Chemical mechanisms in mercury emission control technologies

Olson, Edwin S.; Laumb, Jason D.; Benson, Steven A.; Dunham, Grant E.; Sharma, Ramesh K.; Mibeck, Blaise A.F.; Miller, Stanley J.; Holmes, Mike; Pavlish, John H.

doi:10.1051/jp4:20030462

Cited by 14 publications

(14 citation statements)

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“…29 -32 Previous studies have considered models of C edges comprised of armchair and zigzag sites. [33][34][35][36] The major conclusion from these previous investigations is that the zigzag sites with carbene atoms are the most reactive with the C atom having two unpaired electrons. 37,38 The goal of this work is to identify trends in the adsorption and oxidation of Hg 0 on functionalized edge sites under relevant conditions of the surrounding flue gas.…”

Section: Resultsmentioning

confidence: 99%

Heterogeneous Mercury Reaction Chemistry on Activated Carbon

Wilcox

Sasmaz

Kirchofer

et al. 2011

Journal of the Air & Waste Management Association

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Experimental and theory-based investigations have been carried out on the oxidation and adsorption mechanism of mercury (Hg) on brominated activated carbon (AC). Air containing parts per billion concentrations of Hg was passed over a packed-bed reactor with varying sorbent materials at 140 and 30°C. Through X-ray photoelectron spectroscopy surface characterization studies it was found that Hg adsorption is primarily associated with bromine (Br) on the surface, but that it may be possible for surfacebound oxygen (O) to play a role in determining the stability of adsorbed Hg. In addition to surface characterization experiments, the interaction of Hg with brominated AC was studied using plane-wave density functional theory. Various configurations of hydrogen, O, Br, and Hg on the zigzag edge sites of graphene were investigated, and although Hg-Br complexes were found to be stable on the surface, the most stable configurations found were those with Hg adjacent to O. The Hg-carbon (C) bond length ranged from 2.26 to 2.34 Å and is approximately 0.1 Å shorter when O is a nearest-neighbor atom rather than a next-nearest neighbor, resulting in increased stability of the given configuration and overall tighter Hg-C binding. Through a density of states analysis, Hg was found to gain electron density in the six p-states after adsorption and was found to donate electron density from the five s-states, thereby leading to an oxidized surface-bound Hg complex.

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Section: Resultsmentioning

confidence: 99%

Heterogeneous Mercury Reaction Chemistry on Activated Carbon

Wilcox

Sasmaz

Kirchofer

et al. 2011

Journal of the Air & Waste Management Association

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“…However, this was not observed when H 2 O was omitted, indicating the formation of H 2 SO 4 via NO 2 -oxidized SO 2 , in good agreement with Laumb et al (71) and Olson et al (72). Thus, while NO 2 is important for Hg 0 oxidation and retention as per the mechanism described by Olson et al (69,70), the combination of NO 2 , SO 2 , and H 2 O leads to poisoning of the surface by H 2 SO 4 . Furthermore, adding SO 2 alone and in combination with NO resulted in reduction of the HgCl 2 to Hg 0 , which could also hinder uptake performance.…”

Section: Uptake Of Mercury To Virgin Activated Carbonmentioning

confidence: 95%

“…Large amounts of H 2 SO 4 on an activated carbon surface may block access to pores, thus eliminating the vast majority of the surface area on which oxidation and binding of mercury may occur. On the other hand, small amounts of H 2 SO 4 which do not affect mass transfer of mercury into the inner pores may actually improve the adsorption capacity by creating oxidation sites (69,70). However, a coal combustion flue gas is at an elevated temperature and contains substantial amounts of moisture, oxidants, SO 2 , and SO 3 .…”

Section: Understanding the Effect Of H 2 So 4 On Mercury Uptakementioning

confidence: 97%

“…First, carbenium ion oxidation sites are formed by reaction of HCl with zigzag edge structures. Hg 0 is then oxidized by NO 2 or other oxidizing gases at these oxidation sites (69). The oxidized mercury is then bound to similar zigzag structure carbenium ions which act as Lewis basic sites (70).…”

Section: Oxidation Of Hg On Carbon Surfacesmentioning

confidence: 99%

“…Hg 0 is then oxidized by NO 2 or other oxidizing gases at these oxidation sites (69). The oxidized mercury is then bound to similar zigzag structure carbenium ions which act as Lewis basic sites (70). XPS evidence was found suggesting that NO 2 actively oxidizes sulfur in SO 2 to SO 3 , which, when combined with H 2 O to form H 2 SO 4 , then deactivates the basic binding sites which are necessary for retention of Hg 2+ (71, 72).…”

Section: Oxidation Of Hg On Carbon Surfacesmentioning

confidence: 99%

See 2 more Smart Citations

Understanding the effects of sulfur on mercury capture from coal-fired utility flue gases

Morris

Morita

Jia

2010

Journal of Sulfur Chemistry

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Coal combustion continues to be a major source of energy throughout the world and is the leading contributor to anthropogenic mercury emissions. Effective control of these emissions requires a good understanding of how other flue gas constituents such as sulfur dioxide (SO 2 ) and sulfur trioxide (SO 3 ) may interfere in the removal process. Most of the current literature suggests that SO 2 hinders elemental mercury (Hg 0 ) oxidation by scavenging oxidizing species such as chlorine (Cl 2 ) and reduces the overall efficiency of mercury capture, while there is evidence to suggest that SO 2 with oxygen (O 2 ) enhances Hg 0 oxidation by promoting Cl 2 formation below 100 • C. However, studies in which SO 2 was shown to have a positive correlation with Hg 0 oxidation in full-scale utilities indicate that these interactions may be heavily dependent on operating conditions, particularly chlorine content of the coal and temperature. While bench-scale studies explicitly targeting SO 3 are scarce, the general consensus among full-scale coal-fired utilities is that its presence in flue gas has a strong negative correlation with mercury capture efficiency. The exact reason behind this observed correlation is not completely clear, however. While SO 3 is an inevitable product of SO 2 oxidation by O 2 , a reaction that hinders Hg 0 oxidation, it readily reacts with water vapor, forms sulfuric acid (H 2 SO 4 ) at the surface of carbon, and physically blocks active sites of carbon. On the other hand, H 2 SO 4 on carbon surfaces may increase mercury capacity either through the creation of oxidation sites on the carbon surface or through a direct reaction of mercury with the acid. However, neither of these beneficial impacts is expected to be of practical significance for an activated carbon injection system in a real coal-fired utility flue gas.

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Mercury‐Carbon Surface Chemistry

Olson

2014

Mercury Control

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Chemical mechanisms in mercury emission control technologies

Cited by 14 publications

References 0 publications

Heterogeneous Mercury Reaction Chemistry on Activated Carbon

Heterogeneous Mercury Reaction Chemistry on Activated Carbon

Understanding the effects of sulfur on mercury capture from coal-fired utility flue gases

Mercury‐Carbon Surface Chemistry

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