A hydrophilic polyvinylidene fluoride oil-water separation membrane and a preparation method thereof

Abstract

The application discloses a kind of hydrophilic polyvinylidene fluoride oil-water separation membranes and preparation method thereof, belong to oil-water separation membrane technical field.The preparation method steps include: with 2,2-dimethoxy-2-phenyl acetophenone as photo initiator, 3,6-dioxane-1,8-octane dithiol and polyethylene glycol diacrylate as modifier, by photo initiation mercapto-olefin gradually polymerization method is modified to alkali treated PVDF membrane, and hydrophilic polyvinylidene fluoride oil-water separation membrane is prepared.The application is grafted to PVDF separation membrane surface by photo initiation mercapto-olefin gradually polymerization method, and hydrophilic separation membrane is obtained.The preparation method provided by the application has the characteristics of simple process, low cost and the like, and the prepared hydrophilic membrane can be further developed and utilized as sewage treatment separation membrane, hemodialysis membrane.

Description

Technical Field

[0001] The present invention relates to the technical field of oil-water separation membranes, in particular to a hydrophilized polyvinylidene fluoride oil-water separation membrane and a preparation method thereof. Background Art

[0002] Oily wastewater has a wide range of sources and is generated in many industrial and agricultural processes. Discharging untreated oily wastewater directly can cause serious environmental pollution. For example, directly discharging oily wastewater into rivers, lakes, and oceans can kill aquatic life. Therefore, effective separation and treatment of oily wastewater has significant economic and social value for environmental protection and water conservation.

[0003] In recent years, superhydrophilic or superhydrophobic materials have received widespread attention in the field of oil-water separation. For example, constructing superhydrophobic or superhydrophilic coatings based on mesh materials can effectively remove gasoline, vegetable oil and even crude oil from oily wastewater. However, these materials cannot effectively separate emulsified oils because their pore sizes are much larger than the oil droplet size of the oil-containing emulsion. In comparison, using polymer membranes as separation materials, under pressure-driven conditions, can effectively separate oil-containing emulsions, and has the advantages of low energy consumption and no secondary pollution to water bodies. However, in the membrane separation process, membrane fouling is difficult to avoid. This is because the oil substances and the hydrophobic membrane materials have similar surface energy. The oil substances will be adsorbed on the membrane pores, causing membrane fouling, resulting in reduced permeation flux and deterioration of separation performance.

[0004] One of the ways to improve the anti-pollution performance and oil-water separation performance is to modify the surface of the base membrane by hydrophilization. The hydrophilic functional groups on the membrane surface can tightly bind to water molecules through hydrogen bonds or electrostatic effects to form a hydration layer, prevent the adhesion of oil substances, and play an anti-pollution role. Chinese invention patent CN114405287A discloses a method for preparing an anti-pollution oil-water polyvinylidene fluoride (PVDF) separation membrane. First, hydroxyethyl methacrylate (HEMA) and acrylic acid (AA) are grafted onto the surface of the polyvinylidene fluoride membrane, and the modified membrane is placed in ethylenediamine for cross-linking to form a gelled membrane surface. Further, 2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonic acid propyl) ammonium hydroxide (SBMA) is grafted onto the membrane through atom transfer radical polymerization to construct a highly anti-pollution membrane surface. Chinese invention patent CN108905653A uses trithiocarbonate as a chain transfer group to synthesize a hyperbranched zwitterionic polymer through reversible addition-fragmentation chain transfer active radical polymerization, and then coats it with dopamine on the surface of a PVDF membrane. The membranes prepared by these methods have good oil-water separation performance and anti-pollution performance. However, due to the complex process steps and the use of toxic copper catalysts involved in the preparation process, or the harsh synthesis conditions of hydrophilic polymers, their application range is limited. Chinese invention patent CN107998897A first treats the membrane with a strong base to undergo an elimination reaction to remove the CF bond to form a C=C double bond, and then initiates the grafting of a small molecule hydrophilic thiol compound onto the membrane surface through ultraviolet light. The results show that the minimum static contact angle of the modified membrane obtained is 29.6°, and it does not show superhydrophilic properties. This may be because the grafted hydrophilic compound chain segment is relatively short and cannot cover the membrane surface well.

