Coal, chemicals from Sasol process

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. 

The most prominent player in the field of cresols from coal tar had been SASOL of South Africa that has been operating coal chemical plants using pressure gasification of bituminous coals based on Lurgi process. In these plants, initially phenol and ortho-cresol are separated from the cresylic acid mixture using fractionation, and a mixture rich in cresols (upto 94%) containing some xylenols is produced and the product is marketed as mixed cresols (primarily para cresol, meta cresol, and small percentage of mixed xylenols and a very little quantity of unrecovered phenol). It has been reported that for select customers, SASOL can supply upto 99% pure cresols (metal + para cresols). 

In 1942, about 32 million gallons of aviation fuel were made from coal in Germany. In South Africa, the Sasol process for coal liquefaction has been a major source of gasoline and a variety of other petroleum products and chemicals for more than 50 years. 

Imperial Chemical Industries (ICI) operated a coal hydrogenation plant at a pressure of 20 MPa (2900 psi) and a temperature of 400—500°C to produce Hquid hydrocarbon fuel from 1935 to the outbreak of World War II. As many as 12 such plants operated in Germany during World War II to make the country less dependent on petroleum from natural sources but the process was discontinued when hostihties ceased (see Coal conversion PROCESSES,liquefaction). Currentiy the Fisher-Tropsch process is being used at the Sasol plants in South Africa to convert synthesis gas into largely ahphatic hydrocarbons at 10—20 MPa and about 400°C to supply 70% of the fuel needed for transportation. 

Early developments for producing liquid fuel from coal which can be found in many countries took place in the 1840s in Germany and England. They were the first steps of the petrochemical industry. These processes produced kerosene to fuel German airplanes during World War II and supplied up to 90% of the demand in liquid fuels at that time. Sasol s plants in the Republic of South Africa are the only industrial coal-to-liquid production capability that remains today with an annual production of 7.5 M tonnes of liquid fuels (gas oil, kerosene) and chemical products. 

Fig. 19.24. Block flow diagram of Sasol s coal-to-oil process. (Reprinted from Encyclopedia of Chemical Processing Design, pp. 310, 320, by courtesy of Marcel Dekker, Inc., 1979.)...

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