IDTechEx senior technology analyst, Dr Michael Dent, examines whether Direct Air Capture (DAC) technology has the potential to reverse the impacts of climate change.

DAC technology, which uses carbon capture techniques to strip CO2 from atmospheric air, has generated a lot of excitement around the world. But despite the enthusiasm, the technology is still at a very early stage, is unproven at scale, and is currently far more expensive than point-source carbon capture technology.

The DAC process is similar to an artificial tree; ambient air enters the DAC device and a range of chemical and physical processes extract the CO2 before the rest of the air is released back into the atmosphere.

However, the process is much more efficient than planting trees, requiring less land and fewer resources. For example, Swiss DAC company Climeworks claims that its plant in Hinwil, Switzerland, can remove 900 tonnes of CO2 per year, the equivalent of 36,000 trees.

Commercial DAC methods work via a similar mechanism to point-source carbon capture. First, large fans push ambient air through a filter containing a substance that physically or chemically binds the CO­2, with the CO2-free air being released back into the environment. For example, sodium hydroxide solution will react with CO2 to form a stable sodium carbonate precipitate.

This carbonate can then be heated to produce a high purity gaseous CO2 stream, which also enables the regeneration of the sodium hydroxide.

For CO2 separation, liquid solvents – usually amine-based or caustic – are commonly used to absorb the CO2 from the ambient air.

Alternatively, solid sorbents can be used via a chemisorption mechanism, with heat and vacuum being used to desorb the CO2 and enable reuse of the sorbent.

To date, the most successful processes for capturing CO2 from the ambient air are based on low-temperature solid sorbents and aqueous alkaline solutions.

Several companies around the world are working to commercialize DAC technology.

Arguably the most successful company in the field is Climeworks. This is because Climeworks uses a low-temperature solid sorbent method based on amines supported by a cellulose mesh to capture atmospheric CO2 in an energy-efficient manner.

The company uses a modular design for its “CO2 Collectors”, which it claims reduces costs and supports scalability, and has 15 DAC systems in place across Europe, making it the largest DAC operator in the world.

Another fast-growing company in the field is Carbon Engineering, based in Squamish, British Columbia. Carbon Engineering is taking the opposite approach to Climeworks, aiming to construct a large-scale single facility in the Permian Basin capable of capturing one million tonnes of CO2 every year by 2023-2024.

Carbon Engineering uses a high-temperature aqueous method for capturing atmospheric CO2 based on potassium hydroxide. This method allows continuous capture of CO2, rather than separate capture and regeneration steps.

Despite all the optimism around DAC, the technology still faces some serious hurdles such as high costs.

Although DAC companies have remained fairly tight-lipped, capturing one tonne of CO2 directly from the atmosphere is believed to cost $600-$1,300 using current technology, compared with $40-$80 for capturing one tonne of CO2 from the flue gas stream of a coal-fired power plant.

All DAC technology currently deployed across the world can capture around 50,000 tonnes of CO2 every year, a tiny fraction of global emissions. 

IDTechEx forecasts that DAC capacity will reach 265 million tonnes of CO2 captured by 2030 and could reach eight per cent of global carbon capture capacity by 2040.

DAC is an exciting technology but it is not a silver bullet.

 - Michael Dent undertakes research in life sciences and was previously an innovation consultant at Innovia Technology. He received his PhD in Chemical Biology from Imperial College London.

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