Determination of chemical functionality in asphaltenes by high-resolution solid-state carbon-13 nuclear magnetic resonance spectrometry

Abstract

A solid-state /SUP/1/SUP/3C, /SUP/1H NMR study of two asphaltenes derived from coal-liquid processes is reported. The technique of /SUP/13C dephasing by the /SUP/1H dipolar reservoir is used to resolve both the aromatic and aliphatic NMR absorption bands into tertiary plus secondary components and secondary/tertiary plus primary/quaternary aliphatic components. Integrated intensities of the various resolved absorption bands allow estimations of the percentages of tertiary and quaternary aromatic carbons, as well as those of the secondary/tertiary and primary/quaternary aliphatic carbons. First and second moments of the resolved absorption bands are believed to be correlated with both the kinds and distributions of carbons in these asphaltenes. Studies of these moments suggest that the average number of polynuclear condensed rings in these asphaltenes is much smaller than what is thought to exist in a high-rank anthracite coal. Furthermore, the aliphatic side chains attached to the polynuclear-ring backbone may have large variations in both lengths and branchings.