Sequential thermal dissolution of two low‐rank coals and characterization of their structures by high‐performance liquid chromatography/time‐of‐flight mass spectrometry and gas chromatography/mass spectrometry.

Rationale: Gas chromatography/mass spectrometry (GC/MS) and high‐performance liquid chromatography/time‐of‐flight mass spectrometry (HPLC/TOF‐MS) were used to separate and reveal the molecular characteristics of organic matter in low‐rank coals. Methods: Six soluble portions (SPs) were obtained by sequential thermal dissolution (TD) of two low‐rank coals in the order of cyclohexane, acetone and methanol solvents at 300°C. Organic matter with different molecular characteristics were enriched in eachTD extract, which was further separated and analyzed by GC/MS and HPLC/TOF‐MS using an electrospray ionization source in positive mode to obtain a comprehensive understanding of the structural composition of coals. Results: Low polarity compounds like alkanes and arenes have a better solubility in cyclohexane. Phorone has the highest relative abundance in the acetone SPs, and the main compounds detected in the methanol SPs are alcohols and phenols. According to the data from HPLC/TOF‐MS, most of the oxygen atoms are in the form of carbonyl and alkoxy groups. The nitrogen‐containing compounds in SPs are mainly saturated aliphatic amines and pyridines. The sulfur‐containing compounds mainly exist in the form of thioalkanes and thiophenes. Conclusions: Non‐destructive methods were used to obtain soluble matter from coals, and different chromatographic and mass spectrometric techniques were used to separate and analyze the organic matter in coals. Detailed molecular structural information was obtained for the efficient and clean utilization of low‐rank coals. [ABSTRACT FROM AUTHOR]