(69b) Experimental Results for the Generation of Hydrogen by the Decomposition of Hydrogen Iodide in the Sulfur-Iodine Cycle

The Sulfur-Iodine (S-I) process for thermochemical water decomposition is one of the most promising methods currently being developed for large-scale hydrogen production from nuclear energy. The S-I cycle consists of three key reactions, one of which is the decomposition of HI into H₂ and I₂.

The feed to the HI decomposition step from the Bunsen reaction is HI_x, a mixture of HI, H₂O, and I₂ that must be separated into its components. These separations are complicated by the formation of an azeotrope between HI and water. There have been several approaches to the separation and reaction steps, including reactive distillation, extractive distillation, and electrodialysis coupled to a membrane reactor.

This work studied the separation of I₂ from HI and H₂O by placing the HI₂ into contact with H₃PO₄. In this manner, the HI and water are extracted into the H₃PO₄, facilitating their separation from the distinct I₂ phase. As the H₃PO₄ breaks the azeotrope between HI and H₂O, the HI can then be distilled out of the H₂O/H₃PO₄ solution. Next, the HI is decomposed at approximately 450^oC in the presence of a catalyst. The H₃PO₄ is re concentrated in a boiler and recycled to the extraction column.

Experimental results are reported for the extraction of HI and H₂O from I₂ into H₃PO₄, the extractive distillation of HI from H₂O and H₃PO₄, and the decomposition of HI into H₂ and I₂. Experimental parameters under study include the flow rates of HIx and H₃PO₄ into the extraction column and the feed compositions for both the extraction column and HI distillation column.