In this prototype carbon capture apparatus, a solution of potassium hydroxide is wicked up into polypropylene fibers; circulating air evaporates the water in the solution, concentrating it to very high levels. The white crystals are nearly pure potassium carbonate, formed from carbon removed directly from air.
A University of Toronto team has designed a new method for capturing carbon dioxide directly from the air.
The technique called evaporative carbonate crystallization could cut the hefty price tag of current technologies by 40 percent.
It’s essentially a passive system that leverages capillary action and evaporation to pull CO2 from the atmosphere. This could eliminate some of the most expensive and energy-intensive steps in today’s carbon capture plants.
“We’ve had the technology to capture carbon dioxide (CO2) from flue gases, or even directly from the air, for decades now,” said Professor David Sinton, Interim Director of the University of Toronto’s Lawson Climate Institute and senior author.
“There are even some full-scale plants in operation, but the criticism that the industry always gets—with justification—is that it’s still just too expensive. So, we’ve oriented our team’s approach around radical cost reductions, and that is what this new method of evaporative carbonate crystallization is all about,” Sinton added.
Carbon capture method
The system design is built around long strands of polypropylene fiber, which is basically a common string.
One end dips into a potassium hydroxide solution. The liquid slowly wicks up the string, a process familiar to anyone who’s ever seen a plant draw water.
As the wind blows across the string, it evaporates the water, driving the dissolved potassium hydroxide to extremely high concentration.
“Because we have a very thin layer of extremely concentrated potassium hydroxide, the rate at which it reacts with carbon dioxide speeds way up,” said postdoctoral fellow Dongha Kim.
“We can capture carbon at a much higher rate than with the more dilute solutions used in today’s systems. On top of that, the potassium carbonate salt that we produce doesn’t stay dissolved in solution—instead it forms a solid crystal right on the surface of the fibers,” Kim added.
The captured carbon, which forms solid potassium carbonate crystals on the fibers, resembles “rock candy.”
Interestingly, the carbon captured in a solid form provides a second advantage for the system’s efficiency and cost reduction.
In existing systems, complex chemical plants are required to separate dissolved carbon from the capture liquid, often necessitating the use of additional chemicals and intensive filtration.
But with this new method, the solid crystals are washed off with water, yielding a highly concentrated solution ready for the next step.
Captured gas utilization
The process concludes with the highly concentrated potassium carbonate salts undergoing an electrochemical process.
This step serves a dual purpose: it converts the salts back to pure CO2 gas and simultaneously regenerates the potassium hydroxide capture liquid for reuse in the system.
The captured CO2 gas is then ready for utilization, including storage, injection into underground wells for sequestration, or further processing into valuable carbon-based products such as methanol, ethanol, and ethylene.
A techno-economic analysis revealed that while operating costs remain similar to current methods, the capital costs could plummet by up to 40%.
“If you tour an industrial-scale carbon capture plant, the two biggest things you’ll see are the air contactor, with the fans and blowers, and the chemical plant used to regenerate the capture liquid,” said Sinton. “If you can eliminate both of those, you can save a lot of money.”
Humidity remains a challenge; the process thrives in drier air. Further challenges are anticipated as they scale up to a pilot-scale plant for validation. However, the current study provides strong proof of concept.
The study was published in the journal Nature Chemical Engineering.
The Blueprint
