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

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-8-C-28 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.