Preparation method of electrostatic spinning / polyvinyl alcohol film for oil-water separation

Abstract

The invention discloses a preparation method of an electrostatic spinning / polyvinyl alcohol porous hydrogel film, which is used for efficient oil-water separation. The method comprises the following steps: preparing a polyvinylidene fluoride electrostatic spinning solution, and spinning to obtain a polyvinylidene fluoride electrostatic spinning membrane; uniformly mixing and grinding polyvinyl alcohol and tannic acid; and immersing the electrostatic spinning membrane in the mixed powder, spraying a glutaraldehyde solution for chemical crosslinking, and then immersing the electrostatic spinning membrane in a ferric trichloride solution for physical crosslinking to finally form the porous hydrogel membrane. The film is high in porosity, strong in hydrophilicity, capable of effectively separating an oil-water mixture and preventing oil drops from passing through, and high in separation efficiency. The preparation process is simple, does not need complex equipment, is suitable for large-scale production and is low in cost. The film is high in mechanical strength, good in anti-pollution performance, capable of being repeatedly used, environmentally friendly and capable of meeting the sustainable development requirement.

Description

Technical Field

[0001] The invention relates to the technical field of oil-water separation, and in particular to a method for preparing an electrostatic spinning / polyvinyl alcohol film for oil-water separation. Background Art

[0002] With the acceleration of industrialization and urbanization, the discharge of oily wastewater has become increasingly serious, posing a huge threat to the ecological environment and human health. Oily wastewater often contains tiny oil droplets and stable emulsions, which are difficult to completely remove by traditional methods (such as gravity separation, centrifugal separation or flotation) due to the action of surfactants. The discharge of oily wastewater not only causes water pollution, but also causes irreversible damage to aquatic ecosystems. Therefore, the development of an efficient, economical and environmentally friendly oil-water separation technology has become a global focus.

[0003] Membrane separation technology is considered to be one of the most promising strategies for achieving low-cost and efficient oil-water separation due to its simple operation, low energy consumption and high separation efficiency. It has shown significant advantages in the treatment of micro- / nano-scale surfactant-stabilized oil / water emulsions. In recent years, polyvinyl alcohol (PVA) hydrogel has been widely used in the field of oil-water separation due to its environmental friendliness and strong hydrophilicity. Polyvinyl alcohol hydrogel can effectively adsorb water molecules through its abundant hydrophilic groups to form a stable hydration layer, thereby achieving oil-water separation. However, polyvinyl alcohol hydrogel has some disadvantages that limit its application. On the one hand, its pore structure is dense and the pore size is small, resulting in low water flux, which is difficult to meet the needs of efficient separation; on the other hand, polyvinyl alcohol hydrogel has low mechanical strength and is easily damaged in practical applications, which limits its service life and separation efficiency.

[0004] In order to overcome these shortcomings, current research mainly focuses on improving the performance of polyvinyl alcohol hydrogels by modification methods. For example, the mechanical strength of the hydrogel is enhanced by introducing a cross-linking agent (such as glutaraldehyde), or its pore structure is improved by adding other functional materials (such as nanoparticles). However, although the ice template method commonly used in the prior art can improve the pore structure of polyvinyl alcohol hydrogels to a certain extent, the method has a complex process and requires precise control of temperature and freezing time, which increases the preparation cost and operation difficulty. In addition, the ice template method is difficult to achieve large-scale production, which limits its promotion in practical industrial applications. Summary of the invention

[0005] The present invention aims to simplify the preparation process, reduce production costs, and achieve higher separation efficiency and anti-fouling performance by optimizing the membrane structure.

[0006] To achieve the above object, the present invention provides the following technical solution: a method for preparing an electrospinning / polyvinyl alcohol film for oil-water separation, comprising the following steps:

[0007] Step 1, preparing a polyvinylidene fluoride electrospinning solution, and spinning to obtain a polyvinylidene fluoride electrospinning membrane;

[0008] Step 2, grinding polyvinyl alcohol and tannic acid separately and then mixing and grinding them to obtain polyvinyl alcohol / tannic acid mixed powder;

[0009] Step three, placing the electrospun membrane into the mixed powder and wrapping it evenly, taking it out and spraying it with glutaraldehyde solution, placing it in a closed environment for cross-linking, taking it out and soaking it in ferric chloride solution to obtain an electrospun / polyvinyl alcohol porous hydrogel film.

