Preparation method of nano-modified polyvinylidene fluoride-based composite fiber filter membrane

Abstract

The invention discloses a preparation method of a nano-modified polyvinylidene fluoride-based composite fiber filter membrane, and relates to the technical field of regeneration and purification of transformer insulating oil. According to the invention, ZnSe nanoparticles are adhered to the surface of a PVDF fiber membrane by using an adhesive, so that the nano-modified polyvinylidene fluoride-based composite fiber filter membrane is prepared. The preparation method is simple, the prepared nano-modified polyvinylidene fluoride-based composite fiber filter membrane can meet the purification and filtration requirements in the field of transformer insulating oil, the remarkable purification effect of the aged insulating oil is achieved, and the nano-modified polyvinylidene fluoride-based composite fiber filter membrane has important application prospects in the aspect of purification of the transformer aged insulating oil.

Description

Technical Field

[0001] The invention relates to the technical field of transformer insulating oil regeneration and purification, in particular to a method for preparing a nano-modified polyvinylidene fluoride based composite fiber filter membrane. Background Art

[0002] Oil-filled power transformers are the most basic line of defense for power grid safety. In order to reduce insulation failures in oil-filled electrical equipment and solve the resource waste and environmental pollution problems caused by oil changes, the insulating oil is usually purified after running for a certain period of time.

[0003] Due to the advantages of large specific surface area, small diameter, small pore size and high porosity, polyvinylidene fluoride (PVDF) nanofiber membrane has great application potential in membrane separation technology. The wide application of membrane technology and filtration accuracy have become a research hotspot in today's society.

[0004] The object of the present invention is to provide a method for preparing an efficient super-hydrophobic nano-modified polyvinylidene fluoride-based composite fiber filter membrane that can be used for purifying aged insulating oil. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing a nano-modified polyvinylidene fluoride-based composite fiber filter membrane to solve the problems existing in the above-mentioned prior art and achieve a high-efficiency purification effect on aged insulating oil.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] The present invention provides a method for preparing a nano-modified polyvinylidene fluoride based composite fiber filter membrane, comprising the following steps:

[0008] The ZnSe nanoparticles are adhered to the surface of the PVDF fiber membrane by using an adhesive to obtain the nano-modified polyvinylidene fluoride-based composite fiber filter membrane.

[0009] As a further preferred embodiment of the present invention, the adhesive is polyphthalamide (PPA).

[0010] As a further preference of the present invention, the preparation method comprises the following steps:

[0011] Dispersing ZnSe nanoparticles in a solvent, and adding the adhesive into the dispersion system to obtain a mixed dispersion;

[0012] The ZnSe nanoparticles in the mixed dispersion are adhered to the surface of the PVDF fiber membrane by suction filtration to obtain the nano-modified polyvinylidene fluoride based composite fiber filter membrane.

[0013] As a further preferred embodiment of the present invention, the solvent is one of triethylenetetramine (TETA) and polydimethylsiloxane (PDMS).

[0014] As a further preferred embodiment of the present invention, the mass ratio of the ZnSe nanoparticles to the solvent is 1:(2-4); and the adhesive accounts for 1.2-1.4% of the mass of the mixed dispersion.

[0015] The more preferred preparation process of the present invention is as follows:

[0016] S1. Prepare a spinning precursor solution: dry PVDF powder at 60-80°C for 12-24h; mix N,N dimethylformamide (DMF) and isopropyl alcohol (IPA) to obtain a DMF / IPA mixed solution; add the dried PVDF powder to the DMF / IPA mixed solution at 40-50°C and stir for 40-60min until the mixed solution becomes clear, and then stand for degassing for 40-60min to obtain a spinning precursor solution;

[0017] S2. Preparation of PVDF fiber membrane: At a temperature of 34-36°C and a humidity of 30-38%, the spinning precursor solution after static degassing is sucked into a syringe, the syringe needle is connected to a positive polarity high voltage DC source, the flat-plate collector is connected to a negative polarity high voltage DC source, and electrospinning is performed to prepare a PVDF nanofiber membrane to obtain a PVDF fiber membrane.

