CAS OpenIR
多孔莫来石纤维陶瓷膜制备及其除尘/催化耦合功能
扎西措
Thesis Advisor陈运法
2020-07-01
Degree Grantor中国科学院大学
Degree Name博士
Degree Discipline材料学
Keyword陶瓷膜,Pms过滤,整体式催化剂,锰基复合氧化物,Vocs催化氧化
Abstract

近年来,我国的大气环境污染形势仍然十分严峻,以PM2.5为特征的雾霾天气对环境和人类健康造成极大危害。挥发性有机化合物(VOCs)和细颗粒物(PMs)作为重要的大气污染源,其控制和治理迫在眉睫。在现有的治理方法中,催化氧化是降解VOCs切实可行的处理技术;膜过滤技术则是高效的PMs捕集净化技术。然而,在复合污染条件下,大气具有更强的PM2.5生成趋势,开展集除尘与催化一体化的处理模式对工业源复杂烟气多污染控制显得至关重要,也是目前大气污染治理技术的重要发展方向。多孔陶瓷膜是一种新型的无机分离膜材料,具有耐高温、耐酸碱腐蚀、机械强度高、耐热冲击性良好、可再生、环境友好等优点,在大气污染治理领域具有广泛的应用前景,己成为高温气体净化领域中实现气固分离的关键部件。此外,多孔陶瓷膜可提供丰富的孔道和大比表面积,具有优良的催化剂负载条件。通过对陶瓷膜负载催化剂活性组分,可组装成陶瓷基整体式催化剂,不仅可以过滤细颗粒物,还可以用来催化降解VOCs,可实现陶瓷膜的除尘和催化功能耦合。传统颗粒堆积成型的多孔陶瓷膜,因孔隙率较低、压降大、尺寸难调、自重大而其结构需进一步优化。本课题采用莫来石纤维作基体材料,以高岭土和钾长石等低成本矿物质作高温粘结剂制备出莫来石纤维基多孔陶瓷膜 (PCMs),对其进行表面修饰和催化剂负载等设计,应用到PMs控制和VOCs催化领域,并系统地研究了膜表面结构与性能之间的内在关联。具体内容和主要研究结果如下:(1)多孔陶瓷膜的制备及其PMs过滤性能研究通过铸模压片成型的方法制备了不同纤维含量的多孔陶瓷膜,并测试了样品的除尘性能。结果表明,所制得的陶瓷膜具有轻质多孔、孔道均匀、孔隙率高、机械强度高等特点,经过高温煅烧后,样品具有特殊致密化的三维网状结构。多孔陶瓷膜对0.3-10 μm的PMs具有很高的去除效率。当气流线速度高达1.25 m/min时,样品的压降值低于100 Pa,过滤阻力很小。(2)α-Al2O3/PCMs过滤膜对PMs的控制研究采用喷涂装置在PCMs表面涂覆了一层球形α-Al2O3过滤层。通过调节涂液成分的比例及烧结温度,制备出高效的α-Al2O3/PCMs过滤膜,分析了粘结剂含量及烧结温度对样品相组成、表观密度和PCMs的机械强度的影响,以及球形α-Al2O3过滤层厚度对PMs的过滤效率和压降大小的影响。结果表明:当粘结剂的含量为纤维的50 wt.%,且烧结温度为1250 °C时,样品性能最佳,具有低密度(0.8887 g/cm3)、高孔隙率(70.36%)、均匀孔径(20 -50 μm)、高抗压强度(5.54 MPa)、低线性收缩率(小于0.4%),以及对强酸强碱溶液表现出优异的耐腐蚀性能。经除尘测试证明,α-Al2O3/PCMs对PMs (0.3-10 μm)的去除效率得到了提升。与均质PCMs相比,经表面涂覆后的样品对PMs的去除效率提高了10%以上,体现了陶瓷膜良好的深度除尘性能。(3)Mn-Ce/PCMs 整体式催化剂制备及其VOCs催化性能研究 以PCMs作催化剂载体,锰铈复合氧化物选为催化活性组分,通过溶液浸渍法制备出一系列Mn-Ce基整体式催化剂,并用于挥发性有机化合物(VOCs,以苯为目标气体)的去除。载体PCMs具有独特的相互连接且均匀的孔结构,Mn-Ce复合氧化物活性相均匀地分散在PCMs整体的网络结构中。催化测试结果表明,所有负载催化活性成分的PCMs均对苯的催化氧化具有活性。将Ce引入MnOx中可以提高样品催化性能,当MnOx/CeO2比为3:1时,催化效果最佳,其T90约为240 °C。此外,通入相对湿度为90 vol.%(20 °C)的水蒸气的情况下,催化剂仍保持了高活性及稳定性。催化剂的高活性归因于Mn-Ce复合氧化物低温还原性和丰富的活性氧(OAds),以及与Mn-Ce间的协同作用。本工作为实现陶瓷膜整体式催化剂的过滤和催化功能耦合提供了有效途径。(4)MnxCeyCuz/PCMs整体式催化剂制备及性能Mn-Ce基过渡金属氧化物具有高效且稳定的催化性能,通过将Cu离子引入到Mn-Ce基过渡金属氧化物中,可以进一步提高催化陶瓷膜的催化性能。以PCMs作载体,用溶胶-凝胶法将Cu掺杂的Mn-Ce复合氧化物作为活性组分,制备了PCMs整体式催化剂并用于苯氧化。催化剂活性组分以优异的粘附力均匀地分散在整个PCMs骨架中,并且PCMs催化剂在催化反应过程中为反应气体提供了更多的活性位点。当掺入20%的Cu时,苯的转化率明显提高,T90降为212 °C,表现出更高的活性及稳定性,这是由于大量的活性吸附氧、更多的表面氧空位和低温还原性能引起的。这种负载高活性催化活性组分的纤维陶瓷膜,用于过滤PMs的同时去除VOCs,具有一定的应用前景。;In recent years, air pollution has seriously threatened the living environment and human health. As a coal-based energy consumer, China inevitably produces a variety of volatile organic compounds (VOCs) and fine particulate pollutants (PMs) from coal-fired flue gas, industrial tail gas, waste incineration and biomass combustion, which are the important sources of atmospheric haze pollution. Among the existing treatment methods, catalytic oxidation is a practical treatment technology for efficient degradation of VOCs; for PMs, membrane separation technology is an emerging treatment technology as well. The integrated treatment mode of dust removal and catalysis is an important direction of air pollution control. Porous ceramic membranes, which have more unique properties like