Vanadic acid

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). 

For direct precipitation of vanadium from the salt-roast leach Hquor, acidulation to ca pH 1 without the addition of ammonia salts yields an impure vanadic acid when ammonium salts are added, ammonium polyvanadate precipitates. The impure vanadic acid ordinarily is redissolved in sodium carbonate solution, and ammonium metavanadate precipitates upon addition of ammonium salts. Fusion of the directly precipitated ammonium salts can yield high purity V20 for the chemical industry. Amine solvent extraction is sometimes used to recover 1—3 g/L of residual V20 from the directly precipitated tail Hquors. 

Vanadyl trichloride (VOCI3) [7727-18-6] M 173.3, m-79.5°, b 124.5-125.5°/744mm, 127.16°/760mm, d 1.854, d 1.811. Should be lemon yellow in colour. If red it may contain VCI4 and CI2. Fractionally distil and then redistil over metallic Na but be careful to leave some residue because the residue can become EXPLOSIVE in the presence of the metal USE A SAFETY SHIELD and avoid contact with moisture. It readily hydrolyses to vanadic acid and HCl. Store in a tightly closed container or in sealed ampoules under N2. [Inorg Synth 1 106 1939, 4 80 1953.]... 

Vanadin-saure, /. vanadic acid, -saurean-hydrid, n. vanadic anhydride, vanadium pentoxide, vanadium(V) oxide, V2O6. -stahl, m. vanadium steel, -stickstoff, m. vanadium nitride, -sulfat, n. vanadium sulfate, -ver-bindung, /. vanadium compoimd. 

Vanadium-saure, /. vanadium acid, specif, vanadic acid, -stahl, m. vanadium steel. 

There are several theories about the chemistry of vanadium poisoning. The most prominent involves conversion of VjOj to vanadic acid (H-iVO ) under regenerator conditions. Vanadic acid, through hydrolysis, extracts the tetrahedral alumina in the zeolite crystal structure, causing it to collapse. 

Steam reacts with VjO, to form volatile vanadic acid. Vanadic acid, through hydrolysis, causes collapse of the zeolite crystal. 

Vanadium in the feed poisons the FCC catalyst when it is deposited on the catalyst as coke by vanadyl porphydrine in the feed. During regeneration, this coke is burned off and vanadium is oxidized to a oxidation state. The vanadium oxide (V O ) reacts with water vapor in the regenerator to vanadic acid, HjVO. Vanadic acid is mobile and it destroys zeolite crystal through acid-catalyzed hydrolysis. Vanadic acid formation is related to the steam and oxygen concentration in the regenerator. 

Vanadium and sodium neutralize catalyst acid sites and can cause collapse of the zeolite structure. Figure 10-5 shows the deactivation of the catalyst activity as a function of vanadium concentration. Destruction of the zeolite by vanadium takes place in the regenerator where the combination of oxygen, steam, and high temperature forms vanadic acid according to the following equations ... 

The produced vanadic acid, VO (OH)3, is mobile. Sodium tends to accelerate the migration of vanadium into the zeolite. This acid attacks the catalyst, causing collapse of the zeolite pore structure. 

Synonyms Vanadic anhydride divanadium pentoxide vanadium oxide vanadic acid... 

Both mechanisms discussed above involve an acidic species, and differ primarily in whether that species behaves as a Bronsted or Lewis acid. The vanadic acid approach treats the Y species as a proton donor whereas the oxygen abstraction implies electrophilic attack by V. In either case, it is easy to see how oxygen rich, basic oxides such as MgO function as Y passivators. 

Under FCCU operating conditions, almost 100% of the metal contaminants in the feed (such as nickel, vanadium, iron and copper porphyrins) are decomposed and deposited on the catalyst (2). The most harmful of these contaminants are vanadium and nickel. The deleterious effect of the deposited vanadium on catalyst performance and the manner in which vanadium is deposited on the cracking catalyst differ from those of nickel. The effect of vanadium on the catalyst performance is primarily a decrease in catalyst activity while the major effect of nickel is a selectivity change reflected in increased coke and gas yields (3). Recent laboratory studies (3-6) show that nickel distributes homogeneously over the catalyst surface while vanadium preferentially deposits on and reacts destructively with the zeolite. A mechanism for vanadium poisoning involving volatile vanadic acid as the... 

Synonyms vanadium(V) oxide vanadic acid anhydride vanadic anhydride. 

If the oxidation of graphite by nitric acid is conducted in the presence of catalysts, such as vanadic acid or silver nitrate, mellitic acid, Cl2012H.6, is obtd-... 

The gas can also be prepared by reducing potassium chlorate with oxalic acid,4 or with vanadic acid.5 According to W. Bray, a regular stream of chlorine dioxide is evolved without danger when a mixture of 40 grms. of powdered potassium chlorate, 150 grms. of crystallized oxalic acid, and 20 grms. of water is warmed in an oil bath to 60°. 

Salts of Vanadic Acid. Pour 3-4 ml of a sodium vanadate solution into each of two test tubes. Add to one of them a silver nitrate solution, and to the other a saturated ammonium chloride solution. Write the equations of the reactions. 

Vanadic acid differs also from niobic and tantalic adds in that it forms a number of complex acids with other acids, and a large number of heteropolyvanadates are known. Niobic add and tantalic acid show little tendency to form complex acids oxaloniobates and oxalotanta-lates have, however, been prepared. 

Vanadium Oxydichloride, V02C12.8H20.—By the action of dilute aqueous hydrochloric acid on the two isomeric hydrates of hypo-vanadic acid, two isomeric forms of this compound have been prepared. The green hydrate gives rise to deep green crystals, and the rose hydrate to blue crystals of the same empirical composition.2 Their constitutions are a matter of doubt.3... 

Silver orthovanadate reacts with alkyl halides to give esters of vanadic acid. These are yellow liquids of general formula Alk.3V04, in which Aik. represents the alkyl radical. Esters of orthovanadic acid axe more stable than those of pyro- and meta-vanadic acids that is, the order of stability is the reverse of that which applies to the inorganic salts.3 The following orthovanadates have been prepared —... 

Lead Metavanadate, Pb(VOg)2.—Acid solutions of vanadates on being treated with lead salts give rise to yellow basic vanadates the composition of which varies with the conditions. The precipitation of normal lead vanadate is, therefore, difficult. It has been accomplished by the addition of lead acetate to ammonium metavanadate solution in the presence of acetic acid.2 The lead precipitates contain all the vanadic acid originally present in solution, and precipitation of vanadates with lead salts has, therefore, been employed for the quantitative estimation of vanadium.3 The mineral deschenite consists chiefly of lead metavanadate a portion of the lead is, however, frequently replaced by zinc.4... 

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