Effect of temperature on the solubility of Victorian brown coal in the ionic liquid DIMCARB

The effect of extraction temperature on the solubility of 4 Victorian brown coals (a Yallourn Woody coal and three Loy Yang lithotypes -Dark, Medium Light and Light) in the ionic liquid DIMCARB was investigated using a 100 mL autoclave. The solubility of coal at room temperature is in the order of Light > Medium > Dark > Woody coal, but the effect of temperature on the solubility is related to coal properties. For the Woody, Dark and Medium lithotypes, with higher aromaticity, the soluble yield significantly increased with extraction temperature to 80 °C, then slightly further improved at 120 °C. Elemental analysis, FT-IR and solid 13C NMR analyses indicated that increasing temperature promoted interactions between DIMCARB and the coal and improved the solubilisation. The soluble fractions have higher H/C ratios and aliphaticities than the corresponding residue fractions and raw coals. The extraction temperature affected the distribution of pyrolysis products from the resultant solubles and residues. The solubles have high relative abundance of polycyclic compounds (including diterpenoids and triterpenoids) relative to the corresponding residues and the parent coals. However, increasing extraction temperature leads to decreasing selectivity for triterpenoids and increasing selectivity for long-chain alkanes and alkenes in the pyrolysis products of the soluble fraction. The solubles extracted at 120 °C have similar pyrolysis product distribution to the corresponding raw coals. In the case of the Light lithotype, with high aliphaticity, the highest soluble yield was obtained at room temperature. Extraction at 80 °C reduced the yield significantly, while at 120 °C, the yield slightly increased to be close to that at room temperature. For this case, the soluble fractions have lower H/C molar ratios than the corresponding residues. The relative abundance of triterpenoids in the pyrolysis products of the solubles exhibited the same trend as the soluble yield in DIMCARB versus temperature.