Preparation Of Mullite Fiber-based Porous Ceramic Membrane And Its Coupling Of Dust Filtration And Catalytic Functions

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 controlPorous 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.In addition,porous ceramic membranes can provide abundant pores and large specific surface area,and have excellent catalyst loading conditions.By supporting the ceramic membrane with catalyst active components,it can be assembled into a ceramic-based monolithic catalyst,which not only can filter fine particles,but also can be used to catalyze the degradation of VOCs.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?m 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 ?-Al2O3 membrano 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 ?-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? 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 ?-Al2O3 coating thickness of 150 ?m 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 ?m,99.2%for 1.0 ?m,95.0%for 0.5 ?m and 91.6%for 0.3?m 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 ?m)removal compared to those without ?-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 PCMs 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? and high stability with continuous benzene stream in the presence of 90 vol.%(20?)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 MnxCeyCuz/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? with a high GHSV of 5000 h-1,and showed strong resistance to high humidity(90 vol.%,20?)with long-term stability in continuous benzene stream,which is caused by abundant active adsorbed oxygen,more surficial oxygen vacancy and lower-temperature reducibility.