Oil-water separation membrane as well as preparation method and application thereof

Abstract

The invention discloses a preparation method of an oil-water separation membrane, which comprises the following steps: mixing polyether sulfone powder, polyvinylpyrrolidone and N, N-dimethylformamide, heating and stirring to form a membrane casting solution; putting the prepared membrane casting solution into a constant-temperature oven until bubbles are completely removed; cooling the defoamed membrane casting solution to room temperature, and uniformly coating a glass plate with the membrane casting solution by using a stainless steel scraper; rapidly immersing the glass plate covered with the membrane casting solution in a coagulating bath composed of a chitosan quaternary ammonium salt aqueous solution to carry out a non-solvent induced phase separation process; taking out the solid membrane from the coagulating bath, soaking the solid membrane in deionized water for 24 hours, and replacing water for multiple times during soaking; the preparation and modification of the membrane are carried out at the same time, a firm hydration layer can be constructed, the pollution resistance mechanism of the surface of the membrane can be enhanced, the biological pollution of the surface of the membrane can be reduced while high flux is ensured, the anti-pollution performance of the membrane is improved, the service life of the membrane is prolonged, and the preparation process is simple and easy to implement industrially.

Description

Technical Field

[0001] The present invention relates to the technical field of membrane separation, and particularly to a preparation method and application of an oil-water separation membrane. Background Art

[0002] Water resource pollution has become an important issue affecting the ecological environment and human development. Ultrafiltration technology has been widely used in the water treatment process due to its characteristics such as low energy consumption and easy operation. However, the high cost of raw materials, the complexity of the preparation process, the shortened lifespan caused by membrane fouling, and the cleaning cost have hindered the application of ultrafiltration membranes in industry. Therefore, it is an urgent need to develop an anti-fouling ultrafiltration membrane with simple preparation and low cost.

[0003] As a common chitosan derivative, quaternary ammonium chitosan enhances its water solubility, antibacterial property, and adsorption performance by introducing quaternary ammonium groups. In the field of oil-water separation, quaternary ammonium chitosan is widely used due to its unique properties (such as cationic characteristics, adsorption ability, and film-forming property). Its hydrophilic groups (such as hydroxyl groups and quaternary ammonium groups) can attract a large number of water molecules through hydrogen bonding and electrostatic interaction to construct a firm hydration layer, strengthening the "pollution resistance" mechanism on the membrane surface. At the same time, it can reduce the biological fouling on the membrane surface and extend the service life of the membrane. Summary of the Invention

[0004] In view of the above-mentioned prior art, the present invention provides a preparation method of an oil-water separation membrane, which can construct a firm hydration layer, strengthen the "pollution resistance" mechanism on the membrane surface, reduce the biological fouling on the membrane surface while ensuring high flux, improve the anti-fouling performance of the membrane, and extend the service life of the membrane.

[0005] In order to solve the above technical problems, a preparation method of an oil-water separation membrane proposed by the present invention includes the following steps:

[0006] Step 1) Mix polyethersulfone, polyvinylpyrrolidone, and N,N-dimethylformamide and heat and stir to form a casting solution; wherein, the mass percentages of the polyethersulfone powder, polyvinylpyrrolidone, and N,N-dimethylformamide are: 10 - 20% / 1 - 6% / 74 - 89%, and the sum of the mass percentages is 100%; place the above casting solution in a constant-temperature oven until the bubbles are completely removed;

[0007] Step 2) Slowly cool the degassed casting solution in Step 1 to room temperature in the air, and evenly coat the casting solution on a glass plate with a stainless steel scraper to form a liquid film with a thickness of 200 ± 5 μm on the surface of the glass plate;

[0008] Step 3) Quickly immerse the glass plate covered with the liquid film in a coagulation bath to perform a non-solvent-induced liquid film phase separation process to obtain a solid membrane,

[0009] Step 4) Take out the solid membrane from the coagulation bath and soak it in deionized water for 24 hours, changing the water several times during this period.

[0010] Further, in the preparation method of the present invention, wherein:

[0011] In the said step 1), the process conditions of heating and stirring are: heating to 70 - 80 °C and then stirring for 6 - 12 h. The process conditions for removing bubbles from the casting solution are: the temperature of the constant temperature oven is 60 - 80 °C, and the heating time is 4 - 6 hours until the bubbles are completely removed.

[0012] In the said step 2), the process of uniformly coating the casting solution on the glass plate is: pour the casting solution on one side of the glass plate, and then use a stainless - steel film - scraping rod to uniformly coat the casting solution on the glass plate at a speed of 0.1 m / s according to the required thickness.

