Adsorption of methane, ethane, ethylene, and carbon dioxide on silicalite-l

Choudhary, Vasant R.; Mayadevi, S.

doi:10.1016/s0144-2449(96)00067-x

Cited by 129 publications

(100 citation statements)

References 17 publications

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“…Detailed inspection of the experimental data showed that for ethane, 2-methylpropane, and n-heptane several independent groups provided consistent data, and we used these data as our primary set of experimental data. As basis for calibration, we utilized the experimental data from several different research groups of Cavalcante et al, 29 Jolimaitre et al, 30,31 Eder et al, 32 Zhu et al, [33][34][35] Sun et al, 27,36 and Choudhary et al 37 Whereas inflection points in the isotherms of MFI-type zeolites can be used to calibrate most of the parameters, it does not afford calibration of the parameters for CH 4 . For this molecule, we resorted to AFI-type sieves.…”

Section: Introductionmentioning

confidence: 99%

United Atom Force Field for Alkanes in Nanoporous Materials

et al. 2004

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A novel united atom force field affords accurate and quantitative reproduction of the adsorption properties of linear and branched alkanes in nanoporous framework structures. The force field was generated by adjusting the parameters so as to faithfully reproduce the experimentally determined isotherms (particularly the inflection points) on MFI-type zeolite over a wide range of pressures and temperatures. It reproduces extremely well the Henry coefficients, heats of adsorption, preexponential factors, entropies of adsorption, and maximum loading. It is shown that the extension of the force field from MFI to other nanoporous framework topologies is successful, that it affords the prediction of topology-specific adsorption properties, and that it can be an effective tool to resolve the many discrepancies among experimental data sets.

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Section: Introductionmentioning

confidence: 99%

United Atom Force Field for Alkanes in Nanoporous Materials

et al. 2004

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“…Experimental data are taken from Sun et al [10,16], Choudhary et al [17], and Zhu et al [18,19]. Ethane …”

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confidence: 99%

Force Field Parametrization through Fitting on Inflection Points in Isotherms

et al. 2004

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We present a method to determine potential parameters in molecular simulations of confined systems through fitting on experimental isotherms with inflection points. The procedure uniquely determines the adsorbent-adsorbate interaction parameters and is very sensitive to the size parameter. The inflection points in the isotherms are often related to a subtle interplay between different adsorption sites. If a force field can predict this interplay, it also reproduces the remaining part of the isotherm correctly, i.e., the Henry coefficients and saturation loadings. DOI: 10.1103/PhysRevLett.93.088302 PACS numbers: 82.75.Jn, 47.55.Mh, 66.30.-h The effect of confinement on adsorption and diffusion is still poorly understood despite its importance for practical applications. The performance of molecular sieves in separation and catalytic processes depends critically on the match between sieve topology and the shape and size of the adsorbate [1]. It is therefore of considerable industrial importance to explore the adsorption and diffusion of linear and branched alkanes in different topologies using realistic simulations at the microscopic level [2]. Different parameter sets yield values of diffusivities that differ not only quantitatively but also show a different qualitative dependence on the molecular loading [3]. The critical unresolved question follows: Which of these parameter sets is the most physically realistic one? Here, we hope to remedy this situation.Potential parameter sets can be checked only via comparison with experiment. For diffusion the comparison is complicated by large discrepancies between microscopic and macroscopic experimental measurement methods, and even within the same measurement technique there are many disagreements between various studies. However, adsorption results seem to be well established and provide a more solid basis for a detailed comparison between experiment and simulation. Moreover, a large amount of data exists on adsorption of hydrocarbons in siliceous zeolites.Silicalite-1 (Fig. 1) consists of a three-dimensional pore system with straight parallel channels, intersected by zigzag channels [4]. The channels of approximately 6 Å in diameter lead to shape selectivity, especially for the isomers of hexane, which have dimensions close to the silicalite-1 pores. The linear channels intersect with the zigzag channels 4 times per unit cell. Interestingly, for n-heptane and for the branched alkanes in silicalite-1 a kink in the isotherm is observed [5]. This inflection is directly related to the number of intersections in the structure and occurs at exactly four molecules per unit cell. As these inflections are caused by a subtle interplay between the size and configuration of the molecule and two different adsorption sites, it becomes clear that the adsorbent-adsorbate potential size parameter is the most sensitive parameter in the force field.In general, adsorption in any periodic structure has steps or kinks. The reason is that steps and kinks signal transitions between diffe...

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“…The low-pressure environment facilitates disengagement of the molecule-molecule attraction and gravity that may exist. The mobility of the gas, however, depends on the level of the affinity for the solid medium (Choudhary and Mayadevi 1996). As the gas percolates through the meandering pore pathway, the gas experiences a pressure-driven isothermal expansion and the energy of expansion can be conveniently calculated.…”

Section: Temperature-driven Isobaric Condensation (Adsorption)mentioning

confidence: 99%

“…This might have resulted in the separability of methane from a carbon dioxide/methane gas mixture of as high as 8.17 as reported previously across a zeolite membrane (Othman et al 2009). However, the order of adsorption may be reversed when the material exhibits a greater affinity for carbon dioxide as a result of different cations present in the adsorbent preferentially adsorbing this gaseous species (Othman 2009;Othman and Kim 2008a,b;Choudhary and Mayadevi 1996). T a (K) Gibbs' free energy (kJ)…”

Section: Thermodynamic Functions Of Temperature/pressure-induced Sorpmentioning

confidence: 99%

“…There are many literature reports of thermodynamic adsorption functions centred on a bulk porous adsorbent that treat the diffusion of gas molecules inside the pore and desorption of the gas from the membrane pore in isolation (Marathe 2005;Hung and Bai 2008;Choudhary and Mayadevi 1996;Schindler and LeVan 2008;Xu et al 2008). The permeability and separability of gases across porous membranes were studied from the basis of adsorption and the affinity of the material (Othman et al 2009;Himeno et al 2007;Zhu et al 2006).…”

Section: Introductionmentioning

confidence: 99%

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Thermodynamic Functions of Temperature/Pressure-Induced Sorption across Microporous Membranes: Case Study of Methane and Carbon Dioxide

Othman

Martunus

Fernando

et al. 2010

Adsorption Science & Technology

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This paper introduces a facile technique for the calculation of the thermodynamic properties of a gas across a porous membrane. The calculation assumes that the gas undergoes temperature-driven isobaric condensation, pressure-driven isothermal expansion and temperature-driven isobaric evaporation. The gas is in a disordered and chaotic state in all the three processes as a result of the kinetic energy by the driving forces. A zero entropy value is achievable at a remote distance from the membrane after desorption takes place. The deviation of the entropy from zero for isobaric evaporation is indicative of the irreversibility of the process. In contrast, the convergence of the entropy towards zero for the other two systems is indicative of the near-reversibility of the process.

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Adsorption of methane, ethane, ethylene, and carbon dioxide on silicalite-l

Cited by 129 publications

References 17 publications

United Atom Force Field for Alkanes in Nanoporous Materials

United Atom Force Field for Alkanes in Nanoporous Materials

Force Field Parametrization through Fitting on Inflection Points in Isotherms

Thermodynamic Functions of Temperature/Pressure-Induced Sorption across Microporous Membranes: Case Study of Methane and Carbon Dioxide

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