Coking, aging, and regeneration of zeolites. III. Comparison of the deactivation modes of H-mordenite, HZSM-5, and HY during n-heptane cracking
The rates of deactivation by carbonaceous residues (coke) of HY, H-mordenite, and HZSM-5, which have similar initial activities in n-heptane cracking are quite different: HZSM-5 forms very little coke and is very stable, while HM deactivates much faster than HY. The deactivation mechanisms of these zeolites could be specified by comparing as a function of the coke content: (i) the cracking activity of these zeolites and their capacity for adsorption of n-hexane, (ii) the volume apparently and really occupied by coke, and (iii) the number of coke molecules and of sites on which NH/sub 3/ can no longer be adsorbed. On HY, polyaromatic molecules are very rapidly formed on the strongest acid sites, these molecules obstructing partially or completely the access of the reactant to the acid sites. On HZSM-5 deactivation is initially due to the coverage of the acid sites, located at channel intersections, by alkylaromatics with 1 or 2 rings; later on (above 3% coke content) polyaromatic molecules, formed on the external surface, block access to a part of the pore volume. On HM deactivation is due to pore blockage: even at very low coke contents (1% coke), coke can block the access of n-heptane to a pore volume 10 times greater than the volume really occupied by the coke.
- Research Organization:
- Universite de Poitiers (France)
- OSTI ID:
- 5269482
- Journal Information:
- J. Catal.; (United States), Journal Name: J. Catal.; (United States) Vol. 106:1; ISSN JCTLA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
020400* -- Petroleum-- Processing
ADSORPTION
ALKANES
CATALYTIC CRACKING
CHEMICAL REACTIONS
COKE
COMPARATIVE EVALUATIONS
CRACKING
CRYSTAL STRUCTURE
DEACTIVATION
DECOMPOSITION
DEPOSITION
FLOW BLOCKAGE
HEPTANE
HEXANE
HYDROCARBONS
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
KINETICS
MATERIALS
MICROSTRUCTURE
MINERALS
ORGANIC COMPOUNDS
POROSITY
PYROLYSIS
REACTION KINETICS
SORPTION
THERMOCHEMICAL PROCESSES
ZEOLITES