Preparation of polytetrafluoroethylene catalytic filter based on supercritical CO2 fluid and preparation and application thereof

Abstract

The application discloses a kind of based on supercritical CO2 Fluid preparation polytetrafluoroethylene catalytic filter material and its preparation and application, the method comprises: PTFE needle felt is immersed in anhydrous ethanol, catalyst is added, after ultrasonic immersion or vacuum filtration, it is dried, to obtain catalytic filter material, or coating foam layer on catalytic filter material is dried, baked, to obtain the catalytic filter material containing coating;Catalytic filter material is treated by supercritical CO2 Fluid or supercritical CO2 Microemulsion, after ending, pressure relief obtains the polytetrafluoroethylene catalytic filter material based on supercritical CO2 Fluid;The temperature of supercritical CO2 Fluid is 50-150 DEG C, pressure is 8-35MPa.The application solves the problem that existing catalyst is not combined firmly with PTFE filter material and catalyst active site is easily covered, improves the combination firmness of catalyst and filter material by supercritical CO2 Fluid, exposes covered active site, and improves the activity of PTFE catalytic filter material.

Description

Technical Field

[0001] This invention relates to a polytetrafluoroethylene (PTFE) catalytic filter material, specifically to a method for preparing PTFE catalytic filter material based on supercritical CO2 fluid, and its preparation and application. Background Technology

[0002] Waste incineration is the primary method of municipal solid waste treatment, accounting for over 60% of total waste volume in 2020. Analysis of pollutant emissions from waste incineration reveals dioxins as the most significant pollutant exceeding emission standards. As a typical volatile organic compound (VOC), dioxins are widely recognized by environmental scientists due to their persistent toxicity and difficulty in biodegradation. Therefore, reducing or eliminating dioxin emissions is an urgent problem to solve. Using catalysts to degrade dioxins into carbon dioxide, hydrogen chloride, and water through redox reactions is the most effective and promising method, characterized by low energy consumption, high efficiency, and minimal secondary pollution. The catalyst primarily utilizes the filter bags in baghouse dust collectors as a carrier, degrading dioxins by loading the filter bags. Pure polytetrafluoroethylene (PTFE) membrane filter media offers superior chemical corrosion resistance and tensile strength, making it more suitable as filter bags. Furthermore, considering the unique operating conditions of municipal solid waste incineration, the Technical Guidelines for Fluidized Bed Incineration Engineering of Municipal Solid Waste (RISN-TG016-2014) explicitly recommends prioritizing the use of pure PTFE filter bags. Therefore, using pure PTFE filter media to support catalysts to prepare catalytic filter media is the best choice for removing dioxins from gaseous substances generated by waste incineration.

[0003] The main methods for preparing catalytic filter media include ultrasonic impregnation, vacuum filtration, redox precipitation, and in-situ polymerization. However, catalytic filter media prepared by vacuum filtration and ultrasonic impregnation only physically deposit the catalyst on the surface of the filter media, making it difficult for the catalyst to penetrate the interior and resulting in poor adhesion, leading to easy catalyst detachment. Existing technologies typically cover the surface with a PTFE foam coating to prevent catalyst detachment, but this method causes uneven catalyst loading and coverage of catalyst active sites. The redox method directly places the filter media into the catalyst reaction solution, allowing the generated catalyst to be loaded onto the filter media in situ. In-situ polymerization, based on redox, wraps a negatively charged layer around the surface of the filter media fibers, providing anchor points for the redox precipitation of the catalyst. However, both redox and in-situ polymerization methods suffer from long reaction processes and the use of organic solvents, and these two methods are only used for preparing polyphenylene sulfide catalytic filter media. Furthermore, existing technologies prepare PTFE catalytic filter media by mixing PTFE powder with catalyst powder and then processing it through extrusion, calendering, sintering, and fiber opening. However, this method significantly affects the performance of the prepared PTFE fibers, and most of the catalyst is located inside the fibers, thus failing to effectively degrade dioxins. Therefore, improving the bonding strength between the catalyst and the PTFE filter media and increasing the active sites of the catalyst are of great significance for the industrial application of PTFE catalytic filter media. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing polytetrafluoroethylene (PTFE) catalytic filter media based on supercritical CO2 fluid, and its preparation and application, which solves the problems of weak bonding between the catalyst and PTFE filter media and easy coverage of the active sites of the catalyst by coating in the prior art.

[0005] To achieve the above objectives, the present invention provides a method for preparing polytetrafluoroethylene catalytic filter media based on supercritical CO2 fluid. For polytetrafluoroethylene filter media with catalyst on the surface obtained by loading a catalyst on the surface of polytetrafluoroethylene needle-punched felt, or for catalytic filter media with a coating obtained by coating a foam layer on the surface of polytetrafluoroethylene filter media with catalyst on the surface, the two types of filter media are treated by the following two methods respectively.

