Chromite producers

K. Fischbeck and E. Einecke found that the cathodic polarization of ferrous, cuprous, calcium, and magnesium chromites produces chromic acid, whilst the other chromites are unaffected, and natural chrome ironstone behaves in a like manner, but other commercial chromites are reduced on cathodic polarization, and yield chromic acid on anodic polarization. Chromites behave as an intermediate electrode. 0. Unverdorben observed that chromyl fluoride, prepared by heating a mixture of fluorspar, lead chromate, and sulphuric acid, when passed into water, furnishes an aq. soln. of this oxide. The soln. was treated with silver nitrate, and the washed precipitate of silver chromate decomposed by hydrochloric acid. A. Mans said that anhydrous sulphuric acid or fuming sulphuric acid is not suited for the preparation because of its volatilization with the chromyl fluoride. 

The principal ore is chromite, which is found in Zimbabwe, Russia, Transvaal, Turkey, Iran, Albania, Finland, Democratic Republic of Madagascar, and the Phillippines. The metal is usually produced by reducing the oxide with aluminum. 

Reduction. Hydrogenation of dimethyl adipate over Raney-promoted copper chromite at 200°C and 10 MPa produces 1,6-hexanediol [629-11-8], an important chemical intermediate (32). Promoted cobalt catalysts (33) and nickel catalysts (34) are examples of other patented processes for this reaction. An eadier process, which is no longer in use, for the manufacture of the 1,6-hexanediamine from adipic acid involved hydrogenation of the acid (as its ester) to the diol, followed by ammonolysis to the diamine (35). 

Hydrolysis of primary amides cataly2ed by acids or bases is very slow. Even more difficult is the hydrolysis of substituted amides. The dehydration of amides which produces nitriles is of great commercial value (8). Amides can also be reduced to primary and secondary amines using copper chromite catalyst (9) or metallic hydrides (10). The generally unreactive nature of amides makes them attractive for many appHcations where harsh conditions exist, such as high temperature, pressure, and physical shear. 

Uses ndReactions. Nerol (47) and geraniol (48) can be converted to citroneUol (27) by hydrogenation over a copper chromite catalyst (121). In the absence of hydrogen and under reduced pressure, citroneUal is produced (122). If a nickel catalyst is used, a mixture of nerol, geraniol, and citroneUol is obtained and such a mixture is also useful in perfumery. Hydrogenation of both double bonds gives dimethyl octanol, another useful product. 

Dehydrogenation of citroneUol over a copper chromite catalyst produces citroneUal [106-23-0] in good yield (110). If the dehydrogenation is done under distiUation conditions in order to remove the lower boiling citroneUal as it is formed, polymerization or cyclization of citroneUal is prevented. 

Most synthetic camphor (43) is produced from camphene (13) made from a-piuene. The conversion to isobomyl acetate followed by saponification produces isobomeol (42) ia good yield. Although chemical oxidations of isobomeol with sulfuric/nitric acid mixtures, chromic acid, and others have been developed, catalytic dehydrogenation methods are more suitable on an iadustrial scale. A copper chromite catalyst is usually used to dehydrogenate isobomeol to camphor (171). Dehydrogenation has also been performed over catalysts such as ziac, iadium, gallium, and thallium (172). 

During much of the nineteenth century, the United States was the principal world producer of chromite ore (37). However in the latter twentieth century the United States has become completely dependent on imports from South Africa and Turkey (chromite) South Africa, Zimbabwe, Turkey, and Yugoslavia (ferrochromium) and the Philippines (chromite for refractory brick). 

Around 1800, the attack of chromite [53293-42-8] ore by lime and alkaU carbonate oxidation was developed as an economic process for the production of chromate compounds, which were primarily used for the manufacture of pigments (qv). Other commercially developed uses were the development of mordant dyeing using chromates in 1820, chrome tanning in 1828 (2), and chromium plating in 1926 (3) (see Dyes and dye intermediates Electroplating Leather). In 1824, the first chromyl compounds were synthesized followed by the discovery of chromous compounds 20 years later. Organochromium compounds were produced in 1919, and chromium carbonyl was made in 1927 (1,2). 

