Competitive kinetics study of sulfide oxidation by chlorine using sulfite as reference compound

Abstract

To design and optimize hydrogen sulfide scrubbers working with chlorine, the knowledge of the kinetics of the hydrogen sulfide oxidation is necessary. In this work, the kinetics of the hydrogen sulfide oxidation by sodium hypochlorite was experimentally investigated using a reactor without headspace (100mL gas-tight syringe) and the competitive kinetics method. The sulfite ion was selected as the reference compound. First, the apparent stoichiometries of sulfite anion and hydrogen sulfide chlorinations were determined performing single-compound experiments. Then, the kinetics of the hydrogen sulfide chlorination was studied in the pH range 6–12 performing simultaneous sulfite and sulfide chlorinations. The results demonstrated that sulfide and sulfite oxidation kinetic rates have the same order of magnitude, which validates the choice of the sulfite anion as the reference compound. Kinetic simulations emphasized that the kinetic rates of the oxidation of both compounds were limited by acid–base reactions. The sulfide oxidation in the pH range 6–12 is mainly due to the hydrosulfide (HS−) oxidation by the hypochlorous acid (ClOH) with an associated kinetic constant of 1.2×109Lmol−1s−1 at 25°C.