Kerosenes, hydrocracking

Hydrocracking is the preeminent process for making high quality kerosene and diesel oil (Figure 10.10). 

The major goal of hydroconversion is the cracking of residua with desulfurization, metal removal, denitrogenation, and asphaltene conversion. The residuum hydroconversion process offers production of kerosene and gas oil, and production of feedstocks for hydrocracking, fluid catalytic cracking, and petrochemical applications. 

A flow diagram for a proposed shale oil refinery is shown in Figure 5. An FCC unit is used as the primary cracking process. This refinery produces high-octane gasoline and diesel fuel. Jet fuel also could be produced by severely hydrogenating a kerosene cut (10) from the whole-oil hydrotreater or by using a hydrocracker in place of the FCC. The... 

To remove sulfur, the kerosene and diesel sidecuts are fed to hydrotreaters or hydrodesulfurizers (HDSs). Light gas-oil is fed to a hydrocracker to convert it to diesel and lighter products. The HDS units and hydrocracker consume hydrogen supplied by the catalytic reformer and a hydrogen manufacturing plant. 

Traditionally,has been manufactured only from straight-run components, but in recent years, however, hydrocracking processes (Speight, 1999 Speight and Ozum, 2002) have been introduced that produce high-quality kerosene fractions ideal for jet fuel blending. 

Trickle bed reactors have grown rapidly in importance in recent years because of their application in hydrodesulfurization of naphtha, kerosene, gasoil, and heavier petroleum fractions hydrocracking of heavy gasoil and atmospheric residues hydrotreating of lube oils and hydrogenation processes. In trickle bed operation the flow rates are much lower than those in absorbers. To avoid too low effectiveness factors in the reaction, the catalyst size is much smaller than that of the packing used in absorbers, which also means that the overall void fraction is much smaller. 

The resistance to mass transfer inside the catalyst particle is dealt with as outlined in Chapters 3 and 11. In trickle bed hydrodesulfurization, the gas film resistance is practically zero, since the gas phase is mainly hydrogen. The liquid side and liquid-solid side resistances are negligible with respect to that inside the catalyst, since hydrogen is very soluble in the liquid. The effectiveness factor is generally around 0.5 to 0.6. An additional complication arises when a fraction of the liquid feed is vaporized, such as in hydrodesulfurization of light petroleum fractions (naphtha, kerosene) or in hydrocracking. In such a case the pores of the catalyst are filled with both liquid and vapor. The theory of the effectiveness factor for such a situation still has to be worked out. 

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