The study suggests an energy-efficient way to capture and convert carbon dioxide

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credit: ACS catalysis (2023). doi: 10.1021/acscatal.3c02500

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credit: ACS catalysis (2023). doi: 10.1021/acscatal.3c02500

In the race to cut greenhouse gas emissions around the world, scientists at the Massachusetts Institute of Technology are looking to carbon capture technologies to remove carbon from the most challenging industrial emissions.

The steel, cement and chemical industries are particularly difficult to decarbonise, as carbon and fossil fuels are inherent components of their production. Technologies that can capture carbon emissions and convert them into forms that feed into the production process can help reduce the total emissions from these “hard-to-mitigate” sectors.

But so far, experimental technologies that capture and convert carbon dioxide do so as two separate processes, which themselves require an enormous amount of energy to operate. The MIT team is looking to combine the two processes into a single integrated system that is more energy efficient and can run on renewable energy to capture and convert carbon dioxide from concentrated industrial sources.

In a study just published in ACS catalysisResearchers reveal the hidden function of how carbon dioxide is captured and converted through a single electrochemical process. The process involves using an electrode to attract the carbon dioxide released from the absorbent, converting it into a reusable dilute form.

Others have reported similar demonstrations, but the mechanisms driving the electrochemical reaction have remained unclear. The MIT team conducted extensive experiments to identify this engine, and found that it was ultimately due to partial pressure of carbon dioxide. In other words, the more pure the carbon dioxide that comes into contact with the electrode, the more efficient the electrode will be at capturing and converting the molecule.

Knowing this key driver, or “active species,” can help scientists fine-tune and improve similar electrochemical systems to efficiently capture and convert carbon dioxide in an integrated process.

The results of the study indicate that although these electrochemical systems may not be suitable for highly mitigating environments (for example, to capture and convert carbon emissions directly from the air), they would be well suited for highly concentrated emissions from industrial processes, especially those that are not It has a clear alternative renewed.

“We can, and should, switch to renewables for electricity production,” says study author Petar Gallant, associate professor of career development at MIT. “But industries that are highly decarbonised, such as cement or steel production, are challenging and will take longer.” “. “Even if we get rid of all our power plants, we need some solutions to deal with the emissions from other industries in the short term, before we can fully decarbonise them. And that is where we see a good point, something like this system can that’s convenient.”

Study co-authors from MIT are lead author and postdoctoral researcher Graham Leverick and graduate student Elizabeth Bernhardt, along with Ayesha Ilyani Ismail, John Hui Lu, Arif Arifuzzaman, and Muhammad Khairuddin Arua of Sunway University in Malaysia.

Breaking links

Carbon capture technologies are designed to capture emissions, or “flue gas,” from the stacks of power plants and manufacturing facilities. This is done primarily by using large retrofits to direct the emissions into chambers filled with a “capture” solution – a mixture of amines, or ammonia-based compounds, that chemically bond with carbon dioxide, resulting in a stable form that can be separated from the rest. of flue gas.

High temperatures are then applied, usually in the form of steam from fossil fuels, to liberate the captured carbon dioxide from the amino bond. In its pure form, the gas can then be pumped into storage tanks or underground, mineralized, or converted into chemicals or fuels.

“Carbon capture is a mature technology, as the chemistry has been known for about 100 years, but it requires really large facilities and is very expensive and energy-intensive to operate,” Gallant says. “What we want are technologies that are more agile, flexible and can be adapted to more diverse sources of carbon dioxide. Electrochemical systems can help address this.”

Her group at MIT is developing an electrochemical system that recovers captured carbon dioxide and converts it into a reduced, usable product. It says such an integrated system, rather than a standalone one, could be powered entirely by renewable electricity rather than steam derived from fossil fuels.

Their concept centers around an electrode that can be installed in existing chambers of carbon capture solutions. When a voltage is applied to the electrode, electrons flow to the reactive form of carbon dioxide and convert it into a product using the protons supplied from the water. This makes the absorbent available to bind more carbon dioxide, rather than using steam to do the same.

Gallant had previously demonstrated that this electrochemical process could capture carbon dioxide and convert it into a solid carbonate form.

“We showed that this electrochemical process was possible in very early concepts,” she says. “Since then, there have been other studies that have focused on using this process to try to produce useful chemicals and fuels. But there have been inconsistent explanations for how these reactions work, under the hood.”

Solo company2

In the new study, the MIT team took a magnifying glass under the hood to extract the specific interactions that drive the electrochemical process. In the lab, they produced amino solutions that are similar to the industrial capture solutions used to extract carbon dioxide from the flue gas.

They systematically varied the different properties of each solution, such as pH, concentration and type of amine, then passed each solution through an electrode made of silver, a metal widely used in electrolysis studies and known for its ability to efficiently convert carbon dioxide into carbon. monoxide Then they measured the concentration of carbon monoxide that was converted at the end of the reaction, and compared that number with each other solution they tested, to see which parameter had the greatest effect on the amount of carbon monoxide produced.

In the end, they found that what mattered most was not the type of amine used to capture the carbon dioxide in the first place, as many expected. Instead, it was the concentration of single, free CO2 molecules that avoided binding to the amines but was nonetheless present in solution. This “solo co2Determine the concentration of carbon monoxide that was eventually produced.

“We found it easier to react with single carbon dioxide2compared to CO2 “Leverick shows what was captured by the amine. This tells future researchers that this process could be feasible for industrial streams, as high concentrations of carbon dioxide can be efficiently captured and converted into useful chemicals and fuels.”

“This is not a removal technique, and it’s important to mention that,” Gallant stresses. “The value it brings is that it allows us to recycle CO2 many times over while maintaining existing industrial processes, to reduce associated emissions. Ultimately, my dream is that electrochemical systems can be used to facilitate mineralization and permanent storage of carbon.” a company2Real removal technology. This is a long term vision. And a lot of the science that we’re beginning to understand is a first step toward designing those processes.”

more information:
Graham Leverick et al., Detection of species active in amine-mediated CO reduction to CO in Ag, ACS catalysis (2023). doi: 10.1021/acscatal.3c02500

Journal information:
ACS catalysis

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