Hexadecane cracking reactions

Figure 1. Product distribution of catalytic cracking reaction using n-hexadecane,...

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. 

The structural features of dealuminated zeolite samples were characterized using X-ray powder diffraction, porosimetry and solid-state NMR measurements. Hexadecane cracking was used as a probe reaction to investigate catalytic properties of pure zeolites. 

Catalytic Properties. Catalytic properties were determined for both calcined and steamed zeolites using hexadecane cracking as a test reaction. Hexadecane cracking provides information on zeolite activity and selectivity which can be used to estimate octane production. Data were obtained for both calcined and steamed zeolites at hexadecane conversions from 30% to 70% multiple runs were made for each catalyst. 

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 transformation of n-hexadecane was carried out in a fixed-bed reactor at 220°C under a 30 bar total pressure on bifunctional Pt-exchanged HBEA catalysts differing only by the zeolite crystallites size. The activities of the catalysts and especially the reaction scheme depended strongly on the crystallites size. Monobranched isomers were the only primary reaction products formed with the smallest crystallites, while cracking was the main reaction observed with the biggest crystallites. This was explained in terms of number of zeolite acidic sites encountered by the olefinic intermediates between two platinum particles. 

The hydrocarbons in cmde oil are alkanes, olefins, aromatics, polyaromatics, and organic compounds containing S, N, 0, and heavy metals. Since there are many isomers of aU of these types of molecules, the reactions implied by the preceding equations rapidly approach infinity. A representative reaction of these might be the cracking of hexadecane (number 3 heating oil) into octane and octette (components in gasoline). 

The hydropyrolysis of a representative polycyclic naphthene, i.e., decalin (2), was investigated as a function of reaction temperature (525°-625°C) and hydrogen pressure 500-2000 psig). In addition, a comparison between hydropyrolysis and thermal cracking of 2 was made by doing a parallel study with this compound under nitrogen pressure, using otherwise identical experimental conditions. The apparatus and experimental methods were the same as in the study of n-hexadecane (see Experimental section). 

Other paraffins have also been used for measuring acidity. Neopentane is an attractive compound since protonation of a C-C bond is the preferred primary step for cracking. Corma and coworkers and Guisnet and coworkers used n-heptane in studies of H-Y. Klyachko et al. used octane to characterize the acidities of mordenites and ZSM-5 zeolites. The catalytic activity correlated well with their acidities as determined by calorimetric measurements of the heats of adsorption of ammonia. Higher paraffins such as hexadecane have also been used, but their utility is questionable due to the increased number of secondary reactions that can occur. ... 

K-Hexadecane was chosen as model molecule since it is relatively easy to implement and obtain as a pure body. Its reaction network non-exhaustive on Fig. 29—is representative since it includes all the elementary steps involved in the hydrocracking/hydroisomerisation of heavy paraffinic cuts. After reduction, just six kinetic parameters (two for isomerisation, four for cracking) are required to represent this type of network. 

Apart from the very large number of elementary steps it contains, the reaction network of heavy paraffins is the same as that of w-hexadecane. The apparent kinetic network is unchanged the linear paraffins are isomerised, and then cracked. 

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. 

As we learned more about the hydrocarbon reactions, some similarities to reactions catalyzed by strong acids at much lower temperatures became evident. An additional and different impetus to understanding came from an interlude of thermal cracking studies. At the time we were interested in the thermal cracking of normal paraffins (waxes) for production of alpha olefins. Thermal cracking of n-hexadecane gave products in... 

Wu, G., Katsamura, Y, Matsuura, C., and Ishigure, K. 1997. Radiation effect on the thermal cracking of n-Hexadecane. 1. Products from radiation-thermal cracking. Ind. Eng. Chem. Res. 36 1973-1978 2. A kinetic approach to chain reaction. Ind. Eng. Chem. Res. 36 3498-3504. 

Hierarchical (or mesoporous) zeolites became the focus of the review by Christensen et al. [7]. The main reason behind the development of hierarchical zeolites is to achieve heterogeneous catalysts with an improved porous structure and thereby enhanced performance in alkylation of benzene with alkenes, alkylation, and acylation of other compounds, methanol conversion into hydrocarbons, aromatization processes, isomerization of paraffins, cracking of diverse substrates and raw materials (naphtha, aromatic compounds, hexadecane, vacuum gas oil, and some polymers), and hydrotreating. The reactions that are of interest from the point of view of fine chemicals synthesis occurring on hierarchical zeohtes include aldol condensation, esterification, acetalization, olefin epoxidation, and Beckmarm rearrangement. 

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