Capture carbon dioxide and convert it energy efficiently

These results, which rely on a single electrochemical process, could help reduce emissions from industries that are difficult to decarbonize, such as steel and cement.

In efforts to reduce global greenhouse gas emissions around the world, scientists in Massachusetts Institute of Technology They focus on carbon capture technologies to decarbonize the most challenging industrial emissions.

It is particularly difficult to decarbonize industries such as steel, cement, and chemical manufacturing due to the inherent use of carbon and fossil fuels in their processes. If technologies can be developed to capture carbon emissions and repurpose them into the production process, this could lead to a significant reduction in emissions from these “hard-to-mitigate” sectors.

However, current 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 one integrated, more energy-efficient system that can run on renewable energy to capture and convert carbon dioxide from concentrated industrial sources.

Recent findings on carbon capture and conversion

In a study published September 5 in the journal 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 capture the carbon dioxide released by the absorbent material, converting it into a reusable diluted form.

Others have reported similar demonstrations, but the mechanisms driving the electrochemical reaction have remained unclear. The MIT team conducted extensive experiments to determine this drive, ultimately finding that it was due to the partial pressure of carbon dioxide. In other words, the purer the carbon dioxide that comes into contact with the electrode, the more efficiently the electrode captures and converts the molecule.

Find out what this main, or “active” engine is. Classify“, could help scientists fine-tune and optimize similar electrochemical systems to efficiently capture and convert carbon dioxide in an integrated process.

The study results suggest that although these electrochemical systems may not be suitable for highly dilute environments (for example, to capture and convert carbon emissions directly from the air), they would be well-suited for highly concentrated emissions generated by industrial processes. Especially those that do not have a clear alternative to renewable energy.

“We can and should shift to renewable energy sources to produce electricity,” says study author Petar Galant, associate professor of career development at MIT, class of 1922. “Deeply decarbonizing industries like cement or steel production are challenging and will take time.” Longer. “Even if we get rid of all our power plants, we need some solutions to deal with emissions from other industries in the short term, before we can fully decarbonize them. This is where we see a sweet spot, where something like this system could work.

Co-authors of the study from MIT are lead author and postdoctoral researcher Graham Leverick and graduate student Elizabeth Bernhardt, along with Aisha Iliani Ismail, Jun Hui Low, Arif Arifuzzaman, and Mohd Khairuddin Arua from Sunway University Malaysia.

Understanding the carbon capture process

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

High temperatures are then applied, usually in the form of fossil fuel steam, to release 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 fuel.

“Carbon capture is a mature technology, as the chemistry has been known for about 100 years, but it requires really big facilities, and it’s very expensive and energy-intensive to run,” Gallant points out. “What we want are technologies that are more flexible and 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 turns it into a reduced, usable product. Such an integrated, rather than separate, system could be powered entirely by renewable electricity rather than steam derived from fossil fuels, she says.

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

Gallant has previously demonstrated that this electrochemical process can capture carbon dioxide and turn it into a gas Form of solid carbonate.

“We showed that this electrochemical process was possible in very early concepts,” she says. “Since then, there have been other studies focusing 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.”

Role of Solo CO2

In the new study, the MIT team took a magnifying glass under the hood to tease out the specific reactions that drive the electrochemical process. In the laboratory, they produced amino solutions that resemble industrial capture solutions used to extract carbon dioxide from flue gas. They systematically varied different properties of each solution, such as pH, concentration and type of amine, and 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. They then measured the concentration of carbon monoxide converted at the end of the reaction, and compared this number with every 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 initially trap the carbon dioxide, as many had expected. Instead, it was the concentration of single, free CO2 molecules that avoided binding to the amines but were nonetheless present in the solution. “Single carbon dioxide” determines the concentration of carbon monoxide that is ultimately produced.

“We found that it was easier to react with single carbon dioxide than with carbon dioxide that was captured by the amine,” says Leverick. “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 is important to mention that,” Gallant emphasizes. “The value it brings is that it allows us to recycle CO2 multiple times while maintaining existing industrial processes, to reduce the associated emissions. Ultimately, my dream is that electrochemical systems can be used to facilitate the mineralization and permanent storage of CO2, a true removal technology.” This is a long-term vision, and much of the science we are beginning to understand is a first step toward designing these processes.

Reference: “Detection of active species in amine-mediated carbon dioxide₂ “Reduction to CO2 in Ag” by Graham Leverick, Elizabeth M. Bernhardt, Aisha Iliani Ismail, Jun Hui Lu, A. Arif Al-Zaman, Muhammad Khairuddin Arwa, and Petar M. Gallant*, September 5, 2023, ACS catalysis.
doi: 10.1021/acscatal.3c02500

This research is supported by Sunway University Malaysia.