KINETIC MODELS FOR UNCATALYZED AND POTASSIUM-CATALYZED GASIFICATION OF CHAR BY CARBON DIOXIDE (ADSORPTION, TWO-SITE, CATALYST)
Abstract
A differential packed-bed reactor has been employed to study the gasification of uncatalyzed and 7.5 wt% K(,2)CO(,3)-catalyzed Saran char in carbon dioxide/carbon monoxide mixtures at a total pressure near 1 atm (101.3 kPa). The gasification temperature was varied between 1131 and 1229 K for the uncatalyzed case, and between 922 and 1046 K for the catalyzed case. Gasification rate data were tested with a model which involves two-site adsorption and subsequent dissociation of CO(,2) on the char surface. The results indicate that this model adequately explains both the uncatalyzed and catalyzed gasification data. However, higher concentrations of carbon-oxygen complex, C(O) , exist on the surface during catalyzed gasification. The increase in C(O) weakens carbon-carbon bonds and thus lowers the activation energy for desorption of the C(O) complex. Adsorption of CO and CO(,2) on both catalyzed and uncatalyzed chars was also followed with a volumetric adsorption apparatus at pressures between 1 and 100 kPa and temperatures from 273 to 725 K. The catalyzed char adsorbed an order of magnitude more CO(,2) at 559 K than the uncatalyzed char. Subsequent dissociation of CO(,2) on the carbon surface does not appear to be catalyzed by potassium. Thus, the catalyst's role is to augment the efficiency and/or number of sites for CO(,2) adsorption, thereby creating more oxygen on the surface. The higher rate during catalyzed gasification can be attributed to a combination of increased C(O) and a smaller activation energy for desorption of C(O).
Degree
Ph.D.
Subject Area
Chemical engineering
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