Nitrogen generation by the Pressure Swing Adsorption (PSA) process is a technology that separates N2 from a mixture of gases under pressure according to the special selective adsorption characteristics of the Carbon Molecular Sieves (CMS). Carbon molecular sieve is a non-polar adsorbent, derived from carbonaceous matter, that has different adsorptive rate for oxygen and nitrogen. CMS contains tiny pores of a precise and uniform size that is used as an adsorbent for gases. When the pressure is high enough, the oxygen molecules, which pass through the pores of CMS much faster than the nitrogen molecules, are adsorbed; nitrogen molecules remains free in the gas stream, leaving an enriched N2 gas phase. The CMS releases the oxygen when the system lowers the pressure. This regenerates the CMS so it is ready for another cycle of producing nitrogen enriched air.
CMS looks like small, black grains 1.0x2.0 mm in size and a weight near 650 g/L. Saturation is usually reached near 60 seconds under a pressure of 0.8 Mpa (116 PSI). CMS comes in different grades, which tells you the purity of N2 gas you achieve under a certain pressure. My PSA has about 40kg of CMS-H, which gives me 98.5-99% N2 at a flow rate of 1.05 SCFM (about 30 L/min).