Direct Observation of Asphaltene Nanoparticles on Model Mineral Substrates

Abstract

The propensity for adherence to solid surfaces of asphaltenes, a complex solubility class of heteropolycyclic aromatic compounds from the heavy fraction of crude oil, has long been the root cause of scale deposition and remains an intractable problem in the petroleum industry. Although the adhesion is essential to understanding the process of asphaltene deposition, the relationship between the conformation of asphaltene molecules on mineral substrates and its impact on adhesion and mechanical properties of the deposits is not completely understood. To rationalize the primary processes in the process of organic scale deposition, here we use atomic force microscopy (AFM) to visualize the morphology of petroleum asphaltenes deposited on model mineral substrates. High imaging contrast was achieved by the differential adhesion of the tip between asphaltenes and the mineral substrate. While asphaltenes form smooth continuous films on all substrates at higher concentrations, they deposit as individual nanoparticles at lower concentrations. The size, shape, and spatial distribution of the nanoaggregates are strongly affected by the nature of the substrate; while uniformly distributed spherical particles are formed on highly polar and hydrophilic substrates (mica), irregular islands and thicker patches are observed with substrates of lower polarity (silica and calcite). Asphaltene nanoparticles flatten when adsorbed on highly oriented pyrolytic graphite due to π-π interactions with the polycyclic core. Force-distance profiles provide direct evidence of the conformational changes of asphaltene molecules on hydrophilic/hydrophobic substrates that result in dramatic changes in adhesion and mechanical properties of asphaltene deposits. Such an understanding of the nature of adhesion and mechanical properties tuned by surface properties, on the level of asphaltene nanoaggregates, would contribute to the design of efficient asphaltene inhibitors for preventing asphaltene fouling on targeted surfaces. Unlike flat surfaces, the AFM phase contrast images of defected calcite surfaces show that asphaltenes form continuous deposits to fill the recesses, and this process could trigger the onset for asphaltene deposition.

Distributed Properties of Asphaltene Nanoaggregates in Crude Oils: A Review

“…Adsorption from asphaltene solutions normally gives complete surface coverage by a film of material, but two approaches have been used to image individual nanoaggregates on surfaces. The first approach is to expose the solid substrate to a dilute solution of asphaltenes in toluene, then rinse and dry the sample for imaging. , The second is to expose the substrate to a crude oil, then remove residual liquid portions of the adsorbed asphaltene film by washing with toluene . Deposition from dilute solutions onto mica gave aggregates of height from 1.1 to 4.4 nm depending on the source crude oil, with average lateral dimensions of 16–41 nm.…”

Understanding Asphaltene Fraction Behavior through Combined Quartz Crystal Resonator Sensor, FT-ICR MS, GPC ICP HR-MS, and AFM Characterization. Part I: Extrography Fractionations

“…At the nanoscale level, atomic force microscopy (AFM) is an interesting technique that offers access to three-dimensional information. For asphaltene characterization, AFM has been applied from single asphaltene molecule imaging (Schuler et al) , to observation of asphaltene aggregates in different media/support. − Therefore, AFM is a technique of choice for observation and comparison of the type and form of macroaggregates deposited on metal surfaces or sensors.…”

Porphyrin tripod as a monomeric building block for guest-induced reversible supramolecular polymerisation

“…The attening of nanoparticles can explain the decreased average height of the nanoparticles on HOPG because of the high a nity of the alkyl chains to HOPG. 23,24 Grazing-incidence wide-angle X-ray scattering (GIWAXS) was conducted on the drop-cast lms of DP Zn T. Thus, the in-plane and out-of-plane diffraction of DP Zn T overlapped well (Fig. 2D), indicating the absence of angular dependency in the wide-angle region owing to the formation of spherical nanoparticles.…”