Mechanism of Gas Generation during Low-Temperature Oxidation of Coal and Model Compounds

This study focuses on the mechanism of gas (such as CO and CO2) generation during low-temperature oxidation of coal to provide a better understanding of the progressive phases of coal spontaneous combustion. Considering the formation of coal bodies, the internal structures of different coal bodies vary; therefore, it is difficult to directly use coal samples to study the mechanism of gas generation. In this paper, we use model compounds, which include certain reactive functional groups discovered from real coal bodies, to simulate the gas generation from oxidation of these functional groups. By comparing the gas generation during coal oxidation, we reached conclusions regarding the gas generation mechanism during low-temperature oxidation of coal. It is found that the methylene and methyne groups attached to the aromatic rings are the main functional groups that generate peroxides. The peroxides are unstable and easy to decompose to produce alkoxy radicals and hydroxyl radicals. Then, the alkoxy radicals can generate aliphatic radicals and oxygen-containing groups (aldehyde and carboxyl) through beta-cleavage. Oxygen-containing groups then release CO and CO2, while oxidation, hydrogen adsorption, and other reactions of aliphatic radicals occur, which also release CO and CO2 along with CH4, C2H4, C2H6, and C3H8.