C-13 NMR analysis of soot produced from model compounds and a coal

Soot samples, including the associated organics, produced from an Illinois No. 6 coal (five samples) and two model compounds, biphenyl (three samples) and pyrene (two samples), have been studied by C-13 NMR methods. The coal soot data served as a guide to selection of the temperature range that woul d be most fruitful for investigation of the evolution of aerosols composed of soot and tars that are generated from model compounds. The evolution of the different materials in the gas phase followed different paths. The coal derived soots exhibited loss of aliphatic and oxygen functional groups pri or to significant growth in average aromatic cluster size. Between 1410 and 1530 K, line broadening occurs in the aromatic band, which appears to have a Lorentzian component that is observable at the lower temperature and is quite pronounced at the higher temperature. The data indicate that the aver age aromatic cluster size (the number of carbon atoms in an aromatic ring s ystem where the rings are connected through aromatic bridgehead carbon atom s) may be as large as 80-90 carbons/cluster. The data obtained for the biph enyl samples exhibit a different path for pyrolysis and soot growth. A sign ificant amount of ring opening reactions occurs, followed by major structur al rearrangements, after the initial ring opening and hydrogen transfer pha se. The cluster size not only grows significantly, but the crosslinking str ucture also increases, indicating that soot growth in biphenyl soots consis ts not only of cluster size growth but also cluster cross-linking. The evol ution of pyrene aerosol samples follows still another path. Little evidence is noted for ring opening reactions. Major ring growth has not occurred at 1410 K but cross-linking reactions are noted, indicating the formation of dimer/trimer structures. Although a significant amount of ring growth is no ted, the data are inconclusive regarding the mechanism for ring growth in t he pyrene aerosols between 1410 and 1460 K.