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 C2H4 over C2H6 with a selectivity of 4.1 based on idea adsorbed solution
theory (IAST) for an equimolar C2H4/C2H6 mixture at 298 K and 1 bar, contrasting the C2H6/C2H4 selectivity of 1.8 in UiO-66-ADC
under the same conditions. The enhanced C2H4 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.