Demonstration of the I–S thermochemical cycle feasibility by experimentally validating the over-azeotropic condition in the hydroiodic acid phase of the Bunsen process

Conventional I–S cycle flowsheets suffer from low thermal efficiency and highly corrosive streams. To alleviate these problems, KAIST has proposed the optimal operating condition for the Bunsen reaction and devised a new flowsheet that produces highly enriched HI through spontaneous L–L phase separation and simple flash processes under low pressure. A series of experiments were performed at KAIST to validate the new flowsheet and extend its feasibility. The experimental procedure, measurement method with a rich iodine condition, and results of experiments are discussed in this paper. When the molar ratio of I2/H2SO4 in the feed increased from 2 to 4, the molar ratio of HI/(HI + H2O) in the HIx phase improved from 0.157 to 0.22, which is high enough to generate highly enriched HI gas through flashing. An inverse Bunsen reaction and a sulfur formation were observed when the temperature was increased from 313 K to 343 K and the molar ratio of I2/H2SO4 was decreased from 4 to 1. 10–50 wt% of HI in the feed turned into I2 when an inverse Bunsen reaction and a sulfur formation occurred. The experimental data utilized in the previous parametric study of KAIST has been validated.