Investigation of inverse shape selectivity in alkane adsorption on SAPO-5 zeolite using the tracer chromatography technique

Denayer, Joeri; Ocakoglu, Ahmet; Martens, Johan A.; Baron, Gino V.

doi:10.1016/j.jcat.2004.05.018

Cited by 38 publications

(13 citation statements)

References 12 publications

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“…Adsorption enthalpies, Δ H 0 , and pre-exponential factors, K ′ 0 , were calculated from the temperature dependence of the Henry’s constants using the van’t Hoff equation. A more detailed description of the method is given elsewhere. , …”

Section: Methodsmentioning

confidence: 99%

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Adsorption and Separation of Small Hydrocarbons on the Flexible, Vanadium-Containing MOF, COMOC-2

et al. 2015

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COMOC-2, a flexible vanadium-containing metal-organic framework, was investigated for its adsorption and separation properties of light hydrocarbons. COMOC-2 is an extended version of the MIL-47 framework with 4,4'-biphenyldicarboxylic acid linkers instead of terephthalic acid. Adsorption isotherms of methane to propane, ethylene, and propylene were determined with a gravimetric uptake technique at temperatures between 281 and 303 K. A pronounced breathing effect was observed (in contrast to the more rigid MIL-47 framework) in which the adsorption capacity increases by more than a factor of 2 at a given breathing pressure. The breathing pressure decreases with increasing hydrocarbon molecular weight. The typical two-step isotherms are nearly identical for alkanes and alkenes, in accordance with the nonpolar nature of the material. Binary isotherms of ethane and propane were also measured with the gravimetric uptake technique at different temperatures and total pressures. The mixture isotherms and breathing transition pressures were predicted by relying on the osmotic framework adsorbed solution theory (OFAST). Finally, the separation potential of COMOC-2 for ethane/propane mixtures was looked into using breakthrough experiments for different compositions and different pressures.

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Section: Methodsmentioning

confidence: 99%

“…A more detailed description of the method is given elsewhere. 38,39 Modeling and Prediction of Isotherms. Isotherm fitting for all pure adsorbates showing a two-step adsorption isotherms was performed by fitting a Langmuir equation on the first experimental adsorption step, representing a first structural form of COMOC-2.…”

Section: ■ Introductionmentioning

confidence: 99%

Adsorption and Separation of Small Hydrocarbons on the Flexible, Vanadium-Containing MOF, COMOC-2

et al. 2015

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“…At lower carbon numbers, the monobranched alkanes are preferentially adsorbed over the linear alkanes, with separation factors to 2.9 (Table S2). The preferential adsorption of The Journal of Physical Chemistry C branched n-alkanes, called "inverse shape selectivity", is quite unusual and has been observed in only a few cases (e.g., SAPO-34, 33 SAPO-5, 34 MCM-22, 25e and ZIF-96 35 ). Most porous materials tend to preferentially adsorbed linear chains compared to branched ones.…”

Section: Resultsmentioning

confidence: 99%

Understanding Hydrocarbon Adsorption in the UiO-66 Metal–Organic Framework: Separation of (Un)saturated Linear, Branched, Cyclic Adsorbates, Including Stereoisomers

et al. 2013

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The low coverage adsorption properties of alkanes, alkenes, and aromatics of the linear, branched, and cyclic type (ca. 70 molecules) were studied using inverse pulse gas chromatography at zero coverage on the zirconium metal− organic framework UiO-66 and its functionalized analogues UiO-66-Me, UiO-66-NO 2 , UiO-66-Me 2 in the temperature range 433−573 K. In our study, we determined and analyzed the adsorption enthalpy, Henry constants, and entropic factors. Preferential adsorption of bulky molecules is observed with specific adsorbate and cage size effects, yielding very specific, preferential adsorption. Remarkably high adsorption selectivity factors (up to 14) for cyclo-compared to nalkanes were found. The presence of additional groups (methyl, nitro) on the linkers in the framework influences adsorption properties significantly, mainly by reducing the effective pore size. Whereas increased selectivity is observed for UiO-66-Me, this effect decreases again upon addition of a second methyl group, UiO-66-Me 2 . The latter allows for tuning confinement factors inside the pores, thus adsorption properties of the metal−organic framework. The selective adsorption results from the interaction in the smallest octahedral cage. The extreme confinement in the tetrahedral cage allows for stereoselective separation of disubstituted cycloalkanes and cis/trans alkenes. Monte Carlo simulations were performed for the unfunctionalized UiO-66 framework. First, a comparative study between the force fields Dreiding and UFF is performed with n-alkanes to obtain accurate and reproducible values. The simulations show adsorbate molecular size−adsorbent cage size effects similar to window/cage effects reported for zeolites (e.g., silicalite). Second, adsorption properties were simulated for selected cases, including stereoisomers. Careful analysis of the adsorbate's molecular positioning in the framework confirms the experimental data. The framework's selectivity results from adsorption in the tetrahedral cage at zero coverage. Furthermore, simulations show important contributions of entropic factors to the observed adsorption selectivity.

