Analysis of Botswana coal structural parameters and their correlation to other coal properties

Many countries continue to depend on coal as a significant energy source, with the quality of coal varying considerably based on its chemical and structural composition. A critical aspect influencing coal behavior during utilization is its turbostratic/random-layer/short-range ordered structure, which relates to the arrangement of aromatic sheets, packing, and the presence of oxygen-containing functional groups. This study focused on coal samples from the Morupule, Mmamabula, and Mabesekwa coalfields in Botswana, utilizing X-ray diffraction (XRD), micro-Raman spectroscopy (mRS), and Fourier transform infrared (FTIR) techniques to investigate their turbostratic structure. The findings revealed a predominance of aliphatic structures over aromatic ones, with the FTIR spectrum showing significant -OH and N-H groups, strong phenolic deformation bending (C-O-C), and robust aromatic C-H stretches. The XRD results indicated a random lattice structure with d 002 values ranging from 3.37 to 3.57 Å, while mRS suggested a low degree of crystalline order, with the ratio of D-bands to G-bands (I D /I G ) varying from 0.59 to 1.04. Aromaticity, as determined by XRD, ranged from 0.61 to 0.84, and from FTIR, it ranged from 0.75 to 0.84. These turbostratic structure results indicate the coal samples' potential suitability for combustion, gasification, and liquefaction processes. Principal component analysis (PCA) demonstrated correlations among various structural parameters and the chemical composition, indicating relationships between the structural parameters and coal properties such as nitrogen, hydrogen, and carbon content, as well as ash content and minerals.