Surface-modified nanocomposite hydrogel-based oil-water separation membrane and modification method thereof

Abstract

This invention discloses an oil-water separation membrane with a surface-modified nanocomposite hydrogel and its modification method, belonging to the field of oil-water separation. The method involves a simple filtration and alternating immersion process to modify the surface of various hydrophobic separation membranes with a nanostructured nanocomposite hydrogel layer. The nanocomposite hydrogel is composed of hydrogel and nanoparticles; the hydrogel is formed from polyvinylpyrrolidone and polyphenols, and the nanoparticles are formed by the complexation of iron ions and polyphenols. Compared to smooth hydrogels, the nanostructured hydrogel possesses superior wettability and underwater resistance to high-viscosity oil droplet adhesion, effectively protecting the base membrane and achieving efficient separation of high-viscosity emulsified oil. Compared to conventional methods for modifying separation membranes with nanohydrogels, this strategy has the advantages of simple operation and wider applicability.

Description

Technical Field

[0001] This invention belongs to the field of oil-water separation, specifically relating to a simple and universal surface-modified nanocomposite hydrogel oil-water separation membrane and its modification method. Background Technology

[0002] With the continuous improvement of human living standards and the continuous growth of production, human life is inseparable from various types of oil, inevitably leading to various oily wastewater. Among them, emulsified oil, due to its small oil droplet size, is difficult to separate into oil and water even after long-term storage, making it difficult to treat. Currently, traditional methods for treating emulsified oil include oil flocculation, adsorption, flotation, and deemulsification, but these methods suffer from drawbacks such as low separation efficiency, secondary pollution, and high energy consumption. Membrane separation technology, on the other hand, has received widespread attention in the field of oil-water separation due to its advantages of low energy consumption, high separation efficiency, and no secondary pollution. However, during the oil-water separation process using a separation membrane, under operating pressure, oil droplets in the emulsion, especially high-viscosity oil droplets, easily adhere to the surface of the separation membrane, thereby clogging the separation channels and causing the separation membrane to quickly fail. Therefore, improving the anti-oil adhesion performance of the separation membrane is particularly important. Typically, artificial underwater oleophobic surfaces can be prepared by adding a strong hydration layer and increasing the surface roughness of the material. Hydrogels are well-known water-retaining materials. Most hydrogels contain abundant hydrophilic functional groups, such as hydroxyl, amino, and carboxylic acid groups, which can form a strong hydration layer. Imparting micro / nanostructures to the surface of materials can amplify their inherent wettability. Therefore, introducing nanostructures into the surface of hydrogels can enhance their hydrophilicity. Currently, most methods for introducing nanostructured nanocomposite hydrogels onto membrane surfaces are complex, time-consuming, and generally lack versatility. Therefore, developing a simple and universally applicable strategy for modifying separation membranes with nanocomposite hydrogels is necessary. Summary of the Invention

[0003] To address the shortcomings of existing methods, this invention aims to provide a strategy for modifying separation membranes with nanocomposite hydrogels. This strategy solves both the problems of complex and time-consuming operations in preparing nanocomposite hydrogels and the poor universality of modification strategies. The nanocomposite hydrogel modification strategy involves pre-treating the hydrophobic original membrane through filtration, introducing a pre-coating layer on its surface, and then subjecting it to alternating immersion. A nanocomposite hydrogel is formed on the pre-coating layer, thereby modifying the separation membrane with nanocomposite hydrogels. In the process of using a water-in-water emulsion membrane to treat oil-in-water emulsions, it is crucial to avoid oil clogging the membrane pores, enhance the membrane's anti-oil adhesion properties, and most importantly, reduce the hydrophobic interaction between oil droplets and the base membrane. The strong and stable hydration layer formed by the nanocomposite hydrogel can effectively protect the base membrane, and the nanoparticles can increase the distance between oil droplets and the base membrane during separation, reducing hydrophobic interactions. However, the preparation of traditional nanocomposite hydrogels requires the pre-formation of multiphase interfaces and complex cross-linking and gelation chemical reactions. Meanwhile, many chemical crosslinking agents are toxic and require multiple purification steps to obtain micro / nano structures. Our strategy involves forming nanoparticles on the hydrogel framework while simultaneously forming a hydrogel on the membrane surface during alternating soaking. This method is simple and time-efficient. In this strategy, the pre-coating can stably adhere to the surface of various separation membranes, thus demonstrating the good versatility of this nanocomposite hydrogel-modified separation membrane strategy.

[0004] This invention is achieved through the following technical solution:

[0005] The first aspect of this invention provides a method for modifying an oil-water separation membrane with a surface-modified nanocomposite hydrogel. This method involves modifying the surface of various oil-water separation membranes with a nanocomposite hydrogel through filtration and alternating immersion processes. Introducing a protective coating with excellent anti-oil adhesion properties onto the separation membrane surface is crucial. This protective coating prevents oil droplets from directly contacting the base membrane, thereby protecting the separation membrane from oil contamination. This invention addresses the problem of oil contamination of separation membranes during oil-water separation by introducing a nanocomposite hydrogel onto the membrane surface.

[0006] Furthermore, the aforementioned base membrane is one of polypropylene membrane, polytetrafluoroethylene membrane, and polyvinylidene fluoride membrane.

[0007] The nanocomposite hydrogel of this invention is a novel hydrogel with excellent anti-oil adhesion properties. It is composed of a hydrogel and nanoparticles, wherein the hydrogel is formed by polyvinylpyrrolidone and polyphenols, and the nanoparticles are formed by iron ions and polyphenol complexes. The hydrogel and nanoparticles are formed simultaneously. The nanocomposite hydrogel of this invention exhibits superior anti-oil adhesion properties. The hydrogel can form a strong hydration layer, and the further introduction of nanoparticles can strengthen the hydration layer and increase the distance between oil droplets and the basement membrane, reducing the hydrophobic interaction between oil droplets and the basement membrane. It also exhibits good properties even when facing emulsions formed from high-viscosity crude oil.

[0008] The specific steps for modifying separation membranes with nanocomposite hydrogels include:

[0009] Step 1: Wet the separation membrane with ethanol;

[0010] Step 2: The separation membrane obtained in Step 1 is sandwiched in a filtration device and filtered before and after the solution containing both hydrophilic and hydrophobic groups and a solution containing polyphenols to obtain a pretreated membrane. The purpose of this step is to stabilize the nanocomposite hydrogel on the surface of the separation membrane. The pre-coating formed by the pretreatment adheres stably to the surface of the separation membrane through hydrophobic interactions. At the same time, the surface of the pre-coating contains active sites that can interact with the hydrogel polymer.

[0011] Step 3: Place the pretreated membrane prepared in Step 2 into an aqueous solution containing amide groups and iron ions and react for tens of seconds (preferably 30 seconds). Remove the membrane from the reaction solution and wash it with deionized water to remove excess reaction solution from the surface of the membrane.

[0012] Step 4: Place the separation membrane prepared in Step 3 into an aqueous solution containing polyphenols and react for several tens of seconds (preferably 30 seconds). Remove the separation membrane from the reaction solution and wash it with deionized water to remove excess reaction solution from the surface of the separation membrane.

[0013] Step 5: Place the reaction membrane prepared in Step 4 back into the aqueous solution containing amide groups and iron ions for several tens of seconds (preferably 30 seconds). Remove the separation membrane from the reaction solution and wash it with deionized water to remove excess reaction solution from the surface of the separation membrane, thus obtaining a nano-hydrogel separation membrane with superhydrophilic and super oil-resistant properties.

[0014] Furthermore, the substance containing both hydrophilic and hydrophobic groups is ovalbumin; the polyphenolic substance is tannic acid or gallic acid, or a mixture thereof; the polymer containing amide groups is polyvinylpyrrolidone; and the iron ion solution is either ferric sulfate solution or ferric chloride solution. The concentration of ovalbumin / polyphenolic substance / polymer containing amide groups / iron ions is 0.5 / 0.5 / 1 / 1.25 mg / mL.

[0015] Furthermore, the amount of nanocomposite hydrogel on the surface of the separation membrane can be controlled by the number of alternating depositions in the reaction solution, i.e., by increasing the number of alternating reactions in steps three and four.

[0016] Furthermore, the immersion of the separation membrane in the reaction solution should end with immersion in a mixed solution containing iron ions and polymers containing amide groups.

[0017] In another aspect, the present invention provides an oil-water separation membrane for a surface-modified nanocomposite hydrogel prepared by the above method.

[0018] Compared with the prior art, the beneficial effects of the present invention include:

[0019] 1. This invention combines nanostructures and hydrogels to achieve a nanocomposite hydrogel with super antifouling properties. This hydrogel on the surface of the separation membrane can give the separation membrane super underwater anti-oil adhesion properties, which can solve the problem of the decrease in separation rate and separation efficiency of the separation membrane when processing oil-in-water.

[0020] 2. The modified separation membrane obtained by the composite nano-hydrogel modification strategy has excellent wettability and underwater anti-oil adhesion properties. Water droplets can spread completely within 1 second after contacting the surface of the modified separation membrane. Even after pressing high-viscosity crude oil droplets onto the surface of the modified separation membrane underwater for 23 hours, the oil droplets do not adhere to the surface of the separation membrane. The separation efficiency when treating oil-in-water emulsions formed by crude oil is as high as 99.7%.

[0021] 3. The composite nano-hydrogel can stabilize the surface of the separation membrane. After the modified separation membrane is placed in water rotating at 3000 r / min for 24 hours, placed in air for 5 months, and soaked in aqueous solutions with pH values ​​of 3, 5, 7, 9, and 11 for 12 hours, the nano-hydrogel is still uniformly distributed on the surface of the separation membrane.

[0022] 4. The above-mentioned composite nano-hydrogel modification strategy has the advantages of simple operation, short time, and strong universality. Attached Figure Description

[0023] Figure 1 The flowchart shows the strategy for modifying the separation membrane with nano-hydrogels.

[0024] Figure 2 Scanning electron microscope (SEM) images of the original polyvinylidene fluoride (PVDF) membrane, the modified PVDF membrane, the original polytetrafluoroethylene (PTFE) membrane, the modified PTFE membrane, the original polypropylene (PP) membrane, and the modified PP membrane.

[0025] Figure 3 Image showing the diffusion of water droplets on the surface of the modified polyvinylidene fluoride separation membrane within 1 second;

[0026] Figure 4 The underwater crude oil contact angle of the separation membrane surface before and after modification;

[0027] Figure 5 Images showing crude oil droplets being squeezed onto the surface of a modified separation membrane underwater and crude oil droplets leaving the separation membrane surface after 23 hours of squeezing;

[0028] Figure 6 These are real photographs and optical microscope images of crude oil emulsions before and after separation.

[0029] Figure 7 The underwater crude oil contact angles of the modified polyvinylidene fluoride separation membrane were measured after rinsing with water for 24 hours, placing it in air for 5 months, and immersing it in aqueous solutions with different pH values ​​for 12 hours.

[0030] Figure 8 These are scanning electron microscope (SEM) images of the modified polyvinylidene fluoride (PVDF) separation membrane after processing. Figure 8 a is a scanning electron microscope image of the modified polyvinylidene fluoride separation membrane after rinsing with water for 24 hours. Figure 8 b is a scanning electron microscope image of the modified polyvinylidene fluoride separation membrane after being placed in air for 5 months. Figure 8 c and Figure 8 Images d are scanning electron microscope images of the modified polyvinylidene fluoride separation membrane after immersion in aqueous solutions with pH values ​​of 3 and 11 for 12 hours.

[0031] Figure 9 Scanning electron microscope (SEM) images of polyvinylidene fluoride (PVDF) separation membranes prepared after modifying the number of alternating depositions in the reaction solution, wherein... Figure 9 a is a scanning electron microscope image of the separation membrane obtained after reducing the number of alternating immersion cycles of the polyvinylidene fluoride (PVDF) separation membrane. Figure 9 b is a scanning electron microscope image of the separation membrane obtained after increasing the number of alternating immersions of the polyvinylidene fluoride separation membrane. Detailed Implementation

[0032] The following embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the essence of the present invention should be covered within the scope of protection of the present invention.

