Preparation method of composite filter material based on electrostatic spinning-PTFE foam gradient

Abstract

The invention belongs to the field of industrial flue gas purification, and particularly relates to a preparation method of a composite filter material based on electrostatic spinning-PTFE foam gradient. The preparation method is provided for solving the problems that an existing industrial flue gas filtering material is not high in filtering precision, large in filtering resistance, poor in adaptability in a complex flue gas environment and the like. The preparation method comprises the following steps: firstly, preparing a SiO2 / PI nanofiber layer by using an electrostatic spinning method, coating the SiO2 / PI nanofiber layer with a scraper to form a PTFE foam layer with a gradient structure, and finally, stacking, hot-pressing and compounding a basalt needled felt, a PTFE hot melt adhesive film and a SiO2 / PI nanofiber film coated with a PTFE foam coating film. The industrial flue gas filtering material prepared by the invention has high filtering efficiency and excellent acid resistance, and has a wide application prospect in the field of industrial flue gas purification.

Description

Technical Field

[0001] The invention belongs to the field of industrial flue gas purification, and particularly relates to a method for preparing a gradient composite filter material based on electrospinning-PTFE foam. Background Art

[0002] Air pollutants are complex, primarily consisting of harmful gases and fine particles with a diameter of less than 2.5 μm, which can remain suspended in the air for extended periods. This not only reduces urban visibility and air quality, causing smog, but also, when inhaled, can cause a variety of diseases, including pneumoconiosis, bronchitis, and lung cancer, resulting in irreversible damage to both human health and the ecological environment. In recent years, industrial flue gas filtration technology has garnered significant attention due to its ability to effectively capture particulate matter at the source of emissions. Therefore, developing industrial flue gas filtration materials with simple processes, diverse structures, stable physical and chemical properties, and low cost is crucial to addressing air pollution.

[0003] Currently, electrospun nanofibers feature small diameter, high specific surface area, small pore size, high porosity, and uniform fiber distribution. They are highly effective at capturing tiny particles, achieving efficient filtration. Polyimide, a polymer material containing imide rings, exhibits high strength, high modulus, and excellent thermal stability, making it an ideal high-temperature-resistant material and widely used in high-temperature filtration. Coating composite technology can significantly enhance and expand the functional properties of materials, and is widely used in aviation, automotive, and other fields. In recent years, it has been gradually introduced into the filter material field. PTFE foam coating technology, which imparts excellent filtration performance and chemical stability, has been applied to high-temperature and ultra-high-temperature industrial flue gas filtration. For example, Chinese patent CN201910979064 describes a PTFE foam coating obtained by mixing and stirring a PTFE emulsion, a foaming agent, a flame retardant, and a dispersant, followed by compression and foaming. The resulting PTFE / aramid composite needle-punched product has a reduced average pore size, improved filtration performance, and excellent heat resistance, acid and alkali corrosion resistance, and abrasion resistance. However, this single PTFE foam coating is easily detached due to dust friction, making it difficult to meet filtering requirements in complex environments.

[0004] On this basis, this patented multi-layered structure achieves superior filtration efficiency and lower filtration resistance, while also addressing the limitations of traditional materials and single electrospun nanofiber membranes in complex flue gas environments (such as high temperatures and high corrosion). Furthermore, through an optimized preparation process, this technology reduces costs and improves production efficiency, while ensuring uniform dispersion and chemical stability of the material. This provides a practical solution for the large-scale production and application of industrial flue gas filtration materials. Summary of the Invention

[0005] The present invention provides a method for preparing a gradient composite filter material based on electrospinning-PTFE foam. First, a SiO2 / PI nanofiber membrane is prepared by electrospinning, and then a foam coating agent mainly composed of PTFE emulsion is coated on the SiO2 / PI nanofiber membrane in three layers by a layered coating method. After drying, a gradient PTFE foam coating film is formed thereon. Finally, basalt needle felt, PTFE hot melt adhesive film, and SiO2 / PI nanofiber membrane coated with a gradient PTFE foam coating film are stacked in sequence, with the SiO2 / PI nanofiber membrane side facing the PTFE hot melt adhesive film side, and hot pressed to form a composite filter material. The specific preparation method comprises the following steps:

