Adsorption of Mercury with Modified Thief CarbonsRodolfo Abraham Monterrozo1; Maohong Fan, M.ASCE2; and Morris D. Argyle3

Abstract: In this study, the adsorption performance of elemental mercury onto commercially produced Thief carbons (TCs) and TCs modi-fied with ferric chloride and sodium chloride were investigated. The results indicate that the modifications of Thief carbons not only con-siderably enhanced their mercury sorption capacities but also change their mercury sorption mechanism. For example, modification of a Thiefcarbon with ferric chloride can increase its mercury sorption capacity from 21 μg=g to 206 μg=g (nearly a ten times increase), whereasreducing its surface area from 326 m2=g to 217 m2=g. Ferric chloride is a better modification agent than sodium chloride. Analyses ofthe sorption mechanism with different tools, including X-ray photoelectron spectroscopy (XPS), indicate that physical sorption dominatesraw Thief-carbons-based mercury sorption, whereas chemical sorption plays a much more important role in modified Thief-carbon-basedmercury sorption. The reaction order and activation energy of ferric chloride modified Thief-carbon-based mercury chemisorption are 1 and85:6 kJ=mol·K, respectively. DOI: 10.1061/(ASCE)EE.1943-7870.0000434. © 2012 American Society of Civil Engineers.

CE Database subject headings: Adsorption; Mercury; Carbon.

Author keywords: Adsorption; Mercury; Thief carbons.

Introduction

Global emissions of mercury (Hg) from coal-fired power plants areestimated to be more than 600 t annually, which accounts for ap-proximately one third of the Hg total emissions (USEPA 2005).Mercury is a trace element in coal; nonetheless, its emission intothe environment can be substantial because of the increasing de-mand for energy (USEPA 2005). U.S. coal-fired power plants emitapproximately 48 t of mercury per year (USEPA 2005). On March18, 2005, the U.S. EPA issued the first Clean Air Mercury Rule(CAMR) for the control of mercury emissions from coal-firedpower plants, which requires an overall average reduction in mer-cury emissions of approximately 69% by 2018 (USEPA 2005;Davidson and Clarke 1996).

Three types of mercury must be considered: elemental Hg(0);oxidized forms, Hg(I) or Hg(II); and particulate, Hg(p) (Davidsonand Clarke 1996; Sloss 1995; Tewalt et al. 2001; Western ResearchInstitute 2006; Zeng et al. 2004; Sun et al. 2006; Apogee ScientificInc. 2004; Hutson et al. 2007; O’Dowd et al. 2006). The total mer-cury concentrations of flue gas range from 1 to 35 μg=m3 (O’Dowdet al. 2006). Mercury from coal combustion is released primarily asHg(0) because the thermodynamic equilibrium favors this state atcoal combustion temperatures. Oxidized forms of mercury areeasier to capture by conventional methods, such as electrostatic pre-cipitators, baghouses, and sorbent injection.

People are increasingly interested in using solid sorbents formercury removal, because their applications can be easily realizedthrough injection at appropriate points upstream of an existing par-ticulate device, and activated carbon has been considered to be themost promising sorbent because of its injection suitability, wideavailability, and acceptable prices. To further decrease the costof mercury removal with carbon sorbents, the Department ofEnergy’s National Energy Technology Laboratory (NETL) has de-veloped Thief carbons (TCs). The TC is obtained by inserting alance in or near the flame, extracting a mixture of partially com-busted coal and gas, and reinserting the mixture in the flue gas be-cause its adsorptive properties are suited for mercury removal atcooler flue gas conditions. The tests conducted by NETL havedemonstrated that the mercury sorption capacities of TCs and com-mercial activated carbons are close, but TC-based processes are lessexpensive because the production costs of TCs are lower.

Sorbent surface modification has previously been used for theenhancement of mercury sorption capacity of activated carbon(Zeng et al. 2004; Azhar Uddin et al. 2008; Schofield 2004; Bansalet al. 1988). For example, Zeng et al. (Zeng et al. 2004) demon-strated a five-fold increase of the original mercury sorption capacityby impregnating activated carbon with zinc chloride. Nitric andother acids can also enhance the mercury removal capacity of ac-tivated carbons (Western Research Institute 2006). The change ofsorption mechanism resulting from surface modification is the driv-ing force of sorption capacity of modified activated carbon (Zenget al. 2004; Bansal et al. 1988). However, the study of the surfacemodification of TC for mercury sorption improvement has not beenreported, which is the purpose of this work. The main objectives ofthe current study are to demonstrate the mercury removal capacityof TC and modified TCs, to explain the mechanism of mercuryadsorption by ferric chloride modified Thief carbons and to proposea kinetic model for such adsorption.

