Exploiting the π-bonding for the separation of benzene and cyclohexane in zeolites

Separation of benzene and cyclohexane is one of the greatest challenges in industry. Their close boiling points and similar properties make them difficult compounds to separate. In this context, adsorption-based separation using zeolites or aluminosilicates is a promising technology. In the present work, we combine experimental measurements, density functional theory, and classical simulations to study the targeted separation. We analyse the effect of the sodium content in the adsorption of benzene and cyclohexane in three zeolites with FAU topology; high silica FAU, NaY and NaX. Quasi-equilibrated temperature adsorption and desorption measurements, first principles calculations, and classical simulations reveal the strong interaction between benzene molecules and sodium cations present in aluminosilicates and identify this fact as the key factor for the separation. We have developed a set of parameters to study the targeted separation by fitting to the experimental values and have run Monte Carlo simulations in the Grand-Canonical ensemble to obtain the adsorption isotherms and isobars. In addition, we have performed density functional theory calculations to analyse the specific interaction between benzene or cyclohexane and extra-framework sodium cations. Our results show that NaY and NaX zeolites are able to separate these compounds with extremely high efficiency.