Catalytic Oxidation Performances For VOCs Combustion Over Microfibrous Zeolite Membrane Catalyst

With the fast development of economy, the increasing emission of volatile organiccompounds (VOCs) from petrochemical engineering, transportation and household wastehas posed severe impacts on both the environment and human health. There are plenty oftechniques for VOCs removal like condensation, absorption, membrane separation,adsorption, thermal combustion, catalytic combustion and biodegradation. Catalyticcombustion is one of the most promising techniques for removal of VOCs in air with lowconcentration because of its relatively easy operation, high efficiency as well as lowpollution to the environment. However, most of the traditional fixed bed reactors which arebased on granular or powder shaped catalysts have relatively high mass/heat transfer anddrop pressure, low contact efficiency. Therefore, how to design a novel structured zeolitemembrane catalyst for VOCs removal is a cutting-edge research topic. In this paper, thepreparation, characterization and application of zeolite membrane catalysts for catalyticcombustion of isopropanol were investigated, as well as the reaction dynamics ofisopropanol over the structured zeolite membrane reactor.Firstly, the preparation process of microfibrous zeolite membrane catalystsCo/ZSM-5/PSSF and its catalytic performances for isopropanol combustion in structuredzeolite membrane reactor were studied. ThePSSF support was fabricated through wet lay-uppapermaking and sintering process，then synthesized the ZSM-5zeolite membrane overPSSF support via secondary growth to obtain microfibrous zeolite membrane materialZSM-5/PSSF. The characterization results of XRD, SEM and N2sdsorption/desorptionshowed that a continuous and compact ZSM-5zeolite membrane was successfullysynthesized on PSSF via secondary growth, and the thickness of the zeolite membrane wasabout1.78μm. The cobalt oxides modified microfibrous zeolite membrane catalystCo/ZSM-5/PSSF was prepared by wetness impregnation method with cobalt nitrate asprecursor salts for the catalytic combustion of isopropanol in structured zeolite membranereactor. The results of SEM and EDS mapping indicated that the cobalt oxides were well dispersed on the ZSM-5/PSSF support. The experimental results showed that cobalt loading,calcination temperature, gas hourly space velocity (GHSV) and feed concentration ofisopropanol played an important role in the structure properties and catalytic performancesof the catalysts.The0.5M-Co/ZSM-5/PSSF catalyst presented the best catalytic activity forisopropanol combustion with GHSV of7643h-1and isopropanol feed concentration of3.3mg/L.Secondly, the preparation process of microfibrous zeolite membrane catalystsMn/ZSM-5/PSSF and its catalytic performances for isopropanol combustion in structuredzeolite membrane reactor were investigated. The managanese oxides modified catalystswere synthesized by wetness impregnation methodwith manganese nitrate as precursorsalts.The results of SEM and XPS showed that cationic distribution and microstructure ofthe catalyst was influenced by calcination temperature. The experimental results showedthat the catalytic performance of Mn/ZSM-5/PSSF zeolite membrane catalysts increasedwith the increase of managanese loading and the decrease of calcination temperature, GHSV,isopropanol concentration in feed gas.Mn/ZSM-5/PSSF zeolite membrane catalyst showedmore excellent catalytic activity for isopropanol than granular catalystMn/ZSM-5, thedifference of T50and T90between these two catalysts was about50℃.Thirdly, the preparation process of microfibrous zeolite membrane catalystsCo-Mn/ZSM-5/PSSF and its catalytic performances for isopropanol combustion instructured zeolite membrane reactor were studied. The metal oxides modified ZSM-5zeolite membrane catalysts Co-Mn/ZSM-5/PSSF was prepared by wetness impregnationmethod with cobalt nitrate and manganese nitrate as precursor salts. The result of XPSshowed that cobalt element exsited as Co3+and Co2+，maganese element existed as Mn4+and Mn3+. The result of TG indicated that the microfibrous zeolite membrane catalystsCo-Mn/ZSM-5/PSSF possessed excellent thermal stability. The influence of Co/Mn ratio,GHSV and isopropanol concentration in feed gas on structure properties and catalyticperformances for isopropanol catalytic combustion were discussed.The experimental resultsshowed that the catalytic activity of double-component metal oxides catalyst Co-Mn/ZSM-5/PSSF was much higher than that of Co/ZSM-5/PSSF or Mn/ZSM-5/PSSFcatalyst. T50and T90increased continuously with the increasing of GHSV and feedconcentration of isopropanol, thus decreasing the conversion of isopropanol. The zeolitemembrane catalysts presented the most excellent catalytic activity for isopropanolcombustion with catalysts bed height of1cm, GHSV of7643h-1and feed concentration of3.3mg/L.