Polyelectrolyte microgel modified polyvinylidene fluoride (PVDF) microfiltration membrane as well as preparation method and application thereof

Abstract

The invention discloses a polyelectrolyte microgel modified polyvinylidene fluoride (PVDF) microfiltration membrane as well as a preparation method and application thereof. The preparation method comprises the following steps: (1) neutralizing AMPS and DEA; (2) preparing a P (AMPS-DEA) amphoteric polyelectrolyte modified PVDF (Polyvinylidene Fluoride) casting membrane solution; (3) carrying out ion-induced coordination crosslinking on the P (AMPS-DEA) amphoteric polyelectrolyte in a metal ion solution; and (4) performing osmotic equilibrium in water. According to the modification method disclosed by the invention, the wettability, the water infiltration capacity and the anti-pollution performance of the PVDF flat sheet membrane can be remarkably improved; the construction of an organic-inorganic and ion-covalent molecule hybrid cross-linked network of metal ion induced coordinated cross-linked P (AMPS-DEA) amphoteric polyelectrolyte modified PVDF (polyvinylidene fluoride) enables the modified flat sheet membrane to stand for a long-time circulating oil-water separation test and a harsh chemical environment soaking test, which prove that a hydrophilic polymer is not easy to fall off; the excellent hydrophilic modification stability is realized.

Description

Technical Field

[0001] The invention relates to the field of PVDF flat microfiltration membrane modification, and in particular to a solvent-induced phase-separated amphoteric polyelectrolyte microgel-modified polyvinylidene fluoride PVDF microfiltration membrane and a preparation method and application thereof. Background Art

[0002] With the development of production and life, water pollution is becoming increasingly serious. Membrane separation technology is considered to be one of the important frontier research directions in the separation field because of its continuous automatic operation, small equipment footprint, low energy consumption, no need for chemical addition, and no secondary environmental pollution. PVDF (polyvinylidene fluoride) microfiltration membrane has a wider range of applications and a long service life due to its stable chemical structure. At the same time, its strong hydrophobicity also leads to many problems in the separation process. The main challenges are as follows: The surface energy of the polyfluorine microfiltration membrane is very low, resulting in poor wetting performance and low pure water flux. In addition, the highly hydrophobic polyfluorine microfiltration membrane is more likely to scale when treating aqueous solutions rich in organic pollutants such as oil and protein, and the frequency of membrane cleaning and replacement increases, and the maintenance and operating costs also increase accordingly. Therefore, designing a PVDF microfiltration membrane with high water flux and high anti-fouling performance has broad application prospects.

[0003] At present, the hydrophilic modification methods of PVDF microfiltration membrane mainly include surface modification and bulk modification. Surface modification is mainly to improve the hydrophilicity of PVDF microfiltration membrane by immersing a layer of hydrophilic coating on the surface of PVDF membrane. Shao Lu et al. [Shao Lu, Wang Zhenxing, Ding Shangang. A modification method for preparing highly hydrophilic coating by dopamine-induced sol-gel method [P]. CN201410384326.92014-08-06] soaked the PVDF base membrane in an alkaline dopamine solution to build a layer of gel coating on its surface. The modified PVDF microfiltration membrane has good wettability and water contact angle, but the gel layer on the surface of this modification method has poor stability under variable environments and is prone to aging and shedding. In addition, alkaline solutions will reduce the mechanical properties of PVDF membranes. Regarding bulk modification, Zhang Xiaowei et al. [Zhang Xiaowei, Zhang Longhui, Ni Xiaolu, Shen Zhilin, Ye Dalin. A method for preparing a hydrophilic polyvinylidene fluoride microfiltration membrane [P]. CN202210335289.72022-03-31] designed a hydrophilic copolymer of polyethyleneimine, polyacrylamide, and polyethylene oxide to hydrophilically modify PVDF, and used the volume-increasing effect of the copolymer to improve the retention of the hydrophilic modifier in the PVDF membrane. The water contact angle of the modified PVDF microfiltration membrane was greatly reduced, and the hydrophilicity was improved. The discussion on the anti-fouling performance only stayed on the hydrophilicity and hydrophobicity. Therefore, the surface modification and bulk modification reported so far are difficult to achieve in practical applications for the simultaneous improvement of the water flux and anti-fouling performance of PVDF flat membranes. Summary of the invention

[0004] One of the purposes of the present invention is to provide a method for preparing a modified PVDF filter membrane with simple process, convenient operation, readily available raw materials, low cost, high water flux and long-term anti-fouling ability.

