Oil removal composite fiber membrane as well as preparation method and application thereof

Abstract

The invention discloses a composite fiber membrane and a preparation method and application thereof, the composite fiber membrane comprises a hydrophilic layer and a hydrophobic layer, the hydrophilic layer is a hydrophilic fiber membrane formed by a hydrophilic polymer, the hydrophobic layer is a net structure formed by a hydrophobic polymer, and the net structure covers the surface of the hydrophilic fiber membrane. The composite fiber membrane provided by the invention has high oil-water separation efficiency and flux, and the phenomena that the surface of the fiber membrane is polluted and membrane holes are blocked during oil-water separation are better overcome.

Description

Technical Field

[0001] The present invention relates to the technical field of oil-water separation. Further, it relates to an oil-removing composite fiber membrane, a preparation method thereof, and an application thereof. Background Art

[0002] To actively promote the improvement of water environment quality and continuously deepen the work of improving the quality and efficiency of sewage treatment, one important task is to improve the treatment efficiency of oily sewage. Since the pollution of oily sewage to the water environment is relatively obvious, improving its treatment efficiency has become a normal trend. The treatment of oily sewage is a process for treating wastewater containing grease and oil pollutants. Compared with common oily sewage treatment methods such as gravity separation, hydrocyclone, air flotation, centrifugation, and adsorption, the membrane separation technology has the advantages of low energy consumption, high separation efficiency, simple operation, and no secondary pollution, and has broad application prospects in the field of oil-water separation.

[0003] The membrane separation technology mainly realizes the efficient separation of oil-water mixtures by intercepting the dispersed phase through membrane pores and rapidly transporting the continuous phase. However, due to the relatively stable nature of oil-water emulsions and the widely distributed oil droplets, it is easy to cause surface adhesion and membrane pore blockage, resulting in a sharp decline in membrane separation performance. One solution strategy is to construct a separation membrane with a super-hydrophilic surface and use the principle of mutual repulsion at the oil-water interface to prevent oil droplets from approaching the super-hydrophilic membrane surface. However, this strategy has good effects when separating oil-water mixtures and surfactant-free emulsions, but it cannot maintain a high separation efficiency in a stable small-droplet oil-water emulsion system. Another solution strategy is to construct a Janus membrane, that is, the chemical wetting properties on both sides of the membrane are different. Driven by the surface chemical potential, liquid can undergo anisotropic transport between the cross-sectional layers of the three-dimensional porous membrane material, greatly improving the processing capacity of the oil-water separation process. However, at present, the structural stability of Janus membranes is poor, the recycling performance is not good, the effective service time is short, and the water flux is low, which greatly limits their large-scale application. Summary of the Invention

[0004] To solve the above problems, the present invention provides an oil-removing composite fiber membrane and a preparation method thereof. The fiber membrane has good oil-water separation efficiency and flux, and preferably overcomes the phenomena of surface pollution and membrane pore blockage during oil-water separation.

[0005] First, one object of the present invention is to provide an oil-removing composite fiber membrane.

[0006] Specifically, the oil-removing composite fiber membrane includes a hydrophilic layer and a hydrophobic layer. Among them, the hydrophilic layer is a hydrophilic fiber membrane composed of a hydrophilic polymer, and the hydrophobic layer is a network structure composed of a hydrophobic polymer, and the network structure covers the surface of the hydrophilic fiber membrane.

[0007] The composite fiber membrane provided by the present invention, which consists of a hydrophilic layer and a hydrophobic layer, ensures the flow rate of the water phase through the hydrophilic layer substrate. Through the lipophilic network structure of the hydrophobic layer, tiny oil droplets in the oil-containing polluted water are adsorbed and coalesced to achieve the demulsification and oil removal processes.

[0008] Further, the thickness of the hydrophilic layer in the oil removal composite fiber membrane is 200 - 500 μm; the thickness of the hydrophobic layer is 30 - 100 μm.

