Estudo da contaminação por ferro na presença de enxofre em catalisadores de equilíbrio de FCC

Abstract

FCC (Fluidized Catalytic Cracking) catalysts are used largely in the refining processes of the petroleum industries. During these processes, which occurs in the catalytic cracking units (FCCU), the catalyst is submitted to a hard operational condition, such as steaming at high temperatures and contamination with nickel, vanadium, iron, and sulfur, that promotes its irreversible deactivation. The decrease of accessibility of the catalyst with resulting reduction in bottoms conversion are critical evidence of contamination by iron, usually characterized by nodulation in the outer surface of the catalyst. The phenomenon of particles nodulation is observed only in industrial FCC units, has never been reproduced in the laboratory, although there is some work involving poisoning with iron alone and in the presence of other contaminants such as nickel, vanadium and calcium. The aim of this study was to evaluate the impacts of iron contamination on the properties a commercial catalyst balance obtained from a commercial UFCC. This catalyst was subjected to feedstock cracking contaminated with iron naphthenate and benzothiophene as a sulfur source, in order to verify a synergistic effect between these elements. The experiments were performed in a lab unit MAT (Micro Activity Test) simulating the catalytic cracking. Success was obtained in the contamination of the catalyst by iron (with and without the addition of sulfur) by performing multiple cycles of reaction / regeneration under experimental conditions optimized for this. Analyses of EPR and Mössbauer spectroscopy showed evidence of the formation of iron sulfide precursor and influence the nature of feedstock on the deposited iron species. The distribution of iron settles relatively homogeneous within the particle and the nodulation effects of the outer surface were not observed. Nevertheless, it was possible to simulate the accessibility index drop in the catalyst, as typical iron contamination in the industrial process. The deposition of iron through this protocol resulted in significant damage to the textural properties, such as reducing the volume of micropores, which was reflected in lower activity of the catalyst. The catalytic evaluation showed deterioration in selectivity to coke and fuel gas and reduce the gasoline yield for the doped samples, which can be explained by the action of iron added to promote dehydrogenation reactions to the detriment of cracking. The increase in the residue yield observed suggests that the iron has also caused diffusional restriction of the catalyst. The presence of sulfur in the iron contamination did not significantly alter the catalytic behavior of the poisoned catalyst