In a development that could elicit a sigh of relief from environmentalists and scientists trying to eliminate a major threat to the ozone layer, Yale University scientists reported in the Jan. 19 issue of SCIENCE Magazine that they have discovered a way to convert environmentally damaging CFCs--chlorofluorocarbons such as Freon--into four benign, useful components: sodium chloride (table salt), sodium flouride (an ingredient used in toothpaste), carbon, and carbon dioxide. Most surprisingly, the key to the process is found in rhubarb.

Professor Robert Crabtree and graduate student Juan Burdeniuc used an innocuous compound called sodium oxalate that is found in rhubarb leaves to harmlessly destroy stockpiles of CFCs. "We're very happy that it might make a contribution to the quality of life in the next century," Crabtree said during a news conference. The researchers have applied for a provisional patent of their method.

CFCs such as refrigerants, solvents and cleaning agents have been linked to the shrinking of the ozone layer, which shields the Earth from the sun's ultraviolet radiation. The thinning of the ozone is generally believed to lead to global warming, the destruction of plant life, and increased risk for skin cancer and cataracts.

A safe, inexpensive solution

CFCs have been historically hard to destroy, because they are relatively inert (also the reason they survive so long in the Earth's stratosphere). But the new process, in contrast to the previously known alternatives, is safe, clean, and simple. The CFCs are mineralized by passing them through a bed of sodium oxalate, a harmless powder, which is heated to about the temperature for baking bread.

"This is cutting-edge work," says Craig A. Burton, a chemist at 3M in St.Paul, Minn." Normally, we expect to use extremely high temperatures or highly reactive agents to break [CFCs] up. Any work indicating that they will react in moderate conditions is of great interest."

What makes the development even more practical is that sodium oxalate is relatively inexpensive, at about $40 a pound, and readily available, according to the researchers.

A political issue

Under a 1992 international agreement, 139 countries banned production of CFCs as of Jan. 1. But stockpiles can continue to be used, and developing countries such as China and India have until 2010 to comply. And the United States, which has been internationally criticized for dragging its feet on the elimination of the harmful chemicals, still allows the use of Freon in older vehicles' air conditioners, although alternative refrigerants are now required in new cars and air conditioners.

Manufacturers have also come under fire for stockpiling vast quantities of CFCs in warehouses, arguing that without a practical way to destroy CFCs, they should continue to be used in the United States and the Third World. But, Crabtree notes, if the new process succeeds on an industrial scale, it could prompt manufacturers to make the switch to less environmentally destructive refrigerants more quickly.

Elminating stockpiles

Although CFC production is banned, plenty of Freon remains. In the United States alone, according to automobile-industry estimates, as much as 100 million pounds of it may be stockpiled, where it is becoming a hot item on the black-market.

Professor Mario Molina of MIT, the 1995 Nobel Prize winner in chemistry who proved with two colleagues that CFCs destroy ozone, said the new process would be helpful in eliminating stockpiles but could not remove the CFCs already in the air.

"Like watching a popgun punch holes in steel."

"It's hard to break down CFCs without releasing corrosive by-products," Crabtree says. They're so unreactive, they resist all but the harshest chemical treatments. Previously proposed methods for breaking down CFCs could cause an explosion or fire, and produce corrosive acid gases. "No one thought that CFCs would react with such a mild and unassuming material as sodium oxalate," he says, "It's like watching a popgun punch holes in steel."

The chemists posit that pumping CFCs through sodium oxalate (Na₂C₂O₄) at 290 degrees Celcius causes the powder to surrender two electrons to each CFC gas molecule, which in turn release fluoride and chloride ions. Those ions then hook up with available sodium ions to create salts. Carbon dioxide gas and solid carbon result from the remaining materials.

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