Investigation on Structural and Thermodynamic Characteristics of Perhydrous Bituminous Coal by Fourier Transform Infrared Spectroscopy and Thermogravimetry/Mass Spectrometry

Perhydrous bituminous coal has multi-purpose industrial applications determined mainly by its structural and thermodynamic parameters. The Huainan coalfield in China has a large reserve of perhydrous bituminous coal resource. However, little information is available concerning its physicochemical characteristics. In this study, perhydrous bituminous coal samples from number 13-1 and 8 coal seams were selected from 11 Huainan coal mines. The Fourier transform infrared spectroscopy (FTIR) showed that the chemical structures of perhydrous coal were characterized by relatively low aromaticity, implying that the process of hydrogen enrichment during coalification influenced the reactivity of aromatization and condensation of coal macromolecules. The thermogravimetry/mass spectrometry (TG/MS) experiments were conducted at different heating rates (10, 20, and 30 °C/min). At the heating rate of 20 °C/min, number 13-1 coal seam had similar pyrolysis characteristics as number 8 coal seam. Three pyrolysis stages could be divided at this heating rate, and the main pyrolysis temperature range is 300–600 °C. Variation in heating rates mainly affected the primary pyrolysis stage (450–550 °C) of perhydrous coals. With the increase of heating rates, the maximum weight loss rate of coal and the releasing rates of gaseous species increased. The second- and third-order reaction parameters fitted better representations of the non-isothermal pyrolysis processes of perhydrous coals from the Pan4 coal mine. The apparent activation energy was calculated with values ranging from 78 to 307 kJ/mol.