Sucking CO2: The tech to make direct air capture viable

Sucking CO2 from the air: The technological advances needed to make it viable

Is our sustainable future a wall of fans towering above a barren landscape? Visions of stacks of floating discs that fall into barrels of water before rising again? Triangular-shaped, tent-sized modules equipped with solar panels and material ‘sponges’ to soak up carbon dioxide?

These are just some of the machines being thought up or deployed to extract carbon dioxide from air.

Called direct air capture (DAC), these technologies are designed to remove CO2 from the atmosphere faster than trees, soils, and seaweeds can absorb it, to ensure that any rise above 1.5°C of global heating is only temporary.

Though DAC is still in its infancy, the weight of historical emissions – all the carbon dioxide and other greenhouses gases humans have and are still emitting – means it has become a technological necessity. Planting trees and restoring soils is not enough, experts say.

“In addition to reducing emissions as fast as we can [and] as hard as we can, we have to also remove carbon dioxide from the atmosphere,” Pep Canadell, an earth systems scientist at CSIRO and executive director of the Global Carbon Project, said in a recent Cosmos Briefing about this being the critical decade to arrest climate change.

But the technology we need to suck CO2 from the atmosphere still has a long way to go before it can pull down historic emissions. And its success hinges on investment into research devising ways to make DAC technologies more efficient and reduce energy use, to bring costs down and scale operations up.

“The chemistry of the materials has a huge role to play in really helping to take this technology to market, [and] to surmount the problems that exist with the current technologies,” says Deanna D’Alessandro, a chemist at the University of Sydney working on an industry-led project.

Unlike carbon capture and storage (CCS) which involves capturing and then storing CO2 where it is emitted from coal-fired power stations and gas plants, DAC technologies absorb carbon dioxide straight from the air – a much harder and energy-intensive task.

But the Climate Council says CCS has not been trialled and tested – anywhere in the world – at the scale required to tackle the climate crisis. It says: “When attached to fossil fuel developments – like coal, oil and gas – CCS is not a climate solution, as digging up and burning fossil fuels only adds to the problem.”

A woman holding a flask of purple liquid
Deanna D’Alessandro. Credit: Supplied.

DAC technologies also have shortcomings. Much of that energy goes into powering huge fans that push air through either a solid sponge-like material that traps CO2 or a liquid solution that does the same. The pioneers of direct air capture, Climeworks in Iceland, and Canada-based Carbon Engineering, have built the first commercial carbon-trapping facilities using these two approaches.

Heat is then used to release the trapped CO2 gas into storage canisters, and regenerate the liquid or solid sorbent material so it can soak up more. But heating liquid sorbents requires temperatures of upwards of 800°C. Carbon Engineering burns gas to power its machines and capture those extra emissions too.

To fix those and other problems, D’Alessandro is developing new sorbent materials that are better at plucking CO2 out of the atmospheric mix of oxygen, nitrogen, water vapour and other gases. The goal is a more selective and thereby efficient process powered by cheap, solar energy.

There are a host of other contraptions in the pipeline, with researchers looking at ways to reduce energy inputs using passive systems without fans, where wind blows over large tiles (that could simultaneously shade buildings, to cut solar gain).  Climeworks is also testing how it can recover waste heat from industrial processes and use it to power operations.

Regardless of the technology, operational efficiency and the energy source are key determinants of whether direct air capture technologies extract more CO2 than what is emitted in making the machines and running them.

Since 2010, fewer than 20 direct air capture projects have come online, which collectively remove around 8,000 tonnes of CO₂ each year, according to Dawid Hanak, a process engineer at Cranfield University in the UK. That’s equivalent to the carbon dioxide emitted in producing the world’s energy for seven seconds, in 2021.

The challenge ahead is monumental.

It has been estimated that to keep global heating to below two degrees, DAC projects would need to capture 30 billion tonnes of CO₂ a year from 2080 onwards, and could use as much as a quarter of global energy by 2100.

To do even that, the technology would have to be rolled out – alongside nature-based carbon removal solutions – at a “breathtaking” rate, starting now.

“Critics suggest that the high energy cost and materials used for direct air capture make it prohibitively expensive and so impractical on the tight time scale left to avert catastrophic climate change,” Hanak writes.

However, this kind of rapid advancement is not beyond us. Modelling suggests the expansion of DAC required is not all that different to the rate at which solar and wind power have been deployed.

Costs are falling and plans for another 11 DAC facilities are in advanced stages, according to the International Energy Agency, although their deployment represents only a tenth of what’s needed to achieve net-zero emissions by 2050. Thousands more machines need building.

