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Experimental Results for the Generation of Hydrogen by the Decomposition of Hydrogen Iodide in the Sulfur-Iodine Cycle

Wendi Sweet, Gottfried Besenbruch, L. C. Brown, Robert T. Buckingham, and Benjamin E. Russ. General Atomics, 3550 General Atomics Court, San Diego, CA 92121

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 HIx, 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 450oC 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.