Antioxidants on the thermodynamic properties and radical evolution in coal
Shu Pan, Yanni Zhang, Yu Lan, Xuanhong Du, Yating Zhang, Binde Qin, Nianqiang Li
Abstract
Chemical resistance is a crucial method for preventing and controlling coal spontaneous combustion (CSC). This study aims to investigate the inhibitory effect of antioxidants on oxidative CSC. Three antioxidants-tea polyphenols, melatonin, and β -carotene were selected for this research. Initially, quantum chemistry methods were employed to analyze the reactive sites and the quantity of key free radicals within the antioxidant molecules. Subsequently, the oxidative heat release and changes in free radical characteristics of coal samples treated with antioxidants were examined using a synchronous thermal analyzer and electron paramagnetic resonance spectroscopy. The findings indicate that the variation in the number of reactive sites among different antioxidant molecules is a fundamental factor contributing to the diverse effectiveness in inhibiting CSC. All three antioxidants proved to be effective inhibitors of early coal oxidation, with tea polyphenols demonstrating the most significant inhibitory effect. Macroscopically, the dry cracking temperature and initial exothermic temperature of the coal sample increased by 14.5 °C and 14.8 °C, respectively. Moreover, the apparent activation energy increased by 31.18 kJ/mol and 54.79 kJ/mol in the two reaction stages, showcasing the best inhibitory effect. Microscopically, there was a significant reduction in the concentration, types, and complexity of free radicals in the coal samples treated with antioxidants. Tea polyphenols were particularly effective, reducing the free radical concentration in the coal samples by over 30 % compared to the untreated coal.