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Report No.

Effect of HIx solution concentration on ion-exchange membrane performance in electro-electrodialysis

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

Electro-electrodialysis (EED) has been applied to thermochemical water-splitting iodine-sulfur process for hydrogen production in order to enhance the HI component in the HI-I$$_{2}$$-H$$_{2}$$O mixture (HIx solution). In this paper, HIx solution concentration dependence of the conductivity ($$sigma$$) and transport number ($$t_{+}$$) as the membrane-performance indexes of Nafion 212 and a styrene-grafted poly(ethylene-co-tetrafluoroethylene) (ETFE) membrane was experimentally investigated. From the theoretical analysis for the measurements based on the new EED model, the effects of the H$$^{+}$$ and I$$^{-}$$ content and the diffusion coefficients of H$$^{+}$$ and I$$^{-}$$ in the evaluated membranes on $$sigma$$ and $$t_{+}$$ were as follows: HIx solution concentration dependence of ion contents exhibited a significantly small or different variation in comparison with that of $$sigma$$ and t$$_{+}$$, which indicates that the dominant factors for $$sigma$$ and $$t_{+}$$ would not be ion contents; thereby, the effect of ion diffusion coefficients should not be ruled out. For $$sigma$$ of Nafion 212, H$$^{+}$$ diffusion is the dominant factor because the existence of I$$^{-}$$ was negligible, whereas for the ETFE-St membrane, the effect of I$$^{-}$$ diffusion should be considered. I$$^{-}$$ diffusion could more strongly affect $$t_{+}$$ for the evaluated membranes rather than H$$^{+}$$ diffusion, which indicates that H$$^{+}$$ selectivity of the membranes could be relatively determined by the variation of the I$$^{-}$$ behavior in the membranes.



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Category:Engineering, Chemical



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