A surface-modified composite fiber filter membrane, and a preparation method and application thereof

Abstract

This invention discloses a surface-modified composite fiber filter membrane, its preparation method, and its application, relating to the field of insulating oil filtration. The preparation method involves uniformly stirring PVA powder, solvent, and ZrO2 nanoparticles to obtain a spinning solution; then, using electrospinning technology, a composite fiber filter membrane is prepared from the spinning solution, which can be applied to the filtration and purification of mineral insulating oil. This application utilizes electrospinning technology to prepare the filter membrane, which has advantages such as small fiber diameter, good uniformity, high porosity, and high flux. Introducing ZrO2 nanoparticles into the filter membrane increases the specific surface area, providing impurity adsorption and effectively adsorbing and intercepting trace amounts of moisture and micro-impurities in aged mineral insulating oil. This achieves precise filtration of aged mineral insulating oil, effectively improving its breakdown voltage and reducing resource waste and environmental pollution.

Description

Technical Field

[0001] This invention relates to the field of insulating oil filtration, and more particularly to a surface-modified composite fiber filter membrane, its preparation method, and its application. Background Technology

[0002] Mineral insulating oil is an insulating material made from mineral oil as the base oil, with the addition of antibacterial agents, antifoaming agents, bactericides, etc. Compared with traditional insulating materials, it has the advantages of lower cost and better thermal stability, and is widely used in the power, railway, and petrochemical industries. Among these, mineral insulating oil is the most commonly used in power transformers of all grades, forming an oil-paper insulation system with insulating paper. Pure mineral oil has excellent insulation, arc-extinguishing, and cooling properties, and in my country, many power transformers have been in operation for more than 20 years.

[0003] During the aging process, oil-paper insulation systems continuously generate particulate impurities such as moisture, organic acids, metals, and cellulose. Moisture in aged mineral oil is the number one killer of its insulation performance. Increased moisture content significantly reduces the breakdown voltage of the insulation oil, thereby greatly deteriorating its insulation properties. The decline in mineral oil quality directly leads to a decrease in its insulation, arc-quenching, and cooling performance. Directly replacing the insulation oil is costly and causes a certain degree of resource waste and environmental pollution. Therefore, improving insulation oil purification technology is particularly important. Summary of the Invention

[0004] This invention provides a surface-modified composite fiber filter membrane, its preparation method, and its application. By introducing ZrO2 nanoparticles into the filter membrane to enhance the surface hydrophobic effect, it achieves the interception and adsorption of trace amounts of moisture and impurities in aged mineral insulating oil, thereby purifying the aged mineral insulating oil and effectively improving the breakdown voltage of the aged insulating oil.

[0005] To address the aforementioned technical problems, one objective of this invention is to provide a method for preparing a surface-modified composite fiber filter membrane, comprising the following steps:

[0006] (1) PVA powder is added to a container containing solvent and stirred evenly. ZrO2 nanoparticles are slowly added and stirred evenly. After vacuum standing to remove bubbles, spinning solution is obtained.

[0007] The mass ratio of PVA powder to ZrO2 nanoparticles is (5-7):1, and the particle size of the ZrO2 nanoparticles is 20-40 nm.

[0008] (2) Add the spinning solution to the electrospinning machine and prepare the composite fiber filter membrane by electrospinning technology.

[0009] By adopting the above scheme, the filter membrane prepared by electrospinning technology in this application has small fiber diameter, good uniformity, high porosity and large flux, and high filtration efficiency for micro-sized impurities. Since mineral insulating oil has good hydrophobicity, this application can improve the surface effect of the filter membrane by introducing ZrO2 nanoparticles into the filter membrane, thereby increasing the specific surface area and impurity adsorption. This can hydrophobically block trace amounts of moisture in aged mineral insulating oil. At the same time, the small particle size of ZrO2 nanoparticles can ensure that the pore size of the filter membrane remains small, which can adsorb and intercept micro-sized impurities, thereby achieving precise filtration of moisture and impurities in aged mineral insulating oil, purifying the aged insulating oil and improving the breakdown voltage of the aged insulating oil.

[0010] As a preferred embodiment, in step (1), the PVA powder and ZrO2 nanoparticles are pre-dried at 60-80°C for 20-24 hours.

[0011] As a preferred embodiment, in step (1), the mass ratio of the PVA powder to the solvent is 1:(10-12).

[0012] As a preferred embodiment, the solvent is at least one of methyl phthalate, octyl phthalate, and butyl phthalate.

[0013] As a preferred embodiment, in step (1), the stirring temperature is 35-45℃ and the stirring rate is 350-400r / min.

