A method for preparing a nano-modified polyvinylidene fluoride composite fiber filter membrane

Abstract

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

Description

Technical Field

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

[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 problems of resource waste and environmental pollution caused by oil replacement, the insulating oil is usually purified after a certain period of operation.

[0003] Due to its advantages such as large specific surface area, small diameter, small pore size, and high porosity, polyvinylidene fluoride (PVDF) nanofiber membranes have shown great application potential in membrane separation technology. The wide range of applications of filtration membrane technology and filtration precision have become a hot research topic in today's society.

[0004] The purpose of this invention is to provide a method for preparing a highly efficient superhydrophobic nano-modified polyvinylidene fluoride composite fiber filter membrane suitable for purifying aged insulating oil. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a nano-modified polyvinylidene fluoride composite fiber filter membrane, so as to solve the problems existing in the prior art and achieve a highly efficient purification effect on aging insulating oil.

[0006] To achieve the above objectives, the present invention provides the following solution:

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

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

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

[0010] As a further preferred embodiment of the present invention, the preparation method includes the following steps:

[0011] ZnSe nanoparticles were dispersed in a solvent, and the binder was added to the dispersion system to obtain a mixed dispersion.

[0012] The ZnSe nanoparticles in the mixed dispersion were adhered to the surface of the PVDF fiber membrane by vacuum filtration to obtain the nano-modified polyvinylidene fluoride 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); the adhesive accounts for 1.2-1.4% of the mass of the mixed dispersion.

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

[0016] S1. Preparation of spinning precursor solution: Dry PVDF powder at 60-80℃ for 12-24h; mix N,N-dimethylformamide (DMF) and isopropanol (IPA) to obtain a DMF / IPA mixed solution; add the dried PVDF powder to the DMF / IPA mixed solution at 40-50℃ and stir for 40-60min until the mixed solution is clear, then let it stand for 40-60min to remove bubbles, and obtain the spinning precursor solution.

[0017] S2. Preparation of PVDF fiber membrane: At a temperature of 34-36℃ and a humidity of 30-38%, the spinning precursor liquid after static degassing is drawn into a syringe. The syringe needle is connected to a positive polarity high voltage DC source, and the flat fiber take-up device is connected to a negative polarity high voltage DC source. Electrospinning is performed to prepare PVDF nanofiber membrane, thus obtaining PVDF fiber membrane.

[0018] S3. Preparation of ZnSe / PPA mixed dispersion: ZnSe nanoparticles are placed in a solvent and ultrasonically dispersed at 350 r / min until ZnSe is completely dispersed in the solvent to obtain a dispersion; polyphthalamide (PPA) is added to the dispersion and ultrasonically dispersed for another 2 h to obtain a ZnSe / PPA mixed dispersion.

[0019] S4. Preparation of nano-modified polyvinylidene fluoride composite fiber filter membrane: The PVDF fiber membrane prepared by electrospinning is placed in a vacuum filtration device, and the ZnSe / PPA mixed dispersion is poured into the vacuum filtration device for filtration, so that the modified nano ZnSe particles are uniformly covered on the surface of the PVDF base membrane; the obtained PVDF base fiber filter membrane is dried in a forced-air oven for 12-16 hours at a temperature of 80℃. After drying, the nano-modified polyvinylidene fluoride 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 electrospinning temperature is 34-36℃, the humidity is 30-38%, the voltage is set to 20-22kV, and the liquid pushing speed is 0.75-0.8mL / 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 either triethylenetetramine or polydimethylsiloxane; the mass ratio of ZnSe nanoparticles to 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 consists of a circulating vacuum pump, a sand core funnel, and a conical flask.

[0025] The polyvinylidene fluoride (PVDF) used in this invention as the substrate of the composite nanofiber filter membrane is a high-performance organic electret material. PVDF can be electrospun at room temperature to obtain a hydrophobic nanofiber filter membrane with high porosity. However, the filtration accuracy of a single-layer nanofiber membrane is low. Therefore, a vacuum filtration method is used to cover the surface of the PVDF-based composite fiber filter membrane with zinc selenide nanoparticles to improve the hydrophobicity and charge stability of the base membrane surface. However, since it is difficult for zinc selenide nanoparticles to be uniformly covered on 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, polyphthalamide (PPA) adhesive is used to improve 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 composite fiber filter membrane prepared by this invention has ultra-high hydrophobicity and oleophilicity. At the same time, due to the electrostatic adsorption characteristics of ZnSe nanoparticles, the composite filter membrane has better filtration performance for acidic and polar impurities in oil.

