Step-wise reduction kinetics of Fe2O3 by CO/CO2 mixtures for chemical looping hydrogen generation. (2nd March 2017)

• Record Type: Journal Article
• Authors: Wang, Y.D.; Hua, X.N.; Zhao, C.C.; Fu, T.T.; Li, W.; Wang, W.
• Is Part Of: International journal of hydrogen energy. Volume 42:Number 9(2017)
• Page Start: 5667
• Page End: 5675
• Publication Date: 2017-03-02
• Subjects: Chemical looping hydrogen generation -- Step-wise reduction -- Thermodynamic control -- Kinetic model; Hydrogen as fuel -- Periodicals; Hydrogène (Combustible) -- Périodiques; Hydrogen as fuel; Periodicals; 665.81
• DOI: 10.1016/j.ijhydene.2017.01.159
• Languages: English
• ISSNs: 0360-3199

Abstract

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 Fe2 O3 into three relatively independent steps. The step-wise reduction of Fe2 O3 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 Fe2 O3 → Fe3 O4, Fe3 O4 → 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. Graphical abstract: Highlights: Reduction of Fe2 O3 is decoupled into three independent steps by CO/CO2 mixtures. Kinetics of each stage in the reduction of iron oxide for CLHG was determined. The 2-D geometric contraction model best describes Fe2 O3 → Fe3 O4 and Fe3 O4 → FeO. The FeO → Fe is controlled by nucleation and nuclei growth and diffusion. Activation energies and rate equations of three steps were estimated.