Vanadium content

Vanadium content NF M 07-027 ASTM D 1548 Dissolving ash in acid and colorimetric analysis... 

Ferrovanadium. The steel industry accounts for the majority of the world s consumption of vanadium as an additive to steel. It is added in the steelmaking process as a ferrovanadium alloy [12604-58-9] which is produced commercially by the reduction of vanadium ore, slag, or technical-grade oxide with carbon, ferrosiHcon, or aluminum. The product grades, which may contain 35—80 wt % vanadium, are classified according to their vanadium content. The consumer use and grade desired dictate the choice of reductant. 

An electrolytic process for purifying cmde vanadium has been developed at the U.S. Bureau of Mines (16). It involves the cathodic deposition of vanadium from an electrolyte consisting of a solution of VCI2 in a fused KCl—LiCl eutectic. The vanadium content of the mixture is 2—5 wt % and the operating temperature of the cell is 650—675°C. Metal crystals or flakes of up to 99.995% purity have been obtained by this method. 

In the United States, the largest concentration of atmospheric vanadium occurs over Eastern seaboard cities where residual fuels of high vanadium content from Venezuela are burned ia utility boilers. Coal ash ia the atmosphere also coataias vanadium (36). Ambient air samples from New York and Boston contain as much as 600—1300 ng V/m, whereas air samples from Los Angeles and Honolulu contained 1—12 ng V/m. Adverse pubHc health effects attributable to vanadium ia the ambieat air have aot beea deteroiiaed. lacreased emphasis by iadustry oa controlling all plant emissions may have resulted ia more internal reclamation and recycle of vanadium catalysts. An apparent drop ia consumption of vanadium chemicals ia the United States since 1974 may be attributed, in part, to such reclamation activities. 

Many investigators have also measured the trace metal content of asphalts (68). The catalytic behavior of vanadium has prompted studies of the relation between vanadium content and an asphalt s sensitivity to oxidation (viscosity ratio). The significance of metals in the behavior of asphalts is not yet well understood or defined. 

Liquid fuels require atomization and treatment to inhibit sodium and vanadium content. Liquid fuels can drastically reduce the life of a unit if not properly treated. A typical fuel system is shown in Figure 4-7. The effect of fuels on gas turbines and the details of types of fuel handling systems is given in Chapter 12. 

A double-beam atomic absorption spectrophotometer should be used. Set up a vanadium hollow cathode lamp selecting the resonance line of wavelength 318.5 nm, and adjust the gas controls to give a fuel-rich acetylene-nitrous oxide flame in accordance with the instruction manual. Aspirate successively into the flame the solvent blank, the standard solutions, and finally the test solution, in each case recording the absorbance reading. Plot the calibration curve and ascertain the vanadium content of the oil. 

The vanadium content of heavy fuel oils (expressed as vanadium pentoxide) typically ranges from 50 to 1,000 ppm V205, although 50 to 300 ppm is more the norm. Sodium content typically varies from 10 to 100 ppm Na, depending on the percentage of salty water present in the oil. 

Furnace area and superheater slagging may occur at low furnace or superheater temperatures (below 450-500 °C) due to high vanadium content in fuel oil. These high levels of vanadium in the fuel reduce the eutectic temperature of the noncombustibles, creating a molten deposit that holds unbumed carbon and contributes to a thickening of the slag. The trapped carbon is unavailable for combustion, and this process consequently reduces the overall fuel combustion efficiency. 

Fig. 3. compares the ammonia conversion for nanostructured vanadia/TiOa catalysts pretreated with O2 and 100 ppm O3/O2 gases. The reactions were conducted at 348 K for 3 h. No N2O and NO byproducts were detected in the reactor outlet. It is clear from the figure that higher vanadium content is beneficial to the reaction and ozone pretreatment yields a more active catalyst. Unlike the current catalysts, which require a reaction temperature of at least 473 K, the new catalyst is able to perform at much lower temperature. Also, unlike these catalysts, complete conversion to nitrogen was achieved with the new catalysts. Table 2 shows that the reaction rate of the new catalysts compared favorably with the established catalysts. 

The vanadium content of some fuels presents an interesting problem. When the vanadium leaves the burner it may condense on the surface of the heat exchanger in the power plant. As vanadia is a good catalyst for oxidizing SO2 this reaction may occur prior to the SCR reactor. This is clearly seen in Fig. 10.13, which shows SO2 conversion by wall deposits in a power plant that has used vanadium-containing Orimulsion as a fuel. The presence of potassium actually increases this premature oxidation of SO2. The problem arises when ammonia is added, since SO3 and NH3 react to form ammonium sulfate, which condenses and gives rise to deposits that block the monoliths. Note that ammonium sulfate formation also becomes a problem when ammonia slips through the SCR reactor and reacts downstream with SO3. 

V0x/Zr02 catalysts were designated as ZVx(y)pHz, where x gives the analytical vanadium content (weight percent), y specifies the preparation method (a, adsorption, i, impregnation or acac, acetylacetonate) and z the AV solution pH. The V-content was determined by atomic absorption (Varian Spectra AA-30) after the sample had been dissolved in a concentrated (40%) HF solution. 

The carriers were impregnated to different compositions in terms of vanadium content, K/V ratio, Na/V ratio, Cs/V ratio and sulphur content, cf. Fig. 8. The exact sulphur content is less important since the melt, according to reaction (2), takes up an equilibrium amount of SO3 corresponding to a sulphur to alkali metal molar ratio of about 1 during operation in synthesis gas. The impregnation was carried out by submerging the pellets for a period of time in a surplus of aqueous impregnation liquid prepared from sulphuric acid and water-... 

