Microstructure evolution and higher-molecular-weight gas emission during the low temperature oxidation of coal

Abstract

The higher-molecular-weight gases (HMWGs) released from coal oxidation carry a wealth of information on the mechanism of coal spontaneous combustion. To explore the formation process of HMWGs, the emission of HMWGs and the evolution of active functional groups during coal oxidation were tested using gas chromatography and in-situ FTIR, and the relationship between them was further analyzed using grey relational analysis. It was found that the concentration of most HMWGs changed regularly with the increase in temperature and showed a significant correlation with oxygen concentration. As the temperature increased, the content of alkyl groups changed little at first and then decreased by more than 40%. The content of oxygen-containing functional groups increased gradually by 2–3 times. The production of straight-chain alkanes correlated most strongly with alkyl groups compared to other active groups. While branched alkanes, benzene, aldehydes and ketones showed a higher correlation with the increase of oxygen-containing functional groups. It indicated that the decrease of alkyl groups and the formation of aldehyde groups contributed to the emission of hydrocarbon HMWG. The formation pathways of benzene, aldehydes and ketone during coal oxidation need to be further investigated and verified.