Gas phase tricholoethylene removal at low concentration using activated carbon fiber

Journal f Entiroumemtal Sciences vol 16. No. 1. pp53-55,2004Article 1:|0010742(2004)01-0053-03CLC number: XS11 Document code: AGas phase tricholoethylene removal at low concentration using activatedcarbon fiberLIU Jun, HUANG Zheng-hong, WANG Zhan-sheng, KANG Fei-yu?(1. Department of Environment Scienee and Engineering, Tsinghua University, Beijing 100084. China. E-mail: liujun99@ mails. Tsinghua.edu.en2. Department of Material Science and Engineering, Tsinghua University. Beijing 100084, China)Abstract: The breakthrough adsorption behaviors of gas phase trichloroethylene in a packed bed of activated carbon fibers( ACF)wereestigated. The specific surtace area of the ACF was 600 mig. 1400 m'ig and 1600 m/g, respectively, and the concentration oftrichloroethylene ranged from 270 mg/ m'to 2700 mg/'m. Results showed that the capacity of adsorption increased with increasing specificsurface area, the relationship between the logarithms of 10% breakthrough time and concentration was approximately linear over theexperimental range, the breakthrough time decreased with increasing temperature and humidity. the breakthrough curves at different inletconcentration or different temperature can be predicted by several simple theoretical models with good agreementsKeywords: trichloroethylene; activated carbon fiber; adsorption; breakthrough curveIntroductiTricholoethylene TCE ), as an organic solvent, has been widely concentration and flow raleused in many fields with large quantity, and a large amount of TCEhasIf the adsorptive reaction is a nth order reaction, the half life ofbeen found to be emitted from the users, such mapollution, reactant is inversely proportional to the initial concentration raised toespecially for groundwater( Yu, 2000).It isgnized that (n-1)th power, then Eq (3)can be obtained(Yoon, 1984 b):conventional drinking water treatment processes have low efficiency in(3)removing tricholoethylene fmm water; new process must be used toWhere k, is proportionality constant; F is the flow rate. Eq (Iexposure to volatile organic compounds( vOC s )in water can occur frum Eq (2 )and Eq.(3)can be used to simulate and predict thepathways other than ingestion, inhalation and dermal absorption are also breakthrough curves for various inlet concentrationsimport pathways( Mekone, 1987), and the exposure dose through theIf the adsorption reaction operated under various temperatures,thethree pathways are the same order of magnitude and the major exposure Arhenius'equation is introduced to substitute for the constant kthway is inhalation( Yoshida, 1993). It is necessary to remove thevOCs both in drinking water and the volatiles from drinking watewhere k, is a constant; E is the activation energy R is the gasGranular activated carhon( GAC)has been applied for nany years constant, and T is the absolute temperature. Substitution of Eg. (4)Into control VOCs due to its high micropore volume and low priceEq- (3)gives Eq (5)(Huang, 1999):Recently activated carbon fiber( ACF) has been an interesting topic ofthe removal of vOCs because ACF has uniforrn micropore structuret=mr(5)faster adsorption kinetics, and a lower pressure drop comparing withEq (1), Eq (2)and Eq (5)can be used to simulate und predictCAC. Based on the superior characteristics of ACF, it is considered breakthrough curves under various temperaturefavorable for the treatment of VOCs. There are several reports(Yu1997:Suzuki,1991)about ACF absorbing VOCs in drinking 1 Materials and methodsater,however, few researches has been done to identify the feasibilityThe experiment system included a small ACF holder. a humidifierof ACF removing gas phase TCE at low concentration. In this work, the a tricholoethylene generator section, flow meters, and temperatureffcet of the specifie