A composite membrane material for oil-water separation, its preparation method and application

Abstract

The present invention discloses a method for preparing a composite membrane material for oil-water separation, wherein PVDF is used as a base membrane and MgFe-LDH is used as a functional load. The two are immobilized by dopamine chemical cross-linking to obtain a MgFe-LDH / pDA / PVDF composite membrane material. Also disclosed is a composite membrane material prepared based on the preparation method. Also disclosed is the application of the composite membrane material. The MgFe-LDH / pDA / PVDF composite membrane material of the present invention greatly alleviates the membrane fouling of traditional PVDF membrane materials during oil-water separation, can achieve long-term separation of various emulsions, and exhibits excellent oil-water separation flux.

Description

Technical Field

[0001] The present invention belongs to the technical field of water treatment, and in particular relates to a composite membrane material for oil-water separation, a preparation method thereof, and an application thereof. Background Art

[0002] Wastewater generated during oil extraction, processing, transportation, chemical, mechanical, and food processing often contains significant amounts of oil. Because oily wastewater is less dense than water, it forms an oil film on the surface of receiving water bodies, reducing oxygen levels. Over time, this can lead to hypoxia, the death of aquatic life, and environmental problems. Furthermore, oily wastewater is often potentially carcinogenic, posing a serious threat to human health and aquatic ecosystems. Oily wastewater is primarily classified into three types: floating oil, dissolved oil, and emulsified oil. Emulsified oil refers to tiny oil particles (liquid or semi-solid) that exist in a stable state (not floating or agglomerated). These particles must be demulsified and converted into floating oil before they can be separated. Therefore, emulsified oil is the most difficult type of oil-water emulsion to treat. Currently, the main technologies for treating emulsified oil include pressurized air flotation, chemical coagulation, electrochemical methods, and membrane separation. Pressurized air flotation is typically used in combination with chemical coagulation, offering advantages such as maturity and effectiveness. However, this method requires significant floor space and produces significant amounts of sludge, making subsequent disposal difficult. Electrochemical oil removal is highly efficient and allows for continuous oil-water separation, but the required separation equipment is complex and consumes a lot of electricity, especially as the anode metal is susceptible to corrosion and consumption. In contrast, membrane separation technology, as a new modern water treatment technology, offers advantages such as a small footprint, simple operation, continuous water inflow, low energy consumption, and zero waste generation, demonstrating enormous potential for application in the treatment of oily wastewater.

[0003] The application of membrane separation technology in oil-water separation is mainly based on ultrafiltration (UF). PVDF membrane, as a membrane material with a high degree of compatibility with UF, has become one of the most research-worthy organic polymer membrane materials due to its good chemical stability, high mechanical strength, corrosion resistance, radiation resistance, and UV resistance. It is widely used in the field of oil-water separation. However, since emulsified oil droplets often adhere to the membrane surface or completely fill the membrane pores during the separation process, PVDF membranes are easily contaminated by oil substances, resulting in a sharp drop in flux during the separation of oil-water emulsions, and also manifests as poor long-term separation performance. This not only fails to achieve effective purification of oily wastewater, but may also increase the risk of effluent pollution. Given that PVDF membranes are affected by emulsified oil droplets in oil-water separation applications, improving their resistance to oil pollution is an important way to solve the problem of PVDF membrane pollution.

[0004] Therefore, it is crucial to develop new PVDF membrane materials with special surface properties, and it is necessary to design a new composite membrane material for oil-water separation and its preparation method and application. Summary of the Invention

[0005] The purpose of the present invention is to provide a composite membrane material for oil-water separation, a preparation method and application thereof, so as to solve the problems mentioned in the background art, such as low flux and poor long-term separation performance caused by poor anti-fouling performance of current PVDF membrane materials.

[0006] To achieve the above objectives, the present invention provides a method for preparing a composite membrane material for oil-water separation, wherein PVDF is used as the base membrane and MgFe-LDH is used as the functional load. The two are immobilized by dopamine chemical cross-linking to obtain a MgFe-LDH / pDA / PVDF composite membrane material.