[0010] Specifically, the ratio of the polyvinylidene fluoride electrospinning solution is 12wt%.

[0011] Specifically, the content of polyvinyl alcohol in the polyvinyl alcohol / tannic acid mixed powder is 0-1 wt %.

[0012] Specifically, the concentration of the glutaraldehyde solution is 1-5 wt %.

[0013] Specifically, the step one specifically includes the following steps:

[0014] S1. Adding polyvinylidene fluoride powder into a mixed solution of N,N-dimethylformamide and acetone in a volume ratio of 6:4, stirring at 50° C. for 3 h to obtain an electrospinning precursor solution;

[0015] S2, electrospinning was performed at a high voltage of 15 kV, a flow rate of 0.9 mL / h, a drum rotation speed of 450 rpm, and a distance of 15 cm between the nozzle and the collector to obtain a polyvinylidene fluoride electrospinning membrane;

[0016] S3. The obtained electrospun membrane was placed in an oven at 60° C. for 24 hours to remove excess solvent.

[0017] Specifically, the step three includes the following steps:

[0018] S1, wet the electrospun membrane with ethanol and then place it in deionized water for 3 h for solvent exchange;

[0019] S2, placing the wetted electrospun membrane into the polyvinyl alcohol / tannic acid mixed powder to adhere evenly, taking it out, spraying it evenly with glutaraldehyde solution and placing it in a closed environment for 24 hours to obtain a cross-linked electrospun / polyvinyl alcohol precursor membrane;

[0020] S3. Soak the electrospinning / polyvinyl alcohol precursor film in a ferric chloride solution for 5 hours to obtain a stable electrospinning / polyvinyl alcohol porous hydrogel film.

[0021] The principle and beneficial effects of this technical solution:

[0022] The present invention uses polyvinylidene fluoride electrospinning membrane as a substrate, combined with mixed powder of polyvinyl alcohol and tannic acid, and the cross-linking effect of glutaraldehyde and ferric chloride to form a porous hydrogel film with high porosity, large pore size and excellent hydrophilic properties. The film can adsorb water molecules through its abundant hydrophilic groups to form a stable hydration layer, thereby effectively separating the oil phase and the water phase in the oil-water mixture, while preventing oil droplets from passing through the membrane pores, and achieving efficient oil-water separation.

[0023] The preparation process of the present invention does not require complicated equipment and harsh conditions, is simple to operate, easy to control, has a high film-forming rate, is suitable for large-scale industrial production, and effectively reduces production costs. The prepared electrospinning / polyvinyl alcohol porous hydrogel film has a high porosity and a large pore size, which significantly improves the water flux of the membrane and can quickly process a large amount of oil-water mixture. At the same time, the film has excellent hydrophilic properties, which further enhances its adsorption capacity for the water phase and improves the separation efficiency.

[0024] Through the cross-linking of glutaraldehyde and ferric chloride, the mechanical strength of the film is significantly improved, and it can maintain a stable structure in the complex oil-water separation process, is not easy to break, and prolongs its service life. The film shows good anti-pollution performance during the separation process, and its performance can be restored by simple cleaning after separation. It can be reused many times, further reducing the cost of use and improving resource utilization. At the same time, the materials used are all environmentally friendly materials, meet the requirements of sustainable development, and have no negative impact on the ecological environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the preparation method of the electrospinning / polyvinyl alcohol porous hydrogel film of the present invention;

[0026] Figure 2 This is the bonding mechanism diagram of electrospinning / polyvinyl alcohol porous hydrogel film;

[0027] Figure 3 Schematic diagram of water contact angle and underwater oil contact angle of electrospun / polyvinyl alcohol porous hydrogel film;