[0005] To achieve the above object, the technical solution of the present invention is as follows:

[0006] A method for preparing a polyvinylidene fluoride (PVDF) microfiltration membrane modified with a polyelectrolyte microgel comprises the following steps:

[0007] (1) adding a neutralizing amount of 2-acrylamide-2-methylpropanesulfonic acid (AMPS) and diethanolamine (DEA) into an organic solvent to cause a neutralization reaction to obtain a 2-acrylamide-2-methylpropanesulfonic diethanolamine (AMPS-DEA) monomer solution;

[0008] (2) adding polyvinylidene fluoride (PVDF), a porogen, and an initiator to the AMPS-DEA monomer solution obtained in step (1), mixing them evenly to obtain a prepolymer solution, and polymerizing the prepolymer solution to obtain a casting solution;

[0009] (3) vacuum degassing the obtained casting solution, and immersing it in a solution containing metal ions for more than 1 hour to obtain a film-like material;

[0010] (4) The membrane material obtained in step (3) is immersed in water until osmotic equilibrium is reached to obtain the polyelectrolyte microgel-modified polyvinylidene fluoride PVDF microfiltration membrane.

[0011] Furthermore, the organic solvent is selected from one or more of dimethylacetamide (DMAC), dimethyl sulfoxide, and dimethylformamide.

[0012] Furthermore, in the obtained prepolymer solution, the mass fraction of PVDF is 16wt% to 18wt%, and more preferably 16.5wt% to 17.5wt%.

[0013] Furthermore, in the obtained prepolymer solution, the total mass fraction of AMPS-DEA monomers is 0.6wt% to 0.9wt%.

[0014] Furthermore, in the obtained prepolymer solution, the mass fraction of the porogen is 2wt% to 4wt%, and more preferably 2.5wt% to 3.5wt%.

[0015] Furthermore, in the obtained prepolymer solution, the molar amount of the initiator is 0.1% to 0.5% of the molar amount of the AMPS-DEA monomer, for example, 0.15%, 0.2%, 0.3%, 0.35%, 0.4%.

[0016] Furthermore, the porogen is selected from one or more of polyvinyl pyrrolidone (PVP), hydroxypropyl methylcellulose (HPMC), hydroxypropyl cellulose (HPC), sodium carboxymethyl cellulose (CMC-Na), and polyethylene glycol (PEG).

[0017] Furthermore, the initiator is a free radical initiator or a thermal initiator.

[0018] When the initiator is a thermal initiator, the conditions for crosslinking the prepolymer solution are: stirring the reaction for 8 to 12 hours in a water bath at 60 to 90 degrees Celsius, preferably 70 degrees Celsius. The thermal initiator is selected from one or more of ammonium persulfate (APS), potassium persulfate, hydrogen peroxide, and barium peroxide.

[0019] Furthermore, the temperature of the vacuum degassing of the casting liquid is 60 to 80 degrees, the negative pressure is -0.08 to -0.1 MPa, and the time of the vacuum degassing is 60 to 90 minutes.

[0020] Furthermore, before the casting solution is immersed in the metal ion solution, it is first subjected to a film forming pretreatment, comprising the following steps:

[0021] (1) Leveling the casting liquid; the leveling method includes scraping, spraying, spin coating, casting, etc.; the leveling substrate can be glass; for example, a scraping knife is used to scrape the casting liquid on the glass plate at a uniform speed to form a film;

[0022] (2) Spray a droplet or mist of poor solvent on the surface of the casting solution and leave it there for 5 to 10 minutes. The surface of the casting solution stays in the poor solvent droplet bath, which can cause pre-phase separation on the membrane surface and produce sponge-like pores, limiting the precipitation of the amphoteric polyelectrolyte into the coagulation bath during the phase separation process.

[0023] Furthermore, the poor solvent is water. For example, water mist produced by a humidifier can be used to treat the surface of the leveled casting liquid, and the intensity of the water mist is 1 to 5 mL·min -1 cm -2 .

[0024] Furthermore, the thickness of the casting solution after leveling is 200-400 μm, for example, 200 μm, 250 μm, 300 μm, 350 μm. The thickness of the film is generally slightly smaller than the leveling thickness. Therefore, when the leveling thickness is less than 100 μm, the film thickness is too small, resulting in poor mechanical properties. If the thickness is too large, the membrane pores will collapse easily, resulting in a low equilibrium water flux.

