How to suck carbon dioxide from the sky for fuels and more

June 7, 2018, Cell Press
Carbon Engineering's clean fuel, synthesized from carbon dioxide captured from the air and hydrogen split from water. Credit: Carbon Engineering

Someday, the gasoline you buy might trace its heritage to carbon dioxide pulled straight out of the sky rather than from oil pumped out of the ground. By removing emitted carbon dioxide from the atmosphere and turning it into fresh fuels, engineers at a Canadian firm have demonstrated a scalable and cost-effective way to make deep cuts in the carbon footprint of transportation with minimal disruption to existing vehicles. Their work appears June 7 in the journal Joule.

"The dioxide generated via direct air capture can be combined with sequestration for carbon removal, or it can enable the production of carbon-neutral hydrocarbons, which is a way to take low-cost carbon-free power sources like solar or wind and channel them into fuels that can be used to decarbonize the transportation sector," says lead author David Keith, founder and chief scientist of Carbon Engineering, a Canadian CO2-capture and clean fuels enterprise, and a professor of applied physics and public policy at Harvard University.

Direct air capture technology works almost exactly like it sounds. Giant fans draw ambient air into contact with an aqueous solution that picks out and traps carbon dioxide. Through heating and a handful of familiar chemical reactions, that same carbon dioxide is re-extracted and ready for further use—as a carbon source for making valuable chemicals like fuels, or for storage via a sequestration strategy of choice. It's not just theory—Carbon Engineering's facility in British Columbia is already achieving both CO2 capture and generation.

Carbon Engineering's pilot air contactor, constructed from the same set of cooling tower componentry and design philosophy that will be used at commercial scale. Credit: Carbon Engineering

The idea of direct air capture is hardly new, but the successful implementation of a scalable and cost-effective working pilot plant is. After conducting a full process analysis and crunching the numbers, Keith and his colleagues claim that realizing direct air capture on an impactful scale will cost roughly $94-$232 per ton of carbon dioxide captured, which is on the low end of estimates that have ranged up to $1,000 per ton in theoretical analyses.

That price-point is low enough to use direct air capture to start tackling the roughly 20% of global carbon emissions that result from driving, flying, trucking, and other ways of getting people and goods around. "Electricity from solar and wind is intermittent; we can take this energy straight from big solar or wind installations at great sites where it's cheap and apply it to reclaim and recycle carbon dioxide into new fuel," Keith says, adding that "Making fuels that are easy to store and transport eases the challenge of integrating renewables into the energy system."

The resulting fuels, including gasoline, diesel, and jet fuel, are compatible with existing fuel distribution and transportation infrastructure. Thanks to ultra-low life cycle carbon intensities, they are a promising route for reducing carbon emissions in heavy transportation and other sectors of the energy system that are demanding and difficult to electrify.

This rendering shows Carbon Engineering's proposed air contactor design. This unit would be one of several that would collectively capture 1M tons of CO2 per year. Credit: Carbon Engineering

Centuries of unchecked human carbon emissions also mean that atmospheric carbon dioxide is a virtually unlimited feedstock for transformation into new fuels. "We are not going to run out of air anytime soon," adds Steve Oldham, CEO of Carbon Engineering. "We can keep collecting with direct air capture, keep adding hydrogen generation and fuel synthesis, and keep reducing emissions through this AIR TO FUELSTM pathway."

Keith and Oldham are optimistic that they have reduced scale-up risks by implementing direct air capture at reasonable costs using standard industrial equipment. That means that all the pieces are in place to move on to full-size plants capable of manufacturing 2,000 barrels of fuels per day— totaling over 30 million gallons per year across plants. Commercialization of such plants would allow direct air capture to make a dent in transportation emissions by connecting low-cost renewable energy to low-carbon transportation fuels using Carbon Engineering's AIR TO FUELSTM pathway.

"After 100 person-years of practical engineering and cost analysis, we can confidently say that while air capture is not some magical cheap solution, it is a viable and buildable technology for producing carbon-neutral fuels in the immediate future and for removing carbon in the long run," says Keith.

