Improved solvation routes for the Bunsen reaction in the sulphur iodine thermochemical cycle: Part III–Bunsen reaction in molecular solvents

Operating the Bunsen reaction in a solvent has the potential to increase SI cycle efficiency and decrease operating costs. Analysing the solvent–acid mixtures produced is complicated as additional acid is formed when SO2 comes into contact with water. Tri-n-butyl phosphate (TBP) is suitable for HI extraction; however, it is susceptible to acid catalysed dealkylation, resulting in solvent decomposition and the production of butyl iodide. Cyanex® 923 is found to be superior to TBP in the Bunsen reaction due to its high affinity for HI. Strong orange complexes between HI, SO2 and the phosphoryl group in Cyanex® 923 are formed, giving good product separation, however severely hampering HI recovery. Washing the organic phase with water resulted primarily in the removal of H2SO4. HI could then be recovered either thermally or with a second wash step. nsen reaction in Cyanex® 923 remains far from optimised, however priority should be given to developing a more sophisticated analytical method in order to fully characterise the system.