Influence of hydrothermal upgrading on physical and chemical structures and moisture readsorption characteristics of a lignite

Zhaotong lignite from Yunnan province was hydrothermally upgraded at 150-300 ℃, then the changes of surface oxygen-containing groups were analyzed by Fourier transform infrared spectroscopy, and the evolution of pore structure was identified by nitrogen adsorption isotherm. Constant temperature and humidity incubator were used to investigate moisture readsorption characteristics. The results indicate that the main hydrophilic oxygen-containing functional groups (-OH, -COOH, >C=O) decrease and are removed effectively with increase of upgrading temperature. Large changes occur in pore structures of the treated coal, in which the specific surface area and total pore volume increase firstly then decrease with increasing temperature, moreover tar initially generate at 250-300 ℃. Moisture readsorption performance is restrained effectively under the synergy effect of physical and chemical structures, and the moisture readsorption ratio decreases continuously with increase of upgrading temperature. Environment humidity is a key factor affecting moisture readsorption considering storage of the upgraded lignite. Therefore the situation of hydrothermal upgrading at high temperature and storage at low temperature and low humidity could be more advantageous in terms of enhancing efficiency of lignite upgrading.