Mechanisms of CO and COS formation in the Claus furnace

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 SS, 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 H-2 and S-2 at high temperatures (> 1000 degreesC) 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 <degrees>C, but reaction with either H2O or SO2 was fast above 900 degreesC. Conversion of CS2 by H2O led to CO, H-2, H2S, S-2, and CO2, whereas reaction with SO2 resulted in CO2 and St as the major products. Similar observations were made for the reactions of COS with HzO and SO2. The summary of pathways presented in Scheme 5 shows a complex interlinkage among many reactions involving H2S, CO2, CO, COS, SO2, and S-2, leading to the conclusion that previous explanations of the production of COS from CO f Sg 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.