed of 450 rpm. At this time, the mass content of dry styrene-butadiene rubber in the casting solution is 0.5%. After stirring evenly, continue ultrasonic mixing for 50 minutes;

[0083] (3) The demulsified rubber was then filtered out using a 100-mesh stainless steel mesh screen, and a 20-μm-thick scraper was used to scrape the surface of the ultrafiltration membrane to form a film, obtaining a coating layer with an initial 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 0.06 MPa, the temperature was 60°C, and the drying time was 150 minutes.

[0084] Finally, the membrane was post-treated by washing it in an ultrasonic deionized water bath at an ultrasonic frequency of 50 Hz for 30 min, and then drying it in an oven at a pressure of 0.06 MPa and a temperature of 90°C for 30 min.

[0085] Results The thickness of the coating layer of the prepared composite separation membrane was 0.1 μm.

[0086] 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 200ppm, and the hexane flux at the permeate end was 6.2L / m 2 / bar / h, the water content of hexane at the permeate end was 45ppm. 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 200ppm, and the hexane flux at the permeate end was 6.3L / m 2 / bar / h, the water content in hexane at the permeate end is 46ppm.

[0087] This indicates that the composite separation membrane prepared by the method of the present invention has good stability in organic solvents.

[0088] Example 3

[0089] (1) 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.

[0090] (2) Take another clean beaker and add 10g of styrene-butadiene rubber latex (the rubber content in the latex is 40wt%, and the calculated dry styrene-butadiene rubber is 4g). Use a dropper to take 0.4g of the prepared sodium carboxymethyl cellulose solution and add it to the styrene-butadiene latex. At this time, the mass ratio of sodium carboxymethyl cellulose to dry styrene-butadiene rubber is 0.1%.

[0091] After stirring evenly, slowly add 390g 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 dry styrene-butadiene rubber in the casting solution is 1%. After stirring evenly, continue ultrasonic mixing for 20 minutes;

[0092] (3) The demulsified rubber was then filtered out using a 100-mesh stainless steel sieve, and a 20-μm-thick scraper was used to scrape the surface of the ultrafiltration membrane to form a film, obtaining a coating layer with an initial thickness of 20 μm. The membrane was allowed to stand in air for 10 minutes before forming, and then placed in an oven for further drying. The oven pressure was set to 0.03 MPa, the temperature was 40°C, and the drying time was 200 minutes.

[0093] 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, and then drying it in an oven at a pressure of 0.03 MPa and a temperature of 60°C for 100 min.

[0094] Results The thickness of the coating layer of the prepared composite separation membrane was 0.2 μm.

[0095] 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 200ppm, and the hexane flux at the permeate end was 4.1L / m 2 / bar / h, the water content of hexane at the permeate end was 37ppm. 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 200ppm, and the hexane flux at the permeate end was 4.2L / m 2 / bar / h, the water content in hexane at the permeate end is 37ppm.

[0096] This indicates that the composite separation membrane prepared by the method of the present invention has good stability in organic solvents.

[0097] Example 4

[0098] (1) Weigh 0.35 g of sodium carboxymethyl cellulose using an electronic balance and add it to a beaker. Add 49.65 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.

[0099] (2) Take another clean beaker and add 10g of styrene-butadiene rubber latex (the rubber content in the latex is 40wt%, and the calculated dry styrene-butadiene rubber is 4g). Use a dropper to take 2.3g of the prepared sodium carboxymethyl cellulose solution and add it to the styrene-butadiene latex. At this time, the mass ratio of sodium carboxymethyl cellulose to dry styrene-butadiene rubber is 0.4%.

[0100] After stirring evenly, slowly add 487g of deionized water while stirring. After the deionized water is added, continue stirring for 15 minutes at a stirring speed of 200 rpm. At this time, the mass content of dry styrene-butadiene rubber in the casting solution is 0.8%. After stirring evenly, continue ultrasonic mixing for 60 minutes;

[0101] (3) The demulsified rubber was then filtered out using a 100-mesh stainless steel mesh sieve, and a 20-μm-thick scraper was used to scrape the surface of the ultrafiltration membrane to form a film, obtaining a coating layer with an initial thickness of 20 μm. The membrane was allowed to stand in air for 17 minutes before forming, and then placed in an oven for further drying. The oven pressure was set to 0.05 MPa, the temperature was 45°C, and the drying time was 120 minutes.

[0102] Finally, the membrane was post-treated by washing it in an ultrasonic deionized water bath at an ultrasonic frequency of 45 Hz for 80 min, and then drying it in an oven at a pressure of 0.04 MPa and a temperature of 70°C for 80 min.

[0103] Results The thickness of the coating layer of the prepared composite separation membrane was 0.16 μm.

[0104] 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 200ppm, and the hexane flux at the permeate end was 4.9L / m 2 / bar / h, the water content of hexane at the permeate end was 39ppm. After the experiment, the membrane was immersed in the hexane system for one month and then the experiment was repeated. The hexane water content in the raw liquid was 200ppm, and the hexane flux at the permeate end was 5L / m 2 / bar / h, the water content in hexane at the permeate end is 39ppm.

