The oxidation of aqueous thiols on a graphite intercalation compound adsorbent
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The oxidation of aqueous thiols on a graphite intercalation compound adsorbent Michael G. Conti-Ramsden • K. Nkrumah-Amoako Nigel W. Brown • Edward P. L. Roberts
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Received: 28 September 2012 / Accepted: 8 February 2013 / Published online: 20 February 2013 Ó Springer Science+Business Media New York 2013
Abstract Aqueous phase adsorption of thiols onto a graphite intercalation compound (GIC) adsorbent was shown to be accompanied by surface assisted oxidation of the thiols to their disulfide dimer. This effect was studied for three thiols; ethanethiol, propanethiol and sec-butanethiol. Unlike the case of thiol oxidation on activated carbons in aqueous conditions, the generation of dimer did not affect the adsorbent’s ability to oxidise the thiols in solution in the concentration range studied (0–100 ppm). This was attributed to the nonporous, crystalline nature of the adsorbent. This meant that once formed the dimers migrated from the active sites for thiol oxidation, believed to be mainly at the edges of the graphite planes, onto the hydrophobic basal plane where they could be adsorbed. Oxidation of the GIC adsorbent in the anodic compartment of an electrochemical cell was shown to attenuate the adsorbent’s ability to oxidise thiols. It was inferred that this was a result of a decrease in the amount of CO groups at the plane edges caused by this oxidation process. Keywords Adsorption Oxidation Graphite Mercaptans 1 Introduction The removal of organic sulfur compounds from waste streams presents a challenge shared across several M. G. Conti-Ramsden (&) K. Nkrumah-Amoako E. P. L. Roberts The University of Manchester, Oxford Road, Manchester M13 9PL, UK e-mail: [email protected] N. W. Brown Arvia Technology Ltd. The Innovation Centre, Sci-Tech Daresbury, Keckwick Lane, Daresbury, Cheshire WA4 4FS, UK
industries including the pulp and paper, petroleum refining and waste water treatment industries (Rios et al. 2008). The disagreeable odour of these compounds, which can be a nuisance at concentrations as low as ppb level (Smet and Langenhove 1998), means that wastes in both liquid and gas form have to be controlled at source. Different industries use different techniques to remove these components depending on effluent characteristics such as concentration, volume and required discharge consent (Rafson 1998). Activated carbons are considered a best available technique (BAT) and are used to remove these components by adsorption (Bashkova et al. 2002a). An interesting feature of the removal of thiols using activated carbon is the oxidation of adsorbed thiols to disulfides, a more readily adsorbed hence removed species (Bashkova et al. 2002a). In this paper the ability of a non-porous, electrically conducting graphite intercalation compound (GIC) to adsorb and oxidise thiols is studied. GICs have recently been used as adsorbents in a number of water and gas treatment processes based on fast adsorption coupled with adsorbent regeneration (Conti-Ramsden et al. 2012b; Mohammed et al. 2011; Brown and Roberts 2007; B
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