$1,121.67
Carbon credits for climate change mitigation. Delivery year: 2027. Currently available: 1,390.51 metric tons.
Heirloom Carbon Technologies is a direct air capture (DAC) company included in the Frontier Climate portfolio, dedicated to permanently removing carbon dioxide (CO2) from the atmosphere. Their approach is distinguished by its use of low-cost, earth-abundant limestone (calcium carbonate) to capture CO2, accelerating a natural mineralization process that typically takes years into a cycle that takes just three days.
Heirloom’s technology relies on a “looping” method that continuously recycles limestone to act as a sponge for atmospheric carbon. The process involves several key steps:
Calcination: The cycle begins with crushed limestone (CaCO3), which is fed into an electric kiln powered by renewable energy. Inside the kiln, the material is heated to high temperatures, causing it to separate into carbon dioxide gas and calcium oxide (CaO), also known as quicklime. The CO2 released during this stage is captured and prepared for permanent storage.
Hydration: The remaining calcium oxide is mixed with water to form calcium hydroxide (Ca(OH)2), often referred to as slaked lime. This material is highly reactive and “thirsty” for carbon dioxide.
Carbonation: The calcium hydroxide is spread onto large, vertically stacked trays in a modular facility. These trays act as passive contactors, exposing the material to ambient air. Over a period of approximately three days, the calcium hydroxide naturally bonds with CO2 from the wind, converting back into calcium carbonate (limestone).
Looping: Once the material has fully mineralized and returned to its original limestone state, it is fed back into the kiln, and the cycle repeats. Because the limestone is not consumed but rather recycled, the system is highly efficient in its material usage.
Heirloom operates the first commercial Direct Air Capture facility in the United States, located in Tracy, California. The facility demonstrates the company’s modular approach, which allows for rapid scaling by simply adding more trays and kilns rather than building massive, custom infrastructure.
The carbon captured by Heirloom’s process is permanently sequestered to ensure it does not return to the atmosphere. The company partners with storage providers to inject the CO2 underground into geologic reservoirs or permanently embed it in concrete through partners like CarbonCure, where it mineralizes and strengthens the building material.
Heirloom aims to remove 1 billion tons of CO2 annually by 2035. To achieve this, the company is aggressively driving down costs by leveraging the ubiquity of limestone—which costs approximately $10–$50 per ton compared to thousands of dollars for engineered sorbents—and by utilizing standardized, mass-manufacturable components. The company has also been selected by the U.S. Department of Energy for up to $600 million in funding to develop a regional DAC Hub in Louisiana, further validating its pathway to gigaton-scale removal.