Properties of Nafion 117 in highly acidic environment of Bunsen reaction of I–S cycle

Abstract Membrane electrolysis could be used to carry out Bunsen reaction at much lower levels of excess iodine as compared to the direct contact mode because the two acid phases (sulphuric acid rich and HI rich phases) are separated by an ion exchange membrane. However, undesired permeation of ions or dissolved SO 2 through membrane leads to cross-contamination of the two acid phases. Cross-contamination and resistance of membrane affect the purity of solutions and the energy required for the reaction, respectively. A two-compartment membrane electrolysis cell with Nafion 117 membrane was used to measure cross-contamination arising out of permeation of dissolved SO 2 and/or sulphate ions from anolyte to catholyte and that of iodine/iodide ions from catholyte to anolyte. Permeation was obtained even in absence of current density and the flux increased rapidly with current density. At 1 A/dm 2 , the permeated SO 2 and sulphate ions were ∼12% of total sulphate ions produced in electrolysis which was lower than about 20% of feed sulphuric acid appearing in HI x phase in direct contact mode. The permeated iodine and iodide ions together were less than 3% of iodide ions produced in electrolysis. Areal-resistance of the membrane was measured at different temperatures, and different concentrations of anolyte and catholyte. Areal-resistance of membrane in chemical environment of Bunsen reaction was about 50% more than the values reported in NaCl electrolyte and was found to increase with sulphuric acid concentration.