Kinetics of cumene cracking on HZSM-5
Rate expressions based on the delta mechanism of cumene cracking are applied to cumene cracking on HZSM-5. The fit is good and the resultant parameters confirm that this reaction is very strongly influenced by the steric constraints of the small pore diameter of HZSM-5. The constraints prevent the occurrence of initial bimolecular reactions and reduce the rate of dealkylation, which has a bimolecular reverse reaction, more than the rate of the monomolecular isomerization to n-propyl benzene. The rate of dealkylation is found to be only one order of magnitude faster than isomerization on HZSM-5 while it was found to be two orders of magnitude faster on HY, LaY, and amorphous Si/Al. The coke formed on HZSM-5 is very rich in hydrogen (H/C ratio approx. 2.0) and very low in poisoning activity. The authors believe that this too is the result of the difficulty in achieving the bimolecular transition state necessary for hydrogen transfer and the consequent hardening of the coke. The order of the decay reaction with respect to site concentration is approx. 10/sup 4/ as compared to 2 on HY, LaY, and Si/Al, indicating that a very large number of sites are lost per deactivating event. At the same time the decay rate constant is some 10/sup 14/ times smaller than that on the above catalysts. This suggests that deactivating events are rare (low rate constant) but catastrophic (many sites deactivated per event). It seems that it is the hard coke (low H/C ratio) which is primarily responsible for activity decay. In the case of HZSM-5, decay is very slow and probably takes place by pore blocking rather than site-by-site deactivation, as was clearly the case in other catalysts studied to date.
- Research Organization:
- Nippon Mining Co., Ltd., Saitama, Japan
- OSTI ID:
- 5463822
- Journal Information:
- J. Catal.; (United States), Vol. 109:1
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
CUMENE
CATALYTIC CRACKING
ZEOLITES
CATALYTIC EFFECTS
CATALYSTS
CHEMICAL REACTION KINETICS
COKE
COMPARATIVE EVALUATIONS
DEACTIVATION
DEALKYLATION
DEPOSITION
ISOMERIZATION
KINETIC EQUATIONS
MICROSTRUCTURE
POROSITY
AROMATICS
CHEMICAL REACTIONS
CRACKING
CRYSTAL STRUCTURE
DECOMPOSITION
EQUATIONS
HYDROCARBONS
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
KINETICS
MATERIALS
MINERALS
ORGANIC COMPOUNDS
PYROLYSIS
REACTION KINETICS
THERMOCHEMICAL PROCESSES
020400* - Petroleum- Processing