[0007] In a specific embodiment, the method comprises the following steps:

[0008] S1. Mix N,N'-dimethylformamide (DMF), PVDF, and polyvinylpyrrolidone (PVP), heat and stir to react for a period of time, and then age to remove bubbles to form a casting solution. Pour the casting solution onto a dry and flat glass plate and spread it evenly. Then soak the glass plate in pure water to form a PVDF membrane.

[0009] S2, soaking the PVDF membrane obtained in step S1 in an ethanol solution for a period of time, then immersing it in a Tris-HCl buffer solution, adjusting the pH of the buffer solution, adding dopamine, and performing self-polymerization under certain conditions to obtain a pDA / PVDF membrane;

[0010] S3. Dissolve a solid mixture of magnesium nitrate, ferric nitrate, and urea in ultrapure water to prepare a mixed solution, soak the pDA / PVDF membrane obtained in step S2 in the mixed solution, transfer it to a high-pressure reactor, and react under certain conditions to obtain a MgFe-LDH / pDA / PVDF composite membrane material.

[0011] In a specific embodiment, in step S1, the molar ratio of DMF, PVDF, and PVP is 60-80:10-20:1-10.

[0012] In a specific embodiment, the heating and stirring reaction temperature in step S1 is 40-90° C., the stirring time is 4-24 hours, and the reaction apparatus is a magnetic stirrer.

[0013] In a specific embodiment, in step S2, the pH value of the Tris-HCl buffer solution is adjusted to 7.5-9; the concentration of dopamine (DA) is 5-40 mmol.

[0014] In a specific embodiment, in step S2, the self-polymerization is carried out by shaking, the reaction conditions are shaking at 30-50° C. for 4-20 hours, and the reaction apparatus is a shaker.

[0015] In a specific embodiment, in step S3, the molar ratio of magnesium nitrate, ferric nitrate, and urea is 1.5-6:0.5-3:1-9; after the mixed solution is ultrasonicated for 5-60 minutes, the pH is adjusted to 4-11.

[0016] In a specific embodiment, the reaction temperature in step 3 is 60-180° C., and the reaction time is 6-36 hours.

[0017] The present invention also provides a composite membrane material for oil-water separation, wherein the composite membrane material is prepared by the above-mentioned preparation method.

[0018] The present invention also provides an application of a composite membrane material prepared by the preparation method described above, which is used in the oil-water separation of an emulsion, wherein the emulsion is in a stable state, i.e., tiny oil particles, liquid or semi-solid that do not float or condense, and whose particle size is 0.5 to 25 μm.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The MgFe-LDH / pDA / PVDF composite membrane material prepared in the present invention effectively solves the problem of poor membrane flux and separation performance caused by the poor anti-fouling performance of conventional PVDF membranes, and provides effective reference and experience for the development and implementation of emulsion separation and purification technology based on composite membrane materials.

[0021] The MgFe-LDH / pDA / PVDF composite membrane material of the present invention exhibits good long-term separation effect on emulsions formed by different types of oils.

[0022] In addition to the above-described objects, features and advantages, the present invention has other objects, features and advantages. The present invention is further described in detail below. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0024] Figure 1 This is a comparison chart of the antifouling performance of the PVDF membrane, pDA / PVDF membrane, and MgFe-LDH / pDA / PVDF composite membrane in the present invention;

[0025] Figure 2 is a SEM image of the PVDF membrane of the present invention;

[0026] Figure 3 is a SEM image of the pDA / PVDF membrane of the present invention;

[0027] Figure 4 is a SEM image of the MgFe-LDH / pDA / PVDF composite membrane of the present invention;

[0028] Figure 5 is the WCA diagram of the PVDF membrane in the present invention;

[0029] Figure 6 is the WCA diagram of the pDA / PVDF membrane of the present invention;