[0018] S3, preparing ZnSe / PPA mixed dispersion: placing ZnSe nanoparticles in a solvent, and performing ultrasonic dispersion at a speed of 350 r / min until ZnSe is completely dispersed in the solvent to obtain a dispersion; adding polyphthalamide (PPA) to the dispersion, and continuing ultrasonic dispersion for 2 h to obtain a ZnSe / PPA mixed dispersion;

[0019] S4. Preparation of nano-modified polyvinylidene fluoride based composite fiber filter membrane: Place the PVDF fiber membrane prepared by electrospinning in a vacuum filtration device, and pour the ZnSe / PPA mixed dispersion into the vacuum filtration device for filtration, so that the modified nano ZnSe particles are evenly covered on the surface of the PVDF base membrane; Dry the prepared PVDF-based fiber filter membrane in a blast oven for 12-16 hours, and set the oven temperature to 80°C. After drying, a nano-modified polyvinylidene fluoride based composite fiber filter membrane is obtained.

[0020] In step S1, the PVDF powder accounts for 11-13% of the mass of the mixed solution; the mass ratio of N,N-dimethylformamide to isopropanol is 3:(2-1);

[0021] In step S2, the temperature of electrospinning is 34-36°C, the humidity is 30-38%, the voltage is set to 20-22 kV, and the liquid pushing speed is 0.75-0.8 mL / h.

[0022] In step S3, the mass ratio of ZnSe nanoparticles to PVDF powder is (1-2):1.

[0023] In step S3, the solvent is one of triethylenetetramine and polydimethylsiloxane; the mass ratio of ZnSe nanoparticles to the solvent is 1:(2-4); and polyphthalamide accounts for 1.2-1.4% of the mass of the ZnSe / PPA mixed dispersion.

[0024] Preferably, the vacuum filtration device of the present invention is composed of a circulating vacuum pump, a sand core funnel and a conical flask.

[0025] The polyvinylidene fluoride used as the composite nanofiber filter membrane substrate in the present invention is an organic electret material with excellent performance. PVDF can be obtained by electrostatic spinning at room temperature to obtain a hydrophobic nanofiber filter membrane with high porosity, but the filtration accuracy of a single-layer nanofiber membrane is low. Therefore, zinc selenide nanoparticles are covered on the surface of the PVDF-based composite fiber filter membrane by a vacuum filtration method to improve the surface hydrophobicity and charge stability of the base membrane; but since it is difficult for zinc selenide nanoparticles to evenly cover the filter membrane surface, the PVDF-based composite fiber filter membrane has low surface energy and low hydrophobicity, resulting in poor adhesion between the substrate and the functional layer. Therefore, a polyphthalamide (PPA) adhesive is used to increase the bonding strength between the nanofiltration membrane and the nanoparticles, thereby improving the accuracy and efficiency of the composite fiber filter membrane in purifying insulating oil.

[0026] The nano-modified polyvinylidene fluoride-based composite fiber filter membrane prepared by the present invention has ultra-high hydrophobicity and lipophilicity. At the same time, due to the electrostatic adsorption characteristics of ZnSe nanoparticles, the composite filter membrane has better filtering performance for acidic and polar impurities in oil.

[0027] The present invention discloses the following technical effects:

[0028] The nano-modified polyvinylidene fluoride-based composite fiber filter membrane prepared by the present invention has ultra-high hydrophobicity and purification accuracy, can meet the purification and filtration needs in the field of transformer insulating oil, and achieve a significant purification effect on aged insulating oil.

[0029] The preparation method of the invention is simple and has important application prospects in purifying aged insulating oil of transformers. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0031] Figure 1 The infrared spectra of the nano-modified PVDF-based fiber filter membrane prepared in Example 1 of the present invention and the PVDF-based fiber filter membrane prepared in Comparative Example 1.

[0032] Figure 2 The dielectric loss factor frequency response curves of the nano-modified PVDF-based fiber filter membrane prepared in Example 1 of the present invention and the PVDF-based fiber filter membrane prepared in Comparative Example 1 after filtering No. 25 Karamay mineral oil (aged oil) for 100 days.

