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

Abstract

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 FeOx 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.