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A sulfided Ni/H-erionite catalyst was prepared from the natural mineral, and its catalytic characteristics for hydrocracking n-alkanes were studied. Because of its shape selectivity toward straight chain hydrocarbons, branched products were largely absent and the major cracked product was propane. The observed product distribution could not be explained by simple primary cracking of the feed molecule or by secondary cracking or recombination of the primary products. It is proposed that the feed molecule participated in a set of reactions, including hydrogenation, dehydrogenation, hydrogen transfer, oligomerization and cracking. These reactions are also needed to explain the yield of less than two moles of product from each mole of feed converted. A set of six first order differential equations representing the proposed molecular transformations is shown to fit the product distribution data for n-butane very well. A fit of the n-heptane data was not attempted; however, it is proposed that the mechanism is analogous to that proposed for n-butane. The rate of cracking of n-butane is first order in n-butane concentration, while the rate of n-heptane cracking appeared to follow half order kinetics. For n-butane cracking, the apparent activation energy of all the important reactions are roughly equal, resulting in a product distribution which is nearly independent of temperature. For n-heptane, a larger difference between the apparent activation energy of n-heptane cracking and secondary cracking of its primary products, lead to a temperature dependence in product selectivity.

Etude de la stabilite et de la structure des pores d'une zeolite ZSM5 desaluminee par un traitement chimique avec du CrCl 3

In the 26 years since the term “shape-selective catalysis” was coined by P. B. Weisz and V. J. Frilette [1] to describe the unique catalytic properties of small pore molecular sieve zeolites, great strides in the use of shape-selective zeolites have been made, both scientifically and technologically. Since then, in addition to small pore zeolites, synthetic medium pore zeolites, such as ZSM-5 [2], ZSM-11 [3], ZSM-22 [4], ZSM-23 [5], ZSM-35 [6], ZSM-38 [7], ZSM-48 [8], etc., have been discovered. The availability of these synthetic medium pore zeolites has expanded the realm of “shape selectivity” beyond the original discovery of selective conversion of straight chain molecules to include certain branched molecules, single-ring aromatics, naphthenes, and nonhydrocarbons with a critical molecular dimension smaller than about 6 A.

Methanol, in the presence of toluene, was completely converted to hydrocarbons above 400 °C. However, depending on the ratio of toluene to methanol in the feed mixture and the reaction severity, only a fraction of the methanol participated in the toluene alkylation reaction, with the remainder being converted to gaseous hydrocarbons. Alkylation is found to be ortho/para -directing over the small-crystal ZSM-5, similar to that found with aluminum chloride and amorphous silica/alumina catalysts, whereas the large crystals showed high para selectivity. The catalytic results are shown to be consistent with the diffusion characteristics of the zeolite.