[0028] Figure 4 The scanning electron micrographs of electrospun / polyvinyl alcohol porous hydrogel films PVA-0 to PVA-1;

[0029] Figure 5 The water contact angle and underwater oil contact angle of electrospun / polyvinyl alcohol porous hydrogel film;

[0030] Figure 6 The separation performance of electrospun / polyvinyl alcohol porous hydrogel film for oil-in-water emulsion;

[0031] Figure 7 The separation performance of electrospun / polyvinyl alcohol porous hydrogel films for different oil-in-water emulsions;

[0032] Figure 8 Cycling performance of electrospun / polyvinyl alcohol porous hydrogel films for different oil-in-water emulsions. DETAILED DESCRIPTION

[0033] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments:

[0034] like Figure 1-Figure 7 As shown, an electrospinning / polyvinyl alcohol porous hydrogel film that can be used for oil-water separation comprises the following steps:

[0035] Step 1: prepare a polyvinylidene fluoride electrospinning solution, and perform spinning to obtain a polyvinylidene fluoride electrospinning membrane: add polyvinylidene fluoride powder to a mixed solution of N,N-dimethylformamide and acetone in a volume ratio of 6:4, and stir at 50°C for 3 hours to obtain an electrospinning precursor solution; perform electrospinning at a high voltage of 15 kV, a flow rate of 0.9 mL / h, a drum rotation speed of 450 rpm, and a distance of 15 cm between the nozzle and the collector to obtain a polyvinylidene fluoride electrospinning membrane; place the obtained electrospinning membrane in an oven at 60°C and treat for 24 hours to remove excess solvent.

[0036] Step 2: Grind the polyvinyl alcohol and tannic acid separately and then mix and grind them to obtain a polyvinyl alcohol / tannic acid mixed powder; in the porous hydrogel, the rich pore structure is achieved through the stacking effect between the polyvinyl alcohol and tannic acid particles and their different solubility characteristics.

[0037] Step three, use ethanol to wet the electrospinning membrane, and then place it in deionized water for 3 hours for solvent exchange; place the wetted electrospinning membrane in polyvinyl alcohol / tannic acid mixed powder to adhere evenly, take it out and evenly spray it with glutaraldehyde solution and place it in a closed environment for 24 hours to allow glutaraldehyde and polyvinyl alcohol to undergo acetal reaction to obtain a cross-linked electrospinning / polyvinyl alcohol precursor membrane; soak the electrospinning / polyvinyl alcohol precursor membrane in ferric chloride solution for 5 hours to allow iron ions to react with the metal-phenolic hydroxyl group of tannic acid to obtain a stable electrospinning / polyvinyl alcohol porous hydrogel film.

[0038] Example 1: Polyvinyl alcohol content is 0wt%

[0039] In this embodiment, the content of polyvinyl alcohol is 0 wt%. Figure 6 As shown in Figure 2, the water flux of the membrane prepared by this method during oil-water separation was 29856.68 L·m -2·h -1 bar -1 ; The emulsion flux is 17012.36 L·m -2 ·h -1 bar -1 ; Separation efficiency is 45.6%; COD value is 210.3mg / L -1 This shows that although the absence of polyvinyl alcohol limits the improvement of separation efficiency, its hydrophilicity and mechanical properties can still meet the basic requirements of oil-water separation.

[0040] Example 2: Polyvinyl alcohol content is 0.2wt%

[0041] In this embodiment, the content of polyvinyl alcohol is 0.2 wt %. Figure 6 As shown in Figure 2, the water flux of the membrane prepared by this method during oil-water separation was 25591.45 L·m -2 ·h -1 bar -1 ; The emulsion flux is 14928.34 L·m -2 ·h -1 bar -1 ; Separation efficiency is 79.4%; COD value is 153.2mg / L -1 This indicates that an appropriate amount of polyvinyl alcohol can effectively improve the pore structure of the membrane, thereby increasing the water flux and separation efficiency.

