Petroleum hydrocarbon release behavior study in oil-sediment aggregates: turbulence intensity and chemical dispersion effect
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This study investigated the effects of turbulence and oil dispersants on release of petroleum hydrocarbons in oil-sediment aggregates. A kinetic study showed that the static oil release process could be fitted to the first-order kinetics model. The oil concentration increased with increasing temperature and salinity, while remaining independent of pH. The dispersant desorption ability of petroleum hydrocarbons followed the sequence of: Tween 80 > Tween 85 > Span 80 > DOSS. In the presence of turbulence, the maximum release ratio was 40.28%. However, the combination of dispersants and turbulence had a smaller effect than turbulence alone. Furthermore, residual n-alkanes and PAHs in the sediments were analyzed. The results showed higher proportions of C15-C35 and 2-3 ring PAHs in residual oil. These results can help assess the fate and distribution of oil spills in marine environments.Keywords:
Residual oil
Oil droplet
Total petroleum hydrocarbon
Oil droplet
Fuel oil
Penetration (warfare)
Coalescence (physics)
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The dispersion of oil spilled in water is influenced by chemical dispersants via the modification of the interfacial properties of the oil, such as oil-brine interfacial tension (IFT). In this study, the physical properties and dispersion of oil were measured in order to determine the effects of chemical dispersants on IFT and oil viscosity and the effects on oil droplet formation. In theory, the maximum size of oil droplet that forms under turbulent mixing increases with IFT. Therefore, a reduction in IFT reduces the size distribution of oil droplets. This paper presented the results of an ongoing project aimed at providing quantitative understanding the influence that chemical dispersants have on the size distribution of oil droplets and oil dispersion. Findings showed that a valid approach is to separate the direct effects of chemical dispersants on oil properties, specifically oil-brine IFT and the effects of mixing on dispersion of chemically treated oil. Under constant mixing conditions, the reduction of the maximum oil droplet size that overcomes the breakage process is determined by the effects of chemical dispersant on oil properties. This correlates well with the dispersant-to-oil ratio (DOR) up to the critical micelle concentration (CMC). This good agreement can be attributed to the reduction of IFT with DOR. It was concluded that the reduction of IFT with dispersant concentration is an additional signature of oil composition on droplet formation, while mixing energy is an external parameter that is independent of oil properties. 17 refs., 3 tabs., 9 figs.
Oil droplet
Brine
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Total petroleum hydrocarbon
Degradation
Polycyclic aromatic hydrocarbon
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Abstract After oil spills occur, dispersed oil droplets can collide with suspended particles in the water column to form the oil-mineral aggregate (OMA) and settle to the seafloor. However, only a few studies have concerned the effect of chemical dispersant on this process. In this paper, the mechanism by which dispersant affects the surface properties of kaolin as well as the viscosity and oil-seawater interfacial tension ( IFT ow ) of Roncador crude oil were separately investigated by small scale tests. The results indicated that the presence of dispersant impairs the zeta potential and enhances the hydrophobicity of kaolin. The viscosity of Roncador crude oil rose slightly as the dosage of dispersant increased while IFT ow decreased significantly. Furthermore, the oil dispersion and OMA formation at different dispersant-to-oil ratio ( DOR ) were evaluated in a wave tank. When DOR was less than 1:40, the oil enhancement of dispersant was not significant. In comparison, it began to contribute when DOR was over 1:40 and the effect became more pronounced with the increasing DOR . The adhesion between oil droplets and kaolin was inhibited with the increasing DOR . The size ratio between oil droplets and particles is the significant factor for OMA formation. The closer the oil-mineral size ratio is to 1, the more difficultly the OMA forms.
