Using Atomic Force Microscopy To Detect Asphaltene Colloidal Particles in Crude Oils

Abstract

Asphaltene precipitation is a key problem in the petroleum industry and has been the focus of many studies on their aggregates present in crude oils and on the effects of additives to inhibit their formation and/or deposition. However, most of these studies were performed using model systems, such as asphaltene solutions in organic solvents, making the comparison to real systems more difficult. Herein, we combine different modes (height and phase modes) of atomic force microscopy to identify colloidal particles associated with asphaltene aggregates present in crude oils. Following this methodology, a mica plate is inserted into oil and washed with toluene to remove excess oil. In addition, nanoparticles with dimensions ranging from a few to hundreds of nanometers were observed. Overall, more particles are observed when flocculants, such as heptane, are added, whereas their size decreases when a good solvent for asphaltenes (toluene) is added. Similar colloidal particles are also observed repeating this methodology with asphaltene solutions in toluene, confirming that these somewhat reproduce the asphaltene association observed in crude oils. The addition of an inhibitor, such as dodecylbenzenesulfonic acid, led to observation of more and smaller nanoparticles. The present experimental approach not only confirms the existence of asphaltene colloidal particles in crude oils but also provides an accessible methodology to directly assess how these particles are affected by changes in oil composition or inhibitors.

Fractionation and Characterization of Petroleum Asphaltene: Focus on Metalopetroleomics

“…This work is groundbreaking in the history of asphaltenes, allowing for us to have a direct visual understanding of the structure of some molecules in asphaltenes. This technique is also used to identify colloidal particles associated with asphaltene aggregates present in crude oils and the model system [51]. AFM even allows for direct observations on the specific structure of some biomarkers, such as the characterization of substitution patterns on petroporphyrins [52].…”

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.…”

Recent Developments on the Elucidation of Colloidal Aspects of Asphaltenes and Their Relevance to Oilfield Problems

“…21 The authors of this review were also interested in the direct visualization of these aggregates on the colloidal scale, developing a simple methodology employed in an atomic force microscope that can be accessed in detail in the reference. 61 Figure 6 shows a 3D map of a 1 × 1 μm region, indicating spherical morphology of the particles and their nature as individual units. It is possible to distinguish further that larger objects are formed by the aggregation of smaller units, whose size is (4 ± 1) nm, in height, 61 in agreement with the values calculated by fitting the scattering curves obtained by SAXS.…”

“…61 Figure 6 shows a 3D map of a 1 × 1 μm region, indicating spherical morphology of the particles and their nature as individual units. It is possible to distinguish further that larger objects are formed by the aggregation of smaller units, whose size is (4 ± 1) nm, in height, 61 in agreement with the values calculated by fitting the scattering curves obtained by SAXS. 45 Figure 7 endorses the fact that particles at the micrometer scale are the result of subunits aggregation (roughness in topography map and border meeting of several particles in contrast phase map).…”