This work addresses the discrepancy in the literature regarding the effects of sulfuric acid (H(2)SO(4)) on elemental Hg uptake by activated carbon (AC). H(2)SO(4) in AC substantially increased Hg uptake by absorption particularly in the presence of oxygen. Hg uptake increased with acid amount and temperature exceeding 500 mg-Hg/g-AC after 3 days at 200 °C with AC treated with 20% H(2)SO(4). In the absence of other strong oxidizers, oxygen was able to oxidize Hg. Upon oxidation, Hg was more readily soluble in the acid, greatly enhancing its uptake by acid-treated AC. Without O(2), S(VI) in H(2)SO(4) was able to oxidize Hg, thus making it soluble in H(2)SO(4). Consequently, the presence of a bulk H(2)SO(4) phase within AC pores resulted in an orders of magnitude increase in Hg uptake capacity. However, the bulk H(2)SO(4) phase lowered the AC pore volume and could block the access to the active surface sites and potentially hinder Hg uptake kinetics. AC treated with SO(2) at 700 °C exhibited a much faster rate of Hg uptake attributed to sulfur functional groups enhancing adsorption kinetics. SO(2)-treated carbon maintained its fast uptake kinetics even after impregnation by 20% H(2)SO(4).
Alberta oil-sands petroleum coke is an abundant byproduct of the upgrading of bitumen. The current study aims to improve the current understanding of sulfur added to the surface of petroleum coke through reaction with sulfur dioxide (SO 2 ) and how this is affected by a large excess of oxygen (O 2 ). Particular focus is given to the distribution and speciation of sulfur within the coke particles, as well as its thermal stability. Petroleum coke was activated in SO 2 with and without O 2 in a packed bed reactor at 600-800 °C. The activated cokes were characterized with electron probe microanalysis (EPMA), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). Cross-sectional analysis with EPMA of activated coke particles revealed that sulfur-rich coke particles (i.e., SIAC) could be produced with and without O 2 . Under low SO 2 (3%), high O 2 (18%) conditions, however, O 2 competitively reacted with coke at 600 °C, and SO 2 only reacted to form a sulfur-rich layer after O 2 had been depleted. Analysis with XPS suggested that the sulfur-rich layer of the coke particles was made up of thiophene from the coke plus carbon-sulfur surface complexes, mainly heterocyclic sulfide and disulfide, while the presence of aliphatic sulfide, thiolactone, and thiol could not be ruled out. TGA and DSC analyses confirmed that sulfur added to activated coke via reaction with SO 2 was not elemental in nature. In both N 2 and air, sulfur added via hightemperature reaction with SO 2 is more thermally stable than that of a commercial SIAC sulfurized at lower temperatures. This may have beneficial implications if these SO 2 activated cokes were to be used to capture mercury, since they could be thermally regenerated with minimal loss of active sulfur surface sites while the captured mercury is collected, avoiding the costly and potentially problematic landfill disposal of Hg-containing activated carbon.
Fluid coke is a by-product of bitumen upgrading process and a stockpiled industrial waste produced in large quantities in Alberta, Canada (overall 10,000 tonnes per day). It has been used as a raw material for manufacturing sulfur-impregnated activated carbon (SIAC). Properties of sulfur in the SIAC are critical to the effectiveness of SIAC in adsorbing mercury at ppb levels. K-edge X-ray absorption near edge structure (XANES) spectroscopy was employed to characterize sulfur in two fluid coke samples and their activation products. It was found that about 90% of sulfur in two coke samples is of organic nature, with over 50% of sulfur in the form of thiophene and the rest 40% being organic sulfide. About 10% of sulfur is in the form of oxides, i.e. sulfate. To simulate the coke samples and validate the analytical technique, a mixture of pure sulfur compounds and graphite was prepared and examined with XANES; the results showed good agreement between the actual and measured sulfur contents in specific forms. XANES results were found to be consistent with X-ray photoelectron spectroscopy (XPS) results. The two techniques are complementary to each other; XANES is capable of distinguishing sulfur species at low oxidation states whereas XPS is able to separate some sulfur species with higher oxidation state. The activation process with KOH and SO 2 affected the chemistry of sulfur in fluid coke. XANES surface analysis identified disulfide, sulfide, sulfonate, and sulfate in SIACs and found no thiophene, suggesting a complete removal of thiophene from carbon surface by KOH.
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.
This paper reports the development of an in situ continuous emission monitor (CEM) for measuring elemental mercury (Hg(0)) concentration in the exhaust stream of coal-fired power plants. The instrument is based on the ultraviolet atomic absorption of a mercury lamp emission line by elemental mercury and a light-emitting diode (LED) background correction system. This approach allows an in situ measurement since the absorption of other species such as SO(2) can be removed to monitor the Hg(0) contribution only. Proof of concept was established through a laboratory-based investigation, and a limit of detection, [Hg(0)](min), of 2 microg/m(3) was measured for a 1-min averaged sample and an absorption path length of 49 cm. [Hg(0)](min) is anticipated to be better than 0.2 microg/m(3) across a 7 m diameter stack. Finally, the apparatus was field-tested in a 230 MW coal-fired power plant. The operability of the measurement in real conditions was demonstrated, leading to the first Hg(0) concentration values recorded by the in situ CEM. Comparison with an accepted standard method is required for validation.
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