Anthropocene Magazine · Climate & nature

Circular Chemistry Could Make Cement Production Carbon-Negative

A new approach combining clean energy and direct air capture technology could significantly reduce carbon emissions from cement manufacturing, potentially making it carbon-negative.

Cement production, responsible for about 8% of global CO2 emissions, is notoriously difficult to decarbonize due to high-temperature kilns and the chemical process itself. Researchers from ETH Zurich and Heirloom Carbon Technologies propose a method to cut these emissions by electrifying kilns and using Heirloom's calcium looping direct air capture (DAC) technology.

The proposed system would power cement kilns with clean electricity, reducing emissions from heat. Heirloom's DAC technology would then capture the CO2 released during limestone conversion. This captured CO2 would be compressed and stored underground. The calcium looping process, which cycles calcium between calcium carbonate and calcium hydroxide, aligns with the materials and chemical steps already used in cement manufacturing.

The process involves heating limestone (calcium carbonate) to produce calcium oxide (quicklime) and CO2. In the proposed system, water is added to the quicklime, which then absorbs atmospheric CO2 to revert to limestone, allowing the cycle to continue. Calculations suggest that electrifying kilns and using calcium looping DAC could reduce cement production's climate impact by 78% by 2050.

Heirloom Carbon has been operating a commercial-scale calcium looping DAC plant in California since 2023, capable of capturing 1,000 tonnes of CO2 annually. Lead author Vittoria Bolongaro stated that the technology has a net-negative carbon footprint, meaning these plants remove more CO2 over their lifecycle than they generate.

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