Preparation Of ZSM-5/PSSF Membrane Composites For Removal Of Isopropanol From Air

With the development of global economy and modern industry,environment pollution has attracted much attention worldwide.One of the reason causing the environmental problems is emission of VOCs and many countries begin to take measures to control the discharge of VOCs.Among all the technologies in controlling VOCs,adsorption and catalytic oxidation present unique advantages.Due to the low economic cost and simple operation,adsorption has been the best candidate for removal of VOCs with low concentration.Catalytic oxidation can transform VOCs to CO2 and H2 O in low temperature without producing secondary pollutant.However,traditional fixed bed was usually packed with adsorbent and catalyst in pellet or powder,causing giant bed drop pressure as well as great mass and heat transfer resistance.In order to improve the contact efficiency,reduce the bed drop pressure and intensify the mass and heat transfer,structured material is developed.Micro-fibrous zeolite membrane is one of the structured materials,its good mechanical performance and high contact efficiency makes it a promising structured absorbent/catalyst.In this paper,in situ hydrothermal synthesis and secondary growth are used to synthetize 5A zeolite membrane and ZSM-5 zeolite membrane,Cu-5A zeolite membrane and Cu-ZSM-5 zeolite membrane were prepared by chemical vapor deposition.Besides,adsorption and catalytic dynamics of isopropanol were studied by applied the micro-fibrous ZSM-5 zeolite membrane to compose the structured fixed bed.Firstly,effect of pore structure properties in adsorption performance was taken into consideration by conducting the adsorption experiment with different zeolites as adsorbents,adsorption dynamics of isopropanol in Beta zeolite was also studied,micro-fibrous ZSM-5 zeolite membrane was prepared and used to study the dynamics of isopropanol in structured fixed bed.Experimental results showed that NaY zeolite had the largest adsorption rate but smallest adsorption amount,Beta zeolite had the largest adsorption rate,MCM-41 had only the third largest adsorption amount though it had the greatest BET surface area and pore volume.Characterization of micro-fibrous ZSM-5 zeolite membrane indicated that it had a unique 3D network structure and ZSM-5 zeolite membrane with a thickness of 1.67 ?m was compactly grown in the surface of paper-like stainless steel fiber.Adsorption dynamics of isopropanol reflected that breakthrough curves with shaper slope were observed in structured fixed bed when compared with traditional fixed bed,which revealed an increase in adsorption rate,in other words,reduction in mass transfer.With the increase of inlet concentration and flow rate,the breakthrough curves presented steep slope and breakthrough times shorted.However,when the bed length was changed,even if the breakthrough times varied,the steepness of breakthrough curve was nearly unchanged.LUB theory was applied to analyze the breakthrough curves,parameters showed that bed composition of ZSM-5 zeolite membrane should be controlled in a proper range.Furthermore,Yoon-Nelson and BDST modeling parameters fitted the breakthrough curves well.Secondly,effects of preparation method,loading amount and support patterns on catalytic performance were studied,catalytic performance of isopropanol in granular zeolite catalysts and zeolite membrane catalysts were compared,and catalytic dynamics of isopropanol in ZSM-5 zeolite membrane catalyst were also explored.Experimental results showed that catalysts prepared by CVD showed best catalytic activity followed by catalyst prepared by ion exchange and catalyst prepared by impregnation had the lowest activity.Furthermore,with the increase of metal loading amount,catalyst presented better catalytic performance.Considering effect of pore structure,Cu-NaY had the best catalytic performance,Cu-MCM-41 had good activity in relative higher temperature range,on the contrary,Cu-ZSM-5 presented good activity in low temperature range.Catalytic performance of granular catalysts and membrane catalysts showed that Cu-ZSM-5/PSSF > Cu-ZSM-5 > Cu-5A > Cu-5A/PSSF in catalytic activity,the good activity of Cu-ZSM-5/PSSF was attributed to the unique 3D network structure which strengthen the mass and heat transfer.Besides,catalytic dynamics indicated reduction in catalytic activity with an increase in inlet concentration or flow rate.