(632b) Mercury Adsorption and Oxidation On Brominated Carbon Fibers in Combustion Flue Gas

Coal-fired power plants provided between 45 and 50% of the United States net energy generation in the years between 1999 and 2010. While alternate sources of energy, including natural gas and renewable sources, will continue to grow in importance, coal will remain as a necessary item in the energy portfolio of the US. Furthermore, the rapidly expanding economies of China and India are increasingly reliant on coal power, with upwards of 80% and 60%, respectively, of power consumption in the two countries provided by coal-fired power plants.

The use of coal has several drawbacks, including: the release of hazardous air pollutants (SO₂, NO_x, particulate matter); the release of gases, such as CO₂ with Global Warming Potentials; and the release of trace metals, with high levels of human toxicity, such as mercury. Hazardous air pollutants are largely regulated by the United States Environmental Protection Agency (US EPA) and climate change is currently a research area with intense monetary and manpower support. The release of mercury, Hg, from coal-fired power plants has only recently been regulated by the US EPA in the Mercury and Air Toxics Standards (MATS) ruling in December 2011 and has a direct impact on environmental health, especially in densely populated urban areas surrounded by coal-fired power plants, such as the Great Lakes region and the Eastern Seaboard of the US, as well as many Chinese and Indian urban centers.

In this study, bromine-impregnated carbon fiber (Br-AC) was tested for Hg capture and oxidation. An experimental system has been designed to simulate the combustion flue gas environment (CO₂, H₂O, NO_x, SO₂) where the sorbent is tested. Elemental and total (oxidized + elemental) Hg vapor is introduced from a mercury calibration system (PSA 10.536 Mercury Calibration System, PS Analytical, England) with the concentration of outlet flow measured using a commercial Hg analyzer (PSA 10.525 Sir Galahad System, PS Analytical, England). In this manner, the amount of oxidized Hg (Hg²⁺) can be calculated. Breakthrough curves are obtained for the PBR experiments by measuring the mercury concentration at the reactor outlet. Outlet concentration is plotted as a function of time, and as the outlet concentration approaches that of the inlet, breakthrough is achieved. Results indicate that NO_x (NO and NO₂) promote the oxidation of Hg, while SO₂ prevents the adsorption or oxidation of Hg on the Br-AC. Currently, work is underway in an attempt to determine the oxidation state of Hg, which will help elucidate the mechanism of adsorption and oxidation, and create a better understanding of the Hg adsorption system.