The Sulphur Iodine (SI) thermochemical cycle is a promising route for hydrogen production from water. It requires the processing of a complex solution, termed HIx, which contains HI, H2O, very high concentrations of I-2, plus a range of iodide species. Process efficiency can be improved by dewatering the HIx stream beyond its azeotropic point. This paper reports work aimed at achieving this by pervaporation through a membrane operating at the harsh process conditions involved. Nafion (R) 117 and Nafion (R) 212 are investigated using both a batch and a continuous flow arrangement operating with a range of HI-H2O and HI-H2O-I-2 solution concentrations, up to the expected SI cycle composition. Permeates of almost pure water and reasonable fluxes are seen, and good correspondence is observed between the results from the two rigs. Consideration of the solution-diffusion model suggests that sorption and desorption, as well as diffusion, play a limiting role in the permeate flux. (C) 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.