New Metal Complex Oxygen Absorbents for the Recovery of Oxygen

Abstract

Emerging non-cryogenic technologies for the separation of air use zeolites and microporous “molecular sieve” carbons as moderately selective nitrogen and oxygen adsorbents, respectively.^1,2 While the zeolites have a thermodynamic affinity for N₂, use of carbons relies on a kinetic selectivity for the passage of oxygen into the micropores. It is well known that certain coordination compounds of cobalt and iron reversibly react with oxygen under near ambient conditions.^3,4 Since this is a chemical rather than a physical interaction as is seen with zeolites and carbons, it should be possible to use such metal complexes as O₂ equilibrium sorbents for air separation. We have been conducting a long term research effort to prepare such metal complex oxygen carriers for use in future generation non-cryogenic air separation devices.⁵ The primary interest in such complexes is in their use in pressure or temperature swing processes for the production of inert gas (N₂,Ar) and oxygen.^6,7 For these applications, the oxygen complex could either be used as a circulating liquid or as a solid sorbent. In order to be useful in a commercial process an oxygen complex has to satisfy several requirements. It must (a) bind O₂ rapidly and reversibly, (b) have a high stability (>1 year lifetime), and (c) be accessible via simple synthetic techniques at minimal cost.