PTFE air filtration hollow fiber membrane

Abstract

The invention relates to a PTFE (polytetrafluoroethylene) air filtration hollow fiber membrane, which is characterized in that compared with the traditional similar PTFE air filtration hollow fiber membrane, the microcosmic hole pattern structure of the membrane silk is as follows: the fibril diameter is reduced from 0.35-0.49 mu m to 0.05-0.1 mu m, the fiber spacing is reduced from 1 mu m to 0.05-0.3 mu m, the average hole diameter is reduced from 4.2-4.8 mu m to 1-3 mu m, and the membrane hole is a line gap type hole pattern with the average diameter-length ratio of 30: 0.1. Therefore, the device has a higher interception effect on tiny particles with the particle size of 0.1-0.3 mu m. And the application of large-scale industrial experiments has been obtained.

Description

Technical Field

[0001] A PTFE air filter hollow fiber membrane, particularly a PTFE air filter hollow fiber membrane pore type. Background Technology

[0002] In recent years, research on air filtration using plastic hollow fiber membranes has gradually emerged, especially with the appearance of patents and applications for treating various heavily polluted flue gases using PTFE hollow fiber membranes. However, there is very little publicly available information on the pore design of PTFE hollow fiber membranes used for air filtration. The most comprehensive publicly available information is in the doctoral dissertation "Structural Regulation of PTFE Fiber Membranes and Research on Their Air Filtration Performance" published by Xu Huan, a doctoral student at Zhejiang Sci-Tech University. This dissertation systematically introduces and lists various pore types.

[0003] As can be seen from the list of various design results and references in this paper, the main structural parameters of the PTFE hollow fiber membranes used for air filtration are as follows: average pore size 4.2-4.8 μm; average porosity 55-75%; fibril diameter 0.35-0.49 μm; fiber spacing 1 μm. Experimental results show that the filtration efficiency of particles with a diameter of 2.5 μm can be maintained above 99.99%, and the filtration efficiency of particles with a diameter of 0.3 μm can be maintained at 92-97%.

[0004] Based on the experimental results, the filtration efficiency for 0.3μm cannot meet practical needs. For example, in the case of lead smoke, the main components of lead and its compounds are aerosols of 0.1μm-0.3μm, with a concentration of 50-100mg / m³. The qualified emission standard for regenerated lead is 500μg / m³. This filtration efficiency cannot consistently meet the standard, thus defeating the purpose of using hollow fiber membranes. Summary of the Invention

[0005] The inventors believe that the axial stretching method for producing PTFE hollow fiber membranes, due to their inherent water resistance, oil resistance, high-temperature resistance, and corrosion resistance, has the potential and feasibility for treating heavily polluted flue gas. The poor interception performance for small-diameter particles is due to defects in the pore design, which can be improved. The technical approach to finding a suitable pore shape for effectively intercepting 0.1-0.3μm microparticles lies in precisely controlling factors such as the pushing ratio, pushing speed, pushing pressure, stretching rate, stretching ratio, sintering time, and sintering temperature. Through numerous experiments, the optimal combination of these key parameters can be found through various permutations and combinations. While this appears to be a linear process, the reality is not so simple. As the membrane fibers are continuously thinned and the island ridges shrink to their limit, the supporting force of the membrane fibers weakens, and the axial stretching process cannot continue. At this point, the original equipment and processes become unusable, and linear experiments can no longer continue. Therefore, the applicant and inventors invested significant resources in developing new equipment and improving experimental conditions to enable the experiments to continue. The reason why such a near-limit pore shape could not be found in the past was because the experimental conditions did not support it, and the unsatisfactory pore shape of the membrane fibers was due to insufficient experimentation. After more than ten years of unremitting efforts, the inventors finally found an optimal combination and invented a pore shape suitable for the efficient interception of high-concentration, fine-particle-size dust in PTFE hollow fiber membranes. PTFE hollow fiber membrane products suitable for the efficient interception of high-concentration, fine-particle-size dust have been mass-produced and successfully tested in large-scale industrial experiments. The purpose of this application is to disclose this pore shape design.

[0006] A PTFE air filter hollow fiber membrane, characterized by the following microscopic pore structure: fibril diameter 0.05-0.3 μm, average fibril diameter 0.2 μm, fiber spacing 0.05-0.3 μm, pore length 20-40 μm, average pore diameter 1-3 μm, average porosity 60-70%, and the membrane pores are linear pores with an average diameter-to-length ratio of 30:0.1; macroscopic structure: membrane fiber diameter 3-5 mm, membrane wall thickness 0.2-0.5 mm; and the following conditions: compression ratio 100-150, stretch ratio 3-10 times, and sintering temperature 250-380 degrees Celsius. Attached Figure Description

[0007] Appendix Figure 1 This is a 5000x electron microscope image of the "PTFE air filter hollow fiber membrane" involved in this invention. Since this is only a partial view of a typical sample, Figure 1 This is not the only structural image in this application.

