Abstract

Coal liquefaction incorporates both an increase in the H/C ratio and removal of heteroatoms (S, N, O) and inorganic oxides (ash). Successful industrial processes must incorporate both these steps along with the transport of solid- and slurry-phase material in large-scale processing. The H/C ratio can be increased using high temperatures and pressures and a solvent (generally process derived), or by a catalyst, or by heating rapidly in the absence of a solvent in hydrogen or an inert atmosphere. Sometimes there are advantages to processing coal simultaneously with other fossil fuels such as resids. Typically, such operations, termed coprocessing, result in improved removal of heteroatoms and ash. The use of solids and slurries has resulted in novel reactors and processing steps. Fuel production can be direct, from the coal itself, or indirect, from synthesis gas (CO and H₂) obtained by gasification of the coal. Synthesis gas, in particular, can be used to produce chemicals other than fuels. The production of these chemicals often can be used to make favorable the economics of fuel production from coal.