Capturing Alkanes from Natural Gas by Using a Hydrogen-bonded Organic 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 HOF-MTBA for the effective separation of ternary mixtures of C3H8/C2H6/CH4 and binary mixtures of C2H6/CH4 and C3H8/CH4. Upon solvent exchange, HOF-MTBA 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 HOF-MTBA 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.