Kinetics and Properties of Asphaltene Adsorption on Surfaces

A quartz crystal microbalance (QCM) was used to probe asphaltene adsorption on gold surfaces and hydrophilic and hydrophobic silica particles. The adsorption studies were conducted with solutions of various ratios of pentane solvent to model oil (S/O) and asphaltene concentrations. The adsorption of asphaltenes on solid surfaces at different S/O showed multilayer deposition without reaching equilibrium after 16 h. Adsorption of asphaltenes and other components on the surfaces were detectable well below the onset of precipitation. The amount of material adsorbed increased significantly after the onset of precipitation. Adsorption was more pronounced on the gold surface than on the silica particles. The swelling of the asphaltene aggregates on the surface of the quartz crystal led to restructuring of the adsorbed material on the surfaces, depending on the S/O. For S/O > 0, the swelling effect suggested open nanoaggregate or polymer brush structure. The adsorbed asphaltenes demonstrated more viscoelastic behavior as S/O was increased. The kinetics of the adsorption of asphaltenes on gold at room temperature suggested the formation of very large, slowly diffusing aggregates, even in toluene. These results were not consistent with optical microscopy or other methods.