Flexible zeolitic imidazolate frameworks (ZIFs) for inverse olefin/paraffin separation

This thesis focuses on the synthesis of differently functionalised flexible zeolitic imidazolate frameworks (ZIFs) for the inverse separation of light olefins and paraffins. This separation is fundamental for the production of light olefins such as ethene and propene which are considered to be among the most significant chemical feedstocks in the chemical industry. However, this process is challenging due to the similar chemical and physical properties of light olefins and paraffins and typically this separation is achieved using highly energy-intensive cryogenic distillation at very low pressures and temperatures. A promising less energy-demanding alternative for this separation is represented by selective adsorption on porous and flexible ZIFs, a sub-class of metal-organic frameworks (MOFs) formed by tetrahedral metal ions and imidazole-based linkers. These can preferentially interact with alkanes, favouring their selective adsorption in the pores of the material. In this thesis work, post-synthetic modification (PSM) through solvent-assisted ligand exchange (SALE) with differently functionalised benzimidazole linkers is used to tune the adsorption properties of ZIF-7 and ZIF-9 and increase their performances in ethane/ethene and propane/propene separation.