[0009] Further, the hydrophobic layer is a network structure formed by the interlaced connection of hydrophobic polymer fibers of different thicknesses, preferably a network structure of uneven and irregular meshes, and more preferably a network structure in the shape of leaf veins; the area of the hydrophobic layer covering the hydrophilic layer accounts for 5 - 20% of the total surface area of the hydrophilic layer.

[0010] Preferably, the underwater contact angle of the hydrophilic layer is above 150°, having good superhydrophilicity and underwater oleophobicity, effectively improving the oil removal performance of the composite fiber membrane.

[0011] Preferably, the hydrophilic polymer includes one or a combination of polyacrylonitrile, polyethyleneimine, and polyvinyl alcohol; the hydrophobic polymer includes one or a combination of polydimethylsiloxane, polyvinylidene fluoride, and polypropylene.

[0012] Secondly, the second object of the present invention is to provide a preparation method of the composite fiber membrane of the first object of the present invention.

[0013] Specifically, the preparation method includes the following steps:

[0014] Step 1: Dissolve the hydrophilic polymer in solvent A, and stir well until the hydrophilic polymer is completely dissolved to obtain a spinning solution. The spinning solution is electrospun to obtain a hydrophilic fiber membrane;

[0015] Step 2: Dissolve the hydrophobic polymer in solvent B to obtain a hydrophobic solution;

[0016] Step 3: Place the network template on the hydrophilic fiber membrane prepared in Step 1, pour the hydrophobic solution in Step 2 into the network template to construct a network-structured hydrophobic layer. After drying, remove the network template to obtain the composite fiber membrane.

[0017] Further, the hydrophilic polymer is one or a combination of polyacrylonitrile, polyethyleneimine, and polyvinyl alcohol; more preferably, when the hydrophilic polymer is polyacrylonitrile and polyethyleneimine, the mass ratio of polyacrylonitrile to polyethyleneimine is 3 - 6:1, preferably 4 - 5:1.

[0018] Furthermore, the mass of the hydrophilic polymer accounts for 5 - 10 wt% of the mass of the spinning solution; preferably 6 - 8 wt%; preferably, solvent A is N,N-dimethylformamide.

[0019] Further, the hydrophobic polymer is one or a combination of polydimethylsiloxane, polyvinylidene fluoride, and polypropylene.

[0020] Furthermore, the mass of the hydrophobic polymer accounts for 10-20 wt% of the mass of the hydrophobic solution, preferably 15-18 wt%; preferably, the solvent B is one of n-hexane, chloroform, and toluene.

[0021] Further, in the first step, the electrospinning conditions are as follows:

[0022] The electrospinning voltage is 10-25 kV;

[0023] The spinning flow rate is 0.2-0.5 μL / min;

[0024] The receiving distance is 5-20 cm;

[0025] The receiving time is 40-80 min.

[0026] Finally, the third object of the present invention is to provide the application of the oil-removing composite fiber membrane of the first object of the present invention.

[0027] The composite fiber membrane provided by the present invention is used for removing oil from water-in-oil emulsions. The oil droplets in the emulsion will be intercepted by the hydrophilic layer substrate, and then captured by the reticular structure of the hydrophobic layer, and the oil droplets on the surface of the hydrophilic layer are induced to coalesce, preventing the pollution and blockage of the hydrophilic layer, thereby realizing the oil-removing process of water-in-oil emulsions.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] 1. The present invention provides a composite fiber membrane composed of a hydrophilic layer and a hydrophobic layer. Among them, the hydrophilic layer substrate ensures the flow rate of the water phase passing through and the interception effect on micro-droplets. The hydrophobic layer has excellent super-hydrophobic and lipophilic properties, and its reticular structure with interlaced thickness can adsorb and coalesce micro-oil droplets in oil-containing polluted water, and can efficiently realize the oil-removing separation function of water-in-oil emulsions.

