Analysis of oxidation pathways for characteristic groups in coal spontaneous combustion

This study was designed to clarify the molecular characteristics and reactivities involved in coal spontaneous combustion. In the study, the structures of the characteristic groups –OH, –CHO, –CHOHCH2-, –COOH, –CH2CH2CH3, and –CH2CHCH2 were the research objects. The B3LYP-311G method of DFT was used to construct a molecular structure model for coal spontaneous combustion. Based on quantum-chemistry theory, the oxidation characteristics and reaction pathways of characteristic groups were analysed, and the reaction channels and oxidation products involved in reactions of –CHO, –COOH and –CHOHCH2- moieties were studied. Analyses of the oxidation characteristics and reaction pathways of the characteristic groups showed that the reactions of active groups with oxygen depend on the energies of bonds between the characteristic groups and hydrogen. The smaller the bond energy is, the more exothermic the reaction and the more readily the reaction will take place. When characteristic groups in coal react with oxygen, oxygen first attacks hydrogen atoms directly connected to carbon atoms close to aromatic rings. At normal temperatures and pressures, the rate-determining step of the –CHO conversion to CO2 is decarboxylation of ▪; the rate-determining steps for conversion of –CH2CHOH to CO2 and CO were decarboxylation and decarbonylation of ▪, respectively.