Kinetic study of hydrogen sulfide absorption in aqueous chlorine solution

• Kinetics of H2S oxidation by chlorine is investigated using a well agitated reactor.
• Mass transfer and hydrodynamics performances of the reactor are determined.
• Sensitivity analysis is performed to assess the robustness of the modeling.
• H2S reacts irreversibly with hypochlorous acid and hypochlorite anion.
• Kinetic constants are determined.

Hydrogen sulfide (H2S) is currently removed from gaseous effluents by chemical scrubbing using water. Chlorine is a top-grade oxidant, reacting with H2S with a fast kinetic rate and enhancing its mass transfer rate. To design, optimize and scale-up scrubbers, knowledge of the reaction kinetics and mechanism is requested. This study investigates the H2S oxidation rate by reactive absorption in a mechanically agitated gas–liquid reactor. Mass transfer (gas and liquid sides mass transfer coefficients) and hydrodynamic (interfacial area) performances of the gas–liquid reactor were measured using appropriated physical or chemical absorption methods. The accuracy of these parameters was checked by modeling the H2S absorption in water without oxidant. A sensitivity analysis confirmed the robustness of the model. Finally, reactive absorption of H2S in chlorine solution for acidic or circumneutral pH allowed to investigate the kinetics of reaction. The overall oxidation mechanism could be described assuming that H2S is oxidized irreversibly by both hypochlorite anion ClO− (k = 6.75 × 106 L mol−1 s−1) and hypochlorous acid ClOH (k = 1.62 × 105 L mol−1 s−1).

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