[0006] For polytetrafluoroethylene filter media with catalysts on its surface, the following steps are included:

[0007] Supercritical CO2 fluid is used to treat the catalytic filter media so that the catalyst distributed on the surface of the polytetrafluoroethylene needle-punched felt is embedded between the fibers inside the polytetrafluoroethylene filter media.

[0008] Supercritical CO2 fluid is used because CO2 can be transformed into a fluid at 31.1℃ and 7.37MPa or higher, while other supercritical fluids require higher temperatures and pressures and have higher energy consumption. Furthermore, other supercritical fluids do not have the solubility of supercritical CO2 fluid for many small molecules, and supercritical CO2 fluid is suitable for industrial production.

[0009] For catalytic filter media containing a foam layer, the following steps are included:

[0010] The supercritical CO2 microemulsion with a dynamic-to-static circulation ratio of 1:(3-15) is used to treat the catalytic filter material with a foam layer obtained in step (1), so that the catalyst distributed on the surface of the polytetrafluoroethylene needle-punched felt is embedded between the fibers inside the catalytic filter material with the foam layer. At the same time, the water-soluble components in the coating are extracted by the microemulsion, so that the part of the catalyst covered by the coating is exposed, and the number of catalytic active sites increases. The mixed solution of the microemulsion is sodium di(2-ethylhexyl) succinate sulfonate (AOT)-ethanol solution (AOT is non-toxic and low in cost, which is suitable for industrial production).

[0011] Preferably, in the steps involving polytetrafluoroethylene filter media with a catalyst on its surface and catalytic filter media with a foam layer, the temperature of the supercritical CO2 fluid is 50–150°C, the pressure is 8–35 MPa, and the treatment time is 0.52 h. The temperature and pressure of the supercritical CO2 fluid cause differences in the thermal motion and density of CO2 molecules, resulting in different degrees to which the catalyst is embedded into the filter media fibers.

[0012] Preferably, in the step of using catalytic filter media containing a foam layer, the concentration of sodium di(2-ethylhexyl) succinate sulfonate in the sodium di(2-ethylhexyl) succinate sulfonate-ethanol solution is 0.02-0.15 mol / L, and the mass fraction of ethanol is 1570%.

[0013] Preferably, the step of loading the catalyst onto the surface of the polytetrafluoroethylene needle-punched felt is as follows: immersing the polytetrafluoroethylene needle-punched felt in anhydrous ethanol, adding the catalyst, and then drying it after ultrasonic impregnation or vacuum filtration to obtain a polytetrafluoroethylene filter material with the catalyst on its surface.

[0014] More preferably, the drying temperature after ultrasonic impregnation or vacuum filtration is 80-120℃ and the time is 416h; the catalyst is selected from any one or more of V2O5-WO3-TiO2, MnO2, Ce2O3-CeO2-CuO-MnO2, MnCeO3, CoCrO2, MnO2-Fe2O3-CeO2-CeO2O2, MnO3-WO5-CeO2, and MnCeCoO2.

[0015] More preferably, the mass ratio of the catalyst to the polytetrafluoroethylene needled felt is 1:(0.56).

[0016] Preferably, the step of coating a foam layer on the surface of the PTFE filter material containing the catalyst is as follows: uniformly coating the surface of the PTFE filter material containing the catalyst with a foam finishing liquid, drying at 105°C and calcining at 240°C to obtain a catalytic filter material with a coating; wherein the foam finishing liquid is a mixture of PTFE concentrated dispersion, stabilizer and foaming agent.

[0017] More preferably, in the step of the catalytic filter material containing a foam layer, the mass ratio of the polytetrafluoroethylene concentrated dispersion, the stabilizer and the foaming agent is 1:16:1; the stabilizer is hydroxyethyl cellulose or hydroxypropyl cellulose, and the foaming agent is any one of alkyl glycoside, sodium dodecyl sulfate and sodium fatty alcohol polyoxyethylene ether sulfate foaming agent with a concentration of 6-12 g / L.

[0018] The present invention provides a polytetrafluoroethylene catalytic filter material prepared by the method described above.

[0019] This invention provides an application of the polytetrafluoroethylene catalytic filter material as described above in the degradation of dioxins.

[0020] The present invention relates to the preparation and application of polytetrafluoroethylene (PTFE) catalytic filter media based on supercritical CO2 fluid, which solves the problems of weak bonding between the catalyst and PTFE filter media and easy coverage of the active sites of the catalyst by coating in the prior art, and has the following advantages:

[0021] 1. This invention utilizes the high-pressure permeation effect of supercritical CO2 fluid technology to embed the catalyst, which is only distributed on the surface of PTFE needle-punched felt, into the fibers inside the PTFE filter material, thereby improving the bonding strength between the catalyst and the filter material.

