A flexible hollow fiber composite membrane for oil and gas separation and a method of making the same

Abstract

The application discloses a flexible hollow fiber composite membrane for oil-gas separation and a preparation method thereof, and relates to 2 layers, a flexible matrix in the form of a hollow fiber in the inside, and a functional layer for oil-gas separation in the outside, and the preparation method comprises the following steps: soaking and cleaning matrix materials such as polyamide-imide, polyvinylidene fluoride and zirconium oxide in organic solvents such as isopropyl alcohol, n-hexane and anhydrous ethanol, drying treatment in a blowing drying box after the cleaning is completed, then selecting amorphous fluorine-containing polymer Teflon AF2400, dissolving the Teflon AF2400 in a fluorination liquid according to a certain mass ratio, and uniformly mixing through magnetic heating stirring to obtain a coating modification liquid, and finally preparing the flexible oil-gas separation composite membrane with a thickness of 0.2-2 microns through a liquid phase immersion pulling method. The hollow fiber flexible composite membrane prepared by the application has high oil-gas separation efficiency, short oil-gas balance time and excellent stability, and realizes the separation of fault characteristic gas and insulating oil in oil-filled power equipment such as transformers.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas separation technology, specifically relating to a flexible hollow fiber composite membrane for oil and gas separation and its preparation method. Background Technology

[0002] When thermal or electrical faults occur inside oil-filled electrical equipment, the insulating oil and insulating paper inside the equipment age and decompose, producing seven characteristic gases: hydrogen, methane, ethane, ethylene, acetylene, carbon monoxide, and carbon dioxide. Currently, dissolved gas analysis (DGA) is the most effective means of monitoring and diagnosing faults in oil-filled equipment. By utilizing the characteristic information of dissolved gases in oil, the type and severity of faults in oil-filled equipment can be objectively and accurately described. DGA technology typically requires oil-gas separation first, followed by detection and analysis of the extracted dissolved gases to obtain their composition and content. Oil-gas separation is a crucial step, affecting and even determining the accuracy of subsequent fault gas detection, thus impacting the overall test results.

[0003] Currently, the main methods used for oil-gas separation include dynamic headspace degassing, vacuum complete degassing, and permeate membrane degassing. Among these, dynamic headspace degassing and vacuum complete degassing are prone to producing vaporized oil. This vaporized oil enters the detection chamber, contaminating the downstream gas detection unit and leading to inaccurate detection data. Furthermore, both of these methods are mechanical structures, resulting in high failure rates and high maintenance requirements.

[0004] Oil-gas separation membrane degassing utilizes Teflon membranes to separate oil and gas. When oil-gas separation reaches equilibrium, the concentration of dissolved gases in the oil can be obtained by measuring the concentration of the separated gas according to Henry's Law. This membrane prevents vaporized oil from entering the detection chamber and offers advantages such as simple structure, strong potential adaptability, low energy consumption, and low maintenance costs, making it a promising technology for the future. However, traditional single-layer Teflon membranes are very thin and easily damaged. While Teflon membranes composited with ceramic hollow fiber matrices have been applied, ceramics are brittle materials, making it difficult to guarantee reliability during transportation and long-term use. Therefore, there is an urgent need to develop non-brittle materials as a skeletal support structure to composite with Teflon, forming flexible oil-gas separation membranes for further application.

[0005] Prior art document 1 (CN116328550A) discloses a method for preparing an oil-gas separation membrane for online transformer testing, comprising: Step 1, spreading liquid fluorosilicone rubber on a flat plate and curing it to form a thin film; Step 2, mixing and dispersing Hyflon AD60 with perfluoropolyether thermally conductive liquid evenly, adding α-phase nano-alumina powder, dispersing evenly to obtain a casting solution; Step 3, coating the casting solution onto the thin film, letting it stand, covering it with a pressure plate, heating it to 180-220℃ in a drying oven, and holding it at that temperature for 3-10 hours; Step 4, letting it stand under high pressure for 24-48 hours, then placing it again in a preheated drying oven and holding it at that temperature for 6-12 hours, and cooling it to obtain the final product. However, the shortcomings of this existing technology are that the preparation technology is only applicable to flat sheet membranes and not to hollow fiber membranes. Furthermore, the oil-gas separation membrane prepared by this technology does not demonstrate the stability of the casting liquid separation layer and the stability of long-term operation testing. In addition, the oil-gas separation membrane prepared by this technology has not undergone professional mechanical strength testing, but only tested for whether the membrane ruptures and leaks oil by adding oil pressure to 500 kPa. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a flexible oil-gas separation membrane prepared by using high-molecular materials such as polyamide-imide or polyvinylidene fluoride as a matrix and combining it with Teflon materials, thereby promoting industrial applications and providing a highly reliable flexible hollow fiber composite membrane for oil-gas separation and its preparation method.

