Lawrence Livermore scientists have devised tiny capsules made up of a highly permeable polymer shell and a sodium carbonate solution that actively reacts with and absorbs carbon dioxide (CO₂). Sodium carbonate is typically known as the main ingredient in washing soda, a common household item. The capsules are a lot cheaper and more environmentally friendly than other chemical carbon capture methods, according to the researchers.

Carbon capture and storage (CCS) technology captures carbon emissions and stores them. In theory, this means carbon that would otherwise be emitted into the atmosphere can be locked up somewhere else – without the climate-altering effects. Image: Scottish Carbon Capture & Storage

While renewable energy is catching up, there are still a great deal of coal or natural gas fired power plants operating throughout the world, with many more opening their gates. Instead of going against the wave, scientists are trying to make the best of it and develop carbon capture methods that diminish the levels of greenhouse gases or toxic chemicals that are released in the flue gases.

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Microcapsules containing sodium carbonate solution are suspended on a mesh during carbon dioxide absorption testing. The mesh allows many capsules to be tested at one time while keeping them separated, exposing more of their surface area. Photo by John Vericella/LLNL

In the past decade or so, the industry has become heavily reliant on monoethanol amine (MEA) to capture carbon dioxide before it exits smokestacks. MEA, however, is extremely caustic forcing plants to employ high quality and expensive stainless steel throughout their pipelines where MEA crystals come into contact. Carbonates, on the other hand, are benign and require no additional fitting. This is mainly why the Lawrence Livermore scientists decided to work with sodium carbonate or washing soda, but what really made their work ingenious was the decision to encapsulate the carbon capturing solution.

Microcapsules have become increasingly popular in medicine, agriculture or even cosmetics, but this is the first time they’ve been used for carbon capture. Being spherical, the capsules offer a much greater active surface area, absorbing more CO2 than other solvents.  Putting the carbonate solution inside of the capsules also allows it to be used for CO₂ capture without making direct contact with the surface of equipment in the power plant, as well as being able to move it between absorption and release towers easily, even when it absorbs so much CO₂ that it solidifies, according to Roger Aines, one of the Lawrence Livermore team members.

Unlike more caustic solvents used in capturing CO₂, the microcapsules only react with the gas of interest (in this case CO₂).

“Encapsulation allows you to combine the advantages of solid capture media and liquid capture media in the same platform,” says Jennifer Lewis of Harvard School of Engineering and Applied Sciences, and key author of a paper appearing in the Feb. 5 edition of the journal, Nature Communications.

Washing soda is mined locally, instead of being manufacturing in plants using energy intensive, complex chemical process such as the case with MEA. More importantly, it’s easily recyclable and can be used time and time again.

“It can be reused forever, while amines break down in a period of months to years,” Aines says.

“We think the microcapsule technology provides a new way to make carbon capture efficient with fewer environmental issues,” he says. “Capturing the world’s carbon emissions is a huge task. We need technology that can be applied to many kinds of carbon dioxide sources with the public’s full confidence in its safety and sustainability.”