5. Chemical Response Agents (Other than dispersants)
Spreading and Retraction of Spilled Crude Oil on Seawater
Oil-spills due to release of crude oil from tankers, offshore platforms, drilling rigs, and wells, and of other products such as diesel and bunker fuel, if uncontrolled, may have serious and sometimes long term environmental impact. This paper presents a method for reducing the areal coverage of spilled oil at sea or over other aqueous surfaces. The method can be used to contain spilled oil more efficiently during or after placement of booms.
The surface tension of seawater causes rapid spreading of spilled oil over large distances. However, spreading of oil can be instantly reversed by reducing the surface tension of the seawater by means of minimal quantities of surfactant. A low concentration of a water-soluble surfactant, such as a non-ionic surfactant with low critical micelle concentration, is recommended for maximum effectiveness for the least amount of surfactant. A controlled amount of the surfactant may be continuously deployed at the inner-wall of the boom. The spilled oil is caused to retract away from the boom toward the center of the encircled area. The decrease in area of the spilled oil results in a thicker oil layer that can be removed more effectively by skimming. The deployed surfactant also reduces the amount of oil that adheres to the control boom. The boom can then easily be removed from a remediated oil-spill and reused at a later date with minimal cleaning.
Laboratory observations show how crude oil can migrate over the surface of a model oil-wetted boom. Modification of the spreading behavior of five different crude oils by a non-ionic surfactant, BIO-SOFT®, was investigated. Experiments on spreading and contraction confirmed predictions based on interfacial tension measurements for seawater/air, crude oil/water and crude oil/air before and after release of a very small amount of surfactant. The retraction of crude oil as a function of surfactant concentration is demonstrated by real time video recordings of laboratory experiments.