A modified polyvinylidene fluoride membrane, and a preparation method and application thereof

Abstract

This invention discloses a modified polyvinylidene fluoride (PVDF) membrane, its preparation method, and its application, belonging to the field of gear oil purification technology. The method includes: S1: immersing the PVDF membrane in anhydrous ethanol for activation; S2: immersing the activated PVDF membrane in a citric acid solution, adding polyethyleneimine dropwise to the citric acid solution, adjusting the pH to neutral to alkaline, and reacting to obtain PVDF@CA / PEI; S3: immersing the PVDF@CA / PEI membrane in a glutaraldehyde aqueous solution and stirring to obtain a PVDF@CA / PEI-GA membrane; S4: adding the PVDF@CA / PEI-GA membrane to a cysteine ​​solution, impregnating it, and then removing it to obtain a PVDF@CA / PEI-GA / Cys membrane. This product is used for the removal of metallic impurities from gear oil. The entire synthesis process is simple, efficient, and easy to operate, making it suitable for large-scale production. It overcomes the current difficulty of effectively removing bound metallic impurities from gear oil using physical methods. This adsorbent can effectively remove metallic elements from gear oil, thereby ensuring the reliable and stable long-term operation of the unit equipment.

Description

Technical Field

[0001] This invention belongs to the field of gear oil purification technology, specifically relating to a method for preparing and applying a modified polyvinylidene fluoride membrane. Background Technology

[0002] In industrial production, lubricating oil reduces power loss by decreasing friction in heavy-duty gear transmission devices and provides cooling by dispersing heat. Furthermore, it prevents corrosion and rust on components, reduces operating noise, vibration, and impact between gears, and washes away contaminants, especially between gear teeth, thus reducing wear. Maintaining the oil in a clean state effectively reduces wear on gears and other moving parts, thereby extending gear life. The lubricating performance of oil decreases with equipment operation. Motion and power transmission occur through the interaction and relative motion of each pair of meshing gear teeth in the gear mechanism, inevitably generating friction and producing tiny metal abrasive particles that can damage the stable structure of the gears. Therefore, this places very stringent requirements on the performance of gear oils that lubricate the operating system. In addition to excellent extreme pressure anti-wear properties, cooling properties, and cleaning properties, the gear oil used should also have good thermal oxidation stability, low-temperature performance, and a long service life. Simultaneously, it should have a low coefficient of friction to reduce power loss in gear transmission, ensuring reliable and stable long-term operation of the equipment.

[0003] Waste oil recycling and regeneration is one of the effective measures to save resources. Magnetic iron particles or iron oxides in waste gear oil can be adsorbed by magnetic filters, but iron elements that exist in a non-magnetic bound state cannot be filtered by physical and mechanical methods, which brings great difficulties to the recycling and reuse of waste gear oil. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art in that waste gear oil is difficult to recycle and reuse, the purpose of this invention is to provide a method for preparing and applying a modified polyvinylidene fluoride membrane, so as to solve the technical problem that bound metal impurities in gear oil cannot be effectively removed by physical methods such as mechanical filtration and magnetic filtration.

[0005] To achieve the above objectives, the present invention employs the following technical solution:

[0006] A method for preparing a modified polyvinylidene fluoride (PVDF) membrane includes the following steps:

[0007] S1: The polyvinylidene fluoride membrane is immersed in anhydrous ethanol for activation treatment;

[0008] S2: Immerse the activated polyvinylidene fluoride membrane in a citric acid solution, add polyethyleneimine dropwise to the citric acid solution, adjust the pH to neutral to alkaline to carry out the reaction, and obtain PVDF@CA / PEI;

[0009] S3: Immerse the PVDF@CA / PEI membrane in a glutaraldehyde aqueous solution and stir to react, to obtain the PVDF@CA / PEI-GA membrane;

[0010] S4: Add the PVDF@CA / PEI-GA membrane to the cysteine ​​solution, and after the impregnation reaction, remove it to obtain the PVDF@CA / PEI-GA / Cys membrane.

[0011] As a further improvement of the present invention, the polyvinylidene fluoride membrane is immersed in anhydrous ethanol for 1 to 3 hours.

[0012] As a further improvement of the present invention, the concentration of the citric acid solution is 1-3 mg / mL, and the concentration of the polyethyleneimine solution is 1-3 mg / mL.

[0013] As a further improvement of the present invention, in the process of adjusting the pH to neutral to alkaline, the reaction time is 2 to 5 hours.

[0014] As a further improvement of the present invention, the glutaraldehyde solution has a mass fraction of 0.1% to 0.3%, and the stirring reaction time is 2 to 5 hours.

[0015] As a further improvement of the present invention, the concentration of the cysteine ​​solution is 5-15 mg / mL, and the immersion reaction time is 10-15 h.

[0016] A modified polyvinylidene fluoride membrane obtained by the preparation method described above.

[0017] The above preparation method yields a modified polyvinylidene fluoride membrane used in gear oil purification.

[0018] Furthermore, a modified polyvinylidene fluoride membrane was placed in a filtration device, and gear oil was filtered under a set pressure. The filtered permeate was collected, and the content of each metal element in the permeate was determined.

[0019] The set pressure is 0.1 MPa.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] This invention first utilizes polyvinylidene fluoride (PVDF) as an excellent membrane separation material. PVDF is a semi-crystalline polymer with repeating –(CH2CF2)– units, possessing high mechanical strength, good chemical resistance, and thermal stability, while also exhibiting good anti-aging properties. The modified PVDF membrane prepared in this invention removes metal elements from gear oil through a complexation reaction between the modified molecules on the membrane and metal ions, utilizing the membrane's filtration properties. PVDF exhibits good processability in the preparation of flat sheet membranes, tubular membranes, and hollow fiber membranes. However, PVDF membranes have relatively low surface energy and strong hydrophobicity, making them easily adsorbed by long-chain alkanes, leading to flux attenuation and reduced membrane element production capacity. Therefore, citric acid is used to modify the PVDF membrane. Citric acid is an excellent complexing agent that can react with metal elements to form precipitates, exhibiting a strong complexing ability for metal ions and effectively removing metal elements from oil. Adding polyethyleneimine as a metal ion trapping agent, with its numerous amino groups on the molecular chain, provides a strong chelating ability for some metal ions, thereby enhancing adsorption and effectively improving removal efficiency. Subsequently, glutaraldehyde is used as a crosslinking agent to crosslink polyethyleneimine onto a polyvinylidene fluoride (PVDF) membrane, preparing a stable PVDF@CA / PEI-GA membrane rich in functional groups such as hydroxyl, carboxyl, and amino groups, which can effectively remove metal elements from oil. The addition of cysteine, containing thiol groups, allows the thiol groups to form insoluble thiolates with most metal elements using polydentate ligand structures, thus precipitating the metal ions from the solution. The appropriate introduction of cysteine ​​further enhances the removal of metals.

[0022] The present invention provides a modified polyvinylidene fluoride membrane prepared by the above preparation method, which solves the problem that bound metal impurities in gear oil cannot be effectively removed by physical methods such as mechanical filtration and magnetic filtration. By using the functional groups on the modified polyvinylidene fluoride membrane to form a complex with metal ions, the metal elements in gear oil are removed by utilizing the separation characteristics of the polyvinylidene fluoride membrane.

[0023] The modified polyvinylidene fluoride membrane of this invention is used for the removal of metallic impurities from gear oil. The entire preparation process is simple, efficient, easy to operate, and suitable for large-scale production. The polyvinylidene fluoride membrane can effectively remove metallic elements from gear oil, thereby ensuring the reliable and stable long-term operation of the unit equipment. Detailed Implementation

[0024] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0025] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0026] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0027] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0028] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0029] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0030] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0031] Given the shortcomings of existing technologies in recycling and reusing waste gear oil, it is particularly important to develop a new type of filter membrane for adsorbing and removing metal elements from wind turbine gear oil.

[0032] This invention provides a method for preparing a modified polyvinylidene fluoride (PVDF) membrane, comprising the following steps:

[0033] S1: Immerse the original polyvinylidene fluoride (PVDF) membrane in anhydrous ethanol for cleaning and activation of membrane pores, and then rinse with ultrapure water.

[0034] Optionally, the PVDF membrane is immersed in anhydrous ethanol for 1 to 3 hours;

[0035] S2: Immerse the polyvinylidene fluoride membrane in citric acid (CA) solution, and add polyethyleneimine (PEI) dropwise to the above solution to adjust the pH. React at room temperature, rinse with ultrapure water to remove unreacted substances, and store in ultrapure water. This membrane is denoted as PVDF@CA / PEI.

