Sulfurization of a carbon surface for vapor phase mercury removal – II: Sulfur forms and mercury uptake Wenguo Feng a , Eric Borguet b , Radisav D. Vidic a, * a Department of Civil and Environmental Engineering, University of Pittsburgh, 943 Benedum Hall, Pittsburgh, PA 15261, United States b Department of Chemistry, Temple University, 1901 N. 13th Street, Philadelphia, PA 19122, United States Received 25 October 2005; accepted 18 May 2006 Available online 31 July 2006 Abstract Sulfur forms deposited on carbonaceous surfaces after exposure to hydrogen sulfide were analyzed using XPS and XANES. Higher temperatures promote the formation of organic sulfur and the presence of H 2 S during the cooling process increased elemental sulfur content. Temperatures between 400–600 °C were found to be optimal for producing effective mercury uptake sorbents. The increased amount of sulfur deposited during the cooling process in the presence of H 2 S was very effective towards Hg uptake in nitrogen. Corre- lation of mercury uptake capacity and the content of each sulfur form indicated that elemental sulfur, thiophene, and sulfate are likely responsible for mercury uptake, with elemental sulfur species being the most effective. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Activated carbon; Carbon fibers; Impregnation; X-ray photoelectron spectroscopy; Surface properties 1. Introduction Mercury is a hazardous air pollutant that has attracted significant public health and environmental attention recently. About 150 tons of mercury are emitted annually by anthropogenic sources in the United States [1]. Control of elemental mercury emissions is very difficult due to its high volatility and low solubility. Effective total mercury removal technologies include wet scrubbers, spray dryer adsorption (SDA), and activated carbon injection [2]. Among technologies mentioned above, activated carbon injection is currently considered to be the most promising technology in terms of Hg removal efficiency and reliabil- ity. Although very effective, the high operating cost of this technology [3,4] requires improvements in sorbent perfor- mance to facilitate full scale applications. Previous studies showed that introducing oxygen containing functionalities [5,6] and halogens [7,8] can improve Hg uptake capacity. However, introduction of sulfur onto the carbon surface [9] significantly improved Hg uptake capacity and pro- duced more stable products [10], thus eliminating long- term liabilities of the adsorption technology. Previous studies [11,12] have observed the increase in mercury uptake capacity at relatively high temperatures (about 150 °C) with an increase in sulfur content. Studies by Vidic and co-workers [7,9,10,13–15] showed that the fol- lowing factors are important for mercury uptake by sulfur impregnated sorbents: sulfur content, sulfur forms, sulfur distribution, and pore structure/surface area of the sorbent. Their studies suggested that carbons impregnated with sul- fur at higher temperatures (400–600 °C) performed better than those produced at lower temperatures (25–150 °C). The authors suggested that higher temperatures produced short-chain sulfur allotropes and more uniform sulfur dis- tribution on the sorbent, surface. The impregnation tem- perature was found to be more important than the initial sulfur to carbon ratio [9], which was attributed to the fact that sorbents produced at higher temperatures still retained their high surface area and mesopore structure. 0008-6223/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2006.05.053 * Corresponding author. Tel.: +1 412 624 1307; fax: +1 412 624 0135. E-mail address: vidic@pitt.edu (R.D. Vidic). www.elsevier.com/locate/carbon Carbon 44 (2006) 2998–3004