Polytetrafluoroethylene microporous membrane, preparation method and application thereof

Abstract

The application discloses a kind of polytetrafluoroethylene microporous membrane and preparation method and application, comprising: after the polytetrafluoroethylene microporous membrane after bidirectional stretching is soaked in anhydrous ethanol, impurity is removed and dried;Carrier and auxiliary powder are placed in distilled water, and are fully dispersed using ultrasonic wave to form suspension;After drying, the polytetrafluoroethylene microporous membrane is immersed in suspension and is stationary, then repeatedly pulls in suspension, and is dried and weighed, to obtain the polytetrafluoroethylene microporous membrane of different loadings of carrier and auxiliary powder;Metal salt solution is respectively impregnated into the polytetrafluoroethylene microporous membrane of different loadings prepared in equal volume, and the polytetrafluoroethylene microporous membrane of metal salt solution is obtained after high-temperature treatment.The polytetrafluoroethylene microporous membrane material capable of high-temperature catalytic treatment of flue gas prepared by the method can achieve denitration efficiency of 80% to 90% at 220 to 280 DEG C, and PM 25 removal rate is above 95%.

Description

Technical Field

[0001] This invention relates to the field of filtration materials technology, and in particular to a polytetrafluoroethylene microporous membrane, its preparation method, and its application. Background Technology

[0002] In 2019, the official "Report on the State of China's Ecological Environment" was released. Of the 337 prefecture-level cities and municipalities directly under the central government, only 157 met air quality standards, indicating that air pollution remains a nationwide problem. High-temperature flue gas emitted from industrial production contains large amounts of harmful gases such as nitrogen oxides and dioxins, along with fine particulate matter, resulting in severe air pollution. In recent years, functional membrane filtration technology, as one of the most promising particulate matter capture technologies, has received extensive research attention.

[0003] By filling the membrane with a catalyst, a functional membrane capable of catalytically decomposing harmful gases can be obtained. Previous research has been extensive. For example, Chinese patent CN105771475A discloses a ceramic membrane for high-temperature flue gas filtration and its preparation method. The method involves mixing each component of the filter membrane by ball milling, immersing a support in the mixed membrane slurry, and then drying it at high temperature to obtain the ceramic membrane. Further, Chinese patent CN112778019A discloses a method for preparing a functional ceramic membrane material capable of purifying high-temperature flue gas. This method optimizes the manufacturing process of the dust removal and denitrification functional ceramic membrane material, significantly reducing the preparation cycle. The resulting material has advantages such as uniform catalyst distribution and unobstructed pores. However, the cost of the ceramic membrane itself is too high, and inorganic materials are brittle, easily broken, have a short service life, and poor thermal shock resistance, making them unsuitable for high-temperature flue gas discharged from large chimneys. Chinese patent CN200610154943.5 describes a process where catalyst particles, lubricating oil, and polytetrafluoroethylene (PTFE) resin particles are thoroughly mixed, and PTFE fibers are produced by plunger extrusion. These fibers are then processed using knitting nonwoven fabric equipment to form a high-temperature resistant support material. Finally, the material is bonded to a PTFE microporous membrane at high temperature to form a coating material for waste decomposition. However, this method is too cumbersome to process. Summary of the Invention

[0004] To address the problems mentioned in the background art, this invention provides a polytetrafluoroethylene (PTFE) microporous membrane, its preparation method, and its applications. This membrane can remove high-temperature flue gas and catalytically remove harmful gases, thus expanding the application fields of PTFE microporous membranes. The PTFE microporous membrane of this application is a functional polymer membrane with selective permeability and excellent mechanical and physicochemical properties. This patented catalytic filtration membrane can be applied in high-temperature flue gas environments, and the filter medium possesses characteristics such as high temperature resistance and corrosion resistance. PTFE has excellent chemical corrosion resistance, high and low temperature resistance, weather resistance, and antistatic properties, and also features a long service life and reasonable price, making it widely used in membrane filtration materials. The microporous membrane prepared by the stretching pore-forming method has a special "fiber-node" structure, which can effectively trap dust particles, thereby improving the filtration efficiency of the membrane.

