We have used the hydrogenation of α-methylstyrene in a trickle bed reactor to understand its performance and mechanism. This study emphasizes two steady-state possibilities for such a reactor; one is predictable if we suppose that the reaction rate is limited by mass transfer in the film of liquid trickling on the uniformly wetted catalyst pellets; the other can be explained if the reaction takes place on partly wetted pellets. We also show that the role of the liquid is essential to maintain the catalyst activity by dis solving polymers. This could explain a novel experimental obser vation: a cyclic evolution of the catalyst activity related to the alternative operation of the pellets in gaseous and in liquid phases.T he chemical and petrochemical processes using three-phase reactors are as numerous as they are important. Among these reactors, the trickle bed is one of the most interesting. It offers several advantages over the other threephase reaction vessels: large size apparatus is easily constructed, and the cost of operation is low compared with a stirred tank slurry reactor. For these reasons, the trickle bed reactor is frequently used in the petroleum industry, especially for hydrotreating heavy distillates (hydrocracking, hydrodesulfurization, etc.) (I). Such processes are expanding rapidly at present. On the other hand, the trickle bed reactor also presents some advantages over the fixed bed reactor operating in the vapor phase because it reduces the recirculation of great amounts of the lighter reactants (hydrogen in hydrotreating processes).However, despite the frequent use of the trickle bed reactor in large industrial plants, little is known about its mechanisms. Since the design of such a reactor and the prediction of its performance are still extremely difficult problems for the chemical engineer, several studies have recently been done. Most of these, however, are theoretical (2, 3) or consider only the physical aspects such as pressure drop, fluid holdups, fluid residence time distributions, and hydrodynamic models. (A review of previous work has been reported by Way in 1971 (4), and by Charpentier et al. in 1972 (5).) Little experimental data have been published on the chemical aspects of the operation of the trickle bed reactors. Except for the studies by Satterfield and co-workers {6,7) 164 Downloaded by UNIV LAVAL on December 1, 2014 |

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