Superfine fiber oil-water emulsion separation membrane as well as preparation method and application thereof

Abstract

The invention discloses a superfine fiber oil-water emulsion separation membrane as well as a preparation method and application thereof, and the superfine fiber oil-water emulsion separation membrane is prepared by adding modified graphene in the preparation process of a high-hydrophobicity polyacrylonitrile spinning solution for in-situ polymerization and then performing electrostatic spinning, the high-hydrophobicity polyacrylonitrile spinning solution is prepared from acrylonitrile, a fluorine-containing monomer, allyltriethoxysilane and an organic solution, the modified graphene is prepared by modifying graphene oxide through a cationic surface active agent; the cationic surface active agent has a structure as shown in a formula A. On the basis of a polyacrylonitrile material with high hydrophobicity and stability, the modified graphene with excellent stability, adsorption capacity and mechanical strength is compounded, and the oil-water emulsion separation membrane with excellent separation rate, membrane flux and long-acting stability can be effectively prepared. # imgabs0 #

Description

Technical Field

[0001] The invention relates to the technical field of nanofiber membranes, and in particular to an ultrafine fiber oil-water emulsion separation membrane and a preparation method and application thereof. Background Art

[0002] In recent years, oily wastewater, as a by-product of human production and life, has hindered the process of sustainable development, destroyed the natural environment on which people depend for survival, and posed a huge threat to human life and safety. First, if oily wastewater is not treated or treated incompletely, the harmful substances in it will seep into the ground and converge with rivers, lakes and reservoirs, thereby polluting human freshwater resources; secondly, the density of oily wastewater is smaller than that of water, and it will cover the water surface and isolate oxygen, causing the death of aquatic plants and animals, thereby polluting the natural environment; finally, after oily wastewater is mixed with irrigation water sources, the harmful substances in it may be absorbed by crops and cause great harm to the human body. Therefore, it is particularly urgent to invent an efficient treatment method for oily wastewater.

[0003] In order to solve the above-mentioned effects of oily wastewater, many oil-water separation methods have been developed, including gravity separation, adsorption, membrane separation, etc. Gravity separation refers to the use of the immiscibility of oil and water phases and the difference in density to make the oil phase aggregate on the surface of the water phase, thereby achieving the effect of separation; adsorption refers to the use of adsorbents to adsorb one of the phases to achieve the purpose of separation; membrane separation refers to the use of various thin film materials with special structures to selectively allow one of the phases to pass through, which has the advantages of low energy consumption, convenient operation, and high separation efficiency. Therefore, in the process of studying oil-water separation methods, the preparation of oil-water separation membranes with different functions has become the focus of research by scholars and experts.

[0004] Oil-water separation materials based on superwetting materials are mainly divided into two categories: 1) super hydrophobic / super oleophilic materials; 2) super hydrophilic / super oleophobic materials. With a micro-nanostructured surface, combined with the chemical composition of the material surface, super hydrophilic and underwater super oleophobic separation membrane materials can be prepared, which can efficiently achieve oil-water separation. The current oil-water separation membrane usually uses polyacrylonitrile-based carbon fiber materials, which are widely used in many fields because of their light weight, high specific strength, high specific modulus, high temperature resistance, corrosion resistance, wear resistance, fatigue resistance, electrical conductivity, thermal conductivity and other excellent properties.

[0005] However, the polyacrylonitrile-based carbon fiber materials in the prior art have poor long-term stability, are prone to clogging and damage during the separation process, have a short service life, and have poor hydrophobicity and the size of the membrane materials made. The separation rate of oil-water separation and the membrane flux of the separation process still need to be improved.

[0006] Therefore, there is an urgent need for a microfiber oil-water emulsion separation membrane with excellent separation rate, membrane flux and long-term stability. Summary of the invention

[0007] Purpose of the invention: In view of the defects of the prior art, the purpose of the present invention is to provide an ultrafine fiber oil-water emulsion separation membrane with excellent separation rate, membrane flux and long-term stability, as well as a preparation method and application thereof.

