Hydrocarbon kinetic model

Dente and Ranzi (in Albright et al., eds.. Pyrolysis Theory and Industrial Practice, Academic Press, 1983, pp. 133-175) Mathematical modehng of hydrocarbon pyrolysis reactions Shah and Sharma (in Carberry and Varma, eds.. Chemical Reaction and Reaction Engineering Handbook, Dekker, 1987, pp. 713-721) Hydroxylamine phosphate manufacture in a slurry reactor Some aspects of a kinetic model of methanol synthesis are described in the first example, which is followed by a second example that describes coping with the multiphcity of reactants and reactions of some petroleum conversion processes. Then two somewhat simph-fied industrial examples are worked out in detail mild thermal cracking and production of styrene. Even these calculations are impractical without a computer. The basic data and mathematics and some of the results are presented. 

It is important to characterize FCC feeds as to their molecular structure. Once the molecular configuration is known, kinetic models can be developed to predict product yields. The simplified correlations above do a reasonable job of defining hydrocarbon type and distribution in FCC feeds. Each correlation provides satisfactory results within the range for which it was developed. Whichever correlation is used, the results should be trended and compared with unit operation. 

Figure 4. Effect of methane conversion for 1=5 mA on ethylene, ethane and total Cg hydrocarbon selectivity and yield. Lines from kinetic model discussed below. Solid lines CgH j and C2Hg Dashed lines C2...

In the gas phase, the reaction of O- with NH3 and hydrocarbons occurs with a collision frequency close to unity.43 Steady-state conditions for both NH3(s) and C5- ) were assumed and the transient electrophilic species O 5- the oxidant, the oxide 02 (a) species poisoning the reaction.44 The estimate of the surface lifetime of the 0 (s) species was 10 8 s under the reaction conditions of 298 K and low pressure ( 10 r Torr). The kinetic model used was subsequently examined more quantitatively by computer modelling the kinetics and solving the relevant differential equations describing the above... 

Backman, H., Arve, K., Klingstedt, F. et al. (2006) Kinetic considerations of H2 assisted hydrocarbon selective catalytic reduction of NO over Ag/Al203 Kinetic modelling, Appl. Catal. A 304, 86. 

The kinetic model describes the carbanion polymerization of styrene in a hydrocarbon solvent using n-butyl lithium as the initiator. The mechanism is characterized by four steps ... 

However, the detailed description of the FT product distribution together with the reactant conversion is a very important task for the industrial practice, being an essential prerequisite for the industrialization of the process. In this work, a detailed kinetic model developed for the FTS over a cobalt-based catalyst is presented that represents an evolution of the model published previously by some of us.10 Such a model has been obtained on the basis of experimental data collected in a fixed bed microreactor under conditions relevant to industrial operations (temperature, 210-235°C pressure, 8-25 bar H2/CO feed molar ratio, 1.8-2.7 gas hourly space velocity, (GHSV) 2,000-7,000 cm3 (STP)/h/gcatalyst), and it is able to predict at the same time both the CO and H2 conversions and the hydrocarbon distribution up to a carbon number of 49. The model does not presently include the formation of alcohols and C02, whose selectivity is very low in the FTS on cobalt-based catalysts. 

Kravtsov, A.V., Moizes, O.E., Usheva, N.V., and Yablonskii, G.S. 1988. Kinetic model for hydrocarbon synthesis from CO and H2 accounting for its intragroup distribution. React. Kinet. Catal. Lett. 36 201-6. 

Westbrook, C.K. and Dryer, F.L., Chemical kinetic modeling of hydrocarbon combustion, Prog. Energy Combust. Sci., 1984, 10, 1-57. 

Dunn, I. J. (1968). An interfacial kinetics model for hydrocarbons oxidation, Biotechnol. Bioeng., 11, 467—487. 

A.T., Olozar, M., Bilbao, J., Kinetic modelling of the transformation of aqueous ethanol into hydrocarbons on a HZSM-5 zeolite, Ind. Eng. Chem. Res., 2001, 40, 3467. 

De Visscher, A., Van Eenoo, P., Drijvers, D., and Van Langenhove, H. Kinetic model for the sonochemical degradation of monocyclic aromatic hydrocarbons in aqneons solntion, J. Phys. Chem., 100(28) 11636-11642, 1996. 

