Researchers have revealed how carbon dioxide can be captured and converted using a single electrochemical process in which an electrode like the one pictured covered in bubbles is used to attract the carbon dioxide released from the sorbent and convert it into carbon-neutral products. Credit: John Freidah/MIT MechE
Findings based on a single electrochemical process could help reduce emissions from the hardest-to-decarbonize industries, such as steel and cement.
Scientists in an effort to limit global greenhouse gas emissions around the world HAVE focus on carbon capture technologies to decarbonize the most demanding industrial emitters.
Industries such as steel, cement and chemicals are particularly difficult to decarbonise due to the inherent use of carbon and fossil fuels in their processes. If technologies can be developed to capture carbon emissions and reuse them in the production process, this can lead to significant reductions in emissions from these “hard to reduce” industries.
However, current experimental technologies that capture and convert carbon dioxide do so as two separate processes that themselves require vast amounts of energy. The MIT team is trying to combine these two processes into one integrated and much more energy efficient system that could potentially run on renewable energy to capture and convert carbon dioxide from concentrated industrial sources.
Recent findings on carbon capture and transformation
In a study published Sept. 5 in the journal ACS catalysis, scientists reveal the hidden workings of how carbon dioxide can be captured and converted using a single electrochemical process. The process involves using an electrode to attract carbon dioxide released from the sorbent and convert it into a reduced, reusable form.
Others have reported similar demonstrations, but the mechanisms governing the electrochemical reaction have remained unclear. The MIT team conducted extensive experiments to determine this driver and found that the partial pressure of carbon dioxide ultimately occurred. In other words, the more pure carbon dioxide that comes into contact with the electrode, the more efficiently the electrode can capture and convert the molecule.
Knowledge of this prime mover or “active species‘, may help scientists tune and optimize similar electrochemical systems to efficiently capture and convert carbon dioxide in an integrated process.
The results of the study suggest that while these electrochemical systems would likely not work in very dilute environments (for example, to capture and convert carbon emissions directly from the air), they would be suitable for highly concentrated emissions generated by industrial processes, especially those without an obvious renewable alternative .
“We can and should switch to renewable sources for electricity production. But deep decarbonization of industries like cement or steelmaking is difficult and will take longer,” says study author Betar Gallant, 1922 Associate Professor of Career Development at MIT. “Even if we get rid of all our power plants, we need some solutions to deal with emissions from other industries in the shorter time frame before we can fully decarbonize them. That’s where we see the sweet spot where something like this system could fit in.”
The MIT study was co-authored by lead author and postdoctoral fellow Graham Leverick and graduate student Elizabeth Bernhardt, along with Aisyah Illyani Ismail, Jun Hui Law, Arif Arifutzzaman and Mohamed Kheireddine Aroua of Sunway University in Malaysia.
Understanding the Carbon Capture Process
Carbon capture technologies are designed to capture emissions, or “flue gases,” from the stacks of power plants and manufacturing facilities. This is done primarily through large retrofits that funnel emissions into chambers filled with a “capture” solution—a mixture of amines or ammonia-based compounds that chemically bond with carbon dioxide to create a stable form that can be separated from the rest. flue gas.
High temperatures, typically in the form of fossil fuel generated steam, are then used to release the trapped carbon dioxide from its amine bond. In its pure form, the gas can be pumped into storage tanks or underground, mineralized or further converted into chemicals or fuels.
“Carbon capture is an advanced technology because the chemistry has been known for about 100 years, but it requires really large installations and is quite expensive and energy intensive to operate,” notes Gallant. “We want technologies that are more modular and flexible and can be adapted to more diverse sources of carbon dioxide. Electrochemical systems can help solve this.”
Her group at MIT is developing an electrochemical system that both regenerates captured carbon dioxide and converts it to a reduced, usable product. Such an integrated system, rather than a separate one, she said, could be powered entirely by renewable electricity rather than steam derived from fossil fuels.
Their concept centers on an electrode that would fit into existing chambers of carbon capture solutions. When a voltage is applied to the electrode, electrons flow to the reactive form of carbon dioxide, converting it into a product with the help of protons supplied from the water. This makes the sorbent available to bind more carbon dioxide instead of using steam to do the same.
Gallant previously demonstrated that this electrochemical process can work to capture and convert carbon dioxide into carbon dioxide solid form of carbonate.
“We showed that this electrochemical process was feasible in very early concepts,” he says. “Since then there have been other studies looking at using this process to try to make useful chemicals and fuels. But under the hood, there have been inconsistent explanations of how these reactions work.”
Role “Solo CO2”
In the new study, the MIT team took a magnifying glass under the hood to reveal the specific reactions driving the electrochemical process. In the lab, they created amine solutions that resemble the industrial trapping solutions used to extract carbon dioxide from flue gas. They methodically varied various properties of each solution, such as pH, concentration and type of amine, and then passed each solution around an electrode made of silver—a metal widely used in electrolysis studies and known to efficiently convert carbon dioxide to carbon. oxide of monoxide. They then measured the concentration of carbon monoxide that was converted at the end of the reaction and compared that number to every other solution they tested to see which parameter had the biggest effect on how much carbon monoxide was produced.
In the end, they found that what mattered most was not the type of amine used to initially capture the carbon dioxide, as many had suspected. Instead, it was the concentration of individual, free-floating carbon dioxide molecules that avoided binding with the amines but were still present in the solution. This “solo-CO2” determined the concentration of carbon monoxide that was ultimately produced.
“We found that it was easier to react to this ‘sol’ CO2 compared to CO2 that had been captured by the amine,” Leverick offers. “This tells future researchers that this process could be feasible for industrial streams where high concentrations of carbon dioxide could be efficiently captured and converted into useful chemicals and fuels.”
“This is not a removal technology, and it’s important to state that,” Gallant points out. “The value it brings is that it allows us to recycle carbon dioxide several times while maintaining existing industrial processes with fewer associated emissions. Ultimately, my dream is that electrochemical systems can be used to facilitate the mineralization and permanent storage of CO2 – true removal technology. That’s a longer-term vision. And a lot of the science we’re beginning to understand is the first step toward designing those processes.”
Reference: “Discovery of active species in CO-mediated amine2 Reduction to CO on Ag” by Graham Leverick, Elizabeth M. Bernhardt, Aisyah Ilyani Ismail, Jun Hui Law, A. Arifutzzaman, Mohamed Kheireddine Aroua and Betar M. Gallant*, 5 September 2023, ACS catalysis.
DOI: 10.1021/acscatal.3c02500
This research is supported by Sunway University in Malaysia.
