Nobody paid much attention to the Lotus Exige 270E show car on display at the recent Geneva motor show. Aside from a new stripe job, it looked like every other Exige, and even its tri-fuel (gas/ethanol/methanol) drivetrain seemed ho-hum. We've had bi-fuel cars capable of burning one or the other alcohol, so big deal-this one runs on all three and makes a bit more horsepower. But deep in the press release, they mentioned working on a way to make the methanol it runs on from CO2 pulled out of the air. Holy carbon footprints! Can that be done?
There's a great deal of research underway aimed at extracting carbon-dioxide from the air. You may know about equipment to capture and sequester CO2 from the exhaust streaming out of powerplant smokestacks, and you probably know that similar hardware is impractical for cars and planes (the CO2 weighs about triple what gasoline starts out weighing). But new technology aims to capture CO2 from the ambient atmosphere with stationary scrubbers using vanes covered in CO2-absorbent materials like sodium hydroxide from which the CO2 can be washed and collected. A Los Alamos study suggests the CO2 captured by a scrubber the size of a power-generating windmill could offset coal-generated power equivalent to twice as much as the windmill could generate and that a one-square-meter scrubber could offset the per-capita energy consumption of the average American. And what if we could then turn some of it into an easily distributed liquid fuel?
First off, this process isn't free. Considerable energy goes into these synthetic carbon-based fuels (methanol, butanol, propanol, and some suggest octane can be produced), but then all fuels are energy-storage media. Fossil fuels store solar energy that illuminated the planet over several millennia. The basic science involves converting carbon dioxide into carbon monoxide, then combining that with hydrogen to form methanol. In such a reaction, the CO2 isn't the source of the energy, it's only a building block. The hydrogen provides the energy.
Plants use chlorophyll to turn solar energy into electrons that break down CO2, and various solar-powered catalysts under development use gallium phosphides or rhenium complexes to mimic this task. Hydrogen is generally electrolyzed from water, meaning that the resulting fuel is only as "green" as the energy used to create the hydrogen. Another approach under development at Italy's University of Messina leverages sunlight and a titanium catalyst to split water molecules, releasing hydrogen ions, electrons, and oxygen gas. The electrons reduce the CO2 and bind the carbon using platinum and palladium catalysts inside carbon nanotubes. Keep Googling, and you'll discover more such chemical miracles.
Cars running on carbon fuel derived from recycled atmospheric CO2 would effectively be removed from the global-warming debate-or at least their impact would be constrained to the carbon footprint of the energy expended to produce and distribute the fuel. That's essentially the case with today's zero-emitters-hydrogen fuel cells and battery-powered electric vehicles. Generally speaking, in the near term scaling up for high-volume production of CO2-based fuel will prove cost prohibitive and may not offer sufficient return on energy invested, but further development could change that. Clearly a scientific race is on to see which technology will prove the most environmentally benign and economically feasible energy vector for transportation. I'm on record as bearish on hydrogen. Cellulosic biofuels seem to show some promise, and this latest development has me giving the methanol economy a fresh look. Of course, all the above would get a serious shot in the arm if you cold-fusion scientists would get on the stick.