[0008] Technical solution:

[0009] A superfine fiber oil-water emulsion separation membrane, wherein the superfine fiber oil-water emulsion separation membrane is prepared by adding modified graphene to a highly hydrophobic polyacrylonitrile spinning stock solution during preparation, performing in-situ polymerization, and then performing electrostatic spinning;

[0010] The highly hydrophobic polyacrylonitrile spinning solution comprises acrylonitrile, a fluorine-containing monomer, allyltriethoxysilane and an organic solution;

[0011] The modified graphene is prepared by modifying graphene oxide with a cationic surfactant;

[0012] The cationic surfactant has a structure shown in the following formula A:

[0013]

[0014] The highly hydrophobic polyacrylonitrile spinning stock solution in the present invention can significantly improve the chemical stability and wear resistance of the fiber material prepared from the polyacrylonitrile spinning stock solution based on its copolymerized fluorine-containing monomer and alkenyl silane, and the tertiary amine, carbon fluorine and silane structures in the monomer can effectively change the hydrophobicity of the fiber material, so that it has excellent hydrophobicity, and can be effectively used in the preparation of oil-water emulsion separation membranes.

[0015] Furthermore, the cationic surfactant is prepared by the following steps: in a reactor, N,N,N',N'-tetramethyl-1,6-hexanediamine and an organic solvent are added, the temperature is raised to 50-60°C under nitrogen protection, 3,5-dimethylbenzyl bromide is added after stirring evenly, and the cationic surfactant is prepared after cooling, filtering, washing and drying after keeping warm for 6-8 hours.

[0016] Furthermore, the mass ratio of the N,N,N',N'-tetramethyl-1,6-hexanediamine to 3,5-dimethylbenzyl bromide is 2:4-5; and the organic solvent is selected from one of N,N-dimethylformamide, N,N-dimethylacetamide or dimethyl sulfoxide.

[0017] Furthermore, the modified graphene is prepared by the following steps:

[0018] (1) ultrasonically dispersing graphene oxide in N,N-dimethylformamide to obtain a graphene dispersion;

[0019] (2) adding a graphene dispersion and a cationic surfactant into a reactor, adding hydrazine hydrate after ultrasonic treatment for 30-50 minutes, stirring evenly and transferring to a reactor;

[0020] (3) The reaction vessel is heated to 100-110° C., reacted for 2-3 hours, and then filtered, washed, and dried to obtain modified graphene.

[0021] The present invention modifies graphene oxide by using a cationic surfactant, which can not only improve the dispersibility of graphene and avoid agglomeration, but also significantly improve the hydrophobic effect of graphene due to its multi-branched chains, benzene rings and quaternary ammonium structures. Furthermore, when the modified graphene is in situ polymerized in a polyacrylonitrile system, the hydrophobicity of the prepared membrane material can be further improved.

[0022] Furthermore, the mass ratio of the graphene oxide to the cationic surfactant is 1:2-3.

[0023] Furthermore, the fluorine-containing monomer has a structure as shown in the following formula B:

[0024] In the present invention, the fluorine-containing monomer copolymerized in the highly hydrophobic polyacrylonitrile spinning solution has a tertiary amine structure and a long-chain carbon fluorine structure, which can give the polyacrylonitrile excellent hydrophobicity and chemical resistance, and can improve the dispersibility of the prepared fibers, thereby increasing the number of pores on the fiber surface, significantly improving the membrane flux of the membrane material, and improving the separation efficiency; the copolymerized allyltriethoxysilane has a multi-branched silane structure, which can further improve the hydrophobicity, chemical stability and wear resistance of the membrane material, and significantly improve the service life of the membrane material.

[0025] Furthermore, the molar ratio of acrylonitrile, fluorine-containing monomer and allyltriethoxysilane in the highly hydrophobic polyacrylonitrile spinning solution is (25-30):(5-8):(3-5); the mass ratio of the total mass of each monomer in the highly hydrophobic polyacrylonitrile spinning solution to the modified graphene is 25-30:1.

