Study of the mechanism of the cracking of small alkane molecules on HY zeolites

Journal Article · Sat Aug 01 04:00:00 EDT 1992 · Journal of Catalysis; (United States)

DOI:https://doi.org/10.1016/0021-9517(92)90075-S· OSTI ID:6984531

Shertukde, P V; Marcelin, G; Sill, G A; Hall, W K ^[1]

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1. Univ. of Pittsburgh, PA (United States)

Cracking of i-butane and n-pentane was studied on HY zeolites. These reactions were initiated by the protonation of C-H and C-C bonds by the Broensted acid sites. The pentacoordinated carbonium ions thus formed decomposed into carbenium ions and the products of the initiation reactions, viz., H{sub 2}, CH{sub 4} and C{sub 2}H{sub 6}. These carbenium ions propagated chain reactions, mainly by isomerization followed by hydride transfer. Disproportionation occurred concomitantly. For these small alkanes the contribution of {beta}-scission to product formation was negligible. Chain length (the number of chain cycles per initiation) was defined as the ratio of reactant molecules consumed by hydride transfer to those reacted by protonation, i.e., the ratio of rates of bimolecular propagation to unimolecular initiation. Thus, chain length reflected the average lifetime of the carbenium ions. The extent of protonation was found to increase with the strength of acid sites while the chain length remained relatively constant for preparations of a similar nature. The product distribution obtained was therefore critically dependent on the steady-state population of carbonium ions. Finally the chain reactions were terminated by decomposition of carbenium ions into corresponding alkenes. Mass balances derived from these initiation, propagation, and termination steps were in agreement for both substrates. The product distributions obtained for i-butane and n-pentane cracking were satisfactorily explained on this basis.

• DOE Contract Number: FG02-87ER13774
• OSTI ID: 6984531
• Journal Information: Journal of Catalysis; (United States), Journal Name: Journal of Catalysis; (United States) Vol. 136:2; ISSN 0021-9517; ISSN JCTLA
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
020400* -- Petroleum-- Processing
ALKANES
ALKENES
BROENSTED ACIDS
BUTANE
CATALYSIS
CATALYTIC CRACKING
CATALYTIC EFFECTS
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CRACKING
DECOMPOSITION
ELEMENTS
ETHANE
HYDROCARBONS
HYDROGEN
HYDROGEN COMPOUNDS
HYDROGEN TRANSFER
INORGANIC ACIDS
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
ISOMERIZATION
KINETICS
MASS BALANCE
MATERIALS
METHANE
MINERALS
NONMETALS
ORGANIC COMPOUNDS
PENTANE
PYROLYSIS
RADICALS
REACTION INTERMEDIATES
REACTION KINETICS
SILICATE MINERALS
SYNTHESIS
THERMOCHEMICAL PROCESSES
ZEOLITES