Changes of Aromatic CH and Aliphatic CH in In-situ FT-IR Spectra of Bituminous Coals in the Thermoplastic Range

Abstract

The change in aromatic CH (3030–2950 cm⁻¹) and aliphatic CH (2920–2850 cm⁻¹) of raw and heated coals in the thermoplastic region was investigated by Fourier transform infrared spectroscopy (FT-IR). It was confirmed that the aliphatic CH abundant in coals of high volatiles is closely related to the maximum fluidity of raw coals. The peak area ratio of aromatic CH to aliphatic CH (A_aroCH/A_aliCH) has close relationship with mean reflectance and aromaticity of raw coals. Aliphatic CH and aromatic CH decreased while A_aroCH/A_aliCH increased with increasing temperature in the thermoplastic range. However, the decomposition trend of each coal clearly showed different features. The coal of low fluidity consumed aliphatic hydrogen to release volatile even before entering thermoplastic region while the coal of high fluidity gradually consumed aliphatic hydrogen all through the thermoplastic region even though they have similar volatiles. The difference in decomposition trend of hydrocarbon resulted in different condensation pattern. In addition, according to the application of 2D correlation spectroscopy for analyzing the spectral change of each coal in thermoplastic region, the relations between R₃CH and RCH₃ (2910 cm⁻¹, 2958 cm⁻¹) and between R₂CH₂ and RCH₃ (2923 cm⁻¹, 2958 cm⁻¹) were different. It was suggested that the coal properties was correlated with the different decomposition trend and fluidity.