STEAM GASIFICATION OF GRAPHITE AND CHARS AT TEMPERATURES-LESS-THAN-1000-K OVER POTASSIUM-CALCIUM-OXIDE CATALYSTS

The catalytic steam gasification of graphite and several chars to H2 and CO2 has been studied using a KCaOx catalyst (KCa/C = 0.01 atomic ratio) in a flow reactor system at relatively low temperatures (600-950 K) and in a controlled atmosphere electron microscope (CAEM). A kinetic study of graphite gasification with water was performed. KCaOx appeared to be less sensitive to hydrogen partial pressure that has an inhibiting effect on this reaction than other active catalysts. Evidence was found for water dissociation on the catalyst. Activation energies obtained in the flow reactor system were essentially the same as those for graphite and chars and for various catalysts. The KCaOx catalyst was more resistant to sulfur poisoning than a KNiOx catalyst described in a previous publication. A CAEM study of the KCaOx catalyzed steam gasification of graphite showed: (1) a homogeneous composition of the dispersed K-Ca catalyst mixture; (2) graphite consumption by edge recesssion during steam gasification; (3) an activation energy close to that found in the flow reactor system. The results indicate that steam gasification proceeds via water dissociation and oxygen transfer to the carbon. The rate-controlling step, however, is the CC bond breaking next to a surface carbon-oxygen complex which produces CO2. Chars gasify at rates higher by an order of magnitude than that of graphite. The KCax catalyst exhibits superior poison resistance. © 1990.