An isoreticular series of metal organic frameworks (MOFs) of IFPs (IFP, imidazolate frameworks Potsdam) is investigated for their morphological properties and adsorption behaviour. The materials are characterized phenomenologically with respect to their particle size and tendency of agglomerate formation, and with respect to their internal structure. For this purpose, material densities, pore size distributions, specific inner surfaces, and porosities are determined. The main part of the investigation is based on the analysis of gravimetrically determined adsorption equilibria for carbon dioxide (CO2) and methane (CH4) and their modelling. In this context, two different approaches for the consideration of the buoyancy of the sample are compared. The adjusted measurement data are globally approximated as sets of isotherms at different temperatures with two different modifications of the Langmuir model. Results show that both models are well suited for the interpolation of the experimental data in the temperature range under consideration. Comparison of the heats of adsorption derived from the isosteric method with values extracted from the model equations confirms them as physically consistent. This provides the opportunity to numerically simulate the dynamic separation of CO2/CH4‐mixtures under consideration of the heat tone based on the single component data. The IFPs can be divided phenomenologically into two categories. One is exclusively microporous (IFP‐4, ‐6, ‐7, and ‐8), while the other exhibits hierarchical structures of micropores coupled with mesopores (IFP‐1, ‐2, ‐3, and ‐5). Equilibrium data indicate that the latter are better suited for the separation of CO2/CH4‐mixtures due to their higher selectivities and capacities.

A novel core–shell species for the adsorption-based separation of carbon dioxide (CO2) from methane (CH4) is introduced by hydrothermal synthesis of Ni-MOF-74 on mesoporous spherical Al2O3 carrier substrate. The material was characterized and the shell thickness determined by means of optical and scanning electron microscopy as well as volumetric adsorption and fluid displacement experiments. Kinetic experiments with Ni-MOF-74@Al2O3 core–shell composites carried out at 303.15 K and at pressures up to 10 bar expose remarkably dominating uptake rates for CO2 over CH4. In the contrary Ni-MOF-74@Al2O3 appears to be unselective according to equilibrium data at the same conditions. Dynamic breakthrough experiments of binary CH4/CO2-mixtures (at 303.15 K and 5 bar) prove the prevailing effect of adsorption kinetics and the storage function of the mesoporous core. This statement is supported by a considerable boost in CO2-selectivity and capacity compared to adsorption equilibria measured on pure Ni-MOF-74 by the factor of 55.02 and up to 2.42, respectively.

Sorption measurements of water vapor on an isoreticular series of Imidazolate Frameworks Potsdam (IFP), based on penta-coordinated metal centers with secondary building units (SBUs) connected by multidentate amido-imidate-imidazolate linkers, have been carried out at 303.15 K. The isotherm shapes were analyzed in order to gain insight into material properties and compared to sorption experiments with nitrogen at 77.4 K and carbon dioxide at 273.15 K. Results show that water vapor sorption measurements are strongly influenced by the pore size distribution while having a distinct hysteresis loop between the adsorption and desorption branch in common. Thus, IFP-4 and -8, which solely contain micropores, exhibit H4 (type I) isotherm shapes, while those of IFP-1, -2 and -5, which also contain mesopores, are of H3 (type IV) shape with three inflection points. The choice of the used linker substituents and transition metals employed in the framework has a tremendous effect on the material properties and functionality. The water uptake capacities of the examined IFPs are ranging 0.48 mmol g−1 (IFP-4) to 6.99 mmol g−1 (IFP-5) and comparable to those documented for ZIFs. The water vapor stability of IFPs is high, with the exception of IFP-8.

Based on experimental pure component data for the characterization of the isostructural imidazolate framework Potsdam (IFP) series reported in Part I, a model for the simulation of non‐isothermal dynamic adsorption of CO2/CH4‐mixtures in fixed‐bed columns is presented in this Part II. The robustness of the model is examined and validated, by comparison to experimental breakthrough data at different process conditions, such as varying concentration, temperature, and pressure. Thereby, different predictive methods for the estimation of adsorption equilibria of mixtures are compared (RAST, IAST, ML). The results show that ideal behaviour can be assumed with good accuracy for the system under consideration, except for IFP‐2, which shows significant deviations at increased pressures and temperatures. A detailed kinetic analysis reveals that mass transfer is significantly influenced by micropore diffusion. Thus, only for IFP‐1 the dynamic separation of CO2 and CH4 is equilibrium‐driven, while for the remaining IFPs the kinetic regime dominates the process, which in some cases increases the separation efficiency (IFP‐2 to ‐7) but can also inhibit it (IFP‐8). The determined intracrystalline diffusion coefficients show very good agreement with values for metal organic framework (MOF) compounds of similar structure reported in the literature.