Oxidation of hydrogen sulfide and CO₂ mixtures: Laser-based multi-speciation and kinetic modeling

Hydrogen sulfide (H₂S), encountered in sour natural gas and in fossil fuel refineries, has adverse health and environmental impacts, but also the potential to be a source of clean hydrogen. This work addresses knowledge gaps and inconsistencies in H₂S oxidation measurements and model predictions, emphasizing the scarcity of detailed kinetic modeling of H₂S oxidation in the presence of carbon dioxide (CO₂), a significant component of acid gas. This study leverages a shock tube coupled with laser absorption techniques to investigate the oxidation of mixtures of acid gas (H₂S and CO₂) with high H₂S concentrations, equivalence ratios between 1.5 and 3.0, over the temperature range of 1300 – 1900 K and pressure near 1.3 bar. A detailed kinetic mechanism is proposed and validated through the measurement of time-histories of SO₂, H₂O, and CO, during fuel-rich acid gas oxidation. For the species measurements, we first conducted a comprehensive wavelength analysis for interference-free detection of the target species, providing new temperature-dependent absorption cross-section measurements of SO₂ at its strongest IR band; moreover, we proposed a new laser-based thermometry technique for temperature time-history measurements behind reflected shock waves. The proposed kinetic mechanism is updated based on our recently calculated rate constants for reactions involving sulfurous species using high-level quantum chemistry and master equation calculations. The model outperforms former models at predicting measured time histories across the range of experimental conditions and elucidates different stages of the formation of target species. Important reactions in the new kinetic model are identified and discussed with reference to literature models, highlighting the reasons for the differences in model predictions.