Continuous O2-CO2 production using a Co-based oxygen carrier in two parallel fixed-bed reactors

Abstract

Oxygen-enriched carbon dioxide stream with oxygen concentration higher than 20 vol% was produced continuously by using a Co-based oxygen carrier packed in two parallel fixed-bed reactors operated in a cyclic manner. Oxygen was absorbed by the oxygen carrier with air being fed. An oxygen-enriched carbon dioxide stream was ob- tained when the fixed-bed was regenerated with carbon dioxide as a purge gas. Multiple absorption and desorption cycles indicated that the Co-based oxygen carrier had high cyclic stability. XRD analysis determined the absorbed and desorbed products were Co3O4 and CoO, respectively. The TGA results indicated that Co-based oxygen carrier did not react with NO or SO2 during the desorption stage. This Co-based oxygen carrier offers potential for applications in the O2-CO2 production for the oxy-fuel coal combustion process. La0.1Sr0.9Co0.5Fe0.5O2.6+0.9CO2⇔ 0.9SrCO3+0.05La2O3+0.5CoO+0.25Fe2O3+0.15O2 (1) Sr0.5Ca0.5Co0.5Fe0.5O2.47+CO2⇔ 0.5SrCO3+0.5CaCO3+0.5CoO+0.25Fe2O3+0.11O2 (2) This reversible process makes perovskite material react with CO2 to form carbonate when using CO2 to release O2. In the next step, O2 storage step, the carbonate formed will decompose and gas prod- uct CO2 will be released into air, diluted by N2. This will result into failing to capture CO2 from flue gas (11). So oxygen carrier with high reactivity, high reaction rate, high stability and not reacting with CO2 is critical for CAR O2 production process. It is found that cobalt oxide can be used as oxygen carrier and has all these good characters mentioned above. The storage and release of O2 are based on the following reversible reaction: