Minimizing rare earth content of FCC catalysts: Understanding the fundamentals on combined P-La stabilization

Abstract

Fluidized Catalytic cracking (FCC) is one of the main conversion processes in conventional refineries and employs a multicomponent catalyst with Y zeolite as the main source of activity and selectivity towards value added products. In order to meet the severe requirements of the FCC unit, the hydrothermal stability of this large pore zeolite is traditionally improved by means of controlled hydrothermal treatments that can be combined with acid washing cycles, with rare earth (RE) ion exchange or with a combination of both. Phosphorus has also been described as a hydrothermal stabilization element. Although most of the studies are based on ZSM-5 zeolites, a new Y zeolite containing FCC catalyst, PhinesseTM, was developed recently. This catalyst, based on the partial substitution of RE by P allowed obtaining the same activity and the same yields to the main products as its conventional RE stabilized counterpart in the catalytic cracking of a vacuum gas oil (VGO). In this work, we present a systematic study where the hydrothermal stability of P- and La-free USYs with different dealumination degrees is compared with that of the corresponding USYs containing P or La alone or a combination of both stabilizing elements. The samples have been thoroughly characterized and their catalytic performance has been tested in a MAT unit. According to the results obtained, when using RE alone, only high contents (> 3.5 wt% RE) are able to stabilize the catalysts towards steaming under severe conditions (100% steam, 750 ºC). However, lower RE ( wt%) can lead to similar hydrothermal stabilization when combined with intermediate phosphorus contents (∼1.0 wt%). The results obtained provide the bases for understanding the reasons behind the benefits of this combined P-La stabilization observed for the commercial Phinesse™ catalyst as compared to a high REO catalyst.