[0042] Example 3: Polyvinyl alcohol content is 0.4wt%

[0043] In this embodiment, the content of polyvinyl alcohol is 0.4 wt %. Figure 6 As shown in Figure 2, the water flux of the membrane prepared by this method during oil-water separation was 21300.84 L·m -2 ·h -1 bar -1 ; The emulsion flux is 13358.69 L·m -2 ·h -1 bar -1 ; Separation efficiency is 99.2%; COD value is 55.2mg / L -1 This shows that with the increase of polyvinyl alcohol content, the pore structure and hydrophilicity of the film are further improved, thereby enhancing its oil-water separation performance. Considering the flux, efficiency and COD value of the membrane, the 0.4wt% membrane is the best.

[0044] Example 4: Polyvinyl alcohol content is 0.6wt%

[0045] In this embodiment, the content of polyvinyl alcohol is 0.6 wt %. Figure 6As shown in Figure 2, the water flux of the membrane prepared by this method during oil-water separation was 7972.41 L·m -2 ·h -1 bar -1 ; The emulsion flux is 4841.63 L·m -2 ·h -1 bar -1 ; Separation efficiency is 98.7%; COD value is 63.2mg / L -1 This suggests that too high a PVA content may lead to the densification of the pore structure, thus affecting the water flux.

[0046] Example 5: Polyvinyl alcohol content is 0.8wt%

[0047] In this embodiment, the content of polyvinyl alcohol is 0.8 wt %. Figure 6 As shown in Figure 2, the water flux of the membrane prepared by this method during oil-water separation was 1532.01 L·m -2 ·h -1 bar -1 ; The emulsion flux is 2409.72 L·m -2 ·h -1 bar -1 ; Separation efficiency is 98.2%; COD value is 64.3mg / L -1 This indicates that too high a PVA content will not only reduce the water flux but may also have a certain impact on the separation efficiency.

[0048] Example 6: Polyvinyl alcohol content is 1wt%

[0049] In this embodiment, the content of polyvinyl alcohol is 1 wt%. Figure 6 As shown in the figure, the membrane prepared by this method has blocked membrane pores and no flux during oil-water separation. The porosity and hydrophilicity of the membrane have reached the limit, but the mechanical properties are slightly insufficient. This shows that too high a content of polyvinyl alcohol will lead to blockage of membrane pores and seriously affect the separation performance of the membrane.

[0050] Embodiments 7 to 11

[0051] The effect of glutaraldehyde solution concentration (1wt%, 2wt%, 3wt%, 4wt%, 5wt%) on the mechanical properties and separation performance of the membrane was studied by adjusting the concentration of glutaraldehyde solution in step 3. When the glutaraldehyde concentration was 3wt%, the mechanical properties and separation efficiency of the membrane reached the best balance.

[0052] Performance testing of different oils

[0053] like Figure 7As shown in the figure, different water-in-oil emulsions with and without surfactants were prepared. The electrospinning / polyvinyl alcohol porous hydrogel film has a high separation flux for emulsions without surfactants (water-n-octane, water-n-hexane, water-petroleum ether, water-cyclohexane, water-xylene and water-kerosene), all of which are above 12186.53L·m-2·h-1·bar-1, and the separation efficiency is also above 98.7%. For emulsions containing surfactants (water-n-octane, water-cyclohexane, water-petroleum ether, water-xylene and water-kerosene), the separation flux is about 19685.73L·m-2·h-1·bar-1, and the separation efficiency is greater than 98.2%. In addition, the COD values ​​of these filtrates are all lower than 120mg·L-1 (China's wastewater discharge level 3 standard limit), indicating that the electrospinning / polyvinyl alcohol porous hydrogel film has excellent separation effects on various types of water-in-oil emulsions.

[0054] Cycle Test

[0055] like Figure 8 As shown, 60 water cycles can be performed under the membrane of the terminal filtration device, and the water flux remains above 21304.25L·m-2·h-1·bar-1. The membrane was tested for the separation of kerosene-in-water emulsions. It can be seen that the emulsion flux will decrease from 13735.21L·m-2·h-1·bar-1 to 3919.91L·m-2·h-1·bar-1 within 15 cycles, but the emulsion separation efficiency can reach more than 99.2% during the cycle. After ultrasonic cleaning, the emulsion flux will return to its previous level. Through simple ultrasonic cleaning, the PVDF-PTGF membrane can continuously separate kerosene-in-water emulsions 45 times with a very high separation efficiency.

