A Robust Hydrogen-Bonded Metal–Organic Framework with Enhanced Ethane Uptake and Selectivity

Selective
adsorption of trace C2H6 over C2H4 is important for the industrial purification
of polymer-grade C2H4 (>99.95% purity). For
practical applications, potential adsorbents show high structural
stability while maintaining elevated C2H6 adsorption
even at low pressures. Herein, we report a C2H6-selective metal–organic framework (MOF), viz., Co­(AIN)2 (HAIN = 3-aminoisonicotinic acid), with a twofold
interpenetrated dia structure. Compared to an isoreticular
and unstable Co­(IN)2 (HIN = isonicotinic acid)
without internal hydrogen bonding, this framework exhibits exceptional
structural robustness even under humid conditions because of the presence
of intra- and inter-net hydrogen bonds between carboxylate oxygens
and amino groups of AIN–. Decoration of the internal
polar pore surfaces with groups that form extensive hydrogen bonds
offers a more favorable environment for selective C2H6 adsorption. According to the ideal adsorbed solution theory,
the predicted selectivity for C2H6/C2H4 was found to be 2.98 in C2H6/C2H4 (1:15, v/v) mixtures, which surpasses even the
best-performing MOFs. The C2H6 uptake at 62.5
mbar partial pressure in the single-component isotherm, in C2H6/C2H4 (1:15, v/v) mixtures, was
the highest (63.16 cm3 g–1) among MOF
adsorbents, along with a nearly top-tier separation potential (116.03
cm3 g–1). Molecular modeling illustrates
that the C–H···π interactions of C2H6 with the pore walls are more significant than
those of C2H4, accounting for the improved selectivity
for C2H6 over C2H4 in Co­(AIN)2. The separation performance under dynamic
dry and humid conditions was confirmed by breakthrough experiments. Co­(AIN)2 was shown to be synthesized on a gram
scale and was easily regenerated by inert gas purging. Thus, we demonstrated
that coating of internal pore surfaces with groups that form hydrogen
bonds provides more favorable environments for enhanced structural
stability and C2H6 affinity and selectivity.