Coal, aromatic products from

Coke production was formerly the most important demonstrated technology associated with the direct production of chemicals from coal. Industrial chemicals currently obtained in significant amounts as coke byproducts include benzene, toluene, xylene, naphthalene, anthracene, phenanthrene, phenol, ammonia, ammonium sulfate, sulfitr, and carbon dioxide. The vast majority of aromatics production from coal occurs in Eastern Europe, India, and Japan.75... 

The stability of the products from coal-derived syncrudes must be examined carefully. Many unique compounds are present in these syncrudes peri-condensed aromatics and naphthenes, oxygen compounds, and asphaltene-like hydrocabons. Traces of these compounds may remain in the hydrotreated product and their effect on jet, thermal, and oxidation stabilities cannot be predicted from the behavior of petroleum products. 

FIGURE 15. Gathering the indigo crop, India, around 1900. Aniline was first obtained from indigo, prior to isolation of the aromatic amine from coal tar and synthesis from benzene. Cultivation of the natural product declined following the introduction of synthetic indigo by BASF and Hoechst in 1897. Edelstein Collection... 

There are two factors which distinguish operations in some of these countries from American practice. In the absence of natural gas, petroleum chemicals have to be made from imported liquid hydrocarbon fractions. Compared with America, many of the Europeans countries are relatively well placed on aromatic compounds as by-products from coal processes and the relative price structure may not make manufacture of aromatics from imported oil attractive. 

Benzene (which is the name that was given to the aromatic compound CeUe) is probably the most common and industrially important aromatic compound in wide use today. It was discovered in 1825 by Michael Faraday, and its commercial production from coal tar (and, later on, other natural sources) began in earnest about twenty-five years later. The structure ofbenzene emerged during the 1860s, the result of contributions from several chemists, most famously that of Kekule. 

The hydrogenated product from coal, H-Coal liquid, is more aromatic than shale oil but somewhat comparable in hetero atom content even though a considerable amount of hydrogen has already been added to the product. 

Many valuable chemicals can be recovered from the volatile fractions produced in coke ovens. Eor many years coal tar was the primary source for chemicals such as naphthalene [91-20-3] anthracene [120-12-7] and other aromatic and heterocycHc hydrocarbons. The routes to production of important coal-tar derivatives are shown in Eigure 1. Much of the production of these chemicals, especially tar bases such as the pyridines and picolines, is based on synthesis from petroleum feedstocks. Nevertheless, a number of important materials continue to be derived from coal tar. 

Cyclic Hydrocarbons. The cyclic hydrocarbon intermediates are derived principally from petroleum and natural gas, though small amounts are derived from coal. Most cycHc intermediates are used in the manufacture of more advanced synthetic organic chemicals and finished products such as dyes, medicinal chemicals, elastomers, pesticides, and plastics and resins. Table 6 details the production and sales of cycHc intermediates in 1991. Benzene (qv) is the largest volume aromatic compound used in the chemical industry. It is extracted from catalytic reformates in refineries, and is produced by the dealkylation of toluene (qv) (see also BTX Processing). 

Until the end of World War II, coal tar was the main source of these aromatic chemicals. However, the enormously increased demands by the rapidly expanding plastics and synthetic-fiber industries have greatly outstripped the potential supply from coal carbonization. This situation was exacerbated by the cessation of the manufacture in Europe of town gas from coal in the eady 1970s, a process carried out preponderantly in the continuous vertical retorts (CVRs), which has led to production from petroleum. Over 90% of the world production of aromatic chemicals in the 1990s is derived from the petrochemical industry, whereas coal tar is chiefly a source of anticorrosion coatings, wood preservatives, feedstocks for carbon-black manufacture, and binders for road surfacings and electrodes. 

Until the mid-1950s the main raw material source for the European plastics industry was coal. On destructive distillation coal yields four products coal tar, coke, coal gas and ammonia. Coal tar was an important source of aromatic chemicals such as benzene, toluene, phenol, naphthalene and related products. From these materials other chemicals such as adipic acid, hexamethylenedia-mine, caprolactam and phthalic anhydride could be produced, leading to such important plastics as the phenolic resins, polystyrene and the nylons. 

