ABSTRACT
Direct combustion of coal, although highly developed, is not easily applied to transportation systems such as aircraft or road vehicles. There is considerable interest therefore in the conversion of coal into clean burning gaseous and liquid fuels. The degree of interest is a function of oil prices, which have fluctuated considerably, but in the long term will tend to rise as supplies become scarcer. The production of a fuel with as low a content of pollutants as possible is at least as important as the production of a liquid substitute for oil (105).