[0005] Therefore, in order to solve the problems of complex preparation process and harsh conditions of oil-water separation membrane materials, it is necessary to provide a separation membrane and its preparation method, which not only meets the requirements of significant separation performance of the separation membrane, but also meets the characteristics of low preparation cost, simplified preparation process, and significant anti-pollution and separation performance. Summary of the Invention

[0006] The present invention aims to provide a hydrophilized polyvinylidene fluoride oil-water separation membrane and its preparation method. Using a photoinitiated thiol-olefin stepwise polymerization method, a hydrophilized grafted layer is constructed on the surface of the PVDF membrane. The grafted polymer segments are well distributed on the membrane surface, imparting the modified membrane with excellent oil pollution resistance, oil-containing emulsion separation performance, superhydrophilicity, and underwater superoleophobicity. This method overcomes the complex preparation process and harsh conditions associated with existing PVDF oil-water separation membrane materials.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] One of the technical solutions of the present invention is to provide a method for preparing a hydrophilized polyvinylidene fluoride oil-water separation membrane, comprising the following steps:

[0009] Hydrophilized polyvinylidene fluoride oil-water separation membrane was prepared by modifying alkali-treated PVDF membrane via photoinitiated thiol-ene stepwise polymerization using 2,2-dimethoxy-2-phenylacetophenone (DMPA) as photoinitiator, 3,6-dioxa-1,8-octanedithiol (DOT) and polyethylene glycol diacrylate (PEGDA) as modifiers.

[0010] Preferably, the specific operation steps for modifying the alkali-treated PVDF membrane include: adding 3,6-dioxa-1,8-octanedithiol, polyethylene glycol diacrylate and 2,2-dimethoxy-2-phenylacetophenone to a reaction container, adding a solvent, dissolving to obtain a transparent solution, adding the alkali-treated PVDF membrane, replacing the air with an inert gas and sealing the reaction container, and then reacting under ultraviolet light to obtain a hydrophilized polyvinylidene fluoride oil-water separation membrane.

[0011] More preferably, the concentration of 3,6-dioxa-1,8-octanedithiol in the transparent solution is 20-60 g / L, the concentration of polyethylene glycol diacrylate is 5-120 g / L, and the concentration of 2,2-dimethoxy-2-phenylacetophenone is 0.1-0.6 g / L; and the solvent is anhydrous ethanol.

[0012] More preferably, the power of the ultraviolet light is 10 to 100 W; and the reaction time is 0.5 to 5 h.

[0013] Preferably, the preparation step of the alkali-treated PVDF membrane comprises: adding the PVDF membrane into a preheated alkali solution, immersing the membrane, taking it out, and washing it to neutrality to obtain the alkali-treated PVDF membrane.

[0014] More preferably, the preheating temperature is 50-80° C.; the alkali solution is 0.2-0.6 mol / L NaOH anhydrous ethanol solution; and the immersion time is 10-30 s.

[0015] Preferably, the number average molecular weight of the polyethylene glycol diacrylate is 400 to 2000 g / mol.

[0016] More preferably, the number average molecular weight of the polyethylene glycol diacrylate is 600 g / mol.

[0017] The second technical solution of the present invention is to provide a hydrophilized polyvinylidene fluoride oil-water separation membrane prepared according to the above preparation method.

[0018] The beneficial technical effects of the present invention are as follows:

[0019] The present invention grafts hydrophilic PEGDA onto the surface of a PVDF separation membrane through a photoinitiated thiol-ene stepwise polymerization method to produce a hydrophilic separation membrane. The preparation method provided by the present invention is simple and low-cost. The resulting hydrophilized membrane can be further developed and utilized as a wastewater treatment separation membrane and a hemodialysis membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the SEM image of the PVDF membrane treated with alkali in Example 4.