[0030] Figure 7 is the WCA diagram of the MgFe-LDH / pDA / PVDF composite membrane of the present invention;

[0031] Figure 8 It is the UOCA diagram of the PVDF membrane in the present invention;

[0032] Figure 9 is the UOCA diagram of the pDA / PVDF membrane of the present invention;

[0033] Figure 10 is the UOCA diagram of the MgFe-LDH / pDA / PVDF composite membrane of the present invention;

[0034] Figure 11 This is a diagram showing the cyclic separation effect of the PVDF membrane, pDA / PVDF membrane, and MgFe-LDH / pDA / PVDF composite membrane on engine oil / water emulsion;

[0035] Figure 12 This is a diagram showing the cyclic separation effect of kerosene / water emulsion by the PVDF membrane, pDA / PVDF membrane, and MgFe-LDH / pDA / PVDF composite membrane of the present invention;

[0036] Figure 13 This is a diagram showing the cyclic separation effect of the PVDF membrane, pDA / PVDF membrane, and MgFe-LDH / pDA / PVDF composite membrane on vegetable oil / water emulsions in the present invention;

[0037] Figure 14 This is a diagram showing the cyclic separation effect of the PVDF membrane, pDA / PVDF membrane, and MgFe-LDH / pDA / PVDF composite membrane on n-heptane / water emulsion in the present invention;

[0038] Figure 15 This is a diagram showing the cyclic separation effect of the PVDF membrane, pDA / PVDF membrane, and MgFe-LDH / pDA / PVDF composite membrane on petroleum ether / water emulsion in the present invention;

[0039] Figure 16This is a graph showing the long-term separation performance of the MgFe-LDH / pDA / PVDF composite membrane of the present invention for engine oil / water emulsion;

[0040] Figure 17 This is a graph showing the long-term separation performance of the MgFe-LDH / pDA / PVDF composite membrane of the present invention for kerosene / water emulsion;

[0041] Figure 18 This is a graph showing the long-term separation performance of the MgFe-LDH / pDA / PVDF composite membrane of the present invention for vegetable oil / water emulsion;

[0042] Figure 19 This is a graph showing the long-term separation performance of the MgFe-LDH / pDA / PVDF composite membrane of the present invention for n-heptane / water emulsion;

[0043] Figure 20 This is a diagram showing the long-term separation performance of the MgFe-LDH / pDA / PVDF composite membrane of the present invention for petroleum ether / water emulsion. DETAILED DESCRIPTION

[0044] The embodiments of the present invention are described in detail below. The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0045] The invention discloses a method for preparing a composite membrane material for oil-water separation, which uses PVDF as a base membrane and MgFe-LDH as a functional load, and the two are immobilized by dopamine chemical cross-linking to obtain a MgFe-LDH / pDA / PVDF composite membrane material.

[0046] The specific steps include:

[0047] S1. Mix N,N'-dimethylformamide (DMF), PVDF, and polyvinylpyrrolidone (PVP) in a molar ratio of DMF, PVDF, and PVP of 60-80:10-20:1-10; heat and stir to react at a temperature of 40-90°C for 4-24 hours using a magnetic stirrer; and after aging to remove bubbles, form a casting solution, pour the casting solution onto a dry and flat glass plate and spread it evenly, then soak the glass plate in pure water to form a PVDF membrane.

[0048] S2. Soaking the PVDF membrane obtained in step S1 in an ethanol solution for a period of time, then immersing it in a Tris-HCl buffer solution, adjusting the pH value of the Tris-HCl buffer solution to 7.5-9; adding dopamine, wherein the concentration of dopamine (DA) is 5-40 mmol, and self-polymerizing by shaking. The reaction conditions are shaking at 30-50° C. for 4-20 hours, and the reaction apparatus is a shaker, thereby obtaining a pDA / PVDF membrane;

[0049] S3. Dissolve a solid mixture of magnesium nitrate, ferric nitrate, and urea in ultrapure water to prepare a mixed solution, wherein the molar ratio of magnesium nitrate, ferric nitrate, and urea is 1.5-6:0.5-3:1-9; ultrasonicate the mixed solution for 5-60 minutes, and then adjust the pH to 4-11; immerse the pDA / PVDF membrane obtained in step S2 in the mixed solution, transfer it to a high-pressure reactor, and react at a reaction temperature of 60-180° C. for 6-36 hours to obtain a MgFe-LDH / pDA / PVDF composite membrane material.

