An ultra-fine fiber oil-water emulsion separation membrane, a preparation method thereof and application thereof

Abstract

The application discloses an ultra-fine fiber oil-water emulsion separation membrane and a preparation method and application thereof. The ultra-fine fiber oil-water emulsion separation membrane is prepared by adding modified graphene into a high-hydrophobic polyacrylonitrile spinning solution during in-situ polymerization and then through electrospinning. The high-hydrophobic polyacrylonitrile spinning solution comprises acrylonitrile, fluorine-containing monomer, allyl triethoxysilane and organic solution. The modified graphene is prepared by modifying graphene oxide by a cationic surfactant. The cationic surfactant has a structure shown in the following formula A. On the basis of the polyacrylonitrile material with high hydrophobicity and stability, the modified graphene with excellent stability, adsorption capacity and mechanical strength is compounded, so that the oil-water emulsion separation membrane with excellent separation rate, membrane flux and long-term stability can be effectively prepared.

Description

Technical Field

[0001] This invention relates to the field of nanofiber membrane technology, specifically to an ultrafine fiber oil-water emulsion separation membrane, its preparation method, and its application. Background Technology

[0002] In recent years, oily wastewater, a byproduct of human production and daily life, has hindered the process of sustainable development, damaged the natural environment on which we depend for survival, and posed a significant threat to human life. First, untreated or incompletely treated oily wastewater can seep into the ground and accumulate in rivers and lakes, polluting freshwater resources. Second, oily wastewater, being less dense than water, can cover the water surface, blocking oxygen and causing the death of aquatic plants and animals, thus polluting the natural environment. Finally, when oily wastewater mixes with irrigation water, its harmful substances may be absorbed by crops, also causing significant harm to human health. Therefore, inventing an efficient method for treating oily wastewater is particularly urgent.

[0003] To address the aforementioned impacts of oily wastewater, numerous oil-water separation methods have been developed, including gravity separation, adsorption, and membrane separation. Gravity separation utilizes the immiscibility and density difference between the oil and water phases, causing the oil phase to accumulate on the surface of the water phase, thus achieving separation. Adsorption uses adsorbents to adsorb one phase, achieving separation. Membrane separation utilizes various thin-film materials with special structures, allowing selective permeation of one phase, offering advantages such as low energy consumption, convenient operation, and high separation efficiency. Therefore, in the research of oil-water separation methods, the preparation of oil-water separation membranes with different functions has become a key focus for scholars and experts.

[0004] Oil-water separation materials based on superwetting materials are mainly divided into two categories: 1) superhydrophobic / superoleophilic materials; 2) superhydrophilic / superoleophobic materials. By combining the surface chemical composition with micro / nano-structured surfaces, superhydrophilic and underwater superoleophobic separation membrane materials can be prepared, enabling efficient oil-water separation. Currently, oil-water separation membranes typically use polyacrylonitrile-based carbon fiber materials, which are widely used in various fields due to their excellent properties such as light weight, high specific strength, high specific modulus, high temperature resistance, corrosion resistance, wear resistance, fatigue resistance, electrical conductivity, and thermal conductivity.

[0005] However, the long-term stability of polyacrylonitrile-based carbon fiber materials in the existing technology is poor. They are prone to clogging and damage during the separation process, resulting in a short service life. Furthermore, their hydrophobicity and the size of the membrane materials they are made into are poor. Therefore, the separation rate and membrane flux of oil-water separation still need to be improved.

[0006] Therefore, there is an urgent need for an ultrafine fiber 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 deficiencies of the prior art, the purpose of this 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 its preparation method and application.

[0008] Technical solution:

[0009] An ultrafine fiber oil-water emulsion separation membrane is prepared by adding modified graphene to the high hydrophobic polyacrylonitrile spinning solution for in-situ polymerization, followed by electrospinning.

[0010] The highly hydrophobic polyacrylonitrile spinning solution contains acrylonitrile, a fluorinated monomer, allyltriethoxysilane, and an organic solution.

[0011] The modified graphene was prepared by modifying graphene oxide with a cationic surfactant.

