Vanadium producers

The usual extraction procedure is to roast the crushed ore, or vanadium residue, with NaCl or Na2C03 at 850°C. This produces sodium vanadate, NaV03, which is leached out with water. Acidification with sulfuric acid to pH 2-3 precipitates red cake , a polyvanadate which, on fusing at 700°C, gives a black, technical grade vanadium pentoxide. Reduction is then necessary to obtain the metal, but, since about 80% of vanadium produced is used as an additive to steel, it is usual to effect the reduction in an electric furnace in the presence of iron or iron ore to produce ferrovanadium, which can then be used without further refinement. Carbon was formerly used as the reductant, but it is difficult to avoid the formation of an intractable carbide, and so it has been superseded by aluminium or, more commonly, ferrosilicon (p. 330) in which case lime is also added to remove the silica as a slag of calcium silicate. If pure vanadium metal is required it can... 

This quantitative study (Table 7) showed that the more electrophilic lower valence titanium and vanadium produced decreasing ratios for ethylene and increasing ratios for propylene. This supports the concept that the more electrophilic component shifts the catalysts to mildly cationic, which are more optimum for propylene polymerization. 

Vanadium Produces a fine grain size and improves fatigue strength of the steel, just like molybdenum. 

In contrast to the heterogeneous catalysts which produce polymers with a broad molecular weight distribution MJMf) of 5-30, the compounds containing vanadium produce polymers with a narrow MJM of 2-4. 

The pioneering work of Conant showed that the one-electron reduction of pyridinium ion by low-valent vanadium produces the corresponding carbon radical, which dimerizes to give a homocoupling product. Saveant studied the electrochemical reduction of stable iminium salts, and observed two reduction waves in the polarograms (Scheme 5.27). The first wave corresponds to the one-electron reduction process for which dimerization occurs. This process presumably involves formation of the carbon centered radical. The second wave is concerned with the formation of the amine by two-electron reduction. Wayner performed extensive work on oxidation and reduction potentials of carbon radicals.A modulated... 

Vanadium reacts with most nonmetals at high reaction temperatures (660°C 1,220°F). The compounds of vanadium reflect the varied oxidation states possible for this element. Formal oxidation states of +5 to -1 have been found, with the +4 state being the most stable. The element has good corrosion resistance to alkafi, acid, and salt water. For this reason it is used in rust resistant springs and high speed tools. Approximately 80 percent of the vanadium produced yearly is used as an additive to produce steel that has a resistance to wear. Vanadium oxide is used in ceramics and as a catalyst. SEE ALSO Corrosion Steel. 

On the other hand, throughout that period Free World milling capacity is expected to be well in excess of Free World demand. The milling capacity of the present Free World basic vanadium producers is estimated as 42.5 million pounds for 1973 and is expected to increase to 58.8 million pounds in... 

Much of the vanadium metal being produced is now made by calcium reduction of V2O5 in a pressure vessel, an adaption of a process developed by McKechnie and Seybair. 

Vanadium is used in producing rust resistant and high speed tools steels. It is an important carbide stabilizer in making steels. 

About 80% of the vanadium now produced is used as ferrovanadium or as a steel additive. Vanadium foil is used as a bonding agent in cladding htanium to steel. Vanadium pentoxide is used in ceramics and as a catalyst. 

Alloys with other useful properties can be obtained by using yttrium as an additive. The metal can be used as a deoxidizer for vanadium and other nonferrous metals. The metal has a low cross section for nuclear capture. 90Y, one of the isotopes of yttrium, exists in equilibrium with its parent 90Sr, a product of nuclear explosions. Yttrium has been considered for use as a nodulizer for producing nodular cast iron, in which the graphite forms compact nodules instead of the usual flakes. Such iron has increased ductility. 

Ma.leic Anhydride. The largest chemical use for / -butane is as feedstock for maleic anhydride. A dilute air—butane mixture is passed over a vanadium—phosphoms catalyst 400—500°C to produce maleic anhydride [108-31-6] in good yield. Formerly benzene was used as feedstock, but in the last few years nearly all maleic anhydride in the United States, and an increasing proportion worldwide, is made from butane. 

