Hydrocracking Reaction Kinetics

The usefulness of the of artificial neural networks as a modelling tool is apparent. A more general H-Oil product slate model can be developed by including the feed and catalyst properties. It can also easily be adapted to model the other aspects of the H-Oil process such the hydrotreating and hydrocracking reaction kinetics or coke lay down tendency in the separation units with the appropriate input and output patterns. 

One of the challenges in the EBR modeling is the evalnation of reliable physical parameters. The use of correlations is widely accepted however, for hydrocracking of heavy feedstocks at severe reaction conditions, there are no trustworthy correlations. The cost of the experimentation required for determination of kinetic parameters is quite high, and also the current analytical characterization techniques are sometimes limited to light petroleum fractions. Therefore, additional research is still needed to improve analytical techniques and experimental methodologies that permit proper determination of heavy oil hydrocracking reaction kinetics so that the EBR can be successfully modeled. 

The kinetics of hydrocracking reactions has been studied with real feedstocks and apparent kinetic equations have been proposed. First-order kinetics with activation energy close to 50 kcal/gmol was derived for VGO. The reactions declines as metal removal > olefin saturation > sulfur removal > nitrogen removal > saturation of rings > cracking of naphthenes > cracking of paraffins [102],... 

In view of the complicated reaction kinetics of multicomponent systems, it was not clear whether or not the diffusional effects would also affect the relative rate of conversion of feed molecules in a mixture. To answer this question we studied the hydrocracking of three multicomponent systems. The first was a C5-C8 mixture, a C5 360° C boiling range midcontinent reformate which contained 12.5 wt % n-paraffins including 4.2% n-pentane, 4.3% n-hexane, 2.9% n-heptane, l.l%n-octane, and <1% C9+ n-paraffins, with the remainder isoparaffins and aromatics. The reaction was carried out at 400 psig, 2 H2/HC, 2 LHSV, and 800°F. Secondly, a Cg-Cie mixture... 

The kinetic parameters (apparent activation energies, orders versus hydrogen and hydrocarbon) have been determined for all the isomerization and hydrocracking reactions of n-pentane and 2-methylbutane on a Pt/AljOj catalyst of low dispersion (10% Pt d = 90 A) 40). n-Pentane-2- C and 2-methylbutane-2- C were used to estimate the contributions of cyclic type and bond shift isomerization, respectively. As shown in Table II, the reactions... 

ABSTRACT. The amount of published work on molecular shape-selective catalysis with zeolites is vast. In this paper, a brief overview of the general principles involved in molecular shape-selectivity is provided. The recently proposed distinction between primary and secondary shape-selectivity is discussed. Whereas primary shape-selectivity is the result of the interaction of a reactant with a micropore system, secondary shape-selectivity is caused by mutual interactions of reactant molecules in micropores. The potential of diffusion/reaction kinetic analysis and molecular graphics for rationalizing molecular shape-selectivity is illustrated, and an alternative explanation for the cage and window effect in cracking and hydrocracking is proposed. Pore mouth catalysis is a speculative mechanism advanced for some systems (a combination of a specific zeolite and a reactant), which exhibit peculiar selectivities and for which the intracrystalline diffusion rates of reactants are very low. 

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... 

Kinetics and Mechanism. The hydrocracking reaction is catalyzed by the acid function following the )3-scission mechanism. The paraffin molecule is cracked approximately at a middle position therefore, the production of methane is very low. 

Sue and Sugiyama, Steinberg et al., and Mohanty et al. have written reviews of kinetic studies on hydrocracking reactions. In most of the cited literature, pure compounds or simple mixtures were processed in small isothermal reactors. For example, a publication by Rappaport reported that the rate of hydrocracking for pure normal paraffins increases as shown in Table 5. 

The simple kinetic model for coal liquefaction presented here appears to correlate well the experimentaHy observed effects of space time and temperature on coal solvation and the production of oils. The model must be refined further to account for hydrogen donor and hydrocracking reactions and to properly explain the effect of pressure on the liquefaction process. 

As in the case of other important reactions occurring in the conversion of petroleum fractions, e.g., catalytic cracking and hydrocracking, in the case of visbreaking lumping approach has been widely used for modeling reaction kinetics. Lnmped kinetics is used due to the complexity of visbreaking feed and prodnct, which makes... 

This chapter deals with the noncatalytic hydrodesulfurization (NHDS), hydrodemet-allization (NHDM), and hydrocracking (NHDC) of heavy crude oil and atmospheric residue. Some experiments were carried out in two different bench-scale units equipped with fixed-bed reactors in series operated in adiabatic and isothermal modes. The reactors were loaded with inert material (silicon carbide). Different feedstocks were used for the tests 13°API heavy crude oil, 21°API crude oil, atmospheric residue from the 13°API heavy crude oil, and atmospheric residue from the 21°API crude oil. The effects of pressure, residence time, temperature, and type of feed on noncatalytic reactions and axial reactor temperature profiles are examined. Reaction kinetics of the different noncatalytic reactions is studied by following the power-law approach. 

Catalytic and thermal reactions follow different reaction mechanisms therefore, different reaction orders would be expected. The vacuum residue conversion obtained with catalytic hydrocracking has been properly represented by second-order reaction kinetics (Sanchez and Ancheyta, 2007). Regarding the NHDC reaction, the following expressions can be derived as functions of vacuum residue conversion, kinetic parameters (n reaction order, k kinetic constant), the total mass flow, and the inert material volume ... 

For the case of feed and products of hydrocracking reaction, one property that can be used for the continuous kinetic lumping is the distillation curve data (data of boiling temperature versus weight fraction, wt, where temperature can be transformed into dimensionless temperature, 0). These data depend implicitly on the entities x, that is, 0 = 0(x ). Thus, any change in x entity can provoke a change in composition (wf(0, x)) given by... 

The experimental setup has been modeled as pseudohomogeneous one-dimensional reactor. The classical continuous kinetic model (Laxminarasimhan et al., 1996) was used for hydrocracking reactions thus, the mass balance into the reactor can be represented by an integrodifferential equation as in Equation 11.55. This equation and the following equations are similar to Equations 11.8 through 11.15 in which k has been replaced by 1 hdc (Elizalde and Ancheyta, 2012) ... 

Khorasheh, R, Zainali, H., Chan, E.C., Gray, M.R. 2001. Kinetic modeling of bitumen hydrocracking reactions. Petrol Coal 43 208-218. 

Valarasu, G., Bhaskar, M., Balaraman, K.S. 2003. Mild hydrocracking a review of the process, catalysts, reaction, kinetics and advantages. Petrol. Sci. Technol. 21 1185-1205. 

A single-event microkinetic description of complex feedstock conversion allows a fundamental understanding of the occurring phenomena. The limited munber of reaction families results in a tractable number of feedstock independent kinetic parameters. The catalyst dependence of these parameters can be filtered out from these parameters using catalyst descriptors such as the total number of acid sites and the alkene standard protonation enthalpy or by accounting for the shape-selective effects. Relumped single-event microkinetics account for the full reaction network on molecular level and allow to adequately describe typical industrial hydrocracking data. 

Kinetics studies of the hydrotreatment (and hydrocracking) of VR has led to the conclusion that most of the metals, sulfur and nitrogen removal takes place during the first 50% of the whole VR conversion [119-123], More than one reactor was needed for HDM and HDS of a Maya VR, when HDT is used as feed pretreatment [119,120], Although vanadium removal appears easier and faster than nickel removal, their kinetics results showed very similar values of the activation energy for the demetallization reactions [122],... 

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