CALCIUM-CATALYZED CARBON GASIFICATION IN CO2 AND STEAM

Isothermal CO2 (0.1 MPa) and steam (19.7 KPa) reactivities on pure polymer carbons have been studied at different temperatures as a function of their calcium contents. Ion-exchange and impregnation methods have been used to load the carbons from calcium acetate solutions. Calcium appears to be a very active catalyst for both reactions, its effectivity being much higher in CO2 than in steam. Reactivities in both atmospheres increase linearly with Ca content up to a loading saturation level (LSL) of about 4 wt%. For comparable calcium loading, the catalyst addition method, ion-exchange or impregnation, does not produce any significant difference. Selective CO2 chemisorption has been used to determine the Ca atoms on the surface of the catalyst (and hence its external surface area or dispersion) as functions of both the calcium loading and the preparation method. The results obtained show that CO2 chemisorption is much more suitable than XRD. This allows interpretation of the catalytic activity of Ca in the carbon-gas reactions. Briefly, gasification rates are related to the amount of CO2 chemisorbed. The different catalytic behaviour of calcium catalyst above and below the LSL has been interpreted as being due to catalyst dispersion conditioned by carbon carboxyl groups. Only the exchanged calcium has a catalytic activity, whereas the excess calcium has low dispersion, its mean particle size increases considerably, and does not have additional catalytic activity. © 1990.