The present study investigates the effects of the changes of the catalyst to feedstock ratio (C/O) on FCC cracking using a Y-zeolite-based catalyst. Experiments are developed in a CREC Riser Simulator. This bench-scale mini-fluidized batch unit mimics the operating conditions of large-scale FCC units as follows: It uses temperatures ranging from 510 to 550 °C and reaction times from 3 7 s. For every experiment, 0.2 g of 1,3,5-TIPB is contacted with a 0.12–1g catalyst amount. This is done to achieve a C/O ratio in the range of 0.6–5. Experiments show the effects of increasing the C/O ratio on 1,3,5-TIPB conversion, coke formation, and product selectivity. On this basis, a mechanism involving single catalyst sites for cracking and two sites for coke formation is considered. Coke formation is postulated as an additive process involving coke precursor species, which are either adsorbed on sites in the same particle or adsorbed in close sites in different particles. The proposed mechanism helps explain the results obtained, introducing a rationale for the selection of optimum C/O ratios to yield the highest possible 1,3,5-TIPB conversions with controlled amounts of coke formation. It is anticipated that the findings of this study will have a significant influence on the selection of an optimum C/O ratio for the design and operation of the most advanced FCC risers and downers.

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The present study is a follow-up to a recent authors contribution which describes the effect of the C/O (catalyst/oil) ratio on catalytic cracking activity and catalyst deactivation. This study, while valuable, was limited to one fluidized catalytic cracking (FCC) catalyst. The aim of the present study is to consider the C/O effect using three FCC catalysts with different activities and acidities. Catalysts were characterized in terms of crystallinity, total acidity, specific surface Area (SSA), temperature programmed ammonia desorption (NH3-TPD), and pyridine chemisorption. 1,3,5-TIPB (1,3,5-tri-isopropyl benzene) catalytic cracking runs were carried out in a bench-scale mini-fluidized batch unit CREC (chemical reactor engineering centre) riser simulator. All data were taken at 550 °C with a contact time of 7 s. Every experiment involved 0.2 g of 1,3,5-TIPB with the amount of catalyst changing in the 0.12–1 g range. The resulting 0.6–5 g oil/g cat ratios showed a consistent 1,3,5-TIPB conversion increasing first, then stabilizing, and finally decreasing modestly. On the other hand, coke formation and undesirable benzene selectivity always rose. Thus, the reported results show that catalyst density affects both catalyst coking and deactivation, displaying an optimum C/O ratio, achieving maximum hydrocarbon conversions in FCC units.

The present study establishes the suitability of a kinetic model for the catalytic cracking of 1, 3, 5‐triisopropylbenze (TIPB) using the data obtained in the Chemical Reactor Engineering Centre (CREC) Riser Simulator. The postulated kinetic model accounts for both the TIPB and the various major products formed experimentally, such as: 1, 3‐diisopropylbenzene, isopropylbenzene, benzene, propylene, and coke. It is proven that the proposed kinetics is suitable to describe the chemical concentration changes in a CREC Riser Simulator at various reaction times, partial pressures, temperatures, and C/O (catalyst/feedstock) ratios. It is demonstrated that the proposed kinetics simulates well the experimental data from the CREC Riser Simulator, including an experimentally observed C/O optimum ratio. It is anticipated that this type of kinetic model, accounting for intrinsic kinetics, coke deactivation, and diffusional phenomena, could have significant value in establishing the influence of catalyst solid fluxes, at set hydrocarbon feed fluxes, in both industrial riser and downer fluid catalytic cracking (FCC) units.

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