Limiting long-term global warming to below 1.5°C requires more than just reducing greenhouse gas emissions. The world also needs technologies that can remove and store the hundreds of billions of tonnes of carbon dioxide (CO2) already in the atmosphere, according to climate scenarios outlined in the Intergovernmental Panel on Climate Change’s (IPCC) latest assessment report.
One approach that is gaining increasing attention is direct air capture (DAC), a process that removes CO2 directly from the air. Companies and research teams have spent years developing DAC systems, and Climeworks, a spinoff from ETH Zurich founded in 2009, was one of the first to bring the technology to market. Despite these advances, capturing carbon from the atmosphere remains expensive and energy-intensive.
Protein beads made from food industry waste
Researchers at ETH Zurich have developed a new carbon-trapping material made from an unexpected source: waste from dairy and tofu production.
In a study published in PNASA team led by Professor Raffaele Mezzenga, a materials scientist at ETH Zurich’s Faculty of Health Sciences and Technology, describes how to use whey and by-products from tofu production to absorb CO2.
During the production of dairy products and tofu, large amounts of protein-rich liquid are produced. Only some of it is reused in food production; much of the rest is thrown away. The researchers extracted proteins from this waste stream and assembled them to form long thread-like structures known as amyloid fibrils.
These fibrils were then combined with potassium hydroxide to form porous beads about 0.5 centimeters to 1 centimeter in diameter.
“The resulting material is like a sponge that can absorb large amounts of carbon dioxide via potassium hydroxide,” Mezzenga explains.
Carbon capture performance that outperforms existing methods
When exposed to air, the potassium hydroxide in the beads reacts with CO2 to form bicarbonate, a salt of carbonic acid. This reaction effectively removes carbon dioxide from the atmosphere.
“In tests using air, we were able to extract 97 milligrams of CO2 from one gram of the material,” explains Shudong, a postdoctoral researcher in Metzenga’s group and lead author of the study.
According to Dong, its performance is extremely powerful, exceeding the capacity of traditional DAC technology by 10-50%. He estimates that 1 kg of protein beads could theoretically capture and separate about 100 grams of CO2 during one operating cycle.
low energy carbon removal
Traditional direct air capture systems typically use heat and negative pressure to release the captured CO2 from the holding material. The captured carbon dioxide can be stored or converted into other products and kept out of the atmosphere for long periods of time.
Because this process consumes large amounts of energy, DAC facilities are generally most practical in locations with abundant renewable energy resources.
The ETH Zurich team has developed a different approach. To release the trapped CO2, the researchers spray the protein beads alternately with a weak acid and a weak base for about 10 minutes at room temperature. This process breaks the chemical bonds that hold CO2 together, allowing it to be collected.
Reusable beads support circular economy
Acids, bases, and protein beads can all be reused.
“The synthetic materials used to capture CO2 today degrade quickly,” Dong says. “In contrast, our protein beads are stable over long periods of time.”
Laboratory tests showed that the material maintained its performance after 30 cycles of carbon capture and release without significant loss of efficiency.
Over time, the adsorption capacity will eventually decrease. Mezzenga estimates that they may need to be replaced after a few thousand cycles. However, since the beads are completely organic, they can be reused as agricultural fertilizers or converted into biofuels.
Their biodegradable nature allows this technology to fit into broader circular economy models, potentially reducing waste while continuing to provide value after the beads are retired from carbon capture applications.
“The materials used in this process are non-toxic and food grade,” Mezzenga points out.
The team also conducted a life cycle analysis and found that the new approach pollutes the environment less over its lifetime than existing DAC technology.
Can the technology scale up?
Although the results are promising, additional testing is needed to determine whether this technology can be effectively operated at industrial scale while maintaining high carbon capture capacity.
In the new study, the researchers worked with just a few grams of material in a controlled laboratory environment and captured about 50 grams of CO2.
Mezzenga is optimistic about the future of technology. He has spent nearly 20 years researching amyloid fibrils, which he has previously used to develop biodegradable plastic alternatives and water purification technologies.
“We believe this technology is scalable,” he says.
According to Mezzenga, the spray-based system used to release CO2 is compatible with industrial technologies that are already widely used. Dong plans to continue investigating how this process plays out at scale.
Researchers have not yet calculated the exact cost of capturing one ton of CO2 using this new material. Still, Mezzenga expects it to be significantly cheaper than traditional direct air recovery systems.
“Our technology is cheaper and more sustainable because it requires little energy and is based on widely available waste,” he says. “This could be a game-changer for the future of removing CO2 from the atmosphere.”
