Knowledge Management System Of Institute of process engineering,CAS
|Thesis Advisor||杨传芳 ; 李艳香|
|Place of Conferral||北京|
|Keyword||静电纺丝 聚酰亚胺 纳米纤维 复合滤料 Pm2.5|
随着中国经济的发展，工业煤炭、石油等化石能源使用量剧增，导致空气污染问题越来越严重，雾霾天气频发，严重影响了人们的身体健康，同时给人们的正常生活带来诸多不便。众所周知，雾霾的主要成份为PM2.5，主要来源之一是含尘烟气。有效控制PM2.5的排放，减少甚至消除雾霾天气，需要从源头上提高含尘烟气的净化效率。袋式除尘法是含尘烟气净化的主要方法之一，该方法对小颗粒粉尘的过滤效率可达到99.5%以上，已在除尘过滤领域得到了广泛的应用。袋式除尘器的过滤性能主要受滤料的影响，根据过滤理论分析，滤料过滤效率随纤维直径的减少而增加，因此纳米纤维在空气过滤方面的应用越来越多，但将纳米纤维应用于工业高温含尘烟气过滤的相关研究极少。为将纳米纤维应用于工业过滤中，得到耐高温、高效低阻纳米纤维复合滤料，本研究选择静电纺丝技术制备耐高温聚合物-聚酰亚胺纳米纤维，进行了如下研究工作：首先，确定制备聚酰亚胺（P84）纳米纤维的纺丝条件。通过对比不同湿度、温度下纤维制备过程及所得纤维直径分布、纤维形貌等性质，确定了不同湿度条件下所用溶剂。室温条件下，相对湿度＜30%时使用N,N-二甲基甲酰胺（DMF）作为溶剂，相对湿度＞35%时，使用N-甲基吡咯烷酮（NMP）为溶剂。使用DMF作为溶剂，配制不同浓度的纺丝溶液，研究了溶液质量浓度、电导率、粘度、表面张力及溶剂性质对纳米纤维的影响，确定了合适的纺丝液。调节纺丝电压、接收距离、供液速度等加工参数，确定了不同工艺条件对纺丝稳定性及纤维性质的影响。依据以上结果，选择纺丝溶液质量浓度在9%~15%范围内，纺丝正电压8~15 kV，纺丝负电压0~2 kV，供液速度0.08~0.4 mm/min（2.5 ml注射器），接收转辊转速5 m/min，供液装置左右平移速度0.5 m/min，接收距离9~12 cm。其次，制备了三明治结构纳米纤维复合过滤材料。选择以克重260~350 g/m2的芳纶无纺布为基底支撑层，克重40~60 g/m2的耐高温无纺布为保护层。对比不同纤维粘合方法，选择胶粘法作为粘结固体纤维滤料的方法。为有效控制粘合剂使用量，使粘合剂在基底上均匀喷涂，本论文使用静电喷雾的施胶方式将高温粘合剂均匀涂布在基底层上，通过静电纺丝将直径在100~500 nm的可溶性聚酰亚胺（P84）纳米纤维均匀纺制在此基底上，在纳米纤维表面附上保护层，采用热压固化的方法使三层材料紧密结合，得到三明治结构的耐高温纳米纤维复合过滤材料。测试材料粘结强度，发现施胶超过90 min时，复合滤料粘结强度＞1000 kPa，能够满足工业滤布强度要求。测试含不同粘合剂量、纳米纤维量复合滤料的初始过滤阻力、孔径分布等参数，发心粘合剂对基底本身性能影响较小。最后，使用粒径0.3~10 μm的NaCl颗粒模拟气溶胶，通过气溶胶粒径谱仪检测过滤前后不同粒径粒子的分布及粒子数，从而得到不同复合滤料的过滤效率，结果发现，少量的纳米纤维就可以有效提高材料的过滤效率，使2.0 μm以上颗粒过滤效率达100%，1.0 μm-2.0 μm的颗粒过滤效率达到99.5%以上，而过滤初始阻力低于100 Pa，为纳米纤维应用于工业粉尘过滤提供了可行性的解决方案。预计可用于工业袋式除尘，过滤＜240℃的含尘烟气。
As China economy develops, the usage of coal, oil and other fossil energy has been sharply increased and results in severe air pollution problem and frequent smog, which in turn seriously affects people’s health and brings too much inconvenience to normal life. To effectively control the emissions of PM2.5 and reduce or even eliminate the smog, improving the efficiency of dust collection from the flue gas is of significant importance. Baghouse is one of the main methods used to purify the flue gas containing dust and over 99.5% of the dust could be caught. Therefore, baghouse has been widely applied to dust capture industry. The filtration performance of the baghouse is mainly determined by the filter cloth, and according to the theory of filtration, filtration efficiency increases with the decrease of the diameter of the fiber of the filter media. Therefore, nanofibers have found more frequent use in the field of air filtration. However, there is little research on the application of nanofibers in the field of dust filtration from high temperature flue gas.To apply nanofibers in industrial dust filtration and obtain nanofiber composite filter media with high temperature endurance, high efficiency and low flow resistance, temperature resistant polyimide nanofibers were prepared using electrospinning technique in this research. The following work has been conducted:First, electrospinning conditions for polyimide nanofiber preparation were determined. The workable solvents used at different humidity were determined by the observation of distribution of fiber diameter and fiber morphology at different temperature and humidity. DMF were found to