High temperature chemistry of hydrogen production cycles

Abstract

Studies of the catalyzed decomposition of MgSO/sub 4/ were completed and a manuscript describing the work was prepared. ZnSO/sub 4/, ZnO 2ZnSO/sub 4/, CuSO/sub 4/, and Al/sub 2/(SO/sub 4/)/sub 3/ were also found to yield SO/sub 3/ as the sole gaseous decomposition product, although SO/sub 2/ should predominate at equilibrium. As with other metal sulfate decompositions, a distinct progression of observed pressure with effusion orifice area indicates a significant kinetic barrier. Results obtained with the Zn, Cu, and Al sulfates are consistent with the decomposition mechanism postulated for MgSO/sub 4/. For ZnSO/sub 4/ and ZnO 2ZnSO/sub 4/, derived equilibrium pressures indicate that the oxide and basic sulfate reaction products may be formed in a finely divided state of higher surface free energy and slightly lower thermodynamic stability than the normal macrocrystalline phases. None of the semiconducting oxides found to be catalytically effective with MgSO/sub 4/ had any detectable effect on the decomposition of ZnSO/sub 4/ or ZnO 2ZnSO/sub 4/, but Pt had a substantial catalytic effect on the basic sulfate and a moderate effect on ZnSO/sub 4/. A sample of ZnO 2ZnSO/sub 4/(s) was prepared by thermal decomposition of ZnSO/sub 4/ and submitted to Lawrence Livermore Laboratory for measurement ofmore » high temperature heat content by drop calorimetry; a second sample has been prepared and submitted for low temperature and solution calorimetry at the Albany Metallurgy Research Center of the Bureau of Mines. With CuSO/sub 4/, the solid phase decomposition product was found to be CuO rather than the CuO CuSO/sub 4/ phase reported in static experiments, and the pressures for moderate to large orifices are converging on the SO/sub 3/ equilibrium pressure when extrapolated to zero orifice size. For the smallest orifice sizes, there appears to be a partial catalysis of SO/sub 3/ to SO/sub 2/ and O/sub 2/ by the CuO product.« less