Mixed gas adsorption of carbon dioxide and methane on a series of isoreticular microporous metal–organic frameworks based on 2-substituted imidazolate-4-amide-5-imidates

In this work the adsorption of CO₂ and CH₄ on a series of isoreticular microporous metal–organic frameworks based on 2-substituted imidazolate-4-amide-5-imidates, IFP-1–IFP-6 (IFP = Imidazolate Framework Potsdam), is studied firstly by pure gas adsorption at 273 K. All experimental isotherms can be nicely described by using the Tòth isotherm model and show the preferred adsorption of CO₂ over CH₄. At low pressures the Tòth isotherm equation exhibits a Henry region, wherefore Henry's law constants for CO₂ and CH₄ uptake could be determined and ideal selectivity α_CO2/CH4 has been calculated. Secondly, selectivities were calculated from mixture data by using nearly equimolar binary mixtures of both gases by a volumetric–chromatographic method to examine the IFPs. Results showed the reliability of the selectivity calculation. Values of α_CO2/CH4 around 7.5 for IFP-5 indicate that this material shows much better selectivities than IFP-1, IFP-2, IFP-3, IFP-4 and IFP-6 with slightly lower selectivity α_CO2/CH4 = 4–6. The preferred adsorption of CO₂ over CH₄ especially of IFP-5 and IFP-4 makes these materials suitable for gas separation application.