Membrane technology can provide an alternative, low energy consumption method for air separation. For example, polymeric membranes operating at ambient or warm temperatures can produce oxygen-enriched air (25-50% oxygen). Ceramic membrane can provide high purity oxygen (90% or more), but it needs higher temperature (800-900℃) to work. These ceramic membranes include ion transport membranes (ITM) and oxygen transport membranes (OTM). Membrane gas separation is used to provide oxygen-depleted and nitrogen-rich gas instead of air to fill the fuel tank of jet airliners, thereby greatly reducing the chance of accidental fires and explosions. In contrast, membrane gas separation is used to provide pilots with oxygen-enriched air in high-altitude aircraft without pressurized cabins.
Pressure swing adsorption provides separation of oxygen or nitrogen from the air without liquefaction. The process operates at ambient temperature; the zeolite (molecular sponge) is exposed to high-pressure air, then releases the air and releases the adsorption film of the desired gas. The size of the compressor is much smaller than that of the liquefaction unit. This is how the portable oxygen generator is manufactured to provide oxygen-enriched air for medical purposes. Vacuum swing adsorption is a similar process; the product gas is precipitated from the zeolite at sub-atmospheric pressure.
