Adsorption Of Water Vapor On Hypercrosslinked Polymeric Resin And Its Effect On VOCs Adsorption

Nowadays,adsorption has been recognized as a preferred method for recovering volatile organic compounds(VOCs)at home and abroad,and the key in an adsorption process is usually a porous solid adsorbent.Water vapor is ubiquitous in the actual VOCs adsorption system.Many studies on activated carbon have pointed out that water vapor compete with VOCs and thus influence the adsorption process,resulting in a diminished capacity and a slow adsorption kinetics for the targeted VOCs.However,the studies about the adsorption of water vapor and the competitive mechanism between VOCs and water vapor on hypercrosslinked polymeric resin haven't been reported.The two adsorbents have different surface chemical properties and pore structures.Hence,the conclusions with activated carbon as adsorbents couldn't provide an accurate and systematic theoretical guidance for the adsorption of VOCs on hypercrosslinked polymeric resin with water vapor in the process.In this thesis,we prepared a hypercrosslinked polymeric resin(HPA)as adsorbents,studying the equilibrium,kinetic and dynamic adsorption of water vapor on HPA and the influence of water vapor on the adsorption of VOCs with different physical-chemical properties,comparing with activated carbon(GAC).The aim of the study was to investigate the coupling interaction among water vapor,physical-chemical properties of VOCs and surface chemistry of adsorbents.The main research and results were as follows:(1)The adsorption isotherms,kinetic curves and breakthrough curves of water vapor on HPA and GAC at 298-328K were investigated.All the adsorption isotherms were type V and could be fitted well with Cluster-formation-induced Micropore-filling(CIMF)model,showing a high correlation coefficient(R2>0.98).Adsorption capacity of water vapor on HPA was lower than GAC,positively related with the concentration of oxygenic groups and microporous volume.The adsorption kinetics of water vapor obeyed the LDF model,with high correlation coefficient(R2>0.98).The kinetic rate constants were as following:HPA>GAC,which was just opposite with the concentration of surface functional groups.The kinetic rate constants decreased with the increase of relative humidity(RH),but increased with the temperature.In addition,the breakthrough time of water vapor on HPA was lower than GAC,and it was not affected by RH.But the mass transfer zone(MTZ)become wider with the increase of RH.As the temperature increased,the breakthrough time decreased and the MTZ shortened.(2)The adsorption isotherms of 12 kinds of VOCs(acetone,methyl ethyl ketone(MBK),cyclopentanone,methanol,ethanol,butanol,dichloromethane,1,2-dichloroethane,benzene,toluene,pentane,hexane)on HPA and GAC,with different amount of pre-adsorbed water vapor(PAWV),were determined through static headspace method at 298K.The isotherms of VOCs were type I,and PAWV didn't affect the type of isotherms of VOCs.DR equation was used to fit the characteristic curves of VOCs,with R2>0.90.The negative influence increased with the increase of the amount of PAWV,but decreased with the increase of VOCs concentration.Under the same condition,the reduced percentage of VOCs adsorption capacity effected by PAWV on HPA was lower than GAC.The lower concentration of oxygenic groups could help to reduce the negative influence of PAWV Furthermore,the characteristic adsorption energy of VOCs on HPA and GAC were further characterized using a linear solvation energy relationship(LSER),and the fitted LSER equations were obtained by a multiple regression of the characteristic adsorption energy of 12 VOCs against their solvation parameters.The coefficients of the five-parameter LSER equations showed that both of HPA and GAC interacted with VOC molecules mainly through dispersion and hydrogen-bond basicity(HBB),and the contribution of dispersion was higher.The two interactions decreased with increasing of PAWV amount.For the same serials of VOCs,the reduced percentage of VOCs adsorption capacity decreased with the increase of dispersion and HBB.For the VOCs at different serials,when the HBB were approximate,the reduced percentage of VOCs adsorption capacity increased with the increase of dispersion;while when the dispersion were approximate,the lower of the contribution of HBB was,the bigger of the reduced percentage of VOCs adsorption capacity was.(3)The HPA and GAC column were pre-conditioned under specific RH(0-80%),and then breakthrough curves of VOCs(5-80mg/L)obtained by introducing the acetone,MBK,cyclopentanone,ethanol and hexane into the column.The PAWV had little influence on the dynamic adsorption of acetone,MBK,cyclopentanone,ethanol,while PAWV had an obvious influence on the adsorption of hexane,which was nonpolar and the mass transfer was hindered by PAWV,resulting in the decrease of breakthrough capacity and the wider of the mass transfer zone(MTZ).However,on GAC,the five VOCs were all affected by PAWV,with shorter breakthrough time and wider MTZ.The negative influence of PAW V on the breakthrough capacity of VOCs increased with the increase of RH,but decreased with the increase of VOCs concentrations.The influence of physical-chemical properties of VOCs on their column adsopriton with PAWV in adsorbents was similar to their equilibrium adsorption.(4)The breakthrough curves of VOCs(acetone,MBK,cyclopentanone,ethanol and hexane)on HPA and GAC,co-adsorbed with water vapor,were determined through column adsorption method.The breakthrough capacity decreased with the increase of RH,but the MTZ shortened.Under the same conditions,the reduced percentage of VOCs breakthrough capacity on HPA was lower than that on GAC,and the roll-up peak was smaller.In addition,the roll-up peak of VOCs become smaller and the reduced percentage decreased with the increase of VOCs concentrations.When the concentrations of VOCs were higher than 40mg/L,the breakthrough capacities was not affected by RH.For the VOCs at different serials,the relationship between the influence of water vapor and the properties of VOCs was similar to that of PAWV.While for ketones,the reduced percentage of breakthrough capacity by PAWV were as follows:MBK>acetone>cyclopentanone,which was different with the influence of PAWV in adsorbents,indicating that when the hydrogen-bond interaction between VOCs and water vapor was higher and the VOCs was miscible,the reduced percentage could be decreased.Lastly,by comparing the influence of pre-adsorbed and co-existed water vpaor on the breakthrough adsorption of VOCs,we found that for polar VOCs(acetone,MBK,cyclopentone and ethanol),which was governed by both of HBB and dispersion,the negative influence of latter was more serious than the former.While for nonpolar hexane,governed by only dispersion,the pre-adsorbed water showed more serous influence.