Hougen-Watson kinetics,

Examples of Hougen-Watson kinetic models, which are also called Langmuir-Hinshelwood models, can be derived for a great variety of assumed surface mechanisms. See Butt and Perry s Handbook (see Suggestions for Further reading in Chapter 5) for collections of the many possible models. The models usually have numerators that are the same as would be expected for a homogeneous reaction. The denominators reveal the heterogeneous nature of the reactions. They come in almost endless varieties, but all reflect competition for the catalytic sites by the adsorbable species. 

Butt and Petersen (1988) extended the Langmuir—Hinshelwood—Hougen—Watson kinetics to involve the varying activity (as a result of catalyst deactivation with time) to describe... 

The results can be interpreted in terms of Langmuir-Hinshelwood-Hougen-Watson kinetics. Styrene adsorbs more strongly than octenes and, as a consequence, only after styrene has been converted does the formation of octanes proceed at a high rate. The... 

Exemplary results of modeling processes inside the catalytic layer are presented in Fig. 9. The solid lines show the dependency of the overall effectiveness factor on the relative distribution of the catalyst between the comers and the side regions. The two cases represent two levels of the first-order rate constants, with the faster reaction in case (b). As expected, the effectiveness factor of the first reaction drops as more catalyst is deposited in the comers. The effectiveness factor for the second reaction increases in case (a) but decreases in case (b). The latter behavior is caused by depletion of B deep inside the catalytic layer. What might be surprising is the rather modest dependency of the effectiveness factor on the washcoat distribution. The explanation is that internal diffusion is not important for slow reactions, while for fast reactions the available external surface area becomes the key quantity, and this depends only slightly on the washcoat distribution for thin layers. The dependence of the effectiveness factor on the distribution becomes more pronounced for consecutive reactions described by Langmuir-Hinshelwood-Hougen-Watson kinetics [26]. 

Figure 3. Effectiveness factor versus Thiele modulus at various times of poisoning (Hougen-Watson kinetic model for benzene hydrogenation).

The data fit obtained when benzene hydrogenation is represented by Hougen-Watson kinetic model is poor the results are complicated by changes in equilibrium adsorption constants with extent of poisoning. 

Skrzypek el al. mode (19H5) Skrzypek el al. (1985) developed this model based on the Langmuir-Hinshelwood-Hougen-Watson kinetic model to explain the non-monotonic behaviour observed by Calder-bank (1974). They suggested that the reaction rate behaviour can be related to the Langmuir-Hinshelwood kinetic model for bimolecular reactions, where the surface reaction between o-Xylene and oxygen chemisorbed on the active centers is the rate determining step. The rate of appearance of various components can be written as ... 

Effectiveness factor versus an inappropriate Thiele modulus in a slab Hougen-Watson kinetics. . . . . , , . 384. 

We use the collocation method to solve the next example, which involves five species, two reactions with Hougen-Watson kinetics, both diffusion and external mass-transfer limitations, and nonconstant fluid temperature, pressure and volumetric flowrate. 

Exercise 7.5 Thiele modulus and Hougen-Watson kinetics... 

Consider the Hougen-Watson kinetics of Section 7.4.4. Using Equation 7.58, verify the foEowing limits... 

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