Analysis of asphaltenes by carbon and proton nuclear magnetic resonance spectroscopy

Abstract

Proton and 13C nuclear magnetic resonance spectroscopy has been used to derive a series of parameters of an ‘average molecule’ which characterize complex multicomponent organic mixtures such as asphaltenes. The method developed here is based on a minimum of assumptions and takes explicitly into account the effects of the oxygen atoms on the chemical shift of the adjacent 13C atoms. Moreover, the integrated intensities characterizing ring junction or substituted and unsubstituted carbon atoms are no longer determined on a chemical shift basis but are calculated by using parameters extracted from 1H and 13C spectra. Factors influencing quantitative 13C measurements on asphaltenes in the Fourier transform mode are briefly discussed. The variations of parameters such as the aromaticity factor, the degree of substitution, and the number of aromatic and naphthenic cycles per structural unit are studied as functions of depth of burial for rock samples from the Toarcian Paris basin.