Manufacture The primary iadustrial compounds of chromium made directly from chromite ore are sodium chromate, sodium dichromate, and chromic acid. Secondary chromium compounds produced ia quantity include potassium dichromate, potassium chromate, and ammonium dichromate. 

When relatively small amounts of hydrogen are required, perhaps in remote locations such as weather stations, then small transportable generators can be used which can produce I-I7m h. During production a 1 1 molar mixture of methanol and water is vaporized and passed over a base-metal chromite" type catalyst at 4(X)°C where it is cracked into hydrogen and carbon monoxide subsequently steam reacts with the carbon monoxide to produce the dioxide and more hydrogen ... 

Chromium, 122 ppm of the earth s crustal rocks, is comparable in abundance with vanadium (136 ppm) and chlorine (126 ppm), but molybdenum and tungsten (both 1.2 ppm) are much rarer (cf. Ho 1.4 ppm, Tb 1.2 ppm), and the concentration in their ores is low. The only ore of chromium of any commercial importance is chromite, FeCr204, which is produced principally in southern Africa (where 96% of the known reserves are located), the former Soviet Union and the Philippines. Other less plentiful sources are crocoite, PbCr04, and chrome ochre, Cr203, while the gemstones emerald and ruby owe their colours to traces of chromium (pp. 107, 242). 

The sodium chromate produced in the isolation of chromium is itself the basis for the manufacture of all industrially important chromium chemicals. World production of chromite ores approached 12 million tonnes in 1995. 

When produced by such dry methods it is frequently unreactive but, if precipitated as the hydrous oxide (or hydroxide ) from aqueous chromium(III) solutions it is amphoteric. It dissolves readily in aqueous acids to give an extensive cationic chemistry based on the [Cr(H20)6] ion, and in alkalis to produce complicated, extensively hydrolysed chromate(III) species ( chromites ). 

The presence of catalysts markedly changes the deflagration rate. The greatest rate increase is produced by copper chromite, a well-known hydrogenation catalyst. Some additives which catalyze the process at higher pressures may inhibit it strongly at lower pressures. The catalyst effect is related to catalyst particle-size and concentration, but these factors have not been studied extensively. 

Chromium compounds of high purity can be produced from chromite ore without reduction to the free metal. The first step is the roasting of chromite ore in the presence of sodium carbonate ... 

Two options are being developed at the moment. The first is to produce 1,2-propanediol (propylene glycol) from glycerol. 1,2-Propanediol has a number of industrial uses, including as a less toxic alternative to ethylene glycol in anti-freeze. Conventionally, 1,2-propanediol is made from a petrochemical feedstock, propylene oxide. The new process uses a combination of a copper-chromite catalyst and reactive distillation. The catalyst operates at a lower temperature and pressure than alternative systems 220°C compared to 260°C and 10 bar compared to 150 bar. The process also produces fewer by-products, and should be cheaper than petrochemical routes at current prices for natural glycerol. The first commercial plant is under construction and the process is being actively licensed to other companies. 

A possible method for producing glycerol derivatives can be the reactive distillation in the presence of various oxide and mixed oxide catalysts, such as copper-chromite [3], In this reaction acetol, 1,2- and 1,3-propanediols may be obtained. 

Phthalimide was hydrogenated catalytically at 60-80° over palladium on barium sulfate in acetic acid containing an equimolar quantity of sulfuric or perchloric acid to phthalimidine [7729]. The same compound was produced in 76-80% yield by hydrogenation over nickel at 200° and 200-250 atm [43 and in 75% yield over copper chromite at 250° and 190 atm [7730]. Reduction with lithium aluminum hydride, on the other hand, reduced both carbonyls and gave isoindoline (yield 5%) [7730], also obtained by electroreduction on a lead cathode in sulfuric acid (yield 72%) [7730]. 

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