Characterization of Middle-Temperature
Gasification Coal Tar. Part 2: Neutral Fraction by Extrography Followed
by Gas Chromatography–Mass Spectrometry and Electrospray Ionization
Coupled with Fourier Transform Ion Cyclotron Resonance Mass Spectrometry
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Abstract
A commercial lignite gasification-derived middle-temperature
coal tar (MTCT) was subjected to acid–base extraction to obtain
acidic, basic, and neutral fractions. The neutral fraction was characterized
by mass spectrometry (MS) for hydrocarbon-group-type analysis and
further fractionated by extrography into six subfractions, which were
characterized by gas chromatography–mass spectrometry (GC–MS).
Saturate, aromatic, and resin fractions of the neutral fraction accounted
for 16.4, 47.6, and 36.0 wt %, respectively. The GC–MS analysis
showed that the first neutral subfraction (15.7 wt %) contained alkanes,
alkenes, and cycloalkanes; the second subfraction (52.0 wt %) contained
1–6-ring aromatics; the third subfraction (4.6 wt %) contained
neutral nitrogen compounds, such as indoles, carbazoles, and benzocarbazoles;
the fourth subfraction (8.2 wt %) contained neutral polar compounds,
such as C<sub>8</sub>–C<sub>28</sub> alkyl nitriles and aliphatic
and aromatic ketones, such as 4-, 5-, and 6-ketones and phenyl ketones,
derived from a series of propiophenone to decanophenone; the fifth
subfraction (14.9 wt %) contained 2-ketones and aromatic ketones,
such as acetophenones, indanones, and acetonaphthones; and most of
the sixth subfraction (1.3 wt %) cannot be eluted from GC. Electrospray
ionization (ESI) coupled with Fourier transform ion cyclotron resonance
mass spectrometry (FT-ICR MS) was used to analyze the third neutral
subfraction, which was enriched with neutral nitrogen compounds. In
addition to indoles, carbazoles, and benzocarbazoles, FT-ICR MS analysis
showed that dibenzocarbazoles and tribenzocarbazoles with various
carbon numbers were present in the third neutral subfraction