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

The separation of ethylene (C 2 H 4 ) and propylene (C 3 H 6 ) 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 Al 12 (OMe) 24 [MCl 2 (INA) 4 ] 3 denoted as Al 12 INA-M (HINA = isonicotinic acid, M = Mn, Fe, Co, Cu) featuring ftw topology. Among them, Al 12 INA-Fe showed a high C 3 H 6 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 C 3 H 6 over C 2 H 4 at 298 K, and low synthetic cost ($345.3 per kg). Dynamic breakthrough experiments confirmed effective separation of equimolar mixtures, yielding polymer-grade C 2 H 4 with a productivity of 63.4 L kg –1 and a low purification cost (∼$5.44 per liter of C 2 H 4 ). Theoretical calculations revealed that the separation mechanism originates from molecular sieving effects and stronger host–guest interactions toward C 3 H 6 facilitated by the hydrophobic, methyl-rich cavities and suitable aperture sizes.