Kinetic study on changes in methyl and methylene groups during low-temperature oxidation of coal via in-situ FTIR

It is imperative to have an in-depth understanding of the change in methyl and methylene groups during low-temperature oxidation of coal not only for detecting and preventing coal spontaneous combustion in coal mining industry and for reducing emissions of hazardous gases. The Fourier transform infrared (FTIR) spectroscopy equipped with in-situ reactor cell was introduced to investigate the change in the methyl and methylene groups of different classes of coals (lignite, sub-bituminous and bituminous) during their low-temperature oxidation at temperatures below 230 °C. The reaction kinetics of the methyl and methylene groups was obtained from the real-time measurements of the change in aliphatic hydrocarbon content in coal matrix. These results clearly show that the low-temperature oxidation of coal can be separated into three stages with respect to the activation energies for the change in methyl or methylene groups, which indicates that the reaction regime for the change in methyl or methylene occurrence switches during the spontaneous combustion of coal. At the first and second stages the reaction activation energies of the methyl or methylene groups showed significant difference for the three types of coal, and at the third stage the activation energies were very close for all of the coals. These results indicate that the spontaneous combustion propensity of coals can be evaluated on the basis of the kinetic parameters at the first and second stages. Furthermore, the relationship between the changes in methyl and methylene groups and the emission of carbon oxides (CO2 and CO) was also explored on the basis of the experimental findings.