Irreversible deactivation of fcc catalysts

Abstract

Controlled catalyst deactivation in the laboratory is an essential component in the sequence of tests required for the prediction of catalyst performance in a commercial FCC unit. Conventional single and multiple point deactivation followed by MAT testing gives useful predictions of relative catalyst activities and trends in major yields. These predictions can be enhanced by mathematical modelling based upon specific unit data, but extensions into predicting the yields of individual components within the gasoline and LPG fractions are unreliable. An analysis of the nature of the working equilibrium catalyst shows that it is a complex mixture of age, activity, and metals distributions which work together to generate the final product spectrum. To get closer to predicting this spectrum, it is necessary to simulate an equilibrium catalyst by blending flesh catalyst and a series of mildly and progressively more severely deactivated catalyst samples. The appropriate composition of the blend can be calculated and is a function of the initial catalyst activity, the catalyst decay rates in the laboratory and FCC unit, and the targeted unit catalyst activity and make-up rate. Another major factor in laboratory scale testing lies in the nature of the catalytic testing equipment. Analysis of an FCC riser cracker in terms of catalyst, feedstock, and product contact times indicates that the flow characteristics are crucial to generating the observed product distributions and suggests that, for accuracy, small scale catalytic testing must be carried out in a riser system.