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Synthesis, Application, and Carbonation Behavior of Ca<inf>2</inf>Fe<inf>2</inf>O<inf>5</inf> for Chemical Looping H<inf>2</inf> Production

Ismail, M and Liu, W and Chan, MSC and Dunstan, MT and Scott, SA (2016) Synthesis, Application, and Carbonation Behavior of Ca<inf>2</inf>Fe<inf>2</inf>O<inf>5</inf> for Chemical Looping H<inf>2</inf> Production. Energy and Fuels, 30. pp. 6220-6232. ISSN 0887-0624

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Abstract

© 2016 American Chemical Society. Chemical looping hydrogen production uses the oxidation and reduction of metal oxides, typically iron, to produce hydrogen. This work focuses on the modification of iron oxide with calcium oxide to form an oxygen carrier containing dicalcium ferrite (Ca 2 Fe 2 O 5 ), which presents favorable thermodynamics for achieving higher conversions of steam to hydrogen, compared to chemically unmodified iron oxide. Different methods of synthesis, viz. mechanochemical synthesis and coprecipitation, were used to produce Ca 2 Fe 2 O 5 , and their resulting performances were compared. Consistent with thermodynamic predictions, it was found that CO 2 , or steam, was sufficient to fully regenerate the reduced carriers to Ca 2 Fe 2 O 5 . The cyclic stability of the oxygen carriers were studied in fluidized bed reactors and by thermogravimetric analysis (TGA). Good stability of the materials was observed for up to 50 cycles, with no evidence of agglomeration, even up to 950 °C. The rate of deactivation was found to correlate with the purity of Ca 2 Fe 2 O 5 and the presence of impurity phases such as CaFe 2 O 4 , which had a tendency to segregate into its constituent elemental oxides. Carbonation of the oxygen carriers was examined by TGA, and it was found to occur appreciably only for the reduced carri er (a mixture of CaO and Fe) between temperatures of 500-700 °C and 0.1-0.5 atm of CO 2 , whereas the oxidized carrier (viz. Ca 2 Fe 2 O 5 ) did not carbonate. Fresh and cycled materials were characterized by XRD, SEM, and BET analysis. Ca 2 Fe 2 O 5 is a potentially viable material as an oxygen carrier for hydrogen production; however, because of thermodynamic limitations, it cannot be used for complete fuel oxidation.

Item Type: Article
Subjects: UNSPECIFIED
Divisions: Div A > Energy
Depositing User: Cron Job
Date Deposited: 17 Jul 2017 19:36
Last Modified: 22 Sep 2017 20:12
DOI: