Structural Characteristics of Polycyclic Aromatic Hydrocarbon Isomers in Coal Tars and Combustion Products

4 Isomeric polycyclic aromatic hydrocarbons (PAH) with two to six rings in coal-derived products and in a carbon black were separated, identified, and quantified by using capillary column gas chromatography and gas chromatography-mass spectrometry. A newly synthesized smectic liquid-crystalline polysiloxane and a conventional polymethylsiloxane were utilized as stationary phases. Many previously difficult to separate isomeric PAH (i.e., methylphenanthrenes/methylanthracenes, triphenylene/ chrysene, methylchrysenes, benzofluoranthenes, and pentaphene/benzo[b]chrysene) were identified. The relative abundances of the PAH in these samples were compared and correlated to the reaction conditions during their production. The relationship between abundance and structure for the identified PAH was also discussed. Introduction Coal-derived products and thermally cracked petroleum oils are highly aromatic in nature and contain polycyclic aromatic hydrocarbons (PAH) as major components. Although average descriptive parameters are usually obtained for such materials (i.e., distillation curve, molecular weight range, aromaticity, etc.), it is oftentimes very important to obtain detailed compositional and structural information. Many of the PAH are toxic and/or mutagenic in various biological test systems. The toxicities of various PAH are related to specific structures and positions of ring substitution. The methylphenanthrene and methylchrysene isomers are typical examples. The 1-and 9-methylphenanthrenes are mutagenic, while the other isomers are inactive ( I ) , and 5-methylchrysene is one of the strongest carcinogens, while the other isomers are only moderately carcinogenic (2). Isomeric parent PAH may differ markedly in their activities; benzo[a]pyrene has significantly greater carcinogenicity than benzo[e]pyrene, the relative carcinogenicity varies within the series of dibenzanthracenes, and benzo[g]chrysene appears to be more active than benzo[c]chrysene A number of components of the process oils play important roles in the upgrading processes. Hydrogenated compounds such as tetralin are hydrogen donor solvents for coal liquefaction (5). Cracked gas oils containing highly aromatic compounds are often composed of discontinuous fractions in discrete boiling point ranges. For example