Efficient separation of C4 olefins with fluorinated anion-pillared hybrid ultramicroporous materials by gate-opening and size-sieving effect

In the petrochemical industry, the separation of C4 olefins is crucial but a challenging and energy-intensive process. In this study, two fluorinated anion-pillared hybrid ultramicroporous materials (HUMs), namely KAUST-7 (NbOFFIVE-1-Ni) and KAUST-8 (AlFFIVE-1-Ni), were explored for the efficient separation of ternary C4 olefin mixtures (C4H6/n-C4H8/iso-C4H8) via gate-opening and size-sieving effects. KAUST-7, with a narrow and flexible pore window that completely excludes iso-C4H8, but allows for the absorption of C4H6 and n-C4H8 through gate-opening effects, with a preferential adsorption of C4H6 due to its easier access to the channel. KAUST-8, on the other hand, with a larger pore window size and the strong H-bond interactions between the electronegative fluorine atoms from inorganic anion pillar and the C4 olefin molecules, efficiently separates iso- C4H8 from C4 olefins, as the adsorption of both C4H6 and n-C4H8 is significantly enhanced while iso-C4H8 retains much lower adsorption capacity. The relationship between the structures and separation properties of these materials is discussed, providing insight into the development of efficient separation materials. Fixed bed breakthrough experiments verify the excellent separation performances of KAUST-7 and KAUST-8 for C4H6/n-C4H8/iso-C4H8, highlighting their potential for industrial applications.