An ultramicroporous pillar-layer metal-organic framework for high sieving separation of ethylene from ethane

Developing new techniques and materials for ethylene (C2H4) and ethane (C2H6) separation is an industrially significant but challenging task. Here we report two isoreticular pillar-layer metal-organic frameworks, Co(aip)(bpy)0.5 and Co(aip)(pyz)0.5, for the separation of C2H4/C2H6. The pore apertures of the pillar-layer metal-organic frameworks are rationally controlled by changing the length of the pillar ligands. Significantly, Co(aip)(pyz)0.5 with a shorter pillar ligand shows reduced pore size and molecular sieving separation of C2H4 from C2H6. Co(aip)(pyz)0.5 has a moderate C2H4 capacity of 1.78 mmol/g but ultrahigh C2H4/C2H6 selectivity exceeding 2000 at ambient conditions. The molecular simulation revealed that large torsion angle between the organic linker plane and Co–O bond leads to the high energy barrier for C2H6 to enter into the pore, which results in the molecular sieving separation of C2H4/C2H6. Dynamic breakthrough experiments confirmed the high selectivity of Co(aip)(pyz)0.5 for C2H4. And high-purity C2H4 (>97%) with a C2H4 productivity of 19.1 l/kg can be obtained through the desorption process. Meanwhile, the excellent reusability and moisture stability endow it great potential for applications in adsorptive separation.