[0006] (1) Preparation of SiO2 / PI nanofiber membrane: Heat the DMAC solvent to 50-60°C, then slowly add PI resin, stir thoroughly and then slowly pour in PTFE dispersion, stir thoroughly and then add nano-SiO2 powder, and perform ultrasonic treatment to obtain spinning solution, which is then spun into SiO2 / PI nanofiber membrane using electrospinning technology.

[0007] (2) Preparation of PTFE foam coating membrane: 12-15% solvent was added to PTFE emulsion to prepare foam coating agent, and the foam coating agent was coated on SiO2 / PI nanofiber membrane in three layers by scraper coating method. The foaming ratio of each layer of foam coating agent was 3 times, 5 times and 8 times respectively, and each layer was dried in an oven at 150-180°C for 5-8 minutes after coating, and finally a PTFE foam coating membrane with a gradient structure from fine pores to coarse pores was formed on SiO2 / PI nanofiber membrane.

[0008] (3) Hot pressing bonding: Immerse the basalt needle felt in KH-560 ethanol solution for 5 to 10 minutes, take it out and place it in an oven at 80 to 100 °C for drying. Then, stack the basalt needle felt, PTFE hot melt adhesive film and SiO2 / PI nanofiber membrane coated with gradient PTFE foam coating film in sequence, with the SiO2 / PI nanofiber membrane side facing the PTFE hot melt adhesive film side. The three layers of materials are tightly compounded by hot pressing bonding.

[0009] Preferably, the process parameters of the electrospinning technology in step (1) are a voltage of 18 to 25 kV, a spinning speed of 0.8 to 1.5 mL / h, a humidity of 40 to 60%, and a receiving distance of 15 to 20 cm.

[0010] Preferably, the spinning solution in step (1) contains 65-70% of a DMAC solvent having a viscosity of 0.92 mPa·s, 15-20% of a PI resin, 10-12% of a PTFE dispersion having a solid content of 45-60 wt%, and 3-5% of a nano-SiO2 powder having a particle size of 30 nm.

[0011] Preferably, the foam coating agent in step (2) contains 85-88% of PTFE emulsion with a solid content of 50-60 wt%, 5-8% of ammonium bicarbonate, 4-6% of polyethylene glycol, and 1-3% of silicon carbide whiskers.

[0012] Preferably, the scraper spacing of the scraper coating in step (2) is 0.5 to 0.7 mm, and the coating speed is 0.5 to 1 m / min.

[0013] Preferably, in step (3), the hot pressing temperature is 200-260° C., the hot pressing time is 30-60 s, and the pressure is 0.5-0.8 MPa.

[0014] Preferably, the concentration of the KH-560 ethanol solution in step (3) is 1 to 3 wt%.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] Structural optimization: It adopts a three-layer gradient composite structure with surface gradient PTFE foam coating membrane pre-filtration, middle layer SiO2 / PI nanofiber membrane fine filtration and interception, and bottom layer basalt needle felt support. The filter material pore size is distributed from coarse to fine, which can intercept particles of different particle sizes step by step and significantly improve the filter material's capture efficiency of tiny particles.

[0017] Reasonable control of filtration resistance: The fine-pore to coarse-pore gradient design of the surface gradient PTFE foam coating reduces the initial airflow resistance, the high porosity of the middle layer SiO2 / PI nanofiber membrane reduces the airflow penetration resistance, and the loose structure of the underlying basalt substrate provides a stable channel for airflow. The three work together to ensure high filtration efficiency while keeping the pressure drop at a low level.

[0018] Improved stability: PTFE, PI, basalt, SiO2 and other materials with excellent chemical stability are selected, and a multi-layer composite structure is adopted to ensure that the filter material maintains good acid corrosion resistance in acidic and other corrosive environments.