[0105] This indicates that the composite separation membrane prepared by the method of the present invention has good stability in organic solvents.

[0106] Example 5

[0107] (1) Weigh 0.2 g of sodium carboxymethyl cellulose using an electronic balance and add it to a beaker. Add 49.8 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.

[0108] (2) Take another clean beaker and add 10g of styrene-butadiene rubber latex (the rubber content in the latex is 40wt%, and the calculated dry styrene-butadiene rubber is 4g). Use a dropper to take 2g of the prepared sodium carboxymethyl cellulose solution and add it to the styrene-butadiene latex. At this time, the mass ratio of sodium carboxymethyl cellulose to dry styrene-butadiene rubber is 0.2%.

[0109] After stirring evenly, slowly add 654g of deionized water while stirring. After the deionized water is added, continue stirring for 25 minutes at a stirring speed of 350rpm. At this time, the mass content of dry styrene-butadiene rubber in the casting solution is 0.6%. After stirring evenly, continue ultrasonic mixing for 30 minutes;

[0110] (3) The demulsified rubber was then filtered out using a 100-mesh stainless steel mesh sieve, and a 20-μm-thick scraper was used to scrape the surface of the ultrafiltration membrane to form a film, obtaining a coating layer with an initial thickness of 20 μm. The membrane was allowed to stand in air for 13 minutes before forming, and then placed in an oven for further drying. The oven pressure was set to 0.035 MPa, the temperature was 55°C, and the drying time was 60 minutes.

[0111] Finally, the membrane was post-treated by washing it in an ultrasonic deionized water bath at an ultrasonic frequency of 38 Hz for 200 min. After washing, it was placed in an oven and dried again for 70 min at a pressure of 0.035 MPa and a temperature of 75°C.

[0112] Results The thickness of the coating layer of the prepared composite separation membrane was 0.12 μm.

[0113] 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 200ppm, and the hexane flux at the permeate end was 5.5L / 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 200ppm, and the hexane flux at the permeate end was 5.6L / m 2 / bar / h, the water content in hexane at the permeate end is 43ppm.

[0114] This indicates that the composite separation membrane prepared by the method of the present invention has good stability in organic solvents.

[0115] Comparative Example 1

[0116] (1) Take a clean beaker and add 10g of styrene-butadiene rubber latex, slowly add 561g of deionized water, and stir while adding. After the deionized water is added, continue stirring for 20 minutes at a stirring speed of 300 rpm. At this time, the mass content of dry styrene-butadiene rubber is 0.7%. After stirring evenly, continue ultrasonic mixing for 40 minutes.

[0117] (2) The demulsified rubber was filtered out using a 100-mesh stainless steel sieve. Compared with Example 1, the demulsified styrene-butadiene rubber increased significantly.

[0118] A 20 μm thick scraper was used to scrape the surface of the ultrafiltration membrane to form a film, obtaining a coating layer with an initial thickness of 20 μm; the membrane was formed after standing in the 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 100 minutes.

[0119] Finally, the membrane was post-treated by washing it in an ultrasonic deionized water bath at an ultrasonic frequency of 40 Hz for 60 min, and then drying it in an oven again at a pressure of 0.05 MPa and a temperature of 80°C for 60 min.

[0120] Results The thickness of the coating layer of the prepared composite separation membrane was 0.14 μm.

[0121] 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 200ppm, and the hexane flux at the permeate end was 6.1L / m 2 / bar / h, the water content of hexane at the permeate end was 120ppm. Compared with Example 1, the uniformity of the prepared membrane was not good, the water content of the hexane solvent at the permeate end increased significantly, and the retention rate of the membrane was significantly reduced. After the experiment, the membrane was immersed in the hexane system for one month and then the experiment was repeated. The hexane water content in the raw material solution was 200ppm, and the hexane flux at the permeate end was 7L / m 2 / bar / h, the water content in hexane at the permeate end is 150ppm.

[0122] The results showed that the prepared composite separation membrane had poor uniformity and the overly thin membrane lost its retention performance after being swollen by the solvent, indicating that the addition of water-soluble polymer sodium carboxymethyl cellulose can make the latex particles evenly distributed. In Comparative Example 1, since no water-soluble polymer sodium carboxymethyl cellulose was added, the latex particles were unevenly distributed, resulting in increased membrane defects.

[0123] Comparative Example 2

[0124] (1) 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 can be observed with the naked eye. The resulting solution is uniform and transparent. After a few minutes, almost no bubbles can be observed in the solution.

[0125] (2) In another clean beaker, add 10 g of styrene-butadiene rubber latex. Using a dropper, add 4 g of the prepared sodium carboxymethyl cellulose solution to the styrene-butadiene rubber latex. The mass ratio of sodium carboxymethyl cellulose to dry styrene-butadiene rubber is now 0.3%. Stir thoroughly and continue ultrasonic mixing for 40 minutes. The dry styrene-butadiene rubber content in the casting solution is now 28.6%.

[0126] (3) 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 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 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 60 minutes. After washing, it was placed in an oven for drying for 60 minutes at a pressure of 0.05 MPa and a temperature of 80°C.

