New, Environmentally Friendly Technique For Separating Liquids Invented At UNC-CH

CHAPEL HILL -- An "exciting" new industrial process for separating liquid chemicals from one another -- a technique that promises to cut release of toxic substances into the environment -- has been developed by chemists at the University of North Carolina at Chapel Hill and colleagues.

"Liquid-liquid separations are an important process in many manufacturing industries -- pharmaceuticals, textiles, fine chemicals and natural products such as taxol, an extract from the yew tree that helps fight cancer," said Dr. Joseph M. DeSimone, Mary Ann Smith professor of chemistry at UNC-CH. "Very often these processes need to use organic solvents which are not good for our environment. That's because the solvents are either toxic or flammable or both, and they are expensive.

"What we invented was a process that allows carbon dioxide to be used to replace these organic solvents in liquid-liquid extractions."

A report on the chemical process appears in the Sept. 25 issue of Nature, a scientific journal.

Besides DeSimone, UNC-CH authors are Dr. Andrew I. Cooper, a former postdoctoral fellow; graduate student Jim McLain; Edward T. Samulski, professor and chair of chemistry; Dr. Andrey Dobrynin, postdoctoral research associate; Dr. Michael Rubenstein, professor of chemistry; and graduate student Amy Burke. Other authors include Drs. David Londono and George Wignall of Oak Ridge National Laboratory and John Frechet of the University of California at Berkeley.

The new work employs carbon dioxide, or CO2, because it is a common, inexpensive and harmless gas, DeSimone said. It is the gas humans and animals exhale and also that forms the bubbles in soda and champagne.

The process involves introducing soap-like surfactants into pressurized, or liquid, carbon dioxide that form a 'microenvironment' which allows substances normally not soluble in the gas to become soluble. After pulling the desired compound away from whatever undesirable compound it is mixed with, workers can easily vent the harmless CO2 into the atmosphere or recycle it for further use. What remains is the product chemists are trying to isolate.

Research published in the latest Nature describes how the team used its technique successfully to remove a dye completely from water, the scientist said. The first practical application could come within a couple of years in the textile industry, which releases countless tons of waste water into the environment every year.

"This work opens the door to using environmentally friendly solvents in this very solvent-intensive process," DeSimone said. "We are very excited about the possibilities."

In an accompanying commentary in Nature, Dr. Joan F. Brennecke of the University of Notre Dame said carbon dioxide and ?green chemistry? have become inextricably intertwined in recent years.

"This may seen ironic in light of the bad press it has endured in connection with global warming, but using CO2 as a solvent does not result in any net production," Brennecke wrote. "In fact, most CO2-based processes are designed to recycle and reuse essentially all of the CO2. With this in mind, the excitement about CO2 has developed because of its potential to replace hazardous organic solvents, especially chlorinated liquids and freons."

In June, DeSimone, the youngest person ever to hold a chair at UNC-CH, received the 1997 Presidential Green Chemistry Challenge Award from the U.S. Environmental Protection Agency for his earlier work with carbon dioxide. In 1992, he won a National Science Foundation Young Investigator Award and the following year, the White House named him one of 30 U.S. Presidential Faculty Fellows.