Chemical kinetics of hydrogen sulfide selective oxidation in aqueous iron chelates solutions

The present work concerns the investigation of the chemical kinetics of H2S selective
oxidation into elemental sulfur, by gas absorption and chemical reaction in Fe3+·(ΝΤΑ)
aqueous solutions. By using initial reactivity data, priority is given to the study of intrinsic
kinetics i.e. to avoid interactions with ligand degradation and the presence of sulfur. A wetted
wall gas-liquid reactor was employed under a batch-recycle regime. The conversion of Fe3+ to
Fe2+ chelate was determined over the pH range ca. 3–6, temperature range ca. 30–60°C and
a short overall per run contact time of phases. The penetration theory was used for the
evaluation of intrinsic reaction rate constant and enhancement factor. Activation energy
values determined from the pertinent Arrhenius plots fall in the range, Εa=17.2– 22.8 kcal
mol-1. These values compare satisfactorily with the value Εa=24 kcal mol-1 obtained from a
similar kinetic study performed in a bubble column reactor and indicates a chemical reaction
control of the overall gas absorption phenomenon. Enhancement factors varied in the
respective ranges Ε =2.7–7.5 (pH=3), E=3.2–14.1 (pH=4), E=5.9–17.0 (pH=5), και Ε=6.7–
20.1 (pH=6) indicating a substantial increase of the mass transfer coefficient due to chemical
reaction. For the experimental conditions applied in this study the following kinetic correlation
was validated: