Reaction of carbon with hydrogen sulfide at high temperature (1000-2ooo"C) and low pressure (10~4-10~2 Torr) exhibits the following features: -carbon disulfide CS2 is the only carbonaceous reaction product. There is no indication that CS2 would originate from a secondary reaction of the unstable carbon monosulfide CS. Some decomposition of H2S into its elements is also observed (Figs. l -3).
-as already observed in other high temperature carbon gasification reactions, the intrinsic reactivity of the sample surface is temperature and pressure dependent. Consequently, transitory or stationary rates are observed, depending respectively upon a changing or a stationary surface state of the carbon sample (Fig. 4). The changes in the surface state are more marked for amorphous than for graphitized samples (Fig. 5).
-below 17OO"C, the true reaction order is smaller than one, as a consequence of the high stability of the carbon-sulfur surface complexes.
-for ungraphitized samples, the carbon surface loses slowly and irreversibly its ability to change with changes in pressure and temperature. All these features were previously observed in the reaction of carbon with sulfur vapor: consequently hydrogen sulfide appears to behave simply as a gaseous sulfur carrier. The kinetic behaviour is in agreement with former interpretations assuming presence of peculiar reactive sites, which originate from chemical attack of the solid but disappear due to a surface thermal heating process. Confirming also previous assumptions, sulfur chemisorption strongly affects the reaction kinetics, as shown by the influence of H2S traces on the kinetics of the C-O2 reaction (Fig. 10): -at lower temperatures (< 13WC) there is an important inhibiting effect on the CO production: HIS is adsorbed strongly on the reactive sites which become inaccessible to O2 molecules. -in the intermediate temperature range an enhancing effect is observed which is attributed to a hindrance of thermal healing (caused by chemisorption still present). Finally, the kinetic features as a whole are tentatively summarized in a comprehensive diagram where the consistency of experimental results appears clearly.