Biogenic oxygenates in lignite pyrolysis tars and their thermal cracking revealed by two-dimensional gas chromatography/time-of-flight mass spectrometry (GC x GC-TOFMS)

GC x GC-TOFMS was applied to characterize oxygenates in five lignite tars, which were produced from the pyrolysis of a low-maturity lignite in a two-stage reactor with thermal cracking of volatile matter at a different temperature (500-800 degrees C) and without thermal cracking. The analysis of the two tars obtained by no cracking and cracking at 500 degrees C identified 349 and 469 oxygenates with a higher reliability, respectively. Those oxygenates embraced a considerable variety of biomarker species. Many biomarker compounds were the constituents of essential oils or extracts of plants, including long-chain fatty oxygenates (e.g., linolenic acid, erucic acid and 2-hexyldecanol), terpenoids (e.g., cedrenol, caryophyllene oxide and artemisinin) and aromatic compounds (e.g. vanillin, cinnamic acids and flavoniods). Besides, cellulose-degraded primary compounds (e. g., levoglucosenone and furfural) and lignin-derived guaiacols were detected. The results strongly indicated the preservation of various biogenic compositions in the lignite due to the low microbial activity and immature diagenesis. The study also reported the changes of oxygenate classes with cracking temperature by classifying them into chain fatty oxygenates, alicyclic oxygenates and aromatic oxygenates.