Composite nanofiber filter material for synergistically removing particulate matters and sulfur dioxide and preparation method of composite nanofiber filter material

Abstract

The invention discloses a composite nanofiber filter material for synergistically removing particulate matters and sulfur dioxide and a preparation method of the composite nanofiber filter material, and belongs to the technical field of flue gas purification filter materials. According to the invention, an electrostatic spinning polyimide (PI) nanofiber is used as a substrate, and an amine-functionalized UiO-66-NH2 crystal grows in situ on the surface of the fiber to construct a PI-coated UiO-66-NH2 composite fiber membrane with a core-shell structure. The filter material depends on a surface filtering mechanism of electrostatic spinning nanofibers, and has excellent blowback regeneration performance; the UiO-66-NH2 shell layer can provide abundant Zr-OH defect sites and alkaline amino (NH2) active sites, so that the targeted adsorption and selective removal capability on sulfur dioxide (SO2) is remarkably improved. The prepared composite fiber filter material effectively solves the problems that a traditional fiber filter material is difficult in reverse blowing regeneration, single in function, difficult to synergistically remove particles and SO2 and the like, and can be widely applied to the fields of industrial high-temperature flue gas filtration and deep purification of waste gas.

Description

Technical Field

[0001] This invention belongs to the field of filtration material technology, specifically relating to a composite nanofiber filter material for the synergistic removal of particulate matter and sulfur dioxide, and its preparation method. Background Technology

[0002] Rapid urbanization and industrial expansion have exacerbated global air pollution, with flue gas emitted from high-temperature processes such as coal-fired power plants being a major source of pollution, often containing fine particulate matter (PM2.5). 2.5 A mixture of PM2.5 and sulfur dioxide (SO2). 2.5 SO2 can penetrate deep into the lungs and cause disease, while it damages health and contributes to acid rain. Semi-dry desulfurization is commonly used in small and medium-sized boilers due to its low cost and low water consumption, but its SO2 removal rate is only 70-90%, leaving 150-450 ppm SO2 (approximately 80°C) in the treated flue gas. While baghouse dust collectors can capture particles, their filtration efficiency is limited and the filter bags are prone to clogging. Therefore, how to achieve deep and synergistic purification of SO2 and PM remains a technical challenge, driving research into advanced materials.

[0003] Electrospun nanofibers, due to their high specific surface area and high porosity, have become highly efficient filtration media. Their micropores enable surface filtration and facilitate backflushing regeneration. However, industrial flue gas temperatures are high, placing stringent requirements on the thermal stability of materials. Among existing high-temperature resistant fiber materials, inorganic fiber materials (such as alumina) are heat-resistant but brittle; organic high-temperature resistant fiber materials, such as commonly available commercial PTFE-coated filter media, suffer from problems such as high filtration resistance and poor backflushing regeneration capabilities. Benefiting from its rigid aromatic skeleton and heterocyclic imide units, polyimide (PI) possesses excellent mechanical strength, chemical stability, and heat resistance, making it an ideal material for filtration applications under harsh high-temperature flue gas conditions. Studies have shown that PI nanofibers achieve PM2.5 removal rates exceeding 99.5% over a wide temperature range (e.g., 25-370°C), and even after treatment at 390°C, the PM0.3 filtration efficiency remains at 99.96%. Despite these advantages, polyimide-based filters are primarily designed for particulate matter removal and typically lack the ability to simultaneously capture sulfur dioxide, which limits their application in integrated flue gas purification systems.

[0004] In SO2 removal, porous materials such as activated carbon and zeolites exhibit limited adsorption selectivity or capacity. Metal-organic frameworks (MOFs), due to their tunable pores and chemical tunability, show significant advantages in capturing low-concentration SO2. Among them, zirconium-based MOFs, such as UiO-66, are widely recognized as one of the most practically valuable adsorbents due to their excellent thermal stability and superior chemomechanical properties. Zirconium-based MOFs (such as UiO-66) possess high thermal stability (maintaining structural integrity even at temperatures up to approximately 500°C), ordered structures, and are easily functionalized. They also have readily available precursors and mature large-scale synthesis routes, making them promising candidate materials for the deep removal of low-concentration SO2 from high-temperature industrial flue gas.

