A method for preparing a superhydrophilic, antifouling modified PVDF membrane coupled with a biodemulsifier

Abstract

This invention discloses a method for preparing a superhydrophilic, antifouling modified PVDF membrane coupled with a bio-demulsifier, comprising the following steps: adding tannic acid to a weakly alkaline buffer solution and stirring to obtain solution A, wherein the mass ratio of tannic acid to the weakly alkaline buffer solution is 1:1200~1300; dissolving FeCl3•6H2O in water to obtain an aqueous FeCl3 solution, mixing the FeCl3 aqueous solution with solution A and stirring to obtain solution B, wherein the mass ratio of FeCl3•6H2O to water when FeCl3•6H2O is dissolved in water is 1:1965~1970, and the molar ratio of iron ions to tannic acid in solution B is 1:1.5~2.5; placing the pretreated PVDF membrane in solution B, and performing a co-deposition reaction by constant temperature shaking to obtain membrane M1; drying membrane M1 and placing it in a demulsifier culture medium, and performing constant temperature shaking to obtain membrane M2; drying membrane M2 to obtain the finished product. The preparation method provided in this invention is simple, highly feasible, easy to promote, and has good commercial prospects.

Description

TECHNICAL FIELD

[0001] The application relates to the field of PVDF membranes, in particular to a preparation method of a PVDF membrane modified by super-hydrophilic anti-pollution and coupled with a biological demulsifier. BACKGROUND

[0002] With the development of industrialization, the exploitation scale of petroleum is increasingly expanded, and the amount of oil-containing wastewater generated is increasingly large. Therefore, the treatment of oil-containing wastewater after petroleum exploitation has great significance for reducing water pollution, protecting the environment and resource utilization.

[0003] When the membrane technology is used to treat oil-containing wastewater, the oil-containing wastewater has the advantages of economy, high efficiency, low energy consumption, interception of pollutants, high degree of automation, and no addition of external chemicals, and therefore has great competitive advantages. Polyvinylidene fluoride (PVDF) has been widely used in oil-water separation due to its excellent chemical stability, thermal stability and ultraviolet radiation resistance, and high water flux and separation efficiency. However, the PVDF membrane is easily polluted by adsorbing organic impurities due to its low surface energy and strong hydrophobicity. Therefore, improving the hydrophilicity of the PVDF membrane has practical significance in the field of oil-water separation. SUMMARY

[0004] The application aims to provide a preparation method of a PVDF membrane modified by super-hydrophilic anti-pollution and coupled with a biological demulsifier.

[0005] The application has the advantages of simple preparation method, high feasibility, easy popularization and good commercial prospect.

[0006] To achieve the above-mentioned application purposes, the technical scheme of the application is as follows: a preparation method of a PVDF membrane modified by super-hydrophilic anti-pollution and coupled with a biological demulsifier, comprising the following steps:

[0007] (1) adding tannic acid (TA) into a weak alkaline buffer solution to obtain a solution A by stirring, and the mass ratio of the tannic acid to the weak alkaline buffer solution is 1:1200-1300;

[0008] (2) dissolving FeCl3 6H2O in water to obtain a FeCl3 aqueous solution, mixing the FeCl3 aqueous solution with the solution A to obtain a solution B, and the mass ratio of the FeCl3 6H2O to water when the FeCl3 6H2O is dissolved in water is 1:1965-1970, and the molar ratio of the iron ions to the tannic acid in the solution B is 1:1.5-2.5;

[0009] (3) placing the pretreated PVDF membrane in the solution B, and performing a co-deposition reaction by constant temperature oscillation to obtain a M1 membrane;

[0010] (4) After the M1 film is dried, it is placed into a demulsifier solution, constant temperature oscillation is carried out, an M2 film is obtained, and the M2 film is dried to obtain a finished product.

[0011] Further, the pretreatment in step (3) is to immerse the PVDF original film in anhydrous ethanol for 3-5 hours, and then wash with deionized water.

[0012] Further, the weak alkaline buffer solution is a MOPS buffer solution.

[0013] Further, the constant temperature oscillation in step (3) is oscillation at room temperature for 5-7h.

[0014] Further, the constant temperature oscillation in step (4) is oscillation at room temperature for 5-7h.

[0015] Further, the demulsifier solution is Escherichia coli BL21 / pET28-oxdc culture solution, the bacterial bodies are collected by centrifugation, the bacterial bodies are resuspended with phosphate buffer solution (PBS), the bacterial bodies are broken by ultrasonic, the supernatant is collected after centrifugation. The supernatant is filtered, freeze-dried and concentrated to obtain the demulsifier solution. The Escherichia coli BL21 / pET28-oxdc is preserved in the China General Microbiological Culture Collection Center, the address is No. 1, Beichen West Road, Chaoyang District, Beijing, the preservation date is September 2, 2022, and the preservation number is CGMCC NO. 25643.

