New Insights into Asphaltene Structure and Aggregation by High-Resolution Microscopy

Abstract

Transmission electron microscopy was used to probe the structural properties of asphaltenes and their aggregation behavior. Asphaltenes precipitated by different n-alkanes (n-C5, n-C7, and n-C10) were considered in addition to the interfacial material (IM) extracted from n-C7 asphaltenes. Measurements were first performed with powdered samples dispersed in methanol. Analysis of the amorphous layers observed in their segmented micrographs provided important structural parameters such as the edge-to-edge spacing between particles, the average area and shape factor of these particles, and the rugosity of the layer’s boundary. Short-range order was observed in all samples due to the parallel stacking propensity of asphaltenes. Denser packing and lower particle circularity of the higher alkane asphaltenes resulted in the smallest interparticle spacing. On the other hand, disruption of stacking by the aliphatic side chains was more prevalent in the lower alkane asphaltenes as molecular polydispersity increased. The lower shape factor and average area of the n-C7 IM indicated the presence of smaller particles than in the parent asphaltenes. Furthermore, the much smaller edge-to-edge and interlayer spacings suggested much tighter molecular packing due to the π–π stacking of the small aromatic cores and hydrogen bonding between the fatty acid chains. The higher crystallinity of the IM yielded thin nanosheets that were previously observed in liquid samples. Structure–function relations were also established by comparing micrographs of solid n-C10 asphaltenes to those dispersed in heptol solutions. Crystalline structures seen in the solid samples appeared as small globular clusters in the liquid samples. Their shape and average size were consistent with the Yen–Mullins model.

2022 Pioneers in Energy Research: Oliver Mullins

“…Prof. Kenttämaa from Purdue University provided an in-depth analysis of radical cations of asphaltenes based on collision-activated dissociation (CAD) mass spectrometry . New insights into the asphaltene structure and aggregations were obtained by Prof. Goual at the University of Wyoming using high-resolution electron microscopy . The importance of understanding limitations of each physical technique and assumptions in data interpretation is demonstrated by an original article by Prof. Andersen from the Technical University of Denmark, highlighting the importance of spectral correction in the fluorescence spectroscopic analysis of crude oils and asphaltenes .…”

Asphaltene Precipitation and the Influence of Dispersants and Inhibitors on Morphology Probed by AFM

“…Asphaltene aggregation and self-association (under favorable and unfavorable solubility conditions) have been extensively studied using multiple techniques (optical microscopy, UV-Vis spectroscopy, ultrasmall-, small-and wide-angle scattering, refractive index measurements, quartz crystal resonator (QCR) High Resolution Transmission Electron Microscopy (HRTEM)) [27][28][29][30][31][32][33], indicating that the governing forces driving this phenomenon are primarily of the Van der Waals type, Hydrogen bonding, acid-base interactions and π − π stacking [34][35][36]. The origin of these interactions is the nature of the asphaltene fraction, functionally defined in terms of solubility (soluble in aromatics but insoluble in n-alkanes) and the presence of multiple components (polyaromatic cores, metals, aliphatic chains, heteroatoms and functional groups such as hydroxyl, carbonyl, amine and nitrile, among others) that add to their molecular complexity [37][38][39].…”

Effect of Reservoir Mineralogy on Asphaltene Structure and Remediation Strategy Efficiency

“…Another effective technique for characterizing asphaltene is laser desorption ionization and collision-induced dissociation . Using a transmission electron microscope, the structural characteristics of asphaltene have also been examined; the findings demonstrate the edge–edge spacing of asphaltene particles as well as the rugosity of the border layers . Using the negative ion-mode electrospray (ESI(−)) technique in conjunction with Fourier transform ion cyclotron resonance mass spectrometry, asphaltene and its subfractions were analyzed .…”

“…58 Using a transmission electron microscope, the structural characteristics of asphaltene have also been examined; the findings demonstrate the edge−edge spacing of asphaltene particles as well as the rugosity of the border layers. 59 Using the negative ion-mode electrospray (ESI(−)) technique in conjunction with Fourier transform ion cyclotron resonance mass spectrometry, asphaltene and its subfractions were analyzed. 60 The solubility of the subfraction was shown to be impacted by the aromaticity and heteroatom concentration.…”