Cheap, Safe Way to Destroy Found
In a discovery that could help protect the Earth’s ozone layer from lingering damage, Yale University chemists have devised a safe, inexpensive and simple process that can destroy stockpiles of Freon and other ozone-depleting compounds.
Production of chlorofluorocarbons, used in air conditioners and refrigerators, was banned in the United States and most industrialized nations Jan. 1. But because there is no prohibition on the use of existing stockpiles, many auto parts dealers, mechanics and cooling system repair firms are storing large quantities.
Finding a cheap and safe method of destroying the CFCs is considered to be critical in preventing unwanted supplies from being released into the air, where they damage the ozone layer, which in turn allows more ultraviolet radiation to reach Earth.
Yale chemistry professor Robert H. Crabtree and graduate student Juan Burdeniuc report in Friday’s issue of the journal Science that passing the CFCs over a bed of sodium oxalate, a cheap and readily available material, and heating it to about 550 degrees Fahrenheit transforms the compounds into harmless carbon, salt and sodium fluoride.
Although other techniques are capable of destroying stockpiles of CFCs, they are considered dangerous, costly and inconvenient.
The new process, according to Crabtree and Burdeniuc, requires only simple chemistry and inexpensive materials. Sodium oxalate, which is found naturally in rhubarb leaves, can be purchased for about $40 per pound, and there are no dangerous byproducts, according to the research, which was funded by the U.S. Department of Energy and 3M Co.
In an interview, Crabtree said the idea came from his graduate student, Burdeniuc, who “had an intuition” that sodium oxylate could break down CFCs by feeding electrons in and removing chlorine atoms.
“No one thought that CFCs would react with such a mild and unassuming material as sodium oxalate,” Crabtree said. “It’s the equivalent of watching a pop gun punch holes in steel.”
CFCs were thought to be nearly indestructible because they are remarkably stable compounds that resist chemical reactions. Indeed, their stability is the main reason they became popular in the 1940s. Unlike ammonia and other substances previously used as refrigerants, CFCs are not readily flammable, explosive or toxic.
But in the 1970s, chemists learned that the compounds were not the miracle chemicals they were thought to be. CFCs react in the upper atmosphere to release chlorine that damages ozone that shields the planet from ultraviolet radiation that can cause skin cancer and damage ecosystems.
Manufacture and use of CFCs have declined steadily since 1990, when leaders of industrialized nations signed a pact to phase them out, called the Montreal Protocol.
Still, in 1994, about 300 million pounds were produced in the United States. The compounds are so widely distributed that there is no credible estimate of the volumes still stored.
CFC-free automobile air conditioners, refrigerators and other equipment are in widespread use. But suppliers and repair companies have stockpiled some of the compounds to service older models, especially cars made before 1993.
The method developed by Yale is useful only in eliminating CFCs before they are used, not after they are vented into the atmosphere.
The ozone layer continues to be damaged by the compounds, largely from past use. Once they are in the atmosphere, CFCs continue to thin the ozone layer for decades, perhaps more than 100 years.
Atmospheric chemists predict that the ozone layer won’t start healing until almost the middle of the next century.