[0012] The cationic surfactant has the structure shown in Formula A:

[0013]

[0014] The highly hydrophobic polyacrylonitrile spinning solution of this invention can significantly improve the chemical stability and abrasion resistance of the fiber material obtained by the polyacrylonitrile spinning solution based on its copolymerized fluorine-containing monomers and alkenyl silanes. Furthermore, the tertiary amine, fluorocarbon, and silane structures in its monomers can effectively change the hydrophobicity of the fiber material, giving it excellent hydrophobicity, and it can be effectively applied in the preparation of oil-water emulsion separation membranes.

[0015] Further, 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, and the temperature is raised to 50-60°C under nitrogen protection. After stirring evenly, 3,5-dimethylbenzyl bromide is added, and the reaction is maintained at this temperature for 6-8 hours. After cooling, filtering, washing, and drying, the cationic surfactant is obtained.

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

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

[0018] (1) Graphene oxide was ultrasonically dispersed in N,N-dimethylformamide to prepare a graphene dispersion;

[0019] (2) In the reactor, add graphene dispersion and cationic surfactant, sonicate for 30-50 minutes, add hydrazine hydrate, stir evenly and transfer to the reaction vessel;

[0020] (3) Heat the reactor to 100-110℃ and react for 2-3 hours. Then filter, wash and dry to obtain modified graphene.

[0021] This invention modifies graphene oxide with cationic surfactants, which not only improves the dispersibility of graphene and prevents agglomeration, but also significantly enhances the hydrophobic effect of graphene due to its multi-branched, benzene ring, and quaternary ammonium structure. Furthermore, when the modified graphene is polymerized in situ in a polyacrylonitrile system, the hydrophobicity of the resulting 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 fluorinated monomer has the structure shown in Formula B:

[0024] In this invention, the fluorinated monomers copolymerized in the highly hydrophobic polyacrylonitrile spinning solution have tertiary amine and long-chain fluorocarbon structures, which can endow polyacrylonitrile with excellent hydrophobicity and chemical resistance, and can improve the dispersibility of the resulting 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 abrasion resistance of the membrane material, and significantly improve the service life of the membrane material.

[0025] Furthermore, the molar ratio of acrylonitrile, fluorinated 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 mass of modified graphene is 25-30:1.

[0026] The modified graphene of the present invention can be uniformly dispersed in the membrane material structure. On the one hand, its excellent mechanical strength can support the material structure, thereby giving the membrane material excellent tensile strength, enabling it to withstand stronger liquid impact. On the other hand, the modified graphene can effectively improve the hydrophobicity and oil absorption of the membrane material, significantly improving the separation rate of the membrane material for oil-water emulsions.

[0027] The preparation method of any of the above-mentioned ultrafine fiber oil-water emulsion separation membranes includes the following steps:

[0028] (1) In a reactor, acrylonitrile, fluorinated monomer, allyltriethoxysilane, modified graphene, initiator and organic solvent are added. After heating to 50-70℃, the reaction is carried out for 12-40 hours. After removing residual monomer and bubbles under reduced pressure, the spinning solution is obtained.

[0029] (2) The ultrafine fiber oil-water emulsion separation membrane is prepared by electrospinning under the conditions of anode voltage of 10-12kV, cathode voltage of 2-3kV, injection speed of 0.5-0.8mL / h, receiving distance of 10-15cm, spinning temperature of 45-50℃, and spinning humidity of 15-22%.

[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 using 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 to the high hydrophobic polyacrylonitrile spinning solution for in-situ polymerization and then electrospinning. Based on the polyacrylonitrile material with high hydrophobicity and stability, modified graphene with excellent stability, adsorption capacity and mechanical strength is compounded to effectively prepare an oil-water emulsion separation membrane with 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 solution can significantly improve the chemical stability and wear resistance of the fiber material obtained by the polyacrylonitrile spinning solution based on its copolymerized fluorine-containing monomers and alkenyl silanes. Furthermore, the tertiary amine, carbon fluorine and silane structures in its monomers can effectively change the hydrophobicity of the fiber material, giving it excellent hydrophobicity, and can be effectively applied 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 fluorinated monomer copolymerized from the highly hydrophobic polyacrylonitrile spinning dope has a tertiary amine structure and a long-chain carbon-fluorine structure, which can endow polyacrylonitrile with excellent hydrophobicity and chemical resistance, and can improve the dispersibility of the fiber, 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.

