TiO2/SiO2 nanofluids as novel inhibitors for the stability of asphaltene particles in crude oil: Mechanistic understanding, screening, modeling, and optimization

Determination of the onset of asphaltene flocculation is a key step in studying the asphaltene deposition problems. Therefore, finding an inhibitor to prevent or delay the onset of asphaltene flocculation is inevitable. In this work, first the structural properties of two asphaltene samples extracted from two different Iranian south oilfields were compared. The structural parameters of both asphaltene samples were investigated using elemental analysis, FTIR spectroscopy, and XRD. The onset of asphaltene flocculation for both crude oils A and B was obtained using Near-IR spectroscopy. Asphaltene A from unstable crude oil is characterized by high aromaticity and low hydrogen content, while asphaltene B from stable crude oil shows low aromaticity and high hydrogen content. Then, Near-IR obtains the onset of flocculation by titration of oil samples with n-heptane in the presence of the TiO2/SiO2 nanocomposites at different pH and salinities. Nanoparticles and nanocomposites were characterized using BET, FESEM, EDX, FTIR, XRD and XRF analysis. Modeling and optimization of inhibition of asphaltene flocculation process by TiO2/SiO2 nanofluids were conducted using response surface methodology (RSM). Under optimum conditions (nanocomposite composition = 0.04 wt% (80%TiO2:20%SiO2), salinity = 4.01 wt% for crude oil A and B, pH = 4.87 for A, pH = 3.42 for B), the onset of asphaltene flocculation (the n-heptane volume) increased. For nanofluids stability analysis, one of the optimum nanofluids was compared with the two other nanofluids (SiO2 and TiO2) using visual observation method. The results indicated that high stability and surface area of the 80%TiO2 nanocomposites increase asphaltene adsorption on the particles surface which subsequently increases the onset point. Finally, Polyvinylpyrrolidone (PVP) stabilizer with 1.0 and 2.0 wt% concentrations was used for the stability analysis of the optimum nanofluid using DLS measurement. The results showed that 1.0 wt% PVP was the optimum concentration.