Low-energy carbon capture using food-production byproducts

Direct-air capture (DAC) of carbon dioxide from the atmosphere is required to meet climate goals, but highly effective and inexpensive DAC remains elusive. Researchers at ETH Zurich (www.ethz.ch) have developed a novel approach using waste proteins from dairy and tofu production as CO₂ sorbents. The approach seems to strike an ideal balance among selectivity, capture efficiency and regeneration energy, as well as exhibiting other attributes, such as durability, that could lower costs for both the sorbent material itself and its energy needs.

The unique sorbent materials begin with protein waste from dairy and tofu production. From these waste byproducts, the ETHZ team created amyloid fibrils (AFs), which are highly ordered protein aggregates that result when ordinarily soluble proteins misfold and self-assemble into long, threadlike structures. After the protein isolates are formed into AFs, they are functionalized with hydroxides and molded into ~1-cm dia. microbeads. These microbeads contain multiple CO₂-binding sites within chemically stable nanostructures, the researchers explain.

When the porous beads are exposed to the atmosphere, CO₂ from the air reacts with potassium hydroxide in the pores of the beads, forming hydrogen carbonate and removing the CO₂ from the air.

“Our study provides a milestone in the design of protein sorbents that strike a balance between capture capacity, cost, energy efficiency, stability and sustainability,” says Raffaele Mezzenga, a professor at ETHZ. “Beyond establishing a viable waste-to-materials pathway, we further demonstrate that these functionalized microbeads also efficiently convert CO₂ from packaged food to protein-bicarbonate composites, underscoring their potential reintegration into the food system, for example, as food adsorbents, feed ingredients or fertilizers,” Mezzenga adds.

In tests, the ETHZ researchers found they could extract 97 mg of CO₂ per gram of sorbent material, a level that is 10 to 50% higher than existing DAC methods based on amines. To remove and recover the CO₂, the beads are sprayed with mild acid and base solutions, which can be reused, preparing the beads for another capture cycle. At the end of the beads’ life, they could be used as fertilizer or as biofuel feedstock, the researchers note.

The ETHZ team published their findings in a recent issue of Proceedings of the National Academy of Sciences (PNAS).