[0127] Results The thickness of the coating layer of the prepared composite separation membrane was 5.72 μm.

[0128] 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 200ppm, and the hexane flux at the permeate end was 0.6L / m 2 / bar / h, the water content of hexane at the permeate end was 20ppm. 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 200ppm, and the hexane flux at the permeate end was 0.7L / m 2 / bar / h, the water content in hexane at the permeate end is 20ppm.

[0129] This indicates that the concentration of the casting solution is too high, which seriously affects the permeation flux of the membrane.

[0130] Comparative Example 3

[0131] (1) 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 can be observed with the naked eye. The resulting solution is uniform and transparent. After a few minutes, almost no bubbles can be observed in the solution.

[0132] (2) Take another clean beaker and add 10g of homemade styrene-butadiene latex with low crosslinking degree (latex particle size is 100nm, rubber content in latex is 40wt%). The gel content is about 30% when tested with tetrahydrofuran. Use a dropper to take 4g of the prepared sodium carboxymethyl cellulose solution and add it to the styrene-butadiene latex. At this time, the mass ratio of sodium carboxymethyl cellulose to dry styrene-butadiene rubber is 0.3%.

[0133] After stirring evenly, slowly add 557g 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 dry styrene-butadiene rubber in the casting liquid is 0.7%. After stirring evenly, continue ultrasonic mixing for 40 minutes.

[0134] (3) The demulsified rubber was then filtered out using a 100-mesh stainless steel sieve, and a 20-μm-thick scraper was used to scrape the ultrafiltration membrane surface to form a film, obtaining a membrane with an initial coating layer thickness of 20 μm. The membrane was allowed to stand in the air for 15 minutes to form, 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 100 minutes.

[0135] Finally, the membrane was post-treated. Under the condition of ultrasonic frequency of 40 Hz, the membrane was placed in an ultrasonic deionized water bath for cleaning for 60 minutes. After cleaning, it was placed in an oven for drying for 60 minutes. The oven pressure was 0.05 MPa and the temperature was 80°C.

[0136] Results The thickness of the coating layer of the prepared composite separation membrane was 0.14 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 200ppm, and the hexane flux at the permeate end was 6.1L / m 2 / bar / h, the water content of hexane at the permeate end was 80ppm. 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 200ppm, and the hexane flux at the permeate end was 9.2L / m 2 / bar / h, the water content in hexane at the permeate end is 200ppm.

[0138] This indicates that ordinary styrene-butadiene latex with low cross-linking degree will be dissolved when immersed in hexane solvent, and the membrane's retention capacity will be lost.

[0139] Comparative Example 4

[0140] (1) 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 can be observed with the naked eye. The resulting solution is uniform and transparent. After a few minutes, almost no bubbles can be observed in the solution.

[0141] (2) Take another clean beaker and add 10g of styrene-butadiene rubber latex. Use a dropper to take 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%.

[0142] After stirring evenly, slowly add 557g 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 dry styrene-butadiene rubber in the casting liquid is 0.7%. After stirring evenly, continue ultrasonic mixing for 40 minutes.

[0143] (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 15 minutes before forming and was further dried in an oven at a pressure of 0.04 MPa, a temperature of 50°C, and a drying time of 100 minutes. No post-treatment was performed on the membrane.

[0144] Results The thickness of the coating layer of the prepared composite separation membrane was 0.14 μm.

[0145] 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 200ppm, and the hexane flux at the permeate end was 4.1L / 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 200ppm, and the hexane flux at the permeate end was 4.3L / m 2 / bar / h, the water content in hexane at the permeate end is 42ppm.

[0146] This shows that post-treatment of the membrane can significantly increase the flux of the composite separation membrane.

[0147] 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.

[0148] 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 and deionized water.

2. The composite separation membrane according to claim 1, wherein The casting solution consists of rubber latex, 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 rubber latex 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 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. 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 0.1-0.2 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) first mixing a water-soluble polymer and deionized water to prepare a polymer aqueous solution; (2) mixing the polymer aqueous solution and rubber latex for a second time and then subjecting the mixture to a first ultrasonic treatment to obtain a mixed solution; and diluting the mixed solution with deionized water to obtain a casting solution; (3) The casting solution is coated on the surface of the 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 mass concentration of the high molecular weight polymer aqueous solution is 0.1-5%; And / or, in step (2), the second mixing conditions include: a stirring rate of 10-1000 rpm, a second mixing time of 1-100 min, and a first ultrasonic time of 10-600 min; And / or, in step (3), the post-treatment conditions include: allowing the support layer coated with the casting solution to stand and undergo a first drying treatment, and then immersing the support layer in deionized water for a second ultrasonic cleaning; Preferably, the standing time is 1-30 min; Preferably, the conditions of the first drying treatment include: an oven absolute pressure of 0.01-0.08 MPa, a temperature of 20-80° C., and a drying time of 10-1000 min; Preferably, the second ultrasonic cleaning time is 10-1000 min.

10. The preparation method according to claim 9, wherein The preparation method further comprises: in step (3), subjecting the membrane immersed in deionized water after ultrasonic cleaning 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 40-2800 mesh, preferably 50-500 mesh.

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.