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The aim of this work is to study the adsorption of several hydrocarbons by MIL-101(Cr) in order to find trends in adsorption behavior and relate those to the physicochemical properties of the sorbates. The separation of saturated, unsaturated and cyclic hydrocarbons was investigated on MIL-101(Cr) by means of gas chromatography equipped with a filled column of the MOF. MIL-101(Cr), proved to be very efficient to separate mixtures of saturated, unsaturated or aromatic hydrocarbons. The influence of hydrocarbons branching is evaluated towards their separation. We found that linear hydrocarbons are eluted firstly in the case of the n -hexane isomers series. We also demonstrated that xylenes are partially separated by MIL-101: metaxylene and paraxylene being eluted together, before orthoxylene. MIL-101 behaves therefore as a shape selective material with respect to the isomers of n -hexane, or xylenes. This separation could be predicted by the Henry’s constants which are calculated from the adsorption isotherms of single components by MIL-101(Cr). It is then demonstrated that these Henry’s constants establish a new tool for predicting the separation efficiency of any sorbent.

International audience; Configurational Bias Grand Canonical Monte Carlo simulations have been used to show that the alkane isomer adsorption selectivity of porous MOF materials containing two pore types depends on the orientation of organic linkers' phenyl groups. These simulations were performed at low pressure (0.1 kPa) using mixtures of n-hexane and its branched isomers (2,2-dimethylbutane, 2,3-dimethylbutane and 2-methylpentane). Where possible, we compared the results with our gas chromatography results. In typical 1D narrow pore materials, the linear isomer is usually preferentially adsorbed over its branched isomers. In MOF materials exhibiting a 3D pore system with two pore types, a large one interconnected by smaller pores, the selectivity order is the inverse. Here, we show that this depends on the degree of opening of the access windows, which can allow it to be either ''closed'', or to mimic a small pore channel. The consequence of this is the possibility (in the linear/branched mixture case) for the linear alkane to remain linear and thus maximize its interactions with the pore. The linear/aromatic mixture case considers a mixture of benzene and n-hexane, to show that a more favorable packing efficiency pushes the selectivity towards the aromatic molecule, regardless of the degree of the pore opening, although n-hexane can increase its competitiveness for the adsorption sites in materials where it can remain in mostly linear conformations.

International audience; 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 nhexane 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).

International audience; The adsorption of the xylene mixture onto MIL-101(Cr) has been studied experimentally and theoretically. The adsorption isotherms of the xylene isomers show a high affinity for each isomer with MIL- 101(Cr). This is in good agreement with the enthalpies of adsorption extrapolated at zero coverage, 75 kJ mol 1, 68 kJ mol 1 and 64 kJ mol 1 for o-, m- and p-xylene respectively. The order of these values is consistent with that obtained by the computer simulations. The saturation plateau obtained with p-xylene is higher than that obtained with the adsorption of o- or m-xylene onto MIL-101(Cr). This was discussed in terms of stacking in the cavities of MIL-101(Cr). The filling of the small cavities of MIL-101(Cr) was found more difficult in the case of m-xylene which was interpreted by a weaker interaction with the cavities walls. The chromatographic separation of the xylene mixture was consistent with these results. Different retention times could be found, agreeing the different enthalpies of adsorption for the different isomers. o-Xylene was successfully separated from the xylene mixture.