Kinetic hydrocracking

Because the pore dimensions in narrow pore zeolites such as ZSM-22 are of molecular order, hydrocarbon conversion on such zeolites is affected by the geometry of the pores and the hydrocarbons. Acid sites can be situated at different locations in the zeolite framework, each with their specific shape-selective effects. On ZSM-22 bridge, pore mouth and micropore acid sites occur (see Fig. 2). The shape-selective effects observed on ZSM-22 are mainly caused by conversion at the pore mouth sites. These effects are accounted for in the hydrocracking kinetics in the physisorption, protonation and transition state formation [12]. 

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. 

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],... 

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],... 

Hydrocracking experiments under ideal conditions provided kinetics information characterizing the (3-scission step. On the basis of this work, a classification... 

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... 

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... 

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)... 

Sugioka and Aomura (133) provide kinetic evidence indicating that the rate-determining step in the hydrocracking of aliphatic sulfur compounds over silica-alumina is catalyzed by Brdnsted acid sites. Conversions of reactants were measured by use of a pulse reactor hydrogen was used as the carrier gas. They found that reactivities of mercaptans are in the following order ... 

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. 

Froment, G.F. Kinetic modeling of complex processes. Thermal cracking and catalytic hydrocracking. In Chemical Reactor Technology for Environmentally Safe Reactors and Products, de Lasa, H.I, Dogu, G., Ravella, A., Eds. Kluwer Academic Publishers Dordrecht, 1992 409-424. 

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... 

K-Hexadecane was chosen as model molecule since it is relatively easy to implement and obtain as a pure body. Its reaction network non-exhaustive on Fig. 29—is representative since it includes all the elementary steps involved in the hydrocracking/hydroisomerisation of heavy paraffinic cuts. After reduction, just six kinetic parameters (two for isomerisation, four for cracking) are required to represent this type of network. 

Baltanas, M. A., Van Raemdonck, K. K., Froment, G. F., and Mohedas, S. R., Fundamental kinetic modeling of hydroisomerisation and hydrocracking on noble-metal-loaded Faujasites 1 Rate parameters for hydroisomerisation, Ind. Eng. Chem. Res. 28, 899-910 (1989). 

Kodera, Y., Kondo, T., Isaito, S. Y., and Ukegawa, K., Continuous-distribution kinetic analysis for asphaltene hydrocracking, Energy Fuels 16, 291-296 (2000). 

Martens, G. G. Hydrocracking on Pt/US-Y zeolites Fundamental kinetic modeling and industrial reactor simulation , PhD Thesis, Ghent University (2000). 

---