Dispersing oil slicks

Dispersants are formulated to disperse oil slicks into the sea or another water body. Surface-washing agents, or beach cleaners as they are sometimes called, are surfactant formulations designed to remove oil from surfaces such as beaches. Emulsion breakers and inhibitors are intended to break water-in-oil emulsions or to prevent their formation. 

Neoterge -Super Lux dispersant, oil removal/suspension textile scouring Neoterge -Super Lux dispersant, oil slicks Empimin OP70 Span 20 dispersant, oil slicks greases Lumisorb STT... 

Regardless of the source, the resultant oil slicks are essentially surface phenomena that are affected by several transportation and transformation processes. With respect to transportation, the principal agent for the movement of slicks is the wind, but length scales are important. Whereas small (i.e. relative to the slick size) weather systems, such as thunderstorms, tend to disperse the slick, cyclonic systems can move the slick essentially intact. Advection of a slick is also affected by waves and currents. To a more limited extent, diffusion can also act to transport the oil. 

Dispersants are widely used in many parts of the world to deal with oil spills on the ocean. The objective of adding the dispersant is to emulsify the oil slick... 

Modem oil spill-dispersant formulations are concentrated blends of surface-active agents (surfactants) in a solvent carrier system. Surfactants are effective for lowering the interfacial tension of the oil slick and promoting and stabilizing oil-in-water dispersions. The solvent system has two key functions (1) to reduce the viscosity of the surfactant blend to allow efficient dispersant application and (2) to promote mixing and diffusion of the surfactant blend into the oil film [601]. 

A. Charlier. Dispersant compositions for treating oil slicks on the surface of water (compositions dispersantes pour le traitement de nappes d huile a la surface de I eau). Patent EP 254704, 1988. 

A. Charlier. Dispersant compositions for treating oil slicks on cold water. Patent EP 398860, 1990. 

The physical transport of oil droplets into the water column, called dispersion, is often a result of water surface turbulence but may also result from the application of chemical agents (dispersants). These droplets may remain in the water column or coalesce with other droplets and gain enough buoyancy to resurface. Dispersed oil tends to biodegrade and dissolve more rapidly than floating slicks because of high surface area relative to volume. Most of this process occurs from about half an hour to half a day after the spill. 

Diffusion Flame The flame produced by the spontaneous mixture of fuel vapors or gases and air. Dispersants These are chemicals which reduce the surface tension between oil and water, thus facilitating he breakup and dispersal of an oil slick in the form of an oil-in-water emulsion. Dispersing Agent An adjuvant diat reduces the attraction between particles. 

Some special problems arise at sea. When crude oil is spilled on the ocean, a slick is formed which spreads out from the source with a rate that depends on the oil viscosity. With sufficient energy an O/W emulsion may be formed, which helps disperse oil into the water column and away from sensitive shorelines. Otherwise, the oil may pick up water to form a water-in-oil emulsion, or mousse ( chocolate mousse ). These mousse emulsions can have high water contents and have very high viscosities, with weathering they can become semi-solid and considerably more difficult to handle, very much like the rag-layer emulsions referred to above. The presence of mechanically strong films makes it hard to get demulsifiers into these emulsions, so they are hard to break. See Chapter 9. 

In addition to drifting and evaporation, wind and wave energy advection and turbulence can cause an O/W emulsion to be formed which helps disperse oil into the water column and away from sensitive shorelines [562,563]. These droplets typically become weathered, accumulate suspended fine solids, and settle out [564—567]. For this reason oil-spill response teams may actually promote the formation of O/W emulsions from oil in the slick. 

