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Over geologic timescales, CO₂ chemically binds to minerals and permanently turns to stone. Heirloom is building a direct air capture solution that accelerates this process to absorb CO₂ from the ambient air in days rather than years, and then extracts the CO₂ to be stored permanently underground.

CarbonCapture’s direct air capture machines use solid sorbents that soak up atmospheric CO₂ and release concentrated CO₂ when heated. CarbonCapture’s core innovation is making the capture system modular and upgradeable so that they can swap in best-in-class sorbents as they become available. The captured CO₂ stream is then stored permanently underground.

Airhive is building a geochemical direct air capture system using an ultra porous sorbent structure that can be made out of cheap and abundant minerals. This sorbent reacts rapidly with atmospheric CO₂ when mixed with air in Airhive’s fluidized bed reactor. Coupled with a regeneration process that’s powered by electricity to release the CO₂ for geologic storage, this provides a promising approach to low-cost DAC.

Alkali Earth uses alkaline byproducts, like steel slag, as gravel aggregates for building road surfaces. The calcium- and magnesium-rich minerals in the gravel react with atmospheric CO₂ to form stable carbonates, storing it permanently while cementing the road surfaces. Spreading the gravel across roads increases the surface area exposed to CO₂ and leverages road traffic to agitate the gravel further, accelerating CO₂ uptake.

Banyu uses sunlight to capture CO₂ from seawater and store it permanently. A reusable, light-activated molecule that becomes acidic when exposed to light causes carbon dissolved in seawater to degas as CO₂, which is then compressed for storage. Because only a small portion of the visible light spectrum is needed to trigger the reaction and the light-activated molecule can be reused thousands of times, this is a highly energy-efficient approach to direct ocean removal.

Carbon Atlantis is using a process known as electrochemical pH-swing. Their system uses a solvent to capture CO₂ and an acid to release it. This approach is inspired by recent innovation in Proton Exchange Membrane fuel cells and electrolyzers. Their cell architecture is designed to allow for industrial-sized stacks, and the components of this modular system are readily available and industry-proven, making the process cost-effective and energy-efficient. The CO₂ is then run through Paebbl's mineralization process for permanent storage in construction materials.

CarbonBlue has developed a calcium looping process to remove CO₂ from seawater or freshwater. Their novel mineralization, dissolution and brine hydrolysis regeneration releases CO₂ captured from water without needing any external feedstock of minerals or chemicals. The reactors are highly energy efficient and require a low enough regeneration temperature to enable utilization of waste heat.

CarbonRun enhances the natural ability of river currents to weather abundant, low-cost limestone and reduce river acidity levels. This benefits river ecosystems locally and enhances the rivers’ ability to capture CO₂ from the atmosphere. Rivers, which are natural carbon transport systems, then deliver CO₂ to the ocean for permanent storage in the form of bicarbonate. The alkalinity can be monitored at multiple points throughout the river, simplifying measurement.

EDAC Labs uses an electrochemical process to produce acid and base. The acid is used to start the recovery of valuable metals from mining waste, and the base is used to capture CO₂ from air. The acid and base streams are then combined to produce metals that can be sold for applications such as batteries, and solid carbonates which permanently store CO₂. The EDAC Labs process is energy efficient, uses abundant mine wastes, and produces valuable revenue-generating co-products.

Holocene captures CO₂ from air using organic molecules that can be produced at low cost. In the first step of their process, CO₂ is captured from air when it comes into contact with a liquid solution. In the second step, a chemical reaction crystallizes the material as a solid. That solid is heated up to release the CO₂, minimizing energy wasted in heating water. Their process runs at lower temperatures, further reducing the energy required and increasing energy flexibility.