Simultaneous Solubilities of Oxygen and Sulphur Dioxide in Water: Thermodynamic Data for the Sulphur Family of Thermochemical Cycles

The Sulphur family of thermochemical cycles shows great promise for the massive scale production of hydrogen from water. The decomposition of sulphuric acid is a common stage in the cycles and poses design problems due to the corrosive nature of the solution, the high temperatures involved and the difficult separations required. The work considered here focuses on the oxygen separation stage of the process where, in order for a science based design approach to be taken, thermodynamic data are required for multicomponent phase equilibrium relationships between water, sulphur dioxide and oxygen; H2O-SO2-O2. A bespoke vapour-liquid-equilibrium still is used to measure the simultaneous solubilities of the ternary solution. The results are presented, along with a comparison to a model based on weak electrolyte thermodynamics. The model can be used for flash calculations, necessary for the design of the separation equipment.