Distribution and Structural Analysis of Polycyclic Aromatic Hydrocarbons Abundant in Coal Tar Pitch

High-resolution matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) combined with other analytical techniques and aromatic structure analysis were employed to characterize and identify large polycyclic aromatic hydrocarbons (PAHs) in coal tar pitch and its hexane-soluble fraction. Nonsubstituted aromatics in high abundance up to 850 Da can be extracted successfully with defined molecular formula from MALDI spectra, and mapped systematically into a 50/24 matrix, indicating a structural growth pattern by cooperative ortho-condensation and bay-condensation. The matrix provided a quantitative summary, with their quantity and chemical structures defined essentially by MS intensity and molecular formula of PAHs isomers, respectively. It also revealed a trend that the PAHs grown alternatingly at ortho and bay positions exhibit much higher concentrations than those by ortho- or bay-condensations alone, even though their relative abundance by MS intensity may drop as aromatic rings grow with condensation polymerizations. Such compositional insights may be valuable for better utilization of coal tar pitch as well as understanding the overall reactions that lead to the formation of such a complex mixture including very small and very large polycyclic aromatic compounds.