[0026] The modified graphene of the present invention can be evenly dispersed in the membrane material structure. On the one hand, its excellent mechanical strength can play a role in supporting the material structure, thereby giving the membrane material excellent tensile strength, so that it can withstand stronger liquid impact force; on the other hand, the modified graphene can effectively improve the hydrophobicity and oil absorption effect of the membrane material, and significantly improve the separation rate of the membrane material for oil-water emulsions.

[0027] Any one of the above-mentioned methods for preparing the ultrafine fiber oil-water emulsion separation membrane comprises the following steps:

[0028] (1) Adding acrylonitrile, fluorine-containing monomer, allyl triethoxysilane, modified graphene, initiator and organic solvent into a reactor, heating to 50-70° C. and reacting for 12-40 hours, removing residual monomers and bubbles by decompression, and obtaining a spinning solution;

[0029] (2) Under the conditions of an anode voltage of 10-12 kV, a cathode voltage of 2-3 kV, an injection speed of 0.5-0.8 mL / h, a receiving distance of 10-15 cm, a spinning temperature of 45-50° C., and a spinning humidity of 15-22%, the spinning solution is subjected to electrospinning to obtain the ultrafine fiber oil-water emulsion separation membrane.

[0030] Application of any of the above-mentioned ultrafine fiber oil-water emulsion separation membranes in the field of oil-water separation.

[0031] Furthermore, the ultrafine fiber oil-water emulsion separation membrane is composited with the substrate layer through a low-damage composite device.

[0032] Beneficial effects:

[0033] (1) The ultrafine fiber oil-water emulsion separation membrane provided by the present invention is prepared by adding modified graphene during the preparation of a highly hydrophobic polyacrylonitrile spinning stock solution and then subjecting it to in-situ polymerization and then electrospinning. Based on a polyacrylonitrile material having high hydrophobicity and stability, a modified graphene having excellent stability, adsorption capacity and mechanical strength is compounded, thereby effectively preparing an oil-water emulsion separation membrane having excellent separation rate, membrane flux and long-term stability.

[0034] (2) In the ultrafine fiber oil-water emulsion separation membrane provided by the present invention, the highly hydrophobic polyacrylonitrile spinning stock solution, based on its copolymerized fluorine-containing monomer and alkenyl silane, can significantly improve the chemical stability and wear resistance of the fiber material prepared from the polyacrylonitrile spinning stock solution, and the tertiary amine, carbon fluorine and silane structures in its monomers can effectively change the hydrophobicity of the fiber material, so that it has excellent hydrophobicity, and can be effectively used in the preparation of oil-water emulsion separation membranes.

[0035] (3) In the ultrafine fiber oil-water emulsion separation membrane provided by the present invention, the fluorine-containing monomer copolymerized in the highly hydrophobic polyacrylonitrile spinning solution has a tertiary amine structure and a long-chain carbon fluorine structure, which can give the polyacrylonitrile excellent hydrophobicity and chemical resistance, and can improve the dispersibility of the prepared fibers, thereby increasing the number of pores on the fiber surface, significantly improving the membrane flux of the membrane material, and improving the separation efficiency; the copolymerized allyl triethoxy silane has a multi-branched silane structure, which can further improve the hydrophobicity, chemical stability and wear resistance of the membrane material, and significantly improve the service life of the membrane material.

[0036] (4) In the ultrafine fiber oil-water emulsion separation membrane provided by the present invention, the modified graphene can be uniformly dispersed in the membrane material structure. On the one hand, its excellent mechanical strength can play a role in supporting the material structure, thereby giving the membrane material excellent tensile strength, so that it can withstand stronger liquid impact force; on the other hand, the modified graphene can effectively improve the hydrophobicity and oil absorption effect of the membrane material, and significantly improve the separation rate of the membrane material for oil-water emulsion.

