Affinity of ion-exchange membranes for HI-I-HO mixture

Tanaka, Nobuyuki ; Yamaki, Tetsuya; Asano, Masaharu; Terai, Takayuki*; Onuki, Kaoru

Electro-electrodialysis (EED) has been applied to thermochemical water-splitting iodine-sulfur process for hydrogen production in order to enhance the HI uptake from a HI-I-HO mixture (HIx solution). In this paper, the constitution of the HIx solution absorbed in grafted membranes and in Nafion 212 is evaluated. The affinity of the membranes for the HIx solution is discussed based on the measurement results. The behavior of each component in the membrane was as follows: The strong affinity of the ETFE-St membrane for I was shown because of the formation of a charge-transfer complex with electron-donating aromatic groups, whereas I absorption by Nafion 212 was minimal. The difference of affinity for the ions can be attributed to the formation of the I- complex from I- and I absorbed in the grafted membranes, which was precluded in Nafion 212.