With each succeeding year in the 1950s and 1960s there was a swing away from coal and vegetable sources of raw materials towards petroleum. Today such products as terephthalic acid, styrene, benzene, formaldehyde, vinyl acetate and acrylonitrile are produced from petroleum sources. Large industrial concerns that had been built on acetylene chemistry became based on petrochemicals whilst coal tar is no longer an indispensable source of aromatics. 

Simple aromatic hydrocarbons come from two main sources coal and petroleum. Coal is an enormously complex mixture made up primarily of large arrays of benzene-like rings joined together. Thermal breakdown of coal occurs when it is heated to 1000 °C in the absence of air, and a mixture of volatile products called coal for boils off. Fractional distillation of coal tar yields benzene, toluene, xylene (dimethylbenzene), naphthalene, and a host of other aromatic compounds (Figure 15.1). 

The nmr analyses of the bottoms products given in Table IV show the material to have a large aliphatic content. The aromatic/aliphatic ratios of the fractions are higher than for the whole coal because of the presence of combined phenol reaction with Tetralin reduces these ratios considerably, presumably by transfer of much of this material to the solvent-range product, but some of it must remain in the bottoms as the aromatic/aliphatic ratio of the composite bottoms product from the fractions is higher than that from the whole coal. It was not possible to calculate the contribution that the diluents, excess solvent and combined phenol, made to the aromatic H, but the large monoaromatic content of the bottoms product must be due, in part, to these. 

H NMR and 2H NMR spectra of fractionated coal products from El0 and El9 were recorded and analyzed to determine and 2H composition for each structural position. In our study, y y and 2Hx,v are defined as the fraction of the JH and 2H determined from the integrals of the NMR spectra of a given soluble fraction where y equals HS, BS or BMS and x = y-alkyl, 0-alkyl, a-alkyl or aromatic structural positions. The spectral range of the NMR integrations are given in Table V. 

The polymerization of phenols or aromatic amines is applied in resin manufacture and the removal of phenols from waste water. Polymers produced by HRP-catalyzed coupling of phenols in non-aqueous media are potential substitutes for phenol-formaldehyde resins [123,124], and the polymerized aromatic amines find applications as conductive polymers [112]. Phenols and their resins are pollutants in aqueous effluents derived from coal conversion, paper-making, production of semiconductor chips, and the manufacture of resins and plastics. Their transformation by peroxidase and hydrogen peroxide constitutes a convenient, mild and environmentally acceptable detoxification process [125-127]. 

An important antioxidant for many products is butylated hydroxytoluene (BHT), more properly named 4-methyl-2,6-di-t-butylphenol. Acid-catalyzed electrophilic aromatic substitution of a t-butyl cation at the activated positions ortho to the hydroxy group of /)-cresol yields this product, p-Cresol is obtained from coal tar or petroleum. 

Benzofuran is a colorless organic liquid with an aromatic odor. It is produced by the destructive distillation of coal, and may also be formed during processing of fossil fuels, such as coke production and coal gasification. Limited data indicate that 2,3-benzofuran may partition to soils and sediments from water, but the information available is insufficient to predict the environmental fate of this compound. Substantial bioconcentration in aquatic organisms is not expected based on the physical/chemical properties of 2,3-benzofuran. 

Phenol is produced through both natural and anthropogenic processes. It is naturally occurring in some foods, human and animal wastes, and decomposing organic material, and is produced endogenously in the gut from the metabolism of aromatic amino acids. Phenol has been isolated from coal tar, but it is now synthetically manufactured (EPA, 2002). Currently, the largest use of phenol is as an intermediate in the production of phenolic resins, which are used in the plywood, adhesive, construction, automotive, and appliance industries. Phenol is also used in the production of synthetic fibers such as nylon and for epoxy resin precursors such as bisphenol-A. 

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