Control of pore structure by the solvent effect for efficient ethane/ethylene separation

The purification of ethylene (C2H4) by selective adsorption of small amounts of ethane (C2H6) is a crucial industrial process. However, most porous adsorbents prefer C2H4 over C2H6 due to the increase in kinetic diameter and decrease in quadrupole moment from C2H4 to C2H6. The construction of ethane-selective adsorbents for ethylene purification is therefore a very challenging task. In this study, we designed and synthesized a family of C2H6-selective metal–organic framework (MOF) adsorbents, named Co-1-ina, Co-5-ina and Co-9-ina, through the strategy of crystal engineering using the same metal salt (Co2+) and ligand (isonicotinic acid). Notably, the pore structures and topologies of these materials vary according to the reaction conditions. Among them, Co-9-ina has the highest C2H6 adsorption capacity and C2H6/C2H4 separation performance. The C2H6/C2H4 selectivity of Co-9-ina at 298 K and 1 bar is astoundingly 2.69, which is greater than most C2H6-selective MOFs reported to date. The pyridine rings bind more strongly to C2H6 via van der Waals interactions for ethane adsorption according to theoretical calculations and single crystal structures. The C2H6/C2H4 separation performance for Co-9-ina was further validated by breakthrough studies under dynamic conditions.