Effect of contaminant metals

During the 1980s, antimony was widely used in FCCUs that had a problem with contaminant metals. In the late 1980s, other additives were introduced to combat the contaminant metals, eg. Chevron introduced a bismuth-based additive, which is claimed to provide performance similar to antimony (18). Also in the late 1980s, cracking catalysts were developed with metals traps that appear to be so effective in containing the adverse effects of contaminant metals that additive-type inhibitors are no longer needed (19). 

Figure 5. Effect of contaminant metals on the SOx reduction capability of a blend of DA-250 + 10% Additive R + 0.37% CP-3.

In addition to the simplification of pore structure, assumptions are needed regarding the effects of contaminant metals on the intrinsic activity of the surface. For HDM it appears that the catalyst s intrinsic activity is not significantly affected (see Fig. 42). This is not the case for the HDS reaction, however. Most model formulations also neglect the effects of surface coke on activity since it does not have an impact on long-term stability unless conditions are too severe. 

Laboratory steam deactivations represent a significant compromise in the effort to simulate equilibrium catalyst. Since hydrothermal deactivation of FCC catalysts is not rapid in commercial practice, deactivation of the fresh catalyst in the laboratory requires accelerated techniques. The associated temperatures and steam partial pressures are often in substantial excess of those encountered in commercial units. In some instances, the effect of contaminant metals is measured by an independent test not affiliated with steam deactivation. In subsequent yields testing, interactions between different modes of deactivation may be overlooked. Finally, single mode deactivation procedures can not reproduce the complex profile of ages and levels of deactivation present in equilibrium catalyst. 

Test Methods. Since its inception, the Mitchell Method (MM) or slight variations (often referred to as the Modified Mitchell Method) have been en )loyed by researchers evaluating FCC catalyst as a sin )le, inexpensive, and fast procedure by which to simulate the effect of contaminant metals on catalyst performance. As a fallout of more sophisticated catalytic testing in fixed fluid bed reactors, the method of cycUc metals deposition (CMD) has also emerged as a useful method for introducing metal contaminants. 

Higher catalyst makeup rates or more robust catalyst formulations can offset most of the effects of contaminant metals. Managing the higher CCR levels is best accomplished through the use of external catalyst coolers and possibly operation in a partial combustion mode. 

J. E. HiUis, The Effects of Heavy Metal Contamination on Magnesium Corrosion Peformance, paper 830523, Society of Automotive Engineers, Detroit,... 

A good catalyst is also stable. It must not deactivate at the high temperature levels (1300 to 1400°F) experienced in regenerators. It must also be resistant to contamination. While all catalysts are subject to contamination by certain metals, such as nickel, vanadium, and iron in extremely minute amounts, some are affected much more than others. While metal contaminants deactivate the catalyst slightly, this is not serious. The really important effect of the metals is that they destroy a catalyst s selectivity. The hydrogen and coke yields go up very rapidly, and the gasoline yield goes down. While Zeolite catalysts are not as sensitive to metals as 3A catalysts, they are more sensitive to the carbon level on the catalyst than 3A. Since all commercial catalysts are contaminated to some extent, it has been necessary to set up a measure that will reflect just how badly they are contaminated. 

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. ... 

Kelly JJ, Tate RL (1998) Effects of heavy metal contamination and remediation on soil microbial communities in the vicinity of a zinc smelter. J Environ Qual 27 609-617... 

It was generally agreed that any determinations of trace metals carried out on seawater prior to about 1975 are questionable, principally due to the adverse effects of contamination during sampling, which were then little understood and lead to artificially high results. It is only in the past few years that methods of adequate sensitivity have become available for true ultra-trace metal determinations in water. 

Birds are comparatively resistant to the biocidal properties of cadmium. Adult drake mallards (Anas platyrhynchos) fed up to 200 mg cadmium per kg diet for 90 days all survived with no loss of body weight (White and Linley 1978). Laying hens fed 200 mg Cd/kg diet also survived egg production was suppressed at that concentration but not at lower concentrations (White and Linley 1978). Marine and terrestrial animals, including ducks, have been shown to be particularly abundant in a wildlife community associated with a marine sewer outfall (Brown et al. 1977). These animals were contaminated with high levels of cadmium, as well as zinc and copper, but were apparently protected from the deleterious effects of high metal body burdens by metallothioneins. Amounts... 

Identify potential reaction contaminants. In particular, consider possible contaminants, which are ubiquitous in a plant environment, such as air, water, rust, oil, and grease. Think about possible catalytic effects of trace metal ions such as sodium, calcium, and others commonly present in process water. 

To study the effect of contaminants (chlorides and sulphates) at the interface metal/coating, a set of panels (surface A Sa 3) was prepared and dosed with solutions of NaCl and FeSO in distilled water and methanol. Subsequently, two paint systems (chlorinated rubber and polyurethane) were applied on these contaminated surfaces. 

Catalysts were contaminated with nickel and vanadium according to the method of Mitchell ( ), using metal naphthenates. Prior to blending, all contaminated materials were steamed (1450 F, 4 hrs, 90% steam, 10% air) to age the metals. The selectivity effects of the metals on the non-zeolitic component were determined by blending impregnated non-zeolitic components with 20% of the steamed, uncontaminated high activity zeolitic component such that the overall blend yielded 70% conversion. 

At very low surface areas (about 5 m /g) and constant conversion (70%), the contaminant selectivities are dominated by the matrix composition (Table I). Rare earth and magnesium-containing microspheres were prepared to examine the effects of these metal oxides on catalyst selectivities in the presence of nickel and vanadium. These oxides were chosen because the literature (3,5,10-15) has shown them to be effective at reducing the deleterious effects of vanadium in cracking catalysts. 

VOCs), uranium, and heavy metals. There has been extensive research on various materials for use in PRBs. Metal-based PRBs are common because the reactive material is commercially available at low costs and has been effective on a variety of contaminants. Metal-based PRBs act as selective filters to contaminants and are being developed in response to the need for effective, low-cost technologies to remediate contaminated subsurface environments. The barriers are permeable to water and nontargeted groundwater constituents and impermeable or destructive to the target contaminant(s). 

Due to the particle size of Deloxan THP II and MP, these resins can be used in either batch or fixed bed mode to scavenge transition metals from contaminated process solutions. In this work both modes of operation were investigated. In addition to mode of use, many other variables can influence the effectiveness of a metal scavenger. Oxidation state of the metal, solvent characteristics (polar or nonpolar) and nature of the metal complex (ligands) are just a few of these variables and these were chosen for investigation in this body of work. 

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