The influence of reaction temperature on the cracking mechanism of 2-methylhexane
- Queen's Univ., Kingston, Ontario (Canada)
The cracking of 2-methylhexane on USHY has been studied in the temperature range 400-500[degrees]C. It was found that this reaction leads to the formation of hydrogen, paraffins, olefins, and aromatics ranging from C[sub 1] to C[sub 10]. Of these only hydrogen, C[sub 1]-C[sub 7] compounds, and coke were found to be primary products. Mechanistic considerations indicate that two main processes takes place during 2-methylhexane conversion on USHY: (1) initiation by protolysis on pristine Broensted sites; (2) chain processes involving isomerization, hydrogen transfer, and disproportion. At low temperatures, conversion of 2-methylhexane proceeds to a significant extent via both mechanisms, while at higher temperatures protolytic cracking is the dominant process by far. The authors find that protolysis accounts for 67, 83, and 94% of total conversion of 2-methylhexane at 400, 450, and 500[degrees]C, respectively. The average activation energy for protolytic cracking of 2-methylhexane on USHY was found to be 159 kJ/mol. Hydride abstraction from gas phase 2-methylhexane by C[sub 6]H[sub 13][sup +] and C[sub 7]H[sub 15][sup +] ions lead to the formation of the paraffinic C[sub 6] and C[sub 7] skeletal isomers found in the primary products. In addition to hydride transfer, the set of active bimolecular chain reactions involves some but not all possible disproportionations between feed molecules and carbenium ions in the range C[sub 2]H[sub 5][sup +] and C[sub 5]H[sub 11][sup +]. The probability of initial coke formation was found to decrease with increasing temperature, suggesting a diminished rate of bimolecular reaction between adjacent carbenium ions at higher temperatures. 30 refs., 5 figs., 7 tabs.
- OSTI ID:
- 6879239
- Journal Information:
- Journal of Catalysis; (United States), Journal Name: Journal of Catalysis; (United States) Journal Issue: 2 Vol. 148:2; ISSN 0021-9517; ISSN JCTLA5
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
020400 -- Petroleum-- Processing
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ACTIVATION ENERGY
ALKANES
ALKENES
CATALYSIS
CATALYTIC CRACKING
CATALYTIC EFFECTS
CHEMICAL REACTIONS
CRACKING
CYCLOALKANES
DECOMPOSITION
ENERGY
HETEROGENEOUS CATALYSIS
HYDROCARBONS
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
MATERIALS
MINERALS
ORGANIC COMPOUNDS
OXIDATION
PYROLYSIS
REDUCTION
SILICATE MINERALS
TEMPERATURE DEPENDENCE
TEMPERATURE RANGE
TEMPERATURE RANGE 0400-1000 K
THERMOCHEMICAL PROCESSES
ZEOLITES