Structural Characterization of Large Polycyclic Aromatic Hydrocarbons. Part 2: Solvent-Separated Fractions of Coal Tar Pitch and Naphthalene-Derived Pitch

Complex polycyclic aromatic hydrocarbon (PAH) mixtures separated from a coal tar pitch (CP) and naphthalene pitch (NP) by sequential extraction with heptane and toluene were characterized in detail by applying a multiarray analytical approach. Gas chromatography-mass spectrometry (GC-MS), size exclusion chromatography (SEC), laser desorption ionization-time-of-flight mass spectrometry (LDI-TOFMS), and thermogravimetry (TG) were used to relate the volatility and coking yield of pitch components to their solubility and molecular weight distribution. Spectroscopic analysis, including infrared (IR), ultraviolet-visible (UV-vis), and fluorescence spectroscopy, proved to be useful for measuring specific features of aromatic systems, such as the aromatic content, degree of aliphatic substitution, and size distribution of PAHs of different molecular weights. In particular, it has been shown that the spectroscopic analysis is an essential tool for characterizing very large PAH systems concentrated in the pitch toluene-insoluble fraction. This fraction constitutes a case study of very large, structurally different aromatic compounds, and it is the pitch fraction more relevant for practical applications because of its higher coking tendency and peculiar optical properties.