Nb2O5 Doped SrCo0.8Fe0.2O3-δ Membrane for Oxygen Separator and Membrane Reactor

Dense ceramic membranes such as mixed ionic-electronic conducting (MIEC) membranes used for oxygen separation from air have received considerable attentions. These dense ceramic membranes have 100% selectivity for oxygen and deliver high-pure oxygen product (>99%) which could construct ceramic membrane based air separation unit (CASU). More importantly, they are possible to couple the high-temperature chemical reaction and the separation of feed components and/or reaction products in one ceramic membrane reactor unit (CMRU).

Based on the high-flux dense SCFNb (0.5 wt.% Nb₂O₅ doped in SrCo_0.8Fe_0.2O_3-δ) membrane, we have designed a prototype of CASU with SCFNb thin-tubular membranes. 17-channel CASU system (0.02 m² effective membrane area) was operated under vacuum and sweep mode. A better performance was found under the vacuum mode. At the temperature of 900 °C, the CASU could yield 260 ml (STP) min⁻¹ oxygen with the purity of 99.8%. We further proposed a porous-dense dual-layer composite membrane. A porous Ba_0.3Sr_0.7Fe_0.9Mo_0.1O_3-δ (BSFM) layer was prepared on top of the dense SCFNb layer. The dual-layer composite membrane was expected to play their respective functions and combines the advantages of each layer. Compared with SCFNb single-layer CMRU, no degradation of performance was observed in the dual-layer CMRU during continuously operating for 1500 h at 850 °C under partial oxidation of methane (POM). At 900 °C, oxygen flux of 18.6 ml (STP) cm^-2 min^-1, hydrogen production of 53.67 ml (STP) cm^-2 min^-1, CH₄conversion of 99.34% and CO selectivity of about 94% were achieved.

Acknowledgements

This work was supported by the National Basic Research Program of China (No. 2009CB623406); National Natural Science Foundation of China (No. 20990222, No. 21006047); China Postdoctoral Science Foundation (No. 20090461105, No. 201003581).