Article pubs.acs.org/EF
Investigation on Structural and Thermodynamic Characteristics of Perhydrous Bituminous Coal by Fourier Transform Infrared Spectroscopy and Thermogravimetry/Mass Spectrometry Dun Wu,†,‡ Guijian Liu,*,†,‡ and Ruoyu Sun† †
Chinese Academy of Sciences (CAS) Key Laboratory of Crust-Mantle Materials and Environment, School of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui 230026, People’s Republic of China ‡ State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an, Shaanxi 710075, People’s Republic of China ABSTRACT: 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.
1. INTRODUCTION Perhydrous coal is a type of coal with a higher hydrogen/ carbon (H/C) atomic ratio compared to coals of similar rank.1,2 The increase of the hydrogen content (>6 wt %, on a dry and ash-free basis) in perhydrous coal determines its distinct usefulness in industrial applications.3,4 For example, the perhydrous coal can be used in coal blends to increase the calorific values of low-calorie coal; its enhancement in volatile matter, hydrocarbon oil, and tar generation ability can find applications in producing specific byproducts.5,6 To explore these potentials, it was necessary that we should have a better understanding on the physicochemical characteristics and thermodynamical behaviors of perhydrous coal. Pyrolysis is a useful way to visualize the transition of physicochemical structures and parametrize the thermodynamic processes of coal.7−9 During the pyrolysis processes, the physicochemical structures of coal will be converted and decomposed, generating byproducts, such as tar, char, and gaseous compounds.10 In general, coal pyrolysis can be divided into three stages. In the first low-temperature (
