The present study attempts to understand the use of the flexible porous chromium terephthalate Cr(OH)(O(2)C-C(6)H(4)-CO(2)) denoted MIL-53(Cr) (MIL = Material from Institut Lavoisier) for the separation of mixtures of CO(2) and CH(4) at ambient temperature. The coadsorption of CO(2) and CH(4) was studied by a variety of different techniques. In situ synchrotron X-ray Powder Diffraction allowed study of the breathing of the solid upon adsorption of the gas mixtures and simultaneously measured Raman spectra yielded an estimation of the adsorbed quantities of CO(2) and CH(4), as well as a quantification of the fraction of the narrow pore (NP) and the large pore (LP) form of MIL-53. Quantitative coadsorption data were then measured by gravimetry and by breakthrough curves. In addition, computer simulation was performed to calculate the composition of the adsorbed phase in comparison with experimental equilibrium isotherms and breakthrough results. The body of results shows that the coadsorption of CO(2) and CH(4) leads to a similar breathing of MIL-53(Cr) as with pure CO(2). The breathing is mainly controlled by the partial pressure of CO(2), but increasing the CH(4) content progressively decreases the transformation of LP to NP. CH(4) seems to be excluded from the NP form, which is filled exclusively by CO(2) molecules. The consequences in terms of CO(2)/CH(4) selectivity and the possible use of MIL-53(Cr) in a PSA process are discussed.

Molecular simulations have shown that the metal-organic framework Cu-BTC (Cu 3 (BTC) 2) is an interesting candidate for the separation of CO 2 by adsorption. In this work, the first experimental binary and ternary adsorption data of CO 2 , CH 4 , and CO on the Cu-BTC are reported. These data are analyzed and compared with coadsorption models that are built from pure component isotherm data. Cu-BTC has a CO 2 /CH 4 selectivity of ∼8 and a high delta loading ()difference between adsorption capacity under conditions of adsorption and desorption) and therefore appears to be a good compromise between zeolites, with high selectivity for CO 2 , but low delta loadings, and activated carbons, with high delta loadings, but low selectivity, for pressure swing adsorption applications.