Vanadium pentoxides

The reaction uses a fixed-bed vanadium pentoxide-titanium dioxide catalyst which gives good selectivity for phthalic anhydride, providing temperature is controlled within relatively narrow limits. The reaction is carried out in the vapor phase with reactor temperatures typically in the range 380 to 400°C. 

Vanadium pentoxide, vanadium(V) oxide, V2O5, is the most important compound in this oxidation state. It is a coloured solid (colour due to charge transfer, p. 60), the colour varying somewhat (red -> brown) with the state of subdivision it is formed when vanadium (or some of its compounds) is completely oxidised, and also by heating ammonium vanadate)V) ... 

Commercially, maleic anhydride is prepared more cheaply by the catalytic vapour phase oxidation (in the presence of vanadium pentoxide at about 400°) of benzene with atmospheric oxygen ... 

Fumaric acid is conveniently prepared by the oxidation of the inexpensive furfural with sodium chlorate in the presence of a vanadium pentoxide catalyst ... 

C. Fumaric acid from furfural. Place in a 1-litre three-necked flask, fitted with a reflux condenser, a mechanical stirrer and a thermometer, 112 5 g. of sodium chlorate, 250 ml. of water and 0 -5 g. of vanadium pentoxide catalyst (1), Set the stirrer in motion, heat the flask on an asbestos-centred wire gauze to 70-75°, and add 4 ml. of 50 g. (43 ml.) of technical furfural. As soon as the vigorous reaction commences (2) bvi not before, add the remainder of the furfural through a dropping funnel, inserted into the top of the condenser by means of a grooved cork, at such a rate that the vigorous reaction is maintained (25-30 minutes). Then heat the reaction mixture at 70-75° for 5-6 hours (3) and allow to stand overnight at the laboratory temperature. Filter the crystalline fumaric acid with suction, and wash it with a little cold water (4). Recrystallise the crude fumaric acid from about 300 ml. of iif-hydrochloric acid, and dry the crystals (26 g.) at 100°. The m.p. in a sealed capillary tube is 282-284°. A further recrystaUisation raises the m.p. to 286-287°. 

The vanadium pentoxide catalyst Is prepared as follows Suspend 5 g. of pure ammonium vanadate in 50 ml. of water and add slowly 7 5 ml. of pure concentrated hydrochloric acid. Allow the reddish-brown, semi-colloidal precipitate to settle (preferably overnight), decant the supernatant solution, and wash the precipitate several times by decantation. Finally, suspend the precipitate in 76 ml. of water and allow it to stand for 3 days. This treatment renders the precipitate granular and easy to 6lter. Filter the precipitate with suction, wash it several times with cold 5 p>er cent, sodium chloride solution to remove hydrochloric acid. Dry the product at 120° for 12 hours, grind it in a mortar to a fine powder, and heat again at 120° for 12 hours. The yield of catalyst is about 3 - 5 g. 

Benzoquinone ( quinone ) is obtained as the end product of the oxidation of aniline by acid dichromate solution. Industrially, the crude product is reduced with sulphur dioxide to hydroquinone, and the latter is oxidised either with dichromate mixture or in very dilute sulphuric acid solution with sodium chlorate in the presence of a little vanadium pentoxide as catalyst. For the preparation in the laboratory, it is best to oxidise the inexpensive hydroquinone with chromic acid or with sodium chlorate in the presence of vanadium pent-oxide. Naphthalene may be converted into 1 4-naphthoquinone by oxidation with chromic acid. 

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. 

Vapor-phase oxidation over a promoted vanadium pentoxide catalyst gives a 90% yield of maleic anhydride [108-31-6] (139). Liquid-phase oxidation with a supported palladium catalyst gives 55% of succinic acid [110-15-6] (140). 

Chemically, 2,2,2-trifluoroethanol behaves as a typical alcohol. It can be converted to trifluoroacetaldehyde [75-90-1] or trifluoroacetic acid [76-05-1] by various oxidi2iag agents such as aqueous chlorine solutions (51) or oxygen ia the preseace of a vanadium pentoxide catalyst (52). Under basic conditions, it adds to tetrafluoroethylene and acetylene to give, respectively, 1,1,2,2-tetrafluoroethyl 2/2/2 -trifluoroethyl ether [406-78-0] (53) and... 

