Hydrocracking of Heavy Oils

K. Aimoto, I. Nakamura and K. Fujimoto. Transfer hydrocracking of heavy oil and its model compound. Energy and Fuels, 5, 739-744 (1991). 

Martfnez J, Sdnchez JL, Ancheyta J, Ruiz RS. A review of process aspects and modeling of ebullated bed reactors for hydrocracking of heavy oils. Catal. Rev. Sci. Eng. 2010 52 60-105. 

The catalytic hydrocracking of heavy oil has been well represented by the five-lump kinetic model shown in Figure 6.15 (Sdnchez et al., 2005). Although catalytic and thermal reactions follow different mechanisms, the same kinetic model was used to represent the NHDC. Hydrocracking of vacuum residue was assumed to follow second order as demonstrated earlier, while first order was considered for the other reactions. The reaction rate (r for each lump as a function of the product composition (y and the corresponding kinetic constant k is as follows ... 

FIGURE 6.15 General reaction network for catalytic hydrocracking of heavy oils. 

FIGURE 6.17 Proposed reaction scheme for thermal hydrocracking of heavy oils. 

Sanchez, S., Rodriguez, M.A., Ancheyta, J. 2005. Kinetic model for moderate hydrocracking of heavy oils. Ind. Eng. Chem. Res. 44 9409-9413. 

The EBR technology utilizes a three-phase system, which, in the case of hydrocracking of heavy oil fractions, is composed by gas (mainly hydrogen and partially vaporized hydrocarbons), liquid (the nonvaporized heavy portion of the hydrocarbon feed), and solid (the specially designed catalyst whose physical properties lead to fluidizing within the reactor). Schematic representations of EBRs are shown in Figure 10.1. 

In this section, a five-lump kinetic model and a time-dependent nonselective catalyst deactivation expression are used to represent the reactions occurring during hydrocracking of heavy oils. 

By using the continuous kinetic lumping model for modeling the kinetics of hydrocracking of heavy oils, a reaction order of 1 is assumed for all the pseudocomponents. Hence, for each pseudocomponent, a reaction rate or reactivity is necessary. Thus, a number of reaction rates are present, which in turn generates a distribution of these rates, as given by Equation 11.17. 

Constant B of Equation 11.54, which describes the effect of temperature, is almost twofold that of pressure (constant C) for the three model parameters (a, Uq, and 5). Such values corroborate the statement that the effect of pressure is lower than that of temperature on hydrocracking of heavy oil. When pressure is changed, some physicochemical properties of the reacting system, such as density, viscosity, etc., change, which in turn affect molecular diffusivity of the gas and liquid. Gas formation is enhanced as the pressure is increased however, its effect on fluid dynamics is partially counterbalanced by the great excess of hydrogen, which dominates the gas phase for the hydrodynamics. Hence, not only purely kinetic aspects are involved in the correlation of the parameters of the continuous kinetic model with pressure and temperature, but thermodynamics and hydrodynamics effects of the liquid-gas mixture are also hidden in these parameters. 

Elizalde, L, Ancheyta, J. 2011. On the detailed solution and application of the continuous kinetic lumping modeling to hydrocracking of heavy oils. Fuel 90 3542-3550. 

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