[0056] in conclusion

[0057] In summary, the present invention successfully prepared an electrospinning / polyvinyl alcohol porous hydrogel film by optimizing the polyvinyl alcohol content and glutaraldehyde concentration. The film has high porosity, large pore size and excellent hydrophilicity, and can effectively separate the oil phase and water phase in the oil-water mixture. Its preparation process does not require complex equipment and harsh conditions, is easy to operate, easy to control, and is suitable for large-scale industrial production. By adjusting the content of polyvinyl alcohol and glutaraldehyde, the optimization of film performance can be achieved, thereby meeting different oil-water separation requirements.

[0058] The above is only an embodiment of the present invention, and the common knowledge such as the known specific technical solutions or characteristics in the solution is not described in detail here. For those skilled in the art, without departing from the technical solution of the present invention, several modifications and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing an electrospinning / polyvinyl alcohol porous hydrogel film that can be used for oil-water separation, characterized in that: The following steps are involved: Step 1, preparing a polyvinylidene fluoride electrospinning solution, and spinning to obtain a polyvinylidene fluoride electrospinning membrane; Step 2, grinding polyvinyl alcohol and tannic acid separately and then mixing and grinding them to obtain polyvinyl alcohol / tannic acid mixed powder; Step three, placing the electrospun membrane into the mixed powder and wrapping it evenly, taking it out and spraying it with glutaraldehyde solution, placing it in a closed environment for cross-linking, taking it out and soaking it in ferric chloride solution to obtain an electrospun / polyvinyl alcohol porous hydrogel film.

2. The method for preparing an electrospinning / polyvinyl alcohol porous hydrogel film for oil-water separation according to claim 1, characterized in that: The ratio of the polyvinylidene fluoride electrospinning solution is 12wt%.

3. The method for preparing an electrospinning / polyvinyl alcohol porous hydrogel film for oil-water separation according to claim 1, characterized in that: The content of polyvinyl alcohol in the polyvinyl alcohol / tannic acid mixed powder is 0-1 wt %.

4. The method for preparing an electrospinning / polyvinyl alcohol porous hydrogel film for oil-water separation according to claim 1, characterized in that: The concentration of the glutaraldehyde solution is 1-5 wt %.

5. The method for preparing an electrospinning / polyvinyl alcohol porous hydrogel film for oil-water separation according to claim 1, characterized in that: The step one specifically includes the following steps: S1. Adding polyvinylidene fluoride powder into a mixed solution of N,N-dimethylformamide and acetone in a volume ratio of 6:4, stirring at 50° C. for 3 h to obtain an electrospinning precursor solution; S2, electrospinning was performed at a high voltage of 15 kV, a flow rate of 0.9 mL / h, a drum rotation speed of 450 rpm, and a distance of 15 cm between the nozzle and the collector to obtain a polyvinylidene fluoride electrospinning membrane; S3. The obtained electrospun membrane was placed in an oven at 60° C. for 24 hours to remove excess solvent.

6. The method for preparing an electrospinning / polyvinyl alcohol porous hydrogel film for oil-water separation according to claim 1, characterized in that: The step three specifically includes the following steps: S1, wet the electrospun membrane with ethanol and then place it in deionized water for 3 h for solvent exchange; S2, placing the wetted electrospun membrane into the polyvinyl alcohol / tannic acid mixed powder to adhere evenly, taking it out, spraying it evenly with glutaraldehyde solution and placing it in a closed environment for 24 hours to obtain a cross-linked electrospun / polyvinyl alcohol precursor membrane; S3. Soak the electrospinning / polyvinyl alcohol precursor film in a ferric chloride solution for 5 hours to obtain a stable electrospinning / polyvinyl alcohol porous hydrogel film.

Images