Surface Properties of Coals Upgraded by Hydrothermal Treatment
Xiao-Feng XIE, Akira OHKI, Koichiro MORIMATSU, Tsunenori NAKAJIMA, Hirokazu ODA, Shigeru MAEDA
The properties of coal when the coal was hydrothermally treated at 150-350°C were examined with particular emphasis on the surface properties. The analysis of coal properties includes hygroscopicity, the content of functional groups measured by chemical analysis and FT-IR, elemental analysis, specific surface area, maceral composition, and vitrinite reflectance. Two Australian low rank coals, Loy Yang coal and Yallourn coal, were tested; while a subbituminous coal and a high rank coal were subjected to the same treatment for comparison. When the low rank coals were hydrothermally treated, the hygroscopicity of coal remarkably decreased, becoming comparable to that for high rank coals after the 350°C treatment. The content of carboxyl group greatly decreased as heat treatment temperature (HTT) was raised; whereas decrease in the content of phenolic hydroxyl group was rather small. After the hydrothermal treatment, exinite maceral in the coal almost disappeared and the absorbance for aliphatic carbon in FT-IR spectrum was somewhat raised. From these results, the change in the coal properties during the hydrothermal treatment is discussed.