Structural studies on Illinois no. 6 coal through quinoline extraction

Extraction of two subbituminous and four bituminous coals with quinoline at 350 °C under 4.9 MPa of N₂ pressure was conducted, this giving extract (quinoline-soluble materials) in 65-90 wt % yield. Only the extract from Illinois No. 6 coal (85% yield) was found to be completely soluble in more conventional solvents such as pyridine and N,N-dimethylformamide (DMF). Therefore, the structural study was focused on the extract. Comparison of the structural features of the QS fraction with that of the original coal suggests that bond cleavage reaction occurs during the extraction, this seeming to be partly responsible for solubilization in quinoline. To examine the nature of the extract association, light scattering and size exclusion Chromatographic experiments were conducted in DMF solution. The results indicate that molecular size of the QS is very large even in the polar solvent and this might consist of association of the smaller compounds with ca. 3000 molecular weight. These are discussed briefly.