[0016] The beneficial effects of the present application are:

[0017] 1. In the one-step preparation method, a TA-Fe complex is formed on the surface of the PVDF membrane, and a biological protein demulsifier is coated. On the one hand, the hydrophilic TA-Fe polyphenol metal coating formed on the surface of the membrane and the protein biological demulsifier with amphiphilic properties can improve the hydrophilicity of the PVDF membrane, endow the prepared super-hydrophilic and anti-pollution coupled biological demulsifier modified PVDF membrane with super-hydrophilicity and underwater super-oleophobicity, realize efficient separation of oil-containing wastewater, and at the same time, the membrane has excellent pollution resistance; on the other hand, the amphiphilic protein biological demulsifier connected on the surface of the membrane can improve the separation efficiency of the membrane treatment technology for emulsified oil-containing wastewater with higher stability and smaller oil droplet size.

[0018] 2. The preparation method provided in the present application is simple, high in feasibility, easy to popularize, and has good commercial prospects. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1SEM images of (a) PVDF membrane, (b) finished membrane in Example 1, (c) PVDF-TA membrane, (d) PVDF-TA / Fe membrane;

[0020] Figure 2 Hydrophilic contact angles of (a) PVDF membrane, (b) PVDF-TA / Fe-oxdc membrane, (c) PVDF-TA membrane, (d) PVDF-TA / Fe membrane;

[0021] Figure 3 (a) Oil rejection rate and (b) permeation flux of T / F-2-oxdc modified membrane in separating emulsified oil wastewater;

[0022] Figure 4 (a) COD removal rate and oil removal rate and (b) oil concentration of raw material liquid and filtrate and actual figure of T / F-2-oxdc modified membrane in treating oil-containing wastewater;

[0023] Figure 5 (a) Membrane permeation flux and (b) water flux recovery rate in a cycle test of T / F-2-oxdc modified membrane in treating oil-containing wastewater; DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings.

[0025] Embodiment 1: A method for preparing a PVDF membrane modified by super-hydrophilic anti-pollution and coupled with a biological demulsifier, comprising the following steps: adding tannic acid into a weak alkaline buffer solution to obtain solution A by stirring, wherein the weak alkaline buffer solution is MOPS buffer solution, and the mass ratio of tannic acid to the weak alkaline buffer solution is 1:1200; dissolving FeCl3•6H2O in water to obtain a FeCl3 aqueous solution, mixing the FeCl3 aqueous solution with solution A to obtain solution B, wherein the mass ratio of FeCl3•6H2O to water when FeCl3•6H2O is dissolved in water is 1:1965, and the molar ratio of iron ions to tannic acid in solution B is 1:1.5; placing a pretreated PVDF membrane into solution B, constant temperature oscillation at room temperature for 5 hours to perform a co-deposition reaction, and obtaining a M1 membrane, wherein the pretreatment is soaking the PVDF original membrane in anhydrous ethanol for 3 hours and then washing with deionized water; drying the M1 membrane, and then placing it into a demulsifier solution, wherein the demulsifier solution is obtained by centrifuging the culture solution of Escherichia coli BL21 / pET28-oxdc to collect the bacterial cells, resuspending the bacterial cells with a phosphate buffer solution (PBS), breaking the bacterial cells by ultrasonic, and collecting the supernatant after centrifugation; then filtering and freeze-drying the supernatant to obtain the demulsifier solution; the Escherichia coli BL21 / pET28-oxdc is preserved in the China General Microbiological Culture Collection Center, located at No. 1, Beichen West Road, Haidian District, Beijing, and the preservation date is September 2, 2022, and the preservation number is CGMCC NO. 25643; constant temperature oscillation at room temperature for 5 hours to obtain a M2 membrane, and the M2 membrane is dried to obtain a finished product.