[0013] In the said step 3), the process of non - solvent - induced liquid - film phase separation is: immerse the glass plate covered with the liquid film in the coagulation bath at a constant temperature of 25 °C within 5 seconds, and the phase - transformation process can occur within 1 - 5 minutes; the coagulation bath is an aqueous solution of chitosan quaternary ammonium salt. The mass fraction of the chitosan quaternary ammonium salt aqueous solution is 0.8 - 1.2%.

[0014] In the said step 4), during the 24 - hour immersion of the solid membrane in deionized water, change the water every 2 hours in the first 6 hours, and then change the water every 8 hours.

[0015] Compared with the prior art, the beneficial effects of the present invention are:

[0016] (1) During the preparation process of the oil - water separation membrane of the present invention, in the non - solvent - induced phase - separation process, the reaction surface segregation technology is used to realize the synchronous modification of the membrane surface and membrane pores, and the process of grafting the modifier on the membrane surface is achieved with a single coagulation bath, establishing an in - situ anti - pollution system, and avoiding the disadvantages such as complex surface coating and surface grafting operations and membrane - pore blockage;

[0017] (2) Polyvinylpyrrolidone in the casting solution reacts quickly with chitosan quaternary ammonium salt in the coagulation bath to form a hydrogel layer, which can prevent pollutants from contacting the membrane surface;

[0018] (3) By regulating the concentration of chitosan quaternary ammonium salt in the coagulation bath, the regulation of the membrane structure is realized. While ensuring high flux, the anti - pollution performance of the membrane is improved; the oil - water separation membrane prepared by the present invention is used as a microfiltration membrane or ultrafiltration membrane in the field of water treatment.

[0019] (4) The preparation process is simple, the process flow is short, and the reaction conditions are mild and controllable. Description of the Drawings

[0020] Figure 1Scanning electron microscope photograph of the oil-water separation membrane 1 prepared in Example 1;

[0021] Figure 2 Scanning electron microscope photograph of the oil-water separation membrane 2 prepared in Example 2;

[0022] Figure 3 Scanning electron microscope photograph of the oil-water separation membrane 3 prepared in Example 3;

[0023] Figure 4 Graph comparing the pure water fluxes of the oil-water separation membranes prepared in Examples 1 to 4 and the comparative example;

[0024] Figure 5 Graph comparing the permeation fluxes of the oil-water separation membranes prepared in Examples 1 to 4 and the comparative example;

[0025] Figure 6 Graph comparing the anti-fouling performances of the oil-water separation membranes prepared in Examples 1 to 4 and the comparative example. Detailed implementation mode

[0026] The design concept of a preparation method for an oil-water separation membrane proposed by the present invention is as follows: The preparation and modification of the membrane are carried out simultaneously. The casting solution formula consists of a certain proportion of polyethersulfone, polyvinylpyrrolidone, and N,N-dimethylformamide; polyvinylpyrrolidone in the casting solution reacts rapidly with chitosan quaternary ammonium salt in the coagulation bath to form a hydrogel layer, which can prevent pollutants from contacting the membrane surface. By introducing quaternary ammonium groups, its water solubility, antibacterial property, and adsorption performance are enhanced. Its hydrophilic groups (quaternary ammonium groups) can attract a large number of water molecules through hydrogen bonding and electrostatic interactions, and a firm hydration layer can be constructed to strengthen the "pollution resistance" mechanism on the membrane surface. By regulating the concentration of the chitosan quaternary ammonium salt aqueous solution in the coagulation bath, the regulation of the membrane structure can be achieved. While ensuring high flux, the biological fouling on the membrane surface can be reduced, the anti-fouling performance of the membrane is improved, the service life of the membrane is extended, and the preparation process of the present invention is simple and easy to implement industrially. Extend the service life of the membrane.

[0027] The following further illustrates the present invention in conjunction with the accompanying drawings and specific embodiments, but the following embodiments are by no means any limitation to the present invention.

[0028] Example 1

[0029] The preparation of an oil-water separation membrane is as follows:

[0030] 1) Add 4.8 g of polyethersulfone, 0.8 g of polyvinylpyrrolidone, and 24.3 g of N,N-dimethylformamide (the mass percentages among the three are approximately 16.05% / 2.68% / 81.27%) into a clean threaded bottle, mechanically stir at 70 °C for 8 h, and then place it in a constant temperature oven and let it stand for 4 h at 60 °C to defoam to obtain a casting solution.

[0031] 2) Air-cool the casting solution prepared in step 1) to room temperature. Take a clean, dry and flat glass plate with a length of 15 cm and a width of 10 cm on the test bench. Pour the casting solution on one side of the glass plate, and use a stainless steel film scraping rod to uniformly coat the casting solution on the glass plate at a scraping speed of about 0.1 m / s, initially forming a liquid film with a thickness of 200 ± 5 μm on the glass plate surface.

[0032] 3) Immerse the glass plate covered with the liquid film quickly into an aqueous solution of quaternary ammonium salt of chitosan with a mass fraction of 0.8% for the non-solvent induced phase separation process, that is, immerse the glass plate covered with the liquid film into the coagulation bath at a constant temperature of 25°C within 5 seconds for 5 minutes. The phase inversion process can occur within 5 minutes, thus obtaining a solid film.

[0033] 4) Take out the solid film from the coagulation bath and soak it in deionized water for 24 h. Change the water every 2 hours in the first 6 hours, and then change the water every 8 hours. The finally obtained film is denoted as oil-water separation membrane 1. Figure 1 It is the scanning electron microscope photograph of the oil-water separation membrane 1.

[0034] Perform separation performance testing on the oil-water separation membrane 1 prepared in Example 1. For the pure water flux data of the membrane, refer to Figure 4 , and its value is 394 Lm -2 h -1 bar -1 ; During the separation process of the oil-water emulsion (0.1 wt% pump oil, 0.01 wt% sodium dodecyl sulfate, 99.89 wt% water), for the membrane permeation flux data during 30 min of operation, refer to Figure 5 , and its value is 348 Lm -2 h -1 bar -1 . After cleaning with deionized water for 30 min, the flux recovery rate reaches 82%, as shown in Figure 6 .

[0035] Example 2

[0036] The preparation of an oil-water separation membrane is generally the same as that in Example 1, except that in step 3), the mass fraction of the aqueous solution of quaternary ammonium salt of chitosan used in the coagulation bath is changed from 0.8% to 0.9%. The finally obtained film is denoted as oil-water separation membrane 2. Figure 2 It is the scanning electron microscope photograph of the oil-water separation membrane 2.

[0037] Perform separation performance testing on the oil-water separation membrane 2 prepared in Example 2. For the pure water flux data of the membrane, refer to Figure 4 , and its value is 412 Lm -2 h -1 bar -1; During the separation process of the oil-water emulsion, the membrane permeation flux data for 30 minutes of operation can be seen in Figure 5 , and its value is 370 Lm -2 h -1 bar -1 . After cleaning with deionized water for 30 minutes, the flux recovery rate reaches 95%, as shown in Figure 6 .

[0038] Example 3

[0039] The preparation of an oil-water separation membrane is generally the same as that in Example 1, except that in step 3), the mass fraction of the chitosan quaternary ammonium salt aqueous solution used in the coagulation bath is changed from 0.8% to 1.0%, and the finally obtained membrane is denoted as the oil-water separation membrane 3. Figure 3 This is the scanning electron microscope photo of the oil-water separation membrane 3. The separation performance of the oil-water separation membrane 3 prepared in Example 3 is tested. The pure water flux data of the membrane can be seen in Figure 4 , and its value is 600 Lm -2 h -1 bar -1 ; During the separation process of the oil-water emulsion, the membrane permeation flux data for 30 minutes of operation can be seen in Figure 5 , and its value is 542 Lm -2 h -1 bar -1 . After cleaning with deionized water for 30 minutes, the flux recovery rate reaches 96%, as shown in Figure 6 .

[0040] Example 4

[0041] The preparation of an oil-water separation membrane is generally the same as that in Example 1, except that in step 3), the mass fraction of the chitosan quaternary ammonium salt aqueous solution used in the coagulation bath is changed from 0.8% to 1.2%, and the finally obtained membrane is denoted as the oil-water separation membrane 4.

[0042] The separation performance of the oil-water separation membrane 4 prepared in Example 4 is tested. The pure water flux data of the membrane can be seen in Figure 4 , and its value is 492 Lm -2 h -1 bar -1 ; During the separation process of the oil-water emulsion, the membrane permeation flux data for 30 minutes of operation can be seen in Figure 5 , and its value is 472 Lm -2 h -1 bar -1 . After cleaning with deionized water for 30 minutes, the flux recovery rate reaches 96%, as shown in Figure 6 .

[0043] Comparative Example

[0044] Preparation of an ultrafiltration membrane, the preparation process of which is substantially the same as that of Example 1, except that in step 3), the glass plate covered with the liquid membrane is quickly immersed in deionized water for a non-solvent induced phase separation process; the finally obtained ultrafiltration membrane based on reaction surface segregation is denoted as the comparative membrane.