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

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

[0029] The preparation method of this invention is simple and has important application prospects in the purification of insulating oil during transformer aging. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

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

[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 100 days of filtration of No. 25 Karamay mineral oil (aged oil).

[0033] Figure 3 The water droplet contact angles of the nano-modified PVDF-based fiber filter membrane prepared in Example 1 of this invention and the PVDF-based fiber filter membrane prepared in Comparative Example 1 are compared. Detailed Implementation

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

[0035] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0036] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0037] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

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

[0039] Example 1

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

[0041] (1) Preparation of spinning precursor solution: 11g of PVDF powder was dried in a vacuum drying oven for 16h at a temperature of 60℃. 53.4g of DMF solvent and 35.6g of IPA solvent were weighed and mixed at a mass ratio of 3:2. The resulting DMF / IPA mixed solvent was placed in a glass bottle on a magnetic stirrer at 40℃. The PVDF powder was slowly poured into the DMF / IPA mixed solvent and stirred for 40min. The glass bottle was sealed during stirring until the mixed solution became clear. Then, it was placed in a vacuum drying oven and allowed to stand for 40min to remove bubbles, thus obtaining 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 inside the chamber at 34℃, the humidity at 30%, the voltage at 20kV, and the liquid pushing speed at 0.75mL / h. Slowly draw the deaerated spinning precursor solution into a 10mL syringe, connect the syringe needle to a positive high-voltage DC source, and connect the flat fiber take-up device to a negative high-voltage DC source to prepare the nanofiber membrane, thus obtaining the PVDF fiber membrane.

[0043] (3) Preparation of ZnSe / PPA mixed dispersion: 11g of ZnSe particles were placed in 22g of triethylenetetramine (TETA) and ultrasonically dispersed at 350r / min until ZnSe was completely dispersed in the TETA dispersion to obtain ZnSe dispersion; 0.4g 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 2h to obtain ZnSe / PPA mixed dispersion.

[0044] (4) Preparation of nano-modified polyvinylidene fluoride 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, so that the nano ZnSe particles were uniformly covered on the surface of the PVDF base membrane. Then, it was dried in a forced-air oven for 12 hours at a temperature of 80°C to obtain the nano-modified polyvinylidene fluoride composite fiber filter membrane. The water droplet contact angle of the fiber membrane was tested using an SDC-100 contact angle measuring instrument produced by Dongguan Shengding Precision Instrument Co., Ltd.

[0045] The No. 25 Karamay mineral oil (aged oil) that had been running for 100 days was filtered using a filtration device and the nano-modified PVDF-based fiber filter membrane prepared in Example 1. Before filtration, the membrane sample was cut to a diameter of 5 cm and installed on a sand core. The vacuum pump was turned on to allow the oil sample to flow through the filter membrane, and the performance of the oil samples before and after filtration was tested.

[0046] Example 2

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

[0048] (1) Preparation of spinning precursor solution: 12g of PVDF powder was dried in a vacuum drying oven for 20h at a temperature of 70℃. 52.8g of DMF solvent and 35.2g of IPA solvent were weighed and mixed at a mass ratio of 3:2. The resulting DMF / IPA mixed solvent was placed in a glass bottle on a magnetic stirrer at 45℃. The PVDF powder was slowly poured into the DMF / IPA mixed solvent and stirred for 50min. The glass bottle was sealed during stirring until the mixed solution became clear. After that, it was placed in a vacuum drying oven and allowed to stand for 50min to remove bubbles, thus obtaining 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 inside the chamber at 35℃, the humidity at 34%, the voltage at 20kV, and the liquid pushing speed at 0.75mL / h. Slowly draw the deaerated spinning precursor solution into a 10mL syringe, connect the syringe needle to a positive high-voltage DC source, and connect the flat fiber take-up device to a negative high-voltage DC source to prepare the nanofiber membrane, thus obtaining the PVDF fiber membrane.

[0050] (3) Preparation of ZnSe / PPA mixed dispersion: 12g of ZnSe particles were placed in 36g of triethylenetetramine (TETA) and ultrasonically dispersed at 350r / min until ZnSe was completely dispersed in the TETA dispersion to obtain ZnSe dispersion; 0.63g 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 2h to obtain ZnSe / PPA mixed dispersion.

