Sorption kinetics of linear paraffins in zeolite BEA nanocrystals

Lima, Patrícia M.; Gonçalves, Caroline Vieira; Cavalcante, Célio L.; Cardoso, Dilson

doi:10.1016/j.micromeso.2008.04.022

Cited by 21 publications

(7 citation statements)

References 15 publications

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“…For the measurement of sorption kinetics there are several techniques, one is microscopic (PFG, NMR) and the other is macroscopic (uptake rate, chromatographic) [26][27][28]. Since its introduction by Eic and Ruthven [29] for the measurement of intracrystalline diffusivities in strongly adsorbed species the Zero-Length Column (ZLC) technique has been used extensively for the measurement of sorption rates in porous media due to its apparent simplicity [30][31][32][33]. However, special attention in the use of model parameters from which kinetic data are obtained is required since there are models with the same mathematical form in completely different regimes that when used without previous calculations can produce erroneous results [34].…”

Section: Introductionmentioning

confidence: 99%

Sorption and kinetics of CO2 and CH4 in binderless beads of 13X zeolite

Silva

Schumann

Rodrigues

2012

Microporous and Mesoporous Materials

116

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a b s t r a c tThe sorption equilibrium of CO 2 and CH 4 in binderless beads of 13X zeolite has been investigated between 313 and 373 K and pressure up to 4 atm. The amount adsorbed of CO 2 and CH 4 is around 5.2 mmol/g ads and 1.2 mmol/g ads , respectively, at 313 K and 4 atm. Comparing these values with the ones in literature the value of CO 2 is 20% higher than in CECA 13X binder pellets. It is also found that isotherms are pronounced Type I for CO 2 and almost linear for CH 4 . The CO 2 isotherms were modeled using a simple deviation from Langmuir isotherm that takes into account interaction between adsorbed molecules at adjacent sites (Fowler model) suggesting a moderate repulsion. Henry's constants range from 143 to 11.1 mmol/g ads .atm for CO 2 and 0.45 to 0.27 mmol/g ads .atm for CH 4 between 313 and 373 K, respectively. The heats of sorption at zero coverage are 43.1 kJ/mol for CO 2 and 9.2 kJ/mol for CH 4 .The sorption kinetics has been investigated by the Zero-Length Column technique (ZLC). Recipes to analyze ZLC desorption curves in pellets of adsorbents are reviewed and it is derived a criteria which indicates that for the sorption rate be measured macroscopically the time of the experiment (that should be above a few seconds) is directly calculated with the following expression: t 0:1 ! 7:02 Â 10 Dc. Based on such criteria it is shown that crystal diffusivity of CO 2 in 13X can be measured macroscopically by ZLC, being the same measurement for CH 4 practically impossible. The crystal diffusivity of CO 2 measured experimentally is 5.8 Â 10 À15 m 2 /s and 1.3 Â 10 À15 m 2 /s at 373 and 313 K, respectively. These values are comparable to the ones measured by a frequency response and pulse chromatography techniques reported in literature. The ZLC desorption curves for CH 4 were measured under an equilibrium regime.

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Section: Introductionmentioning

confidence: 99%

Sorption and kinetics of CO2 and CH4 in binderless beads of 13X zeolite

Silva

Schumann

Rodrigues

2012

Microporous and Mesoporous Materials

116

View full text Add to dashboard Cite

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“…The advantage of this method is the elimination of external mass-and heat-transfer resistances by the use of low adsorbate concentrations, very small adsorbent sample amounts as well as high carrier flow rates during desorption. It has been extensively used for diffusivity measurements in zeolites and other molecular sieves (Cavalcante et al 2000(Cavalcante et al , 2003Grande et al 2003, Qiao and Bhatia 2005, Huang et al 2008, Lima et al 2008 and to study diffusion in biporous materials (Brandani 1996), under non-linear conditions (Brandani et al 2000), tracer diffusion and liquid systems .…”

Section: Introductionmentioning

confidence: 99%

Diffusion of linear paraffins in silicalite studied by the ZLC method in the presence of CO2

et al. 2010

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The diffusion behavior of C 4 -C 10 n-alkanes in silicalite-1 has been investigated by using the Zero Length Column method. The diffusivities derived from measurements at different purge rates with different purge gases confirming intracrystalline diffusion control. Data are compared with results reported in the literature for MFI zeolites. The diffusivities were found to be consistent and agree well with data previous obtained by ZLC. However, these data showed a remarkable disagreement with other reported techniques (PFG-NMR, QENS and Permeation). The eventual influence of carbon dioxide (CO 2 ) adsorption on diffusion properties of n-alkanes in silicalite was also investigated. For this purpose, a series of experiments was performed involving hydrocarbons mixed with CO 2 . Data were obtained at 303 K and flow rates between 20 and 80 mL/min. The presence of CO 2 does not seem to influence the intracrystalline transport rate of the investigated light hydrocarbons (n-C 4 and n-C 6 ). On the other hand, the situation for n-C 8 and n-C 10 is more complex. The diffusivity values are higher compared to the previously reported values.

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“…Hence, micropore dimensions were used to calculate the Weisz‐Prater criterion and these values are reported. For the zeotypes, the effective diffusivities were very conservatively estimated by scaling measured diffusivities rather than by calculating diffusivities from molecular properties and pore dimensions. To evaluate diffusion limitations, the largest species in the reaction network was assessed, and reported dimensions of benzosuberone were used in lieu of the (unknown) dimensions of the addition products.…”

Section: Resultsmentioning

confidence: 99%

Intraparticle Diffusional versus Site Effects on Reaction Pathways in Liquid‐Phase Cross Aldol Reactions

et al. 2018

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Chemo- and regioselectivity in a heterogeneously catalyzed cross aldol reaction were directed by tuning the nature of the sites, textural properties, and reaction conditions. Catalysts included sulfonic acid-functionalized resins or SBA-15 with varying particle size or pore diameter, H-BEA zeolites, and Sn-BEA zeotype; conditions were 25 °C to 170 °C in organic media. Benzaldehyde and 2-butanone yielded branched (reaction at -CH - of butanone) and linear (reaction at -CH ) addition and condensation products; and fission of the branched aldol led to β-methyl styrene and acetic acid. Strong acids promoted the dehydration step, and regioselectivity originated from preferred formation of the branched aldol. Both, resins and functionalized SBA-15 materials yielded predominantly the branched condensation product, unless particle morphology or temperature moved the reaction into the diffusion-limited regime, in which case more fission products were formed, corresponding to Wheeler Type II selectivity. For H-form zeolites, fission of the branched aldol competed with dehydration of the linear aldol, possibly because weaker acidity or steric restrictions prevented dehydration of the branched aldol.

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Sorption kinetics of linear paraffins in zeolite BEA nanocrystals

Cited by 21 publications

References 15 publications

Sorption and kinetics of CO2 and CH4 in binderless beads of 13X zeolite

Sorption and kinetics of CO2 and CH4 in binderless beads of 13X zeolite

Diffusion of linear paraffins in silicalite studied by the ZLC method in the presence of CO2

Intraparticle Diffusional versus Site Effects on Reaction Pathways in Liquid‐Phase Cross Aldol Reactions

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