Negative-ion electrospray ionization (ESI) Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was used to study the effect of the pyrolysis temperature (400, 430, 460, 490, and 520 °C) on acidic and neutral nitrogen species in Huadian shale oil. To more accurately analyze the influence, shale oils produced during the heat-up stage were abandoned. The results show that because of the influence of polymerization and cracking reactions, the increase in temperature increases the content of pyrrole, thiophene, furan, phenol, and aromatic ring cores and decreases the content of carboxylic acid, respectively. Among all the heteroatom compounds identified from negative-ion ESI FT-ICR MS, the relative abundance of N1O1, N1O2, N1O3, N2, N2O1, O1, O3, O1S1, and N1S1 species increases, whereas that of O2 and O4 species decreases as the pyrolysis temperature increases. The decrease in the O2 species can be attributed to carboxylic acid with a double-bond equivalence (DBE) value of 1, whereas the increase in the O2 species with DBE values of 7 and 9 can be attributed to the formation of furan, phenol, and aromatic ring by the polymerization reaction at higher pyrolysis temperatures. Although the effect of the reaction temperature on the molecular composition of acidic and neutral nitrogen species is complex, still characteristic rules are found in this study.
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