A linker conformation induced metal–organic framework with high stability and efficient upgrading of natural gas

Natural gas plays an important role in daily life and the petrochemical industry, but there are often large amounts of impurities which prevent the full use of methane in natural gas. Developing excellent adsorbents to purify CH₄ from multi-component mixtures is crucial, but also faces great challenges. Here, by utilizing a ligand conformation preorganization strategy, we employ a flexible nonplanar hexacarboxylate ligand with C2 symmetry to successfully construct a robust microporous metal-organic framework {[Cu₃(bmipia)(H₂O)₃]·(DMF)(CH₃CN)₂}_n (GNU-1, bmipia = 5-[N,N-bis(5-methylisophthalic acid)amion] isophthalate) with an unprecedented topology. More importantly, the obtained GNU-1 not only exhibits good stability in acid-base and water environments, but also shows potential utility as an adsorbent for efficient separation and purification of natural gas under ambient conditions. The adsorption isotherms of GNU-1a (activated GNU-1) exhibit strong binding affinities for C₂H₆ and C₃H₈, a remarkable uptakes of C₃H₈ (6.64 mmol g^-1) and C₂H₆ (4.6 mmol g^-1) and an excellent selectivity of 330.1 and 17.5 for C₃H₈/CH₄ and C₂H₆/CH₄ mixtures, respectively, at 298 K and 1 bar. The breakthrough experiments demonstrate that the ternary CH₄/C₂H₆/C₃H₈ mixtures are completely separated using a fixed-bed separator packed with GNU-1a at ambient temperature and also show great potential for recovering the C₂H₆ and C₃H₈ contents from natural gas. Finally, Grand Canonical Monte Carlo simulations are adopted to ascertain potential gas adsorption mechanisms. This work proves the feasibility of optimizing the structure and pore size of MOF materials by regulating the conformation of ligands for application in the field of light hydrocarbon adsorption/separation.