Stable Radicals Formation in Coals Undergoing Weathering

Coal exposed to the atmosphere air outside absorbs the atmospheric oxygen, which involves physical adsorption and chemisorption to forms surface oxides (including hydro-peroxides).

These weathering processes called Low Temperature Oxidation (LTO), which decrease the energy value of the coal and emit different toxic gasses such as carbon oxides (CO, CO₂), water, hydrogen (H₂) and some low molecular weight organic gases (C_1–5).

The mechanism by which the molecular oxygen interacts with the coal macromolecule suggested occurring in several steps. The main concept is that a chain of radical reactions is taking place, but the exact mechanism is not clear yet. Herein, we aim to explore the coal oxidation process using Electron Paramagnetic Resonance (EPR) spectroscopy. We succeeded to identify various radical species, which depends on the coal rank and the degree of oxidation. Together with other physical methods, we suggested an initial model for the coal oxidation mechanism.