Separation principle of xylene isomers and ethylbenzene with hydrogen-bonded host frameworks via first-principles calculation

Abstract

Separation of molecular isomers, which have similar physical properties, is hardly achieved with conventional separation methods based on phase equilibria. However, using selective inclusion of target molecules into dismantlable molecular framework allows molecular isomers to be effectively separated from one another. For that purpose, we consider the hydrogen-bonded organic framework (HOF), which can undergo solvent-mediated crystallization. Herein, we theoretically elucidated the separation mechanism of the mixture of xylene isomers (i.e., o-, m-, and p-xylene) and ethyl benzene (EB) using guanidinium (G) cation and organosulfonate anion (S) host systems (i.e., 2(G)+4,4′-biphenyldisulfonate (G2BPDS) and 2(G)+2,6-naphthalenedisulfonate (G2NDS) GS-host systems). Density functional theory (DFT) calculations were carried out to investigate separation mechanisms in terms of thermodynamics (i.e., formation energy, interaction energies of guest-host and guest-guest, and vacancy formation energy) and kinetics (i.e., surface energy) considering the solvent-mediated crystallization process. We theoretically predicted that G2BPDS system could effectively separate EB from xylene isomers, and G2NDS system could separate each xylene isomer by sequential separation process.