Thursday, May 13, 2010

Gulf Coast Oil Spill

Here is a bit from an interesting post on the Cocktail Party Physics web site. This post is written by Diandra Leslie-Pelecky is a professor of physics at the University of Texas at Dallas, where she researches biomedical nanomaterials.
In the Gulf Coast, the oil is being treated with dispersants like DISPERSIT and COREXIT. COREXIT is the particular dispersant being used. COREXIT's active components include "light petroleum distillate" (hydrocarbons like mineral spirits and kerosene), propylene glycol (an alcohol and emulsifier, which facilitates the mixing of oil and water and is a primary ingredient in stick deodorant) and organic sulfonic acid salt. The dispersant is dumped on top of the oil. It breaks the giant oil glob into smaller globules, surrounds it with surfactants and disperses it out to sea. Dispersants don't remove the oil, they just break it up into smaller pieces so that it's not as obvious. Natural processes biodegrade the oil over time. Yuck. They've dumped about 190,000 gallons of this stuff in the Gulf at this point.


Some companies are looking to aerogels - gels with so many air pockets that they look like sponges, but are very lightweight. Aerogels pores can be treated to be hydrophobic, which is important because you want a selective mop. If it attracts oil and water, that's not as helpful as just picking up oil. Those technologies aren't ready for use yet. Even after proven effective for picking up oil, they have to be tested for effects on the environment and the animals in the sea.

Most of the sorbents currently being used to deal with oil spils are made from the polymer polypropylene. Selectivity (oil, but not water) limits what we can use in the ocean. Common sorbents for racetracks are clays with pores that suck up and hold oil. The problem with clays and clay substitutes is that they absorb water as well as oil.

Polypropylene is hydrophobic, so fibers absorb oil, but let water pass through. I understand that there is now a polypropylene fiber shortage and its price is going up because of the high demand. Another company, MOP Environmental, uses recycled cellulose fibers that have been surface treated to minimize water absorption. Like the polypropylene, these fibers are placed into mesh bags and formed into booms, sweeps, etc. that can be put in the water and later collected. One of the disadvantages of absorption is that the oil is absorbed so strongly onto the polypropylene, for example, that you can't get it out again. The whole assembly has to be disposed of.

The MOP product also includes some oil-digesting bacteria. I remember during the Valdez disaster people predicting that someday, we would just be able to release bacteria and they would clean up spills in moments. These aren't special bateria, really. Some soil-dwelling bacteria naturally eat oil. Actually, it turns out you can find naturally occurring bacteria that specialize in eating just about anything, from sugar to starch to detergents. A couple of years ago, a 16-year old found a bacteria that eats plastic lunch bags. The problem is producing enough bacteria to make a dent in the millions of gallons of oil in a reasonable time. Also, the specificity of the bacteria as to what oils they will eat can be a problem, as "oil" contains a huge number of different types of hydrocarbon molecules. Most of these bacteria are as picky eaters as three year olds.

One of the more interesting solutions proposed (aside from dropping trash in the pipe to block the oil) also involves using fibers; however, the fibers in question are human hair. Chicken feathers, straw, and wool have all been used to collect oil in the past, but human hair seems to work particularly well. A big advantage is that the oil is adsorbed rather than absorbed. Adsorbed oil forms a very thin layer - a molecule or two thick - at the surface of the hair. Because the molecules are only weakly bound, the oil can be removed, meaning the hair can be reused.
Go read the article. It is filled with interesting facts and science. If you are like me and saw a news story about hair being collected to try and help mop up the oil spill, this article will give you the background physics to understand why that is a good idea.

The site is full of quirky, interesting posting on science by a bunch of women who have their own voice. Lots of fun.

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