Issue |
J. Chim. Phys.
Volume 76, 1979
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Page(s) | 458 - 464 | |
DOI | https://doi.org/10.1051/jcp/1979760458 | |
Published online | 29 May 2017 |
Étude cinétique de la déshydrogénation catalytique de l’isobutane sur le système Al2O3 – Cr2O 3 (à 7,5 % mol. Cr2O2
1
Laboratoire de Chimie Générale, Université Scientifique et Médicale de Grenoble, BP n° 53 X-38041 Grenoble Cedex.
2
Groupe de Physico-Chimie Minérale et de Catalyse, Université Catholique de Louvain, Place Croix du Sud 1, 1348 Louvain-la-Neuve, Belgique.
La cinétique de déshydrogénation de l’isobutane en isobutène est étudiée, en régime dynamique, sur un oxyde mixte Al2O3 – Cr2O3 (à 7,5 % mol. Cr2O3). Après avoir vérifié que la diffusion n’est pas limitative dans les conditions expérimentales choisies, nous proposons une équation de vitesse pour la réaction et suggérons un mécanisme où interviennent deux étapes déterminantes, l’adsorption du réactif et la réaction en surface.
Abstract
The dehydrogenation of isobutane to isobutene over chromia-alumina system has been kinetically investigated at temperatures ranging from 533 to 596 °C. The catalyst containing 92,5 % mol. Al2O3, and 7,5 % mol. Cr2O3 is obtained by quick pyrolysis at 1 050 °C in air of an oxalato complex
(NH4)3[A10,925Cr0,075(C2O4)3].nH2O.
The apparatus is of the flow type. The runs were performed on isobutane and on mixture of isobutane + nitrogen, at atmospheric pressure.
In a preliminary study, calculation shows that diffusion is not controlling in the experimental conditions reported and can be neglected. We measured first the variations in isobuten yield according to the isobutane pressure. The influence of isobutane presse on the initial reaction rate has been studied at several temperature. According to the mechanisms generally reported in the literature in the dehydrogenation of iso and n-butane, the following rate law is proposed, where V is the initial reaction rate and P is the initial isobutanc pressure:
[math]
The rate law implies that the reaction mechanism involves one active site and two rate determining steps: k1 is the reaction rate constant for the isobutane adsorption onto an active site, k2 is the reaction rate constant for adsorbed molecules in the surface. Activation energy for the two elementary steps: E1, and E2 are respectively equal to 27,8 Kcal. Mole- 1 and 12,3 Kcal . Mole- 1.
© Paris : Société de Chimie Physique, 1979