Experimental Section

The TCs were obtained from the Western Research Institute (WRI).The sorbents were prepared from Powder River Basin subbitumi-nous coal. Table 1 shows the temperature at which they were

1Graduate Student, Dept. of Chemical and Petroleum Engineering,Univ. of Wyoming, Laramie, WY 82071.

2Associate Professor, Dept. of Chemical and Petroleum Engineering,Univ. of Wyoming, Laramie, WY 82071 (corresponding author). E-mail:mfan@uwyo.edu

3Adjunct Associate Professor, Dept. of Chemical and Petroleum Engi-neering, Univ. of Wyoming, Laramie, WY 82071; and Associate Professor,Dept. of Chemical Engineering, Brigham Young Univ., Provo, UT 84602.

Note. This manuscript was submitted on March 16, 2011; approved onMay 24, 2011; published online on May 26, 2011. Discussion period openuntil August 1, 2012; separate discussions must be submitted for individualpapers. This paper is part of the Journal of Environmental Engineering,Vol. 138, No. 3, March 1, 2012. ©ASCE, ISSN 0733-9372/2012/3-386–391/$25.00.

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extracted from the furnace. The TC sorbents were modified byimpregnation with 4.85% by weight solutions of NaCl (FisherScientific, 99% purity) and FeCl3 (JT Baker, 95% purity). Theweight ratio of modifying agent (FeCl3 or NaCl) to TCs was1=40; it was determined that with this ratio, a complete or saturatedimpregnation could be achieved. The TCs were modified by mixingappropriate amounts of TCs with the solutions; subsequently, theywere washed, and finally, they were dried for 12 h at 90°C (AzharUddin et al. 2008). The surface areas of nine modified TC samples(3 raw TCs, 3 FeCl3 modified TCs, and 3 NaCl modified TCs) weremeasured by nitrogen physisorption with a Micromeritics Tristar3000 surface area and porosity analyzer.

The mercury removal experimental setup consists of four parts(Fig. 1): a mercury generation unit, a dilution unit, a sorption sys-tem, and equipment for analyzing mercury vapor in the gas stream.Teflon (PTFE) lines (0.635 cm ID) and fittings were used to con-nect all streams. To perform the mercury sorption tests, an airstream flowing at 10.4, 17.06, or 22:6 L=min was introduced asa carrier gas into the chamber of the mercury generator, a VICIMetronics Dynacalibrator 450-548a (1), which generated1;840 ng·Hg=min at 100°C. At these conditions, the total pressurewas 77.5 kPa, which is the approximate atmospheric pressure at the∼2;200 m elevation of the laboratory in which the research wasdone. Because of the small capacity (25 mg of sorbent) of thepacked bed reactor used in this research, only a slip stream(0:05 L=min) of the Hg containing air was passed through thepacked Hg sorption bed (2) held between quartz wool plugs.One of the plugs is located at a notch 0.2 m from one end of a0:5 m × 0:95 cm ID quartz tube. One part of the outlet (postad-soprtion) gas stream was vented to a safe location, whereas the re-maining part was metered by a flow controller (3) and diluted withanother metered (4) air stream provided by air cylinder (5) to reducethe Hg concentration to measurable levels using a TEKRAN 2537-S mercury analyzer (7). The Hg sorption profiles were collectedand recorded using a data acquisition system (10). Blank sorptiontests were performed to determine the Hg sorption capacity of thetested sorbents.

Three factors, the surface areas of sorbents, the Hg concentra-tions in the gas stream, and sorption temperature, were studied fortheir effects on Hg sorption. Raw TCs and FeCl3 modified TCswere tested over sorption temperature ranges of 25–200°C and25–300°C, respectively. The flow rates varied from 10.4 to22:6 L=min. The same tests were conducted for NaCl modifiedTCs. In addition, the kinetics of FeCl3 modified TCs- based Hgadsorption was investigated over temperature and gas flow rateranges of 100–200°C and 10:4–22:6 L=min, respectively.