The carriers were impregnated and calcinated in the laboratory, and the activity was subsequently measured in the set-up shown in Fig. 9. The vanadium content was varied in the range 2-5 wt% and the molar ratios between alkali promoter and vanadium were varied in the ranges 0-4 for K/V, 0-2 for Na/V, and 0-3 for Cs/V. The sulphur content was about the same in all impregnations. The measured activities for 3 catalyst compositions A, B, and C impregnated on the same carrier and with the same vanadium content and molar ratios of K/V and Na/V are given in Table 1. The extrudates are made in the 9 mm Daisy form, which is the special 5-finned ring offered by Haldor Topsoe (Fig. 3). The observed pellet activity is reported as a pseudo-1st order rate constant calculated from... 

Figure 11. Observed activity of 1-2 mm catalyst particles in 0.7% S02 and 7% 02 as a function of vanadium content for fixed molar ratios of K/V, Na/V, and Cs/V.

The evaluation of carriers and catalyst compositions showed that significantly higher SO2 oxidation activity could be achieved with Cs as a promoter under the operating conditions downstream the intermediate absorption tower as demonstrated by the results in Table 1, where the activity compared to the standard product is increased by more than a factor 2. This was clearly sufficient for the introduction of VK69 to the market as a new sulphuric acid catalyst. The activity results for different melt compositions were used to optimise the vanadium content and the molar ratios of K/V, Na/V. and Cs/V. However, the choice of Cs/V was not only a question of maximum activity, because of the significant influence of the Cs content on the raw material costs (the price of caesium is 50-100 times the price of potassium on a molar basis). Here, the economic benefits obtained by the sulphuric acid producer by the marginal activity improvement at high Cs content also had to be taken into account. 

Reduction-oxidation processes, which are the dominant control for uranium mobility and deposit formation, are also responsible for elevated molybdenum and vanadium contents observed associated with mineralization. 

Not only do nickel and vanadium levels rise significantly, but vanadium content may greatly exceed nickel. Because of the absence of vacuum distillation, sodium, iron, copper, and other potential poisons can also appear at very high levels. These may have been present in the crude oil or added by contamination from corrosion, additives, or accidental carryover from desalting. 

In normal operations, however, the RCC unit routinely runs at 6-9000 ppm nickel plus vanadium on feedstocks with as high as 35-75 ppm nickel plus vanadium content. Presently several commercial residuum-type catalysts are giving good performance at these levels. Catalyst manufacturers continue to seek further improvement in performance in terms of activity, selectivity, and catalyst life, while also trying to hold down or even reduce overall cost. 

As shown in Figure 13.2, the intrinsic first-order rate constant of NO reduction increases linearly with the vanadium content whereas the intrinsic first-order rate constant for the oxidation of SO2 increases more than linearly with the vanadia content. This is consistent with the identification of the active sites for reduction... 

The total conversion in the dehydrogenation of ethylbenzene was very low for vanadium free AIPO4-5 and increased with vanadium content. As shown in Fig. 9, the conversion increased with vanadium content in the low conversion region. 

Fig. 9. Effect of vanadium content in VAPO4-5 and V2O5/AIPO4-5 on reactivity at 450 C,...

In the lower range of vanadium content, there were little changes of conversion and selectivities between two modified moleclar sieves. However, the conversion and selectivity toward styrene was significatly imprved at higher vanadium content, which is easily obtained by impregnation method. 

Alumina, iron, nickel, silica, sodium, and vanadium are examples of compounds which can be found in residual fuel ash. If the vanadium content of residual fuel is high, severe corrosion of turbine blades can occur and exhaust system deposit formation can be enhanced. Vanadium-enhanced corrosion can occur at temperatures above 1200°F (648.9°C). 

Virtually all of the reported structural data on titanium alloy hydrides and deuterides indicate that the solute atoms occupy tetrahedral interstitial sites in the metal lattice. Neutron diffraction data obtained for deuterium in Ti/34 atom % Zr and in Ti/34 atom % Nb (17) indicate tetrahedral site occupancy in the bcc /3-phase. Similarly, data reported for deuterium in Ti/19 atom % V and in Ti/67 atom % Nb (18) indicate tetrahedral site occupancy in the fee 7-phase. Crystallographic examination of the 7-phase Ti-Nb-H system (19) reveals that increasing niobium content linearly increases the lattice parameter of the fee 7-phase for Nb contents ranging from 0 to 70.2 atom %. Vanadium, on the other hand, exerts the opposite effect (6) at H/M = 1.85, the 7-phase lattice parameter decreases with increasing vanadium contents. 

Variations in AHh (n — 0) were correlated with variations in the lattice parameter of the parent alloy (28). This correlation presumably reflects the view that the insertion of solute hydrogen atoms becomes more unfavorable as the lattice parameter (and consequently the volume of the interstitial site) decreases. This correlation appears valid in titanium alloy systems for which data are available, except for titanium-vanadium. The lattice parameter of 0-Ti/V decreases (29), but AHh (n — 0) becomes more exothermic as the vanadium content is increased (25, SO). This correlation supports the trend in enthalpy with niobium content observed by Saito and Someno (26). The lattice parameter of 0-Ti/Nb alloys increases with niobium content thus, it is expected that AHh (n — 0) becomes more exothermic. 

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