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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.

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Pyrolysis remains key to all coal utilisation processes such as combustion, gasification and liquefaction. Understanding the thermochemical changes accompanying these processes through pyrolysis would help in defining the technical performance of the processes. With the recent concern for the environment and renewed interest in research on clean coal technology (CCT), hydrogen from coal through the integrated gasification combined cycle has been considered for the proposed hydrogen economy.

In this paper, we explore the use of high resolution transmission electron microscopy (HRTEM) in the degradation of the poly aromatic hydrocarbon (PAH) in coals of different ranks subjected to chemical plus heat treatment. The crystallite diameter on peak (10) approximations, La (10), of 37.6 Å for the high rank coal char at 700 o C fell within the HRTEM's range of minimum-maximum length boundary of 11 x 11 aromatic aromatic fringes (28 -44 Å). The L a (10), 30.5 Å for the low rank lignite chars fell nearly on the minimum-maximum length range of 7 x 7 aromatic fringes (17 -28 Å).The HRTEM results showed that the high rank anthracite chars at 700 o C comprised a higher distribution of larger distribution of larger aromatic fringes (11 x 11 parallelogram catenations). The mechanism for the similarity between coal chars of different ranks was the greater transition occurring in the low rank coals (lignite and sub-bituminous) to match the more resistant medium and high rank coals (bituminous -anthracite). This emphasized that the transitions in the properties of the low rank coals were more thermally accelerated than those of the high rank coals. The total PAHs detected in the coals of different ranks during pyrolysis are dominated by two-and three-ring PAHs. The amount of PAHs increase and then decrease with increase in pyrolysis temperature.

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In this investigation, SAXS and XRD were used to investigate both the physical and chemical changes in six coals of different ranks subjected to heat treatment. The specific surface area which gives an indication of the reactivity of the coal (measures surface area available for reaction) was determined to be in the range of 70.