[0007] The present invention adopts the following technical solution.

[0008] A first aspect of the present invention provides a method for preparing a flexible hollow fiber composite membrane for oil-gas separation, comprising the following steps:

[0009] Step 1, substrate pretreatment: The substrate material is immersed and cleaned in an organic solvent according to a set ratio, and then dried to obtain a substrate material with a clean surface.

[0010] Step 2, preparation of coating modification solution: Select amorphous fluoropolymer Teflon AF2400, dissolve it in fluorinated liquid, and mix it evenly by magnetic heating and stirring to obtain coating modification solution;

[0011] Step 3, preparation of composite membrane by liquid phase dip-coating method: The coating modification liquid obtained in step 2 is transferred into a container, the matrix material obtained in step 1 is placed into the container containing the coating modification liquid, the container is evacuated to a negative pressure within a set range, and the composite membrane is taken out from the coating modification solution by dip-coating method, and vertically hung in a forced-air drying oven for drying treatment to obtain oil-gas separation composite membrane.

[0012] Preferably, in step 1, the matrix material is either polyamide-imide or polyvinylidene fluoride, with a pore size range of 50-200 nm; the organic solvent is either isopropanol, n-hexane, or anhydrous ethanol.

[0013] Preferably, in step 1, the mass ratio of the matrix material to the organic solvent is (1-2):5:(2-5):15, the cleaning time is 1-4 hours, the drying temperature is 40-60°C, and the drying time is 2-3 hours.

[0014] Preferably, in step 2, the concentration of Teflon AF2400 in the prepared coating modification solution is 0.3-1.0 wt%, the fluorinated solution is at least one of FC-40 and FC-770, and the mass ratio of Teflon AF2400 to the fluorinated solution is 1:(2.5-3.5).

[0015] Preferably, in step 2, the magnetic heating temperature is 60-80℃, the magnetic stirring speed is 300-800 r / min, and the dissolution time is 6-12 h.

[0016] Preferably, step 3 specifically includes:

[0017] Step 3.1: Transfer the coating modification liquid into a glass container, seal one end of the substrate material, and place it vertically into the glass container containing the coating modification liquid.

[0018] Step 3.2: Evacuate the glass container to a negative pressure within a set range, so that the coating modification liquid enters the surface of the membrane pores of the substrate material, thereby achieving substrate coating modification.

[0019] Step 3.3: After coating, the composite membrane is removed from the coating modification solution by dip-coating method and hung vertically in a forced-air drying oven for drying to obtain the oil-gas separation composite membrane.

[0020] Preferably, in step 3.2, the set vacuum negative pressure is -0.2 to -0.8 Bar, the immersion coating time is 10-60 s, and the coating ambient temperature is 15-60℃.

[0021] Preferably, in step 3.3, the drying temperature of the coated and modified composite film is 100-140℃, the treatment time is 12-18h, and the immersion and lifting speed is 30-60cm / min.

[0022] Preferably, in step 3.3, the coated and modified oil-gas separation composite membrane is repeatedly processed to achieve a modified layer thickness of 0.2-2 μm.

[0023] A second aspect of the present invention provides a flexible hollow fiber composite membrane for oil-gas separation, which is prepared by the method described above. The flexible hollow fiber composite membrane for oil-gas separation has a flexible matrix in the form of hollow fibers inside and a functional layer on the outside that performs the function of oil-gas separation, and is used for the separation of dissolved gases in transformer oil.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] (1) This invention employs a liquid-phase impregnation-coating method to prepare a flexible hollow fiber composite membrane under a specific range of negative pressure. Polyamide-imide or polyvinylidene fluoride, or other polymeric materials, are used as the matrix and combined with Teflon materials to prepare a flexible oil-gas separation membrane. The process is simple and convenient, providing a non-brittle hollow fiber composite membrane for oil-gas separation. The flexible hollow fiber composite membrane prepared according to this invention was encapsulated into a membrane module for testing. The effective total surface area of ​​the flexible hollow fiber composite membrane is approximately 6.02 cm². 2 Its gas permeability is 9.47 for H2, 5.44 for CO, 4.54 for CH4, 0.63 for C2H4, 0.78 for C2H2, 0.59 for C2H6, and 0.85 for CO2. The high permeability results in a shorter oil-gas separation equilibrium time, and it can be applied to the oil-gas separation unit of the online monitoring device for dissolved gases in transformer oil.

[0026] (2) This invention uses a liquid-phase impregnation-coating method to prepare a flexible hollow fiber composite membrane under a specific range of negative pressure. The coating modification liquid enters the surface of the membrane pores of the matrix material to achieve matrix coating modification. The degree of penetration of the coating modification liquid can be controlled, and the modified layer has better adhesion to the matrix. Compared with hollow fiber composite membranes prepared by coating alone, the modified layer of the composite membrane prepared by this invention is not easy to fall off from the hollow fiber matrix material. After 168 hours of operation, it still maintains good oil-gas separation performance and there is no oil leakage caused by the modification layer falling off. This improves the stability of the hollow fiber composite membrane and obtains an oil-gas separation composite membrane with high oil-gas separation efficiency, short oil-gas balance time and excellent stability. It can be applied to the oil-gas separation unit of the online monitoring device for dissolved gases in oil of oil-filled power equipment. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the process for preparing a flexible hollow fiber composite membrane for oil and gas separation;

[0028] Figure 2 This is a scanning electron microscope image of the outer surface of the flexible oil-gas separation composite membrane prepared using polyvinylidene fluoride in Example 1 of the present invention;

[0029] Figure 3 This is a graph showing the gas permeability performance of the flexible oil-gas separation composite membrane prepared by this invention under different process conditions;

[0030] Figure 4 This is a graph showing the oil-gas separation performance of the flexible oil-gas separation composite membrane prepared in Example 1 of this invention;

[0031] Figure 5 This is a scanning electron microscope image of the cross-section of the flexible hollow fiber composite membrane with polyamide-imide as the matrix in Example 2 of the present invention;

[0032] Figure 6 This is a magnified scanning electron microscope image of a cross-section of the flexible oil-gas separation composite membrane prepared in Example 2 of this invention;

[0033] Figure 7 This is a scanning electron microscope image of the outer surface of the oil-gas separation composite membrane prepared in Comparative Example 1 of this invention. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The embodiments described in this application are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, other embodiments obtained by those skilled in the art without creative effort are all within the protection scope of this invention.

[0035] like Figure 1 As shown, this invention provides a composite membrane for oil-gas separation and its preparation method, the steps of which are as follows:

[0036] Step 1, matrix pretreatment: The matrix material is immersed and cleaned in an organic solvent according to a set ratio. After cleaning, it is dried in a forced-air drying oven to obtain a hollow fiber matrix material with a clean surface.

[0037] In a preferred but non-limiting embodiment of the present invention, the matrix material is an organic polymer membrane such as polyamide-imide or polyvinylidene fluoride, with a pore size range of 50-200 nm, and the organic solvent includes isopropanol, n-hexane, anhydrous ethanol, etc.

[0038] More preferably, the mass ratio of the matrix material to the organic solvents isopropanol, n-hexane, and anhydrous ethanol is (1-2):5:(2-5):15, the cleaning time is 1-4 hours, and the drying temperature is 40-60°C for 2-3 hours.

[0039] Step 2, preparation of coating modification solution: Select amorphous fluoropolymer Teflon AF2400, dissolve it in fluorinated liquid at a certain mass ratio, and mix it evenly by magnetic heating and stirring to obtain coating modification solution;

[0040] In a preferred but non-limiting embodiment of the present invention, the concentration of Teflon AF2400 in the prepared coating modification solution is 0.3-1.0 wt%, and the fluorinated solution is at least one of FC-40 and FC-770;

[0041] More preferably, the mass ratio of Teflon AF2400 to the fluorinated liquid is 1:(2.5-3.5);

[0042] More preferably, the magnetic heating temperature is 60-80℃, the magnetic stirring speed is 300-800 r / min, and the dissolution time is 6-12 h.

[0043] Step 3, preparation of composite membrane by liquid phase dip-coating method: The coating modification liquid obtained in step 2 is transferred into a container, the matrix material obtained in step 1 is placed into the container containing the coating modification liquid, the container is evacuated to a negative pressure within a set range, and the composite membrane is taken out from the coating modification solution by dip-coating method, and vertically hung in a forced-air drying oven for drying treatment to obtain oil-gas separation composite membrane.

