Comparative Study of the Aromaticity of the Coal Structure during the Char Formation Process under Both Conventional and Advanced Analytical Techniques

Six coal samples of different rank, five southern hemisphere and one northern hemisphere, were studied using both conventional and advanced analytical techniques: scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), carbon nuclear magnetic resonance (C NMR), and X-ray diffraction (XRD). Apart from SEM that was used to study the coal to char morphology, the other analytical techniques were used to determine the molecular structural parameter of coal, specifically, the aromaticity, f a. The application of these techniques to the simulation of coal formation revealed the aromaticity to be between 0.86 and 1.03 for lignite, between 0.86 and 1.03 for sub-bituminous, between 0.87 and 1.03 for bituminous, between 0.88 and 1.03 for semi-anthracite, and between 0.94 and 1.03 for anthracite. This reported value for the aromaticity was obtained from the conventional method of analyses. Similar values showing the same consistencies in coal rank were obtained using the FTIR (between 0.66 and 0.79 for lignite, between 0.58 and 0.90 for sub-bituminous, between 0.84 and 1.00 for bituminous, between 0.94 and 1.00 for semi-anthracite, and between 0.97 and 1.00 for anthracite). The values obtained using both C NMR and XRD were at variance from those obtained using both the conventional and FTIR, which call into question the reliability, authenticity, and dependability of these sophisticated and expensive analytical techniques. It is therefore proposed for researchers and coal scientist to rely on the conventional analysis technique of determining aromaticity, which serves as a predictive index for char reactivity, to understand the data obtained from these advanced analytical techniques.