[0021] Figure 2 This is the SEM image of the PVDF-g-PEGDA60 membrane prepared in Example 4.

[0022] Figure 3 This is the surface O element distribution diagram of the alkali-treated PVDF membrane in Example 4.

[0023] Figure 4 This is the surface O element distribution diagram of the PVDF-g-PEGDA60 membrane prepared in Example 4.

[0024] Figure 5 This is a surface wettability analysis diagram of the alkali-treated PVDF membrane in Comparative Example 2 and the PVDF-g-PEGDA60 membrane in Example 4.

[0025] Figure 6 This is the underwater toluene contact angle diagram of the PVDF-g-PEGDA60 film in Example 4.

[0026] Figure 7 This is a diagram of the underwater pump oil adhesion behavior of the alkali-treated PVDF membrane in Comparative Example 2.

[0027] Figure 8 This is a diagram of the underwater pump oil adhesion behavior of the PVDF-g-PEGDA40 membrane in Example 3.

[0028] Figure 9 This is the optical image of the PVDF-g-PEGDA40 emulsion before separation in Example 3.

[0029] Figure 10 This is the optical image of the emulsion after PVDF-g-PEGDA40 separation in Example 3. DETAILED DESCRIPTION

[0030] Various exemplary embodiments of the present invention are now described in detail. This detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terms used in the present invention are only for describing specific embodiments and are not intended to limit the present invention.

[0031] In addition, for numerical ranges in the present invention, it is understood that each intervening value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any stated value or stated range, and any other stated value or intervening value in the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. Although preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention.

[0033] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0034] Example 1

[0035] A PVDF membrane was placed in a 0.5 mol / L NaOH ethanol solution at 80°C for 15 seconds, then washed with copious amounts of pure water until neutral, yielding an alkali-treated PVDF membrane. 2.73 g of DOT, 0.5 g of PEGDA (molecular weight 600 g / mol), and 0.0205 g of DMPA were dissolved in 50 mL of anhydrous ethanol to yield a clear solution. The alkali-treated PVDF membrane was immersed in the clear solution, purged with argon for 15 minutes, and then sealed and irradiated under a 30W UV lamp for 4 hours. Following the reaction, the membrane sample was removed and alternately washed with copious amounts of anhydrous ethanol and pure water, followed by drying. This yielded a hydrophilized polyvinylidene fluoride oil-water separation membrane, designated PVDF-g-PEGDA10.

[0036] The initial contact angle of pure water of the prepared modified membrane PVDF-g-PEGDA10 was 63.6°, which decreased to 41.7° within 30 s.

[0037] Example 2

[0038] A PVDF membrane was placed in a 0.5 mol / L NaOH ethanol solution at 80°C for 15 seconds, then washed with copious amounts of pure water until neutral, yielding an alkali-treated PVDF membrane. 2.73 g of DOT, 1 g of PEGDA (molecular weight 600 g / mol), and 0.0205 g of DMPA were dissolved in 50 mL of anhydrous ethanol to yield a clear solution. The alkali-treated PVDF membrane was immersed in the clear solution, purged with argon for 15 minutes, and then sealed and irradiated under a 30 W UV lamp for 4 hours. Following the reaction, the membrane sample was removed and washed alternately with copious amounts of anhydrous ethanol and pure water, followed by drying. This yielded a hydrophilized polyvinylidene fluoride oil-water separation membrane, designated PVDF-g-PEGDA20.

[0039] The initial contact angle of pure water of the prepared modified membrane PVDF-g-PEGDA20 was 57.8° and decreased to 0° within 11 s.