[0033] Example 1

[0034] A simple and universal nano-hydrogel modified separation membrane strategy for separating high-viscosity emulsified oil in water is described below:

[0035] Polyvinylidene fluoride (PVDF) membrane, polytetrafluoroethylene (PTFE) membrane, and polyethylene (PE) membrane were used as the original separation membranes.

[0036] After wetting the original separation membrane with an ethanol solution, the membrane was clamped into the filter device (the effective filtration area of ​​the separation membrane is 12.57 cm²). 2 ), and then filtered for ovalbumin (0.5 mg / mL) -1 15 mL of solution containing tannic acid (0.5 mg / mL) and 15 mL of solution containing tannic acid (0.5 mg / mL) -1 15 mL of solution was prepared, and then the sample was alternately immersed in a solution containing polyvinylpyrrolidone (1 mg / mL). -1 ) and ferric sulfate (1.25 mg / mL) -1 After reacting in an aqueous solution of tannic acid (0.5 mg / mL) for 30 seconds, the separation membrane was removed and washed with deionized water to remove excess reaction solution from its surface. Then, it was placed in an aqueous solution containing tannic acid (0.5 mg / mL). -1 The membrane was reacted in an aqueous solution containing polyvinylpyrrolidone (1 mg / mL) for 30 seconds, then removed and washed with deionized water to remove excess reaction solution from the membrane surface. The resulting membrane was then placed back into the solution containing polyvinylpyrrolidone (1 mg / mL). -1 ) and ferric sulfate (1.25 mg mL) -1 In an aqueous solution of [a specific ingredient], the reaction is carried out for 30 seconds. Excess reaction solution on the surface of the separation membrane is then washed away with deionized water, yielding a separation membrane with superhydrophilic and underwater superoleophobic properties. The amount of nanocomposite hydrogel on the membrane surface can be controlled by alternating immersion in the reaction solution. The operation procedure is as follows: Figure 1 As shown.

[0037] Scanning electron microscope (SEM) images of the original polyvinylidene fluoride (PVDF) membrane, the modified PVDF membrane (PVDF-Nh2), the original polytetrafluoroethylene (PTFE) membrane, the modified polytetrafluoroethylene (PTFE-Nh2) membrane, the original polypropylene (PP) membrane, and the modified polypropylene (PP-Nh2) membrane are shown below. Figure 2 As shown. Taking a polyvinylidene fluoride (PVDF) separation membrane as an example, when a water droplet is placed on the surface of the modified separation membrane, the water droplet rapidly spreads within 1 second. Figure 3The diffusion of water droplets on the separation membrane surface at 0s, 0.03s, 0.05s, and 1s. Figure 4 Underwater crude oil contact angle before and after membrane modification. For example... Figure 5 As shown, high-viscosity crude oil droplets were forcefully squeezed underwater onto the surface of a modified separation membrane. After 23 hours, the crude oil droplets were pulled away from the membrane surface, and the droplets did not adhere to it. The crude oil emulsion was then treated with the modified separation membrane, as shown... Figure 6 As shown, real photographs and optical microscope images of the emulsion before and after separation are presented. Before separation, the emulsion appears as a colored, unclear liquid with a large number of dispersed crude oil droplets in its optical microscope image. After separation, the filtrate is a colorless and transparent liquid, and no oil droplets are visible in its optical microscope image. The modified separation membrane was subjected to simulated water washing at 3000 r / min for 24 hours, and its underwater crude oil contact angle was measured. The PVDF-Nh2 separation membrane was placed in air for 5 months, and its underwater crude oil contact angle was measured. The PVDF-Nh2 separation membrane was immersed in aqueous solutions with pH values ​​of 3, 5, 7, 9, and 11 for 12 hours, and its underwater crude oil contact angle was measured. All experiments were conducted individually, and the treated separation membranes were tested using scanning electron microscopy. Figure 7 The contact angle of underwater crude oil after PVDF-Nh2 treatment; Figure 8 Here are the corresponding scanning electron microscope images, where, Figure 8 a is a scanning electron microscope image of the modified polyvinylidene fluoride separation membrane after rinsing with water for 24 hours. Figure 8 b is a scanning electron microscope image of the modified polyvinylidene fluoride separation membrane after being placed in air for 5 months. Figure 8 c and Figure 8 Images d are scanning electron microscope (SEM) images of the modified polyvinylidene fluoride (PVDF) separation membranes after immersion in aqueous solutions at pH 3 and 11 for 12 hours.