[0030] 2. The present invention constructs a protruding hydrophobic network structure on the surface of the hydrophilic layer, which can guide and coalesce the oil droplets on the surface of the hydrophilic layer, avoiding the problem that oil droplets accumulate on the surface of the separation membrane and gradually penetrate into the membrane during the oil-water separation process, resulting in membrane pore blockage. The present invention constructs a protruding hydrophobic network structure on the surface of the hydrophilic layer, which can directly adsorb and remove oil droplets efficiently, quickly remove the oil droplets in the oil-water emulsion, and ensure the long-term and efficient separation efficiency of the fiber membrane.

[0031] 3. The present invention constructs a protruding hydrophobic network structure on the surface of the hydrophilic layer. The hydrophobic network structure covers the surface of the hydrophilic membrane and is convex on the surface of the fiber membrane. When oil droplets are blocked on the surface of the fiber membrane, they will gradually approach and adsorb on the hydrophobic network structure under the action of water flow. When the oil droplets are large enough on the hydrophobic fibers, they will break away from the fiber membrane to achieve the effect of oil removal. Moreover, the hydrophobic network structure only occupies a small part of the area of the hydrophilic membrane, ensuring the separation efficiency and flux of the composite fiber membrane.

[0032] 4. The composite fiber membrane provided by the present invention not only has high separation efficiency and flux, but also has the advantages of simple operation, stable properties, low energy consumption, etc. In addition, during the cleaning stage of the fiber membrane, oil droplets are more easily washed off from the lipophilic network structure, which preferably solves the problem of separating oily sewage.

[0033] 5. The composite fiber membrane provided by the present invention can be recycled repeatedly, greatly saving the application cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of a reticular template with a leaf vein-like structure used in Example 1 of the present invention;

[0035] Figure 2 It is a wetting performance diagram of the hydrophilic fiber membrane prepared in Example 1 of the present invention;

[0036] Figure 3 It is a wetting performance diagram of the composite fiber membrane prepared in Example 1 of the present invention;

[0037] Figure 4 It is a comparison diagram before and after the emulsion filtered by the composite fiber membrane prepared in Example 1 of the present invention;

[0038] Figure 5 It is a performance diagram of the separation effect and recycling effect of the composite fiber membranes prepared in Example 1, Comparative Example 1, and Example 2 of the present invention on the emulsion. The abscissa in the figure is the number of times of recycling the composite fiber membrane; the left ordinate and the columnar graph are the separation efficiency (%), and the right ordinate and the curve graph are the separation flux (Lm -2 h -1 )

[0039] Figure 6 It is a schematic diagram of a reticular template with a uniform regular grid reticular structure used in Example 2 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the present invention will be specifically described below in conjunction with specific drawings and embodiments. It is necessary to point out here that the following embodiments are only for further illustration of the present invention and should not be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention still fall within the protection scope of the present invention.

[0041] In the following examples and comparative examples, the raw materials are all commercially available products.

[0042] Example 1

[0043] Step 1: Add polyacrylonitrile and polyethyleneimine (mass ratio 6:1) to the N,N-dimethylformamide solvent, and magnetically stir at room temperature for 24 hours to obtain a polyacrylonitrile / polyethyleneimine solution (concentration 8 wt%). Use a 5 mL syringe to suck up the polyacrylonitrile / polyethyleneimine solution as the electrospinning solution, and use a No. 19 electrostatic needle for spinning. The spinning voltage is 14 kV, the distance from the tip of the needle to the roller is about 15 cm, the roller rotation speed is 60 r / min, the solution feeding rate is 0.3 μL / min, the translation distance is 12 cm, the receiving distance is 12 cm, the receiving speed is 60 r / min, and the receiving time is 60 min. After spinning, remove the aluminum foil and the electrospun fiber membrane on it, and dry it in an oven at 60 °C for 12 hours to obtain the hydrophilic layer.

[0044] Step 2: Add polyvinylidene fluoride to the chloroform solvent to obtain a polyvinylidene fluoride solution (concentration 10 wt%).

[0045] Step 3: Place the laser-etched mesh template (such as Figure 1 ) on the fiber membrane prepared in Step 1, slowly pour the polyvinylidene fluoride solution prepared in Step 2 into the template, and then place the fiber membrane in an oven at 60 °C for drying to finally obtain the composite fiber membrane.

