Adsorption Properties of Microporous Aluminophosphate AIPO4-5

Stach, H.; Thamm, H.; Fiedler, Klaus; Grauert, B.; Wieker, W.; Jahn, E.; Öhlmann, G.

doi:10.1016/s0167-2991(09)60917-4

Cited by 19 publications

(9 citation statements)

References 6 publications

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“…15 Experimentally, the determination of adsorption isotherms of long-chain alkanes can be time-consuming. For example, Stach et al 18 report that measurement of each isotherm for decane in silicalite requires at least two weeks of equilibration. It is therefore an important question whether molecular simulations provide an attractive alternative for estimating the adsorption of long-chain hydrocarbons in the pores of a zeolite.…”

Section: Introductionmentioning

confidence: 99%

Molecular Simulations of Adsorption Isotherms for Linear and Branched Alkanes and Their Mixtures in Silicalite

1999

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The configurational-bias Monte Carlo (CBMC) technique has been used for computing the adsorption isotherms for linear and branched 2-methylalkanes on silicalite. The carbon numbers of the alkanes ranged from four to nine. For branched alkanes inflection behavior was observed for all carbon numbers studied. The inflection was found to occur at a loading of four molecules per unit cell. Below this loading the branched alkanes are seen to be located predominantly at the intersections of the straight and zigzag channels. To obtain loadings higher than four, the branched alkane must seek residence in the channel interiors which is energetically more demanding and therefore requires disproportionately higher pressures; this leads to the inflection behavior. Linear alkanes with six and more carbon atoms also were found to exhibit inflection behavior. Hexane and heptane show inflection due to commensurate "freezing"; the length of these molecules is commensurate with the length of the zigzag channels. This leads to a higher packing efficiency than for other linear alkanes. Available experimental data from the literature are used to confirm the accuracy of the predictions of the CBMC simulations. Furthermore, the temperature dependency of the isotherms are also properly modeled. For purposes of fitting the isotherms we found that the dual-site Langmuir model provides an excellent description of the simulated isotherms for linear and branched alkanes. In this model we distinguish between two sites with differing ease of adsorption: site A, representing the intersections between the straight and zigzag channels, and site B, representing the channel interiors. CBMC simulations of isotherms of 50-50 binary mixtures of C 5 , C 6 , and C 7 hydrocarbon isomers show some remarkable and hitherto unreported features. The loading of the branched isomer in all three binary mixtures reaches a maximum when the total mixture loading corresponds to four molecules per unit cell. Higher loadings are obtained by "squeezing out" of the branched alkane from the silicalite and replacing these with the linear alkane. This "squeezing out" effect is found to be entropic in nature; the linear alkanes have a higher packing efficiency and higher loadings are more easily achieved by replacing the branched alkanes with the linear alkanes. The mixture isotherms can be predicted quite accurately by applying the appropriate mixture rules to the dual-site Langmuir model. This model allows the mixture isotherm to be predicted purely on the basis of the parameters describing the isotherms of the pure components. The sorption selectivity exhibited by silicalite for the linear alkane in preference to the branched alkane in mixtures of C 5 , C 6 , and C 7 hydrocarbon isomers, provides a potential for the development of a novel separation technique based on entropy-driven sorption selectivity.

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Section: Introductionmentioning

confidence: 99%

Molecular Simulations of Adsorption Isotherms for Linear and Branched Alkanes and Their Mixtures in Silicalite

1999

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“…Experimentally, the determination of adsorption isotherms can be quite time consuming, because of the slow diffusion of hydrocarbons in the pores of a zeolite. 5 When mixtures of hydrocarbons are considered, experiments become increasingly complicated. Measurements at the conditions of interest often require a complicated experimental setup (due to high temperature and pressure), and often unwanted side-effects like chemical reactions intrude.…”

Section: Introductionmentioning

confidence: 99%

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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“…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. 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).…”

Section: Introductionmentioning

confidence: 99%

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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Adsorption Properties of Microporous Aluminophosphate AIPO4-5

Cited by 19 publications

References 6 publications

Molecular Simulations of Adsorption Isotherms for Linear and Branched Alkanes and Their Mixtures in Silicalite

Molecular Simulations of Adsorption Isotherms for Linear and Branched Alkanes and Their Mixtures in Silicalite

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

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

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