Nonconventional oil is usually heavy and extra heavy crude or light oil that is relatively unstable. This oil contains varying proportions of larger, more aromatic constituents rather than molecules that can be distilled directly into fuels and petrochemicals. We perform density functional theory (ωB97X-D/6-31G(d,p)) calculations to study the contributions of steric effects and dispersion interactions in a series of dimers and trimers of model hydrocarbons containing fused aromatic and cyclohexyl (referred to in the petroleum literature as naphthenic) rings. The aggregation behavior of these molecules is analyzed in terms of the optimized geometry, atomic charges, interaction enthalpy (ΔH), and Gibbs free energy (ΔG 298 ). The ΔH and ΔG 298 values show that all the dimerization and trimerization processes are exothermic, and only a few are spontaneous at 298 K. The naphthenic hydrogen atoms have a key role in the orientation of the monomers in dimer and trimer aggregates. The interaction among naphthenic hydrogen atoms belonging to adjacent monomers causes steric repulsion. The interaction of naphthenic hydrogen atoms with the π-electronic clouds of aromatic rings in adjacent molecules causes attraction. In both cases, the naphthenic hydrogen atoms cause deviation of the monomer from the initial parallel displaced configuration in dimers and trimers. These results reflect the importance of naphthenic rings and their steric interactions in determining the relationship between structures of nonconventional petroleum constituents and their tendency to aggregate and cause fouling.

Access and use of this website and the material on it are subject to the Terms and Conditions set forth at Density functional theory study of the effects of substituents on the carbon-13 nuclear magnetic resonance chemical shifts of asphaltene model compounds Oliveira, Jackeline S. C.; Da Costa, Leonardo M.; Stoyanov, Stanislav R.; Seidl, Peter R.http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/jsp/nparc_cp.jsp?lang=fr L'accès à ce site Web et l'utilisation de son contenu sont assujettis aux conditions présentées dans le site LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D'UTILISER CE SITE WEB. NRC Publications Record / Notice d'Archives des publications de CNRC:http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/ctrl?action=rtdoc&an=21275738&lang=en http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/ctrl?action=rtdoc&an=21275738&lang=fr READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE.http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/jsp/nparc_cp.jsp?lang=en Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n'arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. Questions? Contact the NRC Publications Archive team atPublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information. NRC Publications Archive Archives des publications du CNRCThis publication could be one of several versions: author's original, accepted manuscript or the publisher's version. / La version de cette publication peut être l'une des suivantes : la version prépublication de l'auteur, la version acceptée du manuscrit ou la version de l'éditeur. For the publisher's version, please access the DOI link below./ Pour consulter la version de l'éditeur, utilisez le lien DOI ci-dessous.http://doi.org/10.1021/ef502078n Energy and Fuels, 29, 5, pp. 2843-2852 Density ABSTRACT: Petroleum asphaltenes are a complex mixture of organic molecules containing mainly fused polyaromatic and naphthenic systems and pendant chains, polar moieties with heteroatoms (S, N, and O), and transition metals. A variety of spectroscopic techniques has been employed to characterize asphaltenes, but their structures remain largely elusive because of the complexity, variety of samples, and assignment limitations. Carbon-13 nuclear magnetic resonance ( 13 C NMR) spectroscopy has contributed extensively to asphaltene characterization. However, proper assignment of 13 C NMR spectra is very challenging because spectra of natural asphaltenes feature a large number of peaks in unusual environments, which may be hard to assign and interpret. We employ the dispersion-corrected ωB97X-D density functional with 6-31G(d,p) basis set to rationalize common trends in the 13 C NMR chemical shifts of asphaltene model compounds. The calculated 13 C NMR chemical shifts for a calib...