Electrochemical production of polysulfides and sodium hydroxide from white liquor: Part II: Electrolysis in a laboratory scale flow cell

Abstract

Electrochemical production of polysulfide-containing white liquor and pure sodium hydroxide solution was investigated at 90°C in a laboratory scale flow cell. A mixed iridium–tantalum oxide coated titanium electrode was used as the anode and the two electrolyte compartments were separated by a cation-exchange membrane. The process was demonstrated at current densities up to 5kAm−2, resulting in high current efficiencies for both products. The previously reported autocatalytic effect of polysulfide ions was confirmed, and its technical implications on the use of three-dimensional electrodes were demonstrated and discussed. The current efficiency was found to depend strongly on the degree of conversion of sulfur(–ii) to sulfur(0). The anode material showed favourable properties, with respect to activity and selectivity, but suffered from limited durability.