Sulfur-containing species in the extraction residue from Xianfeng lignite characterized by X-ray photoelectron spectrometry and electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

Understanding the chemical composition of sulfur-containing species (SCSs) in coals is important because of their negative impact on the environment during coal utilization. In this study, SCSs in the extraction residue (ER) from Xianfeng lignite were characterized through methanolysis combined with X-ray photoelectron spectrometry (XPS) and electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) analyses. The results show that the SCSs on the ER surface include pyrite, aliphatic sulfur, aromatic sulfur, sulfoxide, sulfone, and sulfate. The S₁O_x (x = 0-5), S₂O_x (x = 0-5), and N₃S₁ class species are the main SCSs in the soluble portion from ER methanolysis according to ESI FT-ICR MS analysis. Henicosane-1-thiol and alkylhydroxythiophenecarboxylic acids are dominant in the S₁O_x class species. The S₂O_x class species have double bond equivalent values of 1-14 and carbon numbers of 16-33. Sulfur in the S₂O_x class species is mainly present in thiol groups or S-heterocyclic rings (especially thiophene ring). Methanol can thermally break the -C-O- and -C-S- bonds connected between SCSs and macromolecular moieties in the ER matrix, leading to the release of SCSs.