[0046] Among them, the thickness of the hydrophilic layer is 400 μm; the thickness of the hydrophobic layer is 50 μm, and the hydrophobic layer covers 15% of the total surface of the hydrophilic layer.

[0047] Figure 2 Shows the wettability of the hydrophilic fiber membrane prepared in this example. As can be seen from Figure 2 a and 2b, the contact angle of the hydrophilic fiber membrane with water is 0°, and the contact angle of the oil under water is 156°. It can be seen that the hydrophilic fiber membrane prepared in this example has superhydrophilicity and underwater superoleophobicity.

[0048] Figure 3 Shows the wettability of the composite fiber membrane prepared in this example. As can be seen from Figure 3It can be seen that the contact angle between the composite fiber membrane and water gradually decreases from 72° to 0°, and finally it is completely wetted, which proves that the hydrophobic and oleophilic network structure is successfully modified on the surface of the hydrophilic fiber membrane, affecting the wettability of the membrane surface but not affecting the penetration process of the aqueous phase.

[0049] Figure 4 The front and back comparison diagrams of the oil-in-water emulsion separated by the composite fiber membrane prepared in this example are shown. From Figure 4 it can be seen that the composite fiber membrane removes the oil in the emulsion and has good separation performance and oil removal ability.

[0050] Figure 5 The separation effect and recycling performance of the oil-in-white-oil emulsion separated by the composite fiber membrane prepared in this example are shown. It can be seen from the figure that the composite fiber membrane has good separation efficiency and separation flux, and still has good oil removal effect after being cleaned and reused many times.

[0051] Comparative Example 1

[0052] Step 1: Add polyacrylonitrile and polyethyleneimine (mass ratio 6:1) to N,N-dimethylformamide solvent, and stir magnetically at room temperature for 24 hours to obtain a polyacrylonitrile / polyethyleneimine solution (concentration 8wt%). Use a 5 mL syringe to suck the polyacrylonitrile / polyethyleneimine solution as the electrospinning solution, and use a No. 19 electrostatic needle for electrospinning. The electrospinning voltage is 14 kV, the distance from the tip of the needle to the drum is about 15 cm, the drum rotation speed is 60 r / min, the solution delivery rate is 0.3 μL / min, the translation distance is 12 cm, the receiving distance is 12 cm, the receiving speed is 60 r / min, and the receiving time is 60 min. After electrospinning is completed, remove the aluminum foil and the electrospun fiber membrane on it, and dry it in an oven at 60°C for 12 hours to obtain a hydrophilic layer with a thickness of 400 μm.

[0053] Step 2: Add polyvinylidene fluoride to N,N-dimethylformamide solvent to obtain a polyvinylidene fluoride solution (concentration 10wt%). Use a 5 mL syringe to suck the polyvinylidene fluoride solution as the electrospinning solution, and use a No. 19 electrostatic needle for electrospinning. The electrospinning voltage is 13 kV, the distance from the tip of the needle to the drum is about 12 cm, the drum rotation speed is 60 r / min, the solution delivery rate is 0.2 μL / min, the translation distance is 12 cm, the receiving distance is 12 cm, the receiving speed is 60 r / min, and the receiving time is 5 min. Electrospin the fiber membrane on the hydrophilic layer, and dry it in an oven at 60°C for 12 hours to obtain a composite fiber membrane with a total thickness of 450 μm.

[0054] Figure 5The separation effect and recycling performance of the composite fiber membrane prepared by this comparative example for separating white oil-in-water emulsion are shown. As can be seen from the figure, the separation effect of the composite fiber membrane in this comparative example is slightly reduced, and the separation flux is reduced more significantly.

