Structural effects in the reaction between carbon dioxide and coke doped with various potassium bearing catalytic precur
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I.
INTRODUCTION
THE reaction between coke and carbon dioxide C + CO2 = 2CO
[1]
has been studied extensively in the past. 1-8 The rate of this reaction is influenced by a large number of factors such as the crystallinity of carbon, concentration of active sites on the coke surface, the pore structure of coke, and the nature and the concentration of the inorganic compounds in the coke. 3 Among the inorganic compounds alkali metal oxides, hydroxides, and carbonates are known to be potent catalytic precursors. 9-12 In the blast furnace potassium cyanide is known to form in the bosh region. 13 As the cyanide vapor is carried up by the blast furnace gases, a portion of the cyanide vapor is converted to various other potassium compounds. Although the reaction between coke and carbon dioxide is an important reaction in the blast furnace, the role of KCN in the catalysis of this reaction is not clearly understood. Preliminary experiments in our laboratory indicated that during reaction between coke doped with KCN and carbon dioxide, KCN is partially converted to KOCN and K2CO3. In this study the roles of KCN, KOCN, and K2CO3 in the cokecarbon dioxide reaction were studied by thermogravimetry. The effects of various anionic constituents of the precursors on the rate of the reaction were examined. During the reaction between CO2 and coke doped with various potassium bearing precursors, both potassium and carbon are lost from the coke pellet. Therefore, the changes in the concentration of potassium in the coke samples doped with various catalytic precursors were determined by the atomic absorption spectrometry. Since the precursor-carbon contact is important in the catalysis, the distribution of potassium in the coke structure was examined by the energy dispersion X-ray technique. Furthermore, sulfur is known to influence the M. ALAM, formerly Graduate Student, now Postdoctoral Associate, and T. DEBROY, Associate Professor of Metallurgy, are with the Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802. Manuscript submitted January 2, 1986. METALLURGICALTRANSACTIONS B
coke-CO2 reaction.14 Therefore, the change in the concentration of sulfur during the reaction was also investigated. In the absence of a catalyst in coke, the rate of diffusion of CO2 through the gas boundary layer and the porous coke is often faster than the rate of the intrinsic chemical reaction between coke and CO2. However, when a catalyst is added to coke, the rate of the chemical reaction is significantly enhanced. In catalytic reactions, the need for CO2 to diffuse in the interior of the pellet at an accelerated pace, mandated by the catalytic enhancement of the rate of the reaction, makes the roles of structural parameters relatively more important in determining the overall reaction rate. During the reaction, the specific surface area, pore size distribution, and porosity of the coke change significantly. The influence of these changes on the reaction rate needs to be considered to understand
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