Kinetics of Oxidation of carbonaceous Materials by CO2 and H2O between 1300 degrees C and 1500 degrees C

The kinetics of the oxidation of graphite, metallurgical coke, and glassy c arbon by CO2 and H2O were investigated at temperatures between 1300 degrees C and 1500 degrees C. The experimental technique employed a lance-crucible geometry with continuous gas analysis to measure the reaction rate. The ex periments were designed to ensure that the carbon reaction behavior was in the limited mixed regime, where only a small volume of material close to th e surface is reacting, and external gas phase mass transfer was fast. The r esults demonstrated the importance of internal pore structure, particularly as it develops in the reacted layer during the course of the reaction. Thi s was believed to be responsible for the higher rates measured in graphite than in coke and the time-dependent rate increase that was observed in nonp orous glassy carbon during experiments. For a commercial grade graphite and metallurgical coke, the rate constants depended strongly upon the carrier gas species, indicating that molecular diffusion was the primary transport mechanism in the pores of these materials. In contrast, for a specially pur ified graphite, the rate constant was found to be independent of the carrie r gas species, which suggested Knudsen diffusion control dominates in this carbon. The results are in good agreement with extrapolations of previous w ork carried out at lower temperatures.