[0050] The present invention also provides a composite membrane material for oil-water separation, wherein the composite membrane material is prepared by the above-mentioned preparation method.

[0051] The present invention also provides an application of a composite membrane material prepared by the preparation method described above, which is used in the oil-water separation of an emulsion, wherein the emulsion is in a stable state, i.e., tiny oil particles, liquid or semi-solid that do not float or condense, and whose particle size is 0.5 to 25 μm.

[0052] Example 1

[0053] This embodiment is a method for preparing a MgFe-LDH / pDA / PVDF composite membrane, comprising the following steps:

[0054] (1) N,N'-dimethylformamide (DMF), PVDF, and polyvinylpyrrolidone (PVP) were mixed in a molar ratio of 89:10:1 and heated at 80°C with stirring for 24 h. After aging to remove bubbles, the casting solution was poured onto a dry, flat glass plate and evenly spread. The glass plate was then immersed in pure water to form a PVDF membrane.

[0055] (2) The PVDF membrane obtained in step (1) was immersed in an ethanol solution, and then immersed in 10 mL of Tris-HCl (10 mM) buffer solution. After adjusting the pH of the buffer solution to 9, 10 mM dopamine was added and dopamine (DA) was self-polymerized under oscillation for 4 h to obtain a pDA / PVDF membrane.

[0056] (3) Dissolve Mg(NO3)2·6H2O, Fe(NO3)3·9H2O and urea in ultrapure water at a molar ratio of 1.5:1:2, adjust the pH of the solution to 5, soak the pDA / PVDF membrane obtained in step (2) in the solution, transfer it to a high-pressure reactor, and react at 60°C for 6 hours to obtain a MgFe-LDH / pDA / PVDF composite membrane material.

[0057] Example 2

[0058] The contact angle tests of PVDF membrane, pDA / PVDF membrane and MgFe-LDH / pDA / PVDF composite membrane were carried out. The water contact angle (WCA) results were 137.6°, 86.3° and 0°, respectively. The underwater oil contact angle (UOCA) results were 22.3°, 110.2° and 154.6°, respectively. Figures 5-10 The hydrophilicity of the membrane is indicated by the water contact angle and the underwater oil contact angle. The results show that with the in-situ loading of MgFe-LDH, the hydrophilicity of the membrane increases, which is beneficial for the application of emulsified oil-water separation.

[0059] Example 3

[0060] Prepare a BSA solution with a concentration of 0.5 g / L, and place the PVDF membrane, pDA / PVDF, and MgFe-LDH / pDA / PVDF composite membrane in a low-pressure flat membrane filtration device with an effective membrane area of 4 cm 2 The membrane water flux and BSA antifouling experiments were carried out under constant transmembrane pressure (0.1 MPa). The experimental results showed that the initial water flux of PVDF membrane, pDA / PVDF membrane, and MgFe-LDH / pDA / PVDF composite membrane were 2090 L·m -2 ·h -1 bar -1 、910L·m -2 ·h -1 bar -1 、680L·m -2 ·h -1 bar -1 After a single cycle, the flux recovery rates of PVDF membrane, pDA / PVDF membrane, and MgFe-LDH / pDA / PVDF composite membrane were 51%, 63%, and 91%, respectively. Figure 1 Compared with PVDF membrane and pDA / PVDF membrane, although the flux of MgFe-LDH / pDA / PVDF composite membrane is lower, the flux recovery rate is higher, which proves that MgFe-LDH / pDA / PVDF composite membrane has better anti-fouling performance.

