Fast adsorption and kinetic separation of benzene and cyclohexane/cyclohexene in a microporous metal azolate framework

Abstract

Benzene, cyclohexane, and cyclohexene are essential raw materials in the petrochemical industry. Their separation and purification rely on traditional distillation processes that consume a large amount of energy due to their close boiling points. Here, we describe a new microporous metal azolate framework for mild adsorptive and kinetic separation of the three hexacyclic hydrocarbons. This metal azolate framework exhibits ultrafast benzene adsorption in a short saturation time within seconds and ultrafast kinetic adsorptive separation of benzene/cyclohexane and benzene/cyclohexene. Investigation into the adsorption kinetics of benzene, cyclohexane and cyclohexene reveals a two-step adsorption process, including steps of intraparticle diffusion and surface adsorption, respectively. Also, by adjusting the sample particle size, the adsorption behaviour can be significantly controlled. The large-particle sample achieves a high selectivity for benzene/cyclohexene (94.3) and an inverse selectivity for cyclohexane/cyclohexene, being opposite to the small-particle sample. This highlights the feasibility of controlling adsorption selectivity by manipulating the kinetic steps in porous materials.