Evidence of loss of N2/O2 adsorption selectivity of Li zeolite due to ion exchange between sodium and lithium cations

Generation of oxygen using pressure swing adsorption (PSA) has been commercialized for a few decades. However, the efficiency of the adsorption process in purifying O2 has typically dropped with operating times. In this study, the reasons for the loss of adsorption capacity of zeolite samples collected from a commercial PSA-based O2 generator were investigated. It was illustrated that the adsorption of H2O molecules on a lithium-exchanged low silica X zeolite (Li zeolite) and the replacement of Li+ with Na+ in the zeolite structure were major causes for the loss of selective adsorption of the zeolite. While the H2O molecules could be desorbed and the surface area of the adsorbent could be regained by vacuum heating at 200 °C and 90 kPa, the N2/O2 separation efficiency of the adsorbent could not be recovered. An elemental composition analysis showed that when an active Li zeolite was placed in a high salinity, wet air flow, there occurred vapor-phase ion exchange between Na+ and Li+ cations. The results from this study showed that airborne salinity in a working environment was detrimental to adsorption processes with Li zeolite as the adsorbent.