Chemistry

Bromine Scrub

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Science  09 Feb 2007:
Vol. 315, Issue 5813, pp. 739-741
DOI: 10.1126/science.315.5813.739d

One drawback of power generation from coal combustion is the atmospheric release of toxic mercury previously trapped in the solid coal. Although current emission filtration systems efficiently remove oxidized mercury compounds, they are less effective at trapping the metal in its water-insoluble elemental state. Combustion of chlorine-rich bituminous coals tends to pass less mercury through the filters, an observation that has been attributed to mercury oxidation by the chlorine. Liu et al. therefore explored the capacity of bromine, chlorine's more polarizable congener, to oxidize residual Hg(0) in coal emission streams. Laboratory-scale tests revealed a greater than hundredfold enhancement in the oxidation rate relative to measured chlorination kinetics. Moreover, the reaction was further accelerated by adsorption of the reagents onto fly-ash particles, with little or no inhibition observed from oxygen, CO, water, or HCl. Sulfur dioxide proved mildly inhibitory, whereas NO had a small promoting effect on the fly-ash-mediated oxidation. By extrapolating their data to the higher temperatures of a power plant emission stream, the authors estimate that the addition of 0.4 part per million of bromine to flue gas could oxidize 60% of residual Hg(0). — JSY

Environ. Sci. Technol. 41, 10.1021/es061705p (2007).

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