[0055] Example 2

[0056] Step 1: Add polyacrylonitrile and polyethyleneimine (mass ratio 6:1) to N,N-dimethylformamide solvent, and stir magnetically at room temperature for 24 hours to obtain a polyacrylonitrile / polyethyleneimine solution (concentration 8 wt%). Use a 5 mL syringe to suck up the polyacrylonitrile / polyethyleneimine solution as the electrospinning solution, and use a No. 19 electrostatic needle for electrospinning. The electrospinning voltage is 14 kV, the distance from the tip of the needle to the roller is about 15 cm, the roller rotation speed is 60 r / min, the solution delivery rate is 0.3 μL / min, the translation distance is 12 cm, the receiving distance is 12 cm, the receiving speed is 60 r / min, and the receiving time is 60 min. After electrospinning, remove the aluminum foil and the electrospun fiber membrane on it, and dry it in an oven at 60 °C for 12 hours to obtain the hydrophilic layer.

[0057] Step 2: Add polyvinylidene fluoride to chloroform solvent to obtain a polyvinylidene fluoride solution (concentration 10 wt%).

[0058] Step 3: Place the laser-etched mesh template ( Figure 6 ) on the fiber membrane prepared in Step 1, slowly pour the polyvinylidene fluoride solution prepared in Step 2 into the template, and then place the fiber membrane in an oven at 60 °C for drying to finally obtain the composite fiber membrane.

[0059] Among them, the thickness of the hydrophilic layer is 400 μm; the thickness of the hydrophobic layer is 50 μm, and the hydrophobic layer covers 15% of the total surface of the hydrophilic layer.

[0060] Figure 5 The separation effect and recycling performance of the composite fiber membrane prepared by this example for separating white oil-in-water emulsion are shown. As can be seen from the figure, the composite fiber membrane prepared in this example has good separation efficiency and separation flux for oil-in-water emulsion, and can be cleaned and reused multiple times.

[0061] Example 3

[0062] Step 1: Add polyacrylonitrile and polyethyleneimine (mass ratio 4:1) to N,N-dimethylformamide solvent, and stir magnetically at room temperature for 24 hours to obtain a polyacrylonitrile / polyethyleneimine solution (concentration 10 wt%). Draw the polyacrylonitrile / polyethyleneimine solution with a 5 mL syringe as the electrospinning solution, use a No. 19 electrostatic needle for spinning, the spinning voltage is 18 kV, the distance from the needle tip to the roller is about 15 cm, the roller rotation speed is 60 r / min, the solution delivery rate is 0.35 μL / min, the translation distance is 12 cm, the receiving distance is 12 cm, the receiving speed is 60 r / min, and the receiving time is 40 min. After spinning, remove the aluminum foil and the electrospun fiber membrane on it, and dry it in an oven at 60 °C for 12 hours to obtain the hydrophilic layer.

[0063] Step 2: Add polydimethylsiloxane and a matching curing agent (mass ratio 15:1) to n-hexane solvent to obtain a polydimethylsiloxane solution (concentration 20 wt%).

[0064] Step 3: Place the laser-etched mesh template ( Figure 1 ) on the fiber membrane prepared in Step 1, slowly pour the polydimethylsiloxane solution prepared in Step 2 into the template, and then place the fiber membrane in an oven at 60 °C for drying to finally obtain the composite fiber membrane.

[0065] Among them, the thickness of the hydrophilic layer is 350 μm; the thickness of the hydrophobic layer is 70 μm, and the hydrophobic layer covers 15% of the total surface of the hydrophilic layer.

[0066] The composite fiber membrane prepared in this example has good separation efficiency and separation flux for oil-in-water emulsions, and can be washed and reused multiple times.

[0067] Example 4

[0068] Step 1: Add polyvinyl alcohol to water, and stir magnetically at room temperature for 24 hours to obtain a polyvinyl alcohol solution (concentration 10 wt%). Draw the polyvinyl alcohol solution with a 5 mL syringe as the electrospinning solution, use a No. 19 electrostatic needle for spinning, the spinning voltage is 13 kV, the distance from the needle tip to the roller is about 11 cm, the roller rotation speed is 60 r / min, the solution delivery rate is 0.2 μL / min, the translation distance is 12 cm, the receiving distance is 12 cm, the receiving speed is 60 r / min, and the receiving time is 60 min. After spinning, remove the aluminum foil and the electrospun fiber membrane on it, and dry it in an oven at 60 °C for 12 hours to obtain the hydrophilic layer.

