An Experimental Study on the Effect of Magmatic Thermal Evolution on the Molecular Structure of Low-Rank Coal

Low-rank coal accounts for over half of China’s proven coal reserves. The possibility of coal and gas outbursts in low-rank coal is higher, especially in the m·agmatic thermal evolution area. The complexity of coal’s molecular structure is one of the reasons for problems during the process of mining operations. Different analysis techniques, including XRD, FTIR and Raman spectroscopy, were used to obtain the molecular characteristics of magmatic thermal evolution coal samples and normal coal samples, so that a comparative study could be carried out to investigate the influence of the magmatic thermal evolution effect on the molecular structure of low-rank coal. The ranges of the aromatic interlayer spacing (d₀₀₂), average stacking heights (L_c) and stacking layer number (N_ave) of the thermally evolved coal samples are 3.41–3.51 Å, 22.76–27.02 Å, and 6.68–7.70, respectively. The ranges of the full width at half maximum ratio (F_D1/F_G) and the peak integral intensity ratio (I_D1/I_G) are 2.16–2.19 and 1.55–1.84, respectively. Compared with the normal coal samples, those affected by magmatic thermal evolution have smaller d₀₀₂, I_D1/I_G, and F_D1/F_G values, but larger L_c values. The results indicate that the thermally evolved coal samples have more ordered structures and more developed microcrystalline structure sizes than normal coal samples.