[0022] 2. This invention utilizes supercritical CO2 microemulsion extraction to remove water-soluble stabilizers and foaming agents (the stabilizers are hydroxyethyl cellulose or hydroxypropyl cellulose, and the foaming agents are alkyl glycosides, sodium dodecyl sulfate, or sodium fatty alcohol polyoxyethylene ether sulfate, all of which are soluble in water) from the surface coating of PTFE catalytic filter media, thereby exposing the covered catalytic active sites and improving the activity of the PTFE catalytic filter media. Detailed Implementation

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1

[0025] A method for preparing polytetrafluoroethylene catalytic filter media based on supercritical CO2 fluid, the method comprising:

[0026] (1) 72g of pure PTFE needle-punched felt (purchased from Jiangsu Dongfang Filter Bag Co., Ltd.) was immersed in 10L of anhydrous ethanol, 14.4g of catalyst V2O5-WO3-TiO2 was added, ultrasonically impregnated for 4h, and then dried at 105℃ for 6h to obtain PTFE filter material with catalyst on the surface.

[0027] (2) Place the 78g PTFE filter material obtained in step (1) into a supercritical CO2 fluid autoclave, introduce supercritical CO2 fluid, and remove the PTFE catalytic filter material after the process is completed. The temperature, pressure and working time of the supercritical CO2 fluid are 60℃, 20MPa and 1h respectively.

[0028] The experimental setup for catalytic degradation of dioxins was used to test PTFE catalytic filter media before and after treatment with supercritical CO2 fluid. The results showed that the overall catalytic activity of the PTFE filter media after treatment with supercritical CO2 fluid was increased by 25% compared with that before treatment.

[0029] Example 2

[0030] A method for preparing polytetrafluoroethylene catalytic filter media based on supercritical CO2 fluid is basically the same as that in Example 1, except that:

[0031] In step (1), 78g of pure PTFE needle-punched felt was immersed in 10L of anhydrous ethanol, 20g of catalyst MnCeO3 was added, and after vacuum filtration, it was dried at 110℃ for 4h to obtain 88g of PTFE filter material with catalyst on the surface.

[0032] In step (2), the temperature, pressure and working time of the supercritical CO2 fluid are 80℃, 24MPa and 1.5h, respectively.

[0033] After undergoing the same treatment as in Example 1, the overall catalytic activity of the PTFE filter media increased by 30%.

[0034] Example 3

[0035] A method for preparing polytetrafluoroethylene catalytic filter media based on supercritical CO2 fluid, for coated catalytic filter media, the method comprising:

[0036] (1) 75g of pure PTFE needle-punched felt was immersed in 10L of anhydrous ethanol, 25g of catalyst CoCrO2 was added, and after vacuum filtration, it was dried at 100℃ for 5h to obtain 88g of PTFE filter material with catalyst on the surface; a PTFE concentrated dispersion (PTFE solid content 60%, purchased from Maya) with a mass ratio of 1:16:1, stabilizer hydroxyethyl cellulose and foaming agent alkyl glycoside were mixed, wherein the concentration of alkyl glycoside (R is C9) was 8g / L and the concentration of hydroxyethyl cellulose was 0.5g / L, and a stable foam finishing solution was obtained by stirring at 100 rpm for 20min in a 40℃ water bath; the foam finishing solution was uniformly coated on the surface of the PTFE filter material with catalyst, dried at 105℃ for 120min and calcined at 240℃ for 30min to obtain PTFE catalytic filter material; a 55% ethanol solution was prepared with water, and then a 0.03mol / L LAOT-ethanol solution was prepared;

[0037] (2) Place the AOT-ethanol solution at the bottom of the supercritical CO2 fluid autoclave, and at the same time tie the PTFE catalytic filter material to the yarn frame and place it in the autoclave, with no contact between the AOT-ethanol solution and the PTFE catalytic filter material; the temperature, pressure, time and dynamic-static circulation ratio of the supercritical CO2 fluid introduced are 90℃, 18MPa, 1h and 1min:5min, respectively; the dynamic-static circulation ratio is the ratio of the time the supercritical fluid is circulated by the circulation pump to the time the circulation pump stops running.

[0038] The experimental setup for catalytic degradation of dioxins was used to test PTFE catalytic filter media before and after treatment with supercritical CO2 fluid. The results showed that the overall catalytic activity of the PTFE filter media after treatment with supercritical CO2 fluid was increased by 40% compared with that before treatment.

