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···πinteractions 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.