Study on the kinetic characteristics of stepwise reduction and steam oxidation for the packed-bed chemical looping hydrogen production

Biomass-derived gas chemical looping hydrogen production (CLHP) highlights its potential to produce high-purity hydrogen with recycling waste bioenergy. Investigations on the kinetics characteristics of stepwise reduction and steam/air oxidation are conducted on a thermogravimetric analyzer (TGA) with a bubbler. The research decouples Fe2O3-Fe3O4, Fe3O4-FeO, and FeO-Fe reduction stages by adjusting the partial pressures of CO/CO2. Kinetic equations of stepwise reduction correlating to the reaction temperature and gas concentration are established, with activation energies for the three stages of 9.99 kJ/mol, 82.10 kJ/mol, and 149.32 kJ/mol, respectively. Evolutionary calculations of kinetic models confirms that the Fe2O3 reduction follows a topological chemical reaction pathway. The gas-solid dynamic response characteristics during the reduction process can be qualitatively and quantitatively analyzed, showing regions of Fe, FeO-Fe mixed zone, FeO, Fe3O4-FeO mixed zone, Fe3O4, Fe2O3-Fe3O4 mixed zone, and Fe2O3 distributed alternately along the bed axis. Increasing the oxidation temperature significantly enhance the reaction kinetics of hydrogen production more than reducing the reduction temperature during the steam oxidation process. Above 800 °C, the reaction kinetics of the air combustion stage (Fe3O4-Fe2O3) is not affected by raising temperatures. Overall, this study linked the kinetic mechanism and gas-solid reaction characteristics of reactor beds.