The impact of pyrolysis temperature on the evolution of the maceral and mineral geochemistry in a subbituminous coal

Temperature has a significant effect on the physical and chemical properties of coal. Based on pyrolysis experiments on subbituminous coals rich in inertinite at the Guanbanwusu Coal Mine on the eastern margin of the Ordos Basin, the effect of thermal maturity on the evolution of macerals and minerals is investigated. The results show that the vitrinite reflectance increases from 0.55 % to 2.58 % with increasing temperature from room temperature to 500 °C. When the temperature exceeded 350 °C, stomas began to appear in the vitrinite, and both pore size and pore complexity increased with increasing temperature. The fluorescent properties of liptinite diminished during pyrolysis and disappeared at temperatures above 350 °C. Liptinite is converted to liquid hydrocarbons when the temperature is below 400 °C and splits to gaseous hydrocarbons when the temperature exceeds 400 °C. Vitrinite and liptinite are the main sources of hydrocarbons, and inertinite remains stable during pyrolysis. The total content of major-element oxides is linearly and positively correlated with the conversion rate of the coal sample during pyrolysis. The composition and content of the major minerals in char are similar to those of raw coal, indicating that the minerals of coal remain stable during low-temperature pyrolysis.