ABSTRACT: Thermochemical cycles have great potential for massive scale, carbon-neutral hydrogen production. Of particular interest are the Sulphur Iodine (SI) and the Hybrid Sulphur (HyS) cycles, both having a common step consisting on the high temperature thermal decomposition of H2SO4. The energy requirements are large and there is no known thermodynamic data for this particular system. In order for a design-based approach to be taken for the low temperature separation, accurate vapour-liquid equilibrium data is needed for the decomposition products: SO2-H2O-O2. This work experimentally investigates both the binary SO2-H2O and ternary SO2-O2-H2O system at pressures up to 15 bar and temperatures up to 80° C. Results are compared to a theoretical model based on weak electrolyte thermodynamics. Good correlation between the model and experimental results is seen at low pressures for the binary solution and across the pressure range for the ternary solution. The divergence at high pressures in the binary comparison is thought to be due to the formation of two liquid phases, and the underestimation of the dissolved SO2 salting-out effect. Online spectroscopic measurements are being developed to measure this phenomenon.
International Conference on Hydrogen Production 2011, Thessaloniki, Greece; 01/2011