Reactivity investigation on chemical looping gasification of coal with Iron-Manganese based oxygen carrier

Chemical looping gasification (CLG) of Yunnan lignite with Fe-Mn mixed oxygen carriers (OCs) was performed to achieve high purity synthesis gas and reduce pollutant emissions. The Fe-Mn composite OCs presented the characteristics of oxygen decoupling, and there is a synergistic effect between the active components using various analytical methods. The maximum syngas yield (0.054 mol/g) and the maximum carbon conversion rate (62.9%) were achieved under the following conditions; temperature at 900 °C, steam flow rate at 0.045 ml/min and O/C ratio equal to 1. The OC acts as both oxygen source and catalyst in gasification reaction process, after studying the gasification reaction characteristics between the OC and the model compound. The oxygen transport mechanism and phase evolution law of the OC was revealed by conducting XRD and XPS tests. The migration of lattice oxygen of the OC in CLG transferred from bulk phase to surface phase with the migration pathway of oxygen species OI → OII → OIII, and the OC phase underwent the reduction process of (Mn, Fe)2O3 → (FeO)0.664(MnO)0.336 → Fe/MnO. The reactivity performance of OCs remained stable after 20-cycle redox experiments, indicating that the Fe-Mn OC was a good candidate OC for the CLG process.