A Microporous Zn(bdc)(ted)_0.5 with Super High Ethane Uptake for Efficient Selective Adsorption and Separation of...

Separating light hydrocarbons (C₂H₆, C₃H₈, and C₄H₁₀) from CH₄ is challenging but important for natural gas upgrading. A microporous metal-organic framework, Zn(bdc)(ted)_0.5, based on terephthalic acid (bdc) and 1,4-diazabicyclo[2.2.2]octane (ted) ligands, is synthesized and characterized through various techniques, including powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and porosity analysis. The adsorption isotherms of light hydrocarbons on the material are measured and the isosteric adsorption heats of CH₄, C₂H₆, C₃H₈, and C₄H₁₀ are calculated. The prediction of C2-4/C1 adsorption selectivities is accomplished using ideal adsorbed solution theory (IAST). The results indicate that the material exhibits exceptional characteristics, including a Brunauer-Emmett-Teller (BET) surface area of 1904 m²/g and a pore volume of 0.73 cm³/g. Notably, the material demonstrates remarkable C₂H₆ adsorption capacities (4.9 mmol/g), while CH₄ uptake remains minimal at 0.4 mmol/g at 298 K and 100 kPa. These findings surpass those of most reported MOFs, highlighting the material's outstanding performance. The isosteric adsorption heats of C₂H₆, C₃H₈, and C₄H₁₀ on the Zn(bdc)(ted)_0.5 are higher than CH₄, suggesting a stronger interaction between C₂H₆, C₃H₈, and C₄H₁₀ molecules and Zn(bdc)(ted)_0.5. The molecular simulation reveals that Zn(bdc)(ted)_0.5 prefers to adsorb hydrocarbon molecules with richer C-H bonds and larger polarizability, which results in a stronger dispersion force generated by an adsorbent-adsorbate induced polarization effect. Therefore, the selectivity of C₄H₁₀/CH₄ is up to 180 at 100 kPa, C₃H₈/CH₄ selectivity is 67, and the selectivity of C₂H₆/CH₄ is 13, showing a great potential for separating C2-4 over methane.