Coadsorption of n-Hexane and Benzene Vapors onto the Chromium Terephthalate-Based Porous Material MIL-101(Cr) An Experimental and Computational Study

The adsorption of n-hexane–benzene mixture onto a chromium terephtalate-based porous material (MIL-101(Cr)) has been studied experimentally and theoretically. The adsorption isotherms of the single components show that MIL-101(Cr) has a better affinity for benzene than for n-hexane. This is in good agreement with the enthalpies of adsorption determined at low coverage. Values of −68 kJ·mol–1 and −61 kJ·mol–1 were found for benzene and n-hexane, respectively. These are consistent with the simulated enthalpies of adsorption and also with the benzene/n-hexane selectivities which range between 2 and 3 depending on the equilibrium pressure. The saturation plateau obtained with n-hexane is 30% lower than that obtained with the adsorption of benzene onto MIL-101(Cr). In the case of the mixture of n-hexane–benzene, the saturation plateau is located between those obtained after adsorption of the single components. This is an indication that the coadsorption of n-hexane and benzene does not occur at the expense of one component of the mixture. However, the kinetics of adsorption of the mixture shows that benzene is adsorbed preferentially at low coverage. This is consistent with the chromatographic separation of n-hexane–benzene mixture by MIL-101(Cr).