Problems raised by the application of the usual methods of process identification to the determination of diffusion coefficient of gases in molecular sieves

Bétemps, M.; Scavarda, Serge; Jutard, A.; Mange, Michel

doi:10.1088/0022-3727/10/5/011

Cited by 7 publications

(3 citation statements)

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“…(2.9) imply that the response function might also be obtained by measuring the response of DP(t) to a step-function change in DV. In fact, this was suggested some time ago by Be ´temps et al 12 Within the framework of linear-response theory, DP(t) will be proportional to the convolution integral w(t) DV(t), and hence f DP DPðoÞ / w wðoÞ f DV DV ðoÞ. At long times the response DP(t) will tend to zero.…”

Section: Discussionmentioning

confidence: 94%

The frequency response of sorbate diffusion in one-dimensional channels

Camp

2002

Phys. Chem. Chem. Phys.

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The theoretical diffusion of ideal sorbate molecules along one-dimensional channels containing random sequences of high-energy and low-energy barriers has been studied. This situation might occur in the case of sorbate diffusion in one-dimensional zeolite channels containing two cationic species of different diameters attached to the aluminosilicate framework. Using a master equation with appropriate microscopic transfer rates characterising the transfer of sorbate molecules between neighbouring cells, the frequency response of the number of absorbed molecules to a periodic modulation of the sorbate concentration at the entrances to the channels has been calculated. For channels consisting of about 100 equal-height energy barriers the frequency response function agrees well with the continuum result obtained from the Fickian diffusion equation. Predictions for the frequency response functions when fast and slow microscopic transfer rates operate in each channel have been made. The presence of two distinct transfer rates gives rise to well-resolved low-and highfrequency features. The relevance of these results to experiments on porous materials is discussed.

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Section: Discussionmentioning

confidence: 94%

The frequency response of sorbate diffusion in one-dimensional channels

Camp

2002

Phys. Chem. Chem. Phys.

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“…This periodic variation can be expressed as a sum of sinusoidal variations. For an elementary sinusoidal volume variation, the volume can be written: where ω is the angular frequency and v is the relative amplitude of the volume variation. − …”

Section: Tfr Methodsmentioning

confidence: 99%

Diffusion of Benzene in NaX Zeolite, Studied by Thermal Frequency Response

Malka-Edery

Grenier

2001

J. Phys. Chem. B

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The thermal frequency response technique (TFR) has been used to study the diffusion of benzene in NaX zeolite. The corrected diffusion coefficient is found to be independent of loading between 1.5 and 3.6 mol/cage at 406 K. It is in reasonable agreement with pulsed-field gradient NMR or quasi-elastic neutron scattering methods, but a large discrepancy is observed with the tracer zero length column (TZLC) technique. The activation energy for diffusion determined by TFR, 27 kJ/mol, is in accordance with the TZLC value, but substantially higher than the values reported from the other techniques.

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“…De nombreuses Ctudes de l'interaction gaz-solide en termes d'bnergie ont ktk entreprises pour tenter d'expliquer les phbnomtnes de diffusion et d'adsorption des gaz dans les tamis molCculaires (TM) (Kington et Laing 1955, Dempsey 1967, Kiselev et Lopatkin 1968, Sargent et Whitford 1971, Ruthven et Derrah 1972, Ruthven 1974,1977, Cohen de Lara et Delaval 1978, Barrer 1978. Deux paramhtres ont une importance capitale:…”

Section: Introductionunclassified