surface area, the inlet TE concentration, the controller, The schematic experimental now diagram is shown in Figadsorption temperature and the relatively humidity on the breakthrough High-purity nitrogen was used as the carrier gas. The gas phasecurves was studiedtricholoethylene was generated using temperature- controlled bubbler, andoduced by Yoon and Nelson ( Yootricholoethylene used was AR grade. The now rate through the bubble1984a) has been usedC= Ca 1+ exp[k'(rhumid gas was produced by bubbling the high-purity nitrogen throughWhere C is the exit concentration at breakthrough: Co is the inletvessel filled with water and the humid gas was mixed with dry high-puritynitrogen to get designed relative humidity. The ACF holder was a 15 cmconcentration: k'is a rale constant; r is 50% breakthrough time( raho long, 0.5 em inside diameter glass pipe. The total flow rate and theof exit lo inlet gas concentration of 0.5); and t is the operate time, koperate lemperature was kept at 200 em/ min and 25C. 200 mg ACFcan he express as Ey. (2)"YH中国煤化工hick andomatograph( GC)with ECDCNMHGCorresponding author54v.16was used to analyze the TCE eoncentration of inlet and effluent of the ACF 600, ACF-1400 and ACF-1600, respectively, referring to theiradsorber. The adsorbents used in the study were manufactured byspecific sudace areas, and their physical characteristies of the ACFs areAnsan Activated Carhon Fiber Factory, China. They are denoted as listed in Table I_47Fig. 1 Schematic diagram of experiment apparatushigh-purity nitrogen: 2. tricholocthylene: 3. high-purity water: 4. ACF: 5. gas chromatograph; 6.thermostat;7.flow meterTable 1 Physical properties of activated carbon fiberconcentrations are 2700 my/m, 1900 mg/m, 1360 mg/nt. 540 mg/mCharaeteristiesACF-600 ACF1400 ACF-1600 and 270 mg/m, respectively. The 10% breakthrough time is 150 minBET surface area, m/g1678205 min, 235 min,min and 583 min, accordingly.The减 al pore volume,cm3/gbreakthrough time decreased withMicropore volume. cmis0.1720,3200,432relationship provided a reasonable fit to the data. The relation betweenthe 10% breakthrough time and the inlet concentration is:2 Results and discussiong()=-0.576×log(C0)+4,1762.1 ACF properties effectAnd the correlation coefficient is r=0.99, wherene breakthrough curves of 2700 mg/m'nCE in the bed packed breakthrough time. There is a same result for GAC adsorbing VOCswith different ACEs are shown in Fig. 2. It is obvious that the(Vanosdell, 1996), their result suggestedbreakthrough time increased with the increasing specific surface areamight be cautiously extrapolated to indoor concentration for TCEhis indicates that the higher the specific area of ACF, the higher theIn order to predict the breakthrough curves at different inletadsorption capacity will be. It should be noted that a beginning of particoncentration, Eq (1)and Eq (2)were used to determine k, k'andbreakthrough was observed soon after the beginning and the breakthrough r from the breakthough curve data both at 2700 mg/m and 270 mg/me then exhibited steps in the case of ACF-600. In the previous woThen, the values of t at 2700 mg/m and 270 mg/m'( Kang, 2001)the diffusion time constants(i. e. DIr?)of MEK and Eg(3)to get the parameter n, then n is substituted to Eq (3)to getbenzene for ACF-600 were much less than the value for Ace- 1400, thisvalues of t for different inlet concentrations. Similarly, the values ofindicated that ACF-600 was not suitable for using as adsorbent of vocs k for different inlet concentrations were obtained using Eq.