[0061] Example 4

[0062] The engine oil and water were mixed in a ratio of 1:49 and magnetically stirred for 12 hours to form an emulsion. PVDF membrane, pDA / PVDF membrane, and MgFe-LDH / pDA / PVDF composite membrane were placed in an ultrafiltration cup for a cyclic membrane test. The experimental results showed that after 8 cycles, the separation efficiency of the PVDF membrane and pDA / PVDF membrane for the engine oil / water emulsion was less than 20%, while the separation efficiency of the MgFe-LDH / pDA / PVDF composite membrane remained above 90%. Figure 11 The results show that the MgFe-LDH / pDA / PVDF composite membrane has a good separation effect on the oil / water mixed emulsion and can be recycled multiple times.

[0063] Example 5

[0064] Kerosene and water were mixed in a ratio of 1:49 and magnetically stirred for 12 hours to form an emulsion. PVDF membrane, pDA / PVDF membrane, and MgFe-LDH / pDA / PVDF composite membrane were placed in an ultrafiltration cup for a cyclic membrane test. The experimental results showed that after 8 cycles, the separation efficiency of PVDF membrane and pDA / PVDF membrane for kerosene / water emulsion was less than 20%, while the separation efficiency of MgFe-LDH / pDA / PVDF composite membrane remained above 90%. Figure 12 The results show that the MgFe-LDH / pDA / PVDF composite membrane has a good separation effect on kerosene / water emulsion and can be recycled multiple times.

[0065] Example 6

[0066] Vegetable oil and water were mixed in a ratio of 1:49 and magnetically stirred for 12 hours to form an emulsion. PVDF membrane, pDA / PVDF membrane, and MgFe-LDH / pDA / PVDF composite membrane were placed in an ultrafiltration cup for a cyclic membrane test. The experimental results showed that after 8 cycles, the separation efficiency of PVDF membrane and pDA / PVDF membrane for vegetable oil / water emulsion was less than 20%, while the separation efficiency of MgFe-LDH / pDA / PVDF composite membrane remained above 90%. Figure 13 The results show that the MgFe-LDH / pDA / PVDF composite membrane has a good separation effect on the vegetable oil / water emulsion and can be recycled multiple times.

[0067] Example 7

[0068] n-heptane and water were mixed in a ratio of 1:49 and magnetically stirred for 12 hours to form an emulsion. PVDF membrane, pDA / PVDF membrane, and MgFe-LDH / pDA / PVDF composite membrane were placed in an ultrafiltration cup for a cyclic membrane test. The experimental results showed that after 8 cycles, the separation efficiency of PVDF membrane and pDA / PVDF membrane for the n-heptane / water emulsion was less than 20%, while the separation efficiency of MgFe-LDH / pDA / PVDF composite membrane remained above 90%. Figure 14 The results show that the MgFe-LDH / pDA / PVDF composite membrane has a good separation effect on the n-heptane / water mixed emulsion and can be recycled multiple times.

[0069] Example 8

[0070] Petroleum ether and water were mixed in a ratio of 1:49 and magnetically stirred for 12 hours to form an emulsion. PVDF membrane, pDA / PVDF membrane, and MgFe-LDH / pDA / PVDF composite membrane were placed in an ultrafiltration cup for a cyclic membrane test. The experimental results showed that after 8 cycles, the separation efficiency of PVDF membrane and pDA / PVDF membrane for the petroleum ether / water emulsion was less than 20%, while the separation efficiency of MgFe-LDH / pDA / PVDF composite membrane remained above 90%. Figure 15 The results show that the MgFe-LDH / pDA / PVDF composite membrane has a good separation effect on the petroleum ether / water mixed emulsion and can be recycled multiple times.

