Hydrogen-bonded metal-nucleobase frameworks for highly selective capture of ethane/propane from methane and methane/nitrogen separation

The separation of light hydrocarbons, including C₂H₆ and C₃H₈, is essential to natural gas upgrading. Meanwhile, N₂ removal from CH₄ is also crucial to concentrating low-quality coalbed methane, but the adsorption process is challenging because of the close kinetic diameter. This work reports two hydrogen-bonded metal-nucleobase frameworks (HOF-ZJU-201 and HOF-ZJU-202) capable of efficiently separating C₃H₈/CH₄, C₂H₆/CH₄, and CH₄/N₂. Due to strong affinity for C₃H₈ and C₂H₆, the low-pressure capacity for C₃H₈ (5 kPa) and C₂H₆ (10 kPa) of HOF-ZJU-201a exceeds most adsorbents. The ideal adsorbed solution theory (IAST) selectivity of C₃H₈/CH₄ and C₂H₆/CH₄ is 119 and 45 at ambient conditions. According to density functional theory calculations, surface polarization environments formed by electron-rich anions and electron-deficient purine heterocyclic rings contribute to the selective capture of C₃H₈ and C₂H₆ with greater polarizability. Furthermore, the high CH₄ adsorption capacity (1.73 mmol/g for HOF-ZJU-201a and 1.50 mmol/g for HOF-ZJU-202a at 298 K and 1.0 bar) and excellent CH₄/N₂ selectivity (6.0 for HOF-ZJU-201 at 298 K), as well as dynamic breakthrough experiments of binary CH₄/N₂ gas mixture implied their efficacy in the concentration of low-quality coalbed methane.