The Massachusetts Institute of Technology (MIT) has developed a new technique for magnetically separating oil and water that could be used to clean up oil spills. The idea was presented at the 13th International Conference on Magnetic Fluids in New Delhi yesterday.
Clean up and recovery from an oil spill still remains a challenge. The last big oil spill, The Deep Water Horizon oil spill, also know as the BP oil spill, occured in the Gulf of Mexico in 2010. It is the largest accidental marine oil spill in the history of the petroleum industry. After this disaster, renewed interest emerged on finding new effective methods of cleaning up the spilled oil from the water. Even a competition was born out of frustration over oil clean up efforts. Until now there have been three ways to combat an oil slick on the open sea; a mechanical approach, which comprises the use of a boom to corral and deflect oil and skimmers to collect it, applying dispersants to the slick or, alternatively, burning the oil and manually removing it from the water.
The first tactic has been the preffered approach, because it is the only one removing the oil from the environment. The downside to it is that it is very labour and equipement intensive and you only retrieve a small percentage of the spilled oil. Mechanical clean-up technology tends to work exclusively in placid waters. In choppy waters the recovery efficiency is just 50%. So what you retrieve from the water would be a half water – half oil mixture.
When dispersants are used, they will disperse large amounts of certain oil types from the sea surface by transferring it into the water column. They will cause the oil slick to break up and form water-soluble micelles that are rapidly diluted. The oil is then effectively spread throughout a larger volume of water than the surface from where the oil was dispersed. It can also delay the formation of persistent oil-in-water emulsions. However, laboratory experiments showed that dispersants increased toxic hydrocarbon levels in fish by a factor of up to 100 and may kill fish eggs.
For the controlled burning of oil in open sea you need the right sea surface temperature and enough oil to achieve combustion that could be sustained. Usually oil is spread thin and wide on sea surfaces, so that faces a problem. And moreover, controlled burning does severely impact the air quality and releases all sorts of undesirable gasses into the atmosphere , including mercury.
The first method remains the best, but it is still difficult seperating the oil from the water. Suspending magnetic nanoparticles within the oil turns it into a magnetic liquid known as a ferrofluid. A great deal of research has been done on separating water and ferrofluids, because it seemed like a promising method of extracting oil from contaminated water. The typical method involves pumping a water and ferrofluid mixture through a channel, while magnets outside the channel direct the flow of the ferrofluid, perhaps diverting it down a side channel or pulling it through a perforated wall. This approach can work if the concentration of the ferrofluid is known in advance and remains constant, which unfortunately doesn’t apply in the case of contaminated water from an oil spill.
The MIT researchers made two modifications to this existing ferrofluid method. Instead of placing the magnets on the outside of the stream, they were immersed within it, and instead of being oriented parallel to the flow of the stream, they run perpendicular to it.
The magnets are permanent magnets, and they’re cylindrical. Due to the fact that a magnet’s magnetic field is strongest at its edges, the tips of each cylinder attract the oil much more powerfully than its sides do. In experiments the MIT researchers conducted in the lab, the bottoms of the magnets were embedded in the base of a reservoir that contained a mixture of water and magnetic oil; consequently, oil couldn’t collect around them. The tops of the magnets were above water level, and the oil shot up the sides of the magnets, forming beaded spheres around the magnets’ ends.
MIT’s technology is supposed to improve the 50 % efficiency in choppy waters. The magnetic separation method could be used in conjunction with existing oil recovery techniques such as skimming, which would perform an initial separation. Collecting the 50 % oil and water in a confined space, then putting magnetic nanoparticles in the water and seperating the magnetic oil from the water, so you get clean water and magnetic oil. Then existing technology can be used to remove the magnetic nanoparticles from the oil and the oil can be recovered re-used.
In their experiments, the MIT researchers used a special configuration of magnets, called a Halbach array, to extract the oil from the tops of the cylindrical magnets. Whether the Halbach array would be the most practical way to remove oil from the cylindrical magnets in an actual oil-recovery system remains to be seen. The researchers also need to determine how much water gets dissolved in the oil, and how it can best be removed. “To our eye, you don’t see much moisture in there, but I’m sure that there is some moisture that adheres to it,” Markus Zahn, the Thomas and Gerd Perkins Professor of Electrical Engineering Zahn says. “We might have to run it through multiple cycles.”
Shahriar Khushrushahi, a postdoc in MIT’s Department of Electrical Engineering and Computer Science and lead author on a paper says the technology’s simplicity makes it feasible for large scale manufacture and deployment at sea for days or weeks at a time, where electrical power and maintenance facilities are limited.
Watch MIT’s information video on the technology
Sources: MIT, Treehugger