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.

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.

No abstract

No abstract