A metal azolate framework with small aperture for highly efficient ternary benzene/cyclohexene/cyclohexane separation

Abstract

Separation of ternary C₆ cyclic hydrocarbons, i.e., benzene/cyclohexene/cyclohexane mixtures, is crucial but challenging in the petrochemical industry due to their extremely similar molecular sizes and physical properties. Here, we design and synthesize a new Zn-based metal azolate framework (MAF), MAF-40, with a three-dimensional (3D) honeycomb-like framework and 1D sugar-coated-berry type pore channels. By virtue of the strong coordination bonds and abundant trifluoromethyl groups embedded in the pores, MAF-40 exhibits excellent thermal stability (up to 400 °C) and acid-base stability (within a pH range of 3–11). Moreover, MAF-40 shows ultrahigh benzene selectivity (38.8) from the ternary benzene/cyclohexene/cyclohexane mixtures, attributed to the strong adsorption affinity from fluorine for benzene and markedly different guest diffusion limited by the small aperture, which are confirmed by computational simulations and infrared spectra. Thus, the results indicated that MAF-40 would be a candidate adsorbent for the separation and purification of benzene from C₆ cyclic hydrocarbons, and this work provides a new insight of synthesizing stable MOF materials for separating multicomponent chemical mixtures.