Homogeneous bed expansion of FCC catalysts, influence of temperature on the parameters of the Richardson–Zaki equation

This paper reports some experimental observations on the homogeneous expansion of three FCC catalysts with increasing temperature from ambient up to 650 °C. These catalysts were all characterized by a wide particle size distribution and by nonperfectly spherical particles. The Richardson–Zaki equation was used to describe the homogeneous expansion of these catalysts. Experimental expansion profiles were obtained experimentally with increasing temperature, and the parameters of the Richardson–Zaki equation, n and ut, were estimated. Experimental n and ut values were compared with predictions given, respectively, by the Richardson–Zaki n=n(Ret) correlations employed for liquids and by the drag equation for the settling of an individual particle, using the Stokes law. Experimental n and ut values were also compared with data reported in the literature. For all FCC catalysts, experimental n and ut values were found to be much higher than the predicted ones, with the discrepancy being greater at low temperatures. The homogeneous bed was assumed to be characterized by presence of clusters, whose diameter, dp*, was back-calculated from the ut* values. The values of dp*, which were obtained at temperatures above 100 °C, were found to be of the same order of magnitude as the surface average and volume average mean diameters, indicated as dS and dV, respectively. These findings underlined the importance of defining appropriate mean particle diameters to describe the particlesʹ systems under study. Furthermore, parallel to fluidization tests, thermal analyses were carried out to investigate possible changes in the particlesʹ physical properties as a function of temperature. Results from these tests were compared with fluidization findings in order to highlight the role of the interparticle forces on the stable behaviour of these materials.