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Thief Carbon Catalysts for Oxidation of Mercury in Effluent Stream

National Energy Technology Laboratory

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Technology Marketing Summary
Disclosed in this patent are catalysts for the oxidation of elemental mercury in flue gas. These novel catalysts include iridium
(Ir), platinum/iridium (Pt/Ir), and Thief carbons. The catalyst materials will adsorb the oxidizing agents HCl, Cl2 and other halogen species in the flue gas stream that are produced when fuel is combusted. These adsorbed oxidizing agents can then react with elemental mercury in the stream, which is difficult to capture, and oxidize it to form Hg (II) species, such as mercuric chloride (HgCl2, which is soluble in water and more easily removed from the stream.)
Certain effluent gas streams contain many toxic pollutants, including the heavy metals mercury and cadmium. Much research has been done to develop methods to control mercury emissions from flue gases. These methods employ sorbents, catalysts (including those for selective catalytic reduction (SCR)), scrubbing liquors, flue gas or coal additives, combustion modifications, barrier discharges, and ultraviolet radiation. Existing SCR catalysts are not optimized for selectively oxidizing elemental mercury in effluent streams, and typically achieve only 50 percent oxidation.
The Ir and Pt/Ir catalysts described in this patent adsorb mercury and HCl and Cl2 at high levels. By doing so, they bring together the oxidizing agents HCl and Cl2 with elemental mercury to oxidize most of the mercury to Hg (II) species. Mercury (II) chloride is readily removed by the scrubbing solutions employed for acid gas removal and/or by adsorption on unburned carbon in fly ash captured by ESPs or baghouse filters.
These catalysts exhibit superior anti-corrosion and high-temperature resistance characteristics. Furthermore, when using Thief carbon, which is partially combusted coal removed from the combustion chamber of a power plant using a lance (called a “thief”), the catalyst is self-activated (by adsorbing Cl2 from the flue gas) and disposable.
These mercury oxidation catalysts have the
following advantages:
• They can be used to reduce mercury emis-
sions in coal-burning power plants, incin-
erators, oil-burning boilers and power plants,
and refuse-derived fuel power plants
• They can adsorb mercury, HCl, Cl2 and other
halogen species present in flue gases at high
levels for efficient oxidation of elemental
• Ir-containing catalysts are more temperature-
resistant than currently available catalysts
for mercury removal
• Ir-containing catalysts are more corrosion
resistant than existing mercury removal
catalysts, thus leading to a longer active
• Thief carbons are far less expensive than
conventional gold or palladium catalysts
• Thief carbons are inexpensive enough to
be disposable
Applications and Industries

Reduction of mercury emisssions in coal-burning power plants, incinerators, oil-burning boilers and power plants,and refuse-derived fuel power plants

Patents and Patent Applications
ID Number
Title and Abstract
Primary Lab
Patent 7,776,780
Catalysts for oxidation of mercury in flue gas
Two new classes of catalysts for the removal of heavy metal contaminants, especially mercury (Hg) from effluent gases. Both of these classes of catalysts are excellent absorbers of HCl and Cl.sub.2 present in effluent gases. This adsorption of oxidizing agents aids in the oxidation of heavy metal contaminants. The catalysts remove mercury by oxidizing the Hg into mercury (II) moieties. For one class of catalysts, the active component is selected from the group consisting of iridium (Ir) and iridum-platinum (Ir/Pt) alloys. The Ir and Ir/Pt alloy catalysts are especially corrosion resistant. For the other class of catalyst, the active component is partially combusted coal or "Thief" carbon impregnated with Cl.sub.2. Untreated Thief carbon catalyst can be self-activating in the presence of effluent gas streams. The Thief carbon catalyst is disposable by means of capture from the effluent gas stream in a particulate collection device (PCD).
National Energy Technology Laboratory 08/17/2010
Technology Status
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