Oil droplet
Zeta potential
Mineral oil
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Oil droplet
Zeta potential
Mineral oil
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This work explored the formation mechanism of marine oil snow (MOS) and the associated transport of oil hydrocarbons in the presence of a stereotype oil dispersant, Corexit EC9500A. Roller table experiments were carried out to simulate natural marine processes that lead to formation of marine snow. We found that both oil and the dispersant greatly promoted the formation of MOS, and MOS flocs as large as 1.6-2.1 mm (mean diameter) were developed within 3-6 days. Natural suspended solids and indigenous microorganisms play critical roles in the MOS formation. The addition of oil and the dispersant greatly enhanced the bacterial growth and extracellular polymeric substance (EPS) content, resulting in increased flocculation and formation of MOS. The dispersant not only enhanced dissolution of n-alkanes (C9-C40) from oil slicks into the aqueous phase, but facilitated sorption of more oil components onto MOS. The incorporation of oil droplets in MOS resulted in a two-way (rising and sinking) transport of the MOS particles. More lower-molecular-weight (LMW) n-alkanes (C9-C18) were partitioned in MOS than in the aqueous phase in the presence of the dispersant. The information can aid in our understanding of dispersant effects on MOS formation and oil transport following an oil spill event.
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Aqueous two-phase system
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ABSTRACT The interaction of chemical dispersants and suspended sediments with crude oil influences the fate and transport of oil spills in coastal waters. Recent wave tank studies have shown that dispersants facilitate the dissipation of oil droplets into the water column and reduces the particle size distribution of oil-mineral aggregates (OMAs). In this work, baffled flasks were used to carry out a controlled laboratory experimental study to define the effects of chemical dispersants and mineral fines on the partitioning of crude oil, major fractions of oil, and petroleum hydrocarbons from the surface to the bulk water column and the sediment phases. The dissolved and dispersed oil in the aqueous phase and OMA was characterized using an Ultraviolet Fluorescence Spectroscopy (UVFS). The distribution of major fractions of crude oil (the alkanes, aromatics, resins, and asphaltenes) was analyzed by thin layer chromatography coupled to flame ionized detection (TLC/FID); aliphatic and aromatic hydrocarbons were analyzed by gas chromatography and mass spectrometry (GC/MS). The results suggest that chemical dispersants enhanced the transfer of oil from the surface to the water column as dispersed oil, and promoted the formation of oil-mineral aggregates in the water column. Interaction of chemically dispersed oil with suspended particular materials needs to be considered in order to accurately assess the environmental risk associated with chemical oil dispersant use in particle-rich nearshore and esturine waters. The results from this study indicate that there is not necessarily an increase in sedimentation of oil in particle rich water when dispersants are applied.
Asphaltene
Mineral oil
Oil droplet
Particle (ecology)
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Abstract Although the effects of chemical dispersants on oil droplet sizes and ascent speeds are well‐known, the fate and transport of dispersed oil droplets of different sizes under varying hydrodynamic conditions can be difficult to assess with observations alone. We used a particle tracking model to evaluate the effect of changes in droplet sizes due to dispersant application on the short‐term transport and surface expression of oil released under conditions similar to those following the 3 June 2010 riser cutting during the Deepwater Horizon event. We used simulated injections of oil droplets of varying size and number under conditions associated with no dispersant application and with dispersant application at 50% and 100% efficiency. Due to larger droplet sizes in the no‐dispersant scenario, all of the simulated oil reached the surface within 7 h, while only 61% and 28% of the oil reached the surface after 12 h in the 50% and 100% dispersant efficiency cases, respectively. The length of the surface slick after 6 h was ∼2 km in the no‐dispersant case whereas there was no surface slick after 6 h in the 100% dispersant case, because the smaller oil droplets which resulted from dispersant application had not yet reached the surface. Model results suggest that the application of dispersants at the well head had the following effects: (1) less oil reached the surface in the 6‐12 h after application, (2) oil had a longer residence time in the water‐column, and (3) oil was more highly influenced by subsurface transport.
Oil droplet
Particle (ecology)
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Calanus finmarchicus
Oil droplet
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Oil droplet
Dispersion stability
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