Hydrocracking catalysts kinetics

J.Coreila,A-Monzon,J.B.ButlrR.PlAt)S4l The modelling of the Kinetics of Deactivation of a Commercial Hydrocracking Catalyst in ihe Reaction of Cumene Disproportionation J.CatalysJs 100(1986)149... 

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. 

Kinetics is the study of the rates of reaction. The rates of reaction determine the key properties of a hydrocracking catalyst initial activity, selectivity, stability and product quality. The temperature required to obtain the desired product at the start of the run measures the initial activity. In general, the catalyst activity is a measure of the relative rate of feedstock conversion. In hydrocracking, activity is defined as the temperature required obtaining fixed conversion under certain process conditions. Hydrocracking conversion is usually defined in terms of change of endpoint ... 

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. 

In a detailed kinetic study, Sridhar and Ruthven [256], using nickel supported on Kieselghur (58% Ni), alumina (14% and 40% Ni) and silica-alumina (5% Ni), showed that over all four catalysts the rates of both hydrogenation and hydrocracking could be correlated according to the power rate law equation... 

A study is presented of the synthesis and properties of the novel synthetic zeolite omega. The synthesis variables and kinetics of formation are discussed, as well as the ion exchange, sorption, and thermal properties. By decomposition of imbibed tetra-methylammonium ions and exhaustive treatments of the zeolite with ammonium ions, a pure hydrogen form can be obtained which is a suitable substrate for the preparation of hydrocarbon conversion catalysts. Several catalysts were prepared and utilized to isomerize n-hexane, and to hydrocrack a heavy gas oil. 

In principle, all the kinetic concepts of intercalation introduced for layer-structured silicates hold for zeolites as well. Swelling, of course, is not found because of the rigidity of the three dimensional frame. The practical importance of zeolites as molecular sieves, cation exchangers, and catalysts (cracking and hydrocracking in petroleum industry) is enormous. Molecular shape-selective transport (large differences in diffusivities) and micro-environmental catalysis (in cages and channels)... 

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... 

Miller and Zakarian26 have studied the kinetics of the HDA (hydrofinishing) of hydrocracked and dewaxed 500Ns over noble, base metal, and nickel-tin catalysts, all on a silica-alumina base, at 15.3 MPa total pressure and at temperatures between 220°C and 260°C. The feedstocks employed contained trace quantities of sulfur (up to 19 ppm) and nitrogen (3 to 4 ppm). Since a correlation... 

C.W, Zielke and E. Gorin. Kinetics of Hydrocracking of Coal Extract with Molten Zinc Chloride Catalysts in Batch and Continuous Systems. lEC Proc. Des. Dev. (1969) 546. 

Castano P, Arandes JM, Pawelec B, Olazar M, Bilbao J. Kinetic modeling for assessing the product distribution in toluene hydrocracking on a Pt/HZSM-5 catalyst Industrial and Engineering Chemistry Research 2008 47 1043-1045. 

Catalytic reforming models developed by Kmak and Ramage et al. give a fairly detailed description of the process. In Powell s hydrocracking modeP, the chemical composition parameters are continuous functions of carbon numbers. Quann and Krambeck developed a kinetic model for olefin oligomerization over the ZSM-5 catalyst. 

For the saturation of aromatics in a hydrotreating or hydrocracking unit, equilibrium effects, which favor formation of aromatics, start to overcome kinetic effects above a certain temperature. This causes a temperature-dependent aromatics cross-over effect, which explains the degradation of important middle distillate product properties—including kerosene smoke point and diesel cetane number—at high process temperatures near the end of catalyst cycles. The cross-over temperature is affected by feed quality and hydrogen partial pressure, so it can differ from unit to unit. 

CaUejas, M.A. Martinez, M.T. Hydrocracking of a Maya Residue. Kinetics and Product Yield Distributions, Industrial Engineering Chemistry Research, 38 (9), 1999, 3285. Cooper, B.H. Knudsen, K.G. Ultra Low Sulfur Diesel Catalyst and Processing Options, NPRA Annual Meeting, Paper No. AM-99-06. 

The inspection of catalyst deactivation data from several commercial hydrocracking units reveals another possibility. Kinetic expressions derived from these data indicate with a mechanism in which two PAH condense to form a large PAH Figure 14). In the reactants have side chains, condensation may be accompanied by side-chain cracking. 

These results are interpreted as an influence of the liquid-vapour equilibrium leading to increased effective residence times of products. These residence times depend on the nature of the interface gas-solution or gas-liquid-solid. The contact time of the products with the active metal increases very rapidly with carbon number (e.g. 1 hour for octane in the liquid phase) due to the existence of a condensed phase solution or product in the pore structure of the catalyst. This effect, in addition to the corresponding increase in concentration of heavy hydrocarbons in the condensed phase, modifies the formal kinetic scheme of this complex reaction by the interference of secondary hydrocracking heavy hydrocarbons are converted to methane and linear or branched light hydrocarbons. The simulation of this kinetic network has led to selectivities in excellent accordance with the experimental results. 

A detailed study of many of the reactions is out of the scope of this work. We refer readers to Fromentet al. [10,11,12] for detailed experimental and mechanistic studies. These studies are very useful in the course of detailed catalyst design and kinetic network generation [15,16,17,18], However, neither of these topics is the subject of the current work. We present these reactions in the context of an integrated process model. As mentioned earlier in this work, the typical reactions in the reforming process are dehydrogenation, dehydrocyclization, isomerization and hydrocracking. Table 5.2 shows examples of these reaction classes. 

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