NOVELTY - Preparation of carbon adsorbent pellet composition involves pyrolyzing pellet structure comprising carbon-forming, non-melting binder and non-porous gel-type sulfonated polystyrene precursor, at 750-1000 degrees C under inert atmosphere and conditions suitable to form carbon adsorbent pellet composition having discrete areas of carbonized binder and of carbonized precursor. The carbon adsorbent pellet composition comprises macropores having average pore diameter of 1 mu m or more, and micropores which are capable of selectively admitting 2-3C alkene and excluding 2-3C alkane.    USE - Preparation of carbon adsorbent pellet composition used for pressure swing and temperature swing adsorption process (claimed) for separating 2-3C alkane/alkene mixture.    ADVANTAGE - The 2-3C alkane/alkene mixture is effectively separated using the carbon adsorbent pellet composition.    DETAILED DESCRIPTION - Preparation of carbon adsorbent pellet composition involves pyrolyzing pellet structure comprising carbon-forming, non-melting binder and non-porous gel-type sulfonated polystyrene precursor, at 750-1000 degrees C under inert atmosphere and under conditions suitable to form carbon adsorbent pellet composition having discrete areas of carbonized binder and of carbonized precursor. The carbon adsorbent pellet composition comprises macropores having average pore diameter of 1 mu m or more and total macroporosity of 30% or more, measured by mercury porosimetry, and micropores which are capable of selectively admitting 2-3C alkene and excluding 2-3C alkane, and have total microporosity of 10-30%. INDEPENDENT CLAIMS are included for the following:    (1) carbon adsorbent pellet composition; and    (2) pressure swing or temperature swing adsorption process, which involves feeding gas comprising 2-3C alkane and 2-3C alkene, through separation bed containing the carbon adsorbent pellet composition under pressure swing or temperature swing adsorption conditions such that 2-3C alkane and 2-3C alkene are separated.