[0014] As a preferred option, in step (1), the standing degassing time is 6-8 hours.

[0015] As a preferred embodiment, in step (2), the thickness of the composite fiber filter membrane is 1-1.5 μm.

[0016] As a preferred embodiment, in step (2), the temperature inside the electrospinning machine is controlled at 30-40℃ and the humidity is controlled at 30%-40%.

[0017] As a preferred embodiment, in step (2), the spinning solution is slowly drawn into the syringe of the electrospinning machine, and air bubbles in the syringe are fully removed. A stainless steel needle is used and connected to a positive high-voltage DC source. The flat take-up device is connected to a negative high-voltage DC source. The tin foil is attached to the flat take-up device using conductive adhesive. The distance between the flat take-up device and the syringe is controlled to be 15-17 cm. The pushing speed of the syringe is 0.7-0.8 mL / h to prepare the composite fiber filter membrane.

[0018] To address the aforementioned technical problems, a second objective of this invention is to provide a surface-modified composite fiber filter membrane.

[0019] To address the aforementioned technical problems, a third objective of this invention is to provide an application of a surface-modified composite fiber filter membrane in the field of mineral insulating oil filtration and purification.

[0020] As a preferred embodiment, the following steps are included: cutting the surface-modified composite fiber filter membrane and installing it on the sand core for vacuum filtration of mineral insulating oil, with the vacuum degree set to 0.02-0.05 MPa.

[0021] As a preferred option, the mineral insulating oil is 25# Karamay mineral oil.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] This application uses electrospinning technology to prepare filter membranes, which have the advantages of small fiber diameter, good uniformity, high porosity and large flux. It has high filtration efficiency for micro-sized impurities. By introducing ZrO2 nanoparticles into the filter membrane to increase the specific surface area and provide impurity adsorption, it can hydrophobically block trace amounts of moisture in aged mineral insulating oil and adsorb and intercept micro-sized impurities, thereby achieving precise filtration of moisture and impurities in aged mineral insulating oil. This effectively improves the breakdown voltage of aged insulating oil and reduces the waste of mineral insulating oil resources and environmental pollution. Attached Figure Description

[0024] Figure 1 : These are graphs showing the changes in trace moisture and breakdown voltage of insulating oil after filtration using composite fiber membranes in application examples and comparative application examples of the present invention.

[0025] Figure 2 : This is a water droplet contact angle curve of a surface-modified composite fiber filter membrane in the embodiments and comparative examples of the present invention. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise specified, all raw materials used are commercially available, and the same raw materials are used in parallel experiments.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] Polyvinyl alcohol is sourced from Shanghai Aladdin Biochemical Technology Co., Ltd., model number 1799;

[0032] Polytetrafluoroethylene (PTFE) is sourced from Daikin Industries, Ltd. of Japan, model number DAIKIN PTFE L-5F.

[0033] Example 1

[0034] A surface-modified composite fiber filter membrane is prepared by the following steps:

[0035] (1) Place polyvinyl alcohol (PVA) powder and ZrO2 nanoparticles in a vacuum drying oven for 20 hours in advance and set the drying temperature to 60℃. Use a precision electronic balance to weigh the dried PVA powder and methyl phthalate (DMP) solvent at a mass ratio of 1:10 for PVA powder to solvent, and weigh the dried ZrO2 nanoparticles at a mass ratio of 1:5 for ZrO2 nanoparticles to PVA powder. The ZrO2 nanoparticles selected have a particle size of 20nm.

[0036] (2) Put methyl phthalate (DMP) solvent into a glass bottle and place it on a magnetic stirrer at a temperature of 35°C and a stirring speed of 350 r / min. PVA is slowly poured into the stirring solvent. During the stirring process, the glass bottle is sealed to reduce solvent evaporation. ZrO2 nanoparticles are slowly poured into the stirring solvent. After stirring until the mixed solution is clear and transparent, it is placed in a vacuum drying oven and allowed to stand for 6 hours to remove bubbles.

[0037] (3) The temperature inside the WL-2C high-voltage electrospinning machine is controlled at 30℃ and the humidity is controlled at 30%. The spinning solution is slowly drawn into a 10mL syringe, and the air bubbles in the syringe are fully removed. A stainless steel needle is used and connected to a positive high-voltage DC source. The flat take-up device is connected to a negative high-voltage DC source. The tin foil is attached to the flat take-up device with conductive glue. The distance between the flat take-up device and the syringe is controlled at 15cm. The pushing speed of the syringe is 0.7mL / h. The 1μm composite fiber filter membrane is prepared.

