Stepwise reduction kinetics of iron-based oxygen carriers by CO/CO2 mixture gases for chemical looping hydrogen generation

作者：Zhu, Jie; Wang, Wei^*; Lian, Songjian; Hua, Xiuning; Xia, Zhou

来源：Journal of Material Cycles and Waste Management, 2017, 19(1): 453-462.

DOI：10.1007/s10163-015-0443-2

• Chemical looping hydrogen generation
• Iron-based oxygen carriers
• CO/CO2 mixture gases
• Stepwise reduction kinetics
• Hercynite (FeAl2O4)

Chemical looping hydrogen generation using iron oxides as oxygen carriers is a novel technology to convert carbonaceous substances into hydrogen. The reduction characteristics of oxygen carriers greatly impact the process efficiency. In this work, the oxygen carriers of Fe2O3 60wt%/Al2O3 were prepared by physical mixing method. The stepwise reduction kinetics of this material was investigated at 800-1000 A degrees C in a TGA with a thermodynamics-controlled method. For this method, CO/CO2 mixture gases at the volume ratios of 0.11, 1, and 5.67 were selected as fuels to decouple the continuous reduction of Fe2O3 -> Fe into independent reductions, including Fe2O3 -> Fe3O4, Fe3O4 -> FeO and FeO -> Fe with little mutual influences. The kinetic mechanisms of Fe2O3 -> Fe3O4, Fe3O4 -> FeO and FeO -> Fe were well represented by the nucleation and grain-growth function, the diffusion-controlled function and the phase-boundary-controlled function, respectively. Fe3O4 -> FeO was determined as the rate-limiting step with a lower reaction rate constant (8.89 x 10(-6)-5.60 x 10(-4) s(-1)) and a higher activation energy (234 kJ/mol). By means of XRD analysis, it was also found that Al2O3, usually regarded as the supported component, became active by forming FeAl2O4 with FeO. At 900-1000 A degrees C, FeAl2O4 impacted on the reduction rate of Fe2+-> Fe due to its lower reactivity.

• 出版日期2017-1
• 单位清华大学