[0026] Embodiment 2: A method for preparing a PVDF membrane modified by a super-hydrophilic anti-pollution coupling biological demulsifier, comprising the following steps: adding tannic acid into a weak alkaline buffer solution to obtain solution A by stirring, wherein the weak alkaline buffer solution is MOPS buffer solution, and the mass ratio of tannic acid to the weak alkaline buffer solution is 1:1250; dissolving FeCl3•6H2O in water to obtain a FeCl3 aqueous solution, mixing the FeCl3 aqueous solution with solution A to obtain solution B by stirring, wherein the mass ratio of FeCl3•6H2O to water when FeCl3•6H2O is dissolved in water is 1:1968, and the molar ratio of iron ions to tannic acid in solution B is 1:2; placing a pretreated PVDF membrane into solution B, constant temperature oscillation at room temperature for 6 hours to perform a co-deposition reaction, and obtaining a M1 membrane, wherein the pretreatment is soaking the PVDF original membrane in anhydrous ethanol for 4 hours and then washing with deionized water; drying the M1 membrane, and then placing it into a demulsifier solution, wherein the demulsifier solution is obtained by centrifuging the culture solution of Escherichia coli BL21 / pET28-oxdc to collect the bacterial cells, resuspending the bacterial cells with a phosphate buffer solution (PBS), breaking the bacterial cells by ultrasonic, and collecting the supernatant after centrifugation; then filtering and freeze-drying the supernatant to obtain the demulsifier solution; the Escherichia coli BL21 / pET28-oxdc is preserved in the China General Microbiological Culture Collection Center, located at No. 1, Beichen West Road, Haidian District, Beijing, and the preservation date is September 2, 2022, and the preservation number is CGMCC NO. 25643; constant temperature oscillation at room temperature for 6 hours to obtain a M2 membrane, and the M2 membrane is dried to obtain a finished product.

[0027] Example 3: A method for preparing a superhydrophilic antifouling modified PVDF membrane coupled with a bio-demulsifier, comprising the following steps: adding tannic acid to a weakly alkaline buffer solution and stirring to obtain solution A, wherein the weakly alkaline buffer solution is a MOPS buffer solution and the mass ratio of tannic acid to the weakly alkaline buffer solution is 1:1300; dissolving FeCl3•6H2O in water to obtain an aqueous solution of FeCl3, mixing the aqueous solution of FeCl3 with solution A and stirring to obtain solution B, wherein the mass ratio of FeCl3•6H2O to water when FeCl3•6H2O is dissolved in water is 1:1970, and the molar ratio of iron ions to tannic acid in solution B is 1:2.5; The pretreated PVDF membrane was placed in solution B and oscillated at a constant temperature for 7 hours at room temperature to carry out a co-deposition reaction, resulting in membrane M1. The pretreatment involved immersing the original PVDF membrane in anhydrous ethanol for 5 hours, followed by rinsing with deionized water. After drying the M1 membrane, it was placed in a demulsifier solution, which was Escherichia coli BL21 / pET28-oxdc culture medium. The bacterial cells were collected by centrifugation, resuspended in phosphate-buffered saline (PBS), and disrupted by sonication. The supernatant was collected after centrifugation. The supernatant was then filtered, freeze-dried, and concentrated to obtain a demulsifier solution. The Escherichia coli BL21 / pET28-oxdc was deposited at the China General Microbiological Culture Collection Center (CGMCC), located at No. 3, Courtyard 1, Beichen West Road, Chaoyang District, Beijing, on September 2, 2022, with accession number CGMCC NO.25643. The mixture was shaken at room temperature for 7 hours to obtain the M2 membrane. After drying the M2 membrane, the final product was obtained.

[0028] The pretreated PVDF membrane in the examples is defined as an MO membrane.

[0029] Comparative Example 1: Unlike Example 1, the M0 membrane was placed in solution A of Example 1 and oscillated at a constant temperature for 5 hours at room temperature to carry out a co-deposition reaction to obtain the M1 membrane. After drying the M1 membrane, the superhydrophilic modified PVDF membrane PVDF-TA was directly obtained.

[0030] Comparative Example 2: Unlike Example 1, after drying the M1 membrane, a superhydrophilic modified PVDF membrane PVDF-TA / Fe was directly obtained.

[0031] Depend on Figure 1 It can be seen that the original PVDF membrane has a large pore size, which is significantly reduced after modification with tannic acid alone; the PVDF-TA / Fe membrane modified with both tannic acid and iron ions has a smaller pore size reduction, but the number of pores is also reduced; while the membrane modified with both tannic acid and iron ions and then modified with a demulsifier solution has a significantly smaller pore size and a more uniform pore distribution.

[0032] Depend on Figure 2 It can be seen that (a) is the water contact angle of the original PVDF membrane, which is 127°, showing obvious hydrophobic effect; (b) is the water contact angle of the PVDF-TA / Fe-oxdc membrane, which is 22.4°, which is significantly lower than the original membrane, greatly reducing the hydrophobic performance of the membrane; (c) is the water contact angle of the PVDF-TA membrane, which is 90°, which is slightly lower than the original membrane, but still has strong hydrophobicity; and (d) is the water contact angle of the PVDF-TA / Fe membrane, which is 34.9°, which has a better hydrophilic modification effect than the original membrane, but is slightly worse than the PVDF-TA / Fe-oxdc membrane.

[0033] like Figure 3 As shown in Figure a), the PVDF-TA / Fe-oxdc membrane achieved an oil rejection rate of 96.99% for kerosene emulsion. In Figure b), the initial permeation flux of the PVDF-TA / Fe-oxdc membrane in the kerosene emulsion oil-water separation experiment reached 476 L / m³. -2 h -1 bar -1 As filtration progresses, the membrane permeate flux gradually decreases because the oily filter cake continuously accumulates on the membrane surface, gradually creating greater resistance to subsequent filtration processes. After 10 minutes of membrane separation operation, the flux stabilizes at approximately 10⁶ L / m³. -2 h -1 bar -1 This indicates that the PVDF-TA / Fe-oxdc membrane has good oil-water separation efficiency for kerosene emulsion.

[0034] like Figure 4 As shown in Figure a), the PVDF-TA / Fe-oxdc membrane can achieve a COD removal rate of about 65% in oily wastewater; in Figure b), the filtrate is significantly clearer than the feed liquid, and the oil concentration in the filtrate is significantly reduced.

[0035] like Figure 5 As shown in Figure a), the initial flux of the PVDF-TA / Fe-oxdc membrane can reach 400 Lm during the separation process. -2 h -1 bar -1 Its stable permeation flux is 43 L m -2 h -1 bar -1Figure b) shows that the oil rejection of PVDF-TA / Fe-oxdc membrane reached 95% in the first time. At the same time, PVDF-TA / Fe-oxdc membrane can be reused many times after simple washing with water, and the water flux of the membrane still reached 92.8% after three times of reuse.

[0036] The embodiments described above are only some of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

Claims

1. A method for preparing a PVDF membrane modified with super-hydrophilic anti-fouling and coupled with a biological demulsifier, characterized in that, The method comprises the following steps: (1) adding tannic acid into a weak alkaline buffer solution to obtain solution A by stirring, wherein the mass ratio of tannic acid to the weak alkaline buffer solution is 1:1200-1300; (2) dissolving FeCl3·6H2O in water to obtain an FeCl3 aqueous solution, mixing the FeCl3 aqueous solution with solution A to obtain solution B, wherein the mass ratio of FeCl3·6H2O to water when FeCl3·6H2O is dissolved in water is 1:1965-1970, and the molar ratio of iron ions to tannic acid in solution B is 1:1.5-2.5; (3) placing the pretreated PVDF membrane in solution B, and performing constant-temperature oscillation to perform co-deposition reaction, thereby obtaining M1 membrane; (4) placing the dried M1 membrane in a demulsifier solution, and performing constant-temperature oscillation to obtain M2 membrane, and the dried M2 membrane is the finished product.

2. The method of claim 1, wherein the PVDF membrane is modified with superhydrophilic anti-fouling and coupling biodeemulsifier. The pretreatment in step (3) is to immerse the PVDF original membrane in anhydrous ethanol for 3-5 hours, and then wash with deionized water.

3. The method of claim 1, wherein the PVDF membrane is modified with superhydrophilic anti-fouling and coupled with a biological demulsifier. The weak alkaline buffer solution is MOPS buffer solution.

4. The method of claim 1, wherein the PVDF membrane is modified with super-hydrophilic anti-fouling and coupled with a biological demulsifier. The constant-temperature oscillation in step (3) is oscillation at room temperature for 5-7 hours.

5. The method of claim 1, wherein the PVDF membrane is modified with super-hydrophilic anti-fouling and coupling biodeemulsifier. The constant-temperature oscillation in step (4) is oscillation at room temperature for 5-7 hours.

6. The method of claim 1, wherein the PVDF membrane is modified with super-hydrophilic anti-fouling and coupling biodeemulsifier. The demulsifier solution is obtained by centrifuging the culture solution of Escherichia coli BL21 / pET28-oxdc, resuspending the bacterial cells with phosphate buffer solution (PBS), ultrasonic crushing of the bacterial cells, centrifuging to collect the supernatant, filtering and freeze-drying the supernatant to obtain the demulsifier solution, and the Escherichia coli BL21 / pET28-oxdc is preserved in the China General Microbiological Culture Collection Center, the address is No. 3, Beichen West Road, Chaoyang District, Beijing, the preservation date is September 2, 2022, and the preservation number is CGMCC NO. 25643.

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