Mechanism of SO2 Removal by Carbon

The reaction of SO2 with carbon (C) in the presence of O2 and H2O involves a series of reactions that leads to the formation of sulfuric acid as the final product. The rate-determining step in the overall process is the oxidation of SO2 to SO3. Three SO2 oxidation reactions are possible. Adsorbed SO...

Full description

Saved in:
Bibliographic Details
Published inEnergy & fuels Vol. 11; no. 2; pp. 284 - 291
Main Authors Lizzio, Anthony A, DeBarr, Joseph A
Format Journal Article
LanguageEnglish
Published American Chemical Society 19.03.1997
Online AccessGet full text

Cover

Loading…
More Information
Summary:The reaction of SO2 with carbon (C) in the presence of O2 and H2O involves a series of reactions that leads to the formation of sulfuric acid as the final product. The rate-determining step in the overall process is the oxidation of SO2 to SO3. Three SO2 oxidation reactions are possible. Adsorbed SO2 (C−SO2) can react either with gas phase O2 or with adsorbed oxygen (C−O complex) to form sulfur trioxide (SO3), or gas phase SO2 can react directly with the C−O complex. In optimizing the SO2 removal capabilities of carbon, most studies only assume a given mechanism for SO2 adsorption and conversion to H2SO4 to be operable. The appropriate SO2 oxidation step and role of the C−O complex in this mechanism remain to be determined. The ultimate goal of this study was to prepare activated char from Illinois coal with optimal properties for low-temperature (80−150 °C) removal of sulfur dioxide from coal combustion flue gas. The SO2 adsorption capacity of activated char was found 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 SO2 and conversion to H2SO4. On the basis of these results, a mechanism for SO2 removal by carbon was proposed. The derived rate expression showed SO2 adsorption to be dependent only on the fundamental rate constant and concentration of carbon atoms designated as free sites. Recent studies indicate a similar relationship exists between the rate of carbon gasification (in CO2 or H2O) and the number of reactive sites as determined by transient kinetics experiments. Utilizing the concept of active or free sites, it was possible to produce a char from Illinois coal having an SO2 adsorption capacity surpassing that of a commercial catalytic activated carbon.
Bibliography:ark:/67375/TPS-SX874VXJ-P
Abstract published in Advance ACS Abstracts, February 15, 1997.
Paper presented at the National Meeting of the American Chemical Society, New Orleans, recipient of R. A. Glenn Award from the Division of Fuel Chemistry.
istex:1647A8722F9BDC78EDAAC33E4AB02494B54E41AA
ISSN:0887-0624
1520-5029
DOI:10.1021/ef960197+