Tom Remy

An Amine-Functionalized MIL-53 Metal−Organic Framework with Large Separation Power for CO2 and CH4

Functionalizing the well-known MIL-53(Al) metal-organic framework with amino groups increases its selectivity in CO(2)/CH(4) separations by orders of magnitude while maintaining a very high capacity for CO(2) capture.

Biobutanol Separation with the Metal–Organic Framework ZIF‐8

Bioalcohols, such as bioethanol and biobutanol, are a promising alternative to petroleum-based chemicals. As a fuel, biobutanol has superior properties compared to bioethanol, including a higher energy density and a lower volatility. A major challenge in the economical production of biobutanol as chemical or fuel is its separation from the aqueous medium in which it is produced by the fermentation of biomass. Given the low concentration of the alcohols in the fermentation broth, separation of the butanol fraction via distillation would be energyand cost-intensive. Among alternative separation methods to recover butanol from fermentation broth, adsorption has been identified as the most energy-efficient technique. This requires adsorbents that, besides a high adsorption capacity and stability, have a high affinity towards alcohols (typically, the final butanol concentration is at most 20 g L ) and a low affinity for water. Typical adsorbents (i.e. , most zeolites, silica, and alumina) have a high preference to water and so are not suitable for this particular application. Oudshoorn et al. reported that among the commercially available hydrophobic zeolites, silicalitetype zeolites are the most selective for alcohols, but their adsorption capacity remains low. Although active carbon selectively adsorbs alcohols from water, the recovery of adsorbed alcohols is problematic. Metal–organic frameworks (MOFs) offer new opportunities in adsorption technology, with unprecedented capacities and chemical and structural tunability. Herein, it is demonstrated that the MOF ZIF-8, a member of the zeolitic imidazolate framework (ZIF) family, has promising features for the production of pure biobutanol from its fermentation medium. ZIFs contain tetrahedral Zn atoms linked by imidazolate ligands. A large variety of zeolite-like structures can be obtained by modification of the ligands. ZIFs offer high hydrothermal, chemical, and thermal stabilities. ZIF-8, discovered by Huang et al. , crystallizes into the zeolite sodalite topology, generating a resistant structure with cages of 12.5 connected via hexagonal windows of 3.3 . (Figure S2). Adsorption isotherms on ZIF-8 have been reported for Ar, CO2, CH4, N2, C2H6, C2H4, and H2, and also for longer alkanes, alkenes, and organic compounds. b, 7] Molecular simulations have been used to identify the adsorption sites of H2, N2, and CH4. [8] Selective ZIF-8-membranes have been designed, and their permeability for light gasses has been investigated. 9] ZIF-8 shows an only very low [a] J. Cousin Saint Remi, T. R my, V. Van Hunskerken, S. van de Perre, T. Duerinck, Prof. Dr. G. V. Baron, Prof. Dr. J. F. M. Denayer Department of Chemical Engineering Vrije Universiteit Brussel Pleinlaan 2, 1050 Brussel (Belgium) Fax: (+ 32) 2 629 17 98 E-mail : joeri.denayer@vub.ac.be [b] Dr. M. Maes, Prof. Dr. D. De Vos, Dr. E. Gobechiya, Prof. Dr. C. E. A. Kirschhock Centre for Surface Chemistry and Catalysis Katholieke Universiteit Leuven Kasteelpark Arenberg 23, 3001 Heverlee (Belgium) Supporting Information for this article is available on the WWW under http://dx.doi.org/10.1002/cssc.201100261. Figure 1. Vapor-phase adsorption on ZIF-8. Full symbols: adsorption; open symbols: desorption. a) Adsorption isotherms at 50 8C. b) Adsorption capacity at 50 8C. c) Butanol isotherms at varying temperature. d) Isosteric heat of adsorption as a function of pore filling.

Partially fluorinated MIL-47 and Al-MIL-53 frameworks: influence of functionalization on sorption and breathing properties

Two perfluorinated metal hydroxo terephthalates [M(III)(OH)(BDC-F)]·n(guests) (M(III) = V, MIL-47-F-AS or 1-AS; Al, Al-MIL-53-F-AS or 2-AS) (BDC-F = 2-fluoro-1,4-benzenedicarboxylate; AS = as-synthesized) have been synthesized by a hydrothermal method using microwave irradiation (1-AS) or conventional electric heating (2-AS), respectively. The unreacted or occluded H(2)BDC-F molecules can be removed under vacuum by direct thermal activation or exchange of guest molecules followed by thermal treatment leading to the empty-pore forms of the title compounds [V(IV)(O)(BDC-F)] (MIL-47-F, 1) and [Al(III)(OH)(BDC-F)] (Al-MIL-53-F, 2). Thermogravimetric analysis (TGA) and temperature-dependent XRPD (TDXRPD) experiments indicate that the compounds are stable up to 385 and 480 °C, respectively. Both of the thermally activated compounds exhibit significant microporosity, as verified by N(2), CO(2), n-hexane, o- and p-xylene sorption analyses. The structural changes of 2 upon adsorption of CO(2), n-hexane, o- and p-xylene were highly influenced due to functionalization by -F groups, as compared to parent Al-MIL-53. The -F groups also introduce a certain degree of hydrophobicity into the frameworks, as demonstrated by the H(2)O sorption analyses.

