A team of scientists from Harvard University and the company Carbon Engineering announced on Thursday that they have found a method to cheaply and directly pull carbon-dioxide pollution out of the atmosphere.
the new technique is noteworthy because it promises to remove carbon dioxide cheaply. As recently as 2011, a panel of experts estimated that it would cost at least $600 to remove a metric ton of carbon dioxide from the atmosphere.
The new paper says it can remove the same ton for as little as $94, and for no more than $232. At those rates, it would cost between $1 and $2.50 to remove the carbon dioxide released by burning a gallon of gasoline in a modern car.
Their technique, while chemically complicated, does not rely on unprecedented science. In effect, Keith and his colleagues have grafted a cooling tower onto a paper mill. It has three major steps.First, outside air is sucked into the factory’s “contactors” and exposed to an alkaline liquid. These contactors resemble industrial cooling towers: They have large fans to inhale air from the outside world, and they’re lined with corrugated plastic structures that allow as much air as possible to come into contact with the liquid. In a cooling tower, the air is meant to cool the liquid; but in this design, the air is meant to come into contact with the strong base. “CO2 is a weak acid, so it wants to be in the base,” said Keith.
Second, the now-watery liquid (containing carbon dioxide) is brought into the factory, where it undergoes a series of chemical reactions to separate the base from the acid. The liquid is frozen into solid pellets, slowly heated, and converted into a slurry. Again, these techniques have been borrowed from elsewhere in chemical industry: “Taking CO2 out of a carbonate solution is what almost every paper mill in the world does,” Keith told me.
Finally, the carbon dioxide is combined with hydrogen and converted into liquid fuels, including gasoline, diesel, and jet fuel. This is in some ways the most conventional aspect of the process: Oil companies convert hydrocarbon gases into liquid fuels every day, using a set of chemical reactions called the Fischer-Tropsch process. But it’s key to Carbon Engineering’s business: It means the company can produce carbon-neutral hydrocarbons.
What does that mean? Consider an example: If you were to burn Carbon Engineering’s gas in your car, you would release carbon-dioxide pollution out of your tailpipe and into Earth’s atmosphere. But as this carbon dioxide came from the air in the first place, these emissions would not introduce any new CO2 to the atmosphere. Nor would any new oil have to be mined to power your car.