ZLC Measurements under non-linear conditions

Brandani, Stefano; Jama, Mohamed; Ruthven, Douglas M.

doi:10.1016/s0009-2509(99)00411-x

Cited by 54 publications

(46 citation statements)

References 5 publications

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“…The NZLC experimental results obtained under non-linear conditions diverged at the different flow rates, if the desorption curves were plotted in the form of ln(c/c 0 ) vs. F ·t (purge volume). This confirmed that the NZLC measurements were carried out under conditions of kinetic control (Brandani et al 2000c). In the counter-current binary ZLC measurements (designated as CCZLC), the sample was initially saturated with n-heptane or toluene diluted in a helium flow, and then desorbed with helium containing toluene or n-heptane at the same flow rate.…”

Section: Zlc Measurementssupporting

confidence: 77%

Single component and binary diffusion of n-heptane and toluene in SBA-15 materials

2010

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In this work, the diffusion properties of single component n-heptane and toluene as well as their binary mixtures in two SBA-15 samples with different structural characteristics were studied by the standard Zero Length Column (ZLC) technique under three different concentration levels. A theoretical ZLC desorption model considering the Generalized Maxwell-Stefan (GMS) formulation was developed. Using the independently measured single component equilibrium and kinetic parameters, the model was able to reasonably predict experimental binary ZLC desorption curve for countercurrent diffusion of toluene in the presence of n-heptane. However, there was a significant deviation between model prediction results and experimental data for countercurrent desorption of n-heptane in the presence of toluene. The diffusion of n-heptane is reduced by the presence of toluene, regardless of the relative content of micropores in the intrawall pores, while that of toluene is virtually unaffected by the counter-diffusion of n-heptane. The observed phenomena cannot be addressed by the simple model considering the cross term diffusion effect. The structural property of material and the molecular characteristics of probe molecules were used to account for the difference in the behavior between n-heptane and toluene.

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Section: Zlc Measurementssupporting

confidence: 77%

Single component and binary diffusion of n-heptane and toluene in SBA-15 materials

2010

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“…The experimental desorption plots were fitted using Equations (5)- (7) to obtain the fitting parameters, L, β and Deff/R Table 5. It is seen that the fitted L values, which were used as a criterion for the ZLC model to guarantee that the desorption process is controlled by the kinetics [34,35], are all greater than 5. , which is in reasonably good agreement with the reported results [36,37]. for three xylene isomers increase with the mesoporosities of the Beta zeolites at the measured temperature.…”

Section: Diffusion Resultsmentioning

confidence: 99%

Adsorption and Diffusion of Xylene Isomers on Mesoporous Beta Zeolite

Song

et al. 2015

Catalysts

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Abstract:A systematic and detailed analysis of adsorption and diffusion properties of xylene isomers over Beta zeolites with different mesoporosity was conducted. Adsorption isotherms of xylene isomers over microporous and mesoporous Beta zeolites through gravimetric methods were applied to investigate the impact of mesopores inside Beta zeolites on the adsorption properties of xylene isomers in the pressure range of lower 20 mbar. It is seen that the adsorption isotherms of three xylene isomers over microporous and mesoporous Beta zeolites could be successfully described by the single-site Toth model and the dual-site Toth model, respectively. The enhanced adsorption capacities and decreased Henry's constants (KH) and the initial heats of adsorption (Qst) for the all xylene isomers are observed after the introduction of mesopores in the zeolites. For three xylene isomers, the order of Henry's constant is o-xylene > m-xylene > p-xylene, whereas the adsorption capacities of Beta zeolite samples for xylene isomers execute the following order of o-xylene > p-xylene > m-xylene, due to the comprehensive effects from the molecular configuration and electrostatic interaction. At the same time, the diffusion properties of xylene isomers in the mesoporous Beta zeolites were also studied through the desorption curves measured by the zero length column (ZLC) method at 333-373 K. It turned out that the effective diffusion time constant (Deff/R 2 ) is a growing trend with the increasing mesoporosity, whereas the tendency of the activation energy is just the reverse, indicating the contribution of mesopores to facilitate molecule diffusion by shortening diffusion paths and reducing diffusion resistances. Moreover, the diffusivities of three xylene isomers in all Beta zeolites follow an order of p-xylene > m-xylene > o-xylene OPEN ACCESSCatalysts 2015, 5 2099 as opposed to KH, conforming the significant effects of adsorbate-adsorbent interaction on the diffusion.

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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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ZLC Measurements under non-linear conditions

Cited by 54 publications

References 5 publications

Single component and binary diffusion of n-heptane and toluene in SBA-15 materials

Single component and binary diffusion of n-heptane and toluene in SBA-15 materials

Adsorption and Diffusion of Xylene Isomers on Mesoporous Beta Zeolite

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

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