0000000000427603
AUTHOR
A.v. Orchillés
Catalytic cracking of alkanes on MCM-22 zeolite. Comparison with ZSM-5 and beta zeolite and its possibility as an FCC cracking additive
Abstract N-heptane cracking has been carried out on MCM-22, and its kinetic and decay behaviour is compared with that of ZSM-5 and Beta zeolites. In the case of MCM-22 cracking occurs in the 10-member ring channel system, as well as in the large cavities formed by 12-member rings. Product selectivities show that MCM-22, while presenting features which indicate structural similarities with ZSM-5, it also presents characteristics corresponding to pores or cavities larger than ZSM-5. The selectivities to the individual products together with C1 + C2/iC4, C3/C4, C5/C2, iC4/total C4, and alkane/alkene ratios indicate that MCM-22 has good properties to be used as an FCC octane booster additive sp…
Current views on the mechanism of catalytic cracking
Abstract The cracking mechanisms of hydrocarbons have been reviewed and the kinetic and thermodynamic implications of the different steps, i.e. initiation, chain propagation, and termination, have been discussed. Although the cracking mechanism of olefins and alkylaromatics is well established, the initiation step for the cracking of paraffins is still under debate. The role of Bronsted-type active sites and also the possible influence of extra-framework Al species in the case of zeolite catalysts, especially when commercial feeds and industrial conditions are employed, are presented. The product distribution is determined by the number of propagation events occurring per initiation step, a…
Product selectivity effects during cracking of alkanes at very short and longer times on stream
Abstract Cracking of C 7 , C 10 , C 12 and C 14 n-alkanes, over USY, Beta and ZSM-5 zeolites was carried out in a reaction system which allows to obtain instantaneous conversions at very short times on stream. With this system the influence of operation variables, chain length of the paraffin fed, and catalyst structure on product selectivity was established. Positive and negative effects of catalyst decay on product selectivity were obtained, and this behaviour could be simulated by using a deactivation model in which the rate of deactivation depends on the product concentration. It was observed that olefin/paraffin, branched/normal paraffin, branched/normal olefin ratios and aromatic sele…