X-ray photoelectron spectroscopy (XPS) and X-ray fluores-cence (XRF) tests were performed on some FeCl3 modified TCsto study their Hg sorption mechanism. The XPS tests were per-formed using a Phi-5800 spectrometer with a monochromatic AlKα X-ray source, a hemispherical analyzer, and a multichannel de-tector. The Cls and Hg peaks should be at 284.8 eVand 99–101 eV,respectively (Yang et al. 2007; Hutson et al. 2007; Moulder et al.1992; Brunauer et al. 1938; Suzuki 2002; Beckhoff et al. 2006;McCurdy et al. 2004). The XRF characterization tests were per-formed with a SPECTRO MIDEX XRF spectrometer to test ifHg0 is oxidized to Hg2þ. Table 2 shows the results of the amountof mercury adsorbed to the surface of a sample of FeCl3. Mercury,in this case, was oxidized to Hg2þ, because the compound foundwas HgO. The instrument was operated at 55 kVand 1 mAwith anenergy resolution of 155 eV.

Mercury adsorption kinetics of the FeCl3 modified TC 1298-73-002 sample were studied over a temperature range of 100–200°C.The flow rate of air was regulated to vary the concentration of mer-cury in the gas stream to obtain the sorption kinetics. The Hgremoval efficiencies of all the tests run for kinetic study were keptbelow 10% to obtain initial rate results. The reaction order wasevaluated by calculating the chemisorption on the basis of the sorp-tion rate of Hg0 at different concentrations and then plotting thelogarithm of those rates against the logarithm of the Hg partialpressures. Finally, the activation energy was obtained from anArrhenius plot of the logarithm of k versus �1=T .

Fig. 1. Schematic diagram of the mercury sorption set-up: (1) mercury generation unit; (2) packed bed reactor; (3) porter mass flow controller (FC);(4) porter mass flow controller; (5) zero air cylinder; (6) argon cylinder; (7) mercury analyzer; (8) temperature controller (TC); 9 temperaturecontroller; and (10) data acquisition system

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Results and Discussion: Effect of Different Factorson Adsorption

Surface Area and Modification

The measured surface areas of the nine TC samples (three raw TCs,three FeCl3 modified TCs, and three NaCl modified TCs) rangedfrom 107 to 346 m2g�1 (Table 1). The temperature of the combus-tor at which the three unmodified samples were withdrawn from thecombustor is also shown. The surface areas of the three untreatedsamples increased with the increase in temperature at which theywere withdrawn from the combustor. The surface areas of thetreated samples decrease by approximately 20 to 40% of the un-treated samples, presumably because of pore plugging by the addedFeCl3 or NaCl. The sorption capacities of all the sorbents increasedwith the increase of their surface areas, whereas those of raw TCsare very low, as expected, for activated carbon because they arephysical sorbents (Fig. 2). The breakthrough capacity in Fig. 2was calculated as follows: first, breakthrough is defined as 10% ofthe initial mercury concentration in the inlet continuous stream, andsecond, by obtaining the total amount of mercury adsorbed untilthe breakthrough concentration was reached and amount was di-vided by the weight of the sorbent used. The breakthrough wascalculated by using Fig. 2. For this system, no full isotherm or ad-sorption energy was measured before.

The Hg sorption breakthrough capacities of the different sorb-ents are calculated on the basis of Fig. 2 and listed in Table 3. In

Table 3, the removal efficiencies refer to the maximum amount ofmercury that can be removed during a continuous process and be-fore the sorbent is spent; it is generally expressed as a percentageof the inlet stream. Modified TCs have higher Hg adsorptioncapacities than corresponding raw TCs (Table 3). Furthermore,the FeCl3 modified TCs possess significantly higher Hg sorptioncapacities than the NaCl impregnated samples (Fig. 2 and Table 3).Nevertheless, both have sorption capacities on order of 10 to 100times higher than the unmodified TCs, explained as follows.Although the sorption capacities seem to be correlated to thesorption efficiency in the case of Raw TCs, this fact cannotbe concluded, and it is not the case for surface modified TCs.The sorption efficiency can be more related to the interaction be-tween mercury molecules and the structure of the TC, whereas thecapacity is more likely related to the nature of the adsorption intotal amount of available sites and reactants in the case of thechemisorption.