[0040] Example 3

[0041] A PVDF membrane was placed in a 0.5 mol / L NaOH ethanol solution at 80°C for 15 seconds, then washed with copious amounts of pure water until neutral, yielding an alkali-treated PVDF membrane. 2.73 g of DOT, 2 g of PEGDA (molecular weight 600 g / mol), and 0.0205 g of DMPA were dissolved in 50 mL of anhydrous ethanol to yield a clear solution. The alkali-treated PVDF membrane was immersed in the clear solution, purged with argon for 15 minutes, and then sealed and irradiated under a 30W UV lamp for 4 hours. Following the reaction, the membrane sample was removed and alternately washed with copious amounts of anhydrous ethanol and pure water, followed by drying. This yielded a hydrophilized polyvinylidene fluoride oil-water separation membrane, designated PVDF-g-PEGDA40.

[0042] The initial contact angle of pure water of the prepared modified membrane PVDF-g-PEGDA40 was 12.1° and decreased to 0° within 1.5 s.

[0043] Example 4

[0044] A PVDF membrane was placed in a 0.5 mol / L NaOH ethanol solution at 80°C for 15 seconds, then washed with copious amounts of pure water until neutral, yielding an alkali-treated PVDF membrane. 2.73 g of DOT, 3 g of PEGDA (molecular weight 600 g / mol), and 0.0205 g of DMPA were dissolved in 50 mL of anhydrous ethanol to yield a clear solution. The alkali-treated PVDF membrane was immersed in the clear solution, purged with argon for 15 minutes, and then sealed and irradiated under a 30W UV lamp for 4 hours. Following the reaction, the membrane sample was removed and alternately washed with copious amounts of anhydrous ethanol and pure water, followed by drying. This yielded a hydrophilized polyvinylidene fluoride oil-water separation membrane, designated PVDF-g-PEGDA60.

[0045] The initial contact angle of pure water of the prepared modified membrane PVDF-g-PEGDA60 was 29.9° and decreased to 0° within 3.5s.

[0046] Example 5

[0047] A PVDF membrane was placed in a 0.5 mol / L NaOH ethanol solution at 80°C for 15 seconds, then washed with copious amounts of pure water until neutral, yielding an alkali-treated PVDF membrane. 2.73 g of DOT, 5 g of PEGDA (molecular weight 600), and 0.0205 g of DMPA were dissolved in 50 mL of anhydrous ethanol to yield a clear solution. The alkali-treated PVDF membrane was immersed in the clear solution, purged with argon for 15 minutes, and then sealed and irradiated under a 30W UV lamp for 4 hours. Following the reaction, the membrane sample was removed and washed alternately with copious amounts of anhydrous ethanol and pure water, followed by drying. This yielded a hydrophilized polyvinylidene fluoride oil-water separation membrane, designated PVDF-g-PEGDA100.

[0048] The initial contact angle of pure water of the prepared modified membrane PVDF-g-PEGDA100 was 46.1° and decreased to 0° within 4 s.

[0049] Comparative Example 1

[0050] Taking the unmodified PVDF membrane as comparative example 1, it was measured that the initial contact angle of pure water of the unmodified pure PVDF membrane was 121.8°, which decreased to 119.7° within 30 seconds.

[0051] Comparative Example 2

[0052] Taking the PVDF membrane treated with alkali solution in Example 1 as Comparative Example 2, it was determined that the initial contact angle of pure water of the PVDF membrane treated with alkali solution was 120.8°, which decreased to 118.1° within 30 seconds.

[0053] Figure 1 is a SEM image of the PVDF membrane treated with alkali in Example 4; Figure 2 This is the SEM image of the PVDF-g-PEGDA60 membrane prepared in Example 4.

[0054] Figure 3 This is the surface O element distribution diagram of the PVDF membrane treated with alkali in Example 4; Figure 4 This is the surface O element distribution diagram of the PVDF-g-PEGDA60 membrane prepared in Example 4.

[0055] comprehensive Figures 1 to 4 It can be seen that compared with the alkali-treated PVDF membrane, a uniformly distributed hydrophilic polymer grafted layer can be found on the surface of the modified membrane.

[0056] Surface wettability analysis of membranes

[0057] The PVDF membrane in Comparative Example 1, the alkali-treated PVDF membrane prepared in Comparative Example 2, and the PVDF-g-PEGDA40 membrane and PVDF-g-PEGDA60 membrane prepared in Examples 3 and 4 were used as experimental objects. 2 μl of pure water was dripped from the syringe of the contact angle measuring instrument and suspended above the membrane; the water droplet was slowly moved downward and contacted with the membrane surface until the water droplet was in full contact with the membrane surface; then the syringe was lifted.

[0058] When a water droplet was added to the PVDF membrane, its contact angle decreased from 121.8° to 119.7° within 30 seconds. When a water droplet was added to the alkali-treated PVDF membrane, its contact angle decreased from 120.8° to 118.1° within 30 seconds. When a water droplet was added to the PVDF-g-PEGDA60 membrane, its initial contact angle was only 29.9°, and it quickly dropped to 0° in just 3.5 seconds. When a water droplet was added to the PVDF-g-PEGDA40 membrane, its contact angle dropped from 12.1° to 0° within 1.5 seconds, showing superhydrophilic properties. The above results show that the hydrophilicity of the prepared hydrophilized polyvinylidene fluoride oil-water separation membrane is significantly stronger than that of the pure PVDF membrane and the alkali-treated PVDF membrane. Superhydrophilic properties can be given to the separation membrane by adjusting the monomer ratio in the reaction solution.

[0059] in Figure 5 This is a surface wettability analysis diagram of the alkali-treated PVDF membrane in Comparative Example 2 and the PVDF-g-PEGDA60 membrane in Example 4.

[0060] In addition, the present invention measured the underwater pump oil contact angles of the separation membranes obtained in Examples 1 to 5 and Comparative Examples 1 to 2. The measurement results are shown in Tables 1 and 2.

[0061] Table 1 Underwater pump oil contact angle of each group of separation membranes

[0062]

[0063]

[0064] Table 2 Underwater pump oil contact angle of PVDF-g-PEGDA60 membrane of Example 4

[0065] Name of oil substance Contact angle value (°) rapeseed oil 150.5 soybean oil 151.7 peanut oil 150.6 Toluene 154.8 Petroleum ether 152.4 n-hexane 155.2

[0066] The results in Table 1 and Table 2 show that the hydrophilized polyvinylidene fluoride oil-water separation membrane prepared by the present invention has underwater super oleophobic characteristics. Among them, the underwater toluene contact angle of the PVDF-g-PEGDA60 membrane is shown in FIG. Figure 6 .

[0067] Furthermore, the alkali-treated PVDF membrane in Example 2 and the PVDF-g-PEGDA40 membrane in Example 3 were analyzed. During the test, the separation membrane was immersed in pure water, and then an oil droplet was squeezed out of the needle of the contact angle meter. The oil droplet was slowly moved down and contacted with the membrane surface until the oil droplet was in full contact with the membrane surface; then the syringe was lifted, and the oil droplet left the membrane surface along with the needle tip of the syringe.

[0068] Figure 7 This is a diagram of the underwater pump oil adhesion behavior of the alkali-treated PVDF membrane in Comparative Example 2.

[0069] from Figure 7 It can be seen that the oil droplets will eventually adhere to the surface of the alkali-treated PVDF membrane.

[0070] Figure 8 This is a diagram of the underwater pump oil adhesion behavior of the PVDF-g-PEGDA40 membrane in Example 3.

