An ultramicroporous metal-organic framework based on octahedral-like cages showing high-selective methane purification from a six-component C1/C2/C3 hydrocarbons mixture

Given the crucial significance of using cleaner methane (CH₄) to replace else fossil fuels in remitting energy consumption and preventing environmental degradation, developing prominent adsorbents to purify CH₄ from multicomponent mixtures is fundamentally important but faces great challenges. Cage-based metal-organic frameworks (MOFs) bring about widespread attention in solving numerous separation problems due to their inherent structural preponderances. Herein, we constructed an octahedral-like cages-based MOF (NUM-18) that incorporates two different types of cages within the whole framework and bears abundant Lewis basic sites (naked N atoms) and nonpolar aromatic rings immobilized in the pore surface. Benefitting from its intriguing structural characteristics, the pure-component gas adsorption properties were systematically investigated and indicate that NUN-18a (activated NUM-18) has excellent adsorptive capacities with respect to C2-C3 hydrocarbons than CH₄. The IAST adsorption selectivities for C2/CH₄ are above 14.0, while the adsorption selectivities of C3/CH₄ startlingly surpass 86.0, respectively, all of which forebode that NUM-18a can achieve efficient recovery of C2-C3 hydrocarbons associated with CH₄ purification. Furthermore, the actual separation feasibility for an equimolar 6-component C1/C2/C3 hydrocarbons mixture was examined by simulated dynamic column breakthrough experiments. Finally, molecular simulation calculations were adopted to ascertain potential gas adsorption mechanisms. This work provided a new paradigm for developing novel porous crystalline MOFs materials to separate hyper-complex gas mixtures.