<P> The typical example of carbonization is the Karrick process . The process was invented by Lewis Cass Karrick in the 1920s . The Karrick process is a low - temperature carbonization process, where coal is heated at 680 ° F (360 ° C) to 1,380 ° F (750 ° C) in the absence of air . These temperatures optimize the production of coal tars richer in lighter hydrocarbons than normal coal tar . However, the produced liquids are mostly a by - product and the main product is semi-coke, a solid and smokeless fuel . </P> <P> The COED Process, developed by FMC Corporation, uses a fluidized bed for processing, in combination with increasing temperature, through four stages of pyrolysis . Heat is transferred by hot gases produced by combustion of part of the produced char . A modification of this process, the COGAS Process, involves the addition of gasification of char . The TOSCOAL Process, an analogue to the TOSCO II oil shale retorting process and Lurgi - Ruhrgas process, which is also used for the shale oil extraction, uses hot recycled solids for the heat transfer . </P> <P> Liquid yields of pyrolysis and Karrick processes are generally low for practical use for synthetic liquid fuel production . Furthermore, the resulting liquids are of low quality and require further treatment before they can be used as motor fuels . In summary, there is little possibility that this process will yield economically viable volumes of liquid fuel . </P> <P> One example of a Biofuel - based synthetic fuel process is Hydrotreated Renewable Jet (HRJ) fuel . There are a number of variants of these processes under development, and the testing and certification process for HRJ aviation fuels is beginning . </P>

Which element chemically combines with coal to produce synthetic hydrocarbon fuels