Vanadium sulfides, formation

By far the most important ores of iron come from Precambrian banded iron formations (BIF), which are essentially chemical sediments of alternating siliceous and iron-rich bands. The most notable occurrences are those at Hamersley in Australia, Lake Superior in USA and Canada, Transvaal in South Africa, and Bihar and Karnataka in India. The important manganese deposits of the world are associated with sedimentary deposits the manganese nodules on the ocean floor are also chemically precipitated from solutions. Phosphorites, the main source of phosphates, are special types of sedimentary deposits formed under marine conditions. Bedded iron sulfide deposits are formed by sulfate reducing bacteria in sedimentary environments. Similarly uranium-vanadium in sandstone-type uranium deposits and stratiform lead and zinc concentrations associated with carbonate rocks owe their origin to syngenetic chemical precipitation. 

An additional mechanism affects the deposits formation from the H-Oil reactor, rejection of vanadium and nickel sulfides from the catalyst. In the vacuum tower, asphaltene precipitation was found to be the prevalent fouling mechanism. In asphaltene... 

Bolm and Bienewald discovered in 1995 that some chiral vanadium (IV)-Schiff base complexes were efficient catalysts (1 mol %) for sulfoxidation [71a]. The catalyst 20 was prepared in situ by reacting VO(acac)2 with the Schiff base of a fJ-aminoalcohol (Scheme 6C.8). Reactions were conveniently performed in air at room temperature by slow addition of 1.1 mol equiv. of aqueous hydrogen peroxide (30%). Under these experimental conditions the reaction of methyl phenyl sulfide gave the corresponding sulfoxide in 94% yield and 70% ee. The best enantioselectivity was obtained in the formation of sulfoxide 21 (85% ee). Many structural analogues of catalyst 20 were screened for their efficacy, but none of... 

The group Ib elements—copper, silver, and gold—stand in contradistinction to elements such as rubidium and vanadium. These metals are rather electronegative and soft, and prefer two-coordinate directional bonding. These characteristics are not conducive to the incorporation of these elements into rock-forming oxide matrices, and they therefore form their own minerals, occur in the native state, or reside in trace sulfides in the cmst. They also partition readily into fluid phases, promoting their redistribution in the crust, and the formation of ores. 

The vanadium trioxide (V2O3) and vanadium tetraoxide (V2O4) compounds are typically associated with approximate unbumed carbon levels in the flyash 10 percent. This is consistent with the porphyrin structure of the vanadium in the crude oil, and in the petroleum coke. Nickel can occur as a sulfide, an oxide, or in a vanadate (e.g., nickel pyrovanadate) depending upon combustion condition. For example, r ucing conditions promote formation of sulfide compounds. Some of the conq)ounds shown (e.g., the sodium vanadate compounds) are nK>re commonly associated with oil firing than with petroleum coke firing, as a consequence of the low ash content in petroleum coke and the low... 

For commetcial plants removing only carbon dioxide or carbon dioxide plus low concentrations of hydrogen sulfide, the use of a vanadium base corrosion inhibitor is recommended. For high H2S concentrations, the vanadium inhibitor is unsuitable however, the formation of hydrogen sulfide scale permits operation without an inhibitor. Carbon steel construction is applicable for most equipment. The hindered amines used as promoters have low volatility, good stability, and low foaming tendency at plant operating conditions (Exxon, 1991). 

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