Vanadium organometallic compounds

Organometallic compounds apart, oxidation states below - -2 are best represented by complexes with tris-bidentate nitrogen-donor ligands such as 2,2 -bipyridyl. Reduction by LiAlH4 in thf yields tris(bipyridyl) complexes in which the formal oxidation state of vanadium is -1-2 to —1. Magnetic moments are compatible with low-spin configurations of the metal but. 

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. 

The vanadium-promoted epoxidation method has proved to be valuable in synthetic routes leading to dl-Ci8 Cecropia juvenile hormone20 and lasalocid A.24 The mechanism of vanadium-mediated epoxidation has been elucidated25 but an evaluation of the use of other organometallic compounds as epoxidation reagents is required.26... 

Merox [Mercaptan oxidation] A process for removing mercaptans from petroleum fractions by extracting them into aqueous sodium hydroxide and then catalytically oxidizing them to disulfides using air. The catalyst is an organometallic compound, either a vanadium phthalocyanine supported on charcoal, or a sulfonated cobalt phthalocyanine. Developed by UOP in 1958 and widely licensed by 1994, more than 1,500 units had been built, worldwide. Unzelman, G. H. and Wolf, C. J., in Petroleum Processing Handbook, Bland, W. F. and Davidson, R. L., Eds., McGraw-Hill, New York, 1967, 3-128. 

Physical methods of fractionation of tar sand bitumen usually indicate high proportions of nonvolatile asphaltenes and resins, even in amounts up to 50% wt/wt (or higher) of the bitumen. In addition, the presence of ash-forming metallic constituents, including such organometallic compounds as those of vanadium and nickel, is also a distinguishing feature of bitumen. 

Most complexes of vanadium(IV) with group IV ligands are normally organometallic compounds, which have been reviewed.9... 

Vanadium and nickel are present in parts-per-million quantities in most crude oils, usually in large, oil-soluble organometallic compounds termed porphyrins. The chemical structure of porphyrins is closely akin to the coloring matter in blood and to chlorophyll in plants. 

Distillation concentrates the metallic constituents in the residua (Table 3-5) some can appear in the higher-boiling distillates but the latter may, in part, be due to entrainment. Nevertheless, there is evidence that a portion of the metallic constituents may occur in the distillates by volatilization of the organometallic compounds present in the petroleum. In fact, as the percentage overhead obtained by vacuum distillation of reduced crude is increased, the amount of metallic constituents in the overhead oil is also increased. The majority of the vanadium, nickel, iron, and copper in residual stocks may be precipitated along with the asphaltenes by low-boiling alkane hydrocarbon solvents. Thus, removal of the asphaltenes with n-pentane reduces the vanadium content of the oil by up to 95% with substantial reductions in the amounts of iron and nickel. 

Furthermore, the organometallic compounds (of which nickel and vanadium are the principal constituents) that are present to varying degrees in all residua and in the majority of heavy oils cause catalyst deterioration. Deposition of these metals in any form on to the catalyst leads to catalyst deactivation but the exact mechanism of deactivation is still subject to speculation. Nickel tends to be deposited throughout the catalyst whereas vanadium is usually more concentrated in the outer layers of the catalyst. In either case, catalyst deactivation is certain whether it be by physical blockage of the pores or destruction of reactive sites. 

Residua and heavy oils contain impurities other than sulfur, nitrogen, and oxygen, and the most troublesome of these impurities are the organometallic compounds of nickel and vanadium. The metal content of a residuum or heavy oil can vary from several parts per million (ppm) to more than 1000 parts per million (Table 6-15), and there does seem to be more than a chance relationship between the metals content of a feedstock and its physical properties (Reynolds, 1997 Speight, 1999). In the hydrodesulfurization of the heavier feedstocks the metals (nickel plus vanadium) are an important factor since large amounts (over 150 ppm) will cause rapid deterioration of the catalyst. The free metals, or the sulfides, deposit on the surface of the catalyst and within the pores of the catalyst, thereby... 

Vanadium is present in crudes mainly in the +4 state (58). In fact, up to 50% of the total vanadium in crude oil can be found as V02+ in organometallic compounds such as porphyrins and naphthenates (59-63). During the cracking reaction in a FCCU, these compounds deposit V (probably in the form of VO+2 cations) on the catalyst surface. Then, after steam-stripping and catalyst regeneration, formation of V+5 surface phases occur. The effects of vanadium on FCC properties are more severe than any of the other metals present in petroleum feedstocks. In fact, vanadium causes an irreversible loss of cracking activity which is the result of a decrease in crystallinity, pore volume and surface area of the catalyst, Figure 5. 

Ziegler-Natta Catalysts (Heterogeneous). These systems consist of a combination of a transition metal compound from groups IV to VIII and an organometallic compound of a group I—III metal.23 The transition metal compound is called the catalyst and the organometallic compound the cocatalyst. Typically the catalyst is a halide or oxyhalide of titanium, chromium, vanadium, zirconium, or molybdenum. The cocatalyst is often an alkyl, aryl, or halide of aluminum, lithium, zinc, tin, cadmium, magnesium, or beryllium.24 One of the most important catalyst systems is the titanium trihalides or tetra-halides combined with a trialkylaluminum compound. 

Coordination Chemistry Supported Organotransition Metal Compounds Titanium Organometallic Chemistry Vanadium Organometallic Chemistry Zirconium Hafnium Organometallic Chemistry. 

Complexes containing vanadium in low oxidation states, apart from organometallic compounds, are known with ligands such as bipy, phen, nitric oxide, and tertiary phosphines, which stabihze such oxidation states. Depending on their electronic structure, V and V complexes may be diamagnetic, which permits study by NMR spectroscopy, and EPR spectroscopy has been used to study paramagnetic V complexes. 

Note added in proof. This statement is no longer correct. The Gmelin-Institut has commenced publication of volumes in the 8th edition of Gmelin s Handbuch der anorganische Chemie specifically concerned with organometallic compounds. The first volume describes the derivatives of vanadium and chromium. 

Metals. Metals or organometallic compounds such as arsenic, copper, lead, and vanadium also are poisons to the primary reforming catalysts. Metals are present in trace quantities and are usually removed during normal desul-... 

All heavy crude oil residues have heavy metals such as Ni, V or Fe in their structure. These metals are bonded as organometalic compounds. At high temperatures and for hydrogenation reactions, these compounds are cracked and heavy metals are deposited on the catalyst surface. These metals can also react with hydrogen sulfur from the gas phase to form metal sulfides. The deposition of sulfides of iron, vanadium or nickel leads to irreversible poisoning of the catalyst. This is the difference between catalyst deactivation by metals and deactivation by coke the former leads to an irreversible loss of the catalyst activity. 

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