Carbon molecular sieves (CMS) are adsorbents that can be produced from many different organic sources: bituminous coal, bones, coconut shell, etc. The final micropore size depends on the pyrolysis and activation steps in the manufacturing process [2,3]. The micropore size is generally assumed as uniform. The main use of CMS adsorbent has been the nitrogen production from air [4,5] by means of a kinetic separation where both components are nearly equally adsorbed but diffusion of oxygen is much faster being preferentially adsorbed and the CO /CH separation [6,7].