[0071] Example 9

[0072] Emulsions of engine oil / water, kerosene / water, vegetable oil / water, n-heptane / water, and petroleum ether / water were prepared, and the MgFe-LDH / pDA / PVDF composite membrane was placed in a low-pressure flat membrane filtration device with an effective membrane area of 4 cm2. An oil-water separation experiment was conducted for 1000 minutes under a constant transmembrane pressure (0.1 MPa). The experimental results showed that after 1000 minutes of separation experiment, the separation efficiency of the MgFe-LDH / pDA / PVDF composite membrane for the emulsions of five different types of oil remained stable at above 90%, and the flux was maintained at above 50% of the initial emulsion flux, showing good long-term separation performance for emulsions of various types of oil, such as Figures 16-20 shown.

[0073] The MgFe-LDH / pDA / PVDF composite membrane material of the present invention greatly alleviates the membrane fouling of traditional PVDF membrane materials during oil-water separation, can achieve long-term separation of emulsions of various types of oils, and exhibits excellent oil-water separation flux.

[0074] The above content is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art of the present invention, several simple deductions and substitutions can be made without departing from the concept of the present invention, and all of these should be considered to fall within the scope of protection of the present invention.

Claims

1. A method for preparing a composite membrane material for oil-water separation, characterized in that: Using PVDF as the base membrane and MgFe-LDH as the functional load, the two are immobilized by dopamine chemical cross-linking to obtain a MgFe-LDH / pDA / PVDF composite membrane material; specifically comprising the following steps: S1, DMF, PVDF, and PVP were mixed, heated and stirred for a period of time, and then aged to remove bubbles to form a casting solution. The casting solution was poured onto a dry and flat glass plate and evenly spread. The glass plate was immersed in pure water to form a PVDF membrane; S2, soaking the PVDF membrane obtained in step S1 in an ethanol solution for a period of time, then immersing it in a Tris-HCl buffer solution, adjusting the pH of the buffer solution, adding dopamine, and performing self-polymerization under certain conditions to obtain a pDA / PVDF membrane; S3. Dissolving a solid mixture of magnesium nitrate, ferric nitrate, and urea in ultrapure water to prepare a mixed solution, immersing the pDA / PVDF membrane obtained in step S2 in the mixed solution, transferring the mixture to a high-pressure reactor, and reacting under certain conditions to obtain a MgFe-LDH / pDA / PVDF composite membrane material; in step S3, the molar ratio of magnesium nitrate, ferric nitrate, and urea is 1.5-6:0.5-3:1-9; after ultrasonicating the mixed solution for 5-60 minutes, adjusting the pH to 4-11.

2. The method for preparing a composite membrane material for oil-water separation according to claim 1, characterized in that: In step S1, the molar ratio of DMF, PVDF, and PVP is 60-80:10-20:1-10.

3. The method for preparing a composite membrane material for oil-water separation according to claim 1, wherein: The heating and stirring reaction temperature in step S1 is 40-90° C., the stirring time is 4-24 hours, and the reaction apparatus is a magnetic stirrer.

4. The method for preparing a composite membrane material for oil-water separation according to claim 1, wherein: In step S2, the pH value of the Tris-HCl buffer solution is adjusted to 7.5-9; and the concentration of dopamine is 5-40 mmol.

5. The method for preparing a composite membrane material for oil-water separation according to claim 1, wherein: In the step S2, the self-polymerization is carried out by shaking, and the reaction conditions are shaking at 30-50° C. for 4-20 h, and the reaction apparatus is a shaker.

6. The method for preparing a composite membrane material for oil-water separation according to claim 1, characterized in that: The reaction temperature in step S3 is 60-180° C., and the reaction time is 6-36 hours.

7. A composite membrane material for oil-water separation, characterized in that: The composite membrane material is prepared by the preparation method according to any one of claims 1 to 6.

8. Use of a composite membrane material prepared by the preparation method according to any one of claims 1 to 6, characterized in that: It is used in the oil-water separation of emulsions, wherein the emulsions are small oil particles, liquids or semi-solids that exist in a stable state, that is, do not float or aggregate, and have a particle size of 0.5 to 25 μm.

Images