Kinetic Modeling of the Reaction between Hydrogen and Sulfur and Opposing H2S Decomposition at High Temperatures

The results of the previously reported kinetic study of the reaction between H 2 and sulfur, H 2 + 1 / 2 S 2 = H 2 S, under Claus furnace conditions (Dowling; Hyne; Brown. Ind. Eng. Chem. Res . 1990, 29, 2327), have been reevaluated using a more rigorous analysis. The results of this reinvestigation were found to be consistent with a reversible kinetic model based on the rate expressions, − r H 2 = k r [H 2 ][S 2 ] and − r H 2 S = k d [H 2 S][S 2 ] 1/2, for the H 2 /S 2 recombination and H 2 S decomposition reactions, respectively. The kinetic parameters derived for these rate processes, over the studied temperature range from 600 to 1300 °C, were found to be as follows: A recomb = 3.46 × 10 6 m 3 /(mol.s), E a,recomb = 131.3 kJ/mol; A decomp = 2.26 × 10 9 m 3/2 /(mol 1/2 .s), and E a,decomp = 216.6 kJ/mol. This model has been shown to accurately predict the results of other published kinetic studies on H 2 S decomposition as well as equilibrium predictions for the system, H 2 S/H 2 /S i ( i = 2−8), based on free energy calculations. A free-radical mechanism involving an initial bimolecular step between H 2 S and S 2, as opposed to unimolecular decomposition, is put forward to account for the new form of the H 2 S decomposition rate expression.