Ambient temperature mercury oxidation thermochemistry and kinetics via chlorine and bromine

Document Type

Conference Proceeding

Publication Date

12-1-2010

Abstract

Emissions of gaseous mercury from combustion sources are the major source of Hg in the atmosphere and in environmental waters and soils. Reactions of Hg°(g) with halogens are of interest because they relate to Hg and ozone loss in the Antarctic and Arctic early spring ozone hole events, and the formation of Hg-halides (HgX2) is a method for reduction (capture) of Hg emissions from power generation. The conversion of mercury into mercury bromide and chloride has been studied in a number of recent experimental and theoretical (computational chemistry) papers. Several studies have focused on atmospheric conditions. In this study we use the thermochemistry and kinetics from published theoretical and experimental studies, to compile a mechanism of the reactions considered as contributors to the formation of HgX2, (X = Cl, Br) for atmospheric conditions and to understand the reaction paths and mechanism. Thermochemical properties and kinetic parameters are from literature and from computational chemistry. Elementary reaction mechanisms are assembled and evaluated using microscopic reversibility for all reactions. Temperature and pressure dependence is determined with quantum RRK analysis for k(E) and Master Equation analysis for fall-off. We find initiation by halogen atoms is needed to explain the experimental loss of Hg to HgX2; in general the experiments do not have this source. We further evaluate a Hg insertion reaction into X2 (Hg + X2 = HgX2) that has been reported and find that that models can explain the experimental data only if the barrier for the insertion is significantly lower than evaluated by theory. We conclude that further studies are needed to elucidate the mechanism for the Hg conversion observed in experiments under non photochemical - atmospheric conditions.

Identifier

78751538721 (Scopus)

ISBN

[9780816910656]

Publication Title

Aiche Annual Meeting Conference Proceedings

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