[0036] (4) In the ultrafine fiber oil-water emulsion separation membrane provided by the present invention, modified graphene can be uniformly dispersed in the membrane material structure. On the one hand, its excellent mechanical strength can play a supporting role in the material structure, thereby giving the membrane material excellent tensile strength, so that it can withstand stronger liquid impact. On the other hand, 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 cationic surfactant, which can not only improve the dispersibility of graphene and avoid agglomeration, but also significantly improve the hydrophobic effect of graphene by its multi-branched chain, benzene ring and quaternary ammonium structure. Furthermore, when the modified graphene is polymerized in situ in the polyacrylonitrile system, the hydrophobicity of the membrane material can be further improved. Detailed Implementation

[0038] The present invention will be described below with reference to specific embodiments. It should be noted that the following embodiments are examples of the present invention and are used only to illustrate the invention, not to limit it. Other combinations and various modifications within the scope of the present invention can be made without departing from its spirit or scope.

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

[0040] Preparation of fluorine-containing monomers

[0041] Fluorine-containing monomers are prepared by the following steps:

[0042] In a reactor, 2g of 1H,1H-perfluoro-1-hexanol and 1g of 3-N,N-dimethylaminomethacryloyl chloride were added. Under the protection of 0.1g hydroquinone, the mixture was heated to 60°C and reacted for 12 hours. After cooling, washing, drying, and distillation, the fluorinated monomer was obtained.

[0043] Preparation of cationic surfactants

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

[0045] In a reactor, 2g of N,N,N',N'-tetramethyl-1,6-hexanediamine and 100mL of N,N-dimethylformamide were added. The mixture was heated to 60°C under nitrogen protection and stirred until homogeneous. Then, 5g of 3,5-dimethylbenzyl bromide was added. After reacting at this temperature for 8 hours, the mixture was cooled, filtered, washed, and dried to obtain the cationic surfactant.

[0046] Mass spectrometry data of cationic surfactants: The products were analyzed by LC-MS, and the m / z values ​​of the products were 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) 0.1 g of graphene oxide was ultrasonically dispersed in 100 mL of N,N-dimethylformamide to prepare a graphene dispersion.

[0050] (2) In the reactor, the graphene dispersion prepared above and 0.2g of cationic surfactant were added, and after ultrasonic treatment for 30 minutes, 0.1g of hydrazine hydrate was added. After stirring evenly, the mixture was transferred to the reaction vessel.

[0051] (3) The reaction vessel was heated to 110°C and reacted for 3 hours. After filtration, washing and drying, modified graphene-1 was obtained.

[0052] Preparation of modified graphene-2

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

[0054] Example 1

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

[0056] (1) In a reactor, add 0.3 mol of acrylonitrile, 0.05 mol of 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, heat to 60 °C and react for 24 hours. After removing residual monomers and bubbles under reduced pressure, the spinning solution is obtained.

[0057] (2) The ultrafine fiber oil-water emulsion separation membrane was prepared by electrospinning under the conditions of anode voltage of 12kV, cathode voltage of 3kV, injection speed of 0.6mL / h, receiving distance of 12cm, spinning temperature of 50℃ and spinning humidity of 20%.

[0058] Example 2

[0059] The method is basically the same as in Example 1, except that the content of each component is 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 in Example 1, except that the content of each component is 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 separator membrane.

[0064] Comparative Example 2

[0065] The process is basically the same as in Example 1, except that step (1) is omitted and the spinning solution in step (2) is replaced with a commercially available spinning solution.

