Behavior comparison of films of Mexican bitumen and its asphaltene and maltenes fractions at interfaces

Abstract

The oil industry has been focused on bitumens and heavy oils due to the depletion of petroleum reservoirs. For this reason, we studied the interfacial behavior comparison of films of bitumen and their asphaltene and maltene fractions by means of the Langmuir balance and Brewster angle microscopy at the air–water interface. The films were transferred by Langmuir-Blodgett technique onto mica and grids to be further analyzed by AFM and SEM at different surface pressures. We found that the isotherm behavior of the bitumen depends on the amount of its asphaltene and maltene fractions, although the isotherm behavior of asphaltene and maltene fractions are quite different. BAM images of the bitumen and asphaltene samples show the formation of two- and three-dimensional domains, being the asphaltene domains the most rigid and compact structures. Maltenes seems to form large areas of mono- or bi-molecular films, and their structures are like those reported for lipid monolayers. The AFM images for the bitumen morphology exhibited polydisperse mesostructures with spherical and disk-like shapes, while asphaltene images revealed disk-like microstructures and some of these microstructures coalesce, resulting in the formation of worm-like and other small structures. AFM images of the maltene film revealed that they form a fine plaster that might agglutinates the asphaltenes. SEM images of bitumen film show a smooth and slightly porous surface with some layer detachments, holes and bright spots embedded, while asphaltene images presented porous surfaces with spherical- or drumstick-like structures. Maltene SEM images showed a surface with irregular pores. The results support a better understanding of the bitumen, asphaltene, and maltene fractions and suggest that the interfacial behavior of bitumen presents a synergy between its asphaltene and maltene fractions.