Phenol Hydrogenation to Cyclohexanone

In general, a reaction kinetics following a LHHW model is suitable, but the identification of parameters remains demanding. For some catalysts power-law models may be appropriate, for others not. For example, reaction orders identical with stoichiometric coefficients were suitable for Pd/Al203 doped with different metals. On the contrary, for Pd/MgO reaction orders with respect to phenol ranging from -0.5 to 0.5 were observed [17]. However, the bibliographic search was not able to find a quantitative kinetic model for Pd-type catalysts suitable for reactor design. 

In this project, we make use of platinum-type catalyst on silica gel. Although this is less selective than more modem palladium-based catalysts, kinetic data are available in the literature as an LHHW model [2], better suited for flexible reactor design. The reaction rate equations are  

In the above equations the symbols A, B, C, D designate phenol, hydrogen, cyclohexanone and cyclohexanol. Table 5.7 presents the model parameters at 423 K and 1 atm. The model takes into account the effect of the products on the reaction rate in the region of higher conversion. This feature is particularly useful for describing the product distribution in consecutive catalytic-type reactions. Note that the adsorption coefficients are different in the two reactions. Following the authors, this assumption, physically unlikely, was considered only to increase the accuracy of modeling. 

The above kinetics is valid for small particles when the process rate is controlled by the chemical reaction at the surface. Diffusion effects should be accounted for large-size particles. Table 5.8 presents the calculation of the effectiveness factor [24] for spherical particles of 6 mm diameter and a mixture 1 3 phenol/hydrogen at 2 bar and 423 K. Other data are BET internal surface S = 40m2/g, mean pore radius 150 A, catalyst density pp = 1000kg/m3, particle void fraction = 0.3, 

Observations a kinetic data at 423 K and 1 bar b Arrhenius-type expression for 1,. 

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