Monomolecular and bimolecular mechanisms of paraffin cracking: n-Butane cracking catalyzed by HZSM-5

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

DOI:https://doi.org/10.1016/0021-9517(92)90273-K· OSTI ID:7191280

Krannila, H; Gates, B C ^[1]; Haag, W O ^[2]

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1. Univ. of Delaware, Newark (United States)
2. Mobil Research and Development Corp., Princeton, NJ (United States)

The cracking of n-butane catalyzed by the zeolite HZSM-5 has been characterized by measurements of the conversion determined with a flow reactor at temperatures of 426-523 C and n-butane partial pressures of 0.01-1.00 atm. The primary products, each formed in a first-order reaction, are H[sub 2] + butenes; methane + propylene; and ethane + ethylene. In the limit approaching zero conversion, each compound in each stated pair was formed at approximately the same rates as the other. Propane and a small amount of isobutane were formed as secondary products in second-order reactions. The results are consistent with the occurrence of two simultaneous mechanisms: (1) a monomolecular mechanism proceeding through the pentacoordinated carbonium ion formed by protonation of the n-butane at the two position and (2) a bimolecular hydride transfer proceeding through carbenium ion intermediates. The former proceeds almost to the exclusion of the latter in the limit approaching zero n-butane conversion. The limiting product distribution characterizes the intrinsic selectivity of the collapse of the carbonium ion; at 496 C, the relative rates of decomposition of the carbonium ion to give H[sub 2] + butenes, methane + propylene, and ethane + ethylene are 30 [plus minus] 6, 36 [plus minus] 4, and 34 [plus minus] 5, respectively, with the corresponding activation energies all being approximately 140 kJ/mol. These results provide the first demonstration of stoichiometric dehydrogenation accompanying paraffin cracking.

• OSTI ID: 7191280
• Journal Information: Journal of Catalysis; (United States), Journal Name: Journal of Catalysis; (United States) Vol. 135:1; ISSN 0021-9517; ISSN JCTLA5
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
020400* -- Petroleum-- Processing
ACTIVATION ENERGY
ALKANES
ALKENES
BUTANE
BUTENES
CATALYTIC EFFECTS
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CRACKING
DECOMPOSITION
DEHYDROGENATION
ELEMENTS
ENERGY
ETHANE
ETHYLENE
HYDROCARBONS
HYDROGEN
HYDROGEN TRANSFER
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
KINETICS
MATERIALS
METHANE
MINERALS
NONMETALS
ORGANIC COMPOUNDS
PROPYLENE
PYROLYSIS
REACTION INTERMEDIATES
REACTION KINETICS
SILICATE MINERALS
SYNTHESIS
TEMPERATURE RANGE
TEMPERATURE RANGE 0400-1000 K
THERMOCHEMICAL PROCESSES
ZEOLITES