Ethane-Selective Activated Nitrogen-Doped Carbons for Ethane/Ethylene Separation

Nitrogen-poor and nitrogen-rich heteroatom-doped carbon materials of variable porosity were prepared via a dual cation activation scheme and evaluated as adsorbents for C2H6/C2H4 separation, an inversion of the classic ethylene-selective materials for olefin-paraffin separations, and a difficult and costly process integral to many consumer products and industrial feedstocks. Textural properties (i.e., surface area, pore volume, etc.) were tuned by varying the K2CO3 mole fraction of the activating mixture while N-content remained consistent and, as a result, enabled the investigation of the effect of adsorbent structure on C2H6 and C2H4 adsorption and selectivity. The uptake of C2H6 and C2H4 was determined to be entirely dependent on pore volume and Brunauer–Emmett–Teller surface area (BET SA). However, selectivity was found to be tunable by the surface composition, wherein N-poor carbons demonstrated selectivity for C2H6 whereas N-rich carbons demonstrated selectivity for C2H4. First-principles calculations revealed that increased N-doping led to electron depletion at adjacent carbon atoms such that C2H4 adsorption was promoted.