Abstract
The reduction kinetics of iron-based oxygen carriers significantly affect the efficiency of chemical looping hydrogen generation. Based on the thermodynamics properties of the Fe–CO–CO2 system, CO/CO2 mixtures in different volume ratios can decouple the reduction of Fe2O3 into three relatively independent steps. The step-wise reduction of Fe2O3 was conducted in a thermogravimetric analyzer at 800–900 °C. To investigate the reaction mechanisms, the Hancock–Sharp method and the nonlinear fitting approach were applied to select the kinetic models. The reaction model of step 1 and 2 are geometrical contracting model; the step 3 is controlled by nucleation and nuclei growth model and diffusion model. The activation energy of the three steps including Fe2O3 → Fe3O4, Fe3O4 → FeO and FeO → Fe is estimated to be 34.92 ± 1.24, 70.13 ± 0.88 and 44.12 ± 1.44 kJ/mol, respectively. The rate equations derived from the Arrhenius law were determined to predict the reaction rate at a specific CO concentration.
Published Version
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