[0005] The above-mentioned technical objective of the present invention is achieved through the following technical solution:

[0006] A method for preparing a polytetrafluoroethylene microporous membrane includes the following steps:

[0007] Step (1): Immerse the biaxially stretched polytetrafluoroethylene microporous membrane in anhydrous ethanol to remove impurities and then dry it;

[0008] Step (2): Place the carrier and auxiliary powder in distilled water and disperse them thoroughly using ultrasound to form a suspension;

[0009] Step (3): Immerse the polytetrafluoroethylene microporous membrane dried in step (1) into the suspension obtained in step (2) and let it stand. Then repeatedly lift it in the suspension, dry it and weigh it to obtain polytetrafluoroethylene microporous membranes with different loading amounts of carrier and auxiliary powder.

[0010] Step (4): The metal salt solution is immersed in the polytetrafluoroethylene microporous membranes with different loadings prepared in step (3) in equal volumes, and after high temperature treatment, the polytetrafluoroethylene microporous membranes loaded with metal salt solution are obtained.

[0011] Preferably, the polytetrafluoroethylene (PTFE) microporous membrane has a porosity of 70%–90%, a thickness of 5–10 μm, and an elongation at break of 70%–150%. The PTFE microporous membrane can have any porosity within the range of 70%–90%, such as 70%, 75%, 80%, 85%, or 90%; and any elongation at break within the range of 80%–150%, such as 70%, 90%, 110%, 130%, or 150%.

[0012] In any of the above schemes, it is preferred that in step (2), the carrier is anatase TiO2 with a particle size of 18 nm, an ultrasonic frequency of 20 kHz, and an ultrasonic time of 1 h.

[0013] In any of the above embodiments, it is preferred that, in step (2), the mass ratio of the carrier to the additive powder is 1:0.5 to 1, the particle size of the additive powder is 100 to 200 nm, and the additive powder includes one or a mixture of several of WO3, MnO3, and MoO3. The mass ratio of the carrier to the additive powder can be any value within the range of 1:0.5 to 1, such as 1:0.5, 1:0.6, 1:0.8, or 1:1; the additive powder includes one or a mixture of several of WO3, MnO3, and MoO3 in equal proportions.

[0014] In any of the above embodiments, it is preferred that in step (2), ultrasonication is used to fully disperse the suspension to form a suspension with a mass fraction of 0.8%-1.2%. The mass fraction of the suspension can be any value within the range of 0.8%-1.2%, such as 0.8%, 1%, 1.1%, or 1.2%.

[0015] In any of the above embodiments, the preferred embodiment is that, in step (3), the dried polytetrafluoroethylene microporous membrane is immersed in a suspension and allowed to stand for 1–5 minutes. Then, it is repeatedly pulled up in the suspension at a speed of 1–5 mm / s, dried at 60–100°C, and weighed to obtain a polytetrafluoroethylene microporous membrane with a carrier and additive powder loading of 2–8%. The pulling speed is any value within the range of 1–5 mm / s, such as 1 mm / s, 2 mm / s, 3 mm / s, 4 mm / s, or 5 mm / s. The drying temperature is any value within the range of 60–100°C, such as 60°C, 70°C, 80°C, 90°C, or 100°C.

[0016] In any of the above schemes, it is preferred that, in step (4), the metal salt solution is one or a mixture of several of Cu(NO3)2·3H2O, Fe(NO3)3·9H2O, Co(NO3)2·6H2O, and NH4VO3 / C2H2O4·2H2O.

[0017] The metal salt solution includes at least one of NH4VO3 / C2H2O4·2H2O, Co(NO3)2·6H2O, Cu(NO3)2·3H2O, and Fe(NO3)3·9H2O, and the ratio of NH4VO3 / C2H2O4·2H2O to Co(NO3)2·6H2O, Cu(NO3)2·3H2O, or Fe(NO3)3·9H2O is 1:0.5-1.

