Flocculation of silica particles in a model oil solution: Effect of adsorbed asphaltene.

摘要

The removal of solid particulates from crude oils and hydrocarbon streams is a common challenge in refining. Finding a method for efficient removal of the suspended solids in the oil streams is the main objective of this work. Paraffinic and aqueous treatment and the combination of these two methods were studied in details to determine the efficiency of each method for removal of solid particles from the oil streams. In this study, we investigate the role of adsorbed and precipitated asphaltenes in flocculation and sedimentation of particles from a model oil. Silica particles (1 µm) were suspended in a reacted pitch material (5 wt%) dissolved in toluene to give a model oil (O). In toluene solution, the silica suspension was stabilized by the asphaltenes in the pitch. The onset of asphaltene precipitation was determined to occur at S/O = 0.43 by weight (pentane/oil). At S/O < 0.33, the removal efficiency of silica particles from the oil phase by sedimentation for one hour was poor. Above this ratio, however, the concentration of silica remaining in the supernatant decreased. There was no significant difference in removal efficiency whether the silica particles were hydrophilic or hydrophobic. We did a similar study for removal of other types of solid particles such as clays (∼ 1 µm) which was also successful above S/O = 0.36. Treating the model oil with small amounts of water did not lead to destabilization of the silica suspension in short times. However, paraffinic treatment of the model oil solution in the presence of emulsified water destabilized the silica suspensions at lower S/O (S/O = 0.25) compared to solutions without water (S/O = 0.33) after one hour.;The results obtained from destabilization of silica suspensions showed that asphaltene adsorbs on surfaces even below the visible onset of precipitation. Fourier transform infrared (FTIR) spectroscopy in the region of 2800 - 3000 cm-1 and quartz crystal microbalance (QCM) showed measurable asphaltene adsorption on the surface of the silica before the onset of asphaltene precipitation; however, the amount of adsorption increased significantly beyond this point. QCM measurements on gold and on silica surfaces showed the same trend with S/O. Adsorption was more pronounced on the gold surface than on the silica particles, especially after the onset of asphaltene precipitation.;It was interesting to study the interaction forces between the coated silica particles with asphaltene in oil solutions to have a better understanding of the flocculation mechanism of the silica particles. Therefore, the interaction between asphaltene adsorbed on the gold surface with a gold probe tip was studied by using atomic force microscopy (AFM) in organic solvent (mixture of toluene – pentane). Asphaltenes adhered to the gold surface at various ratios of oil – pentane solution; similar ratios used in the destabilization of silica particles in the model oil. The results from AFM show adsorption of materials with different heights, structures and rupture strengths on the gold substrate. Heterogeneous adsorption of asphaltene aggregates (materials with different heights) were observed on gold surface for various S/O especially above the onset of asphaltene precipitation (S/O>0.43).