Coal Liquefaction

Abstract

AbstractLiquefaction can be direct, from the coal itself, or indirect, from synthesis gas (CO and H2) obtained by gasification of the coal. Coal liquefaction incorporates both an increase in the H/C ratio and removal of heteroatoms (S, N, O) and inorganic oxides (ash). Successful industrial direct liquefaction 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 co‐processing, result in improved removal of heteroatoms and ash. The use of solids and slurries has resulted in novel reactors and processing steps. Indirect liquefaction has as its first step the production of synthesis gas. This mixture can be converted to gasoline‐ or diesel‐range liquid fuels using Fischer‐Tropsch technology. Synthesis gas can also 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. Economic and technical choices between direct and indirect liquefaction are not straightforward. Recent developments in both direct and indirect liquefaction in China and the Middle East have been noteworthy.