Efficient separation of xylene isomers by nonporous adaptive crystals of hybrid[3]arene in both vapor and liquid phases

Abstract

The separation of xylene isomers is a major challenge in the petrochemical industry. However, the traditional distillation method is an energy-intensive process for the separation of xylene isomers. Herein, we develop nonporous adaptive crystals based on hybrid[3]arene H (Hα) for the efficient separation of xylene isomers. Hα shows high selectivity for ortho-xylene from the mixture of xylene isomers in both vapor and liquid phases, with a purity of 90.22% and 99.48%, respectively. The single crystal structure analysis suggests that the selectivity is derived from multiple C–H⋯O and C–H⋯π interactions between H and the preferred guest molecule, ortho-xylene, which is also confirmed by visual study of weak intermolecular interactions and electrostatic potential maps between H and xylene isomers. Besides, the Gibbs free energies of Hα for xylene isomers show that the adsorption energy of Hα for ortho-xylene is lower than that of meta-xylene or para-xylene, further confirming the preferred adsorption of Hα for ortho-xylene. Moreover, Hα is highly recyclable due to the reversible transformation between guest-free and guest-contained structures. This work will afford a new strategy for the separation of other important aromatic isomers and provide inspiration for the use of supramolecular host-based nonporous adaptive crystals in other energy-intensive separation methods.