Solvent extraction of bituminous coals using light cycle oil: Characterization of diaromatic products in liquids

Many studies of the pyrolytic degradation of coal-derived and petroleum-derived aviation fuels have demonstrated that the coal-derived fuels show better thermal stability, both with respect to deposition of carbonaceous solids and cracking to gases. Much previous work at our institute has focused on the use of refined chemical oil (RCO), a distillate from the refining of coal tar, blended with light cycle oil (LCO) from catalytic cracking of vacuum gas oil. Hydroprocessing of this blend forms high concentrations of tetralin and decalin derivatives that confer particularly good thermal stability on the fuel. However, possible supply constraints for RCO make it important to consider alternative ways to produce an "RCO-like" product from coal in an inexpensive process. This study shows the results of coal extraction using LCO as a solvent. At 350°C at a solvent-to-coal ratio of 10:1, the conversions were 30-50 wt % and extract yields 28-40 wt % when testing five different coals. When using lower LCO/coal ratios, conversions and extract yields were much smaller; lower LCO/coal ratios also caused mechanical issues. LCO is thought to behave similarly to a nonpolar, non-hydrogen donor solvent, which would facilitate heat-induced structural relaxation of the coal followed by solubilization. The main components contributed from the coal to the extract when using Pittsburgh coal are di- and triaromatic compounds.