[0025] Furthermore, the metal ion concentration in the metal ion solution is 0.01-0.03 mol / L, for example, 0.015 mol / L, 0.02 mol / L, 0.025 mol / L; the metal ion is selected from one or more of CaCl2, ZnCl2, FeCl3, AlCl3; and the immersion time is 1-24 hours. The metal ion solution is used as a coagulation bath to induce phase separation to form amphoteric polyelectrolyte microgel. Too low a concentration of the metal ion coagulation bath will result in poor coordination effect and failure to form microgel; while too high a concentration will result in an overly strong induction effect, resulting in the precipitation of amphoteric polyelectrolyte base film.

[0026] Furthermore, step (4) is to immerse the membrane material obtained in step (3) in water until the phase separation reaches equilibrium, the equilibrium time is 12 to 36 hours, and the water is changed every 4 to 6 hours.

[0027] The second object of the present invention is to provide a polyelectrolyte microgel-modified polyvinylidene fluoride PVDF microfiltration membrane, which is prepared by the above method.

[0028] The third object of the present invention is to provide the application of the above-mentioned polyelectrolyte microgel-modified polyvinylidene fluoride PVDF microfiltration membrane for gas filtration, liquid filtration, adsorption material, anti-adhesion coating, oil transportation or oil spill interception material.

[0029] The present invention introduces DEA, which has weak alkalinity, high coordination ability and abundant hydrogen bonds, into the membrane system. DEA can undergo an acid-base neutralization reaction with the sulfonic acid group of AMPS, so that the sulfonic acid ion participates in the metal ion coordination reaction after activation, and the sulfonic acid ion itself also participates in the metal ion coordination reaction at the same time. The DEA unit of the obtained P(AMPS-DEA) amphoteric polyelectrolyte contains two hydroxyl groups (-OH) and one ethylamine group (-NH2), and there are abundant intermolecular hydrogen bonds and intramolecular hydrogen bonds. The acid-base neutralization reaction of the amine group will further promote the hydrogen bonding between the DEA unit of the P(AMPS-DEA) amphoteric polyelectrolyte and the PVDF molecule, thereby enhancing the molecular chain entanglement between the DEA unit and the PVDF matrix. During the non-solvent induced phase separation (metal ion coagulation bath) of PVDF microfiltration membrane, the coordination of metal ions with P (AMPS-DEA) will induce the separation of hydrophilic P (AMPS-DEA) and hydrophobic PVDF, thereby causing the PVDF matrix and the dispersed phase amphoteric polyelectrolyte to simultaneously produce two different modes of action: molecular chain entanglement and phase separation. Therefore, an "organic-inorganic, ionic-covalent hybrid cross-linking" gel microphase structure can be formed at the phase separation boundary (membrane surface and membrane pores). This structure can effectively enhance the hydrogen bond interaction between polyampholytes and PVDF molecular chains, and effectively fix the entanglement between molecular chains. In addition, the introduction of inorganic ions can reduce the adhesion of the PVDF microfiltration membrane surface, thereby greatly improving the anti-fouling performance of the PVDF membrane during multiple cycle separations.

[0030] The method for modifying a PVDF high water flux anti-fouling filtration membrane with interpenetrating microgels of hydrophilic polymer chains provided by the present invention has a simple and easy-to-control modification process. The modified flat membrane has both high water flux and high anti-fouling performance. Compared with the general non-electrolyte type hydrophilic polymer, the interaction force between the polyelectrolyte molecular chain and water is more than one order of magnitude higher. Therefore, the amphoteric polyelectrolyte will quickly use metal ion coordination reaction in the strong hydrophobic continuous phase PVDF membrane during the solvent-induced phase separation preparation process to obtain metal ion coordination enhanced microgel. The metal ion coordination enhanced microgel has a more novel two-phase composite structure, in which the continuous phase is a strong hydrophobic PVDF matrix, and the dispersed phase is ion cross-linked to form gel microparticles. Thereby giving the flat membrane excellent anti-fouling performance. This will become a common method for preparing a solvent-induced phase separation amphoteric polyelectrolyte microgel high water flux long-lasting anti-fouling PVDF microfiltration membrane.

[0031] Compared with the prior art, the present invention has the following advantages and significant progress:

[0032] 1) The preparation process of the present invention is simple, the production cycle is short, the process conditions are simple, the raw materials are easily available, and the production cost is low.

