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Surface and Interface Characterization of Asphaltenic Fractions Obtained with Different Alkanes: A Study by Atomic Force Microscopy and Pendant Drop Tensiometry

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journal contribution
posted on 29.10.2018, 00:00 by Iago Oliveira, Larissa Gomes, Elton Franceschi, Gustavo Borges, Juliana F. de Conto, Flávio Cortinas Albuquerque, Claudio Dariva
It is recognized that asphaltenes have a tendency toward aggregation and precipitation. Even at low concentrations, they can adsorb at interfaces/surfaces where each type of interaction plays an important role in different stages of oil production. In order to evaluate the behavior of asphaltenes, it is necessary to conduct studies that allow the understanding of their chemical and physical structure, as well as to assess how they behave interfacially and superficially. By using the Pendant Drop Tensiometry and Atomic Force Microscopy techniques, the present work aims to characterize the interfacial behavior and the surface structure of two asphaltenic fractions obtained through the precipitation using n-heptane and propane as flocculants. Asphaltenic fractions were characterized by Fourier transform infrared spectroscopy, elementary analysis, gel permeation chromatography, and differential scanning calorimetry, to obtain their physicochemical characteristics. Fractions were deposited in glass substrates at different concentrations, and the contact angle between water and the substrate was determined, identifying how the different asphaltenic fractions influence the wettability of the surface, even at low concentrations. When precipitation was conducted using propane, the asphaltenic fraction showed distinct structural characteristics that were obtained by precipitation with heptane. Atomic force microscopy suggested the formation of different surface arrangements between the fractions, caused by the higher presence of resins in the fractions precipitated by propane. The pendant drop tensiometry evidenced that the asphaltenic fraction insoluble in heptane showed greater affinity to migration to the interface, producing films more resistant to the deformation, than the asphaltene fraction insoluble in propane.