Adsorption of asphaltene molecules on functionalized SiO2 nanoparticles at atmospheric and high pressures in heptane/toluene environment: A molecular dynamics simulation study

This molecular dynamics (MD) investigation considers the asphaltene self-association process in the absence and presence of fully hydrophilic spherical SiO2 nanoparticles at pressures of 1 and 300 bar. Our results show that asphaltenes can adsorb onto the surface of nanoparticles through their aromatic rings and polar groups as their total non-bonding energies have been calculated -341 and -299 kJ mol-1 at 1 bar, and -475 and -242 kJ mol-1 at 300 bar, respectively. Additionally, in the presence of SiO2 nanoparticle, total non-bonding energies between asphaltenes experience a 51 % and 85 % reduction at 1 bar and 300 bar, respectively, indicating that asphaltenes are less prone to aggregate with each other in these systems. Increasing the concentration of nanoparticle significantly affect their efficiency. Using one SiO2 nanoparticle causes 17 % increase in the average available surface area of asphaltenes, while using five nanoparticles shows 28 % increment. At high-pressure conditions (300 bar) and in systems with higher concentrations of nanoparticles, unusual peaks emerge in the radial distribution function (RDF) curves. These peaks have been attributed to the formation of 'disordered aggregates' of asphaltenes, stemming from the effect of high pressure and nanoparticles' self-association, respectively. In addition, it is shown that fully hydrophilic SiO2 nanoparticles have a higher tendency to aggregate in toluene rather than in heptane. This shows that oils with lower aliphatic/aromatic ratio can promote aggregation of fully hydrophilic silica nanoparticles.