Capturing CO2 directly from air is chemically, economically viable

per million. This is a factor of 375, notes Sholl, who said the difference in capture efficiency could be partially made up by eliminating the need to transport CO2 removed from flue gas to sequestration locations.

“Because the atmosphere is generally consistent, you could operate the capture equipment wherever you had a sequestration site,” he said. “I don’t think air capture will ever produce carbon dioxide as cheaply as capturing it from flue gas. But on the other hand, it doesn’t seem to be wildly more expensive, either.”

The release notes that based on his work with Global Thermostat, Jones believes that the costs of an optimized process will prove to be even lower than the estimates of Sholl’s team. “Sholl’s paper is important because it shows that direct capture of CO2 from the air can be up to ten times less expensive than had been estimated by others,” he said. “Process improvements based on their initial modeling study could bring costs down even further.”

In its economic analysis, Sholl’s team considered all of the energy that would have to be put into the capture process. The cost estimates did not include the capital cost of establishing the capture facilities because the technology is still too new for reliable projections.

The batch extraction process modeled by the Georgia Tech team involves blowing air through a ceramic honeycomb structure coated with dry amino-modified silica material to capture the CO2, then flowing steam through the structure to release the gas. The technique could produce carbon dioxide that is roughly 90 percent pure.

“The technical challenges are similar to those of flue gas capture: demonstration at scale, demonstration of long-term adsorbent stability and demonstration of process feasibility and stability,” Jones said. “Increased funding for air capture work is needed, because most of the funding invested in carbon capture over the past decade has been directed at flue gas capture.”

Sholl and Jones have also been contributing to work on flue gas treatment, conducting research into adsorbent materials, including theoretical and experimental research into adsorbent alternatives such as metal-organic framework (MOF) materials.

Among their recent papers on direct capture of CO2 from the air are:

• A Journal of the American Chemical Society paper that described the role of zirconium in producing more efficient amine-based adsorbents. “Past work has focused on maximizing the amount of CO2 captured per gram of adsorbent by adding ever-increasing amounts of amines,” Jones explained. “We are the first to show that an alternate strategy is to change the oxide support that the amines lay on, and for a fixed amount of amine, each amine works more efficiently.”
• A paper published in ChemSusChem describing the role played by primary, secondary and tertiary amines in capturing carbon dioxide from ultra-dilute gases like air. “We showed conclusively that primary amines are responsible for CO2 capture from the air, that secondary amines work to some degree, and that tertiary amines don’t absorb from air in any appreciable amount,” Jones said.
• A paper in Industrial & Engineering Chemistry Research that describes detailed cost estimates for the air capture process.

Jones believes air capture should be among the options developed to address global warming produced by increasing levels of carbon dioxide in the atmosphere.

“Initial demonstrations of the air capture process will probably be targeted for applications that can use the carbon dioxide for commercial purposes,” Jones said. “As the technology matures, we envision implementing CO2 capture from the air as a climate stabilization strategy, in parallel with CO2 capture from flue gas and enhanced utilization of alternative energies.”