By DAVID WILLIAMSON
UNC-CH News Services
CHAPEL HILL -- Large volumes of organic and other solvent wastes released into the environment each year by manufacturers and other industries could be reduced by adopting a new chemical technology developed by scientists at the University of North Carolina at Chapel Hill and colleagues, the scientists say.
"More than 30 billion pounds of organic and halogenated solvents are used worldwide each year as process aids, cleaning agents and dispersants, and solvent-intensive industries are considering alternatives that can reduce or eliminate the negative impact that solvent emissions can have on the environment," said Dr. Joseph M. DeSimone, Mary Ann Smith professor of chemistry at UNC-CH and chemical engineering at N.C. State University. "Because of its low cost, wide availability and environmentally and chemically benign nature, carbon dioxide is an attractive solvent alternative for a wide variety of chemical and industrial processes."
Although carbon dioxide's potential as a solvent has been recognized for more than 20 years, the gas -- which humans and animals exhale and which forms the bubbles in soda and champagne -- has worked poorly for that purpose even when highly pressurized into "supercritical" form. Few substances would dissolve in it.
DeSimone and colleagues have found that by combining supercritical carbon dioxide with a special surfactant, or soap-like compound, they could boost carbon dioxide's effectiveness dramatically.
The discovery is described in the Dec. 20 issue of the journal Science. Besides DeSimone, UNC-CH authors of the paper are chemistry graduate students James B. McClain, Douglas E. Betts and Dorian A. Canelas and Dr. Edward T. Samulski, Bosamer professor and chair of chemistry.
"We think this is extremely significant," DeSimone said. "We have shown that when surfactants are added to carbon dioxide, then carbon dioxide goes from being a lousy solvent to a good cleaning solvent, and we have been able to emulsify material in CO2 that normally is insoluble."
In general, soap molecules have a sort of split personality, he explained. Part of the molecule has an affinity for the dispersing agent -- usually water -- while another has an affinity for a contaminant such as dirt. Soap then allows water to lift dirt from fabrics and other materials, and the water is discarded as waste.
With the new technique, the specially-engineered surfactant molecules allow grease, oils, many polymers and machine-cutting fluids to readily combine with carbon dioxide. The modified carbon dioxide is then able to remove contaminants from clothing, for example, or from machined parts resulting in an environmentally sound cleaning process.
Afterward, the carbon dioxide gas is separated from the contaminants, which are collected and reused or destroyed by other means such as incineration, and the carbon dioxide gas is recycled or vented harmlessly into the atmosphere.
Researchers used a technique known as small-angle neutron scattering to test the new method, which involved creating a new surfactant, a fluorinated acrylate compound that combines easily with carbon dioxide. They found the compound worked extremely well in creating two-part, ball-shaped molecular clusters called micelles, the size of which they could alter by adjusting pressure. They also found their new surfactant, or "soap," would break-up non-soluble polystyrene, a kind of plastic.
"Our experiments showed we could reduce the amount of waste generated by at least 100-fold," DeSimone said. "This is an example of a basic science discovery that has implications for society in general. It's also a rare example because it happened so fast, in just a few years."
Co-authors of the Science paper are J. David Londono, Hank D. Cochran and George D. Wignall of Oak Ridge National Laboratory in Oak Ridge, Tenn., and Delia Chillura-Martino and Roberto Triolo of the University of Palermo, Italy.
The National Science Foundation, the Environmental Protection Agency and a consortium of major chemical companies sponsor the UNC-CH research. The university expects to receive royalties from Performance Solutions Inc., a company DeSimone founded that began operating in November to develop and market the new technology through a license agreement.
In 1992, DeSimone won a National Science Foundation Young Investigator Award, and in 1993 was honored by the White House by being named one of 30 U.S. Presidential Faculty Fellows. He joined the UNC-CH faculty in 1990.
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Note: DeSimone can be reached at (919) 962-2166. His email address is firstname.lastname@example.org
Contacts: David Williamson, Juliet Dickey