Dissolution of Baganuur coal analyzed by electron paramagnetic spectroscopy

Experimental studies have been conducted on the solubility of subbituminous coal from Baganuur, Mongolia, in solutions of conventional organic pyridine and modern, "green", imidazolium-based ionic liquid [Bmim]Cl. EPR spectroscopy is employed to investigate the original material and its extraction process. Inertinite-rich Baganuur coal consists of a highly reactive organic fraction of high-gravity ashery residues. As-received coal gives a slightly asymmetric, singlet EPR spectrum at room temperature. After processing with solvents, the inner structure in the spectrum decomposed depending on the used solvent. Various forms of free radical generation were noted. Auxiliary experiments are conducted simultaneously for resolving the type of the radical. Among those radicals, the surface oxygen reactive radicals are revealed and annihilated by mild experimental conditions. In-depth analysis from EPR regarding microwave power dependence and line shape illustrates structural changes occurring during the solubility of coal. Depending on the solvents used, the newly formed charge-transfer complex remained stable. Analysis of line shape reveals the radical interaction, which is subject to Gaussian and Lorentzian laws. The solubility restriction of studied coal in the solvent is a result of the subsequent formation of radicals as a result of Lorentz lines.