[0033] 2) The present invention introduces hydrophilic P (AMPS-DEA) amphoteric polyelectrolyte into PVDF membrane by in-situ polymerization, and forms an entangled structure with PVDF chains. The amphoteric polyelectrolyte is enriched on the surface and membrane pores of the membrane by metal ion induction, giving the microfiltration membrane a high water flux, and forming metal ion cross-linked microgels at the membrane pores. The obtained modified flat membrane can withstand long-term cyclic oil-water separation tests and harsh chemical environment immersion tests, proving that the hydrophilic polymer is not easy to fall off, and has excellent hydrophilic modification stability, and has broad application prospects in the field of hydrophilic modified PVDF microfiltration membranes for water treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of the preparation process of the solvent-induced phase separation amphoteric polyelectrolyte microgel modified PVDF microfiltration membrane of the present application;

[0035] Figure 2 Schematic diagram of the hydrophilic modification principle of the solvent-induced phase separation amphoteric polyelectrolyte microgel-modified PVDF microfiltration membrane in this application. DETAILED DESCRIPTION

[0036] The specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0037] In the following embodiments:

[0038] The PVDF powder used for hydrophilic modification was purchased from San Ai Fu New Material Technology Co., Ltd. with the brand name FR904.

[0039] The preparation method of the amphoteric polyelectrolyte P (AMPS-DEA) microgel modified PVDF casting solution is as follows: polyvinyl pyrrolidone PVP, AMPS-DEA monomer, ammonium sulfate APS, and 17g PVDF are added to 80g DMAC and reacted at 70°C with stirring for 8h.

[0040] The preparation method of solvent-induced phase separation amphoteric polyelectrolyte microgel modified PVDF membrane is as follows: immersing the PVDF / P(AMPS-DEA) membrane after water mist-assisted pre-phase separation in 0.025 mol / L AlCl3 solution for solution-induced ion coordination, and then transferring it to deionized water for phase separation osmotic equilibrium.

[0041] The experimental process and corresponding principles are as follows Figure 1 shown.

[0042] Example 1

[0043] Step 1: 0.50 g AMPS (0.0024 mol) and 0.25 g DEA (0.0024 mol) were dissolved in 80 g DMAC and stirred at 25° C. for 20 min to carry out monomer neutralization reaction to obtain a DMAC solution containing AMPS-DEA monomers.

[0044] Step 2: Add 0.003 g of thermal initiator APS (0.000012 mol), 3 g of pore-forming agent PVP, and 17 g of PVDF to the DMAC solution containing AMPS-DEA monomer obtained in step 1, and react with mechanical stirring at 250 rpm in a 70°C water bath for 8 h to obtain P (AMPS-DEA) amphoteric polyelectrolyte modified PVDF casting solution (the mass fraction of AMPS-DEA monomer in the casting solution is 0.75 wt%).

[0045] Step 3: The casting solution obtained in step 2 is heated at 7-8 cm·s -1 The film was evenly scraped on the glass plate at a speed of 200 μm (the thickness of the scraper was 200 μm), and then the casting liquid was left to level in the air for 20 seconds. The surface of the casting liquid was then subjected to a uniform 3-minute deionized water mist pre-phase separation treatment (the mist output was 3 mL min -1 cm -2 ).

[0046] Step 4: Soak the microfiltration membrane obtained after pre-phase separation in step 3 in a 0.025 mol / L AlCl3 solution for 6 h for metal ion coordination cross-linking.

[0047] Step 5: Soak the microfiltration membrane obtained in step 4 in deionized water for 24 hours, and change the water every 6 hours to remove the residual metal ions and obtain the solvent-induced phase separation amphoteric polyelectrolyte microgel modified Al after phase separation equilibrium. 3+ @PVDF / P(AMPS-DEA) microfiltration membrane.

[0048] Example 2

[0049] Step 1: 0.45 g AMPS (0.0021 mol) and 0.23 g DEA (0.0021 mol) were dissolved in 80 g DMAC and stirred at 25° C. for 20 min to carry out monomer neutralization reaction to obtain a DMAC solution containing AMPS-DEA monomers.

[0050] Step 2: Add 0.003 g thermal initiator APS (0.000012 mol), 3.5 g pore-forming agent PVP, and 16.5 g PVDF to the DMAC solution containing AMPS-DEA monomer obtained in step 1, and react in a 70°C water bath at 250 rpm with mechanical stirring for 8 h to obtain P (AMPS-DEA) amphoteric polyelectrolyte modified PVDF casting solution (the mass fraction of AMPS-DEA monomer in the casting solution is 0.68 wt%).

[0051] Step 3: The casting solution obtained in step 2 is heated at 7-8 cm·s -1 The film was evenly scraped on the glass plate at a speed of 200 μm (the thickness of the scraper was 200 μm), and then the casting liquid was left to level in the air for 20 seconds. The surface of the casting liquid was then subjected to a uniform 3-minute deionized water mist pre-phase separation treatment (the mist output was 3 mL min -1 cm -2 ).