[0037] (5) In the ultrafine fiber oil-water emulsion separation membrane provided by the present invention, the graphene oxide is modified by a cationic surfactant, which can not only improve the dispersibility of graphene and avoid agglomeration, but also its multi-branched chain, benzene ring and quaternary ammonium structure can significantly improve the hydrophobic effect of graphene. Furthermore, when the modified graphene is in situ polymerized in a polyacrylonitrile system, the hydrophobic ability of the prepared membrane material can be further improved. DETAILED DESCRIPTION

[0038] The present invention will be described below in conjunction with specific embodiments. It should be noted that the following embodiments are examples of the present invention and are only used to illustrate the present invention, but not to limit the present invention. Other combinations and various modifications within the concept of the present invention may be performed without departing from the spirit or scope of the present invention.

[0039] The commercially available oil-water separation membrane is a high-strength oil-water separation wastewater recycling and treatment MBR curtain membrane purchased from Lvzeyuan (Zhejiang) Environmental Protection Technology Co., Ltd.; the commercially available spinning stock solution is obtained by mixing PAN fine powder purchased from Dongguan Zhangmutou Hengtai Plastic Raw Materials Business Department with N,N-dimethylformamide; graphene oxide 796034 was purchased from Merck; the remaining reagents and equipment are conventional reagents and equipment in this technical field.

[0040] Preparation of fluorinated monomers

[0041] The fluorinated monomers were prepared by the following steps:

[0042] In the reactor, 2 g of 1H,1H-perfluoro-1-hexanol and 1 g of 3-N,N-dimethylaminomethyl acryloyl chloride were added, and under the protection of 0.1 g of hydroquinone, the mixture was heated to 60° C. and reacted for 12 hours, and then cooled, washed, dried and distilled to obtain the fluorine-containing monomer.

[0043] Preparation of cationic surfactants

[0044] The cationic surfactant was prepared by the following steps:

[0045] In a reactor, 2 g of N,N,N',N'-tetramethyl-1,6-hexanediamine and 100 mL of N,N-dimethylformamide were added, the temperature was raised to 60° C. under nitrogen protection, 5 g of 3,5-dimethylbenzyl bromide was added after stirring, the mixture was kept warm for 8 hours, and then cooled, filtered, washed and dried to obtain the cationic surfactant;

[0046] Mass spectral data of cationic surfactant: The product was analyzed by LC-MS, and the m / z of the product was 205.18 (100.0%), 205.68 (31.6%), and 206.19 (4.8%).

[0047] Preparation of modified graphene-1

[0048] Modified graphene-1 was prepared by the following steps:

[0049] (1) ultrasonically dispersing 0.1 g of graphene oxide in 100 mL of N,N-dimethylformamide to prepare a graphene dispersion;

[0050] (2) Add the graphene dispersion prepared above and 0.2 g of a cationic surfactant into a reactor, add 0.1 g of hydrazine hydrate after ultrasonic treatment for 30 minutes, stir evenly and transfer to a reactor;

[0051] (3) The reactor was heated to 110° C., reacted for 3 hours, and then filtered, washed, and dried to obtain modified graphene-1.

[0052] Preparation of modified graphene-2

[0053] The preparation is basically the same as that of modified graphene-1, except that the cationic surfactant is replaced by an equal amount of sodium dodecylbenzene sulfonate.

[0054] Example 1

[0055] The microfiber oil-water emulsion separation membrane was prepared by the following steps:

[0056] (1) In a reactor, 0.3 mol of acrylonitrile, 0.05 mol of a fluorine-containing monomer, 0.03 mol of allyltriethoxysilane, 1.4 g of modified graphene-1, 0.3 g of azobisisobutyronitrile and 150 mL of N,N-dimethylformamide were added, the temperature was raised to 60° C. and reacted for 24 hours, and residual monomers and bubbles were removed by decompression to obtain a spinning solution;

[0057] (2) Under the conditions of an anode voltage of 12 kV, a cathode voltage of 3 kV, a sample feed rate of 0.6 mL / h, a receiving distance of 12 cm, a spinning temperature of 50° C., and a spinning humidity of 20%, the spinning solution was electrospun to obtain the ultrafine fiber oil-water emulsion separation membrane.