Oxidation of methanol to formaldehyde with vanadium pentoxide catalyst was first patented in 1921 (90), followed in 1933 by a patent for an iron oxide—molybdenum oxide catalyst (91), which is stiU the choice in the 1990s. Catalysts are improved by modification with small amounts of other metal oxides (92), support on inert carriers (93), and methods of preparation (94,95) and activation (96). In 1952, the first commercial plant using an iron—molybdenum oxide catalyst was put into operation (97). It is estimated that 70% of the new formaldehyde installed capacity is the metal oxide process (98). 

The oxidimetric method, which involves the use of soUd vanadium pentoxide as oxidant (103). The vanadium is reduced quantitatively by butyUithium and is determined potentiometricaUy by titration with standard sulfatoceric acid [17106-39-7]. This method gives a direct measure of the actual carbon-bound lithium present when compared to the total titrated alkalinity. 

Oxidation. Naphthalene may be oxidized direcdy to 1-naphthalenol (1-naphthol [90-15-3]) and 1,4-naphthoquinone, but yields are not good. Further oxidation beyond 1,4-naphthoquinone [130-15-4] results in the formation of ortho- h. h5 ic acid [88-99-3], which can be dehydrated to form phthaUc anhydride [85-44-9]. The vapor-phase reaction of naphthalene over a catalyst based on vanadium pentoxide is the commercial route used throughout the world. In the United States, the one phthaUc anhydride plant currently operating on naphthalene feedstock utilizes a fixed catalyst bed. The fiuid-bed process plants have all been shut down, and the preferred route used in the world is the fixed-bed process. 

Monosaccharides such as glucose and fmctose are the most suitable as starting materials. When starch is used, it is first hydrolyzed with oxahc acid or sulfuric acid into a monosaccharide, mainly glucose. It is then oxidized with nitric acid in an approximately 50% sulfuric acid solution at 63—85°C in the presence of a mixed catalyst of vanadium pentoxide and iron(III) sulfate. 

Durene. The oxidation of durene (4) yields pyromeUitic acid [89-05-4] (17) or pyromeUitic dianhydride [89-32-7] (18) directly. The oxidation can be carried out with dilute nitric acid ia solution, with air and catalyst either ia the vapor phase over a soHd vanadium pentoxide-based catalyst or ia the... 

The principal vanadium-bearing ores are generally cmshed, ground, screened, and mixed with a sodium salt, eg, NaCl or Na2C02- This mixture is roasted at ca 850°C and the oxides are converted to water-soluble sodium metavanadate, NaVO. The vanadium is extracted by leaching with water and precipitates at pH 2—3 as sodium hexavanadate, Na V O, a red cake, by the addition of sulfuric acid. This is then fused at 700°C to yield a dense black product which is sold as technical-grade vanadium pentoxide. This product contains a minimum of 86 wt % V20 and a maximum of 6—10 wt % Na20. 

The red cake can be further purified by dissolving it in an aqueous solution of Na2C02- The iron, aluminum, and silicon impurities precipitate from the solution upon pH adjustment. Ammonium metavanadate then precipitates upon the addition of NH Cl and is calcined to give vanadium pentoxide of greater than 99.8% purity. 

Silicon Reduction. The preparation of ferrovanadium by the reduction of vanadium concentrates with ferrosiUcon has been used but not extensively. It involves a two-stage process in which technical-grade vanadium pentoxide, ferrosiUcon, lime, and fluorspar are heated in an electric furnace to reduce the oxide an iron alloy containing ca 30 wt % vanadium but undesirable amounts of siUcon is produced. The siUcon content of the alloy is then decreased by the addition of more V2O5 and lime to effect the extraction of most of the siUcon into the slag phase. An alternative process involves the... 

Because of the strategic nature of many of the uses, vanadium is one of the materials designated in the National Defense Stockpile Inventory. The goals for 1980 for vanadium-containing materials was 907 metric tons of contained vanadium in ferrovanadium, and 6985 t of contained vanadium in vanadium pentoxide. As of March 1981, the inventory consisted of 4911 of contained vanadium in vanadium pentoxide there was no ferrovanadium in the inventory (22). 

Vanadium compounds, including those which may be involved in the production, processing, and use of vanadium and vanadium alloys, are irritants chiefly to the conjuctivae and respiratory tract. Prolonged exposure may lead to pulmonary compHcations. However, responses are acute, never chronic. Toxic effects vary with the vanadium compound involved. For example, LD q (oral) of vanadium pentoxide dust in rats is 23 mg/kg of body weight (24). 

