Ind. Eng. Chem. Process Des. Dev. 1985, 2 4 , 795-802
795
Laboratory Scale Demonstration of the Mg-S-I Cycle for Thermochemical Hydrogen Production Toshlya Kumagal' and Suswnu Mlzuta
Energy Chemistry Division, National ChemlCel Laboratory for Industry, Tsukuba Research Center, Yatabe, Ibaraki 305, Japan
The Mg-S-I thermochemical water-splitting cycle was demonstrated on a laboratory scale. The process design was canied out to a h at the veriflcatbn of repeated H2and O2 production through pwety thermochemical processes below 1273 K (1000 "C).An experimental apparatus was made of quartz and Pyrex glass, and electric furnaces were used. Owing to tbe avoldance of MgSO4-MgI2 separation and of solid transportation processes, the whole system was so simplMe$ as to CMpTISB only three reactors operated in three stages. with satisfactory performance of the system, 30 cycle Operations were successfully repeated with roughly constant production of 0.3 dm3 (0.3 L) of H, and 0.15 dm3 (0.15 L) of O2 per cycle. The tlme requirement for one cycle operation was about 1 h, where all the chemical reactions proceeded and all the reactants were circulated.
Introduction Since thermochemical hydrogen production was widely studied in the 1970's, a number of water-splitting cycles have been proposed (Bamberger and Richardson, 1976; Bamberger, 1978; Carty et al., 1981). Fundamental studies were performed on some of the promising cycles (Veziroglu et al., 1976,1978,1980,1982), where experimental verifications on the consituent reactions of those cycles have been carried out. Among them, the S-I cycle (Norman et al., 1982) and the Ca-Fe-Br cycle'(Nakayama et al., 1984) have been especially developed for a bench-scale operation. However, detailed information on the rate of hydrogen production, the amount of circulating reactants, and the number of times of repeated operations have not been shown in their studies. To the best of present authors' knowledge, demonstrations of the purely thermochemical cycles with more than 10 repeated operations of the whole cycle have never been reported. The authors have been studying the Mg-S-I thermochemical water-splitting cycle, since they presented an addition of magnesium ions for the separation of the HzS04-HI solution in the S-I scheme together with the new cycle proposal'in 1978 (Mizuta et al., 1978; Mizuta and Kumagai, 1979b). The Mg-S-I cycle is expressed as follows
-+ + 273-298
12(c)+ SOz(aq)+ 2Hz0(1)
K
H2S04(aq) 2HI(aq) R(1-1) 343 K
2MgO(c) + H2S04(aq) 2HI(aq) MgS04(aq) + Mg12(aq) R(1-2) MgUaq)
so&)