[0033] Figure 3 The comparison of the water drop contact angle of the nano-modified PVDF-based fiber filter membrane prepared in Example 1 of the present invention and the PVDF-based fiber filter membrane prepared in Comparative Example 1 is shown. DETAILED DESCRIPTION

[0034] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0035] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0036] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0037] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0038] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0039] Example 1

[0040] Preparation of nano-modified polyvinylidene fluoride based composite fiber filter membrane:

[0041] (1) Preparation of spinning precursor solution: Dry 11 g of PVDF powder in a vacuum drying oven for 16 h, and set the drying oven temperature to 60 °C. Weigh 53.4 g of DMF solvent and 35.6 g of IPA solvent in a mass ratio of 3:2 and mix them. Place the obtained DMF / IPA mixed solvent in a glass bottle on a 40 °C magnetic stirrer. Slowly pour the PVDF powder into the DMF / IPA mixed solvent and stir for 40 min. During the stirring process, seal the glass bottle until the mixed solution is clear and place it in a vacuum drying oven for 40 min to degas. Then, obtain the spinning precursor solution.

[0042] (2) Preparation of PVDF fiber membrane (base membrane): Turn on the air dryer and WL-2 electrospinning machine, control the temperature in the box at 34°C, the humidity at 30%, the voltage at 20 kV, and the liquid pushing speed at 0.75 mL / h. Slowly suck the spinning precursor solution after static degassing into a 10 mL syringe, connect the syringe needle to a positive polarity high voltage DC source, and connect the flat-plate collector to a negative polarity high voltage DC source to prepare a nanofiber membrane to obtain a PVDF fiber membrane.

[0043] (3) Preparation of ZnSe / PPA mixed dispersion: 11 g of ZnSe particles were placed in 22 g of triethylenetetramine (TETA) and ultrasonically dispersed at a speed of 350 r / min until ZnSe was completely dispersed in the TETA dispersion to obtain a ZnSe dispersion; 0.4 g of polyphthalamide (PPA) was added to the ZnSe dispersion so that PPA accounted for 1.2% of the total solution mass, and ultrasonic dispersion was continued for 2 h to obtain a ZnSe / PPA mixed dispersion.

[0044] (4) Preparation of nano-modified polyvinylidene fluoride based composite fiber filter membrane: The PVDF fiber membrane was placed in a vacuum filtration device, and the obtained ZnSe / PPA mixed dispersion was poured into the vacuum filtration device for filtration to allow the nano-ZnSe particles to evenly cover the surface of the PVDF base membrane. The membrane was then dried in a blast oven for 12 h at a temperature of 80°C to obtain a nano-modified polyvinylidene fluoride based composite fiber filter membrane. The water drop contact angle of the fiber membrane was tested using an SDC-100 contact angle meter produced by Dongguan Shengding Precision Instrument Co., Ltd.

[0045] The 25th Karamay mineral oil (aged oil) that had been in operation for 100 days was filtered using the filtration device and the nano-modified PVDF-based fiber filter membrane prepared in Example 1. Before filtration, the membrane sample was cut into a diameter of 5 cm and installed on a sand core, and the vacuum pump was turned on to make the oil sample flow through the filter membrane, and the performance of the oil sample before and after filtration was tested.

[0046] Example 2

[0047] Preparation of nano-modified polyvinylidene fluoride based composite fiber filter membrane:

[0048] (1) Preparation of spinning precursor solution: Dry 12 g of PVDF powder in a vacuum drying oven for 20 h, and set the drying oven temperature to 70°C. Weigh 52.8 g of DMF solvent and 35.2 g of IPA solvent in a mass ratio of 3:2 and mix them. Place the obtained DMF / IPA mixed solvent in a glass bottle on a 45°C magnetic stirrer. Slowly pour the PVDF powder into the DMF / IPA mixed solvent and stir for 50 min. During the stirring process, seal the glass bottle until the mixed solution is clear and place it in a vacuum drying oven for 50 min to degas. Then, obtain the spinning precursor solution.

