Study of Supercritical Coal Extraction in Toluene Containing Fluids

The conversion of brown coals and sapropelic coal in toluene containing mixtures with co-solvents (water, ethanol and tetralin) was studied under sub- and supercritical conditions within the temperature range of 375-550°C and at pressures from 7 to 40 MPa. It was found that the extent of coal extraction in the toluene solvent medium, at 400°C, was significantly increased by the addition of small amounts of hydrogen-donor tetralin or ethanol co-solvents. The extract yield from sapropelic coal reached 79-83%, with the gas yield being small. The effect of process variables on extract yields under sub- and supercritical conditions was monitored. Coal extraction in the toluene-tetralin mixtures was found to depend mainly on the hydrogen donor ability of the tetralin co-solvent irrespective of sub-or supercritical toluene states. According to the composition, the bitumen extracted from coals can be used as a feedstock for pitch production. In the water containing mediums, aside from coal liquefaction, coal methanation, hydrolysis and oxidation reactions occurred resulting in the generation of large amounts of methane, hydrogen and carbon dioxide.