[0036] Optionally, the concentrations of the citric acid solution and the polyethyleneimine solution are 1–3 mg / mL; the pH is adjusted to neutral to alkaline, and the reaction time is 2–5 h;

[0037] S3: Immerse the PVDF@CA / PEI membrane in a glutaraldehyde (GA) aqueous solution and stir to react. After washing with ultrapure water, the PVDF@CA / PEI-GA membrane is obtained.

[0038] S4: Add the membrane to a cysteine ​​(Cys) solution, remove it after the impregnation reaction, wash it with ultrapure water and store it in ultrapure water. This membrane is designated as PVDF@CA / PEI-GA / Cys membrane.

[0039] Optionally, the glutaraldehyde solution concentration is 0.1%–0.3%, and the stirring reaction time is 2–5 h; the cysteine ​​solution concentration is 5–15 mg / mL, and the impregnation reaction time is 10–15 h.

[0040] The principle of this invention is as follows:

[0041] Polyvinylidene fluoride (PVDF) is used as an excellent membrane separation material. PVDF is a semi-crystalline polymer with repeating –(CH2CF2)– units, possessing high mechanical strength, good chemical resistance, and thermal stability. PVDF also exhibits good anti-aging properties. The removal of metal elements from gear oil is achieved through complexation reactions between modified molecules on the membrane and metal ions, utilizing the membrane's filtration properties. Citric acid is used to modify the PVDF membrane. Citric acid is an excellent complexing agent, capable of complexing with metal elements to form metal precipitates, exhibiting a strong complexing ability for metal ions and effectively removing metal elements from oil. Polyethyleneimine is added as a metal ion trapping agent. Its molecular chain contains numerous amino groups, exhibiting strong chelating ability for some metal ions, thereby enhancing adsorption and effectively improving removal efficiency. This invention uses glutaraldehyde as a crosslinking agent to crosslink polyethyleneimine onto the PVDF membrane, preparing a stable PVDF@CA / PEI-GA membrane rich in functional groups such as hydroxyl, carboxyl, and amino groups, thus effectively removing metal elements from oil. The addition of cysteine, which contains a thiol group, can form insoluble thiolates with most metal elements using a polydentate ligand structure, thereby precipitating metal ions from the solution. The introduction of an appropriate amount of cysteine ​​can enhance the removal of metals.

[0042] The modified polyvinylidene fluoride membrane prepared by the method of this invention is used for the removal of metal elements from gear oil.

[0043] Specific application methods include: S5: Using the modified PVDF@CA / PEI-GA / Cys membrane to conduct gear oil filtration experiments, different membranes are placed in the filtration device, gear oil is filtered under a certain pressure, the filtered permeate is collected, and the content of each metal element in the permeate is determined.

[0044] Optionally, the filtration pressure is 0.1 MPa.

[0045] This invention is applied to the removal of metallic impurities from gear oil. The entire synthesis process is simple, efficient, easy to operate, and suitable for large-scale production. It overcomes the current difficulty that bound metallic impurities in gear oil cannot be effectively removed by physical methods. This adsorbent can effectively remove metallic elements from gear oil, thereby ensuring the reliable and stable long-term operation of the unit equipment.

[0046] The technical solution of the present invention will be further described in detail below through specific embodiments.

[0047] Example 1

[0048] The preparation method of the lithium-ion battery anode material in this embodiment includes the following steps:

[0049] Step 1: Immerse the original polyvinylidene fluoride (PVDF) membrane in anhydrous ethanol for 2 hours to clean and activate the membrane pores, and then rinse it three times with ultrapure water.

[0050] Step 2: Immerse the polyvinylidene fluoride membrane in 50 mL of 2 mg / mL citric acid (CA) solution, and add 1 mg / mL polyethyleneimine (PEI) dropwise to the above solution to adjust the pH to 7.6. React at room temperature for 3 hours, rinse three times with ultrapure water to remove unreacted substances, and store in ultrapure water. This membrane is designated as PVDF@CA / PEI membrane.

