Membrane air separation begins when air from the atmosphere is compressed to typically 100 psig. The higher the pressure, the higher the purity.

The compressed air is split into a number of streams and directed to a series of membrane separators. A typical process involves many membrane separators. For 20,000 SCFH of nitrogen, about 117 membranes are needed.

Oxygen diffuse out of the membranes at a much faster rate than either argon or nitrogen, and the oxygen rich stream is vented.

The tube-side flow is nearly depleted of oxygen because it has permeated out, and the high purity nitrogen stream is kept as product. Some nitrogen has also permeated, so the recovery of nitrogen is not 100%