Electrochemical direct-air capture of CO2 also produces freshwater from brine

A new electrochemical technology for direct-air capture (DAC) of atmospheric CO2 can also produce freshwater from brackish water or brine waste from desalination or wastewater treatment facilities. The technology, developed by Capture6, a cleantech company based in Berkeley, California, splits the salt content of the water into acid and base solutions, which are then used to capture CO2 from the air and produce valuable byproducts.

The process is based on electrodialysis, a membrane-based separation technique that uses an electric potential to drive ions across selective membranes. By applying a voltage across a stack of alternating anion-exchange and cation-exchange membranes, the salt water is separated into two streams: one with a high pH (base) and one with a low pH (acid). The base stream is then sprayed over a gas diffusion electrode, where it reacts with CO2 from the air to form bicarbonate ions. The acid stream is used to regenerate the base stream by removing the bicarbonate ions and releasing CO2, which can be compressed and stored or utilized in various applications. The remaining water in both streams is purified and recovered as freshwater.

The advantages of this electrochemical DAC technology are its low energy consumption, scalability, and compatibility with renewable energy sources. According to Capture6, the technology can capture CO2 at a cost of $50 per ton, while producing up to 75% of freshwater from the salt water input. The technology can also generate other valuable products, such as calcium carbonate for concrete, lithium salts for batteries, and hydrogen gas for fuel cells.

Capture6 is currently testing its technology at a pilot facility in California, in partnership with Palmdale Water District. The facility uses brine waste from a reverse osmosis desalination plant as the salt water input, and aims to demonstrate the feasibility and performance of the electrochemical DAC process. Capture6 plans to scale up its technology and deploy it in various locations, such as coastal areas, islands, and arid regions, where water scarcity and carbon emissions are major challenges.


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