Cracking selectivity patterns in the presence of chain mechanisms. The cracking of 2-methylpentane
- Queen's Univ., Kingston, Ontario (Canada)
Catalytic cracking of 2-methylpentane on HY has been studied at 400, 450, and 500[degrees]C and a chain reaction mechanism is used to interpret the selectivity of the reaction. The results of a quantitative description of this mechanism show that protolysis of bonds in the feed molecule at 400[degrees]C follows the order (C[sub t]-C[sub s]) > (C[sub s]-C[sub s]) > (C[sub t]-C[sub p] or C[sub s]-C[sub p]) > (C[sub t]-H) in the ratio 0.510/0.416/0.054/0.20, but at 500[degrees], C the order becomes (C[sub t]-C[sub s]) > (C[sub s]-C[sub s]) > (C[sub t]-H) > (C[sub t]-C[sub p] or C[sub s]-C[sub p]) in the ratio 0.625/0.212/0.138/0.025, where p, s, and to refer to primary, secondary, and tertiary carbons. The chain length decreases with increasing reaction temperature. This leads to a pronounced decrease in the formation of isomeric products and an increase in the production of C[sub 1]-C[sub 5] paraffins and C[sub 2]-C[sub 5] olefins. [beta]-Cracking of a parent carbenium ion is very small at 400[degrees]C, but becomes noticeable at 500[degrees]C. The isomerization process consisting of a skeletal rearrangement of the C[sub 6]H[sub 13]S[sup +] ion and a subsequent abstraction of hydride from a feed molecule in the gas phase dominates conversion at lower temperatures. At higher temperatures, however, the appearance of [beta]-cracking of the C[sub 6][sup +] ion and the enhancement of the desorption of parent carbenium ions inhibit isomerization. Molecular hydrogen is initially formed from both the protolysis of a C-H bond in the feed molecule and from the formation of coke. The initial molar probability of coke formation is only 0.010 at 400[degrees]C, while the H/C ratio in the initial coke is 1.96, substantially below the 2.33 ratio present in the feed. Rising temperature results in an increase in the production of hydrogen and the formation of a more hydrogenated coke. 31 refs., 7 figs., 10 tabs.
- OSTI ID:
- 5649862
- Journal Information:
- Journal of Catalysis; (United States), Journal Name: Journal of Catalysis; (United States) Vol. 142:2; 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
ALKANES
ALKENES
CATALYSIS
CATALYTIC CRACKING
CATALYTIC EFFECTS
CHEMICAL REACTIONS
COKE
CRACKING
DECOMPOSITION
HETEROGENEOUS CATALYSIS
HEXANE
HYDROCARBONS
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
ISOMERIZATION
ISOMERS
MATERIALS
MINERALS
ORGANIC COMPOUNDS
OTHER ORGANIC COMPOUNDS
PARAFFIN
PYROLYSIS
SILICATE MINERALS
TEMPERATURE DEPENDENCE
TEMPERATURE RANGE
TEMPERATURE RANGE 0400-1000 K
THERMOCHEMICAL PROCESSES
WAXES
ZEOLITES