Abstract
This paper describes the role of moisture on long-term O2/N2 separation characteristics of a oxygen transport membrane using N, N'-bis(3-methoxysalicylidene)-2-methylpropylenediaminatocobalt(II)with 4-methylaminopyridine as an axial ligand.
Correlations between O2/N2 selectivities of the liquid membrane calculated from the serial double-layer model and concentrations of oxygen adducts as well as deoxygenation properties were investigated.
The O2/N2 selectivity of the liquid membrane calculated from that of the oxygen transport membrane containing the solution dropped from 153 to 2 by treating with O2/N2 mixed gas for 144h, while dropped from 88 to 1.5 by the treatment with wet O2/N2 mixed gas for 24h.
ESR spectra showed that concentrations of the oxygen adducts decreased from 0.4 mol L-1 to 0.065molL-1 by the reaction with O2/N2 mixed gas for 144 h and decreased from 0.4molL-1 to 0.090molL-1 by the reaction with O2/N2 mixed gas for 24h.
The deoxygenation rate of the oxygen adducts generated from the reaction with wet O2/N2 mixed gas decreased remarkably, while the oxygen adducts formed by the reaction with O2/N2 mixed gas remained considerably.
The remarkable reduction of the selectivity of the liquid membrane from that of the oxygen transport membrane containing the solution reacted with wet O2/N2 mixed gas, is due to the rapid decrease in the concentration of oxygen adducts and its deoxygenation rate.
The rapid decrease in the concentration of oxygen adducts generated from the reaction with wet O2/N2 mixed gas for 24 hours suggested to be due to the formation of hydroxides.
Nuclear Magnetic Resonance spectra suggest that slow deoxygenation rate of oxygen adducts from the reaction with wet O2/N2 mixed gas is caused by the exchange of the axial ligand from 4-DMAP to water molecule.
