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Oxygen/Nitrogen-Enriched Air

Oxygen-enrichment and Nitrogen-Enrichment is simple and straightforward using PermSelect® silicone membranes. Since oxygen is roughly twice as permeable than nitrogen, when supplying a feed of compressed air to a PermSelect® module, the permeate will be oxygen rich and the retentate will be oxygen poor (nitrogen rich). The separation properties of silicone enable a maximum permeate oxygen concentration of 34% and retentate nitrogen concentration as high as 99.9 % in a single pass.

Oxygen Enrichment/Nitrogen Enrichment using a PermSelect Membrane ModuleOxygen-Enrichment/Nitrogen-Enrichment using a PermSelect® Membrane Module

Reducing the nitrogen content of air brings advantages in any process where inert nitrogen has a ballast effect. The benefit accrues even at only modest oxygen-enrichment. For example, air with oxygen enriched from 21% to only 30% – an enrichment of only 9% – will contain nearly 40% less nitrogen per unit oxygen.

Shown below is a performance graph of the PermSelect® PDMXA-7500 membrane module. A compressed air feed is supplied at various pressures and flows to the module inlet, and the oxygen rich gas exits as permeate.

Oxygen Enrichment/Nitrogen Enrichment Performance using a PDMXA-7500Oxygen-Enrichment/Nitrogen-Enrichment Performance using a PDMXA-7500
Oxygen enriched air permeate flow: Oxygen enriched air permeate flowOxygen Enriched Air Permeate Flow

Nitrogen enriched air is simultaneously produced as the retentate while oxygen rich air is produced as the permeate. However, unlike the oxygen rich permeate, it is possible to achieve higher levels of nitrogen purity in a single pass as shown in the table below. Note that the stage cut (the fraction of feed air flow loss across the membrane) can be significant at higher levels of purity. Nonetheless, in many applications it is more practical and economical to compromise with a high stage cut in exchange for compactness, simplicity, and lower cost of a membrane system.

Nitrogen enriched air composition achievable at various air feed flows at 45 psi.Nitrogen enriched air composition achievable at various air feed flows at 45 psi. Note that flow is in Liters/min and the nitrogen rich air is at atmospheric pressure.