(2)ue to its lower adsorption kineticsFinally, k' and t were substituted to Eq (1)to predict various inletconcentration breakthrough curves, The simulated and predicted10·AcF600breakthrough curves are shown in Fig. 4. It can be seen that thepredicted breakthrough curves fit the experiment data with relative goodagreementse062.3 Temperature effectThe temperature effect on the breakthrough curve of the ACF iswn in Fig. 5. The operating temperatures were 298K, 323 K and 343K, It is clearly seen that the breakthrough time decreased with increasingoperating temperature. The adsorption behavior of VOcs onto ACF couldphysical adsorption decreases with iFiK. 2 Effect of specific surface area on breakthrougIn order to predict the breakthrough curve of tricholoethylene atCo=2700 mg/m; RH=0; T'=25tdifferent temperatures, for example at 323 K, breakthough curve data of中国煤化工2.2 Concentration effectThe effect of con 10% breakThrough time(ratio ofN MHG298K,2700 mg/mation of 0.1)is show(5)to get theGas phase richoloethylene removal ar low concentralion using activated carom filerbreakthrough time decreased with the inereasing humidity.SomeoneCal, 1996)found that water soluble organic( acetone)showed littledecrease in its adsorption capacity on ACF up to about 90% RH. whileaterer insoluble organic(ound 65% RH2.2■RH0Fig, 3 EReet of inlet concentration on 10% breakthrough time for ACF-1400RH=0;T=25℃SimulatedFig 6 Eect of relative humidity on breakthrough curve for ACF-1400Ca=2700mg/m3,T=25℃130mm3 Conclusions270mgPredictedACF can be used with packed bed for removal of gas phase TCe at0100200300400500600700800900low concentration. The breakthrough eharacteristics dependedthe aCh’sprobreakthrough time increased with the increasing speeifie surface areaFig4 Simulated and predicted breaktarves for ACF-1400 atecreased with increasing operating temperature or humidity. It wasimportant that the breakthrough eurves at various inlet concentrations orRH=0:T=25℃temperatures can be predieted by several simple models with goodparameters(n, k, and E)were applied to eq (1), Eq (2)and Eq5)to predict the breakthrough curve at 2700 mg/m,323K.Thesimulated and predicted breakthrough curves are shown in Fig. 5. It is Referencesn that the predicted breakthrough curve fit the experiment data with Cal M P, Rood M ], Larson S M. 1996. Removal of vOCs from humidified gasgood agreement「J]. Gas Separation&priKang F Y, Huang Z H, Liang K M et a,, 2001. Adsorption of volatile organicompounds in nigrogen streams on the oxidized activated carbon fiber[J]Adsorption Seience Techology, 19(5):423--43HuangC C, Lin Y C, Fang C L, 1999, Dynamic adsorption of organic solventvapors onto a packed bed of activated carbon cbothlJ]. Separation Science andTechnology, 34(4): 555--570L Jw, Yu ZB. Ming G et al., 1997, Trihalomethanes adsorption on activatedbon fiber and ganular activated carion [ J70 mg/m 298KSingled carveMcKone E T, 1987. Human exposure to volatile organic compounds in bouseholdoplication of fiber adsorbents in water treatmentIJJWater Science and Technology, 23: 1649-1658vanosdell D W, Owen M K, Jaffe L B, 1996, voC removal at low contaminantFig. 5 Effect of temperature on breakthrough curve for ACF-140concentration using granular activated carhon[ J]. Joumal of Air &WasteM46(8):883-890kinetics-1. A2.4 Relative humidity effecttheoretical model for respirator cartridlife[J]. American IndustrialAdsorption of vapors from humid air is a complex process. In orderon Yoon y tne Association Journal, 45(8): 509-516theoretical model for respirator cartridgelife and its practical30% and 80%. Fig6 shows the breakthrough curves of TCE at different ysx-ationsL J]. Ameriean Industrial Hygiene Association Joumal, 45(8)process, the relative humidity of the gas stream was designed to be 0Yoshida Kikwu, 1993, Preliminary exposure assessment of volatile chlorinaterelative humidity, apparently the breakthrough time decreased wi中国煤化increasing relative humidity. Adsorbed water in the pores of ACF wouldbe expected to reduce the volumeCNMHfrom groundwater byreducing the adsorption capacityaCF bed. Therefore. the(Received for review October 15, 2002. Aecepted September 20, 2002)