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.