[0052] Step 4: Soak the microfiltration membrane obtained after pre-phase separation in step 3 in a 0.025 mol / L AlCl3 solution for 6 h for metal ion coordination cross-linking.

[0053] Step 5: Soak the microfiltration membrane obtained in step 4 in deionized water for 24 hours, and change the water every 6 hours to remove the residual metal ions and obtain the solvent-induced phase separation amphoteric polyelectrolyte microgel modified Al after phase separation equilibrium. 3+ @PVDF / P(AMPS-DEA) microfiltration membrane.

[0054] Example 3

[0055] Step 1: 0.40 g AMPS (0.0019 mol) and 0.20 g DEA (0.0019 mol) were dissolved in 80 g DMAC and stirred at 25° C. for 20 min to carry out monomer neutralization reaction to obtain a DMAC solution containing AMPS-DEA monomers.

[0056] .Step 2: Add 0.003g thermal initiator APS (0.000012mol), 3.5g pore-forming agent PVP and 16.5g PVDF to the DMAC solution containing AMPS-DEA monomer obtained in step 1, and react with mechanical stirring at 250rpm in a 70°C water bath for 8h to obtain P (AMPS-DEA) amphoteric polyelectrolyte modified PVDF casting solution (the mass fraction of AMPS-DEA monomer in the casting solution is 0.60wt%).

[0057] Step 3: The casting solution obtained in step 2 is heated at 7-8 cm·s -1The film was evenly scraped on the glass plate at a speed of 200 μm (the thickness of the scraper was 200 μm), and then the casting liquid was left to level in the air for 20 seconds. The surface of the casting liquid was then subjected to a uniform 3-minute deionized water mist pre-phase separation treatment (the mist output was 3 mL min -1 cm -2 ).

[0058] Step 4: Soak the microfiltration membrane obtained after pre-phase separation in step 3 in a 0.025 mol / L AlCl3 solution for 6 h for metal ion coordination cross-linking.

[0059] Step 5: Soak the microfiltration membrane obtained in step 4 in deionized water for 24 hours, and change the water every 6 hours to remove the residual metal ions and obtain the solvent-induced phase separation amphoteric polyelectrolyte microgel modified Al after phase separation equilibrium. 3+ @PVDF / P(AMPS-DEA) microfiltration membrane.

[0060] Example 4

[0061] Step 1: 0.55 g AMPS (0.0026 mol) and 0.28 g DEA (0.0026 mol) were dissolved in 80 g DMAC and stirred at 25° C. for 20 min to carry out monomer neutralization reaction to obtain a DMAC solution containing AMPS-DEA monomers.

[0062] Step 2: Add 0.003 g thermal initiator APS (0.000012 mol), 2.5 g pore-forming agent PVP, and 17.5 g PVDF to the DMAC solution containing AMPS-DEA monomer obtained in step 1, and react in a 70°C water bath at 250 rpm with mechanical stirring for 8 h to obtain P (AMPS-DEA) amphoteric polyelectrolyte modified PVDF casting solution (the mass fraction of AMPS-DEA monomer in the casting solution is 0.83 wt%).

[0063] Step 3: The casting solution obtained in step 2 is heated at 7-8 cm·s -1 The film was evenly scraped on the glass plate at a speed of 200 μm (the thickness of the scraper was 200 μm), and then the casting liquid was left to level in the air for 20 seconds. The surface of the casting liquid was then subjected to a uniform 3-minute deionized water mist pre-phase separation treatment (the mist output was 3 mL min -1 cm -2 ).

[0064] Step 4: Soak the microfiltration membrane obtained after pre-phase separation in step 3 in a 0.025 mol / L AlCl3 solution for 6 h for metal ion coordination cross-linking.

[0065] Step 5: Soak the microfiltration membrane obtained in step 4 in deionized water for 24 hours, and change the water every 6 hours to remove the residual metal ions and obtain the solvent-induced phase separation amphoteric polyelectrolyte microgel modified Al after phase separation equilibrium. 3+ @PVDF / P(AMPS-DEA) microfiltration membrane.

[0066] Example 5

[0067] Step 1: 0.60 g AMPS (0.0029 mol) and 0.30 g DEA (0.0029 mol) were dissolved in 80 g DMAC and stirred at 25° C. for 20 min to carry out monomer neutralization reaction to obtain a DMAC solution containing AMPS-DEA monomers.

[0068] Step 2: Add 0.003 g thermal initiator APS (0.000012 mol), 2.5 g pore-forming agent PVP and 17.5 g PVDF to the DMAC solution containing AMPS-DEA monomer obtained in step 1, and react in a 70°C water bath at 250 rpm with mechanical stirring for 8 h to obtain P (AMPS-DEA) amphoteric polyelectrolyte modified PVDF casting solution (the mass fraction of AMPS-DEA monomer in the casting solution is 0.90 wt%).

[0069] Step 3: The casting solution obtained in step 2 is heated at 7-8 cm·s -1 The film was evenly scraped on the glass plate at a speed of 200 μm (the thickness of the scraper was 200 μm), and then the casting liquid was left to level in the air for 20 seconds. The surface of the casting liquid was then subjected to a uniform 3-minute deionized water mist pre-phase separation treatment (the mist output was 3 mL min -1 cm -2 ).

[0070] Step 4: Soak the microfiltration membrane obtained after pre-phase separation in step 3 in a 0.025 mol / L AlCl3 solution for 6 h for metal ion coordination cross-linking.

[0071] Step 5: Soak the microfiltration membrane obtained in step 4 in deionized water for 24 hours, and change the water every 6 hours to remove the residual metal ions and obtain the solvent-induced phase separation amphoteric polyelectrolyte microgel modified Al after phase separation equilibrium. 3+ @PVDF / P(AMPS-DEA) microfiltration membrane.

[0072] Comparative Example 1

[0073] Step 1: Dissolve 0.50 g AMPS and 0.25 g DEA in 80 g DMAC and stir at 25° C. for 20 min to carry out monomer neutralization reaction to obtain a DMAC solution containing AMPS-DEA monomers.

[0074] Step 2: Add 0.5 mol% of thermal initiator APS, 3 g of pore-forming agent PVP and 17 g of PVDF to the DMAC solution containing AMPS-DEA monomer obtained in step 1, and react at 70°C in a water bath with mechanical stirring at 250 rpm for 8 h to obtain P (AMPS-DEA) amphoteric polyelectrolyte modified PVDF casting solution.

[0075] Step 3: The casting solution obtained in step 2 is heated at 7-8 cm·s -1 The film was evenly scraped on the glass plate at a speed of 200 μm (the thickness of the scraper was 200 μm), and then the casting liquid was left to level in the air for 20 seconds. The surface of the casting liquid was then subjected to a uniform 3-minute deionized water mist pre-phase separation treatment (the mist output was 3 mL min -1 cm -2 ).

[0076] Step 4: Soak the microfiltration membrane obtained in step 3 in deionized water for 24 hours, changing the water every 6 hours to remove residual metal ions and obtain an amphoteric polyelectrolyte modified PVDF / P (AMPS-DEA) microfiltration membrane after phase separation.

[0077] Comparative Example 2

[0078] Step 1: Add 0.50 g AMPS monomer, 0.5 mol% thermal initiator APS, 3 g pore-forming agent PVP, and 17 g PVDF to 80 g DMAC solution, and react at 70°C in a water bath at 250 rpm for 8 h to obtain P (AMPS-DEA) amphoteric polyelectrolyte modified PVDF casting solution.

[0079] Step 2: The casting solution obtained in step 1 is heated at 7-8 cm·s -1 The film was evenly scraped on the glass plate at a speed of 200 μm (the thickness of the scraper was 200 μm), and then the casting liquid was left to level in the air for 20 seconds. The surface of the casting liquid was then subjected to a uniform 3-minute deionized water mist pre-phase separation treatment (the mist output was 3 mL min -1 cm -2 ).

[0080] Step 3: Soak the microfiltration membrane obtained after pre-phase separation in step 2 in a 0.025 mol / L AlCl3 solution for 6 h for metal ion coordination cross-linking.

[0081] Step 4: Soak the microfiltration membrane obtained in step 3 in deionized water for 24 hours, and change the water every 6 hours to remove the residual metal ions and obtain the solvent-induced phase separation polyelectrolyte microgel modified Al after phase separation. 3+ @PVDF / PAMPS microfiltration membrane.

[0082] Anti-fouling performance test:

[0083] Step 1: A Tween-80-stabilized oil-in-water emulsion was prepared to simulate real wastewater for evaluating the oil-water separation performance of the membrane: 0.5 g of mineral oil was added to 500 mL of deionized water, 0.1 g of Tween-80 was used as an emulsifier, and then stirred at 6000 rpm for 3 h with a high-speed reflux stirrer to obtain an oil-in-water emulsion.

