Hydrocracking definition

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. 

In ebullating bed reactor, such as the H-coal process, Ni-Mo or Co-Mo alumina catalysts have been used (96). The catalyst definitely improves the oil yields by accentuating aromatic hydrocracking, achieving conversions around 95% at catalyst make-up rates of 1 3%. 

During the last decade, there has been a definite trend towards heavier hydrocracker feedstocks (2). Recognition of the interactions between feed molecular weight and catalyst chemical and physical properties has been necessary to support this trend. 

The values defined in this manner do not represent any probability for rupture of definite carbon-carbon bonds in the feed molecule. This term is meaningless if rearrangement of the carbon skeleton precedes the cracking step. Rather, the values indicate the probability of an n-alkane for being hydrocracked according to the overall cracking reaction in question. These probabilities are useful for a comparison with the relative concentrations of the products formed by hydroisomerization (cf. Table IV). 

The mechanistic background for such a comparison is illustrated in Figure 10 which represents in more detail the pathway of hydroisomerization and hydrocracking of two n-alkanes. Branched carbenium ions are formed via n-alkenes and linear carbenium ions. Then, either desorption or (3 -scission may occur in parallel reactions. Desorption (followed by hydrogenation) of a given carbenium ion yields an iso-alkane with the same carbon skeleton. f3 - scission, on the other hand, yields fragments of definite carbon numbers ( (3 -scissions which would yield or C2... 

While the definitions of the various hydroprocesses are (as has been noted above) quite arbitrary, it may be difficult, if not impossible, to limit the process to any one particular reaction in a commercial operation. The prevailing conditions may, to a certain extent, minimize, cracking reactions during a hydrotreating operation. However, with respect to the heavier feedstocks, the ultimate aim of the operation is to produce as much low-sulfur liquid products as possible from the feedstock. Any hydrodesulfurization process that has been designed for application to the heavier oils and residua may require that hydrocracking and hydrodesulfurization occur simultaneously. 

On the other hand, the results for demetallation, i.e., V and Ni removal, and asphaltenes reduction for both catalysts revealed definite improvements. The improvements for V and Ni removal are on the order of 8-10% and 15-20%, respectively. Similarly, the results presented in Figure 1 show that the presulfided catalyst is more active than the unsulfided catalyst by around 5-10% towards asphaltenes reduction. For hydrocracking, the NiMo/AI2O3 catalyst exhibited around 15% higher conversion for the presulfided catalyst over the untreated catalyst. 

The maximum of the weight loss rate, DTG, is a useful indicator for the reaction kinetics at the corresponding temperatures, T. Below 400 °C represents the kinetics of substance transportation, whereas above 400 °C, it represents the reaction kinetics of pyrolysis. The DTG of 5.3 %/min with a T. of 460 °C for the vacuum residue definitely lies in the reaction kinetic region. The products from hydrocracking experiments exhibit DTG peak maxima at very varying temperatures, and sometimes there is more than one maximum. In Table 4-126 the values of the DTG maxima are hsted and associated with the... 

Solvent deasphalting takes advantage of the fact that aromatic compounds are insoluble in paraffins. Propane deasphalting is commonly used to precipitate asphaltenes from residual oils. Deasphalted oil (DAO) is sent to hydrotreaters, FCC units, hydrocrackers, or fuel-oil blending. In hydrocrackers and FCC units, DAO is easier to process than straight-run residual oils. This is because asphaltenes easily form coke and often contain catalyst poisons such as nickel and vanadium, and the asphaltene content of DAO is (by definition) almost zero. 

In the case of the hydrocracked liquid product, it is complicated to determine the heaviest representative hydrocarbon to define the highest possible boiling point [TBP(h)] since the experimental distillation method is limited to 538°C. Thus, a TBP(h) value needs to be assumed. Once TBP(l) and TBP(h) have been established the dimensionless temperatures are calculated with Equation 11.9. The definition of the TBP(h) sounds arbitrary at first. We indeed know that the... 

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