[0051] Step 3: Immerse the PVDF@CA / PEI membrane in a 0.2% (w / w) glutaraldehyde (GA) aqueous solution and stir for 3 hours. After washing three times with ultrapure water, the PVDF@CA / PEI-GA membrane is obtained. Add the membrane to a 10 mg / mL cysteine ​​(Cys) solution and immerse it at room temperature for 12 hours. Then remove the membrane, wash it with ultrapure water, and store it in ultrapure water. This membrane is designated as the PVDF@CA / PEI-GA / Cys membrane.

[0052] Step 4: The modified PVDF@CA / PEI-GA / Cys membrane was used to conduct a gear oil filtration experiment. The modified membrane was placed in the filtration device, and gear oil was filtered under a pressure of 0.1 MPa. The filtered permeate was collected, and the content of each metal element in the permeate was determined.

[0053] Example 2

[0054] Step 1: Immerse the original polyvinylidene fluoride (PVDF) membrane in anhydrous ethanol for 1 hour to clean and activate the membrane pores, and then rinse it three times with ultrapure water.

[0055] Step 2: Immerse the polyvinylidene fluoride membrane in 50 mL of 1 mg / mL citric acid (CA) solution, and add 1 mg / mL polyethyleneimine (PEI) dropwise to the above solution to adjust the pH to 7.1. React at room temperature for 2 hours, rinse three times with ultrapure water to remove unreacted substances, and store in ultrapure water. This membrane is designated as PVDF@CA / PEI membrane.

[0056] Step 3: Immerse the PVDF@CA / PEI membrane in a 0.1% (w / w) glutaraldehyde (GA) aqueous solution and stir for 2 hours. After washing three times with ultrapure water, the PVDF@CA / PEI-GA membrane is obtained. Add the membrane to a 5 mg / mL cysteine ​​(Cys) solution and immerse it at room temperature for 10 hours. Then remove the membrane, wash it with ultrapure water, and store it in ultrapure water. This membrane is designated as the PVDF@CA / PEI-GA / Cys membrane.

[0057] Step 4: The modified PVDF@CA / PEI-GA / Cys membrane was used to conduct a gear oil filtration experiment. The modified membrane was placed in the filtration device, and gear oil was filtered under a pressure of 0.1 MPa. The filtered permeate was collected, and the content of each metal element in the permeate was determined.

[0058] Example 3

[0059] Step 1: Immerse the original polyvinylidene fluoride (PVDF) membrane in anhydrous ethanol for 3 hours to clean and activate the membrane pores, and then rinse it 3 times with ultrapure water.

[0060] Step 2: Immerse the polyvinylidene fluoride membrane in 50 mL of 3 mg / mL citric acid (CA) solution, and add 2 mg / mL polyethyleneimine (PEI) dropwise to the above solution to adjust the pH to 7.2. React at room temperature for 5 h, rinse three times with ultrapure water to remove unreacted substances, and store in ultrapure water. This membrane is designated as PVDF@CA / PEI membrane.

[0061] Step 3: Immerse the PVDF@CA / PEI membrane in a 0.3% (w / w) glutaraldehyde (GA) aqueous solution and stir for 5 hours. After washing three times with ultrapure water, the PVDF@CA / PEI-GA membrane is obtained. Add the membrane to a 15 mg / mL cysteine ​​(Cys) solution and immerse it at room temperature for 15 hours. Then remove the membrane, wash it with ultrapure water, and store it in ultrapure water. This membrane is designated as the PVDF@CA / PEI-GA / Cys membrane.

[0062] Step 4: The modified PVDF@CA / PEI-GA / Cys membrane was used to conduct a gear oil filtration experiment. The modified membrane was placed in the filtration device, and gear oil was filtered under a pressure of 0.1 MPa. The filtered permeate was collected, and the content of each metal element in the permeate was determined.

[0063] Example 4

[0064] Step 1: Immerse the original polyvinylidene fluoride (PVDF) membrane in anhydrous ethanol for 1 hour to clean and activate the membrane pores, and then rinse it three times with ultrapure water.

[0065] Step 2: Immerse the polyvinylidene fluoride membrane in 50 mL of 1 mg / mL citric acid (CA) solution, and add 3 mg / mL polyethyleneimine (PEI) dropwise to the above solution to adjust the pH to 7.8. React at room temperature for 2 hours, rinse three times with ultrapure water to remove unreacted substances, and store in ultrapure water. This membrane is designated as PVDF@CA / PEI membrane.

