Coal tar naphthalene

The quahty of naphthalene required for phthaUc anhydride manufacture is generally 95% minimum purity. The fixed plants do not require the high (>98%) purity naphthalene product and low (<50 ppm) sulfur. The typical commercial coal-tar naphthalene having a purity ca 95% (freezing point, 77.5°C), a sulfur content of ca 0.5%, and other miscellaneous impurities, is acceptable feedstock for the fixed-bed catalyst process based on naphthalene. 

Fig. 1. Typical coal-tar naphthalene distillation, starting with naphthalene-rich chemical oil.

The main impurity in cmde 78°C coal-tar naphthalene is sulfur which is present in the form of thionaphthene (1—3%). Methyl- and dimethylnaphthalenes also are present (1—2%) with lesser amounts of indene, methylindenes, tar acids, and tar bases. 

Year Coal-tar naphthalene, 10% Petroleum naphthalene, 10 t Total, 10 t Cmde coal-tar naphthalene, 0/kg Petroleum naphthalene, 0/kg... 

The higher price of the petroleum product results from its higher quaUty, ie, higher purity, lower sulfur content, etc. The price of cmde coal-tar naphthalene is primarily associated with that of o-xylene, its chief competitor as phthaUc anhydride feedstock. 

The U.S. naphthalene consumption by markets for 1992 is Hsted in Table 9. The production of phthaHc anhydride by vapor-phase catalytic oxidation has been the main use for naphthalene. Although its use has declined in favor of o-xylene, naphthalene is expected to maintain its present share of this market, ie, ca 18%. Both petroleum naphthalene and coal-tar naphthalene can be used for phthaHc anhydride manufacture. U.S. phthaHc anhydride capacity was 465 X lOM in 1992 (38). 

Naphthalene (qv) from coal tar continued to be the feedstock of choice ia both the United States and Germany until the late 1950s, when a shortage of naphthalene coupled with the availabihty of xylenes from a burgeoning petrochemical industry forced many companies to use o-xylene [95-47-6] (8). Air oxidation of 90% pure o-xylene to phthaUc anhydride was commercialized ia 1946 (9,10). An advantage of o-xylene is the theoretical yield to phthaUc anhydride of 1.395 kg/kg. With naphthalene, two of the ten carbon atoms are lost to carbon oxide formation and at most a 1.157-kg/kg yield is possible. Although both are suitable feedstocks, o-xylene is overwhelmingly favored. Coal-tar naphthalene is used ia some cases, eg, where it is readily available from coke operations ia steel mills (see Steel). Naphthalene can be produced by hydrodealkylation of substituted naphthalenes from refinery operations (8), but no refinery-produced napthalene is used as feedstock. Alkyl naphthalenes can be converted directiy to phthaUc anhydride, but at low yields (11,12). 

U.S. capacity is 455 x 10 t among five producers, as shown in Table 9 (33). All U.S. producers use o-xylene as a feedstock, although Koppers can switch to coal-tar naphthalene. Europe has 20 producers operating 25 plants, 18 of which use o-xylene. Demand growth in North America has averaged less than 3% annually since 1981. Prices in 1992 were 0.77—0.95/kg for molten, and 0.82—1.01/kg for flake (33). 

Methyl iodide Methyl isobutyl carbinol Methyl isoamylacetate cr-methyl styrene Methylene chloride Naphtha (coal tar) Naphthalene Nitromethane... 

Morpholine Naphtha (coal tar) Naphthalene (5-Naphthylamine Nickel carbonyl Nickel metal ST CT CT 1... 

Azeotropic and extractive distillation Distillation processes Extractive distillation(s) argon, 13 460 for aroma isolation, 11 519 atmospheric, 13 646 batch versus continuous, 3 780 of coal-tar naphthalene, 17 78-79 corrosion, 3 779-780 of crude oil, 12 401-402 13 593 debottlenecking, 13 521 in fatty acid neutralization, 22 740 favorable vapor-liquid equilibria, 3 778 feed composition, 3 778 general separation heuristics for, 22 316-317... 

Until 1959, all the phthalic anhydride was made from coal tar naphthalene, the double-benzene ring compound also shown in Figure 18—3 was easily oxidized directly to phthalic acid. But with phthalic anhydride being only a small share of coal oil, and with the demand for phthalic anhydride escalating rapidly, coal tar became an inadequate source. The frantic search for an alternative route led to the development of the recovery process for ortho-xylene from refinery aromatics streams discussed in Chapter 3 and the... 

Two or more benzene rings fused together form a number of polycyclic benzenoid aromatic compounds, naphthalene, anthracene and phenanthrene, and their derivatives. All these hydrocarbons are obtained from coal tar. Naphthalene is the most abundant (5%) of all constituents of coal tar. 

An aromatic compound which is employed along with glycerol in the production of alkyd resins is phthalic anhydride. The conventional process for the manufacture of this chemical has been from the catalytic oxidation of coal tar naphthalene, and annual production of the anhydride in recent years has been around 150,000,000 pounds. In 1946 production was started (4) in a plant of the Oronite Chemical Co. at Richmond, Calif., to produce phthalic anhydride by the oxidation of o-xylene produced in a hydroformer unit of the adjacent Standard Oil Co. of California refinery. The Oronite plant was reported to have a design capacity of 7,000,000 to 8,000,000 pounds per year of 99.7% pure phthalic anhydride. 

All three of these hydrocarbons are obtained from coal tar, naphthalene being the most abundant (5%) of all constituents of coal tar. 

The detoxication of condensed thiophenes was also studied (Maxted and Walker, 16) in connection with the possible detoxication of naphthalene prior to its hydrogenation. The nature and relative abundance of the sulfur-containing poisons which are present in coal-tar naphthalene... 

In coal tar refining, rectification is used to produce a naphthalene fraction which, depending on the separation efficiency of the naphthalene column, can have a naphthalene content rising to over 90%. Table 9.1 shows the composition of a close-cut coal tar naphthalene fraction. 

Table 9.1 Composition of a representative coal tar naphthalene fraction...

Since that time, sulfur-resistant catalysts have been developed. However, the importance of the fluidized-bed phthalic anhydride process is declining since the proportion of raw material costs is about 70% of total production costs, the feedstocks o-xylene and coal tar naphthalene can be more cost-effectively oxidized in fixed-bed reactors. 

Graham, J. J., Young, B.J. Coal Tar Naphthalene Unionfining Erdol, Kohle, Erdgas, Petrochem., 26, 331 (1973)... 

Coal tar naphthalene is oxidized with air over a vana-dia catalyst in a fluidized bed according to the following highly exothermic partial oxidation reaction ... 

Although naphthalene and indeed most polycyclic aromatic hydrocarbons are usually obtained from coal tar, naphthalene can be synthesized by a rather unusual Friedel-Crafts reaction... 

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