Non-cryogenic air separation processes are most likely to be a suitable and cost effective choice when high purity product is not required and/or when the required production rate is relatively small. Systems belong to one of two major technology categories: adsorption processes and membrane diffusion-separation systems. Adsorption-based processes may be described using a number of generic names (Pressure Swing Adsorption or PSA, Vacuum Swing Adsorption or VSA, Vacuum-Pressure Swing Adsorption or VPSA) or by trade names. The same holds true for Membrane separation systems. PSA, VSA and VPSA systems use differences in adsorption of gases on specially-fabricated materials to make the desired separations. Different adsorbents are used for oxygen and nitrogen generation, but the physical appearance and operating principles of the systems are similar. Membrane systems use differences in diffusion rates between, for instance, oxygen and nitrogen or hydrogen and CO2 through the walls of specially designed and fabricated hollow polymer tubes.