ETH Zurich team makes CO2-capturing beads from food waste
Researchers say protein beads made from whey and tofu byproducts captured CO2 from air in lab tests and released it at room temperature.
By Lucas Ferreira · Science & Environment Writer
3 min read
ETH Zurich researchers have developed biodegradable beads from dairy and tofu production waste that can draw carbon dioxide from ambient air. The work matters because direct air capture remains costly and energy-intensive, even as climate models cited by the Intergovernmental Panel on Climate Change call for large-scale removal of CO2 already in the atmosphere.
The team reported the method in the Proceedings of the National Academy of Sciences. ETH Zurich said the researchers used protein-rich liquid byproducts from whey and tofu manufacturing, waste streams that are only partly reused in food production.
According to ETH Zurich, the scientists extracted proteins from those liquids and formed them into amyloid fibrils, long thread-like structures. They then combined the fibrils with potassium hydroxide and shaped the material into porous beads about 0.5 to 1 centimeter wide.
Raffaele Mezzenga, a materials scientist at ETH Zurich and senior author of the study, said the beads act like a sponge because the potassium hydroxide enables them to take up CO2. When the beads sit in air, ETH Zurich said, the potassium hydroxide reacts with carbon dioxide and forms hydrogen carbonate, a salt of carbonic acid.
Lab tests showed high uptake
Zhou Dong, a postdoctoral researcher in Mezzenga’s group and lead author of the study, said the material removed 97 milligrams of CO2 per gram in tests with ambient air. Dong said that result was 10% to 50% above the capacity of conventional direct air capture technologies.
Dong estimated that one kilogram of the beads could capture and isolate about 100 grams of CO2 in one operating cycle. ETH Zurich said the current experiments used only a few grams of material and captured about 50 grams of CO2, leaving scale-up as a key question.
Conventional direct air capture systems often use heat and negative pressure to separate captured CO2 from the materials that bind it, according to ETH Zurich. That energy demand limits where such systems can be practical, with facilities often needing access to abundant renewable power.
The ETH Zurich process releases the captured CO2 without heat. The researchers spray the beads with a mild acid and then a mild base for about 10 minutes at room temperature, which breaks the bonds holding the carbon dioxide so it can be collected, ETH Zurich said.
Researchers cite reuse and lower pollution
The team said the beads, acid and base can be reused. Dong said materials used in today’s CO2 capture systems can break down quickly, while the protein beads stayed stable for a long period in the laboratory.
ETH Zurich said the beads kept working through 30 capture-and-release cycles without a major loss of efficiency. Mezzenga estimated that replacement could be needed after several thousand cycles, and said the organic beads could later be used as fertilizer or converted into biofuel.
Mezzenga said the materials used in the process are non-toxic and food-grade. ETH Zurich also said a life cycle analysis found the approach caused less environmental pollution over its lifespan than existing direct air capture technologies.
The researchers have not calculated the cost of capturing a ton of CO2 with the material. Mezzenga said he expects the cost to be lower than conventional direct air capture because the system uses little energy and relies on a widely available waste product.
Mezzenga said the spray-based release step fits with industrial methods that are already in use. ETH Zurich said Dong will continue testing how the process performs at larger scales.
This story draws on original reporting from ScienceDaily.