Characterization of Oxygen-Containing Species in Methanolysis Products of the Extraction Residue from Xianfeng Lignite with Negative-Ion Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Methanolysis of an extraction residue (ER) from Xianfeng lignite was carried out to obtain extracts 1–4 (E1–E4). The molecular compositions (MCs) of oxygen-containing species (OCSs) in E1–E4 were characterized using negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS). In addition, solid-state 13C nuclear magnetic resonance and X-ray photoelectron spectrometry were used to analyze the carbon types and oxygen functional groups (OFGs) in the ER. The results show that the carbon skeleton structures in the ER are dominated by aliphatic (50.2%) and aromatic (44.9%) carbons. Methylene and methoxy carbons are the most abundant among the aliphatic carbons. Each aromatic cluster contains three rings on average with two substituent groups on each ring. The OFGs in the ER include hydroxy, ether, carbonyl, and carboxyl groups, among which the hydroxy group is the most abundant. The ESI FT-ICR MS analysis shows that the molecular mass distributions of E1–E4 r...