Effects of high-temperature oxygen-deficient oxidation on the surface properties of sub-bituminous coal

The air oxidation of coal releases heat which increases coal temperature, as a result, the spontaneous combustion of coal happens. Generally, coal spontaneous combustion needs to be prevented artificially, however, most of the coal particles still suffer a high-temperature heating process under the oxygen-deficient condition. This paper aims to investigate the effect of high temperature (500°C, 600°C, and 700°C) oxygen-deficient (3% oxygen and 97% nitrogen) oxidation on the surface properties of sub-bituminous coal. SEM and XPS were applied to show the changes of surface properties of sub-bituminous coal. SEM results showed the number of pores and cracks on coal surface increased with the increasing heating temperature, and XPS results showed the content of hydrophobic functional groups on coal surface reduced whereas the content of hydrophilic oxygen-containing functional groups increased after the oxygen-deficient oxidation