[0069] Step 2: Add polypropylene to toluene solvent to obtain a polypropylene solution (concentration 15 wt%).

[0070] Step 3: Place the laser-etched mesh template (Figure 1 ) Place it on the fiber membrane prepared in Step 1, slowly pour the polypropylene solution prepared in Step 2 into the template, and then place the fiber membrane in an oven at 60 °C for drying to finally obtain a composite fiber membrane.

[0071] Among them, the thickness of the hydrophilic layer is 320 μm; the thickness of the hydrophobic layer is 85 μm, and the hydrophobic layer covers 15% of the total surface of the hydrophilic layer.

[0072] The composite fiber membrane prepared in this embodiment has good separation efficiency and separation flux for oil-in-water emulsions, and can be cleaned and reused multiple times.

[0073] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An oil-removing composite fiber membrane, comprising a hydrophilic layer and a hydrophobic layer. The hydrophilic layer is a hydrophilic fiber membrane composed of a hydrophilic polymer, and the hydrophobic layer is a network structure composed of a hydrophobic polymer, and the network structure covers the surface of the hydrophilic fiber membrane.

2. The oil-removing composite fiber membrane according to claim 1, characterized in that the thickness of the hydrophilic layer is 200-500 μm; the underwater contact angle of the hydrophilic layer is above 150°.

3. The oil-removing composite fiber membrane according to claim 1, characterized in that the thickness of the hydrophobic layer is 30-100 μm; the area of the network structure covering the hydrophilic layer accounts for 5-20% of the total surface area of the hydrophilic layer; preferably, the network structure is a network structure formed by the interlaced connection of hydrophobic polymer fibers of different thicknesses; more preferably, it is a leaf vein-like structure.

4. The oil-removing composite fiber membrane according to claim 1, characterized in that the hydrophilic polymer includes one or a combination of polyacrylonitrile, polyethyleneimine, and polyvinyl alcohol; and / or, the hydrophobic polymer includes one or a combination of polydimethylsiloxane, polyvinylidene fluoride, and polypropylene.

5. The preparation method of the oil-removing composite fiber membrane according to any one of claims 1-4, characterized in that the preparation method includes the following steps: Step 1: Dissolve the hydrophilic polymer in solvent A to obtain a spinning solution, and electrospin the spinning solution to obtain a hydrophilic fiber membrane; Step 2: Dissolve the hydrophobic polymer in solvent B to obtain a hydrophobic solution; Step 3: Place the network template on the hydrophilic fiber membrane prepared in Step 1, pour the hydrophobic solution in Step 2 into the network template, and after drying, remove the network template to obtain a composite fiber membrane.

6. The preparation method of the oil-removing composite fiber membrane according to claim 5, characterized in that the hydrophilic polymer includes one or a combination of polyacrylonitrile, polyethyleneimine, and polyvinyl alcohol; and / or, the hydrophobic polymer includes one or a combination of polydimethylsiloxane, polyvinylidene fluoride, and polypropylene.

7. The preparation method of the oil-removing composite fiber membrane according to claim 5, characterized in that the mass of the hydrophilic polymer accounts for 5-10 wt% of the mass of the spinning solution, preferably 6-8 wt%; the solvent A is N,N-dimethylformamide.

8. The preparation method of the oil-removing composite fiber membrane according to claim 5, characterized in that the mass of the hydrophobic polymer accounts for 10-20 wt% of the mass of the hydrophobic solution, preferably 15-18 wt%; the solvent B is one of n-hexane, chloroform, and toluene.

9. The preparation method of the oil-removing composite fiber membrane according to claim 5, characterized in that the electrospinning conditions are: the electrospinning voltage is 10-25 kV; the spinning flow rate is 0.2-0.5 μL / min; the receiving distance is 5-20 cm; the receiving time is 40-80 min.

10. The application of the oil-removing composite fiber membrane according to any one of claims 1-4, characterized in that the composite fiber membrane is used for oil removal from oil-in-water emulsions.

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