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Methanolysis of an extraction residue (ER) from Xianfeng lignite was carried out to obtain extracts 1−4 (E 1 −E 4 ). The molecular compositions (MCs) of oxygen-containing species (OCSs) in E 1 −E 4 were characterized using negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS). In addition, solid-state 13 C 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 E 1 −E 4 range from 150 to 500 u. The O n (n = 1−6) class species are the predominant OCSs in E 1 −E 4 , with 0−14 double bond equivalent (DBE) values and 9−34 carbon numbers (CNs). The most abundant O n class species in E 1 −E 4 are O 2 , O 2 , O 2 −O 3 , and O 3 , respectively. The OCSs in E 4 contain low abundances of O 1 and O 2 class species but relatively high abundances of O 4 −O 6 class species. In addition, the O n class species in E 4 have narrower ranges of DBE values and CNs than those in E 1 −E 3 . A series of acidic species with different DBE values and CNs are assigned to alkanoic acids, alkanedioic acids, alkanetricarboxylic acids, alkylarenols, alkylarenediols, alkylarenetriols, and alkylarenoic acids. With high resolving power and mass accuracy, ESI FT-ICR MS is an effective technique for characterizing MC of the soluble portion from lignites, which will facilitate producing important chemicals from lignites.

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