Several industrial systems involve emulsions, of which the following are worthy of mention. Food emulsions include mayonnaise, salad creams, deserts, and beverages, while personal care and cosmetics emulsions include hand creams, lotions, hair sprays, and sunscreens. Agrochemical emulsions include self-emulsifiable oils that produce emulsions on dilution with water, emulsion concentrates with water as the continuous phase, and crop oil sprays. Pharmaceutical emulsions include anaesthetics (O/W emulsions), hpid emulsions, and double and multiple emulsions, while paints may involve emulsions of alkyd resins and latex. Some dry-cleaning formulations may contain water droplets emulsified in the dry cleaning oil that is necessary to remove soils and clays, while bitumen emulsions are prepared stable in their containers but coalesce to form a uniform fihn of bitumen when apphed with road chippings. In the oil industry, many crude oils (e.g.. North sea oil) contain water droplets that must be removed by coalescence followed by separation. In oil slick dispersion, the oil spilled from tankers must be emulsified and then separated, while the emulsification of waste oils is an important process for pollution control. 

The specific behaviour processes that occur after an oil spill determine how the oil should be cleaned up and its effect on the environment. For example, if an oil evaporates rapidly, cleanup is less intense, but the hydrocarbons in the oil enter the atmosphere and cause air pollution. An oil slick could be carried by surface currents or winds to a bird colony or to a shore where seals or sea lions are breeding and severely affect the wildlife and their habitat. On the other hand, a slick could be carried out to sea where it disperses naturally and has little direct effect on the environment. 

The long-term fate of dispersed oil is not known, although it probably degrades to some extent as it consists primarily of saturate components. Some of the dispersed oil may also rise and form another surface slick or it may become associated with sediment and be precipitated to the bottom. 

Dispersant is a common term used to label chemical spill-treating agents that promote the formation of small droplets of oil that disperse throughout the top layer of the water column. Dispersants contain surfactants, chemicals like those in soaps and detergents, that have molecules with both a water-soluble and oil-soluble component. Depending on the nature of these components, surfactants cause oil to behave in different ways in water. Surfactants or surfactant mixtures used in dispersants have approximately the same solubility in oil and water, which stabilizes oil droplets in water so that the oil will disperse into the water column. This can be desirable when an oil slick is threatening a bird colony or a particularly sensitive shoreline. 

Dispersants must always be applied with a system designed specifically for the purpose. If pesticide spray equipment is used, small droplets form that may blow away and not enough dispersant is deposited onto the oil slick. Unless suitably modified, fire monitors or regular hoses from ships may not result in correct droplet sizes or quantities of dispersant per unit area. Furthermore, the high velocity of the water/dispersant mixture can herd the oil away, resulting in the loss of dispersant to the water column, where it has little effect on oil floating on top of the water. 

Oil-in-water emulsion — Oil droplets dispersed in surrounding water and formed as a result of wave action or by a chemical dispersant. Oil-in-water emulsions show a tendency to coalesce and reform an oil slick when the water becomes calm, although the presence of surface-active agents in the oil or artificially added in the form of chemical dispersants increases the persistence of this type of emulsion. Natural dispersion of large quantities of oil can follow the formation of oil-in-water emulsions and weathering processes such as dissolution, oxidation, and biodegradation may be accelerated due to the large increase in the surface area of the oil relative to its volume. (See also Emulsification, Water-in-oil emulsion.)... 

The technique was used to show the loss of Ci-Cio hydrocarbons in 4-8 hr from four research oil slicks in the ocean surface. Similarly, it showed the loss of this fraction from oil droplets in the water column under the oil slicks in 20-30 min. The hydrocarbon composition measured by gas equilibration showed the hydrocarbons in water under the slick to be residual in the oil droplets with little in true solution in seawater. The same was true for chemically dispersed oil in the Gulf of Mexico. Apparently evaporation quickly removed these hydrocarbons. 

Chemical treatment of a slick usually involves spraying dispersants from ships or aircraft to accelerate the emulsification of the oil. Solvents and agents to reduce surface tension are also utilized to remove oil slicks from the surface of pools and enclosed inshore areas. However, dispersants are not effective on heavy or weathered oils, and some of them are toxic to marine life. Despite these disadvantages, chemical treatment of oil slicks has been instrumental in preserving many threatened coastal habitats. 

Finally, the dispersion of oil slicks resulting from spillage has required an understanding of the way in which surfactants can disintegrate the emulsion (chocolate mousse) which forms spontaneously by the interaction between crude oil and sea water. 

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