291597 Separation of Catalyst Kinetics for Maximizing Gasoline Output, Yield, and Selectivity: A Computational Solution to Catalytic Cracking

Monday, October 29, 2012
Hall B (Convention Center )
Joshua Lansford, Chemical Engineering, University of Virginia, Charlottesville, VA, Dariusz Orlicki, W. R. Grace & Co., Columbia, MD and George M. Bollas, Department of Chemical & Biomolecular Engineering, University of Connecticut, Storrs, CT

The objective of this work is to develop a predictive model for fixed bed and fluid catalytic cracking (FCC) by creating reliable kinetic parameters for a multicomponent catalyst system.  The catalytic cracking unit of a refinery is fed both atmospheric and vacuum distilled gas oil.  The FCC unit uses a zeolite based catalyst at high heat to crack long carbon chains of heavy gasoil into lighter, valuable products.  The zeolite is dispersed throughout an alumina silicate matrix with clay binder.  The heavy carbon molecules adsorb onto the catalyst, lowering the activation energy required to crack the hydrocarbons, while allowing only specific reactions due to the shape selectivity of the zeolite micropores.  Due to coke formation and consequently catalyst deactivation, catalyst is regenerated by burning the deposited coke byproduct. The heat of the catalyst regeneration also provides the necessary energy required for the endothermic cracking reactions. The FCC catalysts consist of microporous zeolite, and macroporous support at various weight or surface area fractions. Each component of the catalyst contributes differently to the selectivity of the process towards valuable products such as gasoline, light cycle oil, liquid petroleum gas and less valuable byproducts such as dry gas and coke. Moreover, in industrial applications blends of catalysts of different compositions are often used to improve the overall activity and selectivity of the process. A computational model was developed to predict yields and conversion of cracking products through lumping of FCC components.  The model incorporates different set of kinetics to account for multicomponent catalyst mixtures and accounts for differing yields of coke in a multicomponent catalyst mixture (i.e., a single blend of zeolite and matrix (support) in the same catalyst formulation, or blends of catalysts of different formulations).  The model successfully uses a 6 lump model to predict effects of changing zeolite to matrix ratios as well as mixing of two entirely different catalysts, without additional fitting of its kinetic parameters. Application of the model to laboratory-scale data of catalysts blends and to catalysts of different zeolite/matrix compositions will be shown, analyzed, and explained using the model. Non-linearities in the experimental results and selectivity trends that would otherwise be impossible to understand, are explained by analyzing the model predictions for the individual catalyst components.

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