be a good solvent when relative humidity was smaller than 30%; NMP worked better as the solvent when relative humidity was greater than 35%. By studying the effect of solution concentration, conductivity, viscosity, surface tension and solvent nature on the nanofibers prepared, a proper formulation of spinning solution was determined using DMF as the solvent. The spinning conditions were screened to ensure the fiber properties and stability through adjusting the spinning voltage, receiving distance, speed of feed supply and other parameters. Based on these, the optimized spinning conditions at room temperature were determined as follows: the spinning solution concentration 9 wt% - 15 wt%, positive spinning voltage 8 - 15 kV, negative voltage 0 - 2 kV, the liquid rate 0.08 - 0.4 mm/min (2.5ml syringes), collect rollover speed 5m/min, feed supply horizontal reciprocating speed 0.5m/min, collection distance 9 - 12cm.Secondly, a composite nanofiber filter media was prepared with sandwiched structure. Aramid non-woven felt with weight of 260 - 350 g/m2 was selected as the base support layer, temperature resistant non-woven fabrics with basis weight of 40 - 60 g/m2 was used as the protection layer. After screening the different fiber bonding methods, adhesive bonding was chosen to combine the different layers together in the composite. The high temperature adhesive was put properly onto the base layer by electrostatic spraying and polyimide (P84) nanofibers of 100 - 500 nm, were uniformly spun on this substrate subsequently. Then protection layer was put on the nanofiber layer, and the three individual layers were combined tightly through hot pressing and curing to form a temperature resistant composite media with nanofibers sandwiched in the middle. Tensile strength test showed that 90 min electrospraying of the adhesive was sufficient enough to endow the composite media with a strength greater than 1000 kPa to meet the application requirement. By measuring the initial flow resistance and pore size of the composite media containing different amount of adhesive and nanofibers, it was found that the adhesive sprayed on the substrate had little effect on the substrate properties.Finally, NaCl particles with diameter of 0.3 - 10 μm were selected to simulate the aerosol for air filtration. The filtration efficiency of different composite filter media developed in this work was determined by counting the particle number and distribution before and after filtration using an aerosol particle counter. It was found that even a small amount of nanofibers in the media could effectively enhance the efficiency of filtration, in which the particles greater than 2.0 μm can be filtered by 100%, particles of 1.0 - 2.0 μm can be removed by over 99.5%, and the initial flow resistance can be as low as lower than 100 Pa. This work provides the necessary information for assessing the possibility of using high-temperature nanofiber filter bag technology to remove industrial dusts, particularly for the dusts from flue gas with temperature under 240 ℃.
|尚磊明. 静电纺聚酰亚胺纳米纤维复合空气过滤材料的制备[D]. 北京. 中国科学院研究生院,2016.|
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