[0018] In any of the above schemes, it is preferred that in step (4), the metal salt solution is immersed in the polytetrafluoroethylene microporous membranes with different loadings prepared in step (3) in equal volumes, and then treated at high temperature in a nitrogen atmosphere at 300-320°C for 2-8 hours to obtain polytetrafluoroethylene microporous membranes with a metal salt solution loading of 6%-12%.

[0019] First, the drying temperature can be any value within the range of 60–100℃, such as 60℃, 70℃, 80℃, 90℃, or 100℃; the drying time can be any value within the range of 2–8h, such as 2h, 3h, 4h, 5h, 6h, 7h, or 8h; the calcination temperature under a nitrogen atmosphere can be any value within the range of 300–320℃, such as 300℃, 310℃, or 320℃; the calcination time can be 2h, 3h, 4h, 5h, 6h, 7h, or 8h; and the metal salt solution loading of the polytetrafluoroethylene microporous membrane can be any value within the range of 6%–12%, such as 6%, 8%, 10%, or 12%.

[0020] The present invention also discloses a polytetrafluoroethylene microporous membrane, which is prepared by any of the above preparation methods.

[0021] The present invention also discloses the application of the above-mentioned polytetrafluoroethylene microporous membrane in removing high-temperature smoke and dust and catalytically removing harmful gases.

[0022] Beneficial effects

[0023] (1) This invention first attaches a carrier to the pores of a polytetrafluoroethylene (PTFE) microporous membrane through impregnation, then attaches one or more active substances to the carrier through impregnation. The metal salts in the solution are adsorbed or stored in the carrier pores by the capillary suction of the porous medium. Finally, a high-temperature treatment is performed to obtain a PTFE microporous membrane loaded with a catalyst. Compared with patent CN200610154943.5, the operation method is simple and convenient, and can effectively reduce production costs.

[0024] (2) The present invention uses equal volume impregnation, and the volume of the metal salt solution used is equal to the volume of the carrier. The solution can be completely absorbed by the carrier, and the loading can be accurately controlled.

[0025] (3) The polytetrafluoroethylene microporous membrane material prepared by the method of the present invention, capable of high-temperature catalytic treatment of flue gas, can achieve a denitrification efficiency of 80%–90% at 220–280°C, and PM2.5 reduction. 2.5 The removal rate reaches over 95%. Attached Figure Description

[0026] Figure 1 PM of different polytetrafluoroethylene microporous membranes prepared for the embodiments and comparative examples of this application 2.5 Filtration efficiency bar chart. Detailed Implementation

[0027] 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 a part of the present invention, and 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, the related materials appearing in subsequent embodiments are all prepared and obtained in the preceding embodiments.

[0028] Example 1

[0029] A method for preparing a polytetrafluoroethylene microporous membrane for removing high-temperature fumes and catalytically removing harmful gases includes the following steps:

[0030] (1) The polytetrafluoroethylene microporous membrane (porosity 85%, membrane thickness 10μm, elongation at break 130% in the warp direction and 80% in the weft direction) provided by Nanjing Zhongcai Membrane Technology Co., Ltd. was first soaked in anhydrous ethanol to remove impurities, and then dried at 60℃.

[0031] (2) Place commercially available carrier anatase TiO2 (particle size 18nm) and auxiliary powder WO3 (particle size 100-200nm) into distilled water. The mass ratio of carrier to auxiliary powder is 1:0.5. Use ultrasound to fully disperse the powder to form a suspension with a mass fraction of 1% (ultrasound frequency 20kHz, ultrasound time 1h).

[0032] (3) Immerse the weighed and dried polytetrafluoroethylene microporous membrane in the suspension and let it stand for 2 minutes. Then, repeatedly lift it in the suspension at 2 mm / s, dry it at 100°C and weigh it. Calculate that the loading of the carrier and auxiliary powder on the polytetrafluoroethylene microporous membrane is 3%.

[0033] (4) The prepared metal salt solutions were impregnated in equal volumes onto polytetrafluoroethylene (PTFE) microporous membranes with different loading amounts. Specifically, a mixed solution of NH4VO3 / C2H2O4·2H2O and Cu(NO3)2·3H2O (ratio 1:0.5) was impregnated in equal volumes onto PTFE microporous membranes already loaded with carrier and additive powder, and then subjected to high-temperature treatment at 300℃ under a nitrogen atmosphere for 6 hours. The mass change before and after the equal-volume impregnation was calculated, and it was found that the loading amount of metal salt solution attached to the microporous membrane after high-temperature treatment was 8%, thus obtaining a PTFE microporous membrane capable of high-temperature catalytic treatment of flue gas.