[0038] Example 2

[0039] A surface-modified composite fiber filter membrane is prepared by the following steps:

[0040] (1) Polyvinyl alcohol (PVA) powder and ZrO2 nanoparticles were placed in a vacuum drying oven and dried for 22 hours. The drying temperature was set to 70℃. The dried PVA powder and butyl phthalate (DBP) solvent were weighed in a ratio of 1:11 using a precision electronic balance. The dried ZrO2 nanoparticles were weighed in a ratio of 1:6 using a ratio of 1:6 using ZrO2 nanoparticles. The ZrO2 nanoparticles were selected with a particle size of 30nm.

[0041] (2) The butyl phthalate (DBP) solvent was placed in a glass bottle and placed on a magnetic stirrer at a temperature of 40°C and a stirring speed of 380 r / min. PVA was slowly poured into the stirring solvent. During the stirring process, the glass bottle was sealed to reduce the evaporation of the solvent. ZrO2 nanoparticles were slowly poured into the stirring solvent. After stirring until the mixed solution was clear and transparent, it was placed in a vacuum drying oven and allowed to stand for 7 hours to remove bubbles.

[0042] (3) The temperature inside the WL-2C high-voltage electrospinning machine is controlled at 35℃ and the humidity is controlled at 35%. The spinning solution is slowly drawn into a 10mL syringe, and the air bubbles in the syringe are fully removed. A stainless steel needle is used and connected to a positive high-voltage DC source. The flat take-up device is connected to a negative high-voltage DC source. The tin foil is attached to the flat take-up device with conductive glue. The distance between the flat take-up device and the syringe is controlled at 15cm. The pushing speed of the syringe is 0.75mL / h. The 1μm composite fiber filter membrane is prepared.

[0043] Example 3

[0044] A surface-modified composite fiber filter membrane is prepared by the following steps:

[0045] (1) Place polyvinyl alcohol (PVA) powder and ZrO2 nanoparticles in a vacuum drying oven for 24 hours in advance and dry at 80°C. Use a precision electronic balance to weigh the dried PVA powder and octyl phthalate (DOP) solvent at a mass ratio of 1:12 for PVA powder to solvent, and weigh the dried ZrO2 nanoparticles at a mass ratio of 1:7 for ZrO2 nanoparticles to PVA powder. The ZrO2 nanoparticles selected have a particle size of 40 nm.

[0046] (2) Put octyl phthalate (DOP) solvent into a glass bottle and place it on a magnetic stirrer at a temperature of 45°C and a stirring speed of 400 r / min. PVA is slowly poured into the stirring solvent. During the stirring process, the glass bottle is sealed to reduce solvent evaporation. ZrO2 nanoparticles are slowly poured into the stirring solvent. After stirring until the mixed solution is clear and transparent, it is placed in a vacuum drying oven and allowed to stand for 8 hours to remove bubbles.

[0047] (3) The temperature inside the WL-2C high-voltage electrospinning machine is controlled at 40℃ and the humidity is controlled at 40%. The spinning solution is slowly drawn into a 10mL syringe, and the air bubbles in the syringe are fully removed. A stainless steel needle is used and connected to a positive high-voltage DC source. The flat take-up device is connected to a negative high-voltage DC source. The tin foil is attached to the flat take-up device with conductive glue. The distance between the flat take-up device and the syringe is controlled at 15cm. The pushing speed of the syringe is 0.8mL / h. The 1μm composite fiber filter membrane is prepared.

[0048] Example 4

[0049] A surface-modified composite fiber filter membrane is prepared in the same way as Example 1, with the same steps, reagents, equipment and process parameters. The difference is that in step (1), the mass ratio of ZrO2 nanoparticles to PVA powder is 1:7.

[0050] Example 5

[0051] A surface-modified composite fiber filter membrane is prepared in the same way as Example 1, with the same steps, reagents, equipment and process parameters used in each step. The difference is that in step (1), the particle size of ZrO2 nanoparticles is 50 nm.

[0052] Comparative Example 1

[0053] A surface-modified composite fiber filter membrane is prepared by the following steps:

[0054] (1) Place the polyvinyl alcohol (PVA) powder in a vacuum drying oven for 20 hours in advance and set the drying temperature to 60°C. Use a precision electronic balance to weigh the dried PVA powder and methyl phthalate (DMP) solvent at a mass ratio of 1:10 for PVA powder and diluent.

