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

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• 作者：Jie Zhu ; Wei Wang ; Songjian Lian…
• 关键词：Chemical looping hydrogen generation ; Iron ; based oxygen carriers ; CO/CO2 mixture gases ; Stepwise reduction kinetics ; Hercynite (FeAl2O4)
• 刊名：Journal of Material Cycles and Waste Management
• 出版年：2017
• 出版时间：January 2017
• 年：2017
• 卷：19
• 期：1
• 页码：453-462
• 全文大小：
• 刊物类别：Earth and Environmental Science
• 刊物主题：Civil Engineering; Waste Management/Waste Technology; Environmental Management;
• 出版者：Springer Japan
• ISSN：1611-8227
• 卷排序：19

文摘

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 °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 × 10−6–5.60 × 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 °C, FeAl₂O₄ impacted on the reduction rate of Fe2+→Fe due to its lower reactivity.