[0038] Example 2

[0039] After wetting the original separation membrane with an ethanol solution, the membrane was clamped into the filter device (the effective filtration area of ​​the separation membrane is 12.57 cm²). 2 ), and then filtered for ovalbumin (0.5 mg / mL) -1 15 mL of solution containing gallic acid (0.5 mg / mL) and 15 mL of solution containing gallic acid (0.5 mg / mL) -1 15 mL of solution was prepared, and then the sample was alternately immersed in a solution containing polyvinylpyrrolidone (1 mg / mL). -1 ) and ferric sulfate (1.25 mg / mL) -1 After reacting in an aqueous solution of tannic acid (0.5 mg / mL) for 30 seconds, the separation membrane was removed and washed with deionized water to remove excess reaction solution from its surface. Then, it was placed in an aqueous solution containing tannic acid (0.5 mg / mL). -1The membrane was reacted in an aqueous solution containing polyvinylpyrrolidone (1 mg / mL) for 30 seconds, then removed and washed with deionized water to remove excess reaction solution from the membrane surface. The resulting membrane was then placed back into the solution containing polyvinylpyrrolidone (1 mg / mL). -1 ) and ferric sulfate (1.25 mg mL) -1 In an aqueous solution of ), the reaction is carried out for 30 seconds to obtain a separation membrane with superhydrophilic and underwater superoleophobic properties.

[0040] Example 3

[0041] After wetting the original separation membrane with an ethanol solution, the membrane was clamped into the filter device (the effective filtration area of ​​the separation membrane is 12.57 cm²). 2 ), and then filtered for ovalbumin (0.5 mg / mL) -1 15 mL of solution containing tannic acid (0.5 mg / mL) and 15 mL of solution containing tannic acid (0.5 mg / mL) -1 15 mL of solution was prepared, and then the sample was alternately immersed in a solution containing polyvinylpyrrolidone (1 mg / mL). -1 ) and ferric chloride (1.25 mg / mL) -1 After reacting in an aqueous solution of tannic acid (0.5 mg / mL) for 30 seconds, the separation membrane was removed and washed with deionized water to remove excess reaction solution from its surface. Then, it was placed in an aqueous solution containing tannic acid (0.5 mg / mL). -1 The membrane was reacted in an aqueous solution containing polyvinylpyrrolidone (1 mg / mL) for 30 seconds, then removed and washed with deionized water to remove excess reaction solution from the membrane surface. The resulting membrane was then placed back into the solution containing polyvinylpyrrolidone (1 mg / mL). -1 ) and ferric chloride (1.00 mg / mL) -1 In an aqueous solution of ), the reaction is carried out for 30 seconds to obtain a separation membrane with superhydrophilic and underwater superoleophobic properties.

[0042] Example 4

[0043] Based on Example 1, the number of alternating soaking times was reduced, i.e., after wetting the original PVDF separation membrane with an ethanol solution, the PVDF separation membrane was clamped into the filter device (the effective filtration area of ​​the separation membrane is 12.57 cm²). 2 ), and then filtered for ovalbumin (0.5 mg / mL) -1 15 mL of solution containing tannic acid (0.5 mg / mL) and 15 mL of solution containing tannic acid (0.5 mg / mL) -1 15 mL of solution was prepared, and then the sample was soaked in a solution containing polyvinylpyrrolidone (1 mg / mL). -1 ) and ferric chloride (1.25 mg mL) -1 After reacting in an aqueous solution of ) for 30 seconds, the separation membrane was removed and washed with deionized water to remove excess reaction solution from the surface of the separation membrane, thus obtaining PVDF-Nh1.

