Hydrogen-assisted Carbon Dioxide Thermochemical Reduction on La 0.9 Ca 0.1 FeO 3-δ Membranes: A Kinetics Study.

Kinetics data for CO2 thermochemical reduction in an isothermal membrane reactor is required to identify the rate-limiting steps. A detailed reaction kinetics study on this process supported by an La0.9 Ca0.1 FeO3-δ (LCF-91) membrane is thus reported. The dependence of CO2 reduction rate on various operating conditions is examined, such as CO2 concentration on the feed side, fuel concentrations on the sweep side, and temperatures. The CO2 reduction rate is proportional to the oxygen flux across the membrane, and the measured maximum fluxes are 0.191 and 0.164 μmol cm-2  s-1 with 9.5 mol% H2 and 11.6 mol% CO on the sweep side at 990 °C, respectively. Fuel is used to maintain the chemical potential gradient across the membrane and CO is used to derive the surface reaction kinetics. This membrane also exhibits stable performances for 106 h. A resistance-network model is developed to describe the oxygen transport process and the kinetics data are parameterized using the experimental values. The model shows a transition of the rate limiting step between the surface reactions on the feed side and the sweep side depending on the operating conditions.