Chemicals from coal-derived

Sasol produces synthetic fuels and chemicals from coal-derived synthesis gas. Two significant variations of this technology have been commercialized, and new process variations are continually under development. Sasol One used both the fixed-bed (Arge) process, operated at about 240°C, as weU as a circulating fluidized-bed (Synthol) system operating at 340°C. Each ET reactor type has a characteristic product distribution that includes coproducts isolated for use in the chemical industry. Paraffin wax is one of the principal coproducts of the low temperature Arge process. Alcohols, ketones, and lower paraffins are among the valuable coproducts obtained from the Synthol process. 

Caldwell, R. D. and Eyerman, S. M., "Chemicals from Coal-Derived Synthetic Crude Oils," Refining of Synthetic Crudes, edited by Martin L. Gorbaty and Brian M. Harney, Advances in Chemistry Series 179, American Chemical Society, Washington D.C., 1979 pp 145-158. 

Chemicals from Coal-Derived Synthetic Crude Oils... 

Caldwell and eyerman Chemicals from Coal-Derived Oils 151... 

A chemistry based on the conversion of synthesis gas has been developed and appHed extensively in South Africa to the production of Hquid fuels and many other products. A small-scale production is used in the manufacture of photographic film materials from coal-derived synthesis gas in the Eastman Kodak plant in Kingsport, Tennessee. However, the principal production of chemicals from coal involves the by-products of coke manufacturing. 

Clearly, the number of chemicals produced from coal-derived synthesis gas can expand as new technologies are developed and favorable economics exist. The most likely such chemicals are those for which processes have been demonstrated but which presently are uneconomic. Relatively small improvements in technology, shifts in feedstock availability and/or... 

Eastman Chemical Co. and Air Products and Chemicals, Inc. Removal of Trace Contaminants from Coal-Derived Synthesis Gas Topical Report, Contract DE-FC22-92PC90543, March 2003. 

In the selection of a raw material, availability and chemical nature are deciding factors. Olefinic and aliphatic chemicals such as ethylene, propylene and methanol are therefore produced from crude oil fractions and suitable natural gas, whereas polynuclear aromatics such as naphthalene, anthracene and pyrene are recovered almost exclusively from coal-derived raw materials. Mononuclear aromatics such as benzene, toluene and xylene occupy a medial position, being obtainable from both crude oil and coal feedstocks. Renewable raw materials are, owing to their chemical structure, particularly suitable for the production of compounds containing oxygen. 

In the first stage of coal liquefaction, finely-crushed coal (particle size <0.1 mm) is slurried with a solvent, to render the coal flowable and pumpable. The choice of solvent is particularly important, since it must be suitable to stabilize the coal fragments and to dissolve the smaller disintegrated molecular moieties. Due to their similarity in chemical nature, coal-derived oils are particularly efficient. Anthracene oil from coal-tar processing was therefore preferred as a solvent, when coal hydrogenation was being developed. 

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. 

In 1980, the last year for which a breakdown has been pubUshed, the amount of benzene derived from coal in the United States was 168,000 t or 2.5% of domestic benzene production. Coal-derived toluene was 0.8% of production, and xylenes from coal were only 0.1% of total chemical production (9). The amounts and proportions of BTX components derived from coal in the United States are expected to be nearly the same today as in 1980. Based on information submitted to the International Trade Commission, approximately 25 companies participated in the coal-tar industry in the United States in 1990. 

Proof of the existence of benzene in the light oil derived from coal tar (8) first estabHshed coal tar and coal as chemical raw materials (see Eeedstocks, COAL chemicals). Soon thereafter the separation of coal-tar light oil into substantially pure fractions produced a number of the aromatic components now known to be present in significant quantities in petroleum-derived Hquid fuels. Indeed, these separation procedures were for the recovery of benzene—toluene—xylene (BTX) and related substances, ie, benzol or motor benzol, from coke-oven operations (8) (see BTX processing). 

There are some chemicals that can be made economically from coal or coal-derived substances. Methanol and CO are used to make acetic anhydride and acetic acid. Methanol itself can be made from synthesis gas over a copper-2inc catalyst (see Feedstocks, coal chemicals). 

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. 

---