Characterization of nitrogen- and oxygen-containing species in methanol-extractable portion from Xinghe lignite

Abstract

Xinghe lignite was sequentially extracted with petroleum ether, carbon disulfide, methanol, acetone, and isometric carbon disulfide/acetone mixed solvent to afford extracts 1–5 (E1–E5) and final residue. According to analysis with positive- and negative-ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS), a series of nitrogen-containing species (NCSs) and oxygen-containing species (OCSs) were identified in E3. The ESI FT-ICR MS resolved ca. 3300 basic and 1300 non-basic compounds, which both have molecular mass distributions ranging from 100 to 700u and dominate in 250–450u. The predominant basic nitrogen compounds are N1Ox and N2Ox (x=0–5) class species with double bond equivalent (DBE) values from 1 to 14 and carbon numbers (CNs) from 10 to 34. Acidic Ox (x=2–6) and non-basic N1Ox (x=0–2) classes are mainly detected in the negative-ion mode. According to DBE distributions and relative contents of different nitrogen/oxygen classes, pyridines and quinolines dominate the basic N1Ox class species, while pyridines with an amino group and aliphatic amines share the characteristic core structures in basic N2Ox class. For non-basic N1Ox class, indoles and carbazoles may be the major nitrogen occurrences. In addition, all the NCSs in E3 have up to 4 aromatic rings. Acidic Ox class species with DBE=1–17 and CN=7–37 are assigned to alkanoic acids, arenepolyols, and arenoic acids, in which arenepolyols and arenoic acids are the main OCSs with up to 5 aromatic rings. Positive- and negative-ion ESI FT-ICR MS proved to be effective techniques for characterizing extractable NCSs and OCSs in coals.