The mechanism of SO{sub 2} removal by carbon
- Illinois State Geological Survey, Champaign, IL (United States)
The goal of this study was to prepare activated char from Illinois coal with optimal properties for low temperature (80-150{degrees}C) removal of sulfur dioxide from coal combustion flue gas. The reaction of SO{sub 2} with carbon in the presence of O{sub 2} and H{sub 2}O involves a series of reactions which leads to the formation of sulfuric acid as the final product. The rate determining step in the overall process is thought to be the oxidation of SO{sub 2} to SO{sub 3}. Three SO{sub 2} oxidation reactions are possible. Adsorbed SO{sub 2} can react either with O{sub 2} or a carbon-oxygen (C-O) complex to form SO{sub 3}, or SO{sub 2} can react directly with the C-O complex. Most studies that seek to maximize the SO{sub 2} removal capability of a carbon material only assume a given mechanism for SO{sub 2} adsorption and conversion to H{sub 2}SO{sub 4} is operable. The role of the C-O complex in this mechanism remains to be determined. In this study, we found the SO{sub 2} also adsorption capacity of a char to be inversely proportional to the amount of oxygen adsorbed on its surface. A temperature programmed desorption technique was developed to titrate those sites responsible for adsorption of SO{sub 2} and conversion to H{sub 2}SO{sub 4}. Based on these results, a mechanism for SO{sub 2} removal by carbon was proposed. The derived rate expression shows SO{sub 2} adsorption to be dependent only an the fundamental rate constant and concentration of carbon atoms we designate as free sites. Recent studies suggest a similar relationship exists between the rate of carbon gasification in carbon dioxide or steam and the number of reactive sites as determined by transient kinetics experiments.
- OSTI ID:
- 370329
- Report Number(s):
- CONF-960376--
- Country of Publication:
- United States
- Language:
- English
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