[0071] from Figure 8 It can be seen that it is difficult for oil droplets to adhere to the surface of the modified membrane PVDF-g-PEGDA40. When the oil droplets detach from the membrane surface, they do not detach from the needle, but are tightly attached to the syringe needle, indicating that the surface of the modified membrane has a high surface energy and almost no oil droplets adhere to it, indicating that the oil pollution resistance of the prepared modified membrane is significantly stronger than that of the alkali-treated PVDF membrane.

[0072] Determination of oil-water separation performance of membranes

[0073] Membranes prepared in Examples 1-5 and Comparative Examples 1-2 were used as experimental subjects. The membrane samples were clamped in a cross-flow membrane filtration cell, and the separation performance of an oil-water emulsion was measured at 0.1 MPa. The emulsion was prepared as follows: 0.2 g of Tween 80 and 1 g of vacuum pump oil were weighed and added to 1000 ml of pure water. The mixture was ultrasonically treated for 30 minutes to obtain a milky white emulsion. The membrane retention data are shown in Table 3.

[0074] Table 3 Emulsion separation performance of each group of separation membranes

[0075] Membrane samples Retention rate (%) Comparative Example 1 PVDF 98.0 Comparative Example 2 Alkali-treated PVDF 97.5 Example 1 PVDF-g-PEGDA10 99.2 Example 2 PVDF-g-PEGDA20 99.3 Example 3 PVDF-g-PEGDA40 99.9 Example 4 PVDF-g-PEGDA60 99.3 Example 5 PVDF-g-PEGDA100 99.1

[0076] Figure 9 This is an optical image of the emulsion before PVDF-g-PEGDA40 separation in Example 3; Figure 10 This is an optical image of the emulsion after PVDF-g-PEGDA40 separation in Example 3. Figure 10 It shows that no distribution of oil droplets was seen after separation.

[0077] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing a hydrophilized polyvinylidene fluoride oil-water separation membrane, characterized in that: The following steps are involved: 3,6-dioxa-1,8-octanedithiol, polyethylene glycol diacrylate, and 2,2-dimethoxy-2-phenylacetophenone are added to a reaction vessel, a solvent is added, and a transparent solution is obtained after dissolution. An alkali-treated PVDF membrane is added, and the air is replaced with an inert gas, and the reaction vessel is sealed. The reaction is then carried out under ultraviolet light to obtain a hydrophilized polyvinylidene fluoride oil-water separation membrane. The concentration of 3,6-dioxa-1,8-octanedithiol in the transparent solution is 20-60 g / L, the concentration of polyethylene glycol diacrylate is 5-120 g / L, and the concentration of 2,2-dimethoxy-2-phenylacetophenone is 0.1-0.6 g / L; the solvent is anhydrous ethanol; The power of the ultraviolet light is 10-100W; the reaction time is 0.5-5h.

2. The method for preparing a hydrophilized polyvinylidene fluoride oil-water separation membrane according to claim 1, characterized in that: The preparation steps of the alkali-treated PVDF membrane include: The PVDF membrane is added into the preheated alkali solution, taken out after immersion, and washed to neutrality to obtain an alkali-treated PVDF membrane.

3. The method for preparing a hydrophilized polyvinylidene fluoride oil-water separation membrane according to claim 2, wherein: The preheating temperature is 50-80° C.; the alkali solution is a 0.2-0.6 mol / L NaOH anhydrous ethanol solution; and the immersion time is 10-30 seconds.

4. The method for preparing the hydrophilized polyvinylidene fluoride oil-water separation membrane according to any one of claims 1 to 3, characterized in that: The number average molecular weight of the polyethylene glycol diacrylate is 400-2000 g / mol.

5. The method for preparing a hydrophilized polyvinylidene fluoride oil-water separation membrane according to claim 4, characterized in that: The number average molecular weight of the polyethylene glycol diacrylate is 600 g / mol.

6. A hydrophilized polyvinylidene fluoride oil-water separation membrane prepared according to the method for preparing a hydrophilized polyvinylidene fluoride oil-water separation membrane according to any one of claims 1 to 5.

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