Hydrocracking ideal

Finally, note that hydrocracking is ideal for obtaining middle distillate cuts that can be used in jet fuel formulation. 

The products obtained from DPM cracking in the present work agree with the results from the literature, mentioned in the Introduction, which indicate that the reaction proceeds via carbocation formation on acidic sites. This implies that the decomposition of DPM does not need the successive intervention of two catalytic sites, like in the "ideal hydrocracking" mechanism. Only acidic sites are sufficient to carry out the reaction. The improved activity of the mixtures when compared to the pure phases must therefore be explained differently. 

Hydrocracking experiments under ideal conditions provided kinetics information characterizing the (3-scission step. On the basis of this work, a classification... 

This picture explains the great differences in product distributions of ideal hydrocracking and catalytic cracking. Furthermore, it is in agreement with the observation that carbon number distributions are similar in ideal hydrocracking of n-alkanes and in catalytic cracking of n-alkenes with the same carbon number (19). 

Ideal hydrocracking of alkanes requires a minimum of seven carbon atoms. This may be derived from Figure 9 in which distributions of the cracked products are compared that were gained with n-hexane (left hand side) and three of its higher homo-... 

No. 2 and 3 seem to be more appropriate to explain the finding that n-hexane is excluded from ideal hydrocracking. 

This is consistent with a most effective role of competitive chemisorption in ideal hydrocracking which minimizes the amount of secondary isomerization. 

The chain length of n-alkanes has a marked influence on reactivities for hydroisomerization, and especially for hydrocracking. To a very small extent a methane and ethane abstracting mechanism, probably hydrogenolysis as predicted in a basic work on bifunctional catalysis (14), is found to be superimposed when lower carbon number feeds (C, Cg, Cg) are used. n-Hexane is excluded from ideal hydrocracking. On the Pt/Ca-Y-zeolite catalyst it is cracked via a mechanism that is mainly hydrogeno-lytic. 

From a practical viewpoint ideal hydrocracking offers an utmost degree of product flexibility. However, as a consequence of the catalysts required contents of poisons in the feed materials such as sulfur and nitrogen compounds are strongly limited. 

The LTFT synthesis is ideally suited for the production of high-quality middle distillates (diesel and jet fuel) after hydrocracking of the long-chain waxes. The waxes themselves can be used as specialty waxes. Finally, the product contains naphtha, which is a feedstock for chemicals. 

Fig. 24. Typical examples of rearrangements of carbon-carbon bonds in isomerization and hydrocracking of paraffins over an ideal and bifunctional large-pore zeolite catalyst (297).

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