[0005] In this study, a bifunctional membrane was designed by combining heat-resistant PI nanofibers with UiO-66-NH2 to simultaneously remove PM and SO2 under high-temperature conditions. PI nanofibers were chosen as the fiber scaffold due to their excellent thermal and mechanical stability, enabling them to withstand the solvothermal conditions required for the in-situ growth of UiO-66. Furthermore, the high specific surface area, high porosity, and interconnected pore network of the nanofiber matrix establish a three-dimensional gas permeation pathway that facilitates mass transport during SO2 adsorption. To further enhance the affinity for acidic SO2 molecules, UiO-66 was functionalized through ligand modification, introducing electron donor amino groups to create basic adsorption sites, which are expected to enhance targeted SO2 binding through acid-base interactions. In addition, the MOF-derived nanotextured surface increases the fiber surface roughness, enhancing particle adhesion and suppressing secondary particle escape during filtration. The membrane's performance in particle filtration and SO2 adsorption was systematically evaluated under conditions relevant to industrial flue gas treatment (including high temperature and repeated adsorption-regeneration cycles) to assess its suitability for complex operating environments.

[0006] This study provides mechanistic insights into the design of integrated nanofiber membranes that combine particulate matter capture with gas adsorption, offering a viable material strategy for advanced and sustainable industrial flue gas purification. Summary of the Invention

[0007] This invention addresses the problems of traditional fiber filter media, such as difficulty in backflushing and regeneration, limited filtration effect, and lack of effective SO2 adsorption function, by providing a composite nanofiber filter material for the synergistic removal of particulate matter and sulfur dioxide, and its preparation method.

[0008] The technical solution adopted by the present invention to achieve its objective is as follows:

[0009] A method for preparing a composite nanofiber filter material for the synergistic removal of particulate matter and sulfur dioxide: First, PI nanofiber substrate is prepared by electrospinning. Then, amine-functionalized UiO-66-NH2 crystals are grown in situ on the fiber surface to construct a core-shell structured PI@UiO-66-NH2 composite membrane. Currently, traditional fiber filter media suffer from problems such as difficult backflushing regeneration, limited filtration efficiency, and lack of effective SO2 adsorption. The proposed material overcomes these shortcomings, possessing excellent particulate matter filtration efficiency and SO2 adsorption performance, while also considering both particulate matter backflushing and SO2 desorption / regeneration effects. This material exhibits a "core-shell" configuration, with a core of high-strength, high-temperature-resistant PI nanofibers and a shell composed of UiO-66-NH2 crystals with high specific surface area and abundant adsorption sites. The specific steps include:

[0010] Step 1: Prepare PAA precursor spinning solution

[0011] PAA precursor spinning solution was prepared by copolymerizing dianhydride monomer BPDA and diamine monomer ODA using DMF as solvent.

[0012] Step 2: Electrospinning process

[0013] The prepared electrospinning precursor solution was injected into a syringe, and the electrospinning parameters were adjusted to obtain PAA nanofiber substrate. The specific parameters are as follows: 16 wt% PAA spinning solution was injected into the syringe, a No. 23 needle was used, the spinning voltage was adjusted to 15 kV, the feed rate was 0.8 mL / h, the receiving distance was 15 cm, and the spinning time was 30-120 min.

[0014] Step 3: Thermal imidization treatment

[0015] PAA nanofiber substrate was heated in a nitrogen atmosphere at a rate of 5 °C / min in the following steps: 100 °C for 2 h, 200 °C for 2 h, and 300 °C for 2 h, and then cooled to room temperature to obtain PI nanofiber substrate.

[0016] Step 4: In-situ growth of UiO-66-NH2

[0017] Zirconium chloride (ZrCl4, 1 mmol), 4-aminoterephthalic acid (BDC-NH2, 1 mmol), and benzoic acid (BZA, 20 mmol) were dissolved in N,N-dimethylformamide (DMF, 60 mL) to form a precursor solution. The PI nanofiber membrane was immersed in this solution and then transferred to a high-pressure reactor with a total volume of 100 mL. The reaction was carried out at 120°C for 2–12 h. After the reaction, the membrane was thoroughly washed three times with DMF and methanol, and then dried under vacuum at 60°C for 12 h to obtain the PI@UiO-66-NH2 composite nanofiber membrane.

