Fuel Out of Thin Air

Copyright © 2011 William Mego

Carbon dioxide is valuable stuff. Everything we eat, for example, started out as carbon dioxide. So did everything we wear and burn for fuel. Far from being a pollutant, carbon dioxide, or CO2, is the stuff of well... everything.

If there weren't CO2 in the air, there would be no plant life and the temperature of the earth would be too low for man to survive. By trapping heat that would otherwise radiate away, CO2 keeps the temperature moderate. But there is in fact an optimal amount of CO2 to have in the atmosphere, about 300 CO2 molecules per million total air molecules. That's what life has adapted to.

When there's more than that, billions of calories of heat become trapped in the oceans, killing many of the things that live there and changing the global weather patterns that allow mankind to survive in its present numbers. The solution, of course, is to take the excess CO2 out of the air.

Plants do that every day, but when they die they rapidly decompose, releasing the CO2 back into the air again. The ancient farmers of South America, however, learned that if they burned the plant material in slow smouldering fires, they could form charcoal, trapping the carbon in the soil.

That not only holds nutrients that would otherwise wash away, and provides home for beneficial micro-organisms, but locks away the carbon perhaps for thousands of years. That forces next year's crops to get their carbon from the air, thus pulling more CO2 out and locking it away.

Although it's essential that we do what those ancient farmers did, it will not lower the amount of CO2 in the air as long as we continuously add more by burning fossil fuels. So where do we get the fuel we need for everything from lighting to transportation? Well, we can get it from the same place that the plants that made that oil and coal did, out of thin air.

Plants remove CO2 from the air by using sunlight to split water. They discard the oxygen and use the hydrogen to "reduce," i.e. add electrons to, CO2. They can't remove as much CO2 as they would like, however, because they can't get enough sunlight. But we don't have the plant's limitations.

Gathering CO2 from air and concentrating it is straightforward, although there's lots of room for improvements. Currently, carbon dioxide can be absorbed on lithium zirconates, various synthetic amines, silver oxide, other metal oxides, ionic liquids, and even the ground up chitin from crabs. In most cases, changing the temperature causes the CO2 to be released from the absorbant in concentrated form.

But what to do with it then? Sequester it, e.g. pump it down some well? No, that wouldn't get us any fuel. Actually Nobel Prize-wining chemist George Olah has had the answer for years: reduce the CO2 to methanol and throw it in the tank of any flex-fuel car. Carbon dioxide is simply used fuel that has been dispersed into the air. We can recover and reuse it forever without hurting the environment.

So how do you actually do that? Well, you need heat to release the CO2 from its absorbant. A solar tower being illuminated by heliostats would work nicely . Then you need a source of hydrogen. Solar electrolysis of water or the thermochemical production of hydrogen in nuclear plants can provide hydrogen at very low cost. Finally, you need to use catalysts to lower the activation energy of the reduction reaction, getting it to happen at reasonable temperatures, catalysts like zirconia, platinum and palladium in carbon nanotubes, and various other organic catalysts . Then behold, fuel out of thin air for (some have estimated) less than 25 cents per gallon.

Once you have methanol, you can easily polymerize it into longer molecules, but it works very well just as it is- as a transportation fuel and in recently designed fuel cells. It's main advantage is that we already have in place the infrastructure for using it. And because you're simply recycling the carbon from the air, it's environmentally benign.

Fourth generation nuclear power plants, as I have written , can easily fulfill our electricity needs, especially for things like electric cars and Personal Rapid Transit , but it will be a long time before we can move beyond the internal combustion personal automobile.

We may not even want to and we may not have to, for the fuel for those cars is all around us. We may not be able to see it in the air, but it's there. And we have just as much of it as Saudi Arabia has.