Kinetics and mechanisms of coal oxidation mass gain phenomenon by TG–FTIR and in situ IR analysis

Coal spontaneous combustion occurs frequently in mining and utilizing processes, which mostly result from the complex dynamic reaction of coal and oxygen. With a focus on the mass gain phenomenon of coal oxidation observed by thermogravimetric analysis, TG–FTIR and in situ IR experiments for a typical Jurassic coal in West China were carried out to identify the kinetics and mechanisms of coal oxidation. The results showed that a mass loss existed both in coal oxidation and pyrolysis process, but the phenomenon of mass gain was particular in coal oxidation process. By FTIR analysis, CO and CO₂ produced in the oxidation process were more than those in the pyrolysis process. By Ozawa method, the apparent activation energy at the initial temperature of mass gain stage was determined to be 43.17 kJ mol⁻¹, which was much less than that at the end temperature of 122.0 kJ mol⁻¹. With in situ IR analysis of Liangshuijing coal during the oxidation and pyrolysis process, the oxidation mass gain mechanism was discussed. It was concluded that the key functional groups for this typical coal oxidation mass gain were carboxyl and carbonyl.