Metal effects fluid cracking catalysts

The first cracking catalysts were acid-leached montmorillonite clays. The acid leach was to remove various metal impurities, principally iron, copper, and nickel, that could exert adverse effects on the cracking performance of a catalyst. The catalysts were first used in fixed- and moving-bed reactor systems in the form of shaped pellets. Later, with the development of the fluid catalytic cracking process, clay catalysts were made in the form of a ground, sized powder. Clay catalysts are relatively inexpensive and have been used extensively for many years. 

Metal contaminants when deposited onto fluid cracking catalysis (FCC) have a serious detrimental effect on the catalysts physicochemical properties (1-21). Vanadium (at levels < 2,000 ppm) generally yield less hydrogen and coke than nickel contaminants in FCC s and its deleterious effects depend on its concentration and... 

Contaminant-Metal Deactivation and Metal-Dehydrogenation Effects During Cyclic Propylene Steaming of Fluid Catalytic Cracking Catalysts... 

Another approach used to reduce the harmful effects of heavy metals in petroleum residues is metal passivation. In this process an oil-soluble treating agent containing antimony is used that deposits on the catalyst surface in competition with contaminant metals, thus reducing the catalytic activity of these metals in promoting coke and gas formation. Metal passivation is especially important in fluid catalytic cracking (FCC) processes. Additives that improve FCC processes were found to increase catalyst life and improve the yield and quality of products. ... 

The most important undesired metallic impurities are nickel and vanadium, present in porphyrinic structures that originate from plants and are predominantly found in the heavy residues. In addition, iron may be present due to corrosion in storage tanks. These metals deposit on catalysts and give rise to enhanced carbon deposition (nickel in particular). Vanadium has a deleterious effect on the lattice structure of zeolites used in fluid catalytic cracking. A host of other elements may also be present. Hydrodemetallization is strictly speaking not a catalytic process, because the metallic elements remain in the form of sulfides on the catalyst. Decomposition of the porphyrinic structures is a relatively rapid reaction and as a result it occurs mainly in the front end of the catalyst bed, and at the outside of the catalyst particles. 

Suib et at. (25, 254) reported the different effects of nickel and vanadium on the catalytic activity and selectivity for the fluid catalytic cracking by a photoluminescence technique and showed that the method is useful in predicting the catalyst deactivation caused by the deposition of metals on surfaces. The activity of the catalyst decreases monotonically with increasing vanadium content. With 1.5 wt% of V, the catalystad lost most of its activity, and with 2.0 wt% of V it became almost completely inactive. Such a deactivation of the catalyst was irreversible, with the extent being closely associated with the surface area covered with vanadium. Moreover, the extent of the deactivation was found to depend on the aging temperature, which was accelerated when aging was carried out under the same conditions normally sized in hydrothermal reactions. 

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