Study On The Adsorption Of Volatile Organic Compounds With Palygorskite

Represented by formaldehyde and benzene,the volatile organic compounds(VOC)are the main components of indoor air pollution,and will seriously endanger human health when the concentration is too high.In this paper,inexpensive palygorskite was used as the main object of study;activated carbon and silica gel as comparative adsorbents;and formaldehyde,ethanol and toluene as adsorbates.The study aimed to explore the effects of the microstructure and physical properties of palygorskite on the adsorption and desorption properties of VOC gas with the use of microscopic characterization experiment and macroscopic adsorption experiment.Besides,the characteristics of adsorption and purification of typical VOC gas and its influence on environmental factors were also investigated.The structure-activity relationship of water and VOC adsorbed by palygorskite was studied by means of constant temperature adsorption experiment.The results showed that the penetrating time of the adsorbent gas through palygorskite was less than that of activated carbon,as well as that of silica gel.The equilibrium adsorption capacities of these adsorbents were activated carbon>silica gel>palygorskite.The pore structure and specific surface area of these adsorbents were measured.The results showed that the pore structure of palygorskite had the same pore size as partial pore,and the average pore size of these adsorbents rank as below:palygorskite>silica gel>activated carbon;the pore structure of palygorskite was not as developed as silica gel and activated carbon.The BET specific surface area of the limestone were activated carbon>silica gel>palygorskite.These results also explained the differences between these adsorbents on equilibrium adsorption.The isothermal adsorption curves of toluene on palygorskite were found similar to typeⅣ and V isotherms adsorption lines through constant temperature adsorption experiment.The adsorption of palygorskite on toluene was mainly adsorption capacity.When the temperature is increased,the adsorption capacity and adsorption rate of palygorskite on toluene would decrease,and the time of penetrating and the equilibrium time of adsorption would increase.There is a certain adsorption competition on the surface of palygorskite between toluene and water.The overall adsorption amount of palygorskite would increase when there is water,but the amount of adsorption of toluene would decrease at the same time.Besides,water vapor could promote the desorption of toluene from palygorskite.The DTG curves of formaldehyde on 404b-3 and kx-3 palygorskite were determined by TPD technique and the results of which were analyzed in combination with the characterization results of two kinds of palygorskite products.The adsorption performance of water and VOC gas on palygorskite and several typical adsorbents was studied by static adsorption and TPD desorption experiments.The results of desorption activation energy showed that the desorption activation energies of formaldehyde on 404b-3 and kx-3 were 20.6 kJ/mol and 29.0 kJ/mol,indicating that the adsorbent can be reused to improve the adsorption force between adsorbent and adsorbate so that to reinforce the adsorption capacity,but which also will increase the difficulty of desorption.Besides,the removal peak of VOC gas molecules on palygorskite kx-3 was wider than that on palygorskite 404b-3 and the differences of DTG curve of formaldehyde on two kinds of palygorskite was mainly in the middle and high temperature section,which was caused by the size and distribution of adsorbent pore size.The kx-3 palygorskite had more micropores,thus enthanced the diffusion resistance of desorbed gas molecules in the pores,which gave rise to higher desorption peak temperature widder desorption peak.While 404b-3 palygorskite had larger diameter,then the channel diffusion resistance of gas molecules inside is smaller and therefore the desorption peak of which is narrower.The comparative experiments of several adsorbents showed that the desorption performance of palygorskite on water and VOC gas was better;the desorption performance of silica gel was the second and the desorption performance of activated carbon was the worst.Especially for toluene gas,activated carbon desorption regeneration performance was far worse than silica gel and palygorskite.