Influence of Aliphatic Species on Coal Molecular Structure During Low-temperature Oxidation of Anthracite Coal

Low-temperature oxidation of anthracite coal has not been extensively investigated. In this study, variations in the structural parameters associated with aliphatic species (e.g., methyl and methylene) in anthracite coal were investigated during low-temperature oxidation (60 °C to 120 °C) using infrared spectroscopy and X-ray diffraction, and the influences on the molecular structure of coal are discussed. The results indicated that the oxidation of aliphatic species is divided into four stages. The aliphatic species were mainly oxidized at Stages 2 (80 °C to 120 °C) and 4 (>170 °C), and only slightly oxidized at Stages 1 (60 °C to 80 °C) and 3 (120 °C to 170 °C). The aliphatic species exhibited two modes of occurrence: at the edges of aromatic structure and in the interlayer spaces, which were mainly oxidized at Stages 2 and 4, respectively. The aliphatic species in the anthracite coal were dominated by those in the interlayer spaces (90.9% methylene and 88.8% methyl), followed by those at the edges (9.1% methylene and 11.2% methyl). The aliphatic species in the interlayer spaces showed a higher chemical stability than that of the species at the edges, resulting in the discontinuous low-temperature oxidation of the aliphatic species. The aliphatic chains in the interlayer spaces ( A ( CH 3 )/ A ( CH 2 )=0.77) were much longer than those at the edges ( A ( CH 3 )/ A ( CH 2 )=0.61), which was mainly attributed to coalification.