Evaluation of Measurement Techniques for the Adsorption of Asphaltenes onto Metal Oxide Nanoparticles
AdvisorHusein, Maen M.
AuthorEzeonyeka, Nkiru Lucia
Committee MemberYarranton, Harvey William
Hill, Josephine Mary
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AbstractThe adsorption of asphaltenes onto nanoparticles (NPs) has received a lot of attention in the recent years owing to its important application in areas such as heavy oil recovery. The effect of the measurement technique on the adsorption isotherms has never been addressed, however. In this work, the adsorption of n-heptane-precipitated asphaltenes, C7-asphaltenes, from toluene model solutions onto three metal oxide NPs; namely Fe2O3, Fe3O4, and Al2O3, was studied. Most results on asphaltenes adsorption employed UV-Vis spectroscopy, especially when using conventional adsorbents. More recently, and with advent of NPs, thermogravimetric analysis (TGA) has also been used. In this investigation, asphaltenes uptake calculated from UV-Vis spectroscopy at three different wavelengths were compared with thermogravimetric analysis (TGA) results. Although the adsorption trends followed Langmuir isotherms, instrument as well as wavelength-dependent adsorption coefficients were obtained. TGA results are believed to be more reliable, provided complete oxidation and account of mass loss due to NPs is attained. UV-Vis measurements, on the other hand, may be impacted by the chemical structure of the asphaltenes sub fractions as well as their state of association. Al2O3 showed the highest adsorption capacity of 385 ± 5 mg/g, followed by Fe3O4 and Fe2O3. However, based on mg/m2, Fe2O3 displayed the highest adsorption capacity. TGA analysis revealed that the NPs promoted the oxidation of adsorbed asphaltenes in a reverse order to their adsorption capacity, qmax (mg/g) (Al2O3 > Fe2O3 ≈ Fe3O4). This trend is in line with a previous observation of mass-dependent thermo-oxidative profile and surface exposure role, rather than a catalyst role, of the NPs.
Schulich School of Engineering