Microsoft Will Use Carbon-Absorbing Rocks to Meet Climate Goals

Summary
A deal with Heirloom Carbon is one of the largest ever purchases of carbon-removal credits.Most of the world’s efforts to remove carbon from the atmosphere use giant, vacuum-like devices that suck in air and isolate the carbon. Microsoft is funding a new approach that uses crushed-up limestone to achieve the same result.
The tech company said Thursday it agreed to buy credits from startup Heirloom Carbon for the removal of up to 315,000 metric tons of carbon dioxide over 10 years. That would amount to a purchase commitment of at least $200 million based on market prices and would offset the equivalent of the annual emissions of around 70,000 gasoline-powered cars.
The deal will help Microsoft neutralize its carbon emissions and is one of the largest ever purchases of carbon-removal credits.
It also shows how carbon removal is quickly becoming a major industry even as the technologies are still developing. Business leaders such as Microsoft and JPMorgan Chase and governments are funding a range of approaches, including burying carbon-rich plant material and tweaks to the ocean’s chemistry that increase carbon absorption.
Heirloom was selected a few weeks ago as a potential recipient of hundreds of millions of dollars from the U.S. government as part of a 2021 infrastructure law program to kick-start the industry. Some of Microsoft’s purchase agreement is tied to Heirloom’s work in a government-funded hub in Louisiana, illustrating how the federal funding is accelerating the sector’s development. It is the first new credit-purchase tied to the government projects.
“All of these different components are really what you need to see this industry take shape," said Shashank Samala, Heirloom’s chief executive. “It’s been pretty crazy momentum for the company."
Founded in 2020, Heirloom hopes to use the Microsoft deal to raise money from investors to build its first large-scale project later this year. The startup will have to contribute funding equivalent to the government grants for the Louisiana effort, which will take much longer.
Limestone naturally absorbs carbon. Heirloom accelerates the natural process so it takes days instead of years. To remove carbon from the air, the company warms up crushed limestone in a kiln heated to about 1,650 degrees Fahrenheit and powered by renewable electricity. That heat separates the carbon dioxide, which is stored underground or in concrete, and leaves a chemical powder called calcium oxide.
That powder is then combined with water to become calcium hydroxide and spread onto trays the size of large desks or picnic blankets. Outside, the calcium hydroxide puffs up like a cookie in the oven as it absorbs carbon dioxide over about three days. The resulting limestone can go back into the kiln to restart the cycle.
Brisbane, Calif.-based Heirloom first used the process to remove a few grams of carbon from the air, then gradually stepped up to removing metric tons. It soon hopes to be removing thousands of metric tons. The goal is to bring down costs faster than competitors through the use of low-cost limestone.
Early this year, the company said carbon it removed from the air was successfully stored in concrete by a Canadian startup called CarbonCure, an industry first. Carbon is typically stored underground in oil-and-gas wells or underground rock formations, but CarbonCure and other companies say an alternative is storing it in concrete, which also makes the product greener.
In the government-backed Louisiana project, Heirloom’s limestone would be used alongside vacuum-like devices from European competitor Climeworks. The carbon would be stored underground by a company called Gulf Coast Sequestration.
Climeworks raised $650 million privately from investors last year, the largest such fundraising for a carbon-removal startup. Oil company Occidental Petroleum also has committed billions of dollars to carbon removal and recently said it would acquire direct-air capture technology startup Carbon Engineering for about $1.1 billion. Occidental also is in talks with the government for federal funding.
Heirloom raised $53 million last year from investors including Bill Gates’ Breakthrough Energy Ventures and Microsoft’s Climate Innovation Fund.
The company’s science builds on academic research on accelerating the carbon-absorbing process using limestone. One of the big challenges is automating the process that moves the limestone trays around. That is a main area of focus for Samala, a longtime automation-industry executive.
As with wind and solar energy, Microsoft expects carbon removal will see technology improvements and cost reductions over time, said Brian Marrs, the company’s senior director of energy and carbon. “We’ve seen this movie before," he said.
Write to Amrith Ramkumar at amrith.ramkumar@wsj.com
