Acid-catalyzed cracking of paraffinic hydrocarbons. 3. Evidence for the protonated cyclopropane mechanism from hydrocracking/hydroisomerization experiments

The mechanism for acid-catalyzed cracking proposed in the first paper of this series, which assumes a protonated dialkylcyclopropane carbonium ion as intermediate instead of a classical carbenium ion, has been applied to rationalize experimental results obtained in the hydrocracking/hydroisomerizati...

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Bibliographic Details
Published in:Industrial & engineering chemistry research 1993-03, Vol.32 (3), p.403-408
Main Author: Sie, S. Tiong
Format: Article
Language:English
Subjects:
02 PETROLEUM
ALKANES
CATALYTIC CRACKING
CHEMICAL REACTION KINETICS
CHEMICAL REACTION YIELD
CHEMICAL REACTIONS
CRACKING
CYCLOALKANES
DECOMPOSITION
HEPTANE
HEXANE
HYDROCARBONS
HYDROCRACKING
ISOMERIZATION
KINETICS
MOLECULAR WEIGHT
ORGANIC COMPOUNDS
PYROLYSIS
REACTION INTERMEDIATES
REACTION KINETICS
THERMOCHEMICAL PROCESSES
YIELDS 020400 > Petroleum-- Processing
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Summary:The mechanism for acid-catalyzed cracking proposed in the first paper of this series, which assumes a protonated dialkylcyclopropane carbonium ion as intermediate instead of a classical carbenium ion, has been applied to rationalize experimental results obtained in the hydrocracking/hydroisomerization of normal paraffins. The new mechanism is shown to be capable of explaining many characteristics of the hydrocracking process which cannot be understood via the classical theory, such as the virtual absence of methane and ethane as cracked products, the relatively low production of propane as compared to the higher hydrocarbons, and characteristic patterns in the branching of the cracked fragments. The new mechanism also makes it clear why crackability increases so rapidly with increasing number of carbon atoms above n-heptane and why n-hexane and lower hydrocarbons are so difficult to crack. An explanation is also offered for the ease with which high selectivities can be achieved in the isomerization of C[sub 5]/C[sub 6], as contrasted with the difficulty of isomerizing C[sub 7+] without significant cracking.
ISSN:0888-5885
1520-5045
DOI:10.1021/ie00015a002