Hydrogen Production by Steam Oxidation of Reduced CaFe2O4 during Chemical Looping Coal Gasification: Equilibrium and Kinetic Analysis

CaFe2O4 reduced during chemical looping coal gasification can be oxidized with steam for production of hydrogen. The conversion and equilibrium data of the oxidation of reduced CaFe2O4 with steam were analyzed using steam concentrations of 10-25 vol % with a balance of helium and the temperature range of 1023-1123 K. Experimental data were evaluated to characterize H-2 production rates and oxidation isotherms. The film diffusion was the controlling step for the oxygen uptake process, and its parameters were determined on the basis of the uptake rate model. The steady-state oxygen uptake data were also evaluated with Langmuir, Temkin, Freundlich, and Dubinin-Radushkevich isotherms. The Langmuir isotherm model correlated the oxidation isotherms best, and the peak uptake capacity decreased with increasing temperatures, which suggests an exothermic process. The negative Gibbs free energy values (-Delta G degrees) implied the spontaneous nature of the uptake process at 1023-1123 K.