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Catalytic Hydrocracking. The advantages of hydrocracking include its ability to handle a wide range of feedstocks that may be difficult to process by catalytic cracking and its flexibility in selectivity between light and middle distillates. The principal objective of hydrocracking is to decrease the molecular weight and boiling point. The main advantages of hydrocracking process are: its flexibility with respect to production of gasoline and middle distillates, quality of its products; ability to handle a wider range of feedstock like cycle oils from other cracking units. The reaction of desulphurisation, denitrogenation and de-oxygenation.

For technical reasons, hydrocracking was only made possible in the late Fifties of the last century. In this process, catalytic cracking is carried out in an atmosphere of hydrogen (300 - 500 m 3 hydrogen per ton of hydrocarbon) with the advantage that impurities, such as sulfur and nitrogen, can be removed from the product easily as hydrogen sulfide and ammonia, respectively. Hydrocracking does not generate any alkenes because hydrogen reacts with the generated forming alkanes with low boiling points instead. Reaction conditions in the hydrocracking process are very drastic with pressures of 80 - 200 bar and temperatures in the range of 270 - 450 °C. The single-stage process employs bi-functional systems consisting of metal sulfides (cobalt, molybdenum and nickel) and aluminum oxide as catalysts.

The disadvantages of this process are moderate yields ( ca. 60%) and very small fractions. Additionally, the activity of the catalysts is lowered by the ammonia formed in the process. To circumvent these problems, a multi-stage process has been developed in which the undesired by-products, ammonia and hydrogen sulfide, are removed in a special reactor before entering the actual cracking process.