Studies on deactivation of cracking catalysts by coke deposition started with the work by Voorhies (1) in 1945, in which coke formation in both, fixed and fluidizxed beds, is expressed by an empirical relation in terms of time on stream, i.e., Coke=At~n. This expression was applied to different types of feedstocks, catalysts and reaction conditions, in terms of parameter A. Since then, this kind of expression, together with the use of lumps, has been employed in FCC reactor modeling works from industry and academia (2-4), and most of the research associated with these studies has been oriented towards the generalization of this type of empirical expression. This idea has also been applied to analyze experiments from micro-activity reactors, either for catalyst evaluation, translation of information between MAT, pilot and industrial units, or for kinetic parameter estimation (5-6). However, what could be convenient for reactor modeling, simulation and control pruposes, is not necessarily useful for improving the understanding of the complex phenomena of coke formation nor is it useful for evaluating catalyst performance. Froment (7, 8) has called attention to the idea that deactivation by coke deposition should be directly related to coke itself, and not to time. This is particularly important when catalyst evaluation using laboratory scale reactors is the main objective. Another aspect that is lacking, is the study of the interactions between active sites, cracking reactions, coke deposition and transport phenomena, which may become very important in assessing catalyst performance.
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