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A better solution for a global warming culprit

Published March 1, 2013

It might not be as divine as transforming water into wine, or as rich as turning lead into gold.

But scientists at the University of Texas, in Arlington, have taken a major step toward converting carbon dioxide, one of the key villains of global warming, into a liquid chemical that, in turn, is key to making plastics and lubricants.

“We all like to think that what we do in the lab has some end use,” says Krishnan Rajeshwar, the university’s interim associate vice-president for research and one of five authors of a paper published in the authoritative journal Chemical Communications.

If the research advances to commercial success — which won’t happen quickly — Rajeshwar’s “some end use” will be a vast understatement.

Here’s a simplified description:

Heat a sheet of copper foil. This causes hairlike “nanorods,” so thin they can be seen only through an electron microscope, to grow. It also induces the copper in the rods to combine with oxygen and produce — no surprise — copper oxide.

Next, the rods are electroplated with another copper compound that contains twice the oxygen of the original.

The whole thing is put into a salty liquid called an electrolyte that’s also infused with carbon dioxide. In sunlight (or under an equivalent lamp in the lab) the copper chemicals react to create an electric current in the electrolyte. The current splits the carbon dioxide molecules.

The end product: methanol.

The goal: Large versions of this process would be installed at coal-burning generating stations or other big carbon dioxide spewers.

When it comes to keeping carbon dioxide out of the atmosphere, most attention is paid to sequestration, which means burying it deep in the Earth or injecting it into ocean water. But this threatens massive leaks from underground sites or, with ocean storage, acidity that’s likely lethal to marine life.

“I’m not a big fan of sequestration,” Rajeshwar says. His group’s work promises, “a much more elegant solution” for carbon dioxide than “trapping it somewhere.”

Researchers have been trying since the mid 1970s to split carbon dioxide. The breakthrough in Texas is that the process is the first without toxic chemicals or costly rare-earth minerals. It’s also extremely efficient, producing barely detectable by-products.

And the nanorods repair themselves, just as plants do when they convert carbon dioxide into carbohydrates. The rods wear down, then, a counter reaction rebuilds them — at least, in the experiments.

Rajeshwar says the process “performed fine,” in the longest test to date, but it lasted only an hour. One of many questions to be answered is whether it’s robust enough for a commercial venture.

Others include how big an area would be required for a system to handle the emissions from a major source, and exactly how much methanol would be produced — although the tests suggest it would be a lot.

And a glitch: Like a can of pop, the process would need pressure to keep sufficient carbon dioxide in the electrolyte. That requires energy, reducing the environmental benefit.

Still, the results are somewhere between incremental and revolutionary, Rajeshwar says.

Why write about it in Green Wheels? After all, methanol isn’t much of a transportation fuel.

It’s highly corrosive, so while it can be mixed with gasoline it’s not ideal in internal combustion. It can be used in small fuel cells, but at the size required for a vehicle it instantly destroys the membrane that makes the device work. It can be upgraded to natural gas, but there’s a glut of that and, Rajeshwar adds, the conversion is “hugely convoluted.”

But there’s more to cars and trucks than fuel. They use massive amounts of plastics and lubricants, and methanol is part of the process that creates many of those materials. I’d say vehicles containing stuff made with carbon dioxide that would otherwise go up in smoke would be a huge green step.

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