While the capture of carbon from flue gas is technically feasible, it has a high energy cost.
A new method could lead to the creation of useful products from the process, while significantly lowering the overall energy cost of carbon capture.
The technique uses a liquid solution containing substances called amines. When flue gas is bubbled through these solutions, the CO2 within it combines with the amine molecules to make chemical species known as adducts.
In typical carbon capture, the next step would be to heat the adducts to temperatures above 150°C in order to release the CO2 gas and regenerate the amines. The released CO2 gas is then compressed so it can be stored. These two steps, heating and compression, account for up to 90 per cent of the energy cost of carbon capture.
Instead of heating the amine solution to regenerate CO2 gas, the team used electrochemistry to convert the carbon captured within it directly into more valuable products.
“What I learned in my research is that if you inject electrons into the adducts in solution, you can convert the captured carbon into carbon monoxide,” said PhD student Geonhui Lee who worked on the project. “This product has many potential uses and you also eliminate the cost of heating and compression.”
Compressed CO2 recovered from smokestacks has limited applications: it is usually injected underground for storage or to enhance oil recovery.
By contrast, carbon monoxide (CO) is one of the key feedstocks for the well-established Fischer-Tropsch process. This industrial technique is widely used to make fuels and commodity chemicals, including the precursors to many common plastics.
Lee developed a device known as an electrolyser to carry out the electrochemical reaction. While she is not the first to design such a device for the recovery of carbon captured via amines, she says that previous systems had drawbacks in terms of both their products and overall efficiency.
“Previous electrolytic systems generated pure CO2, carbonate, or other carbon-based compounds which don’t have the same industrial potential as CO,” she said. “Another challenge is that they had low throughput, meaning that the rate of reaction was low.”
Despite the effectiveness of the electrolyser, the researchers say there is still “some distance” before it can used on a commercial scale.
Earlier this month, a report found that the number of carbon capture and storage (CCS) facilities operating globally has increased by a third in the last year.
