Porphyrins vanadium

The most studied of the Group 5 porphyrins have been compounds with vanadyl and niobium metal ions no electrochemical data have yet been reported for tantalum porphyrins. Vanadium porphyrins have been synthesized as both V(IV) and V(II) complexes. The vanadyl derivatives, represented as (P)VO, generally undergo well-defined reduction and oxidation reactions involving the porphyrin, macrocyle the lower oxidation state V(II) complexes have been prepared as (P)V (L) and (P)V (L)2 derivatives, where P = T(p-Me)PP or OEP and L = THE or PPhMe2, but these species have not been examined as to their electrochemical properties [7]. 

In the heaviest fractions such as resins and asphaltenes (see article 1.2), metal atoms such as nickel and vanadium are found. They belong in part to molecules in the porphyrine family where the basic pattern is represented by four pyrrolic rings, the metal being at the center of this complex in the form Wi - or V0+ (< 3)... 

The sensitivity is very good for nickel and vanadium but for these metals for which distribution data would be of great value, the chromatographic process is the lirniting factor, heavy molecules are not eluted from the column with the exception of some porphyrins. This detector can be used to supply H/C and S/C profiles for hydrocarbon cuts with the chromatograph operating in the simulated distillation mode. 

Porphyrin, octaethyl-, vanadium oxide complex cyclic voltammetry, 4, 399 <73JA5140)... 

No. 6 fuel oil contains from 10 to 500 ppm vanadium and nickel in complex organic molecules, principally porphyrins. These cannot be removed economically, except incidentally during severe hydrodesulfurization (Amero, Silver, and Yanik, Hydrode.suljurized Residual Oils as Gas Turbine Fuels, ASME Pap. 75-WA/GT-8). Salt, sand, rust, and dirt may also be present, giving No. 6 a typical ash content of 0.01 to 0.5 percent by weight. 

Many metals occur in crude oils. Some of the more abundant are sodium, calcium, magnesium, aluminium, iron, vanadium, and nickel. They are present either as inorganic salts, such as sodium and magnesium chlorides, or in the form of organometallic compounds, such as those of nickel and vanadium (as in porphyrins). Calcium and magnesium can form salts or soaps with carboxylic acids. These compounds act as emulsifiers, and their presence is undesirable. 

Low yields of the 5-acetyl-l0,11-epoxy derivative 11 (R = Me) are also obtained by oxidation of 5-acetyl-5//-dibenz[/>,/]azepine (10, R = Me) with iodoxybenzene and vanadium(lll) acetylacetonate, and with iodosobenzene and iron(lll) porphyrin.220... 

Recent developments in the studies of titanium and vanadium porphyrins with special emphasis on oxygen adducts, low valent metalloporphyrins and related systems of sulphur and selenium. R. Gui-lard and C. Lecomte, Coord. Chem. Rev., 1985, 65, 87 (76). 

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. 

In addition to hydrocarbons, petroleum also contains compounds that consist of nitrogen, oxygen, and sulfur (in the minority) as well as trace amounts of metals such as vanadium, nickel, iron, and copper. Porphyrins, the major organometaUic compounds present in petroleum, are large, complex cyclic carbon structures derived from chlorophyll and characterized by the ability to contain a central metal atom (trace metals are commonly found within these compounds). 

Porphyrins organometallic constituents of petroleum that contain vanadium or nickel the degradation products of chlorophyll that became included in the protopetroleum. 

No. 6 fuel oil contains from 10 to 500 ppm vanadium and nickel in complex organic molecules, principally porphyrins. These cannot be... 

Crude oil consists mainly of a mixture of paraffinic, naphthenic, and aromatic hydrocarbons with small amounts of metals-containing heterocyclic compounds. The most abundant metals found in oils are those contained in porphyrin or porphyrin-like complexes (nickel, copper, iron, and vanadium). These... 

Under FCCU operating conditions, almost 100% of the metal contaminants in the feed (such as nickel, vanadium, iron and copper porphyrins) are decomposed and deposited on the catalyst (2). The most harmful of these contaminants are vanadium and nickel. The deleterious effect of the deposited vanadium on catalyst performance and the manner in which vanadium is deposited on the cracking catalyst differ from those of nickel. The effect of vanadium on the catalyst performance is primarily a decrease in catalyst activity while the major effect of nickel is a selectivity change reflected in increased coke and gas yields (3). Recent laboratory studies (3-6) show that nickel distributes homogeneously over the catalyst surface while vanadium preferentially deposits on and reacts destructively with the zeolite. A mechanism for vanadium poisoning involving volatile vanadic acid as the... 

Nickel and vanadium carryover is mainly attributed to volatilization of porphyrins chemically combined with these two elements. Because volatility of the two species is roughly equivalent, carryover of nickel and vanadium are approximately equal. However, because the selectivity detriment of vanadium is so much lower, nickel has always generated the most concern. 

The nitrogen-containing porphyrin ring species can be found in most asphaltic crude oils. The porphyrin ring usually holds a metal ion such as nickel or vanadium. These metals are known as powerful poisons for refining catalysts. 

Some of the metallic constituents were somewhat soluble in the propane-oil portion, but all tended to be concentrated in the asphaltic portion. Although vanadium (0.02% by weight in the original crude petroleum) was present in all fractions, the greater part was found in the cyclohexane and benzene fractions. From the similarity of the absorption spectra of the vanadium concentrates from petroleum and those of synthetic vanadium porphyrin complexes, Skinner arrived at the conclusion that vanadium compounds from the petroleum of the Santa Maria Valley Field in California exist as porphyrin complexes. Additional metallic constituents were detected by Skinner as these became concentrated in the various solvent fractions, including aluminum, titanium, calcium, and molybdenum. 

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