The consequences of steam dilution in catalytic cracking. II. Effect of steam dilution on the selectivity and mechanism in 2-methylpentane cracking over USHY
- Queen`s Univ., Kingston, Ontario (Canada)
The effect of steam dilution in shaping the selectivity of 2-methylpentane cracking has been studied at 400, 450, and 500{degrees}C using a USHY zeolite. The results show that the presence of steam enhances isomerization of the feed and suppresses the production of cracked products. This and other evidence leads to the belief that steam dilution enhances the chain propagating reactions in the mechanism of catalytic cracking. At the same time, steam inhibits chain termination by desorption. The new results is that the presence of steam increases kinetic chain length and the paraffin-to-olefin ratio. The effects of steam dilution are surprisingly strong at lower temperatures but become less significant as temperature rises. All these effects are interpreted in terms of their influence on the elementary steps of the chain mechanism and are principally rendered in terms of a new measure: the reaction path probabilities (RPPs). These describe the likelihood that a feed molecule will be converted by a given reaction. Probabilities of all the reactions of the various ions present in the chain mechanism of 2-methylpentane cracking are quantified by formulating appropriate secondary functions using the RPPs derived from our experimental data. These various {open_quotes}internal{close_quotes} probabilities are used to quantify just how likely are each of the many alternative reactions of a given ion, as reaction conditions change. They allow one to track the effect of changes in reaction conditions, or in catalyst formulation, in unprecedented detail. Moreover, they give a detailed picture of the behavior of elementary processes in this reaction. The authors present and discuss examples of the quantitative information which these methods make available, and the mechanistic interpretations which flow from this information. 45 refs., 12 figs., 6 tabs.
- OSTI ID:
- 501848
- Journal Information:
- Journal of Catalysis, Journal Name: Journal of Catalysis Journal Issue: 2 Vol. 163; ISSN 0021-9517; ISSN JCTLA5
- Country of Publication:
- United States
- Language:
- English
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