[0044] In a preferred but non-limiting embodiment of the present invention, step 3 specifically includes:

[0045] Step 3.1: Transfer the coating modification liquid into a glass container, seal one end of the substrate material, and place it vertically into the glass container containing the coating modification liquid.

[0046] It is worth noting that during this process, the outer surface of the matrix material is ensured to be impregnated with the coating modification liquid, while the coating modification liquid does not penetrate into the interior of the hollow fiber matrix membrane.

[0047] Step 3.2: Evacuate the glass container to a negative pressure within a set range, so that the coating modification liquid enters the surface of the membrane pores of the substrate material, thereby achieving substrate coating modification.

[0048] More preferably, in order to achieve the surface coating modification of the substrate membrane pores, the vacuum negative pressure is required to be set to -0.2 to -0.8 Bar, the immersion coating time is 10-60 s, and the coating environment temperature is 15-60℃.

[0049] Step 3.3: After coating, the composite membrane is removed from the coating modification solution by dip-coating method and hung vertically in a forced-air drying oven for drying to obtain the oil-gas separation composite membrane.

[0050] More preferably, the drying temperature of the coated and modified composite film is 100-140℃, the treatment time is 12-18h, and the immersion and lifting speed in the immersion and lifting method is 30-60cm / min;

[0051] In a preferred but non-limiting embodiment of the present invention, step 3 involves repeating the coating modification process on the composite film to achieve a modified layer thickness of 0.2-2 μm.

[0052] The aforementioned hollow fiber composite membrane for oil-gas separation was applied to the separation of dissolved gases in transformer oil. The gas permeability of the composite membrane was evaluated using nitrogen permeability, and its oil-gas separation effect was evaluated using gas permeability and oil-gas separation equilibrium time.

[0053] In the following embodiments of the present invention, the gas permeation test conditions are as follows: the inlet pressure of the hollow fiber composite membrane is 2.0 bar, the permeation pressure is 1.0 bar, and the nitrogen permeation rate of the hollow fiber composite membrane is obtained under a pressure difference of 1.0 bar. The nitrogen permeation rate of the membrane is calculated based on the permeation flow rate using the following formula:

[0054]

[0055] Among them, Q i Let be the gas volumetric flow rate of gas component i at standard temperature and pressure, Δp be the transmembrane pressure difference, and A be the effective membrane area. Gas permeability is typically represented by a gas permeation unit (GPU), where:

[0056]

[0057] In the following embodiments of the present invention, a scanning electron microscope (Zeiss, EVO18) was used to characterize and analyze the microstructure of the surface and cross-section of the hollow fiber composite membrane for oil-gas separation.

[0058] In the following embodiments of the present invention, before the dissolved gas separation experiment in oil, a hollow fiber composite membrane needs to be encapsulated in the test assembly. The experimental conditions are as follows: during oil circulation, the oil pump speed is set to 300–700 rpm, the oil pressure is approximately 1–2 bar, and after purging with inert gas (N2 or Ar), the gas circulation is started. The gas flow rate is approximately 50–300 ml / min, and the gas pressure is 0.9–1.2 bar. Gas samples are taken at time points of 15 min, 30 min, 45 min, 60 min, 75 min, 90 min, 105 min, 120 min, 150 min, and 180 min after oil-gas separation. The separated dissolved gas in the oil is injected into a gas chromatograph for gas component and concentration detection. Observe whether the concentration of dissolved gas in the oil has reached equilibrium. Use 90% of the gas concentration when the oil and gas separation is completely balanced as the indicator that the oil and gas separation has reached equilibrium. This can determine the equilibrium time of the oil and gas separation membrane. Divide the gas concentration in the gas chamber when the oil and gas separation is completely balanced by the concentration of dissolved gas in the oil to obtain the gas permeability.

[0059] Example 1

[0060] This embodiment provides a hollow fiber composite membrane for oil-gas separation and its preparation method, the steps of which are as follows:

[0061] Polyvinylidene fluoride (PVDF) was used as the hollow fiber matrix material. First, the membrane was immersed and cleaned in anhydrous ethanol for 1 hour, then dried in a forced-air drying oven at 60°C for 3 hours to obtain a clean PVDF hollow fiber membrane. Under magnetic heating and stirring conditions, amorphous fluoropolymer (Teflon AF2400) powder was uniformly mixed in fluorinated liquid FC-770. The mass fraction of Teflon AF2400 was 1 wt%, the heating temperature was 80°C, and the magnetic stirring speed was 500 r / min. After 6 hours, a coating modification solution with completely dissolved Teflon AF2400 was obtained. One end of the PVDF hollow fiber membrane was sealed with hot melt adhesive, and it was placed vertically in a glass container containing the coating modification solution to ensure that the solution did not enter the hollow fiber membrane. By evacuating the glass container to achieve a specific negative pressure range, the coating modification liquid enters the surface of the substrate material membrane pores, thus achieving substrate coating modification. The vacuum degree is -0.5 bar, and the immersion coating time is 60 seconds. After coating, the composite membrane is removed from the coating modification solution using the immersion pull method at a speed of 50 cm / min. It is then transferred to a forced-air drying oven and placed vertically for drying at 120°C for 12 hours to ensure complete solvent evaporation. Finally, the sealing end is cut off to obtain the hollow fiber composite membrane.

[0062] Figure 2 This is a SEM image of the outer surface of the hollow fiber composite membrane in this embodiment, magnified 66 times, compared to the comparative example. Figure 7 The modified layer of the hollow fiber composite membrane prepared in this embodiment has better adhesion to the substrate, and the modified layer is less prone to detachment. The nitrogen permeability of the hollow fiber composite membrane prepared in this embodiment is as follows: Figure 3 As shown in Sample 3, the gas permeability is 78.71 GPU. When the concentration of the coating solution increases and the thickness of the modified layer increases, the gas transmission resistance will increase. Therefore, compared with Sample 1, the concentration of the coating modified solution in Sample 1 is 0.5 wt%, and the gas permeability of Sample 3 is reduced. However, the gas permeability is still relatively high, which is sufficient to support efficient oil-gas separation performance.

[0063] The hollow fiber composite membrane prepared in this embodiment is encapsulated into a membrane module, and the effective total surface area of ​​the hollow fiber composite membrane is approximately 6.02 cm². 2 The gas permeabilities were 9.47 for H2, 5.44 for CO, 4.54 for CH4, 0.63 for C2H4, 0.78 for C2H2, 0.59 for C2H6, and 0.85 for CO2. The equilibrium times for oil-gas separation of these seven gases are as follows: Figure 4 As shown, the equilibration time is approximately 5 hours. Compared to existing technologies, the ceramic-Teflon AF2400 composite membrane has an effective total surface area of ​​30 cm². 2Under the given conditions, the equilibrium time is 10 hours, and this hollow fiber composite membrane exhibits a shorter oil-gas separation equilibrium time. Furthermore, the hollow fiber membrane prepared in this embodiment still maintains good performance after 168 hours of operation, with no oil leakage caused by the detachment of the modified layer. Mechanical strength testing revealed that the composite membrane has a tensile breaking tensile strength of 24.04 MPa, an elongation at break of 23.54%, and a Young's modulus as high as 560 MPa.

[0064] Example 2

[0065] This embodiment provides a hollow fiber composite membrane for oil-gas separation and its preparation method, the steps of which are as follows:

[0066] Polyamide-imide (PAI) was used as the hollow fiber matrix material. First, the membrane was immersed and cleaned in anhydrous ethanol for 1 hour, then dried in a forced-air drying oven at 60°C for 2 hours to obtain a clean PAI hollow fiber membrane. Under magnetic heating and stirring conditions, amorphous fluoropolymer (Teflon AF2400) powder was uniformly mixed in fluorinated liquid FC-770. The mass fraction of Teflon AF2400 was 0.5 wt%. The heating temperature was 60°C, and the magnetic stirring speed was 300 r / min. After 12 hours, a coating modification solution with completely dissolved Teflon AF2400 was obtained. One end of the PAI hollow fiber membrane was sealed with hot melt adhesive, and it was placed vertically in a glass container containing the coating modification solution to ensure that the solution did not enter the hollow fiber tube. By evacuating the glass container to achieve a specific negative pressure, the coating modification liquid enters the surface of the substrate material membrane pores, thus achieving substrate coating modification. The vacuum degree is -0.5 bar, and the immersion coating time is 60 seconds. After coating, the composite membrane is removed from the coating modification solution using the immersion pull method at a speed of 30 cm / min. It is then transferred to a forced-air drying oven and placed vertically for drying at 120°C for 12 hours to ensure complete solvent evaporation. Finally, the sealing end is cut off to obtain the hollow fiber composite membrane.