Which brings us back to the scale of the problem. “If we’re going to scale this industry, we have to think very carefully about where are we going source these materials from and is that going to be sustainable,” says D’Alessandro of the current carbon-trapping sorbent materials that might only last a couple of years before they need replacing. Again, recycling solar panels and wind turbines could provide inspiration.

“Critics suggest that the high energy cost and materials used for direct air capture make it prohibitively expensive and so impractical on the tight time scale left to avert catastrophic climate change,

Dawid Hanak

Ryan Hanna, a research scientist at the University of California San Diego’s Centre for Energy Research, argues that while there are many obstacles to overcome, policy makers shouldn’t wait for fully renewable energy supplies to power direct air capture. Rather, they should deploy as many plants as possible “to push the technology down the learning curve”.

“Such massive CO2 removals hinge on near-term investment to boost the future capacity for upscaling,” Hanna and colleagues wrote in their 2021 paper simulating a wartime-like deployment of DAC as a policy response to the climate crisis.

Australia is slowly catching on, with a few round table discussions held recently to discuss DAC. D’Alessandro says: “We’re well behind the rest of the world.” But, she adds: “with the resources we have, the opportunity is enormous”.

Where Iceland has immense geothermal resources to power Climeworks’ carbon-sucking facilities, Australia has plenty of solar energy and hydropower, and vast geological sites ripe for storing carbon permanently underground, if it can be done safely.

D’Alessandro says early estimates suggest direct air capture and geological storage could be a multibillion-dollar business opportunity for Australia. But when the technology is for now so costly, difficult questions arise: who pays, and to what end?

“If we’re going to scale this industry, we have to think very carefully about where are we going source these materials from.”

Deanna D’Alessandro

A number of global companies such as Microsoft are banking on direct air capture technologies to bury the carbon dioxide they emit. Oil and gas companies are also backing research projects.

The Intergovernmental Panel on Climate Change has said direct air capture “cannot serve as a substitute for deep emissions reductions”. And many scientists have warned direct air capture, like carbon capture and storage, could give big polluters a licence to keep operating or distract from other efforts to slash emissions.

“The reality is that we need it all. Unfortunately, we’ve well and truly used up our carbon budget and now we’re on a knife’s edge,” says D’Alessandro. She acknowledges that the involvement of fossil fuel companies is a real concern, and that there are ethical issues around offsets, but says technological progress will stall without investment – right when we need it most.

Jessica allen
Jessica Allen. Credit: Supplied

“Picking winners at this early stage is really not going to serve us well at all because there are scientific advances that are being made in parallel to the commercial deployment of direct air capture, and we can’t discount that important science that’s happening,” D’Alessandro says. “We need to bring the costs down, so we need new discoveries.”

Jessica Allen, an engineer at the University of Newcastle, takes more of an issue with companies paying to offset their emissions via direct air capture and pledging to decarbonise later. But she admits their investment is needed, albeit problematic: “It’s hard to see how the technology will be developed without it.”

There is another way, however.

“What I’m really interested in is solving more than one problem,” Allen says, and by that she means using the trapped CO2 to manufacture high-value carbon materials rather storing it underground. She’s working on a project to generate solid carbon from captured CO2 to use in batteries, supercapacitors, and save mining the raw materials. Another Australian company, Mineral Carbonation International, is turning CO2 into concrete and plasterboard.  

There is also a big market for renewable jet fuels made from atmospheric CO2 instead of crude oil. Making jet fuel this way and burning it again wouldn’t reduce emissions, but could accelerate progress with direct air capture, Allen says. 

“We need to leverage off these expanding markets of taking CO2 from direct air capture and turning it into products so even though that’s not carbon negative, it’s still low carbon, and it paves the way for carbon-negative technology,” Allen says. “That’s potentially a very positive way forward.”

The world needs to do two things to meet its climate targets, one of which needs to ramp up now

Aaron Tang, a climate policy researcher at Australian National University studying the feasibility of last-ditch efforts to address climate change, says that private sector investment is a driving force behind carbon removal and utilisation technologies. “Even with the vacuum in policy support for carbon dioxide removal in Australia, there are private enterprises that are still investing in this at growing rate,” Tang says.

But, he adds, public sector investment and government incentives are needed to capitalise on private sector momentum. “It doesn’t look great now in terms of where we’re at,” Tang says. “But if things align, we can move very, very quickly – and that’s very much a cause for optimism.”

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