[0034] Example 2

[0035] A method for preparing a polytetrafluoroethylene microporous membrane for removing high-temperature fumes and catalytically removing harmful gases includes the following steps:

[0036] (1) The polytetrafluoroethylene microporous membrane (porosity 90%, membrane thickness 8μm, elongation at break 120% in the warp direction and 70% in the weft direction) provided by Nanjing Zhongcai Membrane Technology Co., Ltd. was first soaked in anhydrous ethanol to remove impurities, and then dried at 60℃.

[0037] (2) Commercially available anatase TiO2 (particle size 18nm) and additive powders MoO3 and WO3 (particle size 100-200nm) are placed in distilled water. The mass ratio of carrier to additive powder is 1:0.8, and the mass ratio of MoO3 and WO3 powder is 1:1. The mixture is fully dispersed by ultrasound to form a suspension with a mass fraction of 1% (ultrasound frequency 20kHz, ultrasound time 1h).

[0038] (3) Immerse the weighed and dried polytetrafluoroethylene microporous membrane in the suspension and let it stand for 2 minutes. Then, repeatedly lift it in the suspension at 3 mm / s, dry it at 80°C and weigh it. The loading of the carrier and auxiliary powder on the polytetrafluoroethylene microporous membrane is calculated to be 4%.

[0039] (4) An equal volume of the prepared mixed solution of NH4VO3 / C2H2O4·2H2O and Co(NO3)2·6H2O (ratio 1:0.5) was impregnated onto a polytetrafluoroethylene microporous membrane loaded with carrier and additive powder, and then subjected to high-temperature treatment at 310℃ under a nitrogen atmosphere for 5 hours. The mass change before and after the equal volume impregnation was calculated, and it was found that the loading of the metal salt solution onto the microporous membrane after high-temperature treatment was 10%, thus obtaining a polytetrafluoroethylene microporous membrane with high-temperature catalytic treatment of flue gas.

[0040] Example 3

[0041] A method for preparing a polytetrafluoroethylene microporous membrane for removing high-temperature fumes and catalytically removing harmful gases includes the following steps:

[0042] (1) The polytetrafluoroethylene microporous membrane (porosity 90%, membrane thickness 8μm, elongation at break 140% in the warp direction and 70% in the weft direction) provided by Nanjing Zhongcai Membrane Technology Co., Ltd. was first soaked in anhydrous ethanol to remove impurities, and then dried at 60℃.

[0043] (2) Place commercially available anatase TiO2 (particle size 18nm) and additive powder MoO3 (particle size 100-200nm) into distilled water. The mass ratio of carrier to additive powder is 1:1. Use ultrasound to fully disperse the powder to form a suspension with a mass fraction of 1% (ultrasound frequency 20kHz, ultrasound time 1h).

[0044] (3) Immerse the weighed and dried polytetrafluoroethylene microporous membrane in the suspension and let it stand for 2 minutes. Then, repeatedly lift it in the suspension at 3 mm / s, dry it at 80°C and weigh it. Calculate that the loading of the carrier and auxiliary powder on the polytetrafluoroethylene microporous membrane is 5%.

[0045] (4) An equal volume of the prepared mixed solution of NH4VO3 / C2H2O4·2H2O and Co(NO3)2·6H2O (ratio 1:1) was impregnated onto a polytetrafluoroethylene microporous membrane already loaded with carrier and additive powder, and then subjected to high-temperature treatment at 320℃ under a nitrogen atmosphere for 5 hours. The mass change before and after the equal volume impregnation was calculated, and it was found that the loading of the metal salt solution onto the microporous membrane after high-temperature treatment was 10%, thus obtaining a polytetrafluoroethylene microporous membrane with high-temperature catalytic treatment of flue gas.

[0046] Example 4

[0047] A method for preparing a polytetrafluoroethylene microporous membrane for removing high-temperature fumes and catalytically removing harmful gases includes the following steps:

[0048] (1) The polytetrafluoroethylene microporous membrane (porosity 90%, membrane thickness 8μm, elongation at break 130% in the warp direction and 90% in the weft direction) provided by Nanjing Zhongcai Membrane Technology Co., Ltd. was first soaked in anhydrous ethanol to remove impurities, and then dried at 60℃.

[0049] (2) Commercially available anatase TiO2 (particle size 18nm) and additives MoO3 and WO3 powder (particle size 100-200nm) are placed in distilled water. The mass ratio of carrier to auxiliary powder is 1:1, and the mass ratio of MoO3 and WO3 powder is 1:1. The mixture is fully dispersed by ultrasound to form a suspension with a mass fraction of 1% (ultrasound frequency 20kHz, ultrasound time 1h).

[0050] (3) Immerse the weighed and dried polytetrafluoroethylene microporous membrane in the suspension and let it stand for 2 minutes. Then, repeatedly lift it in the suspension at 3 mm / s, dry it at 80°C and weigh it. The loading of the carrier and auxiliary powder on the polytetrafluoroethylene microporous membrane is calculated to be 6%.

[0051] (4) An equal volume of the prepared mixed solution of NH4VO3 / C2H2O4·2H2O and Co(NO3)2·6H2O (ratio 1:1) was impregnated onto a polytetrafluoroethylene microporous membrane already loaded with carrier and additive powder, and calcined at 320℃ under a nitrogen atmosphere for 5 hours. The mass change before and after the equal volume impregnation was calculated, and it was found that the loading of the metal salt solution onto the microporous membrane after high-temperature treatment was 10%, and finally a polytetrafluoroethylene microporous membrane with high-temperature catalytic treatment of flue gas was obtained.

[0052] Comparative Example 1

[0053] The polytetrafluoroethylene microporous membrane provided by Nanjing Zhongcai Membrane Technology Co., Ltd. has a porosity of 90%, a membrane thickness of 8μm, and an elongation at break of 140% in the warp direction and 70% in the weft direction.

[0054] Comparative Example 2

[0055] A method for preparing a polytetrafluoroethylene microporous membrane for removing high-temperature fumes and catalytically removing harmful gases includes the following steps:

[0056] (1) The polytetrafluoroethylene microporous membrane (porosity 90%, membrane thickness 8μm, elongation at break 140% in the warp direction and 70% in the weft direction) provided by Nanjing Zhongcai Membrane Technology Co., Ltd. was first soaked in anhydrous ethanol to remove impurities, and then dried at 60℃.

[0057] (2) Place commercially available carrier anatase TiO2 (particle size 18nm) and auxiliary powder WO3 (particle size 100-200nm) into distilled water. The mass ratio of carrier to auxiliary powder is 1:0.5. Use ultrasound to fully disperse the powder to form a suspension with a mass fraction of 1% (ultrasound frequency 20kHz, ultrasound time 1h).

[0058] (3) The weighed and dried polytetrafluoroethylene microporous membrane is immersed in the suspension and left to stand for 2 minutes. Then, it is repeatedly lifted in the suspension at 2 mm / s, dried at 100°C and weighed. The loading of the carrier and auxiliary powder on the polytetrafluoroethylene microporous membrane is calculated to be 3%. Finally, a polytetrafluoroethylene microporous membrane with high-temperature catalytic treatment of flue gas is obtained.

[0059] Dust removal efficiency is measured by membrane permeability and particulate matter (PM2.5) levels. 2.5 Static filtration efficiency was measured using both a fabric air permeability instrument (pressure 200 Pa) and a static filtration efficiency test bench. Denitrification catalytic activity was evaluated using NO conversion rate and tested on a fixed reaction bed. The test gases simulated actual kiln flue gas (NO, O2), reducing gas (NH3), and equilibrium gas (Ar), with the following parameters: sample area 15 cm². 2 The inlet NO concentration is 400 mg / kg, the NH3 concentration is 400 mg / kg, the oxygen content is 10%, and the reaction temperature is 160–260℃.

