Inhibiting effect and mechanism of polyethylene glycol - Citric acid on coal spontaneous combustion

To solve the problems of the existing inhibitors, e.g., low efficiency and high price, a high-efficiency and safe composite inhibitor called polyethylene glycol-citric acid (PEG-CA) has been developed to inhibit coal spontaneous combustion. The inhibition performance and mechanism of PEG-CA were investigated by temperature-programmed and infrared spectroscopy experiments. The temperature-programmed test results showed PEG-CA inhibited the O2 consumption, the production of CO and C2H4, with varying effectiveness at different temperature stages. Polyethylene glycol (PEG) was the dominant inhibitor, with an 85.5% increase in the apparent activation energy of inhibited coal (PEG:CA = 3:1) compared to raw coal at 30–80 °C. Conversely, at 80–170 °C, the inhibited coal (PEG:CA = 1:3) was relatively optimal, with an 81.1% increase in activation energy and a 75% inhibition rate at 150 °C. FTIR results showed the –OH decreased, the ether bonds increased, and the increase rate of –CH3, –CH2- gradually retarded with higher temperature. The PEG-CA inhibited the oxidation of –CH3, –CH2-, as well as the intermediate products and –OH in coal underwent etherification reaction to form numerous ether bonds. The citric acid degraded the transition metal ions in coal, increased the energy of reaction, and inhibited coal spontaneous combustion.