[0055] (2) Put methyl phthalate (DMP) solvent into a glass bottle and place it on a magnetic stirrer at a temperature of 35°C and a stirring speed of 350 r / min. PVA is slowly poured into the stirred solvent. During the stirring process, the glass bottle is sealed to reduce the evaporation of the solvent. After stirring until the mixed solution is clear and transparent, it is placed in a vacuum drying oven and allowed to stand for 6 hours to remove bubbles.

[0056] (3) The temperature inside the electrospinning machine is controlled at 30℃ and the humidity is controlled at 30%. The spinning solution is slowly drawn into a 10mL syringe and the air bubbles in the syringe are fully removed. A stainless steel needle is used and connected to a positive high-voltage DC power source. The flat take-up device is connected to a negative high-voltage DC power source. The tin foil is attached to the flat take-up device with conductive glue. The distance between the flat take-up device and the syringe is controlled at 15cm. The pushing speed of the syringe is 0.7mL / h. The 1μm composite fiber filter membrane is prepared.

[0057] Comparative Example 2

[0058] A surface-modified composite fiber filter membrane is prepared in the same way as Example 1, with the same steps, reagents, equipment and process parameters. The difference is that in step (1), ZrO2 nanoparticles are replaced by an equal amount of SiO2 nanoparticles with a particle size of 20 nm.

[0059] Comparative Example 3

[0060] A surface-modified composite fiber filter membrane is prepared in the same way as Example 1, with the same steps, reagents, equipment and process parameters. The difference is that in step (1), ZrO2 nanoparticles are replaced by an equal amount of TiO2 nanoparticles with a particle size of 20 nm.

[0061] Comparative Example 4

[0062] A surface-modified composite fiber filter membrane is prepared in the same way as that in Example 1, with each step, reagent, equipment and process parameter being the same. The difference is that in step (1), PVA powder is replaced by an equal amount of polytetrafluoroethylene (PTFE).

[0063] Comparative Example 5

[0064] A surface-modified composite fiber filter membrane is prepared in the same way as that in Example 1, with the same steps, reagents, equipment and process parameters. The difference is that the mass ratio of ZrO2 nanoparticles to PVA powder is 1:10.

[0065] Comparative Example 6

[0066] A surface-modified composite fiber filter membrane is prepared in the same way as Example 1, with the same steps, reagents, equipment and process parameters. The difference is that in step (1), the ZrO2 nanoparticles are selected with a particle size of 50 nm.

[0067] Application Example 1-5 and Comparative Application Example 1-6

[0068] The application of a surface-modified composite fiber filter membrane in the filtration and purification of mineral insulating oil includes the following steps:

[0069] The surface-modified composite fiber filter membranes of Examples 1-6 and Comparative Examples 1-6 were cut into membrane samples with a diameter of 4 cm and installed on sand cores for vacuum filtration of aged mineral insulating oil. The aged mineral insulating oil was 25# Karamay. The vacuum degree of the circulating vacuum water pump connected to the filtration device was set to 0.02 MPa. The trace moisture and power frequency breakdown voltage of the filtered mineral oil sample were measured.

[0070] Comparative Application Example 7

[0071] The application of a surface-modified composite fiber filter membrane in the filtration and purification of mineral insulating oil includes the following steps:

[0072] The surface-modified composite fiber filter membrane of Example 1 was cut into a membrane sample with a diameter of 4 cm and installed on a sand core for vacuum filtration of aged FR3 vegetable insulating oil. The vacuum degree of the circulating vacuum water pump connected to the filtration device was set to 0.02 MPa. The trace moisture and power frequency breakdown voltage of the filtered FR3 vegetable insulating oil sample were measured.

[0073] Performance testing

[0074] 1. The insulating oils of the application examples and comparative application examples were tested for trace moisture content according to GB / T 7600-2014 standard. The test results are shown in Table 1 below.

[0075] 2. The insulating oils of the application examples and comparative application examples were subjected to power frequency breakdown voltage tests according to GB / T 507-2002 standard. The test results are shown in Table 1 below.

[0076] 3. Water droplet contact angle: Refer to GB / T 30693-2014 standard and use the SDC-100 contact angle measuring instrument to measure the contact angle of the composite fiber filter membrane used in the corresponding use case and comparative application case. Place a water droplet on the surface of the composite fiber filter membrane and measure the contact angle formed by the water droplet on the surface of the composite fiber filter membrane.

[0077] Table 1 - Performance test results of insulating oil before and after treatment in the application examples and comparative application examples of this application.

[0078]

[0079]

[0080] As shown in Table 1, compared with Comparative Example 1, this application introduces ZrO2 nanoparticles into the composite fiber filter membrane, which can modify the surface of the filter membrane to have a higher specific surface area, making the surface hydrophobic effect more significant. It can hydrophobically block the trace amount of water generated in the aged mineral insulating oil and adsorb and intercept other micro impurities, thereby purifying the aged mineral insulating oil, reducing the water content of the insulating oil, and increasing the breakdown voltage of the insulating oil.

