Molecular structure model construction and pyrolysis characterization of four typical coals: a case study

This paper constructed the molecular structures of four types of coal with different ranks and investigated the correlation between coal molecular structure and pyrolysis characteristics by using 13C NMR, XPS, TG-FTIR, and GC-MS. The results demonstrate that the structural model formulas of lignite (HM), weakly caking coal (RN), long-flame coal (CY), and gas coal (QM) are C104H111NO20S, C93H109NO13, C167H191NO15S, and C142H129N3O9S, respectively. The aromatic structural units of HM and RN consist of benzene and naphthalene, which are connected by ether bonds or aliphatic chains. The molecular structures of HM and RN contain a large amount -OH and -COOH, which are easily broken to generate gases, such as H2O, CO, and CO2 during pyrolysis. The gas yield of RN is 28.90%, which is higher than the others. The ether bonds in HM breakage to form groups are easily combined with each other to form tar, while the aliphatic chains in RN fracture to form fragments to generate gas. The light component (C≦10) is the dominant form of tar in HM and RN, with a content of 95.62% and 87.78%, respectively. Phenols are the dominant components in HM tar; alcohols are the primary components in RN tar. In CY, the aromatic structures consisted of benzene, naphthalene, anthracene, and phenanthrene; the aliphatic structures mainly included cycloalkanes and long-chain alkanes. The QM structural units are dominated by phenanthrene and naphthalene, with the highest aromaticity. The pyrolysis gas in CY and QM is composed of CH4; the tar component consists of alcohols, phenols, and alkanes. The coke yield in RN is the lowest at 52.84%, and QM is the highest at 80.20%.