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 + 1/2S(2) = H2S, 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(H2) = k(r)[H-2][S-2] and -r(H2S) = k(d)[H2S][S-2](1/2), for the H-2/S-2 recombination and H2S decomposition reactions, respectively. The kinetic parameters derived for these rate processes, over the studied temperature range from 600 to 1300 degrees C, were found to be as follows: A(recomb) = 3.46 x 10(6) m(3)/(mol.s), E-a,E-recomb = 131.3 kJ/mol; A(decomp) = 2.26 x 10(9) m(3/2)/(mol(1/2).s), and E-a,E-decomp = 216.6 kJ/mol. This model has been shown to accurately predict the results of other published kinetic studies on H2S decomposition as well as equilibrium predictions for the system, H2S/H-2/S-i (i = 2-8), based on free energy calculations. A free-radical mechanism involving an initial bimolecular step between H2S and S-2, as opposed to unimolecular decomposition, is put forward to account for the new form of the H2S decomposition rate expression.