[0049] (2) Preparation of PVDF fiber membrane (base membrane): Turn on the air dryer and WL-2 electrospinning machine, control the temperature in the box at 35°C, the humidity at 34%, the voltage at 20 kV, and the liquid pushing speed at 0.75 mL / h. Slowly absorb the spinning precursor solution after static degassing into a 10 mL syringe, connect the syringe needle to a positive polarity high voltage DC source, and connect the flat-plate collector to a negative polarity high voltage DC source to prepare a nanofiber membrane to obtain a PVDF fiber membrane.

[0050] (3) Preparation of ZnSe / PPA mixed dispersion: 12 g of ZnSe particles were placed in 36 g of triethylenetetramine (TETA) and ultrasonically dispersed at a speed of 350 r / min until ZnSe was completely dispersed in the TETA dispersion to obtain a ZnSe dispersion; 0.63 g of polyphthalamide (PPA) was added to the ZnSe dispersion so that PPA accounted for 1.3% of the total solution mass, and ultrasonic dispersion was continued for 2 h to obtain a ZnSe / PPA mixed dispersion.

[0051] (4) Preparation of nano-modified polyvinylidene fluoride based composite fiber filter membrane: Place the PVDF fiber membrane in a vacuum filtration device, and pour the obtained ZnSe / PPA mixed dispersion into the vacuum filtration device for filtration to allow the nano ZnSe particles to evenly cover the surface of the PVDF base membrane. Then, dry it in a forced air oven for 14 h at a temperature of 80°C to obtain a nano-modified polyvinylidene fluoride based composite fiber filter membrane.

[0052] The No. 25 Karamay mineral oil (aged oil) that had been in operation for 100 days was filtered using the filtration device and the nano-modified PVDF-based fiber filter membrane prepared in Example 2. Before filtration, the membrane sample was cut into a diameter of 5 cm and installed on a sand core, and the vacuum pump was turned on to make the oil sample flow through the filter membrane, and the performance of the oil sample before and after filtration was tested.

[0053] Example 3

[0054] (1) Preparation of spinning precursor solution: Dry 13 g of PVDF powder in a vacuum drying oven for 24 h, and set the drying oven temperature to 80°C. Weigh 65.25 g of DMF solvent and 21.75 g of IPA solvent in a mass ratio of 3:1 and mix them. Place the obtained DMF / IPA mixed solvent in a glass bottle on a 50°C magnetic stirrer. Slowly pour the PVDF powder into the DMF / IPA mixed solvent and stir for 60 min. During the stirring process, seal the glass bottle until the mixed solution becomes clear and place it in a vacuum drying oven for 60 min to degas. Then, obtain the spinning precursor solution.

[0055] (2) Preparation of PVDF fiber membrane (base membrane): Turn on the air dryer and WL-2 electrospinning machine, control the temperature in the box at 36°C, the humidity at 38%, the voltage at 20 kV, and the liquid pushing speed at 0.75 mL / h. Slowly suck the spinning precursor solution after static degassing into a 10 mL syringe, connect the syringe needle to a positive polarity high voltage DC source, and connect the flat-plate collector to a negative polarity high voltage DC source to prepare a nanofiber membrane to obtain a PVDF fiber membrane.

[0056] (3) Preparation of ZnSe / PPA mixed dispersion: 26 g of ZnSe particles were placed in 104 g of polydimethylsiloxane (PDMS) and ultrasonically dispersed at a speed of 350 r / min until ZnSe was completely dispersed in the PDMS dispersion to obtain a ZnSe dispersion; 1.85 g of polyphthalamide (PPA) was added to the ZnSe dispersion so that PPA accounted for 1.4% of the total solution mass, and ultrasonic dispersion was continued for 2 h to obtain a ZnSe / PPA mixed dispersion.

[0057] (4) Preparation of nano-modified polyvinylidene fluoride based composite fiber filter membrane: Place the PVDF fiber membrane in a vacuum filtration device, and pour the obtained ZnSe / PPA mixed dispersion into the vacuum filtration device for filtration to allow the nano-ZnSe particles to evenly cover the surface of the PVDF base membrane. Then, dry it in a forced air oven for 16 hours at a temperature of 80°C to obtain a nano-modified polyvinylidene fluoride based composite fiber filter membrane.

