Physical properties of low rank coals dried with supercritical carbon dioxide

Three coal samples from low rank coals (Berau and Taiheiyo) were prepared, such as raw coals, dried coals with supercritical carbon dioxide, and thermally dried coals at 110°C. The physical properties of three samples were analysed by a FT-IR spectroscopy, BET surface area measurement, and solvent swelling with pyridine and methanol. The FT-IR spectra of Berau and Taiheiyo coals showed that the infrared absorption for the thermally dried coals was slightly different from those of the raw coals and coals dried with supercritical carbon dioxide. The surface areas of Berau and Taiheiyo coals dried with supercritical carbon dioxide were larger than thermally dried coals. The changes of structures in the coals may be minimized by drying with supercritical carbon dioxide especially at higher pressures. From the swelling experiments with pyridine, the swelling ratio of Berau coal dried with supercritical carbon dioxide was the highest and that of the thermally dried coal was the lowest among the samples. The swelling results of Taiheiyo coal showed almost the same tendency as those of Berau coal. This indicates that the swellability of low rank coals is enhanced by drying with supercritical carbon dioxide.