Composition and structural characteristics of nitrogen-containing species in the soluble organic species of Xianfeng lignite

Xianfeng lignite (XL) was firstly thermal dissolved in the isometric toluene/methanol mixed solvent at 300°C in a stainless-steel autoclave to afford a soluble portion (SPXL) and a residue (RXL), then the nitrogen forms in XL and RXL were characterized with X-ray photoelectron spectroscopy (XPS) analysis, and the nitrogen-containing species (NCSs) in SPXL were identified using gas chromatography/mass spectrometry (GC/MS) and electrospray ionization Fourier transform ion cyclotron mass spectrometry (ESI FT-ICR MS) analyses. The results show that the amount of nitrogen forms in XL is in the order of quaternary-N > pyridinic-N > pyrrolic-N, while quaternary-N in XL is easily dissolved out during thermal dissolution. In total 20 NCSs were detected in SPXL by GC/MS, and most of them are amines. Over three hundreds of NCSs were identified in SPXL by ESI FT-ICR MS, and most of them are the NCSs containing one or three nitrogen atoms. The NCSs containing one nitrogen atom are mainly dominated by N1O1, N1O2 and N1OxS1−2 class species, while most of NCSs containing three nitrogen atoms are N3OxS1−2 class species (x=1−12). The double bond equivalent (DBE) values and carbon number of the NCSs containing one nitrogen atom increase with increasing number of oxygen atoms.