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Although most of the metallic constituents of crude oil are concentrated in the residues, some of the organometallic compounds are actually volatilized at refinery distillation temperatures and appear in the feed to the FCC cracking units. Metal contaminants in the feedstock tend to deposit on the matrix of FCC catalysts wherein they catalyze the combustion of carbon monoxide. Generally, only a portion of the total (25-30%) deposited metal is active. Nickel in FCC feed and iron scale are predominant sources of such contaminants. Iron scale in the flue gas lines, cyclones, and dilute phase of the regenerator can be a cause of afterburning problems. Other metal contaminants such as lead, sodium, and vanadium will act as poisons to the active precious metal contained in CO oxidation promoters. Significant increases in contaminant levels will increase the severity and usage rates for CO promoters. Because the compounds of these metals cannot, in general, be removed from the cracking unit as volatile compounds the usual approach has been to passivate them or render them innocuous under the conditions that are encountered during the cracking process. One passivation method has been to incorporate additives into the cracking catalyst or separate particles that combine with the metals and therefore act as "traps" or "sinks" so that the active zeolite component is protected. The metal contaminants are removed together with the catalyst withdrawn from the system during its normal operation and fresh metal trap is added together with makeup catalyst so as to affect a continuous withdrawal of the deleterious metal contaminants during operation. Depending upon the level of the harmful metals in the feed to the unit, the amount of additive may be varied relative to the makeup catalyst in order to achieve the desired degree of metals passivation.
The existing metal passivator are classified into two categories in terms of function, i.e. the single-function metal passivator which is nickel passivator or vanadium passivator composed of single effective metal like Sb, Sn or Bi; and difunction metal passivator composed of composite metals like Sb--Sn, Sb--Bi, Sb--Re, etc which can simultaneously passivate nickel and vanadium. There are two ways for the addition of metal passivators: one is to add it to the reactor with the catalytic cracking feedstock and this method is usually applied for the liquid metal passivator. The other is to add it to the reactor with the catalyst and this method is usually applied for solid metal passivator such as vanadium trapping agent. Additives proposed for this purpose include the alkaline earth metals and rare earths such as lanthanum and cerium compounds are described in many patents [1-8]. These materials which are typically in the oxide form at the temperatures encountered in the regenerator presumably exhibit a high reaction rate with vanadium to yield a stable, complex vanadate species which effectively binds the vanadium and prevents degradation of the active cracking component in the catalyst.
Antimony and tin are used to passivate the activity of vanadium and nickel on FCC catalyst. Their purpose is to reduce gas make caused by metals catalyzed dehydrogenation. Their effect on CO promotion catalysts is to reduce their activity as well. Thus, the increased use of passivators will increase the severity of the promotion application and the possibility of after burn problems .
In biochemical method a biocatalyst consisting enzyme which degrags porphyrine molecule is used by contacting it in an aquas medium. Embodiments of the biocatalyst can be heme oxygenase and cytochrome C reductase, such as cytochrome C reductase from Bacillus megaterium, catharanthus roseuse, Escherichia coli, animal cells, plant cells or yest cells.
Hossein Salehizadeh et. al. achieved 55% microbial degradation of vanadium oxide octaethyl porphyrin (VOOEP) by mircroorganism Aspergillus sp.MS-100, when the temperature was 30 ï‚°C, pH was 7.0, and the concentration of VOOEP was 20 mg/l for 7 days. Mircroorganism Aspergillus sp.MS-100 were isolated from polluted soil at the Isfahan refinery, Isfahan, Iran .
In an US patent metals were removed from fossil fuel by contacting it (aquas medium) with a biocatalyst selected from the group consisting of an enzyme which degragds porphyrine molecules. Embodiments of the biocatalyst are heme oxygenase and cytochrome C reductase, such as cytochrome C reductase from Bacillus megaterium, catharanthus roseuse, Escherichia coli, animal cells, plant cells or yest cells .
