A method for preparing electrospun-PTFE foam gradient composite filter media

Abstract

This invention belongs to the field of industrial flue gas purification, specifically relating to a method for preparing electrospun-PTFE foam gradient composite filter media. Addressing the problems of low filtration accuracy, high filtration resistance, and weak adaptability to complex flue gas environments in existing industrial flue gas filter materials, this invention provides a preparation method. First, a SiO2 / PI nanofiber layer is prepared using electrospinning, and a PTFE foam layer with a gradient structure is coated onto it using a doctor blade. Finally, basalt needle-punched felt, a PTFE hot-melt adhesive film, and a SiO2 / PI nanofiber membrane coated with a PTFE foam coating are stacked and hot-pressed together. The industrial flue gas filter material prepared by this invention combines high-efficiency filtration with excellent acid resistance, showing broad application prospects in the field of industrial flue gas purification.

Description

Technical Field

[0001] This invention belongs to the field of industrial flue gas purification, specifically relating to a method for preparing electrospun-PTFE foam gradient composite filter media. Background Technology

[0002] In recent years, industrial flue gas filtration technology has received continuous attention due to its ability to effectively intercept particulate matter at the emission source. Therefore, developing industrial flue gas filter materials that are simple to manufacture, structurally diverse, have stable physicochemical properties, and are low-cost is particularly necessary for solving air pollution problems.

[0003] Currently, electrospun nanofibers possess characteristics such as small diameter, high specific surface area, small pore size, high porosity, and uniform fiber distribution, enabling them to effectively capture minute particles and achieve highly efficient filtration. Polyimide, a polymer material with imide rings, exhibits high strength, high modulus, and excellent thermal stability, making it an ideal high-temperature resistant material widely used in high-temperature filtration. Coating composite technology can significantly enhance and expand the functional properties of materials, finding wide application in aerospace, automotive, and other fields, and has been gradually introduced into the field of filtration materials in recent years. Among these, PTFE foam coating technology, due to its ability to impart 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 process where PTFE emulsion, foaming agent, flame retardant, dispersant, etc., are mixed and stirred, then compressed and foamed to obtain a PTFE foam coating agent. The resulting PTFE / aramid composite needle-punched material exhibits a reduced average pore size, improved filtration performance, and good temperature resistance, acid and alkali corrosion resistance, and wear resistance. However, this single PTFE foam coating is prone to peeling off due to dust friction, making it difficult to meet the filtration requirements in complex environments.

[0004] Building upon this foundation, this patent, through a multi-layered structural design, achieves superior filtration efficiency and lower filtration resistance while overcoming the limitations of traditional materials and single electrospun nanofiber membranes in handling complex flue gas environments (such as high temperature and high corrosion). Furthermore, optimized manufacturing processes reduce costs and improve production efficiency, while ensuring uniform material dispersion and chemical stability, providing a practical solution for the large-scale production and application of industrial flue gas filtration materials. Summary of the Invention

[0005] This invention provides a method for preparing electrospun PTFE foam gradient composite filter media. First, a SiO2 / PI nanofiber membrane is prepared by electrospinning. Then, a foam coating agent, primarily composed of PTFE emulsion, is coated in three layers onto the SiO2 / PI nanofiber membrane using a layered coating method. After drying, a gradient PTFE foam coating membrane is formed on top. Finally, basalt needle-punched felt, a PTFE hot-melt adhesive membrane, and the SiO2 / PI nanofiber membrane coated with the gradient PTFE foam coating membrane are stacked sequentially, with the SiO2 / PI nanofiber membrane side facing the PTFE hot-melt adhesive membrane side. The composite filter media is then formed by hot pressing. The specific preparation method includes the following steps:

[0006] (1) Preparation of SiO2 / PI nanofiber membrane: DMAC solvent was heated to 50-60℃, and PI resin was slowly added. After stirring thoroughly, PTFE dispersion was slowly poured in. After stirring thoroughly, nano SiO2 powder was added and ultrasonic treatment was performed to obtain spinning solution. The spinning solution was spun into SiO2 / PI nanofiber membrane using electrospinning technology.