[0066] Step 3: Immerse the PVDF@CA / PEI membrane in a 0.25% (w / w) glutaraldehyde (GA) aqueous solution and stir for 4 hours. After washing three times with ultrapure water, the PVDF@CA / PEI-GA membrane is obtained. Add the membrane to a 6 mg / mL cysteine ​​(Cys) solution and immerse it at room temperature for 11 hours. Then remove the membrane, wash it with ultrapure water, and store it in ultrapure water. This membrane is designated as the PVDF@CA / PEI-GA / Cys membrane.

[0067] Step 4: The modified PVDF@CA / PEI-GA / Cys membrane was used to conduct a gear oil filtration experiment. The modified membrane was placed in the filtration device, and gear oil was filtered under a pressure of 0.1 MPa. The filtered permeate was collected, and the content of each metal element in the permeate was determined.

[0068] Example 5

[0069] Step 1: Immerse the original polyvinylidene fluoride (PVDF) membrane in anhydrous ethanol for 3 hours to clean and activate the membrane pores, and then rinse it 3 times with ultrapure water.

[0070] Step 2: Immerse the polyvinylidene fluoride membrane in 50 mL of 1.5 mg / mL citric acid (CA) solution, and add 1.5 mg / mL polyethyleneimine (PEI) dropwise to the above solution to adjust the pH to 7.4. React at room temperature for 5 h, rinse three times with ultrapure water to remove unreacted substances, and store in ultrapure water. This membrane is designated as PVDF@CA / PEI membrane.

[0071] Step 3: Immerse the PVDF@CA / PEI membrane in a 0.25% (w / w) glutaraldehyde (GA) aqueous solution and stir for 4 hours. After washing three times with ultrapure water, the PVDF@CA / PEI-GA membrane is obtained. Add the membrane to an 8 mg / mL cysteine ​​(Cys) solution and immerse it at room temperature for 12 hours. Then remove the membrane, wash it with ultrapure water, and store it in ultrapure water. This membrane is designated as the PVDF@CA / PEI-GA / Cys membrane.

[0072] Step 4: The modified PVDF@CA / PEI-GA / Cys membrane was used to conduct a gear oil filtration experiment. The modified membrane was placed in the filtration device, and gear oil was filtered under a pressure of 0.1 MPa. The filtered permeate was collected, and the content of each metal element in the permeate was determined.

[0073] Example 6

[0074] Step 1: Immerse the original polyvinylidene fluoride (PVDF) membrane in anhydrous ethanol for 1 hour to clean and activate the membrane pores, and then rinse it 6 times with ultrapure water.

[0075] Step 2: Immerse the polyvinylidene fluoride membrane in 50 mL of 1.3 mg / mL citric acid (CA) solution, and add 2.6 mg / mL polyethyleneimine (PEI) dropwise to the above solution to adjust the pH to 7.6. React at room temperature for 4 hours, rinse 4 times with ultrapure water to remove unreacted substances, and store in ultrapure water. This membrane is designated as PVDF@CA / PEI membrane.

[0076] Step 3: Immerse the PVDF@CA / PEI membrane in a 0.29% (w / w) glutaraldehyde (GA) aqueous solution and stir for 2.5 h. After washing with ultrapure water 4 times, the PVDF@CA / PEI-GA membrane is obtained. Add the membrane to a 13 mg / mL cysteine ​​(Cys) solution and immerse it at room temperature for 14 h. Remove the membrane, wash it with ultrapure water and store it in ultrapure water. This membrane is designated as PVDF@CA / PEI-GA / Cys membrane.

[0077] Step 4: The modified PVDF@CA / PEI-GA / Cys membrane was used to conduct a gear oil filtration experiment. The modified membrane was placed in the filtration device, and gear oil was filtered under a pressure of 0.1 MPa. The filtered permeate was collected, and the content of each metal element in the permeate was determined.

[0078] Example 7

[0079] Step 1: Immerse the original polyvinylidene fluoride (PVDF) membrane in anhydrous ethanol for 3 hours to clean and activate the membrane pores, and then rinse it 3 times with ultrapure water.

[0080] Step 2: Immerse the polyvinylidene fluoride membrane in 50 mL of 1.8 mg / mL citric acid (CA) solution, and add 1.8 mg / mL polyethyleneimine (PEI) dropwise to the above solution to adjust the pH to 7.1. React at room temperature for 2.1 h, rinse 6 times with ultrapure water to remove unreacted substances, and store in ultrapure water. This membrane is designated as PVDF@CA / PEI membrane.

[0081] Step 3: Immerse the PVDF@CA / PEI membrane in a 0.25% (w / w) glutaraldehyde (GA) aqueous solution and stir for 2.5 h. After washing with ultrapure water 4 times, the PVDF@CA / PEI-GA membrane is obtained. Add the membrane to a 7 mg / mL cysteine ​​(Cys) solution and immerse it at room temperature for 14 h. Then remove it, wash it with ultrapure water and store it in ultrapure water. This membrane is designated as PVDF@CA / PEI-GA / Cys membrane.

[0082] Step 4: The modified PVDF@CA / PEI-GA / Cys membrane was used to conduct a gear oil filtration experiment. The modified membrane was placed in the filtration device, and gear oil was filtered under a pressure of 0.1 MPa. The filtered permeate was collected, and the content of each metal element in the permeate was determined.

[0083] The metal removal performance of the PVDF@CA / PEI-GA / Cys membranes prepared in Examples 1-7 of this invention was tested using spectroscopic methods. The results of the tests on the PVDF@CA / PEI-GA / Cys membranes prepared in Examples 1-7 of this invention are shown in Table 1.

[0084] Table 1. Metal removal performance of PVDF@CA / PEI-GA / Cys membranes obtained in Examples 1-7

[0085]

[0086] The above tests show that the modified polyvinylidene fluoride membrane prepared in this embodiment of the invention has an iron removal rate of up to 90.56%, a copper removal rate of up to 88.67%, and a zinc removal rate of up to 89.78%.

[0087] In summary, the modified polyvinylidene fluoride membrane prepared by the above method is applied to the removal of metal elements from gear oil. This invention solves the problem that bound metal impurities in gear oil cannot be effectively removed by physical methods such as mechanical filtration and magnetic filtration. By utilizing the separation characteristics of PVDF membrane, the metal elements in gear oil are removed through the complexation reaction between the functional groups on the modified polyvinylidene fluoride membrane and metal ions.

[0088] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. The application of a modified polyvinylidene fluoride membrane in gear oil purification treatment, characterized in that, The application includes: placing the modified polyvinylidene fluoride membrane in a filtration device, filtering gear oil at a set pressure of 0.1 MPa, and collecting the filtered permeate oil; the method for preparing the modified polyvinylidene fluoride membrane includes the following steps: S1: The polyvinylidene fluoride membrane is immersed in anhydrous ethanol for activation treatment; and it is not pretreated with ferric ions. S2: Immerse the activated polyvinylidene fluoride membrane in a citric acid solution, add polyethyleneimine dropwise to the citric acid solution, adjust the pH to neutral to alkaline to carry out the reaction, and obtain PVDF@CA / PEI; S3: Immerse the PVDF@CA / PEI membrane in a glutaraldehyde aqueous solution and stir to react, to obtain the PVDF@CA / PEI-GA membrane; S4: Add the PVDF@CA / PEI-GA membrane to the cysteine ​​solution, and after the impregnation reaction, remove it to obtain the PVDF@CA / PEI-GA / Cys membrane; The concentration of the citric acid solution is 1–3 mg / mL, and the concentration of the polyethyleneimine solution is 1–3 mg / mL.

2. The application of the modified polyvinylidene fluoride membrane according to claim 1 in gear oil purification treatment, characterized in that, The polyvinylidene fluoride membrane is immersed in anhydrous ethanol for 1 to 3 hours.

3. The application of the modified polyvinylidene fluoride membrane according to claim 1 in gear oil purification treatment, characterized in that, In the process of adjusting the pH to neutral to alkaline, the reaction time is 2-5 hours.

4. The application of the modified polyvinylidene fluoride membrane according to claim 1 in gear oil purification treatment, characterized in that, The glutaraldehyde solution has a mass fraction of 0.1% to 0.3%, and the stirring reaction time is 2 to 5 hours.

5. The application of the modified polyvinylidene fluoride membrane according to claim 1 in gear oil purification treatment, characterized in that, The cysteine ​​solution concentration is 5-15 mg / mL, and the immersion reaction time is 10-15 h.

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