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“…[2][3][4] However, some specific zeolites (e.g., MCM-22, CFI and MFI) also show the so-called inverse alkane adsorption hierarchy, where branched hydrocarbons are preferentially adsorbed versus their linear analogues. 1,[5][6][7] In this context, the development of novel porous materials capable of retaining isomerized The Journal of Physical Chemistry compounds would allow to improve the process significantly, improving efficiency and reducing the final cost.…”

Section: Introductionmentioning

confidence: 99%

“…In a typical isomerization reactor, the product stream contains a mixture of linear, mono- and dibranched isomers that must be separated and for what preferential adsorption of the higher octane number isomer is desired, so that the nonisomerized products can be recycled back to the isomerization unit . Traditionally, isomers separation in conventional adsorbents such as activated carbons, zeolites, and clays with narrow porous networks follow the natural order of size and shape selectivity, i.e., the linear hydrocarbons are preferentially adsorbed due to their smaller kinetic diameter, whereas bulkier ones are partially or totally excluded. − However, some specific zeolites (e.g., MCM-22, CFI, and MFI) show the so-called inverse alkane adsorption hierarchy, where branched hydrocarbons are preferentially adsorbed versus their linear analogues. ,− In this context, the development of novel porous materials capable of retaining isomerized compounds would allow to improve the process significantly, improving efficiency, and reducing the final cost.…”

Section: Introductionmentioning

confidence: 99%

Reverse Hierarchy of Alkane Adsorption in Metal–Organic Frameworks (MOFs) Revealed by Immersion Calorimetry

et al. 2019

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Immersion calorimetry into liquids of different dimensions is a powerful tool to learn about the pore size and shape in nanoporous solids. In general, in the absence of specific interactions with the solid surface, the accessibility of the liquid probe molecule to the inner porosity, and the associated enthalpy value decreases with an increase in its kinetic diameter (bulkier molecules have lower accessibility and packing density). Although this is true for majority of solids (e.g. activated carbons and zeolites), this study anticipates that this is not straightforward in the specific case of MOFs. The evaluation of different hydrocarbons and their derivatives reveals the presence of reverse selectivity for C 6 isomers (2,2-dimethylbutane>2-methylpentane>n-hexane) in UiO-66 and HKUST-1, while size exclusion effects take place in ZIF-8. The immersion calorimetric findings have been compared with vapor adsorption isotherms and computational studies. Monte Carlo simulations suggest that the reverse selectivity in UiO-66 are attributed to the strong confinement of the di-branched hydrocarbons in the small tetragonal cages, while the presence of strong interactions with the open metal sites account for the preferential adsorption in HKUST-1. These results open the gate towards the application of immersion calorimetry for the pre-

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Investigation of inverse shape selectivity in alkane adsorption on SAPO-5 zeolite using the tracer chromatography technique

Cited by 38 publications

References 12 publications

Adsorption and Separation of Small Hydrocarbons on the Flexible, Vanadium-Containing MOF, COMOC-2

Adsorption and Separation of Small Hydrocarbons on the Flexible, Vanadium-Containing MOF, COMOC-2

Understanding Hydrocarbon Adsorption in the UiO-66 Metal–Organic Framework: Separation of (Un)saturated Linear, Branched, Cyclic Adsorbates, Including Stereoisomers

Reverse Hierarchy of Alkane Adsorption in Metal–Organic Frameworks (MOFs) Revealed by Immersion Calorimetry

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