Molecular Characterization of Lignite Extracts of Methanol and Carbon Disulfide/N‑Methyl-2-pyrrolidone by High-Resolution Mass Spectrometry

CS2/N-methyl-2-pyrrolidone (NMP) could extract much more substance from coals than any other solvents. Investigation on the molecular composition of CS2/NMP extracts from lignite is significant for the understanding of high extraction yield and the clean utilization of coal. The methanol-soluble portions from lignites and CS2/NMP extracts of lignites were characterized by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. The yield of CS2/NMP extracts from lignite was quite higher than that of methanol extracts. Furthermore, the yield of methanol-soluble portions from CS2/NMP extracts was far more than that of methanol extracts from lignite. At the level of molecular composition, the relative content of heteroatom compounds with more oxygen atoms, longer side chain, and higher condensation in the CS2/NMP extract was also higher than that in the methanol extract. Despite great difference in the yield and the relative content of components, the distributions of species, molecular weight, carbon number, and double-bond equivalent were similar to those of most organic molecules for the methanol extract and methanol-soluble portions from the CS2/NMP extract. These phenomena suggested that organic molecules with similar structure but different composition, nonuniformly distributed in the coal matrix, were released more in the CS2/NMP extract compared to the single methanol extract.