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

[0008] (3) Hot pressing bonding: Immerse the basalt needle-punched 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 to dry. Then, stack the basalt needle-punched felt, PTFE hot melt adhesive film and SiO2 / PI nanofiber film coated with gradient PTFE foam coating film in sequence, with the SiO2 / PI nanofiber film side facing the PTFE hot melt adhesive film side. The three-layer materials are tightly composited by hot pressing bonding.

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

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

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

[0012] Preferably, in step (2), the spacing between the scrapers used for coating 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 30-60s, and the pressure is 0.5-0.8MPa.

[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: The filter media adopts a three-layer gradient composite structure, consisting of a surface gradient PTFE foam coating membrane for pre-filtration, a middle layer of SiO2 / PI nanofiber membrane for fine filtration and interception, and a bottom layer of basalt needle-punched felt for support. This structure enables the filter media to achieve a hierarchical distribution of pore size from coarse to fine, thereby intercepting particles of different sizes step by step and significantly improving the filter media's capture efficiency for fine 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 bottom 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 media maintains good acid corrosion resistance in acidic and other corrosive environments.

[0019] Cost-effectiveness: By optimizing the preparation process, the cost of production is reduced while ensuring the performance of the filter material, which provides favorable conditions for the large-scale production of industrial flue gas filter materials. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of electrospun PTFE foam gradient composite filter media. Detailed Implementation

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

[0022] Example 1

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

[0024] (1) Preparation of SiO2 / PI nanofiber membrane: DMAC solvent was heated to 50°C, and PI resin was slowly added. After stirring thoroughly, PTFE dispersion was slowly poured in. After stirring thoroughly, nano SiO2 powder was added and ultrasonically treated for 30 min to obtain spinning solution. The spinning solution was spun into SiO2 / PI nanofiber membrane using electrospinning technology.

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

[0026] (3) Hot pressing bonding: The basalt needle-punched felt is immersed in KH-560 ethanol solution for 10 min, taken out and placed in an 80℃ oven to dry. Then, the basalt needle-punched felt, PTFE hot melt adhesive film and SiO2 / PI nanofiber film coated with gradient PTFE foam coating film are stacked in sequence, with the SiO2 / PI nanofiber film side facing the PTFE hot melt adhesive film side. The three-layer material is tightly composited by hot pressing bonding.

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

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

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

[0030] Preferably, in step (2), the spacing between the scrapers used for coating 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 30s, and the pressure is 0.8MPa.

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

[0033] Example 2

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

[0035] (1) Preparation of SiO2 / PI nanofiber membrane: DMAC solvent was heated to 60°C, and PI resin was slowly added. After stirring thoroughly, PTFE dispersion was slowly poured in. After stirring thoroughly, nano SiO2 powder was added and ultrasonic treatment was performed for 30 minutes to obtain spinning solution. The spinning solution was spun into SiO2 / PI nanofiber membrane using electrospinning technology.

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

[0037] (3) Hot pressing bonding: The basalt needle-punched felt is immersed in KH-560 ethanol solution for 5 minutes, then removed and placed in an oven at 100℃ to dry. Then, the basalt needle-punched felt, PTFE hot melt adhesive film and SiO2 / PI nanofiber film coated with gradient PTFE foam coating film are stacked in sequence, with the SiO2 / PI nanofiber film side facing the PTFE hot melt adhesive film side. The three-layer material is tightly composited by hot pressing bonding.

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

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

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

[0041] Preferably, in step (2), the spacing between the scrapers used for coating 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 30s, and the pressure is 0.75MPa.

