Solubility/molecular structure relationships of asphaltenes in polar and nonpolar media

Asphaltenes separated from a Maya type of crude oil were suspended in toluene and later fractionated by solubility in a polar (acetone) and a nonpolar (n-heptane) precipitating solvent. The two sets of derived fractions were characterized using size exclusion chromatography (SEC), elemental analysis, Fourier transform infrared spectroscopy (FTIR), and synchronous fluorescence spectroscopy and proton nuclear magnetic resonance (H-1 NMR) spectroscopy. The results show that the acetone-precipitated asphaltene fractions have larger structural differences compared with those of n-heptane. The average size of the aromatic and aliphatic-substitutions regions of each fraction was also found to correlate with asphaltene solubility in such a way that the smaller the aromatic region and the larger the aliphatic substitution, the greater the solubility. These correlations may provide further explanations as to the role of structural properties on the solubility of asphaltenes in polar and nonpolar media.