Carbon Dioxide: Good for Something?

April 10, 2008 -- The carbon in oil and coal is used to make many useful things: fuel, plastics, paints, detergents, pharmaceuticals...the list is long. Unfortunately, most of that carbon -- especially from fuel -- ends up in the atmosphere as good-for-nothing, climate-change-inducing carbon dioxide.

But is it really good for nothing? Maybe not for long. Chemists are developing strategies to put CO2 to use making products normally derived from oil. These approaches could take a bite out of power plant CO2 emissions that would normally go into the atmosphere.

For instance, CO2 could take the place of the poisonous gas phosgene in production of certain plastics, according to findings released this week at a meeting of the American Chemical Society by Toshiyasu Sakakura of the National Institute of Advanced Industrial Science and Technology in Tsukuba, Japan.

Sakakura and colleagues developed a new catalyst that efficiently converts CO2 and methanol into a plastic precursor whose synthesis currently requires phosgene. Phosgene, which is derived from petroleum, is particularly nasty. It was used as a chemical warfare agent in World War I.

"It does not produce much waste," Sakakura said of the new process. "The waste is just water, so it is simple and clean."

Bringing New Meaning to the Word "Recycled"

Sakakura and other researchers have targeted other processes for making plastics, which are, essentially, long chains of carbon. CO2 can react with a class of chemicals called epoxides to make polycarbonate, the tough, clear plastic used in compact discs, eyeglass lenses, bulletproof windows and more.

Using CO2 in such processes is a challenge, said Thomas Müller of the CAT Catalytic Center in Aachen, Germany, who also presented at the meeting, because it is relatively inert and "low in energy." After all, carbon dioxide is what is left after the energy stored in the chemical bonds of the molecules that make up fuel has been released by combustion.

This means that reactions using CO2 require something else, like methane or an epoxide, to act as a source of energy in creating a stable, higher-energy product like plastics.

"It would be great if you could polymerize CO2 directly," said chemist Geoffrey Coates of Cornell University in Ithaca, NY, referring to the process of linking carbon atoms together. "But you would defeat the laws of nature."

These co-reactants generally come from fossil fuel sources, so these CO2-based processes generally decrease, but do not eliminate, the need for petroleum. Coates has made polymers, for instance, that are 30 to 50 percent CO2.