Ultrasonic extraction and oxidation characteristics of functional groups during coal spontaneous combustion

Abstract The reactions between oxygen molecules and functional groups are the internal cause leading to heat release and the corresponding coal spontaneous combustion. However, the difficult discrimination of the multitudinous functional groups tremendously limits the deep insight into the mechanism of coal-oxygen reactions. Ultrasonic extraction technology, in this case, was utilized to extract the different functional groups from coals. The extracted coal samples were further collected for tests of Fourier infrared (FTIR) spectrum, electron paramagnetic resonance (EPR) spectrum, and thermogravimetric (TG) analysis. The experimental results indicated that Dimethylacetamide (DMAC) had the largest extraction rate in terms of the changes of mass or free radicals. While Acetone exhibited great extraction ability for CH 3 and Cyclohexanone (CYC) could effectively extract C O C . The greatest extraction rate of OH was possessed by N-methylpyrrolidone (NMP). Both TG and differential scanning calorimeter (DSC) tests proved that OH played a dominant role in the oxidation stage of coal. Compared to OH, other functional groups like CH 2 , CH 3 and C O C had fewer effects on the mass change and heat release during coal spontaneous combustion.