Kinetic model, dehydrogenation

In the presence of dibenzyl, octahydrophenanthrene undergoes both dehydrogenation and isomerization. In this study, we use the kinetic model (refer to Figure 1 for structures) ... 

Grenoble, OUis, and coworkers—bifunctional formate mechanism and kinetic model involving formate formation on support, and dehydrogenation on metal. 

Table 5.9 Parameters in LHHW kinetic model for cyclohexanol dehydrogenation.

The Langmuir-Hinshelwood kinetic model describes a reaction in which the rate-limiting step is reaction between two adsorbed species such as chemisorbed CO and 0 reacting to form C02 over a Pt catalyst. The Mars-van Krevelen model describes a mechanism in which the catalytic metal oxide is reduced by one of the reactants and rapidly reoxidizd by another reactant. The dehydrogenation of ethyl benzene to styrene over Fe203 is another example of this model. Ethyl benzene reduces the Fe+3 to Fe+2 whereas the steam present reoxidizes it, completing the oxidation-reduction (redox) cycle. This mechanism is prevalent for many reducible base metal oxide catalysts. There are also mechanisms where the chemisorbed species reacts... 

Note that the mathematical form of the model implies that the rate-limiting step is a dual-site surface reaction between chemisorbed hydrogen and chemisorbed butyraldehyde, and that the reverse reaction is the monomolecular dehydrogenation of chemisorbed butanol. Models of this sort should not be overinterpreted from a mechanistic standpoint. Kinetics models are at best ambiguous indicators of mechanism in that several models typically fit the data equally well. 

A kinetic model for simultaneous activation and deactivation processes in solid catalysts has been applied to kinetic data obtained in isopropyl alcohol dehydrogenation on a Cu/Si02 catalyst. The influence of different catalyst pretreatments on the relevant kinetic parameters of the system has been investigated. 

Facile dehydrogenation is consistent with kinetic models derived from catalytic conversion studies of cyclohexane to benzene. These models predict an ensemble size for the active site of only one atom. On the other hand, surface science studies propose a model where several metal atoms, on the order of seven, are required, and suggest that specific orientation with respect to subsurface metal atoms is needed. Theoretical studies suggest that the key is to bring cyclohexane sufficiently close to the metal such that strong orbital overlap will occur. Small clusters may be even more effective than surfaces. Further experiments are needed to identify the chemical state of the products of the cluster reactions in order to connect the results with the surface science and catalysis results. 

Equation (2) explains the transient deactivation with a model describing reversible and irreversible coke. We can see that the partial pressure of propane in the reactor does not influence the deactivation. This has also been demonstrated in an earlier study of the same system [8]. This observation is consistent with kinetic models for propane dehydrogenation proposed by Loc et al. [13]. They suggested that the rate-determining step is the dissociative adsorption of propane. From this mechanism it follows that the deactivation will be... 

The kinetics of the ODH of n-butane has been investigated for unpromoted and cesium promoted a-NiMoOa catalysts. The reaction rates of dehydrogenation products as functions of the butane and oxygen partial pressures are described by a kinetic model based on the Mars and van Krevelen mechanism. The effects of Cs on the kinetic parameters can be interpreted on the basis of recently published results concerning the properties of those catalysts. 

The kinetic aspect common to all the topics discussed in this chapter is the pyrolysis reactions. The same kinetic approach and similar lumping techniques are conveniently applied moving from the simpler system of ethane dehydrogenation to produce ethylene, up to the coke formation in delayed coking processes or to soot formation in combustion environments. The principles of reliable kinetic models are then presented to simulate pyrolysis of hydrocarbon mixtures in gas and condensed phase. The thermal degradation of plastics is a further example of these kinetic schemes. Furthermore, mechanistic models are also available for the formation and progressive evolution of both carbon deposits in pyrolysis units and soot particles in diffusion flames. 

A Detailed Kinetic Model for the Hydrogenolysis, Isomerization and Dehydrogenation of n-Butane. 

A quantitative kinetic model, denominated TC4, for the catalytic conversion of n-butane is proposed. The model considers 56 elementary reactions, six of them were chosen to occur in heterogeneous phase. The TC4 model can be used to predict the product distribution and the heterogeneous rate constants for a wide range of conditions and on different catalyst types. The model can fit also the experimental data from the isobutane dehydrogenation reaction. A plot, that we have denominated "the graphic s performance of a catalyst", is proposed for the evaluation of the maximum yield of a catalyst with a minimum of experimental data. 

Kinetic model for the oxidative dehydrogenation (ODH) of ethane on a VO /y-AI2O3 catalyst suggested by Klose et ah, 2004a. 

Figure 16.21 Experimental composition obtained in the dehydrogenation of ethylbenzene and the corresponding fitting curves based on the kinetic models.

Hossain, M. M., Atanda, L., Al-Yassir, N., Al-Khattaf, S. (2012). Kinetics modeling of ethylbenzene dehydrogenation to styrene over a mesoporous alumina supported iron catalyst. Chemical Engineering Journal, 207—208, 308—321. 

The complex system of oxidative dehydrogenation that includes different types of reactions was modeled by a set of sixteen reactions. The kinetic model was tested in simulations of various operating conditions. Simulations indicated that staging of oxygen feed improve performance. Experimental data measured over a range of conditions was in good agreement with the model simulations. 

Lee WJ, Froment GF. Ethylbenzene dehydrogenation into styrene Kinetic modeling and reactor simulation. Industrial and Engineering Chemistry Research 2008 47 9183-9194. 

---