[0060] Tests showed that the air permeability of all comparative and example samples was in the range of 7-13 m / min, meeting the air permeability requirements of the membrane. PM 2.5 Filtration efficiency such as Figure 1 As shown, the filtration efficiency of the comparative examples was lower than that of the examples, while the filtration efficiency of all examples was above 95%. This indicates that the polytetrafluoroethylene microporous membrane prepared in this application has high efficiency in filtering PM. 2.5 The ability.

[0061] Table 1 NO conversion rate of different microporous membranes

[0062]

[0063] Table 1 shows the NO conversion rates of Comparative Example 2 and all embodiments. The NO conversion rates of all embodiments reached over 80%. Among them, Example 3 had a higher conversion rate than the other embodiments, reaching 93.8% at 280°C, and the NO conversion rate increased with increasing temperature within the range of 220–280°C.

[0064] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a polytetrafluoroethylene microporous membrane, characterized in that: Includes the following steps: Step (1): Immerse the biaxially stretched polytetrafluoroethylene microporous membrane in anhydrous ethanol to remove impurities and then dry it. Step (2): Place the carrier and auxiliary agent powder in distilled water and disperse them thoroughly using ultrasound to form a suspension. The carrier is anatase TiO2. 2， The anatase TiO2 has a particle size of 18 nm, an ultrasonic frequency of 20 kHz, an ultrasonic time of 1 h, and a mass ratio of carrier to additive powder of 1:0.5~1. The additive powder includes one or a mixture of several of WO3, MnO3 and MoO3, with a particle size of 100~200 nm. Step (3): Immerse the polytetrafluoroethylene microporous membrane dried in step (1) into the suspension obtained in step (2) and let it stand. Then repeatedly lift it in the suspension, dry it and weigh it to obtain polytetrafluoroethylene microporous membranes with different loading amounts of carrier and auxiliary powder. Step (4): The metal salt solution is impregnated onto the polytetrafluoroethylene microporous membranes with different loadings prepared in step (3) in equal volumes. After high temperature treatment, polytetrafluoroethylene microporous membranes loaded with metal salt solution are obtained. The metal salt solution is one or a mixture of several of Cu(NO3)2·3H2O, Fe(NO3)3·9H2O, Co(NO3)2·6H2O, and NH4VO3 / C2H2O4·2H2O.

2. The method for preparing a polytetrafluoroethylene microporous membrane according to claim 1, characterized in that: In step (1), the polytetrafluoroethylene microporous membrane has a porosity of 70%~90%, a thickness of 5~10 μm, and an elongation at break of 70~150%.

3. The method for preparing a polytetrafluoroethylene microporous membrane according to claim 1, characterized in that: In step (2), a suspension with a mass fraction of 0.8%-1.2% is formed by ultrasonic dispersion, with an ultrasonic frequency of 20 kHz and an ultrasonic time of 1 h.

4. The method for preparing a polytetrafluoroethylene microporous membrane according to claim 1, characterized in that: In step (3), the dried polytetrafluoroethylene microporous membrane is immersed in the suspension and left to stand for 1 to 5 minutes. Then, it is repeatedly lifted in the suspension at 1 to 5 mm / s, dried at 60 to 100 °C and weighed to obtain a polytetrafluoroethylene microporous membrane with a carrier and additive powder loading of 2 to 8%.

5. The method for preparing a polytetrafluoroethylene microporous membrane according to claim 1, characterized in that: In step (4), metal salt solutions are immersed in the polytetrafluoroethylene microporous membranes with different loadings prepared in step (3) in equal volumes, and then treated at high temperature for 2-8 h in a nitrogen atmosphere at 300-320 °C to obtain polytetrafluoroethylene microporous membranes with a metal salt solution loading of 6%-12%.

6. A polytetrafluoroethylene microporous membrane, prepared by the preparation method according to any one of claims 1 to 4.

7. The application of the polytetrafluoroethylene microporous membrane according to claim 6 in removing high-temperature smoke and dust and catalytically removing harmful gases.

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