Reduction kinetics of iron-based oxygen carriers using methane for chemical-looping combustion

The performance of three iron-based oxygen carriers (pure Fe ₂O₃, synthetic Fe₂O₃/MgAl ₂O₄ and iron ore) in reduction process using methane as fuel is investigated in thermo-gravimetric analyzer (TGA). The reaction rate and mechanism between three oxygen carriers and methane are investigated. On the basis of reactivity in reduction process, it may be concluded that Fe ₂O₃/MgAl₂O₄ has the best reactivity with methane. The reaction rate constant is found to be in the following order: Fe₂O₃/MgAl₂O₄ > pure Fe ₂O₃ > iron ore and the activation energy varies between 49 and 184 kJ mol^-1. Reduction reactions for the pure Fe ₂O₃ and synthetic Fe₂O₃/MgAl ₂O₄ are well represented by the reaction controlling mechanism, and for the iron ore the phase-boundary controlled (contracting cylinder) model dominates. The particles of iron ore and synthetic Fe ₂O₃/MgAl₂O₄ have better stability than that of pure Fe₂O₃ when the reaction temperature is limited to lower than 1223 K. These preliminary results suggest that iron-based mixed oxygen carrier particles are potential to be used in methane chemical looping process, but the reactivity of the iron ore needs to be increased.