[0058] The No. 25 Karamay mineral oil (aged oil) that had been in operation for 100 days was filtered using the filtration device and the nano-modified PVDF-based fiber filter membrane prepared in Example 3. Before filtration, the membrane sample was cut into a diameter of 5 cm and installed on a sand core, and the vacuum pump was turned on to make the oil sample flow through the filter membrane, and the performance of the oil sample before and after filtration was tested.

[0059] Comparative Example 1

[0060] The only difference from Example 1 is that steps (3)-(4) are not performed. The PVDF fiber membrane obtained in step (2) of Example 1 was directly dried in a blast oven for 14 h, and the oven temperature was set to 80°C to obtain a PVDF-based nanofiber filter membrane. The water drop contact angle of the fiber membrane was tested using an SDC-100 contact angle meter produced by Dongguan Shengding Precision Instrument Co., Ltd.

[0061] The No. 25 Karamay mineral oil (hereinafter referred to as aged oil) that had been in operation for 100 days was filtered using the filtration device and the PVDF-based fiber filter membrane prepared in Comparative Example 1. Before filtering, the membrane sample was cut into a diameter of 5 cm and installed on a sand core, and the vacuum pump was turned on to make the oil sample flow through the filter membrane, and the performance of the oil sample before and after filtration was tested.

[0062] The performance of the filter membranes prepared in the embodiments of the present invention and the comparative examples are shown in Table 1. Among them, the test standard for the water content in insulating oil is GB / T 7600-2014; the test standard for the dielectric loss factor of insulating oil is GB / T 5654-2007; and the test standard for the power frequency breakdown voltage of insulating oil is GB / T 507-2002.

[0063] Table 1

[0064]

[0065] It can be seen from Table 1 that the transformer insulating oil filtered by the nano-modified PVDF-based composite fiber filter membrane of the present invention has excellent performance and has important practical value in insulating oil purification.

[0066] The embodiments described above are only descriptions of the preferred embodiments of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing a nano-modified polyvinylidene fluoride-based composite fiber filter membrane, characterized in that: The following steps are involved: The ZnSe nanoparticles are adhered to the surface of the PVDF fiber membrane by using an adhesive to obtain the nano-modified polyvinylidene fluoride-based composite fiber filter membrane.

2. The preparation method according to claim 1, characterized in that: The adhesive is polyphthalamide.

3. The preparation method according to claim 1, characterized in that: The following steps are involved: Dispersing ZnSe nanoparticles in a solvent, and adding the adhesive into the dispersion system to obtain a mixed dispersion; The ZnSe nanoparticles in the mixed dispersion are adhered to the surface of the PVDF fiber membrane by suction filtration to obtain the nano-modified polyvinylidene fluoride based composite fiber filter membrane.

4. The preparation method according to claim 3, characterized in that: The solvent is one of triethylenetetramine and polydimethylsiloxane.

5. The preparation method according to claim 3, characterized in that: The mass ratio of the ZnSe nanoparticles to the solvent is 1:(2-4); the adhesive accounts for 1.2-1.4% of the mass of the mixed dispersion.

6. The preparation method according to claim 3, characterized in that: The preparation method of the PVDF fiber membrane comprises the following steps: (1) adding PVDF powder to a mixed solution of N,N-dimethylformamide and isopropanol to prepare a spinning precursor solution; (2) The spinning precursor solution is subjected to electrostatic spinning to obtain a PVDF fiber membrane.

7. The preparation method according to claim 6, characterized in that: The PVDF powder accounts for 11-13% of the mass of the mixed solution; the mass ratio of N,N-dimethylformamide to isopropanol is 3:(2-1); the temperature of the electrospinning is 34-36° C., and the humidity is 30-38%.

8. The preparation method according to claim 6, characterized in that: The mass ratio of the ZnSe nanoparticles to the PVDF powder is (1-2):

1.

9. The nano-modified polyvinylidene fluoride-based composite fiber filter membrane prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the nano-modified polyvinylidene fluoride-based composite fiber filter membrane as claimed in claim 9 in the purification of insulating oil.

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