A New Carbon Capture Approach Could Significantly Reduce Costs

Capturing carbon dioxide (CO₂) from industrial plants is a critical strategy in the global effort to mitigate climate change. This process is already employed in various industries, including petrochemical production, cement manufacturing, and fertilizer production.

Now, chemical engineers at the Massachusetts Institute of Technology (MIT) have developed a simple method to make carbon capture more efficient and cost-effective. Their innovation involves adding a commonly used chemical compound to the capture solution.

This breakthrough could drastically reduce costs while enabling the technology to operate using wasted heat or even sunlight, instead of relying on energy-intensive heating methods.

The core of this innovation lies in a chemical compound called tris (tris(hydroxymethyl)aminomethane), which helps stabilize the pH of the CO₂ capture solution. This enables the system to absorb more carbon dioxide at relatively low temperatures.

The new system can release captured CO₂ at just 60°C, a significant improvement over traditional methods, which require temperatures above 120°C to release the trapped carbon.

"A Near-Immediate Solution"

T. Alan Hatton, Professor of Chemical Engineering at MIT and lead author of the study, says: "This is something that can be almost immediately implemented in standard industrial equipment."

Yuhong (Nancy) Gu, a PhD graduate from MIT and now an Assistant Professor at the University of North Carolina, Chapel Hill, is the primary author of the paper, which has been published today in Nature Chemical Engineering.

More Efficient Carbon Capture

Currently, around 0.1% of global carbon emissions are captured and either stored underground or converted into other products. The most common method for capturing CO₂ involves passing exhaust gases through a chemical solution containing amines. These solutions, which are alkaline, allow the CO₂—an acidic gas—to be absorbed.

In addition to traditional amines, carbonates—which are inexpensive and abundant—can also be used to capture CO₂.

However, as CO₂ is absorbed, the pH of the solution drops rapidly, which limits its ability to absorb more gas. The most energy-consuming step in the process is the need to heat the amine or carbonate solution to over 120°C to release the captured CO₂, requiring vast amounts of energy.

A Simple Energy-Saving Change

To enhance the efficiency of carbon capture using carbonates, the MIT team introduced tris to a solution of potassium carbonate. This compound, commonly used in laboratory experiments and found in some cosmetics and COVID-19 mRNA vaccines, acts as a pH regulator, preventing fluctuations in acidity.

When added to the carbonate solution, tris—with its positive charge—neutralizes the negative charge of the bicarbonate ions formed when CO₂ is absorbed. This stabilizes the pH, allowing the solution to absorb three times more CO₂.

Another advantage of tris is its sensitivity to temperature changes. When the CO₂-saturated solution is heated slightly to about 60°C, tris rapidly releases protons, lowering the pH and allowing the captured CO₂ to be released as bubbles.

David Heldbrandt, Associate Professor of Chemical Engineering at Washington State University, who was not involved in the study, comments: "Potassium carbonate is one of the best solvents in carbon capture due to its high chemical stability, low cost, and minimal emissions." He adds, "I believe the electrochemical tris-activated potassium carbonate system holds great potential for carbon capture, especially as the researchers have managed to improve energy efficiency by regenerating the solution at atmospheric pressure, compared to the vacuum-assisted regeneration typically used."

A Simple Switch

To demonstrate the feasibility of their approach, the researchers constructed a continuous-flow reactor for carbon capture. Initially, gases containing CO₂ pass through a tank filled with the carbonate and tris solution, which absorbs the CO₂. The solution is then pumped into a CO₂ regeneration unit, where it is heated to around 60°C to release a pure stream of CO₂.

Once the CO₂ is released, the solution is cooled and returned to the tank for another round of CO₂ absorption and regeneration.

Because the system operates at relatively low temperatures, it offers greater flexibility in terms of energy sources, such as solar panels, electricity, or waste heat generated by industrial plants.

The researchers believe that replacing traditional amines with tris-enhanced carbonate solutions would be relatively simple for industrial facilities. Hatton notes: "The beauty of this method lies in its simplicity. It’s an easy-to-use approach that allows for immediate switching between different types of solutions."

A Long-Term Storage Solution

While some of the captured CO₂ could be used in the production of other chemicals, Hatton emphasizes that most of it will likely be stored in underground geological formations. "You can only use a small portion of the captured CO₂ for chemical production before the market becomes saturated," he explains.

Gu is now investigating whether other additives could further enhance the carbon capture process by accelerating the CO₂ absorption rates.