Alkanes hydrocracking

It is well known that the supported platinum show a high catalytic activity for the dehydrogenation of alkane whereas the supported palladium does not. The results shown in Figure 1 suggest that the dehydrogenation activity of supported metal is not essential for the appearance of the alkane hydrocracking activity. 

Metal clusters in zeolites are catalysts for a number of reactions, including alkene hydrogenation and alkane hydrocracking. The former is an example of shape selective catalysis, whereby straight diain alkenes can enter the zeolite pores and react but branched alkenes cannot enter and so do not substantially react. The latter have been apidied commerdally. Pt dusters in the zeolites KL and BaKL are remarkably selective catalysts for the dehydroi dization of n-hexane to give benzene, and they are now applied commerdally. The origin of the selectivity is still not fully understood, but it may be primarily a consequence of the smallness of the Pt clusters, which consist of only about S or 6 atoms on average, as determined by EXAFS spectroscopy, H2 chemisorption, and electron microscopy. 

A skewed Gaussian-type distribution function can depict the yield distributions. The resulting model reproduces published pilot-plant and commercial data on vacuum gas oil hydrocracking.This has led to the development of a hydrocracking process model." Selective cracking in FCC has also been addressed.Browarzik and Kehlen used a fragmentation-based model for n-alkane hydrocracking. Similar approaches have been used for polymer reaction systems." " ... 

Also in relumped form, single-event microkinetics account for all reactions at molecular level [2,3,13], This requires a molecular composition of the lumps considered. The definition of the lumps in hydrocracking is such that thermodynamic equilibrium can be assumed within the lumps. Per carbon number 12 lumps are considered, i.e., normal, mono-, di- and tribranched alkanes, mono-, di-, tri- and tetracycloalkanes and mono-, di-, tri- and tetra-aromatic components. 

Refineries and petrochemical industry Paraffins, olefins, acetylenes, reformer gas, hydrocracking gas, solvents Sweetening of liquid petrol gas and aromatics, removal of CO2 from olefin containing gases, purification of synthesis gas Normal and branched-chain alkanes... 

Dewaxing is an important specific hydrocracking process used to improve diesel and heating oils by pour-point reduction.88 This is achieved by shape selectivity of certain zeolites allowing selective hydrocracking of long-chain paraffinic waxes to C3—C5 alkanes in the presence of other paraffins.89 Platinum H-mordenite is used in an industrial process.90... 

The platforming catalyst was the first example of a reforming catalyst having two functions.43 44 93 100-103 The functions of this bifunctional catalyst consist of platinum-catalyzed reactions (dehydrogenation of cycloalkanes to aromatics, hydrogenation of olefins, and dehydrocyclization) and acid-catalyzed reactions (isomerization of alkanes and cycloalkanes). Hyrocracking is usually an undesirable reaction since it produces gaseous products. However, it may contribute to octane enhancement. n-Decane, for example, can hydrocrack to C3 and C7 hydrocarbons the latter is further transformed to aromatics. 

Much progress has been made in understanding the catalytic activity of zeolites for several type of reactions. The number of reactions catalyzed by zeolites has been extended, and new multi-component polyfunctional catalysts with specific properties have been developed. In addition to cracking and hydrocracking, reactions such as n-alkane isomerization, low temperature isomerization of aromatic C8 hydrocarbons, and disproportionation of toluene are industrially performed over zeolite-containing catalysts. Moreover, introduction of various compounds (C02, HCl) into reaction mixtures allows one to control the intensity and selectivity of the reactions. There are many reviews on the catalytic behavior of zeolites and even more original papers and patents. This review emphasizes the results, achievements, and trends which we consider to be most important. 

Most multipromoted catalysts have been described for the catalytic reforming of petroleum. For this process it is typical, that several reactions take place simultaneously dehydrogenation of cyclohexanes, dehydroisomerization of alkylcyclopentanes and dehydrocyclization of alkanes. Isomerization, hydrogenolysis, and hydrocracking are also involved in the process. 

The Influence of Chain Length in Hydrocracking and Hydroisomerization of w-Alkanes... 

It was found that hydroisomerization and hydrocracking of n-dodecane over the Pt/Ca-Y-zeolite require low reaction temperatures, a typical value being 275 °C (9). This temperature was chosen in the present work to investigate the influence of chain length on the reactivity of the n-alkanes. In Figure 1 the degree of overall conversion has been plotted versus the superficial... 

Figure 1. Hydroisomerization and hydrocracking of n-alkanes with different chain length (T — 275°C)...

According to Figure 5 a series of elementary reactions are involved in hydroisomerization and hydrocracking of n-alkanes. 

Literature on hydroisomerization of long chain alkanes > is very limited (2, 9,15,16) due to both analytical difficulties and the fact that hydrocracking predominates unless the bifunctional... 

Figure 7. Hydrocracking of n-alkanes with an even carbon number. Distribution of the cracked products.

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