Involvement of Carbon Centered Radicals in Coals Undergoing Oxidative Weathering

Coal is the largest source for fossil fuels for power production (~40% in 2018). Thus, large piles are stored under open air as fuel source. The stored coal undergoes surface reactions (defined as Low Temperature Oxidation LTO). The results are self-heating of the piles, decrease of the calorific value and also emission of different gasses such as carbon oxides (CO, CO₂), water, hydrogen (H₂) and low molecular weight organic gases (C_1–5). In extreme cases, fire eruptions, have been reported.^1,2

It has been suggested that the mechanism by which the molecular oxygen interacts with the coal macromolecule, occurs in several steps in which radicals are involved (a chain of radical reactions). Two types of radicals are observed: aromatic and aliphatic radicals.³ The exact mechanism is not clear yet. We have succeeded to identify various radical species resulting from these LTO processes and measure its spin concentration (#spins/ml) under different atmospheres and temperature range. Several methods utilizing EPR spectroscopy coupled with MATLAB (for simulations quantities parameter) and Origin (for spin concentration), have been used.⁴

Bibliography

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4. Taub, T., Ruthstein, S. & Cohen, H. The involvement of carbon-centered radicals in the aging process of coals under atmospheric conditions: an EPR study. Phys. Chem. Chem. Phys. 20, 27025–27035 (2018).