Vanadium sulphides

Figure 6.19 Magnetic susceptibility of vanadium sulphides as a function of temperature and composition. (After De Vries Haas, 1973.)...

Pb - packing density of catalyst bed., g / cucm. pvC - density of vanadium sulphide (S3V2). g / cucm. 

Ammonium sulphide solution The solution is coloured claret-red, due to the formation of thiovanadates (probably VS ). Upon acidification of the solution, brown vanadium sulphide, V2S5, is incompletely precipitated, and the filtrate usually has a blue colour. The precipitate is soluble in solutions of alkalis, alkali carbonates, and sulphides. 

Vanadium. A residual oil was desulphurized (673 K, 115 atm) with a non-stoicheiometric vanadium sulphide (S/V, 0.8-1.8) formed in situ from VS4 Vanadium sulphide catalysts have been prepared by in situ sulphiding of vanadium complexes, e.g., bis(acetylacetonato)oxovanadium(IV), dissolved in crude petroleum.Vanadium compounds occurring in heavy oils have been activated as desulphurization and demetallization catalysts by treatment with triethylaluminium. Catalysts consisting of vanadium promoted by nickel can be prepared in situ by deposition of the metals from heavy crude oils. Ni-V hds and hdm catalysts on silica or carbon have been claimed. 

Further support for the concept of a sequential reaction leading to metals deposition comes from an analysis of the deposition profiles of vanadium [17]. A kinetic analysis of a two step process for V removal was developed, in which the first step was suggested to involve hydrogenation of the V containing porphyrin, while the second produces deposits of vanadium sulphide on the surface. Increased levels of HzS in the gas stream inhibited HDS of the material but increased HDV. For vanadium, the second reaction leading to metal deposits, with levels of H2S expected in an industrial reactor, was found to be some 85 x faster than the first hydrogenation reaction [17]. Under these conditions, it is not surprising that the bulk of the deposition of vanadium occurs near the pellet surface. 

Assuming that the vanadium deposits consist mainly of vanadium sulphides, it is then possible to extend the arguments of Tamm et al [20] to calculate possible effects of deposition of coke and metals on pore closure. Accepting that 200 mV is a typical surface area for hydrotreating catalysts, it is known that ca 50% of the surface area is lost during the initial deactivation [19-21], It is also known that V deposition occurs in the outermost part of the pellet [20,31,37,38]. As a result, the amount of V needed to provide a monolayer over the surface area available can be calculated to be between 0.034 and 0.079g cm ... 

Vanadium deposits of up to 0.9 g cm have been obtained from Arabian heavy atmospheric residue (figure 4 [20]), inferring ca 10-25 monolayers on the surface. Based on the crystallite dimensions of vanadium sulphide, this corresponds to a deposit some 3-8 nm in depth. Given that the deposit forms, together with coke, on both sides of a pore of diameter ca 20 nm, it is not surprising that the pores are closed off and that the catalyst loses almost all activity [20]. 

A catalytic reaction involving the deposit as the catalyst seems more likely. Hydrotreating reactions have been suggested to be favoured by Ni and V sulphides, albeit at a lower rate of reaction [35]. Welters et al [40] have shown that nickel sulphides in or on a zeolite are active hydroprocessing catalysts and vanadium sulphides have also been found to promote hydrotreating [27], as least to some extent. 

Pore blocking by coke or by vanadium sulphides also restricts access of nickel salts. It has been suggested., that nickel compounds may penetrate further into the pellet as a result, at least in part, of their smaller size [20, 31]. This seems inherently unlikely in that a narrow boiling point cut can be expected to give a general molecular size around the same average. What seems more probable is that the low reactivity of nickel compounds [35] allows greater penetration both of the pellet and of deposits on the pellet. 

If this is the case, then nickel deposition, will also be affected by pore blocking by vanadium. As a result, subsequent removal of nickel should occur near the deposit exterior, as has been observed towards the end of the bed [35]. The resulting improvement in the catalytic activity of the deposit (as compared to the activity of vanadium sulphides) would be significant in view of possible interactions between nickel and molybdenum sulphides, and the role of nickel sulphide in facilitating the distribution of molybdenum sulphide across the surface [44]. 

