CO2 Splitting via Two-Step Solar Thermochemical Cycles with Zn/ZnO and FeO/Fe3O4 Redox Reactions: Thermodynamic Analysis

Two-step thermochemical cycles for CO2 reduction via Zn/ZnO and FeO/Fe3O4 redox reactions are considered. The first, endothermic step is the thermal dissociation of the metal oxide into the metal or a reduced valence metal oxide and O2 using concentrated solar energy as the source of high-temperatur...

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Bibliographic Details
Published in:Energy & fuels 2008-09, Vol.22 (5), p.3544-3550
Main Authors: Gálvez, M. E, Loutzenhiser, P. G, Hischier, I, Steinfeld, A
Format: Article
Language:English
Subjects:
Air pollution caused by fuel industries
Applied sciences
Energy
Energy. Thermal use of fuels
Exact sciences and technology
Pollution reduction
Renewable Energy
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Summary:Two-step thermochemical cycles for CO2 reduction via Zn/ZnO and FeO/Fe3O4 redox reactions are considered. The first, endothermic step is the thermal dissociation of the metal oxide into the metal or a reduced valence metal oxide and O2 using concentrated solar energy as the source of high-temperature process heat. The second, nonsolar, exothermic step is the reaction of the reduced metal/metal oxide with CO2, yielding CO and/or C, together with the initial form of the metal oxide that is recycled to the first step. Chemical equilibrium compositions of the pertinent reactions are computed as a function of temperature and pressure. A second-law thermodynamic analysis for the net reaction of CO2 = CO + 0.5O2 indicates a maximal solar−chemical energy conversion efficiency of 39 and 29% for the Zn/ZnO and FeO/Fe3O4 cycle, respectively. Efficiencies are lower for both cycles yielding C. Major sources of irreversibility are associated with the re-radiation losses of the solar reactor operating at 2000 K and the quenching of its products to avoid recombination.
ISSN:0887-0624
1520-5029
DOI:10.1021/ef800230b