Kinetics of cracking of n-decane and n-hexane on zeolites H-ZSM-5 and HY in the temperature range 500 to 780 K

Journal Article · Thu Oct 01 00:00:00 EDT 1992 · Journal of Catalysis; (United States)

DOI:https://doi.org/10.1016/0021-9517(92)90171-D· OSTI ID:7151626

Riekert, L; Zhou, J -Q ^[1]

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1. Univ. Karlsruhe (Germany)

The kinetics of cracking of n-decane and n-hexane were investigated by observing the composition of the gas phase in contact with zeolite catalysts H-ZSM-5 and HY in a well-mixed closed system (gradientless batch-reactor). Catalyst temperature was varied from 473 K to 773 K, partial pressures of reactant paraffin between 0.5 and 20 mbar. For ZSM-5 the influence of crystal size and of Si/Al-ratio on the kinetics was investigated. At temperatures above 673 K, the rates of cracking on H-ZSM-5 are first order in the partial pressures of paraffin; an estimate of diffusivity under reaction conditions is obtained from the influence of crystal size on observed rates at T > 700 K. Between 473 K and 673 K, the rate of reaction of pure n-decane on H-ZSM-5 exhibits a maximum near 300 C and decreases with temperature to a minimum near 630 K. An induction period followed by autocatalysis was observed with n-decane as reactant in this temperature-range, depending on Si/Al ratio and degree of deactivation of the zeolite. It can be suppressed by addition of olefin to reactant paraffin. These phenomena are also observed in a less pronounced way with dealuminated HY, which deactivates more rapidly. A mathematical model based on a dual pathway of carbenium ion and protolytic cracking as postulated by Haag and Dessau represents the observations qualitatively and in an approximate way also quantitatively.

• OSTI ID: 7151626
• Journal Information: Journal of Catalysis; (United States), Vol. 137:2; ISSN 0021-9517
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
DECANE
CATALYTIC CRACKING
HEXANE
ZEOLITES
CATALYTIC EFFECTS
ALUMINIUM
CHEMICAL REACTION KINETICS
CRYSTAL STRUCTURE
DEACTIVATION
DIFFUSION
GAS ANALYSIS
MATHEMATICAL MODELS
PRESSURE DEPENDENCE
QUANTITY RATIO
SILICON
TEMPERATURE RANGE 0400-1000 K
ALKANES
CHEMICAL REACTIONS
CRACKING
DECOMPOSITION
ELEMENTS
HYDROCARBONS
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
KINETICS
MATERIALS
METALS
MINERALS
ORGANIC COMPOUNDS
PYROLYSIS
REACTION KINETICS
SEMIMETALS
SILICATE MINERALS
TEMPERATURE RANGE
THERMOCHEMICAL PROCESSES
020400* - Petroleum- Processing