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.