[0067] Figure 5 This is a SEM image of the cross-section of the PAI-based hollow fiber composite membrane prepared in this embodiment, magnified 40 times. Figure 6 This is a magnified SEM image of a section of the hollow fiber composite membrane in this embodiment, magnified 1000 times, compared to the comparative example. Figure 7 In this embodiment, the modified layer adheres well to the substrate, and there is no detachment of the modified layer, indicating that this method can obtain a hollow fiber composite membrane with high stability. The hollow fiber composite membrane prepared in this embodiment has a nitrogen permeability of 22.07 GPU, exhibiting good gas permeability performance. When conducting oil-soluble gas separation experiments, the hollow fiber membrane needs to be encapsulated in a membrane module first; the effective total surface area of ​​the encapsulated hollow fiber composite membrane is 101.5 cm². 2The oil-gas separation equilibrium time for dissolved gases (including CH4, C2H2, C2H4, C2H6, CO, CO2, and H2) in the seven types of oils was 4 hours. The equilibrium time was shortened as the volume of the permeate end gas chamber decreased or the effective area of ​​the membrane increased. The oil-gas separation equilibrium time could be further reduced by increasing the number of hollow fiber composite membranes.

[0068] Example 3

[0069] This embodiment provides a hollow fiber composite membrane for oil-gas separation and its preparation method, the steps of which are as follows:

[0070] Polyvinylidene fluoride (PVDF) was used as the hollow fiber matrix material. First, the membrane was immersed and cleaned in anhydrous ethanol for 1 hour, then dried in a forced-air drying oven at 60°C for 3 hours to obtain a clean PVDF hollow fiber membrane. Under magnetic heating and stirring conditions, amorphous fluoropolymer (Teflon AF2400) powder (0.5 wt% Teflon AF2400) was uniformly mixed in fluorinated liquid FC-770. The heating temperature was 80°C, and the magnetic stirring speed was 500 r / min. After 6 hours, a coating modification solution with completely dissolved Teflon AF2400 was obtained. One end of the PVDF hollow fiber membrane was sealed with hot melt adhesive, and it was placed vertically in a glass container containing the coating modification solution to ensure that the solution did not enter the hollow fiber membrane. By evacuating a glass container to achieve a specific negative pressure range, the coating modification solution is allowed to penetrate the surface of the substrate material's membrane pores, achieving substrate coating modification. The vacuum level is -0.5 bar, and the immersion coating time is 60 seconds. After coating, the composite membrane is removed from the coating modification solution using an immersion-pull method at a speed of 50 cm / min. It is then transferred to a forced-air drying oven and placed vertically for drying at 120°C for 12 hours to ensure complete solvent evaporation. The hollow fiber composite membrane is then vertically placed into a glass container containing the coating modification solution, and the above composite membrane preparation process is repeated. Finally, the sealed end is cut off to obtain a hollow fiber composite membrane coated twice using the liquid-phase immersion-pull method under a specific negative pressure range.

[0071] The nitrogen permeability of the hollow fiber composite membrane prepared in this embodiment is as follows: Figure 3 Sample 2, as shown, has a permeability of 187.96 GPU. As the number of coating passes increases and the thickness of the modified layer increases, the gas transport resistance increases. Therefore, compared to Sample 1, the gas permeability of Sample 2 decreases, but it remains relatively high, sufficient to support efficient oil-gas separation performance. The difference between Sample 1 and the preparation method in this embodiment is that the modified layer of Sample 1 is coated once under a specific range of negative pressure; the remaining preparation steps and conditions are the same.

[0072] Example 4

[0073] This embodiment provides a hollow fiber composite membrane for oil-gas separation and its preparation method, the steps of which are as follows:

[0074] Polyvinylidene fluoride (PVDF) was used as the hollow fiber matrix material. First, the membrane was immersed and cleaned in anhydrous ethanol for 1 hour, then dried in a forced-air drying oven at 60°C for 3 hours to obtain a clean PVDF hollow fiber membrane. Under magnetic heating and stirring conditions, amorphous fluoropolymer (Teflon AF2400) powder was uniformly mixed in fluorinated liquid FC-770. The mass fraction of Teflon AF2400 was 1 wt%, the heating temperature was 80°C, and the magnetic stirring speed was 500 r / min. After 6 hours, a coating modification solution with completely dissolved Teflon AF2400 was obtained. One end of the PVDF hollow fiber membrane was sealed with hot melt adhesive, and it was placed vertically in a glass container containing the coating modification solution to ensure that the solution did not enter the hollow fiber membrane. By evacuating the glass container to achieve a specific negative pressure range, the coating modification liquid enters the surface of the substrate material membrane pores, thus achieving substrate coating modification. The vacuum degree is -0.8 bar, and the immersion coating time is 60 seconds. After coating, the composite membrane is removed from the coating modification solution using the immersion pull method at a speed of 50 cm / min. It is then transferred to a forced-air drying oven and placed vertically for drying at 120°C for 12 hours to ensure complete solvent evaporation. Finally, the sealing end is cut off to obtain the hollow fiber composite membrane.

[0075] The hollow fiber composite membrane prepared in this embodiment is encapsulated into a membrane module, and the effective total surface area of ​​the hollow fiber composite membrane is approximately 6.02 cm². 2 The equilibration time is approximately 7 hours. Compared to Example 1, this example uses a vacuum level of -0.8 bar. The higher vacuum level allows for greater penetration of the modified solution into the substrate pores, increasing the thickness of the modified layer and raising gas transport resistance, thus increasing the equilibration time. However, compared to existing technologies, the effective total surface area of ​​the ceramic-Teflon AF2400 composite membrane reaches 30 cm². 2 Even with a balancing time of 10 hours, this hollow fiber composite membrane still exhibits higher oil-gas separation efficiency.

[0076] Comparative Example 1

[0077] This comparative example provides a hollow fiber composite membrane for oil-gas separation and its preparation method, the steps of which are as follows:

[0078] Polyamide-imide (PAI) was used as the hollow fiber matrix material. First, the membrane was immersed and cleaned in anhydrous ethanol for 1 hour, then dried in a forced-air drying oven at 60°C for 2 hours to obtain a clean PAI hollow fiber membrane. Under magnetic heating and stirring conditions, amorphous fluoropolymer (Teflon AF2400) powder was uniformly mixed in fluorinated liquid FC-770. The mass fraction of Teflon AF2400 was 0.5 wt%. The heating temperature was 80°C, and the magnetic rotation speed was 500 r / min. After 6 hours, a coating modification solution with completely dissolved Teflon AF2400 was obtained. One end of the PAI hollow fiber membrane was sealed with hot melt adhesive, and it was vertically immersed in the coating modification solution, ensuring that the solution did not enter the hollow fiber membrane. After coating for 60 seconds, the hollow fiber composite membrane was removed, transferred to a forced-air drying oven, and placed vertically for drying at 120°C for 12 hours to ensure complete solvent evaporation. Finally, the sealed end was cut off to obtain the final hollow fiber composite membrane.

[0079] Figure 7 The SEM image of the outer surface of the hollow fiber composite membrane prepared in this comparative example is magnified 40 times. It can be observed that the modified layer has poor adhesion. The modified layer is prepared on the hollow fiber substrate using only a coating method. Compared to the method of preparing hollow fiber composite membranes under a specific range of negative pressure using liquid phase impregnation and pulling, the modified layer is prone to detachment from the substrate and lacks good stability. The above examples and comparative examples illustrate that this method can prepare hollow fiber composite membranes for oil-gas separation with high oil-gas separation efficiency, short oil-gas equilibrium time, and excellent stability.

[0080] The beneficial effects of this invention are that, compared with the prior art,

[0081] (1) This invention employs a liquid-phase impregnation-coating method to prepare a flexible hollow fiber composite membrane under a specific range of negative pressure. Polyamide-imide or polyvinylidene fluoride, or other polymeric materials, are used as the matrix and combined with Teflon materials to prepare a flexible oil-gas separation membrane. The process is simple and convenient, providing a non-brittle hollow fiber composite membrane for oil-gas separation. The flexible hollow fiber composite membrane prepared according to this invention was encapsulated into a membrane module for testing. The effective total surface area of ​​the flexible hollow fiber composite membrane is approximately 6.02 cm². 2 Its gas permeability is 9.47 for H2, 5.44 for CO, 4.54 for CH4, 0.63 for C2H4, 0.78 for C2H2, 0.59 for C2H6, and 0.85 for CO2. The high permeability results in a shorter oil-gas separation equilibrium time, and it can be applied to the oil-gas separation unit of the online monitoring device for dissolved gases in transformer oil.

[0082] (2) This invention uses a liquid-phase impregnation-coating method to prepare a flexible hollow fiber composite membrane under a specific range of negative pressure. The coating modification liquid enters the surface of the membrane pores of the matrix material to achieve matrix coating modification. The degree of penetration of the coating modification liquid can be controlled, and the modified layer has better adhesion to the matrix. Compared with hollow fiber composite membranes prepared by coating alone, the modified layer of the composite membrane prepared by this invention is not easy to fall off from the hollow fiber matrix material. After 168 hours of operation, it still maintains good oil-gas separation performance and there is no oil leakage caused by the modification layer falling off. This improves the stability of the hollow fiber composite membrane and obtains an oil-gas separation composite membrane with high oil-gas separation efficiency, short oil-gas balance time and excellent stability. It can be applied to the oil-gas separation unit of the online monitoring device for dissolved gases in oil of oil-filled power equipment.

