Sequential Extraction of Coal Tar Pitch and Structural Characterization of Enriched Large Polycyclic Aromatic Hydrocarbons

Abstract Four fractions separated sequentially from a coal tar pitch by two different methods are examined by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI TOF‐MS) and 50/24 matrix analysis, to evaluate both separation effectiveness and characteristics of large polycyclic aromatic hydrocarbons (PAHs) in variable fractions. Both Soxhlet extraction and anti‐solvent precipitation can sequentially produce four fractions that have narrower molecular mass distribution with specific structural features of PAHs. The results show that the overall molecular mass (MM) and ring size of large PAHs abundant in the fractions gradually shift to higher values as solvent strength increases, with some overlap between two adjacent fractions. A broad range of peaks in MS spectra has been resolved as 4‐ to about 25‐ ring PAHs by 50/24 matrix analysis, with some detailed molecular structure elucidated. For example, the PAHs in the light HS fraction include 4 to 11‐ring aromatics with more ortho‐condensed structure. On the other hand, heavier fractions contain more aromatic rings fused by bay‐condensations that result in quaternary aromatic carbons. Besides structural insights, SEM morphologically reveals differences in the extraction effectiveness between Soxhlet and anti‐solvent, due to mass transfer and diffusion limitations in bituminous material.