Diffusion-Ordered Spectroscopy Nuclear Magnetic Resonance as an Alternative Technique to Improve Asphaltene Characterization

Abstract

An asphaltene sample from a light Arabian crude oil was characterized using several analytical techniques, such as thermogravimetric analysis, nuclear magnetic resonance, Fourier transform infrared spectroscopy, and elemental analysis. The results showed that the sample has a high sulfur content and highly condensed aromatic compounds and the average molecular structure is predominantly of continental/island type; however, the presence of a significant amount of methylene carbons in long alkyl chains is clear. A diffusion-ordered spectroscopy nuclear magnetic resonance experiment (DOSY-NMR) was carried out to detect the presence of asphaltene aggregates, evaluate their size, and shed light on the presence of maltenic occluded species and entrained residual solvent. In the DOSY spectrum, some sample signals were attributed to non-asphaltenic molecules, showing that it is possible to achieve key features of the sample complexity in “one shot”.

NMR Spectroscopy Analysis of Asphaltenes

“…However, DOSY results indicates the presence of nanosized aggregates and some remaining solvent molecules (co-removal throughout the asphaltene separation stage applying ASTM D6560-12 process of sonication), and some long alkyl chain species clearly not chemically bonded to the aromatic centers, and the coexistence of archipelago and continental structural patterns. The chemical structure of the asphaltenes analyzed by Junior et al shows only nanosized aggregates at 8 wt % concentration significantly differ from most of the asphaltenes that exhibit micro and macroaggregates even at 3 wt %. , …”

“…A Brazilian group has applied also 1 H DOSY NMR for studying an asphaltene probe derived from a Light Arabian crude oil . The major goals in conducting 1 H DOSY NMR are to determine the existence of asphaltene aggregates, to estimate the dimension of the aggregates, and to discuss the occurrence of maltenes occluded particles and entrained remaining solvent.…”

“…The asphaltene mark is turns out to be bimodal from a wide unimodal behavior when it is closer to the flocculation beginning. There is a direct correlation between relaxation rate of the solvent molecules and asphaltene concentration, which is due to changes of viscosity . The relaxation measurements on asphaltene solutions are performed by dissolving asphaltene in toluene and then by adding n -heptane.…”

Experimental and Theoretical Approach To Determine the Average Asphaltene Structure of a Crude Oil from the Golden Lane (Faja de Oro) of Mexico

“…NMR has proven to be a powerful tool in the determination of asphaltene structures, as shown in the recent review by Ok and Mal . Solution- and solid-state NMR have been used to study asphaltene structure. − Fergoug and Bouhadda studied structural parameters of the asphaltenes derived from the Algerian Hassi Messoud oilfield using 1 H and 13 C liquid NMR, finding that the PAH region contains seven fused aromatic rings (7FAR). Scotti et al concluded, from a liquid-state 1 H and 13 C NMR study, that the most probable number of fused aromatic rings in asphaltene PAHs is seven.…”

NMR Spectroscopy as a Tool for Studying Asphaltene Composition

“…[39] Subsequently, a number of research groups used DOSY NMR spectroscopy to investigate the structure, average size and self-association of the asphaltene aggregates. [1,[24][25][26]29,[43][44][45][46][47][48] A group of authors applied 1 H, 13 C and 1 H DOSY NMR experiments to study the relationship between the structural type (continental or archipelago) and aggregation properties of three different asphaltenes. The obtained results pointed towards the presence of predominantly continental structural type and confirmed the formation of nano-, micro-and macroaggregates, according to different diffusion coefficients.…”