Vapor-Phase Adsorption and Separation of Ethylbenzene and Styrene on the Metal–Organic Frameworks MIL-47 and MIL-53(Al)

Separation of styrene (ST) from ethylbenzene (EB) remains an industrially relevant challenge in the production of polystyrene. Adsorptive separation with metal–organic frameworks (MOFs) is a potential alternative for the conventional vacuum distillation process. Adsorption and separation of ST and EB on the MOFs MIL-47 and MIL-53(Al) were studied under vapor-phase conditions. ST and EB show traditional type I isotherms on MIL-47. Contrarily, ST adsorption isotherms show steep steps on MIL-53(Al) as a result of the breathing of the flexible MOF upon increased adsorbate pressure. The separation potential of both MOFs was investigated by performing vapor-phase breakthrough experiments at total hydrocarbon partial pressures between 1.14 and 16.4 mbar and temperatures between 35 and 90 °C. ST is preferentially adsorbed on both MOFs. Although the MOFs are isostructural, the evolution of selectivity with temperature and pressure is different for both materials due to the different interaction and separation mechanisms.