Activity, cracking

The parameter is a crack propagation velocity and n(e) is a crack activation law driven by the bulk tensile strain e and specified by the Weibull fracture theory... 

ZSM-5 Cracking of cumene and heavy oil Higher cracking activity Higher yield to light olefins [55]... 

Promotion of molecular hydrogen on solid acid cracking activity... 

Dihydroquinoline derivatives offer moderate antioxidant and flex cracking activity with excellent metal poison protection. 

Recent work has shown that strong and weak sites exist in faujasite (11) and it has been proposed that relatively isolated sites are the strong acid sites and are responsible for cracking activity (12). The results obtained in this work imply that strong acid sites are preferred, and that at Si/Al ratios beyond about 3.0 to 4.0 nearly all sites are isolated or strong. Either an increase or decrease in the Si/Al ratio from 3.0 to 4.0 will result in some loss in strong acid sites. 

Silica-alumina mixtures are of great technological importance in the oil industry as catalysts for petroleum processing. The cracking activity is closely linked to surface acidity. Other typical reactions catalyzed by silica-alumina are the dehydration of alcohols and the polymerization of olefins. 

The effect of steam treatment of ZSM-5 on its cracking activity and selectivity was measured with experiments using n-hexadecane feed. With the thermally treated ZSM-5 catalyst, concentration of the unconverted n-hexadecane in the product was not measurable while 507e of the feed was unconverted with the steam treated ZSM-5 catalyst (Table II). The lower limit of conversion with the thermally treated catalyst corresponding to detection limit of n-hexadecane is 99.99%. This lower limit suggests at least an order of magnitude reduction in apparent first order rate constant of the ZSM-5 catalyst upon steam treatment. The small reduction in crystallinity upon steaming cannot fully explain the dramatic activity loss. Loss of active sites due to dealumination of ZSM-5 can be postulated to explain the reduction in activity. 

For the sake of brevity, the yield data for all the individual components are not reported in Table II and subsequent tables. The yield of unreported components (usually Cs-i- olefins and naphthenes) can be calculated as 100 minus percentage yield of the reported components. Results shown in Table ll indicate that thermally treated ZSM-5 produced a high yield of Ce to Ce aromatics, Cs and C4 hydrocarbons. Steam treatment of ZSM-5 reduced cracking activity and increased the selectivity for Cs to C aliphatics at the expense of aromatics. The olefin to paraffin ratio in the product also increased upon steaming. 

Gas Oil Cracking by the Dual Zeolite Catalyst. After the steam pre-treatment, the gas oil cracking activity of REY was about 100 times greater than the activity of the pure matrix catalyst. 

Figure 4. Preservation of cracking activity by metal scavengers.

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