Adsorption and particle size studies of petroleum fluids

Asphaltene is one of the most important constituents of crude oil and is a major cause of precipitation and deposition during oil production, pipeline transportation, and refining. The mechanism that governs asphaltene deposition/adsorption on surfaces has not been well established as yet, probably because of the compositional variations that directly affect the aggregation state of adsorbing species. The adsorption kinetics of asphaltenes on minerals and metals has been the subject of several studies in the past; however most of them were limited to a few solvents or surfaces. Consequently, this extensive study investigates solid-liquid interactions through characterization of the adsorption behavior of several petroleum fluids on different surfaces and establishment of correlations between bulk and surface properties.;In this study, several experimental techniques are employed to investigate crude oil-surface interactions and particle size of adsorbing species in petroleum fluids via adsorption on gold, silica, stainless steel and polystyrene surfaces. A quartz crystal microbalance (QCM-D) technique is used to investigate the adsorption of crude oils and their fractions under flow conditions. Several crude oils are considered at different concentrations in toluene and n-alkane mixtures. The amounts and thicknesses of adsorbed films on different surfaces are determined with good accuracy using liquid loading corrections. A Langmuir-type adsorption with saturation plateaus is observed in all cases where toluene is the solvent but not in n-alkanes or toluene-alkane mixtures where viscoelastic effects are important. X-ray photoelectron spectroscopy (XPS) method is further used to analyze chemical functionalities in asphaltene films adsorbed from toluene and n-alkane on QCM-D crystals. We find that adsorption on various surfaces from toluene shows a high affinity of asphaltenes to hydrophilic surfaces. It is likely that polar functions in asphaltenes become caged inside large clusters or precipitates.;The size of adsorbing species is determined from the diffusion of these species in a concentration range where adsorption is diffusion-controlled. The data agree well with sizes of particles in the bulk phase determined by impedance spectroscopy (IS). This conforms that the kinetic process in the bulk solution is slower than at the interface. The validity of these results is verified by analyzing the size distribution and surface morphology characteristics of deposited oil films on QCM gold crystals using atomic force microscopy (AFM). As expected, the size of asphaltenes increases with concentration due to aggregation and the average value found by AFM is about 2 nm, in agreement with the literature but one order of magnitude larger than values calculated from the diffusion coefficients in QCM-D and IS. On the other hand, the average size of resins obtained from IS method is about 0.5 nm and does not vary much with their concentration in toluene.;Application of the above-mentioned techniques to different crude oils from various origins allows the establishment of fundamental correlations between the particle size of adsorbing species, composition, and physicochemical properties of the crude oils. To our best knowledge, some of these correlations are reported for the first time.