Chemical kinetic modeling of the H/S system:: H2S thermolysis and H2 sulfidation

A detailed chemical mechanism to describe reactions in the H-2-S-2-H2S system has been constructed. The mechanism comprises 21 reactions among the species H2S, S-2, H-2, HSSH, HSS, SH, S, and H. The structure of the mechanism resembles closely that of the H-2-O-2 system. For a few reactions, experimental values for rate constants were taken from the literature, but the kinetics of most of the reactions have been studied theoretically, using a combination of transition state theory for bimolecular reactions, master equation calculations for unimolecular decompositions, and QRRK methods for chemically activated reactions. The mechanism has been validated against a diverse collection of published data for H2S thermolysis in a static cell or in flow reactors, for temperatures ranging from 873 to 1423 K, pressures from 0.04 to 3 bar, and H2S mole fractions from 0.02 to 1. The predictions of the mechanism are sensitive only to the rates of the processes responsible for S-S bond formation, HSS + H reversible arrow 2SH (R8) HSSH (+ M) reversible arrow 2SH (+ M) (R9) HSSH + H reversible arrow H2S +SH (R16) Slight adjustment of these rates allows the data to be modeled accurately. Data for the reverse, hydrogen sulfidation reaction (H-2 + S-2) are also modeled very accurately. This comprehensive chemical kinetic mechanism for the H/S system not only describes a wide range of experimental data but also provides the basis for the construction of accurate models for H2S oxidation in combustion and related systems.