[0084] Step 2: The membrane was compacted at room temperature under a negative pressure of 0.1 MPa for 30 minutes to achieve a stable water flux before the oil-water separation test was started. Each cycle was defined as testing the deionized water flux for 15 minutes and then filtering the oil-in-water emulsion obtained in step 1 for 60 minutes.

[0085] Step 3: Soak the membrane after separation in step 2 in 1% citric acid (CA) solution for ultrasonic washing for 10 minutes and then rinse it with deionized water. Test three cycles continuously and record the oil-water flux in the three cycles as J. p1 , J p2 , J p3 , water flux is recorded as J w1 , J w2 , J w3 .

[0086] Step 4: The flux recovery rate FRR and flux decay rate FDR after the second cycle are used to determine the anti-fouling performance of the filtration membrane. The calculation formula is as follows:

[0087]

[0088] In the formula, J w1 is the stable water flux of the filtration membrane in the first test, in L·m -2 ·h -1 bar -1 ; J w2 is the stable water flux of the filtration membrane in the second test, in L·m -2 ·h -1 bar -1 ; J p1 The oil-water flux of the first test of the filtration membrane, in L·m -2 ·h -1 bar -1 .

[0089] Water flux test:

[0090] Step 1: Solvent-induced phase separation of amphoteric polyelectrolyte microgels modified with Al 3+ @PVDF / P(AMPS-DEA) microfiltration membrane was cut into samples of 5 cm×5 cm.

[0091] Step 2: Fix the sample obtained in step 1 on a surface with an area S of 1.32×10 -3 m 2 On the water flux tester, ensure that there is good air tightness between the sample and the tester.

[0092] Step 3: Add an appropriate amount of deionized water to the measuring cup above the sample fixed in step 2, adjust the test negative pressure P of the water flux tester to stabilize at -0.1MPa, start timing after the deionized water is stably extracted through the flat membrane, pre-press for 30 minutes, perform the first cycle of oil-water separation, and take the stable water flux of the first water cycle.

[0093] Step 4: Calculate the water flux J of the filtration membrane by the ratio of the volume of deionized water extracted to the product of the test time, the test membrane area and the test pressure. w， The calculation formula is as follows:

[0094]

[0095] In the formula, J w is the pure water flux in the first oil-water separation process, in L·m -2 ·h -1 bar -1 ; V is the volume of deionized water extracted, in L; ΔT is the test time, in h; S is the membrane area, in m 2 ; P is the applied pressure, in bar.

[0096] The water flux and anti-fouling performance of the hydrophilic modified PVDF filter membranes obtained in the above examples and comparative examples are shown in Table 1 below:

[0097] Table 1: Water flux and antifouling performance of hydrophilic modified PVDF filtration membrane

[0098]

[0099] In Examples 1 to 5, the total mass of the casting solution base system was controlled to be 100 g, and the content of the AMPS-DEA amphoteric polyelectrolyte monomer was changed (the ratio of the two components remained the same) to prepare the solvent-induced phase separation amphoteric polyelectrolyte microgel modified Al 3+ @PVDF / P(AMPS-DEA) microfiltration membrane; Comparative Example 1 is based on Example 1, but the use of metal ion coagulation bath is eliminated to prepare amphoteric polyelectrolyte microgel modified PVDF / P(AMPS-DEA) microfiltration membrane; Comparative Example 2 is based on Example 1, but the addition of DEA is eliminated, and only PAMPS is polymerized in situ to prepare polyelectrolyte microgel modified Al 3+ @PVDF / PAMPS microfiltration membrane.

[0100] According to the data in Table 1:

[0101] It can be seen from Examples 1 to 5 and Comparative Example 1 that the sample Al of the present invention 3+ @PVDF / P(AMPS-DEA) stable water flux (2571.48~2770.32L·m -2 ·h -1 bar -1 The second and third oil-water separation cycle flux recovery rates (84.3-89.8%) were significantly better than the stable water flux of PVDF / P (AMPS-DEA) microfiltration membrane (1984.24 L·m -2 ·h -1 bar -1 ), the second and third oil-water separation cycle flux recovery rate (56.0%). This is because the original hydrophilic porogen PVP will be lost quickly during multiple cycles and washing, and the formation of microgels is not induced by metal ion coordination. The hydrophilic amphoteric polyelectrolyte P (AMPS-DEA) is easily precipitated from the base membrane into the water during the phase separation process, resulting in the loss of the hydrophilic modifier like the porogen and unable to achieve the effect of long-term modification; while Al 3+ @In the PVDF / P(AMPS-DEA) membrane, microgel phase is formed in the membrane pores and on the membrane surface due to the coordination cross-linking induced by metal ions, which can effectively prevent oil from invading the membrane pores and causing irreversible pollution.

