Capturing Alkanesfrom Natural Gas by Using a Hydrogen-bondedOrganic Framework Composed of Tetracarboxylic Acid

Natural gas upgrading is industrially important for its utilization, wherein the recovery of heavier alkanes, such as ethane (C₂H₆) and propane (C₃H₈) is of certain economic importance. Hydrogen-bonded organic frameworks (HOFs) have shown great potential for separating alkanes. Such a type of porous material is so flexible that it is very challenging to show permanent porosity for gas separation. Here, we report an ultramicroporous hydrogen-bonded organic framework <b>HOF-MTBA</b> for the effective separation of ternary mixtures of C₃H₈/C₂H₆/CH₄ and binary mixtures of C₂H₆/CH₄ and C₃H₈/CH₄. Upon solvent exchange, <b>HOF-MTBA</b> accommodates dichloromethane molecules as a new phase, which can be readily transformed into an open phase after desolvation. Single-component gas sorption experiments show that <b>HOF-MTBA</b> can exhibit high low-pressure uptakes for C₂H₆ (0.71 mmol/g, at 10 kPa and 298 K) and C₃H₈ (1.2 mmol/g, at 5 kPa and 298 K), which are higher than that of many reported adsorbents (0.16–0.73 mmol/g) under the same conditions. The adsorptive selectivities for C₃H₈/CH₄ and C₂H₆/CH₄ are calculated to be 52.7 and 14.0. The breakthrough experiment demonstrates that high-purity CH₄ can be obtained from mixtures of C₃H₈/C₂H₆/CH₄, C₃H₈/CH₄, and C₂H₆/CH₄, respectively.