Transient phenomena in the steam-carbon reaction

Abstract

The kinetics of the reaction of graphite with steam (10 torr pressure) have been investigated in a static reactor over the temperature range 700 to 850°C. Changes in weight of the Graphon sample were determined micro-gravimetrically, and gaseous product evolution was followed mass-spectrometrically. Two parallel reaction pathways were identified. At sites of type I, reaction occurs without detectable formation of stable surface complexes and equimolar amounts of CO and H2 are evolved at a steady rate. It appears that the reaction at these sites is to be identified with that usually observed in conventional studies of the steam-carbon reaction and described by Langmuir-Hinshelwood kinetics. On freshly outgassed (1200° C, − C − C 11 * + H 2 O → C ( − H 2 ) + C O The complex, the precise form of which is unknown, is stable at temperatures below 950° C. The result is that, below 950° C, the type II reaction occurs on outgassed samples only transiently. It does not occur at all on samples previously exposed to steam and not subsequently subjected to outgassing. The availability of dual reaction pathways may help to reconcile conflicting conclusions reached by previous workers as to the formation of hydrogen complexes and their role in the steam-carbon reaction.