Elucidation of the structural features of low-rank coals using two-dimensional gas chromatography/time-of-flight mass spectrometry

Thermal dissolution (TD) and ultrasonic-assisted extraction (UAE) were applied to the extraction of soluble components from Shengli lignite (SL) and Shenfu sub-bituminous coal (SS) using cyclohexane as the solvent. Comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry (GC x GC/TOF-MS) was used to analyze the complex molecular composition of soluble fractions. The powerful separation ability of GC x GC/TOF-MS enriches compounds with similar molecular characteristics. The extracts of SL exhibited a high relative abundance of oxygen-containing compounds, up to 81.10 % in SL100. The extracts of SS had a high relative abundance of hydrocarbons such as 70.30 % in SS100. Meanwhile, those hydrocarbons and oxygenates embraced a considerable variety of biomarkers of coal, which were the constituents of plants and microbes from ancient times, including aliphatic hydrocarbons, sesquiterpenoid compounds, long-chain fatty compounds, furans, and aromatic esters. TD at below 200 degrees C mainly induced the dissociation of intermolecular interactions, but both the dissociation of intermolecular interactions and the partial cleavage of weak covalent bonds at 300 degrees C.