Crude oil droplets

A well-studied example of a bioemulsifier is emulsan, a cell surface-exposed molecule that allows Acinetobacter calcoaceticus RAG-1 to attach to crude oil droplets [123]. Upon depletion of the short-chain alkanes utilised by this strain, the emulsan molecules were released from the bacterial surface, thereby allowing the cells to leave the oil droplet and to find a new substrate. Important positive side-effects of this mechanism seem to be that the remaining emulsan hydrophilises the droplet and prevents both the reattachment of A. calcoaceticus RAG-1 and the coalescence of the used oil droplet with other droplets that still contain unexploited alkanes. Bredholt et al. [124] studied the oil-emulsifying activity of Rhodococcus sp. strain 094. When exposed to inducers of crude-oil emulsification, the cells developed a strongly hydrophobic character, which was rapidly lost when crude-oil emulsification started. This indicated that the components responsible for the formation of cell-surface hydrophobi-city acted as emulsion stabilisers after release from the cells. 

Figure 1.5 Example of a petroleum industry foam containing emulsified crude oil droplets. Photomicrograph by the author.

Figure 1.5 shows an example of an aqueous foam with emulsified and imbibed crude oil droplets residing in its plateau borders. Using a simple model the degree of emulsification and imbibition has been found to correlate quite well with foam sensitivity to oil for a wide variety of foams, oils, and conditions [114]. A limitation of emulsification/imbibition models is that they will only be important for foam lamellae that are thick enough to accommodate realistic emulsion droplet sizes. Typical foam lamellae in porous media appear to have thicknesses on the order of tens of nm [70,71,114,328],... 

To confirm the marked effect of the electrolyte concentration upon the pseudoemuIsion film stability we increased the NaCl concentration to 3 wt % and used DI to investigate the configuration of Salem crude oil droplets in the presence of C AOS surfactant (since this surfactant yields the most stable foam). 

Figure 4. Photomicrograph of an enhanced oil recovery process foam containing emulsified crude-oil droplets. The droplets have traveled within the narrow lamellae to accumulate and sometimes coalesce in the plateau borders of the foam, where they are held preferentially. The presence of such emulsified oil droplets in the foam structure has a destabilizing effect on the foam.

The techniques used for demulsification of a transport emulsion may include raising the temperature of the emulsion, addition of emulsionbreaking additives, addition of diluents to reduce the viscosity of the heavy crude oil, and the use of equipment designed to promote coalescence of the crude-oil droplets. Raising the temperature of the emulsion increases the... 

Electrophoretic Mobility. The electrophoretic mobility of the crude oil droplets as a function of caustic concentration has been determined in relation to enhanced oil recovery (52). It was observed that a maximum in electrophoretic mobility corresponds to a minimum in interfacial tension at the crude oil/caustic interface (Figure 11). The maximum electrophoretic mobility at minimum interfacial tension can be attributed to the ionization of carboxyl groups present in the crude oil, which in turn determine the charge density at the crude oil/caustic interface, depending on NaOH concentration. 

We measured the electrophoretic mobilities of crude oil droplets in alkaline solution using a Zeta Meter (20). Since the droplet sizes were larger than one micron, the zeta potentials were calculated from electrophoretic mobilities using Smoluchowski s formula. 

Fig. 17 shows a photograph of a crude oil droplet dispersed in non-equilibrated aqueous phase consisting of. 02% NaOH and 1% NaCl. The droplet is approximately 16 microns in diameter. 

Preliminary results on the kinetics of coalescence of both the Long Beach and the Huntington Beach crude oil droplets in caustic systems have been presented. 

Figure 23. Differential interferometric (DI) photographs of Salem crude oil droplets at foam surface. Key a, CJ2AOS b, C14AOS and c, C16AOS...

Electrokinetic properties of crude oil droplet dispersed in the aqueous phase provided useful information about the charge groups of the indigenous surfactants in the crude oil which likely act as barriers to the adsorption of added demulsifiers. The pH (and likely ionic content) of aqueous dispersed phase, therefore, plays an important role in the process of droplet coalescence in these systems. 

Petroleum industry foams comprise a mixture of gas with either oil or water, where the gas phase occurs in the form of bubbles dispersed within the liquid. The bubble diameters are typically on the order of 10 to 1000 pm, but may be as large as several centimetres. Although both aqueous and oleic foams may be encountered, the former are by far the most common. Foams and emulsions may also be encountered simultaneously [2], Figure 2 shows an example of an aqueous foam with crude oil droplets residing in its Plateau borders. 