[0019] Cost-effectiveness: Through optimized preparation technology, the cost consumption in the production process is reduced while ensuring the performance of the filter material, providing favorable conditions for the large-scale production of industrial flue gas filter materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the structure of electrospinning-PTFE foam gradient composite filter material. DETAILED DESCRIPTION

[0021] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the specific implementation of the present invention will be further described below in conjunction with the accompanying drawings and specific implementation examples, but the implementation of the present invention is not limited thereto.

[0022] Example 1

[0023] The specific preparation method comprises the following steps:

[0024] (1) Preparation of SiO2 / PI nanofiber membrane: Heat the DMAC solvent to 50°C, then slowly add PI resin, stir thoroughly and then slowly pour in PTFE dispersion, stir thoroughly and then add nano-SiO2 powder, ultrasonically treat for 30 minutes to obtain spinning solution, and use electrospinning technology to spin the spinning solution into SiO2 / PI nanofiber membrane.

[0025] (2) Preparation of PTFE foam coating membrane: 12% solvent was added to PTFE emulsion to prepare foam coating agent, and the foam coating agent was coated on the SiO2 / PI nanofiber membrane in three layers by scraper coating method. The foaming ratio of each layer of foam coating agent was 3 times, 5 times and 8 times respectively, and each layer was dried in an oven at 150°C for 5 minutes after coating, and finally a PTFE foam coating membrane with a gradient structure was formed on the SiO2 / PI hybrid nanofiber membrane.

[0026] (3) Hot pressing bonding: Immerse the basalt needle felt in KH-560 ethanol solution for 10 minutes, take it out and place it in an 80°C oven for drying. Then, stack the basalt needle felt, PTFE hot melt adhesive film and SiO2 / PI nanofiber membrane coated with gradient PTFE foam coating film in sequence, with the SiO2 / PI nanofiber membrane side facing the PTFE hot melt adhesive film side. The three layers of materials are tightly compounded by hot pressing bonding.

[0027] Preferably, the process parameters of the electrospinning technology in step (1) are a voltage of 25 kV, a spinning speed of 0.8 mL / h, a humidity of 40%, and a receiving distance of 15 cm.

[0028] Preferably, the spinning solution in step (1) contains 70% of a DMAC solvent having a viscosity of 0.92 mPa·s, 15% of a PI resin, 10% of a PTFE dispersion having a solid content of 45 wt%, and 5% of a nano-SiO2 powder having a particle size of 30 nm.

[0029] Preferably, the foam coating agent in step (2) contains 88% of PTFE emulsion with a solid content of 50 wt%, 5% of ammonium bicarbonate, 6% of polyethylene glycol, and 1% of silicon carbide whiskers.

[0030] Preferably, the scraper spacing of the scraper coating in step (2) is 0.5 mm, and the coating speed is set to 0.5 m / min.

[0031] Preferably, in step (3), the hot pressing temperature is 260° C., the hot pressing time is 30 s, and the pressure is 0.8 MPa.

[0032] Preferably, the concentration of the KH-560 ethanol solution in step (3) is 1 wt%.

[0033] Example 2

[0034] The specific preparation method comprises the following steps:

[0035] (1) Preparation of SiO2 / PI nanofiber membrane: Heat the DMAC solvent to 60°C, then slowly add PI resin, stir thoroughly and then slowly pour in PTFE dispersion, stir thoroughly and then add nano-SiO2 powder, perform ultrasonic treatment for 30 minutes to obtain spinning solution, and use electrospinning technology to spin the spinning solution into SiO2 / PI nanofiber membrane.

