Adsorption of carbon dioxide, methane and nitrogen on an ultramicroporous copper metal-organic framework

An ultramicroporous copper metal-organic framework (Cu-MOF), Cu(hfipbb)(H₂hfipbb)_0.5 [H₂hfipbb=4,4'-(hexafluoro-isopropylidene) bis(benzoic acid)] was successfully synthesized by a microwave-assisted method (1) with a shorter reaction time and higher MOFs yield. The obtained Cu-MOF sample was characterized with scanning electron microscopy for crystal structure, powder X-ray diffraction for phase structure, and carbon dioxide adsorption at 273K for pore textural properties. Single-component adsorption (adsorption equilibrium and kinetics) of CO₂, CH₄, and N₂ on 1 was measured using a Micromeritics ASAP 2020 adsorption porosimeter at 278, 298 and 318K, and pressures up to 1bar. Isosteric heats of adsorption, Henry's constants, and diffusion time constants were calculated and carefully analyzed. Adsorption equilibrium selectivity (α), adsorbent selection parameter for pressure swing adsorption processes (S), kinetic selectivity and combined separation selectivity (β) for CO₂/CH₄, CO₂/N₂ and CH₄/N₂ binary mixtures were estimated based on the single-component adsorption data. The relative high values of the adsorption selectivities suggest that Cu-MOF is a promising adsorbent for separating CO₂/CH₄, CO₂/N₂ and CH₄/N₂ gas pairs.