[0018] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0019] The PI@UiO-66-NH2 composite nanofiber filter material of this invention has a fine diameter, small pore size, and high porosity. It mainly intercepts particulate matter through a surface filtration mechanism, which can effectively overcome the problem that particulate matter can easily penetrate into the interior of traditional fiber filter materials. It can achieve simple and efficient backflushing regeneration and effectively improve the service life of the filter material.

[0020] The PI@UiO-66-NH2 composite nanofiber filter material of this invention has a fiber surface composed of UiO-66-NH2 crystals with high specific surface area and abundant adsorption sites, which endows the material with the ability to target and adsorb SO2, so that the composite fiber filter material has the dual removal function of particulate matter and SO2.

[0021] The PI@UiO-66-NH2 composite nanofiber filter material of this invention maintains high particulate matter filtration efficiency and SO2 adsorption capacity under high temperature (85℃) flue gas conditions due to the excellent chemical and thermal stability of PI and UiO-66-NH2, and has good adaptability to practical industrial applications.

Claims

1. A method for preparing a composite nanofiber filter material for the synergistic removal of particulate matter and sulfur dioxide, characterized in that, The process includes the following steps: Step 1: Dissolve aromatic dianhydride monomers and aromatic diamine monomers in an organic solvent to carry out a polymerization reaction, and prepare a polyamic acid spinning solution; Step 2: Electrospin the polyamic acid spinning solution to obtain a polyamic acid nanofiber membrane; Step 3: Perform thermal imidization treatment on the polyamic acid nanofiber membrane under an inert atmosphere to obtain a polyimide nanofiber substrate; Step 4: Immerse the polyimide nanofiber substrate in a mixed solution containing a zirconium source, aminophthalic acid ligands, and a regulator for in-situ growth reaction. After the reaction, wash and dry to obtain a composite nanofiber filter material with an amino-based metal-organic framework material loaded on its surface.

2. The preparation method according to claim 1, characterized in that: In step 1, the aromatic dianhydride monomer is 3,3',4,4'-biphenyltetracarboxylic dianhydride, the aromatic diamine monomer is 4,4'-diaminodiphenyl ether, and the organic solvent is N,N-dimethylformamide; in step 3, the inert atmosphere is a nitrogen atmosphere; in step 4, the aminated metal-organic framework material is UiO-66-NH2.

3. The preparation method according to claim 2, characterized in that: In step 4, the zirconium source is zirconium chloride, the aminophthalic acid ligand is 2-aminoterephthalic acid, and the regulator is benzoic acid; the molar ratio of zirconium chloride, 2-aminoterephthalic acid, and benzoic acid is 1:(0.8~1.2):(15~25); the temperature of the in-situ growth reaction is 100°C~150°C, and the time is 2~12 hours.

4. The preparation method according to claim 1, characterized in that: In step 2, the electrospinning process parameters are controlled so that the fiber diameter of the polyamic acid nanofiber membrane after conversion in step 3 is in the range of 100~400 nm and the membrane thickness is in the range of 10~50 μm.

5. A composite nanofiber filter material for the synergistic removal of particulate matter and sulfur dioxide, characterized in that: The filter material comprises a polyimide nanofiber core and an aminated metal-organic framework shell loaded on the surface of the core, forming a core-shell structure; wherein, the fiber diameter of the polyimide nanofiber core is 100~400 nm; the thickness of the aminated metal-organic framework shell is 50~100 nm, and the shell material is UiO-66-NH2 crystal.

6. The composite nanofiber filter material according to claim 5, characterized in that: The filter media has a filtration efficiency of ≥99.5% for particulate matter and a pressure drop ≤200 Pa at the filtration velocity; and / or, the filter media has a dynamic saturated adsorption capacity ≥30 mg g at 25°C and 500 ppm SO2 concentration. -1 .

7. The composite nanofiber filter material according to claim 5, characterized in that: After at least 5 adsorption-desorption cycles, the filter material retains ≥85% of its dynamic adsorption capacity for SO2; and / or, within a temperature range of 55°C to 85°C, the adsorption capacity of the filter material for SO2 remains at more than 60% of its initial adsorption capacity at 25°C.

8. The composite nanofiber filter material according to claim 5, characterized in that: After ten water washing cycles, the pressure drop of the filter media increases by less than 15% of the initial pressure drop, and the total filtration time is greater than 8000 seconds.