Direct Air Capture (DAC) How Cement Plants Can Remove CO₂ from the Atmosphere

Related Vendors

ETH Eidgenössische Technische Hochschule Zürich

Bimos - eine Marke der Interstuhl Büromöbel GmbH & Co. KG

Cement makes up nearly 8% of global CO₂ emissions, but ETH researchers say the industry could flip the script. By pairing cement kilns with Direct Air Capture technology that uses the same core chemistry, a new study finds emissions could drop by up to 78%, with plants ultimately removing more CO₂ than they produce.

Cement is one of the most in-demand building materials of our time. Every year, around four billion tonnes are produced. Cement production is energy-intensive, and greenhouse gases are emitted during the process — particularly during the thermal decomposition of limestone, the most important natural raw material for cement.

In a new study, ETH researchers show that these emissions could be significantly reduced if cement production were combined with a technology for the direct removal of CO₂ from the atmosphere, known as Direct Air Capture (DAC).

According to calculations by researchers in the group led by André Bardow, Professor of Energy and Process Systems Engineering, the climate impact of cement production could be significantly reduced by the year 2050. At present, it is responsible for five to 8 % of global CO₂ emissions. “From a climate perspective, the combination of DAC and cement production is very promising,” as Vittoria Bolongaro stated, a PhD student working with Bardow and lead author of the publication.

Exploiting Synergies

For the study, the researchers collaborated with the US company Heirloom Carbon Technologies. The company is one of the world’s leading developers of DAC based on calcium looping — a process that utilises a chemical cycle involving various calcium compounds. Calcium carbonate is the starting point, i.e. limestone, which is quarried worldwide. DAC plants using calcium looping and cement works operate with the same calcium compounds and employ the same process: limestone is heated until it decomposes into quicklime and CO₂ — a process known as calcination.

In integrated cement production using calcium looping DAC, a kiln powered by electricity rather than fossil fuels, such as coal or gas, is harnessed for calcination. This avoids greenhouse gas emissions from the combustion kiln. At the same time, the CO₂ produced during the calcination process can be captured directly, as it is not contaminated by combustion exhaust gases. According to the study's calculations, electrifying the kiln and using direct CO₂ capture alone could reduce the climate impact of cement production by 78 % by 2050.

Once water has been added to quicklime, the slaked lime absorbs further CO₂ from the atmosphere and is converted back into limestone, which can then be reused as a raw material for cement production. The more often the calcium undergoes this cycle of contact with the air before being processed into cement, the more CO₂ the plant removes from the atmosphere. The CO₂ captured from the atmosphere is not bound in the cement. Instead, it is compressed and transported to underground storage sites.

Real-World Figures

“Heirloom was an ideal partner for us because the company is already operating the first calcium looping DAC systems on a commercial scale,” as Bolongaro underlined. In California, the company has been operating a plant since 2023 with an annual nominal capacity of 1000 tonnes CO₂.

Another, significantly larger plant is due to be built in Louisiana in the upcoming years. “The collaboration was beneficial for both sides: our partner wanted to learn more about the technology’s environmental footprint — and we were able to base our calculations and scenarios on primary industrial data from real-world operations,” explains Bolongaro.

The current study is the first prospective life-cycle analysis for DAC using calcium looping on an industrial scale. In conducting the analysis, the researchers not only considered the operation of the plant, but also all environmental impacts along the process chain; from raw material extraction through the construction and operation of the plant to the storage of the captured CO₂.

Initially, Bolongaro and her team wanted to find out whether larger, commercial plants remove more CO₂ over their entire life cycle than they produce. In a second step, the researchers examined whether the reduction in CO₂ emissions comes at the expense of other environmental factors, such as water or land use.

Their findings showed that by far the largest share of the environmental footprint is attributable to the energy required for the process, as the capture of CO₂ from the air is very energy-intensive. This also applies to other DAC processes. As part of the study, various energy scenarios were therefore tested: operating the plant using the current US electricity mix, drawing on a heavily decarbonised electricity mix comprising wind and solar energy, and employing a fully autonomous system with photovoltaics and battery storage.

“We were able to show that the technology has a net-negative carbon footprint; in other words, commercial calcium looping DAC plants with CO₂ storage remove more CO₂ than they generate over their entire lifecycle,” says Bolongaro. “Depending on the energy mix used in our projections, the efficiency of CO₂ removal by 2050 ranges between 85 and 96 %.” In other words: for every tonne of CO₂ that is captured and stored, 40 to 150 kg of CO₂ are generated in the process chain. This is comparable to figures from other DAC systems. Powering the plant by renewable energy achieves the highest efficiency.

What the Field Trial Still has to Show

“The major advantage of DAC plants using calcium looping is that this technology can be integrated into a well-established cement production process,” explains Bolongaro. The adjustments required to integrate DAC into cement production are relatively straightforward.

First and foremost, additional air contactors are needed to capture CO₂ from the atmosphere. Furthermore, the kiln in which limestone is calcined at high temperatures must be powered by low-carbon or carbon-free energy to ensure the highest possible net removal.

“From a climate perspective, this approach is very promising as a scalable solution that integrates into existing industrial supply chains, while simultaneously driving the decarbonisation of the cement sector forward,” as Bolognaro underlines. A more detailed investigation of the physical and economic limits of this integration is now required.

The key calculations for the study are based on future scenarios up to the year 2050 and assume significant progress in the decarbonisation of the electricity supply. Furthermore, some of the plant components, in particular indirectly heated electric calcining kilns, are not yet in large-scale industrial use. It therefore remains to be seen whether the system can be operated economically; a detailed cost analysis was not part of the study to date.

Consequently, for Bolongaro, the results represent an important starting point that highlights the climate potential of the approach.

Reference: Bolongaro V, Shu DY, McQueen N, Bardow A: Life cycle assessment of solid calcium-looping direct air capture and its synergistic dual use for net-negative cement. Chem Circularity, 4 June 2026, DOI:10.1016/j.checir.2026.100041

(ID:50926984)