[0051] (4) Preparation of nano-modified polyvinylidene fluoride 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, so that the nano ZnSe particles were uniformly covered on the surface of the PVDF base membrane. Then, it was dried in a forced-air oven for 14 hours at a temperature of 80°C to obtain the nano-modified polyvinylidene fluoride composite fiber filter membrane.

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

[0053] Example 3

[0054] (1) Preparation of spinning precursor solution: 13g of PVDF powder was dried in a vacuum drying oven at 80℃ for 24h. 65.25g of DMF solvent and 21.75g ​​of IPA solvent were weighed and mixed at a mass ratio of 3:1. The resulting DMF / IPA mixed solvent was placed in a glass bottle on a magnetic stirrer at 50℃. The PVDF powder was slowly poured into the DMF / IPA mixed solvent and stirred for 60min. The glass bottle was sealed during stirring until the mixed solution became clear. Then, it was placed in a vacuum drying oven and allowed to stand for 60min to remove bubbles, thus obtaining 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 inside the chamber at 36℃, the humidity at 38%, the voltage at 20kV, and the liquid pushing speed at 0.75mL / h. Slowly draw the deaerated spinning precursor liquid into a 10mL syringe, connect the syringe needle to a positive high-voltage DC source, and connect the flat fiber take-up device to a negative high-voltage DC source to prepare the nanofiber membrane, thus obtaining the PVDF fiber membrane.

[0056] (3) Preparation of ZnSe / PPA mixed dispersion: 26g of ZnSe particles were placed in 104g of polydimethylsiloxane (PDMS) and ultrasonically dispersed at a speed of 350r / min until ZnSe was completely dispersed in the PDMS dispersion to obtain ZnSe dispersion; 1.85g 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 2h to obtain ZnSe / PPA mixed dispersion.

[0057] (4) Preparation of nano-modified polyvinylidene fluoride 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, so that the nano ZnSe particles were uniformly covered on the surface of the PVDF base membrane. Then, it was dried in a forced-air oven for 16 hours with the oven temperature set to 80℃ to obtain the nano-modified polyvinylidene fluoride composite fiber filter membrane.

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

[0059] Comparative Example 1

[0060] The only difference from Example 1 is that steps (3)-(4) are omitted. The PVDF fiber membrane obtained in step (2) of Example 1 was directly dried in a forced-air oven for 14 hours at a temperature of 80°C to obtain a PVDF-based nanofiber filter membrane. The water droplet contact angle of the fiber membrane was tested using an SDC-100 contact angle measuring instrument manufactured by Dongguan Shengding Precision Instrument Co., Ltd.

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

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

[0063] Table 1

[0064]

[0065] As can be seen from Table 1, the transformer insulating oil filtered by the nano-modified PVDF-based composite fiber filter membrane of this invention exhibits excellent performance and has significant practical value in insulating oil purification.

[0066] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

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

2. The production method according to claim 1, characterized by, The method comprises the following steps: The ZnSe nanoparticles are dispersed in a solvent, and the adhesive is added to the dispersion system to obtain a mixed dispersion liquid; The ZnSe nanoparticles in the mixed dispersion liquid are adhered to the surface of the PVDF nanofiber membrane by suction filtration to obtain the nanomodified polyvinylidene fluoride-based composite fiber filter membrane.

3. The production method according to claim 2, characterized by, The solvent is one of triethylenetetramine and polydimethylsiloxane.

4. The preparation method according to claim 2, characterized in that, 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 liquid.

5. The preparation method according to claim 2, characterized in that, The method for preparing the PVDF nanofiber membrane comprises the following steps: (1) PVDF powder is added to a mixed solution of N, N-dimethylformamide and isopropyl alcohol to prepare a spinning precursor liquid; (2) The spinning precursor liquid is electrospun to obtain a PVDF nanofiber membrane.

6. The production method according to claim 5, wherein The PVDF powder accounts for 11-13% of the mass of the mixed solution; the mass ratio of the N, N-dimethylformamide to the isopropyl alcohol is 3: (2-1); the temperature of the electrospinning is 34-36℃, and the humidity is 30-38%.

7. The preparation method according to claim 5, characterized in that, The mass ratio of the ZnSe nanoparticles to the PVDF powder is (1-2):

1.

8. The nanomodified polyvinylidene fluoride-based composite fiber filter membrane prepared by the method according to any one of claims 1-7.

9. The application of the nanomodified polyvinylidene fluoride-based composite fiber filter membrane according to claim 8 in the purification of insulating oil.

Images