Dual-Pore Dodecanuclear Al-Oxo Cluster-Based Bimetallic Isonicotinate Frameworks for Selective Propylene/Ethylene Separation.

The separation of ethylene (C2H4) and propylene (C3H6) from methanol-to-olefins (MTO) products remains challenging due to their similar physicochemical properties, whereas conventional cryogenic distillation is energy-intensive. This study addresses the need for cost-effective, efficient adsorbents by developing a series of bimetallic isonicotinate aluminum-based metal-organic frameworks Al12(OMe)24[MCl2(INA)4]3 denoted as Al12INA-M (HINA = isonicotinic acid, M = Mn, Fe, Co, Cu) featuring ftw topology. Among them, Al12INA-Fe showed a high C3H6 adsorption capacity (7.60 mmol g-1 at 1 bar), moderate isosteric heat of adsorption (29.3 kJ mol-1), high IAST selectivity (∼8) for C3H6 over C2H4 at 298 K, and low synthetic cost ($345.3 per kg). Dynamic breakthrough experiments confirmed effective separation of equimolar mixtures, yielding polymer-grade C2H4 with a productivity of 63.4 L kg-1 and a low purification cost (∼$5.44 per liter of C2H4). Theoretical calculations revealed that the separation mechanism originates from molecular sieving effects and stronger host-guest interactions toward C3H6 facilitated by the hydrophobic, methyl-rich cavities and suitable aperture sizes.