257334 Low-Temperature, Manganese Oxide-Based, Thermochemical Water Splitting Cycle

Thursday, November 1, 2012: 9:10 AM
331 (Convention Center )
Bingjun Xu, Chemical Engineering, Caltech, Pasadena, CA and Mark E. Davis, Chemical Engineering, California Institute of Technology, Pasadena, CA

Thermochemical cycles that split water into stoichiometric amounts of hydrogen and oxygen below 1000oC are highly desirable, because they can convert the waste heat from nuclear power plants into chemical energy in the form of hydrogen. We report a manganese-based thermochemical cycle with the highest operating temperature of 850oC that is completely recyclable and does not involve toxic or corrosive components. The thermochemical cycle includes the following 4 steps: (1) thermal treatment of a physical mixture of Na2CO3 and Mn3O4 to produce MnO, CO2, and alpha-NaMnO2 at 850oC, (2) oxidation of MnO in the presence of Na2CO3 by water to produce H2, CO2 and alpha-NaMnO2 at 850oC, (3) Na+ extraction from alpha-NaMnO2 by its suspension in aqueous solutions in the presence of bubbling CO2 at 80oC, and (4) recovery of Mn3O4 by thermally reducing the sodium ion extracted solid produced in step (3) at 850oC. The shuttling of Na+ into and out of the manganese oxides in the hydrogen and oxygen evolution steps, respectively, provides the key thermodynamic driving forces, and allows for the cycle to be closed at temperatures below 1000oC. The production of hydrogen and oxygen is fully reproducible for at least 5 cycles.

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See more of this Session: Fundamentals of Environmental Process and Reaction Engineering II
See more of this Group/Topical: Environmental Division