Entropy effects during sorption of alkanes in zeolites

Krishna, Rajamani; Smit, Berend; Calero, Sofı́a

doi:10.1039/b101267n

Cited by 204 publications

(223 citation statements)

References 34 publications

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“…4,10,12,45 From the simulated isotherms at 300 K up to high pressure (Fig. 8), it was clear that cyclohexane can only adsorb at the intersections.…”

Section: Resultsmentioning

confidence: 98%

Molecular simulations of the adsorption of cycloalkanes in MFI-type silica

Schenk

Smit

Maesen

et al. 2005

Phys. Chem. Chem. Phys.

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A new force field for the simulation of the adsorption of cycloalkanes in nanoporous silica affords a significant improvement over any previously employed force field. The simulated isotherms reproduce the most salient features in the experimental isotherms extremely well. The study of cyclo-pentane, -hexane, and -heptane adsorption in MFI-type silica indicates an inflection for cyclopentane but not for cyclohexane at intermediate pressure. If corroborated by experiments, such an inflection point would afford an excellent calibration point for further force field developments. At low pressures, mixture isotherms of cyclohexane and n-hexane show a temperature dependence on the selectivity in accordance with recent results by J. P. Fox and S. P. Bates, J. Phys. Chem., 2004, 108, 17136. This dependence is caused by a difference in temperature dependence of the Henry coefficient for both molecules. At high pressures entropy effects due to packing always favor the sorption of n-hexane. Furthermore, the influence of the flexibility of the zeolite framework on the adsorption of these rather bulky molecules is investigated. It is found that this influence of the flexibility on the adsorption of cyclohexane is as small as with n-alkanes.

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“…4,10,12,45 From the simulated isotherms at 300 K up to high pressure (Fig. 8), it was clear that cyclohexane can only adsorb at the intersections.…”

Section: Resultsmentioning

confidence: 98%

Molecular simulations of the adsorption of cycloalkanes in MFI-type silica

Schenk

Smit

Maesen

et al. 2005

Phys. Chem. Chem. Phys.

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“…For this type of material, eq 7 cannot be used, and we have to use eq 8 instead where f is the adsorbate fugacity and 1/γ gives the fraction of empty sites as a function of loading for an n-site Langmuir isotherm. 37,[41][42][43] For a single Langmuir isotherm, eq 8 reduces to eq 7. The isotherms and 1/γ as a function of loading for a single-site and dual-site system are shown in Figure 1.…”

Section: Diffusion Theorymentioning

confidence: 99%

Loading Dependence of the Diffusion Coefficient of Methane in Nanoporous Materials

2006

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In this work, we use molecular simulations to study the loading dependence of the self-and collective diffusion coefficients of methane in various zeolite structures. To arrive at a microscopic interpretation of the loading dependence, we interpret the diffusion behavior in terms of hopping rates over a free-energy barrier. These free-energy barriers are computed directly from a molecular simulation. We show that these free-energy profiles are a convenient starting point to explain a particular loading dependence of the diffusion coefficient. On the basis of these observations, we present a classification of zeolite structures for the diffusion of methane as a function of loading: three-dimensional cagelike structures, one-dimensional channels, and intersecting channels. Structures in each of these classes have their loading dependence of the free-energy profiles in common. An important conclusion of this work is that diffusion in nanoporous materials can never be described by one single effect so that we need to distinguish different loading regimes to describe the diffusion over the entire loading range.

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“…Another advantage of performing simulations is the inherent capability of the programs in providing snapshots of adsorbed molecules. Such detailed information on a molecular level has proven to be of considerable importance to our understanding of the driving forces behind the sometimes peculiar shape selective adsorption behavior of hydrocarbon isomers in zeolites [8,9,[11][12][13].…”

Section: Introductionmentioning

confidence: 99%

“…Experimentally, the determination of adsorption isotherms can be quite time consuming because of the slow diffusion of long-chain hydrocarbons in the pores of a zeolite [10]. Molecular simulation can provide a cost-effective way of determining adsorption isotherms [8,9,[11][12][13][14][15][16][17][18][19], especially under conditions not readily amenable to experiments (high pressures and temperatures). Another advantage of performing simulations is the inherent capability of the programs in providing snapshots of adsorbed molecules.…”

Section: Introductionmentioning

confidence: 99%

“…Important in our understanding of the processes involved in these applications is our knowledge of the adsorption behavior of hydrocarbons in zeolitic pores [1][2][3][4][5][6][7][8][9]. This adsorption behavior is usually quantified by means of the adsorption isotherm, which represents the amount of hydrocarbon adsorbed in a pressure range at a given temperature.…”

Section: Introductionmentioning

confidence: 99%

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Molecular simulations of adsorption isotherms of small alkanes in FER-, TON-, MTW- and DON-type zeolites

Ndjaka

Zwanenburg

Smit

et al. 2004

Microporous and Mesoporous Materials

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Computer simulations are a useful tool in the study of the adsorption of alkanes in zeolites, provided the zeolite-alkane interactions are described in an adequate manner. MFI-type zeolites are among the most frequently studied types of zeolite. Consequently, zeolite specific force fields are often parameterized using experimental data obtained on MFI-type zeolites. In this paper we examine whether these force fields can be used to simulate adsorption in other zeolite types. We find that experimentally obtained isotherms of small alkanes on high silica FER-, TON-, MTW-, and DON-type zeolites can be accurately modeled using a single force field.

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Entropy effects during sorption of alkanes in zeolites

Abstract: Recent developments in

Cited by 204 publications

References 34 publications

Molecular simulations of the adsorption of cycloalkanes in MFI-type silica

Molecular simulations of the adsorption of cycloalkanes in MFI-type silica

Loading Dependence of the Diffusion Coefficient of Methane in Nanoporous Materials

Molecular simulations of adsorption isotherms of small alkanes in FER-, TON-, MTW- and DON-type zeolites

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