Chemical looping conversion of CO₂ based on bauxite residue: Thermodynamic behavior and kinetic characteristics

The process of chemical looping conversion of CO₂ based on aluminum industry waste bauxite residue (BR) as oxygen carrier (OC) was proposed, and the thermodynamic behavior and kinetic characteristics were explored. The isothermal reaction performance and cycle stability of chemical looping conversion of CO₂ by three reduced bauxite residue oxygen carriers H₂-RBR1, H₂-RBR2, H₂-RBR3, pure substances H₂-RFe and H₂-RFe₂O₃ were analyzed in a fixed bed reactor. The thermodynamic characteristics of the reaction of CO₂ with FeO_x in bauxite residue oxygen carriers were clarified, and the thermodynamically feasible region of chemical looping conversion was obtained. When the temperature T < 570 °C, the main process of oxidation is Fe→FeO→Fe₃O₄→Fe₂O₃. While the temperature T > 570 °C, the main oxidation process is Fe→FeO→Fe₃O₄→Fe₂O₃. Fe₃O₄ cannot be oxidized to Fe₂O₃ by CO₂ under 1000 °C. The results show that H₂-RBR1 shows the highest CO yield, average CO generation rate, and final utilization rate of oxygen vacancy, which are 5.44 mmol g⁻¹, 340.01 μmol⋅g⁻¹⋅min⁻¹and 60%, respectively. The cycling performance of H₂-RFe₂O₃ and H₂-RBR1 was compared, and the recyclability of H₂-RBR1 is significantly higher than that of H₂-RFe₂O₃. The results showed that the recycling performance of H₂-RBR1 was better than that of H₂-RFe₂O₃. The kinetic characteristics of H₂-RFe, H₂-RFe₂O₃, H₂-RBR1 and H₂-RBR2 chemical looping conversion to CO₂ were analyzed, and the reaction activation energies were 92.79 kJ mol⁻¹, 96.09 kJ mol⁻¹, 27.27 kJ mol⁻¹ and 74.33 kJ mol⁻¹ respectively.