Surface area plays an important role in determining the Hg sorp-tion capacity of a physisorbent because it is directly related to thetotal number of sorption sites in which Hg can be adsorbed (Zenget al. 2004). Physical adsorption apparently dominates the Hg ad-sorption with raw TCs, whereas the NaCl and the FeCl3 impreg-nated TCs depend on both physisorption and chemisorption for theremoval of adsorbed mercury, because of the introduction of Cl�and formation of Cl� surface complexes, Cl2-CnHxOy (Tewalt et al.2001; Bansal et al. 1988). The major interactions between Hg0 andCl� (Zeng et al. 2004; Bansal et al. 1988) are

Hg0 þ ½Cl��↔HgClþ þ 2e ð1Þ

3Hg0 þ 6½Cl��↔3½HgCl2� þ 6e ð2Þ

These reactions may be preceded by the formation of the re-duced chlorine complex on the carbon surface as proposed by Zenget al. and Bansal (Zeng et al. 2004; Bansal et al. 1988) by the fol-lowing reaction

FeCl3 þ CnHxOy↔Fe3þ þ ½Cl3 � CnHxOy�3� ð3Þ

The samples were characterized with XPS measurements be-cause of the capability of such characterization of distinguishingdifferent species in the spent sample, specifically, the organic hal-ide, which confirms that the proposed mechanism is possible. Theorganic halide is a relevant species because it is the precursor of theformation of mercuric chloride. This is confirmed with our XPScharacterization results of the spent FeCl3 modified TC (Fig. 3),which show the organic chloride species on the right side of E3,are present in the region of 198–200 eV. The double peak is a resultof the Cl 2p3=2 and 2p1=2 excitations (Fig. 3). FeCl3 modified TCsare less dependent on the surface area than NaCl modified ones

Table 1. BET Surface Areas of Prepared TC Sorbents

Sample

Preparationtemperature

(°C)

Surfacearea

(m2=g)

Surface area(m2=g) aftermodificationwith FeCl3

Surface area(m2=g) aftermodificationwith NaCl

1298-67-002 932 143.5 107 123

1298-72-001 1,025 254 179 189

1298-73-002 1,039 326 188 217

Table 2. XRF Characterization Test Results Expressed in Weight %Concentration

Element

Concentration in % byweight of sample

1298-73-002 modifiedwith FeCl3, fresh

Concentration in % byweight of sample

1298-73-002 modifiedwith FeCl3, spent

Hg 0 0:171� 0:005

Fe 9:72� 0:09 3:32� 0:02

Cl 6:31� 0:04 5:29� 0:04

Note: Instrument operated at 55 kV and 1 mA with an energy resolutionof 155 eV.

Fig. 2. Effect of surface area on the different sorbents(½Hg�i ¼ 10:1 μg=m3; carrier gas: air; flow rate ¼ 17:06 L=min; T ¼100°C; absolute pressure ¼ 77:5 kPa; and mass of sorbent ¼ 25 mg)

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(Fig. 2 and Table 3), which can be explained by Fe3þ in FeCl3, amuch stronger oxidant than Naþ in NaCl. That is, the oxidant effectis much more relevant in the case of FeCl3 modified TCs than thesurface area effect. It can oxidize Hg0 according to the followingreactions:

2Fe3þ þ Hg0↔2Fe2þ þ Hg2þ ð4Þ

Fe3þ þ Hg0↔Fe2þ þ Hgþ ð5Þ

The XRF characterization shown in Table 2 and the XPS char-acterization in Fig. 4 demonstrate that Fe3þ is the predominant ironspecies. The resulting Hgþ and Hg2þ can form oxides or combinewith Cl� to form stable salts, whereas Naþ cannot oxidize Hg0 atall, which is only physisorbed on TCs, as observed by Huston et al.(Hutson et al. 2007) when they studied the behavior of Hg on sorb-ents impregnated with halide salts.

High resolution XPS characterization of fresh 1298-72-003FeCl3 modified TC before sorption found that FeCl3 exists inthe modified TC because its peak appears at 714 eV, very closeto 711 eV found by Moulder (Moulder et al. 1992) (Fig. 4). InFig. 4, the label ferric chloride refers to the position of ferric chlo-ride in the spectra, that is, at 708 eV. This finding supports thepostulated E4 and E5 attributed to the participation of Fe3þ inoxidizing Hg0.

