Coal liquefaction is a process that converts COAL from a solid state into liquid fuels, usually to provide substitutes for petroleum products. Coal liquefaction processes were first developed in the early part of the 20th century but later application was hindered by the relatively low price and wide availability of crude oil and natural gas. Large scale applications have existed in only a few countries, eg, Germany during WWII and South Africa since the 1960s. The oil crises of the 1970s and the threat of depletion of conventional oil supplies sparked a renewed interest in the production of oil substitutes from coal during the 1980s.
Coal can be liquefied by direct and indirect process routes