[0036] (2) Preparation of PTFE foam coating membrane: 15% solvent was added to PTFE emulsion to prepare foam coating agent, and the foam coating agent was coated on the SiO2 / PI nanofiber membrane in three layers by scraper coating method. The foaming ratio of each layer of foam coating agent was 3 times, 5 times and 8 times respectively, and each layer was dried in an oven at 150°C for 5 minutes after coating, and finally a PTFE foam coating membrane with a gradient structure was formed on the SiO2 / PI hybrid nanofiber membrane.

[0037] (3) Hot pressing bonding: Immerse the basalt needle felt in KH-560 ethanol solution for 5 minutes, take it out and place it in a 100°C oven for drying. Then, stack the basalt needle felt, PTFE hot melt adhesive film and SiO2 / PI nanofiber membrane coated with gradient PTFE foam coating film in sequence, with the SiO2 / PI nanofiber membrane side facing the PTFE hot melt adhesive film side. The three layers of materials are tightly compounded by hot pressing bonding.

[0038] Preferably, the process parameters of the electrospinning technology in step (1) are a voltage of 20 kV, a spinning speed of 1.0 mL / h, a humidity of 50%, and a receiving distance of 18 cm.

[0039] Preferably, the spinning solution in step (1) contains 65% of a DMAC solvent having a viscosity of 0.92 mPa·s, 20% of a PI resin, 12% of a PTFE dispersion having a solid content of 45 wt%, and 3% of a nano-SiO2 powder having a particle size of 30 nm.

[0040] Preferably, the foam coating agent in step (2) contains 85% of PTFE emulsion with a solid content of 54 wt%, 8% of ammonium bicarbonate, 4% of polyethylene glycol, and 3% of silicon carbide whiskers.

[0041] Preferably, the blade spacing of the blade coating in step (2) is 0.5 mm, and the coating speed is set to 0.5 m / min.

[0042] Preferably, in step (3), the hot pressing temperature is 260° C., the hot pressing time is 30 s, and the pressure is 0.75 MPa.

[0043] Preferably, the concentration of the KH-560 ethanol solution in step (3) is 1 wt%.

[0044] Example 3

[0045] The specific preparation method comprises the following steps:

[0046] Preparation of PTFE foam coating membrane: 13% solvent was added to PTFE emulsion to prepare a foam coating agent, and the foam coating agent was coated on the basalt needle felt in three layers using a doctor blade coating method. The foaming ratio of each layer of the foam coating agent was 3 times, 5 times, and 8 times, respectively. After each layer was coated, it was dried in an oven at 180°C for 5 minutes, and finally a PTFE foam coating membrane with a gradient structure was formed on the basalt needle felt.

[0047] Preferably, the foam coating agent in the step contains 87% of PTFE emulsion with a solid content of 60 wt%, 6% of ammonium bicarbonate, 5% of polyethylene glycol, and 2% of silicon carbide whiskers.

[0048] Preferably, the blade spacing of the blade coating in the step is 0.7 mm, and the coating speed is set to 1 m / min.

[0049] Example 4

[0050] The specific preparation method comprises the following steps:

[0051] (1) Preparation of SiO2 / PI nanofiber membrane: Heat the DMAC solvent to 50°C, then slowly add PI resin, stir thoroughly and then slowly pour in PTFE dispersion, stir thoroughly and then add nano-SiO2 powder, perform ultrasonic treatment for 30 minutes to obtain spinning solution, and use electrospinning technology to spin the spinning solution into SiO2 / PI nanofiber membrane.

[0052] (2) Hot pressing bonding: Immerse the basalt needle felt in KH-560 ethanol solution for 5 minutes, take it out and place it in a 100°C oven for drying. Then, stack the basalt needle felt, PTFE hot melt adhesive film and SiO2 / PI nanofiber membrane in sequence, and achieve a tight compound of the two layers of materials by hot pressing bonding.

[0053] Preferably, the process parameters of the electrospinning technology in step (1) are a voltage of 18 kV, a spinning speed of 1.5 mL / h, a humidity of 60%, and a receiving distance of 20 cm.

