The Carbon molecular sieve is a material containing 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, while the coming out nitrogen molecules will be enriched in gas phase. The enriched oxygen air, adsorbed by the CMS, will be released by reducing the pressure. Then the CMS is regenerated and ready for another cycle of producing nitrogen enriched air.