Most attempts to dissociate H2S photolytically involve irradiating an alkaline solution of the gas in which semiconductor particles are suspended. Cadmium sulphide, ruthenium dioxide/cadmium sulphide, titanium dioxide, chromium, platinum, and vanadium sulphides were used [16-18] as the semiconductor which participates by absorbing the incident quanta of light. 

Vanadium Pollution control, e.g. removal of hydrogen sulphide and in manufacture of sulphuric acid Respiratory irritation green-black tongue (transient)... 

Croups Dodecacarbonyidi vanadium (Ammonium sulphide) Triethylphosphine... 

Sulphates, which form part of the ash from the combustion of many fuels, are not harmful to high-alloy steels, but can become so if reduction to sulphide occurs. This leads to the formation of low melting point oxide-sulphide mixtures and to sulphide penetration of the metal. Such reduction is particularly easy if the sulphate can form a mixture of low melting point with some other substance. Reduction can be brought about by bad combustion, as demonstrated by Sykes and Shirley , and it is obviously important to avoid contact with inefficiently burnt fuels when sulphate deposits may be present. Reduction can also be brought about in atmospheres other than reducing ones and the presence of chlorides or vanadium pentoxide has been shown to be sufficient to initiate the reaction. It has also been shown that it can be initiated by prior cathodic polarisation in fused sodium sulphate. The effect of even small amounts of chloride on oxidation in the presence of sulphate is illustrated in Fig. 7.33 . 

Z 1 Niobium 1 Nitrate 1 Osmium 73 a. I Perchlorate Phenols u a o Platinum o 0. 1 5 u 1 Rhodium 1 Rubidium Ruthenium Scandium 1 Selenium Silver I Sodium 1 Strontium 1 Sulphate Sulphides, organic Sulphur dioxide 1 Tantalum 1 Tellurium 1 Thallium Thorium e H 1 Titanium a u ab a 1- I Uranium 1 Vanadium 1 Yttrium 1 Zinc Zirconium... 

Reductant equivalent weights of, 847 Reduction 409 by chromium(II) salts, 409 by hydrogen sulphide, 416 by Jones reductor (zinc amalgam), 410 by liquid amalgams, 412 by silver reductor, 414 by sulphurous acid, 416 by tin(II) chloride, 415 by titanium(II[), 410 by vanadium(II), 410 see also Iron(III), reduction of Reduction potentials 66 Reference electrodes potentials, (T) 554 Relative atomic masses (T) 819 Relative error 134 mean deviation, 134... 

Group 3 Cassiterite from sulphide veins usually contains vanadium, sulphur and wolframite. 

The binary phase diagrams of the titanium oxides and sulphides are very complex with the formation of a very high number of intermediate phases (a similar behaviour is observed also for other intermediate transition metals such as vanadium). In the... 

III. In sulphide ores in which the mineral is associated with hydrocarbons. This class includes the patronite deposits of Peru and various vanadium-bearing asphaltites. It is probable that these asphaltites are the residuary seepage of petroleum deposits, and that they have been formed by the action of (a) hydrocarbons and (6) sulphur or hydrogen sulphide on a fairly porous rock which has been impregnated with a vanadium compound. 

The order of stability of the sulphides of vanadium is not the same as that of the oxides for whilst in the oxygen series the penta-com-pound is stable at a red heat, in the sulphur series the penta-compound is converted into tire trisulplride at this temperature. Again, the trioxide is permanent in hydrogen at intense redness, whilst the trisulphide is reduced to the monosulphide under similar conditions. 

A sulphide in which the vanadium is tetravalent, corresponding to the oxide V02, has not hitherto been prepared. 

Vanadium Oxysulphides.—No vanadium oxysulphides of definite composition have been prepared. By the action of acids on solutions of vanadium pentoxide in ammonium sulphide, or on solutions of alkali vanadates which have been saturated with hydrogen sulphide, brown precipitates are obtained which consist of oxysulphides of variable composition.1... 

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