Stability and performance of nafion-117 membranes for the concentration of HI/water and HI/water/iodine mixtures

Thermochemical water splitting processes for generating hydrogen have been researched for at least 30 yr, in which over 100 chemical cycles have been proposed. Proposed heat sources include nuclear reactors and solar reflectors. One of the most promising cycles is the sulfur-iodine process, where aqueous HI is thermochemically decomposed into H₂ and I₂ at ∼ 400°C. Two membrane materials were identified for their ability to pass water with a high degree of separation from both concentrated HI and HI_x feed streams. Both Nafion-117® and Nafion-112® were effective in the removal of water from these feeds and showed no degradation. Typical in the transport behavior of these membranes was the trade-off between flux and separation performance. With lower water concentrations in the feeds, flux rates decreased while the separation performance increased. Nafion-117® was characterized by more modest water fluxes and high separation factors. Nafion-112® were characterized with substantially higher fluxes, the separation factors were considerably lower. This is an abstract of a paper presented at the AIChE Annual Meeting and Fall Showcase (Cincinnati, OH 10/30/2005-11/4/2005).