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

[0044] Example 3

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

[0046] Preparation of PTFE foam coating film: 13% solvent was added to PTFE emulsion to prepare foam coating agent. The foam coating agent was coated on basalt needle-punched felt in three layers by a doctor blade coating method. The foaming ratio of each layer of 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℃ for 5 minutes. Finally, a gradient structure PTFE foam coating film was formed on basalt needle-punched felt.

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

[0048] Preferably, in the above steps, the blade spacing for the coating process is 0.7 mm, and the coating speed is set to 1 m / min.

[0049] Example 4

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

[0051] (1) Preparation of SiO2 / PI nanofiber membrane: DMAC solvent was heated to 50°C, and PI resin was slowly added. After stirring thoroughly, PTFE dispersion was slowly poured in. After stirring thoroughly, nano SiO2 powder was added and ultrasonic treatment was performed for 30 minutes to obtain spinning solution. The spinning solution was spun into SiO2 / PI nanofiber membrane using electrospinning technology.

[0052] (2) Hot pressing bonding: The basalt needle-punched felt is immersed in KH-560 ethanol solution for 5 minutes, then removed and placed in a 100℃ oven to dry. Then, the basalt needle-punched felt, PTFE hot melt adhesive film and SiO2 / PI nanofiber film are stacked in sequence and hot pressing bonding is used to achieve a tight composite of the two materials.

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

[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 60s, and the pressure is 0.5MPa.

[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]

[0060] The results above show that, compared with Example 3 without the intermediate SiO2 / PI hybrid nanofiber and Example 4 without the PTFE foam layer, Examples 1 and 2 have significantly improved filtration efficiency for 0.5μm particles, and the pressure drop is controlled within 116-143Pa. The quality loss due to acid corrosion is reduced, showing good application prospects.

[0061] 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 can make various specific changes according to different practical needs without departing from the scope and spirit of the present invention, but such changes still fall within the scope of protection of this application.

Claims

1. A method for preparing electrospun-PTFE foam gradient composite filter media, characterized in that, Includes the following steps: S1. Heat the DMAC solvent to 50-60°C, then slowly add PI resin, stir thoroughly, and then slowly pour in the PTFE dispersion. After stirring thoroughly, add nano-SiO2 powder and perform ultrasonic treatment to obtain a spinning solution. Use electrospinning technology to spin the spinning solution into a SiO2 / PI nanofiber membrane. The spinning solution contains 65-70% DMAC solvent, 15-20% PI resin, 10-12% PTFE dispersion with a solid content of 45-60 wt%, and 3-5% nano-SiO2 powder. S2. A foam coating agent is prepared by adding 12-15% solvent to the PTFE emulsion. The foam coating agent is then coated onto the SiO2 / PI nanofiber membrane in three layers using a doctor blade coating method. The expansion ratio of each layer of the foam coating agent is 3 times, 5 times, and 8 times respectively. After each layer is coated, it is dried in an oven at 150-180°C for 5-8 minutes. Finally, a gradient PTFE foam coating film is formed on the SiO2 / PI nanofiber membrane. The foam coating agent contains 85-88% PTFE emulsion with a solid content of 50-60 wt%, 5-8% ammonium bicarbonate, 4-6% polyethylene glycol, and 1-3% silicon carbide whiskers. S3. Immerse the basalt needle-punched felt in KH-560 ethanol solution for 5-10 minutes, remove it and dry it in an oven at 80-100℃. Then, stack the basalt needle-punched felt, PTFE hot melt adhesive film and SiO2 / PI nanofiber film coated with gradient PTFE foam coating film in sequence, with the SiO2 / PI nanofiber film side facing the PTFE hot melt adhesive film side. The three-layer material is tightly composited by hot pressing.

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

3. The preparation method according to claim 1, characterized in that, In S2, the blade spacing is 0.5–0.7 mm, and the coating speed is 0.5–1 m / min.

4. The preparation method according to claim 1, characterized in that, The hot-pressing temperature in S3 is 200-260℃, the hot-pressing time is 30-60s, and the pressure is 0.5-0.8MPa.

5. 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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