Al—Ti Catalyst for cis-l,4-PoIyisoprene. Of the many catalysts that polymerize isoprene, four have attained commercial importance. One is a coordination catalyst based on an aluminum alkyl and a vanadium salt which produces /n j -l,4-polyisoprene. A second is a lithium alkyl which produces 90% i7j -l,4-polyisoprene. Very high (99%) i7j -l,4-polyisoprene is produced with coordination catalysts consisting of a combination of titanium tetrachloride, TiCl, plus a trialkyl aluminum, R Al, or a combination of TiCl with an alane (aluminum hydride derivative) (86—88). 

Vanadium phosphoms oxide-based catalysts ate unstable in that they tend to lose phosphoms over time at reaction temperatures. Hot spots in fixed-bed reactors tend to accelerate this loss of phosphoms. This loss of phosphoms also produces a decrease in selectivity (70,136). Many steps have been taken, however, to aHeviate these problems and create an environment where the catalyst can operate at lower temperatures. For example, volatile organophosphoms compounds are fed to the reactor to mitigate the problem of phosphoms loss by the catalyst (137). The phosphoms feed also has the effect of controlling catalyst activity and thus improving catalyst selectivity in the reactor. The catalyst pack in the reactor may be stratified with an inert material (138,139). Stratification has the effect of reducing the extent of reaction pet unit volume and thus reducing the observed catalyst temperature (hot... 

Butane-Based Fixed-Bed Process Technology. Maleic anhydride is produced by reaction of butane with oxygen using the vanadium phosphoms oxide heterogeneous catalyst discussed earlier. The butane oxidation reaction to produce maleic anhydride is very exothermic. The main reaction by-products are carbon monoxide and carbon dioxide. Stoichiometries and heats of reaction for the three principal reactions are as follows ... 

HDPE resias are produced ia industry with several classes of catalysts, ie, catalysts based on chromium oxides (Phillips), catalysts utilising organochromium compounds, catalysts based on titanium or vanadium compounds (Ziegler), and metallocene catalysts (33—35). A large number of additional catalysts have been developed by utilising transition metals such as scandium, cobalt, nickel, niobium, molybdenum, tungsten, palladium, rhodium, mthenium, lanthanides, and actinides (33—35) none of these, however, are commercially significant. 

Most catalysts for solution processes are either completely soluble or pseudo-homogeneous all their catalyst components are introduced into the reactor as Hquids but produce soHd catalysts when combined. The early Du Pont process employed a three-component catalyst consisting of titanium tetrachloride, vanadium oxytrichloride, and triisobutjlalurninum (80,81), whereas Dow used a mixture of titanium tetrachloride and triisobutylalurninum modified with ammonia (86,87). Because processes are intrinsically suitable for the use of soluble catalysts, they were the first to accommodate highly active metallocene catalysts. Other suitable catalyst systems include heterogeneous catalysts (such as chromium-based catalysts) as well as supported and unsupported Ziegler catalysts (88—90). 

The second type of solution polymerization concept uses mixtures of supercritical ethylene and molten PE as the medium for ethylene polymerization. Some reactors previously used for free-radical ethylene polymerization in supercritical ethylene at high pressure (see Olefin POLYMERS,LOW DENSITY polyethylene) were converted for the catalytic synthesis of LLDPE. Both stirred and tubular autoclaves operating at 30—200 MPa (4,500—30,000 psig) and 170—350°C can also be used for this purpose. Residence times in these reactors are short, from 1 to 5 minutes. Three types of catalysts are used in these processes. The first type includes pseudo-homogeneous Ziegler catalysts. In this case, all catalyst components are introduced into a reactor as hquids or solutions but form soHd catalysts when combined in the reactor. Examples of such catalysts include titanium tetrachloride as well as its mixtures with vanadium oxytrichloride and a trialkyl aluminum compound (53,54). The second type of catalysts are soHd Ziegler catalysts (55). Both of these catalysts produce compositionaHy nonuniform LLDPE resins. Exxon Chemical Company uses a third type of catalysts, metallocene catalysts, in a similar solution process to produce uniformly branched ethylene copolymers with 1-butene and 1-hexene called Exact resins (56). 

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