1988 Volume 1988 Issue 8 Pages 1253-1260
Thermal decomposition of metal sulfates was studied as an oxygen-generating reaction in the thermochemical water splitting process. The cycle using metal (M) sulfates is generally expressed as follows:
I2+SO2+2H2O=H2SO4+2HI.
H2SO4+2HI+2MO=MSO4+MI2+2H2O
MSO4=MO+So2+1/2O2
MI2+H2O=MO+2HI
2HI=H2+I2.
The initial decomposition temperatures obtained by thermogravimetry were related to thermodynamic functions: The equilibrium SO3 pressure at the decomposition temperature was roughly 1×10-4 atm at a heating rate of 2°Cfmin in flowing nitrogen. The decomposition rate of the sulfates is proportional to the surface area of a sample pellet, and not to that of a separate particle. The decomposition rate was in the order: Fe2(SO4)3>CuSO4>CoSO4>NiSO4>ZnSO4>CdSO4, which was nearly th e same as the decreasing order of decomposition temperature. Isothermal kinetic results indicated that sulfates of Fe, Cu, Co and Ni could be candidates for the thermochemical process.
In order to convert the produced oxides into sulfates, Cu and Fe(III) oxides were dissolved into sulfuric acid. The dissolution time, t, obeys and equation: log t= 1/2logE1-[H2SO4]+const. The dissolution rate was proportional to the surface area of a particle.
Thermodynamics show that iodides of Mg, Al and Fe(II) are hydrolyz ed easier than other iodides at low temperatures. For the purpose of composing a cycle using iron, sulfur and iodine, the products of the reaction I2+2S02+H2O+Fe2O2=2FeSO4+2HI were investigated.
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