Reconstructing Asphaltene Average Structures from multi‑technique chemical characterization

Asphaltenes are central to flow assurance and interfacial behavior in crude oils, yet their molecular description remains challenging due to structural heterogeneity and aggregation; here we characterize three asphaltenes from conventional oils of the Neuquen Basin, Argentina (M1322, M1287, M1353), and derive a representative average structure suitable for mechanistic simulation. Our workflow combined sequential precipitation to obtain solids, elemental CHONS analysis for bulk composition, gel permeation chromatography (GPC) for number-average molecular weight (MW), X-ray photoelectron spectroscopy (XPS) to speciate N and S environments, ¹³C NMR to determine aromatic vs aliphatic carbons, and ¹H-NMR to quantify H_a, H_α, H_β, and H_γ populations. These descriptors were integrated to compute average formulas and to assemble internally consistent structural motifs. Apparent GPC MWs were high (6.3 kDa for M1322, 6.8 kDa for M1287, and 4.7 kDa for M1353) exceeding typical ranges reported for asphaltenes; in our interpretation, these elevated values reflect the presence of supramolecular aggregates that traverse the GPC column as larger associating species, rather than isolated molecules. Elemental analysis yielded comparable compositions across samples (C=80–82 wt%, H=7.8–8.0 wt%, N=1.2–1.4 wt%, S=3.9–5.8 wt%, O=4.0–6.3 wt%), enabling formula estimation when combined with MW. NMR indicated 45–48% aromatic carbon and proton populations dominated by H_β (53%) with H_α=19–21%, H_a=10–11%, and H_γ=15–18%, consistent with condensed aromatic cores connected by short aliphatic substituents. XPS showed nitrogen distributed across pyridinic/amine/pyrrolic/quaternary envelopes at sample-dependent proportions, and sulfur dominated by thiophenic contributions (52–75%) with variable sulfoxides. Using measured MW and CHONS for M1322 produced an average composition of C₄₅₈H₅₃₉N₆O₂₂S₁₂ and, correspondingly, a large structural assembly; when an adjusted MW (0.68–0.75 kDa) was considered, the resulting formula and topology aligned with contemporary island/archipelago-type representations. Collectively, these results provide a coherent, data-driven reconstruction of asphaltene architecture for M1322, M1287, and M1353 that captures aromatic core size, aliphatic substitution, and heteroatom functionalities in a manner consistent with their spectroscopic and spectrometric fingerprints; importantly, the reconstructed average structures can be used as inputs for molecular simulations targeting asphaltene–asphaltene and asphaltene–dispersant interactions, supporting predictive studies of aggregation, adsorption, and interfacial modification relevant to mitigation strategies in production systems.