Concentration of HIx solution by electro-electrodialysis using Nafion 117 for thermochemical water-splitting IS process

Yoshida, Mitsunori*; Tanaka, Nobuyuki ; Okuda, Hiroyuki; Onuki, Kaoru

The electro-electrodialysis (EED) for enhancing HI molality in HIx solution (HI-I-HO mixture) of quasi-azeotropic composition was examined at 90 C using Nafion 117 and graphite electrodes. The initial current efficiency of HI molality increase in catholyte varied in the range of 25-80% depending on the operation condition such that the higher iodine molality and the higher weight ratio of anolyte solution to catholyte solution resulted in the higher efficiency. With the progress of EED, the increase rate of the HI molality decreased and, in some cases, concentration limits were observed. Electric conductivity of the HIx solution, overvoltage of the electrode reaction, and voltage drop due to the membrane were measured in the temperature range of 25-120 C, which indicated that the EED cell voltage was governed by the voltage drop due to membrane.