low density, high chemical and thermal stability, high mechanical strength, low thermal conductivity and good thermal shock resistance, are considered the essential component of filtration for the applications associated with high temperature and corrosive environments. However, all the ceramic membranes formed by accumulation of particles have existing problems of low porosity, high pressure drop, heavy self-weight and difficulty in adjusting the size of the ceramic membrane in practical applications. Herein, we successfully prepared a porous PCMs by using mullite fiber as raw material and earth-abundant raw chemicals kaolin and feldspar powder as high temperature binder in a relatively low thermal process. The design of surface modification and catalyst loading was applied to the fields of PMs control and VOCs catalysis. The internal relationship between the surface structure and performance of materials was systematically studied. The specific content and results are as follows:(1) Highly porous ceramic membranes with interconnected pores for high performance dust removalPorous fibrous mullite ceramic membranes with different content of fibers were successfully fabricated by molding method for dust removal. The ceramic membrane of high porous structure having lightweight, uniform and high porosity, high mechanical strength were obtained by using adjustable diameter and length of fibers, the feasible sintering process and the special sinter-locked three-dimensional structure. Interestingly the pressure drop of the fibrous ceramic membrane showed lower than 100 Pa as the airflow linear velocity was as high as 1.25 m?min-1 across the materials. The as-prepared porous ceramic membrane possessed an enhanced dust removal efficiency for dust particles with 3-10 μm in diameter, which are tremendously harmful to human health and environment. The fabricated fibrous porous ceramic membrane showed great potentiality for the utilization in gas filtration processes.(2) Spherical Al2O3-coated PCMs for high-efficiency gas filtrationTo further improve the filtering accuracy of PCMs, the fibrous PCMs with three-dimensional structures were prepared and then coated with a layer of spherical α-Al2O3 membrane on the surface via spray-coating process. The effect of binder composition and sintering temperature on the porosity, phase composition, bulk density and mechanical strength of PCMs, as well as the effect of the coating thickness of spherical α-Al2O3 on PMs filtration efficiency and pressure drop were investigated. The results showed that samples with an added binder weight of 50 wt% and sintered at 1250°C resulted to an optimal structure with material properties such as low bulk density (0.88 g/cm3), high porosity (70.36%), low linear shrinkage (0.40%), high mechanical strength (5.54 Mpa), and excellent corrosion resistance against both acid and alkali solutions. Furthermore, a spherical α-Al2O3 