Molecular Structure and Solubility Determination of Asphaltenes

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Due to their complex chemical structure, identification and characterization of asphaltenes remain a big challenge for researchers in the oil industry. In the current contribution, solution-state two-dimensional (2D) nuclear magnetic resonance (NMR) spectra of the asphaltenes, obtained from either heavy or light crude oil samples, provide information on the chemical structures of asphaltenes at the molecular level. Two-dimensional 1H–13C heteronuclear NMR measurements are particularly useful for differentiating among several structural environments whose signals overlap in the one-dimensional 13C spectra. Both, 2D 1H–13C heteronuclear and 1H–1H homonuclear NMR spectra indicate short- and long-range interactions between different functional groups of the asphaltene samples, revealing even “bay”- and “fjord”-type structures. Based on the NMR correlations between different protons and carbons with different chemical environments, we propose various chemical structures (polyaromatic cores with aliphatic chains, porphyrin derivatives, organic salts). Furthermore, through molecular dynamics simulations, we have obtained Hildebrand solubility parameters of different asphaltene solvents and of two experimental recovered asphaltene structures. Our calculated solubilities are consistent with previous experimental and simulation works.

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