Effect of aromatic solvents in coal liquefaction: residence-time studies

The effect of adding polycondensed aromatic solvents on the liquefaction of a lignite and a bituminous coal was investigated, using a time-sampled reactor system that can rapidly charge reactants into a preheated autoclave and then sample its contents throughout the course of reaction. For both coals, addition of the aromatic solvents significantly increased conversion. The order of effectiveness in the presence of decalin + tetralin was: tetralin < phenanthrene < anthracene/dihydroanthracene < pyrene. The main effect of these solvents on liquefaction behaviour was to increase the oil yield almost immediately after hot-charging of the coal at 425 °C. The solvents also reduced the formation of a plastic phase from the bituminous coal. The mechanistic implications of these results are discussed.