Preparation And Applications Of Microfibrous Fe,V/ZSM-5 Zeolite Membrane Catalyst For Trichloroethylene Catalytic Combustion

With the rapid development of China's modernization drive,the annual increase of exhaust emissions in industrial production and urban construction has brought a series of environmental problems.In particular,emissions of volatile organic pollutants?VOCs?,which are identified as one of the major air pollutants,will increase by 49%by 2020 from 2005 levels.Chlorinated volatile organic compounds?CVOCs?,such as polychloromethanes,polychloroethanes and polychloroethylenes are widely used in solvents,degreasing agents and various commercial products,which have a significant impact on human health and environmental safety.Therefore,highly efficient and economical emission reduction technology has become an urgent need of social production,while low-temperature catalytic combustion technology is considered as one of the most promising emission reduction technologies due to its advantages of simple equipment,low energy consumption and good removal effect.Catalyst is the core of catalytic combustion technology,the traditional fixed bed catalytic reaction device using granular catalyst,there are high heat transfer resistance,low contact efficiency,high bed pressure drop and other problems.And microfiber composite molecular sieve membrane material with larger specific surface area,good thermal stability,chemical stability and considerable mechanical strength can lead to better adsorption separation performance,higher efficiency and lower contact bed pressure drop with great research value in the aspect of industrial waste gas purification.The preparation process and characterization of Fe/ZSM-5/PSSF,and V/ZSM-5/PSSF,as well as the effects of different preparation methods on the catalytic degradation of trichloroethylene in a fixed-bed molecular sieve membrane reactor were all studied in this work.Firstly,the catalytic degradation of trichloroethylene by Fe/ZSM-5/PSSF in a fixed bed molecular sieve membrane reactor was studied.Stainless steel fiber carrier?paper-like stintered stainless steel fibers,PSSF?was prepared by wet layup papermaking and high temperature sintering technology and the secondary growth method is adopted in synthesizing ZSM-5zeolite membrane on fiber surface to get ZSM-5/PSSF composite materials.CVD method and impregnation method were used to load Fe active components on ZSM-5/PSSF molecular sieve membrane and ZSM-5 particles respectively.The physical and chemical properties of the catalysts were analyzed by XRD,BET,SEM,XPS,NH₃-TPD and H₂-TPR.The effect of preparation method,Fe loading,trichloroethylene inlet concentration,gas hourly space velocity and carrier type on the degradation performance were investigated by trichloroethylene catalytic combustion in a structured fixed bed.The SEM characterization indicated that the ZSM-5 membrane with a film thickness of 5?m was successfully grown on the surface of the stainless steel fibers.The BET and XRD characterization indicated that the specific surface area of the catalyst prepared by CVD method was 6 m²/g larger than catalyst prepared by impregnation method and the average particle size of the active component was 9 nm smaller than catalyst prepared by impregnation method.The experimental results showed that the catalytic activity of Fe microfiber composite catalyst was enhanced and then weakened with the increase of Fe loading,the best catalytic activity was exhibited with the actual Fe loading of 5%.And the CVD catalyst showed better catalytic activity with T₉₀ value reduce 17?.The catalytic combustion performance of trichloroethylene over microfiber composite Fe/ZSM-5zeolite membrane catalyst and particle catalyst was compared.The experimental results showed that the by-product selectivity of trichloroethylene on microfiber composite Fe/ZSM-5 zeolite membrane catalyst was significantly better than that of particle catalyst.Secondly,the catalytic degradation of trichloroethylene by V/ZSM-5/PSSF in a fixed bed molecular sieve membrane reactor was studied.CVD method and impregnation method were used to load V active components on ZSM-5/PSSF molecular sieve membrane.The physical and chemical properties of the catalysts were analyzed by BET,SEM,XPS and H₂-TPR.The effect of preparation method,V loading,calcining process and active components type on the degradation performance were investigated by trichloroethylene catalytic combustion in a structured fixed bed.The BET characterization indicated that the specific surface area of the catalyst prepared by CVD method was 7 m²/g larger than catalyst prepared by impregnation method.The XPS characterization indicated that the main valence state of the active component V was V⁵⁺.The experimental results showed that the catalytic activity of V microfiber composite catalyst was enhanced with the increase of V loading.And the CVD catalyst showed better catalytic activity with the T₉₀ of trichloroethylene over 10%V-CVD catalyst was 557?and the trichloroethylene conversion rate over catalyst prepared by impregnation method was83%at corresponding temperature.The catalytic combustion performance of trichloroethylene over microfiber composite Fe/ZSM-5 zeolite membrane catalyst and V/ZSM-5 zeolite membrane catalyst was compared.The experimental results showed that the Fe catalyst is obviously better than V catalyst in catalytic combustion of TCE with difference between T₉₀ is31?and the difference between T₅₀0 is 57?.