| Summary: | Single gas sorption experiments with the C4-hydrocarbons <i>n</i>-butane, <i>iso</i>-butane, 1-butene and <i>iso</i>-butene on the flexible MOFs <i>Cu-IHMe-pw</i> and <i>Cu-IHEt-pw</i> were carried out with both thermodynamic equilibrium and overall sorption kinetics. Subsequent static binary gas mixture experiments of <i>n</i>-butane and <i>iso</i>-butane unveil a complex dependence of the overall selectivity on sorption enthalpy, rate of structural transition as well as steric effects. A thermodynamic separation favoring <i>iso</i>-butane as well as kinetic separation favoring <i>n</i>-butane are possible within <i>Cu-IHMe-pw</i> while complete size exclusion of <i>iso</i>-butane is achieved in <i>Cu-IHEt-pw.</i> This proof-of-concept study shows that the structural flexibility offers additional levers for the precise modulation of the separation mechanisms for complex mixtures with similar chemical and physical properties with real selectivities of >10.
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