Pyrolysis behaviors of model compounds with representative oxygen-containing functional groups in coal over calcium

Calcium has great catalytic potentials to regulate volatiles from low-rank coal pyrolysis to form high-valued products. Due to the complexity of coal structure, it's still no consensus on the catalytic mechanism over calcium catalyst. In this paper, coal-related model compounds with representative O-containing functional groups [1,4-naphthalenedicarboxylic acid, poly (4-vinylphenol) and poly (2,6-dimethyl-1,4-phenylene oxide)] were chosen to study the primary pyrolysis product distribution and composition over calcium components by FTIR, TGA and in-situ pyrolysis vacuum ultraviolet photoionization time-of-flight mass spectrometry. The results show that calcium could be ion-exchanged with the O-containing acidic groups (carboxyl functional group or phenolic hydroxyl group) presented in the model compounds to significantly improve the thermal stability, and the pyrolysis of carboxylic and phenolic compounds in the presence of calcium will not only promote a complex cross-linking reaction for the formation of polymers, but also lead to the formation of ketone compounds. The addition of calcium has no effect on the decomposition modes of ether bond connecting two aromatic rings. In addition, the interaction mode and thermal conversion mechanism between carboxyl groups and calcium component were studied. The benzoic acid, 2-naphthoic acid, anthracene-9-carboxylic acid, and 1-pyrenecarboxylic acid were used to investigate the effect of aromatic ring number on the transformation of carboxyl functional groups under the action of calcium. The results showed that the difference of substitution positions may have a certain effect on the formation of products, but the effect of calcium on the main transformation mechanism of carboxyl functional groups in different aromatic structures is universal.