The ammonium salts of vanadic acid and vanadium pentoxide have been Hsted as toxic constituents in soHd wastes under the Resource Conservation and Recovery Act (27). 

Possibly because of price and performance competition from chromium, titanium, and other transition elements, only about a dozen vanadium compounds are commercially significant of these, vanadium pentoxide is dominant. 

For solvent extraction of a tetravalent vanadium oxyvanadium cation, the leach solution is acidified to ca pH 1.6—2.0 by addition of sulfuric acid, and the redox potential is adjusted to —250 mV by heating and reaction with iron powder. Vanadium is extracted from the blue solution in ca six countercurrent mixer—settler stages by a kerosene solution of 5—6 wt % di-2-ethyIhexyl phosphoric acid (EHPA) and 3 wt % tributyl phosphate (TBP). The organic solvent is stripped by a 15 wt % sulfuric acid solution. The rich strip Hquor containing ca 50—65 g V20 /L is oxidized batchwise initially at pH 0.3 by addition of sodium chlorate then it is heated to 70°C and agitated during the addition of NH to raise the pH to 0.6. Vanadium pentoxide of 98—99% grade precipitates, is removed by filtration, and then is fused and flaked. 

U.S. Stockpile. A U.S. government stockpile goal for vanadium pentoxide of 6985 t contained vanadium was aimounced on May 1, 1980. This is equivalent to 12,470 t of V2O3. At the time of the announcement, the stockpile contained only 4911 of vanadium ia the form of the peatoxide (28). Physical requiremeats are that V2O3 be suppHed as brokea flake, ah. of a size to pass a 2.54-cm screea and not more than 5 wt % to pass a 4.7-mm screen. Packaging ia polyethyleae film iaside 208-L steel dmms and marking of the dmms has been described ia detail (29). 

Other sohd cathode systems that have been widely investigated include those containing lithium cobalt oxide [12190-79-3] LiCo02 (51), vanadium pentoxide [1314-62-17, 20, and higher vanadium oxides, eg, 0 3 (52,53). 

Oxidation. Benzene can be oxidized to a number of different products. Strong oxidizing agents such as permanganate or dichromate oxidize benzene to carbon dioxide and water under rigorous conditions. Benzene can be selectively oxidized in the vapor phase to maleic anhydride. The reaction occurs in the presence of air with a promoted vanadium pentoxide catalyst (11). Prior to 1986, this process provided most of the world s maleic anhydride [108-31 -6] C4H2O2. Currendy maleic anhydride is manufactured from the air oxidation of / -butane also employing a vanadium pentoxide catalyst. 

Vanadium Carbide. Vanadium pentoxide [1314-62-17, V2O5, or vanadium trioxide [1314-34-7] VO3, are the most satisfactory oxides for the preparation of VC. Vanadium pentoxide is best prepared by igniting chemically pure ammonium vanadate [7803-55-6] NH VO, in the presence of moist oxygen to avoid reaction with nitrogen V2O3 is obtained by reduction of V2O3 with hydrogen (see Vanadium compounds). 

The active phase, which is soHd at room temperature, is comprised of mixed potassium and sodium vanadates and pyrosulfates, whereas the support is macroporous siUca, usually in the form of 6—12 mm diameter rings or pellets. The patent Hterature describes a number of ways to prepare the catalyst a typical example contains 7 wt % vanadium pentoxide, 8% potassium added as potassium hydroxide or carbonate, 1% sodium, and 78 wt % siUca, added as diatomaceous earth or siUca gel, formed into rings, and calcined in the presence of sulfur dioxide or sulfur trioxide to convert a portion of the alkah metal salts into various pyrosulfates (81,82). 

When heated in the presence of a carboxyHc acid, cinnamyl alcohol is converted to the corresponding ester. Oxidation to cinnamaldehyde is readily accompHshed under Oppenauer conditions with furfural as a hydrogen acceptor in the presence of aluminum isopropoxide (44). Cinnamic acid is produced directly with strong oxidants such as chromic acid and nickel peroxide. The use of t-butyl hydroperoxide with vanadium pentoxide catalysis offers a selective method for epoxidation of the olefinic double bond of cinnamyl alcohol (45). 

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