(172g) Mathematical Modeling of Catalyst Deactivation by the Presence of Coke Formation in Catalyst Particles
AIChE Spring Meeting and Global Congress on Process Safety
2008
2008 Spring Meeting & 4th Global Congress on Process Safety
Catalysis and Reaction Engineering Division - Jointly Co-sponsored with ACS
Reaction Engineering: Analysis, Design and Modeling
Wednesday, April 9, 2008 - 10:10am to 10:30am
Mathematical modeling of catalyst deactivation by the presence of coke formation
in catalyst particles
M. Gaxiola-Cervantes, J.L. Rico and M.A. Morales-Cabrera
Universidad Michoacana de San Nicolás de Hidalgo, Francisco J. Mújica S/N, Ciudad Universitaria, Col. Felicitas del Rio, México, D.F., C.P. 58060 México
Keywords: diffusion; reaction; catalyst deactivation; mathematical modelling; effectiveness factor; chemical reactors.
Abstract
The catalysts deactivation by coke deposition is a phenomenon frequently found in hydrocarbon conversion processes. Quantitative study of the activity time relation is important to determine the optimum design and operation conditions of chemical reactors [Froment, 2001].
In this work, an approximate solution for a problem of diffusion-reaction in an isothermal catalyst pellet with the presence of coke deposition is developed. The approximation is based on the linearization of the nonlinear reaction terms in the transport equations, by means a Taylor series expansion [Morales-Cabrera et al., 2005]. For the concentration profiles of all reactant species inside the catalyst particle, analytical expressions are obtained by applying the Laplace transform. As consequence, an analytical expression for the effectiveness factor, which is a function of the Thiele modulus and the time, was also derived to study the catalyst activity. And with this tool, the effect of the deactivation on the conversion in a fixed-bed reactor was studied.
The approximate analytical solution was applied to dehydrogenation of 1-buteno into butadiene and considering exponential deactivation functions to the coke deposition (Dumez y Froment, 1976), in catalyst particles with spherical geometry. The deactivation functions included dependence of the coke concentration. The predictions of the concentration profiles and the effectiveness factors were compared with results obtained by the numerical solution of the reactant transport equations and with the experimental data reported by Dumez y Froment, 1976.