[0102] It can be seen from Examples 1 to 5 and Comparative Example 2 that the sample Al of the present invention 3+ @PVDF / P(AMPS-DEA) stable water flux (2571.48~2770.32L·m -2 ·h -1 bar -1 ), the second and third oil-water separation cycle flux recovery rates (84.3-89.8%) are significantly better than Al 3+ @The stable water flux of PVDF / PAMPS microfiltration membrane (1925.67L·m -2 ·h -1 bar -1 ), the second and third oil-water separation cycle flux recovery rate (50.9%). This is due to Al 3+ The hydrophilic modified PAMPS in the PVDF / PAMPS microfiltration membrane is weakly acidic and has a low degree of ionization. It lacks DEA with strong coordination ability, so it has a poor coordination effect with metal ions and cannot form a microgel phase. This results in poor interaction between the modified product and the base membrane, and it cannot be retained for a long time. It will gradually come out during the long-term separation process, causing oil pollution and pore blocking.

[0103] The above embodiments are merely examples of the technical solutions of the present invention. The modification method of the solvent-induced phase separation amphoteric polyelectrolyte microgel for high water flux and long-term antifouling PVDF microfiltration membrane involved in the present invention is not limited to the contents described in the above embodiments, but is subject to the scope defined in the claims. Any modification, supplement or equivalent substitution made by a technician in the field of the present invention on the basis of the embodiment is within the scope of protection required by the claims of the present invention.

Claims

1. A method for preparing a polyvinylidene fluoride (PVDF) microfiltration membrane modified with a polyelectrolyte microgel, characterized in that: The steps include: (1) adding a neutralizing amount of 2-acrylamide-2-methylpropanesulfonic acid and diethanolamine to an organic solvent to cause a neutralization reaction to obtain an AMPS-DEA monomer solution; (2) adding polyvinylidene fluoride, a porogen, and an initiator to the AMPS-DEA monomer solution obtained in step (1), mixing them evenly to obtain a prepolymer solution, and polymerizing the prepolymer solution to obtain a casting solution; (3) vacuum degassing the obtained casting solution, and immersing it in a solution containing metal ions for more than 1 hour to obtain a film-like material; (4) The membrane material obtained in step (3) is immersed in water until osmotic equilibrium is reached to obtain the polyelectrolyte microgel-modified polyvinylidene fluoride PVDF microfiltration membrane.

2. The preparation method according to claim 1, characterized in that: The organic solvent is selected from one or more of dimethylacetamide, dimethyl sulfoxide and dimethylformamide.

3. The preparation method according to claim 1, characterized in that: In the obtained prepolymer solution, The mass fraction of PVDF is 16wt% to 18wt%; The total mass fraction of AMPS-DEA monomer is 0.6wt% to 0.9wt%; The mass fraction of the porogen is 2wt% to 4wt%; The amount of the initiator used is 0.1% to 1% of the molar amount of the AMPS-DEA monomer.

4. The preparation method according to claim 1, characterized in that: The porogen is selected from one or more of polyvinyl pyrrolidone (PVP), hydroxypropyl methylcellulose (HPMC), hydroxypropyl cellulose (HPC), sodium carboxymethyl cellulose (CMC-Na), and polyethylene glycol (PEG).

5. The preparation method according to claim 1, characterized in that: Before the casting solution is immersed in the metal ion solution, it is first subjected to a film forming pretreatment, which includes the following steps: (1) Leveling the casting liquid; (2) Spray a poor solvent in droplet or mist form on the surface of the casting solution and leave it there for 5 to 10 minutes.

6. The preparation method according to claim 5, characterized in that: The poor solvent is water.

7. The preparation method according to claim 5, characterized in that: The thickness of the casting liquid after leveling is 200-400 μm.

8. The preparation method according to claim 1, characterized in that: The metal ion concentration in the metal ion solution is 0.01-0.03 mol / L; the metal ions are selected from one or more of CaCl2, ZnCl2, FeCl3, and AlCl3.

9. A polyelectrolyte microgel-modified polyvinylidene fluoride (PVDF) microfiltration membrane, characterized in that: The method is prepared by any one of claims 1 to 8.

10. An application of the polyvinylidene fluoride (PVDF) microfiltration membrane modified with polyelectrolyte microgel according to claim 9, characterized in that: Used for gas filtration, liquid filtration, adsorption materials, anti-adhesion coatings, oil transportation or oil spill interception materials.

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