Explore further: Keeping captured carbon dioxide in liquid makes it more reactive and easier to concentrate

More information: Joule, Keith et al.: "A process for capturing CO2 from the atmosphere", DOI: 10.1016/j.joule.2018.05.006

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12 comments

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overcurious
3.3 / 5 (6) Jun 07, 2018
As opposed to putting these in the middle of no where; as the illustrations show, wouldn't the be more effective in cities? Like right in downtown area or along highways?
danR
4.7 / 5 (3) Jun 07, 2018
You suck CO2 out of the air by planting trees. Billions of them. For short-term carbon/energy recyclables, quick-growth plants.
danR
3.6 / 5 (5) Jun 07, 2018
...Like right in downtown area or along highways?

There's some merit in that idea: put them where the CO2 concentrations are highest; that should both maximize extraction yields, and efficiency.
barakn
3.8 / 5 (6) Jun 07, 2018
There's not that much merit in that idea. CO2 is relatively well mixed in the lower atmosphere. Combustion sources of CO2 usually release it warmer than the surrounding air, so it balloons upward where it reaches faster winds and mixes quickly. As far as putting it in cities, that would conflict with "we can take this energy straight from big solar or wind installations at great sites where it's cheap." This process will require quite a lot of energy, and placing it near where the energy is produced will reduce transmission losses.
danR
3.7 / 5 (3) Jun 07, 2018
There's not that much merit in that idea. CO2 is relatively well mixed in the lower atmosphere.
Nope. Urban areas have phenomenally higher ppm counts than rural. The mixing process is not immediate, and the updraft phenomenon only occurs significantly in high temperature-differential sources, such as smokestacks. google images:
   CO2 concentrations "urban"
and look for the 'in town' 'out of town' blue and red bar graph.
danR
1 / 5 (1) Jun 07, 2018
' CO2 concentrations "urban"
and look for the 'in town' 'out of town' blue and red bar graph. '

That's a bedroom comparison, in town. Scratch that.

The proper ratio would be ~ 5:4 Urban: Rural
ZoeBell
Jun 07, 2018
This comment has been removed by a moderator.
Dug
2.8 / 5 (4) Jun 07, 2018
The best way to reduce CO2 levels in the future is to start working on benevolent ways to reduce the human population back to sustainable levels of about 1 B.

Regarding the article and fuel from CO2 in the air - this is old news as numerous catalyst have been studied to convert CO2 into fuels. What would be new news and as well most relevant is to know when this technology will be able to compete other current fuel and energy sources - including wind and solar. Providing an EROI for the technology would have made the article meaningful.
ddaye
3 / 5 (2) Jun 07, 2018
The best way to reduce CO2 levels in the future is to start working on benevolent ways to reduce the human population back to sustainable levels of about 1 B.
It's "best" only if there are no tipping points within about a century. Part of the benevolent solution is finding an alternative to a capitalist economy, because for about a hundred years of severe population decrease, there won't be enough young workers to support the elderly whether by direct social security payments or by purchasing retirees' investments. The US for example can't even manage its comparatively trivial baby boomer support costs, which it's known were coming for 70 years. I think for both ecological and societal reasons it's simpler to address the carbon increase directly.
Thorium Boy
1 / 5 (5) Jun 08, 2018
Liberals fiddle while the Canadian economy exists solely because of the U.S. A big part is oil. Kill that, Canadians might find themselves living at the level or Southern Portugal.
Gigel
not rated yet Jun 08, 2018
The best way to reduce CO2 levels in the future is to start working on benevolent ways to reduce the human population back to sustainable levels of about 1 B.

If humanity had done that before each time it faced a limit we would have never progressed. It's time now to do another technological leap and overcome current limitations. The easiest way is probably to gradually renounce fossil fuels in favour of other sources of energy.

Btw, theoretical sustainable levels for the Earth's human population based only on solar energy go up to 1 million billion people (that is what you get if you convert Sun's energy reaching Earth in calorie food with 100% efficiency). In practice, we are not bound to Earth so we can reach and expand over that limit without destroying the environment.

Technology is the key.
alexander2468
2.3 / 5 (3) Jun 08, 2018
The triple whammy oxygen-carbon-oxygen

Carbon is the life blood of life - remove carbon from oxygen permanently from carbon dioxide is the same as lemmings heading for the nearest cliff for the final free fall.

There are higher concentrations of carbon dioxide, but its greatest sources emit this atmospheric gas in extremely diffuse amounts.
This is why oil is the main source for this gas, when this oil is too expensive to drill we require a far more concentrated source of carbon dioxide than sucking air through extraction fans can supply that has taken trees billions of years to concentrate!

As our source of carbon runs out "OIL" our electric cars will come to a grinding halt!

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