Oxygen permeation through O ionic or mixed-conducting ceramic membranes under reaction conditions was analyzed by a simple mathematical model considering different transport mechanisms (with n-type versus p-type flux equations) and oxidation reaction kinetics (extremely fast reaction versus no reaction). Experimental O permeation data for Bi1.5Y0.3Sm0.2O3−δ (BYS) membrane under two different reaction conditions (with methane and ethane) were measured and analyzed by the modelling results. For a membrane under reaction conditions with a specific reducing gas, the O permeation flux depends strongly on the oxidation reaction rate and the reducing gas flow rate. Such dependencies were different for membranes with O permeation controlled by p-type electron transport and those by n-type electron or O vacancy transport. Oxygen permeation flux under the condition of extremely fast reaction was several-fold higher than that under the condition of slow reaction as a result of the decrease of the O partial pressure in the reaction side with increasing reaction rate. The O permeation flux through BYS membrane under the reaction conditions with ethane was about one order of magnitude higher than that with methane because of the significantly faster oxidation reaction with ethane than with methane. The analysis results also suggested that increasing oxidation reaction rate in the reaction side by use of a heterogeneous catalyst could enhance the O permeation flux through an ionic or mixed-conducting ceramic membrane. For a membrane with a fixed O permeation mechanism, increasing gas flow rate lowers the conversion of oxidation reaction in the reaction side (equivalent to a decrease in reaction rate), causing a decrease in the O permeation flux. Varying reactant flow rate may also cause a change in O permeation mechanism leading to a complex permeation flux versus flow rate relationship.

Oxygen Permeation through Oxygen Ionic or Mixed-Conducting Ceramic Membranes with Chemical Reactions. F.T.Akin, J.Y.S.Lin: Journal of Membrane Science, 2004, 231[1-2], 133-46