[0054] Preferably, the spinning solution in step (1) contains 17% PI resin, 11% PTFE dispersion with a solid content of 60 wt%, 4% nano-SiO2 powder with a particle size of 30 nm, and 68% DMAC solvent with a viscosity of 0.92 mPa·s.

[0055] Preferably, in step (2), the hot pressing temperature is 200° C., the hot pressing time is 60 s, and the pressure is 0.5 MPa.

[0056] Preferably, the concentration of the KH-560 ethanol solution in step (2) is 3 wt %.

[0057] The filter material prepared by the above method was made into four samples, and the test data of their filtration efficiency, pressure drop and acid corrosion resistance mass loss are shown in Table 1.

[0058] Table 1

[0059] From the above results, it can be seen that compared with Example 3 without the intermediate layer of SiO2 / PI hybrid nanofibers and Example 4 without the PTFE foam layer, Examples 1 and 2 have significantly improved the filtration efficiency of 0.5 μm particles, and the pressure drop is controlled at 116-143 Pa, and the acid corrosion resistance quality loss is reduced, showing good application prospects.

[0060] Although the present invention has been described in detail by way of preferred embodiments, the present invention is not limited thereto. Those skilled in the art may make various specific changes according to different actual needs without departing from the scope and spirit of the present invention, but they still fall within the scope of protection of this application.

Claims

1. A method for preparing a gradient composite filter material based on electrospinning-PTFE foam, characterized in that: The following steps are involved: S1. Heat the DMAC solvent to 50-60°C, then slowly add the PI resin, stir thoroughly and then slowly pour in the PTFE dispersion, stir thoroughly and then add the nano-SiO2 powder, and perform ultrasonic treatment to obtain a spinning solution, which is then spun into a SiO2 / PI nanofiber membrane using electrospinning technology; S2. Add 12-15% of solvent to PTFE emulsion to prepare a foam coating agent, and apply the foam coating agent to the SiO2 / PI nanofiber membrane in three layers by a doctor blade coating method, wherein the foaming ratio of each layer of the foam coating agent is 3 times, 5 times, and 8 times, respectively, and each layer is dried in an oven at 150-180° C. for 5-8 minutes after coating, finally forming a gradient PTFE foam coating film on the SiO2 / PI nanofiber membrane; S3. Immerse the basalt needle felt in KH-560 ethanol solution for 5 to 10 minutes, take it out and place it in an oven at 80 to 100°C for drying, then stack the basalt needle felt, PTFE hot melt adhesive film and SiO2 / PI nanofiber membrane coated with gradient PTFE foam coating film in sequence, with the SiO2 / PI nanofiber membrane side facing the PTFE hot melt adhesive film side, and achieve tight compounding of the three layers of materials through hot pressing.

2. The preparation method according to claim 1, characterized in that The process parameters of the electrospinning technology in S1 are voltage of 18 to 25 kV, spinning speed of 0.8 to 1.5 mL / h, humidity of 40 to 60%, and receiving distance of 15 to 20 cm.

3. The preparation method according to claim 1, characterized in that The spinning solution in S1 contains 65-70% DMAC solvent, 15-20% PI resin, 10-12% PTFE dispersion with a solid content of 45-60wt%, and 3-5% nano-SiO2 powder.

4. The preparation method according to claim 1, characterized in that The foam coating agent in S2 contains 85-88% of PTFE emulsion with a solid content of 50-60wt%, 5-8% of ammonium bicarbonate, 4-6% of polyethylene glycol, and 1-3% of silicon carbide whiskers.

5. The preparation method according to claim 1, characterized in that The scraper spacing in S2 is 0.5-0.7 mm, and the coating speed is 0.5-1 m / min.

6. The preparation method according to claim 1, characterized in that In the step S3 , the hot pressing temperature is 200-260° C., the hot pressing time is 30-60 seconds, and the pressure is 0.5-0.8 MPa.

7. The preparation method according to claim 1, characterized in that The concentration of the KH-560 ethanol solution in S3 is 1-3 wt %.

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