Hexadecane cracking results

Table V. Hexadecane Cracking Results for Dealuminated Zeolites.

Table VI. Hexadecane Cracking Results for Calcined Zeolites. Product Slate at 50% Conversion...

Dealuminated Y zeolites which have been prepared by hydrothermal and chemical treatments show differences in catalytic performance when tested fresh however, these differences disappear after the zeolites have been steamed. The catalytic behavior of fresh and steamed zeolites is directly related to zeolite structural and chemical characteristics. Such characteristics determine the strength and density of acid sites for catalytic cracking. Dealuminated zeolites were characterized using X-ray diffraction, porosimetry, solid-state NMR and elemental analysis. Hexadecane cracking was used as a probe reaction to determine catalytic properties. Cracking activity was found to be proportional to total aluminum content in the zeolite. Product selectivity was dependent on unit cell size, presence of extraframework alumina and spatial distribution of active sites. The results from this study elucidate the role that zeolite structure plays in determining catalytic performance. 

Light gas compositions are shown in Table VIII for hexadecane cracking at constant 50% conversion. Results are reported as iso-to-normal and olefin-to-paraffin ratios for C4 products. 

Catalyst Performance Relationships. Hexadecane cracking activity of AFS and USY zeolites, when corrected for deactivation effects, shows little or no dependence on framework composition. Rather, as shown in Figure 6, activity appears to be a function of total aluminum content independent of the method of dealumination. This result implies that hexadecane cracking occurs over both framework and extraframework acid sites and that it is the total number of such sites which determines catalytic activity. Hence, extraframework material in the USY samples makes a significant contribution to catalyst activity as reported by others(18.19). 

Gasoline composition from hexadecane cracking over calcined and steamed AFS and USY zeolites can be represented by general correlations as shown in Figure 5. As these correlations are unique to zeolite Y, they indicate that the Y zeolite framework topology plays an important role in the mechanism of product formation. The method of dealumination and subsequent steam treatment lead to various PONA compositions however, these compositions result from a... 

Typical results tor the cracking of the base feedstock, n-hexadecane, are presented in Fig. I, in terms of product distribution. Components are listed as carbon numbers up to Cl5, but also including the amount of coke formed. The product distribution attains a maximum at the C3t C4 and C5 region, following which there is a monotonic decrease in product concentration to 04. An increase then occurs for the C15 concentration and the coke. 

Gasoline selectivity is influenced by both the method of dealumination and steam treatment and, hence, depends on framework acid sites and on presence of extraframework material. Both framework and extraframework sites contribute to the overall zeolite acidity. Framework Al(IV) acid sites are associated with Bronsted acidity whereas extraframework Al(VI) acid sites are associated with Lewis acidity(21). Calcined AFS samples are reported (22) to contain greater Bronsted acidity than USY samples from infrared characterization and to have stronger acidity as measured by ammonia desorption. As a result, the stronger acidity of calcined AFS samples cracks hexadecane to lower molecular weight products than USY. After steaming, the acidities of both AFS and USY are reduced to similar levels and lead to similar gasoline selectivities which are increased relative to the calcined zeolites. 

The effect of quinoline and phenanthrene additions to a n-hexadecane feedstock has been determined for a model four-component FCC catalyst by means of a MAT reactor with analysis of all products and characterisation of the coke produced. Both additions lead to an overall loss in conversion quinoline is considered to act as a poison while phenanthrene participates strongly in coke formation and the resultant coke becomes more aromatic in nature. The cracking propensity and associated coke formation have been measured for a series of FCC catalysts with differing compositions. Increasing amounts of zeolite in a matrix lead to increasing extents of conversion but with little effect on the extent of coke production. However, a pure zeolite gave a very high coke content. 

In this paper, the cracking of n-hexane, n-dodecane and n-hexadecane on ZSM-5 zeolites at about atmosphere and temperatures of 260-400°C were studied. The results showed that both mono-molecular cracking and bimolecular reaction (disproportionation) for n-hexane cracking took place. A network for initial reactions was proposed, and the apparent kinetic parameters of the reactions were estimated. An examination for the factors affecting the product destribu-tion of n-hexadecane indicated that hydrogen transfer on the surface of HZSM-5 zeolites plays an important role in cracking reaction. 

The resulting equation was found empirically by E. B. Burk (3) and M. D. Tilicheev (22). The above-studied mechanism of the cracking of n-paraffins explains the absence of dependence of the cracking rate on reaction extent. This differs from the case of the low molecular weight paraffins experimentally determined by Kasanskaya (6) and Panchenkov and Baranov (19) for n-octane and n-hexadecane. 

The stability of mesoporous material SBA-15 and Al-SBA-15 was investigated under steaming treatment (100 % H2O) at 800 °C for different time. Al-SBA-15 catalyst has been prepared via post-synthesis procedure. The results show that the mesostructure of SBA-15 and Al-SBA-15 can be retained at 800 °C steaming for 8 h, while MCM-41 totally loses its mesostructure under the same condition just for 2 h. Moreover, Al-SBA-15 still has cracking activity of n-hexadecane and Pt/Al-SBA-15 has hydroisomerization activity of n-dodecane to some extent even after steaming treatment at 800 °C for 8 h. Meanwhile, Al-MCM-41and Pt/Al-MCM-41 catalysts totally lose their activity under the same treatment condition just for 2h. 

Alkanes are the dominant initial product at 573 K whereas olefins are dominant at 673 K in the cracking of hexadecane over HY zeolite. This was explained as being the result of more extensive hydrogen transfer at the lower temperature. ... 

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