THE MECHANISM OF CHEMICAL DISPERSION 

 AND THE ROLE OF THE SURFACE-ACTIVE AGENT 



At this point, it would be in order to consider terminology. The chemicals 

 used in the Torrey Canyou incident were basically cleaning agents. They were 

 called detergents . Subsequently, formulations were prepared that were meant 

 solely to disperse oil at sea. These are called dispersants . The word 

 smulsifier is also used in reference to these dispersants. 



The mechanism of chemical dispersion is quite simple. Let us first define 

 a surface-active agent (surfactant) as a compound that has an oil-compatible 



and a water-compatible group. Because of this amphiphatic nature, the surfactant 



located at an oil-water interface is depicted in Figure 1. By its orientation 



at the interface, the surfactant reduces the interfacial tension. The generation 



of interfacial area in the nature of finely dispersed oil droplets is enhanced 

 by the lowering of interfacial tension since: 



W„ = 



K " Y o/w A o/w 



wherein; 



W K is mixing energy, ergs, 



2 



A , is interfacial area, cm , 

 o/w 



Y / is interfacial tension, dynes/cm. 



It can now be appreciated that any surfactant (by definition), because 

 of its molecular configuration, lowers interfacial tension. The more subtle 

 requirements for a selected surfactant to perform as an effective dispersant 

 can now be examined. For example, the dispersed oil droplets, once formed, 

 should be prevented from coalescing. This is shown schematically in Figure 

 2, wherein the hydrophilic portion of the surfactant acts as a "fender" that 

 physically parries droplet collisions. This schematic of the surfactant is 

 somewhat oversimplified since more than one hydrophilic group may exist. 

 This fending characteristic also reduces the tendency of the droplets to stick 

 and thereby wet solid surfaces or to adhere to marine sediments. 



From this brief discussion of the dispersing mechanism, it can be seen 

 that the dispersant acts solely as an agent to enhance the formation of oil 

 droplets. It does not "weight" the droplets in order to sink them. It does 

 not solubilize the oil into the water column. It simply promotes an oil-in- 

 water dispersion. Sinking is a misconception of the behavior /mechanisms of 

 chemical dispersion that has persisted for 10 years! It is surprising that 

 even as recent as a large tanker spill in May 1976, there were reports that 

 it took 1,000 tons of dispersant to "sink" 4,000 tons of oil. 



THE INCENTIVES OF CHEMICALLY DISPERSING OIL 



It is not suggested that chemical dispersion is a panacea to minimize 



oil spill damage in all instances. Where physical containment and recovery 



are feasible, this is the preferred route. The limitations of oil skimmers 



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