Kinetic sieving separation of a gating macrocyclic crystal for purification of propylene

Abstract

Finding an energy-efficient alternative to cryogenic distillation for the room temperature, pressure-swing-adsorptive separation of propylene/propane (C₃H₆/C₃H₈) is challenging due to their physiochemical similarity. Herein, we report a gating macrocyclic crystal facilely prepared by the recrystallization of a macrocyclic arene (i.e., naphthyl-hexnutarene), which exhibits outstanding separation capabilities for C₃H₆/C₃H₈, with a remarkable kinetic selectivity of 76.7 and fast C₃H₆ adsorption kinetics with a diffusional time constant of 0.1727 min⁻¹. The achievement is attributed to the transient motions of a gating methoxy group on the macrocycle that extend toward the contracted pore apertures, effectively amplifying the subtle distinction in guest transport. Furthermore, this crystal demonstrates great potential in actual pressure swing adsorption processes, showcasing energy-saving and efficient regeneration, as evidenced by a low heat of adsorption of 15.4 kJ mol⁻¹ for C₃H₆ and full recovery of adsorption capacity through dynamic vacuum at room temperature, together with merited exclusions of co-present C₂H₆/C₂H₄/CH₄/CO₂/N₂ for C₃H₆ purification.