[0039] Example 4

[0040] A method for preparing polytetrafluoroethylene catalytic filter media based on supercritical CO2 fluid is basically the same as that in Example 3, except that:

[0041] In step (1), 68g of the prepared pure PTFE needle-punched felt was immersed in 10L of anhydrous ethanol, and 23g of catalyst MnO3-WO5-CeO2 was added. After ultrasonic impregnation for 3h, it was dried at 115℃ for 6h to obtain 78g of PTFE filter material with catalyst on the surface. A PTFE concentrated dispersion, stabilizer hydroxypropyl cellulose, and foaming agent sodium dodecyl sulfate were mixed in a mass ratio of 1:16:1, wherein the concentration of sodium dodecyl sulfate was 10g / L and the concentration of hydroxypropyl cellulose was 0.5g / L. The mixture was stirred at 150 rpm for 30min in a 40℃ water bath to obtain a stable foam finishing solution. The foam finishing solution was uniformly coated on the surface of the PTFE filter material with catalyst, and dried at 105℃ for 110min and calcined at 240℃ for 25min to obtain PTFE catalytic filter material. A 45% ethanol solution was prepared with water, and then a 0.06mol / L LAOT-ethanol solution was prepared.

[0042] In step (2), supercritical CO2 fluid is introduced, with fluid temperature, pressure, time, and dynamic-static circulation ratio of 100℃, 24MPa, 1.5h, and 1min:10min, respectively.

[0043] After undergoing the same treatment as in Example 3, the overall catalytic activity of the PTFE filter media increased by 45%.

[0044] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A method for producing a polytetrafluoroethylene catalytic filter material based on supercritical CO2 fluid, characterized by, The catalyst-containing polytetrafluoroethylene filter material is coated with a foam layer to obtain a coated catalyst filter material, which is treated by the following method: The catalyst-containing polytetrafluoroethylene filter material is treated by a supercritical CO2 microemulsion with a dynamic-static circulation ratio of 1: (3-15) to embed the catalyst on the surface of the polytetrafluoroethylene needle felt into the fibers inside the filter material, and the water-soluble components in the coating are extracted by the microemulsion to expose the catalyst covered by the coating; The mixed solution of the microemulsion is a sodium di(2-ethylhexyl) sulfosuccinate-ethanol solution; The dynamic-static circulation ratio is the ratio of the time during which the circulation pump circulates the supercritical fluid to the time during which the circulation pump is stopped; The concentration of sodium di(2-ethylhexyl) sulfosuccinate in the sodium di(2-ethylhexyl) sulfosuccinate-ethanol solution is 0.02-0.15 mol / L, and the mass fraction of ethanol is 15-70 %.

2. The method of claim 1, wherein, The temperature of the supercritical CO2 microemulsion is 50-150 ℃, the pressure is 8-35 MPa, and the treatment time is 0.5-2 h.

3. The method of claim 1, wherein, The preparation steps of the catalyst on the surface of the polytetrafluoroethylene needle felt are as follows: the polytetrafluoroethylene needle felt is immersed in anhydrous ethanol, the catalyst is added, and then the ultrasonic immersion or vacuum filtration is performed, followed by drying.

4. The method of claim 3, wherein, The temperature of the drying after the ultrasonic immersion or vacuum filtration is 80-120 ℃, and the time is 4-16 h.

5. The method of claim 4, wherein, The mass ratio of the catalyst to the polytetrafluoroethylene needle felt is 1: (0.5-6).

6. The method of claim 1, wherein, The step of coating the surface of the catalyst-containing polytetrafluoroethylene filter material with a foam layer is as follows: the foam finishing liquid is uniformly coated on the surface of the catalyst-containing polytetrafluoroethylene filter material, and then dried at 105 ℃ and calcined at 240 ℃ to obtain the coated catalyst filter material; wherein the foam finishing liquid is a mixed solution of polytetrafluoroethylene concentrated dispersion, stabilizer and foaming agent.

7. The method of claim 6, wherein, The mass ratio of the polytetrafluoroethylene concentrated dispersion, stabilizer and foaming agent is 1:16:1; the stabilizer is hydroxyethyl cellulose or hydroxypropyl cellulose; and the foaming agent is any one of alkyl glycoside, sodium dodecyl sulfate and sodium fatty alcohol polyoxyethylene ether sulfate foaming agent, wherein the concentration of alkyl glycoside, sodium dodecyl sulfate and sodium fatty alcohol polyoxyethylene ether sulfate foaming agent is 6-12 g / L.

8. A polytetrafluoroethylene catalyst filter material prepared by the method of any one of claims 1-6.

9. The use of the polytetrafluoroethylene catalyst filter material of claim 8 in the degradation of dioxins.