coating thickness of 150 μm was found to effectively reduced the concentration of PMs from dust-laden air through the filtration tests, achieving enhanced dust removal efficiencies of almost 100% for 3 -10 μm, 99.2% for 1.0 μm, 95.0% for 0.5 μm and 91.6% for 0.3 μm PMs with the pressure drop was only 280 Pa when the airflow linear velocity reached to 2.00 m min?1. The membranes displayed a 10% increase efficiency in fine particles (d=1.0-0.3 μm) removal compared to those without α-Al2O3 coating layer.(3) Monolithic Mn-Ce/PCMs catalysts for benzene oxidationA series of monolithic Mn/Ce-based catalyst of ceramic membranes (PCMs) were prepared through impregnation method for volatile organic compounds (VOCs) removal. The fibrous PCMs possessed a unique interconnected and uniform pore structure, and MnOx-CeO2 active phases were homogenously dispersed into the porous PCMs support. The catalytic activity of samples was measured by using benzene as target VOCs. The results revealed that all catalytic CMs were active for oxidation of benzene. Significantly, the catalytic performance was promoted by introducing Ce species into MnOx. Among all, MnOx-CeO2-3:1 catalyst exhibited the lowest 90% benzene conversion temperature (T90) at 244 °C and high stability with continuous benzene stream in the presence of 90 vol.% (20°C) water vapor under a gaseous hourly space velocity (GHSV) of 5000 h-1, owing to the lower-temperature reducibility and the abundant active oxygen (OAds.) with synergetic effect of MnOx and CeO2. The results indicated a promising way to design a high efficiency dual functional PCMs for the industrial application of removal VOCs while controlling particulate matters (PMs) from hot gases.(4) Monolithic Cu-doped Mn-Ce/PCMs catalysts prepared by sol-gel synthesis for benzene combustionHerein, we prepared PCMs (porosity: 70%) in a facile sintering process, and integrated Cu-doped Mn-Ce oxides into PCMs as monolithic catalysts by sol-gel method for benzene oxidation. Through this method, the catalysts are dispersed evenly throughout the PCMs with excellent adhesion, and the catalytic PCMs provided more active sites for the reactant gases during the catalytic reaction process. All the prepared catalytic PCMs exhibited high catalytic activity for benzene oxidation. Significantly, the monolithic catalyst of Cu0.2Mn0.6Ce0.2/PCMs, obtained the lowest temperature for benzene conversion efficiency of 90% (T90) at 212 °C with a high GHSV of 5000 h?1, and showed strong resistance to high humidity (90 vol.%, 20 °C) with long-term stability in continuous benzene stream, which is caused by abundant active adsorbed oxygen, more surficial oxygen vacancy and lower-temperature reducibility. 

Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/49675
Collection中国科学院过程工程研究所
Recommended Citation
GB/T 7714
扎西措. 多孔莫来石纤维陶瓷膜制备及其除尘/催化耦合功能[D]. 中国科学院大学,2020.
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