Reaction Mechanism of Aldehyde Groups during Coal Self-Heating.

In order to further understand the mechanism of coal self-heating in the initial stage, the aldehyde group was analyzed by using the quantum chemistry methods. The charge distribution, structural parameters, and molecular orbital were analyzed to determine the active sites existing in the structure of aldehyde group. Then, a chemical reaction model including five elementary reaction sequences was established. In elementary reaction E1, the hydrogen of the aldehyde group is captured by hydroxyl to form the aldehyde radical, which provides the reactant and accumulates heat for the subsequent reaction. In elementary reaction E2, the aldehyde radical further reacts to form a carbon-free radical (R) and CO, which is the main source for CO generation during coal spontaneous combustion. In elementary reaction E3, the aldehyde radical is oxidized to a carboxyl radical, providing the reactant for elementary reaction E4, which is directly related to CO generation during coal spontaneous combustion. The thermodynamic parameters of the elementary reactions were further analyzed and confirmed by quantum chemistry methods. The results are helpful for further understanding the pathways of CO generation in the initial stage of coal spontaneous combustion, which provides theoretical support for prediction of coal spontaneous combustion.