[0044] Based on Example 1, the number of alternating soaking times was increased, that is, the PVDF-Nh2 after the operation in Example 1 was again immersed in tannic acid (0.5 mg / mL). -1 The reaction was carried out in an aqueous solution for 30 seconds. The membrane was then removed and washed with deionized water to remove excess reaction solution. Finally, it was placed in a solution containing polyvinylpyrrolidone (1 mg / mL). -1 ) and ferric sulfate (1.25 mg mL) -1 The reaction was carried out in an aqueous solution for 30 seconds. The excess reaction solution on the surface of the separation membrane was washed away with deionized water to obtain PVDF-Nh3.

[0045] The scanning electron microscope images of the obtained PVDF-Nh1 and PVDF-Nh3 are shown below. Figure 9 As shown in a and 9b, combined with the scanning electron microscope images of PVDF-Nh2, the amount of nanocomposite hydrogel on the separation membrane surface increases with the increase of the number of alternating immersions.

[0046] The above description merely illustrates preferred embodiments of the present invention, and while the description is relatively specific and detailed, it should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications, improvements, and substitutions without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A method for modifying an oil-water separation membrane with a surface-modified nanocomposite hydrogel, characterized in that: The modification method involves modifying the surface of various separation membranes with nanocomposite hydrogels through filtration and alternating soaking processes. The nanocomposite hydrogels are composed of hydrogels and nanoparticles; the hydrogels are formed from polyvinylpyrrolidone and polyphenols, and the nanoparticles are formed by the complexation of iron ions and polyphenols. The modification method includes the following steps: Step 1: Wet the separation membrane with ethanol; Step 2: The separation membrane obtained in Step 1 is sandwiched in a filtration device and filtered through reaction solution A to obtain a pretreated membrane. The reaction solution A is a solution containing both hydrophilic and hydrophobic groups and polyphenols. Step 3: Place the pretreated membrane prepared in Step 2 into reaction solution B and react for tens of seconds. Then remove it and wash off the excess reaction solution B on the surface of the separation membrane with deionized water. The reaction solution B is a mixed aqueous solution containing a polymer containing amide groups and iron ions. Step 4: Place the separation membrane treated in Step 3 into reaction solution C and react for several tens of seconds. Then remove it and wash off the excess reaction solution C on the surface of the separation membrane with deionized water. The reaction solution C is an aqueous solution containing polyphenols. Step 5: Place the reaction membrane prepared in Step 4 back into the reaction solution B for several tens of seconds, then remove it and wash off the excess reaction solution B on the surface of the separation membrane with deionized water to obtain a nano-hydrogel separation membrane with superhydrophilic and super oil-resistant properties.

2. The method for modifying the oil-water separation membrane of the surface-modified nanocomposite hydrogel according to claim 1, characterized in that: The separation membrane is one of polypropylene membrane, polytetrafluoroethylene membrane, and polyvinylidene fluoride membrane.

3. The method for modifying the oil-water separation membrane of the surface-modified nanocomposite hydrogel according to claim 1, characterized in that: The substance that simultaneously possesses hydrophilic and hydrophobic groups is ovalbumin.

4. The method for modifying the oil-water separation membrane of the surface-modified nanocomposite hydrogel according to claim 1, characterized in that: The polyphenolic substance is one of tannic acid or gallic acid, or a mixture of both.

5. The method for modifying the oil-water separation membrane of the surface-modified nanocomposite hydrogel according to claim 1, characterized in that: The polymer containing amide groups is polyvinylpyrrolidone.

6. The method for modifying the oil-water separation membrane of the surface-modified nanocomposite hydrogel according to claim 1, characterized in that: The iron ion solution is either ferric sulfate solution or ferric chloride solution.

7. The method for modifying the oil-water separation membrane of the surface-modified nanocomposite hydrogel according to claim 1, characterized in that: The number of alternating reactions in steps three and four is increased before step five, and the amount of nanocomposite hydrogel is controlled by the number of alternating depositions in reaction solutions B and C.

8. An oil-water separation membrane of a surface-modified nanocomposite hydrogel prepared by any one of claims 1 to 7.

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