Experimental and Theoretical Study on Surface Reactivity and CO Generation Mechanism of Bituminous Coal during Room-Temperature Oxidation

To investigate the evolution of the microscopic chemical structure during the oxidation of bituminous coal at room temperature (25 °C) and infer the formation mechanism of carbon monoxide (CO), a self-designed closed-system coal oxidation experimental setup was employed to measure the CO generation from three bituminous coal samples [Duanwang (DW), Linsheng (LS), and Kunning (KN)]. 13C nuclear magnetic resonance and X-ray photoelectron spectroscopy were used to determine the structures and contents of different carbon atoms and surface elemental compositions and chemical states of the coal samples. Molecular models were constructed on the basis of the experimental data, and reactive force field pyrolysis simulation was used to trace the carbon atoms in the generated CO molecules. In combination with the results of interactive Mantel correlation analysis on the Fourier transform infrared experimental data of coal samples oxidized at room temperature for 0, 12, 24, 36, 48, and 60 h, the main functional groups, structures, and evolution of coal involved in CO formation during normal temperature oxidation were determined. The constructed molecular formulas for the coal samples were C154H122O28N2S for DW, C145H114O16N2S2 for LS, and C155H92O16N2S for KN. The formation of CO was related to the transformation of carbonyl (C═O), phenolic hydroxyl (−OH), ether (C–O–C), aromatic, and aliphatic structures in the coal.