[0058] Example 2

[0059] The method is basically the same as Example 1, except that the contents of each component are changed to 0.25 mol of acrylonitrile, 0.08 mol of fluorine-containing monomer, 0.05 mol of allyltriethoxysilane, and 2 g of modified graphene-1.

[0060] Example 3

[0061] The method is basically the same as Example 1, except that the contents of each component are changed to 0.3 mol of acrylonitrile, 0.06 mol of fluorine-containing monomer, 0.04 mol of allyltriethoxysilane, and 1.8 g of modified graphene-1.

[0062] Comparative Example 1

[0063] Commercially available oil-water separation membranes.

[0064] Comparative Example 2

[0065] The process is basically the same as Example 1, except that step (1) is not performed and the spinning solution in step (2) is replaced by a commercially available spinning solution.

[0066] Comparative Example 3

[0067] The method is basically the same as Example 1, except that the modified graphene-1 in step (1) is replaced by an equal amount of N,N-dimethylformamide.

[0068] Comparative Example 4

[0069] The method is basically the same as Example 1, except that the modified graphene-1 in step (1) is replaced by an equal amount of graphene oxide.

[0070] Comparative Example 5

[0071] The method is basically the same as Example 1, except that the modified graphene-1 in step (1) is replaced by an equal amount of modified graphene-2.

[0072] Performance Testing

[0073] Material performance testing: The breaking strength, breaking elongation, pore size distribution and porosity of the products of Examples 1-3 and Comparative Examples 1-5 were tested respectively.

[0074] The test results are shown in the following table:

[0075]

[0076]

[0077] According to the comparison of the test results of Examples 1-3 with Comparative Examples 1 and 2, it can be seen that the ultrafine fiber oil-water emulsion separation membrane provided by the present invention has better mechanical strength, pore size distribution and porosity than the oil-water separation membrane in the prior art, and thus has a better oil-water separation effect.

[0078] According to the comparison of the test results of Examples 1-3 and Comparative Examples 3-5, it can be seen that the modified graphene composited in the ultrafine fiber oil-water emulsion separation membrane provided by the present invention can significantly improve the mechanical strength, pore size distribution and porosity of the membrane material, and improve the oil-water separation effect of the membrane material.

[0079] Separation ability test: prepare an emulsifier-stabilized oil-water emulsion, add 0.05g of emulsifier Tween 80 to 500mL of deionized water, stir until dissolved, then add 5g of hexadecane, stir at 5000rpm for 5h to obtain an emulsifier-stabilized hexadecane / water emulsion; use the products of Examples 1-3 and Comparative Examples 1-5 as oil-water separation membranes, respectively, to separate oil and water from the hexadecane / water emulsion, and test the oil contact angle, membrane flux-1 at the beginning, membrane flux-2 after 1000h of operation, and oil-water separation rate during the separation process.

[0080] The test results are shown in the following table:

[0081] Oil contact angle (°) Membrane flux-1L / (m2·h·bar) Membrane flux-2L / (m2·h·bar) Separation rate (%) Example 1 25 1000 880 99.6 Example 2 24 1050 890 99.6 Example 3 25 1000 880 99.7 Comparative Example 1 45 820 580 95.4 Comparative Example 2 45 800 550 95.1 Comparative Example 3 30 850 680 96.4 Comparative Example 4 30 950 760 97.2 Comparative Example 5 26 950 780 97.9

[0082] According to the comparison of the test results of Examples 1-3 with Comparative Examples 1 and 2, it can be seen that the ultrafine fiber oil-water emulsion separation membrane provided by the present invention has a better oil-water separation rate, membrane flux and long-term stability than the oil-water separation membrane in the prior art, and can be widely used in the field of oil-water separation.

[0083] According to the comparison of the test results of Examples 1-3 and Comparative Examples 3-5, it can be seen that the modified graphene composited in the ultrafine fiber oil-water emulsion separation membrane provided by the present invention can further improve the lipophilic effect of the membrane material, and can significantly improve the oil-water separation rate, membrane flux and long-term stability of the membrane material.

