Pore chemically modified nickel-based metal-organic frameworks for efficient purification of natural gas

Purifying methane from natural gas containing impurities like propane and ethane is a critical chemical process. However, the conventional cryogenic distillation technology necessitates extreme temperature and pressure conditions, leading to substantial energy expenditure. To address these challenges, we present Ni(ina)(2-atp)_0.5 and Ni(3-aia)(2-atp)_0.5, by scaling down the size and incorporating amino-functionalities into both ligands of MCF-19. Ni(ina)(2-atp)_0.5 demonstrated a remarkable adsorption capacity for ethane (C₂H₆) and propane (C₃H₈), registering 62 and 53 cm³/g at 298 K and 100 kPa, respectively, in contrast to its appreciably lower uptake of 10 cm³/g for methane. With a similar adsorption capacity for C₃H₈ and CH₄, the C₂H₆ capacity of Ni(3-aia)(2-atp)_0.5 reached 59 cm³/g. The selectivity of C₂H₆/CH₄ (10/85) by Ni(3-aia)(2-atp)_0.5 was enhanced to 21 from 14 of Ni(ina)(2-atp)_0.5. Higher adsorption capacity and selectivity of Ni(3-aia)(2-atp)_0.5 make it possible to separate multi-component gases. Grand Canonical Monte Carlo simulations were further conducted to investigate the adsorptive interactions within the MOF. The results revealed that two MOF preferentially engage in stronger C-H∙∙∙O and C-H∙∙∙N interactions with C₂H₆ and C₃H₈. These interactions are critical for advancing the purification of methane from ternary mixtures. Experimental validation through adsorption kinetics and dynamic breakthrough experiments confirms that both MOFs yielded a 99.1 % CH₄ purity during the actual natural gas purification process.