Study on the characterization and thermal conversion behavior of sequential extraction products from medium temperature coal pitch

Abstract

To achieve the high value-added clean utilization of medium temperature coal pitch (MTP), five fractions were separated from MTP by the sequential extraction method using n-heptane, n-butanol, toluene, tetrahydrofuran and quinoline as solvents. Briefly, the extracts were analysed using proximate analysis, elemental analysis, fourier infrared spectrum (FTIR), ultraviolet visible spectrum (UV–vis), fluorescence spectrum, and thermogravimetric analysis (TGA) to investigate their structural parameters, aromatic condensation degree and pyrolysis properties. Meanwhile, Raman spectrum, X-ray diffraction (XRD), and polarizing microscope were used to quantitatively analyze the microstructures of thermal conversion products of the extracts. This allowed for investigation of the thermal conversion mechanism and determination of the thermal conversion behavior. In fact, the chain index (CH3/CH2), aromatic index (Iar), aromatic condensation degree and thermal stability of the extracts increase gradually with deeper extraction. Extracts with high aromatic condensation degree are more favorable for the formation of mesocarbon microbeads (MCMBs). However, overly aromatic condensation degree will lead to excessive coalescence of MCMBs. The ideal carbon microcrystalline content increases with higher temperatures during the thermal conversion of the same fraction. But the change of amorphous carbon content has no obvious regularity. The results of this work will provide theoretical and experimental support for the selection of precursors for carbon/graphite materials.