Continuous Age Distribution Method for Catalytic Cracking 2. Understanding Nonidealities

Abstract

In a previous paper, we introduced a novel steam deactivation method, which could in principle reproduce many features of refinery FCC equilibrium catalysts. However, nonideal zeolite decay kinetics had prevented full realization of the potential of the method. Further analysis now shows those kinetic deviations were due to a ubiquitous 10–20% of metastable framework Si in zeolite Y, which is already familiar via the zeolite ultrastabilization process. Unexpectedly high framework Si collapse rates have also been found above 870 °C, but these may not be relevant to the refinery. The effects of these nonidealities can be appropriately excluded by collapsing metastable Si in a mild presteaming at 732 °C and/or by elongating catalyst deactivation time in the method. Variations of the method are then used to demonstrate that the 0–5th age percentile of refinery equilibrium catalyst does substantially contribute to coke and hydride transfer, and that presteaming can be used to systematically effect changes in zeolite mesoporosity, which in turn have a striking linear effect on cracking yields.