[0045] The separation performance of the ultrafiltration membrane prepared in the comparative example was tested, and the pure water flux data of the membrane are shown in Figure 4 , and its value is 359 Lm -2 h -1 bar -1 ; during the separation process of the oil-water emulsion, the membrane permeation flux data after running for 30 min are shown in Figure 5 , and its value is 305 L·m -2 h -1 bar -1 . After cleaning with deionized water for 30 min, the flux recovery rate reached 71%, as shown in Figure 6 .

[0046] In summary, in the preparation method of the present invention, during the non-solvent induced phase separation process, the reaction surface segregation technology is used for the preparation and synchronous modification of the oil-water separation ultrafiltration membrane, and the process of grafting the modifier on the membrane surface is realized with a single coagulation bath, an in-situ anti-fouling system is established. By introducing polyvinylpyrrolidone and chitosan quaternary ammonium salt, a hydrogel is formed on the outer surface of the ultrafiltration membrane to construct a hydrophilic membrane surface, and the membrane fouling is resisted through the hydration layer effect. It can be seen from Figures 1 to 3 that the introduction of chitosan quaternary ammonium salt makes a porous structure formed on the membrane surface, increasing the membrane flux. Through the comparison of the pure water flux, permeation flux and anti-fouling performance of Examples 1 to 4 and the comparative example (see Table 1), it is found that compared with the comparative example, both the pure water flux and the permeation flux of the surface segregation oil-water separation membrane using chitosan quaternary ammonium salt are improved, and the flux recovery rate is significantly improved. In addition, in the preparation method of the present invention, by regulating the concentration of the chitosan quaternary ammonium salt aqueous solution in the coagulation bath, the regulation of the membrane structure can be realized, and while ensuring high flux, the anti-fouling performance of the membrane is improved. The comprehensive performance of the ultrafiltration membrane prepared in Example 3 reaches the optimal value.

[0047] Table 1

[0048]

[0049] The above is only the specific implementation manner disclosed by the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be thought of by those skilled in the art under the inspiration of the technical solutions disclosed by the present invention without departing from the purpose of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for preparing an oil-water separation membrane, characterized in that: The method comprises the following steps: Step 1) polyethersulfone, polyvinyl pyrrolidone and N,N-dimethylformamide are mixed and heated and stirred to form a casting solution; wherein the mass percentages of the polyethersulfone powder, polyvinyl pyrrolidone and N,N-dimethylformamide are: 10-20% / 1-6% / 74-89%, and the sum of the mass percentages is 100%; the casting solution is placed in a constant temperature oven until bubbles are completely removed; Step 2) air-cooling the degassed casting liquid in step 1) to room temperature, and evenly coating the casting liquid on a glass plate with a stainless steel scraper to form a liquid film with a thickness of 200±5 μm on the surface of the glass plate; Step 3) The glass plate covered with the liquid film is quickly immersed in a solidification bath to perform a non-solvent induced liquid film phase separation process to obtain a solid film. Step 4) The solid film is taken out from the coagulation bath and immersed in deionized water for 24 hours, during which the water is changed several times.

2. The preparation method according to claim 1, characterized in that: In the step 1), the process conditions of heating and stirring are: heating to 70-80° C. and stirring for 6-12 hours.

3. The preparation method according to claim 1, characterized in that: In the step 1), the process conditions for removing bubbles from the casting solution are: the temperature of the constant temperature oven is 60-80° C., and the heating time is 4-6 hours, until the bubbles are completely removed.

4. The preparation method according to claim 1, characterized in that: In step 2), the process of uniformly coating the casting liquid on the glass plate is: pouring the casting liquid on one side of the glass plate, and then uniformly coating the casting liquid on the glass plate according to the required thickness with a stainless steel scraper at a speed of 0.1 m / s.

5. The preparation method according to claim 1, characterized in that: In the step 3), the process of the non-solvent induced liquid film phase separation is: immersing the glass plate covered with the liquid film in a coagulation bath at a constant temperature of 25° C. for 5 minutes within 5 seconds, wherein the coagulation bath is a chitosan quaternary ammonium salt aqueous solution.

6. The preparation method according to claim 1, characterized in that: In the step 3), the mass fraction of the chitosan quaternary ammonium salt solution is 0.8-1.2%.

7. The preparation method according to claim 1, characterized in that: In the step 4), the solid membrane is immersed in deionized water for 24 hours, and the water is changed every 2 hours in the first 6 hours, and then every 8 hours.

8. An oil-water separation membrane, characterized in that: The method is prepared according to any one of claims 1 to 7.

9. An application of an oil-water separation membrane, characterized in that: The oil-water separation membrane according to claim 8 is used as a microfiltration membrane or an ultrafiltration membrane in the field of water treatment.

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