Nguyen Nhu Pailes, Farr Tyler P, Bush H Evan, Ambrosini Andrea, Loutzenhiser Peter G
George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia, 30332-0405, USA.
Concentrating Solar Technologies, Sandia National Laboratories, P.O. Box 5800 MS0734, Albuquerque, NM 87185, USA.
Phys Chem Chem Phys. 2021 Sep 15;23(35):19280-19288. doi: 10.1039/d1cp03303d.
Two-step solar thermochemical cycles based on reversible reactions of SrFeO and (Ba,La)SrFeO perovskites were considered for air separation. The cycle steps encompass (1) the thermal reduction of SrFeO or (Ba,La)SrFeO perovskites driven by concentrated solar irradiation and (2) oxidation in air to remove O and produce N. Rate limiting mechanisms were examined for both reactions using a combination of isothermal and non-isothermal thermogravimetry for temperature-swings between 673 and 1373 K, heating rates of 10, 20, and 50 K min, and O pressure-swings between 20% O/Ar and 100% Ar at atmospheric pressure. Evolved O and associated lag due to transport behavior were measured with gas chromatography and used with measured sample temperatures to predict equilibrium compositions from a compound energy formalism thermodynamic model. Measured and predicted chemical equilibrium changes in deviation from stoichiometry were compared. Rapid chemical kinetics were observed as the samples equilibrated rapidly for all conditions, indicative that heat and mass transfer were the rate limiting mechanisms. The effects of bulk diffusion (or gas diffusion through the bed or pellet) were examined using pelletized and loose powdered samples and determined to have no discernable impact.
