Research finds ultrasonics reduce precipitates

By Erin Voegele | November 17, 2010
Posted Dec. 8, 2010

Researchers at Oak Ridge National Laboratory have discovered that treating biodiesel with a high-intensity dose of ultrasonic energy can remove and prevent the formation of precipitates. The project, led by Michael Kass, a researcher in ORNL's Energy and Transportation Science Division, could help overcome one of the primary problems associated with the use of biodiesel in cold climates.

The project was funded internally by ORNL through $20,000 in seed money. Although the project included small-scale preliminary work, Kass said the results have been very intriguing.

Precipitates form in biodiesel when the temperature of the fuel drops to near the cloud point. Although they are not visible, Kass said that those precipitates remain in the fuel even when its temperature increased. In other words, they do not reabsorb into solution. "There are still there," Kass said. "They cause issues with filter plugging and other concerns."

Robert McCormick, a principal engineer with Golden, Colo.-based National Renewable Energy Lab, provided Kass and his team with a paper that summarized the latest work on precipitates. The resulting experimentation revolved around ultrasonically treating soy-based biodiesel samples to determine the effect on precipitates.

"It's a very simple experiment," Kass said, noting that it addressed both preventative precipitate treatment and rehabilitative precipitate treatment. Untreated biodiesel was placed in a beaker and treated with an ultrasonic probe. The sample was then tested under ASTM D6162 to measure filtration time. The results of the initial treated sample showed improvement over the untreated sample. The sample was then spiked with precursors to precipitate formation and refrigerated to drop the temperature. A portion of the sample was then treated with the ultrasonic probe. The study found improved filtration test times with the treated sample. In fact, Kass said the amount of precipitates dropped to nearly the same level as the initial sample.

Since ultrasonic treatment results in localized heating, the researchers also did a control experiment where a biodiesel sample was heated to the same temperature, but without ultrasonic treatment. "When you just heated it up, it did not improve the filtration time," Kass said.

"We know that ultrasound can create localized heating at an interfacial boundary, and if an interfacial boundary exists between the precipitate and the bulk fluid, that would be a point of localized heating, and we thought if we have localized heating, then perhaps we can get that stuff to go back into solution without having to heat the whole sample up, potentially to high temperatures," Kass said.

Although the research did not address the potential impact of ultrasonic treatment on cloud point, Kass said that, in theory, it should. "The other advantage is that if you can [heat the molecules] locally, you can also theoretically keep if from oxidizing as well," he continued.

ORNL has filed a patent on the process. While Kass and his team are not currently working to further research into the process, he said that he thinks it would be good for someone to take the research to the next level.

Additional members of the team include ORNL researchers Maggie Connaster and Samuel Lewis.
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