Modeling the effect of structural changes during dynamic separation processes on MOFs.

A model able to describe the effect of structural changes in the adsorbent or adsorbed phase during the dynamic (breakthrough) separation of mixtures on metal-organic frameworks (MOFs) is presented. The methodology is exemplified for a few pertinent case studies: the separation of xylene isomers and ethylbenzene on the flexible MOF MIL-53 and the rigid MOF MIL-47. At low pressures, no preferential adsorption of any component occurs on both MOFs. Contrarily, at higher pressures separation of ethylbenzene (EB) from o-xylene (oX) occurs on MIL-53 as a result of the breathing phenomenon within the MIL-53 structure. The increase in selectivity, starting from the gate-opening pressure, could be modeled by using a pressure-dependent saturation capacity for the most strongly adsorbed component oX. In the separation of m-xylene (mX) from p-xylene (pX) on the rigid MOF MIL-47, separation at higher pressures is a result of preferential stacking of pX. Here, the selectivity increases once the adsorption of pX switches from a single to a double file adsorption. By implementing a loading dependent adsorption constant for pX, the different unconventional breakthrough profiles and the observed selectivity profile on MIL-47 can be simulated. A similar methodology was used for the separation of EB from pX on MIL-47, where the separation is a result from steric constraints imposed onto the adsorption of EB.

Adsorption and separation of CO2 on KFI zeolites: effect of cation type and Si/Al ratio on equilibrium and kinetic properties.

Selective separation of CO2 is becoming one of the key technologies in the (petro-) chemical industry. This study focuses on the adsorption and separation of CO2 from CH4 on a new low-silica (LS) type of the eight-membered ring KFI zeolite. A series of alkali (Li, Na, K) and alkaline-earth (Mg, Ca, Sr) exchanged samples of the new LS KFI were synthesized and characterized. LS Li-KFI showed the largest pore volume, whereas LS Na-KFI and LS K-KFI were inaccessible for Argon at 87 K. Adsorption of CO2 at 303 K demonstrated the dominant quadrupolar interaction on alkali-exchanged LS KFI samples. LS Li-KFI showed the largest capacities upon high pressure isotherm measurements of CO2 (4.8 mmol/g), CH4 (2.6 mmol/g), and N2 (2.2 mmol/g) up to 40 bar at 303 K. The performance of the new LS KFI was compared to a KFI sample (ZK-5) with a higher Si/Al ratio. Isotherm measurements and dynamic breakthrough experiments demonstrated that ZK-5 samples show larger working capacities for CO2/CH4 separations at low pressure. Li-ZK-5 and Na-ZK-5 show the highest capacities and high selectivities (similar to benchmark 13X).

Biogas upgrading through kinetic separation of carbon dioxide and methane over Rb- and Cs-ZK-5 zeolites

Eight-membered ring (8 MR) zeolites hold large potential for industrial CO2 separations such as biogas separation. They offer large selectivity due to the constrained environment for adsorption, especially when large cations are present in the interconnecting windows. The Rb- and Cs-exchanged ZK-5 zeolites (8 MR KFI type zeolites) were studied for kinetic CO2/CH4 separation. First, Rb-ZK-5 and Cs-ZK-5 were thoroughly characterized via chemical analysis, argon porosimetry, X-ray diffraction and Rietveld refinements. Afterwards, the CO2/CH4 separation potential of both adsorbents was assessed via the measurement of kinetic and equilibrium data (T = 261.15 - 323 K), breakthrough measurements at 303 K (P = 1 - 8 bar), and simulations of their performance. The high occupation of the central 8 MR sites with large cations causes strong diffusional limitations for CH4 on Rb-ZK-5 and Cs-ZK-5. As a result, both zeolites effectively separate CH4 from CO2 with very high selectivities (α = 17 at 1 bar and 303 K). Despite their very large CO2 selectivities, the performance of Rb-ZK-5 and Cs-ZK-5 was still lower than for the benchmark 13X zeolite on a larger scale. Future research needs to further unravel the adsorption mechanism on low-silica 8 MR zeolites and their corresponding potential in separation processes such as biogas purification.