Facile shaping of flexible MIL-53(Al) for effective separation of propylene over propane

A facile granulation approach using polyvinyl butyral (PVB) as a polymer binder was developed to control the textural properties of the flexible metal–organic framework MIL-53(Al). The large pore (LP) structure of MIL-53(Al) contracted after granulation due to a strong interaction between MOF and polymer binder. This contraction enhances propylene's selectivity over propane at saturation pressure (region II), as confirmed by single-component adsorption isotherms. The adsorption kinetics showed faster adsorption of C3H6 compared to C3H8 over time in the case of the granules, while no difference was observed for the powder sample. Breakthrough experiments successfully separated C3H6 over C3H8 using MIL-53(Al)-B10% granules, whereas the pristine MIL-53(Al) powder did not separate the C3H8-C3H6 gas mixture. The breakthrough finding reaffirms that the observed gate-opening effect in MIL-53(Al) within pressure region I is ineffective for separating a mixed gas system containing propane and propylene. The constrained pores of the shaped granules could facilitate strong π-π stacking interactions with C3H6 and decrease the diffusion rate for C3H8 molecules. These findings indicate that the simple granulation approach can modulate the textural properties of flexible MIL-53(Al) and improve its selectivity for C3H6/C3H8 separation resulting from increased MOF-propylene affinity and kinetic factors.