These hazards are reduced drastically by desalting crude oils, a process which consists of coalescing and decanting the fine water droplets in a vessel by using an electric field of 0.7 to 1 kV/cm. 

A knock out vessel may on the other hand be followed by a variety of dehydrating systems depending upon the space available and the characteristics of the mixture. On land a continuous dehydration tank such as a wash tank may be employed. In this type of vessel crude oil enters the tank via an inlet spreader and water droplets fall out of the oil as it rises to the top of the tank. Such devices can reduce the water content to less than 2%. 

To mitigate the effects of corrosion resulting from the presence of salts, it is advantageous to reduce the salt concentration to the range of 3 to 5 ppm. Typically, brine droplets in crude oil are stabilized by a mixture of surface-active components such as waxes, asphaltenes, resins, and naphthenic acids that are electrostatically bound to the droplets surface. Such components provide an interfacial film over the brine droplet, resulting in a diminished droplet coalescence. Adding water to the crude oil can decrease the concentration of the surface-active components on the surface of each droplet, because the number of droplets is increased without increasing component concentration. 

Electrical coalescers, in which a high voltage field is used to break down the stabilising film surrounding the suspended droplets, are used for desalting crude oils and for similar applications see Waterman (1965). 

Bansal, V.K. Chan, K.S. McCallough, R. Shah, D.O. The Effect of Caustic Concentration on Interfacial Charge, Interfacial Tension and Droplet Size A Simple Test for Optimum Caustic Concentration for Crude Oils, J. Canadian Petrol. Tech. 1978,17(1), 69. 

Water may be found in the crude either in an emulsified form or in large droplets. The quantity is generally limited by pipeline companies and by refiners, and steps are normally taken at the wellhead to reduce the water content as low as possible. However, after a spill, water can be introduced by climatic conditions, and the relevant tests (ASTM D96, D954, D1796 IP, 2004) are regarded as important in crude oil analyses. Prior to analyses, it is often necessary to separate the water from a crude oil sample, and this is usually carried out by one of the procedures described in the preliminary distillation of crude petroleum (IP 24). Overall, there are several methods that can be employed for organic semivolatile sample preparation and cleanup procedures (Table 6.4). 

Once reaching a water system, the components of a crude oil or a petroleum hydrocarbon are truly dissolved at a molecular level or apparently soluble at a colloidal level when droplets characterized by radii of tens to hundreds of microns are formed. The apparent solubility of polycyclic aromatic hydrocarbons from oil in an aquatic system is reported by Sterling et al. (2003), who consider that the colloidal concentration of a given hydrocarbon contaminant in aqueous phase, C, is described by the equation... 

Figure 2 Crude desalting (electrostatic desalting). A high-voltage electrostatic field acts to agglomerate dispersed oil droplets for water-oil separation after water wash desalting. (From Ref. 5.)...

The greater the difference in density between the oil droplet and the water phase, the greater the vertical velocity That is, the lighter the crude, the easier it is to treat the water. 

When crude endotoxin from the heptose-less mutant of Salmonella typhimurium is combined with trehalose dimycolate from mycobacteria in oil droplets and injected directly into established tumors (line 10 hepatocellular carcinoma) in syngeneic guinea pigs, rapid regression of the tumors occurs and over 90% of the animals are cured. The three required components for activity in this tumor model are (a) the endotoxin (b) the mycobacterial adjuvant, trehalose dimycolate and (c) a compound satisfying the minimal structural requirement (muramyl dipeptide) for adjuvant activity by bacterial cell wall materials. The mycobacterial cell wall skeleton is able to replace the latter two components. 

Figure 1.3 Photomicrograph of an emulsified droplet of a crude oil, dispersed in the aqueous solution that was used to release it from the mineral matrix in which it was originally held. Note the obvious presence of an interfacial film at the surface of the drop. Photomicrograph by the author.

Not all emulsions exhibit the classical milky opaqueness with which they are usually associated. A tremendous range of appearances is possible, depending upon the droplet sizes and the difference in refractive indices between the phases. An emulsion can be transparent if either the refractive index of each phase is the same, or alternatively, if the dispersed phase is made up of droplets that are sufficiently small compared with the wavelength of the illuminating light. Thus an O/W microemulsion of even a crude oil in water may be transparent. If the droplets are of the order of 1 pm diameter a dilute O/W emulsion will take on a somewhat milky-blue cast if the droplets are very much larger then the oil phase will become quite distinguishable and apparent. Physically the nature of the simple emulsion types can be determined by methods such as [95] ... 

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