The limitation of mixing, therefore, can be fully appreciated. Further- 

 more, in some of the more remote locations where spills have occurred, such 

 as Eleuthera Island, Bahamas, and Chedabucto Bay, Nova Scotia, suitable work- 

 boats are usually not available readily, if at all. 



EFFECT OF RECENT DEVELOPMENTS ON NEED FOR MIXING 



Attention has been focused recently on improving dispersing effectiveness 

 by (1) improving the treatment rate (i.e., the amount of chemical needed to 

 disperse a given amount of oil); and (2) by minimizing and/or eliminating 

 the need for mixing. By improving the treatment rate, a workboat could stay 

 on station longer with its supply of chemicals before returning for resupply. 

 Treatment rates have varied from as low as 1 part of dispersant to 1 part 

 of oil to 1 part of dispersant to greater than 30 parts of oil. In 1974, 

 Warren Spring Laboratory, United Kingdom, described the use of such "improved 

 treating rate" chemicals, which are sometimes called concentrates since the 

 surface-active agent concentration is greater than the conventional 15 to 

 25 percent. The importance of this improvement is cited in the comment by 

 Laboratory personnel that "a spraying vessel carrying concentrate would be 

 capable of remaining at sea up to 10 times longer than one carrying conventional 

 dispersant." 



Elimination of the tedious, time-consuming mixing process has greatly 

 enhanced the scope and potential of chemical dispersion, particularly in the 

 case of large spills. Since mixing is no longer required, aerial application 

 alone would be feasible. Some aircraft uniquely adapted for this service 

 and capable of carrying 1,500 gal of dispersant, such as the Canadair 

 CL-215, can cover up to 3,000 acres (1,215 ha) an hour, based on a speed 

 of 150 kn and a treated swath width of 150 ft (45.6 m). Other aircraft, 

 such as the four-engine C-54s and Constellations, are also available for 

 spraying chemicals. These craft have capacities of between 3,000 and 4,000 

 gal. An entirely new potential for chemical dispersion now exists, therefore. 



THE MECHANISM OF SELF-MIX CHEMICAL DISPERSANTS 



The mechanisms of self-mix chemical dispersants goes beyond the simple 

 thesis represented by Equation (1). In an ideal no-mixing system, true spon- 

 taneous emulsification (or "self-mixing") is postulated to occur in the follow- 

 ing manner. The chemical surfactant formulation is made compatible with the 

 bulk oil. However, when the oil phase comes into contact with a water boundary 

 rather than air, part of the surfactant has a strong driving force to diffuse 

 into the water phase. In this transport process, a small amount of oil "associated" 

 with the surfactant is carried into the water phase. A continuation of this 

 process produces a series of fine oil droplets migrating from the oil phase 

 into the water phase, as schematically shown in Figure 4. 



As indicated in Figure 4, the surfactant formulation is compatible with 

 the crude oil phase as shown in (a). Because of the nature of the specific 

 compounds, however, there is a driving force for part of the formulation to 

 diffuse into the water phase when it contacts an oil/water interface (b). 

 During this diffusion, some oil associated with the surfactant as fine oil 

 droplets is carried along with the surfactant into the water column, as shown 

 in (c). 



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