Co-adsorption and Separation of CO₂−CH₄ Mixtures in the Highly Flexible MIL-53(Cr) MOF

Abstract

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.

Color and Brightness Tuning in Heteronuclear Lanthanide Terephthalate Coordination Polymers

“…For more than a decade, lanthanide-based coordination polymers have attracted great attention, because of their fascinating topologies coupled with their potential applications in gas storage, [1][2][3][4][5][6][7][8] catalysis, [9] separation, [10] luminescence, [11][12][13][14][15][16] and molecular magnetism. [17][18][19] Because lanthanide ions are hard Pearson acids, [20,21] ligands that exhibit donor oxygen atoms have been extensively studied.…”

Enhanced selectivity of CO2 over CH4 in sulphonate-, carboxylate- and iodo-functionalized UiO-66 frameworks

“…Owing to their many fascinating features, MOFs have shown promising performances over conventional adsorbents in separation of gas mixtures. 7,[22][23][24][25][26] Both experiments 27 and computational methods 28,29 have demonstrated that the introduction of polar functional groups in the frameworks significantly enhances the CO 2 adsorption capacity of MOFs. Moreover, MOFs with coordinatively unsaturated metal sites have been shown to adsorb increased amounts of CO 2 .…”

Self-catalysed aerobic oxidization of organic linker in porous crystal for on-demand regulation of sorption behaviours

“…Some flexible PCPs showing gate-opening phenomena and stepped isotherms may be used to solve this problem; however, the real selectivities are usually much lower than those predicted by the singlecomponent isotherms because the non-preferred guest can also enter the opened channel above the gate-opening pressure 50 . We observed that the real C 2 H 6 /CH 4 selectivity (measured by mixed C 2 H 6 /CH 4 with 75:25 molar ratio) of O53 significantly increases from 92 to 140 at C 2 H 6 partial pressure from 4.7 to 5.5 bar, respectively, and remains 113 at C 2 H 6 partial pressure of 8.1 bar (Supplementary Methods and Supplementary Fig.…”