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.
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.
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, which presents the theoretical nitrogen enrichment possible. Users should conduct their own testing to determine if the actual nitrogen enrichment achievable is suitable for their application. 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.
