H₂S_(g) removal using a modified, low-pH liquid redox sulfur recovery (LRSR) process with electrochemical regeneration of the Fe catalyst couple

A modified pH 1.0 liquid redox sulfur recovery (LRSR) process, based on reactive absorption of H₂S_(g) in an acidic (pH 1.0) iron solution ([Fe(III)] = 9-8 g L^-1, [Fe(II)] = 1-2 g L^-1) and electrochemical regeneration of the Fe(III)/Fe(II) catalyst couple, is introduced. Fe(II) was oxidized in a flow-through electrolytic cell by Cl _2(aq) formed on a Ti/RuO₂ anode. pH 1.0 was applied to retard the potential precipitation of predominantly jarosite group Fe(III) species. At pH 1.0, the presence of chloride ions at [Cl^-] = 30 g L^-1 allows for both efficient (indirect) electrochemical oxidation of Fe(II) and efficient H₂S_(g) reactive absorption. The latter observation was hypothesized to be associated with higher concentrations of Fe(III)-Cl complexes that are more highly reactive toward H₂S _(aq) than are free Fe(III) ions and Fe-SO₄ complexes that otherwise dominate pH 1.0 Fe(III) solutions in the absence of a significant Cl^-concentration. At the described operational conditions the rate of Fe(II) oxidation in the experimental system was 0.793 kg Fe h^-1 per m² anode surface area, at a current efficiency of 58%. Electricity cost within the electrochemical step was approximated at $0.9 per kg H₂S_(g) removed.