Benchmark Low-Pressure Ethane Uptake for Ethylene Purification Enabled by a Metal–Organic Framework with Confined Pore Space and Abundant Binding Sites

Removing trace ethane (C₂H₆) from ethylene (C₂H₄)-rich streams is essential for high-purity C₂H₄ production but remains energy-intensive due to their similar physicochemical properties. Adsorptive separation using metal-organic frameworks (MOFs) offers a promising alternative to cryogenic distillation but is limited by insufficient C₂H₆ uptake under industrially relevant low-pressure conditions. Here, we report a microporous copper-based framework, NUC-201Cu, synthesized via an in situ ligand transformation in which cyano groups convert to tetrazole units during assembly. This strategy generates abundant N-rich binding sites within confined pores, thereby strengthening interactions with C₂H₆. Single-component adsorption measurements show that NUC-201Cu achieves a benchmark C₂H₆ uptake of 51.9 cm³ g⁻¹ at 0.06 bar and 298 K and exhibits a distinct adsorption preference over C₂H₄. Ideal adsorbed solution theory (IAST) calculations predict a selectivity of 2.6 for an equimolar C₂H₆/C₂H₄ mixture at 298 K and 1 bar. Theoretical simulations identify tetrazole groups as the dominant C₂H₆ adsorption sites, while dynamic breakthrough experiments confirm efficient separation, enabling the direct production of high-purity C₂H₄. These findings demonstrate that in situ ligand transformation provides an effective approach for constructing highly selective adsorption environments in microporous MOFs, offering promising potential for energy-efficient hydrocarbon separations.