Effect of 915‐MHz low‐temperature microwave irradiation on the molecular structure of coking coal

Abstract

The effect of microwave irradiation on the coking‐coal structure is important to study at the molecular scale to improve the quality of coking coal and optimize the coal‐blending technology for low‐quality coal. Through the characterization of coal structure by Fourier transform infrared spectrometer (FTIR), carbon‐13 nuclear magnetic resonance (13C‐NMR), and X‐ray photoelectron spectroscopy (XPS), the macromolecular structure unit model of coal before and after 915‐MHz microwave irradiation were constructed. A small number of alkyl side chains and cycloalkanes were broken, aromatic structures underwent condensation, and the aromatization of coal structure was increased after 915‐MHz microwave irradiation within 100–150°C. The content of hydroxyl self‐conjugated hydrogen bonds was increased, and the coal had more conjugated structures. Some phenolic hydroxyl groups and other functional groups were oxidized. The content of protonated pyridine and nitrogen oxides were increased, the content of pyridine and pyrrole nitrogen structures were decreased, and some nitrogen structures were oxidized. Mercaptan (thioether) and sulfoxide(sulfone) were partly converted into inorganic sulfur and partly converted into the more stable thiophene structure.