The effect of organic solvent thermal treatment on the physicochemical properties of lignite

Two organic solvents (ethanol and n-hexane) were selected to dewater and upgrade Indonesian lignite under high pressure and moderate temperature. The solid products yield of lignite upgraded by ethanol and n-hexane are 65.1% and 74.4% at 300 degrees C, 17MPa and 300 degrees C, 12MPa, respectively. In addition, the organic solvents upgrading significantly reduced the moisture content, increased the fixed carbon content, decreased the atomic ratios of O/C and H/C, and considerably increased the calorific value of lignite. Numerous porous and large holes were created on the surface of the upgraded lignite due to the extraction of absorbed water and organic matter in raw lignite. Because of the extraction and decomposition of functional groups in the process of upgrading, the content of carboxyl, carbonyl, hydroxyl, and other oxygen-containing functional groups is significantly decreased. Also, the condensation degree of the aromatic ring increased, and the quality of lignite upgraded by n-hexane was better than that of lignite upgraded by ethanol. The content of carbonyl in the lignite decreased from 19.42% to 5.72% after ethanol upgrading and to 2.04% after n-hexane upgrading at 300 degrees C, but the carboxyl groups were decomposed at 300 degrees C. (c) 2015 Curtin University of Technology and John Wiley & Sons, Ltd.