Microsoft-backed start-up Heirloom uses limestone to capture CO2

Just about every industry is working to reduce carbon emissions, but reduction won’t be enough. To prevent the worst effects of global warming, carbon that has already been emitted needs to be removed from the atmosphere, which is why there is a new and fast-growing industry around carbon capture.

Scientists estimate that in order to keep global warming below 1.5 degrees Celsius, about 10% to 20% of the CO2 emitted globally each year needs to be captured and either stored safely or used for something else. New companies are capturing carbon in various new ways. Some, such as Climeworks and Carbon Engineering, use massive fans to pull it out of the air. Charm Industrial takes it out of agriculture by converting biomass into oil.

California-based startup Heirloom has a different approach: using limestone to capture CO2 from the atmosphere. CO2 naturally occurs in limestone. Heirloom removes that CO2 by heating the limestone into a powder and stores the extracted CO2 underground. The remaining powder is then thirsty for more CO2. Heirloom spread that powder out on trays, with a robot determining location for maximum CO2 absorption. A process that naturally takes years is reduced to just three days. Once the powder is full, the process starts again.

“We need to be removing billions of tons of carbon dioxide out of the air, and you know it’s a space that really requires lots of companies, lots of different approaches to go after,” Heirloom CEO Shashank Samala told CNBC.

 “We basically just give super powers to limestone to pull a lot more CO2 much, much faster,” said Samala.

Heirloom’s approach is relatively cheap compared with other types of carbon capture and removal and highly scalable, which made it attractive to investors like Microsoft.

“We identified that Heirloom’s enhanced mineralization approach used widely available materials as passive airflow technologies, [which] means it has a potential to reach a low cost trajectory that’s really been a challenge to this industry as a whole,” said Brandon Middaugh, director of the climate innovation fund at Microsoft.

Heirloom says it plans to deploy its first site next year and aims to remove 1 billion tons of CO2 by 2035. It also sells carbon credits, which allow companies to offset their own CO2 emissions. Buyers include Microsoft, Stripe, Shopify and Klarna.

Besides Microsoft, Heirloom’s backers include Ahren Innovation Capital, Breakthrough Energy Ventures (which is Microsoft co-founder Bill Gates’s climate venture investment firm), Carbon Direct and Lowercarbon Capital. It’s raised $54.3 million to date.