Cracking catalysts experimental procedures

We have used the CPAP technique in two unrelated deactivation investigations. The experimental procedures and analyses are tailored to the individual processes. We show the effect of temperature and coke level in the relative magnitudes of site suppression and pore choking in deactivation by coking during cumene cracking over a zeolite catalyst, and relate results to a simple physical model. For HT of CDL over a supported multimetal catalyst, we show that site suppression is the predominant mode of deactivation by deposition of carbonaceous and metallic materials, at least at large times on stream. 

A problem with monofunctional reactions, e.g., cracking, alkylation, etc. is that they have a tendency to quickly deactivate because of coke deposition. This problem is usually not of concern with bifunctional reactions, e.g., those that employ a metal function in addition to the acid sites. However, we avoided the use of metal function because of the possible unknown modifications that could be introduced to a given sample by the metal deposition procedure. This is especially important when dealing with samples like VPI-5. Thus, to minimize the rate of deactivation, the alkylation experiments were conducted at 463 K. This low temperature introduces another problem, namely, the adsorption of reactants and products. At the experimental conditions employed here, the catalyst bed becomes saturated at time of 10 minutes or less (depending on sample). From this point onward, deactivation is clearly observable via the decrease in conversion with time. The data reported here were obtained at 11-13 minutes on-line. Since meta-diisopropylbenzene proceeds through several reaction pathways that lead to a number of products, it is most appropriate to compare the catalytic data at the constant level of conversion. Here we report selectivities at approximately 25 % conversion. For each catalyst, the results near 25 % conversion were repeated three times to ensure reproducibility. 

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