Harvard scientists: We can prevent climate change by making gasoline out of air
John SextonPosted at 1:21 pm on June 7, 2018
This sounds like the premise of a science fiction novel but it's being reported by the Atlantic so I guess it's real. And I don't mean real in the sense that some scientist wrote down an idea which might work one day with enough improvements in technology. There's a working prototype of this process which has been running since 2015, albeit on a small scale. The idea behind it is to produce gasoline and other fuels by reusing carbon that is already in the air.
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.
The paper which was published Thursday in a new journal claims a full-scale plant could be ready by 2021 if there is enough funding. Here's the description of the existing pilot plant. CE in this paragraph stands for Carbon Engineering, the company that built the project:
CE has operated a pilot plant on a 0.5-hectare industrial site in Squamish, BC, since 2015.
The design goal for the pilot were (1) to test each unit operation for which there is significant technical risk at a scale the equipment supplier judged sufficient to allow specification of commercial-scale hardware, and (2) to test the most important units as components of a closed-loop process. The pilot plant builds on previous prototype data that CE acquired for each unit, and on work with SPX, RHDHV, and Technip to design and size the contactor, pellet reactor, and calciner, respectively. CE's pilot data have been used to refine the commercial-scale plant design described earlier.
What's not clear from the Atlantic piece is how much carbon a full-scale plant could scrub from the atmosphere but the paper does estimate the cost as falling somewhere between $94 and $232 per ton. At the lower range that works out to about a dollar per gallon of gas. Would people pay that much more for recycled gasoline? Would government's subsidize it? Or would the perfect once again become the enemy of the good?
The last step in the process is optional. You don't have to turn the CO2 back into gasoline (or jet fuel). If you wanted, you could bury it and thereby take it out of the atmosphere for good. No doubt that's what the Sierra Club and similar groups would want to see happen (along with leaving oil and gas in the ground). But the beauty of the final step is that it would cover the cost of the other two, making this an approach that improves the amount of carbon going into the atmosphere without draconian changes to our current lifestyles. At least that's what could happen if this plan works at scale.
Tags: climate change CO2 fossil fuels gasoline