The aim of this study was to determine the major pathways leading to COS and CO formation and consumption during the processing of H2S and CO2 in the partially oxidizing conditions of the Claus furnace. Both species were found to be produced by a multitude of pathways, which include the direct reaction of H2S with CO2 to form COS and H2O and the reaction of CO2 with S2, one of the major primary products in a Claus furnace. This last reaction produced SO2 and CO as the major products, with COS being formed in lesser quantities. The dissociation of H2S to H2 and S2 at high temperatures (>1000 °C) was shown to promote a further cascade of reactions stemming from the reduction of COS and CO2, both of which lead to CO. Because of the known formation of CS2 from hydrocarbon carry-over into the furnace, the reactions of CS2 with CO2, H2O, and SO2 were also studied as potential CO- and COS-forming reactions. Reaction with CO2 was slow at <1200 °C, but reaction with either H2O or SO2 was fast above 900 °C. Conversion of CS2 by H2O led to CO, H2, H2S, S2, and CO2, whereas reaction with SO2 resulted in CO2 and S2 as the major products. Similar observations were made for the reactions of COS with H2O and SO2. The summary of pathways presented in Scheme shows a complex interlinkage among many reactions involving H2S, CO2, CO, COS, SO2, and S2, leading to the conclusion that previous explanations of the production of COS from CO + S2 and CO from incomplete combustion dramatically oversimplifies the formation/consumption for these compounds. It also shows that modeling of individual kinetic rate expressions is somewhat impractical.

The pyrolysis of hydrogen sulfide has been studied at residence times between 0.4 and 1.6 s and in the temperature range of 800−1100 °C. A continuous perfectly mixed quartz reactor was used to acquire kinetic data on the thermal dissociation of hydrogen sulfide and elemental sulfur mixtures diluted in argon (95 vol %). The kinetic auto-acceleration effect of sulfur is demonstrated. A detailed radical mechanism is written to account for the experimental results, in particular for the auto-acceleration effect, and validated against experimental results. This pyrolysis kinetic scheme is the first step and core of a complete detailed mechanism capable of modeling the various oxidation reactions encountered in an industrial Claus furnace.

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