Pore Size Reduction in Zirconium Metal-Organic Frameworks for Ethylene/Ethane Separation

Engineering metal-organic frameworks (MOFs) for adsorptive ethylene/ethane separation has shown bright prospects for replacing the energy-intensive cryogenic distillation process. Herein, we demonstrate that pore size reduction in zirconium metal-organic frameworks (Zr-MOFs) can significantly improve their ethylene/ethane separation performance. Two Zr-MOFs based on the acetylenedicarboxylate ligand, UiO-66-ADC and NUS-36, are successfully synthesized. Different from UiO-66-ADC with an fcu topology, NUS-36 possesses a bcu network constructed from 8-connected Zr clusters and organic linkers, leading to ultramicropores smaller than 3.6 Å. NUS-36 selectively adsorbs C ₂ H ₄ over C ₂ H ₆ with a selectivity of 4.1 based on idea adsorbed solution theory (IAST) for an equimolar C ₂ H ₄ /C ₂ H ₆ mixture at 298 K and 1 bar, contrasting the C ₂ H ₆ /C ₂ H ₄ selectivity of 1.8 in UiO-66-ADC under the same conditions. The enhanced C ₂ H ₄ affinity of NUS-36 is attributed to the synergistic enthalpic and entropic effects on gas sorption which are triggered by the congested pore environment. This study demonstrates the effectiveness of the pore size reduction strategy for the design and engineering of suitable MOFs for demanding gas separation processes.