Study on the Effect of DTPMP Inhibitor on Oxidation and Structural Characteristics of Coal Spontaneous Combustion

Preventing coal spontaneous combustion fire by using inhibitor is an effective control measure. The oxidized spontaneous combustion characteristics of coal can reflect the performance of coal, and a suitable structural model can reflect the performance of coal more intuitively, and can also lay the foundation for the study of the action mechanism of the inhibitor. In this study, samples from Baishihu coal mine were selected, and diethylenetriaminepenta-methylenephosphonic acid (DTPMP) was used as a blocking agent to investigate the macromolecular structure, microcrystalline structure changes and oxidation process of coal by X-ray photoelectron spectroscopy (XPS), carbon nuclear magnetic resonance (¹³C-NMR), and Fourier infrared spectroscopy (FTIR). The molecular formula C₁₉₈H₁₆₄O₄₀N₂ and the molecular structure model were obtained. ChemDraw and Materials Studio were used for the experimental data, and high-resolution transmission electron microscopy (HRTEM) was used to verify the aromatic ring structure built to make the constructed structural model more accurate. In the water evaporation stage, the high ring aromatic layer is converted into the low ring number. Furthermore, in the high-temperature stage, the low ring aromatic layer is transformed due to the coking and condensation reaction of the coal sample. With the increase in the treatment temperature, water loss is heavier, oxygen absorption and weight gain are perplexing, and the value of the burnout temperature is higher. The elemental composition of the coal samples was changed after the addition of the hindering agent, and the temperature at which small free radical molecules were produced and the time at which gaseous products appeared during the coal-oxygen reaction were delayed. The characteristic temperature increases with the increase of the resist concentration and the activation energy decreases in the water evaporation stage and increases in the other two stages. The apparent activation energy of the coal-oxygen reaction increases and the reaction becomes more hard and complex to realize. DTPMP mainly reacts with free radicals and reactive oxides and forms an adsorption layer on the coal surface. And the molecular structure of the inhibitor contains several phosphate functional groups, which can react with the oxides in the coal to form phosphate substances and fill the pores in the coal. It can reduce the evaporation of water and the contact of coal samples with oxygen. These mechanisms interact with each other and together reduce the reactivity of the coal and the risk of spontaneous combustion. This study furthers the understanding of coal spontaneous combustion in this mining area, provides a reference for the prevention and control of coal spontaneous combustion.