Characterization of Middle-Temperature Gasification Coal Tar. Part 1: Bulk Properties and Molecular Compositions of Distillates and Basic Fractions

A middle-temperature coal tar (MTCT) was distilled into multiple narrow boiling point fractions. The MTCT and its distillate fractions were subjected to bulk property analysis and molecular compositional characterization by gas chromatography–mass spectrometry. Acid/basic liquid extraction was performed to separate the MTCT into acidic, basic, and neutral fractions, which were characterized by positive-ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. The dominant compounds in MTCT were aromatics, phenols, and normal alkanes. The number of carbon atoms in the substituent chains varied over a relatively broad range for each homology. The composition of narrow distillate fractions varied: light naphtha (240 °C) are a hydrotreating feedstock for clean fuel production. The MTCT had large amounts of acidic and basic components, consisting of oxygen- and nitrogen-containing molecules. The basic fraction accounted for 2.68 wt % MTCT. Only nitrogen compounds in the MTCT could be detected by positive-ion ESI. Most of the oxygen-containing molecules exhibited a weak acidity and were partially extracted into the acidic fraction. Basic nitrogen compounds co-existed in the acidic, basic, and neutral fractions of MTCT. However, the molecular compositions of basic nitrogen compounds were different among these fractions: molecules with low carbon numbers and high aromaticities were found in the acidic and basic fractions, whereas mono-nitrogen basic compounds were abundant in the neutral fraction.