RESEARCH NOTES Modeling of Mercury Oxidation and Adsorption by Cupric Chloride-Impregnated Carbon Sorbents Sang-Sup Lee, †,§ Joo-Youp Lee,* ,‡ Soon-Jai Khang, ‡ and Tim C. Keener † Departments of CiVil and EnVironmental Engineering and Chemical and Materials Engineering, UniVersity of Cincinnati, Cincinnati, Ohio 45221 Cupric chloride-impregnated activated carbon sorbents (CuCl 2 -ACs) showed good performance in Hg 0 oxidation and adsorption in previously published entrained-flow test results. In addition, our previous studies indicated that Hg 0 is oxidized by CuCl 2 -ACs and the resultant oxidized mercury is readsorbed onto the sorbents. This study conducted mathematical modeling to interpret these previous results and better understand the Hg 0 oxidation and adsorption mechanism of CuCl 2 -ACs. As a result, the mathematical modeling results confirmed that Hg 0 oxidation by CuCl 2 -ACs is determined by the injection level of CuCl 2 impregnated onto the sorbents. An increase in CuCl 2 loading in CuCl 2 -ACs was found to increase Hg 0 oxidation but very slightly increased Hg adsorption because an increase in CuCl 2 loading decreased the active CuCl 2 -free carbon sites available for the readsorption of resultant oxidized mercury on the surfaces and inside the pores. 1. Introduction The performance of mercury sorbents has been tested at bench and pilot levels to reduce mercury emissions from coal-fired power plants. Among the sorbents, raw activated carbon has been extensively studied and has shown the capability to adsorb elemental mercury (Hg 0 ) in the presence of other gaseous compounds such as hydrogen chloride (HCl). 1-4 Preimpregna- tion of halogen compounds onto raw activated carbon has been reported to significantly enhance Hg 0 adsorption capability of activated carbon. 3,5-8 Hence chemically treated carbon has also demonstrated good performance in mercury emissions control from subbituminous coal and lignite-burning units which typically generate flue gases with low HCl concentration. 5 However, while the performance of chemically treated activated carbons in Hg adsorption has been examined in these laboratory and field studies and the kinetic models of Hg adsorption onto raw activated carbon have been reported in several studies, 9-11 very few publications are found to investigate the kinetics and mechanisms for Hg 0 oxidation and adsorption by chemically treated carbon sorbents. Cupric chloride-impregnated activated carbon sorbents (CuCl 2 - ACs) demonstrated very similar performance in elemental mercury (Hg 0 ) removal to commercial brominated activated carbon (DARCO Hg-LH) in our previous entrained-flow tests. 12 In addition, Hg 0 oxidation and adsorption characteristics of CuCl 2 -ACs were investigated through our previous experimental studies using fixed-bed and entrained-flow reactor systems. 12,13 These results indicated that CuCl 2 -ACs have different sites for Hg 0 oxidation and adsorption. In addition, significant amounts of effluent oxidized mercury (Hg 2+ ) were found from the entrained-flow tests of CuCl 2 -ACs. While the amount of effluent oxidized mercury was not dependent on the injection rate of CuCl 2 impregnated onto CuCl 2 -ACs, the sum of Hg adsorption and effluent oxidized mercury was found to be dependent on the CuCl 2 injection rate and increased with an increase in the CuCl 2 injection rate. Almost all of the effluent oxidized mercury was also found to be readsorbed onto CuCl 2 -ACs in the filter connected at the end of the entrained-flow portion due to efficient contact with sorbent particles. Therefore, these previous results indicated that elemental mercury (Hg 0 ) is oxidized by CuCl 2 impregnated onto CuCl 2 -ACs and then resultant oxidized mercury seeks different sites of CuCl 2 -ACs for readsorption. 12,13 On the basis of these results, this study conducted further experimental tests and mathematical modeling to understand and ascertain Hg 0 oxidation and adsorption mechanism of CuCl 2 - ACs. 2. Thermochemical Equilibrium Thermochemical equilibrium calculations were conducted to find applicable reactions for Hg 0 oxidation in our entrained- flow tests conducted with a mercury doped air flow. In these calculations, the following reaction equations were assumed to be applicable for Hg 0 oxidation in our entrained-flow tests: The enthalpy and Gibbs free energy values for each com- pound at 300, 400, and 500 K were obtained from the NIST- JANAF thermochemical tables 14 and were determined for each reaction. On the basis of the Gibbs free energy values, the equilibrium constant values were determined for each reaction at different temperatures as summarized in Table 1. On the basis of the equilibrium constant values, Hg 0 oxidation percentages at equilibrium were also determined with respect to temperature. As shown in the table, the formations of mercuric chloride (HgCl 2 ) from reactions 1 and 2 between Hg 0 and CuCl 2 were * To whom correspondence should be addressed: E-mail: joo.lee@ uc.edu. Tel.: 1-513-556-0018. Fax: 1-513-556-0018. † Department of Civil and Environmental Engineering. ‡ Department of Chemical and Materials Engineering. § Present address: Department of Energy Resources Engineering, Stanford University, Stanford, CA 94305. Hg 0 (g) + 2CuCl 2 (s) f HgCl 2 (g) + 2CuCl(s) (1) Hg 0 (g) + CuCl 2 (s) f HgCl 2 (g) + Cu(s) (2) 2Hg 0 (g) + CuCl 2 (s) f 2HgCl(g) + Cu(s) (3) Ind. Eng. Chem. Res. 2009, 48, 9049–9053 9049 10.1021/ie900619v CCC: $40.75  2009 American Chemical Society Published on Web 09/15/2009 Downloaded by UNIV OF CINCINNATI on September 30, 2009 | http://pubs.acs.org Publication Date (Web): September 15, 2009 | doi: 10.1021/ie900619v