To further support this proposed mechanism, the existence of anoxidized form of mercury (Hg2þ) on the spent modified TCs needsto be demonstrated. XPS can potentially be used to determine thepresence of oxidized Hg species on the surface of the spent TCs.However, the peaks of silicon and Hg2þ in the spent TCs arepresent at the same binding energy location of XPS (Moulder et al.1992), and the concentrations of silicon are much higher than thoseof Hg2þ; thus, XPS cannot be used a tool to identify Hg2þ in spentTCs. The source of silicon in the samples is the TC itself, becausecoal contains silicon. An XRF was used in this research to identifyand estimate the quantity of Hg2þ in the spent FeCl3 modified TC1298-73-002. The XRF analyses show that no mercury was foundin raw TC 1298-73-002, but its Hg concentration after sorption was0.0171 % by weight in HgO, which is consistent with the calculatedHg sorption capacity listed in Table 3. The XRF analyses can dis-tinguish the species of mercury because the test shows which com-pounds are present in the sample and not only which elements, seeJanseens et al. (2000).

Temperature Effect

Unlike physical elemental mercury sorption, in which the Hg sur-face binding rate is inversely related to temperature but propor-tional to surface area, the subsequent chemisorption (throughoxidation) of Hg by FeCl3 modified TC has a significant temper-ature dependence according to the Arrhenius equation. This is par-ticularly true in the case of endothermic or entropy driven reactions.Fig. 5 shows the dependence on temperature of raw and FeCl3modified TC 1298-73-002 with respect to its Hg sorption capacityin the mass of mercury adsorbed on per unit mass of sorbent. These

Fig. 3. (Color) High resolution XPS characterization of chlorine com-ponents of fresh 1298-72-003 FeCl3 modified TC (350 W; 45.0°; and58.70 eV)

Fig. 4. (Color) High resolution XPS characterization of iron compo-nents of fresh 1298-72-003 FeCl3 modified TC (350 W; 45.0°; and23.50 eV)

Table 3. Sorption Capacities of Raw and Modified TC Sorbents (½Hg�i ¼ 10:1 μg=m3; Carrier Gas: Air; Flow Rate ¼ 17:06 L=min; T ¼ 100°C;Absolute Pressure ¼ 77:5 kPa; Weight of Sorbent ¼ 25 mg)

Sample

Raw TC FeCl3 impregnated TC NaCl impregnated TC

Surfacearea

(m2=g)Capacity(μgHg=g)

Removalefficiency

(%)

Surfacearea

(m2=g)Capacity(μgHg=g)

Removalefficiency

(%)

Surfacearea

(m2=g)Capacity(μgHg=g)

Removalefficiency

(%)

1298-67-002 143.5 21.27 83 107 188.5 97.2 123 70.19 97

1298-72-001 254 8.96 97 179 195.0 97.7 189 89.19 99

1298-73-002 326 2.49 98.6 188 206.2 99.0 217 108.5 98

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results show that the Hg adsorption capacities of raw TC 1298-73-002 are not only low at all the tested temperature but also decreasewith increasing temperature, which is consistent with the statementthat the adsorption mechanism is in this case is physical. Physisorp-tion shows this behavior because the van der Waals interactions aremore weakly bonded at higher temperatures; therefore, desorptionis more likely to occur. However, the modified TC 1298-73-002shows a different temperature dependence trend. Its Hg sorptioncapacity is very low in the temperature range of 20–150°C in whichphysical sorption dominates, increases with increasing isothermalsorption temperature from 150–225°C, and then decreases with fur-ther increases of sorption temperature. This complex behavior canbe explained as follows. Chemisorption through oxidation controlsthe Hg sorption of the modified TC 1298-73-002 when sorptiontests were conducted above 150°C. Higher temperatures favorthe oxidation, and thus, the chemisorption, of Hg as found inthe temperature range of 150°C–225°C (Fig. 5). However, furtherincreases of sorption temperature are not beneficial to the overallsorption of mercury because some of the mercury compoundsformed through oxidation and chemisorption, such as Hg2O andHgCl2, start to decompose. These observations strongly supportthe chemisorption mechanism induced by the introduction ofFeCl3 to the surface of raw TC.

Initial Hg Concentration

The effect of initial gas phase Hg breakthrough concentration wasstudied in the range of 10 to 25 μg=m3. The data collected for bothraw and FeCl3 modified TCs 1298-73-002 are presented in Fig. 6.Higher initial Hg concentrations lead to increased Hg breakthroughsorption capacity, as expected from Langmurian theory of adsorp-tion isotherms. Fig. 6 shows this tendency, although it cannot beproven with the data obtained that this behavior will persist. Higherconcentrations correspond to lower flow rates. The increase in thesorption capacity at higher concentrations is larger for ferric chlo-ride modified TC than for raw TC. The sorption capacities betweenFig. 6 and Fig. 5 appear different because the vertical axis in Fig. 5is multiplied by a factor of 103.

