The mechanism of paraffin reactions on HY zeolite

Journal Article · Sun Jan 01 04:00:00 EST 1989 · Journal of Catalysis; (USA)

DOI:https://doi.org/10.1016/0021-9517(89)90002-X· OSTI ID:7128607

Abbot, J; Wojciechowski, B W ^[1]

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1. Queen's Univ., Kingston, Ontario (Canada)

The selectivity and kinetics of catalytic cracking of a range of paraffin feedstocks are explained by assuming that cracking occurs only at Bronsted sites. The authors propose that the cracking reaction is initiated through the formation of a pentacoordinated carbonium ion and that subsequent events parallel the reaction of the same paraffin in liquid superacid media. For linear paraffins in the range C{sub 6}-C{sub 16}, direct bond cleavage of the initial carbonium ion produces a gas phase paraffin and an adsorbed carbenium ion which can desorb as an olefin. Rearrangement of the carbonium transition state before cracking is postulated to produce branched paraffins as initial products. Hydride transfer between an adsorbed carbenium ion and a feed molecule leads to the cracking of that feed molecule via {beta}-scission of the resulting carbenium ion. The reaction of linear paraffins is inhibited by the competitive adsorption of product olefins, which also enhance the chain mechanism route but not enough to cause an overall acceleration in cracking rate when olefins are added to a linear paraffin during cracking. For short-chain branched paraffins such as 2-methylpentane, 3-methylpentane, and 2,3-dimethylbutane, C-H bond cleavage to produce molecular hydrogen occurs in parallel with C-C cleavage. In contrast to linear ions, the carbenium ion formed by hydride ion abstraction from a branched feed molecule via the chain process undergoes {beta}-scission more rapidly than does the cleavage of the branched feed molecule through protolysis. Thus the addition of small amounts of olefin to some small branched paraffins produces a significant acceleration in cracking rate. The kinetic model which applies to the reactions of linear paraffins on HY is therefore not valid for these branched paraffins.

• OSTI ID: 7128607
• Journal Information: Journal of Catalysis; (USA), Journal Name: Journal of Catalysis; (USA) Vol. 115:1; ISSN 0021-9517; ISSN JCTLA
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
020400* -- Petroleum-- Processing
ADSORPTION
ALKANES
ALKENES
CATALYSIS
CATALYTIC CRACKING
CATALYTIC EFFECTS
CHEMICAL BONDS
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CLEAVAGE
CRACKING
CRYSTAL STRUCTURE
DECOMPOSITION
ENERGY SOURCES
FOSSIL FUELS
FUELS
GAS OILS
HYDROCARBONS
HYDROGEN TRANSFER
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
KINETICS
MATERIALS
MATHEMATICAL MODELS
MICROSTRUCTURE
MINERALS
ORGANIC COMPOUNDS
PENTANE
PETROLEUM
PETROLEUM FRACTIONS
PETROLEUM PRODUCTS
PYROLYSIS
REACTION INTERMEDIATES
REACTION KINETICS
SORPTION
SURFACE PROPERTIES
THERMOCHEMICAL PROCESSES
ZEOLITES