Studies of hydrogen production by thermochemical cycles, 2

The following three reactions: (1) 2NH4I → 2NH3 + H2 + I2, (2) Na2CO3 + I2 → 2NaI + CO2 + 1/2O2, and (3) 2NaI + 2NH3 + CO2 + H2O → Na2CO3 + 2NH4I, composing a newly proposed I2-Na2CO3 thermochemical water-decomposition cycle were investigated to test the feasibility of this cycle. In reaction 1, NH4I dissociated on sublimation into NH3 and HI so that it was necessary to decompose HI, while preventing the decomposition of NH3, the effectiveness of catalysts was examined, and among these Pt supported on Al2O3 showed the best results with 14 -- 18% of the HI decomposing at 450 -- 6000C, while decomposition of NH3 was 0.4 -- 1%. In reaction 2, when an equivalent amount of I2 reacts with Na2CO3, at temperatures below 7500C the conversion of Na2CO3 increases with the rise in temperature. At 6000C, it also rises with increase of amount of I2 and reaches 100% at 4 times equivalent amount of I2 to Na2CO3. In the 650 -- 7000C range, however, conversion does not exceed 80% even if surplus I2 is used. In reaction 3, by the addition of (NH4)2CO3 to an aqueous solution of NaI including NH3, NaHCO3 and a double salt composed of Na2CO3 and (NH4)2CO3 precipitate. Conversion of NaI increases with rises in the concentration of NH3 and with increases in the amount of (NH4)2CO3 added. The effect of temperature is rather small. (author)