¹³C NMR Analysis of Soot Produced from Model Compounds and a Coal

Abstract

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 13C NMR methods. The coal soot data served as a guide to selection of the temperature range that would 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 prior 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 average aromatic cluster size (the number of carbon atoms in an aromatic ring system where the rings are connected through aromatic bridgehead carbon atoms) may be as large as 80−90 carbons/cluster. The data obtained for the biphenyl samples exhibit a different path for pyrolysis and soot growth. A significant amount of ring opening reactions occurs, followed by major structural rearrangements, after the initial ring opening and hydrogen transfer phase. The cluster size not only grows significantly, but the cross-linking structure also increases, indicating that soot growth in biphenyl soots consists not only of cluster size growth but also cluster cross-linking. The evolution 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 noted, the data are inconclusive regarding the mechanism for ring growth in the pyrene aerosols between 1410 and 1460 K.

Density functional theory molecular modelling and experimental particle kinetics for CO2–char gasification

“…[38,67]. NMR analysis of 1000 however, encounters line broadening which prevents calculation of structural parameters, and thus it cannot predict the aromatic carbon cluster size under these conditions [65]. Line broadening is attributed to aromatic free radicals that begin to change the relaxation behaviour of the aromatic carbons [68].…”

Influence of maceral composition on the structure, properties and behaviour of chars derived from South African coals

“…3. The spectra for the chars exhibited extensive line-broadening in the aromatic region [59] and may be attributed to the formation of aromatic free radicals, which began to change the relaxation behaviour of aromatic carbons [6].…”

FT-IR and 1H NMR characterization of the products of an ethylene inverse diffusion flame

“…Therefore, much of the information available for premixed and diffusion flames comes from solid state NMR and MS analyses [39,[42][43][44]. However, it is difficult to obtain detailed structural information from soot taken from these flames since, in general, significant carbonization or dehydrogenation has taken place.…”