To illustrate these issues better, the pressure at the center of fall-off (F ) is presented in Fig. 20. As seen from this figure, the unimolecular decompositions of small molecules are at their low-pressure limits at atmospheric pressure, and at process temperatures, = feo [M]- Decompositions of larger molecules, on the other hand, are closer to their high-pressure limits. It is important to recognize that the unimolecular decompositions of hydrocarbons from CH4 to CaHg exhibit differing degrees of fall-off under process conditions, and this must be properly accounted for in the development of accurate detailed chemical kinetic models. 

Willems, P, A., and Froment, G. F., Kinetic modeling of the thermal cracking of hydrocarbons. 

For SR of higher hydrocarbons, Rostrup-Nielsen " and Tottrup " postulated a Langmuir-Hinshelwood-Houghen-Watson (LHHW) kinetic model. It was assumed that the hydrocarbon chemisorbs on a dual catalytic site, followed by successive a-scission of the C-C bond. The resulting Ci species react with adsorbed steam to form H2 and CO. The expressions were lit to data for SR of n-Cv on a Ni/MgO catalyst at 500°C the overall rate expression is " " ... 

Recently, Praharso et al also developed a Langmuir-Hinshelwood type of kinetic model for the SR kinetics of i-Cg over a Ni-based catalyst. In their model, it was assumed that both the hydrocarbon and steam dissociatively chemisorb on two different dual sites on the catalyst surface. The bimolecular surface reaction between dissociated adsorbed species was proposed as the ratedetermining step. The following generalized rate expression was proposed ... 

In this section we shall discuss the development of a global kinetic model for DOC. The basic model reactions considered in the DOC model are summarized in Table II. Here the real HC mixture is modeled by two characteristic hydrocarbons—propene and decane. Propene represents more reactive, light hydrocarbons, which practically do not adsorb during cold start, while decane is a representative of heavier hydrocarbons with significant adsorption on... 

This type of rate law is employed in the global DOC kinetic model given in Table II (cf. reaction R5). A typical evolution of the outlet NOx concentration in the course of a slow temperature ramp is shown in Fig. 14. From this type of experiment, the selectivity and inhibition constants A(7) are evaluated, considering exponential temperature dependence, Eq. (36). Again, simpler HC + 02 + NO reaction mixtures with single hydrocarbon are examined first, followed by more complex inlet gas compositions. 

The replenishment of the vacancy can be directly from the gas phase or indirectly from the catalyst. In the latter case, the oxygen mobility within the catalyst is so large that bulk oxygen can diffuse to the vacancy. Then oxygen from the gas phase reoxidizes the lattice on sites which differ from hydrocarbon reaction sites. In a steady state, the rate of catalyst oxidation will be equal to the rate of reduction by the substrate. The steady state degree of reduction, equivalent to the surface coverage with oxygen, is determined by the ratio of these two rates. Kinetic models based on these principles are called redox models, for which the simplest mathematical expression is... 

P. Glarborg, M.U. Alzueta, K. Dam-Johansen, and J.A. Miller. Kinetic Modeling of Hydrocarbon/Nitric Oxide Interactions in a Flow Reactor. Combust. Flame, 115 1— 27,1998. 

E. Ranzi, M. Dente, A. Goldaniga, G. Bozzano, and T. Faravelli. Lumping Procedures in Detailed Kinetic Modeling of Gasification, Pyrolysis, Partial Oxidation, and Combustion of Hydrocarbon Mixtures. Prog. Combust. Sci. Techn., 27 99-139, 2001. 

One exception [124] claims that, for the description of the experimental data obtained at high pressures, it is not necessary to change the kinetic model constructed on the basis of the data obtained at 10 8 to 10 7 Torr. (Only the activation energy for the CO desorption was decreased from 34 to 24.5 kcalmol 1.) This claim does not seem to be confident since the discussed kinetic model was only a unit in the model for the catalytic re-oxidation of CO and hydrocarbons. Experimental and calculated data were only compared on the basis of the observed values, i.e. temperature and the amount of unreacted CO in the output. 

Beltran FJ, Rivas FJ, Alvarez P, Alonso MA, Acedo B. A kinetic model for advanced oxidation processes of aromatic hydrocarbons in water application to phenanthrene and nitrobenzene. Ind Eng Chem Res 1999 38 4189-4-199. 

---