[0066] Comparative Example 3

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

[0068] Comparative Example 4

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

[0070] Comparative Example 5

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

[0072] Performance testing

[0073] Material performance testing: The fracture strength, elongation at break, 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 table below:

[0075]

[0076]

[0077] According to the comparison of the test results of Examples 1-3 with Comparative Examples 1 and 2, 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, the modified graphene composite 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 capability test: Emulsifier-stabilized oil-water emulsions were prepared by adding 0.05 g of emulsifier Tween 80 to 500 mL of deionized water and stirring until dissolved. Then, 5 g of hexadecane was added and stirred at 5000 rpm for 5 h to obtain emulsifier-stabilized hexadecane / water emulsions. The products of Examples 1-3 and Comparative Examples 1-5 were used as oil-water separation membranes to separate the hexadecane / water emulsions. The oil contact angle, initial membrane flux-1, membrane flux-2 after 1000 h of operation, and oil-water separation rate were measured during the separation process.

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

[0081] Oil contact angle (°) Membrane flux - 1 L / (m²·h·bar) Membrane flux - 2 L / (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, the ultrafine fiber oil-water emulsion separation membrane provided by the present invention has 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, the modified graphene composite in the ultrafine fiber oil-water emulsion separation membrane provided by the present invention can further improve the oleophilic 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 embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A microfiber oil-water emulsion separation membrane, characterized in that, The ultrafine fiber oil-water emulsion separation membrane is prepared by adding modified graphene to the high hydrophobic polyacrylonitrile spinning solution for in-situ polymerization, followed by electrospinning. The highly hydrophobic polyacrylonitrile spinning solution contains acrylonitrile, a fluorinated monomer, allyltriethoxysilane, and an organic solution. The modified graphene was prepared by modifying graphene oxide with a cationic surfactant. The cationic surfactant has the structure shown in Formula A: ； The fluorinated monomer has the structure shown in formula B: 。 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: In a reactor, N,N,N',N'-tetramethyl-1,6-hexanediamine and an organic solvent are added, and the temperature is raised to 50-60°C under nitrogen protection. After stirring evenly, 3,5-dimethylbenzyl bromide is added, and the reaction is maintained at this temperature for 6-8 hours. After cooling, filtering, washing, and drying, the cationic surfactant is obtained.

3. The ultrafine fiber oil-water emulsion separation membrane according to claim 2, characterized in that, The mass ratio of N,N,N',N'-tetramethyl-1,6-hexanediamine to 3,5-dimethylbenzyl bromide is 2:4-5; the organic solvent is selected from 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 through the following steps: (1) Graphene oxide was ultrasonically dispersed in N,N-dimethylformamide to prepare a graphene dispersion; (2) In the reactor, add graphene dispersion and cationic surfactant, sonicate for 30-50 minutes, add hydrazine hydrate, stir evenly and transfer to the reaction vessel; (3) Heat the reactor to 100-110℃, react for 2-3 hours, filter, wash and dry to obtain modified graphene.

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

6. The ultrafine fiber oil-water emulsion separation membrane according to claim 1, characterized in that, The molar ratio of acrylonitrile, fluorinated 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 mass of modified graphene is 25-30:

1.

7. The method for preparing the ultrafine fiber oil-water emulsion separation membrane according to any one of claims 1-6, characterized in that, Includes the following steps: (1) In a reactor, acrylonitrile, fluorinated monomer, allyltriethoxysilane, modified graphene, initiator and organic solvent are added, and the temperature is raised to 50-70℃ and reacted for 12-40 hours. After removing the residual monomer and bubbles under reduced pressure, the spinning solution is obtained. (2) The ultrafine fiber oil-water emulsion separation membrane is prepared by electrospinning under the following conditions: anode voltage of 10-12kV, cathode voltage of 2-3kV, injection speed of 0.5-0.8mL / h, receiving distance of 10-15cm, spinning temperature of 45-50℃, and spinning humidity of 15-22%.

8. The application of the ultrafine fiber oil-water emulsion separation membrane according to any one of claims 1-6 in the field of oil-water separation.

9. The application of the ultrafine fiber oil-water emulsion separation membrane according to claim 8 in the field of oil-water separation, characterized in that, The ultrafine fiber oil-water emulsion separation membrane is composited with the substrate layer using a low-damage composite device.

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