[0081] As shown in Table 1, comparative examples 2-3 introduced SiO2 nanoparticles and TiO2 nanoparticles into the filter membrane for surface modification, respectively. However, the filter membrane's filtration and purification effect on aged mineral insulating oil was not as good as that of ZrO2 nanoparticles. The moisture content in the insulating oil after filtration was still high, and the breakdown voltage was relatively low.

[0082] As shown in Table 1, the filter membrane of Comparative Example 4 is made of polytetrafluoroethylene and ZrO2 nanoparticles are introduced for surface modification. However, due to the insufficient compatibility and dispersibility of ZrO2 nanoparticles in the polytetrafluoroethylene system, the hydrophobic effect of the filter membrane surface is poor, resulting in low interception accuracy of trace moisture in aged mineral insulating oil. In addition, the high porosity of the filter membrane leads to poor adsorption and interception accuracy of trace impurities in aged mineral insulating oil, resulting in a low breakdown voltage of the insulating oil after filtration.

[0083] As shown in Table 1, the ZrO2 nanoparticles introduced into the filter membrane of Comparative Example 6 have a particle size of 50 nm, which is relatively large. This results in larger pores in the filter membrane, allowing trace water molecules in the aged mineral insulating oil to easily pass through the pores. Consequently, the interception efficiency of moisture and impurities is low, and the breakdown voltage of the insulating oil remains low.

[0084] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. In particular, it should be noted that any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention for those skilled in the art.

Claims

1. The application of a surface-modified composite fiber filter membrane in the field of mineral insulating oil filtration and purification, characterized in that, The preparation method of the surface-modified composite fiber filter membrane includes the following steps: (1) PVA powder is added to a container containing solvent and stirred evenly. ZrO2 nanoparticles are slowly added and stirred evenly. After vacuum standing to remove bubbles, spinning solution is obtained. The mass ratio of PVA powder to ZrO2 nanoparticles is (5-7):1, and the particle size of the ZrO2 nanoparticles is 20-40 nm. (2) Add the spinning solution to the electrospinning machine and prepare the composite fiber filter membrane by electrospinning technology.

2. The application of the surface-modified composite fiber filter membrane as described in claim 1 in the field of mineral insulating oil filtration and purification, characterized in that, In step (1), the PVA powder and ZrO2 nanoparticles are pre-dried at 60-80 °C for 20-24 h.

3. The application of the surface-modified composite fiber filter membrane as described in claim 1 in the field of mineral insulating oil filtration and purification, characterized in that, In step (1), the mass ratio of the PVA powder to the solvent is 1:(10-12).

4. The application of the surface-modified composite fiber filter membrane as described in claim 1 in the field of mineral insulating oil filtration and purification, characterized in that, The solvent is at least one of methyl phthalate, octyl phthalate, and butyl phthalate.

5. The application of the surface-modified composite fiber filter membrane as described in claim 1 in the field of mineral insulating oil filtration and purification, characterized in that, In step (1), the stirring temperature is 35-45 ℃, the stirring rate is 350-400 r / min, and the settling and degassing time is 6-8 h.

6. The application of the surface-modified composite fiber filter membrane as described in claim 1 in the field of mineral insulating oil filtration and purification, characterized in that, In step (2), the thickness of the composite fiber filter membrane is 1-1.5 μm.

7. The application of the surface-modified composite fiber filter membrane as described in claim 1 in the field of mineral insulating oil filtration and purification, characterized in that, In step (2), the temperature inside the electrospinning machine is controlled at 30-40 ℃ and the humidity is controlled at 30%-40%. The spinning solution is slowly drawn into the syringe, and air bubbles in the syringe are fully removed. A stainless steel needle is used and connected to a positive high-voltage DC source. The flat take-up device is connected to a negative high-voltage DC source. The tin foil is attached to the flat take-up device with conductive glue. The distance between the flat take-up device and the syringe is controlled at 15-17 cm. The pushing speed of the syringe is 0.7-0.8 mL / h. The composite fiber filter membrane is prepared.

8. The application of the surface-modified composite fiber filter membrane as described in claim 1 in the field of mineral insulating oil filtration and purification, characterized in that, Includes the following steps: The surface-modified composite fiber filter membrane is cut and installed on the sand core for vacuum filtration of mineral insulating oil, with the vacuum degree set to 0.02-0.05 MPa.

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