[0008] Appendix Figure 2This is a typical figure from Xu Huan's doctoral dissertation in December 2021, titled "Structural Regulation of PTFE Fiber Membranes and Research on Their Air Filtration Performance." It shows the general pore structure of axially stretched PTFE hollow fiber membranes and has been downloaded from CNKI (China National Knowledge Infrastructure).

[0009] The most significant difference between the two images is as follows: Figure 1 The diameter of the fibrils is much smaller than Figure 2 The fiber spacing is only Figure 2 One-tenth of that, thus achieving a higher interception rate for even smaller particles; Figure 1 The area of ​​the "island ridge" in the middle is much smaller than Figure 2 It's already close to its limit. Therefore, although Figure 1 The fiber density in the latter is higher, yet the average porosity of both can be similar. The effective filtration area is significantly increased, compensating for the increased air resistance caused by the increased fiber density.

[0010] After more than 10 years of effort, the applicant has developed a complete set of specialized equipment and testing systems. Under conditions of a compression ratio of approximately 100-150, a stretching ratio of 30-10, and a sintering temperature of 250-380 degrees Celsius, the applicant has developed and mass-produced the novel structural membrane fibers described in this application. This design has been verified and realized not only in laboratory tests but also in large-scale industrial engineering experiments. The "Hollow Fiber Membrane Heavy Metal Flue Gas Dust Trace Level Treatment Equipment," based on this design, has been included in the "National Catalogue of Major Environmental Protection Technologies and Equipment Encouraged for Development" (2023 Edition) and (2025 Edition). Typical Case: 1. The lead fume trace treatment device for the 120,000 m³ lead melting furnace at Shaoguan Smelter, according to the test report No. 596 (2025) issued by the South China Institute of Environmental Sciences, Ministry of Ecology and Environment, showed that the instantaneous value of upstream particulate matter was 800 mg / m³, the 15-minute average was 275 mg / m³, and lead and its compounds were 53 mg / m³. Downstream particulate matter was "not detected," and lead and its compounds were 0.3 μg / m³. The treatment efficiency reached 99.9994%, and the chimney outlet concentration was better than the atmospheric background standard of 0.7 μg / m³ for lead and its compounds. It has been operating stably since May 2025.

[0011] 2. The 5000 m³ / h trace dust treatment unit in the lead-zinc ore sintering section of Shaoguan Smelter, initially tested using HJ / T397-2007 standards and a Laoying 3012H flue gas analyzer, had a detection limit of 0.4 mg / m². The test results showed an average upstream dust concentration of 2084.4 mg / m³ and an average outlet dust concentration (mg / m³) of "ND" (not detected). A CW-HAT200 Senavi laser dust meter was then used. In weight mode, PM2.5 showed "0 μm / m³" (detection limit 0.3 μg / m³). In particle counting mode, PM2.5 was "0 particles / L" and PM0.3 was "3969 particles / L". The dust concentration at the chimney outlet was close to that of a Class 100,000 cleanroom, indicating a treatment efficiency of 99.99998%.

[0012] 3. The lead fume trace treatment device in the lead melting furnace of the continuous casting and rolling section of Wengyuan Battery Plant, according to the test report No. 668 (2023) issued by the South China Institute of Environmental Sciences, Ministry of Ecology and Environment, shows that the upstream particulate matter average value over 15 minutes is 13.8-123 mg / m³, lead and its compounds are 6.5-42 mg / m³, and downstream particulate matter is "not detected", while lead and its compounds are 0.3-4.3 μg / m³, with a treatment efficiency of 99.9994%. It has been operating stably since May 2023.

[0013] Practice has shown that reducing the diameter and spacing of the fibrils and increasing the fiber density improves filtration efficiency without increasing air resistance. This is mainly due to three improvements: First, the newly designed structure reduces the area occupied by "islands and ridges" in the microstructure of the membrane fibers, increasing the effective working area of ​​the membrane fibers; second, the pore type used in this design is a linear pore, which has the lowest air resistance under the same interception accuracy conditions; and third, the reduction in the pore size of the membrane fibers already provides sufficient inherent filtration accuracy, eliminating the need for the original "powder cake" filtration principle and thus significantly reducing air resistance.

[0014] In summary, the novel PTFE hollow fiber membrane described in this application will become an important material for treating heavily polluted flue gas, especially heavy metal flue gas, and has extremely broad application prospects.

Claims

1. A PTFE air filter hollow fiber membrane, characterized in that, Microscopic pore structure: fibril diameter 0.05-0.3μm, average fibril diameter 0.2μm, fiber spacing 0.05-0.3μm, pore length 20-40μm, average pore diameter 1-3μm, average porosity 60-70%, membrane pores are linear pores with an average diameter-to-length ratio of 30:0.1; Macroscopic structure: membrane fiber diameter 3-5mm, membrane wall thickness 0.2-0.5mm; its conditions are: push-compression ratio 100-150, stretch ratio 3-10 times, sintering temperature 250-380 degrees Celsius.

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