[0084] The above implementation modes are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with this technology to understand the content of the present invention and implement it, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A superfine fiber oil-water emulsion separation membrane, characterized in that: The ultrafine fiber oil-water emulsion separation membrane is prepared by adding modified graphene to the highly hydrophobic polyacrylonitrile spinning solution during preparation, and then performing in-situ polymerization and electrostatic spinning. The highly hydrophobic polyacrylonitrile spinning solution comprises acrylonitrile, a fluorine-containing monomer, allyltriethoxysilane and an organic solution; The modified graphene is prepared by modifying graphene oxide with a cationic surfactant; The cationic surfactant has a structure shown in the following formula A:

2. The ultrafine fiber oil-water emulsion separation membrane according to claim 1, characterized in that: The cationic surfactant is prepared by the following steps: adding N,N,N',N'-tetramethyl-1,6-hexanediamine and an organic solvent into a reactor, heating to 50-60° C. under nitrogen protection, stirring evenly, adding 3,5-dimethylbenzyl bromide, and reacting for 6-8 hours at the same temperature, cooling, filtering, washing, and drying to obtain the cationic surfactant.

3. The ultrafine fiber oil-water emulsion separation membrane according to claim 2, characterized in that: The mass ratio of the N,N,N',N'-tetramethyl-1,6-hexanediamine to 3,5-dimethylbenzyl bromide is 2:4-5; and the organic solvent is selected from one of N,N-dimethylformamide, N,N-dimethylacetamide or dimethyl sulfoxide.

4. The ultrafine fiber oil-water emulsion separation membrane according to claim 1, characterized in that: The modified graphene is prepared by the following steps: (1) ultrasonically dispersing graphene oxide in N,N-dimethylformamide to obtain a graphene dispersion; (2) adding a graphene dispersion and a cationic surfactant into a reactor, adding hydrazine hydrate after ultrasonic treatment for 30-50 minutes, stirring evenly and transferring to a reactor; (3) The reaction vessel is heated to 100-110° C., reacted for 2-3 hours, and then filtered, washed, and dried to obtain modified graphene.

5. The ultrafine fiber oil-water emulsion separation membrane according to claim 4, characterized in that: The mass ratio of the graphene oxide to the cationic surfactant is 1:2-3.

6. The ultrafine fiber oil-water emulsion separation membrane according to claim 1, characterized in that: The fluorine-containing monomer has a structure as shown in the following formula B:

7. The ultrafine fiber oil-water emulsion separation membrane according to claim 1, characterized in that: The molar ratio of acrylonitrile, fluorine-containing monomer and allyltriethoxysilane in the highly hydrophobic polyacrylonitrile spinning solution is (25-30):(5-8):(3-5); the mass ratio of the total mass of each monomer in the highly hydrophobic polyacrylonitrile spinning solution to the modified graphene is 25-30:

1.

8. The method for preparing the ultrafine fiber oil-water emulsion separation membrane according to any one of claims 1 to 7, characterized in that: The following steps are involved: (1) Adding acrylonitrile, fluorine-containing monomer, allyl triethoxysilane, modified graphene, initiator and organic solvent into a reactor, heating to 50-70° C. and reacting for 12-40 hours, removing residual monomers and bubbles by decompression, and obtaining a spinning solution; (2) Under the conditions of an anode voltage of 10-12 kV, a cathode voltage of 2-3 kV, an injection speed of 0.5-0.8 mL / h, a receiving distance of 10-15 cm, a spinning temperature of 45-50° C., and a spinning humidity of 15-22%, the spinning solution is subjected to electrospinning to obtain the ultrafine fiber oil-water emulsion separation membrane.

9. Use of the ultrafine fiber oil-water emulsion separation membrane according to any one of claims 1 to 7 in the field of oil-water separation.

10. The use of the ultrafine fiber oil-water emulsion separation membrane according to claim 9 in the field of oil-water separation, characterized in that: The ultrafine fiber oil-water emulsion separation membrane is compounded with the substrate layer through a low-damage compounding device.

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