Modelling the kinetics of fast catalytic cracking reactions

Abstract

Instantaneous kinetic constants and gasoline selectivities have been determined for catalytic cracking of n‐hexadecane. The pulse technique was used in order to model the sequential build‐up of coke which occurs on cracking catalyst within a riser transport‐line reactor. The total amount of hydrocarbon injected per unit weight of catalyst was between 0 and 10. The mathematical model used to analyze the data was based on the unsteady state mass balance of the microcatalytic reactor with the assumption of plug flow. Results suggest a fast deactivation process during the run with fresh catalyst, while regenerated catalyst showed a slower deactivation. The catalyst regenerated three times evidenced a low apparent activation energy when temperature was increased from 500°C to 550°C.

Fast catalytic cracking of heavy gas oils: modeling coke deactivation

“…From the runs with GX-30 a lower activation energy, 25.3 ± 3.8 kJ/mol, was obtained. Low energies of activation may point, as stated by Chen and Lucki (1986) and Collyer et al (1988), toward intraparticle diffusional limitations in the GX-30 catalyst. It has to be pointed out that this low energy of activation is consistent with values obtained by Kraemer and de and Collyer et al (1988).…”

“…The exponential terms for the stronger active sites, having the bigger decay coefficients, should have a dominant effect for the first few seconds of catalyst time-onstream. Following this, the stronger sites will be coked and the weaker sites will dominate the catalyst operation both in terms of conversion, selectivity to gasoline, and coke fermentation (Collyer et al, 1988). Considering these facts, there is a definite possibility that a single exponential corresponding to the change of activity for the stronger sites could correlate very well the changes of catalytic activities in a riser unit (Kraemer and de Lasa, 1988).…”

“…0888-5885/90/2629-0171102.50/0 1969a,b, 1970; Corella et al, 1985; Habib et al, 1977;Forzatti et al, 1984;Szepe and Levenspiel, 1971;Fuentes, 1985; Weekman, 1968Weekman, ,1979Voltz et al, 1971;Jacob et al, 1976;Collyer et al, 1988). Because bench-scale reactors usually used for these experiments are designed for collecting data for large values of catalyst time-on-stream (1 min or higher), only a few points are normally measured before the first minute.…”