[0083] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a flexible hollow fiber composite membrane for oil and gas separation, characterized in that: Includes the following steps: Step 1, substrate pretreatment: The substrate material is immersed and cleaned in an organic solvent according to a set ratio, and then dried to obtain a substrate material with a clean surface. The set ratio is that the mass ratio of the matrix material to the organic solvent is (1-2):5:(2-5):15; Step 2, preparation of coating modification solution: Select amorphous fluoropolymer Teflon AF2400, dissolve it in fluorinated liquid, and mix it evenly by magnetic heating and stirring to obtain coating modification solution; Step 3, preparation of composite membrane by liquid phase dip-coating method: The coating modification liquid obtained in step 2 is transferred into a container, the matrix material obtained in step 1 is placed into the container containing the coating modification liquid, the container is evacuated to a negative pressure within a set range, and the composite membrane is taken out from the coating modification solution by dip-coating method, and hung vertically in a forced-air drying oven for drying treatment to obtain oil-gas separation composite membrane; The setting range is -0.2 to -0.8 Bar for the vacuum negative pressure.

2. The method for preparing a flexible hollow fiber composite membrane for oil and gas separation according to claim 1, characterized in that: In step 1, the matrix material is either polyamide-imide or polyvinylidene fluoride, with a pore size range of 50-200 nm; the organic solvent is either isopropanol, n-hexane, or anhydrous ethanol.

3. The method for preparing a flexible hollow fiber composite membrane for oil and gas separation according to claim 1, characterized in that: In step 1, the cleaning time is 1-4 hours, and the drying temperature is 40-60°C for 2-3 hours.

4. The method for preparing a flexible hollow fiber composite membrane for oil and gas separation according to claim 1, characterized in that: In step 2, the concentration of Teflon AF2400 in the prepared coating modification solution is 0.3-1.0 wt%, and the fluorinated solution is at least one of FC-40 and FC-770. The mass ratio of Teflon AF2400 to the fluorinated solution is 1:(2.5-3.5).

5. The method for preparing a flexible hollow fiber composite membrane for oil and gas separation according to claim 1, characterized in that: In step 2, the magnetic heating temperature is 60-80°C, the magnetic stirring speed is 300-800 r / min, and the dissolution time is 6-12 h.

6. The method for preparing a flexible hollow fiber composite membrane for oil and gas separation according to claim 1, characterized in that: Step 3 specifically includes: Step 3.1: Transfer the coating modification liquid into a glass container, seal one end of the substrate material, and place it vertically into the glass container containing the coating modification liquid. Step 3.2: Evacuate the glass container to a negative pressure within a set range, so that the coating modification liquid enters the surface of the membrane pores of the substrate material, thereby achieving substrate coating modification. Step 3.3: After coating, the composite membrane is removed from the coating modification solution by dip-coating method and hung vertically in a forced-air drying oven for drying to obtain the oil-gas separation composite membrane.

7. The method for preparing a flexible hollow fiber composite membrane for oil and gas separation according to claim 6, characterized in that: In step 3.2, the immersion coating time is 10-60 s, and the coating ambient temperature is 15-60 ℃.

8. The method for preparing a flexible hollow fiber composite membrane for oil and gas separation according to claim 1, characterized in that: In step 3.3, the drying temperature of the coated and modified composite film is 100-140 ℃, the treatment time is 12-18 h, and the immersion and lifting speed is 30-60 cm / min.

9. The method for preparing a flexible hollow fiber composite membrane for oil and gas separation according to claim 6, characterized in that: In step 3.3, the modified oil-gas separation composite membrane is repeatedly coated to achieve a modified layer thickness of 0.2-2 μm.

10. A flexible hollow fiber composite membrane for oil-gas separation, prepared by the method for preparing a flexible hollow fiber composite membrane for oil-gas separation according to any one of claims 1-9, characterized in that: The flexible hollow fiber composite membrane for oil-gas separation has a flexible matrix in the form of hollow fibers inside and a functional layer on the outside that plays the role of oil-gas separation, and is used for the separation of dissolved gases in transformer oil.

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