Results and Discussion: Reaction Kinetics

Under the given chemisorption conditions (relatively low sorptiontemperatures and Hg sorption efficiencies), the desorption of Hgcan be neglected. As such, the chemisorption rates, ra, can becalculated based on the conversion of Hg0 using the followingequation:

ra ¼ X ×½Hg�iΔt

ð6Þ

where X= Hg0 conversion (%); ½Hg�i = initial concentration of Hg0

in the stream (mol=min); andΔt = time interval of two consecutivesampling points. ra can also be expressed as follows;

ra ¼ kpnHg0 ð7Þ

where k= rate constant of the chemisorption in mol=m3·s; n =sorption order with respect to Hg0; and pHg0= partial pressure ofelemental mercury, so

ln ra ¼ ln k þ n ln pHg0 ð8Þ

The values of k and n can be obtained by using Eq. (8) because nand ln k are the slope and intercept of a plot of ln ra versus

Fig. 5. Comparison of temperature dependence of sorption capacitiesin TC and modified TC sorbents (½Hg�i ¼ 10:1 μg=m3; carrier gas:air; flow rate ¼ 17:06 L=min; and absolute pressure ¼ 77:5 kPa;mass of sorbent ¼ 25 mg)

Fig. 6. Effect of the flow rate on the sorption capacity (carrier gas: air;T ¼ 100°C; mass of sorbent ¼ 25 mg)

Fig. 7. Reaction order of Hg chemisorption on FeCl3 impregnatedTC (ln ra versus ln p, carrier gas: air; T ¼ 100°C; andmass of sorbent ¼ 25 mg)

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ln pHg0 (e.g., Fig. 7 for 100°C), which suggests the sorption orderwith respect to Hg0 is 1. The k values obtained at different temper-atures were plotted in an Arrhenius form of ln k ∼ ð�1=TÞ to obtainthe activation energy of the FeCl3 modified TC 1298-73-002 basedHg0 sorption from the slope of the (e.g., Fig. 8). On the basis of theslope and intercept of the plot, the activation energy, Ea, and pre-exponential factor, A, for Hg0 chemisorption are 85:6 kJ=mol·Kand 2:03 × 106, respectively. The activation energy could be theindicator that the reaction Eq. (3) is the rate limiting step withthe formation of the chlorine halide, which is the precursor ofthe oxidized mercury. The corresponding Arrhenius form of therate constant is

k ¼ Ae�85;578RT ð9Þ

where R= ideal gas constant with units of mol=J K and T has unitsof K.

Conclusions

The mercury sorption capacities of TCs modified with FeCl3 andNaCl are considerably enhanced relative to unmodified TC. Forexample, modification of a TC with ferric chloride can increaseits mercury sorption capacity from 21 to 206 μg=g, despite adecrease in surface area from 326 to 217 m2=g. This increase insorption capacity appears to be caused by a change in its mercurysorption mechanism. Whereas unmodified TC displays a decreas-ing sorption capacity with increasing isothermal sorption temper-atures, which is a hallmark of physisorption processes, theCl-modified forms display more complicated temperature depend-ences that are consistent with chemisorption. FeCl3 is a bettermodification agent than NaCl, with approximately four timeshigher Hg capacity, because Fe3þ can oxidize the Hg to more activeforms that form chlorine compounds, whereas Naþ cannot. TheXPS and XRF characterizations show the presence of surface or-ganic chloride species, FeCl3 and HgO, which support the pro-posed chemisorption mechanism in modified TCs. On the basisof kinetic studies, the observed reaction order is 1, whereas theactivation energy is 85:6 kJ=mol·K for Hg chemisorption onFeCl3 modified TC.

Acknowledgments

The authors would like to thank Jupiter Oxygen, the Departmentof Energy (DOE), and the School of Energy Resources at theUniversity of Wyoming for their financial support. The authorswould like thank Dr. Evan J. Granite in the DOE’s National EnergyTechnology Laboratory, Dr. Khalid Omar in the Western ResearchInstitute, and Mr. Daniel Jakob in the University of ManagementCentre Innsbruck in Austria for their various technical supports.

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Fig. 8. Arrhenius plot for Hg chemisorption on FeCl3 impregnatedTC (ln k versus �1=T , carrier gas: air; T = 100–200°C;absolute pressure ¼ 77:5 kPa; and mass of sorbent ¼ 25 mg)

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