ULTRASONIC IRRADIATION DEMETALATION
The effect of cationic starches on removal of nickel and vanadium from crude oils in the presence of microwaves was investigated. A series of cationic starches with different degrees of substitution (DS), synthesized by a microwave-dry process, were used to remove nickel and vanadium from crude oils. The effects of a number of factors, such as the degree of substitution of cationicstarches, microwave time and cationic starches dose on nickel and vanadium removal rates from the crude oils were investigated. The results indicate that the higher the degree of cation substitution on the cationic starch, the greater the effect of electrostatic adsorption of the heavy metal positive ions. Sample SC4 had the highest degree of substitution in the cationic starch series and had the highest effect on nickel and vanadium removal rates. The optimum conditions for nickel and vanadium removal from crude oils were as follows: (a) amount of SC4 200 mg/L, (b) microwave power 300 W and (c) microwave time 5 min. Under these conditions, the removal rates of nickel from Iranian and Shengli crude oils were 55.33 and 59.64%, respectively, and the removal rates of vanadium were 76.19 and 78.70%, respectively .
The asphaltene fraction [hexane insoluble (HI)] of a vacuum residue (VR) was treated under ultrasonic irradiation at 40Â°C in Tetra hydro furan (THF) or 150Â°C in 1-methylnaphthalene (1-MN) in the presence of an adsorbent composed of modified macro-reticular polystyrene resin. Such a treatment was found effective to convert the asphaltene into the hexane soluble (HS: maltene) without any hydrogen consumption. 61 and 72% of the HI was converted by the adsorption treatment at 40Â°C in THF and 150Â°C in 1-MN, respectively, to HS materials having lower molecular wts. About 65% of the metal contaminants in the original asphaltene remained with the newly formed maltenes after this treatment. Structural analyses of the asphaltene and maltene fractions before and after the treatment suggests decoagulation and/or depolymerisation of the asphaltene into maltene, while the porphyrin moiety becomes soluble, being transformed to the maltene fraction. The roles of polar solvent, ultrasonic irradiation, and adsorbent are discussed based on the above results .
A feasibility study of the decomposition and demetalation of metalloporphyrins by ultrasonic irradiation is presented in a paper by Tu and Yen. Two representative model compounds, NiTPP and VOTPP, were investigated in this ultrasonic process on the laboratory scale. The extent of the decomposition was detected by UV-visible. The metals were measured by ICP/MS. In the initial investigation, the decomposition of metalloporphyrins, which were dissolved in different solvent-water mixtures, was performed under the ultrasonication process. Among these solvents, the chlorinated-type solvents (e.g., chloroform and dichloromethane) achieved a higher efficiency because they generated more oxidizing species under sonication at 20 kHz frequency. Other additives such as surfactant and hydrogen peroxide, which affect the decomposition efficiency, were also investigated. Under optimal condition, the decomposition efficiency reached about 90% in 1 h for both model compounds. An oxidative intermediate existed for both metalloporphyrins under ultrasonication. The decomposition reaction rates of these two compounds followed pseudo-first-order in reactant concentration and were inhibited by initial feed concentration. The dependence of the rate constants on the different initial concentrations could be determined by the Langmuir Hinshelwood equation .
Yasuhiro Shiraishi et. al. studied simultaneous photoreaction and extraction process, employing an oil/water two-phase system. The results for the demetalation, obtained for vanadyl(IV)- and nickel(II)tetraphenylporphyrin dissolved in tetralin, were compared with those obtained for actual atmospheric residue oil. It was found that photochemical reaction was able to demetalize "free"-type metalloporphyrins, but had difficulty in the demetalation of "bound"-type metalloporphyrins, which are associated strongly with the asphaltenic molecules in residue oil. To weaken this association and thus convert the bound type metalloporphyrins to the free-type ones, a hydrogen-donating polar solvent, 2-propanol, was added to the residue oil and photoirradiated. The 2-propanol was then removed by evaporation, and the resulting residue oil was contacted with aqueous HCl solution, into which the resulting vanadium and nickel were successfully removed. According to this latter development of the process, 93% vanadium and 98% nickel were recovered from atmospheric residue and 73% vanadium and 85% nickel from vacuum residue, respectively. The overall demetalation process, involving the recovery of the 2-propanol, has been formulated as an energysaving and safe demetalation process, which is satisfactory for application in the upgrading of heavy residual feedstocks .
Myers et al. (1997) reported an improved sodium desulphurization and demetalation process that was developed by a consortium of three companies comprising Imperial Oil Resources (Esso), Exxon R&E Company, and AEA Technology. The technology was used for the treatment of high-sulfur bitumen .
Removal of Ni and V from crude oils by cationic starch in the presence of microwave irradiation 
% Removal Rate
With out Microwave
In the presence of Microwave