There are methods for enriching oxygen from air by forward and reverse flushing of a zeolite bed - is it used in aircrafts? What is the mechanism that differentially retains N2 and passes O2?
The separation of O2 and N2 in a zeolite (e.g. zolite 5A) is by the differences of their size, for that reason zeolites are so called also molecular sieves, the diffusion is the mechanism responsible of such separation. However, this material does not make an “enrichment” of oxygen in air as a increase of O2 in air, is only the purification of air by removal of CO2. The last molecule can not pass through the molecular sieve mentioned above.
Both O2 and N2 are adsorbed by 5A but N2 has a stronger interaction with 5A due to its quadrupole moment so if you run air throgh a bed of 5A zeolite, more N2 will be adsorbed than O2 so the exiting gas would be richer in O2
I´m agree Agustin, and the enrichment only works using the reverse flushing of gas on the zeolite bed, in order of to maintain the O2 as the only compound exiting the bed.
Thanks! So it it is a physical effect. Next question - how effective would we expect such a bed to be for discriminating against volatile organic compounds such as those from engine exhaust and fuels? Perhaps aromatics (benzene, toluene) or aldehydes and ketones?
Alan Dyer article "Uses of natural zeolites" gives two references for O2 production from air. 'Natural zeolites, occurrence, properties, and use' (eds. L.B.Sand and F.A.Mumpton), Oxford: Pergamon, 1978 Minato, H., & Tamur, T., page 509-13, and Torii, K, page 441-50; Galabova I.M. page 431-40.
The organic molecules will be preferentially adsorbed by the zeolite bed. Actually, water will be adsorbed first, pretty much "poisoning" the bed for any other compound
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