Pressurized air is fed to one end of the hollow fiber membranes. The permeation rates of the water vapour, CO2 and oxygen contained in the air stream are faster than nitrogen and argon and will rapidly diffuse through the fiber walls. The slower diffused nitrogen molecules remain in the fiber bore and are collected as the nitrogen product gas.

Nitrogen purity ranges from 95% to 99.9 %. As purity level increases, more air consumption and membrane modules are required so higher investment appears. That is why precise gas specifications are important in order to obtain maximum economic solution.