A mechanistic study of asphaltene formation and aggregation in presence of metallic-based nanoparticles

Abstract

In this work, the effects of metallic-based nanostructures including iron oxide (Fe2O3), magnesium oxide (MgO) and zinc oxide (ZnO) on asphaltene precipitation and aggregation were explored. The synthesized nanoparticles were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier-transform infrared spectroscopy (FTIR), and Brunauer, Emmett and Teller (BET) methods. Optical microscopy and asphaltene dispersant tests (ADTs) were utilized to discover the effects of nanoparticles on asphaltene stability and the size-growth of asphaltene aggregates in crude oil medium. The interactions of the asphaltene functional groups with metal oxide nanoparticles were evaluated at molecular scale by thermogravimetric analysis (TGA/DTG), FT-IR, and field emission scanning electron microscopy (FESEM). Results of different experiments exhibited that synthesized nanostructures in general postpone the asphaltene onset of precipitation (AOP) and reduce the size of asphaltene aggregates in unstable crude oil medium. MgO nanoparticles with a concentration of 300 ppm had the greatest effect on controlling the asphaltene precipitation and aggregation. The TGA/DTG analysis showed that the oxidation of pure asphaltenes occurs at a temperature of about 425 °C, while the oxidation temperature of asphaltenes adsorbed on ZnO and Fe2O3 nanoparticles occurs at around 330 °C, and for MgO nanoparticles at about 365 °C. In addition, the spectra obtained from the FT-IR analysis for asphaltenes without and with nanoparticles at the wavelengths of 1450 and 2900 cm−1 show the medium C–H stretching bonds that play the most important role in the adsorption of asphaltene on the surfaces of the nanoparticles. Also, the recorded FESEM images of the asphaltene and nanoparticles demonstrated the proper absorption of asphaltenes in the empty spaces between the structures of nanoparticles. According to the results from different experiments and intermolecular analyses, the performance of synthesized nanoparticles for retarding asphaltene precipitation and dispersing the asphaltene aggregates was in order of MgO (300 ppm) > Fe2O3 (300 ppm) > ZnO (700 ppm). The results of intermolecular analyses established the effective adsorption of the asphaltene particles onto the surface of the nanoparticles, which is caused by strong hydrogen interactions between the active sites of the asphaltene and nanoparticles. The findings of this study prove that metal-oxide nanoparticles can be utilized as an economically and environmentally-effective agents for controlling asphaltene formation and aggregation in crude oil.