Separation of High-Purity C₂H₂ from Binary C₂H₂/CO₂ with Robust Al-Based MOFs Constructed with Nitrogen(N)-Containing Heterocyclic Dicarboxylate

The separation of acetylene (C₂H₂) from carbon dioxide (CO₂) holds considerable industrial importance, primarily in acetylene purification. Indeed, the conventional distillation process poses significant energy-consuming due to the similar physicochemical properties, such as kinetic diameters and boiling points of these two gases. In this research, we investigate the potential of three aluminum-based metal-organic frameworks (Al-MOFs), namely Al-L₁, Al-L₂, and Al-L₃, built by nitrogen (N)-containing organic linkers for separating C₂H₂ from C₂H₂/CO₂ mixtures. Among these Al-MOFs, Al-L₃ shows the highest C₂H₂/CO₂ selectivity (4.86) owing to its relatively greater adsorption capacity for C₂H₂ (7.90 mmol g⁻¹) and lower adsorption capacity for CO₂ (2.82 mmol g⁻¹) compared to the other two Al-MOFs. In dynamic breakthrough experiments with an equimolar binary C₂H₂/CO₂ gas mixture, Al-L₃ demonstrates superior separation performance by yielding high-purity C₂H₂ (>99.95%) of 3.73 mmol g⁻¹ through a simple desorption procedure with helium (He) purging at ambient condition. Also, computational simulations employing canonical Monte Carlo and dispersion-corrected density functional theory (DFT-D) methods are conducted to explore the distinctive pore structures of Al-L₁ and Al-L₃. The results emphasize the changes of affinity from variations in the positions of N atoms within pyridine and secondary amine (H–N) groups of three different Al-MOFs. Consequently, Al-L₃ is considered a promising adsorbent for separating high-purity C₂H₂ from binary C₂H₂/CO₂ gas mixtures, and we expect to effectively address challenges related to gas separation in both industrial and scientific fields.