Adsorption equilibria of hydrocarbons on highly dealuminated zeolites

Stach, H.; Lohse, U.; Thamm, H.; Schirmer, Wolfgang

doi:10.1016/s0144-2449(86)80001-x

Cited by 228 publications

(193 citation statements)

References 27 publications

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“…Stach et al 2 and Lohse et al 57 did not observe an inflection at room temperature. Eder and Lercher [58][59][60][61] observed an inflection at T ) 333 K. Yang and Rees 10 also observed that this inflection disappears when the temperature is increased above T ) 383 K. Sun et al 9 state that an inflection is observed in a narrow temperature window (310 < T < 360 K), below and above this temperature window normal type I isotherms are observed.…”

Section: Simulation Techniquementioning

confidence: 90%

“…In our calculations, we have used H ) 1.25 × 10 -3 mmol g -1 Pa -1 . For butane, isotherms have been measured by Thamm, 84 Stach et al, 2 Richard and Rees, 6 Abdul-Rehman, 22 and Shen and Rees. 85 These isotherms gave a Henry coefficient of approximately 1.5 × 10 -2 mmol -1 g -1 Pa -1 .…”

Section: Appendix C: Discussion Of the Experimental Datamentioning

confidence: 99%

“…Adsorption isotherms of pentane in silicalite have been measured by Rakhmatkariev et al 4 and Dubinin et al 5 Dubinin et al 5 report data at low pressures yielding a Henry coefficient of 0.187 mmol -1 g -1 Pa -1 . For hexane, adsorption isotherms have been measured by Stach et al 2 and Richard and Rees. 6 We have used the average of the two Henry coefficients, namely 3.05 mmol -1 g -1 Pa -1 .…”

Section: Appendix C: Discussion Of the Experimental Datamentioning

confidence: 99%

“…The linear and branched alkanes are described with a unitedatom model, i.e., CH 3 , CH 2 , and CH groups are considered as single interaction centers. 24 The bonded interactions include bond-bending and torsion potentials, the nonbonded interactions are described with a Lennard-Jones potential.…”

Section: Modelmentioning

confidence: 99%

“…For example, the isotherms of most linear hydrocarbons in the zeolite silicalite show simple Langmuir behavior. 2 The isotherms of heptane and hexane, however, show an inflection point. Evidence of this surprising inflection behavior can be gleaned by careful analysis of experimental data from various sources.…”

Section: Introductionmentioning

confidence: 99%

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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: Simulation Techniquementioning

confidence: 90%

Section: Appendix C: Discussion Of the Experimental Datamentioning

confidence: 99%

Section: Appendix C: Discussion Of the Experimental Datamentioning

confidence: 99%

Section: Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

1999

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M onte C arlo Simulations for Complex Fluids

Smit

1998

Encyclopedia of Computational Chemistry

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The Dehydrogenation Reaction of Light Alkanes Catalyzed by Zeolites

Furtado¹,

Milas²,

LINS³

et al. 2001

phys. stat. sol. (a)

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The several steps of the dehydrogenation reactions of ethane, propane and isobutane were studied by theoretical methods. Molecular dynamics simulation techniques have been used to study diffusion of the alkanes through the zeolite HZMS-5 framework. Adsorption energies were computed by the methods of molecular mechanics, molecular dynamics and Monte-Carlo. Molecular dynamics was also used to determine the preferred adsorption sites of the alkanes in silicalite and HZMS-5. The mechanism of the chemical reactions at the zeolite's acid site was investigated at the DFT(B3LYP) level of calculation using 6-31G ** and 6-311G ** basis sets, and 3 and 5 T cluster models to represent the zeolite. GIAO/B3LYP calculations were performed on the 3 and 5 T alkyalkoxides and the results were compared with experimental 13 C NMR data.

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Adsorption equilibria of hydrocarbons on highly dealuminated zeolites

Cited by 228 publications

References 27 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

M onte C arlo Simulations for Complex Fluids

The Dehydrogenation Reaction of Light Alkanes Catalyzed by Zeolites

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