Adsorption And Desorption Properties Of VOCs On Molecular Sieve-supported Honeycomb Ceramics

Most VOCs,which are highly volatile,cancerogenic,teratogenetic,mutagenic and inducing photochemical smog,seriously affect human health.At present,as one of the conventional techniques for treating VOCs,adsorption method has become a research hotspot in the field of environmental protection.With molecular sieves as the adsorption materials,rotary adsorption and concentration technique has been developed rapidly and become a mainstream technique for the treatment of low-concentration VOCs in many industries.In this paper,cordierite honeycomb ceramics absorbing materials loaded with HY,NaY,USY?ZSM-5-300 and ZSM-5-360 were prepared by a coating method.With toluene,ethyl acetate,isopropanol and acetone as adsorbents,the adsorption and desorption of single-component and multi-component organic matters by honeycomb ceramics loaded with molecular sieves were investigated.Results on the adsorption and desorption of single-components showed that NaY molecular sieve had the lowest adsorption capacity for toluene,ethyl acetate,isopropanol and acetone.ZSM-5-300 had the highest saturated adsorption capacity for four components,while USY,HY and ZSM-5-360 had medium saturation adsorption capacity.The adsorbents had the lowest desorption temperature on the surface of ZSM-5-300 and ZSM-5-360 molecular sieves.They can be fully desorbed in a temperature range of 180-270 ~oC.The desorption temperature of ZSM-5-300 and ZSM-5-360 were significantly lower than those of NaY,HY and USY molecular sieves,respectively.Moreover,after thermal desorption,there were carbon deposits on the surface of HY and USY molecular sieves.ZSM-5-300 molecular sieve had a higher saturation adsorption capacity and a lower thermal desorption temperature.Thus,it could be used as an ideal adsorption material for VOCs.After examining the influence of adsorption temperature,initial concentration of VOCs and gas flow rate on the adsorption of multi-component VOCs by honeycomb ceramics loaded with ZSM-5-300 molecular sieve,the result showed that all of the penetration curves were S-shaped.The adsorption process by the molecular sieve was an exothermic reaction.When the temperature was raised,the penetration time and adsorption equilibrium time of VOCs were shortened and the adsorption of VOCs was reduced,which was not conducive to the procession of adsorption.When the initial concentration was increased,the penetration time and adsorption equilibrium time were shortened.At a low concentration,the adsorption capacity for all organic matters was relatively fixed,while at a high concentration,the adsorption capacity was significantly reduced.ZSM-5-300 molecular sieve was suitable for the adsorption of VOCs at medium or low concentrations.When the gas flow rate was increased,the penetration time and adsorption equilibrium time of VOCs were shortened.If the gas flow rate was too high or too low,it was not conducive to the procession of adsorption,suggesting that honeycomb ceramics loaded with ZSM-5-300 molecular sieve were suitable for the adsorption of VOCs at medium or low rates.When the gas flow rate was high,the effect was not very good.The multi-component experiment showed that the penetration curves of acetone,toluene and isopropanol presented obvious?humps?,which could be attributed to the fact that four types of VOCs had joint adsorption and competitive adsorption.Comparing the adsorptions of ZSM-5-300 molecular sieve for multi-component VOCs and single-component VOCs,the saturation adsorption capacity of ZSM-5-300 for each single component in the multi-component VOCs was significantly reduced.When multi-component VOCs underwent a thermal desorption,the desorption temperature of each component was lower than that of single-component VOCs,indicating that ZSM-5-300 molecular sieve had a good desorption regeneration effect on multi-component VOCs.The penetration curve of the multi-component VOCs through composite molecular sieves was S-shaped,and the penetration time was decreased with the following order:ethyl acetate>isopropanol>acetone>toluene.ZU13 composite molecular sieve had a mesoporous-microporous structure.The porous structures intersected and the pore walls superposed more significantly.Honeycomb ceramics loaded with ZU13 molecular sieve had a good adsorption effect on multi-component VOCs.When ZU13 and ZU11 composite molecular sieves desorbed VOCs,ethyl acetate,isopropanol and acetone had two desorption peaks,while toluene had only one,which indicated that ZU13 and ZU11 composite molecular sieves had a mesoporous-microporous structure and the full desorption temperature was ZU13>ZU11>ZU31.VOCs could be fully desorbed before 300?.Based on the semi-empirical gas adsorption model proposed by Yoon Nelson,the author fit the experimental data of ZU1 composite molecular sieve and found that the correlation coefficient r~2 of the regression equation of each component in the multi-component VOCs ranged from 0.986 to 0.994.The theoretical model had a good correlation with the experimental data and they fit well.Using the theoretical penetration model,we can predict the variation of the concentration of VOCs in the outlets of the honeycomb ceramics loaded with molecular sieves over time and offer some guidance for engineering applications.